JPH03137532A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To detect with high sensitivity a force acting on a diaphragm by a method wherein a resistance value for a unit length of a second part intersecting a crystal axis perpendicularly is made smaller than the one of a first part along the crystal axis. CONSTITUTION:A P-type region is provided by ion implantation in the vicinity of the peripheral edge of a diaphragm 3 in the central part of an N-type semiconductor chip 1, so as to form a pressure-sensitive resistance 2, and a change in resistance value caused by a piezo resistance effect is utilized. In a pressure- sensitive resistance element thus formed, the resistance value for a unit length differs between a first part along the crystal axis and a second part intersecting the axis perpendicularly, and the resistance value of the later part is smaller than that of the former. On the occasion, a rate at which a change in the resistance of the first part offsets a change in the resistance occurring in the second part is lessened by a pressure acting on the diaphragm, and a large change in the resistance value occurs in the whole of a pressure-sensitive resistance. Accordingly, a high detection sensitivity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pressure sensor equipped with a semiconductor diaphragm, such as a silicon diaphragm.

[Conventional technology]

Semiconductor pressure sensors, which are made by thinning a part of a semiconductor chip to form a pressure-receiving diaphragm, can be easily miniaturized and constructed at low cost, and have excellent heat resistance, moisture resistance, and vibration resistance. , has been in the spotlight in recent years because it can be used even in harsh environments.

FIG. 3 is a partially cutaway perspective view of this semiconductor pressure sensor. A semiconductor pressure sensor includes a plurality of pressure sensitive resistors 2. on the surface of a semiconductor chip 1.・2... is formed, and a diaphragm 3 including these formation areas is thinned by etching from the back side, and when pressure is applied to this diaphragm 3 and distortion occurs, the above-mentioned The pressure is detected by utilizing the change in resistance value caused by the piezoresistive effect in the piezoresistors 2.2. These pressure sensitive resistors 2.2...
・ is, for example, a p-type head region formed on an n-type semiconductor chip l using diffusion or ion implantation technology, and in order to effectively utilize the piezoresistance effect, it is formed within the plane of the diaphragm 3. It is formed along the crystal axis direction of this, for example, along the H10>axis direction. Since the diaphragm 3 originally has a rectangular shape with sides corresponding to the crystal axis direction, the pressure sensitive resistors 2, 2... should be arranged in a manner parallel to one side of the diaphragm 3 as shown in the figure. become.

The output of the semiconductor pressure sensor as described above is - for boat fishing, the output v of a bridge circuit composed of pressure sensitive resistors 2, 2...
It is obtained as 0. The resistance value of pressure sensitive resistor 2, 2... is R
When a resistance value change of ΔR occurs in the pressure sensitive resistor 2 in response to the strain generated in the diaphragm 3 due to pressure reception, the output ■ is expressed by the following equation. is obtained.

However, ■ is the voltage applied to the Brifuji circuit.

As is clear from this equation, in order to improve detection sensitivity,
The resistance value change ΔR may be increased, and for this purpose the pressure-sensitive resistor 2 may be made longer, but the area in which the pressure-sensitive resistor 2 is disposed on the diaphragm 3 is limited. Therefore, in order to increase the length as much as possible within a limited range, a plurality of first portions 2a (see FIG. 4) along the crystal axis direction are arranged, and their ends are made substantially perpendicular to each other. Conventionally, the pressure-sensitive resistor 2 has been formed in such a manner that it is connected and integrated at the second portion 2b (see FIG. 4).

FIG. 4 is an enlarged plan view of the pressure sensitive resistor 2 formed in this manner. This figure shows an example in which the number of first portions 2a arranged in parallel is three, and the pressure sensitive resistor 2 formed by connecting these by two second portions 2b is a flattened inverse as shown in the figure. Forms an S shape. Of course, if the number of parallel arrangement is different, other shapes may be formed.

[Problem to be solved by the invention]

Now, the resistance value change ΔR that occurs in the pressure sensitive resistor 2 due to the pressure received by the diaphragm 3 is expressed by the following equation.

ΔR=(π, σ, +π, σt)・R...(2) However,
π is the piezoresistance coefficient in the pressure sensitive resistor 2, σ is the stress acting on the pressure sensitive resistor 2 due to the pressure applied to the diaphragm 3, and the subscript t indicates the direction along the H10) axis,
The subscript r indicates a direction perpendicular to this.

The resistance value change according to equation (2) occurs in each part of the pressure-sensitive resistor 2, and in the pressure-sensitive resistor 2 as shown in FIG. 4, it occurs in both the first part 2a and the second part 2b. However, since the first portion 2a and the second portion 2b are continuous and substantially orthogonal, the image portion 2a,
2b, and a portion of the resistance change in the first portion 2a is canceled out by the resistance change in the second portion 2b, making it impossible to achieve the originally intended improvement in detection sensitivity. There was a problem.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a semiconductor pressure sensor that enables a large change in resistance value to occur in a pressure-sensitive resistor and improves detection sensitivity.

[Means to solve the problem]

In the semiconductor pressure sensor according to the present invention, the resistance value per unit length is made different between a portion along the crystal axis of the pressure-sensitive resistor formed on the surface of the diaphragm and a portion substantially orthogonal to the crystal axis, so that the resistance value per unit length is made different from the former. It is also smaller.

[Effect]

In the present invention, the resistance value per unit length is smaller in the second portion substantially perpendicular to the crystal axis than in the first portion along the crystal axis, and the resistance change occurring in the first portion due to the pressure acting on the diaphragm is The rate of cancellation due to the resistance change that similarly occurs in the second portion is reduced, and high detection sensitivity is achieved.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof. FIG. 1 is a partially cutaway perspective view of a semiconductor pressure sensor according to the present invention.

The semiconductor pressure sensor according to the present invention, like the conventional one,
A plurality of pressure sensitive resistors 2, 2... are formed on the surface of the semiconductor chip 1, and the semiconductor chip 1 is etched from the back side.
The center of the pressure sensitive resistor 2, 2 is thinned over a predetermined range.
The diaphragm 3 includes a thin diaphragm 3 that includes a forming area near its periphery, and a thick portion that supports the periphery of the diaphragm 3. The pressure-sensitive resistors 2゜2... are, for example, p-type regions formed on the n-type semiconductor chip 1 using diffusion or ion implantation techniques, and the resistance value caused by the piezoresistance effect is The pressure acting on the diaphragm 3 is detected using the change.

FIG. 2 is an enlarged plan view of the pressure sensitive resistor 2. FIG. These pressure sensitive resistors 2.2... Also, as in the past, the diaphragm 3
The first portion 2a is formed along the crystal axis direction, for example, the <1)0> axis direction, as shown in FIG.
(see Fig. 2) are arranged, and their ends are connected at second portions 2b (see Fig. 2) that are substantially perpendicular to each other.
It has an integrated structure with a flat S-shape.

Although the above configuration is similar to the conventional one, the semiconductor pressure sensor according to the present invention has a resistance value RA per unit length of the first portion 2a and a resistance value per unit length of the second portion 2b. R8 is different, and the latter is smaller than the former (Ra>R1+).

Therefore, when stresses σ and σ1 are generated in the pressure sensitive resistor 2 due to the pressure acting on the diaphragm 3, the resistance value change ΔRA in the first portion 2a and the resistance value change ΔR in the second portion 2b are as described in (2) above. From equations (3) and (4), respectively
) is expressed by the formula.

ΔRa” (π, σ, +π, σt)・RA-IIA
...(3) ΔRI= (π, σ, +π, σ,)・
R1・Il, ...(4) However, π1 is pressure sensitive resistor 2
H10) is the piezoresistance coefficient in the axial direction, and π
is the piezoresistance coefficient in the direction perpendicular to this, and 1 and h are the lengths of the first portion 2a and the second portion 2b, respectively. The negative sign on the right side of equation (4) means that the direction of the current in the second portion 2b is different from that in the first portion 2b.
This is because it is approximately orthogonal to that at a.

Therefore, the resistance value change ΔR occurring in the entire pressure sensitive resistor 2
is, ΔR=(π, σ, +π, σ,)・(Rala−Rmlm
)...(5) That is, the resistance value change ΔR in the pressure sensitive resistor 2 is
For the stress caused by the pressure on the diaphragm 3, (RaJa
-Rmj'++). Therefore, the first
．． The rate of change in the conventional semiconductor pressure sensor in which the second portions 2a and 2b have the same resistance value per unit length (Rs=RA) is determined by the difference in length between the image portions 2a and 2b (Il^-Zm
), whereas in the semiconductor pressure sensor according to the present invention in which R1 is made smaller than R1, these differences also act to increase the rate of change, resulting in a large resistance compared to the conventional one. The value change ΔR can be obtained (5)
It is clear from the formula that higher detection sensitivity can be achieved than in the past.

In this embodiment, a case has been described in which three first portions 2a are connected by a second portion 2b, and the pressure-sensitive resistor 2 is formed in a flat S-shape. However, the formation mode of the pressure-sensitive resistor 2 is as follows. It is not limited to this.

〔Effect of the invention〕

As detailed above, in the semiconductor pressure sensor according to the present invention, the resistance value per unit length of the first portion along the crystal axis of the pressure-sensitive resistor on the diaphragm surface and the second portion substantially perpendicular to the crystal axis is In contrast, since the latter is smaller than the former, the rate at which the resistance change caused in the first part due to the pressure acting on the diaphragm is offset by the resistance change similarly caused in the second part is reduced, and the The present invention has excellent effects such as a large resistance value change and high detection sensitivity.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view of a semiconductor pressure sensor according to the present invention, FIG. 2 is an enlarged plan view of its pressure-sensitive resistor, FIG. 3 is a partially cutaway perspective view of a conventional semiconductor pressure sensor, and FIG. is an enlarged plan view of the pressure sensitive resistor. 1... Semiconductor chimp 2... Pressure sensitive resistor 2a...
First part 2b...Second part 3...Diaphragm In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] (1) On the surface of a diaphragm formed by thinning a part of a semiconductor chip, a plurality of first parts along the crystal axis direction are connected by second parts substantially orthogonal to each other, and are integrated with each other. A semiconductor pressure sensor comprising a pressure sensitive resistor, characterized in that the second portion has a resistance value per unit length smaller than that of the first portion.