Sensor module, transducer, voice generator, tactile presentation device, surface inspection device, and electronic apparatus

Abstract

A sensor module comprises a first plate-like member, a piezoelectric element provided on a main surface of the first plate-like member, and a field effect transistor. The piezoelectric element includes: a piezoelectric film having a first main surface and a second main surface facing each other; a reference electrode provided on the first main surface and electrically connected to a reference potential; and a signal electrode provided on the second main surface. The piezoelectric film has a piezoelectric body that is stretched in a stretching direction. The signal electrode is electrically connected to the gate of the field effect transistor. The reference electrode is electrically connected to the source of the field effect transistor.

Description

Sensor module, transducer, sound generator, tactile presentation device, surface inspection device, and electronic device

[0001] The present invention relates to a sensor module using a piezoelectric element.

[0002] As a conventional invention related to a sensor module using a piezoelectric element, for example, a displacement sensor described in Patent Document 1 is known. The displacement sensor described in Patent Document 1 is attached to an object. The displacement sensor described in Patent Document 1 includes an elastic body and a flat film-shaped piezoelectric element attached to the main surface of the elastic body. Electrodes are formed on both main surfaces of the piezoelectric sheet. The piezoelectric sheet contains polylactic acid. The piezoelectric sheet is stretched in a uniaxial direction. The displacement sensor described in Patent Document 1 detects bending and twisting of an object by detecting displacement of the elastic body. Thereby, the displacement sensor described in Patent Document 1 detects a pressing operation of a person.

[0003] International Publication No. 2012 / 137897

[0004] By using a piezoelectric element, the sensor can be made thinner, so that the sensor module can be miniaturized. In addition, the piezoelectric element can respond at high speed. The inventor of the present application focused on these features of the piezoelectric element and studied a new sensor module that enables further application development of the piezoelectric element.

[0005] Therefore, an object of the present invention is to provide a new sensor module that enables further application development of a piezoelectric element.

[0006] A sensor module according to one embodiment of the present invention comprises a first plate-shaped member, a piezoelectric element provided on the main surface of the first plate-shaped member, and a field-effect transistor, wherein the piezoelectric element includes a piezoelectric film having opposing first and second main surfaces, a reference electrode provided on the first main surface and electrically connected to a reference potential, and a signal electrode provided on the second main surface, wherein the piezoelectric film has a piezoelectric body stretched in the stretching direction, the signal electrode is electrically connected to the gate of the field-effect transistor, and the reference electrode is electrically connected to the source of the field-effect transistor.

[0007] In the case of a displacement sensor for detecting human pressing operations, the frequency of the input signal is a low frequency of about 0.1 to 10 Hz. If the charge signal generated by a piezoelectric element is converted into a voltage signal by an integral amplifier circuit, a low-frequency output signal corresponding to the input signal can be obtained with high sensitivity. However, if the time constant of the integral amplifier circuit is optimized for a low frequency of about 0.1 to 10 Hz, the integral amplifier circuit will block high-frequency components of 10 Hz or higher. On the other hand, the sensor module according to the present invention is equipped with a field-effect transistor. The gate of the field-effect transistor is electrically connected to the signal electrode of the piezoelectric element. The source of the field-effect transistor is electrically connected to the reference electrode of the piezoelectric element. In the present invention, the voltage change between the signal electrode and the reference electrode of the piezoelectric element is extracted via the drain voltage of the field-effect transistor, and the input signal is not integrally amplified. Therefore, in the present invention, the input signal can be output with high frequency response via the drain of the field-effect transistor. Accordingly, the sensor module according to the present invention can output the input signal with high sensitivity without blocking it, even if the frequency of the input signal is a high frequency of 10 Hz or higher. Therefore, even if the input signal frequency is high, such as 10 Hz to 20 kHz, the detection accuracy of the sensor module does not deteriorate. As a result, the sensor module can be used not only as a displacement sensor for detecting human pressing operations, but also as a transducer, a tactile sensing device that provides more realistic tactile feedback, a surface inspection device, and even as a sensing device for electronic devices that estimate the object to be detected.

[0008] According to the present invention, it becomes possible to develop new applications for piezoelectric elements.

[0009] Figure 1 is a plan view of the sensor module 1. Figure 2 is a side view of the sensor module 1. Figure 3 is an exploded perspective view of the piezoelectric element 3. Figure 4 is a block diagram showing a specific example of the connection between the sensor module 1 and PC 10A, and the second end E2 of the cable 5. Figure 5 is a circuit diagram when the sensor module 1 is connected to PC 10A. Figure 6 is an input signal IS as an example of an input signal. Figure 7 is an output signal OS1 of the sensor module in a comparative example when the input signal is input signal IS. Figure 8 is an output signal OS2 of the sensor module 1 when the input signal is input signal IS. Figure 9 is a diagram showing the experimental environment for vocal cord sensing using the sensor module 1. Figure 10 is an example of an output signal OS3 as an example of an audio signal. Figure 11 is a block diagram of an electrotactile device ED using the sensor module 1. Figure 12 is a block diagram of a tactile presentation device TPD using the sensor module 1. Figure 13 is a circuit diagram when the sensor module 1 is connected to an oscilloscope 10B. Figure 14 is a plan view of the sensor module 1a. Figure 15 is a side view of sensor module 1a. Figure 16 is a top view of sensor module 1b. Figure 17 is a side view of sensor module 1b. Figure 18 is a top view of sensor module 1c. Figure 19 is a side view of sensor module 1c. Figure 20 is a block diagram of electronic device 100.

[0010] [First Embodiment] (Sensor Module 1) Below, a sensor module 1 according to the first embodiment of the present invention will be described with reference to the drawings. Figure 1 is a plan view of the sensor module 1. Figure 2 is a side view of the sensor module 1. Note that the cable 5 is omitted in Figure 2. Figure 3 is an exploded perspective view of the piezoelectric element 3.

[0011] In the sensor module 1, as an example, directions are defined as follows: As shown in Figure 1, the direction in which the long side of the upper main surface US2 extends is defined as the left-right direction. The direction in which the short side of the upper main surface US2 extends is defined as the front-back direction. As shown in Figure 2, the direction in which the upper main surface US2 and the lower main surface DS2 are aligned is defined as the up-down direction. The left-right direction, front-back direction, and up-down direction are orthogonal to each other. However, the left-right direction, front-back direction, and up-down direction in this specification are directions defined for the convenience of explanation and do not necessarily coincide with the left-right direction, front-back direction, and up-down direction when the sensor module 1 is in use. Also, in each drawing, the left direction and the right direction may be swapped, the front direction and the rear direction may be swapped, and the up direction and the down direction may be swapped.

[0012] As shown in Figure 1, the sensor module 1 comprises a first substrate 2, a piezoelectric element 3, an FET 4, and a cable 5. As shown in Figures 1 and 2, the first substrate 2 is plate-shaped. The first substrate 2 is elastic. In this embodiment, the first substrate 2 is a printed circuit board. The first substrate 2 has opposing upper main surface US2 and lower main surface DS2. The upper main surface US2 and the lower main surface DS2 are rectangular in shape, each having a long side extending in the left-right direction and a short side extending in the front-back direction. The first substrate 2 includes mounting areas for mounting the piezoelectric element 3 and the FET 4, wiring, a signal terminal ST, and a ground terminal GT. The first substrate 2 is an example of the first plate-shaped member according to the present invention. The FET 4 corresponds to a field-effect transistor according to the present invention. Note that the upper main surface US2 and the lower main surface DS2 do not necessarily have to be rectangular in shape.

[0013] As shown in Figure 1, the piezoelectric element 3 is provided on the upper main surface US2 of the first substrate 2. The piezoelectric element 3 is in the shape of a flat film. As shown in Figure 3, the piezoelectric element 3 includes a piezoelectric film 31, a reference electrode 32, and a signal electrode 33.

[0014] The piezoelectric film 31 has opposing first main surface S1 and second main surface S2. The first main surface S1 and the second main surface S2 are arranged in this order along the downward direction. The first main surface S1 and the second main surface S2 are rectangular in shape, each having a long side extending in the left-right direction and a short side extending in the front-back direction.

[0015] The piezoelectric film 31 becomes polarized due to deformation, generating a voltage between the first main surface S1 and the second main surface S2. The voltage generated between the first main surface S1 and the second main surface S2 depends on the amount of deformation of the piezoelectric film 31.

[0016] The piezoelectric film 31 is, for example, a film formed from a chiral polymer. The chiral polymer is, for example, polylactic acid (PLA) such as L-type polylactic acid (PLLA) or D-type polylactic acid (PDLA). The main chain of PLA has a helical structure. PLA has piezoelectric properties when it is uniaxially stretched and its molecules are oriented. The piezoelectric film 31 has a piezoelectric constant of d14 because it contains PLA stretched in the stretching direction OD. PLA is an example of a piezoelectric material according to the present invention.

[0017] The stretching direction OD of the PLA forms a 45-degree angle with respect to both the left-right and front-back directions. Note that the 45-degree angle may be within a range of approximately 45 degrees ± 10 degrees. When the piezoelectric film 31 is stretched or compressed along the left-right direction, a voltage is generated between the first main surface S1 and the second main surface S2. The polarity of the voltage generated by stretching along the left-right direction is opposite to the polarity of the voltage generated by compression along the left-right direction. Similarly, when the piezoelectric film 31 is stretched or compressed along the front-back direction, a voltage is generated between the first main surface S1 and the second main surface S2. The polarity of the voltage generated by stretching along the front-back direction is opposite to the polarity of the voltage generated by compression along the front-back direction. Note that the stretching direction OD of the PLA may form an angle other than 45 degrees with respect to both the left-right and front-back directions.

[0018] The reference electrode 32 is conductive. The material of the reference electrode 32 is, for example, copper. The reference electrode 32 is in the form of a flat film. The reference electrode 32 is provided on the first main surface S1 of the piezoelectric film 31. The reference electrode 32 functions as a reference electrode by being electrically connected to a reference potential. Also, when the reference potential is 0V, the reference electrode 32 functions as a shielding conductor.

[0019] The signal electrode 33 is conductive. The material of the signal electrode 33 is, for example, copper. The signal electrode 33 is in the shape of a flat film. The signal electrode 33 is provided on the second main surface S2 of the piezoelectric film 31. The signal electrode 33 functions as a signal electrode for outputting the voltage generated by the piezoelectric film 31. In this embodiment, the lower main surface of the signal electrode 33 is provided on the upper main surface US2 of the first substrate 2. Alternatively, the signal electrode 33 may be provided on the first main surface S1 and the reference electrode 32 may be provided on the second main surface S2. In this case, the lower main surface of the reference electrode 32 is provided on the upper main surface US2 of the first substrate 2.

[0020] Furthermore, the long sides of the first main surface S1 and the second main surface S2 of the piezoelectric film 31 do not necessarily extend in the left-right direction. That is, the direction in which the long sides of the first main surface S1 and the second main surface S2 of the piezoelectric film 31 extend does not necessarily coincide with the direction in which the long sides of the upper main surface US2 and the lower main surface DS2 of the first substrate 2 extend. Also, the short sides of the first main surface S1 and the second main surface S2 do not necessarily extend in the front-back direction. That is, the direction in which the short sides of the first main surface S1 and the second main surface S2 of the piezoelectric film 31 extend does not necessarily coincide with the direction in which the short sides of the upper main surface US2 and the lower main surface DS2 of the first substrate 2 extend. Moreover, the first main surface S1 and the second main surface S2 do not necessarily have to be rectangular in shape.

[0021] The piezoelectric film 31 may have a piezoelectric constant other than d14. The piezoelectric film 31 may also be a film formed from a piezoelectric material other than a chiral polymer. For example, if the piezoelectric film 31 is a film formed from polyvinylidene fluoride, the piezoelectric film 31 has a piezoelectric constant of d31.

[0022] As shown in Figure 1, the FET 4 is provided on the upper main surface US2 of the first substrate 2. The FET 4 has a gate, a source, and a drain. The FET 4 is a transistor that controls the current between the drain and the source by applying a voltage to the gate. The FET 4 is, for example, a JFET (Junction Field Effect Transistor). In this embodiment, the FET 4 is an N-channel JFET. The gate of the FET 4 is electrically connected to the signal electrode 33 of the piezoelectric element 3 via the wiring of the first substrate 2. The source of the FET 4 is electrically connected to the reference electrode 32 of the piezoelectric element 3 and the ground terminal GT of the first substrate 2 via the wiring of the first substrate 2. The drain of the FET 4 is electrically connected to the signal terminal ST of the first substrate 2 via the wiring of the first substrate 2.

[0023] Figure 4 is a block diagram showing a specific example of the connection between the sensor module 1 and the PC 10A, and the second end E2 of the cable 5. As shown in Figure 4, the cable 5 includes a first core wire CO1, a second core wire CO2, and a phone plug PP. The cable 5 has a first end E1 and a second end E2. The first end E1 is connected to the first board 2. The first core wire CO1 is connected to the signal terminal ST of the first board 2. The second core wire CO2 is connected to the ground terminal GT of the first board 2.

[0024] The phone plug PP is provided at the second end E2 of the cable 5. The phone plug PP is paired with a phone jack provided on an electronic device, etc. The phone plug PP is removable from the phone jack. By inserting the phone plug PP into a phone jack provided on an electronic device, etc., a signal is transmitted to the electronic device, etc. via the phone plug PP and the phone jack. The electronic device, etc., is, for example, a personal computer (PC), a smartphone, or a tablet computer. In this embodiment, the phone plug PP is inserted into a phone jack provided on PC 10A, which is a PC.

[0025] The phone plug PP has a signal terminal SIG, a ground terminal GND, a right channel terminal R, and a left channel terminal L. Each terminal is electrically isolated from the others. In this embodiment, the phone plug PP is a 4-pole mini plug. The right channel terminal R transmits the right audio signal. The left channel terminal L transmits the left audio signal. That is, the phone plug PP can transmit a stereo signal. However, in this invention, the right channel terminal R and the left channel terminal L are not used. Therefore, the phone plug PP does not need to have the right channel terminal R and the left channel terminal L.

[0026] The signal terminal SIG is connected to the first core wire CO1. As described above, the first core wire CO1 is connected to the signal terminal ST of the first board 2. Therefore, the signal terminal SIG is electrically connected to the drain of FET 4. The signal terminal SIG is connected to the microphone input terminal of the phone jack of PC10A.

[0027] The ground terminal GND is connected to the second core wire CO2. As described above, the second core wire CO2 is connected to the ground terminal GT of the first board 2. Therefore, the ground terminal GND is electrically connected to the source of FET 4. The ground terminal GND is connected to the ground input terminal of the phone jack of PC10A.

[0028] In this embodiment, the signal terminal SIG and the ground terminal GND are arranged in this order toward the second terminal E2, but they may also be arranged so that the ground terminal GND and the signal terminal SIG are in that order toward the second terminal E2.

[0029] Figure 5 is a circuit diagram when the sensor module 1 is connected to PC10A. As shown in Figure 5, PC10A is equipped with a pull-up resistor RPU and a capacitor C. Both ends of the pull-up resistor RPU are electrically connected to the power supply Vcc and the microphone input terminal of the phone jack, respectively. One end of capacitor C is electrically connected to the microphone input terminal of the phone jack. The other end of capacitor C is connected to another device within PC10A. The sound signal SS is input to the other device within PC10A. In other words, the microphone input terminal of PC10A is a plug-in power system that supplies power from PC10A to devices other than PC10A. The sound signal SS is amplified when the other end of capacitor C is connected to an amplifier such as an operational amplifier in the other device within PC10A.

[0030] The ground of PC10A is electrically connected to the ground input terminal of the phone jack of PC10A. Therefore, in this embodiment, the reference electrode 32 of the piezoelectric element 3 and the source of the FET 4 are electrically connected to the ground of PC10A.

[0031] (Operation of Sensor Module 1) The operation of sensor module 1 will be explained below in comparison with the sensor module of the comparative example. Figure 6 shows the input signal IS as an example of an input signal. In Figure 6, the horizontal axis is time t, and the vertical axis is the input signal IS. Also in Figure 6, the solid line is the input signal IS, and the dashed line is the low-frequency component of the input signal IS. Figure 7 shows the output signal OS1 of the sensor module of the comparative example when the input signal is input signal IS. In Figure 7, the horizontal axis is time t, and the vertical axis is the output signal OS1. Figure 8 shows the output signal OS2 of sensor module 1 when the input signal is input signal IS. In Figure 8, the horizontal axis is time t, and the vertical axis is the output signal OS2.

[0032] In the comparative example sensor module, the signal electrode 33 and reference electrode 32 of the piezoelectric element 3 are each connected to a charge amplifier. The charge amplifier converts and amplifies the charge generated on the first main surface S1 and the second main surface S2 of the piezoelectric film 31 into a voltage signal using an integral amplifier circuit. In the comparative example sensor module, the output voltage of the charge amplifier becomes the output signal. In the comparative example sensor module, the signal electrode 33 and reference electrode 32 of the piezoelectric element 3 may each be connected to a transimpedance amplifier having an integral amplifier circuit. A significant difference between the comparative example sensor module and the sensor module 1 according to this embodiment is that the signal electrode 33 and reference electrode 32 of the piezoelectric element 3 are each connected to a charge amplifier or transimpedance amplifier having an integral amplifier circuit, rather than to the FET 4. In the sensor module 1 according to this embodiment, the voltage between the drain and source of the FET 4 becomes the output signal.

[0033] For example, an input signal IS as shown in Figure 6 is input to the sensor module 1 according to this embodiment and to the sensor module according to the comparative example. Methods for inputting the input signal IS include, for example, applying vibration having the waveform of the input signal IS to the first substrate 2, or bringing the first substrate 2 into contact with an object so that the displacement of the first substrate 2 is equal to the waveform of the input signal IS.

[0034] For example, in the case of a displacement sensor for detecting human pressing, the frequency of the input signal is a low frequency of about 0.1 to 10 Hz. If the signal electrode 33 and reference electrode 32 of the piezoelectric element 3 are connected to an integral amplifier circuit, a low-frequency output signal corresponding to the input signal can be obtained with high sensitivity. However, if the time constant of the integral amplifier circuit is optimized for a low frequency of about 0.1 to 10 Hz, the integral amplifier circuit will block high-frequency components of 10 Hz or higher. As a result, as shown in Figure 7, the waveform of the output signal OS1 becomes a waveform that extracts the low-frequency components of the input signal IS. Therefore, the detection accuracy of the sensor module in the comparative example deteriorates significantly at frequencies of 10 Hz or higher.

[0035] On the other hand, in the sensor module 1 according to this embodiment, the signal electrode 33 and reference electrode 32 of the piezoelectric element 3 are connected to the gate and source of the FET 4, respectively. In the sensor module 1 according to this embodiment, the voltage change between the signal electrode 33 and the reference electrode 32 of the piezoelectric element 3 is taken via the drain voltage of the FET 4, and the input signal is not integrally amplified. Therefore, the sensor module 1 according to this embodiment can output the input signal IS with high frequency response via the drain of the FET 4. Consequently, even if the frequency of the input signal IS is a high frequency such as 10 Hz to 20 kHz, the sensor module 1 according to this embodiment can output the input signal IS with high sensitivity without blocking it. Therefore, as shown in Figure 8, even if the frequency of the input signal is a high frequency such as 10 Hz to 20 kHz, the output signal OS2 does not deviate from the input signal IS, and the detection accuracy of the sensor module 1 according to this embodiment does not deteriorate.

[0036] Furthermore, the sensor module 1 detects only vibrations of the object to be detected that are mechanically connected to the first substrate 2, without the use of air as an intermediary. This is because even if the air surrounding the sensor module 1 vibrates, the vibration of the first substrate 2 is minimal. Therefore, the sensor module 1 is not affected by air vibrations and is not affected by ambient noise. Note that mechanical connection is not limited to cases where the first substrate 2 and the object to be detected are in direct contact, but also includes cases where the first substrate 2 is indirectly connected to the object to be detected via a solid such as a protective film.

[0037] Furthermore, the output impedance of the piezoelectric element 3 is high, and the signal electrode 33 of the piezoelectric element 3 is susceptible to noise due to electrostatic induction. On the other hand, the output impedance of the FET 4 is low, and the drain of the FET 4 is less susceptible to noise due to electrostatic induction. Therefore, the cable 5 does not need to be a shielded cable. Also, the distance between the FET 4 and the PC 10A can be increased.

[0038] (Application Development of Sensor Module 1, Part 1) The application development of Sensor Module 1 will be explained below with reference to the drawings. Figure 9 shows the experimental environment for vocal cord sensing using Sensor Module 1. Figure 10 is an example of the output signal OS3 as an example of an audio signal. In Figure 10, the horizontal axis is time t, and the vertical axis is the output signal OS3.

[0039] The frequency range of the human voice is approximately 100 Hz to 5 kHz. Therefore, the inventors of this invention hypothesized that by attaching the sensor module 1 to the vicinity of the vocal cords, such as the throat or face, it would be possible to detect the human voice from the vibrations of the skin surface when a person speaks, and conducted experiments. In this experiment, the lower main surface DS2 of the first substrate 2 was attached to the skin near the vocal cords of a person, and the output signal OS3 when a person spoke was confirmed. In this experiment, as shown in Figure 9, an amplification circuit AMP and a waveform display circuit WDC were used. The amplification circuit AMP includes a pull-up resistor RPU and a capacitor C. The signal obtained by amplifying the detection signal DS with the amplification circuit AMP was used as the output signal OS3, and the output signal OS3 was displayed with the waveform display circuit WDC.

[0040] As shown in Figure 10, in this experiment, we were able to obtain an output signal OS3 corresponding to human speech. When a person speaks, the skin near the vocal cords vibrates. The vibration of the skin causes the first substrate 2 to vibrate. The vibration of the first substrate 2 causes the piezoelectric film 31 to expand and contract. The expansion and contraction of the piezoelectric film 31 generates a voltage between the first main surface S1 and the second main surface S2. The sensor module 1 outputs a detection signal DS (voltage between the drain and source of FET 4) that changes due to the vibration of the skin near the vocal cords (vibration of the first substrate 2) via the drain of FET 4. In other words, by mechanically connecting the first substrate 2 to the skin near the vocal cords (detection target), the sensor module 1 functions as a transducer by converting the mechanical vibration of the skin near the vocal cords (detection target) into an electrical signal.

[0041] Furthermore, artificial intelligence may be added to this application. In this case, the artificial intelligence identifies the speaker based on the detection signal DS corresponding to human speech. Therefore, the sensor module 1 functions as a transducer for a speech recognition device.

[0042] Incidentally, in this application development, a drive circuit and a speaker may be further provided. The drive circuit is, for example, an amplifier. The detection signal DS corresponding to a person's speech is transmitted to the drive circuit. The drive circuit amplifies the detection signal DS. The speaker generates sound based on the amplified detection signal DS. That is, the speaker generates sound based on the detection signal DS. Thereby, the speaker can output sound close to the original person's speech. Therefore, the sensor module 1 functions as a transducer of the sound generator.

[0043] Incidentally, in this application development, the detection target is not limited to a person's voice. The detection target may be, for example, a door or a desk. For example, when the first substrate 2 is attached to the surface of a door or a desk, the sensor module 1 can detect the vibration of the door or the desk at the time of knocking. In order to attach the first substrate 2 to the surface of the detection target, the detection target may be a solid.

[0044] As described above, the sensor module 1 detects only the vibration of the detection target that is mechanically connected to the first substrate 2 without using air as a medium. Therefore, it is not affected by the vibration of air and is not affected by ambient noise. The sensor module 1 is particularly effective as a means for detecting a silent voice. Also, since air is not used as a medium, there is no need to provide an air gap and vibration electrodes. Therefore, according to the sensor module 1, the transducer can be miniaturized.

[0045] (Another Application Development of the Sensor Module 1) Next, another application development of the sensor module 1 will be described with reference to the drawings. FIG. 11 is a block diagram of an electro-tactile device ED using the sensor module 1.

[0046] As shown in FIG. 11, the electro-tactile device ED includes a sensor module 1, a control circuit CS, a voltage generation circuit VGC, a positive electrode PE, and a negative electrode NE. The positive electrode PE and the negative electrode NE are each brought into contact with a person's skin. The electro-tactile device ED is an example of a tactile presentation device according to the present invention.

[0047] The control circuit CS includes a pull-up resistor RPU and a capacitor C. The signal terminal ST and the ground terminal GT of the first substrate 2 are connected to the control circuit CS. Thereby, the detection signal DS (the voltage between the drain and the source of the FET4) of the sensor module 1 is input to the control circuit CS. That is, the sensor module 1 outputs the detection signal DS that changes due to the vibration of the first substrate 2 via the drain of the FET4. The detection signal DS is input to the control circuit CS via the pull-up resistor RPU and the capacitor C.

[0048] The voltage generation circuit VGC is connected to the control circuit CS. The control circuit CS generates a voltage in the voltage generation circuit VGC based on the detection signal DS. That is, the voltage generation circuit VGC generates a voltage based on the detection signal DS. For example, the voltage generation circuit VGC generates a voltage obtained by amplifying the detection signal DS.

[0049] The positive electrode PE and the negative electrode NE are connected to the voltage generation circuit VGC. The positive electrode PE and the negative electrode NE output the voltage generated by the voltage generation circuit VGC, cause a weak current to flow through a person's body, and activate the sensory nerves under the person's skin.

[0050] For example, stroke a cloth or an object having irregularities on its surface on the left side surface of the first substrate 2. Thereby, the first substrate 2 vibrates corresponding to the irregularities on the surface of the cloth or the object. Due to the vibration of the first substrate 2, the piezoelectric film 31 expands and contracts. The piezoelectric film 31 generates a voltage between the first main surface S1 and the second main surface S2 due to the expansion and contraction. Thereby, the sensor module 1 outputs the detection signal DS that changes due to the vibration of the first substrate 2 via the drain of the FET4. That is, the sensor module 1 can detect the texture of the cloth or the rough texture of the surface of the object. Note that it is not limited to the case where the first substrate 2 directly contacts the cloth or the object, and the first substrate 2 and the cloth or the object may be indirectly in contact.

[0051] The voltage generation circuit VGC generates a voltage based on the detection signal DS. This causes the positive electrode PE and negative electrode NE to send a weak current through the human body corresponding to the unevenness of the surface of the cloth or object, activating the sensory nerves beneath the skin. Therefore, the texture of the cloth or the roughness of the surface of the object detected by the sensor module 1 can be transmitted to the human body from the positive electrode PE and negative electrode NE. In other words, the electrotactile device ED using the sensor module 1 can provide more realistic tactile feedback.

[0052] (Application Development of Sensor Module 1, Part 3) Below, we will describe another application development for Sensor Module 1 with reference to the drawings. Figure 12 is a block diagram of a haptic presentation device (TPD) using Sensor Module 1.

[0053] As shown in Figure 12, the tactile presentation device TPD comprises a sensor module 1, a drive circuit DC, and an actuator AC.

[0054] The drive circuit DC includes a pull-up resistor RPU, a capacitor C, and an operational amplifier. The signal terminal ST and ground terminal GT of the first board 2 are connected to the drive circuit DC. As a result, the detection signal DS (voltage between the drain and source of the FET 4) from the sensor module 1 is input to the drive circuit DC. That is, the sensor module 1 outputs a detection signal DS that changes due to vibrations of the first board 2 via the drain of the FET 4. The detection signal DS is input to the operational amplifier in the drive circuit DC via the pull-up resistor RPU and capacitor C. The operational amplifier amplifies the detection signal DS.

[0055] The actuator AC is connected to the drive circuit DC. The actuator AC operates based on the amplified detection signal DS. That is, the actuator AC operates based on the detection signal DS. The actuator AC is, for example, an electromagnetic actuator, a piezoelectric actuator, a diaphragm, or a vibrating plate. When a diaphragm or vibrating plate is used as the actuator AC, the diaphragm or vibrating plate vibrates based on the detection signal DS. The diaphragm or vibrating plate may be, for example, a diaphragm or vibrating plate provided in a speaker or the like.

[0056] Similar to the case of the electrotactile device ED, for example, a cloth or an object with an uneven surface is stroked with the left side of the first substrate 2. As a result, the sensor module 1 outputs a detection signal DS that changes due to the vibration of the first substrate 2 via the drain of the FET 4. Similar to the case of the electrotactile device ED, the sensor module 1 can detect the texture of the cloth or the roughness of the surface of the object. Note that the first substrate 2 and the cloth or object are not limited to direct contact; they may also be indirectly in contact.

[0057] Actuator AC operates based on the detection signal DS. This allows Actuator AC to operate in response to the unevenness of the surface of the fabric or object. A person touching Actuator AC can feel the texture of the fabric or the roughness of the object's surface, gaining the sensation of actually touching the surface. In other words, the haptic feedback device TPD using sensor module 1 provides more realistic haptic feedback than the electrotactile device ED.

[0058] [Effects] Sensor module 1 enables the development of new applications for piezoelectric elements. As described above, sensor module 1 can be used not only as a displacement sensor for detecting human pressing operations, but also as a transducer and a tactile sensing device that provides more realistic tactile feedback.

[0059] More specifically, the sensor module 1 includes an FET 4. The gate of the FET 4 is electrically connected to the signal electrode 33 of the piezoelectric element 3. The source of the FET 4 is electrically connected to the reference electrode 32 of the piezoelectric element 3. Therefore, as described above, the sensor module 1 can output the input signal with high frequency response via the drain of the FET 4. Consequently, even if the frequency of the input signal is high, such as 10 Hz to 20 kHz, the output signal does not deviate from the input signal, and the detection accuracy of the sensor module 1 does not deteriorate. As a result, the sensor module 1 can be used not only as a displacement sensor for detecting human pressing operations, but also as a transducer and a tactile sensing device that provides more realistic tactile feedback.

[0060] Furthermore, the FET 4, like the piezoelectric element 3, is provided on the upper main surface US2 of the first substrate 2. Therefore, the diaphragm that vibrates when detecting vibrations of the target object and the circuit board on which the wiring between the piezoelectric element 3 and the FET 4 is mounted can be made common. This makes it possible to miniaturize the sensor module 1. Consequently, the sensor module 1 can be installed in a wider variety of environments.

[0061] Furthermore, the sensor module 1 is equipped with a phone plug PP. The signal terminal SIG of the phone plug PP is electrically connected to the drain of the FET 4. Also, the ground terminal GND of the phone plug PP is electrically connected to the source of the FET 4. Therefore, the sensor module 1 outputs a detection signal DS via the signal terminal SIG of the phone plug PP. The phone plug PP can be plugged into a phone jack provided on a PC, smartphone, or tablet computer (hereinafter referred to as "PC, etc."). Since the sensor module 1 is a device that outputs a frequency signal corresponding to the sound signal connected to the microphone input terminal, it is recognized as a microphone device by software (e.g., device manager) within the PC, etc. Because the sensor module 1 is equipped with a phone plug PP, the detection signal DS can be input to the PC, etc. as a sound signal. Therefore, the detection signal DS can be utilized in audio application programs for the PC, etc. This makes it possible to visualize the vibration waveform of the first board 2 on the PC, etc., perform frequency analysis of the detection signal DS, and even utilize it as a human interface for the PC, etc. Therefore, the range of applications for piezoelectric elements can be greatly expanded.

[0062] Note that if the sensor module 1 is not connected to a PC or the like, it does not need to have a phone plug PP. Figure 13 is a circuit diagram when the sensor module 1 is connected to the oscilloscope 10B. As shown in Figure 13, for example, if the sensor module 1 is connected to the oscilloscope 10B, the sensor module 1 does not need to have a phone plug PP. A pull-up resistor RPU, a capacitor C, and an operational amplifier OP are provided between the sensor module 1 and the oscilloscope 10B, and the ground terminal GT and the negative power supply terminal of the operational amplifier OP are connected to ground. The operational amplifier OP amplifies the signal output via the other end of the capacitor C. By connecting the output terminal of the operational amplifier OP to the oscilloscope 10B, the sensor module 1 can be connected to the oscilloscope 10B.

[0063] [First Modification] Below, a sensor module 1a according to the first modification of the present invention will be described with reference to the drawings. Figure 14 is a plan view of the sensor module 1a. Figure 15 is a side view of the sensor module 1a. Note that the cable 5 is omitted in Figure 15. Note that only the parts of the sensor module 1a that differ from the sensor module 1 will be described, and the rest will be omitted.

[0064] As shown in Figures 14 and 15, the sensor module 1a further comprises a second substrate 6. The second substrate 6 is plate-shaped. In this modified example, the first substrate 2 is a flexible substrate, and the second substrate 6 is a printed circuit board. The elastic modulus of the first substrate 2 is lower than that of the second substrate 6. The second substrate 6 is an example of a second plate-shaped member according to the present invention.

[0065] The second substrate 6 has opposing upper main surface US6 and lower main surface DS6. The upper main surface US6 and lower main surface DS6 are rectangular in shape, each having a long side extending in the left-right direction and a short side extending in the front-back direction. In this modified example, the second substrate 6 includes a mounting area for mounting the first substrate 2 and the FET 4, wiring, signal terminal ST and ground terminal GT, while the first substrate 2 does not include a mounting area for mounting the FET 4, wiring, signal terminal ST and ground terminal GT. Note that the upper main surface US6 and lower main surface DS6 do not necessarily have to be rectangular in shape.

[0066] The first substrate 2 is provided on the upper main surface US6 of the second substrate 6. The first substrate 2 protrudes to the left from the left end of the second substrate 6. As a result, when viewed in the vertical direction (normal to the main surface of the second substrate 6), the first substrate 2 has a first region A1 that does not overlap with the second substrate 6. The piezoelectric element 3 is provided in the first region A1. The FET 4 is provided on the upper main surface US6 of the second substrate 6.

[0067] Because the elastic modulus of the first substrate 2 is lower than that of the second substrate 6, the first substrate 2 is soft and can be bent. Furthermore, the first region A1 is a region that does not overlap with the second substrate 6 when viewed in the direction normal to the main surface of the second substrate 6. Therefore, the piezoelectric element 3 provided in the first region A1 is more easily deformed than the piezoelectric element 3 related to the sensor module 1. Consequently, the sensor module 1a can be made more sensitive.

[0068] [Second Modification] Below, a sensor module 1b according to a second modification of the present invention will be described with reference to the drawings. Figure 16 is a plan view of the sensor module 1b. Figure 19 is a side view of the sensor module 1b. Note that the cable 5 is omitted in Figure 17. Note that only the parts of the sensor module 1b that differ from the sensor module 1 will be described, and the rest will be omitted.

[0069] As shown in Figures 16 and 17, the sensor module 1b further includes a weight 7. The weight 7 is located at the left end of the upper main surface US2 of the first substrate 2. The weight 7 is heavier than both the piezoelectric element 3 and the FET 4.

[0070] Sensor module 1b achieves the same effect as sensor module 1. Furthermore, sensor module 1b is equipped with a weight 7 provided on the first substrate 2. By adjusting the mass of weight 7, the natural frequency of the first substrate 2 can be adjusted to a specific frequency. When the first substrate 2 is vibrated at its natural frequency, the vibration of the first substrate 2 is amplified by resonance. Therefore, sensor module 1b makes it easier to detect specific frequency components.

[0071] The weight 7 may be provided on the lower main surface DS2 of the first substrate 2 or on the side surface of the first substrate 2. Furthermore, the location where the weight 7 is provided is not limited to the left end of the first substrate 2. Also, the weight 7 does not necessarily have to be a separate component from the first substrate 2, and the weight 7 and the first substrate 2 may be integrated together.

[0072] [Third Modification] Below, a sensor module 1c according to a third modification of the present invention will be described with reference to the drawings. Figure 18 is a plan view of the sensor module 1c. Figure 19 is a side view of the sensor module 1c. Note that the cable 5 is omitted in Figure 19. Note that only the parts of the sensor module 1c that differ from the sensor module 1 will be described, and the rest will be omitted.

[0073] As shown in Figures 18 and 19, the sensor module 1c further comprises a pointed member 8. The pointed member 8 is provided at the left end of the lower main surface DS2 of the first substrate 2. The pointed member 8 is a square pyramidal shape that protrudes downward from the lower main surface DS2 of the first substrate 2. The lower end (tip) of the pointed member 8 is pointed. By touching the surface of the object to be detected with the lower end of the pointed member 8, the irregularities of the surface of the object to be detected are detected. The pointed member 8 corresponds to the pointed portion according to the present invention.

[0074] Sensor module 1c achieves the same effect as sensor module 1. Furthermore, sensor module 1c is equipped with a pointed tip. Therefore, by touching the surface of the object to be detected with the tip of the pointed tip, it is possible to detect surface irregularities of the object with higher accuracy than, for example, touching the surface of the object with the left side of the first substrate 2. Thus, sensor module 1c can be used as a sensing device in a surface inspection apparatus.

[0075] The pointed member 8 may be provided on the upper main surface US2 of the first substrate 2 or on the side surface of the first substrate 2. Furthermore, the location where the pointed member 8 is provided is not limited to the left end of the first substrate 2. Also, the pointed member 8 is not limited to a square pyramidal shape. Furthermore, the tip of the pointed member 8 is not limited to the lower end of the pointed member 8. In addition, the pointed member 8 does not necessarily have to be a separate component from the first substrate 2, and the pointed member 8 and the first substrate 2 may be integrated together.

[0076] [Fourth Modification] Below, an electronic device 100 according to the fourth modification of the present invention will be described with reference to the drawings. Figure 20 is a block diagram of the electronic device 100.

[0077] As shown in Figure 20, the electronic device 100 includes a sensor module 1 and a determination circuit 101.

[0078] The determination circuit 101 includes a pull-up resistor RPU and a capacitor C. The signal terminal ST and ground terminal GT of the first board 2 are connected to the determination circuit 101. As a result, the detection signal DS (voltage between the drain and source of the FET 4) from the sensor module 1 is input to the determination circuit 101. That is, the sensor module 1 outputs a detection signal DS that changes due to vibration of the first board 2 via the drain of the FET 4. The detection signal DS is input to the determination circuit 101 via the pull-up resistor RPU and capacitor C.

[0079] The determination circuit 101 analyzes the detection signal DS. In this modified example, the determination circuit 101 includes a memory that pre-stores electrical signals corresponding to mechanical vibrations for each detection target. The memory includes, for example, ROM (Read Only Memory) and RAM (Random Access Memory). Based on the detection signal DS, the determination circuit 101 estimates the detection target.

[0080] According to the electronic device 100, the object to be detected can be estimated. Therefore, the sensor module 1 can be used as a sensing device for the electronic device 100 that estimates the object to be detected.

[0081] The determination circuit 101 may also estimate the detection target by analyzing the detection signal DS using an analysis method such as FFT (Fast Fourier Transform) analysis or wavelet analysis, and extracting vibration characteristics such as the highest frequency.

[0082] Furthermore, the method by which the determination circuit 101 estimates the target of detection is not limited to the method described above; for example, artificial intelligence that has performed machine learning such as deep learning may also be used.

[0083] Furthermore, the determination circuit 101 may have a function to separate the detection signal DS into multiple signals. Specifically, it can separate a detection signal DS containing both audio data and tactile data into audio data and tactile data based on the characteristics of each data. Note that the data to be separated is not limited to audio data and tactile data, but may be other data. From this viewpoint, the electronic device according to the present invention may further include an acceleration sensor or the like that outputs the detection signal to the determination circuit.

[0084] Furthermore, the determination circuit 101 may include a processing unit having an algorithm for estimating noise based on the detection signal DS. In this case, by removing the noise estimated by the processing unit from the detection signal DS, the target to be detected can be estimated with higher accuracy.

[0085] [Other Embodiments] The sensor module according to the present invention is not limited to sensor modules 1, 1a to 1c, but can be modified within the scope of its gist. Furthermore, the structures of sensor modules 1, 1a to 1c may be combined in any way.

[0086] The transducer and tactile presentation device according to the present invention may each include sensor modules 1a and 1b.

[0087] The electronic device according to the present invention may include sensor modules 1a to 1b.

[0088] The present invention has the following configuration.

[0089] (1) A sensor module comprising: a first plate-shaped member; a piezoelectric element provided on the main surface of the first plate-shaped member; and a field-effect transistor, wherein the piezoelectric element includes: a piezoelectric film having opposing first and second main surfaces; a reference electrode provided on the first main surface and electrically connected to a reference potential; and a signal electrode provided on the second main surface, wherein the piezoelectric film has a piezoelectric body stretched in the stretching direction; the signal electrode is electrically connected to the gate of the field-effect transistor; and the reference electrode is electrically connected to the source of the field-effect transistor.

[0090] (2) The sensor module according to (1), wherein the field-effect transistor is provided on the main surface of the first plate-shaped member.

[0091] (3) The sensor module according to (1), further comprising a second plate-shaped member, wherein the field-effect transistor is provided on the main surface of the second plate-shaped member, the first plate-shaped member is provided on the main surface of the second plate-shaped member, the elastic modulus of the first plate-shaped member is lower than that of the second plate-shaped member, the first plate-shaped member has a first region that does not overlap with the second plate-shaped member when viewed in the direction normal to the main surface of the second plate-shaped member, and the piezoelectric element is provided in the first region.

[0092] (4) The sensor module according to any one of (1) to (3), further comprising a weight provided on the first plate-shaped member and heavier than each of the piezoelectric element and the field-effect transistor, wherein the weight is provided on the first plate-shaped member.

[0093] (5) A sensor module according to any one of (1) to (4), further comprising a cable including a phone plug, the phone plug having a signal terminal and a ground terminal, the signal terminal being electrically connected to the drain of the field-effect transistor and the ground terminal being electrically connected to the source.

[0094] (6) A transducer comprising the sensor module described in any of (1) to (5), wherein the first plate-shaped member is mechanically connected to a solid object to be detected, thereby converting the mechanical vibration of the object to be detected into an electrical signal.

[0095] (7) A sound generator comprising the transducer described in (6), and a speaker, wherein the transducer outputs a detection signal that changes due to the vibration of the first plate-shaped member via the drain of the field-effect transistor, and the speaker generates sound based on the detection signal.

[0096] (8) A tactile presentation device comprising: a sensor module as described in any of (1) to (5); and a voltage generation circuit, wherein the sensor module outputs a detection signal that changes due to vibration of the first plate-shaped member via the drain of the field-effect transistor; and the voltage generation circuit generates a voltage based on the detection signal.

[0097] (9) A tactile presentation device comprising a sensor module as described in any of (1) to (5), and an actuator, wherein the sensor module outputs a detection signal that changes due to vibration of the first plate-shaped member via the drain of the field-effect transistor, and the actuator operates based on the detection signal.

[0098] (10) The sensor module according to any one of (1) to (5), further comprising a pointed portion having a pointed tip, which is provided on the first plate-shaped member.

[0099] (11) A surface inspection device comprising the sensor module described in (10), wherein the tip of the sensor module detects surface irregularities by touching the surface of the object to be detected.

[0100] (12) An electronic device comprising: a sensor module as described in any of (1) to (5) and (10); and a determination circuit, wherein the sensor module outputs a detection signal that changes due to vibration of the first plate-shaped member via the drain of the field-effect transistor; and the determination circuit estimates the object to be detected based on the detection signal.

[0101] 1, 1a-1c: Sensor module 2: First substrate 3: Piezoelectric element 4: FET 5: Cable 6: Second substrate 7: Weight 8: Pointed member 10B: Oscilloscope 31: Piezoelectric film 32: Reference electrode 33: Signal electrode 100: Electronic equipment 101: Judgment circuit A1: First region AC: Actuator AMP: Amplifier circuit C: Capacitor CO1: First core wire CO2: Second core wire CS: Control circuit DC: Drive circuit DS: Detection signal DS2, DS6: Lower main surface E1: First end E2: Second end ED: Electrical tactile device GND, GT: Ground terminal IS: Input signal L: Left channel terminal NE: Negative electrode OD: Extending direction OP: Operational amplifier OS1-OS3: Output signal PE: Positive electrode PP: Phone plug R: Right channel terminal RPU: Pull-up resistor S1: First main surface S2: Second main surface SIG, ST: Signal terminals SS: Audio signal TPD: Tactile feedback device US2, US6: Upper main surface VGC: Voltage generation circuit Vcc: Power supply WDC: Waveform display circuit

Claims

1. A sensor module comprising: a first plate-shaped member; a piezoelectric element provided on the main surface of the first plate-shaped member; and a field-effect transistor, wherein the piezoelectric element includes: a piezoelectric film having opposing first and second main surfaces; a reference electrode provided on the first main surface and electrically connected to a reference potential; and a signal electrode provided on the second main surface, wherein the piezoelectric film has a piezoelectric body stretched in the stretching direction; the signal electrode is electrically connected to the gate of the field-effect transistor; and the reference electrode is electrically connected to the source of the field-effect transistor.

2. The sensor module according to claim 1, wherein the field-effect transistor is provided on the main surface of the first plate-shaped member.

3. The sensor module according to claim 1, further comprising a second plate-shaped member, wherein the field-effect transistor is provided on the main surface of the second plate-shaped member, the first plate-shaped member is provided on the main surface of the second plate-shaped member, the elastic modulus of the first plate-shaped member is lower than that of the second plate-shaped member, the first plate-shaped member has a first region that does not overlap with the second plate-shaped member when viewed in the direction normal to the main surface of the second plate-shaped member, and the piezoelectric element is provided in the first region.

4. The sensor module according to any one of claims 1 to 3, further comprising a weight provided on the first plate-shaped member and heavier than each of the piezoelectric element and the field-effect transistor, wherein the weight is provided on the first plate-shaped member.

5. A sensor module according to any one of claims 1 to 4, further comprising a cable including a phone plug, the phone plug having a signal terminal and a ground terminal, the signal terminal being electrically connected to the drain of the field-effect transistor and the ground terminal being electrically connected to the source.

6. A transducer comprising the sensor module according to any one of claims 1 to 5, wherein the first plate-shaped member is mechanically connected to a solid object to be detected, thereby converting the mechanical vibration of the object to be detected into an electrical signal.

7. A sound generator comprising the transducer described in claim 6 and a speaker, wherein the transducer outputs a detection signal that changes due to vibration of the first plate-shaped member via the drain of the field-effect transistor, and the speaker generates sound based on the detection signal.

8. A tactile presentation device comprising: a sensor module according to any one of claims 1 to 5; and a voltage generation circuit, wherein the sensor module outputs a detection signal that changes due to vibration of the first plate-shaped member via the drain of the field-effect transistor; and the voltage generation circuit generates a voltage based on the detection signal.

9. A tactile presentation device comprising: a sensor module according to any one of claims 1 to 5; and an actuator, wherein the sensor module outputs a detection signal that changes due to vibration of the first plate-shaped member via the drain of the field-effect transistor; and the actuator operates based on the detection signal.

10. The sensor module according to any one of claims 1 to 5, further comprising a pointed portion having a pointed tip, provided on the first plate-shaped member.

11. A surface inspection device comprising the sensor module described in claim 10, wherein the tip of the sensor module detects surface irregularities by touching the surface of the object to be detected.

12. An electronic device comprising: a sensor module according to any one of claims 1 to 5 and claim 10; and a determination circuit, wherein the sensor module outputs a detection signal that changes due to vibration of the first plate-shaped member via the drain of the field-effect transistor; and the determination circuit estimates the object to be detected based on the detection signal.

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