CN101348233A - Microstructure Resonant Beam Pressure Sensor - Google Patents

Abstract

Microstructure resonant beam pressure sensor, including upper silicon wafer and lower silicon wafer bonded, the upper silicon wafer includes a rectangular frame and two symmetrical peninsulas opened in the rectangular frame, and the side-by-side arrangement made of titanium nitride The two ends of the two groups of resonant beams are respectively connected to the two peninsulas, and the excitation resistor and the pick-up resistor connected to the lead wire and the electrode are respectively arranged on each resonant beam, and the lower silicon chip is a structure with a mouth-shaped frame. A pressure membrane is arranged in the mouth-shaped frame. The invention adopts titanium nitride as the resonant beam of the pressure sensor. The titanium nitride has a rather high natural resonant frequency, and the precision of the resonant pressure sensor is greatly improved by using the titanium nitride resonant beam. The reason why the high natural resonant frequency can improve the measurement accuracy is because the higher the natural resonant frequency, the greater the movement of the corresponding 0 pressure frequency (the accuracy of the sensor is the ratio of the frequency instability to the corresponding 0 pressure frequency movement) , so the accuracy of the measured pressure is higher.

Description

Microstructure Resonant Beam Pressure Sensor

technical field

The invention relates to a miniature pressure sensor, in particular to a microstructure resonant beam pressure sensor capable of improving the precision of the miniature pressure sensor.

Background technique

The development of Micro Electro Mechanical Systems (MEMS for short) technology and the gradual maturity of its processing technology make it possible to develop MEMS sensors with high integration, low cost, light weight, small size and low power consumption. Become the trend of future sensor research.

For micro-resonant pressure sensors, the external pressure to be measured does not directly act on the resonator, but indirectly changes the stiffness of the resonator through the pressure film, thereby changing the resonant frequency of the beam, so the change of the resonant frequency of the beam can be detected To achieve the purpose of detecting the external pressure, it belongs to the principle of secondary sensitivity. Its characteristics are that, firstly, the resonator is isolated from the medium to be measured, and its vibration will not be affected by the medium. Moreover, the resonator can be placed in a higher vacuum, so that a higher quality factor can be obtained. Secondly, the pressure sensitivity of the sensor can be improved, because the surrounding fixed film has the effect of stress amplification, and the magnification is proportional to the square of the ratio of film size to thickness. The resonant pressure sensor is the pressure sensor with the highest precision at present. It indirectly measures the pressure by detecting the natural frequency of the object, and outputs quasi-digital signals. It can not only directly interface with the computer, but also easily form an instrument that directly displays numbers. In addition to good temperature stability and high sensitivity, resonant pressure sensors also have many advantages such as fast response, wide frequency band, compact structure, low power consumption, small size, light weight, and mass production. Focus on research and development. There are two main parameters that affect the performance of a resonant pressure sensor: the natural resonant frequency of the resonant sensitive element and the mechanical quality factor Q of the resonator. The natural resonant frequency of the resonant sensitive element mainly affects the accuracy of the sensor. The higher the natural resonant frequency, the higher the measurement accuracy of the resonant pressure sensor. The natural resonant frequency of the material is determined by its own conditions and is different from other external conditions. The quality factor of the harmonic oscillator mainly reflects the damping ratio and the degree of energy consumption in the vibration of the harmonic oscillator, and also reflects the steepness of the amplitude-frequency characteristic curve. The factors affecting the Q value of the resonator mainly include: the characteristics of the material itself, the processing technology, the structure of the resonator (boundary conditions and packaging conditions), and the use environment. The resonant pressure sensors developed now use silicon or silicon compounds to make resonant beams. Compared with traditional pressure sensors, the accuracy has been greatly improved, but with the continuous development of science, some industrial applications , especially the modern aerospace field has put forward higher requirements on the accuracy of the resonant pressure sensor (at present, the electrostatic excitation developed by the foreign DRUCK company, the accuracy of the micro-resonant pressure sensor with capacitive pickup is better than 0.01% FS. But At present, the highest precision in China is far from reaching this precision, the main reason is that the beams are made of silicon or silicon compounds, and their natural resonance frequency is not high, so the measurement precision cannot be further improved), the existing precision have been unable to meet their development requirements.

Contents of the invention

The object of the present invention is to provide a microstructure resonant beam pressure sensor capable of greatly improving the accuracy of the resonant pressure sensor.

In order to achieve the above-mentioned purpose, the technical scheme adopted by the present invention is as follows: comprising an upper silicon wafer and a lower silicon wafer bonded together, the upper silicon wafer includes a rectangular frame and two symmetrical peninsulas set in the rectangular frame, formed by nitride The two ends of the two sets of resonant beams made of titanium are connected to the two peninsulas respectively. On each resonant beam, there are excitation resistors and pickup resistors connected to the lead wires and electrodes. The lower silicon chip is a The structure of the mouth-shaped frame is provided with a pressure membrane inside the mouth-shaped frame.

The peninsula of the present invention is arranged on the longitudinal midline of the rectangular frame; the thickness of the mouth-shaped frame is several times of the thickness of the pressure film.

Since the present invention uses titanium nitride as the resonant beam of the pressure sensor, titanium nitride (TiN) has a rather high natural resonance frequency, and the use of the titanium nitride (TiN) resonant beam can greatly improve the precision of the resonant pressure sensor. The reason why the high natural resonant frequency can improve the measurement accuracy is because the higher the natural resonant frequency, the greater the movement of the corresponding 0 pressure frequency, so in the case of the same frequency instability (the accuracy of the sensor is that the frequency is different The ratio of stability to the corresponding 0 pressure frequency movement) precision is also higher, and the present invention adopts double resonant beam structure, double beam structure can obtain two groups of data in exactly the same measurement environment, can greatly be greatly improved by the processing to measurement data The measurement error is reduced, thereby further improving the measurement accuracy.

Description of drawings

Fig. 1 is the overall structural representation of the present invention;

Fig. 2 is a structural diagram of the resonant beam 13 of the present invention;

Fig. 3 is a schematic cross-sectional view of the present invention.

Detailed ways

The structural principle and working principle of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Referring to Fig. 1, the present invention comprises upper silicon chip 11 and lower silicon chip 12 that are bonded, and upper silicon chip 11 comprises a rectangular frame 15 and two symmetrical peninsulas 14 that are offered on the longitudinal center line of rectangular frame 15, made of nitrogen The two ends of the two groups of resonant beams 13 arranged side by side made of titanium dioxide are respectively connected to two peninsulas 14 , and the lower silicon chip 12 has a structure with a mouth-shaped frame 17 , and a pressure film 16 is arranged in the mouth-shaped frame 17 . The thickness of the mouth-shaped frame 17 is several times of the thickness of the pressure membrane 16 .

Referring to FIG. 2 , each resonant beam 13 of the present invention is respectively provided with an exciting resistor 20 and a pickup resistor 21 connected to the lead wire 18 and the electrode 19 .

Referring to Fig. 3, since the upper and lower silicon wafers 11 and 12 are bonded into a whole, the pressure film 16 feels the external force transmitted to the resonant beam 13, which changes the axial mechanical stress of the resonant beam 13, thereby changing the stiffness of the resonant beam , so that the natural resonant frequency of the resonant beam 13 changes, and the pressure measurement is realized by detecting the change of the resonant frequency of the resonant beam 13 .

In the resonant beam pressure sensor of the present invention, the resonant beam 13 adopts electrothermal excitation and piezoresistive vibration pickup: thermal excitation includes electrothermal excitation and photothermal excitation, and there are great differences in their methods, but the excitation principle is the same. It is all through heat diffusion that causes deformation and vibration of the resonant beam 13 . Electrothermal excitation is to apply an alternating voltage on the excitation resistor 20 to cause the resonant beam 13 to generate alternating temperature stress and drive the resonant beam 13 to vibrate. When the vibration frequency is consistent with the natural resonant frequency of the resonant beam 13, the resonant beam 13 resonates , the amplitude reaches a maximum. The vibration of the resonant beam 13 is detected by the pickup resistor 21 . Photothermal excitation is to irradiate the beam through the optical fiber coupling by modulating the semiconductor laser pulse. The beam absorbs the laser light and generates an alternating thermal stress with the same frequency as the modulated light pulse. Under the action of this thermal stress, it is forced to vibrate. When the pulse frequency When equal to the natural resonant frequency of the beam, the beam resonates and the amplitude reaches a maximum. The reason why electrothermal excitation and piezoresistive vibration are used instead of photothermal excitation is because the electrical conductivity of titanium nitride (TiN) is relatively good, and the thermal conductivity is relatively low, so the same excitation voltage is the same excitation power , the temperature rise and the change of resonance frequency generated in the titanium nitride (TiN) beam are relatively large, which is beneficial to improve the sensitivity of the resonant pressure sensor.

Vibration pickup is to detect the vibration of the resonant beam 13 through the vibration pickup resistor 21 . In the present invention, piezoresistive vibration is used. Piezoresistive vibration pickup uses the piezoresistive characteristics of the piezoresistive material whose resistivity is modulated by the stress it receives. A piezoresistor is fabricated on the resonant beam 13. When the resonant beam 13 vibrates, the stress felt by the piezoresistor will periodically The magnitude of the stress is proportional to the amplitude of the beam, and the vibration of the beam can be detected by measuring the change of piezoresistor.

The present invention uses titanium nitride (TiN) as the material of the resonant beam, not only can greatly improve the precision of the resonant pressure sensor, because titanium nitride (TiN) has good machinability, it is sensitive to the resonant pressure sensor Component fabrication is very beneficial.

Claims (3)

1. A microstructure resonant beam pressure sensor, comprising a bonded upper silicon chip (11) and a lower silicon chip (12), characterized in that: said upper silicon chip (11) includes a rectangular frame (15) and The symmetrical two peninsulas (14) set in the rectangular frame (15), the two ends of two sets of resonant beams (13) arranged side by side made of titanium nitride are respectively connected with the two peninsulas (14), in Each resonant beam (13) is respectively provided with an exciting resistor (20) and a pickup resistor (21) connected to the lead wire (18) and the electrode (19). The structure is provided with a pressure film (16) in the mouth-shaped frame (17). 2. The microstructure resonant beam pressure sensor according to claim 1, characterized in that: said peninsula (14) is set on the longitudinal center line of the rectangular frame (15). 3. The microstructure resonant beam pressure sensor according to claim 1, characterized in that the thickness of the mouth-shaped frame (17) is several times the thickness of the pressure film (16).

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