JPH041472Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to a semiconductor pressure transducer that converts pressure into an electrical signal by utilizing the piezoresistive effect of a semiconductor single crystal such as silicon, and in particular relates to a semiconductor pressure transducer that converts pressure into an electrical signal by utilizing the piezoresistance effect of a semiconductor single crystal such as silicon. This invention relates to improvements in semiconductor pressure transducers that effectively realize temperature compensation of the transducer.

<Prior Art> In a conventional semiconductor pressure transducer, for example, a pressure detection element for detecting the pressure to be measured and a temperature detection element for detecting temperature changes of the semiconductor chip are formed on the same semiconductor chip. The measured temperature characteristics are stored in a memory corresponding to each semiconductor pressure transducer, and the characteristics are used to perform correction calculations on the measured pressure obtained by the pressure detection element.

However, measuring the temperature characteristics of each semiconductor pressure transducer and handling a large amount of data as a single unit as characteristic data unique to each semiconductor pressure transducer increases the number of adjustment steps and costs. There are problems that arise.

<Purpose of the invention> In view of the above-mentioned prior art, an object of the present invention is to provide a semiconductor pressure transducer that can realize versatile temperature compensation with a simple configuration.

<Configuration of the present invention> The configuration of the present invention to achieve this object relates to a semiconductor pressure transducer that has a semiconductor single crystal diaphragm and detects the pressure to be measured applied to the diaphragm. at least two pressure gauges with different impurity concentrations formed in the
Ratio b of the output voltages E ₁ and E ₂ of the pressure gauges when the pressure gauges are driven with a constant voltage and the output of each pressure gauge at the reference temperature under any pressure application state
and a calculation means for calculating an output voltage E ₀ of E ₀ =(E ₂ −abE ₁ )/(1−a) using the ratio a of the temperature coefficient of the piezoresistance coefficient of each pressure gauge. It is characterized by outputting an output voltage corresponding to the measured pressure.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

FIG. 1 shows the configuration of a sensor section according to an embodiment of the present invention. A shows a plan view, and B shows a cross-sectional view.
1 is a diaphragm, which has a cylindrical recess 2 provided on one main surface of an n-type silicon single crystal, and further includes a strain-generating part 3 in which the thickness of the single crystal is reduced by forming the recess 2; It has a fixed part 4 around it. The fixing part 4 is fixed to a substrate 6 having a communication hole 5 via a glass thin film 7 by anodic bonding or the like.

As shown in FIG.
A shear stress gauge Gs ₁ functioning as a pressure gauge is formed by diffusion of an impurity of conductivity type P, having a longitudinal direction in the direction of 45°. Furthermore,
The second section is arranged so that the center of the strain-generating part 3 and the horizontal crystal axis <110> are on the line forming the direction of θ, and the longitudinal direction is in the direction of 45° centered on a position close to the shear stress gauge Gs ₁ . A shear stress gauge Gs ₂ is formed by diffusion of P-type impurities. The shear stress gauges Gs ₁ and Gs ₂ are diffused with different impurity concentrations. A pressure P to be measured is applied to the strain-generating portion 3, and the voltage generated by the corresponding strain is detected by shear stress gauges Gs ₁ and Gs ₂ .

Figure 2 shows the configuration of the shear stress gauges Gs ₁ and Gs ₂ . The shear stress gauges Gs ₁ and Gs ₂ have a gauge length l and a gauge width w, and power supply ends 8 and 9 are formed in the longitudinal direction, to which a constant voltage is applied.
When the measured pressure P is applied to the diaphragm 1,
A voltage corresponding to the shear stress τ _s generated by this is applied to the output end 1 formed approximately in the center of the gauge length l.
Obtained from 0,11.

The shear stress gauges Gs ₁ and Gs ₂ are formed by diffusing impurities on the strain-generating portion 3 by changing the concentration of impurities, but the concentration can be changed by thermal diffusion by changing the pre-deposition or drive-in temperature and time.
In ion implantation, this can be easily achieved by changing the conditions.

FIG. 3 shows the relationship between the impurity concentration _Cs , the piezoresistance coefficient π, and the temperature coefficient β of the piezoresistance coefficient. As can be seen from the figure, the coefficients π and β change almost linearly with changes in the surface impurity concentration _Cs .
Further, the temperature coefficient β takes a substantially constant value with respect to temperature.

FIG. 4 is a block diagram showing the overall configuration for obtaining an output voltage corresponding to the pressure to be measured using a shear stress gauge.

A constant voltage V _s is applied to the power supply terminals of each shear stress gauge Gs ₁ , Gs ₂ , and output voltages E _s1 , E _s2 obtained from the output terminals are inputted to the arithmetic circuit PCC. The arithmetic circuit PCC is also configured to have constants a _s and b _s set from the outside, and use these values to perform a predetermined arithmetic operation in the arithmetic circuit PCC to output an output voltage E _s0 .

There are constant current drive and constant voltage drive to drive a shear stress gauge. For example, when driving the shear stress gauge G _s1 with a constant current, the constant current is I _i , the sheet resistance R _sit at an arbitrary temperature t, the shear piezoresistance coefficient π _sit , the shear stress τ _si , and the sheet resistance due to the shear stress τ _si If the change in R _sit is ΔR _sit , the output voltage E _si at this time is expressed as E _si =I _i ·R _sit (ΔR _sit /R _sit ) =I _i ·R _sit ·π _sit ·τ _si .

In this case, since the constant current I _i is naturally not affected by temperature, the output voltage E _si is affected by the temperature coefficients of both the sheet resistance R _sit and the shear piezoresistance coefficient π _sit .

However, in the case of the embodiment shown in FIG. 4 using constant voltage drive, the situation is different, as explained below.

That is, any temperature t of the shear stress gauge G _s1
If the sheet resistance R _svt at , the unit thickness of the sheet resistance is m, and the specific resistance of the shear stress gauge is ρ, it can be expressed as R _svt =ρ/m.

Further, the resistance value R _vt of the shear stress gauge G _s1 can be expressed as R _vt = ρl/mw. From these relationships, the relationship R _svt =WR _vt /l can be obtained. This relationship can be _expressed as
, and if the shear piezoresistance coefficient of the shear stress gauge G _s1 at an arbitrary temperature t (difference from the reference temperature t ₀ ) is π _s1t and the output voltage is E _s1 , then E _s1 = I _i・( WR _vt /l)・π _s1t・τ _s1 .

Here, the product of current (I _i ) and resistance (R _vt ) (I _i・
R _vt ) specifically indicates the applied voltage V _s . In other words, V _s = I _i · R _vt . Using these relationships, E _s1 =(W/l)V _s ·π _s1t ·τ _s1 (1).

Since the applied voltage V _s is supplied as a constant voltage, it is not affected by temperature.

Therefore, the output voltage when driven at constant voltage
Although E _s1 depends on the shape W and l of the gauge, the influence of temperature depends only on the shear piezoresistance coefficient π _s1t and does not depend on the temperature coefficient of sheet resistance.

The embodiment shown in FIG. 4 employs this type of drive system to realize a highly accurate pressure transducer.

Here, if the shear piezo resistance coefficient at the reference temperature is π _s10 and the temperature coefficient of the shear piezo resistance coefficient is β _s1 , then π _s1t = π _s10 (1 + β _s1 t) (2), so this can be expressed as (1 ), E _s1 =w/lV _s π _s10 (1+β _s1 t)τ _s1 (3). Since the shear stress τ _s1 is proportional to the pressure to be measured P, if the proportionality constant is K′ _s1 , then τ _s1 =K′ _s1 P (4). Substituting this into equation (3), we get E _s1 = w/lV _s K′ _s1 π _s10 (1+β _s1 t)P (5), but K _s1 = wV _s K′ _s1 π _s10 /l (constant ), then equation (5) becomes as follows.

E _s1 =K _s1 (1+β _s1 t)P (6) Similar calculations are made for the shear stress gauge Gs ₂ to obtain the following equation.

E _s2 =K _s2 (1+β _s2 t)P (7) Each subscript corresponds to a shear stress gauge Gs ₁ .

Next, each shear stress gauge Gs ₁ , Gs ₂ when an arbitrary pressure is applied at the reference temperature t ₀ (t=0)
From the ratio of the outputs, b _s =K _s2 /K _s1 (8) can be obtained by referring to equations (6) and (7).

Furthermore, for each shear stress gauge Gs ₁ and Gs ₂ , the temperature coefficient β _s1 of the shear piezoresistance coefficient is
The ratio a _s of β _s2 is determined by experiment as shown in the following equation.

a _s = β _s2 / β _s1 (9) From equations (6) to (9) above, E _s0 = K _s2 P, and E _s0 = E _s2 −a _s b _s E _s1 /1−a _s =K We get _s2 P (10).

By executing the calculation shown by this equation (10) in the calculation circuit PCC, an output voltage E _s0 corresponding to the measured pressure P from which the influence of temperature has been removed can be obtained.

FIG. 5 is a plan view of a main part of a diaphragm according to another embodiment of the present invention. The embodiments shown in FIGS. 1 to 4 are cases in which the pressure gauge is constructed using a shear stress gauge, while the embodiment shown in FIG. 5 is a pressure gauge constructed using a vertical stress gauge. The difference is in how they are constructed.

In FIG _{. 5, strain gauges G 1 ,} G ₂ ,
G ₃ and G ₄ are formed in this order by diffusion of impurities. The influence of strain on the resistance of strain gauges G ₁ and G ₄ is equal; for example, as the pressure to be measured P increases, their resistances both increase, and strain gauges G ₂ and
The influence of strain on resistance on G ₄ is such that, for example, G 4 is placed at a position such that its resistance decreases by the same proportion for the same increase in measured pressure P as above.

Furthermore, the horizontal crystal axis passing through the center of the strain-generating portion 3 <110>
Strain gauges G′ ₁ , G′ ₂ , G′ ₃ , and G′ ₄ constituting the vertical stress gauge Gv ₂ are also formed in this order by diffusion of impurities in the direction perpendicular to . vertical stress gauge
The concentration of diffused impurities is different between the group of strain gauges G _{1 to} G ₄ constituting Gv 1 and the group _of strain gauges G′ ₁ to G′ ₄ constituting the vertical stress gauge Gv 2 .

FIG. 6 shows a block diagram of a conversion circuit for converting measured pressure into an electrical signal using a vertical stress gauge. The strain gauges G ₁ to _{G 4} are bridge-connected to each other to form a vertical stress gauge Gv ₁ , whose power supply end 1
A constant voltage V _s is applied to terminals 2 and 13, and the output voltage E _v1 generated at the output terminals 14 and 15 is applied to the arithmetic circuit PCC.
is applied to the input terminal of Also, strain gauge G′ ₁ ~ G′ ₄
are bridge-connected to each other to form a vertical stress gauge Gv ₂ , a constant voltage V _s is applied to its power supply terminals 16 and 17, and an output voltage E _v2 generated at its output terminals 18 and 19 is connected to the other output voltages of the arithmetic circuit PCC. Applied to the input end.

Constants a _v and b _v are also set externally in the arithmetic circuit PCC. An arithmetic circuit using these values
The PCC is configured to perform predetermined calculations and output an output voltage E _v0 .

Next, the operation of the conversion circuit configured as above will be explained. For simplicity, each strain gauge G ₁ ~ _{G 4}
Let the resistance value of be equal at any temperature t, R ₁ ,
The resistance change due to the measured pressure P is measured by strain gauges G ₁ and G ₄
is +ΔR ₁ and strain gauges G ₂ and G ₃ are −ΔR ₁ ,
It becomes as follows.

E _v1 =ΔR ₁ /R ₁ V _s =σ ₁ π _v10 V _s (1+β _v1 t) (11) However, π _v10 is the piezo resistance coefficient at the reference temperature, and β _v1 is the temperature coefficient of the piezo resistance coefficient. Here, assuming that the stress σ ₁ is proportional to the measured pressure P and the proportionality constant is K' _v1 , σ ₁ = K' _v1 P (12), and substituting this into equation (11), E _v1 = K ′ _v1 π _v10 V _s (1+β _v1 t). If K _v1 = K' _v1 π _v10 V _s (constant), then E _v1 = K _v1 (1+β _v1 t) (13).

Similarly, the following equation is obtained for the vertical stress gauge Gv ₂ .

E _v2 = K _v2 (1 + β _v2 t) (14) Each subscript corresponds to the vertical stress gauge Gv ₁ .
Furthermore, the ratio b _v of the output of the vertical stress gauge corresponding to equation (8) with respect to the shear stress gauges Gs ₁ and Gs ₂ is similarly expressed as b _v =K _v2 /K _v1 (15). Similarly, the ratio a _v corresponding to equation (9) becomes the following equation.

a _v = β _v2 / β _v1 (16) From equations (13) to (16) above, assuming E _v0 = K _v2 P, E _v0 = E _v2 −a _v b _v E _v1 /1−a _v = K We get _v2 P (17).

The calculation shown in equation (17) is performed by the calculation circuit PCC.
By performing this operation, an output voltage E _v0 corresponding to the measured pressure P from which the influence of temperature has been removed can be obtained.

In the explanation so far, the case where the diaphragm has a circular shape has been described, but the object of the present invention can be achieved even if the diaphragm is rectangular.

Further, the purpose can also be achieved by diffusing n-type conduction type impurities onto a P-type diaphragm as a stress gauge.

Although the strain gauge shown in FIG. 6 is constructed as a full bridge, the purpose can also be achieved as a half bridge.

<Effects of the invention> As described above in detail with the embodiments, according to the invention, at least two pressure gauges with different impurity concentrations are formed on the diaphragm, and two predetermined constants are Since all that is required is to set the pressure gauge, supply a constant voltage to the pressure gauge, and execute a predetermined calculation, it is possible to realize a semiconductor pressure transducer that can obtain a good temperature compensation effect with a small number of man-hours.

In particular, in this invention, the ratio of the temperature coefficient of the piezoresistance coefficient of each pressure gauge and the ratio of the pressure-strain conversion coefficient are set as constants set externally, so it is necessary to know the absolute values of these. Without,
Moreover, accurate temperature control is not required to obtain these ratios, and therefore an output corresponding to the measured pressure can be obtained with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing the configuration of a sensor section of an embodiment of the present invention, FIG. 2 is a configuration diagram showing the configuration of a shear stress gauge, and FIG. 3 is a characteristic diagram showing the characteristics of each coefficient with respect to impurity concentration. Fig. 4 is a block diagram of obtaining an output voltage corresponding to the pressure to be measured using the shear stress gauge shown in Fig. 1, Fig. 5 is a plan view of the main part of a diaphragm of another embodiment of the present invention, and Fig. is the fifth
FIG. 2 is a block diagram of obtaining an output voltage corresponding to a measured pressure using the vertical stress gauge shown in the figure. DESCRIPTION OF SYMBOLS 1... Diaphragm, 2... Recessed part, 3... Strain-generating part, 4... Fixing part, 5... Communication hole, 6... Substrate,
7... Glass thin film, 8, 9... Power supply end, 10, 1
1...Output end, Gs ₁ , Gs ₂ ...Shear stress gauge,
Gv ₁ , Gv ₂ ... Vertical stress gauge, P ... Pressure to be measured, PCC ... Arithmetic circuit, V _s ... Constant voltage.

Claims (1)

[Scope of utility model registration request] In a semiconductor pressure transducer having a semiconductor single crystal diaphragm and detecting a measured pressure applied to the diaphragm, at least two pressure gauges having different impurity concentrations formed on a strain-generating portion of the diaphragm; The output voltage E ₁ of the pressure gauge when the pressure gauge is driven with a constant voltage and
_{E 0 =} (E ₂ - abE ₁ )/(1-a) output voltage E ₀
1. A semiconductor pressure transducer, comprising a calculation means for calculating the pressure, and outputs an output voltage corresponding to the pressure to be measured.