KR840001795B1 - Semiconductor diaframe type sensor - Google Patents

Abstract

The pressure sensor includes a monocrystalline silicon chip defining recesses on a borosilicate glass substrate in a housing with a hollow extension for connection to a point where pressure is to be determined. Holes in the substrate provide communication between the extension and some of the recesses. Above all the recesses are provided pressure-sensitive diaphragms associated with strain gauges in electrical bridges connected by electrodes and leads to terminals. The chip and substrate are materials with similar coefficients of thermal expansion and are bonded by anoic bonding.

Description

Semiconductor Diaphragm Type Sensor

1 is a stress distribution diagram for explaining the principle of the semiconductor diaphragm sensor of the present invention.

2 is a structural diagram showing an embodiment of a semiconductor diaphragm sensor of the present invention.

FIG. 3 is a Wheatstone brrdge circuit diagram of the piezoresistive element of the drawing of FIG. 2. FIG.

4 and 5 are enlarged explanatory diagrams of the piezoresistive element of FIG.

6 and 7 are structural diagrams in the case where the shape of the diaphragm is deformed.

8 (a) is a nonlinearity diagram of pi.

8 (b) is a nonlinearity diagram of πt.

TECHNICAL FIELD The present invention relates to a semiconductor diaphragm sensor, and more particularly, to an improvement of a semiconductor diaphragm type sensor that converts a pressure or a force into a deformation amount and detects this as a change in electrical resistance.

Conventionally, as shown in Japanese Patent Laid-Open No. 51 (West 1976) -69678, a silicon single crystal substrate has a thick center portion and an outer circumference portion, and a donut-shaped thin portion between them. BACKGROUND ART A semiconductor diaphragm type sensor is formed which is formed so as to form a thin film and has a piezoresistive element formed in a thin film.

Since the sensor has a small film stress generated when the pressure is applied, the linearity with the input pressure is good even at low pressure, and the thinner the width, the better the sensitivity. On the other hand, the piezoresistive element needs a certain length, but when it is formed in a narrow thin film, a plurality of piezoresistive elements are necessarily connected in series.

However, the piezoresistive elements are provided in parallel to a specific crystal axis. However, when a plurality of piezoresistive elements are connected in series, the direction in which the force applied to the piezo resistors is different is different and the linearity between the input pressure and the output voltage is affected. Get mad.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor diaphragm sensor capable of measuring the force or pressure to a low range with high sensitivity and further excellent linearity, eliminating the drawbacks of the conventional prior art.

A feature of the present invention is to use a semiconductor unity as a diaphragm material, to form a thick rigid portion in a thick fixed portion at the periphery thereof, and to spread the thin film therebetween to spread the piezo resistor. A portion where the boundary line between the fixed portion, the distortion portion, and the rigid portion and the distortion portion crosses at right angles with one of the crystal axes of the semiconductor single crystal is a straight line. The point is that it is configured to be.

Next, an embodiment of the present invention will be described with reference to the drawings.

As is well known, the variation in resistance value ΔR / R of a piezoresistive element formed by diffusion on a semiconductor diaphragm is a coefficient when it crosses at a right angle with the coefficient πl (positive) when the current direction and the stress direction of the element are parallel. By pi (part), it is expressed as a first order approximation as follows.

Where? 1 and? T are the stresses in the longitudinal direction and the stresses in the perpendicular direction respectively acting on the piezoresistor.

By the way, the stress distribution on the top of the distortion part (thin) top surface is as shown in FIG. In this stress distribution, it is evident from FIG. 1 that the most effective position in the output sensitivity of the device is near the thin end, even though? T is a negative value. In addition, as described in Example (1) to be described later, in order to maximize the bridge output sensitivity with respect to the input pressure, two piezoresistive elements are formed in the vicinity of the reinforcement rigid part of the thin surface and in the vicinity of the fixed part of the periphery. It is desirable to form a bridge circuit with these.

On the other hand, in order to examine the linearity of such a semiconductor earpiece-type sensor, the present inventors have developed (1) to include the higher order terms of the coefficients and analyze the same. Found significantly worse than that. That is, as shown in FIG. 8A, the nonlinearity of pi is approximately 0 in tensile stress, and 1% in pressure stress of 230 MPa. On the other hand, the non-linearity of is 4.5% in the tensile stress of 230MPa, -3% in the compressive stress of 230MPa, as shown in Figure 8b, there is a significant difference in both. Considering these findings, the linearity will be improved in principle by arranging the piezoresistor in parallel to the axis passing through the diaphragm center.

In addition, the inventors of the present invention conducted an analysis of the relationship between the thin shape of the diaphragm and the straight line, and as a result, the dimension ratio from the center of the diaphragm to the thin end of the minor end was 0.5 or more. It was found that the film stress was reduced and exhibited good linearity by making the thickness of the rigid body portion more than twice the thickness of.

2 shows an embodiment of the semiconductor diaphragm sensor of the present invention, (a) is a plan view, (b) is a sectional view, and shows an example applied to a pressure gauge. In Fig. 2, reference numeral 11 denotes a diaphragm made of a single-crystal single crystal of n-type silicon. For example, a {100} plane substrate is used to make the outer periphery thick and the rigid part of the center part. Except for the center thick portion, which is (32), the groove-shaped portion 33 is formed by anisotropic processing by alkali etching, and the thin portion formed therefrom is formed by the anisotropic processing. The piezoresistive element 5 is formed on the upper surface of the base distortion portion 41 by diffusion of P-type impurities. However, the piezoresistive elements 5 were formed so as to be arranged in plural on the {100} plane with respect to the <100> axis at which πl is the maximum. The piezoresistive elements 51, 53 are located near the central rigid portion 32. In addition, piezo resistors 52 and 54 are formed in the vicinity of the Uijugo government part 31, respectively. As shown in the drawing, the fixing part 31 and the rigid part 32 are configured to have a square in which the angular concentric sides are parallel, and the fixing part 31 and the distortion part 41 and the rigid part ( The boundary line 32) and the distortion part 41 are each configured to be a straight line crossing at right angles to the crystal axis <110> of the semiconductor single crystal. The piezoresistive elements 51 to 54 are formed parallel to the crystal axis at a portion where the boundary line intersects the crystal axis at a right angle, and the four piezoresistive elements are paired with good characteristics among the piezo resistors. By selecting (51) to (54), as shown in Fig. 3, the Wheatstone bridge circuit was fabricated so as to obtain an output differentially and to reduce the temperature influence. In Fig. 3, reference numeral 13 denotes a DC power supply, and 14 denotes an output meter.

In Fig. 2, reference numeral 6 denotes a vapor deposition electrode for squeezing the output (change in resistance value) of the piezoresistive element 5 to the outside to form the bridge circuit described above, for example, vacuum deposition of aluminum. . (7) is a lead wire which connects the deposition electrode 6 on the diaphragm 1 to the terminal electrode 8, and the terminal electrode 8 is formed on the terminal plate 9 which is fixed on the case 10. It is formed by thick film paste such as palladium or plating. The fixing portion 31 of the diaphragm 1 is firmly adhered to the support 12.

Now, when the pressure P is applied in the direction of the arrow in FIG. 2B, the diaphragm 11 bends downward, and the reaction history as shown in FIG. 1 occurs on the plane of the distortion part 41. As shown in FIG. At this time, the piezo resistors 51 and 53 decrease in resistance in response to the compressive stress, and the piezo resistors 52 and 54 increase in resistance in response to the tensile stress. Therefore, the output power corresponding to the pressure can be automatically taken out in the bridge circuit shown in FIG.

4 is an enlarged view of the piezoresistors 51 to 54 shown in FIG. 2, (a) is a plan view, (b) is a sectional view, and FIG. 5 is a view of the piezoresistors 51 therein. It is shown enlarged. This type of sensor usually processes an output signal by installing an external amplifier. In this case, it is necessary to reduce the power consumed by the sensor in consideration of the driving power to various circuit elements and the like used as the amplifier. Therefore, the lower limit of the initial resistance value of a piezoresistive element is determined by the specification of an amplifier. On the other hand, when fabricating a diffusion type piezoresistive element, its initial resistance value is determined by the diffusion impurity concentration and the shape dimension of the piezoresistive element. Among them, the impurity concentration is an important filter for determining the temperature coefficient of the piezoresistive element, and the most appropriate value is preferably determined in view of the temperature characteristic of the sensor. Therefore, in order to obtain a predetermined resistance value, the shape dimension of the piezoresistive element must be changed. However, as is well known, the resistance value is proportional to the length of the piezoresistive element and inversely proportional to the width. As described above, when the lower limit of the initial resistance is achieved in the amplifier shaft, it is often necessary to increase the length of the piezoresistive element and to make the width extremely small. However, simply lengthening the piezoresistive element prevents the conversion of the effective stress-resistance value change as apparent from the stress distribution shown in FIG. In addition, there is a technical limitation to reducing the width of the piezoresistive element. Therefore, in order to make a piezoresistive element having a large resistance value, it is most effective to form a plurality of piezoresistors parallel to each other and to electrically connect them in series. In addition, according to the embodiment shown in FIG. 2, since the boundary lines of the portions forming the piezoresistive elements 51 to 54 are straight lines, the outer rigid part of the central rigid part is compared with the circular one. The structure is suitable for employing the above method. Therefore, in the present invention, as shown in Fig. 5, the piezoresistive elements 51 are constituted by connecting four piezo resistors 511 to 514 in parallel with each other by the connecting conductor 15. The same applies to the piezo resistors 52 to 54. As shown in FIG. 2, the paired piezoresistors 51 to 54 can form four pairs on the diaphragm 1 completely equivalently, and among these four pairs, the sensor As a result, it is possible to select and use the one with the best characteristics, thereby greatly improving mass productivity.

According to the embodiment of the present invention described above

(A) Since the square diaphragm 11 attached to the center rigid body part is used, the linearity to a low pressure range is good and high sensitivity can be measured.

(B) Since the diaphragm 11 having the structure in which the piezoresistive element 5 is formed by diffusion using a semiconductor single crystal having an ideal elastic property, the whole is integral, there are few hysteresis and creep. It can be made excellent in stability.

(C) The four piezoresistive elements 51 to 54 constituting the bridge circuit can be formed at one time by IC technology, and in particular, when a substrate of {100} plane of silicon is used as the substrate, Since anisotropic processing becomes possible, mass productivity improves, and it can make small the influence of a temperature and the nonuniformity of a characteristic.

6 and 7 are structural diagrams in the case where the shape of the diaphragm is changed, respectively (a) is a sectional view, and (b) is a plan view. In FIG. 6, although the outer periphery of the inner and outer periphery center rigid body part 32 of the outer periphery fixing part 31 is all circular, the boundary line min anamorphic part 41 between the fixing part 31 and the anaerobic part 41 is circular. ) And the straight portions 311 and 321 are provided so that only the width of the boundary line between the center rigid portion 32 and the center rigid portion 32 is a straight line with a portion intersecting at any one of the crystal axes of the semiconductor crystal at right angles. Even in the diaphragm 11 having such a configuration, it is easy to form the piezoresistive elements 51 and 54 shown in FIG. 6 near the straight portions 311 and 321 of the distortion part 41, respectively. The same effect can be obtained. In this case, the seismic resistance is improved and the diaphragm 11 has a long life.

In FIG. 7, the diaphragm 11 is formed so that the fixing part 31 and the center rigid part 32 may be square together, and in this case, the piezoresistive element 5 only extends in the longitudinal direction of the distortion part 41. ), But the straight portion of each boundary line that crosses the crystal axis <110> at right angles is long, so that even when the width of the anaerobic portion 41 is narrowed, a plurality of piezoresistive vessels are formed in parallel with each other. These can be connected in series to form a piezoresistive element having a predetermined resistance value, and the nonlinear error can be further reduced by narrowing the width between the rigid portion 32 and the fixed portion 31 of the distortion portion 41. It is said to have an effect.

In addition, although the board | substrate of the {100} surface of a silicon semiconductor single crystal is used in the Example, this invention is not limited to this, You may use another crystal surface. In addition, the semiconductor crystal is not limited to silicon, and a semiconductor material having another piezoresistive effect such as germanium may be used. Moreover, although the case of pressure measurement was demonstrated in the Example, when a force is applied to the central rigid body part 32, a force measurement can also be performed and it has the same effect.

As described above, according to the present invention, there is an effect that the force or the pressure can be measured up to a low range with sensitivity and good linearity.

Claims (1)

It is made of a semiconductor single crystal and has a thick rigid body portion 32 in the center thereof, a thin distortion portion 41 formed around the rigid body portion 32, and a circumference of the distortion portion 41. A semiconductor diaphragm sensor having a ring-shaped fixed portion 31 formed in the upper portion of the semiconductor diaphragm in which one of the semiconductor crystals is formed in the distortion portion 41 in parallel with a crystal axis. A semiconductor diaphragm sensor, characterized in that the distorted portion (41) of the portion where the piezoresistive element is formed is crossed at right angles to the one crystal axis.

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