JPH06207871A - Pressure sensor - Google Patents

Abstract

PURPOSE:To lessen a leak current due to disjunction of a p-n junction and thereby to reduce a drift in a pressure sensor. CONSTITUTION:A p-type silicon substrate 1a having a large-thickness part 2 and a small-thickness diaphragm part 3 is used and a plurality of n-type well regions 10 are formed in a prescribed area of the small-thickness diaphragm part 3. In these n-type well regions 10, gage resistors 4A to 4D each constituted of a p-type diffused region and having a piezo-resistance effect are formed respectively and each of the gage resistors 4A to 4D, is incorporated in a bridge. In this case, each of the n-type well regions 10 is connected electrically by an electrode wiring 11 onto the high-potential side of each of the p-type gage resistors 4A to 4D constructing a bridge circuit and is fixed at the potential.

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 pressure into an electric signal by utilizing the piezoresistive effect of a semiconductor such as silicon, and in particular, a reverse current due to a pn junction used for insulation separation between resistance elements. The present invention relates to a pressure sensor in which (leakage current) is reduced to reduce drift.

[0002]

2. Description of the Related Art Generally, this type of pressure sensor measures strain by generating strain in gauge resistance by introducing pressure and converting resistance change due to the piezoresistive effect of the resistance element into an electric signal to measure the pressure value. And is widely used for various purposes including industrial measurement. As shown in FIGS. 3 (a) and 3 (b), the pressure sensor uses a chip-shaped n-type silicon substrate 1 having a thick part 2 serving as a fixing part and a thin diaphragm part 3 as shown in FIGS. In the thin diaphragm portion 3, a gauge resistor 4 (4 _A to 4 _D ) having a piezoresistive effect formed of a p-type diffusion region is formed.

The silicon substrate 1 is fixed to a supporting member 21 such as a glass tube having a pressure introducing port 22 at the thick portion 2, and when pressure is applied from the introducing port 22, the thin diaphragm portion 3 is formed. Is distorted, which changes the resistance value of the gauge resistor 4. Therefore, if these gauge resistors 4 are incorporated in a bridge circuit and a voltage is applied to the bridge circuit, an output signal corresponding to the pressure, that is, the difference between the pressures P _H and P _{L on} the front and back sides of the thin diaphragm portion 3 is taken out from the bridge circuit. You can

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 that opens this.
The extraction electrode 6 made of aluminum (Al) or the like is formed so as to be electrically connected to the outside, and the connection with the outside is usually performed by wire bonding.

By the way, in the pressure sensor having such a structure, the pn junction separation method is generally used to insulate and separate each gauge resistor formed on the silicon substrate. This is an n-type silicon substrate 1 as shown in FIG.
After each p-type gauge resistor 4 is formed on the substrate 1, a bias electrode 7 is formed on a part of the substrate 1, and the highest potential is applied to this electrode 7 from a power source 8 so that the pn junction 9 is formed. It is intended to perform insulation separation by utilizing high resistance at the time of reverse bias. In FIG. 4, the same reference numerals as those in FIG. 3 indicate the same or corresponding ones.

[0006]

However, the conventional pressure sensor using such pn junction isolation has the p
As shown in FIG. 5 for the n-junction characteristic, the reverse current flowing at the time of reverse bias, that is, the leak current I _L is about 0.4 mA (for example, drive voltage V _B = 5 v, break voltage V _BK = 8 v).
However, there is a problem that the sensor output largely drifts due to the leak current.

In view of the above points, the present invention has been made to solve the above problems, and its purpose is to:
It is an object of the present invention to provide a pressure sensor in which the leakage current due to the pn junction separation is reduced to reduce the drift.

[0008]

To achieve the above object, the present invention provides a pressure sensor for converting pressure into an electric signal by utilizing the piezoresistive effect of a semiconductor, on a semiconductor single crystal substrate of the first conductivity type. A plurality of well regions formed having a second conductivity type different from that of the substrate, and a first conductivity type gauge resistor having a piezoresistor formed in each of the well regions. The gauge resistance is clamped to the high potential side.

[0009]

According to the present invention, the well regions of the second conductivity type are separately formed in each of the gauge resistors of the first conductivity type and fixed to their respective potentials, so that the well regions have potentials close to the gauge resistance. Since it is raised, the potential of the junction becomes small and the leak current is minimized.

[0010]

1 is a schematic view for explaining an embodiment of a pressure sensor according to the present invention. FIG. 1 (a) is a plan view thereof, and FIG. 1 (b) is a thin diaphragm portion B- The B line expanded sectional view is shown, respectively. In this embodiment, as shown in FIG. 1, a chip-shaped p-type silicon substrate 1a having a thick portion 2 serving as a fixing portion and a thin diaphragm portion 3 is used as a semiconductor substrate of the first conductivity type, Plural (four in this example) well regions 10 of the second conductivity type, that is, n-type, different from the substrate are formed in a predetermined region of the diaphragm portion 3.

Gauge resistors 4 (4 _A to 4 _D ) having a piezoresistive effect, which are p-type diffusion regions, are formed in the n-type well regions 10 and SiO 2 is formed on the surface thereof.
The insulating film 5, such as ₂ after having formed by coating, by forming the electrode wiring 11 made of Al or the like having a predetermined pattern on the insulating film 5, as shown in FIG. 2, the gauge resistors 4 _A to 4 _D Is incorporated in the bridge circuit 12.

In this case, each n on the p-type silicon substrate 1a
The well region 10 is electrically connected to the high potential side of each of the p-type gauge resistors 4 _A to 4 _D forming the bridge circuit 12 by the electrode wiring 11 and fixed at that potential. 1 that are the same as or equivalent to those in FIG. 3 are designated by the same reference numerals.

As described above, according to the pressure sensor of this embodiment, the p-type silicon substrate 1a is connected to the lowest potential, and the positive voltage V _B from the drive power source 13 is applied between the input terminals 12 ₁ and 12 _{2 of the} bridge circuit 12. When supplied, each n-type well region 1
0 forms a pn junction with the silicon substrate 1a, and the junction is reverse biased and isolated. In addition, the p-type gauge resistance 4 _A in these n-type well regions 10
To 4 _D, as shown in FIG. 2, it is insulated and isolated pn junction 14 _A to 14 _D are formed is reverse biased between the n-type well region 10, respectively.

Therefore, these p-type gauge resistors 4 _A to 4 _D
By converting the change of the resistance value with respect to the pressure of the bridge circuit 12 into an electric signal, its output terminals 12 ₃ , 12 ₄
The output voltage corresponding to the pressure can be taken out from between. At this time, since each n-type well region 10 is raised to a potential close to the p-type gauge resistors 4 _A to 4 _D , the bias of the pn junction becomes small, and the leak current can be suppressed to the minimum. it can.

Although the p-type silicon substrate is used as the semiconductor single crystal substrate in the above embodiments, the present invention is not limited to this, and an n-type silicon substrate or a substrate having an SOI structure may be used. Many variations are possible, such as by using, or by forming an arbitrary number of gauge resistors in the thin diaphragm in a predetermined region.

[0016]

As described above, according to the present invention, a gauge resistance is formed in a region inside a thin diaphragm on a semiconductor single crystal substrate, and the pressure is measured by utilizing the piezoresistive effect of the gauge resistance. In the sensor, each gauge resistor is formed separately in its opposite conductivity type well region, and these well regions are clamped to the high potential side of each gauge resistor so that the well regions are brought to a potential close to that gauge resistor. The leakage current is minimized because it is increased. Therefore, there is an effect that the drift due to the leak current is reduced and a pressure sensor with stable output can be obtained.

[Brief description of drawings]

1A and 1B are schematic views illustrating an embodiment of a pressure sensor according to the present invention, in which FIG. 1A is a plan view thereof, and FIG. 1B is an enlarged cross-sectional view of a diaphragm portion taken along line BB.

FIG. 2 is an equivalent circuit configuration diagram of the embodiment of FIG.

FIG. 3 is a basic configuration diagram of a pressure sensor according to a conventional example,
(a) is the top view, (b) is sectional drawing.

FIG. 4 is an explanatory diagram of pn junction separation according to the related art.

5 is a pn junction characteristic diagram used for the description of FIG. 4. FIG.

[Explanation of symbols]

1a p-type silicon substrate 2 thick part 3 thin diaphragm part 4,4 _A to 4 _D p-type gauge resistance 5 insulating film 10 n-type well region 11 electrode wiring 12 bridge circuit 13 drive power supply 14 _{A to} 14 _D gauge resistance and well Pn junction with region

Claims (1)

[Claims] 1. A pressure sensor for converting pressure into an electric signal by utilizing the piezoresistive effect of a semiconductor, which is formed on a semiconductor single crystal substrate of the first conductivity type and has a second conductivity type different from this substrate. A plurality of well regions and a first conductive type gauge resistor having a piezoresistive effect formed in each of the well regions, and each well region is clamped to the high potential side of the respective gauge resistor. A pressure sensor characterized in that.