MEMS scanner

Abstract

Disclosed is a MEMS scanner, comprising a mirror, symmetrical torsional beams and a position sensor on the torsional beams, the mirror rotating around a first rotation axis and / or a second rotation axis through the symmetrical torsional beams; the position sensor is a piezoresistive sensor for sensing the torsion angle of the mirror around the first rotation axis and / or the second rotation axis, the first rotation axis being perpendicular to the second rotation axis; wherein the position sensor comprises two center-symmetrical X-shaped piezoresistors forming a Wheatstone bridge structure, each X-shaped piezoresistor comprising a first piezoresistor, a second piezoresistor, a third piezoresistor and a fourth piezoresistor, the distances between the first piezoresistor to the fourth piezoresistor and the center of the X-shaped piezoresistor being equal; the first piezoresistor and the second piezoresistor are connected in series, the length direction thereof being-45° to the corresponding rotation axis; the third piezoresistor and the fourth piezoresistor are connected in series, the length direction thereof being 45° to the corresponding rotation axis, so that the sensitivity of the position sensor can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of micro electro mechanical systems, and particularly relates to a MEMS scanner. BACKGROUND

[0002] With the rapid development of micro-nano processing technology, MEMS (Micro electro mechanical systems) devices have been widely used in industrial production, automobiles, mobile phones, security and other aspects based on their small integration, low power consumption, light weight, and easy mass production. Among them, the MEMS scanner is a kind of MEMS optical device formed by integrating a mirror and a MEMS driver together. The mirror is driven to rotate by the MEMS driver, so as to change the rotation angle of the mirror to realize scanning.

[0003] In the structure of the MEMS scanner, a torsional beam is often used to realize the rotational motion of the mirror by its torsional deformation. A piezoresistive sensor is generally arranged on the torsional beam to detect the stress generated by the torsion and thus detect the torsion angle of the mirror. However, due to the small out-of-plane stiffness of the torsional beam, the mirror is easily caused to move in the out-of-plane under external loads (such as impact, vibration, etc.). The out-of-plane movement of the mirror will cause bending deformation and bending stress on the torsional beam, and the bending stress will also cause the resistance value of the piezoresistive sensor to change, thereby causing the piezoresistive sensor to be unable to accurately perceive the torsion angle of the mirror. Moreover, the MEMS scanner is often used in a vibrating environment (such as a vehicle), and the detection error of the piezoresistive sensor caused by vibration and impact load is easy to cause the error of the mirror motion control, affecting the function of the entire device (such as a laser radar).

[0004] The piezoresistive sensor of the MEMS scanner in the prior art uses a rhombic Wheatstone bridge circuit as the structural layout, which can improve the sensitivity of the sensor, but cannot completely eliminate the interference of the bending deformation on the torsion angle detection. Especially under impact load, the mirror will move in the out-of-plane with a large stroke, causing a large error in the detection of the torsion angle of the mirror, which may cause short-term failure of the device (such as a laser radar), and bring great hidden dangers to driving safety. SUMMARY

[0005] In view of the above problems, the purpose of the present application is to provide a MEMS scanner to improve the sensitivity and anti-interference ability of the position sensor.

[0006] According to a first aspect of the present application, a MEMS scanner is provided, comprising a mirror, symmetrical torsion beams and a position sensor on the torsion beams, the mirror rotates around a first rotation axis and / or a second rotation axis through the symmetrical torsion beams; the position sensor is a piezoresistive sensor for sensing the torsion angle of the mirror around the first rotation axis and / or the second rotation axis, the first rotation axis is perpendicular to the second rotation axis; wherein the position sensor comprises two center-symmetrical X-shaped piezoresistors forming a Wheatstone bridge structure, each of the X-shaped piezoresistors comprises a first piezoresistor, a second piezoresistor, a third piezoresistor and a fourth piezoresistor, the distances between the first piezoresistor to the fourth piezoresistor and the center of the X-shaped piezoresistor are equal; the first piezoresistor and the second piezoresistor are connected in series, the length direction of the first piezoresistor and the second piezoresistor is-45° to the corresponding rotation axis; the third piezoresistor and the fourth piezoresistor are connected in series, the length direction of the third piezoresistor and the fourth piezoresistor is 45° to the corresponding rotation axis.

[0007] Preferably, the symmetrical torsion beams comprise symmetrical two first torsion beams and / or symmetrical two second torsion beams, the first torsion beams rotate around the first rotation axis, the second torsion beams rotate around the second rotation axis.

[0008] Preferably, the position sensor is arranged on the symmetrical first torsion beams and / or the symmetrical second torsion beams.

[0009] Preferably, when the position sensor is arranged on the symmetrical first torsion beams, the two X-shaped piezoresistors are respectively located on the two symmetrical first torsion beams.

[0010] Preferably, the center of each of the X-shaped piezoresistors coincides with the center of the corresponding first torsion beam, and the two X-shaped piezoresistors are symmetrical about the second rotation axis.

[0011] Preferably, under the bending stress of the first torsion beam, the resistance values of the first piezoresistor and the second piezoresistor change in opposite directions, and the resistance values of the third piezoresistor and the fourth piezoresistor change in opposite directions.

[0012] Preferably, when the position sensor is arranged on the symmetrical first torsion beams, the two X-shaped piezoresistors are both located on one of the first torsion beams.

[0013] Preferably, the two X-shaped piezoresistors are arranged along the length direction of the first torsion beam and are respectively located on both sides of the center of the first torsion beam, and the center of each X-shaped piezoresistor is the same distance from the center of the first torsion beam, and the two X-shaped piezoresistors are symmetrical about the perpendicular bisector of the corresponding first torsion beam.

[0014] Preferably, the center of each X-shaped piezoresistor is less than 1 / 4 of the length of the first torsional beam from the center of the corresponding first torsional beam.

[0015] Preferably, when the position sensor is arranged on the symmetrical second torsional beams, the two X-shaped piezoresistors are respectively located on the two symmetrical second torsional beams.

[0016] Preferably, the center of each X-shaped piezoresistor coincides with the center of the corresponding second torsional beam, and the two X-shaped piezoresistors are symmetrical about the first rotation axis.

[0017] Preferably, under the bending stress of the second torsional beam, the resistance values of the first and second piezoresistors change in opposite directions, and the resistance values of the third and fourth piezoresistors change in opposite directions.

[0018] Preferably, when the position sensor is arranged on the symmetrical second torsional beams, the two X-shaped piezoresistors are respectively located on the two symmetrical second torsional beams.

[0019] Preferably, the two X-shaped piezoresistors are arranged along the length direction of the second torsional beam and are respectively located on both sides of the center of the second torsional beam, and the center of each X-shaped piezoresistor is the same distance from the center of the second torsional beam, and the two X-shaped piezoresistors are symmetrical about the perpendicular bisector of the corresponding second torsional beam.

[0020] Preferably, the center of each X-shaped piezoresistor is less than 1 / 4 of the length of the second torsional beam from the center of the corresponding second torsional beam.

[0021] Preferably, the MEMS scanner further comprises a first frame arranged around the mirror surface and connected to a first actuator through the two first torsional beams, and the mirror surface rotates about the first rotation axis under the action of the first actuator.

[0022] Preferably, the MEMS scanner further comprises a second frame, the first frame is connected to the second frame via the two first torsional beams; the second frame is connected to a second actuator through two second torsional beams, and the mirror surface rotates about the second rotation axis under the action of the second actuator.

[0023] Preferably, when the mirror surface moves upward, the resistance values of the two piezoresistors in the X-shaped piezoresistor close to the mirror surface increase, and the resistance values of the two piezoresistors away from the mirror surface decrease; when the mirror surface moves downward, the resistance values of the two piezoresistors in the X-shaped piezoresistor close to the mirror surface decrease, and the resistance values of the two piezoresistors away from the mirror surface increase.

[0024] Preferably, the first and second piezoresistors of one of the X-shaped piezoresistors are connected in series to form a first bridge arm resistor, and the third and fourth piezoresistors are connected in series to form a second bridge arm resistor; the first and second piezoresistors of the other X-shaped piezoresistor are connected in series to form a third bridge arm resistor, and the third and fourth piezoresistors are connected in series to form a fourth bridge arm resistor.

[0025] Preferably, the first, third, fourth and second bridge arm resistors are connected in series to form a Wheatstone bridge structure, a node between the first and second bridge arm resistors is connected to a ground terminal; a node between the third and fourth bridge arm resistors is connected to a working voltage, and a node between the first and third bridge arm resistors and a node between the second and fourth bridge arm resistors are output terminals of the Wheatstone bridge.

[0026] Preferably, each X-shaped piezoresistor comprises a first, second, third and fourth piezoresistance region, and a plurality of contact regions in a substrate, a dielectric layer and a first and second wiring layer on the substrate; wherein the first to fourth piezoresistance regions are located in the substrate and are isolated from each other; the plurality of contact regions are respectively located on both sides of the first to fourth piezoresistance regions; the dielectric layer is covered on the substrate, the first wiring layer is arranged in the dielectric layer to connect the first and second piezoresistance regions in series through the contact regions; and the second wiring layer is located on the dielectric layer to connect the third and fourth piezoresistance regions in series through the contact regions.

[0027] Preferably, the first and / or second wiring layer leads the remaining end of the first to fourth piezoresistance regions out through the corresponding contact regions.

[0028] Preferably, the substrate is of a first doping type, the first to fourth piezoresistance regions and the contact regions are of a second doping type, and the first doping type is opposite to the second doping type.

[0029] Preferably, the doping concentration of the first to fourth piezoresistance regions is less than the doping concentration of the contact regions.

[0030] The MEMS scanner provided by the embodiment of the application comprises a mirror surface, symmetrical torsional beams and a position sensor on the torsional beams, the position sensor is a piezoresistive sensor and is composed of two center-symmetrical X-shaped piezoresistors arranged along the length direction of the torsional beams, each X-shaped piezoresistor comprises four piezoresistors, the four piezoresistors are arranged in the ±45° direction of the rotation axis to form an X shape and each piezoresistor is away from the center of the X shape by the same distance, the bending stress on the torsional beams is distributed in a gradient along the length direction of the torsional beams, and the resistance values of the piezoresistors in the positive bending stress area and the negative bending stress area change in opposite directions under the action of the bending stress so as to offset each other, thereby improving the sensitivity of the position sensor.

[0031] Further, the two X-shaped piezoresistors are arranged on the symmetrical torsional beams respectively, and each X-shaped piezoresistor is located at the center of the corresponding torsional beam, so that the resistance values of the two piezoresistors in series in each bridge arm resistor of the X-shaped piezoresistor change in opposite directions under the bending stress, the influence of the interference motion on the piezoresistive sensor is eliminated, the sensitivity of the position sensor is improved, the accurate control of the motion of the MEMS scanner in the vibration environment is ensured, and the robustness in the vibration environment is further improved.

[0032] Further, the two X-shaped piezoresistors are arranged on the symmetrical torsional beams respectively, and each X-shaped piezoresistor is located at the center of the corresponding torsional beam, so that the resistance values of the two piezoresistors in series in each bridge arm resistor of the X-shaped piezoresistor change in opposite directions under the bending stress, the influence of the interference motion on the piezoresistive sensor is eliminated, the sensitivity of the position sensor is improved, the accurate control of the motion of the MEMS scanner in the vibration environment is ensured, and the robustness in the vibration environment is further improved. BRIEF DESCRIPTION OF DRAWINGS

[0033] The above and other objects, features and advantages of the present application will become more apparent from the following description of the embodiments of the present application taken with reference to the accompanying drawings, in which:

[0034] Figure 1 A stress distribution on the torsional beam under the action of the bending stress in the prior art is shown;

[0035] Figure 2 And Figure 3 Structure schematic diagrams of the MEMS scanner provided by the first embodiment of the application are respectively shown;

[0036] Figure 4 A circuit schematic diagram of the position sensor provided by the embodiment of the application is shown;

[0037] Figure 5a And Figure 5b A top view and a sectional view of the X-shaped piezoresistor provided by the embodiment of the application are respectively shown;

[0038] Figure 6 A structure schematic diagram of the MEMS scanner provided by the second embodiment of the application is shown;

[0039] Figure 7 Fig. 3 shows a structural schematic diagram of a MEMS scanner provided by a third embodiment of the present application;

[0040] Figure 8 Fig. 4 shows a structural schematic diagram of a MEMS scanner provided by a fourth embodiment of the present application;

[0041] Figure 9 Fig. 5 shows a structural schematic diagram of a MEMS scanner provided by a fifth embodiment of the present application. DETAILED DESCRIPTION

[0042] Various embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the various drawings, the same elements are denoted by the same or similar reference numerals. For the sake of clarity, various parts in the drawings are not drawn to scale.

[0043] The specific embodiments of the present application will be further described below in detail with reference to the accompanying drawings and embodiments.

[0044] The prior art MEMS scanner includes a mirror, a first frame surrounding the mirror, and the first frame is connected with a second frame through two symmetrical first torsion beams. The first torsion beams extend along a first rotation axis, and the first torsion beams drive the mirror to rotate around the first rotation axis under the drive of a first actuator. The second frame is connected with a second actuator through two symmetrical second torsion beams, the two symmetrical second torsion beams extend along a second rotation axis, and the two symmetrical second torsion beams drive the mirror to rotate around the second rotation axis under the drive of the second actuator, the second rotation axis is perpendicular to the first rotation axis, thereby realizing two-dimensional scanning.

[0045] The prior art MEMS scanner respectively sets a piezoresistive sensor on one of the first torsion beams and one of the second torsion beams to realize detection of the torsion angle. Each piezoresistive sensor includes a "diamond" Wheatstone bridge composed of four piezoresistors (R1~R4) arranged at the edge of the torsion beam, wherein the piezoresistors have the property that their resistance values change due to stress (piezoresistive effect). The first piezoresistor R1, the second piezoresistor R2, the third piezoresistor R3 and the fourth piezoresistor R4 are connected in series to form a Wheatstone bridge, the node between the first piezoresistor R1 and the fourth piezoresistor R4 is connected with a working voltage Vdd, the node between the second piezoresistor R2 and the third piezoresistor R3 is connected with a ground terminal GND, and the nodes between the first piezoresistor R1 and the second piezoresistor R2 and between the third piezoresistor R3 and the fourth piezoresistor R4 are respectively used as output terminals of the Wheatstone bridge to obtain an output voltage Vout.

[0046] The length direction of the first and third piezoresistors R1 and R3 is +45° to the corresponding rotation axis, and the length direction of the second and fourth piezoresistors R2 and R4 is -45° to the corresponding rotation axis. Under the action of the shear stress generated by the torsion, the stress on the torsion beam is uniformly distributed; but under the action of the bending stress generated by the out-of-plane translation, the stress on the torsion beam is gradiently distributed along the length direction of the torsion beam (see Figure 1 ), so the resistance changes of the first and fourth piezoresistors R1 and R4 are equal, and the resistance changes of the second and third piezoresistors R2 and R3 are equal, thereby affecting the output voltage.

[0047] Figure 2 and Figure 3 respectively show the structural schematic diagram of the MEMS scanner provided by the first embodiment of the application. Referring to Figure 2 and Figure 3 , the MEMS scanner comprises a mirror surface 10, symmetrical torsion beams, and a position sensor 15 located on the torsion beams.

[0048] The symmetrical torsion beams comprise symmetrical first torsion beams 12a and 12b and symmetrical second torsion beams 14a and 14b.

[0049] The MEMS scanner further comprises a first frame 11 surrounding the mirror surface 10, and the first frame 11 is connected with a second frame 13 through the two symmetrical first torsion beams 12a and 12b. The first torsion beams 12a and 12b extend along a first rotation axis (for example, the x-axis), and the first torsion beams 12a and 12b drive the mirror surface 10 to rotate around the first rotation axis (for example, the x-axis) under the drive of a first actuator (not shown in the figure). The second frame 13 is connected with a second actuator (not shown in the figure) through the two symmetrical second torsion beams 14a and 14b, the two symmetrical second torsion beams 14a and 14b extend along a second rotation axis (for example, the y-axis), and the two symmetrical second torsion beams 14a and 14b drive the mirror surface 10 to rotate around the second rotation axis under the drive of the second actuator, the second rotation axis is perpendicular to the first rotation axis (the y-axis is perpendicular to the x-axis), thereby realizing two-dimensional scanning.

[0050] The position sensor 15 is a piezoresistive sensor, and is arranged on the symmetrical first torsion beams 12a and 12b and / or the symmetrical second torsion beams 14a and 14b. The position sensor 15 comprises two center-symmetrical X-shaped piezoresistors forming a Wheatstone bridge structure.

[0051] Specifically, each of the X-shaped piezoresistors includes a first piezoresistor R1, a second piezoresistor R2, a third piezoresistor R3 and a fourth piezoresistor R4, the first piezoresistor R1 and the second piezoresistor R2 are arranged along a direction of -45° with respect to the corresponding rotation axis, the third piezoresistor R3 and the fourth piezoresistor R4 are arranged along a direction of 45° with respect to the corresponding rotation axis, the first piezoresistor R1 to the fourth piezoresistor R4 are cross-placed to form an "X" shape, and the distances between the first piezoresistor R1 to the fourth piezoresistor R4 and the center of the X-shaped piezoresistor are equal to form a central symmetry. The first piezoresistor R1 and the second piezoresistor R2 are connected in series to form a bridge arm resistor, the length direction of which is -45° with respect to the corresponding rotation axis; the third piezoresistor R3 and the fourth piezoresistor R4 are connected in series to form a bridge arm resistor, the length direction of which is 45° with respect to the corresponding rotation axis, i.e., the first piezoresistor R1 to the fourth piezoresistor R4 are arranged along the <110> crystal direction, and the sensitivity is high.

[0052] In the present embodiment, when the position sensor 15 is arranged on the symmetric first torsion beams 12a and 12b (see Figure 2 ), the two X-shaped piezoresistors are respectively located on the two symmetric first torsion beams 12a and 12b, i.e., the X-shaped piezoresistor X1 is located on the first torsion beam 12a, and the X-shaped piezoresistor X2 is located on the first torsion beam 12b. The center of each of the X-shaped piezoresistors coincides with the center of the corresponding first torsion beam, and the two X-shaped piezoresistors are symmetric about the second rotation axis (y-axis).

[0053] Specifically, referring to Figure 4 , the first piezoresistor R1 and the second piezoresistor R2 in the X-shaped piezoresistor are respectively located on the two sides of the perpendicular bisector of the first torsion beam 12a, and the third piezoresistor R3 and the fourth piezoresistor R4 are respectively located on the two sides of the perpendicular bisector of the first torsion beam 12a. The node between the first piezoresistor R1 and the second piezoresistor R2 is not electrically connected with the node between the third piezoresistor R3 and the fourth piezoresistor R4. That is, the two bridge arm resistors are not interconnected at the intersection of the X-shaped piezoresistor. Therefore, the connection wiring between the four piezoresistors can be arranged in two layers of wiring layers respectively to avoid interconnection.

[0054] In the embodiment, the bending stress is distributed from positive to negative along the direction from the mirror surface 10 to away from the mirror surface 10 on each torsion beam (in other embodiments, it can also be distributed from negative to positive), the bending stress of the center position of the torsion beam is 0, and the center of the X-shaped piezoresistor is located at the center of the corresponding torsion beam, that is, the first piezoresistor R1 and the second piezoresistor R2 are located in the positive bending stress region and the negative bending stress region respectively, and the first piezoresistor R1 and the second piezoresistor R2 are subjected to longitudinal stress (stress along the length direction of the piezoresistor) and transverse stress (stress perpendicular to the length direction of the piezoresistor) with opposite signs, so that the bending stress has no effect on the total resistance of the first piezoresistor R1 and the second piezoresistor R2 in series; the third piezoresistor R3 and the fourth piezoresistor R4 are located in the positive bending stress region and the negative bending stress region, and the bending stress also has no effect on the total resistance of the third piezoresistor R3 and the fourth piezoresistor R4 in series, so that the change of the series resistance caused by the bending stress of the two bridge arm resistors of the X-shaped piezoresistor is offset, avoiding the interference of the bending stress on the position sensor 15.

[0055] Further, under the influence of the bending stress, when the mirror surface 10 moves upward, the resistance values of the two piezoresistors of the X-shaped resistor close to the mirror surface 10 become larger, and the resistance values of the two piezoresistors away from the mirror surface 10 become smaller. Specifically, the resistance values of the second piezoresistor R2 and the fourth piezoresistor R4 of the X-shaped piezoresistor X1 located on the first torsion beam 12a and the first piezoresistor R1 and the third piezoresistor R3 of the X-shaped piezoresistor X2 located on the first torsion beam 12b become larger, and the resistance values of the first piezoresistor R1 and the third piezoresistor R3 of the X-shaped piezoresistor X1 located on the first torsion beam 12a and the second piezoresistor R2 and the fourth piezoresistor R4 of the X-shaped piezoresistor X2 located on the first torsion beam 12b become smaller.

[0056] Further, under the influence of the bending stress, when the mirror surface 10 moves downward, the resistance values of the two piezoresistors of the X-shaped resistor close to the mirror surface 10 become smaller, and the resistance values of the two piezoresistors away from the mirror surface 10 become larger. Specifically, the resistance values of the second piezoresistor R2 and the fourth piezoresistor R4 of the X-shaped piezoresistor X1 located on the first torsion beam 12a and the first piezoresistor R1 and the third piezoresistor R3 of the X-shaped piezoresistor X2 located on the first torsion beam 12b become smaller, and the resistance values of the first piezoresistor R1 and the third piezoresistor R3 of the X-shaped piezoresistor X1 located on the first torsion beam 12a and the second piezoresistor R2 and the fourth piezoresistor R4 of the X-shaped piezoresistor X2 located on the first torsion beam 12b become larger.

[0057] Further, the first and second piezoresistors R1 and R2 of one of the X-shaped piezoresistors (e.g. on the first torsion beam 12a) are connected in series to form a first bridge arm resistor, and the third and fourth piezoresistors R3 and R4 are connected in series to form a second bridge arm resistor; the first and second piezoresistors R1 and R2 of the other X-shaped piezoresistor (e.g. on the first torsion beam 12b) are connected in series to form a third bridge arm resistor, and the third and fourth piezoresistors R2 and R4 are connected in series to form a fourth bridge arm resistor. The first, third, fourth and second bridge arm resistors are connected in series to form a Wheatstone bridge structure, the node between the first and second bridge arm resistors is connected to the ground terminal GND, the node between the third and fourth bridge arm resistors is connected to the working voltage Vdd, and the nodes between the first and third bridge arm resistors and between the second and fourth bridge arm resistors are output terminals of the Wheatstone bridge.

[0058] In the present embodiment, when the position sensor 15 is arranged on the symmetric second torsion beams 14a and 14b (see Figure 3 ), the two X-shaped piezoresistors are arranged on the two symmetric second torsion beams 14a and 14b, respectively, i.e. the X-shaped piezoresistor X1 is arranged on the second torsion beam 14a, and the X-shaped piezoresistor X2 is arranged on the second torsion beam 14b. The center of each X-shaped piezoresistor coincides with the center of the corresponding second torsion beam, and the two X-shaped piezoresistors are symmetric about the first rotation axis (x-axis).

[0059] Similarly, under the bending stress of the second torsion beam, the resistance of the first and second piezoresistors R1 and R2 changes in opposite directions, and the resistance of the third and fourth piezoresistors R3 and R4 changes in opposite directions. Specifically, the first and second piezoresistors R1 and R2 are located in the positive and negative bending stress regions, respectively, and the longitudinal stress (stress along the length direction of the piezoresistor) and the transverse stress (stress perpendicular to the length direction of the piezoresistor) acting on the first and second piezoresistors R1 and R2 are opposite in sign, so that the bending stress has no effect on the total resistance of the first and second piezoresistors R1 and R2 connected in series; the third and fourth piezoresistors R3 and R4 are located in the positive and negative bending stress regions, respectively, and the bending stress also has no effect on the total resistance of the third and fourth piezoresistors R3 and R4 connected in series, so that the change in the series resistance of the two bridge arm resistors of the X-shaped piezoresistor caused by the bending stress is offset, avoiding the interference of the bending stress on the position sensor 15.

[0060] As Figure 3As shown, when the mirror surface 10 rotates around the second rotation axis (y axis), the resistance of the first bridge arm resistor formed by the first and second piezoresistors R1 and R2 of the X-shaped piezoresistor X1 on the second torsion beam 14a becomes larger, and the resistance of the second bridge arm resistor formed by the third and fourth piezoresistors R3 and R4 becomes smaller; the resistance of the third bridge arm resistor formed by the first and second piezoresistors R1 and R2 of the X-shaped piezoresistor X2 on the second torsion beam 14b becomes smaller, and the resistance of the fourth bridge arm resistor formed by the third and fourth piezoresistors R3 and R4 becomes larger. Alternatively, when the mirror surface 10 rotates around the second rotation axis (y axis), the resistance of the first bridge arm resistor formed by the first and second piezoresistors R1 and R2 of the X-shaped piezoresistor X1 on the second torsion beam 14a becomes smaller, and the resistance of the second bridge arm resistor formed by the third and fourth piezoresistors R3 and R4 becomes larger; the resistance of the third bridge arm resistor formed by the first and second piezoresistors R1 and R2 of the X-shaped piezoresistor X2 on the second torsion beam 14b becomes larger, and the resistance of the fourth bridge arm resistor formed by the third and fourth piezoresistors R3 and R4 becomes smaller.

[0061] Preferably, the first and second torsion beams are each provided with a position sensor 15, i.e. two X-shaped piezoresistors are arranged on the first torsion beam, and two X-shaped piezoresistors are arranged on the second torsion beam.

[0062] Figure 5a and Figure 5b respectively show a top view and a cross-sectional view (along AA' in Figure 5a ). Referring to Figure 5a and Figure 5b , the position sensor 15 includes two X-shaped piezoresistors, each of which includes a first piezoresistor region 111, a second piezoresistor region 112, a third piezoresistor region 113, a fourth piezoresistor region 114 and a plurality of contact regions 115 in a substrate 110, a dielectric layer 120 and a first wiring layer 130 and a second wiring layer 140 on the substrate 110. Among them, the first piezoresistor region 111 corresponds to the first piezoresistor R1, the second piezoresistor region 112 corresponds to the second piezoresistor R2, the third piezoresistor region 113 corresponds to the third piezoresistor R3, and the fourth piezoresistor region 114 corresponds to the fourth piezoresistor R4.

[0063] In this embodiment, the substrate 110 is a silicon substrate, and the substrate 110 is of a first doping type, for example, n-type. The crystal direction of the substrate 110 is <100> crystal direction, and the length direction of the torsion beam is <100> crystal direction.

[0064] The first to fourth piezoresistive regions 111-114 are located in the substrate 110 and are isolated from each other. A plurality of contact regions 115 are located on both sides of each piezoresistive region, i.e., two contact regions 115 are located on each side of each piezoresistive region. The first to fourth piezoresistive regions 111-114 and the contact regions 115 are of a second doping type, for example, p-type, and are formed by ion implantation from the surface of the substrate 110 downward. The doping concentration of the first to fourth piezoresistive regions 111-114 is less than the doping concentration of the contact regions 115.

[0065] The dielectric layer 120 is covered on the substrate 110, and the dielectric layer 120 has openings above each contact region 115 for the first wiring layer 130 and the second wiring layer 140 to connect with the corresponding contact region 115. The first wiring layer 130 is arranged in the dielectric layer 120 and connects the first piezoresistive region 111 and the second piezoresistive region 112 in series through the corresponding contact region 115.

[0066] The second wiring layer 140 is arranged on the dielectric layer 120 and connects the third piezoresistive region 113 and the fourth piezoresistive region 114 in series through the contact region 115. The first wiring layer 130 and the second wiring layer 140 can be metal or doped polysilicon.

[0067] The first wiring layer 130 and / or the second wiring layer 140 respectively lead out the remaining one end of the first to fourth piezoresistive regions 111-114 through the corresponding contact region 115.

[0068] The MEMS scanner provided by the embodiment of the application comprises a mirror surface, symmetrical torsional beams and a position sensor located on the torsional beams, the position sensor is a piezoresistive sensor and is composed of two center-symmetrical X-shaped piezoresistors arranged along the length direction of the torsional beams, each X-shaped piezoresistor comprises four piezoresistors which are arranged along the ±45° direction of the rotation axis to form an "X" shape and are located at the same distance from the center of the "X" shape, the bending stress on the torsional beams is distributed in a gradient along the length direction of the torsional beams, and the resistance values of the piezoresistors located in the positive bending stress region and the negative bending stress region change in opposite directions under the action of the bending stress, thereby canceling each other out and improving the sensitivity of the position sensor.

[0069] Further, the two X-shaped piezoresistors are arranged on the symmetrical torsional beams respectively, and each X-shaped piezoresistor is located at the center of the corresponding torsional beam, so that the resistance values of the two piezoresistors in series in each bridge arm resistor of the X-shaped piezoresistor change in opposite directions under the bending stress, the influence of the interfering motion on the piezoresistive sensor is reduced, the sensitivity of the position sensor is improved, the accurate control of the motion of the MEMS scanner in a vibrating environment is ensured, and the robustness in the vibrating environment is further improved.

[0070] Figure 6 A structure schematic diagram of a MEMS scanner provided by a second embodiment of the present application is shown. Compared with the first embodiment, the position sensor 15 in the present embodiment is arranged on only one of the torsion beams, i.e. the two X-shaped piezoresistors of the position sensor 15 are arranged on one torsion beam (e.g. the second torsion beam 14a), and the two X-shaped piezoresistors are arranged along the length direction of the torsion beam and are symmetrically distributed on both sides of the center of the second torsion beam 14a and close to the center of the second torsion beam 14a. Specifically, the center of each X-shaped piezoresistor is the same distance from the center of the second torsion beam 14a, and the two X-shaped piezoresistors are symmetric about the vertical bisector of the second torsion beam 14a, i.e. one X-shaped piezoresistor is located in the positive bending stress region and the other X-shaped piezoresistor is located in the negative bending stress region. Preferably, the center of each X-shaped piezoresistor is less than 1 / 4 of the length of the second torsion beam 14a from the center of the second torsion beam 14a. It can be understood that the two X-shaped piezoresistors can also be arranged on the second torsion beam 14b or on the first torsion beam 12a or on the first torsion beam 12b.

[0071] The remaining aspects of the second embodiment are the same as those of the first embodiment, and will not be described here.

[0072] The MEMS scanner provided by the embodiments of the present application has the two X-shaped piezoresistors arranged along the length direction of the torsion beam, and the two X-shaped piezoresistors are arranged on one torsion beam, and the two X-shaped piezoresistors are symmetrically distributed about the vertical bisector of the corresponding torsion beam and close to the center of the torsion beam, which can reduce the influence of the interfering motion (bending stress) on the piezoresistance change of the piezoresistors on the torsion beam, improve the sensitivity of the position sensor, and make the wiring relatively simple compared with the first embodiment.

[0073] Figure 7 A structure schematic diagram of a MEMS scanner provided by a third embodiment of the present application is shown. Compared with the first embodiment, the symmetric torsion beams in the present embodiment only include the symmetric first torsion beams 12a and 12b, and the position sensor 15 is located on the symmetric first torsion beams 12a and 12b. The first torsion beams 12a and 12b extend along the first rotation axis (x-axis).

[0074] The remaining aspects of the third embodiment are the same as those of the first embodiment, and will not be described here.

[0075] The MEMS scanner provided by the embodiment of the present application comprises a mirror surface, symmetrical torsional beams and a position sensor located on the torsional beams, the position sensor is a piezoresistive sensor and is composed of two center-symmetrical X-shaped piezoresistors arranged along the length direction of the torsional beams, each X-shaped piezoresistor comprises four piezoresistors, the four piezoresistors are arranged in the ±45° direction of the rotation axis to form an X shape and the distance from each piezoresistor to the center of the X shape is the same, the bending stress on the torsional beams is distributed in a gradient along the length direction of the torsional beams, and the resistance value of the piezoresistors located in the positive bending stress area and the negative bending stress area changes in opposite directions under the action of the bending stress, thereby offsetting each other and improving the sensitivity of the position sensor.

[0076] Further, the two X-shaped piezoresistors are arranged on the symmetrical torsional beams respectively, and each X-shaped piezoresistor is located at the center of the corresponding torsional beam, so that the resistance value of the two piezoresistors in series in each bridge arm resistor in the X-shaped piezoresistor changes in opposite directions under the bending stress, the influence of the interfering motion on the piezoresistive sensor is reduced, the sensitivity of the position sensor is improved, the accurate control of the motion of the MEMS scanner in the vibration environment is ensured, and the robustness in the vibration environment is further improved.

[0077] Figure 8 A structure schematic diagram of the MEMS scanner provided by the fourth embodiment of the present application is shown. Compared with the third embodiment, the symmetrical torsional beams in the present embodiment only comprise symmetrical first torsional beams 12a and 12b, and the position sensor 15 is located on the symmetrical first torsional beams 12a and 12b. The first torsional beams 12a and 12b extend along the second rotation axis (y axis).

[0078] The remaining aspects of the fourth embodiment are the same as those of the third embodiment, and will not be described here again.

[0079] The MEMS scanner provided by the embodiment of the present application comprises a mirror surface, symmetrical torsional beams and a position sensor located on the torsional beams, the position sensor is a piezoresistive sensor and is composed of two center-symmetrical X-shaped piezoresistors arranged along the length direction of the torsional beams, each X-shaped piezoresistor comprises four piezoresistors, the four piezoresistors are arranged in the ±45° direction of the rotation axis to form an X shape and the distance from each piezoresistor to the center of the X shape is the same, the bending stress on the torsional beams is distributed in a gradient along the length direction of the torsional beams, and the resistance value of the piezoresistors located in the positive bending stress area and the negative bending stress area changes in opposite directions under the action of the bending stress, thereby offsetting each other and improving the sensitivity of the position sensor.

[0080] Further, two X-shaped piezoresistors are respectively arranged on the symmetrical torsional beams, and each X-shaped piezoresistor is located at the center of the corresponding torsional beam, so that the resistance value changes caused by the two piezoresistors in series in each bridge arm of the X-shaped piezoresistor under the bending stress are opposite, the influence of the interfering motion on the piezoresistor sensor is reduced, the sensitivity of the position sensor is improved, and the precise control of the motion of the MEMS scanner in the vibration environment is ensured, and the robustness in the vibration environment is further improved.

[0081] Figure 9 A structure schematic diagram of the MEMS scanner provided by the fifth embodiment of the present application is shown. Compared with the fourth embodiment, the symmetrical torsional beams in the present embodiment only include the symmetrical first torsional beams 12a and 12b, and the position sensor 15 is arranged on only one of the torsional beams, i.e., the two X-shaped piezoresistors of the position sensor 15 are placed on one torsional beam (for example, the first torsional beam 12a), the two X-shaped piezoresistors are arranged along the length direction of the torsional beam and are symmetrically distributed on both sides of the center of the first torsional beam 12a and are as close to the center of the first torsional beam 12a as possible. Specifically, the distance between the center of each X-shaped piezoresistor and the center of the first torsional beam 12a is the same, and the two X-shaped piezoresistors are symmetric about the vertical bisector of the first torsional beam 12a, i.e., one X-shaped piezoresistor is located in the positive bending stress region, and the other X-shaped piezoresistor is located in the negative bending stress region. Preferably, the distance between the center of each X-shaped piezoresistor and the center of the first torsional beam 12a is less than 1 / 4 of the length of the first torsional beam 12a. It can be understood that the two X-shaped piezoresistors can also be placed on the first torsional beam 12b.

[0082] The remaining aspects of the fifth embodiment are the same as those of the fourth embodiment, and will not be described here again.

[0083] The MEMS scanner provided by the embodiments of the present application is composed of two X-shaped piezoresistors arranged along the length direction of the torsional beam, the two X-shaped piezoresistors are arranged on one torsional beam, the two X-shaped piezoresistors are symmetrically distributed about the vertical bisector of the corresponding torsional beam and are close to the center of the torsional beam, the influence of the interfering motion (bending stress) on the piezoresistor change of the piezoresistor sensor on the torsional beam can be reduced, the sensitivity of the position sensor is improved, and the wiring is relatively simple compared with the fourth embodiment.

[0084] In accordance with the embodiments of the present application as described above, these embodiments do not describe all the details, nor limit the present application to only the specific embodiments described. It is obvious that many modifications and changes can be made according to the above description. The present application selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present application, so that those skilled in the art can well utilize the present application and make modifications and uses on the basis of the present application. The present application is limited only by the claims and their full scope and equivalents.

Claims

1. A MEMS scanner, characterized by, The mirror is rotated around a first rotation axis and / or a second rotation axis by the symmetrical torsion beam; The mirror is rotated around a first rotation axis and / or a second rotation axis by the symmetrical torsion beam; The position sensor is a piezoresistance sensor for sensing the torsion angle of the mirror around the first rotation axis and / or the second rotation axis, the first rotation axis being perpendicular to the second rotation axis; The position sensor comprises two center-symmetrical X-shaped piezoresistors forming a Wheatstone bridge structure, Each X-shaped piezoresistor comprises a first piezoresistor, a second piezoresistor, a third piezoresistor and a fourth piezoresistor, the distances between the first piezoresistor to the fourth piezoresistor and the center of the X-shaped piezoresistor being equal; the first piezoresistor and the second piezoresistor are connected in series, the length direction of the first piezoresistor and the second piezoresistor being-45° to the corresponding rotation axis; the third piezoresistor and the fourth piezoresistor are connected in series, the length direction of the third piezoresistor and the fourth piezoresistor being 45° to the corresponding rotation axis, Each X-shaped piezoresistor comprises a first piezoresistor region, a second piezoresistor region, a third piezoresistor region, a fourth piezoresistor region and a plurality of contact regions in a substrate and isolated from each other, the first piezoresistor region corresponding to the first piezoresistor, the second piezoresistor region corresponding to the second piezoresistor, the third piezoresistor region corresponding to the third piezoresistor, and the fourth piezoresistor region corresponding to the fourth piezoresistor, The first piezoresistor and the second piezoresistor are located in positive bending stress regions and negative bending stress regions respectively, the resistance values of the first piezoresistor and the second piezoresistor in the positive bending stress regions and the negative bending stress regions changing in opposite directions under the action of bending stress; the third piezoresistor and the fourth piezoresistor are located in positive bending stress regions and negative bending stress regions respectively, the resistance values of the third piezoresistor and the fourth piezoresistor in the positive bending stress regions and the negative bending stress regions changing in opposite directions under the action of bending stress.

2. The MEMS scanner of claim 1, wherein, The symmetrical torsion beam comprises two symmetrical first torsion beams and / or two symmetrical second torsion beams, the first torsion beam rotating around the first rotation axis, and the second torsion beam rotating around the second rotation axis.

3. The MEMS scanner of claim 2, wherein, The position sensor is arranged on the symmetrical first torsion beam and / or the symmetrical second torsion beam.

4. The MEMS scanner of claim 3, wherein, When the position sensor is arranged on the symmetrical first torsion beam, the two X-shaped piezoresistors are arranged on the two symmetrical first torsion beams respectively.

5. The MEMS scanner of claim 4, wherein, The center of each X-shaped piezoresistor coincides with the center of the corresponding first torsion beam, and the two X-shaped piezoresistors are symmetrical about the second rotation axis.

6. The MEMS scanner of claim 4, wherein, Under the bending stress of the first torsion beam, the resistance values of the first piezoresistor and the second piezoresistor change in opposite directions, and the resistance values of the third piezoresistor and the fourth piezoresistor change in opposite directions.

7. The MEMS scanner of claim 3, wherein, When the position sensor is arranged on the symmetrical first torsion beam, the two X-shaped piezoresistors are arranged on one of the first torsion beams.

8. The MEMS scanner of claim 7, wherein, The two X-shaped piezoresistors are arranged along the length direction of the first torsion beam and are located on both sides of the center of the first torsion beam respectively, and the center of each X-shaped piezoresistor is the same distance from the center of the first torsion beam, and the two X-shaped piezoresistors are symmetrical about the perpendicular bisector of the corresponding first torsion beam.

9. The MEMS scanner of claim 8, wherein, The center of each X-shaped piezoresistor is less than 1 / 4 of the length of the first torsional beam from the center of the corresponding first torsional beam.

10. The MEMS scanner of claim 3, wherein, When the position sensor is arranged on the symmetrical second torsional beams, the two X-shaped piezoresistors are respectively arranged on the two symmetrical second torsional beams.

11. The MEMS scanner of claim 10, wherein, The center of each X-shaped piezoresistor coincides with the center of the corresponding second torsional beam, and the two X-shaped piezoresistors are symmetrical about the first rotation axis.

12. The MEMS scanner of claim 10, wherein, Under the bending stress of the second torsional beam, the resistance values of the first and second piezoresistors change in opposite directions, and the resistance values of the third and fourth piezoresistors change in opposite directions.

13. The MEMS scanner of claim 3, wherein, When the position sensor is arranged on the symmetrical second torsional beams, the two X-shaped piezoresistors are both arranged on one of the second torsional beams.

14. The MEMS scanner of claim 13, wherein, The two X-shaped piezoresistors are arranged along the length direction of the second torsional beam and are respectively arranged on both sides of the center of the second torsional beam, and the center of each X-shaped piezoresistor is the same distance from the center of the second torsional beam, and the two X-shaped piezoresistors are symmetrical about the perpendicular bisector of the corresponding second torsional beam.

15. The MEMS scanner of claim 14, wherein, The center of each X-shaped piezoresistor is less than 1 / 4 of the length of the second torsional beam from the center of the corresponding second torsional beam.

16. The MEMS scanner of claim 3, wherein, Further comprising a first frame arranged around the mirror surface and connected to a first actuator through the two first torsional beams, and the mirror surface rotates about the first rotation axis under the action of the first actuator.

17. The MEMS scanner of claim 16, wherein, Further comprising a second frame, the first frame is connected to the second frame via the two first torsional beams; the second frame is connected to a second actuator through two second torsional beams, and the mirror surface rotates about the second rotation axis under the action of the second actuator.

18. The MEMS scanner of claim 4 or 10, wherein, When the mirror surface moves upward, the resistance values of the two piezoresistors in the X-shaped piezoresistor close to the mirror surface increase, and the resistance values of the two piezoresistors away from the mirror surface decrease; when the mirror surface moves downward, the resistance values of the two piezoresistors in the X-shaped piezoresistor close to the mirror surface decrease, and the resistance values of the two piezoresistors away from the mirror surface increase.

19. The MEMS scanner of claim 1, wherein, The first and second piezoresistors of one of the X-shaped piezoresistors are connected in series to form a first bridge arm resistor, and the third and fourth piezoresistors are connected in series to form a second bridge arm resistor; the first and second piezoresistors of the other X-shaped piezoresistor are connected in series to form a third bridge arm resistor, and the third and fourth piezoresistors are connected in series to form a fourth bridge arm resistor.

20. The MEMS scanner of claim 19, wherein, The first, third, fourth and second bridge arm resistors are connected in series to form a Wheatstone bridge structure, the node between the first and second bridge arm resistors is connected to the ground terminal; the node between the third and fourth bridge arm resistors is connected to the working voltage, and the nodes between the first and third bridge arm resistors and the second and fourth bridge arm resistors are respectively used as the output terminals of the Wheatstone bridge.

21. The MEMS scanner of claim 1, wherein, Each X-shaped piezoresistor further comprises a dielectric layer and first and second wiring layers on the substrate; The first to fourth piezoresistor regions are located in the substrate and are isolated from each other; The plurality of contact regions are respectively located on both sides of the first to fourth piezoresistance regions; A dielectric layer is covered on the substrate, and a first wiring layer is arranged in the dielectric layer to connect the first piezoresistance region and the second piezoresistance region in series via the contact regions; A second wiring layer is arranged on the dielectric layer to connect the third piezoresistance region and the fourth piezoresistance region in series via the contact regions.

22. The MEMS scanner of claim 21, wherein, The first wiring layer and / or the second wiring layer lead out the remaining one end of the first to fourth piezoresistance regions via the corresponding contact regions.

23. The MEMS scanner of claim 21, wherein, The substrate is of a first doping type, and the first to fourth piezoresistance regions and the contact regions are of a second doping type, the first doping type being opposite to the second doping type.

24. The MEMS scanner of claim 21, wherein, The doping concentration of the first to fourth piezoresistance regions is less than the doping concentration of the contact regions.

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