JPH031839B2 - - Google Patents

Description

Detailed Description of the Invention The present invention utilizes the piezoelectric effect of a semiconductor to convert the measured pressure to an electrical quantity and measures it. Concerning the removal of errors.

For example, a semiconductor pressure sensor having the following configuration is well known. As shown in the plan view and the cross-sectional view taken along the line A-A' in _FIGS .
In order to obtain a large piezoelectric effect, a P-shaped diaphragm portion (strain-generating portion) 2 is formed by providing a circular groove 1a in a cross-shaped position of the circular groove 1a in a direction perpendicular to the radial direction. Four piezoresistive elements 3 ₁ , 3 ₂ , 3 ₃ , 3 ₄ having the same resistance value are provided by diffusion to form a pressure detection section, and at the same time, each resistance element is connected to a bridge as shown in the circuit diagram in Figure 1c. They are connected to form a circuit 4 and housed in a case 5 provided with an inlet 5a for the fluid to be pressure tested, as shown in the sectional view of FIG. 1d. As shown in FIG. 1b, each resistance element 3 ₁ , 3 ₂ , 3
₃ and 3 ₄ causes imbalance in the bridge circuit 4, and an output proportional to the pressure P is obtained from the terminals 6a and 6b. Note that in FIG. 1c, 7a and 7b are DC power supply terminals, and in FIG. 1d, 8 is an external connection terminal.

By the way, in this pressure sensor, each piezoresistive element 3 has the same resistance value, and it is desirable that the resistance value is high considering the characteristics of the bridge circuit. Therefore, as shown in the perspective view of FIG. 2, the length l of the resistance element 3 is long and the width a is small;
Since the length of l is limited in relation to the diaphragm portion 2, the width a has to be made small.
That is, when the resistance value of the resistance element is R, the length is l, the width is a, the diffusion depth is b, and the specific resistance is ρ, the resistance value R is given by R=ρ×l/ab. Further, when the surface resistance is ρ _{s ,} it is given by b=l/ρ _s from ρ _s =l/b, and the resistance value R is finally given by R=ρ _s ×l/a. Therefore, since R is regulated by l/a, in order to increase the resistance value, the length l
When the width a is constant, the width a has to be made smaller. However, the resistance element 3 in a small semiconductor pressure sensor
The sizes of ₁ to 3 ₄ are small, for example, 15μ in length and around 4μ in width, and since they are made by photo processing using a mask, the width a must be made completely constant during production. It is difficult to achieve this, and the degree of variation becomes more severe as the width a is made smaller in order to increase the resistance value. For example, width 4μ
Since there may be a variation of about 1μ in relation to the resistance value, if the length l is constant, the resistance value will vary by about 25%. Therefore, it is difficult to make the resistance values of the resistive elements 3 ₁ to _{3 4} the same, and this creates a large imbalance in the bridge circuit 4, which should be in an equilibrium state before the pressure P is applied.

On the other hand, it is ideal that the amount of change in resistance value of the resistance element due to pressure P is selected to be within about 5%. Therefore, the amount of unbalance in the bridge circuit ₄ based on variations in the resistance values of the resistance elements ₃₁ to 34 may exceed the amount of unbalance when pressure is applied, making it difficult to determine what the pressure sensor is measuring. This will result in a situation where there is no such thing. For this reason, the width a has to be made large enough to prevent variations, and as a result, it becomes impossible to obtain a resistor element with a high resistance value, and the sensitivity of the bridge is greatly reduced.

Further, as shown in the relationship diagram of the pressure response force shown in FIG. 3, the magnitude of the stress changes from the fixed end of the diaphragm portion 2 toward the center, and in this case changes from a tensile force to a compressive force. Therefore, in a long resistance element,
This causes a change in the pressure sensitivity distribution over the entire length, and the linearity of the bridge circuit output is disturbed. Furthermore, it is not possible to completely prevent misalignment between the pattern-forming mask for the diaphragm portion 2 and the pattern-forming mask for the resistor element group 3 during manufacture. For this reason, the pressure sensitivity distribution in the length direction of each resistance element is different from that at the normal position for each resistance element, and this causes imbalance in the bridge circuit when pressure is applied, resulting in measurement errors.

The present invention aims to provide a semiconductor pressure sensor that eliminates the dimensional error of the piezoresistive element as described above, measurement error due to positional deviation, etc. at once, and the details thereof will be explained below with reference to the drawings.

FIG. 4 is a plan view showing an embodiment of the present invention, and the features of the present invention are as follows.
That is, one cross-shaped piezoresistance element 9 is provided at the stress generation site of the diaphragm portion 2, with protrusions 9a, 9c, 9b, 9d having a large width and a short length on each side of a substantially square central portion. establish. Electrodes A and B provided at the ends of adjacent protrusions 9a and 9b cause a current to flow as indicated by the arrow in the figure through the central common resistance section 9e, thereby causing a voltage generated in the common resistance section 9e. The descent is carried out by the other adjacent protrusions 9b, 9.
It is characterized in that it is detected by electrodes C and D provided at the ends of d, and an output proportional to the applied pressure P is obtained.

That is, in the present invention, the length of the common resistance part 9e is made smaller than that of the common resistance part 9e, and the change in resistance value due to the pressure P is significantly smaller than that of the common resistance part 9e, so that it hardly becomes a problem, and the resistance value is proportional to the pressure P. This is characterized in that the output to be output is determined by one common resistance section 9e.

In this way, unlike a conventional sensor using four resistance elements, there will be no misalignment of the resistance element group 3 with respect to the diaphragm part 2 during manufacturing, or variations in resistance value between each resistance element due to dimensional errors. There is no. Therefore, not only is there no measurement error due to unbalance of the bridge circuit, but manufacturing is also extremely easy and manufacturing costs can be reduced. In addition, the size of the common resistance portion 9e of the present invention is a square with a small area that is a fraction of that of the conventional sensor, which causes differences in pressure sensitivity in the length direction as in the conventional sensor. Therefore, it is possible to cause a resistance change proportional to only the applied pressure, that is, a resistance change due only to the piezo effect. Therefore, by keeping the current flowing between terminals A and B constant, it is possible to obtain a voltage output that corresponds almost exactly to the measured pressure to be tested, and by increasing the current value, the sensitivity can be enhanced. .

As is clear from the above description, the present invention can provide a pressure sensor that is easy to manufacture and has high measurement accuracy, and is useful for various industrial measurements.

[Brief explanation of drawings]

Figures 1a, b, c, and d are a plan view of a pressure detection part showing an example of a conventional sensor, a sectional view taken along the line A-A', an electric circuit diagram, and a sectional view showing the overall configuration;
FIG. 2 is a shape diagram of a resistive element, FIG. 3 is a relationship diagram of pressure response force of a diaphragm portion, and FIG. 4 is a plan view showing an embodiment of the present invention. 1...Semiconductor substrate, 2...Diaphragm part, 3
... Piezoresistive element group, 3 ₁ , 3 ₂ , 3 ₃ , 3 ₄ ...
Piezoresistance element, 4...Bridge circuit, 5...Case, 5a...Inlet for fluid to be pressure tested, 6a,
6b...Output terminal, 7a, 7b...DC power supply terminal, 8...External connection terminal, 9...Cross-shaped piezoresistive element, 9a, 9b, 9c, 9d...Protrusion part,
A, B, C, D...electrode, 9e...common resistance section.

Claims (1)

[Claims] 1 A cross-shaped piezoresistive element is provided on the surface of the semiconductor substrate on which the diaphragm part is formed and the pressure applied to the test is applied, one of the adjacent protrusions is used as a current supply terminal, the other adjacent protrusion is used as a voltage detection terminal, and the A semiconductor pressure sensor characterized in that a constant current is passed through a current supply terminal, and a voltage drop caused by this is detected by an output of a voltage detection terminal to measure a pressure to be measured.