In-chip resistance adjusting system of silicon piezoresistive pressure chip

Abstract

The invention discloses an in-chip resistance adjusting system for a silicon piezoresistive pressure chip, and relates to the field of zero-point voltage adjustment of the silicon piezoresistive pressure chip. In the prior art, a peripheral resistance network is used for trimming zero-point voltage, so that the size of a sensor is increased, and the temperature resistance of the peripheral resistance network is insufficient. Each bridge arm is connected in series with a group of trimming resistors, the resistance values of the four groups of trimming resistors are equal, each group of trimming resistors is formed by connecting n resistors in parallel or connecting n parallel resistors and m parallel resistors in series, and n and m are both greater than or equal to 2; the four-probe test system is used for measuring the zero-point output voltage of the Wheatstone bridge, controlling the laser to cut the trimming resistor on the bridge arm where the compression resistor is located when the zero-point output voltage is larger than the upper limit value of the preset range, and controlling the laser to cut the trimming resistor on the bridge arm where the compression resistor is located when the zero-point output voltage is smaller than the lower limit value of the preset range. And the laser is controlled to cut the trimming resistor on the bridge arm where the stretching resistor is located, so that the zero point output voltage after cutting is within a preset range. The zero-point output voltage is adjusted.

Description

Technical Field

[0001] This invention relates to the field of zero-point voltage adjustment for silicon piezoresistive pressure chips. Background Technology

[0002] Currently, high-temperature MEMS pressure sensors are based on the piezoresistive effect of single-crystal silicon. They utilize semiconductor planar technology to fabricate four strain gauges on an SOI silicon wafer, forming a closed Wheatstone bridge. An input voltage is applied to a set of diagonal points within the horizontal quadrilateral formed by the four strain gauges. At that time, an output voltage is generated at another set of diagonal points. ,like Figure 1 As shown, the output voltage is expressed as: ， In the formula, —Power supply voltage; —Bridge output voltage; High-temperature MEMS pressure sensors typically fabricate four strain resistors on an SOI silicon wafer using dry etching. Their equivalent circuit is as follows: Figure 1 As shown in the figure , , and Four etched resistor strips form a Wheatstone bridge. On a single-crystal silicon film, the stress region can be divided into a positive stress region and a negative stress region. In the design, the bridge arm resistors ( , The design is in the normal stress region, while the other pair of bridge arm resistors ( , The design is located in a negative stress region. When pressure is applied to the diaphragm, the change in strain resistance is proportional to the pressure.

[0003] When not subjected to external pressure, the sensor output should be as close to zero as possible; existing sensors generally require a zero-point output within ±5mV. Due to the precision limitations of photolithography and dry etching processes, the resistances of the four arms of the Wheatstone bridge cannot be perfectly identical, resulting in a significant zero-point output offset. Current methods for adjusting the zero-point output primarily involve adjusting the zero-point voltage using an external resistor network. However, this method has two drawbacks: 1. Adding an external resistor network to the sensor core increases the sensor's size; 2. The fixed resistors used in the external resistor network lack sufficient temperature resistance to meet the sensor's operational requirements. Summary of the Invention

[0004] The purpose of this invention is to solve the problems of existing methods that use external resistor networks to adjust the zero-point voltage, which increases the size of the sensor and the temperature resistance of the external resistor network is insufficient, thus failing to meet the requirements of the sensor. The invention proposes an in-chip resistance adjustment system for silicon piezoresistive pressure chips.

[0005] Silicon piezoresistive pressure chip on-chip adjustable resistance system, the system comprising strain gauges - The Wheatstone bridge is composed of strain gauges. - Connect them sequentially, for strain gauges and Connection point and strain gauge and When a power supply voltage is applied to the connection point, the strain gauge... and Connection point and strain gauge and A zero-point output voltage is generated at the connection point, which will affect the strain gauge. and As a tensile resistance, strain resistance and As a compressibility resistor, strain gauge , , and The resistance values ​​are all the same; The system also includes four sets of tuning resistors, a laser, and a four-probe testing system; In strain resistance A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the negative terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the zero-point output voltage and the negative terminal. The resistance values ​​of the four sets of adjustment resistors are all equal. Each set of adjustment resistors is composed of n resistors connected in parallel or n parallel resistors connected in parallel with m parallel resistors connected in series. n and m are both greater than or equal to 2. The four-probe testing system is used to measure the zero-point output voltage of the Wheatstone bridge. When the zero-point output voltage is greater than the upper limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the compression resistor is located. When the zero-point output voltage is less than the lower limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the tension resistor is located, so that the zero-point output voltage after cutting is within the preset range.

[0006] Preferably, each set of adjustment resistors includes a resistor. - ,resistance and resistance After parallel connection, the resistance and resistance After being connected in parallel, it is connected in series with the strain gauge on the same bridge arm, and the resistance... and The resistance values ​​are equal, the resistors and The resistance values ​​are equal.

[0007] Preferably, the input voltage 10V, resistor , , and The resistance value is 5040Ω. and The resistance values ​​are all 60Ω. and The resistance of each is 120Ω.

[0008] Preferably, the preset range is within ±5mV.

[0009] Preferably, the change in the zero-point output voltage after slicing is a change of 5mV / step within the range of 0mV to 44mV.

[0010] Preferably, the laser is a 1032nm infrared femtosecond laser.

[0011] The beneficial effects of this invention are: This invention addresses the zero-point output misalignment problem that occurs during the fabrication of high-temperature pressure sensors by designing an on-chip adjustable pressure chip to achieve zero-point adjustment within the chip, thereby reducing the sensor size and enabling it to operate in high-temperature environments.

[0012] The chip's normal pressure output is tested using a four-probe testing system at room temperature. The zero-point output offset is calculated. When the zero-point output is greater than the upper limit of the preset range (±5mV) or less than the lower limit, laser trimming is used for precise adjustment to reduce or eliminate zero-point drift, which can meet the sensor's zero-point output requirements. Attached Figure Description

[0013] Figure 1 The equivalent circuit diagram of the strain gauge on the silicon diaphragm; Figure 2 This is a schematic diagram of the on-chip silicon piezoresistive pressure chip and the adjustment resistor. Figure 3 Equivalent circuit diagram for adjusting the resistor; Figure 4 This is a diagram of the packaging structure of a high-temperature pressure sensor. Detailed Implementation

[0014] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0016] Example 1: In this embodiment, the resistance of the bridge is changed by laser scribing to bring the bridge into a balanced output state.

[0017] Silicon piezoresistive pressure chip on-chip adjustable resistance system, the system comprising strain gauges - The Wheatstone bridge is composed of strain gauges. - Connect them sequentially, for strain gauges and Connection point and strain gauge and When a power supply voltage is applied to the connection point, the strain gauge... and Connection point and strain gauge and A zero-point output voltage is generated at the connection point, which will affect the strain gauge. and As a tensile resistance, strain resistance and As a compression resistor, the resistor , , and The resistance value is 5040Ω; The system also includes four sets of tuning resistors, a laser, and a four-probe testing system; In strain resistance A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the negative terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the zero-point output voltage and the negative terminal. All four sets of adjustment resistors have equal resistance values, and each set includes a resistor. - ,resistance and resistance After parallel connection, the resistance and resistance After being connected in parallel, it is connected in series with the strain gauge on the same bridge arm, and the resistance... and The resistance values ​​are all 60Ω. and The resistance value is 120Ω; The four-probe testing system is used to measure the zero-point output voltage of the Wheatstone bridge. When the zero-point output voltage exceeds the upper limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the compression resistor is located. When the zero-point output voltage exceeds the lower limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the tension resistor is located, so that the zero-point output voltage after cutting is within the preset range.

[0018] like Figure 3 As shown, using strain gauges =5040Ω, 10V power supply as an example ( =10V), adjust the resistor value and adjustment method to obtain the following table: ; because and It is a stretch resistor; increasing the resistance will increase the sensor output. and It is a compression resistor; increasing its resistance will reduce the sensor output. Therefore, the overall impedance adjustment scheme for the chip is as follows: ; As shown in the table above, laser trimming can achieve a 5mV / level variation in the chip's zero-point output within the range of (0~44)mV, which can meet the sensor's zero-point ±5mV specification requirement.

[0019] Example 2: In this embodiment, the resistance of the bridge is changed by laser scribing to bring the bridge into a balanced output state.

[0020] Silicon piezoresistive pressure chip on-chip adjustable resistance system, the system comprising strain gauges - The Wheatstone bridge is composed of strain gauges. - Connect them sequentially, for strain gauges and Connection point and strain gauge and When a power supply voltage is applied to the connection point, the strain gauge... and Connection point and strain gauge and A zero-point output voltage is generated at the connection point, which will affect the strain gauge. and As a tensile resistance, strain resistance and As a compressibility resistor, strain gauge , , and The resistance values ​​are all the same; The system also includes four sets of tuning resistors, a laser, and a four-probe testing system; In strain resistance A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the negative terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the zero-point output voltage and the negative terminal. All four sets of adjustment resistors have equal resistance values, and each set includes a resistor. - ,resistance and resistance After being connected in parallel, they are connected in series with strain gauges on the same bridge arm; The four-probe testing system is used to measure the zero-point output voltage of the Wheatstone bridge. When the zero-point output voltage exceeds the upper limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the compression resistor is located. When the zero-point output voltage exceeds the lower limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the tension resistor is located, so that the zero-point output voltage after cutting is within the preset range.

[0021] resistance - The change in zero-point output voltage after slicing varies depending on the resistance value. Therefore, the resistor value can be set according to the desired voltage level for each zero-point output adjustment range. - The resistance value.

[0022] from Figure 2As can be seen, the positions of the adjustment resistors and silicon piezoresistive pressure chip on the circuit board are such that, since all four sets of adjustment resistors are designed outside the sensitive resistor area, their adjustment does not affect the sensor's accuracy, the temperature performance of the sensitive resistor, or other indicators; it only shifts the sensor's output curve. When the zero-point output of the sensor and chip is too large or exceeds the preset range, laser trimming can be used for precise adjustment based on the output situation, reducing or eliminating zero-point drift and meeting the sensor's temperature drift requirements. This increases the chip's applicability. By designing adjustment resistors within the chip, the influence of these factors can be eliminated, thereby improving the sensor's output performance, yield, and versatility.

[0023] The laser used is a 1032nm infrared femtosecond laser. By adjusting the laser power, it is possible to cut the top silicon layer of 1μm while ensuring that the buried layer of SOI silicon wafer is not damaged.

[0024] High-temperature pressure sensor packaging structure as follows Figure 4 As shown, Figure 4 The chip mentioned refers to the silicon piezoresistive pressure chip described in this embodiment: 1. Chip: The pressure-sensitive chip is made of SOI material and uses the piezoresistive principle for pressure sensing. The front is sealed with glass using an electrostatic sealing process, and there are through holes where the glass is aligned with the chip electrodes.

[0025] 2. The conductive silver paste in the figure is filled into the glass through hole by dispensing. The specific operation is as follows: insert the needle connected to the dispensing machine into the hole of the sensitive chip, set the dispensing machine parameters, and observe that the paste in the hole reaches 1 / 2 to 2 / 3 of the hole depth to complete the filling. The paste can be conductive paste such as silver paste or silver-palladium paste.

[0026] 3. Chip and socket connection method: First, fit the glass preform onto the sintering surface of the socket. Then, align the four holes of the chip filled with silver paste downwards with the four leads and place it onto the socket. Finally, install the socket with the preform and chip on a special graphite fixture. Place it in a sintering furnace and sinter at 400~500℃ for 30 minutes, then allow it to cool naturally.

[0027] 4. The purpose of the support ring in the figure is to support the compensation plate.

[0028] 5. The outer casing material shown in the picture is stainless steel.

[0029] 6. The lead wire material in the figure is Kovar alloy, with an outer gold plating, and is connected to the tube socket assembly by glass sintering.

[0030] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A silicon piezoresistive pressure chip on-chip adjustable resistance system, the system comprising a strain gauge resistor. - The Wheatstone bridge is composed of strain gauges. - Connect them sequentially, for strain gauges and Connection point and strain gauge and When a power supply voltage is applied to the connection point, the strain gauge... and Connection point and strain gauge and A zero-point output voltage is generated at the connection point, which will affect the strain gauge. and As a tensile resistance, strain resistance and As a compressibility resistor, strain gauge , , and The resistance values ​​are all the same; Its features are, The system also includes four sets of tuning resistors, a laser, and a four-probe testing system; In strain resistance A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the positive terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the negative terminal of the zero-point output voltage and the strain gauge. A set of adjustment resistors is connected in series between the zero-point output voltage and the negative terminal. The resistance values ​​of the four sets of adjustment resistors are all equal. Each set of adjustment resistors is composed of n resistors connected in parallel or n parallel resistors connected in parallel with m parallel resistors connected in series. n and m are both greater than or equal to 2. The four-probe testing system is used to measure the zero-point output voltage of the Wheatstone bridge. When the zero-point output voltage is greater than the upper limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the compression resistor is located. When the zero-point output voltage is less than the lower limit of the preset range, the laser is controlled to cut the adjustment resistor on the bridge arm where the tension resistor is located, so that the zero-point output voltage after cutting is within the preset range.

2. The silicon piezoresistive pressure chip on-chip resistance adjustment system according to claim 1, characterized in that, Each set of adjustment resistors includes a resistor. - ,resistance and resistance After parallel connection, the resistance and resistance After being connected in parallel, it is connected in series with the strain gauge on the same bridge arm, and the resistance... and The resistance values ​​are equal, the resistors and The resistance values ​​are equal.

3. The silicon piezoresistive pressure chip on-chip resistance adjustment system according to claim 1 or 2, characterized in that, Input voltage 10V, resistor , , and The resistance value is 5040Ω. and The resistance values ​​are all 60Ω. and The resistance of each is 120Ω.

4. The silicon piezoresistive pressure chip on-chip resistance adjustment system according to claim 1, characterized in that, The preset range is ±5mV.

5. The silicon piezoresistive pressure chip on-chip resistance adjustment system according to claim 3, characterized in that, The change in the zero-point output voltage after slicing is 5mV / step within the range of 0mV to 44mV.

6. The silicon piezoresistive pressure chip on-chip resistance adjustment system according to claim 1, characterized in that, The laser is a 1032nm infrared femtosecond laser.

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