CN108490217A - Contact mode micro-acceleration gauge - Google Patents

Abstract

A contact mode micro accelerometer. It includes a lower base and an upper base, between the lower base and the upper base there are supporting columns, thin plates and several supporting beams and anchor points of the beams, the lower base and the upper base are respectively provided with lower and upper fixed electrodes, and the fixed The surface of the electrode is covered with an insulating layer, the lower and upper surfaces of the thin plate are respectively provided with lower and upper moving electrodes, and the micro accelerometer has a first working state in which the thin plate and the moving electrode are deformed under force but not in contact with the insulating layer and The thin plate and the movable electrode are deformed by force and are in contact with the insulating layer in the second working state. The invention works on the principle that the acceleration force causes the deformation of the moving electrode to change the capacitance between it and the fixed electrode. The invention prevents the short circuit of the moving and fixed electrodes through the insulating layer on the fixed electrode, and provides support for the movable structure by the insulating layer, so it can realize the measurement of high acceleration, and the combined structure of the beam-circular thin plate can effectively suppress the capacitance of the sensor saturation.

Description

Contact Mode Microaccelerometers

technical field

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

Background technique

Accelerometers are widely used in many fields such as industry, military, aviation, and daily life. According to the working principle, micro accelerometers can be divided into capacitive, piezoresistive, piezoelectric and so on. Among them, the capacitive type has the advantages of low power consumption, fast response, and high sensitivity. Its working principle is: a variable capacitor is composed of a fixed electrode and a moving electrode, and the moving electrode is located on the acceleration sensitive structure and moves due to the acceleration force. The magnitude of the acceleration can be known by measuring the capacitance between the moving and fixed electrodes. Traditionally, the active structure of capacitive micro accelerometers mainly adopts a comb structure or a beam-mass structure composed of a beam and a rigid mass, and it is generally believed that the latter has a higher sensitivity. The range of the capacitive micro accelerometer with beam-mass structure is mainly affected by two factors: one is the maximum displacement value of the mass allowed to prevent the short circuit between the moving and fixed electrodes, that is, the initial gap between the moving and fixed electrodes; - Mechanical strength of the mass structure. In recent years, in another type of capacitive microsensor, that is, a capacitive micropressure sensor, a working principle based on contact mode has been proposed: an insulating layer is covered on the fixed electrode or the moving electrode to prevent the short circuit between the electrodes, and withstand The thin plate (film) deformed by the measured pressure is supported by the contact force, so the measuring range of the sensor has been greatly expanded. In addition, the contacting parts of the moving and fixed electrodes are only separated by a thin layer of insulating layer, and the dielectric constant of the insulating layer is generally several times that of vacuum or air. According to the capacitance value, it is inversely proportional to the electrode gap and is related to the dielectric constant. It can be seen that the capacitance value between the electrodes is improved in the contact mode, and the anti-noise ability is also improved, and high sensitivity can be achieved 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 thus has different contact areas with the insulating layer, so as to realize the measurement of pressure. However, for a capacitive microaccelerometer with a beam-mass structure, the above contact mode cannot be directly applied because the mass is a rigid structure and can only do translational motion without deformation.

In previous contact mode capacitive sensors, capacitance saturation is an important factor affecting sensitivity. The so-called capacitance saturation means that when the measured signal reaches a certain value, the capacitance between the moving and fixed electrodes tends to stop changing. One of the main reasons for this phenomenon is that with the increase of the contact area, the area of the remaining undeformed part of the deformed structure becomes smaller and smaller, and the stiffness becomes larger, making deformation more and more difficult. For capacitive micro-accelerometers, if the contact mode is used, the capacitance saturation problem also needs to be considered.

In MEMS, scale effects lead to intermolecular forces—van der Waals forces cannot be ignored. This force increases dramatically with decreasing intermolecular distance. In the contact mode, the distance between the molecules of the moving electrode and the insulating layer is very small on a large area, so the van der Waals force is relatively large. In addition, the relative movement between the moving electrode and the insulating layer also leads to the generation of friction force. According to a large number of literatures, including the literature on contact mode micro pressure sensors, van der Waals force and friction can cause significant hysteresis error (return error) to the sensor. For micro accelerometers, the measured signal often experiences dynamic changes from small to large and then from large to small in a short period of time, so it is more sensitive to hysteresis error.

Contents of the invention

In order to solve the problems in the background technology, the present invention provides a contact mode micro-accelerometer with high-range characteristics that suppresses capacitance saturation and hysteresis errors.

The technical solution adopted by the present invention to solve the technical problem is: a contact mode micro-accelerometer, including: a lower base, an upper base, a support column, a thin plate and several support beams and beam anchors are arranged between the lower base and the upper base point, the lower base and the upper base are provided with fixed electrodes, the surface of the fixed electrodes is covered with an insulating layer, the lower and upper surfaces of the thin plate are provided with moving electrodes, and the micro accelerometer has a thin plate and the moving electrodes to generate force. The first working state is deformed but not in contact with the insulating layer, and the second working state is the thin plate and the moving electrode deformed by force and in contact with the insulating layer.

Several protrusions are arranged on the surface of the insulating layer.

A large number of through holes are arranged on the thin plate.

The thin plate is a circular thin plate and forms a movable structure with the support beams, and the support beams are evenly distributed on the edge of the circular thin plate.

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

When the measured acceleration is non-zero, the first working state is entered, and the circular thin plate and the moving electrode are deformed.

When the measured acceleration value reaches the threshold value, it enters into the second working state, and the movable electrode is in contact with the insulating layer, and the contact area increases as the acceleration increases.

The two moving electrodes on the circular thin plate and the fixed electrodes respectively on the lower and upper substrates form two variable capacitances, and the two variable capacitances form variable differential capacitances. The magnitude of the variable differential capacitance reflects the magnitude of the measured acceleration, and the positive or negative of the variable differential capacitance reflects the positive or negative of the direction of the measured acceleration.

The beneficial effects of the invention are: the insulating layer on the fixed electrode prevents the short circuit of the moving and fixed electrodes, and the insulating layer provides support for the movable structure, has the advantage of high measuring range, and can realize the measurement of high acceleration. The beam-circular thin plate combination structure in the invention can effectively suppress the capacitance saturation of the sensor, and the protrusion on the insulating layer can effectively reduce the hysteresis error.

Description of drawings:

Figure 1 is a cross-sectional view of an embodiment of the present invention (in order to clearly reflect the composition of the device, the proportions of the dimensions in the height direction in the figure differ greatly from the actual situation, the same below).

Fig. 2 is a cross-sectional view of the structure of the present invention along the direction A-A in Fig. 1 .

Fig. 3 is a cross-sectional view of the structure of the present invention along the B-B direction in Fig. 1 .

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

Detailed ways

Embodiments of the present invention will be further described below in conjunction with accompanying drawings:

In an embodiment of the present invention, a contact mode micro-accelerometer includes: a lower base 1, an upper base 8, a support column 12, a thin plate 5, a plurality of support beams 6 and beam anchors are arranged between the lower base 1 and the upper base 8 Point 7, the lower base 1 and the upper base 8 are provided with a lower fixed electrode 2 and an upper fixed electrode 9, and the surfaces of the lower and upper fixed electrodes 2 and 9 are respectively covered with a lower insulating layer 3 and an upper insulating layer 10, and the thin plate The lower and upper surfaces of the 5 are respectively provided with a lower moving electrode 4 and an upper moving electrode 11, and the micro accelerometer has a thin plate 5, the lower moving electrode 4, and the upper moving electrode 11 which are deformed under force simultaneously but are not connected with the lower insulating layer 3 or the upper moving electrode 11. The first working state in which the insulating layer 10 is in contact and the second working state in which the thin plate 5 , the lower moving electrode 4 and the upper moving electrode 11 are simultaneously deformed by force and is in contact with the lower insulating layer 3 or the upper insulating layer 10 .

The fixed electrodes 2 and 9 and the moving electrodes 4 and 11 form two pairs of electrodes, and the two moving electrodes are located on the same deformation body and undergo the same deformation, so these two pairs of electrodes form a variable differential capacitor. Regardless of whether it is in the first working state or the second working state, the size of the differential capacitance reflects the magnitude of the measured acceleration, and the positive or negative of the differential capacitance reflects the positive or negative of the measured acceleration direction, and the differential capacitance structure is conducive to reducing the common mode Interference, improve the test accuracy of the sensor.

The movable structure of the micro-accelerometer is composed of a thin plate 5 and a supporting beam 6. The rigid mass in the traditional beam-mass structure capacitive micro-accelerometer is replaced by a thin plate, and the moving electrode in the beam-mass structure capacitive micro-accelerometer can only be used The translational movement is different. In the present invention, under the action of load, the thin plate and the movable electrode attached thereto are deformed. At the initial stage of the measuring range, the movable electrode is not in contact with the insulating layer covering the fixed electrode, and the micro accelerometer is in the In the first working state, when the measured acceleration is greater than a certain value, the moving electrode is in contact with the insulating layer covering the fixed electrode, and the micro accelerometer enters the second working state, and the measuring range is greatly expanded due to the existence of this state. In the contact mode, the beam is not in contact with the insulating layer, so even when most of the moving electrode is in contact with the insulating layer, the stiffness of the remaining undeformed part of the moving structure is still small enough to effectively suppress capacitance saturation the emergence of the phenomenon.

The thin plate 5 adopts a circular structure. Compared with the rectangular plate, the distribution of deformation and stress on the circular plate is more uniform, which is beneficial to improve the strength of the plate and facilitate the plate to transmit the same load to each support beam, so the circular plate is more suitable for measurement under high acceleration conditions . Because the thin plate is circular, the moving electrodes covering it and the fixed electrodes on the upper and lower substrates are also circular.

The support beams are evenly distributed on the edge of the thin plate and are symmetrical about the center of the thin plate. The shape and size of each beam are the same and the same thickness as the plate they support, and the number of beams is as high as 36. The same thickness of the support beam and the plate can reduce the stiffness difference between the two, and at the same time simplify the processing technology. By adjusting the number, length and width of the beam, the total stiffness of the beam can be changed and the thin plate will not be affected by the large stiffness. Due to the total stiffness of the beam, only translational motion is performed.

There are multiple annular protrusions on the surfaces of the insulating layers 3 and 10 to eliminate or reduce hysteresis errors caused by van der Waals force and friction. Since the van der Waals force is inversely proportional to the cube of the object gap size, and the capacitance is only inversely proportional to the first power of the electrode gap, and the gap between the moving electrode and the insulating layer is at the molecular level, which is much smaller than the distance between the moving and fixed electrodes. (not less than the thickness of the insulating layer), so these protrusions can significantly reduce the van der Waals force and have little effect on the capacitance value. In addition, the existence of these protrusions can also reduce the friction between the moving electrode and the insulating layer, thereby reducing the friction force.

There are a large number of through holes on the thin plate 5, which play the role of reducing air damping.

The processing of this embodiment can adopt the existing common micromachining technology, for example: the movable structure composed of the thin plate 5 and the support beam 6 can be processed on the lower base 1 through the sacrificial layer process, and the connection part with the lower base is the anchor point 7; the upper substrate 8 can be connected to the lower substrate 1 by welding the upper support column 12 with 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 sputtering; the insulation The shape, plane size and distribution position of the protrusions on the layers 3 and 10, the through holes on the thin plate 5, etc. can be flexibly designed according to actual needs and realized by the pattern of the mask plate.

Notes to all technical personnel: Although the present invention has been described according to the above-mentioned specific embodiments, the inventive idea of the present invention is not limited to this invention, and any modification using the inventive idea will be included in the scope of protection of this patent.

Claims (8)

1. a kind of contact mode micro-acceleration gauge, including：Lower substrate（1）, upper substrate（8）, lower substrate（1）With upper substrate（8）It Between be equipped with support column（12）, thin plate（5）With its several supporting beam（6）And its anchor point of beam（7）, it is characterised in that：The lower base Bottom（1）, upper substrate（8）It is respectively equipped with lower fixed electrode（2）, upper fixed electrode（9）, the lower fixed electrode（2）, upper fixed electrode（9）Table Face has been covered each by lower insulating layer（3）, upper insulating layer（10）, the thin plate（5）Upper and lower surface be respectively equipped with lower moving electrode （4）, upper moving electrode（11）, the micro-acceleration gauge is with thin plate（5）With upper and lower moving electrode（4、11）Stress deforms simultaneously But not with lower insulating layer（3）Or upper insulating layer（10）The first working condition and thin plate of contact（5）With upper and lower moving electrode（4、11） Simultaneously stress deformation and with lower insulating layer（3）Or upper insulating layer（10）Second working condition of contact.

2. a kind of contact mode micro-acceleration gauge according to claim 1, it is characterised in that：The upper and lower insulating layer（3、 10）Surface is equipped with several protrusions.

3. a kind of contact mode micro-acceleration gauge according to claim 1, it is characterised in that：The thin plate（5）It is equipped with Several through-holes.

4. a kind of contact mode micro-acceleration gauge according to claim 1 or 3, it is characterised in that：The thin plate（5）For circle Shape thin plate, with the supporting beam（6）Constitute bascule, supporting beam（6）In circular sheet（5）Edge be uniformly distributed.

5. a kind of contact mode micro-acceleration gauge according to claim 4, it is characterised in that：The thin plate（5）On under, Upper moving electrode（4、11）With thin plate（5）Shape is identical, for circle, the upper and lower substrate（1、8）On upper and lower fixed electrode（2、9） Also it mutually should be round.

6. contact mode micro-acceleration gauge according to claim 1, it is characterized in that：In the case of institute's measuring acceleration non-zero Enter first working condition, circular sheet（5）And upper and lower moving electrode（4、11）It deforms.

7. contact mode micro-acceleration gauge according to claim 1, it is characterized in that：After institute's measuring acceleration value reaches threshold value Enter second working condition, lower moving electrode（4）Or upper moving electrode（11）With lower insulating layer（3）Or upper insulating layer（10）Hair Raw contact, and contact area increases with the increase of acceleration.

8. contact mode micro-acceleration gauge according to claim 1, it is characterized in that：Positioned at circular sheet（5）On two Moving electrode（4、11）With two fixed electrodes being located in upper and lower substrate（2、9）Two variable capacitances are constituted, and by the two Variable capacitance constitutes variable differential capacitance.