Improved capacitive sensing in MEMS mirror structures

Abstract

According to certain embodiments, a microelectromechanical system (MEMS) device has a MEMS mirror structure with a rotatable mirror. Rotation of the mirror produces a change in measured capacitance corresponding to the angle of rotation. The MEMS structure is located on an oxide layer deposited on a substrate. A parasitic capacitance exists between the MEMS mirror structure and the substrate. An additional capacitance is provided between the substrate and a DC voltage source. The additional capacitance is much larger than the parasitic capacitance and shunts the parasitic capacitance to ground to minimize its effect on the measured capacitance.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Application No. 17 / 009,513, filed on September 1, 2020, which is incorporated herein by reference for all purposes. Background Art

[0003] Modern vehicles are often equipped with sensors designed to detect objects and terrain features around the vehicle in real time to enable technologies such as lane change assistance, collision avoidance, and autonomous driving. Some commonly used sensors include image sensors (e.g., infrared or visible light cameras), acoustic sensors (e.g., ultrasonic parking sensors), radio detection and ranging (RADAR) sensors, magnetometers (e.g., passive sensing of large ferrous objects such as trucks, cars, or railcars), and light detection and ranging (LiDAR) sensors.

[0004] LiDAR systems typically use a light source and a light detection system to estimate the distance to environmental features (e.g., pedestrians, vehicles, structures, plants, etc.). For example, a light detection and ranging (LiDAR) system can emit a light beam (e.g., a pulsed laser beam) to illuminate a target and then measure the time it takes for the emitted light beam to reach the target and then return to a receiver located near the transmitter or at a known location. In some light detection and ranging (LiDAR) systems, the light beam emitted by the light source can be swept across a two-dimensional or three-dimensional area of ​​interest according to a scanning pattern to generate a "point cloud" containing a collection of data points corresponding to target points in the area of ​​interest. The data points in the point cloud can be updated dynamically and continuously, and can be used to estimate, for example, the distance, size, position, and velocity of an object relative to the light detection and ranging (LiDAR) system.

[0005] Light steering typically includes projecting light in a predetermined direction to help achieve, for example, detection and ranging of objects, illumination and scanning of objects, etc. Light steering can be used in many different application areas, including, for example, autonomous vehicles, medical diagnostic equipment, etc., and can be configured to perform the emission and reception of light. For example, a light steering transmitter can include a micromirror to control the projection direction of light so as to detect / image an image. In addition, a light steering receiver can also include a micromirror to select the direction of incident light to be detected by the receiver to avoid detecting other unwanted signals. A micromirror assembly typically includes a micromirror and an actuator. In the micromirror assembly, the micromirror can be connected to a substrate via a connecting structure (e.g., a torsion bar, a spring, etc.) to form a pivot point. This type of micromirror assembly can be a microelectromechanical system (MEMS) type structure, which can be used in a light detection and ranging (LiDAR) system in an autonomous vehicle, which can be configured to detect objects and determine the corresponding distances of these objects from the vehicle. LiDAR systems typically work by illuminating a target with a light pulse and measuring the characteristics of the reflected return signal. The return signal is typically captured as a point cloud. The width of light pulses often ranges from a few nanoseconds to a few milliseconds.

[0006] A typical electrostatic MEMS mirror consists of a spring, a mirror block, and comb fingers. The mirror block is suspended by mechanical springs, which are usually anchored in the SiO2 / Si substrate, and the mirror block moves when a drive voltage (V) is applied to the comb fingers. Since the overlap area in the comb fingers changes with the displacement of the mirror block, the capacitance (χ) of the comb fingers changes. BC ) and acts as feedback to control the motion of the mirror block. However, the accuracy of capacitance measurement is hampered by parasitic capacitance. The most significant parasitic capacitance is observed at the substrate. This capacitance couples in parallel with the comb capacitance, thus limiting the sensed voltage (ΔV sensed When the parasitic capacitance is large or the impedance (χ) is low, the change in the comb capacitance has the least effect on the sensed voltage. BS +χ CS <<χ BC hour, Small. Therefore, in order to improve sensitivity, the parasitic capacitance needs to be as small as possible. However, the substrate is a fundamental element in the MEMS mirror, and electrical decoupling is extremely difficult and / or almost impossible. Summary of the invention

[0007] The technology disclosed herein generally relates to micro-electro-mechanical system (MEMS) mirrors that can be used, for example, in light detection and ranging (LiDAR) systems or other beam steering systems. More specifically, but not by way of limitation, disclosed herein is a MEMS micromirror comprising a mirror mass that tilts and produces a measurable change in capacitance. The change in capacitance is proportional to the tilt angle of the mirror, and thereby provides a feedback signal to indicate the angle of the mirror. However, measurement errors may be caused by parasitic capacitance. Various inventive embodiments are described herein for minimizing the effects of parasitic capacitance, including systems, modules, devices, components, circuits, materials, methods, etc.

[0008] According to certain embodiments, a MEMS device has a MEMS mirror structure with a rotatable mirror. Rotation of the mirror produces a change in measured capacitance corresponding to the angle of rotation. The MEMS structure is located on an oxide layer deposited / grown on a substrate. A parasitic capacitance exists between the MEMS mirror structure and the substrate. An additional capacitance is provided between the substrate and a direct current (DC) / alternating current (AC) voltage source. The additional capacitance is much larger than the parasitic capacitance and shunts the parasitic capacitance to ground to minimize its effect on the measured capacitance.

[0009] According to some embodiments, a large additional capacitor provides a low impedance element to improve the sensed voltage sensitivity and reduce noise. add ) is built up around the MEMS mirror and / or added to the bottom of the substrate with an additional oxide layer.

[0010] The terms and expressions used in the past are used as descriptive terms rather than limiting, and no equivalents of the features shown and described or portions thereof are intended to be excluded when such terms and expressions are used. However, it is recognized that various modifications are possible within the scope of the claimed systems and methods. Therefore, it should be understood that although the present systems and methods are disclosed in detail through examples and optional features, those skilled in the art should recognize modifications and variations of the concepts disclosed herein, and such modifications and variations are deemed to fall within the scope of the systems and methods defined by the appended claims.

[0011] In one embodiment, a MEMS device for beam steering in a light detection and ranging (LiDAR) system for an autonomous vehicle is provided. The device has a mirror block 304 having a reflective surface 305. There are first and second support springs 302 connected to opposite sides of the mirror block 304 to support the mirror block. First and second common terminals 310 are connected to the first and second support springs 302. A plurality of first comb teeth 306 extend from the mirror block perpendicular to the first and second support springs 302 on first and second sides. There are first and second bias terminals 314 opposite to the first and second sides of the mirror block 304. A set of second comb teeth 312 extend from the first and second bias terminals. The second comb teeth are interlaced with the first comb teeth and partially overlap the first comb teeth. An oxide layer 320 is located below the first and second common terminals and the first and second bias terminals. A substrate 322 is located below the oxide layer. There is a sensed capacitance (C) between the common terminal (C) and the anchor point and bias terminal (B) BC ). The sensed capacitance (C BC ) is proportional to the total overlap between the first comb teeth and the second comb teeth. There is also a first parasitic capacitance (C CS ), and there is a second parasitic capacitance (C BS ). An additional capacitor C is provided between the substrate 322 and the voltage source 606 add The additional capacitance is several times greater than the sum of the first and second parasitic capacitances.

[0012] In one embodiment, the additional capacitance is a structure 602 located outside the first and second common terminals and the first and second bias terminals and located in the same layer as the first and second common terminals and the first and second bias terminals. In one embodiment, the structure includes a rectangular ring 602 that surrounds the first and second common terminals and the first and second bias terminals.

[0013] In one embodiment, the additional capacitance is a second oxide layer 702 on the substrate 322 on the opposite side from the first oxide layer 320. A conductor layer 704 is located on the second oxide layer 702 on the opposite side from the substrate 322. A ground connection 706 is coupled to the conductor layer 704.

[0014] This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used solely to determine the scope of the claimed subject matter. The subject matter should be understood with reference to the corresponding portions of the complete specification of the present disclosure, any or all drawings, and each claim.

[0015] The foregoing as well as other features and examples will be described in more detail in the following description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The features of the various embodiments described above and other features and advantages of certain embodiments of the present invention will become more apparent through the following detailed description in conjunction with the accompanying drawings, in which:

[0017] Figure 1 An autonomous vehicle with a LiDAR system is shown in accordance with certain embodiments;

[0018] Figure 2A shows an example of light projection operation according to some embodiments;

[0019] Figure 2B shows an example of light detection operation according to some embodiments;

[0020] Figure 3 It is a schematic diagram of the structure of a prior art MEMS mirror containing parasitic capacitance;

[0021] Figure 4 yes Figure 3 A cross-sectional view along the straight line A-A';

[0022] Figure 5 yes Figure 3 and Figure 4 Equivalent circuit diagram of the structure;

[0023] Figure 6 is a schematic diagram of a first embodiment of a MEMS mirror having a parasitic capacitance cancellation ring structure according to certain embodiments;

[0024] Fig. 7A According to some embodiments Figure 6 A cross-sectional view along the straight line A-A' in the structure;

[0025] Figure 7B Shows Fig. 7A An alternative embodiment wherein the back side is open for a cavity opening process;

[0026] Figure 8 is a cross-sectional view of a second embodiment of a MEMS mirror having a parasitic capacitance reduction substrate structure according to certain embodiments;

[0027] Fig. 9 is a schematic diagram of a third embodiment of a MEMS mirror having a parasitic capacitance cancellation parallel block structure according to certain embodiments;

[0028] Fig.10 According to some embodiments Figure 6 , Figure 8 and Fig. 9 Equivalent circuit diagram of the structure;

[0029] Fig.11 Yes Figure 6A graph showing the sensed voltage sensitivity of an embodiment of the present invention compared with a typical prior art structure; and

[0030] Fig.12 Yes Figure 6 FIG. 4 is a graph showing sensed voltage noise reduction of an embodiment of the invention compared with a typical prior art structure. DETAILED DESCRIPTION

[0031] Aspects of the present disclosure generally relate to a light detection and ranging (LiDAR) system, and more particularly to reducing parasitic capacitance of a micro-electro-mechanical system (MEMS) micromirror device according to certain embodiments.

[0032] In the following description, multiple examples of MEMS-based micromirror structures are described. For the purpose of explanation, specific configurations and details are set forth to give a thorough understanding of the embodiments. However, it is apparent to those skilled in the art that certain embodiments may be implemented or realized without every detail disclosed. In addition, well-known features may be omitted or simplified to avoid obstructing the understanding of the innovative functions described herein.

[0033] The following high-level overview is intended to give a basic understanding of some of the novel innovations illustrated in the accompanying drawings and in the corresponding description provided below. The technology disclosed herein generally relates to MEMS mirrors that can be used, for example, in light detection and ranging (LiDAR) systems or other beam steering systems. More specifically and without limitation, disclosed herein are MEMS mirrors that include, for example, Figure 6 The MEMS micromirror of the mirror block 304 shown in the figure tilts and produces a capacitance change proportional to the overlap area change, and the overlap area change is proportional to its tilt angle. Therefore, by measuring the capacitance change, the tilt angle can be measured. The capacitance change is proportional to the tilt angle of the mirror, and thus provides a feedback signal to indicate the angle of the mirror. However, measurement errors may be caused by parasitic capacitance between the mirror structure and the substrate. This article describes a variety of innovative embodiments that minimize the impact of parasitic capacitance.

[0034] According to certain embodiments, a MEMS device has a MEMS mirror structure with a rotatable mirror. Rotation of the mirror produces a change in measured capacitance corresponding to the angle of rotation. The MEMS structure is located on an oxide layer deposited on a substrate. A parasitic capacitance exists between the MEMS mirror structure and the substrate. An additional capacitance is provided between the substrate and a DC voltage source. The additional capacitance is much larger than the parasitic capacitance (e.g., 10 to 100 times larger) and shunts the parasitic capacitance to ground to minimize its effect on the measured capacitance.

[0035] In one embodiment, the MEMS mirror structure has comb teeth extending from the mirror block and interleaved with the comb teeth from the bias terminal. The capacitance between the comb teeth is measured to determine the degree of mirror tilt. The mirror is tilted to reflect the light beam and is quickly tilted in different directions to scan an area. The tilt is achieved by a voltage applied across the common (COM) terminal and the bias terminal connected to the mirror block. Different amounts of tilt cause the comb teeth to separate at different angles, thereby changing the overlap area between the comb teeth and thereby changing the capacitance between the comb teeth.

[0036] According to certain embodiments, the large additional capacitance provides a low impedance element to improve the sensed voltage sensitivity and reduce noise. Figure 6 -7 embodiment, the additional capacitor (C add ) are accumulated in a ring structure around the MEMS mirror having. Alternative structures of the ring can be used to allow the additional capacitance to be located near the mirror structure. For example, instead of a continuous ring around the MEMS mirror structure, a series of capacitive regions can be used. Fig. 9 In the embodiment, the additional capacitor (C add ) has two regions, similar to blocks located on either side of the MEMS mirror structure, rather than above or below. This reduces the overall footprint of the chip structure. Alternative geometries can be used to maximize the additional capacitance while preventing the device footprint from becoming too large.

[0037] exist Figure 8 In the embodiment, the additional capacitor (C add ) is added to the bottom of the substrate with the additional oxide layer 702. On the bottom of the added oxide layer, a metal or other conductive layer 704 is added. The metal can be aluminum or another metal or metal compound. Alternatively, a conductive material such as silicide can be used for the most part. This provides a capacitor in which the added oxide layer is the dielectric and the metal layer is the two terminals of the capacitor. The metal layer is connected to a DC voltage or ground to shunt the parasitic capacitance from the sensing node of the capacitor being measured.

[0038] In general, aspects of the invention relate to the implementation of light steering that can be used in many different applications. For example, a LiDAR module of an autonomous vehicle can incorporate a light steering system. The light steering system can include a transmitter and receiver system to steer incident light emitted in different directions around the vehicle and receive reflected light reflected from objects around the vehicle using a sequential scanning process, which can be used to determine the distance between the object and the vehicle to help achieve autonomous driving navigation.

[0039] Light steering can be achieved by one or more micromirror assemblies (e.g., typically part of an array), each micromirror assembly having a movable micromirror and an actuator (or multiple actuators). The micromirrors and actuators can be formed as MEMS on a semiconductor substrate, which allows the MEMS to be integrated with other circuits on the semiconductor substrate (e.g., controllers, interface circuits, etc.), thereby enabling a simpler, easier, more robust and more economically efficient manufacturing process.

[0040] In a micromirror assembly, the micromirror may be mechanically connected (e.g., "anchored") to a semiconductor substrate via a connection structure (e.g., a torsion bar, a torsion spring, a torsion beam, etc.) to form a pivot point and an axis of rotation. As described herein, "mechanical connection" or "connection" may include direct connection or indirect connection. For example, the micromirror may be indirectly connected to a substrate via a connection structure (e.g., a torsion bar or a torsion spring) to form a pivot / connection point. The micromirror may be rotated around a pivot / connection point ("referred to herein as a pivot point") on the axis of rotation by an actuator. In the embodiments presented herein, electrostatic actuators are typically used; however, any suitable type of actuator (e.g., piezoelectric, thermomechanical, etc.) may be implemented, and those skilled in the art having the benefit of the present disclosure should recognize many modifications, combinations, variations, and alternative embodiments thereof.

[0041] In some embodiments, each micromirror can be configured to rotate a certain rotation angle to reflect (and turn) light toward a target direction. The connection structure can be deformed to adapt to the rotation, but the connection structure also has a certain degree of spring stiffness, which changes with the rotation angle and resists the rotation of the micromirror to set the target rotation angle. In order to rotate the micromirror to the target rotation angle, the actuator can apply torque to the micromirror based on the moment of inertia of the mirror and the spring stiffness of the given target rotation angle. Different torques can be applied to rotate (e.g., oscillate) the micromirror at or near the resonant frequency to achieve different target rotation angles. The actuator can then remove the torque, and the connection structure can return the micromirror to its default direction for the next rotation. Based on the mass of the micromirror and the spring constant of the connection structure (shown as a force rod in all figures of the present disclosure), the rotation of the micromirror can be repeated in the form of oscillations, usually at or near the resonant frequency of the micromirror. In various embodiments described throughout the present disclosure, the reference to rotating the micromirror at or near the resonant frequency can be expressed within a specific range of the resonant frequency. For example, "at or close to" the resonant frequency can mean within + / -5% of the resonant frequency, although other tolerances are possible (e.g., + / -1%, + / -2%, + / -3%, + / -10%, etc.), as will be appreciated by those skilled in the art having the benefit of this disclosure. Other terms that can mean "at or close to" in the manner described above include "approximately," "substantially," etc. In some embodiments, the connection structure can be configured on opposite and diametrically opposed sides of a mirror or gimbal.

[0042] In some embodiments, each micromirror can be configured to receive an incident light beam at a common rotation angle with other micromirrors in the array to collectively turn the incident light beam toward a target direction (e.g., in front of a vehicle). In some embodiments, each micromirror can rotate around two orthogonal axes to provide a first projection angle range along a vertical dimension and a second projection angle range along a horizontal dimension. The first projection angle range and the second projection angle range can define a two-dimensional field of view (FOV) in which the projected light is located to detect / scan an object. The FOV can also define a two-dimensional directional range of incident light that can be reflected by an object and detected by a receiver. Less commonly, the LiDAR system can also operate on a single axis (e.g., in the horizontal direction). Those skilled in the art who benefit from the present disclosure should recognize its many implementations and alternative embodiments.

[0043] Typical system environment of some embodiments of the present invention

[0044] Figure 1 An autonomous vehicle 100 capable of implementing various embodiments described herein is shown. The autonomous vehicle 100 may include a LiDAR module 102. The LiDAR module 102 enables the autonomous vehicle 100 to perform object detection and ranging in the surrounding environment. Based on the results of the object detection and ranging, the autonomous vehicle 100 can drive according to the rules of the road and maneuvers to avoid collisions with detected objects. The LiDAR module 102 may include a light steering transmitter 104 and a receiver 106. The light steering transmitter 104 may project one or more light signals 108 in various directions (e.g., incident angles) at different time points using any suitable scanning pattern, and the receiver 106 may monitor the light signal 110 generated by the light signal 108 being reflected by the object. The light signals 108 and 110 may include, for example, light pulses, frequency modulated continuous wave (FMCW) signals, amplitude modulated continuous wave (AMCW) signals, and the like. LiDAR module 102 may detect an object based on receiving light signal 110 and may perform a range determination (e.g., the distance of the object) based on the time difference between light signals 108 and 110, as will be appreciated by those skilled in the art having the benefit of this disclosure. Figure 1As shown, the LiDAR module 102 can transmit a light signal 108 toward the front of the autonomous vehicle 100 at time T1, and receive a light signal 110 reflected by an object 112 (e.g., another vehicle) at time T2. Based on the received light signal 110, the LiDAR module 102 can determine that the object 112 is located directly in front of the autonomous vehicle 100. Moreover, based on the time difference between T1 and T2, the LiDAR module 102 can also determine the distance 114 between the autonomous vehicle 100 and the object 112. Thus, the autonomous vehicle 100 can adjust its speed (e.g., slow down or stop) based on the detection and ranging of the LiDAR module 102 to avoid collision with the object 112.

[0045] Figure 2A and Figure 2B A simplified block diagram of an example of a LiDAR module 200 according to some embodiments is shown. The LiDAR module 200 can be an example of a LiDAR system 102, and can include a transmitter 202, a receiver 204, and a LiDAR controller 206, which can be configured to control the operation of the transmitter 202 and the receiver 204. The transmitter 202 can include a light source 208 and a collimating lens 210, and the receiver 204 can include a lens 214 and a photodetector 216. The LiDAR module 200 can also include a mirror assembly 212 (also referred to as a "mirror structure") and a beam splitter 213. In some embodiments, the LiDAR module 102, the transmitter 202, and the receiver 204 can be configured as a coaxial system to share the mirror assembly 212 to perform a light steering operation, while the beam splitter 213 is configured to reflect incident light reflected by the mirror assembly 212 to the receiver 204.

[0046] Figure 2A An example of a light projection operation according to certain embodiments is shown. To project light, the LiDAR controller 206 can control the light source 208 (e.g., a pulsed laser diode, an FMCW signal source, an AMCW signal, etc.) to emit the light signal 108 as part of a light beam 218. The light beam 218 can diverge when leaving the light source 208 and can be converted into a collimated light beam 218 by the collimating lens 210. The collimated light beam 218 can be incident on the mirror assembly 212, which can reflect the collimated light beam 218 to redirect it along an output projection path 219 to the object 112. The mirror assembly 212 may include one or more rotatable mirrors. Figure 2A A mirror assembly 212 having one mirror is shown; however, the micromirror array may include multiple micromirror assemblies, which may collectively provide the steering capabilities described herein. The mirror assembly 212 may also include one or more actuators ( Figure 2A224 of the output projection path 219 relative to a first dimension (e.g., an x-axis), and the rotation about the second axis 226 may change a second angle 228 of the output projection path 219 relative to a second dimension (e.g., a z-axis). The LiDAR controller 206 may control the actuator to produce different combinations of rotation angles about the first axis 222 and the second axis 226, so that the movement of the output projection path 219 may follow a scanning pattern 232. A range 234 of movement of the output projection path 219 along the x-axis, and a range 238 of movement of the output projection path 219 along the z-axis may define a FOV. An object within the FOV, such as object 112, may receive and reflect the collimated light beam 218 to form a reflected light signal, which may be received by the receiver 204 and detected by the LiDAR module, as described below with reference to FIG. Figure 2B In some embodiments, the mirror assembly 212 may include one or more comb teeth having comb-shaped electrodes (see, e.g., Figure 3 ), as described in further detail below.

[0047] Figure 2B An example of a light detection operation according to certain embodiments is shown. The LiDAR controller 206 can select an incident light direction 239 for the receiver 204 to detect the incident light. This selection can be based on setting the rotation angle of the rotatable mirror of the mirror assembly 212 so that only the light beam 220 propagating along the light direction 239 is reflected to the beam splitter 213, and then the light beam 220 is transferred to the photodetector 216 through the collimator lens 214. With this arrangement, the receiver 204 is able to selectively receive signals related to the ranging / imaging of the object 112 (or any other object within the FOV), such as the light signal 110 generated by the object 112 reflecting the collimated light beam 218, without receiving other signals. As a result, the impact of environmental interference on object ranging and imaging can be reduced, and system performance can be improved.

[0048] Parasitic capacitance in a typical MEMS mirror structure

[0049] Figure 3 Schematic diagram of the structure of a prior art MEMS mirror containing parasitic capacitance. Figure 3A typical electrostatic MEMS mirror structure 300 is shown with springs 302, mirror blocks 304, and comb teeth 306, 312. The mirror blocks 304 are suspended by mechanical springs 302, which are typically anchored in a SiO2 / silicon substrate 308 and anchored at an anchor point and a common terminal (sometimes simply referred to as "common" or "COM") 310. The comb teeth 306 are connected to the mirror blocks 304 and are interleaved with comb teeth 312 connected to an anchor point and a bias terminal (sometimes simply referred to as "bias") 314. Terminal 310 provides the common (COM) terminal of the mirror, both providing a drive voltage and sensing capacitance changes between the comb teeth 306 connected to the mirror blocks 304, and between the interleaved comb teeth 312 connected to the anchor point and bias terminal 314. The anchor point and bias terminal 314 are connected to a bias voltage, which is typically an AC voltage.

[0050] As shown, this structure enables rotation about the axis of spring 302. In another embodiment, not shown to avoid complicating the figure, an additional spring may be provided to provide a second orthogonal axis of rotation of the mirror block 304. Additional staggered comb teeth are then provided, connected to separate bias and COM anchor terminals.

[0051] There are other variabilities in the comb teeth that can help in measuring capacitance (without affecting parasitic capacitance). For example, thickness varies, which also affects the springs because they are made from the same Si film. There are several trade-offs, but higher capacitance is generally desired. Greater area overlap (larger comb teeth and smaller gaps between them) provides greater capacitance and actuation force, but it also reduces the quality factor caused by air friction (damping) between them. The comb tooth gap is also limited by manufacturing; the achievable aspect ratio (device thickness over feature size) is about 20. Higher capacitance is easier to measure and provides greater force, but is limited by manufacturing and reduces the quality factor. Optimizing these trade-offs, the comb tooth capacitance is still not much larger than the parasitic capacitance (because SiO2 is about 2μm thick and has a relative dielectric constant of 4, while air is 1).

[0052] Figure 4 yes Figure 3 A cross-sectional view along the straight line A-A'. Figure 4 As can be seen in the figure, when a drive voltage 318 (V) is applied across the comb teeth 306, 312 between the COM terminal 310 and the bias terminal 314, the mirror block 304 tilts. Since the overlap area in the comb teeth changes with the displacement of the mirror block, the capacitance of the comb teeth changes proportionally and is sensed by the sensing system 316 and used as feedback to control the movement of the mirror block. As shown in the figure, the overlap between the comb teeth 306 and 312 changes, and its capacitance change (ΔC) is proportional to the overlap area change (ΔA), which is proportional to the tilt angle β. However, the accuracy of capacitance measurement is hindered by parasitic capacitance.

[0053] Figure 5 It is the parasitic capacitance Figure 3 and Figure 4 The equivalent circuit diagram of the structure of FIG. The sensing system 316 is shown, which has a sensing power supply V, a sensing voltage V sensed and reference capacitor C ref The sensing capacitance between the interlaced comb teeth is C BC The most significant parasitic capacitance is observed across the substrate, shown as C BS and C CS This parasitic capacitance C BS and C CS and comb capacitance C BC coupled in parallel, thus limiting the sensed voltage (ΔV sensed ) sensitivity. When the parasitic capacitance corresponding to the lower impedance (χ) is large, the change in comb capacitance has the least effect on the sensed voltage. In other words, when χ BS +χ CS <<χ BC hour, Small. Therefore, in order to improve sensitivity, parasitic capacitance needs to be as small as possible. However, the substrate is a basic element in the MEMS mirror, and electrical decoupling is extremely difficult.

[0054] Additional capacitors to reduce parasitic capacitance effects

[0055] Figure 6 FIG. 1 is a schematic diagram of a first embodiment of a MEMS mirror having a parasitic capacitance reduction ring structure according to certain embodiments. The structure is similar to Figure 3 The structure is different in that a ground (GND) terminal 602 is added as a ring around the MEMS mirror structure. The ground terminal 602 provides additional capacitance, as shown in FIG. Fig. 7A , 7B This can be seen in the cross-sectional view along the line AA' shown in FIG. Figure 6 A range of multiple dimensions is shown. In general, the size of the mirror structure before the additional capacitance is added through the ground terminal 602 ranges from 1×1 mm to up to 20×20 mm. Therefore, the total chip size is about 20% to 30% larger than the mirror area to provide space for the additional capacitance. There is a trade-off between footprint (the smaller the better) and capacitance (the larger the better). Typically, the footprint is dominated by the mirror size (from 1×1 mm to 20×20 mm and other possible combinations such as 12×18, etc.), and in one embodiment, the width of the ring should be about ~100-200μm. This width is similar to the width of the anchor and bias terminal 314 and the anchor and COM terminal 310, both of which are in the range of 100-200μm.

[0056] Fig. 7A According to some embodiments Figure 6 A cross-sectional view along the straight line A-A' in the structure of FIG. From this view, a reflective layer 305 can be seen on the mirror block 306. The reflective layer can be aluminum or any other reflective material. The ground (GND) ring 602 provides additional capacitance between the GND terminal 602 and the Si substrate 322, where the SiO2 layer 320 acts as a dielectric. The GND terminal 602 is connected to the ground line 604. In one embodiment, the height of the GND terminal 602 is between 40-200μm, similar to the height of the COM terminal 310. The GND terminal 602 and the bias terminal 314 are etched from the same layer and therefore have the same height in one embodiment. The height of the SiO2 layer 320 is much smaller, at least 20 times smaller, between 1-2μm. The substrate layer 322 is typically 400-500μm. Typically, MEMS are fabricated on a SiO (Silicon on Insulator) wafer consisting of a Si device layer (of which the mirror blocks are made, whose thickness in one embodiment extends from 40 μm to 200 μm), an oxide, and a Si handle layer or substrate. In one embodiment, the Si layer is treated like a metal sheet, which has no effect on the capacitance. The capacitance therefore depends on the oxide given by C = (ε_r area) / thickness, where ε_r is the relative dielectric constant and is different for different oxides.

[0057] In one embodiment, the substrate 322 is subjected to a DC voltage 606 (V dc ) biased and connected to ground 608. In one embodiment, V dc The range of can be between -200 and +200 mV. A ground connection 608 is provided. In one embodiment, V dc The connections can be made through contacts on the back side of the chip. In another embodiment, vias can be provided through other layers, where the metal connections are surrounded by an insulating layer so that all contacts can be made on the top of the chip. The contacts can be made by depositing metal pads, such as aluminum (Al) coatings for wire bonding.

[0058] The DC voltage 606 (V dc ) will eliminate the dynamic capacitance of the Si substrate 322. When the mirror is driven by an AC voltage 318 of up to 200Vpp, some charge consumption can be observed on the substrate. Due to the transition of the Si substrate from charge consumption to charge accumulation or vice versa, the substrate capacitance changes when the driving voltage is applied. In order to avoid this transition and parasitic capacitance changes, a DC bias voltage is applied in the substrate to operate only in the accumulation or consumption state. In theory, this power supply can act as a ground for the substrate (assuming superposition), thereby eliminating DC noise. But in practice, the DC power supply has an output impedance, making the substrate active again. If the consumption problem is handled or tolerated in other ways, an alternative embodiment is to simply ground the substrate.

[0059] In one embodiment, an array of MEMS mirrors is used. The mirrors in the array are mechanically and electrically interconnected so that they can operate synchronously. All connections are around the entire array; isolating each mirror affects optical performance by reducing the fill factor.

[0060] Figure 7B Show Fig. 7A An alternative embodiment in which the back side is open for a cavity opening process using Figure 6 It is shown that the oxide layer 320A and the substrate layer 322A form an open cavity 702.

[0061] Figure 8 7 is a cross-sectional view of a second embodiment of a MEMS mirror with a parasitic capacitance reduction substrate structure according to certain embodiments. The capacitor is added to the bottom of the chip using an oxide layer 702 and a metal layer 704. The metal layer 704 is connected to a ground line 706. The oxide layer 702 can be any number of oxides, such as SiO2, Al2O2, etc. The thickness of the oxide layer 702 affects the total capacitance, but may cause some undesirable stress, so in one embodiment the thickness is optimized accordingly. In various embodiments, a range of thickness values ​​from 0.1 μm to up to 2 μm is used, depending on the film and process.

[0062] like Figure 8 As shown, in one embodiment, the substrate 322 is applied with a DC bias voltage 708 (V dc ), connected to ground line 706. To maximize capacitance, oxide layer 702 and metal layer 704 extend over the entire area of ​​the MEMS mirror structure to the edge of bias region 314. In alternative embodiments, they may extend further, for example, to the edge of the chip, where the MEMS mirror structure is unlikely to extend to the edge of the chip. Alternatively, layers 702 and 704 may extend only beyond one (or more) boundaries of the MEMS mirror structure, for example Figure 8 As shown extending to the right in the figure, both enable contact to the DC voltage 708 and provide additional capacitor area.

[0063] The fabrication of the bottom capacitor can be achieved by a variety of methods, such as physical vapor deposition (PVD), electron beam deposition, thermal evaporation, DC / RF sputtering deposition and / or reactive sputtering deposition. Before dicing and after the MEMS mirror process, the entire wafer is placed on the material source (metal and / or oxide). Both films can be deposited consecutively.

[0064] Fig. 9is a schematic diagram of a third embodiment of a MEMS mirror with a parasitic capacitance reduction parallel block structure according to certain embodiments. In this embodiment, instead of forming a ring for the anchor and ground terminals, two parallel blocks 920 are formed, which have contact terminals 916 for connecting to the ground. The rest of the structure is similar to the ring embodiment, and the contact area is also shown. Similar contact areas can be added to Figure 6 and 8 The structure of the chip can provide a wider contact area. Moreover, the contact area can be moved further to the periphery of the chip.

[0065] Fig. 9 An electrostatic MEMS mirror structure 900 is shown having a spring 902, a mirror block 904, and comb teeth 906, 912. The mirror block 904 is suspended by a mechanical spring 902, which is typically anchored in a SiO2 / silicon substrate 908 and anchored at an anchor and COM terminal 910. The comb teeth 906 are connected to the mirror block 904 and are interleaved with comb teeth 912 connected to an anchor and bias terminal 914. Terminal 910 provides a common (COM) terminal for the mirror, both providing a drive voltage and sensing capacitance changes between the comb teeth 906 connected to the mirror block 904 and the interleaved comb teeth 912 connected to the anchor and bias terminals 914. The anchor and bias terminals 914 are connected to a bias voltage, which is typically ground.

[0066] The structures shown in the drawings herein are illustrative and are not intended to be drawn to scale or to limit possible geometries. For example, the terminal pad rectangular areas 910, 914, and 916 may be further away from the MEMS mirror structure and larger than the MEMS mirror structure shown in the drawings to provide space for wire bonding.

[0067] As shown, this structure enables rotation about the axis of spring 902. In another embodiment, not shown to avoid complicating the figure, an additional spring can be provided to provide a second orthogonal rotation axis of mirror block 904. Additional staggered comb teeth are then provided, connected to the separate COM terminals and bias anchor terminals used. For other embodiments, a similar dual-axis structure can be provided.

[0068] The mirror structures described above and in the accompanying drawings are shown in certain embodiments, and other embodiments may be used. For example, the mirror block may be elliptical rather than rectangular. Alternatively, an elliptical reflective surface may be deposited on the mirror block. Any number of other variations of the mirror structure shape may be used.

[0069] In an alternative embodiment, Figure 6 -7 ring structure and Figure 8 The bottom capacitors of the two transistors are combined to provide greater capacitance while keeping the ring structure relatively narrow to limit the increase in chip area. Fig.10In the example, an external capacitor C_ref is connected, the value of which can also be optimized to obtain maximum sensitivity.

[0070] Fig.10 According to some embodiments Figure 6 , Figure 8 and Fig. 9 The equivalent circuit diagram of the structure. Figure 5 Similarly, a sensing system 1016 is shown, which has a sensing power supply V, a sensed voltage V sensed and reference capacitor C ref In one embodiment, the sensing system 1016 uses a Wheatstone bridge circuit. In one embodiment, the sensing voltage can be driven by a 1-10 MHz signal. The sensing capacitance between the interlaced comb teeth is C BC The most significant parasitic capacitance is observed across the substrate, shown as C BS and C CS This parasitic capacitance C BS and C CS and comb capacitance C BC coupled in parallel, thus limiting the sensed voltage (ΔV sensed ) sensitivity. When the parasitic capacitance corresponding to the lower impedance (χ) is large, the change in comb capacitance has the least effect on the sensed voltage. In other words, when χ BS +χ CS <<χ BC hour, Therefore, in order to improve sensitivity, the parasitic capacitance needs to be as small as possible. This is achieved by adding capacitor 1002 C add To achieve this. Capacitor 1002, C add Corresponding to Fig. 7A Layers 602, 320 and 322, Figure 8 Layers 322, 702 and 704 and Fig. 9 The capacitor formed by layers 920, 908 and 918 in FIG.

[0071] The sensing node is node 1004. The added capacitor 1002 shunts the parasitic capacitance to ground 1006 away from the sensing node. Ground 1006 is the ground terminal of the AC. Therefore, this provides leakage current to ground without affecting the sensing node and thus the measured capacitance C. BC have any significant impact.

[0072] like Fig.10 The equivalent circuit is shown in

[0073] where χ eq1 = x BS ||χ CS ||χGND And x eq2 = x BC ||χ ref ||χ BS ( and ω=2πf).

[0074] Fig.11 Yes Figure 6 FIG. 4 is a graph showing the sensed voltage sensitivity of an embodiment of FIG. 1 compared with a typical prior art structure. Fig.11 and Fig.12 All based on Figure 6 Simulation of several data points in the ring capacitor structure. Fig.11 The graph will be ΔV sensed (Sensitivity) Compared with typical prior art configurations. Fig.11 Shown corresponding to 100×C BC and 10×C BC The additional capacitance of the comb capacitance changes (ΔC BC ) voltage sensitivity With parasitic capacitance (C BS ). As the parasitic capacitance increases, the sensitivity decreases for both cases. As can be seen, the configuration of the present invention shows that the additional impedance χ corresponding to the additional capacitance add values, up to 20% improvement over typical prior art configurations.

[0075] Fig.12 Yes Figure 6 The graph compares the voltage noise reduction of the sensed embodiment of the present invention with the typical prior art structure. (Noise Reduction). Corresponding to the sensitivity of the signal to the parasitic capacitance. As can be seen, this ratio is smaller than the typical prior art case, as shown in the figure. This means that in the case of variable parasitic capacitance, the new configuration of the present invention is not easily affected by noise.

[0076] Manufacturing process

[0077] The MEMS mirror structure is manufactured using semiconductor manufacturing processes. A variety of processes can be used to achieve the structure of the present invention. For example, one process is as follows. The process starts with an SOI wafer, which consists of a SI / SiO2 / Si stack (40-120um / 1-2um / 400-600um). The back is etched, followed by Au or reflective metal deposition and patterning. Next, the Si and SiO2 layers on the front are etched to form a mirror structure. Figure 7BAn alternative embodiment is shown where the back side is open for the cavity process, where a ring configuration is used. For a closed cavity, the Si on the front side of the cavity wafer is etched, and then the second wafer is merged and polished to the desired MEMS structure thickness to form a Si membrane. The reflective metal is then deposited and patterned by Si etching to form the MEMS mirror structure.

[0078] MEMS mirror array

[0079] The MEMS mirror structure described herein can form a part of a micromirror array. The micromirror array can include an array of micromirror assemblies, each of which includes a micromirror and an actuator. In the micromirror assembly, the micromirror can be connected to a substrate by a connecting structure (e.g., a torsion bar, a spring, etc.) to form a pivot, and the micromirror can be driven by an actuator to rotate around the pivot. Each micromirror can be rotated by a certain rotation angle to reflect (and turn) light from a light source to a target direction. Each micromirror can be rotated by an actuator to provide a first projection angle range along a vertical axis and a second projection angle range along a horizontal axis. The first projection angle range and the second projection angle range can define a two-dimensional field of view (FOV) in which the projected light is located to detect / scan an object. The FOV can also define the direction of the incident light reflected by the object detected by the receiver.

[0080] In some examples, the mirror assembly can include two rotatable mirror arrays to perform light steering along a first dimension (e.g., an x-axis) and a second dimension (e.g., a z-axis). In one embodiment, the MEMS mirror array includes: a first rotatable mirror array for receiving and reflecting a light beam from a light source; a second rotatable mirror for receiving a light beam reflected by the first rotatable mirror array; a first actuator array configured to rotate each rotatable mirror of the first rotatable mirror array; and a second actuator configured to rotate the second rotatable mirror. The controller is configured to control the array of first actuators and second actuators to rotate the array of first rotatable mirrors and the second rotatable mirrors, respectively, to set an angle of a first light path relative to the first dimension and to set an angle of a second light path in a second dimension orthogonal to the first dimension, so as to perform one of the following operations: reflect light from the light source along the light path, or reflect input light propagating along the light path to a receiver. In some aspects, the light source is a laser diode.

[0081] In one embodiment, each micromirror will have its own individual additional capacitance. In another embodiment, for Figure 8 The additional capacitance at the bottom of the chip shown may extend across the entire bottom or a large portion of the chip including multiple micromirrors. For a mirror array, in one embodiment, each mirror has its own comb actuator, and the total actuation capacitance is the sum of the capacitance of each mirror. Therefore, the sensing capacitance is the total capacitance.

[0082] In one embodiment, a micromirror array is formed by each micromirror being a separate semiconductor chip. Several mirrors or a mirror array (a mirror array is a chip) are manufactured in a wafer, and then the wafer is cut. Each device is then packaged.

[0083] In one embodiment, a MEMS device for beam steering in a light detection and ranging (LiDAR) system for an autonomous vehicle is provided. The device includes the following elements:

[0084] a mirror block 304 having a reflective surface 305 and at least first and second corresponding sides;

[0085] first and second supporting springs 302, wherein first ends of the first and second supporting springs are connected to the first and second corresponding side surfaces of the mirror block 304 at opposite sides, respectively, to support the mirror block;

[0086] First and second common terminals 310 connected to the first and second support springs 302 at second ends of the first and second support springs, respectively;

[0087] a plurality of first comb teeth 306 extending from the mirror block perpendicularly to the first and second support springs 302 on the first and second sides;

[0088] first and second bias terminals 314, the first and second bias terminals being opposite to first and second sides of the mirror block 304;

[0089] a plurality of second comb teeth 312 extending from the first and second bias terminals, the plurality of second comb teeth 312 being interlaced with the plurality of first comb teeth 306 and partially overlapping the plurality of first comb teeth;

[0090] an oxide layer 320 disposed below the first and second common terminals and the first and second bias terminals;

[0091] a substrate 322 disposed below the oxide layer;

[0092] There is a sensed capacitance (C) between the common terminal (C) and the anchor and bias terminals (B). BC ), which is proportional to the overlap between the first plurality of comb teeth and the second plurality of comb teeth;

[0093] There is a first parasitic capacitance (C CS ), and there is a second parasitic capacitance (C BS );as well as

[0094] The additional capacitor C between the substrate 322 and the voltage source 606 add, wherein the additional capacitance is several times greater than the capacitance of the first and second parasitics combined. In one embodiment, the additional capacitance includes a structure 602 located outside the first and second common terminals and the first and second bias terminals and in the same layer as the first and second common terminals and the first and second bias terminals. In one embodiment, the structure includes a rectangular ring 602 that surrounds the first and second common terminals and the first and second bias terminals.

[0095] In one embodiment, the additional capacitor includes:

[0096] A second oxide layer 702, the second oxide layer being located on a side of the substrate 322 opposite to the first oxide layer 320;

[0097] A conductor layer 704 located on a side of the second oxide layer 702 opposite to the substrate 322 ; and a ground connection 706 coupled to the conductor layer 704 .

[0098] Other variations are within the spirit of the present disclosure. Therefore, although certain examples of the illustrations thereof are shown in the accompanying drawings and described in detail above, a variety of modifications and alternative configurations are easily obtained according to the disclosed technology. However, it should be understood that there is no intention to limit the present disclosure to one or more specific forms disclosed, but rather the purpose is to cover all modifications, alternative structures and equivalents that fall within the spirit and scope of the present disclosure as defined in the appended claims. For example, any example, alternative example, etc. and the concepts thereof may be applied to any other example described in the present disclosure and / or within its spirit and scope.

[0099] For example, instead of the rectangular mirror blocks shown in the drawings, oval or circular mirror blocks may be used. Such mirror blocks may still have extended comb teeth. The adjacent bias terminals may be bent to match the oval shape and have corresponding extended comb teeth. Alternatively, the bias terminals may be rectangular and the extended comb teeth may be different lengths so that they overlap the same amount with the equal length comb teeth of the bias terminals. Alternatively, different amounts of overlap may be provided for comb teeth of different lengths. It is not necessary to have the same amount of overlap, as it is the capacitance change with tilt that is important, not the absolute capacitance.

[0100] The MEMS mirror structure with the additional capacitance of the present invention can be used in a variety of other applications besides LiDAR. The beam steering technology can also be used in other optical systems, such as optical display systems (e.g., televisions), optical sensing systems, optical imaging systems, etc. In various beam steering systems, the light beam can be steered by, for example, a rotating platform driven by a motor, a multi-dimensional mechanical ladder, a current-controlled mirror, a resonant fiber, a MEMS mirror array, or any combination thereof. The MEMS micromirror can be rotated about a pivot or connection point by, for example, a micromotor, an electromagnetic actuator, an electrostatic actuator, or a piezoelectric actuator.

[0101] The MEMS mirror structure with the additional capacitance of the present invention can drive the mirror block by different types of actuators. In some optical steering systems, the emitted or received light beam can be steered by a micromirror array. Each micromirror can rotate around a pivot or connection point to deflect the light incident on the micromirror to the desired direction. The performance of the micromirror can directly affect the performance of the optical steering system, such as the field of view (FOV), the quality of the point cloud, and the quality of the image produced using the optical steering system. For example, in order to increase the detection range and FOV of the LiDAR system, micromirrors with large rotation angles and large apertures can be used, which may lead to an increase in the maximum displacement and moment of inertia of the micromirror. In order to achieve high resolution, a device with a high resonant frequency can be used, which can be achieved using a rotating structure with high stiffness. It may not be easy to achieve such desired performance using electrostatically actuated micromirrors, because the comb teeth used in the electrostatically actuated micromirrors may not provide the required force and torque, and may be disengaged at large rotation angles, especially when the aperture of the micromirror is increased to improve the detection range. Some piezoelectric actuators can be used to achieve large displacements and large scanning angles due to their ability to provide much greater driving force at relatively low voltages than electrostatic actuation types.

[0102] The use of the terms "one", "one", "the" and similar references in the context of describing the disclosed examples (particularly in the context of the appended claims) should be interpreted as covering the singular and the plural, unless otherwise stated herein or explicitly stated to the contrary. Unless otherwise stated, the terms "having", "including" and "comprising" are otherwise interpreted as open terms (i.e., meaning "including but not limited to"). The term "connected" should be interpreted as being partially or completely contained therein, connected to or connected together, even if there is an indirect object therein. The phrase "based on" should be understood as open, not limited in any way, and is intended to be interpreted or otherwise interpreted as "at least partially based on" in any way where appropriate. Unless otherwise stated herein, references to numerical ranges herein are intended only to be a shorthand method of individually citing each individual numerical value falling within the range, and each individual numerical value is incorporated into the specification as if it were individually cited herein. Unless otherwise stated herein or otherwise stated to the contrary by context, all methods described herein can be performed in any suitable order. Unless otherwise specified, the use of any and all examples or exemplary language (e.g., "such as") provided herein is intended only to better illustrate examples of the present disclosure and is not intended to limit the scope of the present disclosure. No language in the specification should be construed as indicating that any non-claimed element is essential to the practice of the present disclosure.

Claims

1. A micro-electromechanical system (MEMS) device for beam steering in a light detection and ranging system for an autonomous vehicle, the device comprising: a mirror block having a reflective surface and at least first and second corresponding sides; first and second supporting springs, wherein first ends of the first and second supporting springs are connected to the first and second corresponding side surfaces of the mirror block at opposite sides, respectively, to support the mirror block; first and second common terminals connected to the first and second support springs, respectively, at second ends of the first and second support springs; a plurality of first comb teeth extending from the mirror block on the first and second sides perpendicular to the first and second support springs; first and second bias terminals, the first and second bias terminals being opposite to the first and second sides of the mirror block; a plurality of second comb teeth extending from the first and second bias terminals, the plurality of second comb teeth being interlaced with and partially overlapping the plurality of first comb teeth; a first oxide layer beneath the first and second common terminals and the first and second bias terminals; a substrate located below the first oxide layer; There is a sensed capacitance (C) between the common terminal (C) and the bias terminal (B). BC ), the sensed capacitance (C BC ) is proportional to the overlap between the plurality of first comb teeth and the plurality of second comb teeth; There is a first parasitic capacitance (CCS) between the common terminal and the substrate, and a second parasitic capacitance (C BS );as well as An additional capacitance is located between the substrate and a voltage source, wherein the additional capacitance is several times greater than the combined capacitance of the first and second parasitics.

2. The MEMS device according to claim 1, wherein: The voltage source is connected to ground.

3. The MEMS device according to claim 1, wherein: The additional capacitance includes a structure outside the first and second common terminals and the first and second bias terminals and located in the same layer as the first and second common terminals and the first and second bias terminals.

4. The MEMS device according to claim 3, wherein: The structure includes a rectangular ring surrounding the first and second common terminals and the first and second bias terminals.

5. The MEMS device according to claim 4, wherein: The rectangular ring is coupled to ground, and the substrate is coupled to a DC voltage source.

6. The MEMS device according to claim 4, wherein: The width of the rectangular ring is between 100-200 μm.

7. The MEMS device according to claim 1, wherein: The additional capacitor comprises: a second oxide layer, the second oxide layer being located on a side of the substrate opposite to the first oxide layer; a conductor layer, the conductor layer being located on a side of the second oxide layer opposite to the substrate; and A ground connection is coupled to the conductor layer.

8. The MEMS device according to claim 7, further comprising: a through hole penetrating the substrate and the second oxide layer; as well as A conductive connector extends through the via to connect to the conductor layer to provide the ground connection from the same side of the MEMS device as the first and second bias terminals and the first and second common terminals.

9. The MEMS device according to claim 7, wherein: The second oxide layer and the conductor layer cover regions corresponding to the mirror block, the spring, the comb teeth, the first and second common terminals, and the first and second bias terminals.

10. The MEMS device of claim 1, further comprising a driving voltage source connected between at least one of the first and second common terminals and at least one of the first and second bias terminals. 11 . The MEMS device of claim 10 , further comprising a sensing system connected between at least one of the first and second common terminals and at least one of the first and second bias terminals.

12. A micro-electromechanical system (MEMS) device comprising: a MEMS mirror structure having a rotatable mirror that produces a change in measured capacitance corresponding to an angle of rotation; a drive voltage source coupled to the MEMS mirror structure; a first oxide layer located below the MEMS mirror structure; a substrate located below the first oxide layer; wherein there is a parasitic capacitance between the MEMS mirror structure and the substrate; and an additional capacitor located between the substrate and the voltage source, wherein the additional capacitor is several times larger than the parasitic capacitor, and the additional capacitor comprises: an additional conductor around the MEMS mirror structure, the additional conductor being separated from the MEMS mirror structure; and A DC bias voltage source is connected to the additional conductor.

13. The MEMS device according to claim 12, wherein: The voltage source is connected to ground.

14. The MEMS device according to claim 12, wherein: The additional capacitance includes a capacitor structure located outside the MEMS mirror structure and in the same layer as the MEMS mirror structure.

15. The MEMS device according to claim 14, wherein: The capacitor structure includes a rectangular ring surrounding the micro-electromechanical system mirror structure.

16. The MEMS device according to claim 15, wherein: The rectangular ring is coupled to ground, and the substrate is coupled to a DC voltage source.

17. The MEMS device according to claim 15, wherein: The width of the rectangular ring is between 100-200 μm.

18. The MEMS device according to claim 12, wherein: The additional capacitor also includes: a second oxide layer, the second oxide layer being located on a side of the substrate opposite to the first oxide layer; The additional conductor includes a conductor layer, wherein the conductor layer is located on a side of the second oxide layer opposite to the substrate; and a ground connection coupled to the conductor layer; Wherein, the DC bias voltage source is connected to the substrate.

19. A micro-electromechanical system (MEMS) device for beam steering in a light detection and ranging system for an autonomous vehicle, the device comprising: a mirror block having a reflective surface and at least first and second side surfaces; first and second supporting springs, wherein first ends of the first and second supporting springs are connected to the first and second side surfaces of the mirror block at opposite sides, respectively, to support the mirror block; first and second common terminals connected to the first and second support springs, respectively, at second ends of the first and second support springs; a plurality of first comb teeth extending from the mirror block on the first and second sides perpendicular to the first and second support springs; first and second bias terminals, the first and second bias terminals being opposite to the first and second sides of the mirror block; a plurality of second comb teeth extending from the first and second bias terminals, the plurality of second comb teeth being interlaced with and partially overlapping the plurality of first comb teeth; a first oxide layer beneath the first and second common terminals and the first and second bias terminals; a substrate located below the first oxide layer; a driving voltage source connected between at least one of the first and second common terminals and at least one of the first and second bias terminals; a sensing system connected between at least one of the first and second common terminals and at least one of the first and second bias terminals; Wherein there is a sensed capacitance (C) between the anchor point and the common terminal (C) and the anchor point and the bias terminal (B) BC ), the sensed capacitance (C BC ) is proportional to the overlap between the plurality of first comb teeth and the plurality of second comb teeth; There is a first parasitic capacitance (C CS ), and there is a second parasitic capacitance (C BS ); as well as an additional capacitance between the substrate and the DC voltage source, wherein the additional capacitance is several times greater than the first and second parasitic capacitances combined; The additional capacitor includes a structure outside the first and second common terminals and the first and second bias terminals and located in the same layer as the first and second common terminals and the first and second bias terminals; Wherein, the structure comprises a rectangular ring, and the rectangular ring surrounds the first and second common terminals and the first and second bias terminals.

20. The MEMS device according to claim 19, wherein: The width of the rectangular ring is between 100-200 μm.

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