JP6972630B2 - Piezoelectric sensor - Google Patents

Description

The present invention relates to a piezoelectric sensor in which a ferroelectric substance is used as a piezoelectric material and a positive piezoelectric effect is enhanced by an electric field application process.

Conventionally, as a piezoelectric sensor including a piezoelectric element using a ferroelectric material as a piezoelectric material, for example, the one described in Patent Document 1 is known. The piezoelectric sensor described in Patent Document 1 is, for example, an ultrasonic sensor element, a vibration sensor element, or the like, which is obtained from a piezoelectric resonance type sensor element having a predetermined resonance frequency and detecting ultrasonic waves or the like, and the element. It is provided with a control means for controlling the signal to be generated.

Specifically, the piezoelectric sensor described in Patent Document 1 includes a piezoelectric layer made of a strong dielectric, a piezoelectric element made of a pair of electrodes sandwiching the piezoelectric layer, a variable DC voltage power supply, a current amplification means, and the like. It includes a frequency measuring means, a frequency input means, and a voltage controlling means.

In the above-mentioned piezoelectric sensor, a piezoelectric element that has received a vibration wave or the like outputs an output signal corresponding to the displacement of the piezoelectric layer, and a predetermined DC bias voltage is applied to this output signal from a variable DC voltage power supply. Then, the current amplification means amplifies the current of the output signal to which a predetermined DC bias voltage is applied, and this output signal is output as a detection signal, and the frequency of the detection signal is measured by the frequency measuring means. NS. After that, a predetermined resonance frequency is input by the frequency input means, and the resonance frequency is compared with the frequency obtained by the frequency measuring means. Then, the voltage control means controls a predetermined DC bias voltage from the variable DC voltage power supply so that these two frequencies match, so that the resonance frequency of the piezoelectric element can be controlled within a predetermined range.

As a result, the resonance frequency of the piezoelectric element can be controlled by the voltage control means after manufacturing, so that it is not necessary to manufacture the piezoelectric element having the adjusted resonance frequency, and the piezoelectric sensor has a low manufacturing cost.

Japanese Unexamined Patent Publication No. 2006-332991

In recent years, it has been studied to increase the sensitivity of a piezoelectric sensor using a ferroelectric material that spontaneously polarizes even when an electric field is not applied as a piezoelectric material. In such a piezoelectric sensor, when the piezoelectric material is deformed by receiving a physical force, an electric charge is generated by the piezoelectric effect. Therefore, theoretically, by increasing the amount of electric charge obtained by the deformation of the piezoelectric material, a piezoelectric sensor with high sensitivity can be obtained.

Here, like the piezoelectric sensor described in Patent Document 1, a bias voltage is applied to a signal based on the amount of charge output from the piezoelectric element, and the bias voltage is based on frequency detection obtained after amplifying the signal. It is also conceivable to control the resonance frequency of the piezoelectric element. However, this method focuses on controlling the resonance frequency of the piezoelectric sensor, and the amount of deformation of the piezoelectric material, that is, the amount of charge obtained from the piezoelectric material with respect to the amount of displacement, without controlling the resonance frequency. It does not increase itself. In addition, a circuit for detecting the resonance frequency is required separately, which complicates the process.

The present invention has been made in view of the above points, and an object of the present invention is to provide a piezoelectric sensor including a piezoelectric element using a ferroelectric material as a piezoelectric material and having higher sensitivity than a conventional piezoelectric sensor. ..

In order to achieve the above object, the piezoelectric sensor according to claim 1 is formed in contact with a piezoelectric layer (13) made of a piezoelectric material (13a) and a piezoelectric layer so as to face each other across the piezoelectric layer. When detecting the charge generated by the displacement of the piezoelectric portion (10) having the first electrode (11) and the second electrode (12) arranged in, and the piezoelectric layer, in advance before the displacement. voltage supply for applying a DC bias voltage for aligning the polarization direction of the piezoelectric material to the first electrode and the (20, 31), Bei give a piezoelectric material is a ferroelectric material, a piezoelectric material layer, The piezoelectric material is thin and has a plurality of spontaneous polarization directions of the piezoelectric material constituting the piezoelectric layer, and the plurality of spontaneous polarization directions are different from each other. The piezoelectric portion is a substrate. The second electrode, the piezoelectric layer, and the first electrode are formed in this order on one surface (50a) of (50), and when a DC bias voltage is applied to the first electrode, the piezoelectric layer is formed. A warping force acts along the normal direction with respect to one surface, and a piezoelectric layer is applied on the first electrode or on the other surface (50b) on the opposite side of one surface when a DC bias voltage is applied to the first electrode. A warp suppressing layer (41) that generates a warping force in the direction opposite to the warping direction is formed, and a third electrode (43) is formed on the warp suppressing layer (41) to suppress warping. The layer is formed on the first electrode and is made of a piezoelectric material different from the piezoelectric material, and when a DC bias voltage is applied to the first electrode, a predetermined voltage is applied to the third electrode. As a result, the piezoelectric layer is a layer that warps in the direction opposite to the warp direction .

As a result, by applying a DC bias voltage to the piezoelectric portion, the polarization directions of the piezoelectric materials constituting the piezoelectric layer can be made uniform to some extent, and the piezoelectric portion can be displaced in this state. The configuration is such that the generated charge can be detected. As a result, the polarization directions of the piezoelectric materials are aligned to some extent, that is, the degree of polarization of the entire piezoelectric layer is increased, so that the positive piezoelectric effect when the piezoelectric portion is displaced is enhanced, and the conventional piezoelectric is enhanced. It is a piezoelectric sensor with higher sensitivity than the sensor.

The reference numerals in parentheses of each of the above means indicate an example of the correspondence with the specific means described in the embodiment described later.

It is a block diagram which shows the structure of the piezoelectric sensor of 1st Embodiment. It is a block diagram which shows the circuit structure of the piezoelectric sensor of 1st Embodiment. It is a figure which shows the relationship between the direction of polarization of a ferroelectric substance in the piezoelectric layer before and after applying a bias voltage, and the direction of an electric field by applying the bias voltage. It is a figure which shows the predicted characteristic of a bias voltage and a piezoelectric constant at the time of electric field application processing. It is sectional drawing which shows the piezoelectric part in the piezoelectric sensor of 2nd Embodiment. It is a figure which shows the function of the warp suppression layer in the piezoelectric sensor of 2nd Embodiment. It is sectional drawing which shows the piezoelectric part in the piezoelectric sensor of 3rd Embodiment. It is a figure which shows the function of the warp suppression layer in the piezoelectric sensor of 3rd Embodiment. It is sectional drawing which shows the piezoelectric part in the piezoelectric sensor of 4th Embodiment. It is a figure which shows the function of the warp suppression layer in the piezoelectric sensor of 4th Embodiment. It is sectional drawing which shows the piezoelectric part in the piezoelectric sensor of 5th Embodiment. It is a figure which shows the function of the warp suppression layer in the piezoelectric sensor of 5th Embodiment. It is a block diagram which shows the circuit structure of the piezoelectric sensor of another embodiment. It is a figure which shows the control of the piezoelectric characteristic by adjusting a bias voltage.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following embodiments, the parts that are the same or equal to each other will be described with the same reference numerals.

(First Embodiment)
The piezoelectric sensor of the first embodiment will be described with reference to FIGS. 1 to 3. In FIG. 2, in order to make the configuration of the entire piezoelectric sensor of the present embodiment easy to understand, the other circuits of the charge detection unit 30 described later, which are connected to the operational amplifier 31, are omitted. FIG. 3 shows the state of polarization of the piezoelectric layer 13 before and after applying a DC bias voltage to the piezoelectric portion 10 including the piezoelectric layer 13 composed of polycrystals of the piezoelectric material 13a described later. Further, in FIG. 3, the direction of polarization of the piezoelectric material 13a described later for each crystal is indicated by an arrow, and components other than the piezoelectric portion 10 and the voltage supply portion 20 are omitted.

The piezoelectric sensor of the present embodiment outputs as a detection signal the amount of deformation of the piezoelectric layer 13 in the piezoelectric portion 10 shown in FIG. 1, that is, the electric charge generated according to the displacement amount, and applies the piezoelectric portion 10 based on the signal. It is used as a sensor to detect physical quantities. The piezoelectric sensor of this embodiment is suitable for being applied to, for example, a gyro sensor.

As shown in FIG. 1, the piezoelectric sensor of the present embodiment has a piezoelectric portion 10 having a first electrode 11 and a second electrode 12 facing each other and a piezoelectric layer 13 sandwiched between both electrodes, and a first one. A voltage supply unit 20 and a charge detection unit 30 connected to the electrode 11 are provided.

In the piezoelectric sensor of the present embodiment, the amount of electric charge generated by the deformation of the piezoelectric layer 13 when a physical force, for example, a colliori force, is applied to the piezoelectric portion 10 to which a predetermined DC bias voltage is applied from the voltage supply unit 20. The charge detection unit 30 detects the signal corresponding to the above. Thereby, the piezoelectric sensor of the present embodiment can detect a predetermined physical quantity acting on the piezoelectric unit 10.

In the present embodiment, the piezoelectric portion 10 has a configuration in which the second electrode 12, the piezoelectric layer 13, and the first electrode 11 are laminated on a substrate made of silicon or the like (not shown in this order) in this order, as shown in FIG. It functions to output a charge corresponding to the amount of displacement of the piezoelectric layer 13 as a signal. In the present embodiment, the piezoelectric unit 10 is configured to output as a signal the electric charge generated by the deformation of the piezoelectric unit 10.

As shown in FIG. 1, the first electrode 11 is an upper electrode formed on the upper surface of the piezoelectric layer 13 and is connected to the voltage supply unit 20. As shown in FIG. 1 or 2, the second electrode 12 is a lower electrode formed on the lower surface of the piezoelectric layer 13 and used as a reference potential, and is a ground electrode in the present embodiment.

As shown in FIG. 3, the piezoelectric layer 13 is composed of a thin film of a piezoelectric material 13a made of a ferroelectric substance such as PZT (abbreviation of lead zirconate titanate). When the piezoelectric layer 13 is deformed for some reason, a piezoelectric effect is generated, and an electric charge corresponding to the amount of displacement thereof is generated. This charge is output as a detection signal and transmitted to the charge detection unit 30 through the first electrode 11.

In the present embodiment, the voltage supply unit 20 has, for example, about several tens of V / μm between the first electrode 11 and the second electrode 12 in order to enhance the positive piezoelectric effect in the piezoelectric layer 13 composed of the ferroelectric substance. It is a power supply that applies a DC bias voltage that generates an electric field to the first electrode 11. The role played by the voltage supply unit 20 will be described in detail later.

In the present embodiment, the charge detection unit 30 includes a charge amplifier that detects the charge when the piezoelectric unit 10 to which the DC bias voltage is applied by the voltage supply unit 20 is deformed, as shown in FIGS. 1 or 2. In the present embodiment, the charge detection unit 30 is configured to include an operational amplifier 31 as a charge amplifier.

Specifically, as shown in FIG. 1 or 2, the first electrode 11 of the piezoelectric section 10 is electrically connected to the voltage supply section 20 and the inverting input terminal of the operational amplifier 31, and the second of the piezoelectric sections 10 is connected. The electrode 12 is a ground electrode. The non-inverting input terminal of the operational amplifier 31 is connected to the charge supply unit 20 and another variable DC voltage source, and the output terminal of the operational amplifier 31 is fed back to the inverting input terminal via the resistor 32.

When a physical force is applied to deform the piezoelectric portion 10, an electric charge is generated, which is transmitted as a signal to the inverting input terminal of the operational amplifier 31, and an amplified signal is output from the output terminal of the operational amplifier 31. Then, the signal output from the output terminal of the operational amplifier 31 is transmitted to a circuit unit that detects a physical quantity (not shown), and detects the physical quantity applied to the piezoelectric unit 10.

In this embodiment, the voltage applied to the non-inverting input terminal of the operational amplifier 31 is the same as the voltage applied to the inverting input terminal together with the first electrode 11 by the voltage supply unit 20. That is, the potential difference between the inverting input terminal and the non-inverting input terminal of the operational amplifier 31 is adjusted so as to be the output of the amount of electric charge corresponding to the amount of displacement of the piezoelectric portion 10. Further, the circuit unit (not shown) is appropriately changed depending on the application of the piezoelectric sensor, for example, when the piezoelectric sensor is a vibration sensor, it is used as a frequency detection circuit.

The above is the configuration of the piezoelectric sensor of this embodiment. Next, a method of manufacturing the piezoelectric sensor of the present embodiment will be described. The piezoelectric sensor of the present embodiment is manufactured by connecting a voltage supply unit 20 and a charge detection unit 30 configured by a known power supply or circuit to the piezoelectric unit 10 obtained by a general method for manufacturing a piezoelectric element. Will be done. Therefore, here, a method of manufacturing the piezoelectric portion 10 will be briefly described.

First, for example, a substrate made of silicon or the like is prepared, and an insulating layer is formed on the surface of the substrate by thermal oxidation or the like. Subsequently, for example, a patterned lower electrode to be the second electrode 12 is formed by sputtering using a mask or the like. If necessary, after forming the second electrode 12 on the entire surface of the substrate surface, patterning may be performed by a photolithography etching method or the like.

After that, the PZT covering the entire surface of the second electrode 12 is formed into a film by, for example, sputtering or a sol-gel method to form the piezoelectric layer 13. Then, the upper electrode to be the first electrode 11 is formed on the piezoelectric layer 13 so as to face the second electrode 12 by, for example, sputtering using a mask. In addition to the above configuration, if necessary, circuit wiring and the like for connecting to the voltage supply unit 20 and the charge detection unit 30, which will be described later, are formed when the first electrode 11 and the second electrode 12 are formed. You may. In this way, the piezoelectric portion 10 used in the piezoelectric sensor of the present embodiment can be manufactured.

Next, the electric field application process of the piezoelectric section 10 by the voltage supply section 20 and the improvement of the positive piezoelectric effect by the electric field application process will be described with reference to FIG.

The "direction of polarization" referred to below means a direction from a negative charge center generated in the crystal lattice due to polarization toward a positive charge center. Further, the "direction of the electric field" described later is a high-potential to low-potential electrode between the second electrode 12 as the reference potential in the piezoelectric portion 10 and the first electrode 11 to which the DC bias voltage is applied. The direction toward. Further, the “positive DC bias voltage” described later is a polarity of the DC bias voltage applied to the first electrode 11 in which the polarization direction of the piezoelectric layer 13 and the direction of the electric field between the electrodes 11 and 12 coincide with each other. Refers to voltage. Strictly speaking, multi-directional polarization also occurs in one crystal of the piezoelectric material 13a, but for convenience in FIG. 3, the direction of polarization of one crystal as a whole is indicated by an arrow for each crystal, and the arrow indicates. Although there are parts where the lengths of the crystals differ due to the relationship shown in the figure, they do not indicate the strength of the degree of polarization for each crystal.

FIG. 3A shows the state of the piezoelectric portion 10 before applying the DC bias voltage. The piezoelectric layer 13 is composed of a ferroelectric substance such as PZT, and as shown in FIG. 3A, has PZT crystals in the layer and is composed of polycrystals.

Here, in general, a ferroelectric crystal is polarized, that is, spontaneously polarized even in a state where an electric field is not applied, and each crystal has a different direction of polarization. Therefore, in a situation where a positive DC bias voltage is not applied by the voltage supply unit 20, the piezoelectric layer 13 has a ferroelectric crystal for each crystal as shown by the arrow in FIG. 3 (a). It is in a state of having a direction of polarization. However, while the polycrystals of the ferroelectric substance constituting the piezoelectric layer 13 have the directions of polarization to some extent, some of the crystals of the polycrystal are of the ferroelectric substance constituting the piezoelectric layer 13. It is a state that points in a direction different from the direction of polarization of other crystals. So to speak, the piezoelectric layer 13 is a state including two or more different directions of polarization.

Even in this state, if the piezoelectric layer 13 is deformed by some action, the electric charge is generated due to the bias of the electric charge in the layer, that is, the positive piezoelectric effect is generated. However, as shown in FIG. 3A, the piezoelectric layer 13 is in a state in which the polarization direction of some of the polycrystals in the layer is different from the polarization direction of the other crystals. It has become. Therefore, since the piezoelectric layer 13 has many different polarization directions, the degree of polarization of the piezoelectric layer 13 as a whole is not yet sufficient. Due to this effect, the piezoelectric portion 10 suppresses the amount of electric charge obtained by the displacement of the piezoelectric layer 13, that is, the positive piezoelectric effect.

On the other hand, FIG. 3B shows a state of the piezoelectric portion 10 in which, for example, a positive DC bias voltage is applied to the first electrode 11.

Here, in the ferroelectric crystal, when an electric field is applied, the direction of spontaneous polarization changes along the direction of the electric field. A polling process is known in which heat or an electric field is applied to a ferroelectric substance to align its polarization direction before use, but some crystals whose polarization direction has changed due to the polling process are known. When this electric field disappears, it returns to the state before the electric field was applied. After this polling process, the ferroelectric crystal that has returned to the direction of polarization before the polling process is aligned with the other polarization directions that are maintained unchanged by the polling process. It is considered that the positive piezoelectric effect of is further enhanced.

Therefore, as shown in FIG. 3B, the piezoelectric layer 13 is in a state where the directions of polarization of the piezoelectric material 13a are aligned for each crystal by the electric field application process in which a positive DC bias voltage is applied to the first electrode 11. Leave it alone. That is, among the polycrystals in the piezoelectric layer 13, the polarization direction of the crystal having a different polarization direction from that of the other crystals remains aligned with the polarization direction of the other crystals by the electric field application treatment. Since it is maintained, the charge bias in the piezoelectric layer 13 becomes large.

The "state in which the directions of polarization are aligned" here does not mean only a state in which the directions of polarization of each crystal of the piezoelectric material 13a are completely the same. Specifically, as shown in FIG. 3B, the "state in which the directions of polarization are aligned" means that the directions of polarization of the piezoelectric material 13a for each crystal are the first electrode 11 and the second electrode 12. It is meant to include a state along the direction X of the electric field applied between them (hereinafter, simply referred to as "direction X of the electric field") to some extent.

In other words, the "state in which the directions of polarization are aligned" is a state in which the directions of polarization of each crystal of the piezoelectric material 13a are aligned to some extent with the direction X of the electric field, and before the DC bias voltage is applied. In comparison with the above, the degree of polarization of the piezoelectric layer 13 as a whole is improved.

When the piezoelectric layer 13 in such a state is deformed, the degree of polarization, that is, the charge bias is larger than that in the state before the DC bias voltage is applied (hereinafter referred to as “initial state”), so that it is the same. The amount of charge obtained will increase with respect to the amount of displacement. That is, in the state where the DC bias voltage is applied to the piezoelectric unit 10 by the voltage supply unit 20, the positive piezoelectric effect of the piezoelectric unit 10 is improved as compared with the initial state.

Specifically, it will be described with reference to the graph of the predicted characteristic of the piezoelectric constant of the piezoelectric layer 13 with respect to the DC bias voltage shown in FIG. The predicted characteristics of FIG. 4 are expected to be theoretically derived in consideration of the fact that the degree of polarization of the entire piezoelectric layer 13 is increased by aligning the polarization directions of the ferroelectric crystals by the electric field application treatment. Is to be done.

In FIG. 4, for example, a rectangular parallelepiped piezoelectric layer 13 and a rectangular parallelepiped first electrode 11 and a second electrode 12 formed on a surface having the largest area and a surface facing the surface of the piezoelectric material 13 are shown. An example of the piezoelectric portion 10 is shown. Specifically, the "bias voltage" in FIG. 4 refers to the DC bias voltage (unit: V) applied to the first electrode 11 of the above-mentioned piezoelectric portion 10, and the "piezoelectric constant" refers to the above-mentioned piezoelectric. Part 10 refers to the piezoelectric constant d ₃₃ (unit: C / N) of the piezoelectric layer 13.

When the bias voltage is zero, that is, when no voltage is applied to the piezoelectric portion 10, the polarization direction of some of the polycrystals in the piezoelectric layer 13 is not aligned with the polarization direction of the other crystals. The amount of electric charge generated with respect to the amount of displacement of the piezoelectric layer 13 can be suppressed. However, since the piezoelectric layer 13 composed of the ferroelectric substance produces a positive piezoelectric effect, as shown at the left end of FIG. 4, the piezoelectric constant of the piezoelectric layer 13 is zero even when the bias voltage is zero, that is, even in the initial state. , It becomes a predetermined value.

Then, as the bias voltage is increased, the directions of polarization of each crystal in the piezoelectric layer 13 are gradually aligned by the electric field application process as described above, so that the piezoelectric constant of the piezoelectric layer 13 is in the initial state. It rises gradually compared to. However, when the bias voltage is further increased, most of the polycrystals in the piezoelectric layer 13 whose polarization direction has not changed are almost eliminated. Therefore, as shown at the right end of FIG. 4, the piezoelectric constant of the piezoelectric layer 13 is set. It is thought that it will reach a plateau at a certain value.

In other words, by applying a bias voltage to the first electrode 11 to apply an electric field to the piezoelectric material 13a, the piezoelectric constant of the piezoelectric layer 13 is increased, and the positive piezoelectric effect of the piezoelectric portion 10 is improved. That is, by using the piezoelectric portion 10 in a state where a predetermined bias voltage is applied, the piezoelectric sensor is compared with a conventional piezoelectric sensor (hereinafter, simply referred to as “conventional piezoelectric sensor”) using a ferroelectric material as a piezoelectric material. It is considered that the amount of charge obtained is improved with respect to the amount of displacement of the portion 10.

According to the present embodiment, since the piezoelectric portion 10 can be used while applying a predetermined bias voltage, the amount of electric charge obtained with respect to the displacement amount of the piezoelectric layer 13 as compared with the conventional piezoelectric sensor. That is, it becomes a piezoelectric sensor with high sensitivity.

(Second Embodiment)
The piezoelectric sensor of the second embodiment will be described with reference to FIGS. 5 and 6. In order to make the configuration easier to understand, the components other than the piezoelectric section 10 are omitted in FIG. 5, and the components other than the piezoelectric section 10 and the voltage supply section 20 are omitted in FIG.

In the piezoelectric sensor of the present embodiment, as shown in FIG. 5, the piezoelectric portion 10 is formed on one surface 50a of the substrate 50 in the order of the second electrode 12, the piezoelectric layer 13, and the first electrode 11, and further, the first electrode 11 is formed. It differs from the first embodiment in that the warp suppressing layer 40 is laminated on the top. In this embodiment, this difference will be mainly described.

The warp suppressing layer 40 is formed on the first electrode 11 and is used to suppress the warp of the piezoelectric portion 10 when a DC bias voltage applied to the first electrode 11 for the purpose of improving the positive piezoelectric effect is applied. It is a layer to be provided.

Specifically, when a DC bias voltage is applied to the first electrode 11 (hereinafter referred to as “when a bias voltage is applied”), the piezoelectric layer 13 is in the plane formed by the piezoelectric layer 13 due to the inverse piezoelectric effect. Shrinks and deforms in the direction of (hereinafter referred to as "in-plane direction").

Due to the in-plane shrinkage stress of the piezoelectric layer 13, the piezoelectric portion 10 is convex on the substrate 50 side as a whole, that is, from one surface 50a of the substrate 50 as shown in FIG. 6A. An action of warping in the Y1 direction toward the other surface 50b occurs. Therefore, when the warp suppressing layer 40 is not formed, the piezoelectric portion 10 may warp so that the substrate 50 side becomes convex when a bias voltage is applied. When the piezoelectric portion 10 is warped in this way, the physical quantity applied to the piezoelectric portion 10 may not be accurately measured.

Therefore, as shown in FIG. 6B, an internal stress in the direction opposite to the contraction stress of the piezoelectric layer 13 when a bias voltage is applied acts, and the entire piezoelectric portion 10 is opposed to the direction in which the side opposite to the substrate 50 side becomes convex. The structure is such that the warp suppressing layer 40 is formed on the first electrode 11. As a result, as shown in FIG. 6B, even if the piezoelectric layer 13 is warped in the Y1 direction when the bias voltage is applied, the piezoelectric portion 10 is opposite to the Y1 direction by the warp suppressing layer 40. It is offset by the action of warping in the Y2 direction.

Specifically, when a bias voltage is applied to the first electrode 11, contraction stress is generated on the one side 50a side of the piezoelectric layer 13, and tensile stress is generated on the opposite side of the one side 50a. Therefore, the warp suppressing layer 40 in which the shrinkage stress is generated on the piezoelectric layer 13 side and the tensile stress is generated on the opposite side of the piezoelectric layer 13 is formed on the piezoelectric layer 13. As a result, the tensile stress of the piezoelectric layer 13 is canceled by the contraction stress of the warp suppressing layer 40, and the piezoelectric portion 10 is suppressed from being warped to the extent that the detection of the physical quantity is hindered when the bias voltage is applied. It becomes.

The warp suppressing layer 40 is made of a material generally used in a manufacturing process of a known semiconductor device such as _{SiO 2 or SiN, and is formed by a vacuum film forming method such as sputtering.} The internal stress of the warp suppressing layer 40, that is, the force extending in the in-plane direction can be controlled by adjusting the film forming conditions of the above material, and is adjusted by a known method such as adjusting the film forming temperature and the film thickness. can.

The warp suppression layer 40 is formed on the first electrode 11 in the present embodiment, but is a film having an internal stress such that the piezoelectric layer 13 warps in the direction opposite to the warp direction when a bias voltage is applied. Is formed, for example, it may be formed on the other surface 50b or on another part. The material, film thickness, and the like of the warp suppressing layer 40 are arbitrary and are appropriately adjusted according to the configuration of the piezoelectric layer 13.

According to the present embodiment, similarly to the first embodiment, the piezoelectric sensor has a high sensitivity because it can be used while the predetermined bias voltage is applied to the piezoelectric portion 10. Further, the piezoelectric sensor can suppress the warp of the piezoelectric portion 10 when a bias voltage is applied, and can stably detect the physical quantity acting on the piezoelectric portion 10.

(Third Embodiment)
The piezoelectric sensor of the third embodiment will be described with reference to FIGS. 7 and 8. In order to make the configuration easier to understand, the components other than the piezoelectric section 10 are omitted in FIG. 7, and the components other than the piezoelectric section 10 and the voltage supply section 20 are omitted in FIG.

In the piezoelectric sensor of the present embodiment, as shown in FIG. 7, the piezoelectric portion 10 has the piezoelectric portion 10 of the second embodiment in which the warp suppressing layer 40 is replaced with the warp suppressing layer 41 and the third electrode 43. It differs from the above-mentioned second embodiment in that it has a structure. In this embodiment, this difference will be mainly described.

The warp suppressing layer 41 is provided to cause a warping action on the opposite side to the warping action generated on the piezoelectric layer 13 when a bias voltage is applied, and to suppress the warping of the piezoelectric portion 10 as a whole. The warp suppressing layer 41 is made of any piezoelectric material different from the ferroelectric material, for example, AlN, ZnO, ScAlN, or the like.

A third electrode 43 is formed on the warp suppressing layer 41. The first electrode 11, the piezoelectric layer 13, and the second electrode 12 are conveniently used as the first piezoelectric portion, and the first electrode 11, the warp suppression layer 41, and the third electrode 43 form the second piezoelectric portion. .. Similar to the warp suppression layer 40 in the second embodiment, the second piezoelectric portion has a Y2 direction side opposite to the Y1 direction, which is the warp direction of the first piezoelectric portion, when a bias voltage is applied to the first piezoelectric portion. It is configured to warp so as to be convex. As a result, the piezoelectric portion 10 has a structure in which warpage when a bias voltage is applied is suppressed.

Specifically, the piezoelectric layer 13 contracts and deforms in the in-plane direction when a bias voltage is applied, as described in the second embodiment, so that the substrate 50 side becomes convex, that is, the figure. A warping action occurs so that the Y1 direction side shown in 8 becomes convex. Therefore, in order to prevent the piezoelectric portion 10 from warping as a whole when a bias voltage is applied, as shown in FIG. 8, the second piezoelectric portion is convex on the Y2 direction opposite to the Y1 direction in which the first piezoelectric portion warps. It suffices to drive so that the warping action works so as to become. That is, the warp of the piezoelectric portion 10 is suppressed by exerting a stress in the direction opposite to the stress of the first piezoelectric portion in the warp suppressing layer 41 of the second piezoelectric portion and canceling the stress of the first piezoelectric portion.

In the present embodiment, the warp suppressing layer 41 is made of a piezoelectric material different from the ferroelectric substance. Ferroelectrics have the property that their polarization direction is reversed when a voltage exceeding the coercive electric field is applied. Therefore, although the ferroelectric substance deforms to shrink in the in-plane direction of the layer, the in-plane direction thereof. This is because it does not deform to extend to. That is, in order to have a configuration in which a force that extends the second piezoelectric portion in the in-plane direction acts, it is necessary to use a piezoelectric material that extends the warp suppressing layer 41 in the in-plane direction, that is, a dielectric material different from the ferroelectric material. ..

The material and film thickness of the warp suppressing layer 41 are arbitrary and may be appropriately changed according to the configuration of the first piezoelectric portion. Further, the third electrode 43 is connected to a drive power source different from the voltage supply unit 20 in order to drive the second piezoelectric unit. Further, in the present embodiment, the third electrode 43 and the first electrode 11 are used as a pair of electrodes for driving the second piezoelectric portion, but an electrode is formed separately from the first electrode 11 and the first electrode is used. It may be used together with 3 electrodes 43.

According to the present embodiment, as in the second embodiment, the piezoelectric portion 10 can be used while a predetermined bias voltage is applied to the piezoelectric portion 10, the piezoelectric sensor has high sensitivity, and the piezoelectric portion 10 is used when the bias voltage is applied. It becomes a piezoelectric sensor that can stably detect physical quantities by suppressing the warpage.

(Fourth Embodiment)
The piezoelectric sensor of the fourth embodiment will be described with reference to FIGS. 9 and 10. In order to make the configuration easier to understand, the components other than the piezoelectric section 10 are omitted in FIG. 9, and the components other than the piezoelectric section 10 and the voltage supply section 20 are omitted in FIG.

In the piezoelectric sensor of the present embodiment, as shown in FIG. 9, the piezoelectric portion 10 is formed on the substrate 50, the first piezoelectric portion formed on one surface 50a of the substrate 50, and the other surface 50b on the opposite side of the one surface 50a. It differs from the second embodiment in that it is composed of the warp suppressing layer 42 formed in the above. In this embodiment, this difference will be mainly described.

The warp suppressing layer 42 is a layer formed for the same purpose as the warp suppressing layers 40 and 41, and as shown in FIG. 9, the fourth electrode 421, the piezoelectric film 423, and the fourth electrode 421 are placed on the other surface 50b of the substrate 50. The configuration is such that the five electrodes 422 are stacked in this order.

In the present embodiment, the warp suppressing layer 42 has the same configuration as, for example, the first piezoelectric portion. Specifically, the piezoelectric film 423 is made of the same ferroelectric material as the piezoelectric layer 13. When the bias voltage is applied to the first piezoelectric portion, the warp suppression layer 42 contracts in the in-plane direction when the fourth electrode 421 is set as the reference potential and the DC bias voltage is applied to the fifth electrode 422. Deform. That is, the warp suppressing layer 42 is driven at the same time as the first piezoelectric portion when the bias voltage is applied to the first piezoelectric portion, and as shown in FIG. 10, the warp suppressing layer 12 is warped so that the Y1 direction side of the piezoelectric layer 13 becomes convex. Corresponds to the third piezoelectric portion in which the action of warping so as to be convex on the Y2 direction side opposite to the action of warping works. As a result, the piezoelectric portion 10 has a structure in which warpage when a bias voltage is applied is suppressed.

In the warp suppression layer 42, the direction of polarization of the ferroelectric substance constituting the piezoelectric film 423 is aligned with the direction of the electric field between the fourth electrode 421 and the fifth electrode 422, similarly to the first piezoelectric portion. The direction of the electric field is set to be opposite to the direction of the electric field of the first piezoelectric portion. As a result, the first piezoelectric portion and the warp suppressing layer 42, which is the third piezoelectric portion, have an action of warping in opposite directions, and the stress of the first piezoelectric portion is canceled by the stress of the third piezoelectric portion. Therefore, the warp of the piezoelectric portion 10 when the bias voltage is applied is suppressed.

Further, another DC bias voltage power supply different from the voltage supply unit 20 is connected to the fifth electrode 422. Further, each of the fourth electrode 421, the piezoelectric film 423, and the fifth electrode 422 corresponds to the first electrode 11, the piezoelectric layer 13, and the second electrode 12 of the first piezoelectric portion, and has the same material and film thickness. It may be configured as such, or it may be configured differently. The configurations of the fourth electrode 421, the piezoelectric film 423, and the fifth electrode 422 are arbitrary and may be appropriately changed depending on the configuration of the first piezoelectric portion.

According to the present embodiment, as in the second embodiment, the piezoelectric portion 10 can be used while a predetermined bias voltage is applied to the piezoelectric portion 10, the piezoelectric sensor has high sensitivity, and the piezoelectric portion 10 is used when the bias voltage is applied. It becomes a piezoelectric sensor that can stably detect physical quantities by suppressing the warpage.

(Fifth Embodiment)
The piezoelectric sensor of the fifth embodiment will be described with reference to FIGS. 11 and 12. In FIGS. 11 and 12, in order to make the configuration easy to understand, the components other than the piezoelectric portion 10 are omitted.

The piezoelectric sensor of the present embodiment includes a substrate 50, a first piezoelectric portion formed so that the piezoelectric portions 10 are arranged side by side on one surface 50a of the substrate 50 in a state of aligning the longitudinal directions, and a warp suppressing layer 44. It is composed of. Further, as shown in FIG. 11, the first piezoelectric portion and the warp suppressing layer 44 are in the in-plane direction formed by one surface 50a when a bias voltage is applied to the first piezoelectric portion, and are in the longitudinal direction of the first piezoelectric portion. The configuration is such that a warping action occurs along the Z2 direction perpendicular to the Z1 direction.

Specifically, as shown in FIG. 12, the first piezoelectric portion is counter-convex so that the Z3 direction side, which is the direction from the first piezoelectric portion toward the warp suppression layer 44 along the Z2 direction when a bias voltage is applied, is convex. It is said that the structure causes the above-mentioned action. More specifically, in the present embodiment, the first piezoelectric portion is configured to have a warping action so that the Z3 direction side becomes convex at the center position in the longitudinal direction, as shown by the white arrow in FIG. ing. On the other hand, as shown by the white arrow in FIG. 12, the warp suppressing layer 44 is configured to have a warping action so that the side in the Z4 direction opposite to the Z3 direction becomes convex at the center position in the longitudinal direction. The piezoelectric sensor of this embodiment is different from the second embodiment in these respects. In this embodiment, this difference will be mainly described.

The warp suppressing layer 44 is provided to suppress warping so that the Z3 direction side of the piezoelectric portion 10 becomes convex when a bias voltage is applied to the first piezoelectric portion. The warp suppressing layer 44 is made of a pair of electrodes 441 and 442 and a ferroelectric material, and is composed of a piezoelectric film 443 sandwiched between the pair of electrodes.

Specifically, as shown in FIG. 12, in the present embodiment, the first piezoelectric portion has an action in which the piezoelectric layer 13 warps so that the Z3 direction side becomes convex at the center position in the longitudinal direction when a bias voltage is applied. Is configured to occur. Then, as shown in FIG. 12, the warp suppressing layer 44 is arranged so that the longitudinal direction is aligned with the longitudinal direction of the first piezoelectric portion in order to suppress the warp of the piezoelectric portion 10. The warp suppression layer 44 is configured to warp so that the Z4 direction side becomes convex at the center position in the longitudinal direction when another DC bias voltage (not shown) is applied. As a result, the stress generated in the first piezoelectric portion when the bias voltage is applied to the first piezoelectric portion is canceled by the stress generated in the warp suppressing layer 44, and the warp of the entire piezoelectric portion 10 when the bias voltage is applied is suppressed. It becomes.

In the above example, the first piezoelectric portion warps so as to be convex on the Z3 direction side at the center position in the longitudinal direction, and the warp suppressing layer 44 is convex on the Z4 direction side at the center position in the longitudinal direction. An example in which a warping action occurs is described. However, the warp suppression layer 44 may be configured to warp so that the direction opposite to the first piezoelectric portion becomes convex when a bias voltage is applied. Therefore, the direction of action of the warp of the first piezoelectric portion and the direction of action of the warp of the warp suppressing layer 44 may be opposite to the above. Further, in either of these configurations, the first piezoelectric portion is in a state where it is apparently hardly deformed when a bias voltage is applied, that is, the sides along the longitudinal direction thereof are linear. The "state in which there is almost no deformation" here does not mean only the state in which the first piezoelectric part is not warped at all when the bias voltage is applied, but also the state in which the first piezoelectric part is slightly warped to the extent that the detection of the physical quantity is not hindered. Also includes.

Further, in the present embodiment, the warp suppressing layer 44 has an action of suppressing the piezoelectric portion 10 from warping along the normal direction (hereinafter, simply referred to as “normal direction”) with respect to one surface 50a of the substrate 50 by some force. Is small. Therefore, in order to prevent the piezoelectric portion 10 from warping along the normal direction, the piezoelectric portion 10 may be configured to have a thicker plate thickness of the substrate 50 in the normal direction, if necessary.

The material and film thickness of the pair of electrodes 441 and 442 of the warp suppressing layer 44 and the piezoelectric film 443 are arbitrary and are appropriately changed according to the configuration of the first piezoelectric portion. Further, FIG. 12 shows an example in which the warp suppressing layer 44 is formed completely independently of the first piezoelectric portion, but the warp suppressing layer 44 is not limited to this, and for example, the piezoelectric film 443 is piezoelectric. It may be configured integrally with the body layer 13 and only a pair of electrodes may be configured independently of the first piezoelectric portion. In this case, a DC bias voltage is applied to the electrode 442 on the substrate 50 side of the warp suppression layer 44, and the electrode 441 on the opposite side to the substrate 50 is used as a ground electrode, whereby a force that warps on the side opposite to the first piezoelectric portion. Will work.

According to the present embodiment, as in the second embodiment, the piezoelectric portion 10 can be used while a predetermined bias voltage is applied to the piezoelectric portion 10, the piezoelectric sensor has high sensitivity, and the piezoelectric portion 10 is used when the bias voltage is applied. It becomes a piezoelectric sensor that can stably detect physical quantities by suppressing the warpage.

(Other embodiments)
The piezoelectric sensor shown in each of the above embodiments shows an example of the piezoelectric sensor of the present invention, and is not limited to each of the above embodiments, but is within the scope of the claims. Can be changed as appropriate.

(1) For example, in the first embodiment, an example in which a power supply is directly connected as a voltage supply unit 20 for applying a DC bias voltage to the first electrode 11 of the piezoelectric unit 10 to form the circuit configuration shown in FIG. 2 has been described. .. However, since the circuit configuration may be such that a DC bias voltage is applied to the first electrode 11, the circuit configuration may be shown in FIG. 13, for example.

Specifically, assuming a virtual short circuit of the operational amplifier 31, a power supply that applies a DC bias voltage only to the non-inverting input terminal is connected, and the output terminal is fed back to the inverting input terminal via a resistor. Then, as a result of the operational amplifier 31 working to make the potential difference between the non-inverting input terminal and the inverting input terminal zero (virtual short circuit), a DC bias voltage is applied to the first electrode 11 electrically connected to the inverting input terminal. It will be applied. As a result, the operational amplifier 31 serves as a voltage supply unit 20, and although it is not necessary to connect a power supply that applies a DC bias voltage to the first electrode 11, the piezoelectric sensor has an enhanced positive piezoelectric effect of the piezoelectric unit 10. ..

(2) As shown in FIG. 14, the piezoelectric sensor of each of the above embodiments has a change in piezoelectric constant and manufacturing variation due to deterioration of the piezoelectric layer 13 over time by appropriately adjusting the DC bias voltage applied to the first electrode 11. It is possible to cope with the fluctuation of the piezoelectric constant due to. In FIG. 14, the piezoelectric characteristic of (a) shown by the solid line shows the piezoelectric characteristic of the piezoelectric layer 13 in the state immediately after production, that is, the initial state, and the piezoelectric characteristic of (b) shown by the broken line is another. The piezoelectric characteristics of the piezoelectric layer 13 of the piezoelectric portion 10 of the production lot or the piezoelectric layer 13 after deterioration over time are shown.

Specifically, as shown in FIG. 14, the piezoelectric layer 13 shows the piezoelectric property of (a) shown by a solid line in the initial state, but the piezoelectric property deteriorates with the passage of time and is shown by a broken line. This is the piezoelectric characteristic of (b). In this case, as shown in FIG. 14, even if the same DC bias voltage V1 is applied by the voltage supply unit 20, the obtained piezoelectric constant α1 decreases to α2 as the piezoelectric characteristics decrease, so that the positive piezoelectric effect is exhibited. The degree of improvement also decreases. Therefore, by adjusting the DC bias voltage from V1 to V2 and keeping the obtained piezoelectric constant at α1, the amount of charge obtained based on the displacement amount of the piezoelectric portion 10 becomes about the same as the initial state, and the piezoelectric constant. Can respond to fluctuations in. Further, even when the piezoelectric constant of the piezoelectric layer 13 is different due to the manufacturing variation, it is possible to cope with the same.

When adjusting the DC bias voltage, it is necessary to use a known piezoelectric characteristic measuring means in addition to the configuration of the piezoelectric sensor.

(3) In each of the above embodiments, the case where a variable bias voltage power supply is used for the voltage supply unit 20 has been described, but the voltage supply unit 20 does not necessarily have to be integrated with the piezoelectric sensor, and the DC bias voltage is applied. It may be a wiring that can be applied, and may be configured to connect a power supply separately.

(4) In the first embodiment, it is described that it is suitable to apply the piezoelectric sensor to, for example, a gyro sensor. Applicable. Further, the piezoelectric sensor of the present invention is not limited to a gyro sensor or the like, and can be applied to an ultrasonic sensor, a vibration sensor, or the like, and may be applied to other devices.

(5) In each of the above embodiments, the first electrode 11 to which the DC bias voltage applied by the voltage supply unit 20 is applied is arranged on the opposite side of the substrate, and the second electrode 12 is arranged on the substrate side, but the reverse is true. It may be arranged as.

10 Piezoelectric part 11 1st electrode 12 2nd electrode 13 Piezoelectric layer 13a Piezoelectric material 20 Voltage supply part 30 Charge detection part 31 Operational amplifiers 40, 41, 42, 44 Warp suppression layer

Claims (3)

A first electrode (11) and a second electrode (11) formed in contact with the piezoelectric layer (13) made of the piezoelectric material (13a) and arranged so as to face each other across the piezoelectric layer. 12), and the piezoelectric portion (10) having the
When detecting the electric charge generated by the displacement of the piezoelectric layer, the voltage supply unit (20, 31) for applying a DC bias voltage for aligning the polarization directions of the piezoelectric material to the first electrode in advance before the displacement. ) And, with
The piezoelectric material is a ferroelectric material and is
The piezoelectric layer is formed into a thin film, and the piezoelectric material constituting the piezoelectric layer has a plurality of spontaneous polarization directions, and the plurality of spontaneous polarization directions are different from each other. And
The piezoelectric portion has a configuration in which the second electrode, the piezoelectric layer, and the first electrode are formed in this order on one surface (50a) of the substrate (50), and the DC bias voltage is applied to the first electrode. When applied, a force that warps the piezoelectric layer along the normal direction with respect to the one surface acts on the piezoelectric layer.
A warp suppressing layer (41) is formed on the first electrode to generate a warping force in the direction opposite to the warping direction of the piezoelectric layer when the DC bias voltage is applied to the first electrode. And
A third electrode (43) is formed on the warp suppressing layer.
The warp suppression layer is made of a dielectric material different from the piezoelectric material, and when the DC bias voltage is applied to the first electrode, a predetermined voltage is applied to the third electrode. A piezoelectric sensor that is a layer that warps in a direction opposite to the warp direction of the piezoelectric layer. The first electrode of the piezoelectric portion is connected to the voltage supply portion.
The second electrode of the piezoelectric portion has a reference potential and is set to a reference potential.
The voltage supply unit is connected to an inverting input terminal of an operational amplifier (31) that constitutes a part of a charge detection unit (30) in which the piezoelectric unit outputs a signal corresponding to the amount of charge generated by the displacement of the piezoelectric layer. ,
A variable DC voltage power supply is connected to the non-inverting input terminal of the operational amplifier.
The electric charge generated by the displacement of the piezoelectric layer is detected based on the potential generated in the output terminal of the operational amplifier.
The piezoelectric sensor according to claim 1, wherein the potential applied to the first electrode by the voltage supply unit and the potential applied to the non-inverting input terminal by the DC voltage power supply are the same. Of the piezoelectric portions, the first electrode is an inversion of an operational amplifier (31) that constitutes a part of a charge detection unit (30) in which the piezoelectric portion outputs a signal according to the amount of charge generated by the displacement of the piezoelectric layer. Connected to the input terminal,
The second electrode of the piezoelectric portion has a reference potential and is set to a reference potential.
A variable DC voltage power supply is connected to the non-inverting input terminal of the operational amplifier.
The piezoelectric sensor according to claim 1, wherein the operational amplifier functions as the voltage supply unit that applies the potential of the output terminal generated by the voltage applied to the non-inverting input terminal to the first electrode. ..

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