JPS6143868B2 - - Google Patents

Description

[Detailed description of the invention]

For example, the present invention can be applied to a load or force applied to fixation,
Alternatively, the present invention relates to a mechanical-electrical converter for detecting a mechanical quantity such as the pressure of a liquid, gas, or fluid and converting it into an electrical quantity, and particularly relates to a mechanical-electrical converter that utilizes the piezoresistance effect of a semiconductor. In the specification of Japanese Patent Application No. 51-137954 (Japanese Patent Publication No. 57-58791) previously filed by the present applicant, an elastic substrate made of silicon single crystal is fixed to the surface of the base at its periphery. A strain-generating part is formed in the center where strain occurs due to external pressure, a P-type semiconductor strain-electrical conversion element is formed on the surface of this strain-generating part, and the strain-electrical conversion element is proportional to the strain of the strain-generating part. In a mechanical-electrical converter configured to detect electrical output, (length of the short axis on the surface of the strain-generating portion)/(thickness of the strain-generating portion) is set within a range of 2 to 150, And the average conductivity of the strain-electric conversion element is 3.7×10 ² to 6.0×10 ² (1/
A mechanical-electrical converter that is set within the range of Ωcm) and driven by a constant current power supply, so that the output relative to external pressure is always constant without being affected by changes in ambient temperature. It has been proposed as a self-temperature compensated mechanical-electrical converter. In this case, the above-mentioned "length of the short axis" is specified by the "diameter at the surface of this strain-generating part" if the strain-generating part is circular, and if the strain-generating part is polygonal, " It is specified by the length of the shortest axial line that passes through the center of the surface of this strain-generating part and is drawn on this surface. By the way, when a bridge circuit is constructed using the strain-to-electrical conversion element in such a mechanical-to-electrical converter, as described above, although the output is stable against changes in ambient temperature, the mechanical-to-electrical conversion is Due to the influence of assembly errors of the device, structural variations in the strain-generating part of the elastic substrate, and variations in the gauge factor and resistance value of each strain-electrical conversion element, even under a constant input current, the Output values vary. To adjust this variation and obtain a constant output for a constant pressure, a variable resistor is connected between the input terminals of each mechanical-electrical converter, and this variable resistor This can be resolved by adjusting the current flowing through the circuit. However, in this method, due to the addition of a variable resistor, the current flowing through the bridge circuit is not constant with respect to temperature and has temperature characteristics. That is, if the combined resistance Rb of the bridge circuit and the value of the parallel resistance are Rp, the current I ₁ becomes I ₁ = I × Rp / Rb + Rp, and while the combined resistance Rb of the bridge circuit generally has a positive resistance temperature characteristic, Assuming that the resistance value of the parallel resistance Rp remains virtually unchanged with respect to temperature, I ₁
will decrease with increasing temperature. Therefore, when a constant current is applied to the bridge circuit, even in the case of a mechanical-electrical converter that is self-temperature compensated so that the output sensitivity is constant with respect to temperature, the output sensitivity is changed by the resistor Rp added in parallel. The good temperature characteristics of the
The smaller the value of Rp and the smaller the value of the output adjustment ratio (I ₁ /I), the larger it becomes. The present invention has been made to eliminate such drawbacks, and its purpose is to maintain the output temperature characteristics of the above-mentioned mechanical-electrical converter stably without being affected by ambient temperature, while maintaining constant current. The aim is to adjust the current flowing into the bridge circuit from the power supply over a wide range. In order to achieve this object, the structural features of the present invention include an elastic substrate made of silicon single crystal on the surface of the base, and a strain-generating portion that is fixed at its periphery and that is strained by external pressure at its center. A P-type semiconductor strain-to-electrical conversion element is formed on the surface of the strain-generating portion, and a constant current power supply is connected to the P-type semiconductor strain-to-electrical conversion element, so that the strain is proportional to the strain in the strain-generating portion. In a mechanical-electrical converter configured to detect electrical output, (length of the short axis on the surface of the strain-generating portion)/(thickness of the strain-generating portion) is set within a range of 2 to 150, The strain-electric conversion elements are formed to form a bridge circuit as four strain-electric conversion elements having an average conductivity within the range of 3.7×10 ² to 6.0×10 ² (1/Ωcm). , and at least one fixed resistor having approximately the same average conductivity and approximately the same resistance temperature characteristics as the strain-to-electrical conversion element is formed at the zero strain portion of the surface of the elastic substrate at the input end of the bridge circuit or The reason is that it is connected to the output end. However, by configuring the present invention in this way, when driven by a constant current power supply,
The output of the bridge circuit is determined based on the relationship between the average conductivity of each strain-electrical conversion element determined as described above and the ratio of the thickness of the strain-generating portion to the length of the short axis line, so that the output of the bridge circuit responds to changes in ambient temperature. Not only can the temperature output error be suppressed to a minimum without being affected, but also the adjustment circuit can maintain the stable output temperature characteristics of the bridge circuit while also controlling the temperature output from the constant current power supply. The current flowing into the circuit can be adjusted over a wide range, and as a result, in this type of mechanical-electrical converter, assembly errors, structural variations in the strain generating part, and gauge factors of each strain-electrical conversion element can be reduced. It is possible to easily and accurately adjust output variations with respect to a constant pressure caused by variations in resistance values, etc., by simple operations. Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIGS. 1 and 2 show the main parts of a mechanical-electrical converter embodying the present invention, and are designated by the reference numeral 1 in the figures.
0 indicates an elastic substrate made of silicon single crystal, and 20 indicates a base. The elastic substrate 10 is bonded to the upper surface 21 of the base 20 at its periphery, and on the upper surface 11a of the circular strain-generating portion 11 formed in a thin shape at the center thereof, there is a groove as shown in FIGS. 1 and 2. As shown, four P-type semiconductor strain-to-electric conversion elements g ₁ to _{g 4} are integrally formed by diffusion in a portion of the oxide film 12 by a diffusion planar method. In this case, the ratio of the diameter of the surface of the strain-generating portion 11 to the thickness of the strain-generating portion is within the range of 2 to 150.
Furthermore, if the strain-generating portion 11 is polygonal, the ratio specified here is the length of the shortest axis drawn on the surface passing through the center of the surface of the strain-generating portion (i.e., the length of the short axis). ) corresponds to the ratio of the thickness of the homogeneous strain part. Each strain-electric conversion element g ₁ to g is 2.4×
It has an impurity concentration within the range of 10 ²⁰ to 40 × 10 ²⁰ (atoms/cm ³ ), and when a bridge circuit is configured with this element and a constant current is supplied to the bridge circuit, the output of the bridge circuit is It is designed to be stable within the allowable error range. Also, each strain -
Electric conversion elements _g1 to _g4 have four leads ₁ to ₄ .
(deposited on the upper surface of the oxide layer 12) are connected to form a bridge circuit G (see iso-ambient temperature in FIG. 3A). In addition, in FIG. 3A, leads ₁ and ₂ and leads ₃ and ₄
are the input terminal and output terminal of the bridge circuit G, respectively. Note that the surface impurity concentration of each strain-electric conversion element g ₁ to _{g 4} is 2.4×10 ²⁰ to 4.0×10 ²⁰ as described above.
(atoms/cm ³ ).As is well known, the positive temperature characteristic α of the resistance of this type of strain-electrical conversion element is based on the surface impurity concentration of the strain-electrical conversion element. As the surface impurity concentration increases, the negative temperature coefficient β of the gauge factor of the strain-electric conversion element changes to become minimum at a predetermined surface impurity concentration, and increases almost linearly as the surface impurity concentration increases. However, when a mechanical-electrical converter employing such a strain-electrical conversion element is driven by a constant current power supply, the output temperature error is proportional to the sum α + β of the temperature coefficients of resistance and gauge factor. There is one surface impurity concentration on the high-concentration side and one on the low-concentration side, respectively, where the sum +β becomes zero. Focusing on this point of view, it was experimentally found that the impurity concentration was 2.4×10 ²⁰ to 4.0×10 ²⁰ (atoms/ ^cm3 ). Further, the reason why the ratio of the surface diameter of the strain-generating portion 11 to the thickness of the strain-generating portion 11 is limited to 2 to 150 is as follows. 1. The surface impurity concentration of each strain-electric conversion element g ₁ to _{g 4} is set within the range of 2.4×10 ²⁰ to 4.0×10 ²⁰ (atoms/cm ³ ) as described above, and the diameter of the strain-generating portion 11 is 3 (mm), and the thickness of the same strain part 11 is 20 (μ) ~
When an experiment was performed by changing the value within a range of 100 (μ), the temperature error in the output of each strain-electric conversion element g ₁ to _{g 4} was within the allowable error range. In other words,
The surface impurity concentration of each strain-electric conversion element g ₁ to g ₄ is
Set within the range of 2.4×10 ²⁰ to 4.0×10 ²⁰ (atoms/cm ³ ), (diameter of strain-generating portion)/2 (2× thickness of strain-generating portion)
If it is set to 15 to 75, the temperature error of the output for each strain-diameter g ₁ to _{g 4} will fall within the allowable error range. 2 Also, the above ratio, that is, (direction of strain-generating part)/(2
× strain-generating portion thickness) is 75, the diameter of the strain-generating portion is too large compared to the thickness, the strain-generating portion is deflected, and the strain-diameter output characteristic becomes very poor, and the ratio When is smaller than 1, the thickness of the strain-generating portion is too large compared to the diameter, and such a strain-generating portion does not actually serve as a strain-diameter sensing portion. In addition, each of the above-mentioned grounds is based on the fact that the strain-generating portion is, for example, a polygon, and the ratio is (length of the short axis on the surface of the strain-generating portion)/(2×thickness of the strain-generating portion). The same holds true. Next, the configuration of the main part of the present invention will be explained.
A fixed resistor 30 is provided on the upper surface of the elastic substrate 10.
As shown in the figure, each strain-diameter g ₁ to _{g 4} is diffused and formed in the outer zero strain portion of the strain-generating portion 11 . This fixed resistor 30 has approximately the same impurity concentration and approximately the same resistance temperature characteristics as the strain-electrical conversion elements _g1 to _g4 , and is connected at one end to the lead ₁ via the auxiliary lead ₅ , and at the other end. Auxiliary lead at the end
₆ , each auxiliary lead ₅ , ₆
is deposited on the top surface of the oxide film 12 (see FIGS. 1 and 3A). Furthermore, a variable resistor 40 constituting an external circuit is connected between the auxiliary lead ₆ and the lead ₂ , as shown in FIG. 3A.
The current supplied between the terminals ₁ and ₂ is adjusted, and the fixed resistor 30 and variable resistor 40 form an adjustable ambient temperature. By the way, by connecting the adjustment circuit consisting of the fixed resistor 30 and the variable resistor 40 between the input terminals ₁ and ₂ of the bridge circuit G in this way,
The range in which the output of the bridge circuit G provided in the mechanical-electrical converter can be adjusted without impairing its temperature characteristics will be discussed. In this case, since the output of the bridge circuit G is proportional to the current flowing through the bridge circuit G, we will focus on the relationship between the input current of the bridge circuit G and the fixed resistor 30 and variable resistor 40 of the adjustment circuit. think about. In FIG. 3A, the input terminal of bridge circuit G
When a constant current I (unchanged with respect to temperature) is supplied between ₁ and ₂ by a constant current power supply S, the bridge circuit G
If the ambient temperature is t, _the current I ₁ flowing into the
...(1) However, Rb: input terminal ₁ of bridge circuit G,
₂ (Output terminals ₃ and ₄ are open)
Each strain at ambient temperature T as seen from -
Combined resistance value of electrical conversion elements g ₁ to g ₄ n, m; constant nRb; resistance value of fixed resistor 30 mRb; resistance value of variable resistor 40
(It is assumed that it does not change with respect to temperature.) Therefore, the current adjustment ratio flowing between input terminals ₁ and ₂ of bridge circuit G is P=I ₁ (t)/I=n+m/1+n+m...(2) Also, If the resistance change in the combined resistance value Rb when the ambient temperature changes from t to t+△t is △Rbt, then
The resistance change of the fixed resistor 30 is nΔRbt. Therefore, I ₁ (t+△t) = n(Rb+△Rbt)+mRb/Rb+△Rbt+n
(Rb+△Rbt)mRb・I...(3) Therefore, the rate of change of current I ₁ due to temperature is Q=I ₁ (t+△t) - I ₁ (t)/I ₁ (t) = -m/ {(1+n)(1+α△t)+m}(n+m) ・α△t ...(4) However, α=(△Rbt/Rb)(I/△t) Therefore, equations (2) and (4) To find the relationship between current adjustment P and current change rate Q due to temperature, α=
If 1.4910 ^-3 /C is used, a graph as shown in FIG. 4 will be obtained. In FIG. 4, a graph is drawn in which the constant n of the resistance value of the fixed resistor 30 is used as a parameter.
Straight line a corresponds to the case where n=0, and curves b, c, d
correspond to the cases where n=2, 3, and 4, respectively. Straight line a connects the variable resistor 40 to the input terminal of the bridge circuit G.
₁ and ₂ (obtained by a conventional adjustment method), the current change rate Q increases as the current adjustment ratio P becomes smaller. Therefore, in order to minimize the change in temperature characteristics, the current change rate Q is set to -1 (%/100℃).
If the current adjustment ratio P is to be kept within the range of 1 to 0.93, the adjustment range of the current adjustment ratio P is limited to 1 to 0.93. On the other hand, when n=3, for example, even if the variable resistor 40 is changed from infinity to zero and the current adjustment ratio P is changed in the range of 1 to 0.75, the current change rate Q is -
Stay within 1 (%/100℃). Also, n=4
In this case, the adjustable range of the current adjustment ratio P is 1 to
0.8, which is slightly narrower than the field where n=3,
It is much wider than when n=0. As a result, if the resistance value of the fixed resistor 30 is set to approximately three times the combined resistance value Rb of the bridge circuit G, then when the current change rate Q is kept within -1 (%/100°C), the current adjustment ratio P The adjustable range is 1 to 0.75. In the above embodiment, an example was explained in which the fixed resistor 30 and the variable resistor 40 were connected in series, but instead of this, the fixed resistor 30 and the variable resistor 40 were connected in the bridge circuit G as shown in FIG. 3B. input end
₁ and ₂ may be connected in parallel to each other. Therefore, the relationship between the rate of change Q of the current I ₁ and the current adjustment ratio P in this case is shown by the broken lines b ₁ , c ₁ , d ₁ in FIG _. , c ₃ , and d ₁ correspond to n=2, 3, and 4, respectively. For example, when n=3, the current change rate Q
If it is kept within -1 (%/100℃), the current adjustment ratio P can be set to 0.75 by adjusting the variable resistor 40.
It can be varied within the range of ~0.7. Similarly, n
= 4, the adjustable range of the current adjustment ratio P is
It is 0.8-0.75. In addition, in the above embodiment, the series circuit of the fixed resistor 30 and the variable resistor 40 shown in FIG.
By combining the fixed resistor 30 and the variable resistor 40 shown in the figure in parallel, the adjustable range of the current adjustment ratio P can be further expanded. For example, when n=3, the current adjustment ratio P 1~
Even if it is changed within the range of 0.7, the current change rate due to temperature remains within -1 (%/100°C). Embodiment 2 FIG. 5 shows a second embodiment of the present invention. In this embodiment, a fixed resistor 30a is connected to a front fixed resistor 30 on the outer zero strain part of the strain generating part 11 on the upper surface of the elastic substrate 10. and are formed by diffusion with each strain-diameter g ₁ to _{g 4} . This fixed resistor 30a has approximately the same impurity concentration and approximately the same resistance temperature characteristics as the strain-electrical conversion elements _g1 to _g4 , and one end thereof is connected to the lead 2 via the auxiliary lead ₇ , and the other end is connected to the lead ₂ via the auxiliary lead 7. It is connected to the auxiliary lead ₈ at the end. Further, as for the connection circuit of the variable resistor 40 to each fixed resistor 30, 30a, various circuits can be constructed as shown in the table below (see FIG. 6).

[Table] Therefore, in Table 1, the relationship between the current change rate Q and the current adjustment ratio P due to temperature will be explained in the case where a combinational circuit that switches from the connection circuit 1 to the connection circuit 2 is adopted, for example. In the connection circuit 1, only the series circuit of the fixed resistor 30 and the variable resistor 40 is connected to the constant current power supply S and the input terminals ₁ and ₂ of the bridge circuit G.
connected between. The equivalent circuit constructed in this way is the same as that shown in FIG. 3A, with n
=3, the relationship between the current change rate Q due to temperature and the current adjustment ratio P becomes a curve C in FIG. Also,
In the connection circuit 2, a fixed resistor 30a and a variable resistor 4
Only the series circuit with 0 is connected between the input terminals ₁ and ₂ of the bridge circuit G, as in the case of the connection circuit 1. Then, the resistance value of the fixed resistor 30a is n ₁ Rb,
If n ₁ =2, the relationship between the current change rate Q and the current adjustment ratio P becomes curve b in FIG. 4. As a result, song c
By combining and b, the adjustable range of the current adjustment ratio P becomes 1 to 0.67, which is wider than that of the previous embodiment. At this time, the current change rate Q is -1
(%/100℃) or less. As another example, if a combinational circuit that switches from connection circuit 1 to connection circuit 5 in Table 1 is adopted, and if n=3 in connection circuit 1, then
The relationship between the current change rate Q and the current adjustment ratio P is the curve e in FIG. 7 (same as the curve c in FIG. 4). Also,
In the connection circuit 5, a fixed resistor 30a and a variable resistor 4 are connected.
It is connected between the input terminals ₁ and ₂ of the bridge circuit G together with a series circuit with 0, a fixed resistor 30a, and a constant current power supply S. Therefore, assuming n=3, n ₁ =2,
When the relationship between the current change rate Q and the current adjustment ratio Q is determined in the same manner as in the first embodiment, a curve f in FIG. 7 is obtained. As a result, by combining both curves e and f, the adjustable range of the current adjustment ratio P is 1
~0.54, which is even wider. At this time, the current change rate Q is -1 (%/100°C) or less. In addition, in this embodiment, when connecting circuits 1 and 2 and 1 and 5 are combined, n=
3. An example in which n ₁ = 2 has been explained, but the current change rate Q can be set to -1 (%/100
℃) while keeping the current adjustment ratio P from 1 to
It can be adjusted within a range of 0.5. Next, a modification of the second embodiment will be described. In this modification, two fixed resistors 30b and 30c are used in place of the fixed resistors 30 and 30a described in the second embodiment. As shown in FIG. 8, on the upper surface of the elastic substrate 10, the strain-to-electric conversion elements _g1 to _g4 are diffused and formed in the outer zero strain part of the strain generating part 11. Each of these fixed resistors 30b, 30
The elements c have approximately the same impurity concentration and approximately the same resistance-temperature characteristics as the prestrain-electrical conversion elements g ₁ to _{g 4} , and are connected in series to each other via the auxiliary lead ₁₀ . The fixed resistor 30b is connected at one end to the lead ₁ via the auxiliary lead ₉ ,
On the other hand, the fixed resistor 30c has an auxiliary lead at one end.
Connected to ₁₁ . In addition, each fixed resistor 30b,
Regarding the connection circuit of the variable resistor 40 to the variable resistor 30c, various circuits can be constructed as shown in the table below.

[Table] Therefore, in this modification, by combining each of the connection circuits 1 to 4 shown in Table 2, the current change rate is substantially the same as that described in the second embodiment above. The relationship of current adjustment ratio P to Q is obtained. In each of the above embodiments and modifications, the resistance value of each fixed resistor 30 to 30c is determined by the bridge circuit G.
Although an example has been described in which the resistance value Rb is an integral multiple of the combined resistance value Rb, the present invention is not limited to this. Note that it is practical for the resistance value of each of the fixed resistors 30 to 30c to be approximately 5 Rb or less. Further, in each of the above embodiments and modifications, an example was explained in which each of the fixed resistors 30 to 30c and the variable resistor 40 were connected to the input terminal of the bridge circuit G. Even if it is connected to the output end of , substantially the same effects as in the above embodiments and modifications can be obtained. Further, when implementing the present invention, the elastic substrate 10
Each strain-electrical conversion element g ₁ to _{g 4} and each fixed resistor 30 to 30c are placed on the surface of 3.7×10 ² to 6.0×10 ² by, for example, ion implantation or epitaxial method.
It may be formed to have an average conductivity within the range of (1/Ωcm). In this case, since the evaluation method of impurity concentration generally differs depending on the method of forming the strain-electric conversion element, the surface impurity concentration set by the diffusion planar method is 2.4 × 10 ²⁰ to 4.0 × 10 ²⁰ (atom/
cm ³ ) and average conductivity 3.7×10 ² to 6.0×10 ² (1/Ω
cm) (determined by the well-known Stein method and four-probe method), and within the range of this converted average conductivity, the strain-electrical conversion element formed by epitaxial method or ion implantation and each fixed resistor. The average conductivity was kept within range. Further, in each of the embodiments and modifications described above, it is assumed that the resistance value of the variable resistor 40 does not change with respect to temperature, but this is not the case with commercially available variable resistors, and the resistance value varies depending on the temperature. However, even if such a variable resistor is employed as the variable resistor in the present invention, its influence on the relationship between the current adjustment ratio P and the current change rate Q due to temperature can be substantially ignored. Furthermore, in each of the above embodiments and modifications, an embodiment has been shown in which the fixed resistors 30, 30a, 30b, and 30c are diffused and formed in the zero strain part outside the strain generating part on the surface of the elastic substrate, but the fixed resistors in the present invention The formation location is not limited to this, but it is also possible to adopt an embodiment in which the fixed resistance is diffused and formed on the surface of the strain-generating portion in a zero-strain region where tensile force and compressive force are exactly balanced. . Further, in each of the above embodiments and modifications, as described above, the circular strain generating portion 11 is provided on the elastic substrate 10.
, and the ratio of the surface diameter of the strain-generating portion 11 to the thickness of the strain-generating portion is set within the range of 2 to 150, but the invention is not limited to this.
The strain-generating portion 11 is formed into a polygonal shape, for example, and the same strain portion has the length of the short axis of the surface of the strain-generating portion (the shortest axis drawn on the surface passing through the center of the surface of the strain-generating portion). The ratio of 2 to 150 may be set in the range of 2 to 150.

[Brief explanation of the drawing]

Figure 1 is a plan view of essential parts of a mechanical-electrical converter embodying the present invention, Figure 2 is a cross-sectional view of the same, and Figures 3A and 3B show a variable resistor connected to the mechanical-electrical converter of Figure 1. FIG. 4 is a graph showing the relationship between the current adjustment ratio P and the current change rate Q, and FIG. Figure 6 shows an equivalent circuit in which a variable resistor is connected to the mechanical-electrical converter shown in Figure 5, and Figure 7 shows the current adjustment ratio P.
FIG. 8 is a graph showing the relationship between the current change rate Q and the current change rate Q, and FIG. 8 is a machine diagram showing a modification of the second embodiment shown in FIG.
FIG. 9, which is a plan view of the main part of the electrical converter, is an equivalent circuit diagram in which a variable resistor is connected to the mechanical-electrical converter shown in FIG. 8. Explanation of symbols, 10...Elastic substrate, 11...Strain-generating portion, 20...Base, 30-30c...Fixed resistor,
40...variable resistor, _g1 to _g4 ...distortion-electric conversion element, G...bridge circuit, ₁ , ₂ ...input terminal, ₃ , ₄ ...output terminal, S...constant current power supply.

Claims (1)

[Scope of Claims] 1. An elastic substrate made of a silicon single crystal is fixed to the surface of the base at its periphery, and a strain-generating portion is formed in the center thereof where strain occurs due to external pressure, and the surface of this strain-generating portion is fixed to the surface of the base. A P-type semiconductor strain-electric conversion element is formed in the P-type semiconductor strain-electric conversion element, and by connecting a constant current power source to the P-type semiconductor strain-electric conversion element, an electrical output proportional to the strain of the strain generating portion is detected. In the mechanical-electrical converter, (length of short axis on the surface of the strain-generating portion)/(thickness of the strain-generating portion) is set within the range of 2 to 150, and the strain-electrical conversion element is A bridge circuit is formed as four strain-electric conversion elements having an average conductivity within the range of 10 ² to 6.0×10 ² (1/Ω·cm), and the strain-electric conversion elements and An adjustment circuit in which at least one fixed resistor having approximately the same average conductivity and approximately the same resistance temperature characteristic is formed in a zero strain portion on the surface of the elastic substrate is connected to the input end or output end of the bridge circuit. Mechanical-electrical converter.