JPH04332837A - Manufacture of hydraulic pressure sensor - Google Patents

Abstract

PURPOSE:To reduce an error due to a change in temperature without enlarging the diameter of a seal film, by eliminating the effect of the change in temperature on a pressure transmitting medium by making negative 4 temperature coefficient of an output of a pressure-sensitive semiconductor before incorporation in a container. CONSTITUTION:A pressure-sensitive semiconductor chip 1 has a diaphragm whereon strain gages are formed and an output signal processing circuit of a bridge composed of the strain gages. A seal film 2, a spacer 3 supporting this film, a container stem 4 supporting the chip 1 and a cap 5 are joined together and a pressure transmitting medium 9 is sealed hermetically in a space formed by the seal film 2, the spacer 3 and the stem 4. A liquid for measuring a pressure entering a container through hole 15 of the cap 5 applies the pressure to the diaphragm of the chip 1 through the intermediary of the seal film 2 and the medium 9. At this time, a temperature coefficient of an output before incorporation in the container is made negative by adjustment of the output signal processing circuit, so as to offset an error occurring in the medium 9 due to a change in temperature. In this way, precision is made high, it is made unnecessary to enlarge the dimensions of the seal film 2 and a sensor can be made small in size.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to a diaphragm provided in a semiconductor element through a liquid containing a pressure to be measured, and the resistance value of a strain gauge resistor formed on the diaphragm changes due to deformation of the diaphragm. The present invention relates to a method of manufacturing a hydraulic pressure sensor that detects pressure by doing so.

0002

[Prior Art] Conventionally, in semiconductor hydraulic pressure sensors for detecting water pressure or oil pressure, if a pressure medium such as water or oil comes into direct contact with the pressure-sensitive chip, the circuit integrated in the chip may be contaminated or damaged. Therefore, the structure is such that insulating silicone oil or silicone gel is sealed to indirectly transmit the media pressure of water or oil. The pressure medium and the silicone oil or gel are separated by a corrugated sealing membrane made of a highly corrosion-resistant material such as elastic stainless steel SUS316L. This sealing film protects the chip from the pressure medium and has the function of absorbing fluid pressure changes due to volumetric expansion and contraction associated with temperature changes of the enclosed silicone oil and silicone gel. However, if the deformation of the seal membrane is not sufficient in response to the volumetric expansion of the enclosed medium when the temperature rises, the stress of the seal membrane becomes large and the hydraulic pressure of the enclosed medium increases. This increase in fluid pressure causes errors, so by increasing the diameter of the seal membrane, the amount of deformation of the seal membrane is sufficiently increased, and the stress of the seal membrane is reduced, thereby reducing the temperature dependence of the sensor output. Ta.

0003

Problems to be Solved by the Invention Such hydraulic pressure sensors are normally used in a temperature range of -20°C to 100°C. In order to eliminate the influence of stress on the seal membrane due to volumetric expansion and contraction of the enclosed pressure transmission medium due to temperature changes within this range, the effective (movable) diameter of the seal membrane is increased to increase the hydraulic pressure of the pressure transmission medium. must be kept within a few percent of full scale. On the other hand, there is a demand for products to be smaller and lighter, and for this purpose it is necessary to reduce the diameter of the seal membrane. However, as the diameter of the seal membrane is made smaller, the amount of deformation is reduced, so the fluid pressure changes due to temperature changes are large, and the diameter of the seal membrane is reduced by several percent. There was a problem in which it was not possible to maintain an error within In addition, it is possible to increase the amount of deformation by making the seal membrane thinner or by making it flat from a corrugated one, but these methods generate large distortions in the seal membrane material and cause the offset voltage to shift. be. Therefore, it was necessary to increase the diameter of the seal membrane.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a hydraulic pressure sensor that solves the above problems and reduces errors due to temperature changes without increasing the diameter of the seal membrane.

[0005]

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing a hydraulic pressure sensor of the present invention includes a diaphragm portion in which a strain gauge is formed and an output signal processing circuit of a bridge made up of the strain gauge. A semiconductor element whose output after processing has a predetermined negative temperature coefficient is supported on the bottom plate of the container, and a sealing film fixed to the upper lid of the container having an opening is connected to the semiconductor element supporting surface of the bottom plate of the container. The space between them shall be sealed with a pressure transmission medium. Then, it is effective to adjust the resistance value of the thin film resistor connected in series to the diffused resistor in the output signal processing circuit so that the output has a predetermined negative temperature coefficient.
It is effective to perform this adjustment by laser trimming. It is also effective to use precipitation hardening stainless steel as the material for the seal membrane.

[0006]

[Operation] If the output signal produced by processing the output signal of the gauge resistance bridge is made to have no temperature dependence by processing the output signal in the processing circuit, the semiconductor element is placed in a container and then the pressure transmission medium is enclosed. , the output has a positive temperature coefficient due to changes in hydraulic pressure due to expansion and contraction of the pressure transmission medium due to temperature changes. If the output of the output signal processing circuit before being placed in the container has a negative temperature coefficient that offsets its positive temperature coefficient, the sensor output after being placed in the container will not be affected by the temperature change of the pressure transmission medium. It disappears. The negative temperature coefficient of such an output is
In order to compensate for the temperature dependence of the strain gauge, this can be easily obtained by increasing the resistance value by trimming a thin film resistor connected in series with a diffused resistor having a large positive resistance temperature coefficient in the output signal processing circuit. In addition, by using precipitation hardened stainless steel with high tensile strength as the material for the seal membrane, the occurrence of distortion in the seal membrane is reduced, and the temperature dependence of the sensor output due to temperature changes in the pressure transmission medium is reduced. can.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of a hydraulic pressure sensor manufactured according to the present invention. In order to protect the chip from waves, a thin corrugated sealing membrane 2 made of precipitation-hardened stainless steel such as SUS630 and having an effective diameter of 10mm and a thickness of 30μm is provided, and a spacer 3 is used to support this. 2. The spacer 3, the container stem 4, and the cap 5 are connected to each other by welding or silver soldering. The pressure sensitive chip 1 is attached to the adhesive 6 via the pedestal 7.
The gauge resistance output signal processing circuit on the pressure sensitive chip 1 and the lead wire 8 are connected by a conductive wire 13. Then, silicone oil, for example, is injected from the injection pipe 10 as the pressure transmission medium 9 into the space surrounded by the seal membrane 2, the spacer 3, and the stem 4.
The injection tube is sealed off. The liquid whose pressure is to be measured enters the container through the hole 15 in the cap 5, and the pressure is applied to the sealing membrane 2.
is applied to the diaphragm of the pressure-sensitive chip 1 via the pressure transmission medium 9. FIG. 2 is a circuit diagram of the output signal processing circuit, and the double squares are diffused resistors formed by diffusing impurities into the chip. A power supply voltage is applied from the VCC terminal to the connection point A between the gauge 21 and the gauge 23 of the bridge circuit constituted by the strain gauges 21 to 24, and the connection point B between the gauge 22 and the gauge 24 is connected to earth potential by the GND terminal. Connected. A connection point C between the gauge 21 and the gauge 22 of the bridge circuit is on one side of the bridge output terminal, and the potential at point C decreases due to pressure applied from the surface of the diaphragm of the pressure-sensitive chip 1 on which the strain gauge is formed. This potential is impedance-converted by a voltage follower circuit including an operational amplifier OP1. A differential amplifier is constituted by operational amplifier OP1 and resistors 35, 36, 43, and 51. Connection point D between gauge 24 and gauge 23 of the bridge circuit is the other side of the bridge output terminal, and the potential at point D rises due to pressure applied from the strain gauge surface. A differential voltage between this potential and the output potential of OP1 is amplified by this differential amplifier and output to the Vout terminal. The amplification of this circuit, ie the pressure sensitivity of the sensor, is adjusted by trimming the thin film resistor 35. The resistor 51 is a variable resistor provided outside the chip, and by changing the resistance value, the pressure sensitivity can be adjusted similarly to the resistor 35. The diffusion resistance 43 is, for example, 3000 to 4000 ppm.
It has a large positive temperature dependence of /℃, and has a thin film resistance of 3
6 are connected in parallel, the amplification degree of the differential amplifier is made to have a positive temperature dependence, and the negative temperature dependence of the signal voltage caused by pressurization of the strain gauge bridge is compensated for. The thin film resistors 31 and 32, the resistors 41 and 42, and the variable resistor 52 provided outside the chip are resistors related to zero potential compensation and adjustment. The resistors 41 and 42 have positive temperature coefficients like the resistor 43, and by trimming either of the thin film resistors 33 or 34, which are connected in series and have a temperature coefficient one order of magnitude smaller, the sensor output terminal V
It is possible to adjust the temperature characteristics of the zero potential of out in both positive and negative directions. Therefore, first, the resistor 32 was trimmed using a laser to lower the output level to a predetermined value, and then the resistor 33 was trimmed and made larger to restore the output level to the original value and make it temperature dependent in the negative direction. . FIG. 3 shows the temperature dependence of the output characteristics measured at this stage, and the output of the Vout terminal connected to the operational amplifier OP2 has a temperature coefficient of 15 mV/° C. in the negative direction.

The metal stem 4 supporting the pressure sensitive chip 1 having such an output temperature coefficient and the spacer 3 combined with the sealing film 2 are welded together, and silicone oil 9 having a viscosity of 100 cSt is injected through the injection pipe 10. Seal membrane 2, spacer 3
, filling the hollow formed by the stem 4 and inserting the injection tube 10
were welded and sealed. A hydraulic pressure sensor was manufactured in this way.

FIG. 4 shows the temperature dependence of the output characteristics of a hydraulic pressure sensor in which a pressure sensitive chip with no temperature dependence of output is assembled in the same manner without laser trimming of the resistor 32. As shown in the figure, this case has an output temperature coefficient of about 15 mV/°C in the positive direction. Therefore, in a hydraulic sensor incorporating the pressure-sensitive chip 1 having the temperature dependence shown in FIG. As shown in FIG. 5, the output characteristics were consistent at each temperature. By adjusting the span level of this pressure sensor using externally attached resistors 51 and 52, a compact hydraulic pressure sensor with even higher accuracy can be manufactured.

0010

[Effects of the Invention] According to the present invention, errors caused by expansion and contraction of the pressure transmission medium during temperature changes are offset by making the temperature coefficient of the output of the pressure-sensitive semiconductor chip itself negative before it is incorporated into the container. By doing so, we were able to obtain a highly accurate hydraulic pressure sensor whose output characteristics do not change even when the temperature changes. Therefore, it is no longer necessary to increase the size of the seal membrane, and it has become possible to downsize hydraulic sensors such as water pressure sensors or oil pressure sensors. Furthermore, since the temperature coefficient of the output can be easily adjusted by laser trimming of the thin film resistor, the industrial effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a hydraulic pressure sensor in which the present invention is implemented.

[Figure 2
]Circuit diagram of a hydraulic pressure sensor in which the present invention is implemented

[Figure 3] Output characteristic diagram with the temperature of the pressure-sensitive chip as a parameter after diffusion resistance trimming

[Figure 4] Output characteristic diagram with temperature as a parameter for a hydraulic pressure sensor using a pressure-sensitive chip without trimming the diffused resistance

[Fig. 5] Output characteristic diagram using temperature as a parameter of a hydraulic pressure sensor manufactured according to an embodiment of the present invention.

[Explanation of symbols]

1 Pressure-sensitive semiconductor chip 2 Seal membrane 3 Spacer 4 Stem 5 Cap 7 Pedestal 9 Pressure transmission medium 10 Injection tube 15 Hole

Claims (4)

[Claims] Claim 1: A semiconductor element comprising a diaphragm portion on which a strain gauge is formed and an output signal processing circuit of a bridge made up of the strain gauge, and whose output after processing has a predetermined negative temperature coefficient is mounted on the bottom plate of a container. A method of manufacturing a hydraulic pressure sensor, comprising: sealing a pressure transmission medium in a space between a sealing membrane fixed to a container top lid having an opening and a semiconductor element supporting surface of a container bottom plate. 2. The method of manufacturing a hydraulic pressure sensor according to claim 1, wherein the resistance value of a thin film resistor connected in series with the diffused resistor in the output signal processing circuit is adjusted so that the output has a predetermined negative temperature coefficient. 3. The method of manufacturing a hydraulic pressure sensor according to claim 2, wherein the resistance value of the thin film resistor is adjusted by laser trimming. 4. The method of manufacturing a hydraulic pressure sensor according to claim 1, wherein precipitation hardening stainless steel is used as the material of the sealing film.