JPH0442612B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an integrated pressure sensor, and more particularly to a temperature compensation circuit suitable for semiconductor integration of a sensor portion and a pressure detection signal amplification circuit portion.

A circuit for compensating for temperature-related variations in the sensitivity of a semiconductor pressure sensor is described, for example, in US Pat. No. 3,836,796. The basic configuration is shown in Figure 1. This compensation circuit consists of transistor 1, a resistor R1 connected between its collector and base, and a resistor _R1 connected between its collector and base.
It consists of a resistor R ₂ connected between the emitters, and is connected in series with a bridge-configured strain gauge circuit G ₁ to _{G 4} . This temperature compensation circuit is generally known as an nVbe circuit.

The inter-terminal voltage Vcom of the compensation circuit is a voltage obtained by multiplying the base-emitter voltage Vbe of the transistor 1 by a constant determined by the resistors _R1 and _R2 . Therefore, select resistor R ₁ and resistor R ₂ appropriately, and set the voltage
The temperature characteristics of Vcom compensate for the sensitivity of the pressure sensor.

The sensitivity of pressure sensors generally decreases at higher temperatures. To compensate for this decrease in sensitivity, the bridge terminal voltage of the pressure sensor can be increased. That is, it is sufficient to lower the voltage Vcom between the terminals of the compensation circuit. Base-emitter voltage of transistor 1
Since Vbe decreases as the temperature rises, the inter-terminal voltage Vcom of the compensation circuit decreases, making it possible to increase the bridge terminal voltage of the pressure sensor.

This type of temperature compensation circuit has Japanese Patent Application Laid-open No. 49-119675.
Some of them are described in the publication. This compensation circuit uses a fixed resistor, a variable resistor, and a transistor used as a heat-sensitive element to supply a current according to the temperature to the bridge circuit of the pressure sensor, or a Zener diode or the like is added to supply a current according to the temperature. A means for supplying voltage to a bridge circuit of a pressure sensor is proposed.

For the above USP3836796 pressure sensor, the power supply voltage
When Vcc changes, the terminal voltage Vcom of the compensation circuit including transistors is hardly affected, whereas the bridge terminal voltage is affected one-to-one. Therefore, the amount of change in Vcom due to temperature changes is almost unaffected by changes in power supply voltage Vcc and remains constant; therefore, as power supply voltage Vcc increases, the proportion of terminal voltage Vcom in the total decreases. When temperature compensation is insufficient and the power supply voltage drops, there is a drawback of overcompensation.

On the other hand, in the pressure sensor disclosed in JP-A-49-119675, current or voltage depending on the temperature is supplied only to the bridge circuit, but there is no consideration given to miniaturization, especially integration, and the bridge circuit is No consideration was given to compensation including the temperature characteristics of the amplifier circuit that amplifies the pressure detection signal and outputs it to the next stage.

Incidentally, recently, for the purpose of downsizing the pressure sensor or making it easier to handle the signal, a method has been proposed in which the pressure sensor part and the amplification circuit part of the pressure detection signal are integrated. In this case, the diffusion gauge resistor constituting the bridge of the pressure sensor is formed, for example, by diffusion on the surface of the silicon diaphragm. Further, a resistor that determines the amplification degree of the amplifier circuit portion is also formed on the surface of the silicon substrate outside the diaphragm region.

While the bridge output Vout is generally several tens of mV, the sensor output Eout, which will be described later, is several volts due to the requirements of the equipment that receives this output Eout.
Is required. Therefore, the amplification degree of the amplifier circuit integrated on the silicon substrate is at least
100 times more required. Therefore, the ratio of the feedback resistance to the resistance connected to the input side is 100
The resistance value becomes more than twice that, for example, several 100 kΩ. Making this resistor on-chip requires a huge amount of area, which makes it difficult to secure the area and also increases the cost of the chip. Therefore,
It is considered more practical to form a thin film on a chip or a thick film resistor.

In such a structure, the resistor connected to the input side to determine the amplification degree of the amplifier circuit and the feedback resistor are made of different materials and have different configurations, resulting in a difference in temperature coefficient between the two resistors. Even if the decrease in sensitivity due to temperature in the bridge section of the pressure sensor is sufficiently compensated for, the output voltage Vout obtained from the integrated pressure sensor will be affected by changes in the amplification degree of the amplifier circuit section due to temperature. Become.

All of the above-mentioned conventional techniques, which lack consideration for integration including the amplifier circuit, have the drawback of not being able to perform precise temperature compensation including the amplifier circuit.

Among the pressure sensor part and its amplifier circuit part integrated on a substrate on which a diaphragm is formed, the object of the present invention is to not only change the sensitivity of the pressure sensor part due to temperature, but also to improve the resistance of the pressure sensor part that determines the amplification degree of the amplifier circuit part. It is an object of the present invention to provide a pressure sensor equipped with a compensating means that comprehensively compensates for temperature including fluctuations caused by temperature, and furthermore, its temperature compensation characteristics do not change even if the power supply voltage fluctuates.

In order to achieve the above object, the present invention forms a stress sensing element consisting of a plurality of diffused resistors whose resistance value changes depending on pressure on the front surface of a semiconductor substrate whose back surface is processed into a diaphragm, and from this stress sensing element. An integrated type in which an amplifier circuit including an amplification factor setting resistor formed on the surface of a semiconductor substrate and whose resistance value changes depending on temperature is arranged on the surface of the semiconductor substrate outside the diaphragm in order to amplify the signal at a predetermined amplification factor. In the pressure sensor, a constant current driving means is formed on the surface of the semiconductor substrate and drives a plurality of diffused resistors of the stress sensing element with a constant current to remove the influence of a power supply voltage, and a transistor and a diffused resistor are formed on the surface of the semiconductor substrate. and a constant current changing means that changes the set current of the constant current driving means based on changes in the Vbe voltage of the transistor that changes depending on the temperature and the resistance value of the diffused resistance element, and detects changes in power supply voltage and stress. This paper proposes an integrated pressure sensor equipped with a compensation circuit that comprehensively compensates for changes in sensitivity characteristics due to temperature of the element and changes in amplification factor due to temperature of the amplifier circuit.

More specifically, the constant current changing means changes the Vbe of the plurality of transistors having different emitter areas.
A voltage-current conversion circuit that includes a circuit that obtains a voltage proportional to absolute temperature based on the voltage, and a plurality of the diffusion resistance elements having different impurity concentrations, and converts the voltage proportional to the absolute temperature into a set current of the constant current driving means. It consists of.

In the present invention, first, the influence of fluctuations in power supply voltage on the detection signal of the stress sensing element having a bridge configuration is basically eliminated by driving the bridge at a constant current.

Next, in order to meet the demand for integrating and miniaturizing stress-sensing elements and amplifiers, it is necessary to mix a metal film resistor with a small temperature coefficient and a diffused resistor with a large temperature coefficient in the amplification factor determining element of the amplifier. Therefore, the influence of temperature change on the overall output sensitivity due to the mixed use of a metal film resistor and a diffused resistor is determined by changing the set current of the constant current circuit according to the temperature.

Specifically, by using the temperature dependence of Vbe of a transistor, the difference in Vbe of two transistors ΔVbe
is used as a parameter. Furthermore, the temperature coefficients of the plurality of diffused resistors are adjusted by the impurity concentration, and the set current of the constant current circuit is changed according to the temperature based on the differential voltage ΔVbe.

FIG. 2 is a diagram showing an example of a change in sensitivity with respect to temperature of a silicon diaphragm pressure sensor. This characteristic is the characteristic when the pressure sensor having the bridge configuration shown in FIG. 1 is driven at a constant voltage.

For details, see ``Structural Analysis of Semiconductor Pressure Sensors for Industrial Instruments,'' No. 105 of the Proceedings of the Hitachi Regional Conference, jointly sponsored by the Japan Society of Mechanical Engineers and the Japan Society of Precision Mechanical Engineers, held on September 25, 1981. As shown, the impurity concentration of the diffused resistance does not have a large effect on sensitivity, but the mechanical factor of the difference in linear expansion coefficient between the silicon diaphragm and the die to which it is attached has a large effect on sensitivity. That is, the value of stress that would normally occur in the silicon diaphragm only due to pressure is affected by thermal strain, resulting in a change in the sensitivity of the pressure sensor.

More specifically, FIG. 2 shows the characteristics of a pressure sensor in which a silicon diaphragm is bonded to borosilicate glass. This characteristic is expressed by the following empirical formula.

Vout(T)=Vout(T ₀ ) {1+ξ(1/T-1/T
₀ )}...(1) However, ξ differs depending on the sample, but is, for example, 233K.

An example of the basic system configuration of an integrated pressure sensor equipped with temperature compensation means according to the present invention is shown in FIG. Diffusion gauge resistors _G1 to _G4 constituting the bridge of the pressure sensor section are diffused on the silicon diaphragm surface. 2 is a temperature compensation circuit according to the present invention, and 3 is an amplifier forming a detection signal amplification circuit together with resistors R ₃ and R ₄ .

As already mentioned, the output of bridges G ₁ to _{G 4}
While Vout is generally several tens of mV, the sensor output Eout from the amplifier circuit 3 is required to be several volts. Therefore, the amplification degree of the amplifier circuit portion 3, R ₃ and R ₄ integrated on the silicon substrate must be at least 100 times. Therefore, the ratio of the feedback resistor R ₄ to the resistor R ₃ connected to the input side is 100 times or more, resulting in a resistance value of several hundred kΩ, for example. If this resistor _R4 is made on-chip, a huge area will be required, which will also be reflected in the cost of the chip. Therefore, a resistance of such a value is
It can be formed as a thin film or as a thick film on the chip.

In this way, since the materials of the resistor R3 connected to the input side of the amplifier ₃ and the feedback resistor _R4 are different to determine the amplification degree of the amplifier circuit,
Even if a difference occurs in the temperature coefficients of both resistors R3 and R4 and the decrease in sensitivity due to temperature of the bridge portion of the pressure sensor is sufficiently compensated for, the output voltage Eout obtained from the integrated pressure sensor is , R ₃ , and R ₄ due to temperature changes.

Therefore, next, this amplifier circuit part 3, R ₃ , R ₄
The principle of temperature compensation, including compensation for the influence of changes in the degree of amplification due to temperature, will be explained.

Assuming that the bridge formed by the diffusion gauge resistors G ₁ to _{G 4} is driven by a constant current Ib(T), the output Eout of the pressure sensor is Eout(T)=R ₄ /R ₃ Vout( T) …(2) Vout(T)=K(1+αdr)Ib(T) …(3) Substituting equation (3) into equation (2), Eout(T)=R ₄ /R ₃ (1+αr) K(1+αdr)
Ib(T)...(4) where K: proportionality constant αdr: temperature change in sensitivity of constant current drive bridge ar: temperature change in resistance.

Now, if the impurity concentration of the resistance R ₃ is chosen to be the same as that of the diffusion gauge resistance, then equation (4) becomes Eout=R ₄ /R ₃ K(1+β)Ib(T)...(5) However, β=αdr−αr becomes. Here, if R ₄ is a metal thin film resistor whose temperature coefficient of resistance is extremely small compared to R ₃ , β is the temperature change in the sensitivity of the constant current drive bridge, and ξ (1/T −1/T ₀ ).
Therefore, Eout is Eout(T)=R ₄ /R ₃ K{1+ξ(1/T-1/T
₀ )Ib(T)}...(6). From this equation (6), in order to make Eout independent of temperature, it is necessary to set Ib(T)=Ib(T ₀ )1/1+ξ(1/T-1/T ₀ )...(7) I understand that. Further transforming equation (7), Ib(T)=Ib(T ₀ )T/T ₀ ÷{1+T ₁ −ξ/T ₀ ²
(T−T ₀ )}…(8). In the example of the characteristics shown in FIG. 2 at T ₀ =293K, that is, 20° C., (T ₀ −ξ)/T ₀ ² is 7×10 ⁻⁴ K ⁻¹ , which is a value that can be realized with a diffused resistor. As is clear from equation (8), Ib consists of a term proportional to T and a term that suppresses it.

Now, FIG. 4 shows an example of a detailed circuit of the temperature compensation circuit 2, which is a circuit that realizes the temperature characteristic of the drive current shown by equation (8). In the figure, 20 and 3
0 is a constant current source that supplies constant current to transistors 40 and 50, respectively, 60 and 70 are differential amplifiers, 80 is a transistor for converting voltage into current, and R ₅ , R ₆ , and R ₇ are diffused resistors or Thin film resistor or thick film resistor.

When the ratio of the emitter areas of the transistors 40 and 50 is γ, the difference in Vbe between the two is ΔVbe=Tk/qlnγ (9) where k is Boltzmann's constant and q is the amount of charge. Therefore, the output current Ib(T) is Ib(T)=TkR ₆ /qR ₅ R ₇ (lnγ)=kR ₆₀ /qR ₅₀ R ₇₀
(lnγ)T/1+( _α5 + _α7 − _α6 )(T− _T0 )…(10) From equations (8) and (10), kR ₆₀ lnγ/qR ₅₀ R ₇₀ = Ib(T ₀ )/T ₀ …(11) α ₅ + α ₇ − α ₆ = T ₀ −ξ/T ₀ ² , the respective resistance values R ₅₀ , R ₆₀ , R ₇₀ and resistance temperature coefficient at temperature T ₀ It turns out that you should choose . As is well known, the temperature coefficient of diffused resistance largely depends on the impurity concentration, so
An impurity concentration that satisfies the above conditions may be selected. In the characteristics shown in Figure 2, R ₇ is a metal thin film or thick film resistor with an extremely small temperature coefficient, and R ₆
If the impurity concentration Ns of R 5 is 4 × 10 ¹⁸ cm ^-3 and the impurity concentration Ns of R ₅ is 2 × 10 ¹⁹ cm ^-3 , a temperature coefficient of resistance that satisfies the above equation can be obtained, and equation (1) and experimental results can be obtained. A good approximation can be seen between.

Note that the slope shown in FIG. 2 may become smaller depending on the relationship between the silicon diaphragm and the die. In this case, if ξ becomes small and (T ₀ - ξ)/T ₀ ² must be made large, the temperature coefficient of resistance must have a large difference, so R ₇
It is also necessary to use a diffused resistor with a large resistance temperature coefficient.

As explained above, in this embodiment, the bridge is driven by a constant current Ib, and this Ib does not depend on the power supply voltage Vcc, but depends on the transistor-specific voltage Vbe and the temperature coefficient α of the diffusion gauge resistance. It can be seen that the temperature compensation characteristics are not affected by fluctuations in the power supply voltage because the temperature compensation characteristics are determined in such a way that they can be determined according to the temperature control characteristics. In other words, the temperature-dependent transistor base temperature is not affected by the power supply voltage.
By using the emitter voltage Vbe and the diffusion resistance, it is possible to accurately compensate for the sensitivity temperature of the entire semiconductor pressure sensor, including the temperature change of the amplification factor determining element of the amplifier circuit.

According to the present invention, not only fluctuations in power supply voltage but also
It is possible to accurately compensate for the sensitivity of the entire semiconductor pressure sensor, including the temperature change of the amplification factor determining element of the amplifier circuit.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of an example of temperature compensation of a conventional pressure sensor, Fig. 2 is a diagram showing the temperature sensitivity characteristics of a silicon pressure sensor, and Fig. 3 is a diagram showing the principle of temperature compensation of a pressure sensor according to the present invention. FIG. 4 is a diagram showing a more specific embodiment of the temperature compensation shown in FIG. 3. 2...Temperature compensation circuit, 3...Detection signal amplifier,
20, 30... constant current source, 40, 50... transistor for absolute temperature proportional voltage calculation, 60, 70...
Differential amplifier, 80...Transistor for voltage/current conversion, _R5 , _R6 , _R7 ...Resistor for temperature compensation.

Claims (1)

[Claims] 1. A stress sensing element consisting of a plurality of diffused resistors whose resistance value changes depending on pressure is formed on the front surface of a semiconductor substrate whose back surface is processed into a diaphragm, and a signal from the stress sensing element is transmitted to a predetermined level. An integrated pressure sensor, wherein an amplifier circuit including an amplification factor setting resistor formed on the surface of the semiconductor substrate and whose resistance value changes depending on the temperature is disposed on the surface of the semiconductor substrate outside the diaphragm for amplification at an amplification factor. A constant current driving means formed on the surface of the semiconductor substrate and driving a plurality of diffused resistors of the stress sensing element with a constant current to remove the influence of a power supply voltage, and a transistor and a diffused resistor formed on the surface of the semiconductor substrate. constant current changing means for changing the set current of the constant current driving means based on changes in the Vbe voltage of the transistor which changes depending on the temperature and the resistance value of the diffused resistance element, What is claimed is: 1. An integrated pressure sensor comprising a compensation circuit that comprehensively compensates for changes in sensitivity characteristics due to temperature of the stress sensing element and changes in amplification factor due to temperature of the amplifier circuit. 2. The integrated pressure sensor according to claim 1, wherein the constant current changing means includes a circuit that obtains a voltage proportional to absolute temperature based on the Vbe voltage of the plurality of transistors having different emitter areas, and an impurity. An integrated pressure sensor comprising a voltage-current conversion circuit that includes a plurality of the diffusion resistance elements having different concentrations and that converts a voltage proportional to the absolute temperature into a set current of the constant current driving means.