JP2573535Y2 - Pressure sensor - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor for converting a pressure into an electric signal by utilizing a piezoresistance effect of a semiconductor such as silicon, and more particularly to a pressure sensor having a function of detecting a static pressure and a temperature as well as a differential pressure. Things.

[0002]

2. Description of the Related Art Generally, a pressure sensor of this type generates a strain in a gauge resistance by introducing pressure, and converts a resistance change of the resistance element due to a piezoresistance effect into an electric signal to measure a pressure value. It is widely used for various applications including industrial measurement. As shown in FIGS. 4A and 4B, this pressure sensor uses a chip-shaped n-type silicon substrate 1 provided with a thick part 2 and a thin diaphragm part 3 as fixed parts, as shown in FIGS. , the thin diaphragm portion 3, has a structure obtained by forming the gauge resistors 4 (4 ₁ to 4 ₄₎ having a piezo resistance effect made of p-type diffusion region.

The silicon substrate 1 is fixed to a support member 31 such as a glass tube provided with a pressure inlet 32 at the thick portion 2. When a pressure is applied from the inlet 32, the thin diaphragm portion 3 is formed. Is distorted, whereby the resistance value of the gauge resistor 4 changes. Therefore, incorporation of these gauge resistors 4 to the bridge circuit, when a voltage is applied thereto is removed from the bridge circuit pressure, i.e. an output signal corresponding to the differential pressure of the pressure P _H and P _L of the front and back surfaces of the thin diaphragm portion 3 be able to.

Here, the surface of the silicon substrate 1 on which the gauge resistor 4 is formed is covered with an insulating film 5 such as SiO _2, and the gauge resistor 4 is passed through a contact hole opened.
An extraction electrode 6 made of aluminum (Al) or the like is formed so as to be electrically connected to the outside, and connection to the outside is usually made by wire bonding.

When such a pressure sensor is used as a pressure transmitter for industrial measurement, the pressure sensor has a built-in static pressure detecting circuit and a built-in temperature detecting circuit for detecting the ambient temperature and detecting the ambient temperature. There are things that let me. This has its equivalent circuit configuration as shown in FIG. 5, forms a differential pressure detection bridge circuit 11 comprised of p-type gauge resistors 4 to the thin diaphragm portion 3 ₍₄₁ to ₄₎ on the silicon substrate 1 At the same time, gauge resistances 12 ₁ to 12 similar to the gauge resistance 4 are provided in a predetermined region of the thick part 2 on the outer periphery thereof.
12 ₄ static pressure temperature detecting bridge circuit 12 consisting of the temperature detecting bridge circuit 13 consisting of the temperature detecting element _131-134 are integrally formed. The respective input terminals of the bridge circuits 11 to 13 are commonly connected to the power supply terminals 10a and 10b to which a constant voltage V is applied.
3 is always driven.

[0006] Such a pressure sensor is a silicon substrate 1
Gauge resistors 4 _1- arranged on the thin diaphragm section 3 above
4 ₄ while measuring the differential pressure by a bridge circuit 4 constituted by, gauge resistors 12 ₁ formed respectively on the thick portion 2
With measuring a static pressure by a bridge circuit 12 which is constituted by 12 _4, by measuring the temperature by a bridge circuit 13 constituted by a temperature detecting element _131-134, static pressure against the differential pressure by the subsequent electric circuits, the temperature To compensate for the effect of In FIG. 5, symbols V ₁ , V ₂ and V ₃ indicate a differential pressure, a static pressure and a temperature output, respectively. In the same figure, the same reference numerals as those in FIG. 4 indicate the same or corresponding ones.

[0007]

However, in the above-mentioned conventional pressure sensor, current is shunted at the time of measurement because power is constantly supplied to each of the bridge circuits 11 to 13 for detecting differential pressure, static pressure and temperature. As a result, the current supplied to each bridge circuit is reduced, which is a factor that lowers the S / N ratio. This has been particularly noticeable in the case of two-wire transmission.

[0008] In view of the above points, the present invention has been made to solve the above-described problems.
An object of the present invention is to provide a pressure sensor having a function of detecting a differential pressure, a static pressure, and a temperature, in which a supply current at the time of measurement to each detection circuit is increased to improve an S / N ratio.

[0009]

According to the present invention, there is provided a pressure sensor for measuring pressure utilizing a piezoresistive effect of a semiconductor, the pressure sensor being formed integrally on a semiconductor single crystal substrate. A detection circuit, a static pressure detection circuit, and a temperature detection circuit are provided, and power is supplied to these differential pressure, static pressure, and temperature detection circuits periodically.

[0010]

In the present invention, the power supply to the differential pressure detection circuit, the static pressure detection circuit and the temperature detection circuit formed on the semiconductor single crystal substrate is not performed simultaneously, but is performed periodically (cyclically). The supply current at the time of measurement to the detection circuit increases.

[0011]

1 is a schematic view for explaining an embodiment of a pressure sensor according to the present invention, wherein FIG. 1 (a) is a plan pattern diagram of the sensor section, and FIG. 1 (b) is an equivalent view thereof. Various circuit diagrams are shown. In this embodiment, as shown in FIG. 1, a chip-shaped n-type silicon substrate 1 having a thick portion 2 serving as a fixed portion and a thin diaphragm portion 3 is used, and the thin diaphragm portion 3 has a piezoresistive effect. Gauge resistance 4 (4 _1-
The point that a bridge circuit 11 for differential pressure detection composed of 4 ₄ ) is formed and the surface thereof is coated with an insulating film 5 such as SiO ₂ is the same as that of the conventional example of FIG. thick predetermined area of the wall portion 2 on the silicon substrate 1, the gauge resistor 4 and the same gauge resistors 12 ₁ to 12 ₄ differential bridge circuit 12 for output pressure consisting of lower first impurity concentration as a temperature detecting element The temperature detection bridge circuit 13 composed of the resistance layers 13 ₁ and 13 ₄ and the second resistance layers 13 ₂ and 13 ₃ having a high impurity concentration is integrally formed.

A constant voltage applied between the power supply terminals 10a and 10b is applied to the bridge circuits 11 to 13 for detecting the differential pressure, the static pressure and the temperature by the rotary switch 14 which operates in synchronization with sampling at the time of measurement. by sequentially switching the V, which is intended to supply at a constant period T each of the voltage V _P, V _S, the V _T as shown in FIG.

In this case, in the temperature detecting bridge circuit 13, the first resistance layers 13 ₁ and 13 ₄ having a low impurity concentration are composed of p-type diffusion layers formed in the same manner as the respective gauge resistors 4 and have a temperature coefficient. For example, about 3000 ppm / ° C. Further, the second resistance layers 13 ₂ and 13 ₃ having a high impurity concentration are used as the wiring diffusion lead layers 2 of the respective gauge resistors 4.
It is formed of a p-type diffusion layer formed in the same manner as in Example 1, and has a temperature coefficient of, for example, about 1500 ppm / ° C.
Therefore, by converting a change in resistance value of the resistance layers 131 to 134 due to a change in temperature into a voltage signal by the bridge circuit 13, an output signal corresponding to the temperature can be obtained.

In FIG. 1, reference numeral 21 denotes each gauge resistor 4 (4 _A
To 4 _D ), a diffusion lead layer for wiring connecting between them, 22 is an Al lead for leading out the diffusion lead layer 21, 23 is a lead terminal for detecting a differential pressure, and 24 is a gauge resistance ( _A).
To _D ), a diffusion lead layer for wiring connecting between the elements, 25 denotes an Al lead for leading out the diffusion lead layer, and 26 denotes a lead terminal for detecting static pressure. Reference numeral 27 denotes an Al lead for connecting each of the first resistance layers, reference numeral 28 denotes an Al lead for connecting each of the first and second resistance layers, and reference numeral 29 denotes a lead terminal for temperature detection. In the same figure, the same reference numerals as those in FIG. 4 indicate the same or corresponding ones.

As described above, according to the pressure sensor of this embodiment, the bridge circuit 11 for detecting the differential pressure,
A bridge circuit 12 for detecting a static pressure and a bridge circuit 13 for detecting a temperature are formed, respectively.
13 is separately supplied only at the time of sampling for measurement, so that each of the bridge circuits 11-
13 can be increased, so that the S / N ratio can be improved. This will be described in detail with reference to the circuit of FIG.

In FIG. 3, each of the bridge circuits 11-
13, for example, the error at one output point a in the bridge circuit 11 is Δv, the input voltage is V, and the insulation resistance value of a pn junction that insulates and separates each of the gage resistors constituting the bridge circuit formed on the silicon substrate is R _1. When the resistance value of each gauge resistance of the bridge circuit, that is, the resistance value of the sensor resistance is R ₂ , the combined resistance R ₀ is

[0017]

(Equation 1)

## EQU1 ## At this time, if the current flowing into the bridge circuit is i, this current i is

[0019]

(Equation 2)

## EQU1 ## The error Δv is expressed by the following equation.

[0021]

(Equation 3)

Thus, when the equation (2) is substituted into the equation (3) for calculation, the error Δv is obtained as an approximate value by the following equation.

[0023]

(Equation 4)

Therefore, as is apparent from the equation (4), R ₂ /
As the value of R ₁ is small, the error Δv is reduced. Thus, the sensor resistance R ₂ to form a bridge circuit may be as small as possible, but the current consumption increases by decreasing the sensor resistance R _2. Therefore, according to the present embodiment,
By which is adapted to feed only at the time of sampling of the measurement, to lower the sensor resistance R _2, since the bridge circuit can be separately powered, without increasing the current consumption, S /
N can be increased.

In the above embodiment, the case where an n-type silicon substrate is used as a semiconductor single crystal substrate is shown. However, the present invention is not limited to this, and a p-type silicon substrate or a substrate having an SOI structure may be used. Many modifications are possible, such as using a temperature detecting circuit formed in a thick portion on the outer periphery of a thin diaphragm with a sensor element other than a resistance layer having a different impurity concentration.

[0026]

As described above, according to the present invention, in a pressure sensor for measuring pressure utilizing the piezoresistive effect of a semiconductor, a differential pressure detecting circuit integrally formed on a semiconductor single crystal substrate, and a static pressure By supplying power to the detection circuit and the temperature detection circuit simultaneously and cyclically, the supply current at the time of measurement to each detection circuit is increased, and therefore, a pressure sensor with a good S / N ratio can be obtained. There is.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an embodiment of a pressure sensor according to the present invention, wherein (a) is a plan pattern diagram of the sensor unit,
(b) is an equivalent circuit diagram.

FIG. 2 is a timing chart of a power supply voltage applied to each bridge circuit of FIG.

FIG. 3 is an explanatory diagram for explaining the above embodiment.

FIG. 4 is a basic configuration diagram of a conventional pressure sensor;
(a) is a plan view and (b) is a cross-sectional view.

FIG. 5 is a schematic explanatory view of a conventional pressure sensor.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 n-type silicon substrate 2 thick portion 3 thin diaphragm portion 4, 4 ₁ to 4 ₄ p-type gauge resistor 5 insulating film 10 a, 10 b power supply terminal 11 bridge circuit for differential pressure detection 12 bridge circuit for static pressure detection 13 temperature detection Bridge circuit 14 Rotary switch

Claims (1)

(57) [Scope of request for utility model registration] 1. A pressure sensor for measuring pressure utilizing a piezoresistive effect of a semiconductor, comprising a differential pressure detection circuit, a static pressure detection circuit, and a temperature detection circuit integrally formed on a semiconductor single crystal substrate. Differential pressure,
A pressure sensor wherein power supply to a static pressure and temperature detection circuit is periodically performed.