Mirror driving apparatus and method for manufacturing thereof

The present invention relates to a mirror driving apparatus, a method for controlling a mirror driving apparatus, and a method for manufacturing a mirror driving apparatus. In particular, the present invention relates to a mirror driving apparatus for changing the reflection direction and the focus position of incident light to be used for information communication or distance measurement.

A mirror driving apparatus for changing the reflection direction and the focus position of light incident on a mirror by causing bending deformation of a beam supporting the mirror to thereby change the posture and the displacement of the mirror has been known. For example, WO2003/062899 (Patent Document 1) discloses an optical switch in which a mirror device and piezoelectric elements made up of piezoelectric thin films, electrodes, and elastic members, are formed on a substrate. A voltage is applied to the electrodes to cause flexure deformation of the piezoelectric thin films, which causes the mirror device to rotate about the rotational axis. The mirror device is thus driven.

Patent Document

PTD 1: WO2003/062899

Technical Problem

In the optical switch of WO2003/062899, a strain absorber connects the mirror device to the elastic member. In this optical switch, different voltages are applied to respective piezoelectric thin films so as to drive the mirror device. In this case, particularly if a beam on which the piezoelectric thin film is mounted and the mirror device are formed as a single unit by a technology such as MEMS (Micro Electro Mechanical Systems) technology, stress is easily exerted on the mirror device when the optical switch is driven, which could result in deterioration of the flatness of the mirror device. This is due to the action of the strain absorber disposed between the beam and the mirror device for connecting the beam and the mirror device together. Deterioration of the flatness of the mirror device could degrade the properties of light reflected from the mirror device.

The present invention has been made in view of the above problem. An object of the present invention is to provide a mirror driving apparatus that can suppress deterioration of the flatness of the mirror device by reducing stress between the mirror device and the beam on which the piezoelectric material is mounted, even when the beam and the mirror device are formed as a single unit, as well as a method for controlling the mirror driving apparatus and a method for manufacturing the mirror driving apparatus.

Solution to Problem

A mirror driving apparatus of the present invention includes a reflector and a pair of beam portions. The reflector is capable of reflecting incident light. The pair of beam portions is adjacent to the reflector to sandwich the reflector between the beam portions as seen in plan view. The pair of beam portions includes: a pair of first beams directly adjacent to the reflector to sandwich the reflector between the first beams; and a pair of second beams each coupled to one side of a corresponding one of the first beams, the one side being opposite to the reflector with respect to the corresponding one of the first beams. A plurality of electrodes are spaced from each other on a main surface of each of the pair of first beams, a piezoelectric material being interposed between the main surface and the plurality of electrodes. The first beams of the pair of first beams are displaceable crosswise to the main surface in respective directions opposite to each other. First boundary portions directly adjacent to the reflector and directly adjacent to the pair of first beams are displaceable crosswise to the main surface, and the pair of first beams is smaller in width than the reflector. The pair of second beams is displaceable in a direction connecting the pair of first beams and the pair of second beams, along a main surface of the second beams. Respective voltages of opposite polarities are applicable to a first electrode and a second electrode of the plurality of electrodes, the first electrode being located at a smaller distance from the reflector than a distance between the second electrode and the reflector, the second electrode being adjacent to the first electrode. The reflector is configured to be inclined about an axis by deformation of the piezoelectric material caused by the voltages, the axis being orthogonal to a line connecting the reflector and the first boundary portions between the reflector and the pair of first beams. Respective voltages identical in absolute value and opposite in polarity to each other are applied to the first electrode for one first beam of the pair of first beams and the first electrode for the other first beam of the pair of first beams, the one first beam being different from the other first beam. Respective voltages identical in absolute value and opposite in polarity to each other are applied to the second electrode for the one first beam of the pair of first beams and the second electrode for the other first beam of the pair of first beams. A plurality of rows each including the pair of first beams and the pair of second beams are arranged. A first row and a second row that are included in the plurality of rows are arranged to cross each other as seen in plan view.

According to a method for manufacturing a mirror driving apparatus of the present invention, a reflector capable of reflecting incident light is formed. A pair of beam portions adjacent to the reflector to sandwich the reflector between the beam portions as seen in plan view is formed. The pair of beam portions includes: a pair of first beams directly adjacent to the reflector to sandwich the reflector between the first beams; and a pair of second beams each coupled to one side of a corresponding one of the first beams, the one side being opposite to the reflector with respect to the corresponding one of the first beams. A plurality of electrodes are spaced from each other on a main surface of each of the pair of first beams, a piezoelectric material being interposed between the main surface and the plurality of electrodes. The first beams of the pair of first beams are displaceable crosswise to the main surface in respective directions opposite to each other. First boundary portions directly adjacent to the reflector and directly adjacent to the pair of first beams are displaceable crosswise to the main surface, and the pair of first beams is smaller in width than the reflector. The pair of second beams is displaceable in a direction connecting the pair of first beams and the pair of second beams, along a main surface of the second beams. Respective voltages of opposite polarities are applicable to a first electrode and a second electrode of the plurality of electrodes, the first electrode being located at a smaller distance from the reflector than a distance between the second electrode and the reflector, the second electrode being adjacent to the first electrode. The reflector is configured to be inclined about an axis by deformation of the piezoelectric material caused by the voltages, the axis being orthogonal to a line connecting the reflector and the first boundary portions between the reflector and the pair of first beams. Respective voltages identical in absolute value and opposite in polarity to each other are applied to the first electrode for one first beam of the pair of first beams and the first electrode for the other first beam of the pair of first beams, the one first beam being different from the other first beam. Respective voltages identical in absolute value and opposite in polarity to each other are applied to the second electrode for the one first beam of the pair of first beams and the second electrode for the other first beam of the pair of first beams. A plurality of rows each including the pair of first beams and the pair of second beams are arranged. A first row and a second row that are included in the plurality of rows are arranged to cross each other as seen in plan view.

Advantageous Effects of Invention

According to the present invention, the first beams located relatively closer to the reflector are displaceable crosswise to the main surface of the first beams, while the second beams are displaceable in the direction connecting the first beams and the second beams, along the main surface of the second beams. Stress between the reflector and the first beams connected to the reflector can therefore be reduced and accordingly deterioration of the flatness of the reflector can be suppressed.

FIG. 1 is a perspective view showing an overall configuration of a mirror driving apparatus in a first example of Embodiment 1.

FIG. 2 is a schematic plan view showing the overall configuration of the mirror driving apparatus in the first example of Embodiment 1.

FIG. 3 is a schematic cross-sectional view along line III-III in FIG. 2 .

FIG. 4 is a schematic enlarged plan view of region IV defined by a dotted line in FIG. 2 , particularly a schematic enlarged plan view showing a first example of the shape of an upper electrode as seen in plan view and a first example of the shape of a second beam as seen in plan view.

FIG. 5 is a schematic enlarged plan view showing a second example of the shape of the second beam as seen in plan view, which is different from FIG. 4 .

FIG. 6 is a schematic enlarged plan view showing a third example of the shape of the second beam as seen in plan view, which is different from FIG. 4 .

FIG. 7 is a schematic enlarged plan view showing a second example of the shape of the upper electrode as seen in plan view, which is different from FIG. 4 .

FIG. 8 is a schematic cross-sectional view showing a first step of a method for manufacturing the mirror driving apparatus in Embodiment 1.

FIG. 9 is a schematic cross-sectional view showing a second step of the method for manufacturing the mirror driving apparatus in Embodiment 1.

FIG. 10 is a schematic cross-sectional view showing a third step of the method for manufacturing the mirror driving apparatus in Embodiment 1.

FIG. 11 is a schematic cross-sectional view showing a fourth step of the method for manufacturing the mirror driving apparatus in Embodiment 1.

FIG. 12 is a schematic cross-sectional view showing a fifth step of the method for manufacturing the mirror driving apparatus in Embodiment 1.

FIG. 13 is a schematic cross-sectional view showing a sixth step of the method for manufacturing the mirror driving apparatus in Embodiment 1.

FIG. 14 is a schematic cross-sectional view showing a seventh step of the method for manufacturing the mirror driving apparatus in Embodiment 1.

FIG. 15 is a schematic enlarged cross-sectional view of one piezoelectric element extracted from FIG. 2 .

FIG. 16 is a schematic enlarged cross-sectional view illustrating deformation when a positive voltage is applied to an upper electrode of the piezoelectric element in FIG. 15 .

FIG. 17 is a schematic enlarged cross-sectional view illustrating deformation when a negative voltage is applied to the upper electrode of the piezoelectric element in FIG. 15 .

FIG. 18 is a schematic enlarged view illustrating deformation of a beam of the whole of one of the first beam portions extracted from FIG. 2 , caused by voltage application to a piezoelectric clement.

FIG. 19 is a schematic enlarged view illustrating deformation of a beam of a mirror portion and two first beam portions as a whole extracted from FIG. 2 , caused by voltage application to piezoelectric elements.

FIG. 20 is a schematic enlarged view showing dimensions of the mirror portion and components of a first beam portion in FIG. 19 as well as inclination angles with respect to the X direction.

FIG. 21 is a graph showing a relation between a ratio of the radius of a reflective mirror to the beam length, and coefficient α that minimizes an angle error at a first boundary portion of the beam.

FIG. 22 is a schematic plan view showing an overall configuration of a mirror driving apparatus in a second example of Embodiment 1.

FIG. 23 is a schematic plan view showing an overall configuration of a mirror driving apparatus in a first example of Embodiment 2.

FIG. 24 is a schematic plan view showing an overall configuration of a mirror driving apparatus in a second example of Embodiment 2.

In the following, embodiments of the present invention are described based on the drawings.

A description is given, using FIGS. 1 to 4 , of a configuration of a mirror driving apparatus in a first example of the present embodiment. For the sake of convenience of description, X direction, Y direction, and Z direction are used. In FIG. 1 , the width in the Y direction of a beam is drawn wider relative to other drawings for the sake of ease of visual recognition. In FIGS. 1 to 4 , the X direction is a direction connecting a reflective mirror portion M to first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 . In the X direction, first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 extend. The Y direction is orthogonal to the X direction as seen in plan view. Specifically, the Y direction crosses the direction in which first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 extend. The Z direction is a direction in which electrodes 12 BL 1 , 14 BL 1 and a piezoelectric film 13 BL 1 are stacked on a first beam 11 BL 1 of first beam portion BL 1 .

Referring to FIGS. 1, 2, and 3 , a mirror driving apparatus 100 in the first example of the present embodiment mainly includes a reflective mirror portion M, a pair of first beam portions BL 1 , BR 1 (a pair of beam portions), and a pair of second beam portions BL 2 , BR 2 (a pair of beam portions). First beam portion BL 1 which is one of the pair of first beam portions is located adjacent to the left side, in the X direction in FIGS. 1, 2, and 3 , of reflective mirror portion M. First beam portion BR 1 which is the other of the pair of first beam portions is located adjacent to the right side, in the X direction in FIGS. 1, 2, and 3 , of reflective mirror portion M. Likewise, second beam portion BL 2 which is one of the pair of second beam portions is located adjacent to the left side, in the X direction in FIGS. 1, 2, and 3 , of first beam portion BL 1 , i.e., located away from reflective mirror portion M. Second beam portion BR 2 which is the other of the pair of second beam portions is located adjacent to the right side, in the X direction in FIGS. 1, 2, and 3 , of first beam portion BR 1 , i.e., located away from reflective mirror portion M.

Reflective mirror portion M, the pair of first beam portions BL 1 , BR 1 , and the pair of second beam portions BL 2 , BR 2 are each made up of a beam 11 , a lower electrode 12 , a piezoelectric film 13 , and an upper electrode 14 . A description is given first of a manner in which beam 11 , lower electrode 12 , piezoelectric film 13 , and upper electrode 14 are arranged.

Beam 11 is supported by a left end EL and a right end ER that are respectively a left side end and a right side end in the X direction in FIGS. 1, 2 and 3 , and extends linearly in the X direction between left end EL and right end ER. Herein, beam 11 in reflective mirror portion M is a reflective mirror 11 M, respective portions of beam 11 in the pair of first beam portions BL 1 , BR 1 are first beams 11 BL 1 , 11 BR 1 , and respective portions of beam 11 in the pair of second beam portions BL 2 , BR 2 are second beams 11 BL 2 , 11 BR 2 . Beam 11 is therefore made up of reflective mirror 11 M, a pair of first beams 11 BL 1 , 11 BR 1 , and a pair of second beams 11 BL 2 , 11 BR 2 .

Reflective mirror 11 M of reflective mirror portion M is formed as a reflector capable of reflecting incident light, like a common mirror. Lower electrode 12 is a thin-film electrode formed on a main surface of each of the pair of first beams 11 BL 1 , 11 BR 1 , and has a rectangular shape as seen in plan view, for example. The main surface of each of first beams 11 BL 1 , 11 BR 1 is the surface of first beams 11 BL 1 , 11 BR 1 that extends along the XY plane and faces upward along the Z direction. Lower electrode 12 on the main surface of first beam 11 BL 1 is a lower electrode 12 BL 1 , and lower electrode 12 on the main surface of first beam 11 BR 1 is a lower electrode 12 BR 1 . Lower electrode 12 thus includes lower electrode 12 BL 1 of first beam portion BL 1 and lower electrode 12 BR 1 of second first beam portion BR 1 .

Piezoelectric film 13 is a thin-film member formed on the main surfaces of lower electrodes 12 BL 1 , 12 BR 1 that face upward along the Z direction and formed to overlap lower electrodes 12 BL 1 , 12 BR 1 , and has a rectangular shape as seen in plan view, for example. Piezoelectric film 13 on the main surface of lower electrode 12 BL 1 is piezoelectric films 13 BL 1 , 13 BL 2 . Piezoelectric film 13 BL 1 is located at a shorter distance from reflective mirror portion M relative to the distance between piezoelectric film 13 BL 2 and reflective minor portion M, and piezoelectric film 13 BL 1 and piezoelectric film 13 BL 2 are spaced from each other. Piezoelectric film 13 on the main surface of lower electrode 12 BR 1 is piezoelectric films 13 BR 1 , 13 BR 2 . Piezoelectric film 13 BR 1 is located at a shorter distance from reflective mirror portion M relative to the distance between piezoelectric film 13 BR 2 and reflective mirror portion M, and piezoelectric films 13 BR 1 and 13 BR 2 are spaced from each other. Piezoelectric film 13 thus includes a pair of piezoelectric films 13 BL 1 , 13 BL 2 of first beam portion BL 1 , and a pair of piezoelectric films 13 BR 1 , 13 BR 2 of first beam portion BR 1 .

Upper electrode 14 is a thin-film electrode formed to overlap the main surfaces of piezoelectric films 13 BL 1 , 13 BL 2 , 13 BR 1 , 13 BR 2 that face upward along the Z direction, and have a rectangular shape as seen in plan view, for example. Upper electrode 14 formed directly on piezoelectric films 13 BL 1 , 13 BL 2 , 13 BR 1 , 13 BR 2 is upper electrodes 14 BL 1 , 14 BL 2 , 14 BR 1 , 14 BR 2 . Upper electrode 14 BL 1 and upper electrode 14 BL 2 are spaced from each other, and upper electrode 14 BR 1 and upper electrode 14 BR 2 are spaced from each other. Upper electrode 14 thus includes a pair of upper electrodes 14 BL 1 , 14 BL 2 of first beam portion BL 1 and a pair of upper electrodes 14 BR 1 , 14 BR 2 of first beam portion BR 1 .

A reflective film 14 M is formed on the main surface, which faces upward along the Z direction, of reflective mirror 11 M corresponding to beam 11 in reflective mirror portion M. Reflective film 14 M is the same layer and made from the same material and at the same time as upper electrodes 14 BL 1 , 14 BL 2 , 14 BR 1 , 14 BR 2 . Reflective film 14 M is formed on the main surface, which faces upward along the Z direction, of reflective mirror 11 M, in order to enhance the function of reflecting incident light, as a mirror of reflective mirror 11 M.

A description is now given, from a different point of view from the above, of the configuration of reflective mirror portion M, the pair of first beam portions BL 1 , BR 1 , and the pair of second beam portions BL 2 , BR 2 .

Referring again to FIGS. 2 and 3 , in reflective mirror portion M disposed in a central portion with respect to the X direction, reflective mirror 11 M as a part of beam 11 and reflective film 14 M on the main surface of reflective mirror 11 M are stacked in this order. Reflective mirror 11 M and reflective film 14 M have a circular shape as seen in plan view, for example.

First beam portion BL 1 is disposed on the left side, in the X direction, of reflective mirror portion M. First beam 11 BL 1 is thus adjacent to reflective mirror 11 M in one direction from reflective mirror 11 M, i.e., adjacent to the left side, in the X direction, of reflective mirror 11 M, as seen in plan view. In first beam portion BL 1 , first beam 11 BL 1 as a part of beam 11 , lower electrode 12 BL 1 , a pair of piezoelectric films 13 BL 1 , 13 BL 2 , and a pair of upper electrodes 14 BL 1 , 14 BL 2 are stacked in this order. Both piezoelectric film 13 BL 1 and piezoelectric film 13 BL 2 are stacked on lower electrode 12 BL 1 . On piezoelectric film 13 BL 1 , upper electrode 14 BL 1 having a shape and an area substantially identical to those of piezoelectric film 13 BL 1 is stacked. On piezoelectric film 13 BL 2 , upper electrode 14 BL 2 having a shape and an area substantially identical to those of piezoelectric film 13 BL 2 are stacked. The area of upper electrode 14 BL 1 / 14 BL 2 is therefore approximately a half of the area of lower electrode 12 BL 1 .

First beam portion BR 1 is disposed on the right side, in the X direction, of reflective mirror portion M. First beam 11 BR 1 is thus adjacent to reflective mirror 11 M in the other opposite direction from reflective mirror 11 M, i.e., adjacent to the right side, in the X direction, of reflective mirror 11 M, as seen in plan view. In first beam portion BR 1 , first beam 11 BR 1 as a part of beam 11 , lower electrode 12 BR 1 , a pair of piezoelectric films 13 BR 1 , 13 BR 2 , and a pair of upper electrodes 14 BR 1 , 14 BR 2 are stacked in this order. The relation in shape and area between electrodes for example is similar to that between corresponding electrodes in first beam portion BL 1 . In this way, a pair of beam portions adjacent to reflective mirror 11 M that are specifically first beam portion BL 1 and first beam portion BR 1 as well as second beam portion BL 2 and second beam portion BR 2 are arranged, with reflective mirror 11 M sandwiched between the beam portions in the X direction as seen in plan view.

In this way, a pair of first beams 11 BL 1 , 11 BR 1 is formed. Over the main surface of first beam 11 BL 1 , upper electrodes 14 BL 1 , 14 BL 2 as a plurality of electrodes are spaced from each other with piezoelectric films 13 BL 1 , 13 BL 2 as a piezoelectric material interposed therebetween. While two upper electrodes 14 BL 1 , 14 BL 2 are formed as a plurality of electrodes, the number of the electrodes is not limited to this and three or more upper electrodes 14 may be formed. Likewise, over the main surface of first beam 11 BR 1 , upper electrodes 14 BR 1 , 14 BR 2 as a plurality of electrodes are spaced from each other with piezoelectric films 13 BR 1 , 13 BR 2 as a piezoelectric material interposed therebetween. Over first beam 11 BR 1 , three or more upper electrodes 14 may be formed.

Second beam portion BL 2 is disposed on the left side of first beam portion BL 1 in the X direction, and second beam portion BR 2 is disposed on the right side of first beam portion BR 1 in the X direction. Accordingly, second beams 11 BL 2 , 11 BR 2 are adjacent to first beams 11 BL 1 , 11 BR 1 respectively and located away from reflective mirror 11 M as seen in plan view. Specifically, second beam 11 BL 2 is located on the left side of first beam 11 BL 1 away from reflective mirror portion M in the X direction, and second beam 11 BR 2 is located on the right side of first beam 11 BR 1 away from reflective mirror portion M in the X direction.

Thus, the pair of beam portions adjacent to reflective mirror 11 M includes the pair of first beams 11 BL 1 , 11 BR 1 and the pair of second beams 11 BL 2 , 11 BR 2 . First beams 11 BL 1 , 11 BR 1 are directly adjacent to reflective mirror 11 M to sandwich reflective mirror 11 M between the first beams. Second beams 11 BL 2 , 11 BR 2 are coupled to the opposite sides, to reflective mirror 11 M, of first beams 11 BL 1 , 11 BR 1 .

Beam 11 is usually formed as a single unit into which reflective mirror 11 M, the pair of first beams 11 BL 1 , 11 BR 1 , and the pair of second beams 11 BL 2 , 11 BR 2 are all integrated, and beam 11 is formed of a single member. The embodiment, however, is not limited to this. Specifically, “first beam 11 BL 1 adjacent to reflective mirror 11 M in one direction from reflective mirror 11 M as seen in plan view” described herein may be reflective mirror 11 M and its adjacent first beam 11 BL 1 that are formed either as a single unit or as separate beams 11 connected to each other. The same is applied to “first beam 11 BR 1 adjacent to reflective mirror 11 M in the other direction from reflective mirror 11 M as seen in plan view.”

Second beam portion BL 2 is formed of second beam 11 BL 2 as a part of beam 11 . Second beam portion BR 2 is formed of second beam 11 BR 2 as a part of beam 11 . Referring to FIG. 4 , preferably second beam 11 BL 2 has an H shape as seen in plan view, in which a central portion of second beam 11 BL 2 in the X direction, which is a part of second beam 11 BL 2 , is narrower than the remaining portion to have a smaller width in the Y direction, for example. The shape of second beam 11 BL 2 , however, is not limited to this. For example, referring to FIG. 5 , second beam 11 BL 2 may be shaped to have two cantilevers extending in the negative Y direction as seen in plan view. Specifically, a pair of cantilevers on one side and the other side in the X direction of second beam 11 BL 2 extends to protrude in the negative Y direction from the remaining portion of second beam 11 BL 2 . Alternatively, referring to FIG. 6 , second beam 11 BL 2 may be shaped to have two cantilevers in the positive Y direction and two cantilevers in the negative Y direction so that a portion of second beam 11 BL 2 continuing in the X direction from first beam 11 BL 1 is located between the cantilevers in the positive Y direction and the cantilevers in the negative Y direction as seen in plan view. The shapes shown in FIGS. 4 to 6 are applied not only to second beam 11 BR 1 but also to second beam 11 BR 2 .

Upper electrodes 14 BL 1 , 14 BL 2 in FIG. 4 each have a rectangular shape extending in the X direction as seen in plan view. The shape as seen in plan view of upper electrodes 14 BL 1 , 14 BL 2 , however, is not limited to this. For example, referring to FIG. 7 , each of upper electrodes 14 BL 1 , 14 BL 2 may be shaped so that it extends generally in the X direction in which beam 11 extends, and is bent to extend back and forth multiple times along the Y direction, as seen in plan view. In this way, stress in the longitudinal direction of beam 11 , namely X direction, generated in lower electrode 12 and upper electrode 14 when beam 11 is deformed, can be alleviated, and thus breakage due to fatigue of the metal material can be prevented. This contributes to reliable operation of mirror driving apparatus 100 . This is applied not only to upper electrodes 14 BL 1 , 14 BL 2 but also to upper electrodes 14 BR 1 , 14 BR 2 .

Left end EL and right end ER are disposed respectively at the left end and the right end of the entire mirror driving apparatus 100 in the X direction. Left end EL and right end ER act as fixing portions on the opposite ends in the X direction for fixing the whole mirror driving apparatus 100 made up of parts including beam 11 . Left end EL is adjacent to second beam portion BL 2 (second beam 11 BL 2 ) and opposite to reflective mirror 11 M in the X direction, and right end ER is adjacent to second beam portion BR 2 (second beam 11 BR 2 ) and opposite to reflective mirror 11 M in the X direction. Although not shown specifically in FIGS. 2 to 4 , each of left end EL and right end ER may be formed to include a part of the region of beam 11 (i.e., formed as a part of a single unit including first and second beams 11 BL 1 , 11 BL 2 for example), or formed as a separate member from beam 11 for example.

In mirror driving apparatus 100 , each of the pair of first beams 11 BL 1 , 11 BR 1 is displaceable crosswise to the main surface which extends along the XY plane and on which lower electrode 12 , piezoelectric film 13 , and upper electrode 14 are stacked, namely displaceable in the Z direction. In other words, each of first beams 11 BL 1 and 11 BR 1 is deformable in the XZ plane. Moreover, one of first beams 11 BL 1 and 11 BR 1 can be displaced upward along the Z direction while the other can be displaced downward along the Z direction. In other words, first beams 11 BL 1 and 11 BR 1 can be displaced in respective directions different from each other along the Z direction crossing the main surface which extends along the XY plane and on which upper electrode 14 is disposed. Specifically, first beams 11 BL 1 and 11 BR 1 can be displaced in opposite directions along the Z direction crossing the main surface. For example, first beam 11 BL 1 can be displaced upward along the Z direction while first beam 11 BR 1 can be displaced downward along the Z direction.

In contrast, each of the pair of second beams 11 BL 2 , 11 BR 2 is displaceable in the direction connecting the pair of first beams 11 BL 1 , 11 BR 1 and the pair of second beams 11 BL 2 , 11 BR 2 , along the main surface of second beams 11 BL 2 , 11 BR 2 , i.e., displaceable in the X direction. In other words, second beams 11 BL 2 , 11 BR 2 are not intended to be displaceable in the Z direction (except for slight shift due to error).

At first boundary portions CL 1 , CR 1 , reflective mirror 11 M is directly adjacent to first beams 11 BL 1 , 11 BR 1 respectively as seen in plan view. “Adjacent” herein means that reflective mirror 11 M and first beams 11 BL 1 , 11 BR 1 may be formed as a single beam 11 , or may be separate parts of beam 11 that are connected together, as mentioned above. “Directly adjacent” herein means that reflective mirror 11 M and first beam 11 BL 1 / 11 BR 1 are arranged continuously with no part interposed therebetween, so that they are located directly side by side.

First boundary portions CL 1 , CR 1 are displaceable in the direction crossing the main surface on which elements such as piezoelectric films 13 BL 1 , 13 BL 2 of first beams 11 BL 1 , 11 BR 1 are formed, i.e., displaceable in the Z direction. In other words, first boundary portions CL 1 , CR 1 are displaceable following displacement of the pair of first beams 11 BL 1 , 11 BR 1 .

Second boundary portion portions CL 2 , CR 2 which forms form the boundary between first beam 11 BL 1 / 11 BR 1 and second beam 11 BL 2 / 11 BR 2 adjacent to first beam 11 BL 1 / 11 BR 1 , are displaceable in the direction connecting first beams 11 BL 1 , 11 BR 1 and second beams 11 BL 2 , 11 BR 2 , along the main surface of second beams 11 BL 2 , 11 BR 2 , i.e., displaceable in the X direction. In other words, second boundary portion CL 2 , CR 2 are not intended to be displaceable in the Z direction (except for slight shift due to error).

A description is now given of respective materials for the members of mirror driving apparatus 100 and how they are connected electrically.

Beam 11 is made of single-crystal silicon without electrical conductivity, for example. Beam 11 may be any elastic material that may be flexed as a result of stretch/contraction of piezoelectric film 13 caused by application of an electric field. Lower electrode 12 is formed of a platinum thin film, for example. Platinum is suitable as a material for a base on which the material for piezoelectric film 13 is deposited. Piezoelectric film 13 is made of lead zirconate titanate (PZT) as a piezoelectric material. Upper electrode 14 and reflective film 14 M are formed of a gold thin film. Gold exhibits high reflectivity for light. Gold is therefore suitable as a material for reflective film 14 M for further increasing the reflectivity of reflective mirror 11 M for light. The materials for lower electrode 12 and upper electrode 14 are not limited to the above-described ones, and may be any material allowing voltage to be applied to piezoelectric film 13 .

Lower electrode 12 BL 1 is electrically insulated from upper electrodes 14 BL 1 , 14 BL 2 by piezoelectric films 13 BL 1 , 13 BL 2 located therebetween in the direction in which they are stacked. Lower electrode 12 BR 1 is also electrically insulated from upper electrodes 14 BR 1 , 14 BR 2 by piezoelectric films 13 BR 1 , 13 BR 2 located therebetween in the direction in which they are stacked. While electrical interconnection from each electrode is not shown in FIGS. 2 to 4 , each electrode can be electrically connected to a power source external to mirror driving apparatus 100 . Although not shown specifically in FIGS. 2 to 4 , lower electrode 12 BL 1 is electrically connected to lower electrode 12 BR 1 by an external power source connected by leads, and the potential of these lower electrodes 12 BL 1 , 12 BR 1 is a reference potential.

Lower electrode 12 BL 1 and lower electrode 12 BR 1 may be electrically insulated from each other, or may be electrically connected to each other.

A description is now given of a method for manufacturing above-described mirror driving apparatus 100 with reference to FIGS. 8 to 14 .

Referring to FIG. 8 , an SOI (Silicon on Insulator) substrate 20 is prepared in which a silicon layer 10 made of single-crystal silicon, a silicon oxide film layer 15 formed of a silicon oxide film, and a silicon layer 11 S made of single-crystal silicon, for example, are stacked in this order.

Referring to FIG. 9 , lower electrode 12 , specifically a thin-film pattern of lower electrodes 12 BL 1 , 12 BR 1 , is formed by the common photolithography technique (deposition and patterning) and etching on the main surface of silicon layer 11 S which is the uppermost layer, in the Z direction, of SOI substrate 20 . The main surface of silicon layer 11 S is a surface opposite to the surface thereof facing silicon oxide film layer 15 , i.e., the main surface is a surface facing upward. Lower electrodes 12 BL 1 , 12 BR 1 are formed in a region which is to form first beam portion BL 1 and a region which is to form first beam portion BR 1 . Accordingly, first beam portions BL 1 , BR 1 are formed. A central portion, in the X direction, of silicon layer 11 S of first beam portions BL 1 , BR 2 are formed as reflective mirror 11 M and defined as a region to form reflective mirror portion M. In other words, the process shown in FIGS. 8 and 9 forms reflective mirror 11 M capable of reflecting incident light, and first beams 11 BL 1 , 11 BR 1 adjacent to reflective mirror 11 M in one direction from reflective mirror 11 M and the other direction therefrom, respectively.

Referring to FIG. 10 , on the main surface, which faces upward along the Z direction, of lower electrodes 12 BL 1 , 12 BR 1 , piezoelectric film 13 , specifically a thin-film pattern of piezoelectric films 13 BL 1 , 13 BL 2 , 13 BR 1 , 13 BR 2 is formed by the common photolithography technique and etching.

Referring to FIG. 11 , a thin-film pattern of upper electrodes 14 BL 1 , 14 BL 2 , 14 BR 1 , 14 BR 2 of upper electrode 14 is formed to completely match and overlap the pattern of piezoelectric films 13 BL 1 , 13 BL 2 , 13 BR 1 , 13 BR 2 , respectively, as seen in plan view. Accordingly, on each of respective main surfaces of the pair of first beams 11 BL 1 , 11 BR 1 , a plurality of (two, for example) electrodes 14 BL 1 , 14 BL 2 / 14 BR 1 , 14 BR 2 are formed to be spaced from each other with piezoelectric film 13 interposed.

At the same time, particularly in a region to form reflective mirror portion M, a thin-film pattern for reflective film 14 M which is the same layer as upper electrode 14 BL 1 for example is formed on silicon layer 11 S. Accordingly, a part of beam 11 directly below the region where reflective film 14 M is formed is a part where reflective mirror 11 M is formed. Reflective mirror portion M is thus formed.

Referring to FIG. 12 , SOI substrate 20 , particularly silicon layer 11 S is partially patterned and etched to form the shape of second beams 11 BL 2 , 11 BR 2 of second beam portions BL 2 , BR 2 as shown in FIG. 4 , for example. Preferably, the partial etching of silicon layer 11 S is accomplished by inductive coupling type reactive ion etching called ICP-RIE (Inductive Coupled Plasma Reactive Ion Etching), for example. Second beam portions BL 2 , BR 2 are formed as regions where the shape of second beams 11 BL 2 , 11 BR 2 are formed. Second beam 11 BL 2 / 11 BR 2 is adjacent to first beam 11 BL 1 / 11 BR 1 and located opposite to reflective mirror 11 M as seen in plan view. Beam 11 also includes first boundary portions CL 1 , CR 1 and second boundary portions CL 2 , CR 2 as boundaries between corresponding regions.

As described above in connection with the process steps, respective ranges of regions to form first beam portions BL 1 , BR 1 , the region to form reflective mirror portion M, and the regions to form second beam portions BL 2 , BR 2 are clearly defined. Accordingly, reflective mirror portion M, first beam portions BL 1 , BR 1 , and second beam portions BL 2 , BR 2 are formed. In other words, a pair of beam portions adjacent to reflective mirror 11 M is formed so that reflective mirror 11 M is located between these beam portions in the X direction as seen in plan view, i.e., first beam portion BL 1 and first beam portion BR 1 as well as second beam portion BL 2 and second beam portion BR 2 are formed. The pair of beam portions includes first beams 11 BL 1 , 11 BR 1 located directly adjacent to reflective mirror 11 M so that reflective mirror 11 M is sandwiched therebetween, and second beams 11 BL 2 , 11 BR 2 located opposite to reflective mirror 11 M with respect to first beams 11 BL 1 , 11 BR 1 . Silicon layer 11 S as an uppermost layer of the SOI substrate is formed as beam 11 . On the outside in the X direction, i.e., on respective ends in the X direction, of second beam portions BL 2 , BR 2 , left end EL and right end RE may be formed. In FIGS. 12 to 14 , left end EL and right end ER are formed.

Referring to FIG. 13 , silicon layer 10 of reflective mirror portion M, first beam portions BL 1 , BR 1 , and second beam portions BL 2 , BR 2 is removed by ICP-RIE, for example. Accordingly, beam 11 is entirely supported by silicon layer 10 of left end EL and right end ER, for example.

Referring to FIG. 14 , silicon oxide film layer 15 of reflective mirror portion M, first beam portions BL 1 , BR 1 , and second beam portions BL 2 , BR 2 is removed by dry etching using tetrafluoromethane CF 4 , for example.

As shown in FIG. 2 , the final shape of reflective mirror portion M including reflective mirror 11 M is a circular shape for example as seen in plan view, while the final shape of other portions such as first and second beam portions BL 1 , BL 2 is an elongate shape as seen in plan view. Therefore, in the steps of FIGS. 12, 13, and 14 for example, unnecessary regions of SOI substrate 20 are removed to form the shape as seen in plan view as shown in FIG. 2 . In this way, mirror driving apparatus 100 shown in FIGS. 2 to 4 is formed.

As seen from the above, mirror driving apparatus 100 in the present embodiment can be formed by applying the so-called semiconductor microfabrication technology or MEMS device technology in which deposition, patterning, and etching for example are repeatedly performed on a silicon substrate, for example. Using the above-described manufacturing method, all of reflective mirror 11 M of reflective mirror portion M, first beams 11 BL 1 , 11 BR 1 of first beam portions BL 1 , BR 1 , and second beams 11 BL 2 , 11 BR 2 of second beam portions BL 2 , BR 2 of mirror driving apparatus 100 in the present embodiment are formed as a single beam 11 .

In the following, a description is given of an operation of and a method for controlling mirror driving apparatus 100 in the present embodiment, and then a description is given of the function and effect of the present embodiment. Referring first to FIGS. 15 to 17 , an operational principle of a piezoelectric element as an element of mirror driving apparatus 100 in the present embodiment is described.

Referring to FIG. 15 , FIGS. 15 to 17 mentioned below show an extracted region of first beam portion BL 1 in which about a right half, in the X direction, of first beam 11 BL 1 and lower electrode 12 BL 1 , as well as piezoelectric film 13 BL 1 and upper electrode 14 BL 1 located directly above them are stacked, and an operational principle of deformation of this region for example is described.

In first beam portion BL 1 of mirror driving apparatus 100 , lower electrode 12 BL 1 and upper electrode 14 BL 1 are disposed opposite to each other with respect to the Z direction with piezoelectric film 13 BL 1 interposed therebetween to form a piezoelectric element. Likewise, a piezoelectric element in which lower electrode 12 BL 1 and upper electrode 14 BL 2 are opposite to each other with piezoelectric film 13 BL 2 interposed therebetween, a piezoelectric element in which lower electrode 12 BR 1 and upper electrode 14 BR 1 are opposite to each other with piezoelectric film 13 BR 1 interposed therebetween, and a piezoelectric element in which lower electrode 12 BR 1 and upper electrode 14 BR 2 are opposite to each other with piezoelectric film 13 BR 2 interposed therebetween, are formed.

For these piezoelectric elements each, a voltage can be applied between a pair of electrodes 12 and 14 sandwiching piezoelectric film 13 in the top-bottom direction to thereby apply an electric field to piezoelectric film 13 . Therefore, a voltage applied between lower electrode 12 BL 1 and upper electrode 14 BL 1 in FIG. 15 causes an electric field to be applied, in the film thickness direction, namely Z direction, to piezoelectric film 13 BL 1 sandwiched between these electrodes. Accordingly, depending on the direction of the electric field, piezoelectric film 13 BL 1 stretches/contracts in the direction along the main surface, i.e., XY plane. Piezoelectric film 13 BL 1 thus deforms to warp a part of first beam 11 BL 1 over which piezoelectric film 13 BL 1 is deposited.

Referring to FIG. 16 , when a positive voltage is applied to upper electrode 14 BL 1 and a negative voltage is applied to lower electrode 12 BL 1 for example, a downward electric field along the Z direction is applied to piezoelectric film 13 BL 1 between these electrodes. At this time, if piezoelectric film 13 BL 1 is deformed to stretch along the main surface along the XY plane, first beam 11 BL 1 located directly below the piezoelectric film is warped in a convex shape protruding upward along the Z direction. Consequently the stack of the piezoelectric element is entirely warped in a convex shape protruding upward along the Z direction.

Referring to FIG. 17 , when a negative voltage is applied to upper electrode 14 BL 1 and a positive voltage is applied to lower electrode 12 BL 1 for example, an upward electric field along the Z direction is applied to piezoelectric film 13 BL 1 between these electrodes. At this time, if piezoelectric film 13 BL 1 is deformed to contract along the main surface along the XY plane, first beam 11 BL 1 located directly below the piezoelectric film is warped in a convex shape protruding downward along the Z direction. Consequently the stack of the piezoelectric element is entirely warped in a convex shape protruding downward along the Z direction. As seen from the above, depending on the direction of the electric field applied to piezoelectric film 13 of the piezoelectric element, one of stretch and contraction occurs. It is therefore possible to change the direction of the warp of piezoelectric film 13 by changing the polarity of the voltage (positive or negative) applied to upper electrode 14 , and to change the curvature of the warp of piezoelectric film 13 by changing the magnitude of the voltage applied to upper electrode 14 . In other words, depending on the polarity (positive/negative) and the magnitude of the voltage between upper electrode 14 and lower electrode 12 , warp of beam 11 directly below them can be controlled.

Such a nature of deformation of the piezoelectric element is used to control the inclination angle and the displacement for example of reflective mirror portion M including reflective mirror 11 M of mirror driving apparatus 100 . Referring next to FIGS. 18 to 21 , a method for controlling mirror driving apparatus 100 using the piezoelectric elements is described.

Regarding FIGS. 18 to 20 , beam 11 in each region such as first beam portion BL 1 is considered, and it is supposed that basically beam 11 is deformed following deformation of piezoelectric film 13 deposited directly above beam 11 . Referring to FIG. 18 , both the region in which upper electrode 14 BL 1 is located and its adjacent region in which upper electrode 14 BL 2 is located in first beam portion BL 1 , are considered.

When mirror driving apparatus 100 is actually driven, a voltage of a certain polarity is applied to upper electrode 14 BL 1 as a first electrode located relatively closer to reflective mirror 11 M, out of a plurality of (two) upper electrodes 14 BL 1 , 14 BL 2 arranged in first beam portion BL 1 , and a voltage of the opposite polarity is applied to upper electrode 14 BL 2 as a second electrode located adjacent to upper electrode 14 BL 1 . Specifically, the potential of lower electrode 12 BL 1 (see FIG. 15 ) is used as a reference potential, a positive voltage +V 1 is applied to upper electrode 14 BL 1 , and a negative voltage −V 2 opposite in polarity to upper electrode 14 BL 1 is applied to upper electrode 14 BL 2 , where |V 1 |>|V 2 |.

As shown schematically in FIG. 18 , in a part of the piezoelectric element including upper electrode 14 BL 1 , first beam 11 BL 1 is deformed to protrude upward along the Z direction, while in a part of the piezoelectric element including upper electrode 14 BL 2 , first beam 11 BL 1 is deformed to protrude downward along the Z direction. The part of the piezoelectric element including upper electrode 14 BL 1 has radius of curvature R 1 , the part of the piezoelectric element including upper electrode 14 BL 2 has radius of curvature R 2 , and R 2 >R 1 holds. The warp of the part of first beam 11 BL 1 directly below upper electrode 14 BL 1 is therefore larger than the warp of the part of first beam 11 BL 1 directly below upper electrode 14 BL 2 .

The length in the X direction of upper electrode 14 BL 1 is substantially identical to that of upper electrode 14 BL 2 . There is thus an inversely proportional relation between radius of curvature R 1 , R 2 and central angle θ 1 , θ 2 of the arc formed in the X direction due to the warp of beam 11 .

Because radius of curvature R 1 is smaller than radius of curvature R 2 , the right end in the X direction of beam 11 corresponding to upper electrode 14 BL 1 is inclined downward along the Z direction at the coordinate position (Z>0) higher than a reference position (Z=0) in the Z direction in FIG. 18 . First boundary portion CL 1 located at the right end in the X direction of the beam corresponding to upper electrode 14 BL 1 is adjacent to reflective mirror 11 M of reflective mirror portion M, and therefore, the right side in the X direction of reflective mirror 11 M is rotationally displaced to be inclined downward along the Z direction, following the aforementioned inclination of beam 11 at first boundary portion CL 1 . Thus, deformation of piezoelectric film 13 caused by a voltage applied to the piezoelectric element in mirror driving apparatus 100 is used to incline reflective mirror 11 M.

FIG. 18 considers only first beam 11 BL 1 of first beam portion BL 1 . Referring next to FIG. 19 , a description is given of application of a voltage to the piezoelectric element and deformation inclination of each region in the case where not only first beam 11 BL 1 but also reflective mirror portion M, first beam portion BR 1 and second beam portions BL 2 , BR 2 of mirror driving apparatus 100 are considered.

Referring to FIG. 19 , respective voltages of the same absolute values and opposite polarities are applied to upper electrode 14 BL 1 , which is a first electrode for first beam 11 BL 1 of the pair of first beams 11 BL 1 , 11 BR 1 , and upper electrode 14 BR 1 , which is a first electrode for the opposite first beam 11 BR 1 . Respective voltages of the same absolute values and opposite polarities are also applied to upper electrode 14 BL 2 , which is a second electrode for first beam 11 BL 1 of the pair of first beams 11 BL 1 , 11 BR 1 , and upper electrode 14 BR 2 , which is a second electrode for the opposite first beam 11 BR 1 . Specifically, positive voltage +V 1 is applied to upper electrode 14 BL 1 while negative voltage −V 1 of the same absolute value and the opposite polarity is applied to upper electrode 14 BR 1 , similarly to FIG. 18 . Negative voltage −V 2 is applied to upper electrode 14 BL 2 while positive voltage +V 2 of the same absolute value and the opposite polarity is applied to upper electrode 14 BR 2 , similarly to FIG. 18 .

At this time, as shown schematically in FIG. 19 , first beam 11 BR 1 corresponding to the part of the piezoelectric element including upper electrode 14 BR 1 deforms in a convex shape protruding downward along the Z direction, while first beam 11 BR 1 corresponding to the part of the piezoelectric element including upper electrode 14 BR 2 deforms in a convex shape protruding upward along the Z direction. The part of the piezoelectric element including upper electrode 14 BR 2 has radius of curvature R 1 , the part of the piezoelectric element including upper electrode 14 BL 2 has radius of curvature R 2 , and R 2 >R 1 holds, like first beam 11 BL 1 . Therefore, the left end in the X direction of beam 11 corresponding to upper electrode 14 BR 1 is inclined upward along the Z direction at the coordinate position (Z<0) lower than the reference position (Z=0) in the Z direction in FIG. 19 . First boundary portion CR 1 located at the left end in the X direction of the beam corresponding to upper electrode 14 BR 1 is adjacent to reflective mirror 11 M of reflective mirror portion M, and therefore, the left side in the X direction of reflective mirror 11 M is rotationally displaced to be inclined upward along the Z direction, following the aforementioned inclination of beam 11 at first boundary portion CR 1 .

At second boundary portion CL 2 between first beam 11 BL 1 and second beam 11 BL 2 and second boundary portion CR 2 between first beam 11 BR 1 and second beam 11 BR 2 , beam 11 is located at the reference coordinate position (Z=0), and second beams 11 BL 2 , 11 BR 2 are entirely maintained at the Z=0 position.

Thus, the deformation of beam 11 in FIG. 19 as a whole has point symmetry with respect to Y coordinate 0 of the Y axis at the center of reflective mirror 11 M in the X direction. Beam 11 in FIG. 19 corresponding to reflective mirror portion M, first beam portions BL 1 , BR 1 , and first boundary portions CL 1 , CR 1 is displaceable in the Z direction, while beam 11 corresponding to second boundary portions CL 2 , CR 2 and second beam portions BL 2 , BR 2 is located at the Z=0 position and is not displaced in the Z direction.

In the case where beam 11 of reflective mirror portion M and first beam portions BL 1 , BR 1 is formed as a single unit as shown in FIGS. 8 to 14 , for example, the process for forming beam 11 can be further simplified. In this case, however, beam 11 is more likely to be affected by stress from other members constituting mirror driving apparatus 100 , as compared with the case where the portions of beam 11 between the aforementioned regions are formed as separate members. If beam 11 is configured to have first boundary portions CL 1 , CR 1 between reflective mirror 11 M and first beams 11 BL 1 , 11 BR 1 that are not displaced in the Z direction but only displaceable in the XY direction, the flatness of reflective mirror 11 M could be deteriorated. This is for the following reason. In the case where first beams 11 BL 1 , 11 BR 1 and first boundary portions CL 1 , CR 1 cannot be shifted in the Z direction by deformation of beam 11 when the piezoelectric element is driven, beam 11 is subjected to moment about the Y axis to cause deformation of reflective mirror 11 M.

In view of the above, mirror driving apparatus 100 of the present embodiment is configured to have a pair of first beams 11 BL 1 , 11 BR 1 that are displaceable in the Z direction crossing the main surface of beam 11 . Likewise, first boundary portions CL 1 , CR 1 are displaceable in the Z direction crossing the main surface of beam 11 . Accordingly, the possibility that beam 11 is subjected to moment about the Y axis as mentioned above to cause deformation of reflective mirror 11 M can be reduced.

First beam 11 BL 1 is displaced upward along the Z direction in FIG. 19 while first beam 11 BR 1 is displaced downward along the Z direction in FIG. 19 . Thus, first beams 11 BL 1 and 11 BR 1 are displaceable in respective directions different from each other (opposite directions) with respect to the Z direction. It is therefore possible to cause both first beams 11 BL 1 and 11 BR 1 to be inclined downward to the right respectively at first boundary portion CL 1 and first boundary portion CR 1 for example as shown in FIG. 19 . Reflective mirror 11 M sandwiched between these first boundary portions CL 1 and CR 1 can thus be kept linear, namely flat in FIG. 19 , and deterioration of the flatness of reflective mirror 11 M can be suppressed.

If the whole of beam 11 including second beams 11 BL 2 , 11 BR 2 for example is displaceable in the Z direction, there is disadvantageously no region for cancelling displacement in the X direction resulting from displacement in the Z direction of beam 11 of first beam 11 BL 1 for example. In view of this, each of the pair of second beams 11 BL 2 , 11 BR 2 of mirror driving apparatus 100 in the present embodiment is displaceable in the direction connecting the pair of first beams 11 BL 1 , 11 BR 1 and the pair of second beams 11 BL 2 , 11 BR 2 , along the main surface of second beams 11 BL 2 , 11 BR 2 , namely displaceable in the X direction. Second boundary portions CL 2 , CR 2 are also displaceable in the X direction. These regions are hardly displaced in the Z direction. Therefore, a change in length in the X direction resultant from displacement of first beams 11 BL 1 , 11 BR 1 in the Z direction can be absorbed to be cancelled.

Second beam 11 BL 2 / 11 BR 2 displaceable in the X direction and non-displaceable in the Z direction is located adjacent to first beam 11 BL 1 / 11 BR 1 and opposite to reflective mirror 11 M. In other words, second beam 11 BL 2 / 11 BR 2 is located at a longer distance from reflective mirror 11 M relative to the distance between first beam 11 BL 1 / 11 BR 1 and reflective mirror 11 M. The portion displaceable in the X direction (only) is thus located away from reflective mirror 11 M. Therefore, even when second beams 11 BL 2 , 11 BR 2 and second boundary portions CL 2 , CR 2 are displaced in the X direction only, the possibility that beam 11 is affected by this displacement and subjected to moment about the Y axis resulting in deformation of reflective mirror 11 M can be reduced.

First beams 11 BL 1 , 11 BR 1 and first boundary portions CL 1 , CR 1 are displaceable in the Z direction while second beams 11 BL 2 , 11 BR 2 and second boundary portions CL 2 , CR 2 are displaceable in the X direction (only) in the manner show in FIG. 19 as described above. This is because the inflection direction is controlled by voltage application to the piezoelectric elements. Specifically, referring again to FIG. 19 , respective voltages of the same absolute values and opposite polarities are applied to upper electrode 14 BL 1 of first beam portion BL 1 located relatively closer to reflective mirror 11 M and upper electrode 14 BR 1 of first beam portion BR 1 located relatively closer to reflective mirror 11 M. Accordingly, one of upper electrode 14 BL 1 and upper electrode 14 BR 1 can be deformed in a convex shape protruding upward along the Z direction while the other thereof can be deformed in a convex shape protruding downward along the Z direction, and respective radii of curvature of these electrodes can be made substantially identical to each other. Thus, one of the pair of first boundary portions CL 1 , CR 1 can be deformed at a position higher than Z=0 and the other can be deformed at a position lower than Z=0, so that the displacement has point symmetry with respect to Y=0 and both are inclined downward to the right with respect to the X direction. In this way, reflective mirror 11 M located between first boundary portions CL 1 and CR 1 can be inclined without causing deformation such as curve of the mirror.

Reflective mirror 11 M can be inclined by voltage application to the piezoelectric elements to cause rotational displacement about the Y axis, even when no member supports beam 11 in the Y direction.

In first beam portion BL 1 , respective voltages of opposite polarities are applied to upper electrode 14 BL 1 located relatively closer to reflective mirror 11 M and upper electrode 14 BL 2 , and therefore, one of upper electrode 14 BL 1 and upper electrode 14 BL 2 can be deformed in a convex shape protruding upward along the Z direction and the other can be deformed in a convex shape protruding downward along the Z direction. Beam 11 can be inflexed so that the Z coordinate of second boundary portion CL 2 is 0 even when the Z coordinate of first boundary portion CL 1 is not 0 and beam 11 is inclined with respect to the Z direction. The point of inflection is located at the boundary between upper electrode 14 BL 1 and upper electrode 14 BL 2 where the direction of curve is inverted with respect to the Z direction. In this way, second boundary portion CL 2 and second beam 11 BL 2 located further away from reflective mirror 11 M can be displaced in the X direction (only) while being kept at the Z coordinate 0.

A description is further given of the method for controlling mirror driving apparatus 100 , specifically a control method for more reliably suppressing deterioration of the flatness of reflective mirror 11 M.

Voltage application to upper electrodes 14 BL 1 , 14 BL 2 , 14 BR 1 , 14 BR 2 can be controlled as described above to thereby control the posture of reflective mirror 11 M, specifically the inclination direction and the inclination angle of reflective mirror 11 M. Consideration is now given to inclination of reflective mirror 11 M and inclination of first boundary portion CL 1 between first beam portion BL 1 and reflective mirror 11 M. While the following description is of first boundary portion CL 1 between first beam portion BL 1 and reflective mirror 11 M, basically the same is applied as well to first boundary portion CR 1 between first beam portion BR 1 and reflective mirror 11 M.

FIG. 20 shows first beam portion BL 1 and reflective mirror portion M extracted from FIG. 19 . Referring to FIG. 20 , in order to make zero the stress generated particularly in first boundary portion CL 1 of beam 11 , the following Formula 1 and Formula 2 may be satisfied. Specifically, Z direction coordinate Zb of first boundary portion CL 1 between first beam 11 BL 1 and reflective mirror 11 M, Z direction coordinate Zm of the first boundary portion CL 1 -side end of reflective mirror 11 M, X direction radius r of reflective mirror 11 M, inclination angle θm of reflective mirror 11 M with respect to the X axis, and inclination angle θb of first boundary portion CL 1 of first beam 11 BL 1 with respect to the X axis may satisfy

Zb=Zm=r tan θ m   Formula 1

θ b=θm=θ 1−θ2  Formula 2

where θ 1 in Formula 2 is the central angle of the arc formed by the region overlapping upper electrode 14 BL 1 as seen in plan view, as a result of voltage application to upper electrode 14 BL 1 of first beam portion BL 1 , and corresponds to angle θ 1 in FIG. 18 , and θ 2 in Formula 2 is the central angle of the arc formed by the region overlapping upper electrode 14 BL 2 as seen in plan view, as a result of voltage application to upper electrode 14 BL 2 of first beam portion BL 1 , and corresponds to angle θ 2 in FIG. 18 .

θ 1 and θ 2 satisfying the above-specified relation can be determined to make zero the stress generated in first boundary portion CL 1 . There are, however, multiple solutions for θ 1 and θ 2 satisfying this relation. For the sake of practical application, it is supposed that the following two conditions 1) and 2) are met.

1) The X direction dimension of upper electrode 14 BL 1 is equal to the X direction dimension of upper electrode 14 BL 2 .

2) Angle θ 1 and angle θ 2 have the relation defined by the following Formula 3, i.e., the ratio between angle θ 1 and angle θ 2 is kept at a certain value determined by mirror driving apparatus 100 . Specifically, θ 1 and θ 2 satisfy the relation:

θ1=α·θ2  Formula 3

where α is a constant. An electric field is applied to piezoelectric films 13 BL 1 , 13 BL 2 of the piezoelectric element so as to meet the relation defined by Formula 3.

Referring to FIG. 21 , the horizontal axis of the graph represents the ratio of the mirror radius, i.e., the value of the X direction radius r of reflective mirror 11 M (see FIG. 20 ), to the beam length, particularly the X direction length of first beam 11 BL 1 . The vertical axis of the graph represents the value of coefficient α that minimizes an angle error under a certain condition of the X direction dimension of first beam 11 BL 1 and that of reflective mirror 11 M. More specifically, depending on the ratio of the X direction dimension of reflective mirror 11 M to the X direction dimension of first beam 11 BL 1 in each mirror driving apparatus 100 , the value of coefficient α is determined so that an error amount between Zb and Zm is minimized, i.e., the stress generated in first boundary portion CL 1 is zero. This graph is referenced to determine the value of α.

Central angles θ 1 , θ 2 of respective arcs generated by deformation of first beam portion BL 1 depends on the voltages applied to upper electrodes 14 BL 1 , 14 BL 2 (see FIG. 18 ). Therefore, depending on the ratio of the value of radius r of reflective mirror 11 M to the X direction length of first beam 11 BL 1 represented by the horizontal axis in FIG. 21 , the ratio between applied voltages |V 1 | and |V 2 | in FIG. 18 is set. Accordingly, the stress generated in first boundary portion CL 1 and reflective mirror 11 M can be reduced sufficiently and deterioration of the flatness of reflective mirror 11 M can be suppressed. In other words, first beam 11 BL 1 and reflective mirror 11 M which are adjacent to each other with first boundary portion CL 1 in between can be inclined at the same angles to suppress generation of stress in first boundary portion CL 1 as well as deterioration of the flatness of reflective mirror 11 M.

Once the value of constant α depending on respective dimensions of the relevant members is determined, θb is set. Moreover, the X direction length of first beam 11 BL 1 is determined. Then, the value of θm is determined by Formula 2 and replaced into Formula 1. The value of Zb is determined accordingly. Once θm is determined, the value of Zb can also be determined by replacing θm and the value of r into Formula 1. For example, supposing that inclination angle θm falls in a range of ±10°. The ratio of an error of Zb with respect to Zm is then determined from radius r of reflective mirror 11 M. The determined ratio is 0.2% or less. Specifically, if radius r of reflective mirror 11 M is 500 μm, the error of the Z direction displacement is 0.1 μm or less. Accordingly, in terms of practical application, the error of the value of Zb with respect to Zm is sufficiently small. It is therefore possible to sufficiently reduce the stress generated in first boundary portion CL 1 and reflective mirror 11 M and suppress deterioration of the flatness of reflective mirror 11 M.

In the example shown in FIGS. 18 to 20 , reflective mirror 11 M is inclined downward to the right. The above description, however, is applied as well to reflective mirror 11 M inclined downward to the left.

Other functions and effects of the present embodiment are described one by one in the following. Regarding mirror driving apparatus 100 in the present embodiment, generation of stress in first boundary portions CL 1 , CR 1 and reflective mirror 11 M when the mirror is driven can be suppressed, and therefore, improvement of the stiffness of reflective mirror 11 M for the purpose of suppressing deformation of reflective mirror 11 M is unnecessary.

Mirror driving apparatus 100 having the above-described characteristics can be formed easily by applying the manufacturing method described above and shown in FIGS. 8 to 14 . In particular, from silicon layer 11 S of SOI substrate 20 , beam 11 as a single unit including respective regions of reflective mirror portion M, first beam portion BL 1 , and second beam portion BL 2 can be formed so that these regions are substantially identical to each other in terms of the Z direction thickness. It is therefore unnecessary that only reflective mirror 11 M is formed thicker than other regions of beam 11 , or it is unnecessary to join a separate member which is to form the mirror portion and has a greater thickness. Beam 11 can therefore be formed more easily.

In mirror driving apparatus 100 , piezoelectric film 13 on first beam 11 BL 1 for example is divided into a plurality of (two) piezoelectric films, i.e., piezoelectric film 13 BL 1 and piezoelectric film 13 BL 2 . Piezoelectric film 13 can thus be divided into a plurality of films to alleviate or prevent influence of the polarity of the voltage applied to one of the regions of the divided piezoelectric film of the piezoelectric element on the other region. It is therefore possible to deform each of the regions of the divided piezoelectric film of first beam 11 BL 1 with higher precision, and control the posture of reflective mirror 11 M with higher precision.

A description is given, using FIG. 22 , of a configuration of a mirror driving apparatus in a second example of the present embodiment. Referring to FIG. 22 , basically mirror driving apparatus 101 in the second example of the present embodiment has a similar configuration to that of mirror driving apparatus 100 in the first example, and therefore, the same component as that of mirror driving apparatus 100 is denoted by a similar reference character to that of mirror driving apparatus 100 . As to the features of the second example similar to those of the first example, the description thereof is not repeated herein.

In mirror driving apparatus 101 in FIG. 22 , first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 extend in the circumferential direction of circular reflective mirror 11 M (reflective film 14 M) as seen in plan view. In this respect, the configuration of mirror driving apparatus 101 differs from that of mirror driving apparatus 100 in which first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 extend linearly, i.e., radially in the radial direction of circular reflective mirror 11 M (reflective film 14 M) as seen in plan view.

In mirror driving apparatus 101 , a pair of first beams includes: first beam 11 BL 1 adjacent to reflective mirror 11 M in one direction from reflective mirror 11 M, specifically leftward along the X direction; and first beam 11 BR 1 adjacent to reflective mirror 11 M in the opposite direction from reflective mirror 11 M, specifically rightward along the X direction. Second beam 11 BL 2 is adjacent to first beam 11 BL 1 and opposite to reflective mirror 11 M with respect to first beam 11 BL 1 , and second beam 11 BR 2 is adjacent to first beam 11 BR 1 and opposite to reflective mirror 11 M with respect to first beam 11 BR 1 . On the main surface of first beam 11 BL 1 , upper electrodes 14 BL 1 , 14 BL 2 are spaced from each other and piezoelectric films (not shown) are interposed between the upper electrodes and the main surface. On the main surface of first beam 11 BR 1 , upper electrodes 14 BR 1 , 14 BR 2 are spaced from each other and piezoelectric films (not shown) are interposed between the upper electrodes and the main surface. Elements such as upper electrodes 14 BL 1 , 14 BL 2 also extend in the circumferential direction of reflective mirror 11 M.

The basic operation of mirror driving apparatus 101 can be considered as similar to that of mirror driving apparatus 100 . Specifically, first beams 11 BL 1 , 11 BR 1 are displaceable in respective directions different from each other (opposite to each other) along the Z direction crossing the main surface which extends along the XY plane and over which upper electrode 14 is deposited. In contrast, the pair of second beams 11 BL 2 , 11 BR 2 is displaceable in the direction connecting the pair of first beams 11 BL 1 , 11 BR 1 and the pair of second beams 11 BL 2 , 11 BR 2 , along the main surface of second beams 11 BL 2 , 11 BR 2 , specifically in the direction along the circumferential direction of reflective mirror 11 M. Reflective mirror 11 M and first beam 11 BL 1 are directly adjacent to each other with first boundary portion CL 1 in between, while reflective mirror 11 M and first beam 11 BR 1 are directly adjacent to each other with first boundary portion CR 1 in between. First boundary portions CL 1 , CR 1 are displaceable in the Z direction crossing the main surface of first beams 11 BL 1 , 11 BR 1 . In contrast, second boundary portion CL 2 between first beam 11 BL 1 and second beam 11 BL 2 and second boundary portion CR 2 between first beam 11 BR 1 and second beam 11 BR 2 are displaceable in the direction along the main surface of second beams 11 BL 2 , 11 BR 2 , i.e., the circumferential direction.

As seen from the above, mirror driving apparatus 101 differs from mirror driving apparatus 100 in terms of the direction in which first and second beam portions BL 1 , BL 2 , BR 1 , BR 2 extend and their shapes as seen in plan view. Other features of the configuration and the operation of these members are basically similar to those of mirror driving apparatus 100 . The functions and effects of mirror driving apparatus 101 are therefore basically similar to those of mirror driving apparatus 100 . It should be noted that the first and second beam portions of mirror driving apparatus 101 extend in a region close to the outer circumference of reflective mirror 11 M, along the circumferential direction thereof. In this way, the size of mirror driving apparatus 101 as a whole as seen in plan view can be reduced relative to mirror driving apparatus 100 .

Moreover, since the beam portions each extend in the circumferential direction, generation of large stress in regions adjacent to first boundary portions CL 1 , CR 1 can be suppressed. In this way, deterioration of the flatness of reflective mirror 11 M can be suppressed.

A description is given, using FIG. 23 , of a configuration of a mirror driving apparatus in a first example of the present embodiment. Referring to FIG. 23 , basically mirror driving apparatus 200 in the first example of the present embodiment has a similar configuration to that of mirror driving apparatuses 100 , 101 in Embodiment 1, and therefore, the same component as that of mirror driving apparatuses 100 , 101 is denoted by a similar reference character to that of mirror driving apparatuses 100 , 101 . As to the features of mirror driving apparatus 200 similar to those of mirror driving apparatuses 101 , 102 , the description thereof is not repeated herein.

Mirror driving apparatus 200 in FIG. 23 includes first and second beam portions that are specifically first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 extending in the X direction from reflective mirror portion M as seen in plan view, and additionally first beam portions BU 1 , BD 1 and second beam portions BU 2 , BD 2 extending in the Y direction from reflective mirror portion M as seen in plan view. In other words, mirror driving apparatus 200 includes, in addition to the components of mirror driving apparatus 101 , a pair of first beam portions BU 1 , BD 1 (a pair of beam portions) and a pair of second beam portions BU 2 , BD 2 (a pair of beam portions).

Regarding mirror driving apparatus 200 , the features of the configuration and the operation of first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 are similar to those of mirror driving apparatus 100 in Embodiment 1. Regarding mirror driving apparatus 200 , the features of the configuration and the operation of first beam portions BU 1 , BD 1 and second beam portions BU 2 , BD 2 extending in the Y direction are similar to those of first beam portions BL 1 , BR 1 and second beam portion BL 2 , BR 2 .

Specifically, first beam portion BU 1 includes a first beam 11 BU 1 , a lower electrode, a piezoelectric film, and upper electrodes 14 BU 1 , 14 BU 2 similar to those of first beam portion BL 1 (some of them are not shown). Likewise, first beam portion BD 1 includes a first beam 11 BD 1 , a lower electrode, a piezoelectric film, and upper electrodes 14 BD 1 , 14 BD 2 similar to those of first beam portion BR 1 . Second beam portion BU 2 includes a second beam 11 BU 2 similar to that of second beam portion BL 2 , and second beam portion BD 2 includes a second beam 11 BD 2 similar to that of second beam portion BR 2 .

First beam 11 BU 1 which is one of the pair of first beams is adjacent to reflective mirror 11 M in one direction from reflective mirror 11 M, specifically upward along the Y direction, while the other first beam 11 BD 1 is adjacent to reflective mirror 11 M in the other direction from reflective mirror B, specifically downward along the Y direction. Second beam 11 BU 2 is adjacent to first beam 11 BU 1 and opposite to reflective mirror 11 M with respect to first beam 11 BU 1 , while second beam 11 BD 2 is adjacent to first beam 11 BD 1 and opposite to reflective mirror 11 M with respect to first beam 11 BD 1 .

Regarding beam 11 , reflective mirror 11 M and first beam 11 BU 1 are directly adjacent to each other at first boundary portion CU 1 , while reflective mirror 11 M and first beam 11 BD 1 are directly adjacent to each other at first boundary portion CD 1 . Moreover, regarding beam 11 , first beam 11 BU 1 and second beam 11 BU 2 are directly adjacent to each other at second boundary portion CU 2 , while first beam 11 BD 1 and second beam 11 BD 2 are directly adjacent to each other at second boundary portion CD 2 .

First beams 11 BU 1 , 11 BD 1 and first boundary portions CU 1 , CD 1 are displaceable in respective directions different from each other (opposite to each other) along the Z direction crossing the main surface. Second beams 11 BU 2 , 11 BD 2 and second boundary portions CU 2 , CD 2 are displaceable along the Y direction connecting first beams 11 BU 1 , 11 BD 1 and second beams 11 BU 2 , 11 BD 2 , along the main surface of second beams 11 BU 2 , 11 BD 2 .

As seen from the above, in the present embodiment, a plurality of rows each including a pair of first beams and a pair of second beams are arranged. Specifically, two rows, specifically a first row including a pair of first beams 11 BL 1 , 11 BR 1 and a pair of second beams 11 BL 2 , 11 BR 2 , and a second row including a pair of first beams 11 BU 1 , 11 BD 1 and a pair of second beams 11 BU 2 , 11 BD 2 are included. Any number of these rows may be included. The first row extends linearly in the X direction, and the second row extends linearly in the Y direction. The first row and the second row thus cross each other (e.g., orthogonal to each other) as seen in plan view.

Mirror driving apparatus 200 in the present embodiment can be used to suppress deformation of reflective mirror 11 M due to moment about the Y axis exerted on first and second beam portions BL 1 , BR 1 , BL 2 , BR 2 extending in the X direction, and deformation of reflective mirror 11 M due to moment about the X axis exerted on first and second beam portions BU 1 , BD 1 , BU 2 , BD 2 extending in the Y direction. Moreover, voltage application to upper electrodes 14 BU 1 , 14 BU 2 , 14 BD 1 , 14 BD 2 can be controlled independently of voltage application to upper electrodes 14 BL 1 , 14 BL 2 , 14 BR 1 , 14 BR 2 . It is therefore possible to control displacement of reflective mirror 11 M about the Y axis independently of displacement of reflective mirror 11 M about the X axis, and freely change the posture of reflective mirror 11 M about any of the Y axis and the X axis. Accordingly, the direction in which incident light is reflected can be changed more freely as compared with Embodiment 1.

A description is given, using FIG. 24 , of a configuration of a mirror driving apparatus in a second example of the present embodiment. Referring to FIG. 24 , basically mirror driving apparatus 201 in the second example of the present embodiment has a similar configuration to that of mirror driving apparatus 200 in the first example, and therefore, the same component as that of mirror driving apparatus 200 is denoted by a similar reference character to that of mirror driving apparatus 200 . As to the features of the second example similar to those of the first example, the description thereof is not repeated herein.

In mirror driving apparatus 201 in FIG. 24 , first beam portions BL 1 , BR 1 , BU 1 , BD 1 and second beam portions BL 2 , BR 2 , BU 2 , BD 2 extend in the circumferential direction of circular reflective mirror 11 M (reflective film 14 M) as seen in plan view. In this respect, the configuration of mirror driving apparatus 201 differs from that of mirror driving apparatus 200 in which first beam portions BL 1 , BR 1 , BU 1 , BD 1 and second beam portions BL 2 , BR 2 , BU 2 , BD 2 extend linearly, i.e., radially in the radial direction of circular reflective mirror 11 M (reflective film 14 M) as seen in plan view.

First beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 of mirror driving apparatus 201 are basically similar to those of mirror driving apparatus 101 in Embodiment 1, and therefore, the detailed description thereof is not repeated. First beam portions BU 1 , BD 1 and second beam portions BU 2 , BD 2 of mirror driving apparatus 201 are also basically similar to first beam portions BL 1 , BR 1 and second beam portions BL 2 , BR 2 .

As described above, the features of the configuration and the operation of each beam portion of mirror driving apparatus 101 extending circumferentially are basically similar to those of each beam portion of mirror driving apparatus 100 extending linearly. Likewise, the features of the configuration and the operation of first beam portions BU 1 , BD 1 and second beam portions BU 2 , BD 2 of mirror driving apparatus 201 extending circumferentially are basically similar to those of first beam portions BU 1 , BD 1 and second beam portions BU 2 , BD 2 of mirror driving apparatus 200 extending linearly. The detailed description of the features of the configuration and the operation of first beam portions BU 1 , BD 1 and second beam portions BU 2 , BD 2 of mirror driving apparatus 201 is therefore not repeated.

Basically mirror driving apparatus 201 has both the functions and effects of mirror driving apparatus 101 and those of mirror driving apparatus 200 . Specifically, the direction in which incident light is reflected can be changed more freely as compared with Embodiment 1 and the whole mirror driving apparatus 201 can be downsized. Meanwhile, deterioration of the flatness of reflective mirror 11 M can also be suppressed.

The foregoing features of the embodiments (and examples included in the embodiments) may be applied in appropriate combination that meets technical consistency.

It should be construed that embodiments disclosed herein are given by way of illustration in all respects, not by way of limitation. It is intended that the scope of the present invention is defined by claims, not by the description above, and encompasses all modifications and variations equivalent in meaning and scope to the claims.

10 , 11 S silicon layer; 11 beam; 11 BL 1 , 11 BR 1 , 11 BU 1 , 11 BD 1 first beam; 11 BL 2 , 11 BR 2 , 11 BU 2 , 11 BD 2 second beam; 11 M reflective mirror; 12 , 12 BL 1 , 12 BR 1 lower electrode; 13 , 13 BL 1 , 13 BL 2 , 13 BR 1 , 13 BR 2 piezoelectric film; 14 , 14 BL 1 , 14 BL 2 , 14 BR 1 , 14 BR 2 , 14 BU 1 , 14 BU 2 , 14 BD 1 , 14 BD 2 upper electrode; 14 M reflective film; 15 silicon oxide film layer; 20 SOI substrate; 100 , 101 , 200 , 201 mirror driving apparatus; BL 1 , BR 1 , BU 1 , BD 1 first beam portion; BL 2 , BR 2 , BU 2 , BD 2 second beam portion; CL 1 , CR 1 , CU 1 , CD 1 first boundary portion; CL 2 , CR 2 , CU 2 , CD 2 second boundary portion; EL left end; ER right end; M reflective mirror portion