JPH0257933A - Pressure sensor - Google Patents

Abstract

PURPOSE:To perform stable pressure measurement by conducting a current through heating resistors, heating a semiconductor single crystal substrate, and controlling the temperature at a constant value. CONSTITUTION:Metallic film resistors comprising thin nickel films are evaporated on a silicon chip 11 of a diaphragms 11a, and heating resistors Rh1 and Rh2 are formed. A Wheatstone bridge is formed with four gage resistors R1-R4 which are formed on the diaphragm 11. The diaphragm 11a including the resistors R1-R4 is heated with the resistors Rh1 and Rh2, and the temperature is controlled at a constant temperature. Therefore, the temperature of a strain- gage forming part is kept at the constant temperature which is not affected with temperature in an outer environment. The strain gage outputs a specified electric signal corresponding to only pressure change, and stable pressure measurement can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a pressure sensor for measuring fluid pressure, and particularly to a pressure sensor using a strain gauge formed in a semiconductor single crystal substrate.

[Prior Art] In recent years, semiconductor pressure sensors that utilize the piezoresistance effect, in which the resistivity of a semiconductor crystal changes when an external force is applied to the semiconductor crystal, have been used in various fields including automobiles as small, lightweight, and highly sensitive pressure sensors. It is used in As this type of semiconductor pressure sensor, a diffusion type semiconductor pressure sensor is known, in which a thin film diaphragm is processed and formed in the center of a semiconductor single crystal substrate such as silicon, and a diffused resistance layer is formed on this diaphragm to form a strain gauge. In particular, silicon pressure sensors using a diaphragm on a silicon single crystal substrate are being utilized.

In silicon pressure sensors, fluid pressure is measured by detecting changes in diffusion resistance in response to strain due to fluid pressure applied to the diaphragm. Usually, the strain is such that the resistance value increases or decreases with respect to fluid pressure. A pair of gauges constitutes a Wheatstone bridge, which is connected to a constant current or constant voltage power source to convert it into an electrical signal and measure fluid pressure.

Semiconductor pressure sensors react sensitively to external heat and mechanical strain, so they are designed to be unaffected by these, and to avoid non-linearity in semiconductors due to external environmental temperature changes, including temperature changes in the fluid being measured. A temperature compensation circuit is connected to compensate for temperature characteristics. For example, in the Wheatstone bridge for the silicon pressure sensor mentioned above, a compensation resistor is connected in series or parallel to the gauge resistor,
One method is to give the feedback resistance of an amplifier circuit made up of operational amplifiers a temperature characteristic.

Furthermore, as described in Japanese Patent Publication No. 59-41134,
There is also a technology that performs temperature compensation by inserting a pressure-insensitive gauge resistor and a fixed resistor connected in parallel into the feedback circuit of the output stage operational amplifier, and this is expected to provide highly accurate temperature compensation.

[Problem to be solved by the invention]

The above technique has the advantage that the temperature compensation resistor is the same gauge resistor as the strain gauge and can be formed in the same step when forming the strain gauge on the semiconductor single crystal substrate. However, it is not easy to accurately adjust the resistance value of the temperature-compensating gauge resistor, that is, the diffused resistor, to a predetermined value. Further, trimming is also required to adjust the resistance value of the fixed resistor connected in parallel. Furthermore, although the above-mentioned technique can respond to temperature changes in the fluid to be measured to a certain extent, it remains a passive response and there is a limit to the range of temperature changes that can be accommodated.

Therefore, an object of the present invention is to actively heat the strain gauge forming part and control its temperature to a constant temperature, so that stable pressure measurement can be performed even for a fluid to be measured that has a large temperature change range. do.

[Means for Solving the Problems] In order to achieve the above object, the present invention has one surface as a pressure-receiving surface for the reference pressure, and the other surface as a pressure-receiving surface for the fluid to be measured through a communication passage. In a pressure sensor that detects the pressure of the fluid to be measured by forming a strain gauge in a semiconductor single crystal substrate as a pressure receiving surface and converting the strain generated in the strain gauge into an electric signal, The heating resistor is provided with a heating resistor disposed on the semiconductor single crystal substrate, and is connected to a heating control circuit that energizes the heating resistor to control heating of the semiconductor single crystal substrate to a constant temperature.

In particular, a silicon substrate formed with a diaphragm portion that is arranged to close a communication path that communicates with a fluid source to be measured and introduces the fluid to be measured, and that deforms in response to pressure fluctuations of the fluid to be measured; a strain gauge formed on the diaphragm portion, and a metal film resistor attached to the diaphragm portion in proximity to the strain gauge, and heating the diaphragm portion to a constant temperature by applying electricity to the metal film resistor. It is recommended to connect a heating control circuit to control the temperature.

[Operation] In the pressure sensor configured as described above, the reference pressure is applied to one pressure receiving surface of the semiconductor single crystal substrate, and the measured fluid pressure from the measured fluid source is applied to the other pressure receiving surface. . These pressure differences cause strain in the semiconductor single crystal substrate containing the strain gauge, and this strain is converted into an electrical signal by the strain gauge.

In this case, a heating resistor provided on the semiconductor single-crystal substrate near the strain gauge is energized and heated by the heating control circuit, and the semiconductor single-crystal substrate is heated to a constant temperature higher than, for example, the maximum temperature of external environmental temperature changes. controlled. Then,
The temperature of the strain gauge forming portion is maintained at a constant temperature that is not affected by the external environmental temperature, and the strain gauge outputs a predetermined electrical signal in response only to pressure changes.

[Embodiments] Preferred embodiments of the pressure sensor of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the pressure sensor of the present invention.
A silicon wheel crystal substrate is used as the semiconductor single crystal substrate according to the present invention, and the central portion of the square silicon chip 11 is processed into a thin film with a thickness of several + μm to form a diaphragm lla. Four strain gauges of a diffused resistance layer are formed on this diaphragm lla by diffusion of boron or the like. That is,
As shown in FIG. 2, diffused resistors, ie, gauge resistors R1 to R4, are formed in the center of the diaphragm lla.

These gauge resistors R1 to R4 have a high gauge factor, and the gauge resistors R1, R3 and the gauge resistors R2, R4 are arranged opposite each other, and when pressure is applied to the diaphragm lla, the gauge resistors R1, R3 have a positive Resistance value change (R+ΔR
) occurs, and a negative resistance value change (
R-ΔR) are placed at the positions where R-ΔR) occurs.

As is clear from FIG. 2, the diaphragm 11a
Heating resistors according to the present invention are arranged on both sides of the upper gauge resistors R1 to R4. That is, a metal film resistor such as a thin nickel film is deposited on the silicon chip 11 on the diaphragm 11a to form the heating resistor Rh1. Rh2 is formed. These heating resistors Rhl and Rh2 have positive temperature coefficients of resistance, and their gauge factors are much smaller than those of R1 to R4, so that changes in resistance due to strain are negligible. Note that the number of these gauge resistors R1 to R4 is not limited to four, but may be a desired number as necessary.

The silicon chip 11 having the above structure is a cylindrical body made of the same material, ie, silicon, and is joined by solder to a pedestal 12 whose end surface has gold vapor-deposited thereon. Thus, one opening of the hollow part of the pedestal 12 is connected to the silicon chip 1.
It faces the back surface of the first diaphragm 11a.

The pedestal 12 to which the silicon chip 11 is bonded is made of Kovar, which has a disc shape with gold vapor-deposited on the surface opposite to the bonding surface of the silicon chip 11, and has a communicating hole in the center and a plurality of holes around it. It is soldered to the center of the stem 13.

Therefore, the hollow portion of the base 12 and the communication hole of the stem 13 match and communicate with each other. A hole with a larger diameter is provided around the communication hole of the stem 13, and one end of the pressure vibrator 23 is fitted into this hole.

Miki's lead bin 14 is installed in the hole around the communicating hole of the stem 13.
(Only the inner tree is shown in Figure 1) is inserted through the gauge resistor R formed on the diaphragm lla.
1, R2, gauge resistance R1, R4 and gauge resistance R3,
Each of R4 is brought together at both ends and wire-bonded to each of the three lead pins 14 using a gold wire. Further, the connection point between the gauge resistors R2 and R3 is grounded via a doped pin 15. That is, a Wheatstone bridge is formed by the four gauge resistors R1 to R4 formed on the diaphragm 11a, and its input/output terminals are connected to an external circuit via the lead pin 14 and the terminal 24 connected thereto. It is configured.

Heating resistance Rh1. One end of each Rh2 is grounded via a lead pin 15, the other end is connected to a lead pin 16, and is connected to a heating control circuit to be described later via a terminal 24.
It is configured to be energized as appropriate to generate a predetermined amount of heat.

The gaps between the hole in the stem 13 and the lead bins 14 to 16 are hermetically sealed. Then, the flange portion of the cup-shaped metal case 21 is joined around the stem 13 by resistance welding, and the stem 13 and the case 2
1, a sealed vacuum reference pressure chamber 25 is defined between the two. Incidentally, a communication hole is drilled in the case 21, and after joining the stem 13 and making the inside of the reference pressure chamber 25 a vacuum state, or after filling the reference pressure chamber 25 with gas at a predetermined pressure, the communication hole is plugged with solder. You can also do this.

The sensor element configured as described above includes an inch housing 31 having a tubular connecting portion 31a in the center and an accommodating portion 31b having a large diameter hole communicating with a communication hole in the connecting portion 31a; It is housed in a cup-shaped outer housing 32 that is joined to the outer housing 32, and is filled with resin 33.

At this time, the open end of the pressure vibrator 23 faces the open end of the communication hole of the connecting portion 31a with the filter 34 in between, and the O-ring 35 is inserted into the gap between the accommodating portion 31b and the pressure vibrator 23.

One surface of the diaphragm 11a of the silicon chip 11, that is, the front surface, becomes a pressure receiving surface for the reference pressure in the reference pressure chamber 25, and the other surface, that is, the back surface, serves as a pressure receiving surface for the pedestal 12 and the stem 13.
It communicates with a fluid pressure source (not shown) through the communication hole, the pressure guiding vibrator 23, and the connecting portion 31a of the inner housing 31, and serves as a pressure receiving surface for fluid pressure.

The connection part 31a of the pressure sensor is connected to a fluid pressure source, for example, an intake pipe of an internal combustion engine, and the fluid pressure, that is, the intake pipe pressure, that is, the intake negative pressure is applied to the diaphragm lla of the silicon chip 11.
transmitted to. When intake negative pressure is transmitted to the back surface of diaphragm lla, gauge resistance R1 on diaphragm lla
A stress corresponding to the pressure difference between the pressure inside the reference pressure chamber 25 and the pressure inside the reference pressure chamber 25 is generated between R4 and R4. In this embodiment, since the inside of the reference pressure chamber 25 is set to a vacuum, the stress corresponds to the absolute value of the intake pipe pressure. According to this stress, the resistivity of the gauge resistors R1 to R4 changes due to the piezoresistance effect.

On the other hand, a constant voltage is applied to the Wheatstone bridge made up of these gauge resistors R1 to R4 by a piece of lead bin 14, and the gauge resistors R1 to R4
A voltage corresponding to the change in resistivity of the lead bin 14 is outputted via the other two lead bins 14 and the terminal 24. Although a gas flow is generated due to the pressure difference between the connecting portion 31a and the inside of the pressure-guiding vibrator 23, the filter 34 prevents dust and the like from entering the diaphragm lla portion.

In addition, current is supplied to the heating resistors Rhl and Rh2 via the lead bin 16 by a heating control circuit, which will be described later, and generates a predetermined amount of heat, which heats the nearby gauge resistors R1 to R4 and controls them to a constant temperature. . That is, the gauge resistors R1 to R4 are heated to a constant temperature that is not affected by temperature changes in the external environment including the fluid to be measured.

FIG. 3 shows an electrical circuit diagram of the pressure sensor, in which the Wheatstone bridge composed of the gauge resistors R1 to R4 is connected to resistors R5 to R8 and operational amplifiers OPI and OP.
A differential amplifier circuit consisting of 2 is connected to the constant voltage power supply VCC.
It is connected to the. As a result, the output of the Wheatstone bridge is amplified to become the output VO, and a predetermined impedance conversion is performed.

Further, a Wheatstone bridge is separately constituted by the resistors R11, R12 and R13 including the heating resistors Rhl and Rh2 having a positive resistance temperature coefficient, and the heating control circuit 3 is constituted together with the operational amplifier OP3 and the transistor Tri.

In the heating control circuit 3, the heating resistor Rh1. A current is supplied to Rh2 to generate heat, which heats the diaphragm lla including the nearby gauge resistors R1 to R4. And heating resistance Rhl
, Rh2 increase in resistance as the temperature rises, and when a predetermined heating temperature is reached and the equilibrium condition of the Wheatstone bridge is satisfied, the output of the operational amplifier OP3 becomes a low level and the transistor Tri is cut off, causing the heating resistor Rh+.

The exothermic action of Rh2 stops.

On the other hand, a diaphragm ll including gauge resistors R1 to R4
When the temperature of a decreases, and therefore the temperature of the heating resistors Rhl and Rh2 decreases, and the resistance value decreases, the equilibrium condition of the Wheatstone bridge collapses, the output of the operational amplifier OP3 becomes high level, the transistor Tri is driven, and the above-mentioned state occurs. Similarly, power supply current is supplied until a predetermined heating temperature is reached.

The diaphragm Ila including the gauge resistors 11i% R1 to R4 is heated and controlled to a constant temperature by the heating resistors Rhl and Rh2 as follows. That is, the heating resistance Rhl
, Rh2 resistance value (respectively Rh+.

The temperature characteristics of Rh2) are expressed by the following equation.

Rhl Tomi Rh. (1+αT).

Rh2 =Rh2゜(1+αT) Here, Rhl. , Rh2° is the reference resistance value of Rh, , Rh2, T is the temperature of both, and α is the temperature coefficient.

Then, from the Wheatstone bridge equilibrium condition, R+5
(Rh+a+Rh*.)(1+αT)=R11R12, T= [RIIRI2-RI3(Rh+o+Rhzo)]/R
+sα.

Here, R11+R1□+R13 are each resistance R11
゜Resistance values of R12 and R13 are shown.

The temperature T of the heating resistors Rhl and Rh2 can be controlled to a constant temperature by the heating control circuit 3 regardless of the ambient temperature.

Therefore, the resistance value Rth n is set so that this temperature T becomes a predetermined value higher than the upper limit of the operating temperature range as a pressure sensor.
R12+Rl! +Rh By setting lo+Rh20 and the temperature coefficient α, the gauge resistors R1 to R4 arranged near the heating resistors Rhl and Rh2 are controlled to a constant temperature higher than the above upper limit value. In other words, the heating temperatures of the heating resistors Rhl and Rh2 are controlled so that the temperatures of the nearby gauge resistors R1 to R4 are maintained at a constant temperature higher than the upper limit of the ambient temperature at the time of pressure detection.

Gauge resistors R1 to R4 have large gauge factors and predetermined temperature characteristics, but since the ambient temperature at the time of pressure detection is heated to a level that does not cause resistance value fluctuations due to temperature characteristics, the gauge resistors R1 to R4 represent resistance values using only the detected pressure as a parameter. That is, the temperature of the gauge resistors R1 to R4 is maintained at a constant temperature higher than the ambient temperature during use, and therefore the output of the Wheatstone bridge is . is a function of pressure only.

The circuit elements including operational amplifiers OPI to OP3 that constitute the electric circuit shown in FIG. 3 are mounted on a thick film resistance board (not shown), and together with the pressure sensor shown in FIG. 1 are mounted on a printed wiring board (not shown). The senna unit is configured by disposing the senna unit. This sensor unit is used, for example, to measure intake pipe pressure of an internal combustion engine. In addition, I of the above electric circuit
It is also possible to further advance the C conversion and incorporate it into the pressure sensor shown in FIG.

In the above example, the heating resistor Rhl.

A metal thin film resistor with a low gauge factor is used as Rh2, and pressure is applied to the diaphragm lla, causing the heating resistor Rh.
Even when strain occurs in L and Rh2, the resistance value does not change, and the resistance value is substantially a function only of temperature. However, it is also possible to use the same diffused resistors as the gauge resistors R1 to R4 as the heating resistors Rhl and Rh2. However, since the gauge resistance, that is, the diffused resistance, naturally has a large gauge factor, it must be configured to reduce this.

For example, as shown in Fig. 4, a heating resistor Rhl is placed at a portion where the resistance value increases when pressure is applied in a predetermined direction.
It is necessary to form the heating resistor Rh2 in a portion where the resistance value decreases and arrange it so that the changes in both resistance values in response to pressure changes are canceled out. As a result, the heating resistance Rhl,
The overall resistance value of Rh2 does not change with respect to pressure changes, and is a function only of temperature. Therefore, silicon chip 11
When forming the gauge resistors R1 to R4, the heating resistors Rhl and Rh2 can be formed at the same time.

[Effects of the Invention] Since the present invention is configured as described above, it produces the effects described below.

That is, the heating resistor is controlled to a constant temperature by the heating control circuit, and the strain gauge formed on the semiconductor single crystal substrate can be maintained at a constant temperature higher than the upper limit temperature in the operating state. Stable pressure measurement can be performed without being affected by environmental temperature changes.

Further, even if moisture is mixed in the fluid to be measured, the semiconductor single crystal substrate is kept in a high-temperature atmosphere by the heating resistor, so it will not freeze.

In particular, with metal film resistors attached to the diaphragm, the resistance value can be heated to a constant temperature as a function only of the temperature coefficient, so it is stable without being affected by pressure fluctuations in the diaphragm. Heating control can be performed.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of an embodiment of the pressure sensor of the present invention, FIG. 2 is a plan view of a silicon chip in the pressure sensor of the above embodiment, and FIG. 3 is an electrical circuit diagram of the pressure sensor of the above embodiment. , FIG. 4 is a plan view of a silicon chip showing another embodiment of the heating resistor in the pressure sensor of the above embodiment. 11...Silicon chip (semiconductor single crystal substrate) 11a
...Diaphragm. 12...Pedestal. 14.15.16...Lead bin. 23... pressure vibration. 25...Reference pressure chamber. R1 to R4... Gauge resistance.

Claims (2)

[Claims] (1) A strain gauge is formed in a semiconductor single crystal substrate, with one surface as a pressure receiving surface for the reference pressure and the other surface as a pressure receiving surface for the pressure of the fluid to be measured and communicating with the source of the fluid to be measured via a communication path. , a pressure sensor that detects the pressure of the fluid to be measured by converting strain occurring in the strain gauge into an electrical signal, comprising a heating resistor disposed on the semiconductor single crystal substrate in proximity to the strain gauge; A pressure sensor characterized in that a heating control circuit is connected to conduct electricity to a resistor to control heating of the semiconductor single crystal substrate to a constant temperature. (2) A silicon substrate formed with a diaphragm portion that is arranged to close a communication path that communicates with a fluid source to be measured and introduces the fluid to be measured, and that deforms in response to pressure fluctuations of the fluid to be measured; and the silicon substrate. A strain gauge formed on the diaphragm part in the diaphragm part, and a metal film resistor attached to the diaphragm part in proximity to the strain gauge, and the metal film resistor is energized to control heating of the diaphragm part to a constant temperature. A pressure sensor characterized by being connected to a heating control circuit.