JPH03194401A - Semiconductor strain detecting circuit - Google Patents

Abstract

PURPOSE:To attain accurate temperature compensation with simple constitution by offsetting temperature variation in voltage developed across a temperature insensitive element against the temperature characteristics of a strain detecting element. CONSTITUTION:The semiconductor strain detecting circuit 7 is constituted by composing a bridge circuit 9 of strain detecting elements R1-R2 and connecting the temperature insensitive element Rx which does not vary in resistance value with temperature to the circuit 9 in parallel. Then a constant current source 10 is connected to the circuit 9, which is driven to output a voltage V0. Consequently, the temperature variation of the temperature insensitive element Rx is offset against the temperature characteristics of the strain gauges R1-R4 to perform the temperature compensation of output sensitivity DELTAV0.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor strain detection circuit equipped with a semiconductor strain detection element.

2. Description of the Related Art Conventionally, the technology of semiconductor strain detection circuits equipped with strain detection elements has been applied in various fields. As a first example, strain sensing elements (hereinafter referred to as strain gauges) are formed on a diaphragm of a Si (silicon) substrate, and each of these strain gauges constitutes a Wheatstone bridge circuit to create a pressure sensor. This is applied to the measurement of various pressures. FIG. 10 shows a bridge circuit 1 constructed using these strain gauges R1 to R1, and is driven by a constant current source 2. At this time, V to the output
is ΔV=GRε engineering (1).

However, G: Gauge factor R: Resistance factor of strain gauge at no strain: Current value From this, ΔV for a constant strain ε (i.e., sensitivity)
The temperature characteristics of are determined by the temperature characteristics of G and R (■ is constant due to constant current source). FIG. 11 shows the relationship between the temperature coefficient of sensitivity and the surface impurity concentration when driven by the constant current source 2. In this case, G has a negative gauge factor temperature coefficient and R has a positive resistance temperature coefficient, so the surface impurity concentration is 2 X 10"atoms/cm' or 2 X
By setting 10''ato[Ils/Cm, the two can be canceled out and the temperature fluctuation of Δ■ can be reduced.

Problem to be Solved by the Invention Figure 12 shows the relationship between the rate of change in sensitivity and the ambient temperature based on the sensitivity at 35°C when the bridge circuit 1 is driven by the constant current source 2 as shown in Figure 10. It shows. From this, if the temperature range is 0 to 45°C, the sensitivity fluctuation will be within ±0.3%.

In a wide temperature range of -20 to 80°C, it fluctuates by more than ±1%. Pressure sensors with such fluctuation characteristics are used in equipment that requires high measurement accuracy in the temperature range of -20°C to 80°C, and in particular, the fluctuation range must be suppressed to ±0.3% or less due to the measurement accuracy. When applied to such a device, the above-mentioned method of performing temperature compensation by canceling each other out cannot meet the requirements.

Conventionally, there is a method disclosed in Japanese Patent Publication No. 59-41134 as a means for dealing with such problems.

That is, as shown in FIG. 13, strain gauges R0 to R4
is used to drive the pressure conversion circuit 3 constituting the bridge circuit 2 with a constant voltage. In this case, strain gauge R1
Temperature compensation is performed by connecting the temperature-sensitive resistor Rp formed by the same process as ~R1 to the feedback section of the amplifier circuit in parallel with the temperature-insensitive resistor Ro, thereby suppressing the rate of change in output sensitivity due to temperature. ing. Note that the surface impurity concentration of the strain gauges R1 to Rp at this time is 2
X I O1t ~ 8 X 1017 atoms/cm
' is used. However, in this case, a complicated circuit is required as shown in FIG. 13, and as shown in FIG. Therefore, there is a problem in that the manufacturing process of the substrate becomes extremely troublesome.

Means for Solving the Problems The present invention provides a semiconductor strain detection circuit in which strain detection elements are formed on the surface of a substrate, and the strain generated on the substrate is detected by connecting these strain detection elements to a bridge circuit. The strain sensing element and a temperature-insensitive element whose resistance value does not change with temperature are connected to the bridge circuit in parallel, and a constant current source is connected to the bridge circuit provided with the temperature-insensitive element to drive it. .

Operation In this way, the temperature-insensitive element is connected in parallel to the bridge circuit and driven by a constant current source, and the temperature change (positive characteristic) of the voltage appearing across the temperature-insensitive element and the sensitivity temperature characteristic of the strain detection element (
By offsetting the negative characteristics), a wide temperature range (-
It becomes possible to suppress fluctuations in output sensitivity over a temperature range of 20 to 80'C), and more accurate temperature compensation can be performed with a simpler configuration.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 7. FIG. 1 shows the configuration of this circuit without distortion. That is, this semiconductor strain detection circuit 7 constitutes a bridge circuit 9 using strain detection elements R1 to R4 (hereinafter referred to as strain gauges 8). A temperature-insensitive element Rx whose resistance value does not change with temperature is connected in parallel to this bridge circuit 9. The bridge circuit 9 in which the temperature-insensitive elements Rx are connected in parallel is connected to a constant current source 10, and is driven by the constant current source 10 to output an output voltage of V.

FIG. 3 shows a cross-sectional shape of an n-type Si substrate 11 as a substrate. A strain gauge 8 is formed on the surface of the substrate by diffusing boron or the like by ion implantation or the like. Its surface impurity concentration Cs is 2×10”~l,
5 x 10"atoms/cm', which is
The formation can be controlled by the conditions of the diffusion process.

However, in FIG. 1, it is assumed that all the resistors R1 to R4 have the same resistance value R, and at this time, the resistance value of the entire bridge also becomes R.

In such a configuration, it is now assumed that the resistances R1 to R4 have changed by ΔR4 to ΔR4, as shown in FIG. In this case, ΔR8 to ΔR1 are approximately equally represented by ΔR. Therefore, ΔR5 and -ΔR4, -Δ
R1 and ΔR2 cancel each other out, so that the resistance value of the entire bridge when strain is applied also becomes R.

In such a state, the output ■. ΔV appearing in (Output sensitivity) can be expressed as G・ε・Ra・■ (2).

Now, the temperature characteristics of G (gauge factor) and R when C5=9X10"a toms/cm' are shown in FIGS. 4 and 5.

Note that the ratio is shown based on the reference temperature T=30°C.

From this equation (2), 8■ for a constant ε. It can be seen that is determined by G and Ra (ε and ■ are constant), and therefore, its temperature characteristics are also determined by the product of G and Ra. Therefore, −
R so that the GRa in the range of 20°C to 80”C is equal.
We determined x. That is, G (-20) Ra (-20
) G (80) Ra (80) ... (4) Therefore, from this, Rx is Rx determined by this formula (6) in a bridge circuit (resistance value R
The measurement results of the temperature characteristics of Ra when connected in parallel with
As shown in the figure. Then, as shown in Figure 1, the Rx is connected to a bridge circuit and driven by a constant current generator. Figure 17 shows the temperature characteristics of . Therefore, this gives -20
It can be seen that the fluctuation is less than ±0.3% over a wide temperature range from ℃ to 80℃. Note that the characteristic results in FIG. 7 are G (T) Ra (T) expected from equation (2).
The temperature characteristics were almost the same as those of .

As mentioned above, the temperature-insensitive element Rx is connected in parallel to the bridge circuit of the resistor R, and a constant current ■ is caused to flow, and the temperature change of Vi (positive characteristic) and the sensitivity temperature characteristic of strain gauges R1 to R4 (negative characteristic) are calculated. By canceling out the output sensitivity Δ■. Temperature compensation can be performed. In addition, by determining Rx using the same procedure when the value of the surface impurity concentration Cs is between 2X10'7 and 1.5X10'', and configuring the configuration as shown in Fig. 1, the temperature fluctuation of ΔV0 can be suppressed by ± We were able to suppress it to 0.3% or less.

Next, a second embodiment of the present invention will be described based on FIGS. 8 and 9. Now, as in the first embodiment, when there is no distortion in FIG. 8, R,=R,=R, and when distortion is applied as shown in FIG. 9, the values of R1 and R2 change. At this time, if ΔR, = 8R, = ΔRa, then the resistance value of the series resistor of the two strain gauges will be 2R regardless of the presence or absence of strain. In this case, the output ΔV appearing at vo due to the strain ε. can be expressed as.

Also, Vi is ■１ I (2R/2Rx) becomes.

Here, from the relationship of equation (3), equation (9) becomes =G・ε・R
It can be transformed as a・■...(10).

This shows that the equation (10) is equal to the equation (2). Therefore, in the case of this embodiment as well, similarly to the first embodiment, by determining the surface impurity concentration, Rx, of the strain gauge 8, the output sensitivity can be kept below ±0.3% in the range of -20 to 80°C. Temperature fluctuations can be suppressed.

In the embodiments described so far, the structure in which the P-type strain gauge 8 is diffused on the n-type Si substrate 11 has been described, but the structure is not limited to this. Even when the n-type strain gauge 8 is diffused, the same temperature compensation method can be applied at an appropriate surface impurity concentration.

Further, the present invention can be applied not only to the diffusion type strain gauge 8 but also to thin film semiconductor strain gauges such as bulk single crystal Si strain gauges, polycrystalline silicon, amorphous silicon, and the like. moreover,
It can also be applied to strain gauges using compound semiconductors.

Effects of the Invention The present invention provides a semiconductor strain detection circuit in which strain detection elements are formed on the surface of a substrate, and which detects strain generated on the substrate by connecting these strain detection elements to a bridge circuit. A temperature-insensitive element whose resistance value does not change with respect to temperature is connected in parallel to the bridge circuit, and a constant current source is connected to the bridge circuit equipped with the temperature-insensitive element to drive it. A temperature-insensitive element is connected in parallel to a bridge circuit and driven by a constant current source, and the voltage that appears across the temperature-insensitive element changes with temperature (positive characteristic).
By offsetting the sensitivity temperature characteristic (negative characteristic) of the strain detection element, it is possible to suppress fluctuations in output sensitivity over a wide temperature range (-20 to 80 degrees Celsius), and this makes it possible to improve accuracy with a simple configuration. It is possible to perform good temperature compensation.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing the first embodiment of the present invention, Fig. 2 is a circuit diagram showing the situation when distortion occurs in the circuit, Fig. 3 is a longitudinal cross-sectional side view of the silicon substrate, and Fig. 4 5 is a characteristic diagram showing the temperature characteristic of the gauge factor G, FIG. 5 is a characteristic diagram showing the temperature characteristic of the resistance value R, FIG. 6 is a characteristic diagram showing the temperature characteristic of the resistance value Ra, and FIG. 7 is a characteristic diagram showing the temperature characteristic of the resistance value R. FIG. 8 is a circuit diagram showing the second embodiment of the present invention, FIG. 9 is a circuit diagram showing the state when distortion occurs in the circuit, and FIG. 10 is a conventional circuit diagram. Figure 11 is a circuit diagram showing the bridge configuration, Figure 11 is a characteristic diagram showing the relationship between sensitivity temperature coefficient and surface impurity concentration, Figure 12 is
FIG. 13 is a characteristic diagram showing the relationship between sensitivity and temperature, FIG. 13 is a circuit diagram showing another conventional bridge configuration example, and FIG. 14 is a configuration diagram showing the state of the substrate on which the circuit is formed. 8... Strain detection element, 9... Bridge circuit, ]O... Constant current source, 11... Silicon substrate, Rx... Temperature insensitive element Applicant Rico Co., Ltd. 3 / Figure T ("C) - T ('C) - T ("の"") Figure JD, IZ Figure Jai1口! T (@C) J JIi俤珪

Claims (1)

[Claims] In a semiconductor strain detection circuit in which strain detection elements are formed on the surface of a substrate, and the strain generated in the substrate is detected by connecting these strain detection elements to a bridge circuit, the resistance value of the strain detection element and the temperature are determined. A semiconductor strain detection circuit characterized in that a temperature-insensitive element that does not change is connected in parallel to the bridge circuit, and a constant current source is connected and driven to the bridge circuit including the temperature-insensitive element.