Patent Description:
A pressure sensor is known that detects a distortion of a membrane (also referred to as a diaphragm) by resistance change using a piezoresistive effect. In such a pressure sensor, the distortion due to the deformation of the membrane is detected by a resistance change of a resistor provided on the membrane.

In recent years, there has been a demand for low power consumption of a pressure sensor. For example, a technique is proposed in which electric power is intermittently supplied to a bridge circuit included in a pressure sensor by pulse driving (see Patent Document <NUM>).

However, the pressure sensor that intermittently supplies electric power has a problem with inability to detect a momentary pressure abnormality generated at the timing when the electric power supply is turned off.

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

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

In addition to the pressure detection circuit measuring pressure with the bridge circuit by the resistors, the pressure sensor according to the present invention includes the piezoelectric body disposed on the membrane and the changeover unit switching electric power supply to the pressure detection circuit based on a detection signal from the piezoelectric body. In such a pressure sensor, for example, pressure can be detected only in a required pressure range by stopping or restarting electric power supply based on the detection signal, and electric power consumption can thus be reduced. Moreover, since the piezoelectric body is disposed on the membrane, the changeover unit can accurately stop or restart the electric power supply based on the detection signal from the piezoelectric body, and it is possible to prevent detection omission of pressure change. In addition, the piezoelectric body generates a piezoelectric effect due to a deformation of the membrane. Thus, such a pressure sensor can reduce the electric power required for detecting the deformation of the membrane by the piezoelectric body and supplying the electric power by the switching unit, and this respect also contributes to the reduction of power consumption.

For example, the resistors included in the pressure detection circuit comprise:.

The third strain region is located on the outer circumferential side of the second strain position for arranging the second resistor and the fourth resistor and is in a comparatively wide range on the membrane. Thus, the degree of freedom in layout can be secured by disposing the piezoelectric body in the third strain region. Moreover, since the third strain region is wide, it is possible to use the piezoelectric body including a comparatively large-sized first piezoelectric portion, and the piezoelectric body having such a first piezoelectric portion can generate a larger electromotive force by deformation of the membrane. When the detection signal is large, the circuit for amplifying the signal can be smaller or omitted, and this respect also contributes to the miniaturization of the device. Moreover, when the detection signal is large, noise can be reduced, and it is thus possible to improve the accuracy of the detection by the piezoelectric body and the sensor by the changeover unit.

For example, the piezoelectric body may comprise a plurality of first piezoelectric portions, and
the changeover unit may switch electric power supply to the pressure detection circuit based on a signal obtained by summing detection signals from the plurality of first piezoelectric portions.

The third strain region is wide as described above and is thus suitable for arranging a plurality of first piezoelectric portions. Moreover, the changeover unit can increase the detected value of the signal based on the signal obtained by summing the detection signals generated from strains in the same direction in the plurality of first piezoelectric portions. Thus, in such a pressure sensor, the circuit for amplifying signals can be smaller or omitted, and this contributes to the miniaturization of the pressure sensor. Moreover, noise can be reduced if the detection signals are large, and it is thus possible to improve the accuracy of detection by the piezoelectric body and switching by the changeover unit.

For example, the piezoelectric body may comprise a second piezoelectric portion disposed in a fourth strain region generating a strain in the same direction as the second strain position on the membrane, and the changeover unit switches electric power supply to the pressure detection circuit based on a signal of difference between a detection signal from the first piezoelectric portion and a detection signal from the second piezoelectric portion. Thus, in such a pressure sensor, the circuit for amplifying signals can be smaller or omitted, and this contributes to the miniaturization of the pressure sensor. Moreover, noise can be reduced if the detection signals are large, and it is thus possible to improve the accuracy of detection by the piezoelectric body and switching by the changeover unit.

The directions of detected strains are different, and the detection signals having reverse signs are output, between the first piezoelectric portion and the second piezoelectric portion. Thus, the detection value (absolute value) of the signal can be increased by a signal difference between the detection signal from the first piezoelectric portion and the detection signal from the second piezoelectric portion.

For example, the piezoelectric body comprises a thin film piezoelectric body made of a thin film.

When the piezoelectric body is the thin film piezoelectric body, this contributes to the miniaturization of the device.

For example, the pressure sensor according to the present invention may comprise:.

Since the fillet portion is formed, the third strain region formed on the membrane is wider as compared with when no fillet portion is formed. Thus, in such a pressure sensor, it is easy to enlarge the first piezoelectric portion or arrange a plurality of first piezoelectric portions and is possible to improve the accuracy of detection by the piezoelectric body and switching by the changeover unit.

Hereinafter, the present invention is described based on 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> that is deformed in response 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> with a flow path 12b for transmitting pressure to the stem <NUM>, a holding member <NUM> for fixing the stem <NUM> to the connection member <NUM>, a substrate portion <NUM> wired to an electrode portion or the like 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 circumference of the connection member <NUM>. The flow path 12b formed inside the connection member <NUM> tightly communicates with a pressure chamber as a measurement target by fixing the pressure sensor <NUM> via the screw groove 12a.

As shown in <FIG>, the stem <NUM> has a bottomed (upper bottom) cylindrical outer shape and is provided at one end of the flow path 12b in 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 flow path 12b of the connection member <NUM> are tightly connected using the holding member <NUM>, and the pressure as a measurement target 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 a side wall <NUM> (see <FIG>), and is deformed according to the pressure transmitted from the flow path 12b. The membrane <NUM> has an inner surface 22a that comes into contact with the pressure fluid and an outer surface 22b that is opposite to the inner surface 22a. A pressure detection circuit <NUM> and a piezoelectric body <NUM> (see <FIG>) mentioned below, electrode portions (not shown), and the like are provided on the outer surface 22b side of the membrane <NUM>.

The substrate portion <NUM> including wirings, electrode portions, and the like electrically connected to the pressure detection circuit <NUM> and the piezoelectric body <NUM> formed on the outer surface 22b of the membrane <NUM> is fixed to the holding member <NUM> shown in <FIG>. 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, and the stem <NUM> inserts a through hole formed at the center of the substrate portion <NUM>.

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

As shown in <FIG>, the pressure sensor <NUM> includes: a pressure detection circuit <NUM> detecting a deformation of the membrane <NUM> with a bridge circuit formed by a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4; and the piezoelectric body <NUM> detecting the deformation of the membrane <NUM> independently from the pressure detection circuit <NUM>. The pressure detection circuit <NUM> includes at least four resistors R1 to R4 arranged on the outer surface 22b of the membrane <NUM>. As with the resistors R1 to R4, the piezoelectric body <NUM> is also disposed on the outer surface 22b of the membrane <NUM>.

As shown in the schematic plan view of the upper part of <FIG>, the resistors R1 to R4 included in the pressure detection circuit <NUM> include the first resistor R1 and the third resistor R3 arranged on a first circumference <NUM> and the second resistor R2 and the fourth resistor R4 arranged on a second circumference <NUM>. As shown in the schematic cross-sectional view of the lower part of <FIG>, the first circumference <NUM> is a first strain position that generates a predetermined strain characteristic on the membrane <NUM>, and the second circumference <NUM> is a second strain position that generates a strain characteristic different from that on the first circumference <NUM> (first strain position) on the membrane <NUM>.

As shown in <FIG>, the first circumference <NUM> (first strain position) is a circumference of a circle having a radius larger than that of the second circumference <NUM> (second strain position) and is located on the outer circumferential side of the second circumference <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>, whereas a positive strain +ε (tensile strain) is generated on the second circumference <NUM>. In this way, preferably, the strain characteristic on the first circumference <NUM> (first strain position) and the strain characteristic on the second circumference <NUM> (second strain position) are in different directions (relation in which the symbols are different and cancel each other out).

The pressure detection circuit <NUM> shown in <FIG> includes four resistors R1 to R4. However, the number of resistors R1 to R4 included in the pressure detection circuit <NUM> is not limited to only four. For example, the pressure detection circuit <NUM> may form a bridge circuit as shown in <FIG> with five or more resistors.

In the pressure detection circuit <NUM> shown in <FIG>, the number of resistors R1 and R3 arranged on the first circumference <NUM> and the number of resistors R2 and R4 arranged on the second circumference <NUM> are both two. However, the number of resistors R1 and R3 arranged on the first circumference <NUM> and the number of resistors R2 and R4 arranged on the second circumference <NUM> may be three or more. The number of resistors R1 and R3 arranged on the first circumference <NUM> and the number of resistors R2 and R4 arranged on the second circumference <NUM> may be the same or different.

As shown in the plan view of the upper part of <FIG>, the piezoelectric body <NUM> includes a first piezoelectric portion 35a. The first piezoelectric portion 35a is disposed in a third strain region <NUM> that generates a strain in the same direction as the first circumference <NUM> (first strain position) on the membrane <NUM>. As shown in the schematic cross-sectional view of the bottom part of <FIG>, when the membrane <NUM> receives a predetermined positive pressure from the inner surface 22a, the same negative strain -ε (compressive strain) as on the first circumference <NUM> is generated in the third strain region <NUM> of the membrane <NUM>.

As shown in <FIG>, the first piezoelectric portion 35a of the piezoelectric body <NUM> is disposed in the third strain region <NUM> on the center side of the first circumference <NUM>. However, the disposition of the first piezoelectric portion 35a is not limited to this, and the first piezoelectric portion 35a may be disposed in the third strain region <NUM> on the outer circumferential side of the first circumference <NUM> or may be disposed on the first circumference <NUM>. The third strain region <NUM> includes the first circumference <NUM>.

<FIG> is a conceptual diagram illustrating an example of a circuit formed with the pressure sensor <NUM>. As shown in <FIG>, the first to fourth resistors R1 to R4 included in the pressure detection circuit <NUM> form a bridge circuit. An output signal Vout of the pressure detection circuit <NUM> is input to a pressure signal input unit <NUM> of a microprocessor <NUM> via an amplifier <NUM>. Although not illustrated in <FIG>, an electrode portion for supplying electric power to the first to fourth resistors R1 to R4 constituting the pressure detection circuit <NUM> or transmitting the output signal Vout of the pressure detection circuit <NUM> by the first to fourth resistors R1 to R4 is formed on the membrane <NUM>. The pressure detection circuit <NUM> is electrically connected to the substrate portion <NUM> via the electrode portion and a connection wiring <NUM> (see <FIG>).

As shown in <FIG>, the piezoelectric body <NUM> including the first piezoelectric portion 35a is not connected to the pressure detection circuit <NUM> at least on the membrane <NUM> and can detect a strain independently from the pressure detection circuit <NUM>. A detection signal Vtr1 of the first piezoelectric portion 35a is input to the detection signal input unit <NUM> of the microprocessor <NUM>.

As shown in <FIG>, the pressure sensor <NUM> includes a changeover unit <NUM> for switching electric power supply to the pressure detection circuit <NUM> based on a detection signal Vtr from the piezoelectric body <NUM>. The microprocessor <NUM>, the changeover unit <NUM>, and the amplifier <NUM> shown in <FIG> can be arranged, for example, on the substrate portion <NUM>, but their arrangement is not limited.

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

The switch control unit <NUM> controls the changeover unit <NUM> based on the detection signal Vtr of the piezoelectric body <NUM> based on the detection signal Vtr1 by the first piezoelectric portion 35a. In the pressure sensor <NUM>, as shown in <FIG>, since the piezoelectric body <NUM> includes one first piezoelectric portion 35a, the detection signal Vtr of the piezoelectric body <NUM> input to the pressure signal input unit <NUM> is the same as the detection signal Vtr1 by the first piezoelectric portion 35a.

<FIG> is graphs showing output results of a pressure P, the detection signal Vtr, and the output signal Vout in the pressure sensor <NUM> including the circuit shown in <FIG>. The vertical axes of the graphs shown in <FIG> indicate the height of the pressure P and signal intensities of the detection signal Vtr and the output signal Vout, and the horizontal axes of the graphs indicate the time t. The graphs shown in <FIG> assume a case where a positive strain is generated in the third strain region <NUM> for disposing the first piezoelectric portion 35a. As shown in <FIG>, however, even when a negative strain is generated in the third strain region <NUM>, it can be considered in the same manner, for example, provided that the strain is regarded as an absolute value.

As shown in the left region of <FIG>, when the pressure of the pressure fluid as a measurement target of the pressure sensor <NUM> is kept low, a strain or a change in strain generated in the third strain region <NUM> is small, and the detection signal Vtr detected by the piezoelectric body <NUM> is thus smaller than a predetermined value VL. In this case, the switch control unit <NUM> shown in <FIG> determines that the detection signal Vtr is not the predetermined value VL or more via the detection signal input unit <NUM> and keeps the switch of the changeover unit <NUM> in the OFF state.

When the switch of the changeover unit <NUM> shown in <FIG> is in the OFF state, no electric power is supplied to the pressure detection circuit <NUM>. Thus, as shown in the left part of the lower graph in <FIG>, the pressure detection circuit <NUM> detects no strain, and the value of the output signal Vout from the pressure detection circuit <NUM> does not change. The predetermined value VL for switching ON/OFF of electric power supply can be determined based on, for example, pressure and pressure fluctuation that trigger the pressure detection by the pressure sensor <NUM>.

Next, as shown in the right region of <FIG>, when the pressure of the pressure fluid as a measurement target of the pressure sensor <NUM> rises, a strain or a change in strain generated in the third strain region <NUM> becomes large, and the detection signal Vtr detected by the piezoelectric body <NUM> becomes the predetermined value VL or more (time T1). In this case, the switch control unit <NUM> shown in <FIG> determines that the detection signal Vtr becomes the predetermined value VL or more via the detection signal input unit <NUM> and switches the switch of the changeover unit <NUM> to the ON state.

When the switch of the changeover unit <NUM> shown in <FIG> is in the ON state, electric power is supplied to the pressure detection circuit <NUM>. Thus, as shown in the right part of the lower graph in <FIG>, the pressure detection circuit <NUM> including the first to fourth resistors R1 to R4 detects a strain of the membrane <NUM> generated by pressure, and the value of the output signal Vout from the pressure detection circuit <NUM> changes depending on the pressure P. The switch of the changeover unit <NUM> may be kept in the ON state until a predetermined timing even after the detection signal Vtr becomes smaller than the predetermined value VL and may be switched from ON to OFF corresponding to the detection signal Vtr becoming smaller than the predetermined value VL (see <FIG>).

As described above, in the pressure sensor <NUM>, no electric power is supplied to the pressure detection circuit <NUM> forming a bridge circuit until the piezoelectric body <NUM> detects a deformation of the membrane <NUM> with the detection signal Vtr exceeding the predetermined value VL. Thus, the pressure sensor <NUM> can achieve low electric power consumption. Moreover, since the pressure sensor <NUM> constantly detects the pressure as a measurement target using the piezoelectric body <NUM>, the electric power supply is appropriately switched by the changeover unit <NUM> even if the pressure rises momentarily, and detection omission of pressure change can be prevented.

The pressure detection accuracy of the piezoelectric body <NUM> is sufficient as long as the electric power supply by the changeover unit <NUM> can be switched appropriately and may be lower than the pressure detection accuracy of the pressure detection circuit <NUM> forming a bridge circuit.

As with the pressure detection circuit <NUM>, the piezoelectric body <NUM> detects a deformation of the membrane <NUM> corresponding to the pressure. Unlike the pressure detection circuit <NUM> using the resistors R1 to R4, however, the piezoelectric body <NUM> is polarized with the deformation of the membrane <NUM> and has a spontaneous potential difference on its surface. Thus, the piezoelectric body <NUM> can function as a sensor for switching electric power supply to the pressure detection circuit <NUM> even without supplying electric power from the outside, and the wiring to the piezoelectric body <NUM> formed on the membrane <NUM> is simple.

In the circuit shown in <FIG>, a predetermined voltage can be applied to the piezoelectric body <NUM>, for example, for improvement in the accuracy of the detection signal Vtr. Even in such a case, since the piezoelectric body <NUM> hardly flows electric current, the pressure detection using the piezoelectric body <NUM> can significantly reduce the electric power consumption as compared with the detection using the resistors R1 to R4.

The stem <NUM> including the membrane <NUM> as shown in <FIG> and the pressure detection circuit <NUM> and the piezoelectric body <NUM> provided on the membrane <NUM> are manufactured, for example, as follows. First, the stem <NUM> including the membrane <NUM> is manufactured by machining. The material of the stem <NUM> is not limited as long as it generates an appropriate elastic deformation, and examples thereof include metals and alloys such as stainless steel.

Next, a semiconductor thin film or a metal thin film is formed on the membrane <NUM> with an insulating film interposed therebetween, a piezoelectric thin film is further partially formed, and these thin films are subjected to a fine processing with a semiconductor processing technique, such as laser processing and screen printing, so as to form the pressure detection circuit <NUM> including the first to fourth resistors R1 to R4 and the first piezoelectric portion 35a as shown in <FIG>. If necessary, an insulating surface layer may be formed on the upper surfaces of the pressure detection circuit <NUM> and the first piezoelectric portion 35a. The pressure sensor <NUM> including the piezoelectric body <NUM> with the first piezoelectric portion 35a made of a thin film piezoelectric body and manufactured using the semiconductor processing technique is advantageous for miniaturization.

<FIG> is a schematic plan view illustrating an arrangement of the resistor <NUM> and a piezoelectric body <NUM> in a pressure sensor <NUM> according to Second Embodiment. The pressure sensor <NUM> according to Second Embodiment is similar to the pressure sensor <NUM> according to First Embodiment, except that the arrangement of a first piezoelectric portion 135a included in the piezoelectric body <NUM> is different from that in the pressure sensor <NUM> shown in <FIG>. The pressure sensor <NUM> according to Second Embodiment is described focusing on the differences from the pressure sensor <NUM> according to First Embodiment, and common matters are not described.

The piezoelectric body <NUM> of the pressure sensor <NUM> includes one first piezoelectric portion 135a, and the first piezoelectric portion 135a is disposed in the third strain region <NUM> that generates a strain in the same direction as the first strain position. The location of the piezoelectric body <NUM> is not limited as long as a strain can be detected on the membrane <NUM>, but the restrictions on the arrangement and size of the piezoelectric body <NUM> can be relaxed by disposing the piezoelectric body <NUM> in the third strain region <NUM> formed in a wide range on the membrane <NUM> and generating strains in the same direction. Thus, the pressure sensor <NUM> including the first piezoelectric portion 135a disposed in the third strain region <NUM> can adopt, for example, the large-sized first piezoelectric portion 135a so as to increase the pressure detection sensitivity by the piezoelectric body <NUM>. If the piezoelectric body <NUM> has a high detection sensitivity, it may be possible to omit or reduce a circuit such as an amplifier for amplifying the detection signal, and this is advantageous from the viewpoint of reduction of power consumption and miniaturization.

As shown in <FIG>, the first piezoelectric portion 135a can align the direction and magnitude of the strain to be detected with respect to the first resistor R1 and the third resistor R3 by disposing the first piezoelectric portion 135a on the first circumference <NUM> (first strain position). In such a pressure sensor <NUM>, the correspondence between the detection signal of the piezoelectric body <NUM> and the output signal of the pressure detection circuit <NUM> by the resistor <NUM> can be determined with a higher accuracy, and the changeover unit <NUM> (see <FIG>) of the pressure sensor <NUM> can thus be operated with high accuracy. As for the common matters with the pressure sensor <NUM> according to First Embodiment, the pressure sensor <NUM> exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a schematic plan view illustrating an arrangement of the resistor <NUM> and a piezoelectric body <NUM> in a pressure sensor <NUM> according to Third Embodiment. The pressure sensor <NUM> according to Third Embodiment is similar to the pressure sensor <NUM> according to Second Embodiment, except that the pressure sensor <NUM> is different from the pressure sensor <NUM> shown in <FIG> in that the piezoelectric body <NUM> includes a plurality (two in <FIG>) of first piezoelectric portions 235a. The pressure sensor <NUM> according to Third Embodiment is described focusing on the differences from the pressure sensor <NUM> according to Second Embodiment, and common matters are not described.

The piezoelectric body <NUM> of the pressure sensor <NUM> includes two first piezoelectric portions 235a, and the two first piezoelectric portions 235a are arranged in the third strain region <NUM> that generates a strain in the same direction as the first strain position. In the pressure sensor <NUM>, both of the two first piezoelectric portions 235a are arranged on the first circumference <NUM> (first strain position), but the arrangement of the first piezoelectric portions 235a is not limited to this. In the piezoelectric sensor <NUM>, either or both of the two first piezoelectric portions 235a may be arranged in the third strain region <NUM> excluding the first circumference <NUM>.

In the pressure sensor <NUM>, detection signals Vtrl from the two first piezoelectric portions 235a are input to the detection signal input unit <NUM> of the microprocessor <NUM> shown in <FIG>. <FIG> is a conceptual diagram illustrating a processing of the detection signal by the microprocessor <NUM> of the pressure sensor <NUM>. As shown in <FIG>, the microprocessor <NUM> calculates a detection signal Vtr obtained by summing the detection signals Vtr1 from the plurality of first piezoelectric portions 235a. Then, the changeover unit <NUM> of the pressure sensor <NUM> switches electric power supply to the pressure detection circuit <NUM> based on the detection signal Vtr obtained by summing the detection signals Vtr1 from the plurality of first piezoelectric portions 235a (see <FIG>).

In such a pressure sensor <NUM>, the signal detected by the piezoelectric body <NUM> can be strengthened by summing the detection signals Vtr1 from the plurality of first piezoelectric portions 235a, the changeover unit <NUM> can operate more precisely. As for the common matters with the pressure sensor <NUM> according to Second Embodiment, the pressure sensor <NUM> exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a schematic plan view illustrating an arrangement of the resistor <NUM> and a piezoelectric body <NUM> in a pressure sensor <NUM> according to Fourth Embodiment. The pressure sensor <NUM> according to Fourth Embodiment is different from the pressure sensor <NUM> shown in <FIG> in that the piezoelectric body <NUM> includes a second piezoelectric portion 335b in addition to a first piezoelectric portion 335a. In other respects, however, the pressure sensor <NUM> according to Fourth Embodiment is similar to the pressure sensor <NUM> according to Second Embodiment. The pressure sensor <NUM> according to Fourth Embodiment is described focusing on the differences from the pressure sensor <NUM> according to Second Embodiment, and common matters are not described.

As shown in <FIG>, the piezoelectric body <NUM> of the pressure sensor <NUM> includes the first piezoelectric portion 335a and the second piezoelectric portion 335b. The first piezoelectric portion 335a is similar to the first piezoelectric portion 135a shown in <FIG> and is disposed in the third strain region <NUM> on the membrane <NUM>. The second piezoelectric portion 335b includes, for example, a thin film piezoelectric body as with the first piezoelectric portion 335a and is disposed in a fourth strain region <NUM> on the membrane <NUM>. The fourth strain region <NUM> is a region that generates a strain in the same direction as the second circumference <NUM>, which is a second strain position for arranging the second resistor R2 and the fourth resistor R4 on the membrane <NUM> (see <FIG>).

In the pressure sensor <NUM>, a detection signal Vtrl from the first piezoelectric portion 335a and a detection signal Vtr2 from the second piezoelectric portion are input to the detection signal input unit <NUM> of the microprocessor <NUM> shown in <FIG>. <FIG> is a conceptual diagram illustrating a processing of the detection signal in the microprocessor <NUM> of the pressure sensor <NUM>. As shown in <FIG>, the microprocessor <NUM> calculates a detection signal Vtr of the difference between the detection signal Vtr1 from the first piezoelectric portion 335a and the detection signal Vtr2 from the second piezoelectric portion 335b. Then, the changeover unit <NUM> of the pressure sensor <NUM> switches electric power supply to the pressure detection circuit <NUM> based on the detection signal Vtr of the difference between the detection signal Vtr1 from the first piezoelectric portion 335a and the detection signal Vtr2 from the second piezoelectric portion 335b (see <FIG>).

In such a pressure sensor <NUM>, since the signal detected by the piezoelectric body <NUM> can be strengthened by obtaining the detection signal Vtr of the difference between the detection signal Vtr1 from the first piezoelectric portion 335a and the detection signal Vtr2 from the second piezoelectric portion 335b, the changeover unit <NUM> can operate more accurately. As for the common matters with the pressure sensor <NUM> according to Second Embodiment, the pressure sensor <NUM> exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a conceptual diagram illustrating a circuit of a pressure sensor <NUM> according to Fifth Embodiment. The circuit of the pressure sensor <NUM> shown in <FIG> is different from the circuit of the pressure sensor <NUM> shown in <FIG> in that the detection signal Vtr1 of the first piezoelectric portion 35a is input to the detection signal input unit <NUM> after passing through a diode bridge <NUM>. In other respects, however, the circuit of the pressure sensor <NUM> shown in <FIG> is similar to the circuit of the pressure sensor <NUM> according to First Embodiment. The pressure sensor <NUM> according to Fifth Embodiment is described focusing on the differences from the pressure sensor <NUM> according to First Embodiment, and common matters are not described.

When the detection signal Vtr1 of the first piezoelectric portion 35a is a negative voltage, the diode bridge <NUM> shown in <FIG> inverts and outputs the detection signal Vtr1. Thus, in the detection signal Vtr of the piezoelectric body <NUM> input to the detection signal input unit <NUM> shown in <FIG>, a positive signal responding to the deformation of the membrane <NUM> is input regardless of whether the pressure rises or falls.

<FIG> is graphs showing an example of output results of a pressure P, the detection signal Vtr, and the output signal Vout in the pressure sensor <NUM> including the circuit shown in <FIG>. As shown in the left region of <FIG>, when the pressure of the pressure fluid as a measurement target of the pressure sensor <NUM> is kept high, the strain or change in strain generated in the membrane <NUM> is small, and the detection signal Vtr detected by the piezoelectric body <NUM> and input to the detection signal input unit <NUM> is thus smaller than a predetermined value VL. In this case, the switch control unit <NUM> shown in <FIG> keeps the switch of the changeover unit <NUM> in the OFF state.

When the switch of the changeover unit <NUM> shown in <FIG> is in the OFF state, no electric power is supplied to the pressure detection circuit <NUM>. Thus, as shown in the left part of the lower graph of <FIG>, the pressure detection circuit <NUM> detects no strain, and the value of the output signal Vout from the pressure detection circuit <NUM> does not change.

Next, as shown in the right region of <FIG>, when the pressure of the pressure fluid as a measurement target of the pressure sensor <NUM> decreases, the detection signal Vtr detected by the piezoelectric body <NUM> and input to the detection signal input unit <NUM> becomes the predetermined value VL or more (time T1). In this case, the switch control unit <NUM> shown in <FIG> determines that the detection signal Vtr becomes the predetermined value VL or more via the detection signal input unit <NUM> and switches the switch of the changeover unit <NUM> to the ON state.

When the switch of the changeover unit <NUM> shown in <FIG> is in the ON state, electric power is supplied to the pressure detection circuit <NUM>. Thus, as shown in the right part of the lower graph of <FIG>, the pressure detection circuit <NUM> including the first to fourth resistors R1 to R4 detects a strain of the membrane <NUM> generated by pressure, and the value of the output signal Vout from the pressure detection circuit <NUM> changes depending on the pressure P.

As described above, in the pressure sensor <NUM>, since the diode bridge <NUM> is disposed between the first piezoelectric portion 35a and the detection signal input unit <NUM>, even when the pressure rises as shown in <FIG> or drops as shown in <FIG>, the electric power supply to the pressure detection circuit <NUM> can be started by a predetermined pressure fluctuation as a trigger. As for the common matters with the pressure sensor <NUM> according to Second Embodiment, the pressure sensor <NUM> exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a conceptual diagram illustrating a circuit of a pressure sensor <NUM> according to Sixth Embodiment. The circuit of the pressure sensor <NUM> shown in <FIG> is different from that of the pressure sensor <NUM> according to First Embodiment in that a changeover unit <NUM> is not a switch controlled by the microprocessor <NUM> as shown in <FIG>, but is configured by a transistor <NUM> or the like. In other respects, however, the circuit of the pressure sensor <NUM> shown in <FIG> is similar to the circuit of the pressure sensor <NUM> shown in <FIG>. The pressure sensor <NUM> according to Sixth Embodiment is described focusing on the differences from the pressure sensor <NUM> according to First Embodiment, and common matters are not described.

As shown in <FIG>, the changeover unit <NUM> of the pressure sensor <NUM> is achieved by a circuit consisting of a resistance Ro1, two resistances Ro2, a comparator <NUM>, and a transistor <NUM>. In the changeover unit <NUM> shown in <FIG>, the transistor <NUM> is disposed at the entrance from the power supply voltage VDD to the pressure detection circuit <NUM>, and the electric power supply to the pressure detection circuit <NUM> is switched by the transistor <NUM>. The detection signal Vtr1 of the first piezoelectric portion 35a is binarized by the comparator <NUM> and input to the third terminal of the transistor <NUM>. As a result, ON/OFF of the electric power supply to the pressure detection circuit <NUM> is switched based on the detection signal Vtr1 from the first piezoelectric portion 35a.

<FIG> is graphs showing an example of output results of a pressure P, the detection signal Vtrl, and the output signal Vout in the pressure sensor <NUM> including the circuit shown in <FIG>. As with the circuit of the pressure sensor <NUM> shown in <FIG>, also in the circuit of the pressure sensor <NUM>, as shown in <FIG>, the deformation of the membrane <NUM> is detected by the first piezoelectric portion 35a, and the changeover unit <NUM> can switch electric power supply to the pressure detection circuit <NUM> based on the detection signal Vtr1. As for the common matters with the pressure sensor <NUM> according to First Embodiment, the pressure sensor <NUM> exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a conceptual diagram showing a circuit of a pressure sensor <NUM> according to Seventh Embodiment. The circuit of the pressure sensor <NUM> shown in <FIG> is different from the circuit of the pressure sensor <NUM> shown in <FIG> in that the detection signal Vtr1 of the first piezoelectric portion 35a is input to a comparator <NUM> after passing through a diode bridge <NUM>. In other respects, however, the circuit of the pressure sensor <NUM> shown in <FIG> is similar to the circuit of the pressure sensor <NUM> according to Sixth Embodiment. The pressure sensor <NUM> according to Seventh Embodiment is described focusing on the differences from the pressure sensor <NUM> according to Sixth Embodiment, and common matters are not described.

As with the diode bridge <NUM> shown in <FIG>, when the detection signal Vtr1 of the first piezoelectric portion 35a is a negative voltage, the diode bridge <NUM> shown in <FIG> inverts and outputs it. Thus, a positive signal responding to the deformation of the membrane <NUM> is input to the comparator <NUM> shown in <FIG> regardless of whether the pressure rises or falls.

<FIG> is graphs showing an example of output results of a pressure P, the detection signal Vtrl, and the output signal Vout in the pressure sensor <NUM> including the circuit shown in <FIG>. As with the circuit of the pressure sensor <NUM> shown in <FIG>, also in the circuit of the pressure sensor <NUM>, as shown in <FIG>, the deformation of the membrane <NUM> is detected by the first piezoelectric portion 35a, and the changeover unit <NUM> can switch electric power supply to the pressure detection circuit <NUM> based on the detection signal Vtr1. As for the common matters with the pressure sensor <NUM> according to Sixth Embodiment, the pressure sensor <NUM> exhibits effects similar to those of the pressure sensor <NUM>.

<FIG> is a schematic cross-sectional view of a pressure sensor <NUM> according to Eighth Embodiment. The pressure sensor <NUM> is different from the pressure sensor <NUM> shown in <FIG> in that the pressure sensor <NUM> includes a fillet portion <NUM>. In other respects, however, the pressure sensor <NUM> is similar to the pressure sensor <NUM> according to First Embodiment. The pressure sensor <NUM> according to Eighth Embodiment is described focusing on the differences from the pressure sensor <NUM> according to First Embodiment, and common matters are not described.

As shown in <FIG>, the fillet portion <NUM> connects between the side wall <NUM> connected to an outer edge <NUM> of the membrane <NUM> and the inner surface 22a of the membrane <NUM>. In particular, the fillet portion <NUM> is connected not to the entire inner surface 22a of the membrane <NUM>, but only to a predetermined range of the inside of the outer edge <NUM> of the membrane <NUM>.

The fillet portion <NUM> gradually becomes thinner from the side wall <NUM> toward the center of the membrane <NUM> and is not connected to a fourth strain region <NUM> on the center side of the membrane <NUM>. The fillet portion <NUM> may be made of the same material as the side wall <NUM> or the inner surface 22a of the membrane <NUM> or may be made of a different material.

In the pressure sensor <NUM> including the fillet portion <NUM>, a ratio of the third strain region <NUM> to the fourth strain region <NUM> tends to be larger than that in the pressure sensor <NUM> including no fillet portion. Thus, the pressure sensor <NUM> including the fillet portion <NUM> shown in <FIG> can easily have a sufficient disposition space when the first piezoelectric portion 25a is disposed in the third strain region <NUM>. Thus, the pressure sensor <NUM> can increase the detection output of the piezoelectric body and is advantageous for miniaturization. As for the common matters with the pressure sensor <NUM> according to First Embodiment, the pressure sensor <NUM> exhibits effects similar to those of the pressure sensor <NUM>.

Claim 1:
A pressure sensor (<NUM>) comprising:
a membrane (<NUM>) generating a deformation in response to pressure;
a pressure detection circuit (<NUM>) including at least four resistors (R1-R4) arranged on the membrane and detecting the deformation of the membrane with a bridge circuit formed by the resistors;
the pressure sensor characterized that it comprises: a
piezoelectric body (<NUM>) disposed on the membrane and detecting the deformation of the membrane; and
a changeover unit (<NUM>) switching electric power supply to the pressure detection circuit based on a detection signal from the piezoelectric body.