JPH0262928A - Thin film pressure sensor - Google Patents

Abstract

PURPOSE:To easily control a resistance value by patterning strain gauges longer than the length between electrodes and connecting them. CONSTITUTION:An SiO2 film is laminated as an insulator 2 on a diaphragm made of stainless steel and n-type polycrystalline Si is laminated thereupon as a strain gauge 3 by a plasma VCD method and patterned in an optional shape. The gauge 3 is provided where stress is applied sufficiently. Then an electrode wiring pattern 4 is provided by laminating Al through a metal mask. Then the gauge 3 is about 0.6mum in film thickness and 50mum in film width and this is extended around in a U shape and patterned to about 2mm overall length, thereby obtaining high resistance of about 3.5kOMEGA. The length between electrodes is set to about 600mum and those range length and position are enough to indicate the stress remarkably. Thus, the shape of the strain gauge is selected properly to easily the desired high resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film pressure sensor, and more particularly to a thin film pressure sensor that effectively controls the resistance value of its strain gauge.

[Prior Art] In recent years, semiconductor strain gauges that utilize the Biesot effect, in which the resistance value of a semiconductor changes with stress, have been widely used in pressure sensors, acceleration sensors, and the like. As for pressure sensors, one example is a thin film pressure sensor in which a semiconductor thin film such as polycrystalline silicon is formed as a strain gauge on a diaphragm such as stainless steel with an insulating film interposed therebetween. For example, two proposals by the inventors (patent application 1986-
55975), as shown in Figures 4 (a) and (b).
As shown in the figure, there is a diaphragm 1 made of stainless steel, silicon oxide (S i 02 ) as an insulator 2 formed on the surface of the diaphragm, and an n-type diaphragm laminated on this insulator as a strain gauge by plasma CVD. It consists of a polycrystalline silicon pattern 3 and an electrode wiring pattern 4 for supplying power to the strain gauge and for measuring output voltage. To explain the operation in such a configuration, when pressure is applied to the diaphragm 1.

The resistance value of the strain gauge changes, and by measuring this change ffi, it becomes possible to detect the pressure.

[Problems to be Solved by the Invention] However, the thin film pressure sensor having the conventional configuration described above has the following drawbacks.

The resistance value of a thin film semiconductor strain gauge used in a semiconductor pressure sensor must be controlled to a high resistance value, especially when driving the thin film semiconductor strain gauge with a constant current.

The following methods are available for this control, but all of them have serious drawbacks that cannot be ignored. Each control method and its drawbacks will be described below.

(1) When forming a semiconductor thin film by the famous plasma CVD method without reducing the impurity concentration by controlling the film forming conditions, it is difficult to uniformly reduce the impurity concentration. In particular, when attempting to form an n-type high-resistance strain gauge in which electrons with high mobility serve as carriers, reliability may be affected because various conditions such as gas pressure and RF power become unstable regions of the plasma. Therefore, it becomes impossible to form a film with a high temperature. Thus, it is not easy to control the impurity concentration and ensure a highly accurate resistance value.

(2) How to reduce the film thickness of a strain gauge To explain this with reference to the drawings, in the relationship diagram of film thickness, resistance value, and its variation in Figure 3, if the film thickness is made thinner, the resistance value will naturally increase. On the other hand, the thinner the film thickness is, the more the variation in resistance value increases (for example, the hunting area in Figure 2 has a satisfactory resistance value, but the variation is large, causing problems in use).

Furthermore, the thin film thickness also causes defects such as pinholes. Therefore, it is extremely difficult to control the resistance value to a high value by changing the film thickness.

(3) How to narrow the strain gauge membrane width If the strain gauge membrane width is narrowed, durability will be significantly reduced when stress is repeatedly applied to the pressure sensor, so defects such as peeling of the strain gauge will be avoided. arise. In addition, when forming strain gauges during manufacturing, patterning accuracy decreases, resulting in large variations in resistance values, and can easily cause defects such as pinholes, resulting in a decrease in manufacturing yield. becomes.

(4) Method of increasing the length of the strain gauge This will be explained with reference to the drawings, as shown in the relationship between stress and the position of the strain gauge on the diaphragm in Figures 5 (a) and (b). In addition, there is a stress distribution in the diaphragm 1, and if the length of the strain gauge is increased.

This results in an undesirable result in that the strain gauge is located at a position that is not subjected to stress. In the case of a strain gauge in such a state, even if it is subjected to stress, the change in resistance of the strain gauge is small, resulting in a pressure sensor with poor sensitivity and cannot be put into practical use.

In view of the above-mentioned conventional problems, the present invention provides a thin film pressure sensor that is free from defects and variations during manufacturing and whose accuracy and sensitivity do not deteriorate during use. It is an object.

[Means for Solving the Problems] In order to achieve the above objects, two thin film pressure sensors according to the present invention are formed by connecting a pattern made of electrodes and the electrodes via an insulator on a diaphragm. In addition, in the thin film pressure sensor including a pattern of a strain gauge made of a semiconductor thin film, the strain gauge is patterned to be longer than the length between the electrodes and wired.

[Operation] According to the above configuration, the pattern (that is, the shape) of the strain gauge can be arbitrarily changed at the optimum position.

This does not simply increase the length of the strain gauge, but rather it can be used in the most ideal position, that is, within a small range of stress distribution, or at the same electrode position and length as before, such as a 9-curve, U-shaped or By patterning a strain gauge in an arbitrary shape such as a zigzag shape, and by forming it into such a configuration.

Since the length of the strain gauge can be increased, the resistance value can be easily controlled. Furthermore, since this configuration does not control the impurity concentration, film thickness, or film width of the strain gauge, which are other resistance value control methods, it is difficult to prevent defects such as skin shedding caused by these controls. It becomes possible.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram for explaining a first embodiment of the present invention, and FIG. 2 is a diagram for explaining second and third embodiments of the present invention.

In the first embodiment shown in FIG. 1, silicon oxide (S i 02
) film is laminated, and plasma CV is applied as a strain gauge on top of this.
N-type polycrystalline silicon is laminated to a thickness of approximately 0.6 μm using the D method. Then, it is patterned into an arbitrary shape by photolithography. At this time, the strain gauge is installed at a position where sufficient stress is applied. Next, an electrode wiring bar pattern 4 for supplying power to the strain gauge and measuring the output voltage was provided by laminating aluminum layers through a metal mask. In the first embodiment, the film thickness is approximately 0.6 μm.
,and.

This is a strain gauge with a membrane width of approximately 50 μm.

As shown in the figure, the total length is approximately 2.0 mm when routed in a 30-character shape.
Patterning of mm strain gauge.

It was possible to obtain a high resistance of approximately 3.5 Ω, which was the initially desired resistance. Although the length between each electrode was set to approximately 600 μm, the range length and its position are sufficient to express stress clearly, depending on the skin lightening film thickness, resistance value, and its position. This is clear from the relationship diagram with variations (Figure 3) and the open relationship diagram between stress and the position of the strain gauge on the diaphragm (Figure 5).

The second and third embodiments are examples of a thin film pressure sensor in which the arbitrary shape of the strain gauge between the electrodes is determined to be a more effective shape, and will be described below with reference to the drawings. When a strain gauge is placed on a diaphragm, it must be placed in consideration of the strain direction dependence of the strain gauge sensitivity.

This characteristic varies depending on the type of semiconductor thin film constituting the strain gauge and its type (p-type or n-type). An example of this is illustrated by the drawing (FIG. 2).

FIG. 2(a) is a graph showing the strain direction dependence of strain gauge sensitivity for n-type polysilicon deposited by plasma CVD and n-type polysilicon. The vertical axis is the strain gauge sensitivity. , the horizontal axis is the radial direction at 0 degrees above the level (
0°) is the angle of the distortion direction. As shown in the figure, in the n-type, when the distortion direction is zero degrees (0°), the sensitivity is maximum on the negative side, and when the distortion direction is 90 degrees, the sensitivity is zero (zero). On the other hand, the p-type has maximum sensitivity on the positive side when the strain direction is zero degrees (0°), but the sensitivity decreases as the strain direction angle increases.

At approximately Nakaoka point between 45 degrees and 90 degrees, the sensitivity becomes zero (zero),
When the distortion direction angle further increases to 90 degrees, sensitivity begins to be shown on the negative side. Examples of implementation based on these reasons are listed below.

Second embodiment: An N-type strain gauge is bent into a U-shape or the like and arranged.

As shown in Figure 2(b), the strain direction of the diaphragm (
In other words, this is a thin-film pressure sensor that has a large number of zero-degree components (in other words, a long length) in the radial direction to achieve high sensitivity.

Third embodiment: A p-type strain gauge is bent into a U-shape or the like and arranged.

As in the second embodiment, as shown in FIG. 2(b), a large number of zero degree components (i.e., long) are arranged in the diaphragm distortion direction (radial direction) to obtain high sensitivity. Thin film pressure sensor.

Incidentally, FIG. 2(c) is a diagram showing an example of component arrangement of a good strain gauge in FIG. 2(b) in the second and third embodiments. It is a figure which shows the example of component arrangement|positioning of an unfavorable strain gauge.

[Effects of the Invention] As explained above, according to the present invention, by appropriately selecting the shape of the strain gauge, a desired height can be easily achieved without changing the impurity substances, film thickness, and film width of the strain gauge. You can get the resistance value. This is a thin film pressure sensor that eliminates the defects and variations that occur during the manufacturing of conventional thin film pressure sensors, and eliminates the conventional problem of reduced measurement accuracy and sensitivity during use. It is not a thin film pressure sensor that uses other resistance value control methods that were used to solve sensor problems, such as controlling the impurity concentration, film thickness, or film width of strain gauges, so it is a thin film that eliminates the drawbacks caused by these control methods. It is a pressure sensor.

[Brief explanation of the drawing]

FIG. 1: A first embodiment of a thin film pressure sensor according to the present invention. FIG. 2: A diagram illustrating second and third embodiments of a thin film pressure sensor according to the present invention. is plasma C
A graph showing the strain direction dependence of strain gauge sensitivity for n-type polysilicon and p-type polysilicon deposited using the VD method. ) is an unfavorable component arrangement of the strain gauge in comparison with (b). Figure 3 shows the relationship between the film thickness, resistance value, and variation of the thin film pressure sensor.・A conventional thin film pressure sensor, (a
) is a diagram showing the arrangement of strain gauges on the diaphragm, (b
) is a cross-sectional view taken along line A-A in (a). FIG. Figure 1 (b) shows the relationship between the placement position of the strain cage and the distribution of strain stress generation on the upper surface of the diaphragm. Diaphragm 2 Insulator 3 Strain gauge 4 Electrode patent application Person Komatsu Ltd. Agent (patent attorney) Oka 1) Japanese Shunga 2 (a) Figure 1 Figure 2 (b) Man 2 (C) Figure 4 (a)

Claims (1)

[Claims] In a thin film pressure sensor having a strain gauge made of a semiconductor thin film on a diaphragm with an insulating layer interposed therebetween and a metal electrode pattern wiring the strain gauge, the length of the strain gauge connected by the electrodes is set to be longer than the length between the electrodes. A thin film pressure sensor characterized by a long strain gauge pattern.