JPS63228764A - Thin-film pressure sensor - Google Patents

Abstract

PURPOSE:To improve the characteristics of a sensor by arranging a pressure- sensitive resistance layer pattern in a peripheral section so as to pass on the edge of the thin section of a diaphragm. CONSTITUTION:Resistance layer pressure-sensitive patterns R2, R4 are disposed at the central section of a stainless diaphragm. Pressure-sensitive resistance patterns R1, R3 are arranged so as to run parallel with the patterns R2, R4 and pass on the periphery of a thin section. Accordingly, when uniform pressure is applied to the whole surface of a case (c), strain gages are disposed at a position where strain-stress is minimized on the periphery, and a position where strain-stress is maximized in the vicinity of the center, thus acquiring a linearly high sensor having high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film pressure sensor, and particularly to the arrangement of strain gauges thereof.

[Prior art and its problems] With the progress of semiconductor technology, conductor pressure sinks that utilize the piezoresistance effect of semiconductors such as silicon and germanium have been attracting attention in recent years.

One of them consists of a diaphragm made of stainless steel,
A hydrostatic pressure sensor has been proposed in which a film such as a silicon thin film or the like is formed on the diaphragm via an insulating layer.

For example, the thin film pressure pincer (hereinafter referred to as thin film pressure pincer) proposed by Rira of the present invention (Patent No. 61-111377) is
As shown in FIGS. 5(a) and (b), a diaphragm 1 made of stainless steel, silicon oxide (SiO2) I<2 as an insulating layer formed on the surface of the diaphragm 1,
N-type microcrystal silicon (μc-
A pressure-sensitive resistance layer consisting of s r > m4, an electrode wiring pattern 5 made of an aluminum layer for feeding power to the pressure-sensitive resistance layer, and a silicon oxide layer 7 for covering and protecting the gauge structure. It is composed of a passivation film consisting of.

The pressure-sensitive resistance layer 4 of the gauge metropolitan area is composed of four pressure-sensitive resistance layer patterns R1 to R4, and has six electrode wiring patterns E1 to [6] for supplying power to these patterns. If this gauge part is shown as a Kasada circuit, it constitutes a bridge circuit as shown in Fig. 6, and the electrode wiring patterns E2 and E5, which are caused by changes in the resistance value of the pressure-sensitive resistor layer due to strain caused by pressure, are connected to each other. Pressure is measured by detecting voltage changes between the two.

In other words, when there is no load (when there is no strain), the resistance values of the pressure-sensitive resistance layer patterns R1 to R4 are all set to be the same R.

If pressure P is applied to the diaphragm 1 as shown in FIG.
Because it is a 4IllI structure with and placed in the center,
Pressure-sensitive resistive layer patterns R1 and 1<3 are subjected to compressive stress, R
+ΔR, while the pressure-sensitive resistance layer patterns R2 and R4 receive tensile stress and become R-Δ1.

Assuming that Vln is applied between the electrode wiring patterns El and E6, the four pressure-sensitive resistance layer patterns R1 when no load is applied.
, R2, R3, and R4 are all equal, so the electrode wiring pattern E2. The potentials between E5 are equal and the voltage between them is V-
It is O.

Therefore, when a load such as the pressure P shown in Fig. 7 is applied,
The pressure-sensitive resistance layer patterns R1 and R3 are 1<tΔ[, and the pressure-sensitive resistance layer patterns R2 and R4 are R−Δ1, and the electrode wiring pattern E2. Voltage between E5 V = 2 (ΔR/R)・Vl
It becomes n.

In this way, a voltage corresponding to the negative voltage is outputted, subjected to processing such as amplification in an amplifier section (not shown), and outputted to an external circuit.

By the way, the arrangement of the pressure-sensitive resistance layer pattern, that is, the strain gauge, on the diaphragm is determined from the stress distribution on the die hair phragm so as to obtain the highest sensitivity.

In other words, assuming that a uniformly distributed load is applied to a disk whose peripheral edge is fixed, the radial stress of the diaphragm, σ, is.

Tangential stress σ. was calculated from the following formula, and the strain gauges were arranged accordingly.

...(2) p: Load t: Thickness of the disk C: Boisson's ratio r: Radius of the disk (a) shows the curve σ1. It becomes as shown by σθ. Therefore, as shown in FIG. 8(b), large pressure-sensitive resistance patterns R2, R4 and R1, R3 are formed at the positions of the diaphragm where the stress is the largest and the position where the stress is the smallest.

In other words, the pressure-sensitive resistance layer patterns R1 and R3 are located inside the edge IE of the thin portion of the diaphragm. Ii! It is placed. (FIG. 8fc) is a side view of FIG. 8(b). ) However, such conventional thin film pressure sensor+y
However, there was a problem in that the linearity of the pressure-output characteristics was not good. As a result of repeated inquiries from various directions, the following facts were discovered.

That is, the actual sensor does not exist on a diaphragm, but is fixed inside the case.

For this reason, it was found that the stress distribution after the case was housed was slightly different from the stress distribution according to equations (1) and (2) above, and the strain gauge was not placed at the optimal position.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to optimize the position of a strain gauge and to provide a thin film pressure sensor with high Senna characteristics.

[Means for Solving the Problems] Accordingly, in the present invention, two patterns on the peripheral side of the pressure-sensitive resistance layer of a thin film pressure sensor having four pressure-sensitive resistance layer patterns are point-symmetrical to each other, and the diaphragm is It is arranged so as to pass over the periphery of the thin part.

(Function) In the present invention, the finite element method is used instead of the pattern position of the pressure-sensitive resistance layer, which is calculated assuming that a uniformly distributed load is applied to a disk whose peripheral edge is fixed, and which is placed inside the edge of the thin part of the diaphragm. It is placed at the position calculated by. In other words, it is calculated that a uniform load is applied to the entire case surface extending to the edge of the case C where the diaphragm is supported, and the position where the stress strain is the smallest on the periphery and the position where the stress strain is the smallest near the center. Since the strain gauge is disposed at the position where the strain gauge increases, a thin film pressure sensor with high sensitivity and high linearity can be obtained.

Preferably, the two outer pressure-sensitive resistance layer patterns are formed so as to extend in the normal direction from the periphery of the thin portion of the diaphragm by equal distances inside and outside.

In this case, as shown in Figure 1 (C), two people are placed at the maximum and minimum peaks of the stress distribution calculated by the finite element method.
Two pressure-sensitive resistance layer patterns are arranged (Fig. 1(a)
)(b)) Therefore, 1
By reducing the deviations in the values of 6 to 1, deviations in the characteristics of the sensor can be significantly reduced and stable characteristics can be obtained.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIGS. 1(a) and 1(fb) are diagrams schematically showing the pattern arrangement of the a-relief pressure sensor according to the embodiment of the present invention.

This thin film pressure sensor is characterized in that the position of the pressure sensitive resistor layer pattern on the peripheral side is located outside of the conventional position, and the thickness t of the thin part is 0.64rR*, and the diameter is R1=0.
Length 11 extending in the tangential direction at positions 2ii apart =
0.3 order, the second and fourth pressure sensitive resistance layer patterns R2 and R4 with width W1 = 0.05H, and the thin portions parallel to the second and fourth pressure sensitive resistance layer patterns R2 and R4. Length 12 = 0.3att, width w2 = 0.05, extending by 0.15am in the normal direction with the periphery E as the center
and third pressure-sensitive resistance layer patterns R1 and R3.

FIGS. 2(a) to 2(f) show 7iiJI of the embodiment of the present invention.
g! It is a manufacturing process diagram of a pressure sensor.

First, as shown in FIG. 2(a), a film with a thickness of about 1 to 100 ml is coated on the surface of a stainless steel diaphragm 1 by plasma CVD.
10 layers of silicon oxide layer 12 are deposited.The deposition conditions at this time are a substrate temperature of 550°C, silane (SIH4),
) and hydrogen (H2) gas LLSi 1-14 /H2=
1/201 power 100W.

Next, by plasma CVD method, a film with a thickness of 11JIJ was formed.
A polycrystalline silicon layer 3' of the mold type is deposited. The deposition conditions at this time were a temperature of 550° C., S i +−+ 4/t12=1/20 to 1/′50, and a power of 100 W.

After this, a film thickness of 1
A layer of aluminum is deposited and an aluminum layer pattern 14' is formed by photolithography. (FIG. 2(C)) Here, reactive ion etching (RIE) using tetrachloromethane (CCJ!4) plasma was used for etching the aluminum layer.

Furthermore, as shown in FIG. 2(d), using the aluminum layer pattern 14' as a mask, an n-type polycrystalline silicon layer 1 is formed.
3' is selectively removed by reactive ion etching using detrafluoromethane (C'4).

Then, the portions of the n-type polycrystalline silicon layer that will become the pressure sensitive resistance layer patterns R1...R4 are exposed. 2(e) and 2(f), the aluminum layer is selectively removed and a badge 1 film 15 is formed to form pressure sensitive resistor layer patterns 13 (R1...R4). )) and the main wiring pattern 14 (El...[6), a 1tWtlQ pressure sensor is completed. Here, FIG. 2(e) is a diagram showing the AA cross section of FIG. 2(f).

The output (vertical axis)-pressure (horizontal axis) characteristic of the thin film pressure sensor formed in this way is as shown by curve a in Fig. 3, and compared to the conventional one shown in Fig. 8 (aHb) and (c). Compared to curve IIb showing the output-pressure characteristics of the example thin film pressure sensor, the linearity is significantly improved.

In addition, Fig. 4 shows the deviation from linearity of the output voltage ΔV/V
It shows the relationship between (%) and pressure (horizontal axis), and from the comparison between curve a showing the thin film pressure sensor of the present invention and curve fI2b showing the conventional thin film pressure sensor, it can be seen that the thin film pressure of the present invention It can be seen that the linearity of the sensor has been significantly improved.

Furthermore, in the conventional thin film pressure sensor 1, the pressure is 500 kg/
The resistance value change △R/R for ruR2 full scale is:
3% for second and fourth pressure sensitive resistance layer patterns R2°R4
, O8 in the first and third pressure sensitive resistance layer patterns R1 and R3.
7%, but due to the improved gauge position, the thin film pressure sensor of the present invention has the first and third pressure sensitive resistance layer patterns R1
, R3 becomes 2%. In this way, sensitivity is significantly improved.

Therefore, the design standard for the thickness of the diaphragm can be loosened to the extent that the sensitivity is improved, so that durability can be improved.

As is clear from comparing Figure 1 (aHb) and Figure 1 (C), the pressure-sensitive resistor layer pattern is placed at the minimum and maximum positions of the C value in the stress distribution diagram. It is thought that the linearity has been improved and the sensitivity has also been greatly improved.

[Effect of Brahma]

As explained above, according to the present invention, a full-bridge circuit is formed using two sets of pressure-sensitive resistor layer patterns arranged symmetrically in the center and at the periphery. The thin film pressure sensor υ is designed to measure the Fj force by measuring the output change between the terminals due to stress strain when .
Since it is extended so as to pass over the edge of the thin portion of the diaphragm, sensitivity is improved and the linearity of the output characteristics is greatly enhanced.

[Brief explanation of drawings]

FIGS. 1(a) and fb) are explanatory diagrams showing the pattern arrangement of the pressure-sensitive resistance layer of the thin film pressure sensor according to the embodiment of the present invention, and FIG. 1(C) is a diagram showing the stress distribution obtained by the finite element method. , FIGS. 2(a) to 2(f) are manufacturing process diagrams of the same thin film pressure sensor, FIG. 3 is a comparison diagram of the output-pressure characteristics of the thin film pressure sensor of the present invention and a conventional thin film pressure sensor, and FIG. The figure shows a comparison of deviations from the same linearity. Figures 5 (a) and (b) show a conventional thin film pressure sensor. Figure 1 and Figure 6 are equivalent circuit diagrams of the same sensor. Figure 7 is , an explanatory diagram showing the pressure detection mechanism of the same sensor, and Figs. 8(a), (b), and (c) are explanatory diagrams showing the stress distribution and the same pattern arrangement used in the design of a conventional thin film pressure sensor. It is. 1.11... Diaphragm, 2,12... Silicon oxide layer, 3... Binder layer, 4.13... Pressure sensitive resistance layer (pattern), 5.14... Electrode wiring pattern, 6
... Gauge part, 7, 15... Passivation film. Figure 1 (α) Figure 1 (b) Figure 1 (C) Figure 2 (α) Figure 2 (b) Figure 2 (C) Section 3 OTOO200300400500 P (kg/mm2) Figure 4 Figure 8 (Q) Figure 8 (b) Figure 8 (C)

Claims (2)

[Claims] (1) A bridge circuit is constructed by arranging two sets of pressure-sensitive resistor layer patterns, one at the center and one at the periphery, on the surface of a diaphragm having a circular thin part so that each set is point symmetrical. , a thin film pressure sensor configured to detect stress by measuring changes in output between terminals due to stress strain, wherein the pressure-sensitive resistor layer pattern at the peripheral edge portion passes over the peripheral edge of the thin portion of the diaphragm. A thin film pressure sensor characterized by being disposed in. (2) The thin film pressure according to claim (1), wherein the pressure-sensitive resistance layer pattern of the peripheral portion is a pattern having a center at the peripheral edge of the thin portion and extending in the normal direction. sensor.