CN110040680A - The MEMS microgravity sensor chip with quasi- zero stiffness characteristic is preloaded based on electric heating - Google Patents

Abstract

A MEMS microgravity sensor chip with quasi-zero stiffness characteristics based on electrothermal preloading, including a single crystal silicon substrate, a silicon dioxide insulating layer grown on the single crystal silicon substrate, and a single crystal silicon structural layer bonded to the silicon dioxide insulating layer, The MEMS acceleration sensor chip is made in the single crystal silicon structure layer; the MEMS acceleration sensor chip includes a chip frame, and a group of electrode anchor points are respectively arranged at its four corners, and an electrothermal drive unit composed of a V-shaped beam is connected between each group of electrode anchor points. The beam is connected with an intermediate arm, the intermediate arm is connected by a limit self-locking mechanism, a spring and a mass block, and the limit self-locking mechanism cooperates with the chip frame; except for the electrode anchor point and the chip frame, the rest of the monocrystalline silicon substrate and The silicon dioxide insulating layer is corroded; the spring is loaded with axial displacement by the electrothermal effect, and the mass block can obtain a working range with quasi-zero stiffness in the vertical direction without reducing the vertical stiffness of the spring, which can be used for microgravity Acceleration detection has the characteristics of simple structure and so on.

Description

MEMS microgravity sensor chip with quasi-zero stiffness characteristics based on electrothermal preloading

technical field

The invention relates to the technical field of acceleration sensors, in particular to a MEMS microgravity sensor chip with quasi-zero stiffness characteristics based on electrothermal preloading.

Background technique

The earth's gravity field contains rich physical information. With the gradual deepening of human production activities, the measurement environment and indicators of gravitational acceleration become more stringent, and people's demand for high-resolution, high-precision microgravity acceleration detection technology is increasing. eager. With the iterative development of manufacturing technology, micro-electromechanical systems (MEMS) acceleration sensors with small size, low energy consumption and high precision are increasingly becoming the mainstream instead of traditional acceleration sensors. Whether using optical, capacitive or resonant measurement methods, a spring-mass system with high sensitivity is the core structure for realizing low-g acceleration measurement, which is of great significance to the field of high-precision microgravity measurement.

Sandia National Laboratories has proposed an in-plane acceleration sensor based on submicron wavelength grating detection technology. The sensor has nano-g (1 nano-g=9.81×10 ^-9 m/s ² ) resolution; it uses Four sets of folded springs are used to suspend the mass, combined with the nano-sized differential grating structure to obtain a high-resolution signal, but the resonance frequency of the spring-mass system itself is not too low, and the sensitivity of the main structure of the chip has room for improvement.

Middlemiss and others of the University of Glasgow applied the MEMS manufacturing process to the acceleration sensor, and used the anti-spring structure to design the spring-mass system of the acceleration sensor, and obtained a system with ultra-low in-plane vibration resonance frequency; however, the characteristic size of the anti-spring structure is very small , the manufacturing process is very demanding, and there is a shortcoming of narrow bandwidth.

To sum up, since the sensitivity of the spring-mass system in the vertical direction is inversely proportional to its stiffness in this direction, if the vertical stiffness of the spring is simply reduced in order to improve its sensitivity, the bearing capacity of the system will also decrease. , that is, the mass of the connected mass decreases and the acceleration it can withstand is also very small, so the sensitive direction stiffness of the main structure of the existing in-plane motion MEMS acceleration sensor cannot be made very low, and the sensitivity of the mass is limited, and the low g The resolution of value detection still needs to be improved.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a MEMS microgravity sensor chip with quasi-zero stiffness characteristics based on electrothermal preloading, using electrothermal effect to load the spring with axial displacement, without directly reducing the spring Under the premise of vertical stiffness, the mass block can obtain a working range with high sensitivity in the vertical direction, and at the same time, the original bearing capacity of the system to the mass of the mass block or large acceleration is not changed, so it can be used for the detection of microgravity acceleration value. And it has the characteristics of batch production, low cost and simple structure.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A MEMS microgravity sensor chip with quasi-zero stiffness characteristics based on electrothermal preloading, comprising a single crystal silicon substrate 1, a silicon dioxide insulating layer 2 grown on the single crystal silicon substrate 1, and a bond on the silicon dioxide insulating layer 2 A single crystal silicon structure layer 3 is combined, a metal electrode layer 4 is deposited on the electrode anchor point 3-2 of the single crystal silicon structure layer 3, and a MEMS acceleration sensor chip is fabricated in the single crystal silicon structure layer 3;

The MEMS acceleration sensor chip includes a chip frame 3-7, four corners of the chip frame 3-7 are respectively provided with a group of electrode anchor points 3-2, and an array is connected between the two electrode anchor points 3-2 of each group. The V-shaped beam of the structure constitutes an electric heating drive unit 3-1. A middle arm 3-3 is horizontally connected in the middle of the V-shaped beam. The middle arm 3-3 is connected with one end of the limit self-locking mechanism 3-4, and the limit self-locking The mechanism 3-4 cooperates with the chip frame 3-7, the other end of the limit self-locking mechanism 3-4 is connected with the head end of the spring 3-5, and the tail end of the spring 3-5 is connected with the mass block 3-6; electric heating drive The unit 3-1, the middle arm 3-3, the limit self-locking mechanism 3-4, the spring 3-5, and the mass block 3-6 constitute the main part of the sensor chip, which is manufactured by an integrated MEMS process, all of which are fixedly connected; After removing the electrode anchor point 3-2 and the chip frame 3-7, the monocrystalline silicon substrate 1 and the silicon dioxide insulating layer 2 under the remaining part will be etched away, so that the main part of the sensor chip becomes a suspended structure;

After the electrothermal drive unit 3-1 axially loads the spring 3-5, the linear stiffness of the MEMS acceleration sensor chip in its sensitive direction can be changed. By changing the loading voltage and the structural parameters of the spring 3-5, the MEMS acceleration sensor chip can be accurately Adjustable in zero stiffness interval.

The limiting self-locking mechanism 3-4 adopts a cam compression self-locking structure, which moves along the loading force and squeezes vertically with the arc of the chip frame 3-7, and passes through the chip frame 3-7. The arc of 7 is pressed to form self-locking.

The length of the single side beam of the V-shaped beam of the electrothermal drive unit 3-1 is 1000-1200 μm, the width is 30-40 μm, the middle angle between the V-shaped beams is 166-172°, and the spacing between the V-shaped beams is 70-70 μm. 80μm.

The springs 3-5 adopt an Euler buckling beam structure, the beam width is 30-34 μm, the span at both ends is 3000-3100 μm, and the center deflection distance is 55-60 μm.

The growth thickness of the silicon dioxide insulating layer 2 is 2-3 μm.

The thickness of the single crystal silicon structure layer 3 is 40 μm, and the plane size is 13 mm×16 mm.

Compared with the prior art, the beneficial effects of the present invention are:

On the basis of the layout of the symmetrically arranged spring suspension mass blocks, each spring is equipped with an electrothermal drive unit. The input end of the electrothermal drive unit is a low-voltage DC power supply, and the component structure is simple. After the chip is fabricated as a whole, the electrothermal effect is used to load the spring with axial displacement, so that the four groups of springs are in a compressed preload state at the initial equilibrium position. By rationally designing parameters such as electrothermal drive unit, spring size, preload, etc., the force-displacement curve of the mass block near the initial equilibrium position can be modulated to be nonlinear without directly reducing the vertical stiffness of the spring. It has quasi-zero stiffness characteristics along the in-plane vibration direction within the range without reducing the original bearing capacity of the system to the mass of the mass block or large acceleration. By changing the loading voltage and spring structure parameters, the length of the quasi-zero stiffness interval can also be achieved. Adjustment, that is, changing the working range as needed. Therefore, when the weight of the mass is constant, the vibration of the mass in the vicinity of the equilibrium position is amplified, and the sensitivity is improved as much as possible.

The chip of the invention has a simple structure, and can be easily produced by adopting a mature micro-nano process method. In the future, it can be combined with high-resolution displacement detection technologies such as light intensity difference and grating to measure microgravity acceleration, and can be easily integrated into microgravity acceleration sensor products with small size, high precision and high resolution, suitable for low frequency Signal detection can well meet application and market demands.

Description of drawings

FIG. 1 is an isometric view of a three-dimensional structure of the present invention.

FIG. 2 is a front view of the single crystal silicon structure layer 3 of the present invention.

FIG. 3 is a front view of the single-crystal silicon structure layer 3 of the present invention in a state of being loaded and self-locked by electricity.

FIG. 4 is a schematic diagram of the loading state of the electrothermal driving unit 3-1 and the limiting self-locking mechanism 3-4 of the present invention.

FIG. 5 is a schematic diagram of the force after the spring-mass block of the present invention is loaded.

FIG. 6 is a force-displacement curve diagram of the spring-mass mass of the present invention after loading.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

Referring to FIG. 1, a MEMS microgravity sensor chip with quasi-zero stiffness characteristics based on electrothermal preloading includes a single crystal silicon substrate 1, and a silicon dioxide insulating layer 2 is grown on the single crystal silicon substrate 1, and the growth thickness is 2 ~3 μm, a single crystal silicon structural layer 3 is bonded on the silicon dioxide insulating layer 2 , a metal electrode layer 4 is deposited on the electrode anchor point 3-2 of the single crystal silicon structural layer 3 , and in the single crystal silicon structural layer 3 A MEMS acceleration sensor chip is fabricated; the thickness of the single crystal silicon structure layer 3 is 40 μm, and the plane size is 13 mm×16 mm.

2 and 3, the MEMS acceleration sensor chip includes a chip frame 3-7, the four corners of the chip frame 3-7 are respectively provided with a group of electrode anchor points 3-2, each group of two electrode anchor points 3- 3 groups of V-shaped beams in an array structure are connected between 2 to form an electric heating drive unit 3-1, and a middle arm 3-3 is horizontally connected between the 3 groups of V-shaped beams, the middle arm 3-3 and the limit self-locking mechanism One end of 3-4 is connected, the limit self-locking mechanism 3-4 is matched with the chip frame 3-7, the other end of the limit self-locking mechanism 3-4 is connected with the head end of spring 3-5, the tail of spring 3-5 is connected The end is connected with the mass block 3-6; the electrothermal drive unit 3-1, the middle arm 3-3, the limit self-locking mechanism 3-4, the spring 3-5, and the mass block 3-6 constitute the main part of the sensor chip, Manufactured by an integrated MEMS process, all of which are fixed connections; except for the electrode anchor point 3-2 and the chip frame 3-7, the monocrystalline silicon substrate 1 and the silicon dioxide insulating layer 2 below the rest will be etched away, making the sensor chip The main part of the spring 3-5 becomes a suspended structure; because the limit self-locking mechanism 3-4 and the mass block 3-6 connected with the head and tail ends of the spring 3-5 have a larger structural size than the spring 3-5, it can be regarded as a rigid body and does not occur. Deformation, so the transmitted deformation only makes the spring 3-5 buckling; the electric heating drive unit 3-1 pushes the spring 3-5 to move axially after being heated and expands, and the limit self-locking mechanism 3-4 connected with it moves with it until It is limited and locked by the chip frame 3-7, and the end of the spring 3-5 is fixed at one position, that is, a certain amount of compression is generated inside the spring 3-5, so that the mass 3-6 is compressed in the four groups of springs 3-6. -5 degrees of freedom of movement in the plane of the chip is achieved under the support.

Referring to FIG. 4 , the limiting self-locking mechanism 3-4 adopts a cam compression self-locking structure, which moves along the loading force and squeezes vertically with the arc of the chip frame 3-7. When the left end of the limit self-locking mechanism 3-4 is in contact with the side of the chip frame 3-7, the expansion stroke of the V-beam electric heating drive unit 3-1 reaches the design upper limit, and at the same time is pressed by the arc of the chip frame 3-7 form self-locking.

The length of the single side beam of the V-shaped beam of the electrothermal drive unit 3-1 is 1000-1200 μm, the width is 30-40 μm, the middle angle between the V-shaped beams is 166-172°, and the spacing between the V-shaped beams is 70-70 μm. 80 μm; the spring 3-5 adopts Euler buckling beam structure, the beam width is 30-34 μm, the span at both ends is 3000-3100 μm, and the center deflection distance is 55-60 μm.

The working principle of the present invention is:

The electrocaloric effect and thermal expansion effect of silicon material are utilized. When a DC voltage is applied on the metal electrode layer 4, the electrothermal driving unit 3-1 of the single crystal silicon material will have a current passing through it. Due to the resistance of the single crystal silicon, corresponding heat will be generated. Under the combined action, the generated heat and the dissipated heat will eventually reach a balance, and the temperature on the electrothermal drive unit 3-1 will also be in a stable state higher than the ambient temperature, and the interior of the silicon material will expand under the temperature field. Connected to the electrode anchor point 3-2, the vertical movement of the electrothermal drive unit 3-1 is restricted, and finally the deformation movement can only be generated along its symmetry axis; due to the limit self-locking mechanism 3- 4. The mass block 3-6 has a larger structural size than the spring 3-5, which can be regarded as a rigid body without deformation, so the transmitted deformation only causes the Euler beam to buckle; the electrothermal drive unit 3-1 expands when heated Then push the spring 3-5 to move axially, and the limit self-locking mechanism 3-4 connected with it moves along with it until it is locked by the chip frame 3-7; the end of the spring 3-5 is also fixed at a position, That is, a certain amount of compression is generated inside the spring 3-5, and the mass block 3-6 can move in a single degree of freedom along the sensitive direction under the support of the four groups of compressed springs 3-5. For the Euler beam structure with fixed ends, the relationship between the axial load P and the axial displacement y can be written as:

L is the original span at both ends of the spring, q ₀ is the center deflection distance of the beam, P _e =π ² EI/L ² is the critical load for Euler beam buckling, E is the elastic modulus of single crystal silicon, I is the Euler beam The moment of inertia of the cross-section of the tension beam.

Referring to Figure 5, the Euler buckling beams on both sides have the axial stiffness K _axis . Since the boundary conditions at the head end of the Euler buckling beam are fixed, the simplified model of the supporting masses 3-6 can be equivalent to the hinge support at the head end of the spring. The last _vertical spring with a constant stiffness K; the left picture shows the force model when the chip is in the initial equilibrium position. Due to the upper and lower symmetry, it can be simplified as a mass 3-6 supported by a set of compression springs 3-5; when After the mass 3-6 is shifted downward and balanced at the new position, the force model is as shown in the figure on the right; considering the case where the mass 3-6 is shifted downward from the equilibrium position, the mass 3-6 is subjected to The dimensionless vertical force of Dimensionless offset from equilibrium position The relationship can be written as:

F is the vertical force on the mass block 3-6, the stiffness ratio K is the _vertical stiffness of the spring-mass block, the compression ratio a is the span at both ends of the Euler beam after compression, is the dimensionless offset of the origin of the coordinate system, is the dimensionless span at both ends of the spring.

Will right Derivative to get the vertical kinematic stiffness of the system exist season Obtain λ ₀ satisfying the quasi-zero stiffness interval:

Referring to Figure 6, when the loading voltage and the structural parameters of springs 3-5 meet the required conditions of λ ₀ , the force-displacement curve of the chip near the initial equilibrium position presents a nonlinear characteristic with quasi-zero stiffness. By changing the loading voltage and the spring 3-5 structural parameters, the length of the quasi-zero stiffness interval can also be adjusted.

In the low-frequency microgravity acceleration measurement, the relationship between the acceleration A received by the mass block and the offset u of the equilibrium position can be written as:

A=ω ₀ ² ·u,

is the undamped natural angular frequency of the system, and k and m are the stiffness and mass of the system in a certain direction, respectively. By detecting the displacement u by means of optics, capacitance, etc., the acceleration of the mass block can be obtained. In the present invention, since the chip works in the quasi-zero stiffness range, its stiffness can approach 0, so when the acceleration A is constant, the displacement u generated by the mass block can become very large, that is, the sensitivity is greatly improved, which makes it very suitable for low-frequency signal detection with low g value.

Claims (6)

1. a kind of preload the MEMS microgravity sensor chip with quasi- zero stiffness characteristic, including monocrystalline substrate based on electric heating (1), it is characterised in that: there is silicon dioxide insulating layer (2) growth in monocrystalline substrate (1), silicon dioxide insulating layer is bonded on (2) There are monocrystal silicon structure layer (3), metal electrode layer (4) is deposited on the electrode anchor point (3-2) of monocrystal silicon structure layer (3), in list Production has MEMS acceleration sensor chip in crystal silicon structure sheaf (3)；

The MEMS acceleration sensor chip, including chi frame (3-7), the quadrangle of chi frame (3-7) are respectively equipped with 1 It organizes electrode anchor point (3-2), the V-type beam that array structure is connected between every group of two electrode anchor points (3-2) forms an electric heating Driving unit (3-1), V-type beam intermediate lateral are connected with an intermediate arm (3-3), intermediate arm (3-3) and limit self mechanism (3- 4) one end connection, limit self mechanism (3-4) and chi frame (3-7) cooperate, the other end of limit self mechanism (3-4) with The head end of spring (3-5) connects, tail end and mass block (3-6) connection of spring (3-5)；Electrothermal drive unit (3-1), intermediate arm (3-3), limit self mechanism (3-4), spring (3-5), mass block (3-6) constitute the main part of sensor chip, pass through Integrated MEMS technology manufacture, is to be fixedly connected；Electrode anchor point (3-2) and chi frame (3-7) are removed, under rest part The monocrystalline substrate (1) and silicon dioxide insulating layer (2) in face will be corroded, and the main part of sensor chip is made to become hanging Structure；

After electrothermal drive unit (3-1) is axially loaded to spring (3-5) progress, MEMS acceleration sensor chip can be changed and existed The linear rigidity of its sensitive direction can be realized MEMS acceleration biography by changing on-load voltage and spring (3-5) structural parameters The quasi- zero stiffness section of sensor chip it is adjustable.

2. a kind of MEMS microgravity sensor preloaded based on electric heating with quasi- zero stiffness characteristic according to claim 1 Chip, it is characterised in that: the limit self mechanism (3-4) uses cam pressing self-locking structure, acts on along loading force Lower movement, and vertical extruding occurs with the circular arc of chi frame (3-7), shape is compressed by the circular arc of chi frame (3-7) At self-locking.

3. a kind of MEMS microgravity sensor preloaded based on electric heating with quasi- zero stiffness characteristic according to claim 1 Chip, it is characterised in that: the V-type beam unilateral side beam length of the electrothermal drive unit (3-1) is 1000~1200 μm, width 30 ~40 μm, V-type beam centre angle is 166~172 °, and the spacing between V-type beam is 70~80 μm.

4. a kind of MEMS microgravity sensor preloaded based on electric heating with quasi- zero stiffness characteristic according to claim 1 Chip, it is characterised in that: the spring (3-5) uses Euler's buckling girder construction, and deck-siding is 30~34 μm, and both ends span is 3000~3100 μm, center deflection is away from being 55~60 μm.

5. a kind of MEMS microgravity sensor preloaded based on electric heating with quasi- zero stiffness characteristic according to claim 1 Chip, it is characterised in that: the growth thickness of the silicon dioxide insulating layer (2) is 2~3 μm.

6. a kind of MEMS microgravity sensor preloaded based on electric heating with quasi- zero stiffness characteristic according to claim 1 Chip, it is characterised in that: the monocrystal silicon structure layer (3) with a thickness of 40 μm, planar dimension is 13mm × 16mm.