JPH041471Y2 - - Google Patents

Description

[Detailed description of the invention] <Industrial field of application> The present invention 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 semiconductor pressure transducers using gauges.

<Prior art> A conventional semiconductor pressure transducer has a pressure detection element that detects the pressure to be measured and a temperature detection element that detects temperature changes of the semiconductor chip formed on the same semiconductor chip. The measured temperature characteristics are stored in a memory corresponding to each semiconductor pressure transducer, and this characteristic is 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 that achieves this objective is to place a conduction type of P type and a crystal axis of When a constant current is supplied to the input end of this shear type gauge, the voltage E si generated at the output end, the voltage E _Ri at the input end, and the voltage E _Ri at the input end of the shear type gauge. Using the voltage E _sv at the output terminal when a constant voltage is supplied, the voltage E _Ri0 at the input terminal when a constant current is supplied to the input terminal of the shear type gauge at the reference temperature, and the constant C, E ₀ = and calculation means for calculating an output voltage E ₀ of E _si 1−CE _SV /E _Si /E _Ri /E _RiO −1,
It is characterized by outputting an output voltage E ₀ corresponding to the measured pressure applied to the diaphragm.

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

FIG. 1A shows a plan view of a main part of a diaphragm according to an embodiment of the present invention, and FIG. 1B shows a sectional view of a sensor section. Reference numeral 1 denotes a diaphragm, which has a rectangular recess 2 provided on one principal surface of a silicon single crystal, and further includes a strain-generating portion 3 in which the thickness of the single crystal is reduced by forming the recess 2.
and a fixing 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. Strain part 3
On the top, a shear type gauge 8 is formed in the direction of the <100> axis at 45 degrees with respect to the vertical crystal axis <110> direction passing through the center, and the conductivity type is P type due to the diffusion of impurities. A pressure P to be measured is applied to the diaphragm 1 from above to cause strain, which is detected by a shear type gauge 8.

Figure 1C shows an enlarged view of the configuration of the shear type gauge. The shear gauge shown in FIG. 1C has a gauge length l and a gauge width w, and input ends 9 and 10 are formed in the longitudinal direction of this shear type gauge, to which a voltage or current is applied. When the measured pressure P is applied to the diaphragm 1, a voltage corresponding to the resulting shear stress _τs is obtained from output ends 11 and 12 formed approximately at the center of the gauge length l.

FIG. 2 is a block diagram of a conversion circuit that uses the sensor section shown in FIG. 1 to convert the measured pressure P into a corresponding voltage _E0 .

An input end 9 of the shear type gauge 8 is connected to one end of a constant current source CCS via a switch SW ₁ , and the other end is connected to an input end 10 of the shear type gauge 8. Furthermore, the input terminal 9 is connected to one terminal of the constant voltage source CVS via switch SW ₂ , and the other terminal is connected to the input terminal 10.
It is connected to the. The input ends 9, 10 of the shear type gauge 8 are also connected to the amplifier Q ₁ via the switch SW ₃ .
connected to the input end of the Output ends 11 and 12 of shear gauge 8 are connected to an amplifier via switch SW ₄ .
It is connected to the input of Q ₂ , and is also connected to the input of amplifier Q ₃ via switch SW ₅ . These switches SW ₁ to SW ₅ are controlled by an oscillator OSC. The switch groups SW ₁ and SW ₅ are opened and closed at the same time, and the switch groups SW ₂ , SW ₃ and SW ₄ are also opened and closed at the same time, but these switch groups operate complementary to each other.

The output of amplifier Q ₁ is connected to the input of divider Q ₄ , while each output of amplifiers Q ₂ and Q ₃ is connected to the subtracter
Connected to each input end of _Q5 . The output of the divider _Q4 and the output of the subtractor _Q5 are connected to each input of the divider _Q7 via a subtractor _Q6 . Output voltage E ₀ is obtained from the output of divider Q ₇ . Note that a voltage E _Ri0 is set at the other end of the input of the divider _Q4 . Amplifiers Q ₁ to _{Q 3} , dividers Q ₄ , Q ₇ , subtracters Q ₅ , Q ₆ and the like constitute an arithmetic circuit PCC.

The operation of the circuit shown in FIG. 2 constructed as above will now be described.

First, switch SW ₁ is closed by the oscillator OSC,
A constant current I _i is supplied to the shear type gauge 8 from a constant current source CCS. Shear type gauge 8 at arbitrary temperature t
If the resistivity per unit thickness, that is, the sheet resistance is R _spt , the shear piezoresistance coefficient is π〓 _pt , and the shear stress is τ _p , then the output voltage E _si is E _si = I _i R _spt (ΔR _spt /R _spt ) =I _i R _spt π〓 _pt τ _p (1) If the sheet resistance at the reference temperature t ₀ is R _sp0 and the shear piezo resistance coefficient is π〓 _p0 , then R _spt = R _sp0 (1+f(t)) (2) π〓 _pt = π〓 _p0 (1+g(t) ) (3) becomes. Here, f(t) can be expressed by a polynomial of temperature as shown in the following equation, assuming that α ₁ , α ₂ , ... are the rate of change in sheet resistance with temperature.

f(t)=α ₁ t+α ₂ t ² +… (4) Also, g(t) can be expressed by the temperature polynomial as shown below, assuming that the temperature change rate of the piezoresistance coefficient is β ₁ , β ₂ , ~ Ru.

g(t)=β ₁ t+β ₂ t ² +… (5) Substituting equations (2) and (3) into equation (1), E _si = I _i R _sp0 π〓 _p0 τ _p (1+f( t))(1+g(t)) (6) If we set t _p = KP (K: constant) and A = I _i R _sp0 π〓 _pt K, then E _si = AP (1+f(t) )(1+g(t)) (7). This output voltage E _si is input to amplifier Q ₂ via switch SW ₄ . This output voltage E _si is an output corresponding to the measured pressure P including a function of temperature.

Next, between the input ends 9 and 10 of the shear type gauge 8, which is formed so that a constant current I _i flows in the direction of the crystal axis <100> on the surface of the diaphragm 1 whose crystal plane is the (100) plane, An output voltage E _Ri corresponding to this constant current I _i is generated, but the point that this output voltage E _Ri is not affected by the stress applied to the diaphragm 1 will be explained.

When stress is applied to diaphragm 1, the electric field strength in the silicon crystal (E _x , E _y , E _z )
and the current density (J _x , J _y , J _z ), ρ is the resistivity under no stress, Δρij (tensor,
If i and j are indices) are changes in resistivity due to stress, then the following relationship holds true according to Ohm's law.

E _x E _y E _z = ρ + Δρ _xx Δρ _xy Δρ _xz Δρ _xy ρ + Δρ _yy Δρ _yz Δρ _xz Δρ _yz ρ + Δρ _zz ×J _x J _y J _z ...(8) However, x is the input terminal 9, 10 where the current is input (<100> axis), Y indicates the direction of the output ends 13, 14 perpendicular to the direction of this current, and Z indicates the direction perpendicular to the plane of the paper. When stress is applied to the crystal, the resistivity is A〓=1/ρΔρ _xx Δρ _yy Δρ _zz Δρ _yz Δρ _xz Δρ _xy , and the piezoresistance coefficient is Aβ=π ₁₁ π ₁₂ π ₁₃ π ₁₄ π ₁₅ π ₁₆ π ₂₁ π ₂₂ π ₂₃ π ₂₄ π ₂₅ π 26 π ₃₁ π ₃₂ π ₃₃ π ₃₄ π ₃₅ π ₃₆ π ₄₁ π ₄₂ π ₄₃ π _{44 π 45} π ₄₆ π ₅₁ π ₅₂ π ₅₃ π ₅₄ π ₅₅ π ₅₆ π ₆₁ π ₆₂ π ₆₃ π ₆₄ π ₆₅ π ₆₆ , and regarding the stress, σ _x , σ _y , and σ _z are the stress components in the X direction, Y direction, and Z direction, respectively, and τ _yz , τ _xz ,
Letting τ _xy be the shear stress component, A = σ _x σ _y σ _z τ _yz τ _xz τ _xy . The relationship between these is A〓＝A〓・A〓...(9).

Using equations (8) and (9) above, and considering J _Y = J _Z = 0 since the current flows only in the X-axis direction, the X-direction component E _x of the electric field is calculated as follows: (E _x /ρ )=J _x (1+π ₁₁ σ _x +π ₁₂ σ _y +π ₁₃ σ _z +π ₁₄ τ _yz +π ₁₅ τ _xz +π ₁₆ τ _xy )……(10
) becomes. (E _y /ρ) and (E _z /ρ) can be found in the same way, but will be omitted here.

Here, π ₁₄ and π ₁₅ are zero in the case of a cubic crystal, regardless of the direction of the current flowing through the gauge, so equation (10) is (E _x /ρ) = J _x (1 + π ₁₁ σ _x + π ₁₂ σ _y + π ₁₃ σ _z + π ₁₆ τ _xy ) ...(11).

The output voltage E _Ri has the relationship E _Ri = E _x・l I _i = J _x・m・w, where m is the unit thickness of the sheet resistance, so substitute these relationships into equation (11). And using the relationship (ρl/mw) = R _t (gauge resistance of shear type gauge), E _Ri = R _t・I _i (1 + π ₁₁ σ _x + π ₁₂ σ _y + π ₁₃ σ _z + π ₁₆ τ _xy ) ...(12) becomes.

By the way, for π ₁₁ and π ₁₂ , if the angle between the current direction and the <100> axis is θ, θ=0, that is, when the current direction is in the <100> direction, the normally used value of the <110> axis is 70×10. ^-12 dyn/cm ² , 7×10 ^-12 dyn/cm ² and -1×10 ^-12 dyn/cm ² , respectively.
and π ₁₃ is −1× regardless of θ.
10 ^-12 dyn/cm ² and π ₁₆ is zero.

Therefore, when θ = 0, the term of the piezoresistance coefficient π in () can be ignored, so E _Ri = R _t・I _i , which is not affected by stress, and therefore the temperature coefficient of the piezoresistance coefficient There is no influence due to

If R ₀ is the gauge resistance at the reference temperature, R _t is expressed as R _t = R ₀ (1+f(t)), so E _Ri is E _Ri = I _i R ₀ (1+f(t))... (13) becomes. Here, I _i R ₀ is the voltage that occurs between input terminals 9 and 10 at the reference temperature, so if we set E _Ri0 = I _i R ₀ , equation (13) becomes E _Ri = E _Ri0 (1 + f(t)) (14) is shown as

This voltage is a function of temperature and is input to amplifier Q ₂ via switch SW ₃ controlled by oscillator OSC. Note that the output voltage E _Ri0 is the voltage between the input terminals 9 and 10 at the reference temperature t ₀ , and the output voltage E Ri0 is the voltage between the input terminals 9 and 10 at the reference temperature t _0.
is preset to the input.

Next, the oscillator OSC turns off the switch _SW1 and turns on the switches _SW2 and _SW5 . In this state, a constant voltage V _s is applied between the input ends 9 and 10 of the shear type gauge 8 from the constant voltage source CVS. here,
The sheet resistance of the shear type gauge 8 at an arbitrary temperature t is
If R _svt , the unit thickness of the sheet resistance is m, and the specific resistance of the pressure gauge is ρ, it can be expressed as R _svt =ρ/m.

Further, the resistance value R _vt of the shear type gauge 8 can be expressed as R _vt =ρl/mw. From these relationships, the relationship R _svt =WR _vt /l can be obtained. Substituting this relationship into the constant current drive equation (1), and assuming that the shear piezoresistance coefficient at an arbitrary temperature t of the shear type gauge 8 is π〓 _vt and the output voltage is E _sv , E _sv = I _i (WR _vt /l)・π〓 _vt・τ _p .

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 _sv = (W/l)V _s・π〓 _vt・τ _p (15). The applied voltage V _s is supplied from a constant voltage source CVS and is not affected by temperature.

Therefore, the output voltage when driven at constant voltage
E _sv depends on the shape W and l of the gauge, but the influence of temperature depends only on the shear piezoresistance coefficient π〓 _vt and does not depend on the temperature coefficient of sheet resistance corresponding to equation (2). If the shear piezo resistance coefficient at the reference temperature t ₀ is π〓 _v0 , then π〓 _vt = π〓 _v0 (1+g(t)) (16), so by substituting this into formula (15), we get the following formula: .

E _sv = w/lV _s π〓 _v0 (1+g(t))τ _p (17) Here, if we transform equation (17) using τ _p = KP, we get B=w/lV _s π〓 _v0 K ( 18) becomes. B represents the output voltage when a constant voltage is supplied to the shear type gauge 8 and a unit pressure is applied at the reference temperature _t0 , and takes a constant value. Therefore, the equation (17) becomes E _sv =BP(1+g(t)) (19).

This output voltage E _sv is input to the amplifier Q ₃ via the switch SW ₅ controlled by the oscillator OSC.

Based on the output voltages expressed by the above equations (7), (14), and (19), the calculation circuit PCC performs calculations to remove the influence of temperature as follows.

From equation (14), f(t)=E _Ri /E _Ri0 −1 (20) From equation (19), g(t)=E _sv /BP−1 (21) From equation (7), f(t)g Assuming (t)≪1, E _si = AP(1+f(t))(1+g(t)) ≒AP(1+f(t)+g(t)) (22) Add equations (20) and (21) to equation (22) Substituting E _si = AP (E _Ri /E _Ri0 +E _sv /BP-1) Here, if we set A/B = C and E ₀ = AP, then E ₀ = E _si 1-CE _SV /E _Si /E _RV /E _RiO −1 (23). This equation is modified to calculate E ₀ =E _si −CE _sv /E _Ri /E _RiO −1 (24) in the arithmetic circuit PCC. In the arithmetic circuit PCC, divider Q ₄ calculates the output voltage E _Ri of amplifier Q ₁ (gain is assumed to be 1 for simplicity) and the set voltage.
Execute division that takes the ratio of E _Ri0 to E _Ri0 , subtract 1 from the output using subtractor _Q6 , and divide the output by (E _Ri /E _Ri0 ) - 1 _. Enter into device Q ₇ .
On the other hand, the output voltage E _si of amplifier Q ₂ (gain is assumed to be 1 for simplicity) and the output voltage CE _sv of amplifier Q ₃ (gain C) are subtracted by subtractor Q ₅ to produce an output E _si −CE _sv . .
The divider _Q7 calculates the ratio between the output of the subtractor _Q6 and the output of the subtractor _Q5 to obtain the result of the calculation of equation (24).

As described above, the output voltage E ₀ corresponding to the measured pressure P from which the influence of temperature has been removed is obtained.

In the above embodiments, the shape of the diaphragm is described as being rectangular, but the shape is not limited to this and may be circular or other shapes. The shape of the shear type gauge is not limited to the shape shown in the embodiment, but any shape can be used as long as it can obtain the same effect.

<Effect of the invention> As explained above in detail along with the examples,
According to the present invention, a shear type gauge is formed on a silicon diaphragm, and by driving it with a constant current or constant voltage, the voltage at the input end or output end of the gauge is detected and a simple predetermined calculation is performed. A semiconductor pressure transducer that is unaffected by temperature can be realized simply by doing this. Therefore, reliability is high and adjustment man-hours can be significantly reduced.

[Brief explanation of the drawing]

Fig. 1A is a plan view of the main part of a diaphragm according to an embodiment of the present invention, Fig. 1B is a sectional view of the sensor section, and Fig.
Figure C is an enlarged view of the configuration of the shear type gauge.
FIG. 2 shows a conversion circuit that converts the output voltage of the sensor section shown in FIG. 1 into pressure. DESCRIPTION OF SYMBOLS 1... Diaphragm, 3... Strain part, 4... Fixed part, 5... Communication hole, 6... Substrate, 7... Glass thin film, 8... Shear type gauge, 9, 10... Input end, 11, 12... Output end, P... Pressure to be measured,
CCS...constant current source, CVS...constant voltage source, OSC...
...Oscillator, PCC ... Arithmetic circuit, V _s ... Constant voltage, I _i
... Constant current, E ₀ ... Output voltage.

Claims (1)

[Claims for Utility Model Registration] An input end is formed on the strain-generating part of a semiconductor single crystal diaphragm whose crystal plane is in the (100) direction, and whose conductivity type is P type and whose crystal axis is in the <100> direction. A shear type gauge with an output end formed near the center in a direction perpendicular to the crystal axis, and a voltage E _si generated at the output end when a constant current is supplied to the input end of the shear type gauge. The voltage E _Ri at the input terminal, the voltage E _sv at the output terminal when a constant voltage is supplied to the input terminal, and the voltage E _Ri0 at the input terminal when a constant current is supplied to the input terminal at a reference temperature. and a calculation means for calculating an output voltage _E0 of E0= _Esi [1-C( _Esv / _Esi )]/[( _ERi / _ERi0 ) _-1 ] using a constant C,
A semiconductor pressure transducer characterized in that it outputs the output voltage E ₀ corresponding to the measured pressure applied to the diaphragm.