JPS5923119B2 - semiconductor strain gauge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor strain gauge, and particularly to a semiconductor strain gauge in which a strain gauge element is arranged on the surface of a diaphragm made of a semiconductor single crystal.

A semiconductor strain gauge using a silicon diaphragm made of a semiconductor semi-crystal, for example, a silicon single crystal, uses the silicon single crystal itself as a diaphragm having a fixed part and a strain-generating part, and a plurality of strain gauge elements are diffused thereon. These strain gauge elements are formed in a predetermined position using technology and wired in a Wheatstone bridge, making it possible to effectively convert the strain that occurs within the diaphragm plane into an electrical signal. .

The operating principle of this silicon diaphragm is based on the piezoresistance effect of semiconductors, and it has superior performance in terms of output characteristics than strain gauges made of metal conductors when converting physical quantities converted into strain into electrical signals. ing. FIG. 1 shows an example of the arrangement of strain gauges in a conventional semiconductor strain gauge, in which strain gauge elements are arranged along the 110〉 axis on a silicon diaphragm 1 having a (100) plane orientation. , each pair of radial strain gauges 2, 3, 4, 5 in which the direction of the current flowing through the strain gauge element and the radial stress acting on the silicon diaphragm 1 are parallel, and
Each pair of tangential strain gauge elements 6, 7, 8, 9, in which the direction of the current flowing through the strain gauge elements and the tangential stress acting on the silicon diaphragm 1 are parallel, is located near the end of the silicon diaphragm 1 at the center of the diaphragm 1. It is diffused and formed at a position equidistant X from.

Generally speaking, in semiconductor strain gauges, in order to effectively convert strain into electrical signals, four strain gauge elements provided on a silicon diaphragm 1 are configured into a 4-active Wheatstone bridge (full bridge) as shown in Figure 2. do. In FIG. 2, 22, 23, 24, 25 represent strain gauge elements;
When arranging 24 and 25, for example, the strain gauge element 2
2 and 24 are arranged as lines A in Fig. 3, and strain gauge elements 23 and 25 are arranged as shown in lines B in the same figure. can be obtained as the output of the bridge. In FIG. 3, strain and resistance change are plotted on the horizontal and vertical axes, respectively. By adopting such a configuration, the characteristics as a semiconductor strain gauge are extremely excellent, a large output can be obtained, and nonlinear errors are small. However, this semiconductor strain gauge, like general semiconductor devices, is extremely affected by the ambient temperature.

This change in output due to temperature can be electrically compensated for by installing a circuit outside the semiconductor strain gauge, and the semiconductor strain gauge shown in Figure 1 can also compensate for the high output performance obtained at room temperature by using an external circuit to compensate. It is maintained even when the ambient temperature changes. However, it has become clear that the influence of ambient temperature affects not only the output but also nonlinear errors, and it has become clear that the temperature compensation described above is insufficient. That is, when the strain gauge elements are arranged as shown in FIG. 1, there is a relationship between temperature and nonlinear error as shown in FIG. 4. In this figure, the horizontal and vertical axes represent temperature and nonlinear error, respectively, and C represents the radial strain gauge element 2 (or 3, 4,
5) characteristics, D is the tangential strain gauge element 6 (or 7, 8
,9). That is, radial strain gauge elements 2, 3, 4, 5 and tangential strain gauge elements 6, 7,
8 and 9, the influence of temperature on the nonlinear error of the resistance change with respect to each strain is significantly different, so it becomes clear that the influence of the nonlinear error of the electrical signal, that is, the bridge output, on the strain becomes large, and therefore, Conventional semiconductor strain gauges have a significant drawback in that the allowable temperature range is extremely small. The purpose of the present invention is to provide a semiconductor strain gauge of this type with a wide allowable temperature range.
at least a pair of radial strain gauge elements arranged on a diaphragm surface made of a semiconductor single crystal, in which a radial stress acting on the diaphragm surface and a current direction are parallel;
In a semiconductor strain gauge having at least one pair of tangential strain gauge elements in which the tangential stress acting on the diaphragm surface and the current direction are parallel, the diaphragm surface is
111) has a plane orientation, and is characterized in that the distances from the center of the diaphragm of the radial strain gauge element and the tangential strain gauge element are different.

The present invention was made based on the results of studies on conventional semiconductor strain gauges of this type by the present inventors.

For example, in the conventional semiconductor strain gauge shown in FIG. 1, four strain gauge elements constituting one full bridge are arranged as close as possible. This is because there are large variations in the initial resistance values of each strain gauge element when manufacturing the elements, so the four strain gauge elements that make up one full bridge are placed as close together as possible, thereby minimizing the variation in initial resistance values. This is to reduce the deviation of the zero point of the blitz output. In other words, when considering the arrangement of strain gauge elements that minimizes the nonlinear error of the bridge output under the constraint that the four strain gauge elements that make up one full bridge are placed as close as possible, the radius Directional strain gauge elements and tangential strain gauge elements will be formed equidistant from the center of the silicon diaphragm.

For example, in FIG. 1, the position of distance X from the center of the silicon diaphragm can be obtained as the position that minimizes the non-linear error, and this position of X is the position of the radial and tangential strain gauge elements. The non-linear error of the two types of strain gauge elements is not necessarily small;
Since the signs of the values are opposite, the nonlinear error is only minimized by the cancellation effect when the bridge is configured. Moreover, near the end of the silicon diaphragm, the stress changes sharply with respect to position, so the nonlinear error of the strain gauge element itself also changes sharply with respect to position. Therefore, if this positioning method is used, the characteristics such as non-linear errors will greatly change due to positional deviation of the strain gauge element caused by errors in processing the silicon diaphragm.
However, with the current situation where semiconductor manufacturing technology has improved, especially in a series of processes for manufacturing elements such as diffusion technology, photo etching, and photo masks, even at locations on the diaphragm at different distances from the center of the diaphragm,
It was found that the variation in the initial resistance value of the strain gauge element can be reduced.

Based on the results of this study, the positions of the radial strain gauge element and the tangential strain gauge element on the diaphragm are changed completely independently, and for all mutually independent full bridges in which the relative positional relationship of both strain gauge elements is different, The strain gauge element of the present invention was obtained by examining nonlinear errors and their temperature effects.Furthermore, since the (100) plane used as the diaphragm surface has anisotropy in the piezoresistance coefficient, the strain gauge element It is easily affected by variations depending on the placement location, and on the other hand, as a diaphragm surface (
111) surface, the piezoresistance coefficient of this surface is isotropic, so such variations can be eliminated. Examples will be described below. FIG. 5 shows an example of this, in which a silicon diaphragm 11 made of an n-type silicon single crystal and having an isotropic (111) plane orientation is aligned along any crystal axis passing through the center of the diaphragm. Then, a pair of radial strain gauge elements 21 and 31 are placed at a distance XRl from the center of the silicon diaphragm 11, and a pair of radial strain gauge elements 41 and 51 are placed at a distance XR2 from the center of the silicon diaphragm 11, for example, using a P-type material such as boron. A pair of tangential strain gauge elements 61 and 81 are formed by diffusion of impurities, and a pair of tangential strain gauge elements 71 and 91 are positioned at a distance XT2 as a radial strain gauge element. It was formed in a similar way,
They are arranged so that XR>XT.

That is, these strain gauge elements 21 and 61, 31 and 7
By combining strain gauge elements 1, 41 and 81, and 51 and 91, the strain gauge elements are arranged so as to constitute four types of independent full bridges. This silicon diaphragm 11 is made by forming a concave hole on the side opposite to the surface on which the strain gauge element is formed of an n-type silicon single crystal wafer, and using the silicon single crystal itself having such a concave hole as a diaphragm. Therefore, the arrangement of the strain gauge elements is designed based on this concave hole.

Therefore, when manufacturing this diaphragm, it is fully conceivable that the position of this strain gauge element will equivalently deviate from the design value. However, in the case of this embodiment, even if this positional deviation occurs, there is little variation among the rods in various characteristics of the semiconductor strain gauge, so precision is not required for such positional deviation. In addition, in this example, four types of full bridges with different characteristics are configured, and even if variations occur, by changing the combination of strain gauge elements that make up the full bridge, variations in various characteristics can be corrected. can be accommodated.
Therefore, there is no need to require strict positional deviation accuracy when machining a concave hole in a silicon diaphragm, and the machining yield is improved. In addition, since there is no variation due to the strain gauge position on the diaphragm, the radial strain gauge element and the tangential strain gauge element can be placed at positions where the temperature effects of these nonlinear errors can be eliminated, thereby reducing the nonlinear error. Temperature effects can be reduced.

As described above, the semiconductor strain gauge of this embodiment has the advantage of being able to eliminate the serious drawback of conventional semiconductor strain gauges, such as the temperature effect of non-linear errors, and having small variations in characteristics due to manufacturing processes. It has a great effect.

That is, the semiconductor strain gauge of the present invention provides a semiconductor strain gauge of this type that has a wide allowable temperature range, and has great industrial effects.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the arrangement of strain gauge elements of a conventional semiconductor strain gauge, Figure 2 is a circuit diagram also showing the operating principle of the strain gauge, Figures 3 and 4 are characteristic diagrams, and Figure 5. FIG. 2 is an explanatory diagram showing the arrangement of strain gauge elements of the semiconductor strain gauge of the present invention. 11... Silicon diaphragm, 21, 31,
41, 51... Radial strain gauge element, 61,
71, 81, 91...Tangential strain gauge elements.

Claims (1)

[Scope of Claims] 1. At least one pair of radial strain gauge elements in which the radial stress acting on a diaphragm surface made of a semiconductor single crystal and the current direction are parallel, and the tangential stress and current acting on the diaphragm surface. In a semiconductor strain gauge having at least one pair of tangential strain gauge elements whose directions are parallel to each other, the diaphragm surface has a (111) plane orientation, and the radial strain gauge element and the diaphragm of the tangential strain gauge element A semiconductor strain gauge characterized by different distances from the center. 2. The semiconductor strain gauge according to claim 1, wherein a bridge is formed by the pair of radial strain gauge elements and the pair of tangential strain gauge elements. 3. The radial strain gauge element constituting the bridge and the tangential strain gauge element located closer to the center of the diaphragm than the radial strain gauge element act as a bridge against strain occurring on the diaphragm surface. 3. The semiconductor strain gauge according to claim 2, wherein the semiconductor strain gauge is disposed at a position where the temperature effect of non-linear error of the output signal is substantially reduced. 4. The semiconductor strain gauge according to claim 1, wherein the semiconductor is silicon, and the radial strain gauge element and the tangential strain gauge element are formed by impurity diffusion.