JP7816938B2 - Pressure Sensor - Google Patents

Description

The present invention relates to a pressure sensor that detects strain caused by deformation of a membrane by measuring changes in the resistance of a resistor.

In recent years, various technologies have been proposed for pressure sensors that utilize the piezoresistive effect. For example, Patent Document 1 describes a pressure sensor that has a membrane (diaphragm), multiple resistors formed on the membrane, and a temperature measuring element formed on the membrane.

The multiple resistors formed on the membrane form a detection circuit (strain gauge) consisting of a bridge circuit. When the membrane receives pressure from the pressurized fluid and generates strain, the resistance value changes by an amount proportional to the amount of strain. By detecting the output signal from the detection circuit at this time, it is possible to measure the change in the resistance value of the multiple resistors, i.e., the pressure applied to the membrane.

The temperature sensor element formed on the membrane is a resistive element, such as a thermistor, and changes its resistance value in response to changes in the temperature of the pressurized fluid. Therefore, by detecting the output signal of the temperature sensor element, it is possible to measure the temperature of the pressurized fluid, and based on this temperature information, errors contained in the output signal of the detection circuit (errors caused by the temperature dependency of resistance changes in the resistor) can be corrected.

In order to miniaturize the pressure sensor or improve the accuracy of temperature measurement, it is desirable to form the temperature sensor in the area where multiple resistors are located, i.e., the area where distortion occurs in the membrane. However, in this case, if the membrane is subjected to pressure from the pressurized fluid and generates distortion, the resistance change of the temperature sensor due to the influence of this distortion cannot be ignored, and there is a risk that an error corresponding to this resistance change will be superimposed on the output signal of the temperature sensor beyond the allowable amount. As a result, the accuracy of the temperature information obtained from the output signal of the temperature sensor cannot be guaranteed, and it is difficult to perform accurate temperature correction on the output signal of the detection circuit.

Japanese Patent Application Publication No. 11-094667

The present invention was made in consideration of these issues, and its purpose is to provide a pressure sensor that can perform temperature detection or temperature correction with high accuracy.

In order to achieve the above object, the pressure sensor according to the present invention comprises:
a membrane that deforms in response to pressure;
a plurality of sensor resistors formed on the membrane and constituting a detection circuit;
a compensation resistor formed on the membrane for detecting temperature;
The compensation resistor has an external resistor formed on an external substrate different from the membrane and electrically connectable to one end of the compensation resistor.

For example, when the correction resistor and external resistor are not electrically connected, the temperature of the pressurized fluid (hereinafter referred to as the virtual temperature) can be measured by detecting the output signal (hereinafter referred to as the provisional output signal) of the correction resistor. However, the provisional output signal may contain not only the resistance change of the correction resistor caused by temperature changes in the pressurized fluid, but also the resistance change of the correction resistor caused by distortion of the membrane.

Therefore, by detecting the output signal of the correction resistor while the correction resistor and external resistor are electrically connected, it is possible to identify the resistance change of the correction resistor due to the distortion of the membrane. That is, if the temperature conditions are similar between the location where the correction resistor is placed and the location where the external resistor is placed, when a resistance change occurs in the correction resistor in response to a temperature change in the pressurized fluid, a resistance change also occurs in the external resistor at a similar rate. Therefore, the resistance changes of each resistor in response to the temperature change cancel each other out, and the output signal of the correction resistor (e.g., the voltage division value between the correction resistor and the external resistor located between the power supply line and ground) theoretically becomes equal to the resistance change of the correction resistor due to the distortion of the membrane. Therefore, the true temperature of the pressurized fluid can be determined by subtracting the resistance change of the correction resistor due to the distortion of the membrane from the detected value of the provisional output signal described above.

In this way, the pressure sensor of the present invention can accurately detect the temperature of the pressurized fluid and, based on that temperature information, accurately correct errors contained in the output signal of the detection circuit (errors caused by the temperature dependency of the resistance change of each sensor resistor). Furthermore, as described above, because the resistance change of the correction resistor caused by membrane distortion can be removed from the detected value of the provisional output signal, there is no problem even if the correction resistor is formed in the area where distortion occurs in the membrane, which allows for the miniaturization of the pressure sensor and the improvement of temperature measurement accuracy.

The external substrate may be made up of a plurality of external substrates, the external resistor may be made up of a plurality of external resistors, each of the plurality of external substrates may be formed with a respective one of the plurality of external resistors, and the correction resistor and the plurality of external resistors may form a bridge circuit. This configuration makes it possible to obtain the output signal of the correction resistor as a differential output of the bridge circuit, avoiding the effects of bias voltage, noise, etc., and accurately reading resistance changes in the correction resistor caused by distortion of the membrane. Furthermore, by forming each external resistor on each external substrate, the placement of each external resistor can be freely adjusted by appropriately adjusting the installation position of each external substrate, thereby increasing the degree of freedom in the placement of each external resistor.

The external resistor may be composed of multiple external resistors, and the multiple external resistors may be formed on the external substrate, with the correction resistor and the multiple external resistors forming a bridge circuit. Even with this configuration, as described above, the output signal of the correction resistor can be obtained as a differential output of the bridge circuit, making it possible to precisely read resistance changes in the correction resistor caused by membrane distortion while avoiding the effects of bias voltage, noise, etc. Furthermore, because each external resistor is formed on the same substrate, the temperature conditions at each location where each external resistor is placed are similar. Therefore, each external resistor will undergo similar temperature changes, preventing errors from being included in the output signal of the correction resistor due to differences in temperature changes between the external resistors.

Preferably, the external substrate and the membrane are made of materials with similar thermal properties. This configuration makes it possible to achieve similar temperature conditions between the position where the correction resistor is located and the position where the external resistor is located. This means that the correction resistor and the external resistor undergo similar temperature changes, preventing errors caused by differences in the temperature changes of the resistors from being included in the output signal of the correction resistor and enabling highly accurate detection of resistance changes in the correction resistor caused by distortion of the membrane.

Preferably, the device has a disconnecting unit that disconnects the electrical connection between the correction resistor and the external resistor. When measuring the resistance change of the correction resistor due to a temperature change in the pressurized fluid (when measuring the virtual temperature), the electrical connection between the correction resistor and the external resistor is disconnected and the output signal (provisional output signal) of the correction resistor is detected. This avoids interference with the circuit including the external resistor and prevents the provisional output signal from containing errors due to the influence of the external resistor. In other words, as described above, the provisional output signal may contain not only the resistance change of the correction resistor due to a temperature change in the pressurized fluid but also the resistance change of the correction resistor due to distortion of the membrane, but it is possible to prevent errors due to the influence of the external resistor from being further included in this signal.

Preferably, the correction resistor further includes a first conductive path and a second conductive path electrically connectable to one end of the correction resistor, the external resistor being electrically connected to the second conductive path, and the disconnecting unit comprising a switch for switching the electrical connection of the correction resistor between the first conductive path and the second conductive path. By switching the electrical connection of the correction resistor to the first conductive path with the switch, a state in which the correction resistor and the external resistor are electrically disconnected can be established, and a process for measuring the temperature (temporary temperature) of the pressure fluid can be performed based on the output signal (temporary output signal) of the correction resistor. Furthermore, by switching the electrical connection of the correction resistor to the second conductive path with the switch, a state in which the correction resistor and the external resistor are electrically connected can be established, and a process for detecting resistance changes in the correction resistor due to distortion of the membrane can be performed based on the output signal of the correction resistor.

Preferably, the device further includes a substrate portion to which the external substrate is fixed, the external substrate being arranged adjacent to the periphery of the membrane, and the external resistor formed on the external substrate being arranged near the correction resistor formed on the membrane. This configuration makes it possible to make the temperature conditions between the position where the correction resistor is arranged and the position where the external resistor is arranged similar, allowing for highly accurate detection of resistance changes in the correction resistor caused by distortion of the membrane.

FIG. 1 is a schematic cross-sectional view of a pressure sensor according to a first embodiment of the present invention. FIG. 2 is a schematic plan view of the pressure sensor shown in FIG. FIG. 3 is a schematic plan view showing the configurations of the detection circuit, the temperature measurement circuit, and the distortion measurement circuit shown in FIG. FIG. 4A is a circuit diagram showing a circuit configuration when a voltage dividing resistor is electrically connected to one end of the correction resistor shown in FIG. FIG. 4B is a circuit diagram showing a circuit configuration when an external resistor is electrically connected to one end of the correction resistor shown in FIG. FIG. 5A is a diagram showing the relationship between the temperature change of the pressure fluid and the voltage value of the output signal of the correction resistor in the circuit shown in FIG. 4B. FIG. 5B is a diagram showing the relationship between the distortion occurring in the membrane and the voltage value of the output signal of the compensation resistor in the circuit shown in FIG. 4B. 6A is a circuit diagram showing a state in which a voltage dividing resistor is electrically connected to one end of a correction resistor in a circuit configured to be switchable between the circuit shown in FIG. 4A and the circuit shown in FIG. 4B using a switch. FIG. 6B is a circuit diagram showing a state in which an external resistor is electrically connected to one end of the correction resistor in the circuit shown in FIG. 6A. FIG. 7 is a schematic plan view showing the configurations of the detection circuit, temperature measurement circuit, and strain measurement circuit of a pressure sensor according to a second embodiment of the present invention. FIG. 8 is a circuit diagram showing the configuration of a bridge circuit made up of the correction resistor shown in FIG. 7 and a plurality of external resistors. FIG. 9A is a circuit diagram showing a state in which a voltage dividing resistor is electrically connected to one end of the correction resistor. FIG. 9B is a circuit diagram showing a state in which an external resistor is electrically connected to one end of the correction resistor in the circuit shown in FIG. 9A. FIG. 10A is a diagram showing the relationship between the temperature change of the pressure fluid and the voltage value of the output signal of the correction resistor in the circuit shown in FIG. FIG. 10B is a diagram showing the relationship between the distortion occurring in the membrane and the voltage value of the output signal of the correction resistor in the circuit shown in FIG. FIG. 11 is a schematic plan view showing the configurations of the detection circuit, temperature measurement circuit, and strain measurement circuit of a pressure sensor according to a third embodiment of the present invention.

The present invention will now be described based on the embodiments shown in the drawings.

A pressure sensor 10 according to a first embodiment of the present invention is a pressure sensor that utilizes the piezoresistive effect and detects strain due to deformation of a membrane by a change in resistance of a resistor. As shown in Figure 1 , the pressure sensor 10 has a connecting member 12, a holding member 14, a substrate portion 16, an external substrate 18, and a stem 20.

The connecting member 12 is used to secure the pressure sensor 10 to the object to be measured. A thread groove 12a is formed on the outer surface of the connecting member 12. The thread groove 12a has a shape that allows it to be screwed into a thread groove formed in the object to be measured. A flow path 12b is formed inside the connecting member 12 and is used as a flow path for pressure fluid. By securing the pressure sensor 10 to the object to be measured via the thread groove 12a, it is possible to hermetically connect the flow path 12b to the pressure chamber that is the object to be measured.

The retaining member 14 is used to secure the stem 20 to the connecting member 12. The retaining member 14 is placed on the upper surface of the connecting member 12 and has a ring-shaped outer shape. A through-hole is formed in the center of the retaining member 14, allowing the stem 20 to be inserted (placed) inside. A portion of the stem 20 (the flange portion 21, described below) can be secured between the retaining member 14 and the connecting member 12.

The stem 20 has a cylindrical outer shape with a bottom (upper bottom) and is provided at one end of the flow path 12b in the connecting member 12. The stem 20 is made by machining a metal or alloy such as stainless steel. There are no particular restrictions on the material of the stem 20, as long as it generates appropriate elastic deformation.

The stem 20 has a flange portion 21, a membrane 22, and a side wall portion 23. The side wall portion 23 has a cylindrical outer shape. One end of the side wall portion 23 is closed by the membrane 22, while the other end of the side wall portion 23 is open. The flange portion 21 is provided on the opening side of the stem 20 and protrudes radially outward from the opening edge formed at the other end of the side wall portion 23. By fixing the flange portion 21 so that it is sandwiched between the pressing member 14 and the connecting member 12, it is possible to fix the stem 20 to the connecting member 12 with the opening of the stem 20 airtightly connected to one end of the flow path 12b of the connecting member 12.

The membrane 22 is the part through which the pressure to be measured is transmitted, and forms the upper base of the stem 20. The membrane 22 is thinner than other parts of the stem 20 (such as the sidewall 23), and generates deformation (distortion) in response to the pressure transmitted from the flow path 12b (pressure received from the pressurized fluid). The membrane 22 has an inner surface 22a that comes into contact with the pressurized fluid, and an outer surface 22b opposite the inner surface 22a. The outer surface 22b of the membrane 22 is provided with a detection circuit 30, a temperature measurement circuit 41, and electrodes 51-56, which will be described later (see Figure 3).

The substrate portion 16 is fixed to the upper surface of the retaining member 14 and has a ring-shaped outer shape. A through-hole is formed in the center of the substrate portion 16, allowing the stem 20 to be inserted (placed) inside. Electrode portions 57-64 (Figure 2) are formed on the substrate portion 16, and the electrode portions 57-62 of the substrate portion 16 are electrically connected to the electrode portions 51-56 on the membrane 22 via connection wiring 80 formed by wire bonding or the like. The electrode portions 57-64 formed on the substrate portion 16 are electrically connected to, for example, signal lines, power supply lines, or ground.

The external substrate 18 is constructed separately from the substrate portion 16 and is fixed to the upper surface of the substrate portion 16 with fasteners such as screws 82 or adhesive. The strain measurement circuit 42 and electrode portions 65-66 (Figure 2), which will be described later, are provided on the upper surface of the external substrate 18. Examples of materials that can be used to construct the external substrate 18 include stainless steel, copper alloy, aluminum alloy, and steel. The external substrate 18 may also be constructed from the same material as the stem 20.

The thermal properties of the external substrate 18 are preferably similar (substantially identical) to those of the membrane 22. That is, the external substrate 18 is preferably made of a material having similar thermal properties to those of the membrane 22. Examples of thermal properties include, but are not limited to, thermal conductivity, specific heat, coefficient of thermal expansion, latent heat, and melting temperature.

The external substrate 18 is preferably arranged adjacent to the membrane 22 on the outside (periphery) of the membrane 22. As described below, in this embodiment, an external resistor Re is provided on the external substrate 18, and a correction resistor Rc is provided on the membrane 22. The external substrate 18 is arranged close to the membrane 22 (particularly the position on the membrane 22 where the correction resistor Rc is provided) so that the temperature conditions (temperature environment) are similar between the position where the correction resistor Rc is provided and the position where the external resistor Re is provided. For example, the external substrate 18 may be arranged along the outer periphery of the membrane 22.

Furthermore, from the viewpoint of maintaining the same temperature conditions between the position where the correction resistor Rc is disposed and the position where the external resistor is disposed, it is preferable that the position (height) of the surface of the external substrate 18 in the Z-axis direction be approximately equal to the position (height) of the surface of the membrane 22 in the Z-axis direction. From the viewpoint of maintaining the position (height) of the surface of the external substrate 18 in the Z-axis direction be approximately equal to the position (height) of the surface of the membrane 22, it is preferable that the position (height) of the surface of the external substrate 18 in the Z-axis direction be between the position (height) of the inner surface 22a of the membrane 22 and the position (height) of the outer surface 22b of the membrane 22 in the Z-axis direction.

As described above, the membrane 22 is provided with the detection circuit 30, temperature measurement circuit 42, electrodes 51-56, etc. These components will be described below with reference to Figures 2 and 3. As shown in Figure 2, the detection circuit 30 has sensor resistors R1-R4 and is formed in the strain generation area of the membrane 22.

In Figure 3, the upper part shows a schematic cross-sectional view of the stem 20, and the lower part shows a schematic plan view of the stem 20. The strain generation region of the membrane 22 consists of a first strain region 24 that generates strain characteristics in a predetermined direction and a second strain region 26 that generates strain characteristics in the opposite direction to that of the first strain region 24. The first strain region 24 of the membrane 22 receives pressure (positive pressure) from the inner surface 22a and generates a negative strain -ε (compressive strain), while the second strain region 26 of the membrane 22 receives pressure (positive pressure) from the inner surface 22a and generates a positive strain +ε (tensile strain). As such, it is preferable that the strain characteristics in the first strain region 24 and the second strain region 26 are in different directions (different signs that cancel each other out).

The first strain region 24 and the second strain region 26 are each formed concentrically around the center O of the membrane 22. The second strain region 26 is located a predetermined distance radially from the center O of the membrane 22 and is formed in the center of the membrane 22. The first strain region 24 is formed outside (on the outer periphery) of the second strain region 26 and is located a predetermined distance radially from the second strain region 26 of the membrane 22. The outer edge 27 of the membrane 22 is connected to the side wall 23 of the stem 20.

The sensor resistors R1 to R4 that make up the detection circuit 30 are pressure detection elements that generate strain in response to the deformation of the membrane 22, and are configured so that their resistance value changes due to the piezo-resistance effect depending on the amount of strain.

The sensor resistors R1 to R4 are fabricated, for example, by patterning a conductive thin film (such as a semiconductor thin film or a metal thin film) made of a specific material into a meandering shape. The conductive thin film is patterned using microfabrication techniques such as laser processing or screen printing, using semiconductor processing techniques. The conductive thin film is formed on the membrane 22 by a thin-film method such as sputtering or vapor deposition, with an insulating film sandwiched between them. However, if the membrane 22 is made of an insulating material such as alumina and the outer surface 22b of the membrane 22 is insulating, the conductive thin film may be formed directly on the outer surface 22b of the membrane 22 without forming an insulating film. An example of a conductive thin film is a strain-sensitive resistive film containing Cr and Al.

Sensor resistors R1 and R3 are formed in the first strain region 24 and are arranged opposite each other across the center O of the membrane 22. Sensor resistors R2 and R4 are formed in the second strain region 26 and are arranged opposite each other across the center O of the membrane 22. The direction in which sensor resistors R1 and R3 face each other is approximately perpendicular to the direction in which sensor resistors R2 and R4 face each other. The arrangement of sensor resistors R1 to R4 is not limited to the arrangement shown in the figure and may be changed as appropriate.

The detection circuit 30 is formed on the upper surface of the membrane 22, spanning the first strain region 24 and the second strain region 26, and has an outer shape consisting of a circular ring (elliptical ring). The detection circuit 30 is a bridge circuit, and in this embodiment, constitutes a Wheatstone bridge. However, the configuration of the detection circuit 30 is not limited to the configuration shown in the figure, and the detection circuit 30 may constitute other bridge circuits.

In the detection circuit 30, sensor resistors R1 and R2 are connected via connection point 71, sensor resistors R1 and R4 are connected via connection point 72, sensor resistors R3 and R4 are connected via connection point 73, and sensor resistors R2 and R3 are connected via connection point 74. In other words, sensor resistors R1 to R4 are electrically and physically connected to each other via connection points 71 to 74.

Connection point 71 is electrically connected to electrode portion 51, connection point 72 is electrically connected to electrode portion 52, connection point 73 is electrically connected to electrode portion 53, and connection point 74 is electrically connected to electrode portion 54.

The electrodes 51-54 are fabricated, for example, by patterning a conductive thin film (such as a semiconductor thin film or a metal thin film) made of a predetermined material into a predetermined shape using a method similar to that used for the sensor resistors R1-R4. The same applies to the electrodes 55 and 56 described below. Each of the electrodes 51-54 is formed on the outer edge 27 of the membrane 22, but the positions of the electrodes 51-54 are not limited to those shown in the figure and may be formed anywhere between the first strain region 24 and the outer edge 27, for example.

Each of the connection points 71-74 and each of the electrode portions 51-54 are continuously connected by a conductive thin film patterned into the predetermined shape described above. However, each of the connection points 71-74 and each of the electrode portions 51-54 may also be connected by wire bonding, for example.

As shown in FIG. 2, electrode portion 51 is electrically connected to electrode portion 57 formed on substrate portion 16 by wire bonding or the like, electrode portion 52 is electrically connected to electrode portion 58 formed on substrate portion 16 by wire bonding or the like, electrode portion 53 is electrically connected to electrode portion 59 formed on substrate portion 16 by wire bonding or the like, and electrode portion 54 is electrically connected to electrode portion 60 formed on substrate portion 16 by wire bonding or the like. Electrodes 57-60 are fabricated on substrate portion 16, for example, by the same method as electrode portion 51, etc. The same applies to electrodes 61-64, which will be described later.

The electrode unit 58 is electrically connected, for example, to a power supply line, and power (bias voltage) is supplied to the detection circuit 30 from the power supply line via the electrode unit 58 and the electrode unit 52. The electrode unit 60 is electrically connected, for example, to ground.

Electrode unit 57 is connected to, for example, a control unit (not shown) of pressure sensor 10, and the voltage (V+) at connection point 71 is output as a detection signal to the control unit via electrode unit 57 and electrode unit 51. Electrode unit 59 is connected to, for example, a control unit (not shown) of pressure sensor 10, and the voltage (V-) at connection point 73 is output as a detection signal to the control unit via electrode unit 59 and electrode unit 53. The control unit is configured, for example, by an IC such as an MCU, FPGA, or ASIC.

By amplifying the voltage value V+ of the detection signal output from electrode unit 57 (electrode unit 51) and the voltage value V- of the detection signal output from electrode unit 59 (electrode unit 53) using, for example, a differential amplifier with gain A, it is possible to obtain the output voltage V from the detection circuit 30 and detect the fluid pressure acting on the membrane 22 based on the output voltage V.

However, because the resistance change of the sensor resistors R1 to R4 formed in the membrane 22 is temperature dependent, the output signal of the detection circuit 30 (the output voltage V described above) may contain an error due to the temperature dependency of the resistance change of the sensor resistors R1 to R4. In other words, the output signal of the detection circuit 30 may contain an error not only due to the resistance change of the sensor resistors R1 to R4 caused by distortion of the membrane 22, but also due to the resistance change of the sensor resistors R1 to R4 caused by temperature changes in the pressure fluid.

In order to measure the error resulting from the temperature dependency of the resistance change of the sensor resistors R1 to R4 (the resistance change of the sensor resistors R1 to R4 resulting from the temperature change of the pressure fluid) and perform temperature correction on the output signal of the detection circuit 30 based on the measured value, the pressure sensor 10 is provided with a temperature measurement circuit 41, as shown in Figure 3. The configuration of the temperature measurement circuit 41 is described below.

The temperature measurement circuit 41 is formed on the membrane 22 and has a correction resistor Rc. The correction resistor Rc is a resistor for detecting temperature, and changes its resistance value in response to temperature changes in the pressurized fluid, for example. The correction resistor Rc is formed independently of (and not electrically connected to) the detection circuit 30, and is preferably formed on the outer edge 27 of the membrane 22, which is relatively less susceptible to distortion of the membrane 22. This is to prevent the correction resistor Rc from changing its resistance value in response to distortion of the membrane.

However, at least a portion of the correction resistor Rc may be formed in a distortion-generating region of the membrane 22 that is relatively susceptible to distortion of the membrane 22. As will be described later, this embodiment is provided with a circuit (distortion measurement circuit 42) that makes it possible to measure changes in the resistance of the correction resistor Rc caused by distortion of the membrane 22. Therefore, even if the correction resistor Rc is placed in such a position, it is possible to accurately identify changes in the resistance of the correction resistor Rc caused by temperature changes in the pressurized fluid.

For example, at least a portion of the correction resistor Rc may be formed at any position between the first strain region 24 and the outer edge portion 27. Alternatively, a portion of the correction resistor Rc may be formed at any position between the first strain region 24 and the second strain region 26.

The correction resistor Rc is fabricated, for example, by patterning a conductive thin film (such as a semiconductor thin film or a metal thin film) made of a predetermined material into a predetermined shape using the same method as the sensor resistors R1 to R4.

When viewed as a whole, the extension direction of the correction resistor Rc is, for example, approximately aligned with the circumferential direction of the membrane 22 (the correction resistor Rc extends in a meandering pattern along the circumferential direction of the membrane 22). However, the extension direction of the correction resistor Rc is not limited to this, and the correction resistor Rc may, for example, extend radially along the radial direction of the membrane 22.

As shown in FIG. 2, one end of the correction resistor Rc is electrically and physically connected to an electrode portion 55 formed on the membrane 22, and the other end of the correction resistor Rc is electrically and physically connected to an electrode portion 56 formed on the membrane 22. The electrode portion 56 is electrically connected to an electrode portion 62 formed on the substrate portion 16 by wire bonding or the like, and is electrically connected to, for example, ground.

The electrode portion 55 is electrically connected to an electrode portion 61 formed on the substrate portion 16 by wire bonding or the like. The electrode portion 61 is electrically connected to, for example, a control portion (not shown) of the pressure sensor 10, and the voltage (Vo) at the connection point 75 can be output to the control portion via the electrode portion 61 as an output signal of the correction resistor Rc (a signal indicating the resistance change of the correction resistor Rc).

The connection point 75 can be electrically connected to a power supply line (not shown) via a first conductive path 75a. A voltage-dividing resistor Rt (see FIG. 6A) is inserted between the power supply line and the connection point 75, and a bias voltage Vdd1 (FIG. 3) is supplied to the temperature measurement circuit 41 (correction resistor Rc). The voltage-dividing resistor Rt may be provided in a control unit such as an ASIC.

The connection point 75 can be electrically connected to the external resistor Re via the second conductive path 75b. Electrode portions 63 and 65 are provided between the external resistor Re and the connection point 75.

It is preferable that a disconnecting unit be provided at the connection point 75 to disconnect the electrical connection between one end of the correction resistor Rc and the external resistor Re. For example, as shown in Figures 6A and 6B, a switch 83 may be provided as a disconnecting unit at the connection point 75. In this case, the switch 83 can switch the electrical connection of one end of the correction resistor Rc to either the first conductive path 75a or the second conductive path 75b. Note that the switching of the switch 83 is controlled by, for example, a control unit (not shown) of the pressure sensor 10.

As described above, when performing temperature compensation on the output signal of the detection circuit 30, the output signal of the correction resistor Rc is output to the control unit via the electrode unit 61 (Figure 2). At this time, the electrical connection between one end of the correction resistor Rc and the external resistor Re is disconnected, and as shown in Figure 6A, one end of the correction resistor Rc is electrically connected to the voltage-dividing resistor Rt. The output signal of the correction resistor Rc is then detected by the control unit. This avoids interference with the external resistor Re (distortion measurement circuit 42) and prevents errors due to the influence of the external resistor Re from being included in the output signal of the correction resistor Rc.

It is also possible to physically and electrically connect the first conductive path 75a and the second conductive path 75b at the connection point 75 without installing the release unit described above at the connection point 75. In this case, however, it is preferable to provide a means for preventing interference between the circuit on the first conductive path 75a side and the circuit on the second conductive path 75b side.

When one end of the correction resistor Rc is electrically connected to the first conductive path 75a of the first conductive path 75a and the second conductive path 75b, the correction resistor Rc and the voltage-dividing resistor Rt are electrically connected, forming the circuit shown in FIG. 4A or 6A. In this circuit, the output voltage Vo at connection point 76 (corresponding to electrode 61 shown in FIG. 2) is equal to the voltage at connection point 75 shown in FIG. 3 and is obtained, for example, via electrode 61 shown in FIG. 2. The output voltage Vo is the value obtained by dividing the bias voltage Vdd1 supplied via the first conductive path 75a by the voltage-dividing resistor Rt and the correction resistor Rc.

When one end of the correction resistor Rc is electrically connected to the first conductive path 75a, the output signal (output voltage Vo of the electrode portion 61) of the correction resistor Rc is detected via the electrode portion 61 (Figure 2). This detection value can then be used to measure the resistance change (temperature of the pressure fluid) of the sensor resistors R1 to R4 caused by temperature changes in the pressure fluid. Therefore, temperature compensation can be performed on the output signal of the detection circuit 30 based on this measurement value. In this way, measuring the resistance change (temperature of the pressure fluid) of the sensor resistors R1 to R4 caused by temperature changes in the pressure fluid based on the detection value of the output signal of the correction resistor Rc is referred to as the "temperature measurement mode."

As shown in FIG. 2, the correction resistor Rc is formed on the membrane 22. Therefore, resistance changes of the correction resistor Rc are affected to some extent by distortion of the membrane 22. That is, when the membrane 22 is subjected to pressure from the pressure fluid and generates distortion, the resistance value of the correction resistor Rc changes due to the distortion. Therefore, the output signal of the correction resistor Rc detected in the temperature measurement mode (output voltage Vo shown in FIG. 4A or 6A) may contain an error not only due to resistance changes caused by temperature changes in the pressure fluid, but also due to resistance changes caused by distortion of the membrane 22. Therefore, the output signal of the correction resistor Rc detected in the temperature measurement mode may not accurately reflect the resistance changes of the sensor resistors R1 to R4 caused by temperature changes in the pressure fluid (temperature of the pressure fluid). Therefore, even if temperature correction is performed on the output signal of the detection circuit 30 based on this output signal, the accuracy of the temperature correction may not be guaranteed.

In order to accurately determine the resistance change of the correction resistor Rc due to temperature changes of the pressure fluid (pressure fluid temperature), it is necessary to measure the resistance change of the correction resistor Rc due to distortion of the membrane 22 and remove the resistance change of the correction resistor Rc due to distortion of the membrane 22 from the output signal of the correction resistor Rc detected in temperature measurement mode. Therefore, in this embodiment, a distortion measurement circuit 42 is provided in the pressure sensor 10 to measure the resistance change of the correction resistor Rc due to distortion of the membrane 22. The configuration of the distortion measurement circuit 42 is described below.

The distortion measurement circuit 42 is formed on the external substrate 18 and has an external resistor Re. The external resistor Re is fabricated, for example, by patterning a conductive thin film (such as a semiconductor thin film or a metal thin film) made of a predetermined material into a predetermined shape using a method similar to that used for the correction resistor Rc. Unlike the correction resistor Rc, the external resistor Re is not formed on the membrane 22 and is therefore not affected by distortion. Therefore, the external resistor Re does not substantially undergo resistance changes due to distortion, but only changes in resistance due to temperature.

One end of the external resistor Re is electrically and physically connected to an electrode portion 65 formed on the external substrate 18. The electrode portion 65 is electrically connected to an electrode portion 63 formed on the substrate portion 16 by wire bonding or the like. The electrode portion 63 is electrically connected to the second conductive path 75b. For example, as shown in FIG. 6B , the switch 83 switches the electrical connection destination of one end of the correction resistor Rc to the second conductive path 75b, thereby electrically connecting the external resistor Re to one end of the correction resistor Rc.

As shown in FIG. 2, the other end of the external resistor Re is electrically and physically connected to an electrode portion 66 formed on the external substrate 18. The electrode portion 66 is electrically connected to an electrode portion 64 formed on the substrate portion 16 by wire bonding or the like. The electrode portion 66 is electrically connected to, for example, a power supply line, and a bias voltage Vdd2 (FIG. 3) is supplied to the distortion measurement circuit 42 from the power supply line via the electrode portion 64 and the electrode portion 66.

When one end of the correction resistor Rc is electrically connected to the second conductive path 75b of the first conductive path 75a and the second conductive path 75b, the correction resistor Rc and the external resistor Re are electrically connected, forming the circuit shown in FIG. 4B or 6B. In the circuit shown in FIG. 6B, the electrical connection of one end of the correction resistor Rc can be switched from the first conductive path 75a to the second conductive path 75b by the switch 83.

In this circuit, the output voltage Vo at connection point 76 (corresponding to electrode unit 61 shown in Figure 2) is equal to the voltage at connection point 75 shown in Figure 3 and is obtained, for example, via electrode unit 61 shown in Figure 2. The output voltage Vo is the value obtained by dividing the bias voltage Vdd2 supplied via the second conductive path 75b between the external resistor Re and the correction resistor Rc, and is expressed by the following equation (1):

If a temperature change ΔT occurs in the correction resistor Rc and a temperature change ΔT occurs in the external resistor Re due to a temperature change in the pressurized fluid, the output voltage Vo' of the correction resistor Rc after the temperature change is expressed by the following equation (2). In equation (2), the temperature resistance coefficients of the correction resistor Rc and the external resistor Re are defined as TCR.

As shown in equation (2), when the temperature of the correction resistor Rc changes by ΔT, the resistance of the correction resistor Rc changes by ΔRc (ΔRc = Rc * TCR * ΔT). Similarly, when the temperature of the external resistor Re changes by ΔT, the resistance of the external resistor Re changes by ΔRe (ΔRe = Re * TCR * ΔT). However, when resistance changes ΔRc and ΔRe occur in both the correction resistor Rc and the external resistor Re, as shown in equation (2), the resistance change rate of the correction resistor Rc (1 + TCR * ΔT) is equal to the resistance change rate of the combined resistor consisting of the correction resistor Rc and the external resistor Re (1 + TCR * ΔT). Therefore, these changes cancel each other out, and the output voltage Vo' after the temperature change is expressed by the same equation as the output voltage Vo before the temperature change. In other words, as shown in Figure 5A, the output voltage Vo does not change with temperature changes and always remains constant.

On the other hand, if distortion ε occurs in the correction resistor Rc due to distortion of the membrane 22, the output voltage Vo' of the correction resistor Rc after the distortion occurs is expressed by the following equation (3). In equation (3), the sensitivity of the correction resistor Rc is k.

As shown in equation (3), when the strain applied to the correction resistor Rc changes by ε, the resistance of the correction resistor Rc changes by ΔRc (ΔRc = k ε Rc). As is clear from equation (3), the output voltage Vo' is a function in which the magnitude of the strain ε is a variable. Therefore, as shown in Figure 5B, the output voltage Vo' changes by an amount corresponding to the magnitude of ε.

In other words, when the correction resistor Rc and the external resistor Re are electrically connected (when the circuit shown in Figure 4B is formed), changes in the resistance of the correction resistor Rc due to temperature changes in the pressure fluid do not appear as changes in the output voltage Vo (see Figure 5A), and changes in the output voltage Vo of the correction resistor Rc always represent changes in the resistance of the correction resistor Rc due to distortion of the membrane 22. Therefore, by detecting the output voltage Vo, it is possible to measure changes in the resistance of the correction resistor Rc due to distortion of the membrane 22. In this way, measuring changes in the resistance of the correction resistor Rc due to distortion of the membrane 22 based on the detected value of the output signal of the correction resistor Rc is called the "strain measurement mode."

As described above, the output signal of the correction resistor Rc detected in the temperature measurement mode may include resistance changes of the correction resistor Rc due to distortion of the membrane 22, in addition to resistance changes of the correction resistor Rc due to temperature changes of the pressurized fluid. In contrast, the output signal of the correction resistor Rc detected in the strain measurement mode theoretically includes only resistance changes of the correction resistor Rc due to distortion of the membrane 22. Therefore, by taking the difference between the detected value of the output signal of the correction resistor Rc detected in the temperature measurement mode and the detected value of the output signal of the correction resistor Rc detected in the strain measurement mode, the resistance changes (errors) due to distortion of the membrane 22 can be removed from the detected value of the former output signal.

This allows accurate identification of only the resistance change of the correction resistor Rc due to temperature changes in the pressure fluid from the output signal of the correction resistor Rc detected in temperature measurement mode (i.e., identification of the true temperature of the pressure fluid), and accurate temperature correction can be performed on the output signal of the detection circuit 30.

Here, for formula (2) to hold, the resistance change rate of the correction resistor Rc (1 + TCR ΔT) and the resistance change rate of the combined resistor consisting of the correction resistor Rc and the external resistor Re (1 + TCR ΔT) must be substantially equal; in other words, the TCR of the correction resistor Rc and the TCR of the external resistor Re must be substantially equal, and the temperature change ΔT of the correction resistor Rc and the temperature change ΔT of the external resistor Re must be substantially equal.

Therefore, in order for the above assumptions to hold true, it is preferable that the material making up the external resistor Re be the same as the material making up the correction resistor Rc, or a material with similar temperature characteristics (temperature coefficient of resistance, etc.). For example, it is preferable that the difference between the TCR of the external resistor Re and the TCR of the correction resistor Rc be ±100 ppm or less.

Furthermore, as shown in FIG. 2, the external resistor Re formed on the external substrate 18 is preferably positioned near the correction resistor Rc formed on the membrane 22. In this case, it is possible to make the temperature conditions between the position where the external resistor Re is positioned and the position where the correction resistor Rc is positioned similar. Therefore, the temperature change ΔT of the correction resistor Rc and the temperature change ΔT of the external resistor Re are approximately equal, and the resistance change of the correction resistor Rc caused by distortion of the membrane 22 can be detected with high accuracy.

Furthermore, by forming the external substrate 18 and the membrane 22 from materials with similar thermal properties, it is possible to achieve similar temperature conditions between the position where the external resistor Re is located and the position where the correction resistor Rc is located. Therefore, the external resistor Re and the correction resistor Rc undergo similar temperature changes, preventing errors caused by differences in the temperature changes of the correction resistor Rc from being included in the output signal. This enables highly accurate detection of resistance changes in the correction resistor Rc caused by distortion of the membrane 22.

As explained above, the pressure sensor 10 according to this embodiment is capable of detecting the temperature of the pressurized fluid with high accuracy, and can accurately correct errors contained in the output signal of the detection circuit 30 (errors resulting from the temperature dependency of the resistance changes of the sensor resistors R1 to R4) based on that temperature information. Furthermore, because the resistance change of the correction resistor Rc resulting from distortion of the membrane 22 can be removed from the detected value of the output signal detected in temperature measurement mode, there is no problem even if the correction resistor Rc is formed in the region where distortion occurs in the membrane 22, which allows for the pressure sensor 10 to be made more compact and for temperature measurement to be more accurately performed.

Second Embodiment Next, the configuration of a pressure sensor 10A according to a second embodiment of the present invention will be described. In the drawings, components common to the pressure sensor 10 of the first embodiment are designated by common reference numerals, and descriptions thereof will be omitted.

As shown in FIG. 7, the pressure sensor 10A has three external substrates 18_1 to 18_3 and three external resistors Re1 to Re3. External resistor Re1 is formed on external substrate 18_1, external resistor Re2 is formed on external substrate 18_2, and external resistor Re3 is formed on external substrate 18_3.

The three external substrates 18_1 to 18_3 are each constructed separately and are arranged at a predetermined distance from one another. It is preferable that the external substrates 18_1 to 18_3 be arranged close to one another, so that the temperature conditions (temperature environment) of the external resistors Re1 to Re3 formed on each substrate are similar.

The three external substrates 18_1 to 18_3 are preferably arranged close to the membrane 22 (particularly the position on the membrane 22 where the compensation resistor Rc is provided) so that the temperature conditions are similar between the position where the compensation resistor Rc is located and the positions where the external resistors Re1 to Re3 are located. For example, the external substrates 18_1 to 18_3 may be arranged along the outer periphery of the membrane 22.

From the viewpoint of similar thermal properties, it is preferable that external substrates 18_1 to 18_3 are each composed of substrates made of materials with similar thermal properties. Also, from the viewpoint of similar thermal properties, it is preferable that external substrates 18_1 to 18_3 are each composed of substrates with the same shape, size, or height. Furthermore, it is preferable that the surface positions (heights) of external substrates 18_1 to 18_3 are approximately equal to each other, and preferably approximately equal to the surface position (height) of membrane 22. In other words, it is preferable that the Z-axis position of the surface of external substrates 18_1 to 18_3 is between the Z-axis position of the inner surface 22a of membrane 22 (Figure 1) and the Z-axis position of the outer surface 22b of membrane 22.

The external resistors Re1 to Re3 may be resistors similar to the external resistor Re in the first embodiment. Alternatively, the external resistors Re1 to Re3 may be resistors having a different shape, size, or resistance value from the external resistor Re in the first embodiment. Furthermore, the external resistors Re1 to Re3 may each have the same shape, size, or resistance value. Alternatively, at least one of the external resistors Re1 to Re3 may be a resistor having a different shape, size, or resistance value from the other resistors.

The materials that make up the external resistors Re1 to Re3 are preferably the same material or materials with similar temperature characteristics, so that their temperature characteristics are similar. In this case, when the temperature environment of the external resistors Re1 to Re3 changes in response to a change in the temperature of the pressurized fluid, for example, it is possible to cause a similar temperature change ΔT to occur in each of the external resistors Re1 to Re3.

The external resistors Re1 to Re3 are electrically connected via electrodes formed on the external substrates 18_1 to 18_3 and the substrate portion 16 (Figure 2) by wire bonding or wiring on the substrate portion 16.

More specifically, electrode 65 electrically connected to one end of external resistor Re1 is electrically connected to connection point 75, and electrode 66 electrically connected to the other end of external resistor Re1 is electrically connected to electrode 68 electrically connected to the other end of external resistor Re2. Electrode 67 electrically connected to one end of external resistor Re2 is electrically connected to electrode 70 electrically connected to the other end of external resistor Re3. Electrode 69 electrically connected to one end of external resistor Re3 is electrically connected to connection point 79. Connection point 79 is electrically connected to electrode 56 formed at the other end of correction resistor Rc.

A connection point 77 electrically connected to the electrode portion 66 and the electrode portion 68 is electrically connected to a power supply line, and a connection point 79 electrically connected to the electrode portion 56 and the electrode portion 69 is electrically connected to ground. A connection point 76 electrically connected to the electrode portion 65 and the electrode portion 55 is connected to a control unit (not shown) of the pressure sensor 10, and a voltage V ₊ (an intermediate potential between the external resistor Re1 and the correction resistor Rc connected in series) at the connection point 76 is output to the control unit as a detection signal. A connection point 78 electrically connected to the electrode portion 67 and the electrode portion 70 is connected to a control unit (not shown) of the pressure sensor 10, and a voltage _V- (an intermediate potential between the external resistor Re2 and the external resistor Re3 connected in series) at the connection point 78 is output to the control unit as a detection signal.

As shown in FIG. 8, the correction resistor Rc and the multiple external resistors Re1 to Re3 form a bridge circuit, and in the distortion measurement mode, the differential output between the voltage V ₊ at the connection point 76 and the voltage _V- at the connection point 78 becomes the output voltage Vo2 (Vo2 = V ₊ - _V- ) of the output signal of the correction resistor Rc.

As shown in Figures 9A and 9B, a switch 83 (release unit) may be provided at the position of the connection point 75. As shown in Figure 9A, when the switch 83 is electrically connected to the first conductive path 75a, the temperature measurement mode is activated, a series circuit consisting of the voltage dividing resistor Rt and the correction resistor Rc is formed, and the output voltage Vo1 at the connection point 76 is output to the control unit (not shown) of the pressure sensor 10 as an output signal of the correction resistor Rc. The detected value of the output voltage Vo1 mainly indicates the resistance change of the correction resistor Rc due to temperature changes of the pressurized fluid (the output voltage Vo1 also includes the resistance change of the correction resistor Rc due to distortion of the membrane 22).

As shown in FIG. 9B , when switch 83 is electrically connected to second conductive path 75b, the strain measurement mode is activated. A bridge circuit is formed consisting of correction resistor Rc and external resistors Re1 to Re3. Output voltage V ₊ at node 76 and output voltage _V− at node 78 are output as output signals from correction resistor Rc (bridge circuit) to a control unit (not shown) of pressure sensor 10. The control unit calculates the difference between output voltages V ₊ and _V− as an output voltage (differential output) Vo2. The detected value of output voltage Vo2 indicates the change in resistance of correction resistor Rc due to distortion of membrane 22. As shown in FIG. 10B , the detected value of output voltage Vo2 is a function of the magnitude of distortion ε. As shown in FIG. 10A , output voltage Vo2 remains constant regardless of temperature changes (ΔT).

Therefore, by subtracting the detected value of the output signal detected in the strain measurement mode (output voltage Vo2) from the detected value of the output signal detected in the temperature measurement mode (output voltage Vo1), it is possible to remove the resistance change of the correction resistor Rc caused by the distortion of the membrane 22 from the detected value of the output signal detected in the temperature measurement mode. This not only enables accurate temperature detection of the pressurized fluid, but also enables accurate correction of errors contained in the output signal of the detection circuit 30 (errors caused by the temperature dependency of the resistance change of each of the sensor resistors R1 to R4) based on that temperature information.

In this way, the same effects as in the first embodiment can be obtained in this embodiment. Furthermore, because the output signal of the correction resistor Rc can be obtained as a differential output of the bridge circuit, it is possible to remove the bias voltage from the output signal (output voltage), as shown in Figure 10B, and it is possible to precisely read the resistance change of the correction resistor Rc caused by distortion of the membrane 22. Furthermore, the effects of noise superimposed on the output signal of the correction resistor Rc can be mitigated.

In addition, in this embodiment, by forming external resistors Re1 to Re3 on the external substrates 18_1 to 18_3, respectively, the placement of the external resistors Re1 to Re3 can be freely adjusted by appropriately adjusting the installation positions of the external substrates 18_1 to 18_3, thereby increasing the degree of freedom in the placement of the external resistors Re1 to Re3.

Third Embodiment Next, the configuration of a pressure sensor 10B according to a third embodiment of the present invention will be described. In the drawings, components common to the pressure sensor 10A of the second embodiment are designated by the same reference numerals, and descriptions thereof will be omitted.

As shown in FIG. 11, pressure sensor 10B in this embodiment differs from pressure sensor 10A in the second embodiment in that all of external resistors Re1 to Re3 are formed on a single external substrate 18. External resistors Re1 to Re3 may be formed on external substrate 18 in the arrangement shown in the figure. Alternatively, they may be formed on external substrate 18 so as to be arranged in a line. Although not shown in detail, a release unit such as switch 83 (FIGS. 9A and 9B) may be provided at connection point 75.

This embodiment also achieves the same effects as the second embodiment. In addition, in this embodiment, because the external resistors Re1 to Re3 are formed on the same substrate, the temperature conditions at each position where the external resistors Re1 to Re3 are placed are similar. Therefore, the external resistors Re1 to Re3 each undergo similar temperature changes, preventing errors caused by differences in the temperature changes of the external resistors Re1 to Re3 from being included in the output signal of the correction resistor Rc.

Note that the present invention is not limited to the above-described embodiments and can be modified in various ways within the scope of the present invention.

In each of the above embodiments, the voltage dividing resistor Rt shown in Figure 4A is not essential and may be omitted. In this case, in temperature measurement mode, one end of the correction resistor Rc may be connected to a current source, and a current may be supplied to the correction resistor Rc via the current source to obtain the output signal of the correction resistor Rc.

In the first embodiment described above, the position of the external substrate 18 is not limited to the position shown in FIG. 1 and may be changed as appropriate. For example, the external substrate 18 may be positioned adjacent to the membrane 22.

In the second embodiment described above, the number of external substrates may be two. In this case, one of the external resistors Re1 to Re3 may be formed on one external substrate, and the remaining two external resistors may be formed on the other external substrate.

DESCRIPTION OF SYMBOLS 10, 10A, 10B...Pressure sensor 12...Connecting member 12a...Thread groove 12b...Flow path 14...Retaining member 16...Substrate portion 18, 18_1 to 18_3...External substrate 20...Stem 21...Flange portion 22...Membrane 22a...Inner surface 22b...Outer surface 23...Side wall portion 24...First strain area 26...Second strain area 30...Detection circuit 41...Temperature measurement circuit 42...Strain measurement circuit 51 to 70...Electrode portion 71 to 79...Connection point 80...Connection wiring 82...Screw R1 to R4...Sensor resistor Rc...Compensation resistor Re, Re1 to Re3...External resistor

Claims (4)

a membrane that deforms in response to pressure;
a plurality of sensor resistors formed on the membrane and constituting a detection circuit;
a compensation resistor formed on the membrane for detecting temperature;
an external resistor formed on an external substrate different from the membrane and electrically connectable to one end of the compensation resistor;
the external substrate is made up of a plurality of the external substrates,
the external resistor comprises a plurality of external resistors,
a plurality of external resistors are formed on each of the plurality of external substrates,
The compensation resistor and the plurality of external resistors form a bridge circuit. a membrane that deforms in response to pressure;
a plurality of sensor resistors formed on the membrane and constituting a detection circuit;
a compensation resistor formed on the membrane for detecting temperature;
an external resistor formed on an external substrate different from the membrane and electrically connectable to one end of the compensation resistor;
A pressure sensor in which the external substrate and the membrane are formed from materials having similar thermal properties. a membrane that deforms in response to pressure;
a plurality of sensor resistors formed on the membrane and constituting a detection circuit;
a compensation resistor formed on the membrane for detecting temperature;
an external resistor formed on an external substrate different from the membrane and electrically connectable to one end of the compensation resistor;
a disconnecting portion that disconnects the electrical connection between the compensation resistor and the external resistor. a first conductive path and a second conductive path electrically connectable to one end of the compensation resistor;
the external resistor is electrically connected to the second conductive path,
4. The pressure sensor according to claim 3 , wherein the canceling unit is a switch that switches the electrical connection of the correction resistor between the first conductive path and the second conductive path.