JPH034568A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To hold down the fluctuation and the zero shift of an output voltage so as to enable a pressure sensor of this design to execute a highly sensitive and a very accurate measurement by a method wherein a low resistive layer pattern connecting four piezoresistors with four electricity outlets is reduced in area near the electricity outlets. CONSTITUTION:A semiconductor pressure sensor is constituted in such a manner that a recess is provided to the (100) surface of a single crystal Si to form a rectangular diaphragm 1 and a pedestal which serves a pressure introduction section surrounding the recess on the rear side is joined to a thick part 2 of a board 3. Four piezoresistors 4 serving as a stress sensor are arranged on the side of the board 3 opposite to the recess surrounding the diaphragm 1 to sense a stress applied onto the diaphragm 1. A low resistive pattern 6 which connects the four resistors 4 in a Wheastone bridge is formed on the thick part 2. An electricity outlet 5 of metal is provided to four corners of the board 3 coming in ohmic contact with the resistive layer 6 respectively. A constriction (slit) 7 is provided near each of the outlets 5 respectively to control the path of holes which flow from the resistors 4.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (Industrial Field of Application) The present invention relates to a pressure sensor, and more particularly to a semiconductor substrate pressure sensor with a thin film diaphragm.

(Conventional technology) Semiconductor pressure sensors are known in the prior art.

It uses a thin film diaphragm that responds to pressure differences across its sides. As shown in FIG. 2, a recess is formed on one surface of a rectangular single crystal semiconductor substrate (13) to form a thin film diaphragm (11) in the center.
A piezoresistor (14) as a stress sensor is arranged around the surface opposite to the recessed portion 1).

The thick part (1
A low-resistance layer pattern (16) connecting four electrical take-out portions (15) and four piezoresistors (14) arranged in 2).
) is formed. The reason why a metal wiring pattern is not used to connect the four piezoresistors (14) to the electrical outlet (15) is because thermal distortion occurs due to the large difference in thermal temperature coefficient between the thin film diaphragm (11) and the metal wiring. This is to avoid the influence of mechanical hysteresis of metal wiring. A pedestal made of a square prism with a circular hole or a cylindrical tube is bonded to the thick part around the recess so as to surround the recess on the back side of the thin film diaphragm (11) of the semiconductor substrate (13).

(Problems to be Solved by the Invention) In the conventional semiconductor pressure sensor described above, the current path flowing through the low resistance layer pattern (16) changes over time, and the Wheatstone bridge composed of four piezoresistors (14) changes over time. A phenomenon in which the output offset voltage fluctuates appears. This is because the potential distribution of the oxide film on the top of the low-resistance layer pattern (16) changes due to the movement of ions (thermally and electrically), and the carrier distribution on the wide-area low-resistance layer surface changes, and holes flow through this. This is because it affects the route.

In order to avoid this phenomenon, it is sufficient to limit the use of the above-mentioned low-resistance layer, but metal wiring that replaces this layer is expected to cause the above-mentioned hysteresis and deterioration of temperature characteristics. Also,
When the low-resistance layer pattern (16) is made into strips to limit the current path, the resistance value of the low-resistance layer pattern increases, and the non-pressure resistance part of the resistor forming the Wheatstone bridge increases, causing piezoresistance. connected in series, the increase in overall resistance reduces the actual sensitivity. Furthermore, this causes an increase in offset variations.

Therefore, the object of the present invention is to realize a semiconductor pressure sensor that can suppress the fluctuation of the output voltage after the power is turned on, has a small amount of zero shift, and can stably perform high-sensitivity, high-precision pressure measurement. This is also the purpose of the present invention.

[Structure of the invention]

(Means for Solving Problem m1) The semiconductor pressure sensor of the present invention has four electrical leads arranged in a thick wall around each piezoresistor and a substrate so that the four piezoresistors form a Wheatstone bridge. In this configuration, the low resistance layer pattern connecting the parts is shaped so that the area is narrowed in the vicinity of the electrical lead-out part.

(Function) In the semiconductor pressure sensor of the present invention, the maze current is limited by limiting the current path of holes flowing in the low resistance layer connecting piezoresistors in the vicinity of the electrical extraction part, and the electrical extraction Stabilizes the potential of the area. This stabilizes the output offset voltage of the Wheatstone bridge and outputs a highly accurate and reliable pressure signal.

(Example) Hereinafter, the present invention will be described in detail based on the example shown in the drawings.

FIG. 1 shows a semiconductor pressure sensor according to an embodiment of the present invention.
As shown in FIG. 1, the semiconductor pressure sensor of this embodiment consists of a rectangular (100) single crystal silicon substrate
A rectangular thin film diaphragm (
1), and a pedestal (not shown) that also serves as a pressure introduction part is bonded to the thick part (2) of the substrate (3) so as to surround the recess on the back side of the thin film diaphragm (1). . Four piezoresistors (4) as stress sensors are placed around the thin film diaphragm (1) on the surface of the single crystal silicon substrate (3) opposite to the recess, and sense the stress applied to the thin film diaphragm (1). That's what I do. This piezo resistance (
4) is formed on the surface of the substrate (3) at an optimal location in the surface area determined by the shape of the sensor, for example, by diffusion of an impurity such as boron or by ion implantation. Low resistance layer pattern (6) connecting four piezoresistors (4) to form a Wheatstone bridge
is formed over a wide area around the thin film diaphragm (1) and over the thick part (2). This low resistance layer is formed by diffusing an impurity such as boron at a high concentration.

A low resistance layer (6) is placed on the four corners of the rectangular silicon substrate (3).
Metal electrical lead-out portions (5) that are in ohmic contact with are respectively arranged. In the vicinity of the electricity extraction part (5) of the low resistance layer pattern (6), there is an aperture (slit) (7) for restricting the path of holes flowing from the piezoresistor (4).
) is provided. The aperture (7) is made of N-type substrate with a higher concentration and the same conductivity type as the N-type substrate that divides the low-resistance layer into two.
It is also possible to insert a + layer.

In the semiconductor pressure sensor of this embodiment configured as described above, the electrical extraction portion (5) is connected to the piezoresistor (4).
The low resistance layer pattern (6) up to the thin film diaphragm (1
) to the thick part (2) and approximately 4
Since it is symmetrical, variations in surface impurity concentration that affect the temperature characteristics of the offset voltage are alleviated. Furthermore, since the pressure-insensitive series resistance value that causes a decrease in sensitivity can be reduced, high sensitivity can be maintained. Furthermore, since the aperture (slit) (7) exists so that the flow of holes always passes through the electrical extraction part (5), stray holes are less likely to occur, and the potential of the electrical extraction part (5) is stable over a long period of time.

〔Effect of the invention〕

As detailed above, according to the present invention, the low-resistance layer pattern that connects the four piezoresistors to the electrical outlet so as to form a Wheatstone bridge is narrowed and narrowed near the electrical outlet. Since the structure minimizes the use of metal wiring, temperature hysteresis is reduced.

Even if there is a change in the voltage distribution of the surface oxide film that affects the flow of holes after electricity is applied, the holes always pass through the electricity extraction part without straying, so the offset voltage is stabilized. Thereby, it is possible to provide a highly reliable semiconductor pressure sensor that has a small amount of offset shift and is capable of highly sensitive and highly accurate pressure measurement.

[Brief explanation of the drawing]

FIG. 1 is a top view of a semiconductor pressure sensor according to an embodiment of the present invention, and FIG. 2 is a top view of a conventional semiconductor pressure sensor. 1... Thin film diaphragm, 2... Thick part of substrate, 3
... Single crystal silicon substrate, 4... Piezoresistor, 5.
・・Electricity extraction part, 6 ・・Low resistance layer pattern, 7・・
・Aperture.

Claims (1)

[Claims] Four piezoresistors are arranged around the surface opposite to the recess of a thin film diaphragm formed by forming a recess on one surface of a (100) plane semiconductor substrate, and each piezoresistor is connected to a Wheatstone bridge. A semiconductor pressure sensor in which a low resistance layer pattern connecting four electrical lead-out parts arranged in a thick part around a substrate is formed in a shape with a narrowed area near the electrical lead-out parts.