JPS5938746B2 - semiconductor strain gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises a silicon diaphragm in which a concave hole is formed on one side of an N-type silicon single crystal wafer, and a plurality of P-type piezoresistive strain gauge elements arranged on the other side. Particularly, it relates to a semiconductor strain gauge formed by bridge-connecting parts (11
0) This relates to a semiconductor strain gauge in which two types of piezoresistive strain gauge element groups, a radial strain gauge element group and a circumferential strain gauge element group, are arranged on the surface of a silicon diaphragm having a plane orientation.

Examples of the arrangement of conventional semiconductor strain gauges are shown in FIGS. 1 and 2.

The conventional example shown in Fig. 1 is made of N-type silicon single crystal (
100) 2 arranged with the <110> axis passing through the center on the surface of the silicon diaphragm 1 having a plane orientation as the center of symmetry.
A pair of radial strain gauge elements 2 and 3 and this <110>
It is constituted by two integral circumferential strain gauge elements 4 and 5 arranged with the center of symmetry about an axis perpendicular to the axis (<110> axis on the (100) plane).

Such strain gauge elements 2, 3, 4, 5 are formed by diffusing impurities such as boron, and 2, 3
The four gauges 04 and 5 form a bridge to function as a semiconductor gauge. In the conventional example shown in FIG. 2, <
A pair of radial strain gauge elements □18 are arranged with the center of symmetry about the 111> axis, and a pair of circumferential strain gauge elements are arranged with the center of symmetry about the <112> axis passing through the center of the surface of the silicon diaphragm 6. It is composed of gauge elements 9 and 10.
The means for forming such strain gauge elements □, 8, 9, and 10 and the structure as a semiconductor gauge are the same as those shown in FIGS.
The common feature of the conventional examples described above is that all the strain gauge elements are formed at the same distance from the center of the silicon diaphragm,
Moreover, its position is close to the end of the silicon diaphragm.

The first purpose of the conventional structure having the above-mentioned characteristics is to reduce the imbalance of the zero points of the bridge by suppressing as much as possible the variation in resistance value that occurs when the four strain gauge elements are formed by diffusion.

A second purpose is to increase the output voltage sensitivity of the bridge to stress generated on the surface of the silicon diaphragm, for example when pressure is applied to the silicon diaphragm. Furthermore, a third object is to obtain a highly accurate semiconductor strain gauge by minimizing the non-linear error of the bridge output with respect to pressure, for example, using the first object as a constraint. However, although the conventional example can almost fully satisfy the above-mentioned first and second objectives, it does not necessarily have a configuration that can satisfy the second objective. When a uniaxial stress acts on a single strain gauge element, the non-linear error due to the stress due to resistance change of the strain gauge element is greater when the direction of current flowing through the element is perpendicular to the stress direction than when it is parallel. It has been found through experiments that the non-linearity error is large and that the change in non-linearity error due to ambient temperature is also large. In the conventional example, these basic studies have not been sufficiently conducted, and the constraint conditions for achieving the first objective have been an obstacle, and strain gauge elements for obtaining high-precision semiconductor strain gauges have not been developed. However, we have not yet reached a truly stable and optimal arrangement of . Therefore, in the conventional example, even if the non-linear error is small at room temperature, it shows an extremely large change due to changes in ambient temperature, and furthermore, the concave shape formed at the center and back surface of the surface where the strain gauge element is formed. This shows an extremely large change in the relative position of the strain gauge element caused by the deviation from the center of the circular hole.

In other words, in the conventional example, if high accuracy is aimed at, the allowable temperature range becomes narrow, and conversely, if the allowable temperature range is widened, the accuracy drops significantly, and furthermore, there are problems in that the variations in characteristics between product rods are extremely large. was. An object of the present invention is to solve the above-mentioned problems in the prior art, and to provide a semiconductor strain gauge with low non-linearity error and its temperature influence, that is, high accuracy, wide allowable temperature range, high sensitivity, and small variation between product rods. is to provide.

The feature of the present invention is that {110
} Passing through the center on the diaphragm surface having the plane orientation 11
A group of radial strain gauge elements is arranged along the 1〉 axis, and a group of circumferential strain gauge elements is arranged along the 112〉 axis passing through the apex on the diaphragm surface. The object of the present invention is to employ a configuration in which the distance to the center of the flange is smaller than the distance from the radial strain gauge element group to the center of the diaphragm.

Generally, it is considered that radial stress σ and circumferential stress σθ act on the silicon diaphragm surface, as shown in FIG.

Therefore, if the resistance change rates of the radial strain gauge element and the circumferential gauge element are respectively (ΔB/R)R and (ΔVR)T, these can be approximated by the following equations. 1 cry
′ ▲ PeZ7已! Here, πt is the piezoresistance coefficient when the current and stress are parallel, and π is the piezoresistance coefficient when the current and stress are orthogonal. The orientation shows a distribution as shown in FIG. 4 with respect to the in-plane crystal axis orientation, and the {110} plane orientation, which is used in the conventional example shown in FIG. The distribution shown in the figure is shown.

When the four strain gauge elements are assembled into a bridge and this is excited by a constant current E6, the bridge output voltage V is approximately given by the following equation.

As described above, the nonlinear error of a single strain gauge element is larger when the current direction is directly parallel to the stress direction than when it is parallel to the stress direction. Applying this to each of the radial strain gauge element and the circumferential strain gauge element, the position where the nonlinear error of each strain gauge element is minimized is near the position where σθ is zero for the former (point A in Figure 3). In the latter case, σ is near zero (point B in FIG. 3). That is, the position where the non-linear error of the circumferential strain gauge element is minimized is closer to the center of the silicon diaphragm than the position where the non-linear error of the radial strain gauge element is minimized. However, the reason why the nonlinear error at room temperature is minimized at the optimal position near the end of the diaphragm in the conventional example is only due to the canceling effect of the bridge constituted by the strain gauge element, and in fact, the third As shown in the figure, the stress near the end of the diaphragm changes sharply with respect to position, and the above-mentioned canceling effect is extremely unstable.〇Line NL (V)
is given approximately, and the fundamental difference between the conventional example and the present invention will become clearer.

Here, NL(R) indicates a nonlinear error of the radial strain gauge element, and NL(T) indicates a nonlinear error of the circumferential strain gauge element.

On the other hand, at the position of the radial strain gauge element and circumferential strain gauge element that minimizes the non-line-of-line error as described above, the axial orientation of each strain gauge element that maximizes the bridge output sensitivity is (1) As is clear from equations and equations (2), πt is the maximum axis, and it can be seen from FIG. 5 that this is the <111> axis in the conventional example shown in FIG. 2 and the present invention.

For this reason, in the present invention, the current direction of each strain gauge element is made to match the crystal axis direction.
Note that even if the crystal axes are shifted during manufacturing, the effects of the present invention will not be impaired as long as πt in FIG. 5 does not change sharply. FIG. 6 shows an embodiment of the present invention.

The embodiment shown in FIG. 6 is made of N-type silicon single crystal {110
} having a plane orientation passing through the center on the surface of the silicon diaphragm 11, and parallelly arranged with the 111〉 axis as the center of symmetry.
radial strain gauge elements 12 and 13, and two circumferential strain gauge elements 14, which are also arranged with the 112〉 axis passing through the center on the surface of the silicon diaphragm 11 as the center of symmetry,
15.

These strain gauge elements 12, 13, 14, 15 are formed by diffusing impurities such as boron on the surface of the silicon diaphragm 11, and are formed from the center of the circumferential strain gauge elements 14, 15. The distance to the center of the silicon diaphragm 11 is determined by the radial strain gauge element 12,
13 to the center of the silicon diaphragm 11. Furthermore, these four strain gauge elements 12 are connected by a conductor such as At.
, 13, 14, and 15 are connected to a bridge, thereby converting a strain conversion physical quantity such as pressure into an electrical signal. As described above, according to the present invention, it is possible to realize a semiconductor strain gauge with small nonlinear errors and their temperature effects, that is, high accuracy, a wide allowable temperature range, and high output sensitivity. , it is possible to extremely minimize variations in various properties between rods that occur during the manufacture of silicon diaphragms.

[Brief explanation of drawings]

Figures 1 and 2 are layout diagrams of strain gauge elements in conventional examples, Figures 3, 4, and 5 are illustrations of characteristics of semiconductor strain gauges, and Figure 6 is an illustration of an embodiment of the present invention. It is. 1, 6, 11... Silicon diaphragm, 2,
3, 7, 8, 12, 13... Radial strain gauge element, 4, 5, 9, 10, 14, 15... Circumferential strain gauge element.

Claims (1)

[Claims] 1 In a semiconductor strain gauge in which a plurality of P-type strain gauge elements are formed on a diaphragm surface having {110} plane orientation made of N-type silicon single crystal, and some of them are bridge-connected, the center on the diaphragm surface The radial strain gauge element is placed at a position where the <111> axis passes through the center and the circumferential stress is almost zero, and the <112> axis passes through the center of the diaphragm surface.
＞A semiconductor strain gauge characterized in that a circumferential strain gauge element is arranged at a position on the axis where radial stress is approximately zero.