CN103675348B - Z axis capacitance type micromechanical accelerometer - Google Patents

Abstract

The invention discloses a Z-axis capacitive micromachine accelerometer, belonging to the technical field of inertial sensors in micromechanical electronic systems, comprising: a glass base, a torsion structure layer bonded on the glass base, and sputtered on the glass base The twisted structure layer includes four subunits with the same structure, and any three subunits are equivalent to another subunit rotated 90 degrees, 180 degrees, and 270 degrees clockwise or counterclockwise, respectively. get. The present invention increases the sensitivity of the micromechanical accelerometer by reducing the ratio of the detection capacitor polar plate facing area to the polar plate spacing, and the fully symmetrical torsional structure layer makes the common mode rejection ratio of the structure large and reduces the zero point deviation of the output signal. shift.

Description

Z-axis capacitive micromachined accelerometer

technical field

The invention discloses a Z-axis capacitive micro-machine accelerometer, which belongs to the technical field of inertial sensors in micro-machine electronic systems.

Background technique

Micromachined accelerometers are one of the most successful devices in microelectromechanical systems. They have broad application prospects in the military and civilian fields, and have huge social and economic benefits. Improving performance indicators is currently the research focus in the field of micromachined accelerometers. .

The Z-axis capacitive micromachined accelerometer acts on the mass block through the acceleration in the Z-axis direction. The mass block drives the movement of the support beam, and the comb teeth or flat plate on the mass block also move correspondingly. When the comb tooth or flat plate and the fixed When the distance between the capacitance pairs formed by the plates or the distance between the pole plates changes, it means that the corresponding capacitance changes, and the magnitude of the capacitance change is related to the acceleration in the Z-axis direction. The Z-axis capacitive micromachined accelerometer senses the acceleration in the Z-axis direction by detecting the magnitude of the capacitance change.

There are generally two types of Z-axis capacitive micromachined accelerometers. One is the up-and-down translation type. When the acceleration in the Z-axis direction changes, the mass block supported by the support beam moves in parallel up and down in the Z-axis direction. Differential capacitors are formed directly above and below the mass block. The whole structure is a "sandwich" bread structure. This solution has many layers of accelerometers, which is difficult to manufacture, and the movable mass block moves up and down in parallel. The distance is small, and the sensitivity of the accelerometer is small. . The other is torsion type. The mass block is supported by the beam. When the acceleration in the Z-axis direction changes, the left and right parts of the mass block supported by the support beam will twist relative to the axis corresponding to the support beam. The position of the mass block on one side rises, and the other side The position of the mass block decreases, and the corresponding left and right capacitances change due to the change in the ratio of the polar plate facing area to the polar plate spacing. In this way, the fixed capacitance plate is arranged horizontally with the mass block and the support beam, and the processing is relatively easy. Yang Zhenchuan, Liu Xuesong, Hao Yilong, etc. from Peking University introduced a comb-tooth capacitive Z-axis accelerometer and its preparation method (CN 1605871A), including a glass base, movable electrodes and fixed electrodes, support beams and anchor points, movable The electrode takes the support beam as the axis, and its two sides have poor quality. It belongs to the torsion Z-axis capacitive micromachined accelerometer, but because the change of the detection capacitance only depends on the torsion angle of the support beam, and has nothing to do with the fixed electrode, so the sensitivity of the accelerometer smaller.

Contents of the invention

The technical problem to be solved by the present invention is to propose a Z-axis capacitive micro-mechanical accelerometer in view of the deficiencies of the above-mentioned background technology.

The present invention adopts following technical scheme for realizing above-mentioned purpose of the invention:

Z-axis capacitive micromachined accelerometer, including: a glass base, a torsion structure layer bonded on the glass base, a gold electrode layer sputtered on the glass base, the torsion structure layer includes four subunits with the same structure, any three A subunit is equivalent to another subunit rotated clockwise or counterclockwise by 90 degrees, 180 degrees, and 270 degrees respectively;

Wherein, each of the subunits includes: a quadrilateral mass of symmetrical structure, a support beam connected to the quadrilateral mass, a hollowed-out area is left on the local mass on one side of the symmetric axis of the quadrilateral mass, and the quadrilateral mass There are comb teeth attached to the symmetrical first side and the second side of the block, and the horizontal comb teeth attached to the first side of the quadrilateral mass block have an included angle of 90 degrees with the vertical direction of the subunit attached to the quadrilateral mass block. The angle between the vertical comb teeth on the second side of the mass block and the horizontal direction of the associated subunit is 90 degrees, and the horizontal comb teeth of each subunit overlap with the vertical comb teeth of adjacent subunits to form a comb capacitor pair .

As a further optimization scheme of the Z-axis capacitive micromachined accelerometer, the quadrilateral mass block is an isosceles trapezoidal mass block, and the mutually symmetrical first and second sides of the quadrilateral mass block are two sides of an isosceles trapezoid. hypotenuse.

As a further optimization solution for the Z-axis capacitive micromachined accelerometer, the hollowed-out area is a triangular area.

The present invention adopts the above-mentioned technical scheme, and has the following beneficial effects:

(1) Increase the sensitivity of the micromechanical accelerometer by reducing the ratio of the detection capacitor polar plate facing area to the polar plate spacing;

(2) Each unit of the structural layer is identical, and the common mode rejection ratio of the structure is large, which can reduce the zero offset of the output signal;

(3) The isolation distance of the electrode layout is large, and the cross-coupling of the output signal is small: Since the electrode layout is in the middle of each unit, the corresponding detection electrodes are far away from each other, so the cross-coupling of the output signal is relatively small.

Description of drawings

Figure 1 is a cross-sectional view of a typical z-axis capacitive micromachined accelerometer.

Fig. 2 is a sectional view of the z-axis capacitive micromachined accelerometer of the present invention.

FIG. 3 is a structural diagram of a Z-axis capacitive micromachined accelerometer involved in the present invention.

Fig. 4 is a structural diagram of a twisted structural layer.

FIG. 5 is a structural diagram of the second subunit A2.

FIG. 6 is a schematic diagram of the Z-axis capacitive micromachined accelerometer connected to an external circuit through metal leads.

7 is a schematic diagram of the capacitive comb teeth of each subunit in the Z-axis capacitive micromachined accelerometer.

Explanation of the symbols in the figure: A1-A4 are the first to fourth subunits in sequence, M2 is the isosceles trapezoidal mass block, K21, K22 are rectangular support beams, H11, H21, H31, H41 are horizontal comb teeth, H12, H22, H32, H42 are vertical comb teeth, J11, J21, J22, J31, J41 are anchor points, S1, S2, S3, S4 are electrodes.

Detailed ways

Below in conjunction with accompanying drawing, the technical scheme of invention is described in detail:

For a typical Z-axis capacitive micromachined accelerometer as shown in Figure 1, in order to ensure that the movable mass is torsion under the action of acceleration, the left side of the mass is raised and the right is lowered after the torsion, and the difference between the movable mass and the left and right fixed detection masses The ratio of the facing area of the plates corresponding to the capacitance to the distance between the plates decreases. Because the torsional stiffness is relatively large, the capacitance change is relatively small, so the sensitivity of the accelerometer is relatively small.

The Z-axis capacitive micromachined accelerometer of the present invention is improved on a typical Z-axis capacitive micromachined accelerometer. The dotted line in Fig. 2 is the state of the active mass structure at initial balance, and there are two active detections on the left and right of the central mass mass block. When there is an acceleration in the Z-axis direction, the left end of the middle active mass is twisted upwards, and the right end is twisted downwards. Under this condition, the proof mass is also supported by the support beam. Rotate downward, such that one twists upward and the other twists downward, the ratio of the facing area of the two mass blocks to the distance will be greatly reduced, and the changing capacitance will increase. Similarly, under the action of acceleration in the Z-axis direction, the right-end proof mass is designed to rotate upwards, so that the central movable mass is twisted downward, and the right-end proof mass is rotated upward, and the ratio of the facing area of the two masses to the distance is will be greatly reduced, and the changing capacitance will be similarly increased. In this way, the parallel connection of the two detection capacitors can further increase the sensitivity of the accelerometer.

As shown in Figure 3, the Z-axis capacitive micromachined accelerometer related to the present invention is used to measure the one-dimensional acceleration in the vertical direction, including: a glass base, a single crystal silicon torsion structure layer bonded on the glass base, sputtering A gold electrode layer on a glass pedestal. The glass base is used to support the twisted structure layer of single crystal silicon, the backside of the twisted structure layer of single crystal silicon is etched with a bonding area, and the gold electrode layer is arranged with signal wires.

As shown in Figure 4, the torsion structure layer includes: a central active mass unit and a detection unit, the central active mass unit and the detection unit are symmetrical about the center of mass of the torsion structural layer, and the central active mass unit includes a center of mass symmetrical about the torsion structural layer. The first subunit A1, the third subunit A3, and the detection unit include a second subunit A2 and a fourth subunit A4 that are symmetrical about the center of mass of the twisted structure layer. The first to fourth subunits A1 , A2 , A3 , A4 are arranged in a clockwise direction, and may also be arranged in a counterclockwise direction.

Take the torsion structure layer composed of the first to fourth subunits A1, A2, A3, and A4 arranged in a clockwise direction as an example: each subunit has the same structure, and the second subunit A2 includes, as shown in Figure 5: an isosceles trapezoid Mass M2, rectangular support beams K21, K22 connected with isosceles trapezoidal mass, multiple horizontal combs H21 attached to the left hypotenuse of trapezoidal mass M2, multiple horizontal combs H21 attached to the right hypotenuse of trapezoidal mass M2 Vertical comb H22. A hollow area is left on the local mass block on one side of the symmetry axis of the trapezoidal mass M2. The hollow area can be triangular or other shapes, and the size of the hollow area can be designed as required. The vertical angle between the horizontal comb H21 and the second subunit is ninety degrees, the horizontal angle between the vertical comb H22 and the second subunit is ninety degrees, the length of the horizontal comb H21, the vertical comb H22 and The width can be adjusted according to design needs. The distance between adjacent horizontal comb teeth H21 and vertical comb teeth H22 can also be adjusted according to design requirements. The rectangular support beam K21 is connected to the long base of the trapezoidal mass M2, and the rectangular beam K22 is connected to the short base of the trapezoidal mass M2. The rectangular supporting beam K21 is fixed on the base through the anchor point area J21, and the rectangular supporting beam beam K22 is fixed on the base through the anchor point area J22. The anchor point area J21 and the anchor point area J22 are rectangular, and the area size can be changed as required. The trapezoidal mass M2 and the comb teeth attached to it are suspended in the air under the support of the anchor points J21 and J22. The second sub-unit A2 is force-balanced with respect to the support beams K21 and K22 in the vertical plane direction.

The third subunit A3 can be obtained by rotating the second subunit A2 clockwise ninety degrees, the vertical comb teeth H22 in the second subunit A2 and the horizontal comb teeth H31 in the third subunit A3 overlap together, but do not The contacts form comb-tooth capacitor pairs. From a three-dimensional perspective, it is necessary to ensure that the comb teeth of the two sub-units overlap at an appropriate height in static state. The overlapping height is related to the geometric dimensions of the support beams in the two sub-units and the position where the support beams are connected to the mass blocks they support. Since the four sub-units in the present invention are identical, the geometric dimensions of the supporting beam and the position where the beam is connected to the mass block supported can be adjusted according to the design requirements, thereby adjusting the overlapping height of the comb teeth. By analogy, the third subunit A3 is rotated 90 degrees clockwise to obtain the fourth subunit A4, and the vertical comb teeth in the third subunit A3 overlap with the horizontal comb teeth in the fourth subunit A4 to form a comb capacitor Right; the fourth subunit A4 is rotated 90 degrees clockwise to obtain the first subunit A1, and the vertical comb teeth in the fourth subunit A4 overlap with the horizontal comb teeth in the first subunit A1 to form a comb capacitor pair . The horizontal comb H11 in the first subunit and the vertical comb H42 in the fourth subunit constitute the first comb capacitor pair, the vertical comb H12 in the first subunit and the horizontal comb H21 in the second subunit Constitute the second comb-tooth capacitor pair, the horizontal comb-tooth H31 in the third subunit and the vertical comb-tooth H22 in the second sub-unit form the third comb-tooth capacitor pair, the vertical comb-tooth H32 in the third sub-unit and the fourth The horizontal comb teeth H41 in the subunit form a fourth comb tooth capacitance pair.

The Z-axis capacitive micromachined accelerometer needs to be connected to the external circuit through metal leads. As shown in Figure 6, the metal electrode layer on the glass base has four electrodes S1, S2, S3, and S4. Electrode S1 is connected to the anchor region J11 through anodic bonding, electrode S2 is connected to the anchor region J21 through anodic bonding, electrode S3 is connected to the anchor region J31 through anodic bonding, and electrode S4 is connected to the anchor region through anodic bonding. Point area J41 is connected. The electrodes S1 , S2 , S3 , and S4 respectively provide electrical signal connections for the first, second, third, and fourth subunits A1 , A2 , A3 , and A4 in turn. The shapes of the electrodes S1, S2, S3, and S4 can be adjusted according to needs, and the distance between the electrodes is large, which can reduce the cross-coupling effect of the output signal.

The central active mass unit and the detection unit can be interchanged. When measuring the Z-axis acceleration, a set of centrally symmetrical subunits is fixed as the central active mass unit, and another set of centrally symmetrical subunits is the detection unit. The central active mass unit and The detection unit can move during the measurement process. Compared with the technical solution in which only the central active mass unit is active in the existing Z-axis capacitive micromachined accelerometer, the solution of the present invention increases the distance between the central active mass unit and the detection unit. The relative torsion angle in the detection further reduces the ratio of the facing area of the detection capacitance plate to the distance between the plates, and increases the sensitivity of the accelerometer.

As shown in Figure 7, taking the pair of the first subunit A1 and the third subunit A3 as the central active mass unit, and the pair of the second subunit A2 and the fourth subunit A4 as the detection pair unit as an example, in Under the action of acceleration in the Z-axis direction, the vertical comb H22 of the second subunit A2 moves downward, and the horizontal comb H21 moves upward; the vertical comb H32 of the third subunit A3 moves downward, and the horizontal comb H31 moves upward; The vertical comb teeth H42 of the fourth subunit A4 move downwards, and the horizontal comb teeth H41 move upwards; the vertical comb teeth H12 of the first subunit A1 move downwards, and the horizontal comb teeth H11 move upwards. Taking the second sub-unit A2 as an example, the size of the second comb-tooth capacitor pair is C21, and the size of the fourth comb-tooth capacitor pair is C23. Under the action of acceleration in the Z-axis direction, the vertical comb teeth H12 of the first sub-unit A1 move downward , the horizontal comb H21 of the second subunit A2 moves upwards, so that the ratio of the facing area of the detection capacitance plate corresponding to C21 to the distance between the plates decreases, and the size of C21 decreases by △C21, the horizontal comb of the third subunit A3 The tooth H31 moves upward, and the vertical comb tooth H22 of the second subunit A2 moves downward, so that the ratio of the facing area of the detection capacitor plate corresponding to C23 to the distance between the plates also decreases, and the size of C23 decreases by △C23. Under the action of Z-axis acceleration, both C21 and C23 decrease, and the size of the decrease is △C21+△C23. In the same principle, taking the fourth subunit A4 as an example, the size of the first comb-tooth capacitance pair is C41, and the size of the third comb-tooth capacitance pair is C43. Under the action of acceleration in the Z-axis direction, the horizontal comb-tooth H11 Moving upwards, the vertical comb H42 of the fourth subunit A4 moves downwards, so that the ratio of the facing area of the detection capacitor plate corresponding to C41 to the distance between the plates decreases, and the size of C41 decreases by △C41; the third subunit A3 The vertical comb H32 of the fourth subunit A4 moves downward, and the horizontal comb H41 of the fourth subunit A4 moves upward, so that the ratio of the facing area of the detection capacitor plate corresponding to C43 to the distance between the plates decreases, and the size of C43 decreases by △C43. Under the action of Z-axis acceleration, both C41 and C43 decrease, and the decrease is △C41+△C43. Short-circuit the electrodes S2 and S4 through the signal line as a lead for testing the equivalent capacitance, and short-circuit the electrodes S1 and S3 through the signal line as another lead for testing the equivalent capacitance. When the acceleration in the Z-axis direction is 0, The test capacitance is C21+C23+C41+C43; when the acceleration in the Z-axis direction is not 0, the test capacitance is C21+C23+C41+C43-△C21-△C23-△C41-△C43, and the change is △ C21+△C23+△C41+△C43. The amount of change is much larger than that of a single comb-tooth capacitance pair, so the sensitivity is increased.

In summary, the present invention has the following advantages:

(1) Increase the sensitivity of the micromachined accelerometer by reducing the ratio of the facing area of the detection capacitor plate to the plate spacing;

(2) Each unit of the structural layer is identical, and the common mode rejection ratio of the structure is large, which can reduce the zero offset of the output signal;

(3) The isolation distance of the electrode layout is large, and the cross-coupling of the output signal is small: Since the electrode layout is in the middle of each unit, the corresponding detection electrodes are far away from each other, so the cross-coupling of the output signal is relatively small.

Claims (3)

1. Z-axis capacitive micromachined accelerometer, comprising: a glass base, a twisted structure layer bonded on the glass base, and a gold electrode layer sputtered on the glass base, characterized in that: the twisted structure layer includes Four subunits with the same structure, any three subunits are equivalent to another subunit rotated 90 degrees, 180 degrees and 270 degrees clockwise or counterclockwise respectively; Wherein, each of the subunits includes: a quadrilateral mass of symmetrical structure, a support beam connected to the quadrilateral mass, a hollowed-out area is left on the local mass on one side of the symmetric axis of the quadrilateral mass, and the quadrilateral mass There are comb teeth attached to the symmetrical first side and the second side of the block, and the horizontal comb teeth attached to the first side of the quadrilateral mass block have an included angle of 90 degrees with the vertical direction of the subunit attached to the quadrilateral mass block. The angle between the vertical comb teeth on the second side of the mass block and the horizontal direction of the associated subunit is 90 degrees, and the horizontal comb teeth of each subunit overlap with the vertical comb teeth of adjacent subunits to form a comb capacitor pair . 2. The Z-axis capacitive micromachined accelerometer according to claim 1, characterized in that: the quadrilateral mass is an isosceles trapezoidal mass, and the quadrilateral mass is symmetrical to each other on the first side and the second side The sides are the two hypotenuses of the isosceles trapezoid. 3. The Z-axis capacitive micromachined accelerometer according to claim 1 or 2, wherein the hollowed-out area is a triangular area.