Actuator, switch using the actuator, and method of controlling the actuator

1. Field of the Invention

The present invention relates an actuator for use in electronic devices, a method of controlling the actuator, and a switch including the actuator.

2. Related Art

A conventional actuator of a micro-electro-mechanical system (MEMS) is disclosed in Japanese Patent Laid-Open Publication No. 2000-188050. The actuator includes an arm having an elastic property, and is supported on a substrate. A positive voltage is applied to one of respective electrodes provided on the substrate and the arm, and a negative voltage is applied to the other of the electrodes, thereby producing an electrostatic force. This electrostatic force causes the arm to deform toward the substrate. A movable contact provided on the arm accordingly contacts a fixed contact provided on the substrate, thus allowing the actuator to operate as a switch.

In this actuator, the distance between the electrostatic electrodes becomes the largest at an initial position in which the arm is straight. In order to drive the arm at a high speed from the initial position, a large electrostatic force is required, thus requiring an increased a voltage applied to the electrodes. The deforming arm returns by an elastic force after the electrostatic force is released, and a speed of return is limited.

Another conventional actuator includes an arm deforming by a piezoelectric drive. In this actuator, when a movable contact contacts a fixed contact, the arm may vibrate, accordingly generating a noise.

While being used as micro-switches, conventional actuators of MEMS have not be able to be used in a switch required to have a large driving speed, such as a switch for switching the connection of transmitting and receiving signals of a portable telephone.

An actuator includes a base, an arm having an elastic property and supported by the base, electrostatic-driving electrodes provided on the base and the arm, respectively, and a piezoelectric-driving layer. The piezoelectric-driving layer includes a first electrode layer on the arm, a piezoelectric layer on the first electrode layer, and a second electrode layer on the piezoelectric layer.

This actuator can be driven quickly with a low voltage.

FIG. 1 is a perspective view of a switch including an actuator according to an exemplary embodiment of the present invention.

FIG. 2 is a side view of the switch according to the embodiment.

FIG. 3 is a side view of another switch according to the embodiment.

FIG. 4 is a top view of still another switch according to the embodiment.

FIG. 5A is a front view of the switch shown in FIG. 4 .

FIG. 5B is a side view of the switch shown in FIG. 4 .

FIG. 6 is a side view of the switch for illustrating a method of manufacturing the switch according to the embodiment.

FIG. 7 is a side view of the switch for illustrating another method of the manufacturing the switch according to the embodiment.

FIG. 8 is a side view of still another switch according to the embodiment.

FIG. 1 is a perspective view of switch 2 including actuator 1 in accordance with an exemplary embodiment of the present invention. Actuator 1 includes base 3 , arm 4 , piezoelectric-driving layer 7 , and electrostatic-driving electrodes 8 A and 8 B. Switch 2 includes actuator 1 , and contacts 9 , 10 A, and 10 B. Base 3 has surface 3 A having an insulating property. Arm 4 has end 4 A, a supported portion supported by base 3 , and extends parallel to surface 3 A of base 3 . Arm 4 has a plate shape and has an elastic property. Arm 4 has surface 4 B facing surface 3 A of base 3 , and has surface 4 C opposite to surface 4 B. Piezoelectric-driving layer 7 includes electrode layer 6 A provided on surface 4 C of arm 4 , piezoelectric layer 5 provided on electrode layer 6 A, and electrode layer 6 B provided on piezoelectric layer 5 . Electrostatic-driving electrode 8 A is provided on surface 3 A of base 3 . Electrostatic-driving electrode 8 B is provided on surface 4 B of arm 4 and faces electrostatic-driving electrode 8 A. Power supply 101 applies a direct-current (DC) voltage between electrode layers 6 A and 6 B of piezoelectric-driving layer 7 . Power supply 102 applies a voltage between electrostatic-driving electrodes 8 A and 8 B. Contact 9 is provided on surface 4 B at end 4 D of arm 4 . Contacts 10 A and 10 B are provided on surface 3 A of base 3 and face contact 9 . Arm 4 has movable portion 4 F including end 4 D different from end 4 A supported by base 3 .

Base 3 and arm 4 are made of silicon, and may be made of elastic material having an insulating surface, such as a metal having a surface to which an insulating process is performed.

An operation of switch 2 will be described below. Power supply 102 applies a DC voltage between electrostatic-driving electrodes 8 A and 8 B so as to produce an electrostatic force between electrostatic-driving electrodes 8 A and 8 B facing each other, thereby causing arm 4 to deform toward base 3 . Further, power supply 101 applies a voltage between electrode layers 6 A and 6 B of piezoelectric-driving layer 7 to cause piezoelectric layer 5 to shrink and expand, thereby causing arm 4 to deform in direction 2 A perpendicular to surface 3 A of base 3 . Arm 4 deforming toward surface 3 A of base 3 causes contact 9 provided at end 4 D to contact contacts 10 A and 10 B, thereby connecting contact 10 A electrically with contact 10 B.

In order to cause arm 4 to deform from initial position S 1 at which no voltage is applied between electrode layers 6 A and 6 B and between electrostatic-driving electrodes 8 A and 8 B, power supply 102 needs to apply a high voltage between electrostatic-driving electrodes 8 A and 8 B. In switch 2 , power supply 101 applies a voltage between electrode layers 6 A and 6 B of piezoelectric-driving layer 7 to cause arm 4 to deform toward surface 3 A of base 3 . That is, within range D 1 from initial position S 1 to position S 2 at which arm 4 deforms, a force toward surface 3 A produced by piezoelectric-driving layer 7 mainly causes arm 4 to deform, while the electrostatic force produced by electrostatic-driving electrodes 8 A and 8 B is smaller than the force produced by piezoelectric-driving layer 7 . Then, arm 4 further deforms from position S 2 to position S 3 for allowing contact 9 to contact contacts 10 A and 10 B. Position S 2 is closer to position S 3 , i.e., surface 3 A of base 3 , than initial position S 1 is. Within range D 2 from position S 2 to position S 3 , the electrostatic force produced by electrostatic-driving electrodes 8 A and 8 B causes arm 4 to deform in addition to the force produced by piezoelectric-driving layer 7 . In order to cause arm 4 to deform further within range D 2 , the electrostatic force produced between electrostatic-driving electrodes 8 A and 8 B mainly works, while the force produced by piezoelectric driving layer 7 is smaller than the electrostatic force produced by electrostatic-driving electrodes 8 A and 8 B. The distance between electrostatic-driving electrodes 8 A and 8 B at position S 2 is shorter than that at initial position S 1 , accordingly allowing the voltage applied between electrostatic-driving electrodes 8 A and 8 B to be small. This allows arm 4 to deform quickly, and further decreases the voltage applied between electrostatic-driving electrodes 8 A and 8 B, thus allowing switch 2 to be used in devices, such as portable telephones, requiring operation at a low voltage.

If arm 4 deforms only with the force of piezoelectric-driving layer 7 , the elastic property of arm 4 may cause arm 4 to vibrate. In switch 2 , the electrostatic force increases as electrostatic-driving electrode 8 A and 8 B get close to each other, and suppresses the vibration of arm 4 , thereby reducing a noise. When arm 4 is kept at position S 3 , the electrostatic force produced between electrostatic-driving electrodes 8 A and 8 B mainly keeps arm 4 at position S 3 , while the force produced by piezoelectric layer 7 is smaller than the electrostatic force produced between electrostatic-driving electrodes 8 A and 8 B.

When arm 4 deforms only with the electrostatic force between electrostatic-driving electrodes 8 A and 8 B, arm 4 returns to initial position S 1 only by the elastic property of arm 4 after the deforming of arm 4 . This operation limits a speed at which arm 4 returns to initial position S 1 . In switch 2 of the embodiment, power supply 101 applies a voltage having a reverse polarity between electrode layers 6 A and 6 B of piezoelectric-driving layer 7 to cause arm 4 to receive a force away from surface 3 A of base 3 , thereby allowing arm 4 to return to initial position S 1 quickly.

FIG. 3 is a side view of switch 1002 including another actuator 1001 of the embodiment. In FIG. 3 , components of switch 2 shown in FIGS. 1 and 2 are denoted by the same reference numerals, and their descriptions are omitted. Actuator 1001 further includes via-conductor 13 for electrically connecting electrostatic-driving electrode 8 A on arm 4 with electrode layer 6 A of piezoelectric-driving layer 7 . Thus, electrostatic-driving electrode 8 A and piezoelectric-driving layer 7 are provided with electric potentials identical to each other. Via-conductor 13 penetrates between surface 4 B and surface 4 C of arm 4 . Electrostatic-driving electrode 8 B on surface 3 A of base 3 is grounded. Piezoelectric layer 5 is polarized so as to expand in surface direction 5 A when an electric field from electrode layer 6 A to electrode layer 6 B is applied to piezoelectric layer 5 . Power supply 102 applies a positive voltage to electrode layer 6 A, and electrode layer 6 B is grounded so as to expand piezoelectric layer 5 , accordingly causing arm 4 to deform toward surface 3 A of base 3 . At this moment, electrostatic-driving electrodes 8 A and 8 B attract each other, thereby causing contact 9 provided at end 4 D of arm 4 to contact contacts 10 A and 10 B and electrically connecting contact 10 A with contact 10 B. Then, electrode layer 6 A and electrostatic-driving electrode 8 A are grounded, and power supply 101 applies a positive voltage to electrode layer 6 B. Electrostatic-driving electrode 8 B is grounded, thereby eliminating the electrostatic force causing electrostatic-driving electrodes 8 A and 8 B to attract each other. Further, a shrinking force of piezoelectric layer 5 and the elastic property of arm 4 cause end 4 D of arm 4 to move away from surface 3 A, thus disconnecting contact 10 A from contact 10 B.

In switch 1002 , a positive voltage and a zero potential (grounding) are applied alternately between (a) electrode layer 6 A and electrostatic-driving electrode 8 A and (b) electrode layer 6 B so as to cause arm 4 deform and return. When arm 4 deforms toward surface 3 A, the respective forces produced by piezoelectric-driving layer 7 and electrostatic-driving electrodes 8 A and 8 B are used. When deforming arm 4 moves away from surface 3 A to return, the respective forces produced by piezoelectric-driving layer 7 and the elastic property of arm 4 are used. This operation allows actuator 1001 to activate switch 1002 quickly with low voltages.

FIG. 4 is a top view of switch 2002 including still another actuator 2001 of the embodiment. FIGS. 5A and 5B are a front view and a side view of switch 2002 , respectively. In FIGS. 4 , 5 A and 5 B, components identical to those of switch 2 shown in FIGS. 1 and 2 are denoted by the same reference numerals, and their descriptions are omitted. Instead of piezoelectric-driving layer 7 of actuator 1 shown in FIGS. 1 and 2 , actuator 2001 includes piezoelectric-driving layers 7 A, 7 B, and 7 C. Instead of contacts 10 A and 10 B of switch 2 shown in FIGS. 1 and 2 , switch 2002 includes contacts 110 A, 110 B, and 110 C provided on surface 3 A,

As shown in FIGS. 5A and 5B , piezoelectric-driving layer 7 A includes electrode layer 106 A provided on surface 4 C of arm 4 , piezoelectric layer 105 provided on electrode layer 106 A, and electrode layer 106 B provided on piezoelectric layer 105 . Piezoelectric-driving layer 7 B includes electrode layer 206 A provided on surface 4 C of arm 4 , piezoelectric layer 205 provided on electrode layer 206 A, and electrode layer 206 B provided on piezoelectric layer 205 . Piezoelectric-driving layer 7 C includes electrode layer 306 A provided on surface 4 C of arm 4 , piezoelectric layer 305 provided on electrode layer 306 A, and electrode layer 306 B provided on piezoelectric layer 305 . At an initial position at which no voltage is applied to the electrostatic-driving electrodes and the electrode layers, contact 110 B is located beneath contact 9 and faces contact 110 B.

As shown in FIG. 4 , piezoelectric-driving layers 7 A and 7 B are provided at positions symmetric with each other about axis 4 E passing through supported end 4 A of arm 4 and end 4 D having contact 9 thereon. Contact 110 B is provided between contacts 110 A and 110 C.

An operation of actuator 2001 and switch 2002 will be described below. A voltage is not applied between electrode layers 106 A and 106 B of piezoelectric-driving layer 7 A, while voltages are applied between electrode layers 206 A and 206 B of piezoelectric-driving layer 7 B, between electrode layers 306 A and 306 B of piezoelectric-driving layer 7 C, and between electrostatic-driving electrodes 8 A and 8 B. Then, a force in direction 2002 C produced by piezoelectric-driving layer 7 C, a force in direction 2002 D produced by piezoelectric-driving layer 7 B, and an electrostatic force produced by electrostatic-driving electrodes 8 A and 8 B work together. These forces cause arm 4 to deform in direction 2002 A shown in FIG. 5A , and cause contact 9 to contact contacts 110 A and 110 B, thereby electrically connecting contact 110 A with contact 110 B. Then, the voltage applied between electrostatic-driving electrodes 8 A and 8 B is changed into zero, the polarities of the voltages applied between electrode layers 206 A and 206 B and between electrode layers 306 A and 306 B are reversed. This operation allows forces to be produced by piezoelectric-driving layers 7 B and 7 C and the elastic property of arm 4 to cause arm 4 to return to the initial position, thereby electrically disconnecting contact 110 A from contact 110 B. Similarly, a voltage is not applied between electrode layers 206 A and 206 B of piezoelectric-driving layer 7 B while voltages are applied between electrode layers 106 A and 106 B of piezoelectric-driving layer 7 A, between electrode layers 306 A and 306 B of piezoelectric-driving layer 7 C, and between electrostatic-driving electrodes 8 A and 8 B. Then, a force in direction 2002 C produced by piezoelectric-driving layer 7 C, a force in direction 2002 E produced by piezoelectric-driving layer 7 B, and the electrostatic force produced by electrostatic-driving electrodes 8 A and 8 B are applied to arm 4 . These forces cause arm 4 to deform in direction 2002 B shown in FIG. 5A , and cause contact 9 to contact contacts 110 B and 110 C, thereby electrically connecting contact 110 B with contact 110 C. Then, the voltage applied between electrostatic-driving electrodes 8 A and 8 B is changed to zero, and the polarities of the voltages applied between electrode layers 106 A and 106 B and between electrode layers 306 A and 306 B are reversed. This operation allows forces to be produced by piezoelectric-driving layers 7 A and 7 C and the elastic property of arm 4 to cause arm 4 to return to the initial position, thereby disconnecting contact 110 B from contact 110 C.

Switch 2002 can be used as a single-pole double-throw (SPDT) switch for use in dual-band portable telephones operating in two different transmitting/receiving systems, such as a global system for mobile communication (GSM) system and a digital communication service (DCS) in European portable telephone communication systems. Contact 1110 B may be used as an antenna terminal, contact 110 A may be used as a transmitting terminal, and contact 110 C may be used as a receiving terminal. The contacts switch a single antenna to connect the antenna selectively with transmitting and receiving circuits.

For use in such high-frequency circuits, switch 2002 is required to have an isolation between contacts 110 A, 110 B, and 110 C when these contacts do not contact one another. An inductor may be connected in parallel with a parasitic capacitance between the contacts to provide the isolation, and a parallel resonance frequency of them is determined to be a frequency band requiring the isolation.

The positions of the contacts and switches may be arranged appropriately, thereby allowing the switch of this embodiment to be used as a switch supporting multi-bands, such as a single-pole three-throw (SP3T) switch and a double-pole double-throw (DPDT) switch.

In each of actuators 1 , 1001 , and 2001 of the embodiment, arm 4 is supported by base 3 at end 4 A. However, arm 4 may be supported at both ends, providing the same effects.

Then, a method of manufacturing switch 2 will be described below. FIG. 6 is a side view of switch 2 for illustrating a method of manufacturing switch 2 . Electrostatic-driving electrode 8 B and contacts 10 A and 10 B are formed by sputtering on surface 3 A of base 3 made of silicon. Then, electrostatic-driving electrode 8 A and contact 9 are formed on dummy layer 11 made of silicon dioxide. Then, dummy layer 11 is mounted on surface 3 A and contacts 10 A and 10 B except portion 3 B of surface 3 A supporting end 4 A of arm 4 . Arm 4 made of silicon is formed on electrostatic-driving electrode 8 A, contact 9 , dummy layer 11 , and portion 3 B of surface 3 A. Then, electrode layer 6 A, piezoelectric layer 5 made of lead zirconate titanate (PZT), and electrode layer 6 B are formed on arm 4 , thus forming piezoelectric-driving layer 7 on arm 4 . Then, dummy layer 11 is removed, providing switch 2 .

FIG. 7 is a side view of switch 2 for illustrating another method of manufacturing switch 2 . Device 12 can be mounted on switch 2 . When piezoelectric layer 5 of PZT is formed, switch 2 is heat-treated at temperatures of about 600° C. Device 12 , being a device having small heat resistance, such as a surface acoustic wave (SAW) filter, may be broken due to the heat treatment. As shown in FIG. 7 , piezoelectric-driving layer 7 including piezoelectric layer 5 and arm 4 are formed together, and device 12 is mounted on base 3 separately from piezoelectric-driving layer 7 and arm 4 . Then, arm 4 is mounted on base 3 . Thus, device 12 having a small heat resistance can be combined with switch 2 including piezoelectric layer 5 .

FIG. 8 is a side view of switch 3002 including still another actuator 3001 according to the embodiment. In FIG. 8 , components identical to those of switch 2 shown in of FIGS. 1 and 2 are denoted by the same reference numerals, and their descriptions are omitted. Instead of piezoelectric-driving layer 7 of actuator 1 shown in FIG. 1 , actuator 3001 includes piezoelectric-driving layer 107 provided on surface 4 B. Piezoelectric-driving layer 107 includes electrode layer 406 A provided on surface 4 B, piezoelectric layer 405 provided on electrode layer 406 A, and electrode layer 406 B provided on piezoelectric layer 405 . Piezoelectric-driving layer 107 , electrostatic-driving electrode 8 A, and contact 9 are provided on a single surface, surface 4 B of arm 4 , hence being formed at a high productivity.