Patent Description:
There is a known pressure sensor utilizing the piezoresistive effect to detect a strain of a membrane (also referred to as a diaphragm) by resistance change. In such a pressure sensor, a strain due to a deformation of the membrane is detected by a resistance change of a resistor disposed on the membrane.

In recent years, it has been required to reduce the power consumption of the pressure sensor. For example, a technique of intermittently supplying power to the bridge circuit included in the pressure sensor by pulse driving is proposed (see Patent Document <NUM>). Further pressure sensors are known from Patent Documents <NUM> to <NUM>.

However, the pressure sensor that intermittently supplies power has a problem that it cannot detect a momentary pressure abnormality that occurs when the power supply is turned off.

The present invention provides a pressure sensor capable of reducing power consumption and preventing omission of detection of pressure change.

To solve the above object, a pressure sensor according to the present invention comprises:.

Since the pressure sensor according to the present invention includes a second circuit capable of detecting strain independently from a bridge circuit configured to detect pressure change, the second circuit can detect strain generated in the membrane even if no electric power is supplied to the first circuit. Since the fifth circuit included in the second circuit is disposed at the first strain position or the second strain position where the first to fourth resistors of the first circuit are arranged or a position where a strain characteristic in the same direction as them occurs in the membrane, the pressure sensor can precisely detect the generation of pressure change to be detected. Thus, the pressure sensor according to the present invention can reduce electric power supply to the first circuit and achieve low electric power consumption while preventing the detection omission of pressure change by the second circuit.

The pressure sensor according to the present invention comprises a switching unit for switching electric power supply to the first circuit using a detection signal from the second circuit.

Such a pressure sensor can achieve low electric power consumption by stopping electric power supply to the first circuit while the second circuit is not detecting signal. For example, the detection omission of pressure change can be prevented by restarting electric power supply to the first circuit triggered by the detection of signal by the second circuit.

For example, the fifth resistor may be at least partly disposed at the first strain position located on the outer peripheral side of the second strain position on the membrane.

Since the first strain position is located on the outer peripheral side of the second strain position, the space for being able to dispose the fifth resistor at the first strain position is larger than that at the second strain position. Thus, such a pressure sensor can use the fifth resistor having a comparatively large size and a high resistance value for the second circuit and can effectively reduce electric power consumption in the second circuit.

For example, the fifth resistor may include a plurality of thin film resistors made of thin films, and the second circuit may include a connection portion for connecting the thin film resistors in series.

When the second circuit includes the fifth resistor made of a plurality of thin film resistors and a connection portion for connecting the thin film resistors in series, it is possible to increase the resistance value of the fifth resistor and effectively reduce the electric power consumption in the second circuit. The pressure sensor using the thin film resistors can be manufactured by effectively forming a plurality of thin film resistors having different resistance values on the membrane and is productive.

For example, the fifth resistor may include a first thin film resistor made of a thin film disposed at the first strain position located on the outer peripheral side of the second strain position on the membrane and a second thin film resistor made of a thin film disposed in a third strain region where a strain having a different size from the first strain position but in the same direction occurs on the membrane, and the second circuit may include a connection portion for connecting the first thin film resistor and the second thin film resistor in series.

In such a pressure sensor, the fifth resistor is disposed using not only the first strain position but also a third strain position where a strain having a different size from the first strain position but in the same direction occurs, and it is thereby possible to increase the resistance value of the fifth resistor and more effectively reduce the electric power consumption in the second circuit.

A resistance value of the fifth resistor may be higher than that of any of the first to fourth resistors in a state where the membrane is not deformed.

When such a fifth resistor is included, the electric power consumption in the second circuit can be reduced effectively.

Hereinafter, the present invention is described based on the embodiments shown in the figures.

<FIG> is a schematic cross-sectional view of a pressure sensor <NUM> according to the present invention. The pressure sensor <NUM> includes a membrane <NUM> configured to produce deformation corresponding to pressure. In the embodiment shown in <FIG>, an upper bottom of a stem <NUM> is the membrane <NUM>. In addition to the stem <NUM> including the membrane <NUM>, the pressure sensor <NUM> includes a connection member <NUM> provided with a passage 12b for transmitting pressure to the stem <NUM>, a holding member <NUM> for fixing the stem <NUM> to the connection member <NUM>, and a substrate portion <NUM> wired to an electrode portion on the membrane <NUM>, and the like.

As shown in <FIG>, a screw groove 12a for fixing the pressure sensor <NUM> to a measurement target is formed on the outer periphery of the connection member <NUM>. Since the pressure sensor <NUM> is fixed by the screw groove 12a, the passage 12b formed inside the connection member <NUM> airtightly communicates with a pressure chamber as the measurement target.

As shown in <FIG>, the stem <NUM> has a bottomed (upper bottom) tubular outer shape and is disposed at one end of the passage 12b of the connection member <NUM>. The stem <NUM> is provided with a flange portion <NUM> on the opening side and is fixed to the connection member <NUM> by sandwiching the flange portion <NUM> between the holding member <NUM> and the connection member <NUM>. The opening of the stem <NUM> and the passage 12b of the connection member <NUM> are airtightly connected using the holding member <NUM>, and the pressure to be measured is transmitted to the membrane <NUM> of the stem <NUM>.

The membrane <NUM>, which is the upper bottom of the stem <NUM>, is thinner than other parts of the stem <NUM>, such as the side wall, and is deformed corresponding to the pressure transmitted from the passage 12b. The membrane <NUM> includes an inner surface 22a configured to contact with a pressure fluid and an outer surface 22b opposite to the inner surface 22a. A first circuit <NUM> and a second circuit <NUM> mentioned below (see <FIG>), the electrode portion, and the like are provided on the outer surface 22b side of the membrane <NUM>.

The substrate portion <NUM> having a wiring, an electrode portion, and the like electrically connected to the first circuit <NUM> and the second circuit <NUM> formed on the outer surface 22b of the membrane <NUM> is fixed to the holding member <NUM>. The electrode portion of the substrate portion <NUM> and the electrode portion on the membrane <NUM> are electrically connected via a connection wiring <NUM> or the like formed by wire bonding or the like. The substrate portion <NUM> has a ring outer shape. The stem <NUM> is inserted in a through hole formed at the center of the substrate portion <NUM>.

<FIG> is a conceptual diagram illustrating an arrangement of resistors and the electrode portions in the pressure sensor <NUM> according to First Embodiment. The upper part of <FIG> is a schematic cross-sectional view of the stem <NUM>, and the lower part of <FIG> is a schematic plan view of the stem <NUM> viewed from the upper side, which is the outer surface 22b side of the membrane <NUM>.

As shown in <FIG>, the pressure sensor <NUM> includes the first circuit <NUM> configured to form a bridge circuit and detect strain and the second circuit <NUM> capable of detecting strain independently from the first circuit <NUM>. The first circuit <NUM> and the second circuit <NUM> are formed on the outer surface 22b of the membrane <NUM>.

As shown in the schematic plan view of the lower part of <FIG>, the first circuit <NUM> includes a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4. The resistors R1-R4 are separately arranged on a first circumference <NUM>, which is a first strain position that produces a predetermined strain characteristic responding to the pressure applied to the inner surface 22a of the membrane <NUM>, and a second circumference <NUM>, which is a second strain position that produces a strain characteristic in a direction different from that at the first strain position.

As shown in <FIG>, the first circumference <NUM> is a circumference of a circle having a radius larger than that of the second circumference <NUM> and is located on the outer peripheral side of the second circumference <NUM> in the membrane <NUM>. For example, when the membrane <NUM> receives a predetermined positive pressure from the inner surface 22a, a negative strain - ε (compressive strain) is generated on the first circumference <NUM>, but a positive strain + ε (tensile strain) is generated on the second circumference <NUM>. Preferably, the strain characteristic on the first circumference <NUM> (the first strain position) and the strain characteristic on the second circumference <NUM> (the second strain position) are in mutually different directions (relation in which the symbols are different and cancel each other out).

Among the first to fourth resistors R1-R4 included in the first circuit <NUM>, the first resistor R1 and the third resistor R3 are arranged on the first circumference <NUM>. On the other hand, among the first to fourth resistors R1-R4 included in the first circuit <NUM>, the second resistor R2 and the fourth resistor R4 are arranged on the second circumference <NUM>.

<FIG> is a conceptual diagram illustrating an example of a circuit formed by using the pressure sensor <NUM>. As shown in <FIG>, the first to fourth resistors R1-R4 included in the first circuit <NUM> form a bridge circuit. An output signal S1 of the first circuit <NUM> is input to a pressure signal input unit <NUM> of a microprocessor <NUM> via an amplifier <NUM>. As shown in <FIG>, first electrode portions <NUM>-<NUM> for supplying electric power to the first circuit <NUM> or transmitting the output signal S1 of the first circuit <NUM> are formed on the membrane <NUM>. The first circuit <NUM> is electrically connected to the substrate portion <NUM> via the first electrode portions <NUM>-<NUM> and a connection wiring <NUM> (see <FIG>).

As shown in the schematic plan view of the lower part of <FIG>, the second circuit <NUM> includes a fifth resistor R5 disposed on the first circumference <NUM>, which is the first strain position. The fifth resistor R5 of the second circuit <NUM> may be disposed on the second circumference <NUM>, but is preferably disposed on the first circumference <NUM> located on the outer peripheral side of the second circumference <NUM> from the viewpoint of increasing the resistance value of the fifth resistor R5. This is because the space for being able to dispose the fifth resistor R5 is larger on the first circumference <NUM>. In particular, when the fifth resistor R5 is a thin film resistor made of a thin film (described below), the resistance value of the fifth resistor R5 can be larger as the disposition space is larger. The fifth resistor R5 partly or entirely produces a strain characteristic in the same direction as the first circumference <NUM>, but may be disposed at a position where a strain having a size different from that of the first circumference <NUM> occurs.

As shown in <FIG>, the fifth resistor R5 includes a plurality of first thin film resistors R51 made of thin films arranged on the first circumference <NUM>. The second circuit <NUM> includes connection portions <NUM> for connecting the first thin film resistors R51 to each other, and the first thin film resistors R51 are connected in series by the connection portions <NUM> to form the fifth resistor R5.

The second circuit <NUM> is not connected to the first circuit <NUM> at least on the membrane <NUM> and can detect strain independently from the first circuit <NUM>. As shown in <FIG>, second electrode portions <NUM> and <NUM> for supplying electric power to the second circuit <NUM> and transmitting a detection signal S2 of the second circuit <NUM> are formed on the membrane <NUM>.

As shown in <FIG>, the detection signal S2 from the second circuit <NUM> including the fifth resistor R5 is input to a detection signal input unit <NUM> of the microprocessor <NUM>. As shown in <FIG>, the pressure sensor <NUM> includes a switching unit <NUM> for switching electric power supply to the first circuit <NUM>. The microprocessor <NUM>, the switching unit <NUM>, and the amplifier <NUM> shown in <FIG> can be arranged, for example, on the substrate portion <NUM>, but their arrangement locations are not particularly limited.

The switching unit <NUM> includes a switch disposed on the substrate portion <NUM> (see <FIG>). When the switch is turned on, electric power is supplied to the first circuit <NUM>. When the switch is turned off, electric power supply to the first circuit <NUM> is stopped. ON/OFF of the switching unit <NUM> is controlled by a switch control unit <NUM> of the microprocessor <NUM>.

The switch control unit <NUM> controls the switching unit <NUM> by using the detection signal S2 from the second circuit <NUM>. <FIG> is a graph illustrating an example of output results of the detection signal S2 and the output signal S1 in the pressure sensor <NUM> including the circuit shown in <FIG>. The horizontal axis of the graph shown in <FIG> represents the strain generated in the fifth resistor R5 or the pressure applied to the membrane <NUM>. The graph shown in <FIG> assumes a case where a positive strain occurs in the fifth resistor R5, but even in a case where a negative strain occurs in the fifth resistor R5 as shown in <FIG>, it can be considered in the same way, for example, if the strain is an absolute value.

As shown in the left region of <FIG>, when the pressure of the pressure fluid to be measured of the pressure sensor <NUM> is low and the strain generated in the fifth resistor R5 is smaller than a predetermined value X1, an output value of the detection signal S2 detected in the second circuit <NUM> is smaller than a predetermined value Y1. The switch control unit <NUM> shown in <FIG> recognizes that the detection signal S2 is smaller than the predetermined value Y1 via the detection signal input unit <NUM> and maintains the switch of the switching unit <NUM> in the OFF state.

When the switch of the switching unit <NUM> shown in <FIG> is in the OFF state, electric power is not supplied to the first circuit <NUM>. Thus, as shown in <FIG>, the first circuit <NUM> does not detect distortion, and the value of the output signal S1 from the first circuit <NUM> does not change. The predetermined value X1 for switching ON/OFF of electric power supply is determined as an upper limit of a range in which pressure detection by the pressure sensor <NUM> is unnecessary or as a value smaller than the upper limit.

As shown in the right region of <FIG>, when the pressure of the pressure fluid to be measured of the pressure sensor <NUM> is high and the strain generated in the fifth resistor R5 is a predetermined value X1 or more, an output value of a detection signal S2 detected in the second circuit <NUM> is a predetermined value Y1 or more. The switch control unit <NUM> shown in <FIG> recognizes that the detection signal S2 is the predetermined value Y1 or more via the detection signal input unit <NUM> and maintains the switch of the switching unit <NUM> in the ON state.

When the switch of the switching unit <NUM> shown in <FIG> is the ON state, electric power is supplied to the first circuit <NUM>. Thus, as shown in <FIG>, the first circuit <NUM> detects distortions of the first to fourth resistors R1-R4 caused by pressure, and the value of the output signal S1 from the first circuit <NUM> changes depending on the distortions and pressure. In the pressure sensor <NUM>, when the strain generated in the fifth resistor R5 is smaller than the predetermined value X1, electric power is not supplied to the first circuit <NUM> forming the bridge circuit. Thus, the pressure sensor <NUM> can achieve low power consumption. Moreover, since the pressure sensor <NUM> constantly detects the pressure to be measured by using the second circuit <NUM>, the electric power supply can be switched appropriately by the switching unit <NUM> even when a momentary pressure rise occurs, and it is possible to prevent omission of detection of pressure change.

The pressure detection accuracy of the second circuit <NUM> is sufficient as long as the electric power supply by the switching unit <NUM> can be switched appropriately and may be lower than the pressure detection accuracy of the first circuit <NUM> forming the bridge circuit. From the viewpoint of lowering the electric current value flowing through the second circuit <NUM> to reduce the electric power consumption in the second circuit <NUM>, the resistance value of the fifth resistor R5 in the second circuit <NUM> is preferably higher than any of the resistance values of the first to fourth resistors R1-R4 included in the first circuit <NUM> in the state where no strain is generated.

The stem <NUM> including the membrane <NUM> as shown in <FIG> and the first circuit <NUM> and the second circuit <NUM> provided on the membrane <NUM> are manufactured, for example, as below. First, the stem <NUM> including the membrane <NUM> is manufactured by machining. The material of the stem <NUM> is not particularly limited as long as it produces an appropriate elastic deformation and is, for example, a metal or an alloy such as stainless steel.

Next, the first circuit <NUM> including the first to fourth resistors R1-R4, the second circuit <NUM> including the fifth resistor R5, the first electrode portions <NUM>-<NUM>, and the second electrode portions <NUM> and <NUM> as shown in <FIG> are formed by forming a semiconductor thin film or a metal thin film on the membrane <NUM> with an insulating film interposed therebetween and subjecting this thin film to laser processing, microfabrication by a semiconductor processing technique such as screen printing, or the like. If necessary, an insulating surface layer may be formed on parts other than the first and second electrode portions <NUM>-<NUM>, <NUM>, and <NUM>, such as the upper surface of the first circuit <NUM> or the second circuit <NUM>.

<FIG> is a conceptual diagram illustrating an example of a circuit formed by using a pressure sensor <NUM> according to Second Embodiment. Except for a switching unit <NUM> and a microprocessor <NUM> arranged on the substrate portion <NUM>, the pressure sensor <NUM> according to Second Embodiment is similar to the pressure sensor <NUM> according to First Embodiment. The pressure sensor <NUM> according to Second Embodiment is explained for only differences from the pressure sensor <NUM> according to First Embodiment, and common maters are not explained.

The pressure sensor <NUM> is similar to the pressure sensor <NUM> shown in <FIG> in terms of the first circuit <NUM> and the second circuit <NUM> formed on the membrane <NUM>. However, the switching unit <NUM> of the pressure sensor <NUM> according to First Embodiment is controlled by the switch control unit <NUM> of the microprocessor <NUM>, but the switching unit <NUM> of the pressure sensor <NUM> is different from this. That is, the switching unit <NUM> of the pressure sensor <NUM> is achieved by a circuit of resistors Ro1, Ro2, Ro3, and Ro4, a comparator <NUM>, and a transistor <NUM> shown in <FIG>.

In the switching unit <NUM> shown in <FIG>, the transistor <NUM> is disposed at the entrance from a power supply voltage VDD to the first circuit <NUM>, and the electric power supply to the first circuit <NUM> is switched by the transistor <NUM>. A detection signal S2 binarized by the comparator <NUM> is input to a third terminal of the transistor <NUM>. As a result, ON/OFF of electric power supply to the first circuit <NUM> is switched by using the detection signal S2 from the second circuit <NUM>.

As with the pressure sensor <NUM> shown in <FIG>, the pressure sensor <NUM> shown in <FIG> can also switch electric power supply so as to supply electric power to the first circuit <NUM> only when the pressure is equal to or higher than a predetermined pressure as shown in <FIG>. As shown in <FIG>, the pressure sensor <NUM> can switch electric power supply so as to supply electric power to the first circuit <NUM> only when the pressure is lower than a predetermined pressure by replacing the inputs to the comparator <NUM>.

<FIG> is a graph showing an example of output results of the detection signal S2 and the output signal S1 in the pressure sensor <NUM> including the circuit shown in <FIG>. The horizontal axis of the graph shown in <FIG> represents the strain generated in the fifth resistor R5 or the pressure applied to the membrane <NUM>. As with <FIG>, the graph shown in <FIG> assumes that a positive distortion is generated in the fifth resistor R5.

As shown in the left region of <FIG>, when the pressure of the pressure fluid to be measured by the pressure sensor <NUM> is low and the strain generated in the fifth resistor R5 is smaller than a predetermined value X1, an output value of the detection signal S2 detected in the second circuit <NUM> is smaller than a predetermined value Y1. The detection signal S2 converted to Hi via the comparator <NUM> is input to the third terminal of the transistor <NUM> shown in <FIG>, and the transistor <NUM> makes it possible to supply electric power to the first circuit <NUM> by the power supply voltage VDD.

In this state, as shown in the left region of <FIG>, the first circuit <NUM> detects strains of the first to fourth resistors R1-R4 caused by pressure, and the value of the output signal S1 from the first circuit <NUM> changes responding to the pressure of the fluid.

As shown in the right region of <FIG>, when the pressure of the pressure fluid to be measured by the pressure sensor <NUM> is high and the strain generated in the fifth resistor R5 is a predetermined value X1 or more, the output value of the detection signal S2 detected in the second circuit <NUM> is a predetermined value Y1 or more. A detection signal S2 converted to Low via the comparator <NUM> is input to the third terminal of the transistor <NUM> shown in <FIG>, and the transistor <NUM> makes it impossible to supply electric power to the first circuit <NUM> by the power supply voltage VDD.

In this state, electric power is not supplied to the first circuit <NUM>. Thus, as shown in the right region of <FIG>, the first circuit <NUM> does not detect strain, and the value of the output signal S1 from the first circuit <NUM> does not change. The predetermined value X1 for switching ON/OFF of electric power supply is determined as an upper limit of a range in which pressure detection by the pressure sensor <NUM> is required or as a value larger than the upper limit.

In the pressure sensor <NUM> according to Second Embodiment, the second circuit <NUM> is driven using the power supply voltage VDD common to the first circuit <NUM>, and it is thereby unnecessary to separately generate a voltage applied to the fifth resistor R5 of the second circuit <NUM>. Since the pressure sensor <NUM> achieves the switching unit <NUM> with a simple circuit, the operation reliability of the switching unit <NUM> is high, and the calculation amount of the microprocessor <NUM> for processing the output signal S1 can be reduced.

<FIG> is a conceptual diagram illustrating an arrangement of the first circuit <NUM>, a second circuit <NUM>, and the electrode portion in a pressure sensor <NUM> according to Third Embodiment and an equivalent circuit of the first circuit <NUM> and the second circuit <NUM>. The pressure sensor <NUM> according to Third Embodiment is similar to the pressure sensor <NUM> according to First Embodiment except that a fifth resistor R15 of the second circuit <NUM> includes a first portion R15-<NUM> and a second portion R15-<NUM>. The pressure sensor <NUM> according to Third Embodiment is explained for only differences from the pressure sensor <NUM> according to First Embodiment, and common matters are not explained.

As shown in <FIG>, the fifth resistor R15 of the second circuit <NUM> includes the first portion R15-<NUM> and the second portion R15-<NUM> arranged separately in two locations on the first circumference <NUM>. The first portion R15-<NUM> and the second portion R15-<NUM> are similar to the fifth resistor R5 shown in <FIG> and have a structure in which three first thin film resistors R51 are connected in series by the connection portion <NUM> (See <FIG>).

As shown in <FIG>, the first resistor R1 and the third resistor R3 of the first circuit <NUM> are arranged between the first portion R15-<NUM> and the second portion R15-<NUM> on the first circumference <NUM>. The first portion R15-<NUM> and the second portion R15-<NUM> are connected electrically via second electrode portions <NUM> and <NUM>.

As shown in <FIG>, the bridge circuit formed by the first circuit <NUM> of the pressure sensor <NUM> is similar to the first circuit <NUM> of the pressure sensor <NUM>. As shown in <FIG>, the fifth resistor R15 included in the second circuit <NUM> of the pressure sensor <NUM> is configured by connecting the first portion R15-<NUM> and the second portion R15-<NUM> in series with the connection portion <NUM>. The connection portion <NUM> may connect them via the substrate portion <NUM> shown in <FIG> or may directly connect them on the membrane <NUM>. One of second electrode portions <NUM> and <NUM> shown in <FIG> is connected to the detection signal input unit <NUM> (see <FIG>), and the other is grounded.

In the pressure sensor <NUM> according to Third Embodiment, since the fifth resistor R15 is disposed separately at two locations on the first circumference <NUM>, it is possible to increase the resistance value of the fifth resistor R15 and reduce electric power consumption of the second circuit <NUM>. Since the fifth resistor R15 is disposed on the first circumference <NUM> similarly to the first resistor R1 and the third resistor R3 of the first circuit <NUM>, the pressure sensor <NUM> can accurately detect the pressure for switching electric power supply and the strain. The pressure sensor <NUM> according to Third Embodiment exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a conceptual diagram illustrating an arrangement of the first circuit <NUM>, a second circuit <NUM>, and the electrode portion in a pressure sensor <NUM> according to Fourth Embodiment and an equivalent circuit of the first circuit <NUM> and the second circuit <NUM>. The pressure sensor <NUM> according to Fourth Embodiment is similar to the pressure sensor <NUM> according to First Embodiment except that a fifth resistor R25 of the second circuit <NUM> includes a first portion R25-<NUM>, a second portion R25-<NUM>, and a third portion R25-<NUM>. The pressure sensor <NUM> according to Third Embodiment is explained for only differences from the pressure sensor <NUM> according to First Embodiment, and common matters are not explained.

As shown in <FIG>, the fifth resistor R25 of the second circuit <NUM> is disposed separately at three locations on the first circumference <NUM>, which is the first strain position, and on a third circumference <NUM> and a fourth circumference <NUM> as a third strain region where a strain having a different size (e.g., <NUM>/<NUM>) on the first circumference <NUM> but in the same direction (e.g., compression) occurs on the membrane <NUM>. The first portion R25-<NUM> of the fifth resistor R25 disposed on the first circumference <NUM> is similar to the fifth resistor R5 shown in <FIG> and has a structure in which three first thin film resistors R51 are connected in series by the connection portion <NUM> (see <FIG>).

As shown in <FIG>, the second portion R25-<NUM> of the fifth resistor R25 disposed on the third circumference <NUM> has a structure in which the second thin film resistors R52 made of thin films are connected in series by connection portions. Likewise, the third portion R25-<NUM> of the fifth resistor R25 disposed on the fourth circumference <NUM> has a structure in which the third thin film resistors R53 made of thin films are connected in series by connection portions.

As shown in <FIG>, the third circumference <NUM> is located on the inner circumference side of the first circumference <NUM>, and the fourth circumference <NUM> is located on the outer circumference side of the first circumference <NUM>, but both of them produce a strain in the same direction as on the first circumference <NUM>. As shown in <FIG>, the second circuit <NUM> of the pressure sensor <NUM> includes a connection portion <NUM> for connecting the first portion R25-<NUM> made of the first thin film resistor R51 and the second portion R25-<NUM> made of the second thin film resistor R52 in series. Likewise, the second circuit <NUM> of the pressure sensor <NUM> includes a connection portion <NUM> for connecting the first portion R25-<NUM> made of the first thin film resistor R51 and the third portion R25-<NUM> made of the third thin film resistor R53 in series. One of the second electrode portions <NUM> and <NUM> shown in <FIG> is connected to the detection signal input unit <NUM> (see <FIG>), and the other is grounded.

As shown in <FIG>, the second circuit <NUM> of the pressure sensor <NUM> includes not only the first portion R25-<NUM> disposed on the first circumference <NUM>, but also the second portion R25-<NUM> and the third portion R25-<NUM> arranged on the third circumference <NUM> and the fourth circumference <NUM>, and these are connected in series by the connection portions <NUM> and <NUM> to form the fifth resistor R25. Such a second circuit <NUM> can effectively increase the resistance value in a limited area on the membrane <NUM> and is thereby advantageous from the viewpoint of low electric power consumption.

As shown in <FIG>, the bridge circuit formed by the first circuit <NUM> of the pressure sensor <NUM> is similar to the first circuit <NUM> of the pressure sensor <NUM>. In addition, the pressure sensor <NUM> according to Fourth Embodiment exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a conceptual diagram illustrating an arrangement of the first circuit <NUM>, a second circuit <NUM>, and the electrode portion in a pressure sensor <NUM> according to Fifth Embodiment and an equivalent circuit of the first circuit <NUM> and the second circuit <NUM>. The pressure sensor <NUM> according to Fifth Embodiment is similar to the pressure sensor <NUM> according to Fourth Embodiment except that a fifth resistor R35 of the second circuit <NUM> includes a fourth portion R35-<NUM>, a fifth portion R35-<NUM>, and a sixth portion R35-<NUM>. The pressure sensor <NUM> according to Fifth Embodiment is explained for only differences from the pressure sensor <NUM> according to Third Embodiment, and common matters are not explained.

As shown in <FIG>, the fifth resistor R35 of the second circuit <NUM> includes first to third portions R25-<NUM> to R25-<NUM> similar to the fifth resistor R25 of the second circuit <NUM> shown in <FIG>. In addition, the fifth resistor R35 includes fourth to sixth portions R35-<NUM> to R35-<NUM>. The fourth portion R35-<NUM> of the fifth resistor R35 is disposed on the first circumference <NUM> similarly to the first portion R25-<NUM>, the fifth portion R35-<NUM> of the fifth resistor is disposed on the third circumference <NUM> similarly to the second portion R25-<NUM>, and the sixth portion R35-<NUM> of the fifth resistor R35 is disposed on the fourth circumference <NUM> similarly to the third portion R25-<NUM>. Except for the positions on the first to third circumferences <NUM>, <NUM> and <NUM>, the fourth to sixth portions R35-<NUM> to R35-<NUM> are similar to the first to third portions R25-<NUM> to R25-<NUM>.

As shown in <FIG>, the first to third portions R25-<NUM> to R25-<NUM> and the fourth to sixth portions R35-<NUM> to R35-<NUM> of the fifth resistor R35 are connected in series via a connection portion <NUM> and the like. Such a second circuit <NUM> can effectively increase the resistance value in a limited area on the membrane <NUM> and is thereby advantageous from the viewpoint of low electric power consumption. The pressure sensor <NUM> according to Fifth Embodiment exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a schematic cross-sectional view of a pressure sensor <NUM> according to Sixth Embodiment. The pressure sensor <NUM> according to Sixth Embodiment is similar to the pressure sensor <NUM> according to Sixth Embodiment except that a membrane <NUM> is a flat metal plate and is not the bottom surface of the stem <NUM>. The pressure sensor <NUM> according to Fifth Embodiment is explained for only differences from the pressure sensor <NUM> according to First Embodiment, and common matters are not explained.

The membrane <NUM> is fixed to an end face 512a of a housing <NUM> so as to close a passage 512b of the housing <NUM>. A pressure detection circuit <NUM> is formed on an upper surface of the membrane <NUM> via an insulating film <NUM>. The pressure detection circuit <NUM> includes the first circuit <NUM> and the second circuit <NUM> shown in <FIG>. The pressure sensor <NUM> includes the substrate portion <NUM> similarly to the pressure sensor <NUM> shown in <FIG>.

The flat membrane <NUM> is fixed to the end surface 512a of the housing <NUM> by welding or the like. The area of the insulating film <NUM> is smaller than that of the membrane <NUM>, and the membrane <NUM> is partly exposed from the insulating film <NUM>. Thus, the membrane <NUM> can easily be fixed to the housing <NUM> by contacting an electrode with the exposed membrane <NUM> and performing resistance welding.

The pressure sensor <NUM> includes the metal plate membrane <NUM> and is thereby advantageous for miniaturization. In addition, unlike the stem <NUM> (see <FIG>), the metal plate is easily processed in a general semiconductor factory and is productive. The pressure sensor <NUM> according to Fifth Embodiment exhibits effects similar to those of the pressure sensor <NUM>.

Hereinbefore, the pressure sensor according to the present invention is explained with reference to the embodiments, but the present invention is not limited to these embodiments and, needless to say, may include many other embodiments and modifications. For example, the shapes and fixation structures of the stem <NUM> and membranes <NUM> and <NUM> shown in <FIG> and <FIG> are merely examples, and the pressure sensor of the present invention can employ any other shapes and fixation structures in which a membrane can be deformed appropriately corresponding to pressure. The membrane of the pressure sensor is not limited to only the stem or the metal plate shown in the embodiments and can be a membrane made of other shapes and materials.

Hereinafter, the present invention is explained in more detail with reference to examples, but the explanation of these examples does not limit the present invention in any way.

In the examples, using the pressure sensor <NUM> according to Second Embodiment as shown in <FIG>, the values of electric current consumed at the sensor ON time and the sensor OFF time were calculated in each of parts A1-A5 of a circuit included in the pressure sensor <NUM>. The resistance values used for the calculation were a resistance Rbr of the bridge circuit (a resistance of the bridge circuit by the first to fourth resistors R1-R4): <NUM> kΩ, the fifth resistor R5: <NUM> kΩ, the resistance Ro1: <NUM> kΩ, the resistance Ro2: <NUM> MΩ, the resistance Ro3: <NUM> MΩ, and the resistance Ro4: <NUM> kΩ. The power supply voltage VDD was 5V. The results are shown in Table <NUM>.

Claim 1:
A pressure sensor (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) comprising:
a membrane (<NUM>, <NUM>) configured to produce deformation corresponding to pressure;
a first circuit (<NUM>) including a first resistor (R1) and a third resistor (R3) arranged at a first strain position (<NUM>) where a predetermined strain characteristic occurs on the membrane (<NUM>, <NUM>) and a second resistor (R2) and a fourth resistor (R4) arranged at a second strain position (<NUM>) where a strain characteristic in a different direction from the first strain position (<NUM>) occurs and configured to form a bridge circuit and detect strain; and
a second circuit (<NUM>, <NUM>, <NUM>, <NUM>) including a fifth resistor (R5, R15, R25, R35) disposed at a position where a strain characteristic in the same direction as the first strain position (<NUM>) or the second strain position (<NUM>) in the membrane (<NUM>, <NUM>) occurs and capable of detecting strain independently from the first circuit (<NUM>),
characterized in that
the pressure sensor (<NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>) further comprises a switching unit (<NUM>, <NUM>) for switching electric power supply to the first circuit (<NUM>) using a detection signal (S2) from the second circuit (<NUM>, <NUM>, <NUM>, <NUM>).