Silicon-based micro-machined vibratory gyroscope with an I-shaped structure

This invention belongs to micro-electromechanical systems MEMS and micro inertial measurement technique, especially a silicon-based micro-machined vibratory gyroscope with an I-shaped structure.

Silicon-based micro-machined gyroscope is an angular rate measurement inertial sensor, fabricated with micro-machined process, and can be integrated with its readout circuit on one silicon chip, having advantages on low volume, low-cost, light-weight and good reliability, showing great worth in both military and civilian applications.

Nowadays, the performance of silicon micro-machined gyros has progressed from ordinary car level to near tactical level ldeg/h, however, applications such as vibration and temperature have poor performance, especially vibration environment. Dual mass tuning fork gyroscope is a known structure having good vibration immunity, but due to the existence of many low-order vibration modes, fabrication errors and high-Q factor, it still has a large vibration error, which affects its practical application.

An-ping Qiu and Qin Shi proposed a dual mass vibrating gyroscope in 2007 200710133223.5, which comprises two proof masses connected with up and down crossbeams via support systems, and bounded with a pair of torsion levers to the pedestals. Experiment results indicate the proposed gyroscope has properties of low error, high sensitivity and good performance under static environment. However, this structure can only link with anchors via a middle torsion lever, resulting in poor structural stability; meanwhile, this gyroscope has several low-order modes near the operational modes, in a vibrating environment, these modal motions have a great influence on the gyroscope output. In addition, the stiffness of the torsion lever affects the frequency of the gyroscope detection mode, and the torsion lever is directly connected to the anchor point, its rigidity is affected by the fabrication stress and the package stress, thereby affecting the gyroscope output and deteriorating its temperature performance.

TRONICS MICROSYSYTEMS S.A. reported a micro-machined z-axis gyroscope in 2014 WO 2014/094996 A1, the z-axis micro-gyroscope adopts the same structure as the ZL 200710133223.5 gyroscope, which also formed by two proof masses, and connected with up and down crossbeams via support systems, and the crossbeams are bounded with coupled support beam to the fixed pedestals. In addition, this patent also lists several coupled support beam instances, including its structural style and arrangement method. However, the structural proposal of the patent application has the same technical problems as the ZL 200710133223.5 gyroscope.

The invention aims to provide a silicon micromachined gyroscope with small error, high mechanical sensitivity, low vibration sensitivity and low temperature sensitivity, which can realize the motion decoupling of the drive mode and detection mode, large amplitude vibration and detection output decoupling.

The technical solution of this invention is a silicon-based micro-machined vibratory gyroscope with an I-shaped structure which measures the angular rate perpendicular to a base, and comprises a top monocrystalline silicon, a middle monocrystalline silicon, and a bottom monocrystalline silicon; the top monocrystalline silicon being arranged with signal input and output lines is the silicon micro gyroscope packaged cover plate; the middle monocrystalline silicon is where the gyroscope mechanical structures are fabricated; the bottom monocrystalline silicon is a gyroscope substrate with fixed pedestals; the middle monocrystalline silicon layer is sealed in a closed cavity formed by top and bottom monocrystalline silicon layers; the middle monocrystalline silicon layer comprises sub-structures, I-shaped frame, torsion levers, multi-folded beams and isolation structure; the two substructures are arranged in an I-shaped frame symmetrically, by connecting the drive beams with an I-shaped frame; the I-shaped frame is connected with isolation structures through torsion levers and multi-folded beams distributed at the top and lower end of the I-shaped frame; the isolation structures are bonded with the fixed pedestals on the bottom monocrystalline silicon, so that the mechanical structures on middle monocrystalline silicon layer are suspended between the top single crystal silicon and the bottom single crystal silicon.

Compared with previous arts, this invention has the following notable improvements: (1) The silicon micromachined gyroscope structure is connected with the isolation structure through four multi-folded beams and the up, middle and down torsion levers, which increases the stability of the structure and improves the structural vibration immunity; (2) The silicon micromachined gyroscope structure is connected with the isolation structure through four multi-folded beams and the up, middle and down torsion levers, which increases its stiffness along z-axis and overcomes the stiffness limitation caused by the small thickness of MEMS fabrication process; (3) The two sub-structures are connected by an I-shaped frame to increase the stiffness in the x direction and the stiffness in the y direction of the gyroscope structure, effectively suppressing the influence of the in-phase force, such as vibration and shock; (4) The drive support beam and the detection support beam are connected to the I-shaped frame, and the I-shaped frame passes through the torsion lever and multiple-folded beams to the isolation structure, and the isolation structure is connected with the fixed pedestals. This connection way greatly reduces the influence of processing stress and package stress, and reduces the temperature error; (5) The two sub-structures are connected together by an I-shaped frame, and then the torsion levers and the multi-folded support beams are connected with the fixed pedestals to realize the movement of the tuning fork of the two sub-structures; (6) The drive motion and detection motion of the two sub-structures are opposite to each other, forming a differential comb capacitance detection, achieving detection output decoupling and suppressing interfering signals; (7) The two substructures are symmetrically arranged side by side, increasing the output signal twice as the output signal of a single mass; (8) Two sets of support beams are used to separate the drive part from the detection part, thus decoupling the movement of the drive direction and the detection direction, thereby reducing the error signal.

The following sections describe this invention with attached figures.

FIG. 1 is the schematic of silicon-based micro-machined vibratory gyroscope with an I-shaped structure.

FIG. 2 is the schematic of drive resonator of silicon-based micro-machined gyroscope.

FIG. 3 is the schematic of another silicon-based micro-machined vibratory gyroscope with an I-shaped structure.

FIG. 4 is the schematic of comb structure for open-loop sensing scheme of silicon-based micro-machined gyroscope.

FIG. 5 is the schematic of comb structure for closed-loop sensing scheme of silicon-based micro-machined gyroscope.

FIG. 6 is the schematic of a silicon-based micro-machined vibratory gyroscope according to one embodiment of the present invention.

This patent introduces a silicon-based micro-machined vibratory gyroscope with an I-shaped structure, which measures the angular rate perpendicular to a base, is characterized by a top monocrystalline silicon 7 , a middle monocrystalline silicon 8 , and a bottom monocrystalline silicon 9 as shown in FIG. 6 . The top monocrystalline silicon 7 being arranged with signal input lines 10 and signal output lines H is the silicon micro gyroscope packaged cover plate. The middle monocrystalline silicon 8 is where the gyroscope mechanical structures are fabricated. The bottom monocrystalline silicon 9 is a gyroscope substrate with fixed pedestals. The middle monocrystalline silicon layer is sealed in a closed cavity formed by top and bottom monocrystalline silicon layers. The middle monocrystalline silicon layer comprises of sub-structures, I-shaped frame, torsion levers, multi-folded beams and isolation structure. The two substructures are arranged in an I-shaped frame symmetrically, by connecting the drive beam with an I-shaped frame, the I-shaped frame is connected with an isolation structure through a torsion levers and a multi-folded beam distributed at the top and lower end. The isolation structure is bonded with the fixed pedestal on the bottom monocrystalline silicon, so that the mechanical structures on middle monocrystalline silicon layer are suspended between the top single crystal silicon and the bottom single crystal silicon.

According to FIG. 1 , for the silicon-based micro-machined vibratory gyroscope with an I-shaped structure, the gyroscope mechanical structure on the middle monocrystalline silicon layer 8 consist of first sub-structure 100 , second sub-structure 200 , I-shaped frame 2 , first multi-folded beam 3 a , second multi-folded beam 3 b , third multi-folded beam 3 c , fourth multi-folded beam 3 d , first torsion lever 4 a , second torsion lever 4 b , first isolation structure 5 a and second isolation structure 5 b . The first sub-structure 100 and second sub-structure 200 are identical in composition and structure, and disposed in an I-shaped frame 2 symmetrical to y axis y axis direction is from bottom to top, and x axis direction is from left to right. First sub-structure 100 is connected to the I-shaped frame 2 by first drive support beam 104 a , second drive support beam 104 b , third drive support beam 104 c , and fourth drive support beam 104 d . Second sub-structure 200 is connected to the I-shaped frame 2 by fifth driving support beam 204 a , sixth driving support beam 204 b , seventh driving support beam 204 c , and eighth driving support beams 204 d . The I-shaped frame 2 is connected to first isolation structure 5 a above the I-shaped frame 2 by first multi-folded beam 3 a , second multi-fold beam 3 b and first torsion lever 4 a . The I-shaped frame 2 is connected to the second isolation structure 5 b below the I-shaped frame 2 by third multi-folded beam 3 c , fourth multi-folded beam 3 d and second torsion lever 4 b . First isolation structure 5 a is bonded to first fixing pedestal 6 a and second fixing pedestal 6 b on the bottom monocrystalline silicon, and second insulating structure 5 b is bonded to the third fixing pedestal 6 c and fourth fixed pedestal 6 d on the bottom monocrystalline silicon.

The first sub-structure 100 of the I-shaped silicon micro-mechanical vibration gyroscope in this invention comprises first rectangular frame 101 , first detection support beam 102 a , second detection support beam 102 b , third detection support beam 102 c , fourth detection support beam 102 d , first drive resonator 105 a , second drive resonator 105 b , first movable detection comb fingers 107 , first fixed detection comb fingers 108 , first detection comb fixed electrode 106 a and second detection comb fixed electrode 106 b . First movable detection comb fingers 107 which is arranged on first rectangular frame 101 constitute a detection comb capacitance with first fixed detection comb fingers 108 arranged on first and second detection comb fixed electrodes 106 a , 106 b , and the first and second detection comb fixed electrodes 106 a , 106 b are bonded to the fixed pedestal of the bottom monocrystalline silicon. The upper end of the first rectangular frame 101 is connected to first drive resonator 105 a by first detection support beam 102 a and second detection support beam 102 b , and the lower end of first rectangular frame 101 is connected to second drive resonator 105 b by third detection support beam 102 c and fourth detection support beam 102 d . First drive support beam 104 a and second driving support beam 104 b on first drive resonator 105 a are connected to I-shaped frame 2 , third driving beam 104 c and fourth driving beam 104 d on second driving resonator 105 b are connected to I-shaped frame 2 .

The second sub-structure 200 comprises second rectangular frame 201 , fifth detection support beam 202 a , sixth detection support beam 202 b , seventh detection support beam 202 c , eighth detection support beam 202 d , third driving resonator 205 a , fourth driving resonator 205 b , second movable detection comb fingers 207 , second fixed detection comb fingers 208 , third detection comb fixed electrode 206 a and fourth detection comb fixed electrode 206 b . A second motion detection comb figures 207 disposed on second rectangular frame 201 , and second fixed detection comb figures 208 disposed on the third and fourth detection comb fixed electrodes 206 a , 206 b constitute a comb-capacitor detection capacity. The forth comb fixed electrodes 206 a , 206 b are bonded to the corresponding fixed pedestals on the bottom monocrystalline silicon. The upper ends of second rectangular frames 201 are connected to third drive resonator 205 a by fifth detection support beam 202 a and sixth detection support beam 202 b ; the lower end of the second rectangular frame 201 is connected to fourth drive resonator 205 b through seventh detection support beam 202 c and eighth detection supporting beam 202 d . Fifth driving support beam 204 a and sixth driving support beam on the third driving resonator 205 a are connected to the I-shaped frame 2 , and seventh driving beam 204 c and eighth driving beam 204 d on fourth driving resonator 205 b are connected to the I-shaped frame 2 .

According to FIG. 1 and FIG. 2 , for the silicon-based micro-machined vibratory gyroscope with an I-shaped structure, the first drive resonator 105 a is identical in composition and structure with the second drive resonator 105 b are exactly the same. First drive resonator 105 a consists of first transverse bar 103 a , first drive support beam 104 a , second drive support beam 104 b , first comb beam 111 a , second comb beam 111 b , third comb beam 111 c , fourth comb beam 111 d , first drive comb fixed electrode 110 a , second drive comb fixed electrode 110 b , third drive comb fixed electrode 110 c , fourth drive comb fixed electrode 110 d , first drive detection comb fixed electrode 109 a and second drive detection comb fixed electrode 109 b . First drive support beam 104 a and second drive support beam 104 b are located at both ends of first transverse bar 103 a and are perpendicular to first transverse bar 103 a . The first, second, third, and fourth comb beams 111 a , 111 b , 111 c , 111 d are vertically arranged on first transverse bar 103 a and are sequentially arranged on first drive support beam 104 a and second drive support beam 104 b . Both sides of the second comb beam 111 b and third comb beam 111 c are provided with movable drive combs, constituting a drive capacitor with fixed drive combs on first drive comb fixed electrode 110 a , second drive comb 110 , third drive comb fixed electrode 110 c , and fourth drive comb fixed electrode 110 d . One side of first comb beam 111 a and fourth comb beam 111 d are provided with movable drive comb, constituting a drive sense capacitor with fixed drive combs on first drive detection comb fixed electrode 109 a and second drive detection comb fixed electrode 109 b . An AC voltage with DC bias is applied to first drive comb fixed electrode 110 a and third drive comb fixed electrode 110 c , and second drive comb fixed electrode 110 b and fourth drive comb fixed electrode 110 d are applied with an inverting AC voltage to create a bilateral drive; first drive detection comb fixed electrode 109 a and second drive detection comb fixed electrode 109 b are applied with a pair of reversed DC voltage to form a differential capacitance detection.

According to FIG. 1 and FIG. 3 , first driving resonator 105 a of the silicon-based micro-mechanical vibratory gyroscope with an I-shaped structure of the present invention has the same composition and structure as the second driving resonator 105 b . First transverse bar 103 a for first drive resonator 105 a is located at the upper ends of first rectangular frame 101 , and second transverse bar 103 b of second drive resonator 105 b is located at the lower ends of the first rectangular frame 101 . First transverse bar 103 a and the second transverse bar 103 b are integrated to form the outer rectangular frame 112 of the first rectangular frame 101 . Third transverse bar 203 a for the drive resonator 205 a is located at the upper ends of second rectangular frame 201 , and fourth transverse bar 103 b of fourth drive resonator 205 b is located at the lower ends of second rectangular frame 201 . Third transverse bar 203 a and the forth transverse bar 203 b are integrated to form the second outer rectangular frame 212 of the second rectangular frame 201 . Compared with the structure in FIG. 1 , the structure is exactly the same except that first rectangular frame 112 and second rectangular frame 212 in the driving resonator are integrated.

The silicon-based micro-machined vibratory gyroscope with an I-shaped structure of the present invention can adopt two schemes of open-loop and closed-loop. FIG. 4 is a schematic view of the detecting comb structure of the gyro open loop detection. The detection comb structure for open loop detection consists of first detection comb fixed electrode 106 a , second detection comb fixed electrode 106 b , third detection comb fixed electrode 206 a , fourth detection comb fixed electrode 206 b , first fixed detection comb fingers 108 , second fixed detection comb fingers 208 and first moveable detection comb fingers 107 , second moveable detection comb fingers 207 . First, second, third, and fourth detection comb fixed electrodes 106 a , 106 b , 206 a , 206 b , first and second fixed detection comb fingers 108 , 208 and first moveable detection comb fingers 107 , second moveable detection comb fingers 207 constitute four pairs of sense comb capacitors. The fixed detection comb on first detection comb fixed electrode 106 a and the corresponding moveable detection comb constitute first detection capacitance D 1 , and the fixed detection comb on second detection comb fixed electrode 106 b and corresponding moveable detection comb constitute second detection capacitance D 2 , and the comb arrangement of first detection capacitance D 1 and second detection capacitance D 2 are anti-symmetric and constitute a differential detection topology to detect first rectangular frame 101 displacement in the y-axis direction. The fixed detection comb on third detection comb fixed electrode 206 a and the corresponding moveable detection comb constitute third detection capacitance D 3 , and the fixed detection comb on fourth detection comb fixation electrode 206 b and the corresponding moveable detection comb constitute fourth detection capacitance D 4 , and the arrangement of third detection capacitance D 3 and fourth detection capacitance D 4 is anti-symmetric, constituting a differential detection topology to detect second rectangular frame 201 displacement in the y-axis direction. The arrangement of the comb of first detection capacitor D 1 and third detection capacitor D 3 is anti-symmetric, and the arrangement of second detection capacitor D 2 and fourth detection capacitor D 4 is antisymmetric. First detection capacitor D 1 is added to third detection capacitor D 3 and second detection capacitance D 2 is added to fourth detection capacitance D 4 , the influence of the same-direction movement on the output is suppressed.

The detection comb structure of the closed-loop detection is shown in FIG. 5 . the detection comb structure of the gyroscope for closed loop detection consist of first detection comb fixed electrode 106 a , second detection comb fixed electrode 106 b , third detection comb fixed electrode 206 a , fourth detection comb fixed electrode 206 b , first force comb fixed electrode 106 c , second force comb fixed electrode 106 d , third force comb fixed electrode 206 c , fourth force comb fixed electrode 206 d , first fixed detection comb fingers 108 , second fixed detection comb fingers 208 , first moveable detection comb fingers 107 , and second moveable detection comb fingers 207 . First fixed detection comb fingers 108 is also provided on first force comb fixed electrode 106 c and second force comb fixed electrode 106 d , and the third force comb fixed electrode 206 c , the second fixed detection comb fingers 208 is also arranged on the fourth force comb fixed electrode 206 d . The first and second moveable detection comb fingers 107 , 207 and the first and second fixed detection comb fingers 108 , 208 on the first, second, third, and fourth detection comb fixed electrodes 106 a , 106 b , 206 a , 206 b and the first, second, third, and fourth force comb fixed electrodes 106 c , 106 d , 206 c , 206 d constitute four pairs of force comb capacitors. The fixed detection comb on first detection comb fixed electrode 106 a and the corresponding moveable detection comb constitute the first detection capacitance D 1 , and the fixed detection comb on the second detection comb fixed electrode 106 b and the corresponding movable detection comb constitute the second detection capacitor D 2 . The comb arrangement of the first detection capacitance D 1 and second detection capacitance D 2 are anti-symmetric and constitute a differential detection topology to detect first rectangular frame 101 displacement in the y-axis direction. The fixed detection comb on third detection comb fixed electrode 206 a and the corresponding moveable detection comb constitute third detection capacitor D 3 , and the fixed detection comb on fourth detection comb fixed electrode 206 b and the corresponding movable detection comb constitute fourth detection capacitor D 4 , and the comb arrangement of third detection capacitance D 3 and fourth detection capacitance D 4 are anti-symmetric and constitute a differential detection topology to detect second rectangular frame 201 displacement in the y-axis direction. The fixed detection comb on first force comb fixed electrode 106 c and the corresponding movable detection comb constitute first force capacitor A 1 , and the fixed detection comb on the second force comb fixed electrode 106 d , and the corresponding moveable detection comb constitute second force capacitor A 2 , and the fixed detection comb on third force comb fixed electrode 206 c and the corresponding moveable detection comb constitute third force capacitor A 3 , and fourth force fixed detection comb on the comb fixed electrode 206 d and the corresponding movable detection comb constitute fourth force capacitor A 4 . A voltage is applied to the first, second, third, and fourth force comb electrodes 106 c , 106 d , 206 c , 206 d to generate an electrostatic force; detection capacitances D 1 -D 4 and force capacitors A 1 ˜A 4 form a closed-loop detection, controlling the first and second rectangular frames 101 , 201 in a balanced position.

The drive force can be generated by applying a pair of differential AC drive voltages with a DC bias via input route on top monocrystalline silicon layer on first fixed drive electrode 110 a , third fixed drive electrode 110 c and second fixed drive electrode 110 b , fourth fixed drive electrode 110 d of first sub-structure 100 . It can be expressed as

in which, n represents the number of movable drive comb fingers, ε is the dielectric constant, h and d stand for the thickness and gap of combs, U d and U a represent the DC and AC component of drive voltage, and ω d is its frequency.

Similarly, drive force can be generated by applying in-phase drive voltage on second sub-structure 200 . Since the comb fingers arrangement of first and second sub-structures 100 , 200 is antisymmetric, the generated drive forces are out-of-phase.

Consequently, the moveable structures of first and second sub-structures 100 , 200 play simple harmonic motion along drive axis under the drive force. The displacement can be expressed as 2 when the drive force frequency equals to the resonant frequency of drive mode.

in which, F d0 represents the amplitude of drive force, k x is the stiffness along X-axis, Q x is the quality factor of drive mode. It corresponding velocity is

When a Z-axis angular rate ω z applied on the gyroscope, the Coriolis acceleration along Y-axis can be derived as

a c = 2 ⁢ ω z ⁢ V ⁢ ⁢ sin ⁢ ⁢ φ = 2 ⁢ ⁢ ω z ⁢ ω d ⁢ F d ⁢ ⁢ 0 ⁢ Q x k x ⁢ sin ⁢ ⁢ φ ⁢ ⁢ sin ⁢ ⁢ ω d ⁢ t ( 4 )

in which φ represents the angle between input angular rate and oscillation velocity.

Suppose the drive mass is m a , the Coriolis force applied on the sense proof mass is

F c =−m d a c =−2 m d ω z V sin φ  (5)

The directions of Coriolis inertial force and Coriolis acceleration are out-of-phase, therefore, the Coriolis forces on first rectangular frame 101 and second rectangular frame 201 are out-of-phase. The first rectangular frames 101 a nd second rectangular frames 201 play simple harmonic motion along sense Y axis with the Coriolis forces. In this way, the gap variation between moveable and fixed sense comb fingers follows the same trend of the first rectangular frames 101 and second rectangular frame 201 . The capacitances difference can be readout by interface circuit via output route on top monocrystalline silicon layer and converts it to voltage. The total output voltage is a sum of readout voltages of first sub-structures 100 and second sub-structures 200 and proportional to the input angular rate. The input angular rate direction can be determined by comparing the phase between phase detector's input and output voltage.