CN108490217B

CN108490217B - Contact mode micro-accelerometer

Info

Publication number: CN108490217B
Application number: CN201810253047.7A
Authority: CN
Inventors: 李凯; 彭志辉
Original assignee: Wenzhou University
Current assignee: Wenzhou University
Priority date: 2018-03-26
Filing date: 2018-03-26
Publication date: 2020-08-25
Anticipated expiration: 2038-03-26
Also published as: CN108490217A

Abstract

A contact mode micro accelerometer. The micro-accelerometer comprises a lower substrate and an upper substrate, wherein a support column, a thin plate, a plurality of support beams and anchor points of the beams are arranged between the lower substrate and the upper substrate, the lower substrate and the upper substrate are respectively provided with a lower fixed electrode and an upper fixed electrode, the surface of the fixed electrode is covered with a plurality of convex insulating layers, the lower surface and the upper surface of the thin plate are respectively provided with a lower moving electrode and an upper moving electrode, and the micro-accelerometer has a first working state that the thin plate deforms under the stress of the moving electrode but does not contact with the insulating layers and a second working state that the thin plate deforms under the stress of the moving electrode and contacts with the insulating layers. The invention works by utilizing the principle that the acceleration force causes the deformation of the moving electrode so as to change the capacitance between the moving electrode and the fixed electrode. The invention prevents the short circuit of the stop and the fixed electrode through the insulating layer positioned on the fixed electrode, and provides the support for the movable structure by the insulating layer, thereby realizing the measurement of high acceleration, effectively inhibiting the capacitance saturation of the sensor by the beam-circular thin plate combined structure, and effectively inhibiting the hysteresis error by the bulge on the insulating layer.

Description

Contact mode micro-accelerometer

Technical Field

The invention relates to the field of micro-electro-mechanical systems, in particular to a contact mode micro-accelerometer.

Background

The accelerometer is widely applied to various fields such as industry, military, aviation, daily life and the like. According to the working principle, the micro-accelerometer can be classified into a capacitance type, a piezoresistive type, a piezoelectric type and the like. The capacitance type has the advantages of low power consumption, quick response, high sensitivity and the like, and the working principle is as follows: the variable capacitor is composed of a fixed electrode and a moving electrode, wherein the moving electrode is positioned on the acceleration sensitive structure and moves due to the action of acceleration force, and the magnitude of the acceleration can be known by measuring the capacitance value between the moving electrode and the fixed electrode. The movable structure of the traditional capacitive micro-accelerometer mainly adopts a comb structure or a beam-mass block structure consisting of a beam and a rigid mass block, and the latter is generally considered to have higher sensitivity. The range of a capacitive micro-accelerometer with a beam-mass structure is mainly affected by two factors: the maximum displacement value of the mass block allowed for preventing the short circuit of the moving electrode and the fixed electrode, namely the initial gap of the moving electrode and the fixed electrode, and the mechanical strength of the beam-mass block structure. In recent years, in another capacitive micro-sensor, namely a capacitive micro-pressure sensor, an operation principle based on a contact mode is proposed: the insulating layer is covered on the fixed electrode or the moving electrode to prevent short circuit between the electrodes, and the thin plate (film) deformed by the pressure to be measured is supported by the contact force, so the measuring range of the sensor is greatly expanded. In addition, the contact parts of the movable and fixed electrodes are only separated by a thin insulating layer, and the dielectric constant of the insulating layer is generally several times of that of vacuum or air, so that the capacitance between the electrodes is improved in a contact mode according to the fact that the capacitance is inversely proportional to the electrode gap and directly proportional to the dielectric constant, the noise resistance is improved, and high sensitivity can be realized within a certain acceleration range. In the contact mode, the thin plate in the capacitive micro-pressure sensor deforms differently due to different pressures and has different contact areas with the insulating layer, so that the pressure is measured. However, for the capacitive micro accelerometer using the beam-mass structure, since the mass is a rigid structure, it can only do translational motion without deformation, and the above contact mode cannot be directly applied.

In conventional touch mode capacitive sensors, the problem of capacitance saturation is an important factor affecting sensitivity. The term "saturation of capacitance" means that the capacitance between the moving and fixed electrodes tends to stop changing after the measured signal reaches a certain value. One of the main reasons for this is that as the contact area increases, the remaining undeformed portion of the deformed structure becomes smaller and smaller in area and greater in stiffness, making deformation more and more difficult. For capacitive micro accelerometers, the problem of capacitance saturation is also considered when using the touch mode.

In microelectromechanical systems, scale effects cause intermolecular forces-van der waals forces that are not negligible. This force increases sharply with decreasing intermolecular distance. In the contact mode, the distance between the molecules of the moving electrode and the insulating layer is very small in a large area, so that van der waals force is large. In addition, the relative motion between the moving electrode and the insulating layer also causes the generation of friction. As is known from a large number of documents, including those relating to contact mode micro-pressure sensors, van der waals forces, frictional forces can cause significant hysteresis errors (return errors) to the sensors. For microaccelerometers, the measured signal often undergoes dynamic changes from small to large and then large to small in a very short time, and is more sensitive to hysteresis errors.

Disclosure of Invention

In order to solve the problems in the background art, the invention provides a contact mode micro-accelerometer with high range characteristics, which can inhibit capacitance saturation and hysteresis errors.

The technical scheme adopted by the invention for solving the technical problems is as follows: a contact mode micro accelerometer comprising: the micro-accelerometer comprises a lower substrate, an upper substrate, wherein anchor points of support columns, a thin plate, a plurality of support beams and beams are arranged between the lower substrate and the upper substrate, fixed electrodes are arranged on the lower substrate and the upper substrate, insulating layers cover the surfaces of the fixed electrodes, moving electrodes are arranged on the lower surface and the upper surface of the thin plate, and the micro-accelerometer has a first working state that the thin plate is deformed under the stress of the moving electrodes but is not in contact with the insulating layers and a second working state that the thin plate is deformed under the stress of the moving electrodes and is in contact with the insulating layers.

The surface of the insulating layer is provided with a plurality of bulges.

A large number of through holes are formed in the thin plate.

The thin plate is a circular thin plate, a movable structure is formed by the thin plate and the supporting beams, and the supporting beams are uniformly distributed on the edge of the circular thin plate.

The moving electrode on the thin plate is the same as the thin plate in shape and is circular, and the fixed electrodes on the lower substrate and the upper substrate are correspondingly circular.

And under the condition that the measured acceleration is nonzero, the first working state is entered, and the circular thin plate and the moving electrode are deformed.

And when the measured acceleration value reaches a threshold value, the second working state is entered, the moving electrode is contacted with the insulating layer, and the contact area is increased along with the increase of the acceleration.

Two movable electrodes on the circular thin plate and fixed electrodes on the lower and upper substrates form two variable capacitors, and the two variable capacitors form a variable differential capacitor. The magnitude of the variable differential capacitance reflects the magnitude of the measured acceleration, and the positive and negative of the variable differential capacitance reflects the positive and negative of the direction of the measured acceleration.

The invention has the beneficial effects that: the insulating layer on the fixed electrode prevents short circuit of the fixed electrode and provides support for the movable structure, so that the device has the advantage of high range and can realize measurement of high acceleration. The beam-circular thin plate combined structure can effectively inhibit the capacitance saturation of the sensor, and the protrusion on the insulating layer can effectively reduce the hysteresis error.

Description of the drawings:

fig. 1 is a cross-sectional view of an embodiment of the present invention (in order to clearly reflect the structure of the device, the ratio of the dimensions in the height direction in the drawing is greatly different from the actual situation, the same applies below).

Fig. 2 is a cross-sectional view of the inventive structure in the direction a-a of fig. 1.

Fig. 3 is a cross-sectional view of the inventive structure taken in the direction B-B of fig. 1.

Fig. 4 is a cross-sectional view of an insulating layer.

Detailed Description

The embodiments of the invention will be further described with reference to the accompanying drawings in which:

in an embodiment of the present invention, a contact mode micro accelerometer includes: the micro-accelerometer comprises a lower substrate 1, an upper substrate 8, a support column 12, a thin plate 5, a plurality of support beams 6 and anchor points 7 of the beams are arranged between the lower substrate 1 and the upper substrate 8, the lower substrate 1 and the upper substrate 8 are provided with a lower fixed electrode 2 and an upper fixed electrode 9, the surfaces of the lower fixed electrode 2 and the upper fixed electrode 9 are respectively covered with a lower insulating layer 3 and an upper insulating layer 10, the lower surface and the upper surface of the thin plate 5 are respectively provided with a lower moving electrode 4 and an upper moving electrode 11, and the micro-accelerometer has a first working state that the thin plate 5, the lower moving electrode 4 and the upper moving electrode 11 are simultaneously stressed and deformed but are not in contact with the lower insulating layer 3 or the upper insulating layer 10 and a second working state that the thin plate 5, the lower moving electrode 4 and the upper moving electrode 11 are simultaneously stressed and deformed and are in contact with.

The

fixed electrodes

2 and 9 and the

movable electrodes

4 and 11 form two pairs of electrodes, and the two movable electrodes are positioned on the same deformation body and are deformed identically, so that the two pairs of electrodes form a variable differential capacitor. No matter in first operating condition or second operating condition, the size of differential capacitance reflects the size of the acceleration that is surveyed, and the positive and negative nature of differential capacitance reflects the positive and negative nature of the acceleration direction that is surveyed, and differential capacitance structure is favorable to reducing common mode interference moreover, improves the test accuracy of sensor.

The invention relates to a micro-accelerometer, in particular to a micro-accelerometer with a micro-accelerometer active structure, which comprises a thin plate 5 and a supporting beam 6, wherein the thin plate replaces a rigid mass block in a traditional beam-mass block structure capacitive micro-accelerometer, and only can make translational motion different from a moving electrode in the beam-mass block structure capacitive micro-accelerometer. In the contact mode, the beam does not contact the insulating layer, so that even under the condition that most of the area of the movable electrode is contacted with the insulating layer, the rigidity of the rest undeformed part of the movable structure is still small enough, and the phenomenon of capacitance saturation can be effectively inhibited.

The sheet 5 adopts a circular structure. Compared with a rectangular plate, the circular plate has more uniform distribution of deformation and stress, is favorable for improving the strength of the plate and transferring loads with the same magnitude to each supporting beam, and is more suitable for measurement under the condition of high acceleration. Because the thin plate is circular, the moving electrode covered on the thin plate and the fixed electrodes positioned on the upper substrate and the lower substrate are also circular.

The supporting beams are uniformly distributed on the edge of the thin plate and are symmetrical about the center of the thin plate, the shape and the size of each beam are the same and are as thick as the plate supported by the beams, and the number of the beams is up to 36. The equal thickness of the supporting beam and the plate can reduce the rigidity difference between the supporting beam and the plate, and can simplify the processing technology, and the total rigidity of the beam can be changed and the thin plate can not only do translational motion because the rigidity is far greater than the total rigidity of the beam by adjusting the number, the length and the width of the beam.

There are a plurality of annular projections on the surfaces of the

insulating layers

3 and 10 to eliminate or reduce hysteresis errors caused by van der waals forces and frictional forces. Since the van der waals force is inversely proportional to the third power of the gap size of the object, the capacitance is inversely proportional to the first power of the electrode gap, and the gap size of the contact part of the moving electrode and the insulating layer is in the molecular size level and is much smaller than the distance between the moving electrode and the fixed electrode (not smaller than the thickness of the insulating layer), the van der waals force can be remarkably reduced by the bulges, and the influence on the capacitance value is very little. In addition, the existence of the bulges can also reduce the friction between the movable electrode and the insulating layer, thereby reducing the friction force.

The thin plate 5 is provided with a large number of through holes to play a role in reducing air damping.

The processing of the present embodiment can adopt the existing common micro-processing technology, such as: the movable structure formed by the thin plate 5 and the support beam 6 can be processed on the lower substrate 1 by a sacrificial layer process, and the connection part of the movable structure and the lower substrate is an anchor point 7; the upper substrate 8 may be connected to the lower substrate 1 by welding with the support posts 12 on the lower substrate 1; the

fixed electrodes

2 and 9, the

insulating layers

3 and 10 and the moving

electrodes

4 and 11 can be completed by a sputtering process; the shapes, the plane sizes and the distribution positions of the bulges on the

insulating layers

3 and 10, the through holes on the thin plate 5 and the like can be flexibly designed according to actual needs and realized by the patterns of the mask plate.

The skilled person should understand that: although the invention has been described in terms of the above specific embodiments, the inventive concept is not limited thereto and any modification applying the inventive concept is intended to be included within the scope of the patent claims.

Claims

1. A contact mode micro accelerometer comprising: lower base (1), go up base (8), be equipped with support column (12), sheet metal (5) and its a plurality of supporting beam (6) and anchor point (7) of roof beam thereof between lower base (1) and last base (8), its characterized in that: lower basement (1), last basement (8) are equipped with down decide electrode (2), go up decide electrode (9) respectively, decide electrode (2), go up decide electrode (9) surface and cover respectively and have lower insulating layer (3), upper insulation layer (10), the lower, upper surface of sheet metal (5) is equipped with down moving electrode (4), last moving electrode (11) respectively, lower, upper insulation layer (3, 10) surface is equipped with a plurality of archs, the micro-accelerometer has sheet metal (5) and lower, upper moving electrode (4, 11) atress simultaneously and takes place to warp but not with the first operating condition of lower insulating layer (3) or upper insulation layer (10) contact and sheet metal (5) and lower, upper moving electrode (4, 11) atress simultaneously warp and with lower insulating layer (3) or upper insulation layer (10) contact's second operating condition.

2. A contact mode microaccelerometer as claimed in claim 1 wherein: the thin plate (5) is provided with a plurality of through holes.

3. A contact mode microaccelerometer according to claim 1 or 2 wherein: the thin plate (5) is a circular thin plate, a movable structure is formed by the thin plate and the supporting beams (6), and the supporting beams (6) are uniformly distributed on the edge of the circular thin plate (5).

4. A contact mode microaccelerometer according to claim 3 wherein: the lower and upper moving electrodes (4, 11) on the thin plate (5) are the same as the thin plate (5) in shape and are circular, and the lower and upper fixed electrodes (2, 9) on the lower and upper substrates (1, 8) are also correspondingly circular.

5. The contact mode microaccelerometer according to claim 1 wherein: when the measured acceleration is not zero, the first working state is entered, and the circular thin plate (5) and the lower and upper moving electrodes (4, 11) are deformed.

6. The contact mode microaccelerometer according to claim 1 wherein: and when the measured acceleration value reaches a threshold value, the second working state is entered, the lower moving electrode (4) or the upper moving electrode (11) is contacted with the lower insulating layer (3) or the upper insulating layer (10), and the contact area is increased along with the increase of the acceleration.

7. The contact mode microaccelerometer according to claim 1 wherein: two movable electrodes (4, 11) positioned on the circular thin plate (5) and two fixed electrodes (2, 9) respectively positioned on the lower substrate and the upper substrate form two variable capacitors, and the two variable capacitors form a variable differential capacitor.