CN116892917A - Compact microelectromechanical angular rate sensor - Google Patents

Abstract

Embodiments of the present disclosure relate to compact microelectromechanical angular rate sensors. MEMS angular rate sensors are proposed, having two pairs of suspended masses micromachined on a semiconductor layer. The first pair includes two masses that are opposite and mirror images of each other. The first pair of masses has a driving structure for generating mechanical vibrations in a linear direction. The second pair of masses comprises two masses opposite and mirrored from each other. The second pair of masses is coupled to the first pair of driving masses with coupling elements. Two pairs of masses are coupled to a center bridge. The center bridge has a differential configuration for excluding any external disturbances. Each of the two pairs of masses includes a different portion for detecting different linear and angular motions.

Description

Compact microelectromechanical angular rate sensor

Technical Field

The present disclosure relates to a microelectromechanical system having enhanced mechanical properties, reduced size, and improved stability and sensitivity.

Background

In general, microelectromechanical systems (MEMS) are produced by micromachining layers of semiconductor material. The semiconductor material is deposited onto or grown on the sacrificial layer. The sacrificial layer may be removed by etching techniques to allow the semiconductor layer to move freely or oscillate as a film or cantilever. MEMS with small dimensions (typically microns) are widely used for sensing applications of integrated circuits.

MEMS are used for Angular Rate Sensors (ARS) and gyroscopes. MEMS-based ARS includes multiple masses movable in a linear direction as well as in a rotational direction. In these sensors, angular velocity may be detected based on displacement of the masses in response to any motion. The displacement may be detected based on a change in capacitance. The capacitance is generated by capacitive coupling between suspended semiconductor layers, which may be arranged in a parallel plate configuration, wherein a plurality of electrodes are fixed in parallel with a plurality of masses. The movable mass detects movement of the MEMS in various directions.

MEMS-based ARS typically include a symmetrical structure to detect motion in all directions. The movable structure of the ARS may have two pairs of masses, wherein each pair of masses has a symmetrical characteristic. The symmetric feature provides the ability to reject external disturbances when the mass is coupled to the differential detection structure. In this case, any possible external disturbance has the same or substantially similar effect (due to the symmetrical features) on both masses of a pair of masses. Thus, in the differential mode, the influence of the disturbance can be excluded from the readout process.

Each of the plurality of masses of the MEMS-based ARS may include a drive structure coupled with a sense structure. The drive structure may comprise drive electrodes, wherein the drive electrodes convert the electrical signals into mechanical movements of a drive mass coupled to the drive electrodes. The electrical signal may be an Alternating Current (AC) having a resonant frequency, which results in mechanical oscillation of the drive mass at a mechanical frequency corresponding to the resonant frequency. The oscillation frequency provides a biasing motion to enable the sensing structure to detect triaxial motion. In particular, a circuit coupled to the drive electrode may generate an oscillation frequency having a phase and an amplitude of the oscillating motion.

Disclosure of Invention

The present disclosure relates to a microelectromechanical system (MEMS) sensor for sensing triaxial motion (e.g., angular velocity). The architecture of the MEMS sensor is enhanced to improve both stability and sensitivity, with the sensor operating as an Angular Rate Sensor (ARS).

In one embodiment of the present disclosure, the MEMS-based ARS includes two pairs of suspended masses that are micromachined or otherwise formed from a single semiconductor or silicon layer. Each pair includes two masses that are opposite and mirror images of each other. The first pair of masses has a driving structure for generating an oscillation frequency in a linear direction. The first pair of masses may be referred to as "drive masses". The second pair of masses is coupled to the driving mass with coupling elements, wherein the coupling elements transfer the oscillating motion of the driving mass to the second pair of masses at the same resonant frequency. The first pair of masses and the second pair of masses are coupled to and surround the center bridge. The center bridge has a differential configuration for excluding any external disturbances. Each of the first and second pairs of masses detects different linear and angular motions. The configuration of the mass increases the stability and sensitivity of the MEMS sensor to triaxial motion.

Drawings

Aspects of the disclosure are best understood from the following detailed description when read with the accompanying drawing figures. It is noted that the various features are not drawn to scale.

FIG. 1A is a schematic top view of a microelectromechanical system according to an embodiment of the disclosure;

FIG. 1B is an enhanced view of the MEMS of FIG. 1A;

FIG. 1C is an enhanced view of the MEMS of FIG. 1A;

FIG. 1D includes more details of the MEMS of FIG. 1A;

FIG. 1E is an enhanced view of the center bridge of the MEMS of FIG. 1A;

FIG. 2A is an enhanced view of a spring of the MEMS of FIG. 1A;

FIG. 2B is a schematic illustration of the spring of FIG. 2A under an applied stress; and

fig. 2C is an enhanced view of a portion of the mass of fig. 2A.

Detailed Description

Fig. 1A is a schematic top view of a microelectromechanical system (MEMS) sensor 100, according to an embodiment of the disclosure. The MEMS sensor 100 may be an Angular Rate Sensor (ARS) or a tri-axis gyroscope configured to detect three-dimensional motion (e.g., x, y, and z in fig. 1A). The gyroscope may be a single silicon layer micromechanical element. The MEMS sensor 100 has a rectangular shape that is symmetrical along a first symmetry axis 100A and a second symmetry axis 100B.

The MEMS sensor 100 includes a substrate 102 coupled to a plurality of suspended masses. The plurality of suspended masses (112, 113, 115, 117) are coupled by coupling elements (128, 129, 130, 131) positioned at corners of adjacent masses. The coupling elements enable both driving and sensing of the movement of the masses. The MEMS sensor 100 includes a single drive system and three independent sense axes formed in a single crystal silicon layer. The plurality of suspended masses are micromachined in a monocrystalline silicon layer. The motion on the three independent shafts is sensed by displacement signals that are converted to electrical signals by parallel plate stators placed under the plurality of suspended mass blocks. In various embodiments, a parallel plate stator is formed in a single crystal silicon layer. As will be described in more detail below, the plurality of masses, the plurality of drive structures, the springs or elastic elements, and the sense electrodes are all formed of monocrystalline silicon or a semiconductor layer. The substrate 102 may be a semiconductor material such as silicon, silicon-on-insulator, or other suitable material.

The plurality of suspended masses includes a first mass 112 and a second mass 113 opposite and mirrored from the first mass 112. The plurality of suspension masses further includes a third mass 115 and a fourth mass 117, the fourth mass 117 being opposite and mirrored from the third mass 115.

The drive system includes a first drive structure 180 and a second drive structure 181 positioned in the fourth mass 117 and the third mass 115, respectively. The substrate 102 has a first edge 104 opposite a second edge 106 and a third edge 107 opposite a fourth edge 109. The first edge 104 is spaced apart from the second edge 106 by a distance S1. The distance S1 also extends from the outermost edge of the first spring 196 to the outermost edge of the second spring 197 (see fig. 1C).

In some embodiments, the length of the third edge 107 is the same as the length of the fourth edge 109, and the length of the fourth edge 109 is equal to or substantially equal to the distance S1. The third edge 107 is spaced apart from the fourth edge 109 by a distance L1. In some embodiments, the length of the first edge 104 is the same as the length of the second edge 106, and the length of the second edge 106 is equal to or substantially equal to the distance L1.

The first mass 112 has a maximum dimension D4 adjacent the first edge 104 (as shown in fig. 1B), and the second mass 113 has a maximum dimension adjacent the second edge 106. The largest dimension of the second mass 113 is substantially similar or identical to the largest dimension D4 of the first mass 112. For clarity of drawing, the second mass is not shown in fig. 1B. The third mass 115 includes a maximum end or dimension that is closer to the third edge 107 than the fourth edge 109. The fourth mass 117 includes a maximum end or dimension S2 that is closer to the fourth edge 109 than the third edge 107. The maximum dimension of the third mass 115 is substantially similar or identical to the maximum dimension S2 of the fourth mass 117. For clarity of drawing, the third mass 115 is not shown in fig. 1C.

The first and second drive structures 180, 181 include capacitive combs 180a, 181a (also referred to as comb drive actuators). Capacitive comb 180a is closer to fourth edge 109 than spring 166 and capacitive comb 181a is closer to third edge 107 than spring 166 a. Capacitive combs 180a, 181a provide actuation of the drive mass.

The first and second drive structures are configured to drive all four masses in a "heartbeat" manner. Fig. 1C depicts more details of the first and second drive structures 180, 181. The first drive structure 180 is adjacent or contiguous with the fourth edge 109 and the second drive structure is adjacent or contiguous with the third edge 107.

Center bridge 108 is centered between a plurality of suspended masses 112, 113, 115, and 117. In some examples, the center bridge 108 includes a square, rectangular, or polygonal frame 402. In fig. 1A, center bridge 108 includes four sides, each of which includes a flexible or resilient extension 402 a-402 d from the center bridge to one of the plurality of suspended masses 112, 113, 115, and 117. Each of the flexible extensions 402 a-402D is coupled in an opening extending from the center bridge 108 to one of the springs 116, 116a, 166, and 166a (more details are described in fig. 1B-1D). Within square frame 402 of center bridge 108, there are resilient elements (described in more detail in FIG. 1E) coupled to substrate 102 with four anchors 422a, 424a, 426a, and 428 a.

Each of the plurality of masses 112, 113, 115, and 117 includes a smaller end adjacent to the center bridge 108. The small end portions of masses 112 and 113 surround center bridge 108 (see extensions 120a, 120B in fig. 1B and symmetrical extensions of mass 113). The portions of the small ends of masses 112, 113 are located between the small ends of masses 115, 117 and center bridge 108. The extensions 402a, 402c extend from the center bridge 108 and pass through the distance between the small ends of the masses 112, 113.

The first mass 112 is coupled to the third mass 115 with a coupling element 128 and to the fourth mass 117 with a coupling element 130. The second mass 113 is coupled to the third mass 115 with a coupling element 129 and to the fourth mass 117 with a coupling element 131. The plurality of masses 112, 113, 115, and 117 are generally trapezoidal or truncated triangular in shape. The coupling elements 128-131 are coupled to the plurality of masses 112, 113, 115 and 117 at intermediate portions of the sloped sides of the trapezium or truncated triangle. In some examples, coupling elements 128-131 are drive springs that pull first mass 112 and second mass 113 when third mass 115 and fourth mass 117 are driven by first drive structure 180 and second drive structure 181. Coupling elements 128 and 130 have folded ends 128a and 130a adjacent first edge 104, adjacent anchors 132a, 134a, respectively (more details are depicted in fig. 1B). Coupling elements 129 and 131 have folded ends 129a and 131a adjacent second edge 106, adjacent anchors 132b, 134b, respectively (not shown for clarity of illustration).

To illustrate further features of the first mass 112, fig. 1B provides an enhanced view of the region 101 of fig. 1A. The region 101 includes portions of the first mass 112 and the third and fourth masses 115, 117. The second mass 113 includes similar features as described for the first mass 112 in fig. 1B, which is in a mirror-image orientation about the axis of symmetry 100B.

The first detection structure 110 comprises a plurality of openings 111 in the first mass 112 between the first edge 104 and the central bridge 108, the plurality of openings 111 being closer to the first edge 104 than the central bridge 108. A first spring 116 is located within the opening 114 in the first mass 112. The openings 114 are located between the plurality of openings 111 and the center bridge 108. A first portion 120 of the first mass 112 is located between the opening 114 and the center bridge 108, and a second portion 122 of the first mass is located between the opening 114 and the plurality of openings 111. The first portion 120 is closer to the center bridge 108 than the second portion 122 of the first mass 112.

The first portion 120 corresponding to the minimum size has a size D1 in the first direction y. Rigid extension 120a extends from center bridge 108 between flexible extensions 402a and 402 d. Rigid extension 120b extends around center bridge 108 between flexible extensions 402c and 402 d. The second portion 122 of the mass has a dimension D2 in the first direction y. The connecting portions 122a, 122b of the mass are coupled between the first portion 120 and the second portion 120 along the sides 114a, 114b of the opening 114. Side 114a is closer to extension 120a than side 114 b. Dimension D2 is greater than dimension D1. This difference between dimensions D1 and D2 results in first mass 112 having a truncated triangular or trapezoidal shape, wherein the area of first portion 120 closer to center bridge 108 is smaller than the area of second portion 122 closer to first edge 104.

The coupling elements or springs 130, 128 are coupled to the second portion 122 of the mass, i.e. the middle portion of the mass. From this position, springs 128, 130 extend at an angle away from the center bridge, but remain within the boundaries of the anchor (e.g., anchor 134 a).

The extensions 120a and 120b of the first mass 112 provide additional sensitivity during the detection phase. Thus, the extensions 120a and 120b allow for more significant movement to be detected than the portion of the first mass 112 that is away from the center bridge 108 (e.g., the second portion 122).

In various embodiments, a second spring 124 and a third spring 126 are coupled between the first edge 104 and the second portion 122. The second and third springs 124, 126 participate in the driving motion of the MEMS sensor 100 and detect motion about a third direction z that is transverse to the first and second directions x, y. Adjacent the first edge 104, the second spring 124 is located between the end 128a and the detection structure 110. Adjacent the first edge 104, the third spring 126 is located between the end 130a and the detection structure 110. The second spring 124 is separated from the third spring 126 by the detection structure 110. The coupling element 130 is closer to the third spring 126 than the second spring 124 of the first mass 112. The second spring 124 is a folded spring that includes a thin extension 127 extending from a first end 132 to a second end 138. The first end 132 is coupled to the substrate 102 by anchors 132a, and the second end 138 is coupled to an opening 139 in the first mass 112. Anchor 132a is closer to first edge 104 than opening 139. The thin extension 127 comprises a first folding element 127a extending along the first direction y and a second folding element 127b extending into the opening 139 of the first mass 112 along the second direction x.

The third spring 126 is a folded spring that includes a thin extension 137 that extends from the first end 134 to the second end 140. The first end 134 is coupled to the substrate 102 by anchors 134a, and the second end 140 is coupled to an opening 141 in the first mass 112. Anchor 134a is closer to first edge 104 than opening 141. The thin extension 137 comprises a first folding element 137a extending along the first direction y and a second folding element 137b extending into the opening 141 of the first mass 112 along the second direction x. Dimension D3 between first end 132 and first end 134 is greater than dimension D2. Dimension D3 is less than length L1 of first edge 104.

The first mass 112 includes a third portion 136 aligned with and adjacent to the plurality of openings 111. The third portion 136 is located between the second portion 122 and each of the second spring 124 and the third spring 126. The third portions 136 are located on both sides of the plurality of openings 111. The third portion 136 extends from the coupling element 128 to the coupling element 130 in the first direction y. The third portion 136 has a dimension D4 in the first direction y that is greater than the dimension D2. Dimension D4 is smaller than dimension D3.

The second end 138 of the second spring 124 extends into an opening 139 in the third portion 136 in the second direction x. The second end 140 of the third spring 126 extends into an opening 141 in the third portion 136 in the second direction x. Third portion 136 includes an opening 143 around anchor 144 and an opening 145 around anchor 146. In various embodiments, anchors 144, 146 may operate as stops for first mass 112. Opening 143 is separated from opening 145 by detection structure 110. The opening 143 is closer to the second spring 124 than the third spring 126, and the opening 145 is closer to the third spring 126 than the second spring 124.

In some embodiments, the first spring 116 has a folded configuration. The folded structure of the first spring 116 includes two separate loops 116b, 116c, the loops 116b and 116c being coupled together with a joint 116 d. Ring 116c is coupled to first portion 120 and ring 116b is coupled to second portion 122. Ring 116c is closer to center bridge 108 than ring 116 b. In some examples, ring 116c is directly coupled to center bridge 108 along second direction x by way of extension 402 d. Extension 402c is free to move independently of first portion 120. The folded configuration of the springs 116 provides flexibility for the first mass 112 to oscillate at the drive frequency in the second direction x, while the extension 402d provides flexibility for the first mass 112 to move in the third direction z.

The detection structure 110 comprises a plurality of electrodes 110a. Each of the plurality of electrodes 110a includes a structure 118. The structure 118 includes a movable electrode 118a and a fixed electrode 118b. The movable electrode 118a is part of the first mass 112, and the fixed electrode 118b is coupled to the substrate 102 (e.g., via an anchor). The plurality of electrodes 110a may include a plurality of movable electrodes 118a arranged parallel to one another along the first direction y, with each movable electrode 1180a being capacitively coupled to a respective fixed electrode 118b. The detection structure 110 may detect a motion about a third direction z, for example, a yaw motion (yaw motion). In this case, the detection structure 110 forms a yaw frame. The yaw movement changes the distance between the movable electrode 118a and the fixed electrode 118b. The capacitively coupled movable electrode 118a and fixed electrode 118b form an equivalent capacitance that can be read by an external readout circuit coupled to the MEMS sensor 100. The change in distance between the movable electrode 118a and the fixed electrode 118b has an adverse effect on the equivalent capacitance of the detection structure 110. Thus, the external readout circuit detects the yaw motion by reading out the change in the equivalent capacitance of the detection structure 110.

To illustrate further features of the fourth mass 117, fig. 1C provides an enhanced view of the region between the fourth edge 109 and the symmetry axis 100A of fig. 1A. The region of fig. 1C includes portions of the fourth mass 117 and the first and second masses 112, 113. The third mass 115 includes similar features as described for the fourth mass 117 in fig. 1C, in a mirror image orientation about the axis of symmetry 100A.

The second detection structure 160 is located in an opening 161 in the fourth mass 117 between the fourth rim 109 and the center bridge 108. The third spring 166 is located within an opening 164 in the fourth mass 117. Opening 164 is located between opening 161 and center bridge 108. The first portion 170 of the fourth mass 117 is located between the opening 164 and the center bridge 108, and the second portion 172 of the fourth mass 117 is located between the opening 164 and the opening 161. The first portion 170 is closer to the center bridge 108 than the second portion 172 of the fourth mass 117. Opening 164 is closer to center bridge 108 than opening 161.

The first portion 170 has a dimension D5 in the second direction x. The extensions 170a and 170b extend along the extension 402a toward the center bridge 108. Extension 170b is closer to first mass 112 than extension 170 a. The second portion 172 has a dimension D6 in the second direction x. Dimension D6 is greater than dimension D5. This difference between dimensions D5 and D6 results in a truncated triangular or trapezoidal shape of the fourth mass 117, wherein the first portion 170 closer to the center bridge 108 than the second portion 172 is smaller than the second portion 172 closer to the edge 109 than the first portion 170.

The extensions 170a and 170b of the fourth mass 117 provide additional sensitivity during the detection phase. Thus, the extensions 170a and 170b result in more significant movement being detected than a portion of the fourth mass 117 that is farther from the center bridge 108 (e.g., the second portion 172).

In various embodiments, the drive structure 180 is located between the fourth edge 109 and the second detection structure 160. The fourth mass 117 includes a third portion 186. The third portion 186 is aligned with the opening 161 and is adjacent to the opening 161. The third portions 186 are located on both sides of the opening 161 in the second direction x. The third portion is located between the second portion 172 and the drive structure 180 in the first direction y. The third portion 186 extends from the coupling element 130 to the coupling element 131 in the second direction x. The dimension D7 of the third portion 186 in the second direction x is greater than the dimension D6.

The fourth spring 174 extends along the second direction x from the opening 161 along the side 168 of the drive structure 180. The fifth spring 176 extends along the second direction x from the opening 161 along the side 168 of the drive structure 180. The sides 168 of the drive structure 180 are tangential to the detection structure 160. The fourth spring 174 is separated from the fifth spring 176 in the second direction x by the detection structure 160. The coupling element 130 is closer to the fourth spring 176 than the fifth spring 174 of the fourth mass 117.

The fourth spring 174 is a fold-over spring having a thin extension extending from the first end 182 to the second end 188. The first end 182 is coupled to the substrate 102 by an anchor 182a and the second end 188 is coupled to the drive structure 180. The fifth spring 176 is a fold-over spring having a thin extension extending from the first end 184 to the second end 190. The first end 184 is coupled to the substrate 102 by an anchor 184a and the second end 190 is coupled to the drive structure 180. The dimension D8 of the detection structure 160 in the second direction x is substantially the same as the distance of the first end 182 and the first end 184 in the second direction x. Dimension D8 is smaller than dimension D5.

The drive structure 180 includes openings 191, 192, and 193. Opening 191 is closer to coupling element 131 than openings 192 and 193 in the second direction x. The opening 193 is closer to the coupling element 130 than the openings 191 and 192 in the second direction x. The opening 192 is closer to the detection structure 160 than the openings 191 and 193 in the second direction x. Anchors are located in each of openings 191, 192, and 193. The drive structure 180 further comprises a pair of parallel electrodes 194 extending from the opening 192 to the opening 191 in the second direction x, and a pair of parallel electrodes 195 extending from the opening 192 to the opening 193 in the second direction x. Parallel electrode pairs 194 and 195 are separated by opening 192 and coupled to substrate 102 with a plurality of anchors. One of the parallel electrodes 194 is closer to the fourth edge 109 and is coupled to the side of the drive structure 180 closer to the fourth edge 109 with a plurality of movable electrodes (comb teeth 180a depicted in fig. 1A). The other electrode of the parallel electrode 194 is closer to the opening 161 and the spring 176, and is coupled to the side of the drive structure 180 closer to the opening 161 and the spring 176 using a plurality of movable electrodes (comb teeth 180a depicted in fig. 1A). One of the parallel electrodes 195 is closer to the fourth edge 109 and is coupled to the side of the drive structure 180 that is closer to the fourth edge 109 using a plurality of movable electrodes. The other electrode of the parallel electrode 195 is closer to the opening 161 and the spring 174 and is coupled to the sides of the drive structure 180 closer to the opening 161 and the spring 174 using a plurality of movable electrodes.

The folding spring 196 is located between the opening 191 and the fourth edge 109 in the first direction y. The spring 196 extends from the drive structure 180 to the second edge 106 along the second direction x. The end of the spring 196 near the second edge 106 is coupled to the substrate 102 with a pair of anchors. The folding spring 197 is located between the opening 193 and the first edge 104 in the first direction y. The spring 197 extends from the drive structure 180 to the first edge 104 along the second direction x. The end of the spring 197 near the first edge 104 is coupled to the substrate 102 with a pair of anchors. In addition to springs 174 and 176, folding springs 196 and 197 provide flexibility in oscillating fourth mass 117 in first direction y at the drive frequency.

Folding structure 198 has a first end 198a, which first end 198a is coupled to opening 191 and extends along a side of coupling member 131, and folding structure 198 is coupled to portion 186 with a second end 198 b. The extension of the folded structure 198 proximate the first end 198a folds and extends in the first direction y. The extension of the folded structure 198 proximate the second end 198b extends in the second direction x. The fold structure 199 has a first end 199a, the first end 199a being coupled to the opening 193 and extending along a side of the coupling element 130, and the fold structure 199 being coupled to the portion 186 with a second end 199 b. The extension of the fold structure 199 near the first end 199a folds and extends in the first direction y. The extension of the fold 199 near the second end 199b extends in the second direction x. Folding structures 198 and 199 provide flexibility in oscillating fourth mass 117 along third direction z and in moving about third direction z (e.g., yaw movement).

In some embodiments, the third spring 166 has a folded configuration. The folded structure includes two separate loops 166b, 166c coupled together by a joint 166 d. Ring 166c is coupled to first portion 170 and ring 166b is coupled to second portion 172. In some examples, ring 166c is directly coupled to center bridge 108 along first direction y via extension 402 a. Ring 166c is closer to center bridge 108 than ring 166 b. Extension 402a is free to move independently of first portion 170. The folded configuration of the spring 166 provides flexibility for the fourth mass 117 to oscillate at the drive frequency in the first direction y, while the extension 402a provides flexibility for the fourth mass 117 to move along the third direction z.

The detection structure 160 includes parallel electrodes 163 extending along the second direction x. The parallel electrodes 163 are coupled to the substrate 102 with a plurality of anchors (not shown for clarity). The electrode 163a of the parallel electrode 163 is closer to the driving structure 180 than the electrode 163 b. The electrode 163a is coupled to a side of the drive structure 180 with a plurality of movable electrodes. Electrode 163b is closer to portion 172 than electrode 163a and is coupled to the sides of portion 172 with a plurality of movable electrodes. The detection structure 160 may detect movement in the first direction y, including driving movement. The driving motion changes the distance between the movable and fixed electrodes 163a, 163b on the substrate 102. The change in distance has an adverse effect on the equivalent capacitance of the detection structure 160. The equivalent capacitance may be read by an external readout circuit coupled to the MEMS sensor 100. Accordingly, the MEMS sensor 100 detects the driving motion based on the change in the equivalent capacitance of the detection structure 160.

Fig. 1D is a more detailed view of the MEMS sensor 100 of fig. 1A. Region 123 in first mass 112 shows the boundaries of electrode 123a (not shown for clarity of drawing) formed in substrate 102. An electrode 123b (not shown for clarity of drawing) having the same shape as the region 123 is formed on the substrate 102 within the second mass 113. Region 123 has a shape that aligns with the shape of the combination of portions 120 and 122. Region 123 surrounds opening 114 and extends along the sides of center bridge 108. The shape of the region 123 in the portion 122 has a larger dimension along the first direction y and a smaller dimension along the second direction x than the portion 120. Electrode 123a combines with portions 120, 122 to form a capacitance. The capacitance varies with the position of the portions 120, 122. The spring 116 and extension 402d connected to the center bridge 108 provide movement of the portions 120, 122 in a third direction z, such as roll movement. An external readout circuit coupled to MEMS sensor 100 reads out the change in capacitance from electrode 123a on substrate 102. In some examples, the roll motion generates higher kinetic energy on the portion 120 than the portion 122, which results in a higher displacement of the portion 120 than the portion 122. Thus, portion 120 is more efficient than portion 122 when MEMS sensor 100 detects roll motion.

Region 125 in fourth mass 117 shows the boundaries of electrode 125a (not shown for clarity of the drawing) formed in substrate 102. An electrode 125b (not shown for clarity of drawing) having the same shape as the region 125 is formed on the substrate 102 within the third mass 115. Region 125 has a shape that aligns with the shape of the combination of portions 170 and 172. The region 125 surrounds the opening 164 and extends along the sides of the extension 402 a. The shape of the region 125 in the portion 172 has a larger dimension than the portion 170 along both the first direction y and the second direction x. The electrode 125a combines with the portions 170, 172 to form a capacitance. The capacitance varies with the position of the portions 170, 172. Spring 166 and extension 402a connected to center bridge 108 provide movement of portions 170, 172 in a third direction z, such as pitching movement. An external readout circuit coupled to the MEMS sensor 100 reads out the change in capacitance from the electrode 125a on the substrate 102. In some examples, pitch motion generates higher kinetic energy on portion 170 than portion 172, which results in a higher displacement of portion 170 than portion 172. Thus, portion 170 is more efficient than portion 172 when MEMS sensor 100 detects pitch motion.

To illustrate further features of center bridge 108, FIG. 1E provides an enhanced view of center bridge 108 of FIG. 1A. Center bridge 108 includes a square, rectangular, or polygonal frame 402. Internally, the frame 402 includes a first resilient structure 430a and a second resilient structure 430b. The first elastic structure 430a is symmetrical and mirror-images the second elastic structure 430B about the symmetry axis 100B. The first elastic structure 430a is closer to the extension 402d than the elastic structure 430b. A center point 450 located at the center of the frame 402 has a circular connection between the first extension 450a and the second extension 450 b. The first extension 450a connects the extension 402a into the extension 402c along the first direction y. The second extension 450b connects the center point of the first elastic structure 430a into the center point of the second elastic structure 430b along the second direction x. The first extension 450A extends along the symmetry axis 100B, and the second extension 450B extends along the symmetry axis 100A.

The first resilient structure 430a has a first end 422 and a second end 428. The first and second ends 422, 428 are coupled to the substrate 102 with anchors 422a, 428a, respectively. The elastic structure 430a has a thin extension folded between the first end 422 and the second end 428. The center point of the spring structure 430a has a cross-connect with the extension 450 b. The second resilient structure 430b has a first end 424 and a second end 426. The first and second ends 424, 426 are coupled to the substrate 102 with anchors 424a, 426a, respectively. The elastic structure 430b has a thin extension folded between the first end 424 and the second end 426. The center point of the elastic structure 430b has a cross-interconnection with the extension 450 a.

Extension 402d is coupled to frame 402 with a trapezoidal connection 414. The connector 414 has an opening 414a. The straight extension 420 is located inside the opening 414a. Extension 420 has a first end 416 and a second end 418. The first and second ends 416, 418 are coupled to the substrate 102 with anchors 416a, 418a, respectively. The first end 416 is closer to the extension 402a than the second end 418. Extension 402b is coupled to frame 402 with a trapezoidal connection 404. The connector 404 has an opening 404a. The straight extension 410 is located inside the opening 404a. Extension 410 has a first end 406 and a second end 408. The first and second ends 406, 408 are coupled to the substrate 102 with anchors 406a, 408a, respectively. The first end 406 is closer to the extension 402a than the second end 408.

Fig. 2A shows a quarter of the MEMS sensor 100 of fig. 1A between the symmetry axis 100A and the symmetry axis 100B. The stop 302 is positioned between the fourth mass 117 and the second mass 113. The stops are symmetrically positioned for the other quarter of the MEMS sensor 100. The stop 302 has an angular shape to prevent any excessive deflection of the fourth mass 117 and the second mass 113 (and the corresponding masses in the other quarter) in the first direction y and the second direction x. The stop 304 improves the robustness of the MEMS sensor 100 compared to available MEMS sensors for ARS applications.

Fig. 2B is an enlarged region 301 of the spring 166 of the fourth mass 117 in fig. 2A. The region 301 is repeated symmetrically for the other masses. Spring 266 is equivalent to spring 166 within opening 164. The opening 164 is equivalent to the boundary 367. Boundary 367 protects spring 266 from any excessive deflection. Excessive deflection increases the mechanical stress on the spring 266, which may damage the thin extension of the folded structure. Boundary 367 limits mechanical stress by reducing the space of movement of spring 266 within boundary 367.

Spring 266 in fig. 2B flexes under mechanical stress. The spring 266 has a limited space according to the boundary 367 to oscillate in the first direction y. In this case, the spring 266 contacts the boundary 367 in the point 368 and stops moving in the first direction y. The greatest mechanical stress acts on portion 370 of spring 266. Without the boundary 367, the spring 266 may move beyond the point 368, which results in a mechanical stress on the portion 370 that is greater than the maximum mechanical stress. In this case, a crack or fracture may occur in the portion 370. Thus, the boundary 367 protects the spring 266 from these potential damages.

Fig. 2C is an enlarged region 401 of the fourth mass 117 of the MEMS sensor 100 in fig. 2A. Region 401 is identical to masses 112, 113, 115, and 117 in fig. 1A. Region 401 has a hollow structure or opening. The hollow structure comprises a plurality of holes that repeat in a period 501 in both the first and second directions y, x. Each of the plurality of holes is square with a fixed dimension 502. Dimension 502 and period 501 define the resonant frequency of the hollow structure. By decreasing each of the size 502 and the period 501, the resonant frequency increases.

The MEMS sensor 100 of the present disclosure is capable of detecting triaxial motion. Triaxial motion includes driving motion, pitching motion, yawing motion and rolling motion. The driving motion includes a motion of the MEMS sensor 100 in a first direction y. As shown in fig. 1A-1E, springs 196, 197, 174, and 176 of fourth mass 117 (and corresponding springs of third mass 115) maintain the driving motion of MEMS sensor 100 at the resonant frequency (generated by the external oscillator). Additionally, the springs 116 of the first mass 112 and the springs 166 of the fourth mass 117 (and the corresponding springs of the second and third masses 113, 115) control the driving motion of the masses. The coupling elements 128, 129, 130 and 131 convert the generated driving motion of the third and fourth masses 115, 117 in the first direction y into a driving motion of the first and second masses 112, 113 in the second direction x. The driving motion of the mass may be an oscillating motion at a resonant frequency. The driving motion of the first mass 112 and the second mass 113 is inverted. Thus, the driving motion of the third mass 115 and the fourth mass 117 is anti-phase.

The pitching motion is a motion of the MEMS sensor 100 between the first direction y and the third direction z. The pitching motion is a rotational motion about the second direction x. During pitch motion, extension 402a and extension 402c operate in a sense mode in combination with center bridge 108 while providing free movement of third and fourth masses 115, 117 in accordance with pitch motion. The extensions 170a and 170b of the first portion 170 in the fourth mass 117 (and the corresponding extensions in the third mass 115) have a maximum displacement along the third direction z compared to the other portions of the fourth mass 117. The displacement may be read as a change in capacitance. Thus, the extensions 170a and 170b (and corresponding extensions in the third mass 115) increase the amplitude of the motion and thus increase the sensitivity of the MEMS sensor 100 to pitching motion.

The roll motion is the motion of the MEMS sensor 100 between the second direction x and the third direction z. The roll motion is a rotational motion about a first direction y. During roll motion, extension 402b and extension 402d operate in a sensing mode in combination with center bridge 108 while providing free movement of first mass 112 and second mass 113 in accordance with the roll motion. The extensions 120a and 120b of the first portion 120 (and the corresponding extensions in the second mass 113) in the first mass 112 have a maximum displacement along the third direction z compared to the other portions of the first mass 112. The displacement may be read as a change in capacitance. Thus, the extensions 120a and 120b (and corresponding extensions in the second mass 113) increase the amplitude of the motion and thus increase the sensitivity of the MEMS sensor 100 to tilting motion.

The yaw motion is a motion of the MEMS sensor 100 between a first direction y and a second direction x. The yaw movement is a rotational movement about a third direction z. During the yaw motion, the springs 126, 124, 196 and 197 of the first and fourth masses 112, 117 (and the corresponding springs in the second and third masses 113, 115) operate in a sense mode while providing free motion of the masses in accordance with the yaw motion. The portion 136 of the first mass span 112 (and the corresponding portion in the second mass 113) has a maximum displacement about the third direction z compared to the other portions of the first mass 112. The displacement may be read as a change in capacitance. Thus, the portion 136 of the first mass 112 (and the corresponding portion in the second mass 113) increases the amplitude of the orientation around the third direction z, and thus increases the sensitivity of the MEMS sensor 100 to yaw motion.

The MEMS sensor 100 of the present disclosure operates as an Angular Rate Sensor (ARS) or a multi-axis gyroscope. Zero Rate Level (ZRL) stability with respect to temperature is an important parameter managed in MEMS gyroscopes. In general, reducing the size of the sensor has a tradeoff with ZRL stability with respect to temperature, which is related to the sensing quality factor (Q factor) of the sensor. In the MEMS sensor 100 of the present disclosure, although the size of the sensor is reduced as compared to conventional MEMS gyroscopes, the enhancement of the Q factor of the sensor also provides high ZRL stability with respect to temperature. By reducing the size 502 and period 501 of the hollow structure in fig. 2C, the Q-factor of the mems sensor 100 is enhanced.

The robustness of the MEMS sensor 100 of the present disclosure is enhanced by varying aspects of the anchors or stops as compared to conventional MEMS gyroscopes. Anchors 146 and 144 of first mass 112 (and corresponding anchors of second mass 113) in fig. 1B are in-plane anchors that enhance the robustness of MEMS sensor 100. Additionally, the boundary 367 depicted in FIG. 2B enhances the robustness of the MEMS sensor 100 by protecting the spring from any potential damage due to excessive deflection.

In general, applying any strain to a MEMS gyroscope changes the sensitivity of the gyroscope, which is referred to as scale factor bias. This is because of the frequency mismatch between the drive frequency and the sense frequency. Typically, the sensing frequency is higher than the driving frequency. For a conventional MEMS gyroscope, the mismatch should be compensated for by a stiffness change of the elastic structure of the MEMS gyroscope. However, in the MEMS sensor 100 of the present disclosure, the sensing frequency is lower than the driving frequency. Thus, the scale factor offset is reduced, thereby enhancing sensitivity stability.

The present disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. Of course, these are merely examples and are not limiting. For example, in the following description, forming a first feature over or on a second feature may include embodiments in which the first feature and the second feature are formed in direct contact, and may also include embodiments in which additional features may be formed between the first feature and the second feature such that the first and second features are not in direct contact. Additionally, the present disclosure may repeat reference numerals/symbols in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as "below," "beneath," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature as illustrated in the figures. In addition to the orientations shown in the drawings, the spatially relative terms are intended to encompass different orientations of the device in use or operation. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

An apparatus may be summarized as including: a microelectromechanical sensor, the microelectromechanical sensor comprising: a substrate having a first edge; a center bridge; a first detection structure located between the first edge and the center bridge; and a first suspended mass located between the first edge and the center bridge, the first suspended mass comprising: a first opening; a first spring positioned in the first opening; a first portion located between the first opening and the central bridge, the first portion having a first dimension in a first direction, the first portion having an extension extending along a side of the central bridge in a second direction transverse to the first direction; and a second portion located between the first opening and the first detection structure, the second portion having a second dimension in the first direction, the second dimension being greater than the first dimension.

The first suspended mass may include a second spring between the first edge and the second portion and a third spring between the first edge and the second portion, the second spring being separated from the third spring by the first detection structure.

The microelectromechanical sensor may include: a first drive spring coupled to a first side of the first suspended mass; and a second drive spring coupled to the second side of the first suspended mass, the second drive spring being closer to the third spring than the second spring of the first suspended mass.

The first suspended mass may include a third portion extending from the second portion, the third portion aligned with and overlapping the first detection structure.

The third portion may be coupled to the second spring and the third spring.

The third portion may be coupled to the first drive spring and to the second drive spring.

The center bridge may include: a center spring structure; a plurality of first anchors coupled to the substrate and to the central spring structure; and an outer frame surrounding the first plurality of anchors and coupled to the central spring structure.

The center bridge may include: a first extension extending from the outer frame into the first suspended mass, the extension of the first portion of the first suspended mass being closer to the central spring structure than the first extension of the central bridge along the second direction.

An apparatus may be summarized as including: a microelectromechanical sensor, the microelectromechanical sensor comprising: a substrate having a first edge opposite a second edge; a center bridge; a first detection structure between the first edge and the central bridge; a second detection structure located between the second edge and the center bridge; a first suspended mass located between the first edge and the center bridge, the first suspended mass comprising: a first opening; a first spring positioned in the first opening; a first portion located between the first opening and the center bridge, the first portion having an extension extending along a side of the center bridge; and a second portion located between the first opening and the first detection structure; and a second suspended mass located between the second edge and the center bridge, the second suspended mass comprising: a second opening; a second spring positioned in the second opening; a first portion located between the second opening and the center bridge, the first portion having an extension extending along a side of the center bridge; and a second portion located between the second opening and the second detection structure.

The microelectromechanical sensor may include: a third suspended mass coupled to the center bridge and located between the first and second suspended masses; and a fourth suspended mass aligned with the third suspended mass along a first direction, the first suspended mass aligned with the second suspended mass along a second direction transverse to the first direction, the fourth suspended mass coupled to the center bridge.

The microelectromechanical sensor may comprise a first drive structure spaced apart from the central bridge by the third suspended mass and a second drive structure spaced apart from the central bridge by the fourth suspended mass.

The microelectromechanical sensor may comprise a third detection structure located between the first drive structure and the third suspended mass, and a fourth detection structure located between the second drive structure and the fourth suspended mass.

The third suspended mass may include: a third opening; a third spring positioned in the third opening; a first portion located between the third opening and the center bridge, the first portion having an extension extending along a side of the center bridge; and a second portion located between the third opening and the third detection structure.

The fourth suspended mass may include: a fourth opening; a fourth spring positioned in the fourth opening; a first portion located between the fourth opening and the center bridge, the first portion having an extension extending along a side of the center bridge; and a second portion located between the fourth opening and the fourth detection structure.

The microelectromechanical sensor may include: a first L-shaped anchor is coupled to the substrate and is located between the extension of the first portion of the first suspended mass and the extension of the first portion of the third suspended mass.

The microelectromechanical sensor may include: a second L-shaped anchor coupled to the substrate and located between the extension of the first portion of the first suspended mass and the extension of the first portion of the fourth suspended mass; a third L-shaped anchor coupled to the substrate and located between the extension of the first portion of the third suspended mass and the extension of the first portion of the second suspended mass; and a fourth L-shaped anchor coupled to the substrate and located between the extension of the first portion of the second suspended mass and the extension of the first portion of the fourth suspended mass.

A method of sensing angular rate by a microelectromechanical sensor may be summarized as including: driving the first mass with a first driving structure and the second mass with a second driving structure, the driving comprising an oscillating movement at a driving frequency; coupling the drives of the first and second masses to the third and fourth masses by coupling elements, each of the coupling elements being coupled between two of the masses; detecting a driving motion with a first detection structure of the first mass and a second detection structure of the second mass, the first detection structure being located between the first driving structure and the center bridge, and the second detection structure being located between the second driving structure and the center bridge; detecting a yaw motion with a third detection structure of the third mass and a fourth detection structure of the fourth mass; detecting pitch motion by a first extension of the first mass and a second extension of the second mass, the first extension extending from the first detection structure towards the central bridge, wherein a dimension of the first extension closer to the central bridge is smaller than a dimension of the first extension closer to the first detection structure, the second extension extending from the second detection structure towards the central bridge, wherein a dimension of the second extension closer to the central bridge is smaller than a dimension of the second extension closer to the second detection structure; and detecting a roll motion by a third extension of the third mass and a fourth extension of the fourth mass, the third extension extending from the third detection structure towards and along a side of the center bridge, the fourth extension extending from the fourth detection structure towards and along a side of the center bridge.

The sensing frequency may be less than the driving frequency.

The driving movement of the first mass may be controlled by a first spring and the driving movement of the second mass may be controlled by a second spring, the first extension extending around the first spring and the second extension extending around the second spring.

The detection of the driving motion, yaw motion, pitch motion and roll motion may be detected in a differential mode by the symmetrical structure of the center bridge.

The various embodiments described above may be combined to provide further embodiments. Aspects of the embodiments can be modified, as necessary, to employ concepts of the various patents, applications and publications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the present disclosure.

Claims (20)

1. An apparatus, comprising:

A microelectromechanical sensor, comprising:

a substrate having a first edge;

a center bridge;

a first detection structure located between the first edge and the central bridge; and

a first suspended mass between the first edge and the center bridge, the first suspended mass comprising:

a first opening;

a first spring located in the first opening;

a first portion located between the first opening and the central bridge, the first portion having a first dimension in a first direction, the first portion having an extension extending along a side of the central bridge in a second direction transverse to the first direction; and

a second portion located between the first opening and the first detection structure, the second portion having a second dimension in the first direction, the second dimension being greater than the first dimension.

2. The apparatus of claim 1, wherein the first suspended mass comprises a second spring between the first edge and the second portion and a third spring between the first edge and the second portion, the second spring being separated from the third spring by the first detection structure.

3. The apparatus of claim 2, wherein the microelectromechanical sensor comprises:

a first drive spring coupled to a first side of the first suspended mass; and

a second drive spring is coupled to a second side of the first suspended mass, the second drive spring being closer to the third spring than the second spring of the first suspended mass.

4. The apparatus of claim 3, wherein the first suspended mass includes a third portion extending from the second portion, the third portion aligned with and overlapping the first detection structure.

5. The apparatus of claim 4, wherein the third portion is coupled to the second spring and the third spring.

6. The apparatus of claim 5, wherein the third portion is coupled to the first drive spring and to the second drive spring.

7. The apparatus of claim 1, wherein the center bridge comprises:

a center spring structure;

a plurality of first anchors coupled to the substrate and to the central spring structure; and

an outer frame surrounding the first plurality of anchors and coupled to the central spring structure.

8. The apparatus of claim 7, wherein the center bridge comprises:

a first extension extending from the outer frame into the first suspended mass, the extension of the first portion of the first suspended mass being closer to the center spring structure than the first extension of the center bridge along the second direction.

9. An apparatus, comprising:

a microelectromechanical sensor, comprising:

a substrate having a first edge opposite a second edge;

a center bridge;

a first detection structure located between the first edge and the central bridge;

a second detection structure located between the second edge and the central bridge;

a first suspended mass between the first edge and the center bridge, the first suspended mass comprising:

a first opening;

a first spring located in the first opening;

a first portion located between the first opening and the central bridge, the first portion having an extension extending along a side of the central bridge; and

a second portion located between the first opening and the first detection structure; and

a second suspended mass between the second edge and the center bridge, the second suspended mass comprising:

A second opening;

a second spring positioned in the second opening;

a first portion located between the second opening and the central bridge, the first portion having an extension extending along a side of the central bridge; and

a second portion located between the second opening and the second detection structure.

10. The apparatus of claim 9, wherein the microelectromechanical sensor comprises:

a third suspended mass coupled to the center bridge and located between the first and second suspended masses; and

a fourth suspended mass aligned with the third suspended mass along a first direction, the first suspended mass aligned with the second suspended mass along a second direction transverse to the first direction, the fourth suspended mass coupled to the center bridge.

11. The apparatus of claim 10, wherein the microelectromechanical sensor comprises a first drive structure spaced apart from the center bridge by the third suspended mass and a second drive structure spaced apart from the center bridge by the fourth suspended mass.

12. The apparatus of claim 11, wherein the microelectromechanical sensor comprises a third detection structure located between the first drive structure and the third suspended mass and a fourth detection structure located between the second drive structure and the fourth suspended mass.

13. The apparatus of claim 12, wherein the third suspended mass comprises:

a third opening;

a third spring located in the third opening;

a first portion located between the third opening and the central bridge, the first portion having an extension extending along a side of the central bridge; and

a second portion located between the third opening and the third detection structure.

14. The apparatus of claim 13, wherein the fourth suspended mass comprises:

a fourth opening;

a fourth spring located in the fourth opening;

a first portion located between the fourth opening and the central bridge, the first portion having an extension extending along a side of the central bridge; and

a second portion located between the fourth opening and the fourth detection structure.

15. The apparatus of claim 14, wherein the microelectromechanical sensor comprises: a first L-shaped anchor is coupled to the substrate and is located between the extension of the first portion of the first suspended mass and the extension of the first portion of the third suspended mass.

16. The apparatus of claim 15, wherein the microelectromechanical sensor comprises:

a second L-shaped anchor coupled to the substrate and located between the extension of the first portion of the first suspended mass and the extension of the first portion of the fourth suspended mass;

a third L-shaped anchor coupled to the substrate and located between the extension of the first portion of the third suspended mass and the extension of the first portion of the second suspended mass; and

a fourth L-shaped anchor is coupled to the substrate and is located between the extension of the first portion of the second suspended mass and the extension of the first portion of the fourth suspended mass.

17. A method of sensing angular rate by a microelectromechanical sensor, the method comprising:

driving the first mass with a first driving structure and driving the second mass with a second driving structure, the driving comprising an oscillating movement at a driving frequency;

coupling the drives of the first and second masses to third and fourth masses by coupling elements, each of the coupling elements being coupled between two of the masses;

Detecting a driving motion with a first detection structure of the first mass and a second detection structure of the second mass, the first detection structure being located between the first driving structure and a center bridge, and the second detection structure being located between the second driving structure and the center bridge;

detecting a yaw motion with a third detection structure of the third mass and a fourth detection structure of the fourth mass;

detecting pitch motion by a first extension of the first mass extending from the first detection structure towards the central bridge, wherein a dimension of the first extension closer to the central bridge is smaller than a dimension of the first extension closer to the first detection structure, and a second extension of the second mass extending from the second detection structure towards the central bridge, wherein a dimension of the second extension closer to the central bridge is smaller than a dimension of the second extension closer to the second detection structure; and

the roll motion is detected by a third extension of the third mass extending from the third detection structure towards and along the side of the center bridge and a fourth extension of the fourth mass extending from the fourth detection structure towards and along the side of the center bridge.

18. The method of claim 17, wherein a sensing frequency is less than the driving frequency.

19. The method of claim 17, wherein the driving motion of the first mass is controlled by a first spring and the driving motion of the second mass is controlled by a second spring, the first extension extending around the first spring and the second extension extending around the second spring.

20. The method of claim 17, wherein the detection of the driving motion, the yaw motion, the pitch motion, and the roll motion is differential mode detected by a symmetrical structure of the center bridge.