CN201673168U - Low Stress Silicon Microresonant Accelerometer - Google Patents

Abstract

The utility model discloses a low-stress silicon micro-resonant accelerometer. The accelerometer structure is fabricated on two layers of single crystal silicon, the mechanical structure of the accelerometer is fabricated on the upper single crystal silicon chip, and metal is deposited on the upper surface of the mechanical structure. As a signal input/output line, the lower layer of single crystal silicon is the substrate of the accelerometer, and the mechanical structure of the accelerometer consists of a mass block, an upper resonator, a lower resonator, two upper-end first-level lever amplification mechanisms, and two lower-end first-level lever amplification mechanisms. Mechanism, intermediate stress release frame, upper end stress release frame and lower end stress release frame, the upper resonator and the lower resonator are symmetrically located in the middle of the mass block, and the lower end of the upper resonator and the upper end of the lower resonator are released through the intermediate stress The frame is connected with the middle fixed base. The utility model greatly reduces the processing residual stress and the thermal stress caused by the temperature change of the working environment, improves the stability of the resonant frequency of the resonator, and the amplification factor of the lever amplification mechanism is close to the ideal value.

Description

Low Stress Silicon Microresonant Accelerometer

technical field

The utility model belongs to the micro-inertia sensor technology in MEMS, in particular to a low-stress silicon micro-resonant accelerometer.

Background technique

Micro-electro-mechanical systems (MEMS for short) is a multidisciplinary cutting-edge high-tech field developed in recent years. MEMS uses the silicon micromachining technology developed from semiconductor technology, mainly using silicon as the material, to produce a three-dimensional structure on the silicon wafer with a size in the order of microns, suspended and movable, to realize the perception and control of external information, and It can be integrated with signal processing and control circuits to form a multifunctional micro system. Micro-electromechanical systems have the characteristics of small size, low cost, high reliability, and easy mass production. They can be widely used in aerospace, military, communications, biomedicine, and many other fields. They are considered as emerging technologies or even leading technologies for the 21st century. one.

Silicon micro accelerometer is a typical MEMS inertial sensor. Its research began in the early 1970s, and there are various forms such as capacitive, piezoelectric, piezoresistive, thermal convection, tunnel current and resonance. The unique feature of the silicon microresonant accelerometer is that its output signal is a frequency signal, and its quasi-digital output can be directly used in complex digital circuits, which has high anti-interference ability and stability, and eliminates the need for other types of acceleration In order to avoid the inconvenience of signal transmission, it is directly connected to the digital processor.

At present, the silicon microresonant accelerometer is generally composed of a resonant beam and a sensitive mass. The acceleration is converted into an inertial force by the sensitive mass. The inertial force acts on the axial direction of the resonant beam to change the frequency of the resonant beam. By testing the resonant frequency Calculate the measured acceleration.

In 2006, Fan Shangchun of Beijing University of Aeronautics and Astronautics proposed a new resonant accelerometer for the previous resonant accelerometers (Fan Shangchun, Renjie. A resonant micromachined accelerometer, Beijing University of Aeronautics and Astronautics, CN1844931A). The structure is composed of a mass block, a support beam, a tuning fork and a mechanical amplification system. The tuning fork is located in the middle of the mass block and arranged symmetrically up and down adjacent to each other, which overcomes the shortcomings of uneven material and ambient temperature that have a great influence on the device and the low utilization rate of the mass block. . However, the mass block of this structure is supported by two supporting beams in the middle, so the stability and shock resistance of the accelerometer are relatively poor. In addition, the structural form of the supporting beam of the structure is a cantilever beam, which has poor ability to release residual stress.

In 2008, Qiu Anping of Nanjing University of Science and Technology disclosed a silicon microresonant accelerometer (Qiu Anping, Shi Qin, Su Yan. Silicon microresonant accelerometer, Nanjing University of Science and Technology, application number: 2008100255749), the structure is composed of silicon and glass Layer composition, the mechanical structure is fabricated on a single crystal silicon wafer, and glass is used as a substrate. The mechanical structure is composed of a mass block, a resonator and a lever amplification mechanism. The resonator is located in the middle of the mass block and is arranged symmetrically adjacent to each other. The mass block is supported by folded beams at its four corners. The shortcomings that have a great impact on the device improve the stability and impact resistance of the structure. The two layers of the structure are made of silicon and glass, and the thermal expansion coefficients of the two are different. At the same time, the resonant beam and the lever of the structure are directly connected to the fixed base, so that the thermal stress caused by the processing residual stress and the temperature change of the working environment is large. Resonant accelerometers have poor frequency stability. The resonator of this structure adopts comb teeth, and the edge effect of the comb teeth reduces the linearity of the resonator vibration, thereby reducing the frequency stability. In addition, the folded beam supporting the mass block of the structure is a three-fold beam, which increases the cross-axis sensitivity of the structure.

Contents of the invention

The purpose of the utility model is to provide a silicon micro-resonance accelerometer with low stress, high frequency stability, low cross-axis sensitivity and strong impact resistance.

The technical solution to realize the purpose of this utility model is: a kind of low-stress silicon microresonant accelerometer, the accelerometer structure is made on two layers of single crystal silicon, the accelerometer mechanical structure is made on the upper layer single crystal silicon chip, and the mechanical structure Metal is deposited on the upper surface as the signal input/output line, and the lower layer of single crystal silicon is the substrate of the accelerometer. The upper resonator and the lower resonator are symmetrically located in the middle of the mass block, and the lower end of the upper resonator and the lower resonator The upper end of the upper resonator is connected to the middle fixed base through the intermediate stress release frame; the upper end of the upper resonator is respectively connected to the output ends of the two upper-end first-stage lever amplifying mechanisms, and the fulcrum end of the upper-end first-stage lever amplifying mechanism is connected to the upper-end stress releasing frame. It is connected with the upper fixed base, and the lower end of the lower resonator is respectively connected with the output ends of the two lower first-stage lever amplifying mechanisms, and the fulcrum end of the lower-end first-stage lever amplifying mechanism is connected with the lower fixed base through the lower stress release frame; up and down The input ends of the end-level lever amplification mechanism are respectively connected to the mass block; the mass block is respectively connected to four fixed bases located at the four corners of the mass block through four U-shaped beams, and all the fixed bases are installed on the fixed base of the lower monocrystalline silicon. On the bonding point of the base, the mechanical structure part of the upper layer is suspended above the part of the single crystal silicon substrate of the lower layer.

Compared with the prior art, the utility model has significant advantages: (1) the structural layer and the substrate layer of the accelerometer all adopt monocrystalline silicon, and the resonator and the first-stage lever amplification mechanism all pass the stress release frame and the fixed base Connected, and the resonant beam of the resonator is connected with the stress relief frame through the connecting block. These methods greatly reduce the residual stress of processing and the thermal stress caused by the temperature change of the working environment, and improve the stability of the resonant frequency of the resonator, and the leverage The magnification of the amplifying mechanism is close to the ideal value; (2) The fulcrum end, input end and output end of the first-level lever amplifying mechanism all adopt thin beam structures, so the axial tensile stiffness and bending stiffness of the fulcrum end and output end are very large Small, and the axial direction of the thin beam at the fulcrum end is perpendicular to the axial direction of the lever, realizing the magnification close to the theoretical value of the traditional lever amplification mechanism; (3) The structure of the drive electrode and detection electrode of the resonator adopts the flat plate electrode , which greatly reduces the edge effect of the electric field, improves the linearity of the vibration of the resonant beam, and improves the frequency stability; (4) the mass block is connected to the fixed base at its four corners through an axisymmetric U-shaped beam. The axisymmetric U-shaped beam can not only The residual stress is effectively released, and the cross-axis sensitivity of the accelerometer is also reduced, and the support beams of the mass block are arranged at the four corners to improve the impact resistance of the accelerometer structure.

Below in conjunction with accompanying drawing, the utility model is described in further detail.

Description of drawings

Fig. 1 is a schematic structural view of the low-stress silicon microresonant accelerometer of the present invention.

Fig. 2 is a schematic structural view of the amplification mechanism of the primary lever of the present invention.

Fig. 3 is a schematic diagram of the structure of the resonator of the present invention.

Detailed ways

In conjunction with Fig. 1, the low-stress silicon microresonant accelerometer of the utility model, the accelerometer structure is made on two layers of single crystal silicon, the mechanical structure of the accelerometer is made on the upper layer of single crystal silicon wafer, and metal is deposited on the upper surface of the mechanical structure As a signal input/output line, the lower layer of monocrystalline silicon is the substrate of the accelerometer, and the mechanical structure of the accelerometer consists of a mass block 1, an upper resonator 2a, a lower resonator 2b, two upper-level lever amplification mechanisms 3a, 3b, two A lower end primary lever amplifying mechanism 3c, 3d, an intermediate stress releasing frame 5a, an upper end stress releasing frame 5b and a lower end stress releasing frame 5c are formed, and the structures of the upper and lower four primary lever amplifying mechanisms are exactly the same. The upper resonator 2a and the lower resonator 2b are symmetrically adjacent to each other in the middle of the mass block, which can reduce the unevenness of the material and the asymmetry caused by processing, so that the structural parameters of the upper and lower resonators 2a and 2b are consistent, and the resonance can be effectively realized Frequency differential output. The lower end of the upper resonator 2a and the upper end of the lower resonator 2b are connected to the middle fixed base 4a through the middle stress relief frame 5a, and the middle stress relief frame 5a and the middle fixed base 4a are located on the upper resonator 2a and the lower resonator 2b between. The stress release frame 5a can release the processing residual stress, and at the same time reduce the thermal stress caused by the temperature change of the working environment. The upper end of the upper resonator 2a is respectively connected to the output ends 11a, 11b of the two upper-end first-stage lever amplifying mechanisms 3a, 3b, and the fulcrum ends 9a, 9b of the upper-end first-stage lever amplifying mechanisms 3a, 3b are connected to the upper-end stress release frame 5b. Connected to the upper fixed base 4b, the lower end of the lower resonator 2b is respectively connected to the output ends 11c, 11d of the two lower-level lever amplifying mechanisms 3c, 3d, and the fulcrum ends 9c, 3d of the lower-level lever amplifying mechanisms 3c, 3d, 9d is connected to the lower fixed base 4c through the lower end stress release frame 5c; the input ends 10a, 10b, 10c, and 10d of the upper and lower end primary lever amplification mechanisms 3a, 3b, 3c, and 3d are respectively connected to the mass block 1; the mass block 1 passes through The four U-shaped beams 6a, 6b, 6c, 6d are respectively connected to four fixed bases 7a, 7b, 7c, 7d located at the four corners of the mass block 1, and all the fixed bases 4a, 4b, 4c, 7a, 7b, 7c , 7d are installed on the bonding point of the fixed base of the lower layer of single crystal silicon, so that the upper layer of the mechanical structure is suspended above the lower layer of the single crystal silicon substrate. Among them, four U-shaped beams 6a, 6b, 6c, 6d and fixed bases 7a, 7b, 7c, 7d are located on the four corners of the mass block 1, which increases the stability of the accelerometer and improves its impact resistance. Moreover, the axially symmetrical U-shaped beams 6a, 6b, 6c, and 6d not only effectively release residual stress, but also reduce cross-axis sensitivity. Each of the four U-shaped beams 6a, 6b, 6c, 6d is an axisymmetric structure.

In conjunction with Fig. 2, the upper and lower end level lever amplification mechanisms 3a, 3b, 3c, 3d of the utility model low-stress silicon microresonant accelerometer are input by levers 8a, 8b, 8c, 8d, fulcrum ends 9a, 9b, 9c, 9d Ends 10a, 10b, 10c, 10d and output ends 11a, 11b, 11c, 11d, fulcrum ends 9a, 9b, 9c, 9d and input ends 10a, 10b, 10c, 10d are located at the upper ends of levers 8a, 8b, 8c, 8d , while the output ends 11a, 11b, 11c, 11d are located at the lower ends of the levers 8a, 8b, 8c, 8d, the fulcrum ends 9a, 9b, 9c, 9d, the input ends 10a, 10b, 10c, 10d and the output ends 11a, 11b, 11c , 11d have adopted thin beam structure, and the axis of fulcrum end 9a, 9b, 9c, 9d and the axis of lever 8a, 8b, 8c, 8d are perpendicular to each other. For the micro-lever, when the axial tensile stiffness of the fulcrum end and the output end is larger, and the bending stiffness of the fulcrum beam and the output end is smaller, the magnification of the lever will approach the ideal value, so the fulcrum end 9a, output end 11a and The input ends 10 a all adopt a thin beam structure, for example, when the width of the lever is 40 μm, the width of the thin beam is 6 μm×80 μm. When the fulcrum end of the lever amplification mechanism is a thin beam, the influence of the stress on the lever amplification factor is also greatly reduced. The axial direction of the thin beam 9a at the fulcrum end is perpendicular to the axial direction of the lever 8a, which also makes the magnification of the lever close to the ideal value.

In conjunction with Fig. 3, each resonator 2a, 2b of the low-stress silicon microresonant accelerometer of the present invention consists of two resonant beams 12a, 12b, two movable electrodes 13a, 13b, two fixed drive electrodes 14a, 14b, four One fixed detection electrode 15a, 15b, 15c, 15d and two connecting blocks 16, 17, two resonant beams 12a, 12b are arranged side by side and grouped together by connecting blocks 16, 17 at both ends, one connecting block 16 is connected to the corresponding The first-level lever amplifying mechanism is connected (as a connection block 16 of the upper resonator 2a is connected with the upper-end first-level lever amplifying mechanism 3a, 3b, and another connection block 16 is connected with the middle stress release frame 5a; a connection block of the upper resonator 2b It is connected with the lower end primary lever amplification mechanism 3c, 3d, and the other connecting block is connected with the intermediate stress release frame 5a), and the other connecting block 17 is connected with the middle fixed base 4a through the intermediate stress releasing frame 5a, and the other connecting block 17 And the middle stress release frame 5a can greatly reduce the influence of residual stress on the resonant beams 12a, 12b. The outer sides of the two resonant beams 12a, 12b are respectively connected to a movable electrode 13a, 13b, and the outer sides of the two movable electrodes 13a, 13b are respectively provided with a fixed driving electrode 14a, 14b to form a driving capacitor. The four fixed detection electrodes 15a, 15b, 15c, 15d are respectively arranged between the movable electrodes 13a, 13b and the resonant beams 12a, 12b, and the movable electrodes 13a, 13b and the fixed detection electrodes 15a, 15b, 15c, 15d form detection capacitors. The resonator adopts double-sided driving, and an AC voltage with a DC bias is applied to the left fixed driving electrode 14a, and an anti-phase AC voltage with a DC bias is applied to the right fixed driving electrode 14b, thereby ensuring the resonant beams 12a, 12b The working mode is anti-phase vibration mode. The movable electrodes 13a, 13b, fixed drive electrodes 14a, 14b and fixed detection electrodes 15a, 15b, 15c, 15d of the lower and upper resonators 2a, 2b are all planar electrodes.

The low-stress silicon microresonant type accelerometer of the utility model is used for measuring the input acceleration of y direction, when there is the acceleration a input along y direction, produces inertial force F=-ma on mass block, and this inertial force acts on respectively On the four first-stage lever amplification mechanisms, under the action of lever amplification, the force acting on each resonant beam of the resonator is

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; Ama</span>}}{\mathrm{<span\; class="notranslate">\; 4</span>}}$

In the formula, A is the magnification factor of the first-stage lever magnification mechanism. The force on the upper resonator is pressure, and the resonance frequency decreases, while the force on the lower resonator is tension, and the resonance frequency increases. The frequency difference between the two resonators is

Δf=2f ₀ κAma

In the formula, κ is a constant related to the structural parameters of the resonant beam. It can be seen that the frequency difference between the upper and lower resonators is proportional to the input acceleration, and the input acceleration can be measured by detecting the frequency difference between the upper and lower resonators.

Claims (5)

1. A low-stress silicon micro-resonance type accelerometer is characterized in that: the accelerometer structure is made on two layers of monocrystalline silicon, and the accelerometer mechanical structure is made on the upper monocrystalline silicon chip, and the upper surface of the mechanical structure is deposited The metal is used as the signal input/output line, and the lower layer of monocrystalline silicon is the substrate of the accelerometer. The mechanical structure of the accelerometer consists of a mass [1], an upper resonator [2a], a lower resonator [2b], and two upper first-level levers. Amplifying mechanism [3a, 3b], two lower-end one-stage lever amplifying mechanisms [3c, 3d], intermediate stress releasing frame [5a], upper end stress releasing frame [5b] and lower end stress releasing frame [5c], the upper resonator [2a] and the lower resonator [2b] are symmetrically located in the middle of the mass block up and down, the lower end of the upper resonator [2a] and the upper end of the lower resonator [2b] pass through the middle stress release frame [5a] and the middle fixed base [4a] is connected; the upper end of the upper resonator [2a] is respectively connected with the output ends [11a, 11b] of the two upper-end first-level lever amplification mechanisms [3a, 3b], and the upper-end first-level lever amplification mechanisms [3a, 3b] The fulcrum end [9a, 9b] is connected with the upper fixed base [4b] through the upper end stress release frame [5b], and the lower end of the lower resonator [2b] is respectively connected with the two lower end first-level lever amplification mechanisms [3c, 3d] The output ends [11c, 11d] are connected, and the fulcrum ends [9c, 9d] of [3c, 3d] of the lower level lever amplification mechanism are connected with the lower fixed base [4c] through the lower end stress release frame [5c]; the upper and lower ends The input ends [10a, 10b, 10c, 10d] of the primary lever amplification mechanism [3a, 3b, 3c, 3d] are respectively connected to the mass block [1]; the mass block [1] passes through four U-shaped beams [6a, 6b . ] installed on the fixed base bonding point of the lower layer of monocrystalline silicon, so that the upper mechanical structure part is suspended above the lower layer of the monocrystalline silicon substrate. 2. The low-stress silicon microresonant accelerometer according to claim 1, characterized in that: the upper and lower end level lever amplification mechanisms [3a, 3b, 3c, 3d] are composed of levers [8a, 8b, 8c, 8d], Pivot end [9a, 9b, 9c, 9d] input end [10a, 10b, 10c, 10d] and output end [11a, 11b, 11c, 11d] composition, fulcrum end [9a, 9b, 9c, 9d] and input end [10a, 10b, 10c, 10d] are located at the upper end of the lever [8a, 8b, 8c, 8d], while the output end [11a, 11b, 11c, 11d] is located at the lower end of the lever [8a, 8b, 8c, 8d], the fulcrum Ends [9a, 9b, 9c, 9d], input ends [10a, 10b, 10c, 10d] and output ends [11a, 11b, 11c, 11d] all adopt thin beam structures, and the fulcrum ends [9a, 9b, 9c , 9d] and the axial direction of the lever [8a, 8b, 8c, 8d] are perpendicular to each other. 3. The low-stress silicon microresonant accelerometer according to claim 1, characterized in that: each of the four U-shaped beams [6a, 6b, 6c, 6d] is an axisymmetric structure. 4. The low-stress silicon microresonant accelerometer according to claim 1, characterized in that: each resonator [2a, 2b] consists of two resonant beams [12a, 12b], two movable electrodes [13a, 13b] ], two fixed drive electrodes [14a, 14b], four fixed detection electrodes [15a, 15b, 15c, 15d] and two connection blocks [16, 17], two resonant beams [12a, 12b] are arranged side by side And through the connection blocks [16, 17] at its two ends, one connection block [16] is connected with the corresponding first-level lever amplification mechanism, and the other connection block [17] is fixed to the middle through the middle stress release frame [5a] The bases [4a] are connected, the outer sides of the two resonant beams [12a, 12b] are respectively connected to a movable electrode [13a, 13b], and the outer sides of the two movable electrodes [13a, 13b] are each provided with a fixed driving electrode [14a, 14b ], forming a drive capacitor, four fixed detection electrodes [15a, 15b, 15c, 15d] are respectively arranged between the movable electrodes [13a, 13b] and the resonant beam [12a, 12b], the movable electrodes [13a, 13b] and the fixed The detection electrodes [15a, 15b, 15c, 15d] form a detection capacitor. 5. The low-stress silicon microresonant accelerometer according to claim 4, characterized in that: the movable electrodes [13a, 13b], the fixed drive electrodes [14a, 14b] and the fixed Detection electrodes] 15a, 15b, 15c, 15d] are flat electrodes.

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