JPS6154271B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diaphragm type semiconductor pressure sensor that utilizes a piezoresistance effect, and particularly to a semiconductor pressure sensor suitable for absolute pressure measurement.

A semiconductor pressure sensor is typically configured as follows. That is, as shown in FIGS. 1 and 2, a thin part is provided at the center of a chip 1 of a silicon single crystal substrate with a plane orientation of (100), and this is used as a diaphragm (strain part) 2.
Gauge resistors R ₁ to _{R 4} are formed thereon by impurity diffusion so that their respective resistance values are as uniform as possible. This chip 1 is adhered to a silicon single crystal pedestal 4 with an adhesive, and the back surface of the diaphragm 2 is used as a vacuum chamber 3. When pressure R is applied to the diaphragm 2, the resistance values of the gauge resistances R ₁ and R ₃ decrease, and the resistance values of the gauge resistances R ₂ and R ₄ increase. Therefore, as shown in Fig. 3, if the gauge resistors R ₁ to _{R 4} are bridge-connected and a constant voltage is applied to obtain the bridge output V,
This output V is proportional to the pressure P.

By bridge-connecting them in this way, diffused resistors originally have the disadvantage of having a very large temperature coefficient, but this can be canceled out and zero drift and sensitivity changes due to temperature can be reduced. ing.

Incidentally, the gauge resistors R ₁ to _{R 4} are usually designed and manufactured so that their resistance values are substantially uniform when the diaphragm 2 is in an unstrained state. However, in the case of absolute pressure measurement, it is usually used to measure a pressure range of 1 atmosphere or more. In this case, the changes in each resistance value will be as shown in Figure 4,
When the diaphragm 2 is not strained in vacuum, each resistance value is similar within the range of manufacturing variations, but when pressure is applied within the critical usage range, the gauge resistance R ₁ , R ₃ and R ₂ , R ₄ have very different resistance values. If the resistance values differ greatly in this way, even if the temperature coefficient is the same, the amount of change will differ greatly.
As shown in the figure, the bridge output V is greatly affected by temperature changes, and this effect becomes more pronounced as the measured pressure increases.

An object of the present invention is to provide a semiconductor pressure sensor that is improved so as to alleviate the adverse effects caused by the above-mentioned temperature changes. It is characterized in that it is designed and manufactured so that each resistance value of the gauge resistor is as close as possible within the working pressure range.

Next, one embodiment of the present invention will be described. For example, as shown in Figure 6, the resistance value of the pair of gauge resistors R ₁ and R ₃ whose resistance value increases with pressurization is the resistance value of the pair of gauge resistors R ₂ and R ₄ whose resistance value decreases with pressurization. It is designed and manufactured so that the offset value ΔR is smaller than the value when the diaphragm is in a non-strained state. Then, in the case of FIG. 6, when the diaphragm is pressurized and reaches the lower limit of the operating pressure state, the resistance values become approximately equal. Therefore, within this usage range, the resistance values of gauge resistors R ₁ and R ₃ and the resistance values of gauge resistors R ₂ and R ₄ do not differ significantly, and therefore the change due to temperature is also smaller than before. Become. Therefore, as shown in Figure 7, the bridge output V is almost unaffected by temperature changes at the lower end of the operating range, and although it does have an effect at the upper end of the operating range, the degree is small and compared to the conventional one. The result is a marked improvement.

Further, the offset value ΔR of the resistance value is not limited to being set to be equal at the lower limit pressure of the working pressure range, but can also be set to be equal at any point within the working pressure range. For example, as shown in Figure 8, if the offset values △R are set to be approximately equal at the center of the working pressure range, the temperature characteristics of the bridge output V will become as shown in Figure 9, and in principle the temperature characteristics will change. Most favorable.

As described above with respect to the embodiments, according to the present invention, the resistance value of the diffused resistor constituting the gauge resistor is designed and manufactured to have an offset value, and each resistance value of the gauge resistor is set within the working pressure range. Since the values are made to be as close as possible, the adverse effects of temperature changes can be alleviated.

[Brief explanation of the drawing]

Figures 1 to 5 are for explaining the conventional example. Figure 1 is a plan view, Figure 2 is a vertical sectional view, and Figure 3 is a longitudinal sectional view.
4 is a graph showing the relationship between pressure and the resistance value of the gauge resistor. FIG. 5 is a graph showing the relationship between pressure and bridge output V. FIG. 6 is a graph showing the relationship between pressure and bridge output V. A graph showing the relationship between the pressure applied to the first embodiment and the resistance value of the gauge resistance, FIG. 7 a graph showing the relationship between the pressure applied to the same embodiment and the bridge output V, and FIG. 8 a graph showing the relationship between the pressure applied to the first embodiment and the bridge output V. A graph showing the relationship between the pressure applied to the example and the resistance value of the gauge resistance,
Figure 9 shows the pressure applied to the same example and the bridge output V.
It is a graph showing the relationship between 1...chip, 2...diaphragm, 3...vacuum chamber, 4...pedestal, _R1 to _R4 ...gauge resistance.

Claims (1)

[Claims] 1. In a semiconductor pressure sensor in which a plurality of gauge resistors are formed by impurity diffusion on a diaphragm made of a semiconductor single crystal substrate, and are formed on the back surface of the diaphragm and in a vacuum chamber, the resistance value of the gauge resistors is within the working pressure range. A set of gauge resistors whose resistance value increases when pressurized has a smaller resistance value when the diaphragm is in the unstrained state than a set of gauge resistors whose resistance value decreases when pressurized so that the resistance values are approximately the same. A semiconductor pressure sensor characterized by: