JPS5925393B2 - Semiconductor strain gauge diaphragm - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a semiconductor pressure transducer that converts pressure into an electrical signal by utilizing the piezoresistance effect of a semiconductor single crystal such as silicon, and particularly relates to a semiconductor pressure transducer that converts pressure into an electrical signal. This relates to a diaphragm.

Figure 1a shows the configuration conventionally used as a semiconductor strain gauge type diaphragm made of a semiconductor single crystal.
and b.

The diaphragm 10 has a circular recess 11 provided on one main surface of the silicon single crystal, and the thinner part of the single crystal due to the formation of the recess 11 becomes a strain-generating part 13, and the peripheral fixed part 14 Therefore, it is fixed to a mounting base 15 having a communication hole 16 with an adhesive 17. On the strain generating part 13, semiconductor strain gauges 1, 2, 3, 4 are formed by diffusion of impurities.
is formed, and when pressure p is applied from the outside, the strain-generating portion 1
3 is a semiconductor strain gauge, and piezoresistors 1, 2, 3, and 4 change. FIG. 1a shows the arrangement of semiconductor strain gauges on the diaphragm 10, in which a pair of radius gauges 1 and 2 are provided in the direction of the crystal axis 110〉 passing through the center on the strain-generating part 13; A pair of tangent gauges 3 and 4 are provided at right angle positions (only one pair of each is shown in the figure,
Others are omitted).

These radius gauges 1, 2 and tangent gauges 3, 4 are connected to form a Wheatstone bridge. The centers of radius gauges 1, 2 and tangent gauges 3, 4 used here are at the same distance from the center of the recess, and the distance r from the center of the recess is
The ratio L between the radius a and the radius a of the strain-generating portion is approximately 0.8.
a However, such conventional semiconductor pressure transducers using semiconductor strain gauge diaphragms do not always have sufficiently satisfactory sensitivity.

An object of the present invention is to provide a semiconductor strain gauge type diaphragm suitable for precision measurement that can obtain the largest output. It has a recess, and has a plurality of strain gauges arranged in the radial direction and tangential direction in the strain-generating part with a thickness h corresponding to the recess in the second main surface, and a mounting base is installed at the peripheral part of the semiconductor single crystal. In the diaphragm fixed to the diaphragm, the crystal plane of the diaphragm has a (110) plane orientation, and the piezoresistive strain gauge constituting the radius gauge is along the <111> axis passing through the center of the strain-generating part of the diaphragm, c is h
, and the total length of the radius gauge is arranged within a-c (a is the radius of the strain-generating portion). When a semiconductor strain gauge type diaphragm is used, for example, as a pressure gauge, the first requirement is that its output signal be accurately proportional to the pressure, and the second requirement is that the output signal be large.

To do this, it is first necessary to select the crystal axis with the largest piezoresistance coefficient, which is a sensitivity coefficient. In order to meet this need, the present invention employs a (110) plane as the diaphragm surface, and a configuration in which the radius gauge is set on the 111〉 axis passing through the center of the strain-generating portion. This is due to the piezoresistance coefficient π in the longitudinal and lateral directions of the (100) plane orientation. and πΣ are approximately Σπ44 and -Σπ44 (π44 is the piezoresistance coefficient), respectively, whereas πL and πT in the 111〉 crystal axis direction in a silicon single crystal with the (110) plane orientation are approximately Σπ44 and -Σπ44, respectively. -Xπ44. Next, it is necessary to form the gauge at the location of the highest stress.

It is well known that when a peripherally fixed model diaphragm is used as a pressure-strain conversion element, the closer it is to the fixed part, the greater the strain (or stress) becomes. Figure 2a
shows the situation; the horizontal axis of this figure represents the position from the center in r/a, and the vertical axis represents stress (KI impact). σ and σ1 indicate the stress in the radial direction and the tangential direction, respectively, and these σ and σt are A,
It is expected that the fixed part will rise to the position of r/a=1 as shown in B. However, the peripheral part 1 of the recess of the diaphragm
2 is formed with a certain radius of curvature C as shown in FIG. 2b. This radius of curvature C is set approximately at the strain-generating portion 13 in order to avoid a decrease in fracture pressure due to stress concentration in this portion.
be equal to the plate thickness h. Therefore, the stress in the portion corresponding to this portion is lower than in the case of the ideal model diaphragm, as shown in D and E in the same figure. This shows that it is not best to provide the gauge at the outermost periphery of the strain-generating section 13, and what is more problematic is that this section is greatly affected by variations in machining the recess. If the variation is large, it may reach 20(f).

That is, the change in resistance of the strain gauge placed on the diaphragm is expressed by the product of the piezoresistance coefficient and the stress, as shown in the following equation.

The resistance change (P) of the radius gauge is r The low resistance change (brown?) of the tangential gauge. Therefore, if a strain gauge is formed in a part where the stress is disordered, such as the area around the recess 12, the characteristics will be disordered. In this case, variations in processing and other factors can be directly measured as variations in characteristics.

Therefore, the present invention defines the gauge position.

FIG. 3 shows the arrangement positions of the gauges around the strain-generating part, and the same parts as in FIG. 1 are given the same reference numerals.
In this figure, if the radius of the strain-generating portion 13 is a, the radius of curvature of the peripheral portion 12 of the strain-generating portion is c, the length of the gauge is 2L, and the distance from the center of the diaphragm to the center of the gauge is r, then the gauge is the strain-generating portion. The following conditions are required to avoid interference with the periphery (x≧0).

r+L≦a-c ・・・・・・・・・・・・・・・
...(3) In order to avoid stress concentration at the end and ensure the pressure resistance of the diaphragm, if the radius of curvature of the peripheral part of the strain-generating part is c, then from equations (3) and (4), the position r of the gauge is It is necessary to arrange it to satisfy the requirements.

In order to detect high stress under this restriction, it is necessary to reduce the gauge length 2L. However, these gauges are used connected to a constant current excitation bridge as shown in Figure 4, and the output E, is EO2ΔRIx+RF6lx=
R7YOIx...(6) Here, ΔR...
...Resistance change of the strain gauge R...Resistance value F of the strain gauge...Gauge factor ε of the strain gauge...Strain σ...Stress 1 ...Excitation current x π...Piezoresistance coefficient Y in equations (1) and (2)...
...Young's modulus, so in order to obtain a large output signal, it is necessary to increase the gauge resistance R, and therefore it is not desirable to reduce the gauge length 2L.

On the other hand, in the present invention, in order to ensure the effective length of the strain gauge of 2L, strips having a length n of ↓ are arranged in the radial direction, and these low resistance bodies are connected in series.
Gauge resistance value was secured.

Note that, strictly speaking, a proportional relationship does not hold between the pressure p and the stress σ.

Membrane stress and the like handled in so-called large displacement problems are included as non-linear terms, and there is also a non-linear term for the stress σ of the piezoresistance coefficient itself. Regarding these points, according to the study results of the present inventors, the input pressure P and the bridge output voltage E. It has become clear that the linearity between the two is highly dependent on the arrangement of the strain gauges, and a semiconductor strain gauge type diaphragm with good linearity can be obtained by arranging the tangential gauge slightly inside the radius gauge. However, even in this case, a practical problem is that it is necessary to make the output signal as large as possible and to ensure the linearity of both signals.

The present invention was obtained as a result of such considerations. below,
An example will be explained.

FIGS. 5A and 5B show one embodiment, and the same parts as in FIG. 1 are given the same reference numerals.

The diaphragm is made of silicon single crystal with n-type conductivity (
011) The strain generating portion 13 and the fixing portion 14 are formed by a recessed portion provided on the back surface. The radius of curvature c around this concave portion is equal to the thickness h of the strain-generating portion 13, and the fixing portion 14 is airtightly bonded to the mounting base 15, and the material of the mounting base 15 is silicon to ensure adhesive strength. It is joined to the diaphragm 10 using a gold-silicon eutectic alloy. 111 on the strain-generating portion 13 of the diaphragm 10
Strain gauges 21, 22; 31, 32 arranged radially along the axes, i.e.
41, 42; 51, 52 are formed by diffusion of p-type impurities, and are arranged at positions that satisfy equation (5). Strain gauges 23, 24:33, 34:4 are arranged tangentially on the 45th axis from the 110〉 axis.
3,44:53,54 are formed in the same manner as described above,
Between these radial gauges, for example 21 and the tangential gauge 24, there are provided an aluminum evaporated wiring 25 for bridge connection and a wiring 26 connected to the electrode 5. When a pressure p is applied to the surface of the semiconductor strain gauge diaphragm constructed in this way from the direction of the arrow in FIG.
At this time, the radius gauges 21 and 22 show a positive resistance change according to equation (1) based on the piezoresistance effect, and the tangent gauges 23 and 24 show (2 ) shows a negative resistance change according to the equation (6), so by making the bridge connection shown in Figure 4, it is possible to obtain an output according to the equation (6), and since the stress σ or strain ε is approximately proportional to the pressure, The bridge output voltage e is approximately proportional to the pressure p.

FIGS. 6A and 6b show still other embodiments, and the fifth
The difference from the figure is the configuration of the radius gauge.

The same parts as in FIG. 5 are given the same reference numerals. The radius gauge of this embodiment consists of four strain gauge strips 21a, 21b, 21c, and 21d arranged parallel to the <111> axis, and connected in series by connecting members 6b, 6c, and 6d made of low resistance materials. Both ends are connected to electrodes 5a, 5b via connecting members 6a, 6e. These strain gauge strips are formed of a p-type impurity diffusion layer as in the previous embodiment, and the low resistance members 6a, 6b, . . . and electrodes 5a, 5b are formed by vapor deposition or the like. The midpoint in the length direction of these strain gauge strips is formed at a position that satisfies equation (5). FIG. 6b shows a cross section taken along line FF in FIG. 6a, and 7 indicates an oxide film. Even when using a radius gauge with such a configuration, the same effects as in the embodiment shown in FIG. 5 can be obtained.
However, since the effective part of the strain gauge strip is located in the periphery of the strain-generating part, it has excellent sensitivity and a large output can be obtained.

As described above, in the semiconductor strain gauge type diaphragm described in this example, (1) the radius gauge and the connection gauge are arranged on the crystal axis having the maximum sensitivity, and the radius gauge is arranged in the periphery of the strain-generating part. Since large stress can be detected intensively, the output signal is large and linearity between pressure and output voltage can be ensured.

(2) Since the radius of curvature of the diaphragm recess is made almost equal to the thickness of the strain-generating portion, the pressure resistance of the diaphragm can be ensured, and the strain gauge is configured so that it does not cover the curvature of the periphery of the diaphragm recess. Therefore, variations in characteristics due to stress disturbances are small.

As described above, it is possible to provide a semiconductor strain gauge type diaphragm using the strain gauge type diaphragm of the present invention, which has great industrial effects.

[Brief explanation of the drawing]

FIG. 1a is a plan view of essential parts of a conventional semiconductor strain gauge type diaphragm, FIG. 1b is a cross-sectional view of the same, FIG. Figure 2b is a cross-sectional view of the main part of the diaphragm.
FIG. 3 is a sectional view of the main part of the diaphragm, FIG. 4 is a bridge circuit diagram, FIG. 5a is a plan view of the main part of an embodiment, FIG. 5b is a sectional view, and FIG. is a plan view of the main part of another embodiment, and FIG. 6b is taken along the line FF in FIG. 6a.
FIG. DESCRIPTION OF SYMBOLS 10... Diaphragm, 12... Peripheral part (of the recessed part of the diaphragm), 13... Strain generating part, 14... Fixing part, 21, 22, 31, 32, 41, 42, 51, 52.
・Radius gauge, 23, 24, 33, 34, 43, 44
, 53, 54... tangent gauge, 21a, 21b, 21
c, 21d, 21e...Strain gauge strips, 6a, 6
b, 6c, 6d...low resistance member, 5a, 5b... electrode.

Claims (1)

[Claims] 1. A radius of curvature c around the concave portion on the first principal surface of the semiconductor single crystal.
and a plurality of strain gauges arranged in a radial direction and a tangential direction in a strain-generating portion with a thickness h corresponding to the recess of the second main surface of the semiconductor single crystal, In a diaphragm fixed to a mounting base at the periphery of a semiconductor single crystal, the crystal plane of the diaphragm has a (110) plane, and the piezoresistive strain gauge constituting the radius gauge passing through the center of the
111> axis, the c is equal to the h, and the total length of the radius gauge is within a-c (a is the radius of the strain-generating part). . 2. The radius gauge is arranged at a position that satisfies the relationship of r/a≈1−[h+L]/a, where 2L is the length of the radius gauge in the radial direction. Semiconductor strain gauge type diaphragm. 3. The semiconductor strain gauge type diaphragm according to claim 1 or 2, wherein the radius gauge comprises a plurality of strips parallel to each other and connected in series by a low resistance element. 4. A semiconductor strain gauge type diaphragm according to any one of claims 1 to 3, wherein the semiconductor is silicon.