CN100449265C - A horizontal axis micromachined gyro and its preparation method - Google Patents

Abstract

The invention relates to a horizontal axis micromechanical gyro and its preparation method, which is characterized in that it includes an outer frame, an inner frame, a driving electrode, a driving feedback electrode, a driving mode elastic beam, a detection electrode, a detection mode elastic beam and an anchor point, the drive electrodes and the drive feedback electrodes both use two sets of transverse comb capacitors, the outer frame is connected to the anchor point fixed on the substrate through the elastic beam of the drive mode, the drive electrodes and the drive feedback electrodes The movable electrode of the electrode is connected to the outer frame, the movable electrode of the detection electrode is connected to the inner frame, and the detection electrode is two sets of unequal-height vertical comb capacitors for differential detection. The dynamic elastic beams are four groups of combined torsion beams, one end of each group of combined torsion beams is connected to the inner frame, and the other end is connected to the outer frame. The preparation method adopted in the present invention adopts conventional MEMS process equipment, which can realize mass production. The process is simple, compatible with Z-axis gyro and accelerometer technology, and can be used to realize a single-chip three-axis gyro or a miniature inertial measurement unit (MIMU).

Description

A horizontal axis micromachined gyro and its preparation method

technical field

The invention relates to a capacitive micromechanical gyroscope and a preparation method thereof, in particular to a horizontal axis micromechanical gyroscope adopting vertical comb capacitance detection and a preparation method thereof.

Background technique

Micromachined gyroscopes are a class of inertial sensors that use the Coriolis force to measure the angular rate of rotation of an object. Due to the use of micro-electromechanical system (MEMS) technology, micro-mechanical gyroscopes have the advantages of small size, light weight, and low cost. They have very broad application prospects in inertial navigation, weapon guidance, automobiles, and consumer electronics. In order to obtain the complete information of the object's rotation, it is necessary to detect the angular velocity signals of three axes at the same time, which requires a three-axis gyroscope. A three-axis gyro can be realized by assembling three single-axis devices orthogonally, but the error during assembly makes it difficult for the three detection axes to be completely orthogonal, which limits the performance of the three-axis gyro and increases the processing cost. . Using MEMS technology, three single-axis gyroscopes can be processed on a single chip at the same time. The orthogonal alignment between the axes is automatically realized through structural design, which avoids assembly problems and can reduce the volume and weight of the entire system. The gyro structure of each unidirectional axis in the three-axis gyroscope realized by this technology can be independently optimized, so that higher performance can be obtained.

Integrating three single-axis gyroscopes on one chip, on the one hand, the compatibility between the Z-axis gyroscope and the X-axis and Y-axis gyroscopes must be considered when selecting a design scheme, and the process scheme that can realize a high-aspect-ratio structure should also be considered. Increase the inertial mass and sensitive capacitance of the gyro; on the other hand, in order to improve the quality factor (Q value) of the gyro drive and detection mode to improve the performance of the gyro, the movement of the gyro drive and detection direction should minimize the air pressure film damping, Such as the use of variable area comb electrodes. A gyroscope that can obtain a higher Q value when working in an atmospheric environment can eliminate the need for vacuum packaging, reducing the processing cost of the gyroscope. Because the driving and detection modes of the Z-axis gyroscope move in the plane, it is easy to use the high aspect ratio MEMS process to realize the design of the gyroscope with a higher Q value, such as the gyroscope design scheme of Seong-HyokKim et al. (Proc.Transducers2001). For the X and Y axis gyroscopes that need to detect out-of-plane motion in the Z direction, it is difficult to realize variable area sensitive capacitors due to the limitations of MEMS technology. Existing solutions mostly use variable gap parallel plate capacitors, such as W. Geiger in Germany, etc. Human-designed gyro structure (Sensors & Actuators A, 95). Since the sensitivity of the variable-gap plate capacitor is inversely proportional to the gap, in order to ensure high sensitivity, the gap between the plate electrodes should not be too large, which will cause a large air damping, and must work in a low-voltage or vacuum environment, and this type of capacitor Difficult to achieve differential detection. Huikai Xie et al. in the United States designed a gyroscope structure (Sensors and Actuators-Physical) that uses vertical comb capacitance for detection. This gyroscope is implemented in a CMOS MEMS process, but its sensitive capacitance depends on the interconnection in the CMOS process. The number of layers and thickness of the wiring makes it difficult to obtain a large sensitive capacitance, and there is a large stress in the process, which limits the performance of the device.

Contents of the invention

The object of the present invention is to provide a horizontal-axis micromechanical gyroscope with high sensitivity and capable of differential detection of vertical motion in the Z direction and a preparation method thereof.

To achieve the above object, the present invention takes the following technical solutions: a horizontal axis micromachined gyroscope, characterized in that: it includes an outer frame, an inner frame, a drive electrode, a drive feedback electrode, a drive mode elastic beam, a detection electrode, a detection mode state elastic beams and anchor points, the driving electrodes and the driving feedback electrodes both use two sets of transverse comb capacitors, the outer frame is connected to the anchor points fixed on the substrate through the elastic beams in the driving mode, and the The movable electrodes of the drive electrodes and the drive feedback electrodes are connected to the outer frame, the movable electrodes of the detection electrodes are connected to the inner frame, and the detection electrodes are two sets of unequal-height vertical comb capacitors for differential detection , the detection mode elastic beams are four groups of combined torsion beams, one end of each group of combined torsion beams is connected to the inner frame, and the other end is connected to the outer frame.

The two sets of unequal-height vertical comb-tooth capacitors of the detection electrodes are composed of movable electrodes and fixed electrodes inserted adjacent to each other with a height difference, and the movable electrodes of one set of capacitors are shorter than the fixed electrodes, Another set of said capacitors has movable electrodes longer than the fixed electrodes.

The two sets of unequal-height vertical comb capacitors of the detection electrodes are composed of adjacently inserted movable electrodes and fixed electrodes with height differences at both ends, and the position of the movable electrodes of one set of capacitors is higher than that of the fixed electrodes. High, the position of the movable electrode of the other group of capacitors is lower than that of the fixed electrode.

The four groups of combined torsion beams for the detection mode elastic beam respectively include a rigid part and four beams, and one end of the four beams is respectively connected to the end of the rigid part.

A method for preparing a horizontal-axis micromachined gyroscope, comprising the following steps: (1) using a double-polished N-type silicon wafer; (2) forming a photoresist mask and a composite mask composed of silicon oxide on the silicon wafer to The photoresist is used as a mask to etch deep grooves, and the depth of the deep grooves determines the height difference between the fixed electrode and the movable electrode; (3) Remove the photoresist mask, and use silicon oxide as a mask to etch shallow grooves, shallow grooves The depth determines the gap between the movable electrode and the substrate; (4) Remove silicon oxide, and the surface of the silicon wafer is doped by ion implantation or diffusion process to form an ohmic contact; (5) Make a metal electrode on the glass substrate, As the lead electrode of the micromechanical gyroscope; (6) anodic bonding, realize the alignment and bonding of the glass substrate and the silicon wafer, and thin the silicon wafer to an appropriate thickness; (7) mask etching release structure, complete Fabrication of comb-tooth capacitive micromachined gyroscope.

The mask etching release structure is an etching release structure using an aluminum mask as a mask to complete the preparation of a single-end unequal-height comb micromechanical gyroscope.

The mask etching release structure includes the following steps: (1) forming a composite mask composed of a photoresist mask and an aluminum mask on the surface of the silicon wafer, and etching a deep groove with the photoresist as a mask; (2) Remove the photoresist mask, etch the silicon wafer with the aluminum mask as a mask, and complete the preparation of the double-terminal unequal-height comb capacitance micromechanical gyroscope.

Because the present invention adopts the above technical scheme, it has the following advantages: 1. The present invention effectively reduces the driving mode and detection mode due to the drive electrode, the drive feedback electrode and the detection electrode are all realized by variable-area comb-tooth electrodes. Damping, which increases the sensitivity of the gyro. 2. Since the detection electrode of the present invention adopts a vertical comb capacitor, its sensitivity has nothing to do with the gap between the movable electrode and the substrate, so the air damping of the driving and detection modes can be further reduced by increasing the gap between the movable electrode and the substrate. 3. Due to the effective reduction of air damping, the gyroscope can obtain a higher Q value in the atmospheric environment, and can work without vacuum packaging, which can reduce the processing cost of the device. 4. The gyro structure of the present invention realizes the vertical motion of the high aspect ratio structure, so that the entire gyro structure can be realized by a high aspect ratio process, and the gyro can obtain larger inertial mass and sensitive capacitance, which is beneficial to improving the performance of the device. 5. The present invention adopts conventional MEMS process equipment to produce the product of the present invention. The process is simple and compatible with Z-axis gyroscope and accelerometer process. It can be used to realize single-chip three-axis gyroscope or miniature inertial measurement unit (MIMU), and can realize large Mass manufacturing.

Description of drawings

Figure 1a and Figure 1b are schematic cross-sectional views of single-ended unequal height vertical comb capacitors of the present invention

Figure 2a and Figure 2b are cross-sectional schematic diagrams of double-ended unequal height vertical comb capacitors of the present invention

Fig. 3 is the structure schematic diagram of combined torsion beam of the present invention

Fig. 4 is a structural representation of the present invention

Fig. 5a～Fig. 5g are the schematic diagrams of the preparation process of the present invention

Figure 6a and Figure 6b are schematic diagrams of another embodiment of the preparation process of the present invention

Detailed ways

For the convenience of describing the present invention, the structure of the single-ended unequal-height vertical comb capacitor, the double-ended unequal-height vertical comb capacitor and the combined torsion beam involved in the present invention will be described first.

As shown in Figures 1a and 1b, the single-ended unequal-height vertical comb capacitor includes movable electrodes 1 and fixed electrodes 2 arranged at intervals, and the movable electrodes 1 and fixed electrodes 2 adopt single-ended (upper or lower) unequal heights. structure, forming two sensitive capacitors 3,4. Wherein the movable electrode 1 of the sensitive capacitor 3 is shorter than the fixed electrode 2 (as shown in Figure 1a), and the movable electrode 1 of the sensitive capacitor 4 is longer than the fixed electrode 2 (as shown in Figure 1b), when the movable electrode 1 is upward ( or downward) vertical movement, according to the height setting of the fixed electrode 2 and the movable electrode 1, the electrode overlapping area of the sensitive capacitor 3 decreases (or remains unchanged), that is, the sensitive capacitor 3 decreases (or remains unchanged) ; The electrode overlapping area of the sensitive capacitor 4 remains unchanged (or decreases), that is, the sensitive capacitor 4 remains unchanged (or decreases). The differential result of the two sensitive capacitors 3 and 4 is proportional to the vertical displacement of the movable electrode 1, so it can be used for vertical displacement detection. The above analysis does not consider the influence of the fringe electric field on the capacitance. If the fringe electric field is included, the variation of a single capacitance changes and deviates from linearity, but the differential result of capacitance still maintains a linear relationship, so it can be used for actual detection.

As shown in Figures 2a and 2b, the double-ended unequal-height vertical comb capacitor is an improvement on the basis of the aforementioned single-ended unequal-height comb capacitor structure, including movable electrodes 1 and fixed electrodes 2 arranged at intervals, The movable electrode 1 and the fixed electrode 2 adopt a double-terminal unequal height structure to form two sensitive capacitors 5 and 6 . The position of the fixed electrode 2 of the sensitive capacitor 5 is lower than that of the movable electrode 1 (as shown in FIG. 2 a ), and the position of the fixed electrode 2 of the sensitive capacitor 6 is higher than that of the movable electrode 1 (as shown in FIG. 2 b ). As shown in Figures 2a and 2b, when the movable electrode 1 moves upward (or downward) vertically, the electrode overlapping area of the sensitive capacitor 5 decreases (or increases), that is, the sensitive capacitor 5 decreases (or increases) ; The electrode overlapping area of the sensitive capacitor 6 increases (or decreases), that is, the sensitive capacitor 6 increases (or decreases). The differential results of the two sensitive capacitors 5 and 6 are proportional to the vertical displacement of the movable electrode 1, and can be used for vertical displacement detection. Compared with the aforementioned single-ended unequal-height vertical comb-tooth capacitor, the detection sensitivity and linearity of the double-ended unequal-height vertical comb-tooth capacitor are improved.

As shown in Figure 3, the combined torsion beam 7 is composed of four support beams 71, 72, 73, 74 connected to a rigid member 8, wherein two support beams 71, 72 are connected with fixed points, and the other two support beams 73, 74 Connected to the inertial mass (the inertial mass is the structure connected to the beam in the gyroscope, which will be described in detail below). When the inertial mass moves vertically, the combined torsion beam 7 twists about the support beams 71 and 72, thereby realizing the vertical movement of the structure with a high aspect ratio. The combined torsion beam 7 can reduce the equivalent elastic stiffness of the inertial mass in the Z direction and improve the displacement sensitivity in the Z direction. In actual use, more than two combined torsion beams 7 must be used to ensure the vertical movement of the inertial mass.

As shown in Figure 4, the present invention adopts the horizontal axis micromechanical gyroscope of vertical comb capacitance detection, and it comprises driving electrode 9, driving feedback electrode 10, detecting electrode 11,12, driving modal elastic beam 13, detecting modal elastic beam 14 and anchor point 15. The driving electrodes 9 of the gyroscope include two sets of electrodes, adopting a push-pull driving mode, and the driving feedback electrodes 10 also include two sets of electrodes, which respectively provide feedback signals for the two sets of driving electrodes 9 . The driving electrodes 9 and the driving feedback electrodes 10 can be implemented with transverse comb-teeth electrodes to increase the amplitude of vibration modes and reduce air damping. The present invention adopts a double frame 16, 17 structure, and the outer frame 16 is connected with the anchor point 15 through the driving mode elastic beam 13, and is fixed on the substrate of the device. The inner frame 17 of the present invention is integrated with the movable electrodes of the detection electrodes 11 and 12 and the connection between the electrodes, and is connected with the outer frame 16 through the detection mode elastic beam 14 . There are four groups of detection modal elastic beams 14, and the structure of each group of detection modal elastic beams 14 is the structure and motion mode of the aforementioned combined torsion beam 7, wherein the inner frame 17 of the gyroscope and the movable electrodes of the detection electrodes 11, 12 and The connecting part between the electrodes is equivalent to the inertial mass connected by the beams 73 and 74 in the combined torsion beam 7; the outer frame 16 of the gyroscope is equivalent to the fixed point where the beams 71 and 72 in the combined torsion beam 7 are connected. The two sets of detection electrodes 11 and 12 of the present invention adopt the aforementioned single-ended or double-ended vertical comb capacitors with unequal heights to realize differential detection. The detection electrode 11 is located in the middle, and the detection electrode 12 is symmetrically located on both sides (the gray part in the figure is the fixed electrode). The comb teeth of the movable electrodes on both sides of the fixed electrode near the middle are longer, and the comb teeth of the movable electrodes near the fixed electrodes on both sides are longer. Shorter, the sum of the overlapping areas between the movable electrodes and the fixed electrodes in the detection electrodes 12 on both sides is equal to the sum of the overlapping areas between the movable electrodes and the fixed electrodes in the middle detection electrode 11 . Wherein, the detection electrode 11 adopts the structure form of capacitor 3 or 5 (as shown in FIG. 1a or 2a ), and the detection electrode 12 adopts the structure form of capacitor 4 or 6 (as shown in FIG. 1b or 2b ). The drive axis of the micromechanical gyroscope of the present invention is parallel to the substrate direction (Y axis), the detection axis is perpendicular to the substrate (Z axis), and the angular velocity input axis is parallel to the substrate direction, orthogonal to the drive axis and detection axis (X axis) .

The micromechanical gyroscope of the present invention uses the Coriolis force to measure the angular velocity of the object. As shown in Figure 4, the Y-axis is driven during work, so that the entire structure vibrates along the Y-axis. When the system has an X-direction angular velocity (rotating with the X direction as the axis) At this time, the inner frame 17 and the movable electrodes of the detection electrodes 11 and 12 and the connecting parts between the electrodes will vibrate up and down (along the Z axis) under the constraint of the torsion beam 7, thereby causing a change in capacitance, and obtaining the detection result moving in the Z axis .

The horizontal axis micromechanical gyroscope of the present invention can adopt the following preparation methods:

Embodiment 1: The following steps are adopted when making a single-ended unequal-height comb-tooth capacitance horizontal-axis micromechanical gyroscope:

1. The starting material is a double-polished N-type (100) silicon wafer 18 (as shown in FIG. 5a ), with a thickness of 400±10 microns;

2, at first form silicon oxide 19 mask on silicon wafer 18, then on silicon wafer 18, form the compound mask (as shown in Figure 5 b) that photoresist 20 and silicon oxide 19 form, then use photoresist 20 as The deep groove 21 is etched by the mask, and the depth of the deep groove 21 determines the height difference between the lower ends of the fixed electrode 2 and the movable electrode 1;

3. As shown in FIG. 5C, the photoresist mask 20 is removed, and the shallow groove 22 is etched using the silicon oxide 19 as a mask. The depth of the shallow groove 22 determines the gap between the movable electrode 1 and the glass substrate;

4. As shown in FIG. 5d, the silicon oxide 19 is removed, and the surface of the silicon wafer 18 is doped with ion implantation or diffusion process 23 to form an ohmic contact;

5. As shown in FIG. 5e, metal electrodes 25 are made on the glass substrate 24 as the lead electrodes of the gyroscope;

6. As shown in FIG. 5f, align and bond the glass substrate 24 and the silicon wafer 18 to realize anodic bonding, and thin the silicon wafer 18 to an appropriate thickness;

7. As shown in FIG. 5g, use the aluminum mask 26 as a mask to etch the release structure to form the movable electrode 1 and the fixed electrode 2 of the capacitor, and complete the preparation of the single-ended unequal-height comb capacitor horizontal axis micromechanical gyroscope ( as shown in Figure 1b).

Embodiment 2: The following steps are adopted when making a double-ended unequal-height comb capacitor horizontal axis micromechanical gyroscope:

1. The initial process is consistent with the above single-end unequal-height comb micromechanical gyroscope process, that is, steps 1 to 6 in Example 1 are used, and then the following steps are carried out;

2. As shown in FIG. 6a, a composite mask composed of a photoresist mask 27 and an aluminum mask 28 is formed on the surface of the silicon wafer 18, and the photoresist is used as a mask to etch a deep groove 29;

3. As shown in FIG. 6b, remove the photoresist mask 27, etch the silicon wafer 18 with the aluminum mask 28 as a mask, form the movable electrode 1 and the fixed electrode 2 of the capacitor, and complete the double-ended unequal height comb teeth Fabrication of capacitive horizontal axis micromachined gyroscopes.

Claims (7)

1, a kind of horizontal axis micromechanical gyroscope, it is characterized in that: it comprises outer frame, inner frame, drive electrode, drive feedback electrode, drive modal elastic beam, detection electrode, detection modal elastic beam and anchor point, described driving The electrodes and the driving feedback electrodes both use two sets of transverse comb capacitors, the outer frame is connected to the anchor point fixed on the substrate through the driving mode elastic beam, and the movable electrodes of the driving electrodes and the driving feedback electrodes are connected to the The outer frame is connected, the movable electrode of the detection electrode is connected to the inner frame, the detection electrodes are two sets of unequal-height vertical comb capacitors for differential detection, and the detection modal elastic beams are four groups Combined torsion beams, one end of each group of combined torsion beams is connected to the inner frame, and the other end is connected to the outer frame. 2. A horizontal-axis micromechanical gyroscope according to claim 1, characterized in that: the two sets of unequal-height vertical comb-tooth capacitors of the detection electrodes are composed of adjacently inserted movable electrodes with a height difference at one end and The movable electrodes of one group of capacitors are shorter than the fixed electrodes, and the movable electrodes of the other group of capacitors are longer than the fixed electrodes. 3. A horizontal-axis micromechanical gyroscope as claimed in claim 1, characterized in that the two sets of vertical comb-tooth capacitors with unequal heights of the detection electrodes are formed by adjacently inserted movable electrodes with height differences at both ends. It is composed of fixed electrodes, and the position of the movable electrodes of one group of capacitors is higher than that of the fixed electrodes, and the position of the movable electrodes of the other group of capacitors is lower than that of the fixed electrodes. 4. A horizontal-axis micromechanical gyroscope according to claim 1, 2 or 3, characterized in that: the four sets of combined torsion beams for the detection of modal elastic beams respectively include a rigid member and four beams, so One ends of the four beams are respectively connected to the ends of the rigid parts. 5. A method for preparing a horizontal axis micromachined gyroscope, comprising the following steps: (1) Double-throwing N-type silicon wafers are used; (2) Form a composite mask composed of a photoresist mask and silicon oxide on the silicon wafer, etch a deep groove with the photoresist as a mask, and the depth of the deep groove determines the height difference between the fixed electrode and the movable electrode; (3) Remove the photoresist mask, etch the shallow groove with silicon oxide as the mask, and the depth of the shallow groove determines the gap between the movable electrode and the substrate; (4) Silicon oxide is removed, and the surface of the silicon wafer is doped by ion implantation or diffusion process to form an ohmic contact; (5) Make metal electrodes on the glass substrate as the lead electrodes of the micromechanical gyroscope; (6) Anodic bonding, to realize the alignment and bonding of the glass substrate and the silicon wafer, and to thin the silicon wafer to an appropriate thickness; (7) The mask is etched to release the structure, and the preparation of the comb-tooth capacitive micromachined gyroscope is completed. 6. A method for manufacturing a horizontal-axis micromechanical gyroscope according to claim 5, characterized in that: the mask etching release structure is an etching release structure using an aluminum mask as a mask, and the single-ended unequal Preparation of high-comb micromechanical gyroscope. 7. The method for manufacturing a horizontal-axis micromachined gyroscope according to claim 5, wherein said mask etching release structure comprises the following steps: (1) Form a composite mask composed of a photoresist mask and an aluminum mask on the surface of the silicon wafer, and use the photoresist as a mask to etch deep grooves; (2) Remove the photoresist mask, etch the silicon wafer with the aluminum mask as a mask, and complete the preparation of the two-terminal unequal-height comb capacitance micromechanical gyroscope.

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