JPH01199476A - Pressure sensor - Google Patents

Abstract

PURPOSE:To enable the constitution of resistors included in a compensation circuit without increasing resistor elements and processes such as soldering and the like in number by a method wherein resistors of the compensation circuit formed of the same material as a distortion gauge are constructed on a diaphragm. CONSTITUTION:A thin film pressure sensor is provided, where a distortion gauge 3 is provided to the rear of a diaphragm pressure sensing face through an insulating film 2 and compensation resistance circuits R5 and R6, formed of the same material as the distortion gauge 3, for temperature, a zero point, and the like are provided onto the face where the gauge 3 is formed. For instance, the resistors R5 and R6 are provided between contact points of electrode wirings E4 and E6 and an applied voltage source Vin onto the face of the diaphragm 1 where the distortion gauge 3 (R1-R4) is formed. In this process, the thin film pressure sensor is structured in such a manner that the SiO2 film 2 is laminated on a stainless steel 1 as an insulating film, next the distortion gauge 3 and the resistors R5 and R6 are formed of a polycrystalline silicon thin film, and wiring patterns (E1-E5) of an electrode 4 are formed thereon. A transistor Tr is connected between the wirings E4 and E6 and with wiring E7 and E8 in an externally attaching manner.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) Various sensors have been developed using semiconductor strain gauges that utilize the piezo effect, which shows a large resistance change when strain is applied to a semiconductor.

One of them is a thin film pressure sensor in which a diaphragm is made of metal such as stainless steel, and a strain gauge made of a semiconductor thin film such as an amorphous silicon thin film is formed on the diaphragm with an insulating film interposed therebetween.

The present invention provides a circuit for compensating the temperature or zero point of the FLL film pressure sensor strain gauge, in which the structure of the compensation circuit whose resistance element is made of the same material as the strain gauge, and the pressure receiving part and restraint part of the pressure sensor are kept apart. This invention relates to a structure that reduces the adverse effects of restraint on a pressure receiving part.

(Conventional technology) A thin film pressure sensor will be explained.

As shown in FIG. 6(a), a cross-sectional view of the thin film pressure sensor, fiF! A strain gauge 3 consisting of a diaphragm 1 made of stainless steel, a polycrystalline silicon layer pattern formed on the surface of the diaphragm 1 via a silicon oxide (S i Ot ) III 2 as an insulating film, and the strain gauge. 3, and a bassinet base 6 made of a silicon nitride layer to protect the sensor part 5 made of the strain gauge 3 and the electrode 4. And the same figure (
As shown in b), the sensor section 5 is composed of patterns R, -R4 of four strain gauges 3 and wiring patterns E, -E of six electrodes 4 for feeding these. When this sensor section 5 is shown in an equivalent circuit, as shown in FIG. 2(C), it constitutes a bridge circuit, in which electrode wiring patterns E8 and E are generated due to a change in resistance of the strain gauge 3 due to strain caused by pressure.

The pressure is measured by detecting the voltage change between the two.

Incidentally, semiconductor elements have a drawback in that their characteristics are highly dependent on temperature. However, the repeatability with respect to temperature is poor, and after compensation, this characteristic actually increases the reliability of the device.

In the case of a semiconductor thin film pressure sensor, the resistance value of the strain gauge changes with temperature as well as the inherent resistance value of the strain gauge and the change in resistance due to pressure. Therefore, in a bridge circuit that combines strain gauges, both the pressure sensitivity and the zero point change depending on the temperature.

Since the accuracy of a pressure sensor is determined by how well temperature compensation is performed, various methods have been tried in the past.

The following method uses a constant voltage driven pressure sensor.
It uses a combination of transistors and resistors to offset temperature fluctuations in strain gauge sensitivity.

FIG. 7 shows an equivalent circuit diagram of a pressure sensor incorporating the temperature compensation circuit 7.
A transistor Tr and a resistor Rs,
Connect with Ra.

The sensitivity of the thin film pressure sensor is as shown in Figure 8(a).
The temperature is high (it decreases linearly as it gets higher) (a)
, where sensitivity refers to the magnitude of the pressure that the pressure sensor receives and the rate of change in resistance value caused by it. In other words, the higher the sensitivity, the higher the accuracy.

On the other hand, the voltage drop of the transistor used for temperature compensation decreases as the temperature increases. In other words, if the input terminal is kept constant, as shown in Figure 8(b),
The voltage applied to the sensor section via the transistor increases (b).

When the voltage applied to the sensor section increases, it cancels out the decrease in sensitivity of the sensor section due to temperature, and in the end, it is possible to maintain constant sensitivity even if the temperature rises (Fig. 8 (ago). In this way, temperature compensation A thin film pressure sensor incorporating an element for temperature compensation is highly reliable and its sensitivity does not change due to temperature. - Such a temperature compensation element is incorporated outside the thin film pressure sensor as shown in Figure 9. ing.

The thin film pressure sensor 100 is built into a case 101, and together with the case 101, it is a case for external circuits! It will be incorporated into 02. Inside the case +02 is a printed circuit board 104 to which an amplifier 105 and a temperature compensation element 106 are connected, and the case 102 is closed by a Ji 103. The output of the Ill5 pressure sensor 100, temperature compensated by the temperature compensating element 106 on the printed circuit board 104, is amplified by the amplifier 105 and output to an external circuit (not shown).

Furthermore, conventionally, when a sensor module is incorporated into a pressure transducer or other object to be measured, the position where the sensor module is restrained is almost on the same plane as the pressure receiving surface (FIG. 5(b)).

(Problem to be Solved by the Invention) In the temperature compensation circuit described above, the rate of change in voltage drop due to temperature of the transistor used does not necessarily match the rate of change in sensitivity decrease due to temperature of the strain gauge. Therefore, by using two resistance elements R5 and R6 and changing the ratio of the two resistances of the resistance elements, the value of the temperature dependence of the voltage drop can be freely changed. To accurately correct sensitivity by matching the rate of change in sensitivity reduction.

Conventionally, this resistive element is connected to the external print 1 of the thin film pressure sensor.
! Board! It was connected to 04. Since the thin film pressure sensor is very small, it is difficult to connect the transistor and two resistive elements to the printed circuit board 104 by soldering, or to connect it to the electrodes of the pressure sensor. Furthermore, the increase in the number of parts and processes required to connect two resistive elements means that the factors that reduce yield in the process, as well as factors that reduce yield due to defective parts or poor contact between parts, greatly increase. there were.

Furthermore, when the pressure sensor is restrained and pressure is applied, the shape of the restrained area changes, and the restraint position shifts as shown in FIG. 5(c). If the restraining part is close to the pressure-receiving surface as in the past, even a slight shift in the restraining position will cause a large change in the stress distribution on the diaphragm (Figure 5 (b)), which will have a negative effect on the linearity of the output characteristics with respect to pressure. There was a problem with the impact.

(Means and effects for solving the problem) (+) The resistance for temperature compensation of the thin film pressure sensor is not constructed using a resistance element, but is constructed as a strain gauge of the thin film pressure sensor. Use materials that are

In other words, when forming a strain gauge, polycrystalline silicon 111
9 etc., and patterning is performed, and at the same time, a resistor is also patterned and provided.

The wiring between the sensor section and the resistor is also formed at the same time using the same material as the electrode wiring pattern of the sensor section.

A desired resistance value can be obtained by arbitrarily changing the shape of the polycrystalline silicon thin film etc. that forms the resistance part.
Therefore, the value of the temperature dependence of the voltage drop of the transistor can be matched with the rate of change of the sensitivity reduction of the strain gauge without using a resistance element.

(2) In a thin film pressure sensor in which a strain gauge is provided on the back side of the diaphragm pressure-receiving surface via an insulating film, a step is provided between the diaphragm restraining surface and the diaphragm pressure-receiving surface, that is, by moving the restraining surface away from the pressure-receiving surface. , to eliminate the influence of changes in the restraint position when pressure is applied.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

First, the compensating resistor will be explained.

First Embodiment FIG. 1 shows (a) a plan view and (b) a plan view of the first embodiment of the present invention.
) As shown in FIG. 1(a), which shows a cross-sectional view, a resistor tA is placed on the forming surface of the strain gauges 3 (R1 to R,) of the diaphragm l.
15% + Rh is formed between the contacts of the electrode wirings E4, E, and the applied voltage rjIXVin (not shown).

As shown in FIG. 1(b), in this embodiment, the thin film pressure sensor is made of Si as an insulating film on stainless steel.
A film 2 of O is laminated, then a strain gauge 3 and resistors R2, R, are formed of a polycrystalline silicon thin film, and a wiring pattern of tli4 (E, to El) is formed thereon.

The transistor Tr is externally connected between E4 and E, and between E, , and E (not shown). The equivalent circuit of this thin film pressure sensor is the same as that shown in FIG.

FIGS. 2(a) to 2(e) show process diagrams of the first embodiment of the present invention and will be described.

(1) As shown in Figure 2 (a), on the stainless steel diaphragm l,! ! a111 as S i Oz N'
1 is laminated to a thickness of about 7 μm by plasma CVD.

(2) As shown in FIG. 2(b), a polycrystalline silicon thin film of approximately 0.5 μm is deposited on the S i O film by plasma CVD using silane gas as a raw material.

(3) As shown in Fig. 2(c), three strain gauge patterns (R, ~R,) and resistance patterns (Rs, R,
−) is formed. At this time, by changing the shape of the resistance pattern, a desired resistance value can be obtained and the temperature dependence value of the transistor of the compensation circuit can be changed.

The resistance value of this resistance pattern (Rs, R6) changes when strain occurs, so in order to maintain a constant value, it must be formed at a position around the diaphragm that will not be strained by pressure. .

(4) As shown in Figure 2(d), strain gauges (R1 to R
, ) and resistors (Rs, R, ) are formed, a gold kI4 electrode 4 made of aluminum (Al) or the like is scraped, and a wiring pattern (E1 to E-) is formed by a photolithography process for wiring. .

(5) As shown in FIG. 2(e), SiN++I! is used as a passivation film to protect the strain gauge, resistor, and wiring pattern. Approximately 5,000 layers will be stacked using the plasma CVD method.

The thin film pressure sensor is completed through steps F-F. This thin film pressure sensor is constructed in a case 101 as shown in FIG.
The case 101 and ' are incorporated into a case 102 for an external circuit.

Inside the case 102 is a printed circuit board 104 to which an amplifier 105 and a temperature compensation transistor are connected.
The case 102 is closed by a lid 103. Between the transistor on the printed circuit board 104 and the electrodes E4 to E1 of the iIM pressure sensor, El and E are bonding wires (
(not shown), the temperature compensation circuit is completed, and the output of the pressure sensor is amplified by the amplifier 105 and output to an external circuit (not shown).

By using the '389 pressure sensor having such a configuration, when configuring a temperature compensation circuit, a resistor can be formed without increasing the number of parts and processes.

Although this embodiment describes a circuit for temperature compensation for sensitivity, it is not limited to this, and can also be applied to, for example, a circuit for temperature compensation for zero points, a circuit for zero point compensation for variations between strain gauges, etc. It is.

Second Embodiment As a second embodiment shown in FIG. 3, the resistances Rs and Ri of the circuit for temperature compensation for sensitivity and the resistance R7 for zero point compensation due to variations between each strain gauge are placed on the diaphragm of a thin film pressure sensor. (a) A plan view, (b) a cross-sectional view, and (C) an equivalent circuit diagram when a transistor is externally connected as a temperature compensation element of the formed example.
in* (not shown), and strain gauges (R,
~R1) and resistances Rs and R4 for temperature compensation for sensitivity.
Polycrystalline silicon is laminated and patterned as a resistor R1 of a circuit for zero point compensation due to variations between strain gauges. Then, we layer and pattern metals such as A-strain,
The thin film pressure sensor is completed by forming electrode wiring (El-Es) and laminating a passivation film (not shown). In this embodiment, E and E are connected, and the contact point and E,
By outputting a voltage from the electrode, two coarse zero point adjustment resistors are added to R1 and a fine zero adjustment resistor is added to R1.

Third Embodiment FIG. 4 shows (a) a plan view and (b) a plan view of the third embodiment of the present invention.
FIG. The equivalent circuit diagram when the temperature compensation element is externally connected is the same as the second embodiment (Fig. 3(C)).
In this embodiment, as shown in FIG. 4(a), the strain gauge 3 (R
1 to R,) have a high resistance because they are substantially long patterns, and accordingly, the zero point compensation resistor Rt also has a high resistance. Therefore, unlike the second embodiment of the present invention, it is not necessary to form the zero point compensation resistor into a substantially wide pattern such as a dogleg shape.

In addition, in this example, since the coarse adjustment resistor R1 for zero point compensation is arranged on the same circumference with respect to the center of the diaphragm l, the film thickness distribution when forming the pressure sensitive layer (the thickness at the center of the diaphragm is thickest and toward the outside). thinning) can be ignored. Therefore, it is possible to reduce the variation in the resistance value per coarse adjustment resistor divided into a plurality of pieces, and to perform compensation with high accuracy.

In this embodiment, as shown in FIG. 4(b),
2 is a SiO□-layer, but the stainless steel diaphragm l
1ll (for example, a non-doped polycrystalline silicon film with a thickness of about 0.3 μm) having an intermediate coefficient of linear expansion may be laminated between the insulator M2 and the insulation M2 as a buffer layer to alleviate the difference in coefficient of linear expansion between the two.

Fourth Embodiment Next, improvement of the linearity of the output characteristics of the pressure sensor will be explained.

FIG. 5 shows the constraint position dependence of the stress distribution on the diaphragm l of the pressure sensor.
b) A conventional diaphragm is shown.

Figure 5(b) shows the cross-sectional shape of a conventional diaphragm.
The restraint position 1a and the diaphragm pressure receiving part 1b are at almost the same height, and the stress distribution changes greatly when the restraint part shifts slightly from ■, ■5■, ■.
Figure (a) shows the cross-sectional shape of the diaphragm of the present invention, and shows the restraint position! There is a step between a and the diaphragm pressure receiving part 1b, and the restraint position 1a and the diaphragm pressure receiving part 1b are separated.0 With the structure of the present invention, even if the restraint part is shifted from ■ to ■, the stress distribution will be maintained. There is no change in

Therefore, even if the restraint position shifts as shown in FIG. 5(C) when pressure is applied, the restraint part does not have an adverse effect on the pressure receiving part, and the linearity is greatly improved. In the example, the nonlinearity was reduced to about ⅓ (FIG. 5(d)).

(Effects of the Invention) According to the invention set forth in claim 1 of the present invention, the resistance of the compensation circuit is formed on the diaphragm using the same material as the strain gauge, so there is no need to increase the number of components of the resistance element. Furthermore, the resistor of the compensation circuit can be constructed without increasing the number of steps such as soldering. Therefore, factors such as a decrease in yield due to defects, poor contact, etc. that occur during processes such as soldering are eliminated, and the yield is improved. moreover,
The resistor is made of the same material and formed in the same process as the strain gauge, so
Since the resistor can be formed without changing the process of the thin film pressure sensor, the process time is not increased at all by forming the resistor.

According to the invention set forth in claim 2 of the present invention, even if the restraining position shifts during pressure application, there is no change in the stress distribution of the diaphragm, and the linearity of the output characteristics of the pressure sensor is improved.

[Brief explanation of the drawing]

FIG. 1 is (a) of a thin film pressure sensor according to an embodiment of the cylinder 1 of the present invention.
FIG. 2 is a plan view and (b) a cross-sectional view; FIG. 3 is a process diagram;
A plan view, (b) a sectional view, and (c) an equivalent circuit diagram.
) Cross-sectional view FIG. 5(a) is a graph showing the constraint position dependence of the stress distribution of the diaphragm of the 1119 pressure sensor according to the present invention, and FIG. 5(b) is a graph showing the constraint of the stress distribution of one diaphragm of the conventional thin film pressure sensor. Graph showing position dependence, Figure 5 (C)
is a diagram showing the deviation of the diaphragm restraint position when pressure is applied,
FIG. 5(d) is a graph showing the improvement in linearity according to the present invention. Figure 6 shows a conventional 71 gll pressure sensor (a) cross-sectional view, (b) plan view, and (C) equivalent circuit diagram. a) is a diagram showing the relationship between the sensitivity and temperature of a thin film pressure sensor; FIG. 8(b) is a diagram showing the relationship between temperature and voltage applied to the sensor section via a temperature compensation element; It is a diagram in which a pressure sensor, a circuit, etc. are assembled into a case. l...Diaphragm 4...Electrode la...Restriction position lb...Diaphragm pressure receiving part 2...Insulating film 5...Sensor part 3...Strain gauge 6...Bancibasin film 7...・Temperature compensation circuit R7...Resistance for zero point compensation

Claims (2)

[Claims] (1) In a thin film pressure sensor in which a strain gauge is provided on the back side of a diaphragm pressure receiving surface via an insulating film, the temperature of the strain gauge formed on the strain gauge forming surface is
A pressure sensor characterized by being provided with a resistance circuit for compensating for zero points, etc. (2) A thin film pressure sensor in which a strain gauge is provided on the back side of a diaphragm pressure receiving surface via an insulating film, characterized in that a step is provided between the restraining surface of the diaphragm and the diaphragm pressure receiving surface.