JPH02263132A - Zero-point adjusting circuit for semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To perform zero-point adjustment and temperature with high accuracy by forming a resistor for the zero-point adjustment of a bridge circuit composed of strain gauges in the same process with the strain gauges. CONSTITUTION:Respective resistors R1 - R4 are diffusion layers formed on the same substrate as a semiconductor substrate where the strain gauges RA - RD constituting the bridge circuit are formed and the line width of the diffusion layers is equal to the width of the strain gauges RA - RD. The strain gauges RA - RD which constitute the bridge circuit and the respective resistors R1 - R4 of a zero-point adjusting circuit are formed in the same process at the same time and resistance values of the strain gauges RA - RD and the temperature coefficients of the resistors R1 - R4 to the resistance values are nearly equal. Consequently, the resistors R1 and R2 which can be trimmed are only trimmed to adjust the zero point of the bridge circuit, thereby performing high-accuracy temperature compensation and zero-point adjustment.

Description

[Detailed Description of the Invention] [Summary] The present invention enables zero point adjustment and zero point adjustment by creating a resistor for zero point adjustment for a bridge circuit composed of strain gauges in a semiconductor pressure sensor in the same process as the above strain gauge. Both temperature compensations can be achieved with high accuracy.

[Industrial application field]

The present invention relates to a zero point adjustment circuit for a semiconductor pressure sensor, and more particularly to a zero point adjustment circuit for a semiconductor pressure sensor that is excellent in temperature compensation of a bridge circuit in a semiconductor pressure sensor.

[Conventional technology]

Pressure sensors are very widely available;
Its applications are wide-ranging, including measurement in various industries, physical and chemical fields, medical fields, automobiles, automatic machinery, robots, and hydraulic and pneumatic equipment.

The above pressure sensor uses a metal strain gauge type pressure sensor in which a strain gauge is attached directly to a metal diaphragm, etc., and a silicon single crystal as a diaphragm, with a strain gauge attached to a part of its surface. ) strained semiconductor pressure sensors (diffusion-type semi-solid pressure sensors) that have a diffusion resistance layer formed thereon.

The metal strain gauge type pressure sensor mentioned above has the disadvantage that it is very difficult to bond the strain gauge and is not suitable for mass production.Semiconductor pressure sensors with high accuracy, high reliability, and excellent productivity are used for automobiles. It has come to be used in various fields including.

A semiconductor pressure sensor is used, for example, by arranging two diffusion resistance layers in the center and the periphery of a diaphragm and connecting them to a bridge. The strain gauge made of the diffused resistance layer is more sensitive to temperature changes than to pressure changes, and temperature compensation as well as zero point adjustment are essential in the semiconductor pressure sensor.

FIGS. 4 and 5 are circuit configuration diagrams of a conventional semiconductor pressure sensor configured to perform such zero point adjustment and temperature compensation.

As shown in FIGS. 4 and 5, conventionally, strain gauges G, , G2°G 3 , , whose resistance changes in response to changes in physical quantities.
When configuring a so-called full bridge circuit by arranging G 4 on four sides, the strain gauges G, , G
2. G3. Strain gauges G+ and G2 are used as a method to zero-adjust the bridge output due to unbalanced resistance values of G.
, G3, and G4, a method has been adopted in which external zero-point adjustment variable resistors R1, R2, and R3 are inserted in series or in parallel. However, in the conventional method as described above, even if the bridge output is adjusted to zero by zero point adjustment, a variable resistor for zero point adjustment (RI, or RI, R2) is used.

I also changed the resistance temperature coefficient at the point where R,) was inserted,
Therefore, thermal output due to temperature change (bridge output caused by thermal stress applied to strain gauges G1'+ G2, G3.Ga due to temperature change, or bridge output caused by variation in temperature characteristics of each strain gauge due to temperature change) This has a serious drawback in that the zero point moves during use as a result of increasing the .

For this reason, for example, as shown in FIG. 6, strain gauge G3. G
4 are connected in series with resistors R4R5, and strain gauges 03. It is known that external resistors Rb and R7 are connected in parallel to G4 to perform not only zero point adjustment but also temperature compensation (Japanese Patent Laid-Open No. 56
-14023).

However, in this way, the series resistor R4 of the external LJ,
Even if R5 and parallel resistors R6 and R7 are provided to perform zero point adjustment and temperature compensation, the bridge output becomes zero after zero point adjustment and measurement of zero point temperature characteristics, and the above-mentioned method is used so that the zero point temperature characteristics can be compensated. The resistance values of the series resistors R,', R and the parallel resistors R, , R7 are calculated, and the resistance values of the resistors R,', R7 are calculated so that a resistance value equal to the calculated result is obtained.
,R,.

R6, R? It was necessary to trim the area.

Furthermore, if the zero point output value and zero point temperature characteristics are measured again, and if the bridge output does not become zero or the temperature compensation characteristics are not good, then Perform trimming and finely adjust the resistance value of each resistor.

Usually, by repeating the above-mentioned operation many times by trial and error, a semiconductor pressure sensor having a practical zero-point output and temperature compensation can be obtained.

[Problem to be solved by the invention]

As mentioned above, in the conventional bridge circuit, it is necessary to perform complicated work that requires a great deal of time and effort to obtain a practical circuit, which has the problem of low productivity and difficulty in reducing costs. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a zero point adjustment circuit for a semiconductor pressure sensor that allows easy zero point adjustment and zero point temperature compensation.

[Means to solve the problem]

To achieve the above object, the present invention provides a semi-integrated pressure sensor in which a bridge circuit consisting of a plurality of strain gauges is entirely formed on a semiconductor diaphragm constructed by etching a semiconductor substrate. In a zero point adjustment circuit for a semiconductor pressure sensor→no° for performing zero point adjustment, the zero point adjustment circuit is connected to the bridge circuit of the semiconductor pressure sensor ◇;1. a plurality of resistors, including a one-rimmable resistor for zero point adjustment connected in series or in parallel to the diaphragm, the plurality of resistors being formed on the same substrate as the semiconductor substrate on which the diaphragm is formed; The strain cage is characterized by comprising a diffusion layer having the same line width as the strain cage.

The resistor in the zero point adjustment circuit may include a unit resistor having a predetermined resistance value, which is made of a diffusion layer having the same line width as the strain gauge, and is connected in series or in parallel, as described in claim 2, for example. It is formed by connecting multiple pieces through a conductive material.

[For production]

The zero point adjustment circuit for a semiconductor pressure sensor of the present invention according to claim 1 includes a semi-circular pressure sensor for adjusting the zero point of the bridge output of the semiconductor pressure sensor formed by forming a bridge circuit consisting of a plurality of strain gauges. In the zero-point adjustment circuit of ``S'', each resistor of the zero-point adjustment circuit is a diffusion layer formed on the same semiconductor substrate as the strain gauge forming the bridge circuit, and the line of the diffusion layer is The width is the same as that of the strain gauge.

Therefore, it is possible to simultaneously form the strain gauges that make up the bridge circuit and the resistors of the zero point adjustment circuit in the same process, and the line width of the strain gauges that make up the bridge circuit and each resistor of the zero point adjustment circuit can be formed at the same time. Since the line widths are the same, the resistance value of the strain cage and the temperature coefficient of the resistance value of each resistor in the zero point adjustment circuit are almost the same.

Therefore, by simply trimming the trimmable resistor in the zero point adjustment circuit and adjusting the bridge circuit's zero point (adjusting the offset voltage to zero), there is no need to separately install a temperature compensation resistor. However, the zero point temperature characteristics
This makes it possible to obtain a semiconductor pressure sensor with a high degree of accuracy. Also,
Since the bridge circuit and the zero point adjustment circuit can be formed on the same chip, it becomes possible to manufacture a large number of chips on a wafer at high speed using the semiconductor manufacturing process.

Further, in the zero point voltage adjustment circuit Q for a semiconductor pressure sensor according to claim 2, the trimmable resistor for zero point adjustment in the circuit is made of a diffusion layer having the same line width as the strain gauge. A unit resistor with a predetermined resistance value,
Since it is constructed by connecting multiple resistors in series or in parallel via conductive members, the resistance value of the above-mentioned I/rimmable resistor can be set with very high precision by trimming, and the bridge output It becomes possible to perform zero point adjustment with very high precision.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram of a semiconductor pressure sensor 1 which is an embodiment of the present invention. In the figure, the bridge circuit body is formed by selectively expanding or ion-implanting boron, for example, on a diaphragm formed by etching the central part of an n-type silicon substrate of several angles. . Diffused resistors Rn, Rn, Re, RD, which are strain gauges of the semiconductor pressure sensor 1 (hereinafter, diffused resistors R11, R++, Rc, Rn are referred to as strain gauges R
A, R11RC, RD) constitutes a closed circuit with four sides, and between the opposing strain gauges RA and RC and between the terminals between strain gauge RB and strain gauge R9 (
In the same figure, a constant current source 1 is connected between the terminals B and C), and a resistive element R2 whose resistance value can be adjusted by trimming is connected between the terminals in parallel with the constant current source . It is connected in series as a resistor. Note that the resistance elements R1 and R2 will be hereinafter referred to as trimming resistance elements R, , R2. Further, a resistive element R3 and a resistive element R6 are connected in series between one terminal of the other opposing terminals and a connection portion F between the resistive element R5 and the resistive element R2. Then, an output voltage ■ is applied to the other terminal from between the connecting portion E of the resistive element R3 and the resistive element R4. I'm trying to get a U+.

In the above configuration, the strain gauges RA, RB+ RCI RD and the zero point adjustment resistance elements R+, R2, R:l, and R4, which constitute the bridge except for the constant current source (■), are all mounted on a single n-type silicon substrate. Elementary (B o r o
n) selection expansion +1J1. Alternatively, they are formed in an integrated manner by performing ion implantation.

To explain in more detail, the strain gauges RA, Ra, Rc, Ro and the zero point adjustment resistance elements R+, Rz, 'R3, R4 that constitute the bridge circuit are all formed with the same line width d.

In addition, the trimming resistance elements R+, Rz are formed by connecting a plurality of unit diffused resistors 10 made of P-type silicon in series or in parallel, each having the same line width d as that of the strain gauges RA, Re, Rc, and RD, as shown in FIG. It is constructed by wiring with an electrode member 30 made of A#-3t, Aβ, etc., which can make good ohmic contact with the unit diffused resistor 10 through the contact hole 20. In addition, the above Aj2-3i,
A7! The electrode member 30 is formed by a sputtering method, a thin vacuum deposition method, or the like.

In addition, in the same figure, unit diffused resistors 10-
1. The part where the line width of the electrode member 30 formed between 10-2 and the single unit diffused resistor 103 is narrower is as follows.
The trimming portion 33 (33-1) is cut by fuse trimming or laser, and a voltage is applied to both ends of the trimming portion 33 (331) via a probe to burn out the trimming portion 33 during fuse trimming. An electrode pad 32 is formed for applying .

The trimming resistance elements R, , R2 and the zero point adjustment resistance elements R, , R4 of the above configuration are both strain gauges RA,
It is formed by the same process as Rs, Rc, and Rn (selective boron diffusion or ion implantation). Incidentally, it has been confirmed that the temperature coefficient of a diffused resistor formed by selective diffusion or ion implantation in the same process depends on the line width.

Therefore, strain gauges RA, RB, Rc, RD and zero point adjustment resistance elements R, , R2, R, , R, which are formed in the same process and have the same line width, all have the same temperature coefficient. become. For this reason, the zero point compensation circuit composed of the zero point adjustment resistive elements R+, R2, R3, and Ra is adjusted, and the strain gauges RA, Rn1. R
By performing zero point adjustment to zero the offset voltage of the bridge circuit consisting of C and Re, the zero point temperature characteristics are guaranteed even if the ambient temperature of the chip on which the semiconductor pressure sensor 1 is formed changes.

The reason why the bridge circuit described above is driven by constant current rather than constant voltage driving is because the sensitivity of semiconductor strain gauges generally tends to decrease as the temperature rises, and the resistance value of semiconductor strain gauges is generally positive. This is to use the characteristic of having a temperature coefficient of , to cancel the decrease in sensitivity due to a rise in temperature by a change in resistance value.

Next, a method of zero point adjustment of the diffusion type semiconductor pressure sensor 1 having the above configuration will be explained.

First, before adjustment, the potential of the terminal A is ■. is the connection part E
Let's consider it as if the potential is higher than the potential ■.

The trimming section 33 is connected to a fuse so that the resistance value of the trimming resistance element R2 becomes large in order to equalize the potentials V and the potentials and make the differential output zero.
Trimming or cutting by laser is performed to raise the potential VF of the connection portion F. Eventually, when the potential 6 becomes equal to the potential VA, the differential output becomes zero, and the zero point adjustment is completed. In order to know how the potential V and the potential (2) change during this time, the current flowing through the strain gauge R8 is set to 19, and the current flowing through the resistance element R3 is
, the current flowing through R4 is represented by 14, and the potential changes by adjusting the resistance value of the trimming resistance element R1 or the trimming resistance element R2 by trimming,
When the change in current is expressed by adding Δ in front of the symbol representing the potential and current, ΔV, = Δ10 Rn + Δ1. R3 and Δ■, -ΔIDRD+Δ14 (Rs ”R4)
becomes. Here, if the resistance values of resistance elements R3, Ra and strain gauge RD are set so that R3>>RD, R4>RD, the ID is disabled.

= 0, therefore, the ΔIn Rn of the front two can be considered to be approximately zero. Therefore, ΔVF−ΔVE
It can be approximated as (R3+R4)/R:l, and the adjusted voltage (initial offset I voltage) vE at the connection point E can be amplified by (R3+R4)/Rz times and measured at the connection point F.

By measuring the voltage at the connection point F in this way, it is possible to perform 1-rimming adjustment while measuring the amplification value of the initial offset voltage VE of the bridge circuit, and by trimming the trimming resistance elements R1 and R2, the zero point can be adjusted. Adjustments can be made with very high precision and easily. In other words, since a minute voltage change at the connection point E can be measured as a large voltage change at the connection point F, highly accurate zero point adjustment is possible.

On the other hand, the potential V of the terminal A. is the potential of the connection point E ■
If the resistance value is smaller than 2, zero point adjustment can be performed in the same manner as in the above case by performing trimming so that the resistance value of the trimming resistance element R1 becomes larger.

Further, as described above, the resistance elements R, , R2R:l,
R4 and the strain gauges RA, RE, RCR9 have the same line width and are formed in the same process, so the trimming resistance elements R+, Rz and the resistance elements R3, R4 for zero point adjustment are Strain gauges RA, RB, Rc
, Ro has the same temperature coefficient of resistance. Therefore, R.A.
= RAo (10αT), RB −RBO(l+αT
), Rc = Rc.

(l 10 αT), Rn-RDO (1+αT), R
, -R,o(,1+αT), R2=R20(1+αT)
, R3=R3o(1-1-αT'), R4""R
There is a relationship of no (14αT). However, the resistance value with the subscript O (RAG, RBO, RCO, RDO,
RIG, R20, R30°R40) is the resistance value of the resistance element at the temperature t0°C at the time of zero point adjustment, α is the resistance temperature coefficient, and T is the temperature t at the time of the zero point adjustment. ℃ and an arbitrary temperature t3℃.

When the bridge circuit having the above relationship is driven with a constant current, at temperatures t and 'c, VA = VAo (l to αT) and VE = VEO (1 + αT), so that the zero point output V of the bridge circuit. LIT is] 5 VOIIT -VA VE -(VAOVEO
) (1+αT) and temperature. ■4゜■, when adjusting the zero point of °C. By making fine adjustments so that the temperature changes to an arbitrary temperature t1° C. after the zero point adjustment is completed, it is possible to reduce the temperature fluctuation at the zero point (offset voltage) with a sufficiently high degree of accuracy. In addition, V in the above formula. ,■,. are the temperature t at the time of zero point adjustment, respectively.
. 'C is the potential of the terminals Δ and E.

Next, a method of trimming the trimming resistance elements R, , R, will be explained with reference to FIG.

As shown in the figure, the trimming resistance element R1 or R2
is a resistance element R11 consisting of unit diffused resistors 101.10-2 connected in parallel, and a resistance element Rb consisting only of unit diffused resistors 103 connected in series with respect to the composite resistance Rh+.
z, and further includes a resistor element R63 consisting of a series-connected resistor 10-4 and 10-5 connected in series to the resistor element Rbz.

Here, if the resistance value of the unit diffused resistor 10 is R8, R.

Rb+=, Rbz=Ro,
Rbz=2R.

becomes.

Similarly, although not particularly shown in FIG. 2, resistive elements Rb4 (-4RO), Rbs (=8RO), etc. are connected in series to the resistive element Rh2 in sequence.
・Rbn (=2−2・RO) is formed by connecting a plurality of unit diffused resistors IO in series. Here, the resistance elements Rh+, Rh□, Rbx+...R5, are respectively bit 1, bit 2, bit 3,...bit n
A resistive element Rb++ connected in series is defined as a resistive element Rb++
The trimming resistance elements R1 and R2 consisting of Rbz+ Rb3+ . . . Rb will be referred to as n-bit trimming resistance elements.

As described above, the resistance elements Rbl+ Rb2+ Rb3+ configuring the trimming resistance elements R+ and Rz
...The resistance value of Rbn increases by 2 as it becomes a high-order bit.
It is designed to increase as a power of . By the way, ANA
The electrode material 30 made of μmSi or the like has high conductivity, and its electrical resistance value is a unit diffused resistance of 1
This is a very small value compared to the resistance value of 0. Therefore, which trimming section 33 (33-1, 33-
2, 33-3, . . . ) are also trimming resistors RI in the uncut state.

The resistance value of R2 is approximately equal to the total resistance value of the electrode material 30.

When the trimming portion 33-1 in FIG. 2 is cut by fuse trimming or laser, the resistance value of the trimming resistance elements R, , R, becomes approximately R0/2.

Further, when only the trimming portion 33-2 is cut by trimming, the resistance value of the trimming resistance elements R1+R2 becomes Ro.

In this way, the total resistance value RLoLm of the trimming resistance elements R1 and Rz is determined by the combination of fuse trimming or the trimming section 33 cut by laser, as follows: Rtotm = Rh+ + Rbz+ Rb3...
・Rb, 1+ ・ ・ ・ n R6X n (X+, X2,
If (i=1.2.3·=n) is cut, X becomes "1", and if the trimming part 33-1 is not cut, X becomes "0") can.

Therefore, n resistance elements Rb+ + Rb, z+
Rb,.

The trimming resistance elements R+ and R2 are
By trimming or cutting the trimming portion 33 with a laser, it is possible to set 2'' types of resistance values. Therefore, the resistance value R6 of the unit diffused resistor 10 can be made smaller, and the resistance element Rh, (i=1°2, · By increasing the bits of . . . n), fine adjustment with high precision becomes possible.

Further, FIG. 3 is a diagram showing another embodiment of a semiconductor pressure sensor to which the present invention is applied. In FIG. 3, the same parts as shown in FIG. 2 are designated by the same reference numerals. The device shown in FIG. 3 is provided with a zero point adjustment circuit similar to the zero point adjustment circuit provided on the terminal B side on the terminal A side of the device shown in FIG. In FIG. 3, resistance element R7 is connected to the resistance element R8, and resistance element R8 is connected to the resistance element R4.
The trimming resistance element R6 corresponds to the resistance element R8, and the trimming resistance element R6 corresponds to the trimming resistance element R2. In this example, R7/ (R,? + R11) is changed to R3/ (R3+R
4) By setting the value to be larger, coarse adjustment can be made on the terminal A side and fine adjustment can be made on the terminal B side, which expands the adjustment range in which the actual zero point can be obtained and allows for even more fine adjustment. Be able to make adjustments.

〔Effect of the invention〕

In the zero point adjustment circuit for a semiconductor pressure sensor according to claim 1, the strain gauge of the bridge circuit and the resistor of the zero point voltage adjustment circuit are formed on the same semiconductor substrate, and are formed of diffusion layers having the same line width. Therefore, by forming the strain gauge and the resistor of the zero point adjustment circuit in the same process, it is possible to make the temperature coefficients of the strain gauge and the resistor of the zero point adjustment circuit almost the same. Therefore, by simply adjusting the zero point of the bridge circuit output, it is possible to obtain a semiconductor pressure sensor with excellent zero point temperature characteristics without the need to provide a special temperature compensation resistor. Furthermore, since the semiconductor pressure sensor and the zero point adjustment circuit of the semiconductor pressure sensor can be manufactured on the same semiconductor substrate, that is, the semiconductor pressure sensor and the zero point adjustment circuit of the semiconductor pressure sensor can be integrated into one chip. It becomes possible to simultaneously manufacture a large number of semiconductor pressure sensor chips with zero-point adjustment circuits, and the mass production effect makes it possible to reduce manufacturing costs.

Further, according to the semiconductor pressure sensor according to claim 2, the trimming versatile resistor used for zero point adjustment in the zero point voltage adjustment circuit according to claim 1 is arranged in a diffusion layer having the same line width as the strain gauge. Since it is constructed by connecting a plurality of unit resistors having a predetermined resistance value in series or in parallel via a conductive member, any conductive member can be cut from the fuse 1 by rimming or laser etc. By performing resistance trimming, it becomes possible to adjust the resistance value of the trimmable resistor for zero point adjustment with high precision, and it becomes possible to perform zero point adjustment of the bridge circuit output with very high precision.

[Brief explanation of drawings]

Fig. 1 is a circuit configuration diagram of a semiconductor pressure sensor which is an embodiment of the present invention; Fig. 2 is a configuration diagram of zero point adjustment resistance elements R+ and R2; Fig. 3 is another embodiment to which the present invention is applied. Figure 4 is a circuit diagram showing an example of a conventional semiconductor pressure sensor; Figure 5 is a circuit diagram showing another example of a conventional semiconductor pressure sensor; Figure 6 is a circuit diagram showing another example of a conventional semiconductor pressure sensor. 1 is a circuit configuration diagram of a conventional semiconductor pressure sensor capable of zero point adjustment and temperature compensation. RA, Rn, Rc, R. ...Strain gauge (diffused resistance), R,, R2, R,,, R6 ... Trimming resistance element (diffused resistance) R3, R,, R
7, RI] ...Resistance element (diffused resistance).

Claims (2)

[Claims] (1) Zero point adjustment of a semiconductor pressure sensor for adjusting the zero point of the bridge circuit output of a semiconductor pressure sensor formed by forming a bridge circuit consisting of a plurality of strain gauges on a semiconductor diaphragm formed by etching a semiconductor substrate In the circuit, the zero point adjustment circuit comprises a plurality of resistors including a trimmable resistor for zero point adjustment connected in series or parallel to a terminal of the bridge circuit of the semiconductor pressure sensor, and the plurality of resistors A zero point adjustment circuit for a semiconductor pressure sensor, comprising: a diffusion layer having the same line width as the strain gauge formed in the same semiconductor substrate on which the diaphragm is formed. (2) The trimmable resistor in the zero point adjustment circuit is formed by connecting a unit resistor having a predetermined resistance value made of a diffusion layer having the same line width as the strain gauge in series or in parallel through a conductive member. 2. The zero point adjustment circuit for a semiconductor pressure sensor according to claim 1, characterized in that a plurality of the zero point adjustment circuits are connected.