CN100394154C - Piezoresistive high frequency dynamic low pressure sensor - Google Patents

Abstract

A piezoresistive high-frequency dynamic low-voltage sensor is composed of a piezoresistive sensitive component, a sensor base, a transfer circuit and an outgoing cable. The piezoresistive sensitive component is composed of a silicon piezoresistive sensitive element and a glass ring. The sensitive element is a force sensitive C-type or E-type square planar silicon diaphragm, the front of the diaphragm is covered with Si ₃ N ₄ and SiO ₂ layers, the front of the force-sensitive area has a Wheatstone full bridge and leads electrodes, and the hard frame on the back edge of the force-sensitive area is covered with Si ₃ N ₄ and SiO ₂ layers and welded to the glass ring, the electrode is welded to the inner lead of the gold wire, the other side of the glass ring is fixed to the circular pit surface of the pressure-input end of the sensor base through the metal ring, and the back of the silicon chip is connected to the sensor base. The pressure end surface is quasi-flush, the other end of the inner lead is welded to the transfer circuit, the core wire of the lead cable is welded to the transfer circuit, the sensor base is screwed to the sensor cap, and the lead cable is drawn out through the bottom of the cap and is based on the crimp cap Fixed on the cap of the sensor, the transfer circuit and the lead-out cable have a high-frequency bandwidth amplification circuit indirectly to realize the high-frequency amplification of the transmission signal.

Description

Piezoresistive high frequency dynamic low pressure sensor

technical field

The invention relates to a piezoresistive high-frequency dynamic low-voltage sensor, in particular to a high-frequency dynamic piezoresistive low-voltage sensor based on MEMS (Micro Electro Mechanical System) silicon micromachining technology, especially suitable for aerodynamic tests (commonly known as Wind tunnel test), water conservancy engineering, aerospace, weapon test, dynamic pressure measurement of ships, etc.

Background technique

The silicon micromachining technology of MEMS (Micro Electro Mechanical System) technology was used in the production of piezoresistive pressure sensors in the late 1970s. Using the piezoresistive effect of silicon, a certain crystal on a silicon wafer was used in a planar integrated circuit process. Direction, the strain detection piezoresistors made by oxidation diffusion or ion implantation doping, photolithography and other methods at a certain position, and interconnected to form a test Wheatstone strain bridge. Using double-sided alignment photolithography, silicon anisotropic etching and other silicon three-dimensional processing technologies, the substrate silicon wafer is made into a force-sensitive thin film structure fixed around the periphery to replace the traditional mechanical grinding process of silicon cups. The silicon piezoresistive pressure sensor manufactured by the silicon micromachining process has the advantages of low range, high sensitivity and high natural frequency of the silicon piezoresistive pressure sensor.

Kulite uses a C-type flat membrane force-sensing structure; in order to improve the linearity and frequency response at low ranges, Endevco uses a double-island membrane structure, both of which have their own advantages and disadvantages.

When used for dynamic measurement, the sensor is generally required to have a high dynamic frequency response. For this reason, the package of the sensor cannot form a lumen, and the pressure-sensitive diaphragm must directly face the facing pressure. The silicon chip of the high-frequency pressure sensor product packaged by Kulite company has good dynamic frequency response performance, but it is covered with a laser-drilled metal film cap in front of the front of the silicon chip. This structure seriously affects the use of dynamic frequency response. ring.

Contents of the invention

In order to solve the above problems, the present invention provides a MEMS technology-based high-frequency high-frequency sensor with high dynamic response frequency, high sensitivity, strong anti-interference, rise time below μS level, low range, and excellent dynamic performance that can be used for pressure dynamic testing. Dynamic piezoresistive low pressure sensor.

Technical scheme of the present invention is constituted like this:

A piezoresistive high-frequency dynamic low-voltage sensor, composed of piezoresistive sensitive components, sensor base, transfer circuit and lead-out cables,

1. The piezoresistive sensitive component is composed of a silicon piezoresistive sensitive element and a glass ring. The silicon piezoresistive sensitive element is a square silicon diaphragm with a square force sensitive area. The front side of the silicon diaphragm is covered with _SiO2 layer and Si ₃ N ₄ layers, the front of the force-sensitive area has a Wheatstone strain full bridge and leads to the resistance electrode, the hard frame on the back edge of the force-sensitive area is covered with Si ₃ N ₄ layers and SiO ₂ layers in turn and welded to polished Pyrex or GG -17 glass ring pieces to form the piezoresistive sensitive component, and the resistance electrode is welded to one end of the inner lead of the gold wire;

2. The circular concave surface of the sensor base pressure inlet is bonded or welded with a metal ring piece, the outer surface of the metal ring piece is flush with the end surface of the sensor base pressure inlet port, and the glass of the piezoresistive sensitive component The other side of the ring piece is pasted on the inner surface of the metal ring piece, so that the back side of the silicon diaphragm of the piezoresistive sensitive component and the end face of the pressure inlet port of the sensor base are quasi-flush packaged, and the other end of the inner lead wire of the gold wire is welded to the switch To connect the circuit, the core wire of the lead-out cable is welded to the transfer circuit to realize the conduction between the inner lead wire of the gold wire and the corresponding core wire;

3. The tail of the sensor base is screwed to the sensor tube cap used to package the sensor, the lead cable is drawn out through the bottom opening of the sensor tube cap, and is fixed to the sensor tube cap based on the crimping cap.

As a further improvement of the present invention, the back of the square planar silicon diaphragm has a C-shaped structure, and the film part surrounded by the hard frame on the back edge of the force-sensitive area exposes the silicon chip, and the film part surrounded by the hard frame on the back edge of the force-sensitive area The silicon chip is exposed, and the thickness of the silicon diaphragm relative to the pressure range of the sensor is 0-200Kpa-2MPa is 50μ-150μ.

As a further improvement of the present invention, the back side of the planar silicon diaphragm has an E-shaped structure, and the back side of the force-sensitive area is provided with a central island covered with _Si3N4 layers and _SiO2 layers _in sequence, surrounded by the central island and the edge hard frame. The formed membrane part exposes the silicon chip, and the thickness of the silicon diaphragm corresponding to the pressure range of the sensor is 0-10Kpa-200KPa is 15μ-60μ.

As a further improvement of the present invention, the metal ring piece is integrated with the sensor base.

As a further improvement of the present invention, the square planar silicon diaphragm adopts silicon single crystal with high Young's modulus of elasticity.

As a further improvement of the present invention, the resistance of the Wheatstone strained full bridge has a resistance value below 1KΩ.

As a further improvement of the present invention, the switching circuit is a PCB switching board (14) fixed in the cavity of the sensor base.

As a further improvement of the present invention, the transfer circuit and the lead-out cable are indirectly provided with an integrally packaged high-frequency bandwidth amplifier circuit to realize high-frequency amplification of transmission signals. The high-frequency bandwidth amplifier circuit has a bandwidth up to 100KHz and a rise time of 1μS .

As a further improvement of the present invention, the high-frequency bandwidth amplifying circuit is composed of two-stage amplifying circuits. The first-stage amplifying circuit adopts an amplifier AD620 with a unity gain bandwidth as high as 1 MHz and a magnification factor of 5-10 times, and the second-stage amplifying circuit adopts Amplifier OP37 with unity gain bandwidth up to 30MHz and 10-40x magnification.

As a further improvement of the present invention, the thickness of the polished Pyrex or GG-17 glass ring is 2-4mm, the inner wire of the gold wire is φ25-φ40μm, and the piezoresistive high-frequency dynamic low-voltage sensor has a natural frequency of 138K-600KHz, 0 -40KHz to 0-200KHz bandwidth and 1.0-0.2μS rise time.

The beneficial effects of the present invention are:

The contact-sensitive material of the high-frequency dynamic low-pressure sensor adopts silicon single crystal with high Young's modulus of elasticity, and the pressure-sensitive diaphragm is a square-shaped silicon diaphragm with a very small size, which is fixed around the periphery. The silicon piezoresistive element is made by micromachining technology, so the sensitive element has a high natural frequency above 100KHz up to 1500KHz, an extremely fast rise time of 1μS-0.2μS, and a low frequency response characteristic as low as zero Hz.

Square planar silicon diaphragm adopts C-type or E-type island membrane composite mechanical structure design to solve the problem of low range sensitivity. Since the pressure sensing surface of the force-sensitive chip of the low-range pressure sensor is 1-2mm lower than the pressure inlet port of the sensor base, it is a typical quasi-flush package design, and the center hole of the metal ring in this quasi-flush package design is facing In the force-sensing area of the force-sensing silicon chip, there is only a 1-2mm cylindrical hole between the pressure inlet port and the force-sensing chip, without forming a T-shaped lumen effect, so the sensor has excellent dynamic test performance and anti-light interference Response frequency that fully meets the requirements of the dynamic test test.

When the test requires that the lead wire of the sensor is too long, in order to avoid interference, when the user requires the sensor to output a high-level signal, an integrated high-frequency broadband amplifier is used to achieve a magnification of 50-400 times, ensuring that the sensor can reach the bandwidth used. 100KHz, high dynamic frequency response with dynamic amplitude-frequency error less than 1%, and rise time less than 1μS, while avoiding its weakness of small signal and large noise.

Description of drawings

Fig. 1 is the sectional structure schematic diagram of the C-type square planar silicon diaphragm with force-sensitive region of the present invention;

Fig. 2 is the sectional structure schematic diagram of the E-type square planar silicon diaphragm with force-sensitive region of the present invention;

Fig. 3 is a schematic diagram of the structure of the piezoresistive sensitive component formed by the square planar silicon diaphragm and the Pyrex glass ring sheet of the present invention and the internal and external leads;

Fig. 4 is a schematic structural view of the sensor quasi-flush package of the present invention;

Fig. 5 is the structural representation of the sensor with high-frequency broadband amplifier of the present invention;

Fig. 6 is a schematic circuit diagram of the high-frequency broadband amplifier involved in the present invention.

Figures 1 to 6 are further explained as follows:

1-Si ₃ N ₄ layers 13-○ ring

2-SiO _2- layer 14-PCB interposer board

3-Membrane 15-Exit cable

4-edge hard frame

5-Central island 16-Sensor cap

7-Pyrex glass ring piece 17-Crimping cap

8-metal ring piece 18-fixed plate frame

10-Square silicon diaphragm 19-Transfer cable

11-Gold wire inner lead 20-High frequency broadband amplifier

road

12-sensor base

Detailed ways

The high-frequency dynamic low-pressure sensor adopts the MEMS silicon micromachining process to make the peripheral fixed square planar film and uses the quasi-flush package to eliminate the influence of the lumen effect on the dynamic test and realize the real-time measurement of the dynamic pressure. It adopts high-frequency broadband The amplifier ensures a sufficiently high frequency response while avoiding its weakness of small signal and large noise. The implementation steps are realized as shown in Figure 1 to Figure 6:

Figure 1 is a C-type square planar silicon diaphragm with a square force-sensitive area. The double-sided polished silicon wafer used as an elastic element is firstly covered with a 1 μm thick _SiO2 layer 2 on both sides by traditional thermal oxidation technology during MEMS technology processing. Then use the standard LPCVD method to cover the Si ₃ N ₄ layer 1 with a thickness of 3000A on both sides, and use two photolithography techniques to etch away the Si ₃ N ₄ layer and SiO ₂ on the parts other than the square force-sensitive area on the front side of the silicon diaphragm. layer, and keep the Si ₃ N ₄ layer and SiO ₂ layer covered by the edge hard frame. _The above-mentioned silicon wafers are anisotropically etched in _the KOH etching solution according to the standard silicon micromachining technology, and the C _- type elastic Mechanically sensitive structures. Using double-sided photolithography technology and ion implantation doping technology, a Wheatstone strain full bridge is fabricated at a specific position on the front side of the square planar silicon diaphragm, and the electrodes of the strain resistance are drawn out. Those not described in detail above are all standard integrated circuit processes.

Figure 2 is an E-type square planar silicon diaphragm with a square force-sensitive area. The double-sided polished silicon wafer used as an elastic element is first covered with a 1 μm thick _SiO2 layer 2 on both sides by traditional thermal oxidation technology in MEMS technology processing. Then use the standard LPCVD method to cover the Si ₃ N ₄ layer 1 with a thickness of 3000 Å on both sides, and use two photolithography techniques to etch away the Si ₃ N ₄ layer and the film position on the back of the silicon diaphragm equivalent to the central island in the future. Si ₃ N ₄ layer and SiO ₂ layer, keep the SiO ₂ layer covered by the center island, and keep the Si ₃ N ₄ layer and SiO ₂ layer covered by the edge hard frame. The above-mentioned silicon wafer is etched anisotropically in KOH etching solution according to the standard silicon micromachining technology, and the island-membrane composite elastic-mechanical sensitive structure is formed due to the corrosion masking effect of the _SiO2 layer reserved on the island. Using double-sided photolithography technology and ion implantation doping technology, a Wheatstone strain full bridge is fabricated at a specific position on the front of the island-membrane composite elastic chip, and the electrodes of the strain resistance are drawn out. Those not described in detail above are all standard integrated circuit processes.

Fig. 3 is a piezoresistive sensitive group composed of square planar silicon diaphragms in Fig. 1 or Fig. 2, and the edge hard frame area and the polished Pyrex glass ring 7 with a thickness of 2-4mm are welded together by electrostatic bonding process. Then use 4 or 5 φ25-φ40μm gold wires 11 as inner leads, weld one end of the gold wire to the electrode lead-out block of the Wheatstone strain full bridge with a special gold wire ball welding machine, and connect the glass ring The other side is pasted on a piece of metal ring sheet 8 with a small hole of ф0.5-1.2mm and a thickness of 1-2mm with epoxy resin glue to form a pressure sensitive component.

Fig. 4 is a schematic diagram of the sensor structure of the quasi-flush package. The metal ring piece 8 of the force-sensitive component shown in Fig. 3 is bonded with epoxy glue or laser welded to the pit in the center of the pressure inlet port of the sensor base 12, Make the outer side of the metal ring just flush with the end face of the pressure inlet port of the sensor base. It is also possible to design the metal ring piece and the sensor base as one, and then glue the end of the glass ring without the silicon chip to the position corresponding to the metal ring piece with epoxy glue. The other end of the gold wire inner lead 11 is welded to the PCB adapter board 14, and the core wire of the sensor lead cable 15 is welded to the corresponding PCB board, so as to realize the transfer of the inner and outer leads.

The sensor base tail is screwed to the sensor tube cap 16 for packaging the sensor, the lead-out cable is drawn out through the sensor tube cap bottom opening, and is fixed on the sensor tube cap based on the crimping cap 17, the sensor base tail is connected to the sensor tube cap. O-rings 13 may be provided between the sensor caps and between the crimping cap and the sensor cap.

Fig. 5 is a schematic diagram of the structure of a sensor with a two-stage amplifying circuit. The gold wire inner lead is connected to the high-frequency broadband amplifying circuit 20 through a PCB adapter board and an adapter cable. The high-frequency broadband amplifying circuit is based on the sensor cavity. The solid plate frame 18 is fixed, and then the core wire of the lead-out cable is welded to the high-frequency broadband amplifier circuit, thereby realizing high-frequency amplification of the sensor signal.

When the test requires that the lead wire of the sensor is too long, so in order to avoid interference and the user requires the sensor to output a high-level signal, an integrated high-frequency broadband amplifier is used. The amplifier has a bandwidth as high as 0-100KHz and a rise time of 1μS and extremely low low frequency noise.

The high-frequency bandwidth amplifying circuit is composed of two-stage amplifying circuits. The first stage adopts AD620 with a unity gain bandwidth of only 1MHz. times low magnification, so AD620 still has a frequency response of 800KHz at this time, because it has a higher slew rate and small signal amplification, it can ensure a rise time of 1μS; The high-frequency instrument amplifier OP37 with a unity gain bandwidth of 30MHz adopts a magnification ratio of 10-40 times, so it has a high enough frequency response guarantee, and at the same time avoids its weakness of small signal and large noise.

Fig. 6 is the circuit schematic embodiment of the high-frequency broadband amplifier involved in the present invention, and this high-frequency broadband amplifier is made up of three parts, wherein:

1. LM317 and R5, D1, C6, and C7 form a constant current power supply for the sensor to provide work. According to the formula I=1.25/R, the size of R5 determines the constant current provided by LM317, and D1, C6, and C7 form a constant current. The filter circuit is used to remove the interference and noise of the power supply.

2. AD620 and R1, C1, C8, C9, C2, R2 form the first stage amplification of the high-frequency broadband amplifier, R1 is a fixed resistor, and its value is R=49.4K/(G-1), (G =4~10) Connected between pins 1 and 8 of AD620, the magnification of this stage is fixed at 4 to 10 times, so that AD620 has lower noise and higher frequency response under this magnification; C1 spans Connected between pins 2 and 3 of AD620 to filter out 800-1MHz sensor input noise; C8 and C9 are used to filter out the interference noise of the AD620 working power supply; C2 and R2 form the AD620 amplified output signal, which is the filter of the OP37 input signal The circuit filters out its signal interference.

3. OP37 and C3, C4, C5, R3, R4, W2 and R3, W1 form the second stage of amplification of the amplifying circuit, W1, W2 are three-terminal adjustable resistors (potentiometers), R3, W2, R4 are connected across On the 1st, 7th and 8th feet of the OP37, this part forms the zero offset circuit of the OP37 as the zero adjustment circuit of the high-frequency broadband amplifier, and R3 and W1 are respectively connected across the 2nd, 6th and 6th feet of the OP37. Between the power supply and the ground is used as the adjustment of the magnification of the second-stage amplifying circuit, and C3, C4, and C5 form the power supply and signal output filter of the second-stage amplifying circuit, and are used as a filter circuit for signal interference of the second-stage amplifying circuit

The measuring range of this high-frequency dynamic low-pressure sensor is controlled by the thickness of a square silicon diaphragm with a square force-sensitive area processed by micromachining. The control of the diaphragm thickness is completed by an anisotropic etching process and a precision-controlled thickness-controlled four-electrode chemical etching device. . The square planar silicon diaphragm (10) has a C-shaped structure on the back, and the thickness of the silicon diaphragm relative to the pressure range of the sensor is 0-200Kpa-2MPa is 50μ-150μ; The thickness of the silicon diaphragm in the range of 0 ~ 10Kpa-200KPa is 15μ-60μ.

The distance between the back of the silicon diaphragm of the high-frequency dynamic low-pressure sensor and the pressure port of the sensor base is 1-2mm, which is a typical quasi-flush package design, which eliminates the influence of the pressure lumen effect on its dynamic test and fully guarantees The dynamic frequency response characteristics of the sensor fully meet the response frequency required by the dynamic pressure test.

The high-frequency dynamic low-voltage sensor can achieve a 50-400 times magnification through a two-stage amplified broadband amplifier, which ensures that the sensor can achieve a high dynamic frequency response with a gain bandwidth of 800KHz and a rise time of less than 1μS, while avoiding its small signal Noisy weakness.

The high-frequency dynamic low-pressure sensor has excellent performance, stability, and strong anti-interference ability, and can be used for high-sensitivity dynamic pressure tests in aerodynamic tests and other working conditions, and has a good market prospect.

The main performance index of product of the present invention is;

1. Range: 0～10KPa-2MPa, output sensitivity: 15～100mV or 0-5V

2. Accuracy: 0.1%～0.01%FS

3. Natural frequency: 0～150-600KHz

4. Use bandwidth: 0～50-200KHz

5. Rise time: 1-0.2μS

6. Time stability: ≤0.1mV

7. Temperature stability: ≤5×10 ^-4 /°C·FS.

Claims (10)

1. A piezoresistive high-frequency dynamic low-voltage sensor is composed of piezoresistive sensitive components, sensor base (12), switching circuit and lead-out cable (15), characterized in that: 1) The piezoresistive sensitive component is composed of a silicon piezoresistive sensitive element and a glass ring. The silicon piezoresistive sensitive element is a square silicon diaphragm (10) with a square force sensitive area, and the front of the silicon diaphragm is covered with SiO ₂ layers (2) and Si ₃ N ₄ layers (1), the force-sensing area has a Wheatstone strain full bridge on the front and leads to resistance electrodes, and the force-sensing area has a hard frame (4) on the back edge of the SiO ₂ layer (2 ) and Si ₃ N ₄ layers (1) and welded to polished Pyrex or GG-17 glass ring (7) to form the piezoresistive sensitive component, and the resistance electrode is welded to one end of the gold wire inner lead (11); 2) The surface of the pressure inlet port of the sensor base is bonded or welded with a metal ring (8), and the outer surface of the metal ring is flush with the end face of the pressure inlet port of the sensor base. The other side of the glass ring of the component is pasted on the inner side of the metal ring to realize the quasi-flush packaging of the back of the silicon diaphragm of the piezoresistive sensitive component and the end face of the pressure inlet port of the sensor base, and the other end of the inner lead of the gold wire is welded To the transfer circuit, the core wire of the lead-out cable is welded to the transfer circuit to realize the conduction between the gold wire inner lead and the corresponding core wire; 3) The tail of the sensor base is screwed into the sensor tube cap (16) for packaging the sensor, the lead-out cable is drawn out through the bottom opening of the sensor tube cap, and is fixed to the sensor tube cap based on the crimping cap (17). 2. A kind of piezoresistive high-frequency dynamic low-pressure sensor as claimed in claim 1, it is characterized in that, the back side of the square planar silicon diaphragm (10) has a C-shaped structure, and the hard frame on the back side of the force-sensitive area is surrounded by The silicon chip is exposed at the part of the membrane (3). 3. A kind of piezoresistive high-frequency dynamic low-voltage sensor as claimed in claim 1, is characterized in that, this square planar silicon diaphragm (10) back side has E-type structure, and this force-sensitive area back side is provided with and covers SiO ₂ layers (2) Central island (5), the silicon chip is exposed at the film (3) surrounded by the central island and the edge hard frame. 4. A piezoresistive high-frequency dynamic low-voltage sensor as claimed in claim 1, wherein the metal ring is integrated with the sensor base. 5 . A piezoresistive high-frequency dynamic low-voltage sensor as claimed in claim 1 , wherein the square planar silicon diaphragm adopts a silicon single crystal with a high Young's modulus of elasticity. 6. A piezoresistive high-frequency dynamic low-voltage sensor as claimed in claim 1, wherein the resistance of the Wheatstone strained full bridge has a resistance value below 1KΩ. 7. A piezoresistive high-frequency dynamic low-voltage sensor according to claim 1, wherein the switching circuit is a PCB switching board (14) fixed in the cavity of the sensor base. 8. A kind of piezoresistive high-frequency dynamic low-voltage sensor as claimed in claim 1, 2 or 3, it is characterized in that, the high-frequency bandwidth amplifying circuit (20) of integrated package is indirectly arranged between the switching circuit and the lead-out cable , to achieve high-frequency amplification of transmission signals, the high-frequency bandwidth amplifier circuit has a bandwidth up to 100KHz and a rise time of 1μS. 9. A piezoresistive high-frequency dynamic low-voltage sensor as claimed in claim 8, wherein the high-frequency bandwidth amplifying circuit is composed of two-stage amplifying circuits, and the first-stage amplifying circuit adopts a unit gain bandwidth up to 1MHz. Amplifier AD620 and 5-10 times magnification, the second stage amplifier circuit adopts amplifier OP37 with unity gain bandwidth up to 30MHz and 10-40 times magnification. 10. A kind of piezoresistive high-frequency dynamic low-pressure sensor as claimed in claim 1, 2 or 3, is characterized in that, the thickness of the polished Pyrex or GG-17 glass ring sheet is 2-4mm, and the inner lead wire of the gold wire is φ25-φ40μm, the piezoresistive high-frequency dynamic low-voltage sensor has a natural frequency of 138K-600KHz, a bandwidth of 0-40KHz to 0-200KHz, and a rise time of 1.0-0.2μS.

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