JP2001272293A - Pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pressure sensor for surely detecting a failure when a resistance value of a bridge circuit changes because of failure. SOLUTION: Reference electric-potential generating circuits 2 where resistors RE and RF which does not change resistance value when a pressure is applied generate a reference electric-potential are connected in parallel on one end side and the other end side of the bridge circuit. Electric-potential difference VBC at two middle points B and C of the bridge circuit is compared to electric- potential differences VCE and VBE between the electric potential at the middle points B and C and a reference electric-potential of the reference electric- potential generating circuit 2, for judging the disorder of the bridge circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor for detecting pressure.

[0002]

2. Description of the Related Art Conventionally, in a pressure sensor, a thin diaphragm portion is formed on a semiconductor substrate, and two pressure detecting elements (gauge resistors) are formed at a central portion and a peripheral portion of the diaphragm portion, respectively. Make up the circuit. When pressure is applied to the diaphragm, the resistance value of the pressure detecting element changes due to the piezoresistance effect, and as a result, a potential difference (output voltage) occurs at the midpoint potential of the central and peripheral pressure detecting elements. . The pressure sensor performs an appropriate amplification and adjustment process on the output voltage to output an electric signal corresponding to the pressure.

[0003]

As described above, the pressure sensor amplifies and adjusts the potential difference output from the bridge circuit. Therefore, for example, if the bridge circuit generates an erroneous potential difference due to contamination, damage, or the like, an erroneous electric signal may be output as it is.

A pressure sensor having a function of detecting a failure of such a pressure sensor is disclosed in Japanese Patent Application Laid-Open No. 10-50671.
No. 8 discloses a pressure sensor. This pressure sensor divides the diaphragm part into two parts from the center in order to detect the abnormal state of stress distribution in one diaphragm,
A bridge circuit is formed for each of them, and the voltage output of both is compared to detect a deviation to detect a failure. However, in this pressure sensor, the diaphragm is moved from the center by 2
Divided. For this reason, there is a problem that the sensing unit for detecting the pressure is twice as large as the conventional one, and the area of the diaphragm becomes large, so that it is difficult to reduce the size of the pressure sensor.

[0005] Some pressure sensors form a pressure reference chamber by attaching a sensor chip to a pedestal by anodic bonding, and perform pressure detection based on a pressure difference between the pressure reference chamber and an external pressure. . The attachment of the sensor chip to the pedestal in this pressure sensor is usually performed in a vacuum to prevent oxidation of the aluminum wiring and the like formed on the sensor chip. Therefore, the pressure reference chamber is in a vacuum state (zero pressure in absolute pressure).

When this pressure sensor is used for pressure detection at a location where a very high pressure is applied (for example, brake fluid pressure detection), it is necessary to make the pressure changing in a wide range correspond to the voltage range used as the sensor output. Therefore, the sensitivity of the pressure sensor is set low.

[0007] Therefore, there is a problem that a failure cannot be detected only by monitoring the normal sensor output.

[0008] The case where the bonding between the sensor chip and the pedestal is peeled off is a case where the pressure reference chamber communicates with the outside and the reference chamber pressure becomes substantially equal to the external pressure. Even if the same pressure is detected as two systems of signals as in the detection method and the signals are compared with each other, a similar signal appears, so that failure detection cannot be performed.

In view of the above problems, an object of the present invention is to provide a pressure sensor capable of reliably detecting a failure when the resistance value of the bridge circuit changes due to the failure, and further reducing the size. Another object is to provide a simple pressure sensor.

It is another object of the present invention to detect a failure due to poor airtightness of a reference chamber formed by bonding a sensor chip and a pedestal.

[0011]

In order to achieve the above object, according to the first aspect of the present invention, a gauge resistor (RA to RD) which changes its resistance value when a pressure is applied to a thin portion provided on a semiconductor substrate. A pressure sensor having a bridge circuit formed according to (1) and (2), wherein a reference potential generating circuit (11, 12) configured to generate a reference potential by a resistance (RE, RF) that does not change in resistance value when pressure is applied to the pressure sensor. The potential difference (V _BC ) at the two middle points (B, C) of the bridge circuit and the potential difference (V) between the potential at the middle point and the reference potential of the reference potential generating circuit are connected in parallel to one end and the other end of the circuit. _CE , V _BE ) to determine the failure of the bridge circuit.

Thus, when the resistance value of the bridge circuit changes due to a failure, it is possible to reliably detect the failure.

According to a second aspect of the present invention, there is provided a bridge
The gauge resistance of the circuit is divided by the divided gauge resistance (RA
1, RA2, RB1, RB2, RC1, RC2, RD
1, RD2), the two midpoints of the bridge circuit
(B, C) potential difference (V _BC) And the split gauge resistance
Of the intermediate terminals (B1, B2, C1, C2)
Terminal with the same potential when no pressure is applied to the
Potential difference (V_B1C1, V_B2C2) And the ratio
Comparing the failure of the bridge circuit.
And

[0014] Even with such a configuration, when the resistance value of the bridge circuit changes due to a failure, the failure can be reliably detected as in the first aspect of the invention.

Further, according to the present invention, the potential difference between the terminals (A, D) at one end and the other end of the bridge circuit and the first and second intermediate terminals (B, C) of the bridge circuit is provided. V _AB , V _CD , V _AC , V _BD ) are compared to determine the failure of the bridge circuit.

[0016] Even with such a configuration, similarly to the first aspect of the invention, when the resistance value of the bridge circuit changes due to a failure, the failure can be reliably detected.

Further, the invention according to claim 4 is characterized in that a failure determination of a bridge circuit is performed using an output signal obtained by amplifying a potential difference by an amplifier circuit.

According to a fifth aspect of the present invention, in the thin film portion (2) of the semiconductor substrate (1), two gauge resistors (RA, RD; RB, RC) provided in the direction orthogonal to each other.
Bridge circuit (10) formed by pressure detection
A pressure sensor that outputs an electric signal corresponding to the pressure from the bridge circuit, wherein the pressure sensor is provided at a portion of the thin portion where the pressure detection bridge circuit (10) is not formed. A failure detection circuit (1) that outputs an electrical signal with a sensitivity different from that of the detection bridge circuit
3, 14, 53), and failure determination means for determining failure of the pressure detection bridge circuit based on the outputs of the pressure detection bridge circuit and the failure detection circuit.

Thus, the output of the pressure detecting bridge circuit (10) having different sensitivities and the failure detecting circuit (13,
By using the outputs of (14, 53), when the output of the pressure detection bridge circuit (10) changes due to a failure, the failure can be reliably detected.

Further, only two gauge resistors (RA, RD; RB, RC) constituting a pressure detecting bridge circuit are arranged in the diaphragm portion of the conventional pressure sensor in the direction orthogonal to each other. The rest is an unused area. According to the fifth aspect of the present invention, since the failure detection circuit is provided in an unused area of the diaphragm, a pressure sensor having a failure detection function with a sensing unit having a size similar to that of a conventional pressure sensor is provided. As a result, the size of the pressure sensor can be reduced.

Further, according to the present invention, there is provided a storage means (31) for storing in advance a correspondence relationship between each output value of the pressure detection bridge circuit and the failure detection circuit, and the failure determination means comprises: It is characterized in that a failure determination of the pressure detection bridge circuit is performed based on whether or not each output value of the pressure detection bridge circuit and the failure detection circuit at an arbitrary pressure point satisfies the correspondence.

The fault detecting circuit can be constituted by one or more gauge resistors, as in the invention of claim 7, and further, as in the invention of claim 8, It can be a bridge circuit (13, 14).

According to a ninth aspect of the present invention, the pressure detection bridge circuit and the failure detection circuit are each formed of a diffusion resistor.
The tenth aspect of the present invention is characterized in that the pressure detection bridge circuit is constituted by a diffusion resistor, and the failure detection circuit is constituted by a thin film resistor. Further, as the failure detecting circuit, a capacitive sensor can be used as in the eleventh aspect of the present invention.

Further, in the twelfth aspect of the present invention, the failure determination means is provided on the semiconductor substrate (1) provided with the pressure detection bridge circuit and the failure detection circuit.

According to a thirteenth aspect of the present invention, there is provided a sensor having a sensor chip (60, 70) formed of a semiconductor substrate having a thin diaphragm portion formed thereon, and a pedestal to which the sensor chip is attached. Chip and pedestal (6
In the pressure sensor in which the reference chamber (60a) is provided between the pressure sensor and the pressure sensor, gauge resistances (Ra to R) are provided in the diaphragm.
a pressure detection bridge circuit formed by d) is provided, the pressure detection bridge circuit outputs an electric signal corresponding to the pressure, and is disposed at a portion different from the pressure detection bridge circuit. And a failure detection bridge circuit formed by the gauge resistors (Ra 'to Rd'), which outputs an electric signal corresponding to the pressure with a sensitivity different from that of the pressure detection bridge circuit. And the failure detection bridge circuit has high sensitivity, and the pressure detection bridge circuit has low sensitivity.

As described above, by providing a high-sensitivity failure detection bridge circuit in addition to the low-sensitivity pressure detection bridge circuit, the reference chamber formed by bonding the sensor chip and the pedestal has poor airtightness. Failure detection can be performed.

According to a fourteenth aspect of the present invention, the gauge resistor forming the failure detection bridge circuit is provided near the center of the diaphragm and near the periphery of the diaphragm. Claim 15
In the invention described in (1), the gauge resistance forming the failure detection bridge circuit is provided in a portion where the tensile stress is applied most and a portion where the compressive stress is applied most in the diaphragm portion.

With such a configuration, the failure detection bridge circuit can have high sensitivity.

According to a sixteenth aspect of the present invention, the gage resistance forming the pressure detection bridge circuit is provided at an intermediate position between the center and the periphery of the diaphragm. Further, in the invention according to claim 17, the gauge resistance forming the pressure detection bridge circuit is provided at a portion where the tensile stress is the smallest and a portion where the compressive stress is the smallest among the diaphragm portions. It is characterized by.

With such a configuration, the pressure detection bridge circuit can have low sensitivity.

According to the present invention, the semiconductor substrate has a (110) plane orientation, and the gauge resistor forming the failure detection bridge circuit has the first direction as the longitudinal direction. It is characterized by comprising a first gauge resistor and a second gauge resistor whose longitudinal direction is a second direction perpendicular to the first gauge resistor.

As described above, by making the longitudinal directions of the first gauge resistor and the second gauge resistor different from each other, the amount of change in the resistance value of the gauge resistor with respect to the surface stress can be made different. For this reason, for example, even if the first gauge resistance and the second gauge resistance are arranged in the vicinity, an electric signal corresponding to the pressure can be output by the first and second gauge resistances.

[0033] The invention according to claim 19 is characterized in that the failure detection bridge circuit is constituted by a full bridge circuit having four gauge resistors.
When the fault detection bridge circuit is configured with a full bridge circuit in this manner, higher sensitivity can be achieved than when a half bridge circuit is configured.

According to a twentieth aspect of the present invention, in a pressure sensor having a diaphragm portion and a pressure reference chamber (60a) isolated by the diaphragm portion, a pressure detecting element formed at or around the diaphragm portion is provided. Ra to Rd), a circuit for outputting an electric signal corresponding to the pressure is provided, and further, a function of determining that both surfaces of the diaphragm section have substantially the same pressure is provided.

As described above, by judging that both surfaces of the diaphragm section have substantially the same pressure, it is possible to detect a failure due to poor airtightness of the reference chamber formed by bonding the sensor chip and the pedestal. .

According to the twenty-first aspect of the present invention, a pressure detecting circuit is provided by pressure detecting elements (Ra to Rd) formed at or around the diaphragm, and an electric signal corresponding to the pressure is output. A failure detection circuit that outputs an electrical signal corresponding to pressure with a sensitivity different from that of the pressure detection circuit, wherein the failure detection circuit has high sensitivity and the pressure detection circuit has low sensitivity. .

As described above, by setting the failure detection circuit to have high sensitivity and the pressure detection circuit to have low sensitivity, failure detection due to poor airtightness of the reference chamber formed by bonding the sensor chip and the pedestal is performed. be able to.

In this case, as described in claim 22, the pressure detecting element is formed of a gauge resistor, and the change in the resistance value caused by the pressure change of the gauge resistor forming the failure detecting circuit and the change in the resistance of the gauge resistor forming the pressure detecting circuit. When comparing the resistance value change with the pressure change, the gauge resistor may be arranged so that the resistance value change of the failure detection circuit is larger.

According to a twenty-third aspect of the present invention, there is provided a method for diagnosing a failure in a pressure sensor having a diaphragm portion and a pressure reference chamber (60a) isolated by the diaphragm portion, the method comprising: forming a diaphragm on or around the diaphragm portion; If the output value of the circuit that outputs the electric signal corresponding to the pressure by the pressure detection elements (Ra to Rd) outputs an output value that can be considered that both surfaces of the diaphragm portion have become substantially the same pressure, it is regarded as a failure. It is characterized by:

As described above, when an output value that can be regarded as having substantially the same pressure on both sides of the diaphragm portion is output, it is regarded as a failure, and the reference chamber formed by bonding the sensor chip and the pedestal has a poor airtightness. Failure detection can be performed.

The reference numerals in parentheses of the above-mentioned means indicate the correspondence with the concrete means described in the embodiments described later.

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment to which the present invention is applied will be described below with reference to FIGS. The pressure sensor according to the present embodiment measures a pressure such as a brake fluid pressure of a brake device or a fuel pressure of a fuel injection device in a vehicle.

FIGS. 1A and 1B show a circuit configuration of the pressure sensor of the present embodiment, and FIG. 2 shows a partial cross section of the pressure sensor. As shown in FIG. 1A, the pressure sensor includes a bridge circuit 10 in which four gauge resistors (diffusion resistors) RA, RB, RC, and RD are bridge-connected.

As shown in FIG. 2, the bridge circuit 10 is formed on the thin diaphragm 2 of the silicon substrate 1. A broken line in FIG. 1 indicates the diaphragm section 2. Of the resistors constituting the bridge circuit 10, two resistors RA and RD are formed at the center of the diaphragm, and the other two resistors RB and RC are formed at the periphery of the diaphragm. When pressure is applied to the diaphragm portion, a stress displacement occurs, and the resistance values of the resistors RA to RD change in the direction of the arrow in FIG. 1 due to the piezoresistance effect, that is, the resistance values of the resistors RA and RD decrease. , Resistance R
B and RC are configured so that their resistance values increase.

The pressure sensor of this embodiment has a reference potential generation circuit 11 for generating a reference potential by resistance division.
Are connected in parallel to one end and the other end of the bridge circuit 10. The reference potential generation circuit 11 includes two resistors RE and RF connected in series. The resistors RE and RF are arranged in a portion that is not affected by the stress displacement caused by the pressure application, and are configured so that the resistance value does not change even when pressure is applied to the diaphragm portion. The reference potential is
These resistors RE and RF are created by resistance division.

The resistors RA to RF have the same shape and the same shape so as not to be affected by patterning, temperature, and the like.
They should be formed in the same step so as to have the same resistance value.

A constant voltage Vcc is applied between a terminal A on one end (power supply side) and a terminal D on the other end (ground side) of the bridge circuit 10, and a midpoint B between the resistors RA and RB and the resistors RC and RD. The potential difference (voltage) V _BC of the middle point potential at the middle points B and C is output using the middle point C as an output terminal. With this voltage V _BC , the pressure applied to the diaphragm portion of the silicon substrate can be measured. Terminals A and D
A similar effect can be obtained even if a constant current is applied during this period.

In this embodiment, the bridge circuit 10
In order to determine the failure of the circuit, the potential difference V _CE and V _BE between the midpoint potential at the midpoint E of the reference potential generation circuit 11 and the midpoint potentials at the midpoints B and C of the bridge circuit 10 are output. I have.

As shown in FIG. 1B, the voltage V _BC ,
V _CE and V _BE are output to amplification adjustment circuits 20, 21 and 22, respectively. The amplification adjustment circuits amplify those signals and output signals Out (BC), Out (CE) and Out (B).
E). These output signals Out (BC), Out (CE), Out (BE)
Is output to a failure determination circuit (comparison circuit) 30, and the failure determination circuit 30 is configured to perform failure determination of the bridge circuit as described later.

The failure determination circuit 30 may be provided in the pressure sensor, or may be provided in an external device such as an ECU. When the failure determination circuit 30 is provided in the pressure sensor, the external terminals are three terminals of a power supply terminal A, a ground terminal D, and a terminal for outputting Out (BC).
When provided in an external device, Out (CE), Out
It is necessary to increase the number of terminals to the outside such as the terminal for outputting (BE).

Hereinafter, the failure determination of the bridge circuit will be described.

Since the resistance values of the resistors RA to RF are all the same, the midpoint potential at the two midpoints B and C of the bridge circuit 10 and the midpoint potential at the midpoint E of the reference potential generating circuit 11 are equal to the pressure. It is equal when no voltage is applied. Therefore, when the potential of the terminal E is used as a reference, Equation 1 is established between the potential differences V _BC , V _CE , and V _BE between the terminals B, C, and E.

[0053]

V _BC = V _CE = V _BE = 0 Further, when pressure is applied to the diaphragm portion of the silicon substrate, the potential at the terminal B rises and the potential at the terminal C falls. At this time, since the resistances RE and RF are arranged in a portion not affected by the pressure application, the potential at the terminal E does not change. The resistors RA and RD have the same resistance change amount, and similarly the resistors RB and RC have the same resistance change amount. Therefore, the absolute value of the potential change amount at the terminals B and C becomes equal. Therefore, with reference to the potential of the terminal E, each potential difference V
Equation 2 holds between _BC , V _CE , and V _BE .

[0054]

| V _BC | = 2 × | V _CE | = 2 × | V _BE | Therefore, the failure of the bridge circuit is determined by comparing the absolute values of the voltages V _BC , V _CE , and V _BE. It becomes possible. That is, when the above equation (2) is satisfied, it can be determined that a normal pressure application state is established, and when the above equation (2) does not hold, it can be determined that a failure has occurred in the bridge circuit.

Since the changes in the potential differences V _BC , V _CE , and V _BE are very small, it is difficult to determine the failure of the bridge circuit using these voltage values. Therefore, in the present embodiment, the output signals Out (BC), Out (CE), and Out after the voltages VBC, VCE, and VBE are amplified and adjusted using the amplification adjustment circuits 20, 21, and 22 of different systems.
By comparing and determining (BE) in the failure determination circuit 30, the failure of the bridge circuit is determined. That is, it is determined whether Expression 3 holds.

[0056]

| Out (BC) | = 2 × | Out (CE) |
= 2 × | Out (BE) | With this configuration, in addition to the failure determination of the bridge circuit 10, the failure of the amplification adjustment circuits 20, 21, and 22 can be determined simultaneously.

As described above, in the pressure sensor using the bridge circuit 10, by providing the reference potential generating circuit which is not affected by the application of the pressure to the diaphragm, the change in the bridge resistance value due to, for example, a disconnection or a short circuit is obtained. When a failure occurs, the failure can be reliably detected.

(Second Embodiment) Next, a second embodiment will be described with reference to FIG. The pressure sensor according to the second embodiment includes a first reference potential generation circuit 1
In this embodiment, a second reference potential generation circuit 12 is added to the configuration of FIG. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. Although not shown, similar to the first embodiment, an amplification adjustment circuit and a failure determination circuit of another system are provided.

The second reference potential generation circuit 12 generates a reference potential by resistance division, like the first reference potential generation circuit 11, and is connected in parallel to one end and the other end of the bridge circuit 10. ing. The second reference potential generation circuit 12 includes two resistors RG and RH connected in series. The resistances RG and RH are arranged in a portion that is not affected by the stress displacement caused by the application of the pressure to the diaphragm,
The configuration is such that the resistance value does not change even when pressure is applied to the diaphragm portion.

The resistors RA to RH have the same shape and the same shape so as not to be affected by patterning, temperature, and the like.
They should be formed in the same step so as to have the same resistance value.

Hereinafter, the failure determination of the bridge circuit in the second embodiment will be described.

When pressure is applied to the diaphragm portion of the silicon substrate, the potential at point B rises and the potential at point C falls. At this time, the resistors RE, RF and R
Since G and RH are arranged at a position not affected by the pressure application, the potentials at the points E and F do not change. Since the resistance change amounts of the resistors RA and RD are equal, and similarly the resistance change amounts of the resistors RB and RC are equal, the absolute values of the potential change amounts at the points B and C are equal.
Therefore, based on the potentials at points E and F, the potential differences VBC, VCE, VBE, VCF, and VBF are:
Equation 4 holds.

[0063]

| VBC | = 2 × | VCE | = 2 × | VBE |
= 2 × | VCF | = 2 × | VBF | Similarly, output signals Out (BC), Out (CE) obtained by amplifying and adjusting each of the potential differences VBC to VBF by the amplifying circuit.
Equation 5 holds between Out (BE), Out (CF), and Out (BF).

[0064]

| Out (BC) | = 2 × | Out (CE) |
= 2 × | Out (BE) | = 2 × | Out (CF) | =
2 × | Out (BF) | Therefore, it is possible to determine whether or not a failure has occurred in the bridge circuit by determining whether or not Expression 4 or Expression 5 holds.

In Equations 4 and 5 of the second embodiment, since the number of conditional expressions increases as compared with Equations 2 and 3 of the first embodiment, it is possible to more reliably determine the failure of the bridge circuit.

In the second embodiment, two reference potential generation circuits 11 and 12 are provided, but more reference potential generation circuits may be provided.

Further, it is not always necessary to judge all the equations included in Equations 4 and 5, and at least the potential difference between the middle points B and C, the potential of the middle points B and C, and the reference potential generation circuit 1
A configuration may be adopted in which the potential difference between the reference potentials 1 and 12 is compared.

(Third Embodiment) Next, a third embodiment will be described with reference to FIG. The pressure sensor of the third embodiment is different from the first embodiment in that the bridge circuit 1
0 is different, and no reference potential generating circuit is provided. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. Although not shown, an amplification adjustment circuit and a failure determination circuit are provided as in the first embodiment.

In the third embodiment, the four gauge resistors (resistors) RA, RB, RC, and RD of the bridge circuit 10 are each equally divided into two, so that eight divided gauge resistors (divided resistors) RA1, RA1, RA2, RB1, RB2, R
C1, RC2, RD1, and RD2 are formed. At this time, the eight resistors RA1 to RD2 are all formed to have the same resistance value, and are configured such that the resistance values change in the direction of the arrows, respectively, by applying pressure to the diaphragm portion of the silicon substrate.

A constant voltage Vcc is applied between the two terminals A and D in the bridge circuit, and a middle point B between the resistors RA and RB and a middle point C between the resistors RC and RD are used as output terminals. A potential difference (voltage) V _BC of the midpoint potential is output. With this voltage V _BC , the pressure applied to the diaphragm portion of the silicon substrate can be measured.

The bridge circuit according to the third embodiment further includes
The potential of the intermediate terminal B1 of the division resistors RA1 and RA2 and
And the potential of the intermediate terminal C1 of the divided resistors RC1 and RC2.
Difference V _B1C1And an intermediate terminal B2 of the divided resistors RB1 and RB2.
And the potential of the intermediate terminal C2 of the divided resistors RD1 and RD2.
Potential difference V from potential_B2C2Is configured to output
You.

Here, attention is paid to respective potentials at the intermediate terminal B1 of the division resistors RA1 and RA2 and at the intermediate terminal C1 of the division resistors RC1 and RC2. When pressure is applied to the diaphragm, the potential at the terminal B1 rises and the potential at the terminal C1 falls. At this time, the resistance RA
1, RA2, RD1, and RD2 have the same resistance change amount, and the resistors RB1, RB2, RC1, and RC2 have the same resistance change amount.

Therefore, the potential difference V between the intermediate terminals B1 and C1 is
The absolute value of _B1C1 is the potential difference V _BC of the midpoint potential at midpoints B and C.
Is divided by the number of divisions of the resistors RA and RC (2 in this embodiment) and multiplied by the number of division resistors (1 in this embodiment) existing between the terminals B1 and C1 and the power supply terminal A. Equals the value. Similarly, the potential difference V _B2C2 between the intermediate terminals B2 and C2
Also, the potential difference V _BC of the midpoint potential at terminals B and C is
It is divided by the number of divisions of B and RD, and becomes equal to a value obtained by multiplying the number of division resistances between the terminals B2 and C2 and the ground terminal D.

Therefore, the potential difference V _BC between the middle _points B and C, the potential difference V _B1C1 between the intermediate terminals B1 and C1, and the potential difference V B1 and C2
Equation 6 holds between the potential differences V _B2C2 .

[0075]

| V _BC | = 2 × | V _B1C1 | = 2 × | V _B2C2 | _Further , an output signal Out (BC) obtained by amplifying and adjusting each of the voltages V _BC , V _B1C1 , and V _B2C2 by an amplification adjustment circuit of another system. ), O
Equation 7 holds between ut (B1C1) and Out (B2C2).

[0076]

| Out (BC) | = 2 × | Out (B1C
1) | = 2 × | Out (B2C2) | Therefore, if it is determined whether Expression 6 or Expression 7 is satisfied, it is possible to determine the failure of the bridge circuit.
That is, the terminals B1 and C1, the terminal B2, which are a combination of the potential difference VBC between the terminals B and C and the intermediate terminals having the same potential when no pressure is applied to the diaphragm portion.
By comparing the potential differences V _B1C1 and V _{B2C2 at} C2 and C2, it is possible to determine the failure of the bridge circuit.

In the above formulas 6 and 7, the failure of the bridge circuit is determined by a plurality of equations.
V _BC | = 2 × | V _B1C1 | or | V _BC | = 2 × | V
_B2C2 | or | Out (BC) | = 2 ×
| Out (B1C1) | or | Out (BC) | =
If any of 2 × | Out (B2C2) |
It is possible to determine the failure of the bridge circuit. In this case,
Failure can be detected by comparing the two potential differences, and the circuit configuration can be simplified.

In the third embodiment, all of the four resistors RA to RD of the bridge circuit are divided into two. However, the number of divisions may be further increased. For example, the resistors RA to RD are divided into three as shown in FIG.
When 1 to RD3 are formed, Expression 8 holds.

[0079]

[Equation 8] | V_BC| = 3 × | V_B1C1| = 3 × | V_B4C4| =
3/2 | V_B2C2| = 3/2 | V_{B3 C3}| Combination of resistors RA and RC, or resistor RB
And RD should be the same number of divisions.
These combinations may be different numbers of divisions.

(Fourth Embodiment) Next, a fourth embodiment will be described with reference to FIG. As shown in FIG. 6, the pressure sensor according to the fourth embodiment includes a bridge circuit 10 in which four gauge resistors (resistances) RA, RB, RC, and RD are connected in a bridge. Are the same as those conventionally used. Although not shown, an amplification adjustment circuit and a failure determination circuit are provided as in the first embodiment.

Hereinafter, the failure determination of the bridge circuit in the fourth embodiment will be described.

When pressure is applied to the diaphragm, the midpoint potential at terminal B rises and the midpoint potential at terminal C falls. At this time, the potentials at the terminals A and D do not change.
Since the resistance change amounts of the resistors RA and RD are equal, and similarly the resistance change amounts of the resistors RB and RC are equal, the absolute values of the potential change amounts at the points B and C are equal.

Therefore, the potential difference V _AC between the terminals A and C, the potential difference V _BD between the terminals B and D, the potential difference V _AB between the terminals A and B, and the potential difference V _CD between the terminals C and D are expressed by the following equation (9). Are simultaneously satisfied.

[0084]

| V _AC | = | V _BD | and | V _AB | = | V _CD | Therefore, by comparing the absolute values of the voltages V _AC , V _BD , V _AB , and V _CD , the bridge circuit Failure can be determined. That is, when Equation 9 is satisfied, it can be determined that a normal pressure application state is established, and when Equation 9 is not satisfied, it can be determined that a failure has occurred in the bridge circuit.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a plan view of a diaphragm portion of the pressure sensor according to the fifth embodiment.
FIG. 8 is a circuit diagram showing a schematic configuration of the pressure sensor according to the fifth embodiment.

As shown in FIGS. 7A and 7B, the fifth
In the pressure sensor according to the embodiment, in addition to the diffusion resistors RA to RD forming a bridge circuit for pressure detection, a diffusion resistor RI for failure detection is formed in a region of the diaphragm 2 of the silicon substrate 1. Here, the predetermined area is
This is a region where the balance between the radial stress and the circumferential stress of the stress generated by the application of the pressure is broken, and is a region deviated from the center of the diaphragm 2.

Further, an insulating oxide film 3 is formed thereon. A contact hole is formed in the oxide film 3, an aluminum wiring (not shown) is patterned thereon, and a protective film (passivation film) 4 is formed thereon.

Further, the silicon substrate in the fifth embodiment has a (100) plane orientation, and <110>
The crystal axes are orthogonal to each other. As shown in FIG. 7A, diffusion resistors RA to RD forming a pressure detection bridge
Are arranged two each along two <110> crystal axis directions.

As shown in FIG. 8, the failure detection resistor RI is connected in parallel to the pressure detection bridge circuit 10 together with the reference resistor Rref. The pressure detection bridge circuit 10 includes:
A potential difference (voltage) between two midpoint potentials generated by applying pressure to the diaphragm section 2 is output. On the other hand, the failure detection resistor RI is configured to increase its resistance value by applying pressure to the diaphragm unit 2 and outputs a voltage corresponding to the resistance value. The output signals of the pressure detection bridge circuit 10 and the failure detection resistor RI are amplified and adjusted by the amplification adjustment circuit, respectively, and then output to the failure determination circuit 30. The failure determination circuit 30 determines the failure of the bridge circuit 10. It is configured as follows.

Next, the failure determination of the pressure sensor according to the fifth embodiment will be described. First, at two or more arbitrary pressure points, a storage circuit (storage means) 31 stores the output voltage value of the pressure detection bridge circuit 10 and the output resistance value of the failure detection resistor RI with respect to the application of pressure to the diaphragm section 2.
In advance. Thus, the change characteristic of the output value of the pressure detection bridge circuit 10 and the failure detection resistance RI
Of the output value can be obtained. The output of the bridge circuit 10 and the output of the resistor RI change in proportion to the change in stress. These are configured to have different output change characteristics, and a fixed relationship is established between these outputs. That is, if the pressure sensor operates normally, the output of the bridge circuit 10 and the output of the resistor RI at a certain pressure point always have the same value.

Therefore, when the pressure sensor is operating,
The output of the bridge circuit 10 is compared with the output of the resistor RI,
If the relationship between these output values does not satisfy the relationship stored in the storage circuit 31, it can be determined that the bridge circuit 10 is not outputting a normal output value.

Further, only two gauge resistors RA to RD constituting a pressure detecting bridge circuit are arranged in the direction perpendicular to the diaphragm portion of the pressure sensor having the conventional structure, and the remaining portion is not provided. It is used area. In the fifth embodiment, since the failure detection resistor RI is provided in an unused area of the diaphragm, it is possible to provide a pressure sensor having a failure detection function with a sensing unit having the same size as a conventional pressure sensor. Thus, the size of the pressure sensor can be reduced.

In the fifth embodiment, a diffused resistor is used as the failure detection resistor RI. However, the present invention is not limited to this. For example, a thin film resistor may be used. Further, the failure detection circuit is configured by one resistor, but is not limited thereto, and may be configured by a plurality of resistors. For example, when a fault detection circuit is configured by two resistors connected in series, the midpoint potential may be used as an output.

(Sixth Embodiment) Next, a sixth embodiment of the present invention will be described with reference to FIGS. FIG. 9A is a plan view of a diaphragm portion of the pressure sensor according to the sixth embodiment, and FIG. 9B is a cross-sectional view taken along line BB of FIG. 9A.

As shown in FIG. 9A, the silicon substrate 1
The diaphragm portion 2 has eight diffusion resistors RA to RD,
RJ to RM are formed, and these diffusion resistors form two bridge circuits 10 and 13. That is,
The diffusion resistances RA to RD (open in the figure) are connected so as to constitute a bridge circuit 10 for pressure detection, and diffusion resistances RJ to RM (cross hatched in the figure) are provided inside the bridge circuit for pressure detection. It is connected so as to form a bridge circuit 13 for failure detection. The silicon substrate of this embodiment has a (110) plane orientation, and has a <100> crystal axis and a <100> crystal axis.
110> crystal axis exists orthogonal to each other. Resistance RA, R
D, RJ, and RM are formed in the <100> crystal axis direction, and resistors RB, RC, RK, and RL are formed in the <110> crystal axis direction.

As shown in FIG. 9B, in the pressure sensor according to the sixth embodiment, a diffusion resistor serving as a P-type diffusion layer is formed on an N-type silicon substrate, and an insulating oxide film is formed thereon. 3
Are formed. A contact hole is formed in the oxide film 3, an aluminum wiring (not shown) is patterned thereon, and a protective film 4 is formed thereon. Instead of the N-type silicon substrate, a silicon substrate obtained by epitaxially growing an N-type layer on a P-type silicon substrate may be used.

FIG. 10 shows output characteristics of the two bridge circuits 10 and 13 with respect to stress fluctuation. The output characteristics of the bridge circuits 10 and 13 of the pressure sensor are determined by the arrangement of the resistors in the diaphragm unit 2. In the sixth embodiment, the two bridge circuits 10 and 13 are provided at different positions in the diaphragm unit 2, and FIG.
As shown by 0, the output change characteristics (sensitivity) are different with respect to the pressure applied to the diaphragm 2. In the sixth embodiment, the pressure detection bridge circuit 10 is configured to have higher sensitivity, in other words, to have a higher output change rate with respect to pressure fluctuation.

FIG. 11 shows a schematic circuit configuration of the pressure sensor according to the sixth embodiment. As shown in FIG. 11, the voltage supplied from the constant voltage power supply is converted to a constant voltage (for example, 5 V) via a voltage adjustment circuit 40, and then supplied to bridge circuits 10 and 13 that perform sensing. The two bridge circuits 10 and 13 are connected in parallel and output midpoint potentials VB and VC and midpoint potentials VF and VG, respectively.
The outputs of the two bridge circuits 10 and 13 are switched by first and second switching circuits 41 and 42,
After being amplified by the first and second data storage units 45, 4
6 is stored in a form that can be compared by the failure determination circuit 30. The failure determination circuit 30 makes a failure determination based on the output values of the two bridge circuits 10 and 13. Note that the first and second switching circuits 41 and 42
The timing is controlled by the timing circuit 44 so that data error does not occur.

Next, the failure detection of the pressure sensor according to the sixth embodiment will be described. First, the change characteristics of the output voltage value of the pressure detection bridge circuit 10 and the change characteristics of the output voltage value of the failure detection bridge circuit 13 with respect to the application of pressure to the diaphragm unit 2 are stored in the storage circuit 31 in advance. . In order to obtain these output value change characteristics, the bridge circuits 10, 13 at at least two or more pressure points are required.
What is necessary is just to know the output value of. At this time, bridge circuit 1
Considering that the output values of 0 and 13 do not always change linearly with pressure fluctuations, it is desirable to take any three or more output values in order to obtain more accurate change characteristics.

A fixed relationship as shown in FIG. 10 is established between the outputs of these two bridge circuits 10 and 13. That is, if the pressure sensor is operating normally, two bridge circuits 10 at a certain pressure point,
13 always have the same value. Therefore, when the pressure sensor is operating, the output of the pressure detection bridge circuit 10 and the output of the failure detection bridge circuit 13 are compared, and the relationship between these output values is stored in the storage circuit 31. Is not satisfied, it can be determined that the bridge circuit 10 is not outputting a normal output value.

In the pressure sensor according to the sixth embodiment, when it is determined that a failure has occurred, the failure determination circuit 30
Represents the sensor output in the normal output voltage range (for example, 0.5 to
It is configured to forcibly shift out of the range of 4.5 V) (diag area) and output a signal indicating occurrence of abnormality.

In the diaphragm of the conventional pressure sensor, only two gauge resistors RA to RD constituting a pressure detection bridge circuit are arranged in a direction orthogonal to each other, and the remaining portion is not yet provided. It is used area. In the sixth embodiment, since the failure detection bridge circuit 13 is provided in an unused area of the diaphragm, a pressure sensor having a failure detection function with a sensing unit having a size similar to that of a conventional pressure sensor is provided. As a result, the size of the pressure sensor can be reduced.

In the sixth embodiment described above, (1
10) Although a silicon substrate having a plane orientation was used, the present invention is not limited to this, and a silicon substrate having a (100) plane orientation shown in FIG. 12 may be used. In the (100) plane orientation, two <110>
The crystal axis directions are orthogonal to each other. When a silicon substrate having a (110) plane orientation is used, each resistor must be provided at a position having a different stress distribution as shown in FIG. 9A, whereas a silicon substrate having a (100) plane orientation is used. When used, each gauge resistor can be evenly arranged at a position where stress distribution is equal. For this reason, the degree of deformation of the silicon substrate due to the temperature change, the degree of change in the generated stress, and the like can be made the same for each resistor, and thermal errors can be reduced.

(Seventh Embodiment) Next, a seventh embodiment of the present invention will be described with reference to FIG. The pressure sensor according to the seventh embodiment is different from the pressure sensor according to the sixth embodiment in that the failure detection bridge circuit 13 is formed of four thin film resistors. The same parts as those in the sixth embodiment are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIGS. 13A and 13B, in the pressure sensor of the seventh embodiment, a diffusion resistance R
A to RD are formed, and an insulating oxide film 3 is formed thereon. On the oxide film 3, thin film resistors RN to RQ made of, for example, polysilicon are formed. The four diffusion resistors RA to RD constitute a pressure detection bridge circuit 10, and the four thin film resistors RN to RQ constitute a failure detection bridge circuit. Each of the thin film resistors RN to RQ is formed at a position farther from the center of the diaphragm than the diffusion resistors RA to RD.

Since the thin-film resistance has a lower gauge factor than the diffusion resistance, the pressure detection circuit 10 and the failure detection circuit 13 have different output characteristics. That is, in the present embodiment, the pressure detection bridge circuit 10 has a higher output with respect to stress fluctuation. Therefore, according to the configuration of the pressure sensor of the seventh embodiment, the output of the pressure sensor is compared with the output of the failure detection bridge circuit, as in the sixth embodiment. Abnormal values can be detected.

In the seventh embodiment, the diffused resistor and the thin-film resistor are formed at different positions in the diaphragm. However, they can be arranged in layers at the same position in the diaphragm 2. Even with such a configuration, since the gauge factors of the diffusion resistance and the thin-film resistance are different, different output characteristics can be provided between the pressure detection circuit and the failure detection circuit.

(Eighth Embodiment) Next, an eighth embodiment of the present invention will be described with reference to FIG. The pressure sensor according to the eighth embodiment uses a metal diaphragm instead of a silicon substrate. As shown in FIGS. 14A and 14B, the pressure sensor includes a metal stem 50 having a circular diaphragm portion 50a, and a silicon substrate 51 bonded to the diaphragm portion 50a.
This configuration is such that pressure detection is performed based on a and the deformation of the silicon substrate 51.

The metal stem 50 has a hollow cylindrical shape and is made of a metal having a low coefficient of thermal expansion and a low coefficient of thermal expansion (such as Kovar having a coefficient of thermal expansion close to that of silicon). A pressure medium is introduced into the metal stem 50 from one end in the direction of the arrow in the drawing, and pressure is applied to a diaphragm 50a formed at the other end.

The silicon substrate 51 is fixed to the diaphragm 50a via a glass layer 52 made of low melting point glass or the like. The silicon substrate 51 has a (100) plane orientation, and constitutes a pressure detection bridge circuit.
The diffusion resistors RA to RD and the four thin film resistors RN to RQ that constitute the failure detection bridge circuit are formed.
The diffusion resistances RA to RD and the thin film resistances RN to RQ are determined by the rotation angle θ.
They are only shifted.

According to the configuration of the pressure sensor of the eighth embodiment, a failure can be detected by comparing two bridge outputs having different output change characteristics with respect to a stress change, similarly to the above embodiment.

(Ninth Embodiment) Next, a ninth embodiment of the present invention will be described with reference to FIG. FIG. 15A is a plan view of a diaphragm portion of the pressure sensor according to the ninth embodiment, and FIG. 15B is a cross-sectional view taken along line E-E. The pressure sensor according to the ninth embodiment is different from the above-described embodiment in that a capacitive sensor is used as a failure detecting circuit. The description is omitted here.

As shown in FIG. 15A, in the pressure sensor of the ninth embodiment, in addition to the four diffusion resistors RA to RD constituting the pressure detection bridge circuit 10, A capacitive sensor 53 is provided at the center as a failure detection circuit. The pressure detection bridge circuit 10 and the capacitive sensor 53 are electrically connected in parallel.

The capacitance type sensor 53 measures the pressure by using the change in the capacitance value between two electrodes, and the diaphragm formed on the silicon substrate 1 as shown in FIG. The portion 2 and the thin-film electrode 53a made of polycrystalline silicon arranged so as to face each other constitute a capacitance. When pressure is applied to the diaphragm portion 2, the distance between the diaphragm portion 2 and the thin film electrode 53a becomes short, and the capacitance between the diaphragm portion 2 and the thin film electrode 53a increases.
The capacitive sensor 53 outputs the capacitance value as an electric signal.

Normally, since the capacitive sensor 53 can obtain an output larger than that of the bridge circuit 10 composed of a diffusion resistor, the bridge circuit 10 and the capacitive sensor 53 obtain outputs having different output characteristics with respect to a stress change. be able to.

Therefore, according to the configuration of the pressure sensor of the present embodiment, the failure can be detected similarly to the above embodiment by comparing the output of the pressure detection bridge circuit 10 with the output of the capacitive sensor 53. It becomes possible.

(Tenth Embodiment) Next, a tenth embodiment of the present invention will be described.
An embodiment will be described with reference to FIGS. FIG.
FIG. 16A is a perspective view of the pressure sensor according to the present embodiment, and FIG. 16B is a cross-sectional view taken along line FF. FIG.
5A is a diagram illustrating a relationship between a position where a diffusion resistance is formed and a stress generated by pressure, FIG. 5A is a front view of a pressure sensor according to the present embodiment, FIG. 5B is a GG cross-sectional view of FIG. (c) is a diagram showing the magnitude of the x-direction component σxx of the stress generated by the pressure on the x-axis of the diaphragm surface when pressure is applied to the diaphragm from the surface direction.

The pressure sensor according to the present embodiment is different from the pressure sensor according to the sixth embodiment in that a sensor chip 60 having a diaphragm formed thereon is bonded to a base 61 and a pressure reference chamber 6 is formed.
0a is formed, and the bridge circuit for pressure detection and the bridge circuit for failure detection are both half bridge circuits formed by two diffusion resistors Ra, Rb and Ra ', Rb'. Are different.

Diffusion resistors Ra, Rb and Ra ', Rb'
Is formed on the surface layer of the sensor chip 60 composed of a silicon substrate having a (110) plane orientation. Both the diffusion resistors Ra and Rb are arranged near the middle position between the peripheral edge and the center of the diaphragm shown by the broken line. Specifically, as shown in FIG. 17C, the diffusion resistance Ra is formed near the position where the amount of positive change in the resistance value is the minimum, that is, in the vicinity of the position where the tensile stress is the minimum. The diffusion resistance Rb is formed near the position where the amount of the negative change is minimum, that is, near the position where the compressive stress is minimum. The diffusion resistances Ra ′ and Rb ′ are equal to one diffusion resistance Ra ′.
Are arranged near the periphery of the diaphragm, and the other diffused resistor Rb 'is arranged almost at the center of the diaphragm. Specifically, as shown in FIG. 17C, the diffusion resistance Ra ′ is formed near the position where the amount of positive change in the resistance value is the maximum, that is, near the position where the tensile stress is the maximum. Where the amount of negative change is maximum,
That is, the diffusion resistance R is set near the position where the compressive stress is maximized.
b ′ is formed.

In such a configuration, since the amount of change in the resistance of the diffusion resistances Ra and Rb with respect to the application of pressure to the diaphragm is small, the bridge circuit for detecting pressure has low sensitivity, and the diffusion with respect to the application of pressure to the diaphragm is reduced. Since the amount of change in the resistance values of the resistors Ra 'and Rb' is large, the failure detection bridge circuit has high sensitivity.

As described above, by providing a high-sensitivity bridge circuit separately from the one for pressure detection, the sensor chip 60
Pressure reference chamber 60, such as when the bonding between
Failure detection due to poor airtightness a can be performed. Therefore, the failure can be detected by the high-sensitivity bridge circuit while the output corresponding to the product specification is generated by the low-sensitivity bridge circuit.

FIG. 18 shows a schematic circuit configuration of the pressure sensor of the present embodiment. As shown in this figure, the pressure sensor forms a bridge circuit for pressure detection by diffusion resistances Ra and Rb and dummy resistances 62 and 63 provided in a portion different from the diaphragm part, and also includes a diffusion resistance Ra ′. , Rb ′ and a dummy resistor 64, 65 provided at a portion different from the diaphragm portion form a bridge circuit for failure detection.

The potential difference at each middle point of the pressure detecting bridge circuit is amplified by an amplifier circuit 66 having a temperature compensation function, and is output to the outside as a sensor output via an output circuit 67. The potential difference at each midpoint of the failure detection bridge circuit is amplified by an amplifier circuit 68 having a temperature compensation function, and then compared with a predetermined reference voltage Vref by a comparison circuit 69. The comparison result is input to an output circuit 67. It is supposed to be. When the output of the bridge circuit corresponds to the output at the time of failure, a signal indicating a failure is output from the comparison circuit 69 to the output circuit. When such a signal is input, the output circuit 67 outputs the sensor signal. The output is forcibly shifted out of the normal output voltage range (diag region), and a signal indicating the occurrence of an abnormality is output.

As described above, by providing the bridge circuit having two sensitivities of low sensitivity and high sensitivity, the low sensitivity bridge circuit is used for pressure detection, and the high sensitivity bridge circuit is used for failure detection. In addition, failure detection due to poor airtightness of the pressure reference chamber 60a can be performed.

(Eleventh Embodiment) Next, an eleventh embodiment of the present invention will be described.
An embodiment will be described with reference to FIGS. FIG.
(A) is a front view of the pressure sensor in the present embodiment, FIG.
9B is a cross-sectional view taken along the line HH of FIG. 9A, and FIG. 19C is an x-direction component of stress generated by pressure on the diaphragm surface x-axis when pressure is applied to the diaphragm from the surface direction. FIG. 9 is a diagram illustrating the magnitude of σxx. FIG. 20 is a diagram illustrating a circuit configuration of the pressure sensor according to the present embodiment.

The pressure sensor of the present embodiment is different from that of the tenth embodiment in that the number of bridge circuits for detecting a failure is four.
This is a point that a full bridge circuit composed of two diffusion resistors Ra 'to Rd' is used.

In this case, the diffusion resistance Rc ′ is
The diffusion resistance Rd 'is formed at a position where a resistance value change (tensile stress) corresponding to the diffusion resistance Ra' is obtained.

As described above, the bridge circuit for failure detection is a full bridge circuit composed of four diffused resistors Ra 'to Rd', whereby a more sensitive bridge circuit can be obtained.

(Twelfth Embodiment) Next, a twelfth embodiment of the present invention will be described.
An embodiment will be described with reference to FIGS. FIG.
(A) is a front view of the pressure sensor in the present embodiment, FIG.
1B is a cross-sectional view taken along the line II of FIG. 1A, and FIG. 21C is an x-direction component of stress generated by pressure on the x-axis of the diaphragm surface when pressure is applied to the diaphragm from the surface direction. FIG. 9 is a diagram illustrating the magnitude of σxx. FIG. 22 is a diagram illustrating a circuit configuration of the pressure sensor according to the present embodiment.

The pressure sensor according to the present embodiment is different from the eleventh embodiment in that a pressure detection bridge circuit is used.
This is a point that a full bridge circuit composed of two diffusion resistors Ra to Rd is used.

In this case, the diffusion resistance Rc is formed at a position where a resistance value change (compression stress) corresponding to the diffusion resistance Rb is obtained, and the diffusion resistance Rd is obtained at a resistance value change (tensile stress) corresponding to the diffusion resistance Ra. Is formed at the position shown.

As described above, by forming the pressure detection bridge circuit as a full bridge circuit composed of four diffusion resistors Ra to Rd, a bridge circuit with higher sensitivity can be obtained.

(Thirteenth Embodiment) Next, a thirteenth embodiment of the present invention will be described.
An embodiment will be described with reference to FIG. FIG. 23A is a front view of the pressure sensor according to the present embodiment, and FIG.
FIG. 23A is a cross-sectional view taken along the line JJ of FIG. 23A, and FIG. 23C is a graph showing the x-direction component σxx of the stress generated by the pressure on the x-axis of the diaphragm surface when pressure is applied to the diaphragm from the surface direction. FIG. 9 is a diagram illustrating the magnitude of a direction component σyy.

The pressure sensor according to the present embodiment is a tenth pressure sensor.
Compared to the embodiment, in the surface layer portion of the sensor chip 70 formed of a silicon substrate having a (100) plane orientation, the longitudinal direction (current path) of the diffusion resistances Ra and Ra ′ and the diffusion resistances Rb and Rb ′ is different. Are different.

The piezoresistance effect on the Si (100) surface is
Since the resistance change amount ΔR has a property of being proportional to the stress difference (σxx−σyy), when the resistance value change amount of the diffusion resistance (here, the diffusion resistances Ra and Ra ′) whose x direction is the longitudinal direction is ΔR. , The resistance change amount of the diffusion resistance (here, the diffusion resistances Rb and Rb ′) whose longitudinal direction is the y direction is substantially −ΔR, and has different change characteristics even when the same pressure is applied. are doing.

For this reason, in the present embodiment, σxx and σy
A diffusion resistor Ra having a longitudinal direction in the x direction is provided at a portion where the difference from y is the smallest, and a diffusion resistor Rb having a longitudinal direction in the y direction is provided.
A diffused resistor Ra 'having a longitudinal direction in the x direction is provided and a diffused resistor Rb' having a longitudinal direction in the y direction is provided.

In such a configuration, the diffusion resistance Ra,
The pressure detection bridge circuit composed of Rb has low sensitivity, and the failure detection bridge circuit composed of the diffusion resistors Ra ′ and Rb ′ has high sensitivity. Therefore,
With the configuration of the present embodiment, effects similar to those of the tenth embodiment can be obtained.

(Fourteenth Embodiment) Next, a fourteenth embodiment of the present invention will be described.
An embodiment will be described with reference to FIG. FIG. 24A is a front view of the pressure sensor according to the present embodiment, and FIG.
FIG. 24A is a cross-sectional view taken along the line KK of FIG. 24A, and FIG. 24C is a graph showing the x-direction component σxx of the stress generated by the pressure on the x-axis of the diaphragm surface when pressure is applied to the diaphragm from the surface direction. FIG. 9 is a diagram illustrating the magnitude of a direction component σyy.

The pressure sensor according to the present embodiment is different from the thirteenth embodiment in that a bridge circuit for detecting a failure is provided by four.
This is a point that a full bridge circuit composed of two diffusion resistors Ra 'to Rd' is used.

In this case, the diffusion resistance Rc ′ is formed at a position where the y-direction is the longitudinal direction and a resistance value change (compression stress) corresponding to the diffusion resistance Rb ′ is obtained. Further, the diffusion resistance Rd ′ is formed at a position where the x direction is the longitudinal direction and a resistance value change (tensile stress) corresponding to the diffusion resistance Ra ′ is obtained.

As described above, the bridge circuit for failure detection is a full bridge circuit composed of four diffused resistors Ra 'to Rd', so that a more sensitive bridge circuit can be obtained.

(Fifteenth Embodiment) Next, a fourteenth embodiment of the present invention will be described.
An embodiment will be described with reference to FIG. FIG. 25A is a front view of the pressure sensor according to the present embodiment, and FIG.
FIG. 25A is an LL cross-sectional view of FIG. 25A, and FIG. 25C is an x-direction component σxx of a stress generated by a pressure on the x-axis of the diaphragm surface when pressure is applied to the diaphragm from the surface direction, and similarly, y FIG. 9 is a diagram illustrating the magnitude of a direction component σyy.

The pressure sensor according to the present embodiment is different from the fourteenth embodiment in that the pressure detection bridge circuit has four bridge circuits.
This is a point that a full bridge circuit composed of two diffusion resistors Ra to Rd is used.

In this case, the diffusion resistor Rc is formed at a position where the longitudinal direction is the y direction and a change in resistance value (compression stress) corresponding to the diffusion resistor Rb is obtained. Also, the diffusion resistance Rd
Is formed in a position where the longitudinal direction is the x direction and a change in resistance value (tensile stress) corresponding to the diffusion resistance Ra is obtained.

As described above, the bridge circuit for detecting pressure is a full bridge circuit composed of four diffusion resistors Ra to Rd, so that a bridge circuit with higher sensitivity can be obtained.

(Other Embodiments) In the above embodiments, the resistors constituting the bridge circuit are configured to have the same resistance value. However, the resistance values of the resistors are the same due to manufacturing variations and the like. In consideration of the case where resistance does not occur, a resistor (variable resistor) for performing trimming adjustment may be provided in the vicinity of each resistor on the circuit so that the resistance value of each resistor becomes equal.

In the failure determination of the bridge circuit in each of the above embodiments, the determination is made based on whether or not the output values to be compared match. However, in consideration of the manufacturing variation of the pressure sensor and the detection accuracy, the determination is made to some extent. May be provided. For example, in Expression 2, | V _BC | = 2 × | V _CE |, | V _BC | =
2 × | V _CE | ± α (α: tolerance).

Further, in the first to fourth embodiments, the failure of the bridge circuit is determined by comparing the potential differences (voltages) at a certain point in time. However, the amount of change in the potential difference over a predetermined time is compared. The failure determination of the bridge circuit may be performed.

In the fifth to ninth embodiments,
The failure detection circuit is not limited to the arrangement of each embodiment, and the failure detection circuit can be arranged at an arbitrary position in the diaphragm section as long as it can have an output characteristic different from that of the pressure detection circuit.

Further, in the third embodiment, the case where the failure detection is performed by using the potential of the dividing point of the equally divided resistor has been described as an example. However, it is not always necessary to perform the equal dividing. The present invention is applicable to any other configuration as long as the resistors arranged on the two sides are divided at a point where the electric potential becomes equal when no pressure is applied and the failure is detected using the electric potential at the divided point. Can be applied.

Further, in the thirteenth embodiment,
The diffused resistors Ra and Rb and the diffused resistors Ra 'and Rb' are arranged so as to be displaced from the center of the diaphragm in the x-direction. However, such an arrangement is not necessarily required. For example, as shown in FIG. 26, the diffusion resistances Ra and Rb are shifted in the x direction from the center of the diaphragm, and the diffusion resistances Ra ′ and
Rb 'may be shifted in the y direction from the center of the diaphragm.

Similarly, regarding the diffused resistors Ra, Rb, Ra ′ to Rd ′ in the fourteenth embodiment, FIG.
As shown in (a), the diffusion resistances Ra and Rb are shifted from the center of the diaphragm in the x direction, and the diffusion resistances Ra 'to R'
d 'may be shifted from the center of the diaphragm in the y direction. Further, as shown in FIG. 27B, the diffusion resistors Ra, Rb, Ra ', and Rb' are shifted in the x direction from the center of the diaphragm, and the diffusion resistors Rc 'and Rd' are shifted in the y direction from the center of the diaphragm. The arrangement may be shifted.

Similarly, regarding the diffusion resistances Ra to Rb and Ra ′ to Rd ′ in the fifteenth embodiment, FIG.
As shown in (a), the diffusion resistances Ra ′ to Rd are shifted in the x direction from the center of the diaphragm part, and the diffusion resistances Ra ′ to Rd are shifted.
d 'may be shifted from the center of the diaphragm in the y direction. Further, as shown in FIG. 28 (b), the diffusion resistances Ra, Rb, Ra ', Rb' are shifted in the x direction from the center of the diaphragm part, and the diffusion resistances Rc, Rd, R
c ′ and Rd ′ may be displaced from the center of the diaphragm in the y direction.

However, the arrangements shown in FIGS. 26 to 28 are merely examples, and the present invention can be applied to arrangements not shown in these figures.

In the tenth and subsequent embodiments, since a pressure sensor for detecting an extremely high pressure (50 atm or more) is taken as an example, a high-sensitivity failure detection circuit is separately provided. A pressure sensor that detects (1 to 10 atm) eliminates this need. The case will be described below.

Assuming that the pressure reference chamber 60a is evacuated in FIG. 16, the diaphragm normally flexes slightly toward the reference chamber under atmospheric pressure, and further flexes toward the reference chamber with pressurization. At a pressure lower than the atmospheric pressure, that is, at a negative pressure, the degree of bending gradually decreases, and when the absolute pressure is zero, the bending of the diaphragm portion is eliminated. In a pressure sensor that assumes only pressurization, a signal indicating a negative pressure is abnormal, but if the airtightness of the pressure reference chamber 60a is broken, the upper and lower pressures of the diaphragm become the same. , That is, a state in which the absolute pressure is virtually zero occurs.

Therefore, using the circuit configuration shown in FIG.
If the output corresponding to the vicinity of the absolute pressure of zero or the negative pressure is detected, the failure mode of poor airtightness of the pressure reference chamber 60a can be detected.

Further, a pressure range slightly higher than the target pressure of the circuit configuration in FIG.
A circuit configuration shown in FIG. 30 is also conceivable as a circuit configuration targeting 0 atm. That is, in FIG.
In this figure, two systems are provided with the amplifiers 66 and 66 '. With such a circuit configuration,
It is possible to increase the sensitivity of the failure detection circuit.

In the tenth and subsequent embodiments, the pressure sensor of the type in which the diaphragm is formed by reducing the thickness of the semiconductor substrate and the gauge resistance is formed on the surface of the substrate has been described. In the case of a sensor, the present invention relating to detection of poor airtightness can be applied. That is, the present invention can be applied to other types of pressure sensors such as a capacitance type.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a circuit configuration of a pressure sensor according to a first embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the pressure sensor according to the first embodiment.

FIG. 3 is a circuit diagram illustrating a circuit configuration of a pressure sensor according to a second embodiment.

FIG. 4 is a circuit diagram illustrating a circuit configuration of a pressure sensor according to a third embodiment.

FIG. 5 is a circuit diagram showing a modified example of the pressure sensor of the third embodiment.

FIG. 6 is a circuit diagram illustrating a circuit configuration of a pressure sensor according to a fourth embodiment.

FIG. 7 is a plan view of a diaphragm section of a pressure sensor according to a fifth embodiment.

FIG. 8 is a circuit diagram illustrating a circuit configuration of a pressure sensor according to a fifth embodiment.

9A is a plan view of a diaphragm of a pressure sensor according to a sixth embodiment, and FIG. 9B is a cross-sectional view taken along line BB of FIG. 9A.

FIG. 10 is a characteristic diagram illustrating output characteristics of two bridge circuits in the pressure sensor according to the sixth embodiment.

FIG. 11 is a circuit diagram illustrating a schematic configuration of a pressure sensor according to a sixth embodiment.

FIG. 12 is a plan view of a diaphragm showing a modification of the pressure sensor of the sixth embodiment.

FIG. 13A is a plan view of a diaphragm of the pressure sensor according to the seventh embodiment, and FIG. 13B is a cross-sectional view taken along the line CC of FIG.

FIG. 14A is a plan view of a diaphragm portion of the pressure sensor according to the eighth embodiment, and FIG. 14B is a cross-sectional view taken along line DD of FIG.

FIG. 15A is a plan view of a diaphragm portion of the pressure sensor according to the ninth embodiment, and FIG. 15B is a cross-sectional view taken along line EE of FIG.

FIG. 16A is a perspective view of a pressure sensor according to a tenth embodiment, and FIG. 16B is a sectional view taken along line FF.

FIG. 17 is a diagram showing a relationship between a position where a diffusion resistance of a pressure sensor is formed and a stress generated by pressure in a tenth embodiment.

FIG. 18 is a diagram illustrating a circuit configuration of a pressure sensor according to a tenth embodiment.

FIG. 19 is a diagram showing a relationship between a position where a diffusion resistance of a pressure sensor is formed and a stress generated by pressure in an eleventh embodiment.

20 is a diagram showing a circuit configuration of the pressure sensor shown in FIG.

FIG. 21 is a diagram showing a relationship between a position where a diffusion resistance of a pressure sensor is formed and a stress generated by pressure in a twelfth embodiment.

FIG. 22 is a diagram showing a circuit configuration of the pressure sensor shown in FIG. 21.

FIG. 23 is a diagram illustrating a relationship between a position where a diffusion resistance of a pressure sensor is formed and a stress generated by pressure in a thirteenth embodiment.

FIG. 24 is a diagram illustrating a relationship between a position where a diffusion resistance of a pressure sensor is formed and a stress generated by pressure in a fourteenth embodiment.

FIG. 25 is a diagram showing a relationship between a position where a diffusion resistance of a pressure sensor is formed and a stress generated by pressure in a fifteenth embodiment.

FIG. 26 shows diffused resistors Ra, Rb, and R shown in another embodiment.
It is a figure which shows the example of arrangement | positioning of a 'and Rb'.

FIG. 27 shows diffused resistors Ra, Rb, and R shown in another embodiment.
It is a figure which shows the example of arrangement | positioning of a'-Rd '.

FIG. 28 shows diffused resistors Ra to Rd and R shown in another embodiment.
It is a figure which shows the example of arrangement | positioning of a'-Rd '.

FIG. 29 is a diagram showing a circuit configuration of a pressure sensor shown in another embodiment.

FIG. 30 is a diagram showing a circuit configuration of a pressure sensor shown in another embodiment.

[Explanation of symbols]

10, 13 bridge circuit, 11, 12 reference potential generation circuit, 20, 21, 22 amplification control circuit, 30 failure determination circuit, RA to RD, RI, RJ to RM, RN to RQ
Gauge resistance.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroaki Tanaka 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso Corporation (72) Inventor Yasutoshi Suzuki 1-1-1, Showa-cho, Kariya City, Aichi Prefecture Denso Corporation (72) Inventor Seiichiro Ishio 1-1-1, Showa-cho, Kariya-shi, Aichi Prefecture Inside Denso, Inc. (72) Inventor Yukihiko Tanizawa 1-1-1, Showa-cho, Kariya-shi, Aichi F-term (reference) ) 2F055 AA40 BB20 CC02 DD05 EE14 FF45 FF49 GG16 GG31 4M112 AA01 BA01 BA07 CA05 CA10 CA12 DA17 DA18 EA03 EA04 EA06 FA11 GA03

Claims (23)

[Claims] A pressure detecting bridge circuit (10) formed by gauge resistors (RA to RD) that change in resistance value when pressure is applied to a thin portion (2) provided on a semiconductor substrate (1). A reference potential generating circuit (11, 12) configured to generate a reference potential by resistances (RE, RF) that do not change in resistance value when the pressure is applied; The potential difference (V _BC ) at two middle points (B, C) of the bridge circuit, and the potential difference (V _CE , between the potential at the middle point and the reference potential of the reference potential generation circuit) V _BE ), the failure of the pressure detection bridge circuit is determined. 2. A pressure detecting bridge circuit (10) formed by gauge resistances (RA to RD) that change in resistance value when pressure is applied to a thin portion (2) provided on a semiconductor substrate (1). Wherein the gauge resistance of the bridge circuit is divided into divided gauge resistances (RA1, RA2, RB1, RB2, RC1, RC1, R2).
C2, RD1, RD2), the potential difference (V _BC ) at the two middle points (B, C) of the bridge circuit, and the intermediate terminals (B1,
B2, C1, C2), the pressure detection bridge circuit is determined to be faulty based on the potential difference (V _B1C1 , V _B2C2 ) in the combination of the intermediate terminals having the same potential when no pressure is applied to the thin portion. Pressure sensor characterized by the above-mentioned. 3. A thin portion provided on a semiconductor substrate (1).
(2) Gauge resistor that changes resistance value with application of pressure
A pressure sensor formed by anti- (RA to RD)
A pressure sensor having a bridge circuit (10), wherein terminals (A,
D) and first and second intermediate terminals of the bridge circuit
(B, C) potential difference (V_AB, V_CD, V_AC, V _BD)
And determining the failure of the pressure detection bridge circuit based on
Pressure sensor. 4. The pressure sensor according to claim 1, wherein the failure determination of the bridge circuit is performed using an output signal obtained by amplifying the potential difference by an amplifier circuit. 5. In a thin film portion (2) of a semiconductor substrate (1), two gauge resistors (R) are provided in a direction orthogonal to each other.
A, RD; RB, RC) is a pressure sensor provided with a pressure detection bridge circuit (10) formed by the pressure sensor, wherein the bridge circuit outputs an electric signal according to pressure from the bridge circuit. The pressure detection bridge circuit (1)
A failure detection circuit (13, 14, 53) which is provided in a portion where no (0) is formed and outputs an electric signal according to the pressure with a sensitivity different from that of the pressure detection bridge circuit (13, 14, 53)
And a failure determination means for determining failure of the pressure detection bridge circuit based on each output of the pressure detection bridge circuit and the failure detection circuit. 6. A storage circuit (31) for storing in advance a correspondence relationship between respective output values of the pressure detection bridge circuit and the failure detection circuit, wherein the failure determination means includes the pressure detection bridge circuit. 6. The pressure sensor according to claim 5, wherein the failure determination of the pressure detection bridge circuit is performed based on whether each output value of the failure detection circuit satisfies the correspondence. 7. The fault detecting circuit includes one or more fault detecting gauge resistors (RI, RJ to RM, RN to RQ).
7. The method according to claim 5, wherein
Pressure sensor. 8. The failure detection gauge resistor (RJ to RJ).
The pressure sensor according to claim 7, wherein M, RN to RQ) constitute a bridge circuit (13, 14). 9. The pressure sensor according to claim 7, wherein each of the pressure detection bridge circuit and the failure detection circuit includes a diffusion resistor. 10. The pressure detection bridge circuit according to claim 7, wherein the pressure detection bridge circuit comprises a diffused resistor, and the failure detection circuit comprises a thin film resistor. Pressure sensor. 11. The circuit according to claim 5, wherein the failure detection circuit comprises a capacitive sensor (53).
Or the pressure sensor according to 6. 12. The semiconductor device according to claim 5, wherein said failure determination means is provided on said semiconductor substrate provided with said pressure detection bridge circuit and said failure detection circuit. A pressure sensor according to any one of the preceding claims. 13. A sensor chip (60, 7) constituted by a semiconductor substrate on which a thin diaphragm portion is formed.
0) and the pedestal (6
1), wherein a reference chamber (60a) is provided between the sensor chip and the pedestal, wherein the diaphragm includes a pressure detecting sensor formed by a gauge resistor (Ra to Rd). A bridge circuit is provided,
The pressure detection bridge circuit outputs an electric signal corresponding to the pressure, and a gauge resistor (R) disposed at a different portion from the pressure detection bridge circuit.
a ′ to Rd ′), and a failure detection bridge circuit is configured to output an electric signal corresponding to pressure with a sensitivity different from that of the pressure detection bridge circuit. A pressure sensor, wherein the failure detection bridge circuit has high sensitivity and the pressure detection bridge circuit has low sensitivity. 14. The failure detecting bridge circuit according to claim 13, wherein the gauge resistors forming the failure detection bridge circuit are provided near a center of the diaphragm and near a periphery of the diaphragm. Pressure sensor. 15. The gage resistance forming the failure detection bridge circuit is provided in a portion of the diaphragm portion where a tensile stress is applied most and a portion where a compressive stress is applied most. Pressure sensor. 16. The pressure sensing bridge circuit according to claim 13, wherein the gauge resistor is provided at a middle position between a central portion and a peripheral portion of the diaphragm portion. 4. The pressure sensor according to any one of the above. 17. The gauge resistance forming the pressure detecting bridge circuit is provided in a portion of the diaphragm portion where the tensile stress is the smallest and a portion where the compressive stress is the smallest. A pressure sensor according to any one of claims 13 to 15. 18. The semiconductor substrate having a plane orientation of (110).
A gauge resistor forming a fault detection bridge circuit includes a first gauge resistor having a first direction as a longitudinal direction and a second gauge direction perpendicular to the first gauge resistor. 14. The pressure sensor according to claim 13, further comprising a second gauge resistor having a direction. 19. The fault detecting bridge circuit according to claim 13, wherein the fault detecting bridge circuit is a full bridge circuit having four gauge resistors.
4. The pressure sensor according to any one of the above. 20. A pressure sensor having a diaphragm part and a pressure reference chamber (60a) isolated by the diaphragm part, wherein a pressure is detected by pressure detecting elements (Ra to Rd) formed in or around the diaphragm part. A pressure sensor comprising: a circuit for outputting an electric signal corresponding to the pressure; and a function of determining that both surfaces of the diaphragm section have substantially the same pressure. 21. A pressure sensor having a diaphragm section and a pressure reference chamber (60a) isolated by the diaphragm section, wherein pressure detection is performed by pressure detecting elements (Ra to Rd) formed at or around the diaphragm section. A failure detection circuit that outputs an electric signal according to pressure with a sensitivity different from that of the pressure detection circuit, wherein the failure detection circuit has a circuit. A pressure sensor having high sensitivity, wherein the pressure detection circuit has low sensitivity. 22. The pressure detecting element is formed as a gauge resistor, and changes in resistance value according to a pressure change of the gauge resistor forming the failure detection circuit and changes in a pressure of the gauge resistor forming the pressure detection circuit. 22. The gauge resistance according to claim 21, wherein the gauge resistance is arranged such that a change in resistance of the failure detection circuit is larger than a change in resistance.
Pressure sensor. 23. A method for diagnosing a failure of a pressure sensor having a diaphragm portion and a pressure reference chamber (60a) isolated by the diaphragm portion, comprising: a pressure detecting element (Ra) formed at or around the diaphragm portion. To Rd), the output value of the circuit that outputs the electric signal corresponding to the pressure outputs an output value that can be considered that both surfaces of the diaphragm portion have become substantially the same pressure. Sensor failure detection method.