JPS62160772A - Semiconductor pressure sensor and pressure measuring device - Google Patents

Abstract

PURPOSE:To obtain a voltage proportional to the change in pressure, by providing another diffused layer in one diffused layer, which has specified concentration and area, on a diaphragm formed with a silicon semiconductor, forming a synthesized resistor body, reducing the change in pressure sensitivity dependent on the change in temperature, and constituting a bridge circuit using four pieces of the semiconductor pressure sensors. CONSTITUTION:A first impurity layer 2 is formed on a silicon semiconductor 3 by epitaxial growing and the like. A second impurity layer 5 is formed in the first diffused layer by the similar means. Terminals 4 and 4a are formed thereon with a specified interval being provided. An SiO2 layer 6 is provided on the first and second impurity layers in order to insulate both terminals. The first diffused layer 2 and the second diffused layer 5 are considered to be an assembled body of two kinds of resistors in the longitudinal and lateral directions. A pressure measuring device using these parts includes a Whetstone bridge circuit in order to pickup detected signal as enlarged and accurately as possible. A constant voltage source 14 is connected between input terminals 12 and 13. An output voltage is picked from between output terminals 15 and 16. Thus the temperature dependency of pressure sensitivity can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention (Field of Industrial Application) The present invention relates to an improvement in the temperature characteristics of a semiconductor pressure sensor and a pressure measuring device using this semiconductor pressure sensor.

(Prior Art) Sensors using semiconductors have recently attracted attention as a means of converting pressure into electrical signals.

Products using silicon semiconductors are considered particularly promising in that they meet the requirements of pressure sensors, such as low cost, high reliability, and miniaturization.

Semiconductor pressure sensors generally utilize piezoresistance effects. Sensors that utilize this piezoresistance effect generate stress changes within the semiconductor crystal due to strain caused by external forces.
Due to this, one unit of electronic energy changes. As a result, the resistance value changes. Therefore, by measuring one change in this resistance value, the applied pressure can be measured.

[Problem that the invention seeks to solve]

However, since semiconductor pressure sensors have strong temperature dependence, a temperature compensation circuit is required to accurately measure pressure. There are two types of temperature effects. One is the temperature variation of the output voltage, and the other is the temperature variation of the output voltage relative to the minimum pressure.

Generally, the former is called span variation, and the invader is called offset variation.

In conventional semiconductor pressure sensors, a circuit must be provided to compensate for these two temperature fluctuations, but this complicates the circuit, causing problems in terms of increased cost and reliability.

In order to solve this problem, the invention of Japanese Patent Publication No. 57-26430 [Silicon Drain Gauge] (hereinafter referred to as Prior Application 1) and Japanese Patent Application No. 60-138591 filed by the present applicant [Semiconductor pressure sensor and pressure measurement] There is an application (hereinafter referred to as "Prior Application 2") for "Device".

The present invention solves the problems of the above-mentioned conventional techniques by using means different from those of these prior applications.

``Structure of the Invention'' [Means for Solving the Problems] In order to solve the above problems, the present invention provides a first impurity layer having a predetermined concentration and area on a diaphragm formed of a silicon semiconductor. A second impurity layer is formed in the first impurity layer, a resistor is formed by connecting appropriate locations of the second impurity layer, and the shape of the resistor is determined on the diaphragm. By using the arrangement of the resistor and the relationship between the formation direction of the resistor and the crystal axis of the diaphragm, the semiconductor pressure sensor is configured so that the temperature change in the pressure sensitivity of the resistor is small. A bridge circuit is constructed using four of them, and a current is applied from a constant voltage source between the input terminals of this bridge circuit, so that 1q of voltage proportional to the change in pressure is applied between the output terminals of the bridge circuit. .

The difference between the present invention and the technology related to Prior Application 1 is that
The above technology requires limiting the impurity concentration of the resistor to a specific value, but the present invention solves the problems of the above-mentioned conventional example without limiting the impurity concentration to a specific value. They are different in that they can solve the problem.

Further, the difference between the present invention and the technology related to Prior Application 2 is that in the technology of Prior Application 2, two resistors are formed independently, whereas in the present invention, one resistor is formed in one diffusion layer. The difference is that two diffusion layers are provided to form a composite resistor.

(Example) Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 is a plan view (a) and a cross-sectional view (b) showing a configuration example of a semiconductor pressure sensor according to the present invention, and FIG. 2 is a current with respect to resistance between terminals shown in the semiconductor pressure sensor of FIG. Figure 3 is an equivalent circuit diagram of the resistance distribution shown in Figure 2, Figure 4 is a diagram schematically showing the distribution of the bus in Figure 2, and Figure 4 is a diagram showing a bridge circuit using four semiconductor pressure sensors. Figure 5 is a diagram showing the pressure measurement @ arrangement according to the invention, Figure 5 is a diagram showing how the semiconductor pressure sensor shown in Figure 1 is distorted due to pressure being applied, and Figure 6 is a diagram showing the thin part of the diaphragm. Cross-sectional view (A) and plan view (A) showing the semiconductor pressure sensor placed above
B), FIG. 7 is a plan view showing another example, FIG. 8 is a diagram showing the relationship between surface concentration and piezo coefficient, and FIG. Figure 10 is a diagram showing the relationship between n-type silicon temperature and piezo coefficient component π44, and Figure 11 is a diagram showing the relationship between n-type silicon piezo coefficient component π11's 1 degree coefficient and electron 9 is a diagram showing the relationship with concentration, which was determined from the slope of the graph in FIG. 9. Figure 12 is a diagram showing the relationship between the temperature coefficient of n-type silicon piezoelectric coefficient component π44 and hole concentration, Figure 13 is a diagram showing the relationship between the resistance temperature coefficient of n-type silicon and specific resistance, and Figure 14 is a diagram showing the relationship between the temperature coefficient of resistance and specific resistance of n-type silicon. The figure is a diagram showing the relationship between the resistance temperature coefficient and specific resistance of n-type silicon. In addition, the starting prefectures in Figures 13 and 14 are 5olid 5tate ele
ctron, 11 pp 639-646. f
eb (1968). Figure 15 is Figure 9 or 10
A diagram showing the relationship between the component πI++πd4 of the piezo coefficient obtained from the figure and the surface electron concentration or surface hole concentration. Figure 16 is a diagram showing the relationship between the piezo coefficient component πI++πd4 and the surface electron concentration or surface hole concentration. concentration or hole l
N! Figure 17 is a diagram showing that the sign of the piezo coefficient is different when resistors 2 and 5 are placed on the diaphragm, and (C) and (d) are diagrams showing that the crystal axis and the resistance It is a figure showing the relationship with body direction.

In addition, Figs. 8 to 10 are J, of apply, p
hys, 34, no, 2 pp313-318jeb
This is an excerpt from y1963.

In FIGS. 1(a) and (b), 3 is a silicon semiconductor, 2 is a first impurity layer formed on the silicon semiconductor 3 by means such as thermal diffusion, ion implantation, epitaxial growth, etc., and 5 is a first impurity layer. a second impurity layer formed in the diffusion layer by the same means as the first impurity layer 2; terminals 4 and 4a are formed on the second impurity layer 5 at a predetermined interval; is the first. This is a SiO□ layer formed on the second impurity layer to insulate between terminals.

In such a configuration, when looking at the first diffusion layer 2 and the second diffusion layer 5, they can be considered as a combination of two types of resistors, one in the vertical direction and the other in the horizontal direction. In this case, output terminal 4
, 48 can be divided into a resistor 10 for the X component and a resistor 20 for the Y component as shown in Figure 2, and can be replaced with an equivalent circuit as shown in Figure 3. I can do it.

The change in resistance (detection signal) obtained by a semiconductor pressure sensor is small. For this reason, in pressure measuring devices,
In order to extract this detection signal as large and accurately as possible,
Usually, as shown in Figure 4, Wheatstone Bridge (
A circuit (hereinafter simply referred to as a bridge) is constructed.

Although only one resistor is shown in FIGS. 1A and 1B, four pairs of resistors are formed when forming a bridge circuit. If the resistance value of the resistor 10 in the equivalent circuit shown in FIG.
a −1/(r + +r2 ) −RM. Then, so as to function as a bridge circuit, opposite sides (R+ and R4, R2 and R3) are configured so that their resistance changes in the same direction in response to applied pressure, and adjacent sides change their resistance in opposite directions.

A constant voltage source 14 is connected between input terminals 12 and 13, and output voltage eO is taken out between output terminals 15 and 16.

In order to explain the operation of the pressure measuring device using the full bridge circuit shown in FIG. 4, the operation will be explained using FIG. 3 which shows the basic configuration.

It is assumed that the resistors 10 and 20 are both arranged at positions where they operate as strain resistors when strain is applied to the single crystal diaphragm. For example, as shown in FIG. 5, the arrangement is such that stress is applied to the resistor when the state B changes from no strain to the state C where strain is applied.

Generally, the sensitivity of a strain resistor is determined by the piezo coefficient π (Cn12/
dyn) T; Table mg, Definition GE (1) Formula theal.

Δρ/ρ−π・σ (+) Here, ρ: Specific resistance (Ωcm > Δρ: Change in specific resistance (Ωcm) σ: Stress applied to the resistor (dyn/cm2) This can be expressed as the resistance Ifr of the resistor. Expressing this, a term for the shape change of the resistor is added, but in the case of semiconductors, the value of π is large, so equation (2) may be used.

Δr/r−(1+2ν)ε+π·σ 〜π畢σ (2) Here, σ: Boisson's ratio ε: strain amount The temperature coefficient of this piezo coefficient π is formulated as in equation (3).

π −π o (1-t β T )
(3
) Here, β: temperature coefficient of Biezo coefficient (dcg-')
π0: Piezo coefficient at reference temperature To: T: TohH measured temperature Also, the temperature coefficient of the resistance value of the resistor itself is set as shown in equation (4).

r − r, (1+ a T )
(4) Here, α: resistance temperature system rIl(deg-
')ro:! 3 Resistance value at quasi-temperature TO When stress is applied to the resistor and the temperature changes, the change in resistance value is expressed by the following equation from equations (2) and (3).

Δγ/γ−π・σ−πo (1+βT)σ (5)
Also, as shown in Fig. 4, using four resistors shown in Fig. 3,
A bridge circuit is configured, and a constant voltage source 14 is connected to terminals 12 and 13.
When connected, the voltage eo appearing at the output terminals 15 and 16 is expressed by equation (6).

M γ eo - E (6) A: Voltage E of constant voltage source 14 Therefore, when considering the change in output voltage eo due to temperature, that is, the temperature dependence Δγ as a pressure sensor (pressure measuring device). You can think of '7.

π1: Piezo coefficient of the resistor 10 π2: Considering the dependence of the piezo coefficient of the resistor 20 on the east, πlo*'IO...The piezo coefficient and resistance value πzo l r of the resistor 10 at the temperature To. ...Piezo coefficient and resistance value β1 of the resistor 20 at temperature To, α1...Temperature coefficient of the piezo coefficient and temperature coefficient β2 of the resistance value of the resistor 10. α2...Temperature coefficient of piezo coefficient of resistor 20 and temperature coefficient of resistance value σ1. σ2... Stress applied to the resistor Here, the values of α and β are the 11th when the resistor is n-type silicon. From FIG. 13, in the case of n-type silicon, it can be found from FIGS. 12 and 14.

In Figures 13 and 14, α has a specific resistance of 1O-20C.
Since the minimum value is taken at 1, α becomes as shown in Figure 16.
There are two resistivities corresponding to the values of .

In Figure 16, if we select the m degree of impurity corresponding to (2) as the degree of impurity 'a of the resistor, α1 - α2 (9) π10 σI”β1 +m7r,.β2−β2)T
]...0ω Here, if the first term of equation 00) is A1 and the second term is 8, then A
=π,. -cyl+mπZ.・cy2”-Q
(11) Yo9”−・(π,.,σ,+mπυσ2
)11,000, and it is possible to obtain a resistor element whose resistance value changes with stress but whose resistance value does not change with temperature.

Next, when constructing an actual pressure sensor using the above resistor elements, it is constructed so that the relationship as described above is established,
We will use a concrete example to prove that the temperature dependence of pressure sensitivity can be reduced.

For example, if a resistor is arranged on a diaphragm as shown in FIG. 6, the angle of π1° in equation (10) will depend on the crystal plane of the diaphragm and the direction in which the resistor is arranged.

The piezo coefficient of πz0 changes. For example, the 11th and 12th
From the figure, in order to satisfy equation (12), β1 × O1 β2 × 0, so (π1°・σ+ ) ・(m7rzo・(72) <Q
It must be (13). This can be achieved by the following means.

(1) The arrangement direction of the resistor (tangential direction and radial direction on the diaphragm)...that is, piezo coefficient πIQ +
When realizing the present invention by means of making the polarity of πlO positive or negative, for example, the means of (1),
As shown in Fig. 17, the (1
10) Arrange two types of resistors in the direction.

At this time, the piezo coefficient values of the resistor for the χ and y components are:
As shown in (c) and (d) of FIG. 17, π1゜〉0. πz
o<O, and formula (13) is satisfied.

Therefore, from the form of equation (12), there is a condition that B=O. Here, π1゜・σ1・βl+mπzo・σ2
- An example of means for actually achieving β2=O will be described.

The resistance value of the resistor, its arrangement on the silicon semiconductor diaphragm, the relationship between the formation direction of the resistor and the crystal axis of the diaphragm, the combination of impurity a degree, etc. are determined in advance so that the above formula is satisfied. do.

Here, at the moment when the resistor is formed on the silicon semiconductor diaphragm, πIQ, π101 σ嘗, σ2°β1.
The value of β2 is determined.

Therefore, the adjustment means is to adjust the resistance ratio m. This resistance ratio m can be adjusted by an empirical method. For example, forming a plurality of resistors and selecting a good resistor, or the first. It can be adjusted by changing the shape of the second diffusion layer, how to connect its terminals, etc.

FIG. 7 shows another embodiment. In this example, the diffusion layer 2 is formed to have a relatively wide area, and a plurality of terminals 40a to 40e are provided in this second diffusion layer. A terminal (for example, configured to connect 40a and 40e) serves as an optimal resistor.

The above specific explanation is an example of implementing the present invention, and the present invention is not limited thereto. For example, n-type silicon can be used, and various combinations of crystal planes and resistor arrangement directions are possible.

Further, in the above, it is assumed that α-value − α2 in equation (9), but even if this does not hold, it is possible to create a piezoresistance element (q) whose pressure sensitivity does not depend on temperature.

C. "Effects of the Present Invention" As described above, according to the present invention, the following effects can be obtained.

(2) A semiconductor pressure sensor with strain sensitivity and low temperature dependence of strain sensitivity can be realized relatively easily.

■ Non-linearity of stress and resistance value changes can be improved.

[Brief explanation of drawings]

FIG. 1 is a plan view (a) and a cross-sectional view (b) showing a configuration example of a semiconductor pressure sensor according to the present invention, and FIG. 2 is a resistance between terminals shown in the semiconductor pressure sensor of FIG. FIG. 3 is a diagram schematically showing the resistance distribution, which is not shown in FIG. A diagram showing such a pressure measuring device, FIG. 5 is a diagram showing how pressure is applied to the semiconductor pressure sensor shown in FIG. 1 and distortion occurs, and FIG. 6 is a diagram showing the semiconductor pressure sensor shown in FIG. FIG. 7 is a plan view showing another embodiment, and FIG. 8 is a diagram showing the relationship between surface concentration and piezo coefficient. Figure 9 is a diagram showing the relationship between the temperature of n-type silicon and the component π11 of the piezo coefficient, Figure 10 is a diagram showing the relationship between the temperature of n-type silicon and the component π44 of the piezo coefficient, and Figure 11 is a diagram showing the relationship between the temperature of n-type silicon and the component π44 of the piezo coefficient. A diagram showing the relationship between the temperature coefficient of the component πI+ of the n-type silicon piezo coefficient and the electron concentration,
Figure 12 is a diagram showing the relationship between the temperature coefficient of n-type silicon piezoelectric coefficient component π44 and Hall m degrees, and Figure 13 is n
A diagram showing the relationship between the temperature coefficient of resistance and specific resistance of type silicon,
Figure 14 is a diagram showing the relationship between the temperature coefficient of resistance and specific resistance of n-type silicon, Figure 15 is the piezo coefficient component π1 tube, π44, and surface electron 11 degree or surface electron coefficient determined from Figure 7 or Figure 8. Figure 16 shows the relationship with hole concentration.
Figure 3 or Figure 14 shows the existence of two electrons or holes si that have the same temperature coefficient of resistance despite having different concentrations. Figures 17 (a) and (b) show the presence of a resistor on the diaphragm. (C) and (d) are diagrams showing the relationship between the crystal axis and the resistor orientation. . 10.20...Resistance body, 3...Silicon single crystal,
14... constant voltage source. Figure 1 Chopsticks 3 Figure 73 Figure 5 Figure 7 Figure 6 Figure 9 Temperature °C Figure 10 Radiation °C Figure 13 Hm ja JI'[<rl-Cfi] Figure 14 Jiji 1 Mr. 2 in (n-cm)

Claims (2)

[Claims] (1) A first impurity layer having a predetermined concentration and area is formed on a diaphragm made of a silicon semiconductor, a second impurity layer is formed in the first impurity layer, and a second impurity layer is formed in the first impurity layer.
A resistor is formed by connecting appropriate locations of the impurity layer, and the shape of the resistor, the arrangement of the resistor on the diaphragm,
A semiconductor pressure sensor configured such that a temperature change in pressure sensitivity in the resistor is reduced by using the relationship between the direction in which the resistor is formed and the crystal axis of the diaphragm. (2) forming a first impurity layer having a predetermined concentration and area on a diaphragm formed of a silicon semiconductor; forming a second impurity layer in the first impurity layer; and forming a second impurity layer in the first impurity layer;
A bridge circuit is constructed using four semiconductor pressure sensors in which resistors are formed by connecting appropriate points of the impurity layer of A pressure measuring device that obtains a voltage between terminals that is proportional to the change in pressure.