Optical actuator, method for manufacturing same, and optical actuator device

Abstract

Provided is an optical actuator which uses an oxide ferroelectric material and which is capable of large deformation at a faster pace. This optical actuator that is driven by irradiation light comprises a dielectric film composed of perovskite and a protective film composed of an amorphous oxide. Distortion is imparted to the dielectric film from the protective film, and the dielectric film is deformed by the reverse piezoelectric effect induced by irradiation light. A conductive electrode film may be further provided between the dielectric film and the protective film. The dielectric film is composed of Ba1-xSrxTiO3 (0 ≤ x ≤ 0.5) or PLTZ.

Description

Optical actuator, its manufacturing method, and optical actuator device

[0001] The present invention relates to an optical actuator, and more particularly to an optical actuator using an oxide ferroelectric thin film, a manufacturing method thereof, and an optical actuator device.

[0002] Optically driven actuators (hereinafter referred to as "optical actuators") that convert light into mechanical movement differ from electrically driven actuators that convert electricity into mechanical movement in that they do not require a power source or wiring to drive the actuator, allowing for weight reduction and a simplified structure. They also allow remote control using light, offering excellent properties not found in electrically driven actuators. Optical actuators that use organic materials and are driven by light-induced conversion of the chemical bonds of the organic materials (photoisomerization) have been proposed (see, for example, Non-Patent Document 1). However, because they utilize photoisomerization, they require two types of light sources to operate as actuators, and have problems such as a slow drive speed that makes high-speed modulation difficult and a limited number of repetitions.

[0003] In response to this, an optical actuator has been proposed that uses an oxide ferroelectric material instead of an organic material, and is driven by utilizing the piezoelectric effect of electrons and holes generated by irradiating the oxide ferroelectric material with light (see, for example, Non-Patent Document 2).

[0004] Y. Chen, J. Yang, X. Zhang, Y. Feng, H. Zeng, L. Wang, et al., Mater. Horiz. 2021, 8, 728-757C. Chen and Z. Yi, Adv. Funct. Mater. 2021, 31, 2010706

[0005] However, in the past, it was difficult to produce thin films of oxide ferroelectric materials, and bulk oxide ferroelectrics were used, resulting in problems such as the deformation amount being minute at a few nm and the resonant frequency being low at 80 Hz or less.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical actuator that uses an oxide ferroelectric material and is capable of larger deformation at higher speeds.

[0007] One aspect of the present disclosure is an optical actuator that is driven by irradiated light, the optical actuator including a dielectric film made of perovskite and a protective film made of amorphous oxide, wherein strain is applied to the dielectric film from the protective film, and the dielectric film is deformed by an inverse piezoelectric effect caused by irradiated light.

[0008] Another aspect of the present disclosure is an optical actuator further including a conductive electrode film between the dielectric film and the protective film.

[0009] Another aspect of the present disclosure is a method for producing a substrate comprising the steps of: preparing an aluminum oxide single crystal substrate or an yttria-stabilized zirconia single crystal substrate; and depositing a water-soluble film of CaO and a water-soluble film of BaO on the substrate. １－ｘ Sr ｘ TiO ３ a step of epitaxially growing a dielectric film made of SiO2 (0≦x≦0.5) or PLTZ on the substrate; a step of forming a protective film made of amorphous oxide on the dielectric film to produce an as-grown film made of a substrate, a water-soluble film, a dielectric film, and a protective film; and a step of immersing the as-grown film in a solution to dissolve the water-soluble film and separating an oxide ferroelectric sheet made of the dielectric film and the protective film from the substrate.

[0010] The optical actuator according to the present invention has sufficient displacement and is capable of high-speed, highly reliable, and repeated operation. Furthermore, it can be made smaller and simpler than electrically driven actuators, and can be remotely operated in environments including physiological saline.

[0011] 1 is a schematic diagram of an as-grown film according to a first embodiment of the present invention; 2 is a schematic diagram of an oxide ferroelectric sheet according to a first embodiment of the present invention; 3 is a schematic diagram showing an example of a process for obtaining an oxide ferroelectric sheet by immersing an as-grown film in pure water and dissolving the water-soluble film; 4 is a schematic diagram showing an example of a process for obtaining an oxide ferroelectric sheet by immersing an as-grown film in pure water and dissolving the water-soluble film; 5 is a photograph showing an example of a process for obtaining an oxide ferroelectric sheet by immersing an as-grown film in pure water and dissolving the water-soluble film; 6 is a photograph showing an example of a process for obtaining an oxide ferroelectric sheet by immersing an as-grown film in pure water and dissolving the water-soluble film; 7 is a diagram showing electric polarization when the electric field of the oxide ferroelectric sheet is changed; 8 is a diagram showing current when the electric field of the oxide ferroelectric sheet is changed; 9 is a diagram showing the relative permittivity and dielectric loss when the electric field of the oxide ferroelectric sheet is changed; 10 is a diagram showing the displacement when the electric field of the oxide ferroelectric sheet is changed; 11 is an enlarged photograph showing the driving characteristics of an oxide ferroelectric sheet. 1 is an enlarged photograph showing the driving characteristics of an oxide ferroelectric sheet. It shows the relationship between the irradiation time of a UV laser beam on an oxide ferroelectric sheet and the displacement amount. It shows the relationship between the laser energy density of UV laser beam and the displacement amount of an oxide ferroelectric sheet. It is an energy band diagram explaining the operating principle of an optical actuator using an oxide ferroelectric material. It shows a measuring device for measuring the driving characteristics of an oxide ferroelectric sheet in physiological saline. It shows the measurement results of measuring the driving characteristics of an oxide ferroelectric sheet in physiological saline. It is a schematic diagram of an apparatus used to evaluate the high-frequency light driving characteristics of an optical actuator. It shows the amplitude intensity when the frequency of UV laser beam incident on an oxide ferroelectric sheet is changed. It shows the phase change when the frequency of UV laser beam incident on an oxide ferroelectric sheet is changed. It is a schematic diagram of an as-grown film according to a second embodiment of the present invention. It is a schematic diagram of an oxide ferroelectric sheet according to a second embodiment of the present invention. It is a photograph showing an example of a process of obtaining an oxide ferroelectric sheet by immersing an as-grown film in pure water and dissolving the water-soluble film. It shows the r-plane Al ２ O ３ 1 shows the results of X-ray diffraction (XRD) measurement of an oxide ferroelectric sheet before peeling when a single crystal substrate is used. ２ O ３1 shows the results of X-ray diffraction (XRD) measurement of the oxide ferroelectric sheet after peeling when a single crystal substrate is used. ２ O ３ 1 shows the results of ψ-scan measurement of X-ray diffraction of an oxide ferroelectric sheet before peeling when a single crystal substrate is used. 1 shows the results of X-ray diffraction (XRD) of an oxide ferroelectric sheet before peeling when a YSZ (110) single crystal substrate is used. 1 shows the results of X-ray diffraction (XRD) of an oxide ferroelectric sheet after peeling when a YSZ (110) single crystal substrate is used. 1 shows the results of X-ray diffraction (ψ-scan) of an oxide ferroelectric sheet before peeling when a YSZ (110) single crystal substrate is used. 1 shows the ferroelectric hysteresis loop of an oxide ferroelectric sheet. 1 shows the changes in relative permittivity and dielectric loss when the voltage applied to the oxide ferroelectric sheet is changed. 1 shows an atomic force microscope (AFM) photograph of the surface of a YSZ single crystal substrate. 1 shows the results of X-ray diffraction of an as-grown film fabricated by reusing a YSZ single crystal substrate. 1 shows the results of X-ray diffraction (XRD) of an as-grown film according to a third embodiment of the present invention. 1 is an X-ray diffraction (XRD) measurement result of an oxide ferroelectric sheet according to a third embodiment of the present invention; 2 is an enlarged photograph of an oxide ferroelectric sheet; 3 is a ferroelectric hysteresis loop of an oxide ferroelectric sheet using PLZT; and 4 is a measurement result of the driving characteristics of an oxide ferroelectric sheet.

[0012] As mentioned above, optical actuators using oxide ferroelectric materials have been proposed instead of optical actuators using organic materials, but in the past it was not possible to fabricate large-area thin films of oxide ferroelectric materials without cracks, so bulk oxide ferroelectric materials were used instead of thin films. As a result, the displacement when irradiated with light was small, at a few nm, and the resonance frequency was low, at 80 Hz or less, so sufficient characteristics were not obtained for use as an actuator.

[0013] In response to this, the inventors discovered that a crack-free single crystal thin film of oxide ferroelectric can be obtained by the method described below (patent application "Japanese Patent Application No. 2023-113031" by the same applicant), and also discovered that a good optical actuator can be realized by applying this oxide ferroelectric thin film to an optical actuator, and thus completed the present invention.

[0014] First Embodiment In a first embodiment of the present invention, a method for manufacturing an oxide ferroelectric sheet (a thin film of an oxide ferroelectric material) will be described. Fig. 1A is a perspective view of an as-grown film 10 according to a first embodiment of the present invention.

[0015] As shown in FIG. 1A, first, SrTiO ３ A (001) single crystal substrate 1 is prepared. Subsequently, Sr is deposited on the single crystal substrate 1 by pulsed laser deposition (PLD). ３ Al ２ O ６ The water-soluble film 2 is epitaxially grown at a substrate temperature of, for example, 700° C. to 800° C. The water-soluble film 2 has a thickness of, for example, 20 nm to 100 nm.

[0016] Subsequently, a single-crystal dielectric film 3 is epitaxially grown on the water-soluble film 2 by using pulsed laser deposition (PLD). The substrate temperature is, for example, 700° C. to 800° C. The dielectric film 3 is made of perovskite, particularly Ba. １－ｘ Sr ｘ TiO ３ (0≦x≦0.5), for example, BaTiO ３ The dielectric film 3 has a thickness of, for example, 100 nm to 500 nm and extends in the c-axis direction.

[0017] Subsequently, a conductive electrode film 4 is deposited at room temperature on the dielectric film 3. The electrode film 4 is made of crystallized ITO (Indium Tin Oxide). The film thickness is, for example, 0 nm to 100 nm, which means that the electrode film 4 may be omitted. The electrode film 4 may be made of amorphous ITO (a-ITO), RuO ２ may be.

[0018] Subsequently, the protective film 5 is deposited at room temperature on the electrode film 4. The protective film 5 is made of a-Al２ O ３ The protective film 5 is made of a-SiO ２ may be.

[0019] Through the above steps, an as-grown film 10 is formed on the single crystal substrate 1, in which the water-soluble film 2, the dielectric film 3, the electrode film 4, and the protective film 5 are laminated.

[0020] Finally, the as-grown film 10 is immersed in pure water to dissolve the water-soluble film 2. This causes the laminate of the dielectric film 3, electrode film 4, and protective film 5 to be peeled off from the single crystal substrate 1, yielding an oxide ferroelectric sheet 100 as shown in FIG.

[0021] 2A and 2B are schematic diagrams showing an example of a process for obtaining an oxide ferroelectric sheet 100 by immersing the laminated as-grown film 10 in pure water to dissolve the water-soluble film 2. Specifically, SrTiO ３ On the (001) single crystal substrate 1, 50 nm of Sr ３ Al ２ O ６ Water-soluble film 2, 300 nm BaTiO ３ Dielectric film 3, 100 nm ITO electrode film 4, 1000 nm a-Al ２ O ３ After the protective films 5 are laminated in order, the water-soluble film 2 is dissolved and removed by immersion in pure water.

[0022] FIG. 2A is a schematic diagram of the as-grown film 10 before immersion in pure water, and shows the SrTiO ３ On the (001) single crystal substrate 1, epitaxially grown Sr ３ Al ２ O ６ Water-soluble film 2 and BaTiO ３ The dielectric film 3 is formed in pseudomorphic alignment with the single crystal substrate 1. ３ Al ２ O ６ Water-soluble film 2 and BaTiO ３ The crystal lattice structure of the dielectric film 3 is also shown.

[0023] FIG. 2B is a schematic diagram of the oxide ferroelectric sheet 100 after the water-soluble film 2 has been removed by immersion in pure water, where a flat oxide ferroelectric sheet 100 is obtained.

[0024] FIG. 2C is a photograph of the surface of the as-grown film 10 viewed from the protective film 5 side after 60 minutes and 120 minutes of immersion in pure water, and shows that the peeled area increases with the passage of time.

[0025] In this way, even if the water-soluble film 2 is removed, the dielectric film 3 is subjected to strain (residual stress) from the protective film 5, so that the occurrence of cracks due to shrinkage of the dielectric film 3 is prevented.

[0026] 2D is a surface photograph taken of the oxide ferroelectric sheet 100 peeled off from the single crystal substrate 1 and placed on a glass substrate, and it can be seen that a crack-free oxide ferroelectric sheet 100 is obtained. The shape (warpage) of the oxide ferroelectric sheet 100 can be controlled by the film thickness of the water-soluble film 2, and a flat oxide ferroelectric sheet 100 as shown in FIG. 2D can be obtained by setting the water-soluble film 2 to a thickness of 50 nm.

[0027] Next, the characteristics of the obtained oxide ferroelectric sheet 100 will be described. Here, a 300 nm single crystal BaTiO ３ Dielectric film 3, 100 nm ITO electrode film 4, 1000 nm a-Al ２ O ３ The oxide ferroelectric sheet 100 shown in FIG. 2B, which is made up of three layers including the protective film 5, will be described.

[0028] 3 to 6 show the BaTiO ３ The dielectric characteristics of the dielectric film 3 when an electric field is applied in the film thickness direction are shown.

[0029] FIG. 3 shows BaTiO ３ This is a ferroelectric hysteresis loop of the dielectric film 3, where the horizontal axis represents the electric field and the vertical axis represents the electric polarization. ３ The dielectric film 3 exhibits clear ferroelectric inversion, and dielectric polarization occurs even at an applied voltage of 0, with a remanent polarization of 23 μC / cm ２ It can be seen that the film has excellent ferroelectric properties.

[0030] FIG. 4 shows BaTiO ３ This shows the current characteristics of the dielectric film 3, with the horizontal axis representing the electric field and the vertical axis representing the current. When the direction of the electric field is reversed, a current flows, demonstrating that the film has excellent ferroelectric properties.

[0031] Figure 5 shows the relative permittivity (top) and dielectric loss (bottom) when the electric field is changed. The horizontal axis is the electric field, and the vertical axis is the relative permittivity ε Ｔ The right side is the dielectric loss tanδ. The high relative dielectric constant ε is about 1800 to about 2000. Ｔ Furthermore, the dielectric loss tan δ is a very low value of about 0.08, which is preferable as a ferroelectric material.

[0032] FIG. 6 shows BaTiO ３ This shows the piezoelectric properties of the dielectric film 3. The horizontal axis represents the electric field, and the vertical axis represents the amount of displacement. When the electric field is changed, the BaTiO ３ It can be seen that the shape of the dielectric film 3 changes and that it has a piezoelectric constant of 300 to 750 pm / V, particularly 600 pm / V.

[0033] Next, the driving characteristics when the oxide ferroelectric sheet 100 according to the first embodiment of the present invention is used as an optical actuator will be described.

[0034] 7A and 7B are enlarged photographs showing the driving characteristics of the oxide ferroelectric sheet 100. Fig. 7A is an enlarged photograph of the oxide ferroelectric sheet 100 adhered to the tip of a glass rod using a UV-curable adhesive. The glass rod is located at the back of the photograph, and the BaTiO ３ It is bonded to the dielectric film side.

[0035] As can be seen from Fig. 7A, the oxide ferroelectric sheet 100, which is approximately 2 mm x 2 mm in size, maintains its flatness (stands on its own) with a portion of it attached to the tip of the glass rod. As mentioned above, the oxide ferroelectric sheet 100 is made of 300 nm BaTiO ３ Dielectric film 3, 100 nm ITO electrode film 4, 1000 nm a-Al ２ O ３ It comprises a protective film 5 .

[0036] FIG. 7B is a photograph of the oxide ferroelectric sheet 100 adhered to the glass rod as viewed from the side. The oxide ferroelectric sheet 100 is composed of BaTiO ３ Dielectric film 3, ITO electrode film 4, a-Al ２ O ３ The left side shows the case where UV laser light was not irradiated, and the right side shows the case where UV laser light was irradiated. The UV laser light used was laser light with a wavelength of 266 nm, and was irradiated in air.

[0037] In Fig. 7B, the light-colored (white) dashed line represents the position of the oxide ferroelectric sheet 100 when not irradiated with UV laser light, and the black dashed line represents the position when irradiated with UV laser light. As can be seen from Fig. 7B, the oxide ferroelectric sheet 100 is displaced to the right by a displacement amount (Δd) by irradiation with UV laser light.

[0038] Here, BaTiO ３ The band gap of the dielectric film 3 is 3.2 eV, so approximately 90% of the UV laser light with a wavelength of 266 nm is absorbed. When irradiated with UV laser light, the oxide ferroelectric sheet 100 exhibits a displacement (Δd) of approximately 52 μm, and the displacement (Δd) / length ratio is calculated to be 3.7%. This value is the highest displacement (Δd) / length ratio (e.g., less than 0.3%) of currently reported ferroelectric-type light-driven actuators. The displacement (Δd) refers to the displacement at the end of the oxide ferroelectric sheet 100, and the length refers to the distance from the fixed part of the oxide ferroelectric sheet 100 (the part attached to the glass rod) to the displacement measurement point.

[0039] 8 shows the relationship between the irradiation time of the UV laser light and the displacement (Δd), with the horizontal axis representing time and the vertical axis representing the displacement (Δd). From top to bottom, the graph shows the cases where the on / off cycle of the UV laser light is 2.0 seconds, 1.0 seconds, 0.5 seconds, and 0.2 seconds, i.e., the frequency is 0.5 Hz, 1.0 Hz, 2.0 Hz, and 5.0 Hz. The UV laser light is on in the gray-colored areas and off in the uncolored areas. The UV laser light is irradiated in air.

[0040] As can be seen from Figure 8, when the UV laser light is turned on, the oxide ferroelectric sheet 100 is displaced, and when the UV laser light is turned off, the oxide ferroelectric sheet 100 returns to its original position. Furthermore, when the UV laser light is turned on, the displacement (Δd) reaches a saturated displacement of approximately 52 μm after approximately 1.4 seconds and remains substantially constant. On the other hand, when the UV laser light is turned off, the displacement (Δd) returns to 0 μm after approximately 0.1 seconds. In this way, the oxide ferroelectric sheet 100 can be repeatedly displaced with good reproducibility by turning a single light source on and off.

[0041] 9 shows the relationship between the laser energy density of the UV laser light (wavelength 266 nm) and the displacement (Δd) of the oxide ferroelectric sheet 100, with the horizontal axis representing the laser energy density and the vertical axis representing the displacement (Δd). As can be seen from Fig. 8, the laser energy density and the displacement are in a directly proportional relationship, and it can be seen that the displacement (Δd) can be controlled by adjusting the laser intensity of the UV laser light.

[0042] Furthermore, conventional optical actuators utilize the phase transition of oxide layers or the piezoelectric effect of bulk dielectric films, so they are difficult to operate using pulsed lasers or lasers with a power of 150 mW / cm. ２ ~8.5 x 10 ９ mW / cm ２ In contrast, the optical actuator using the oxide ferroelectric thin film according to this embodiment requires a continuous laser with a high energy density of 10 to 200 mW / cm. ２ It is possible to achieve large displacement / length ratios of 0.8 to 3.7% using a continuous laser with low energy density of about 1000 .mu.m.

[0043] 10 is a diagram illustrating the operating principle of an optical actuator using an oxide ferroelectric material. An optical actuator using an oxide ferroelectric material is driven by strain caused by the inverse piezoelectric effect due to photovoltaic power.

[0044] That is, as can be seen from FIG. 3, the BaTiO ３The dielectric film 3 has ferroelectric polarization in the film thickness direction. Therefore, when the energy band structure is viewed, the valence band maximum (VBM) and conduction band minimum (CBM) are tilted in the polarization direction, as shown in Figure 10. In Figure 10, the left-right direction is the film thickness direction, i.e., the polarization direction.

[0045] BaTiO ３ When the dielectric film 3 is irradiated with UV laser light having a wavelength of 266 nm, which has energy greater than the band gap, BaTiO ３ Holes and electrons are formed in the valence band and conduction band of the dielectric film 3. The slope of the valence band and the conduction band separates the holes and electrons, forming BaTiO ３ An electromotive force is generated in the thickness direction of the dielectric film 3 due to the photovoltaic effect. The inverse piezoelectric effect caused by this electromotive force causes the BaTiO ３ A displacement occurs in the dielectric film 3, driving the optical actuator.

[0046] When considering the application of optical actuators to fluidic microdevices and microchips, it is important that the optical actuator operates not only in air but also in an electrolyte (e.g., physiological saline). Figures 11A and 11B show the driving characteristics of the oxide ferroelectric sheet 100 in physiological saline, with Figure 11A showing an overview of the device used to measure the driving characteristics and Figure 11B showing the measurement results.

[0047] As shown in Figure 11A, the oxide ferroelectric sheet 100 was fixed in a quartz glass beaker filled with saline, and UV laser light (wavelength 266 nm) was irradiated from outside the beaker. Figure 11B shows the relationship between the irradiation time of the UV laser light and the displacement amount (Δd), with the horizontal axis representing time and the vertical axis representing the displacement amount (Δd). As can be seen from Figure 11B, the oxide ferroelectric sheet 100 is displaced depending on whether the UV laser light is turned on or off. In this way, it was confirmed that the oxide ferroelectric sheet 100 can be driven by UV laser light even in saline.

[0048] Next, the high-frequency optical drive characteristics of the optical actuator according to the embodiment of the present invention were evaluated. FIG. 12 is a schematic diagram of the optical actuator device used to evaluate the high-frequency optical drive characteristics. As in FIG. 7A, an oxide ferroelectric sheet 100 bonded to a glass rod was irradiated with continuous UV laser light having a wavelength of 266 nm using an electrically controlled optical chopper as an optical intensity modulator. By using an electrically controlled optical chopper, the on / off frequency of the UV laser light can be changed between 0.2 kHz and 10 kHz. Here, an optical chopper was used as the optical intensity modulator, but a mechanical shutter or a modulator using an electro-optical element or an acousto-optical element capable of higher-speed modulation can also be used.

[0049] The displacement of the oxide ferroelectric sheet 100 was measured using a probe beam consisting of continuous laser light with a wavelength of 532 nm. The probe beam is irradiated onto the surface of the oxide ferroelectric sheet 100, reflected from the surface, and then incident on a position sensitive detector (PSD). The position sensitive detector (PSD) converts the difference between the integrated light intensities A and B, which correspond to the displacement within the two divided regions shown in the figure, into a voltage, which is then amplified by a lock-in amplifier to detect the displacement as a voltage value.

[0050] Figure 13A shows the amplitude intensity (displacement) when the frequency of the UV laser light incident on the oxide ferroelectric sheet 100 is changed, and Figure 13B shows the change in phase when the frequency of the UV laser light incident on the oxide ferroelectric sheet 100 is changed. The frequency was changed from 200 Hz to 10 kHz, and Figures 13A and 13B show enlarged views of the range from 6 to 10 kHz. The incident UV laser light used had a wavelength of 266 nm and an output of 0.7 W. In Figure 13A, the horizontal axis represents the frequency of the UV laser light, and the vertical axis represents the amplitude intensity of the oxide ferroelectric sheet 100. In Figure 13B, the horizontal axis represents the frequency of the UV laser light, and the vertical axis represents the phase.

[0051] The amplitude versus frequency curve in FIG. 13A shows positive and negative peaks in amplitude intensity at frequencies of 7.8 kHz and 8.3 kHz. Furthermore, the phase versus frequency curve in FIG. 13B shows a negative peak with a phase of 130° at a frequency of 8 kHz. These behaviors resemble the electrical response of a piezoelectric vibrator at its resonant frequency. These results demonstrate that mechanical resonance is induced in the oxide ferroelectric sheet 100 by using an on / off cycle of UV laser light with a frequency of 8 kHz. In other words, an optical actuator using the oxide ferroelectric sheet 100 can be driven in response to an on / off cycle of UV laser light with a frequency exceeding 8.3 kHz.

[0052] In the embodiment of the present invention, a single-wavelength UV laser beam is used to drive the optical actuator, but the light source may be a single-wavelength UV laser, an ultraviolet pulse laser light source, an ultraviolet LED light source, etc. Furthermore, the ultraviolet spectrum of a broadband lamp light source (xenon lamp light source, deuterium lamp light source) may be extracted using a filter and used as the light source.

[0053] Here, it is possible to use visible light as a light source for driving the optical actuator, but while this light source is easy to obtain, the visible light component contained in ambient light may be irradiated onto the optical actuator, causing malfunction. In this regard, light with a wavelength of 280 nm or less is not included in ambient light (sunlight) and is in the so-called solar blind region. By using ultraviolet light, which is included in the solar blind region, as a light source, it is possible to prevent malfunction of the optical actuator without the need to separate it from ambient light using a filter or other shading measures.

[0054] In this way, an optical actuator using the thin film oxide ferroelectric sheet 100 according to an embodiment of the present invention can be driven using UV laser light with an on / off frequency of 8 kHz, which is significantly faster than the 80 Hz that could be achieved with optical actuators using conventional bulk oxide ferroelectric films.

[0055] As described above, the optical actuator according to the embodiment of the present invention uses a thin oxide ferroelectric sheet, thereby realizing an optical actuator that has sufficient displacement and is capable of high-speed, highly reliable, and repeated operation. This optical actuator can be made smaller and simpler than electrically driven actuators, and can also be remotely operated in environments including electrolytes such as physiological saline. Furthermore, an optical actuator device that drives such an optical actuator can also be realized.

[0056] Second Embodiment In the first embodiment of the present invention, SrTiO ３ On the (001) single crystal substrate 1, Sr ３ Al ２ O ６ In the above description, a water-soluble film (sacrificial layer) made of r-plane Al is epitaxially grown, and an oxide ferroelectric sheet (a thin film of an oxide ferroelectric material) is formed thereon. ２ O ３ The following describes a case where a water-soluble film (sacrificial layer) made of CaO is formed on a single crystal substrate or a

[110] -oriented YSZ (Yttaria-Stabilized Zirconia) single crystal substrate, and an oxide ferroelectric sheet is then formed thereon.

[0057] As shown in FIG. 14A, first, r-plane Al ２ O ３ A single crystal substrate or a

[110] -oriented YSZ single crystal substrate 11 is prepared. Next, a water-soluble film 12 made of CaO is epitaxially grown on the single crystal substrate 11 using pulsed laser deposition (PLD). The substrate temperature is, for example, 700°C to 800°C. The film thickness of the water-soluble film 12 is, for example, 50 nm to 100 nm.

[0058] Next, a Ba film having a perovskite structure was formed on the water-soluble film 12 in the same manner as in the first embodiment. １－ｘ Sr ｘ TiO ３ (0≦x≦0.5) Dielectric film 3, here BaTiO ３ Dielectric film 3 (300 nm), ITO electrode film 4 (50 nm), Al ２ O ３A glass protective film 5 (1000 nm) is formed on each of the layers to form an as-grown film 20. Note that the thicknesses of the layers shown here are merely examples.

[0059] Next, as shown in FIG. 14B, the as-grown film 20 is immersed in pure water to dissolve the water-soluble film 12, and BaTiO ３ dielectric film 3, ITO electrode film 4, Al ２ O ３ An oxide ferroelectric sheet 100 consisting of a glass protective film 5 is obtained.

[0060] 15 shows surface photographs of the as-grown film 20 viewed from the protective film 5 side immediately after immersion of the as-grown film 20 in pure water, and after 100, 200, 300, and 310 minutes have elapsed. It can be seen that the peeled area increases with the passage of time, and after 310 minutes, the oxide ferroelectric sheet 100 is completely peeled off from the substrate 11.

[0061] As in the case of the first embodiment, even if the water-soluble film 2 is removed, the dielectric film 3 is subjected to strain (residual stress) from the protective film 5, thereby preventing cracks from occurring due to shrinkage of the dielectric film 3. Also, the ITO electrode film 4 may be omitted.

[0062] FIG. 16A shows the r-plane Al ２ O ３ 16B shows the results of X-ray diffraction (XRD) measurement of the oxide ferroelectric sheet before peeling when a single crystal substrate is used. ２ O ３ 16A and 16B show the results of X-ray diffraction (XRD) measurement of the oxide ferroelectric sheet after peeling when a single crystal substrate was used. In Fig. 16A and Fig. 16B, the horizontal axis represents the diffraction angle (2θ) and the vertical axis represents the diffraction intensity. Both before peeling (Fig. 16A) and after peeling (Fig. 16B), BaTiO ３ Diffraction peaks of 001 and 002 originating from the BaTiO ３ It can be seen that a dielectric film was obtained. The peak indicated by PETsub is a peak derived from the PT substrate to which the highly oriented oxide ferroelectric sheet 100 was attached.

[0063] Also, FIG. 16C shows the r-plane Al２ O ３ This shows the results of ψ-scan measurement of X-ray diffraction of the oxide ferroelectric sheet 100 before peeling when using a single crystal substrate 11, where the horizontal axis represents the rotation angle (ψ) around the normal to the substrate, and the vertical axis represents the diffraction intensity. ３ The diffraction peak of 003 originating from BaTiO was detected, and the BaTiO was uniaxially oriented in the c-axis direction. ３ It is clear that a film was obtained.

[0064] 17A shows the results of X-ray diffraction (XRD) measurement of the oxide ferroelectric sheet before peeling when a YSZ (110) single crystal substrate is used, and FIG. 17B shows the results of X-ray diffraction (XRD) measurement of the oxide ferroelectric sheet 100 after peeling when a YSZ (110) single crystal substrate is used. In FIGS. 17A and 17B, the horizontal axis indicates the diffraction angle (2θ), and the vertical axis indicates the diffraction intensity. r-plane Al ２ O ３ Similar to the case where the single crystal substrate 11 was used, BaTiO ３ Diffraction peaks of 001 and 002 originating from the BaTiO ３ It can be seen that a dielectric film was obtained.

[0065] 17C shows the results of ψ scan measurement of X-ray diffraction of the oxide ferroelectric sheet 100 before peeling when a YSZ (110) single crystal substrate 11 is used, where the horizontal axis represents the rotation angle (ψ) around the normal to the substrate, and the vertical axis represents the diffraction intensity. ３ The diffraction peak of 103 originating from the BaTiO crystalline structure was detected, and the BaTiO crystalline structure was uniaxially oriented in the c-axis direction. ３ It is clear that a film was obtained.

[0066] 18A is a ferroelectric hysteresis loop of the oxide ferroelectric sheet 100, where the horizontal axis represents the electric field and the vertical axis represents the electric polarization. ３ The dielectric film 3 exhibits clear ferroelectric inversion, and dielectric polarization occurs even at an applied voltage of 0, with a remanent polarization of 20 μC / cm ２ It can be seen that the film has excellent ferroelectric properties.

[0067] 18B shows the change in the relative permittivity and dielectric loss when the voltage applied to the oxide ferroelectric sheet 100 is changed, with the horizontal axis representing the voltage and the vertical axis representing the relative permittivity (left side) and dielectric loss (right side). ３ The dielectric film 3 has a high relative dielectric constant ε of about 200 to about 500. Ｔ Furthermore, the dielectric loss tan δ is a very low value of about 0.04, which is preferable as a ferroelectric material.

[0068] 19 is an atomic force microscope (AFM) photograph of the surface of the YSZ single crystal substrate 11 after ultrasonic cleaning with pure water after peeling off the oxide ferroelectric sheet 100. The surface irregularities within a 5 μm × 5 μm area were 1.14 nm or less, and a flat substrate surface was obtained even after peeling, demonstrating that the substrate can be reused.

[0069] FIG. 20 shows a YSZ single crystal substrate 11 that has been reused to form a CaO water-soluble film 12 and a BaTiO ３ Dielectric film 3, ITO electrode film 4, Al ２ O ３ 20 shows the results of X-ray diffraction measurement of the as-grown film 20 prepared by depositing the glass protective film 5, where the horizontal axis represents the scattering vector and the vertical axis represents the scattering intensity. As shown in FIG. 20, the as-grown film 20 shows peaks derived from the YSZ single crystal substrate 11 as well as peaks derived from the CaO water-soluble film 12 and BaTiO ３ Diffraction peaks originating from the dielectric film 3 and the ITO electrode film 4 were detected, and it was found that a good as-grown film 20 could be formed even when the YSZ single crystal substrate 11 was reused.

[0070] As described above, by using CaO as the material of the water-soluble film 12, SrTiO ３ Instead of the (001) single crystal substrate 1, a cheaper r-plane Al ２ O ３ The oxide ferroelectric sheet 100 can be produced using a single crystal substrate or a

[110] -oriented YSZ single crystal substrate, and the production cost of the oxide ferroelectric sheet 100 can be reduced.

[0071] In addition, r-plane Al ２ O ３For single crystal substrates and YSZ single crystal substrates with

[110] orientation, SrTiO ３ It is also possible to make the substrate area larger than that of a (001) single crystal substrate.

[0072] Furthermore, r-plane Al ２ O ３ In the case of a single crystal substrate or a

[110] -oriented YSZ single crystal substrate, by using CaO as the material of the water-soluble film 12, it becomes possible to reuse the substrate after peeling off the oxide ferroelectric sheet 100.

[0073] Third Embodiment In a third embodiment of the present invention, the dielectric film 3 is made of Ba. １－ｘ Sr ｘ TiO ３ Instead of the ferroelectric film (0≦x≦0.5), the oxide ferroelectric sheet 100 was fabricated using PLZT (La-modified lead zirconate titanate).

[0074] Specifically, as in the first embodiment, SrTiO ３ A (001) substrate was prepared, and Sr ３ Al ２ O ６ Water-soluble film (50 nm), PLZT dielectric film (200 nm), ITO electrode film (50 nm), Al ２ O ３ A glass protective film (1000 nm) was then laminated to form an as-grown film. Note that the thicknesses shown here are merely examples.

[0075] 21 shows the results of X-ray diffraction (XRD) measurement of the as-grown film, with the horizontal axis representing the diffraction angle (2θ) and the vertical axis representing the diffraction intensity. Diffraction peaks of 001 and 002 originating from PLZT were detected, indicating that a c-axis oriented PLZT dielectric film was formed.

[0076] Then, it is immersed in pure water. ３ Al ２ O ６ The water-soluble film was dissolved, and the PLZT dielectric film (200 nm), ITO electrode film (50 nm), and Al ２ O ３ An oxide ferroelectric sheet was prepared, which was made of a glass protective film.

[0077] As in the case of embodiment 1, even if the water-soluble film is removed, the dielectric film is subjected to strain (residual stress) from the protective film, so that the occurrence of cracks due to shrinkage of the dielectric film is prevented. Also, the ITO electrode film may be omitted.

[0078] 22 shows the results of X-ray diffraction (XRD) measurement of the oxide ferroelectric sheet after peeling, where the horizontal axis represents the diffraction angle (2θ) and the vertical axis represents the diffraction intensity. Even after peeling, the 001 and 002 diffraction peaks derived from PLZT were detected, indicating that a c-axis oriented PLZT dielectric film was obtained in the oxide ferroelectric sheet after peeling from the substrate.

[0079] FIG. 23 is an enlarged photograph of the oxide ferroelectric sheet, in which millimeter-sized crack-free areas are obtained.

[0080] Fig. 24 shows the ferroelectric hysteresis loop of the oxide ferroelectric sheet using PLZT, where the horizontal axis represents voltage and the vertical axis represents electric polarization. As can be seen from Fig. 24, a clear ferroelectric hysteresis loop was observed even when using a PLZT dielectric film, demonstrating that the film has ferroelectricity.

[0081] Figure 25 shows the measurement results of the driving characteristics of the oxide ferroelectric sheet, showing the relationship between the irradiation time of the UV laser light and the displacement (Δd), with the horizontal axis representing time and the vertical axis representing the displacement (Δd). As shown in Figure 7B, the displacement (Δd) refers to the displacement at the end of the oxide ferroelectric sheet 100. The UV laser light was switched on and off every second. As can be seen from Figure 25, when the UV laser light was turned on, the oxide ferroelectric sheet 100 displaced, and when the UV laser light was turned off, the oxide ferroelectric sheet 100 returned to its original position, demonstrating the reproducibility of the displacement. Thus, even when a PLZT dielectric film is used, the oxide ferroelectric sheet 100 can be displaced with good reproducibility by turning a single light source on and off.

[0082] In the third embodiment, SrTiO ３ (001) substrate, Sr ３ Al ２ O ６A PLZT ferroelectric film was formed on the water-soluble film. ２ O ３ It can also be fabricated on a single crystal substrate, a

[110] oriented YSZ single crystal substrate, or a CaO water-soluble film.

[0083] The optical actuator using the thin film oxide ferroelectric sheet of the present invention can be applied to electronics technologies such as MEMS devices, microrobots, filters, and microfluidic devices, as well as medical technologies.

[0084] REFERENCE SIGNS LIST 1, 11 Single crystal substrate 2, 12 Water-soluble film 3 Dielectric film 4 Electrode film 5 Protective film 10, 20 As-grown film 100 Oxide ferroelectric sheet

Claims

1. An optical actuator that is driven by irradiated light, comprising: a dielectric film made of perovskite; and a protective film made of amorphous oxide, wherein strain is applied to the dielectric film from the protective film, and the dielectric film is deformed by the inverse piezoelectric effect caused by irradiated light.

2. The optical actuator according to claim 1, further comprising a conductive electrode film between the dielectric film and the protective film.

3. The dielectric film is Ba １－ｘ Sr ｘ TiO ３ 3. The optical actuator according to claim 1, wherein the optical actuator is made of (0≦x≦0.5) or PLTZ.

4. The protective film is amorphous Al ２ O ３ or amorphous SiO ２ 3. The optical actuator according to claim 1, comprising:

5. The electrode film is ITO or RuO ２ The optical actuator according to claim 2 , 6. The optical actuator according to claim 1 or 2, wherein the thickness of the dielectric film is 100 nm to 500 nm.

7. The optical actuator according to claim 1 or 2, wherein the protective film has a thickness of 10 nm to 1 μm.

8. The dielectric film is BaTiO with a piezoelectric constant of 300 to 750 pm / V. ３ The optical actuator according to claim 3 , wherein 9. An optical actuator according to claim 1 or 2, wherein the irradiated light is a UV laser light of a single wavelength.

10. The optical actuator according to claim 1 or 2, wherein the deformation resonates with irradiation light having an on / off cycle of 8 kHz.

11. An optical actuator device comprising: an optical actuator according to claim 1 or 2; a light source which irradiates the optical actuator with ultraviolet light; and a modulator which is disposed between the optical actuator and the light source and which modulates the intensity of the ultraviolet light.

12. The optical actuator device according to claim 11, wherein the wavelength of the ultraviolet light is 280 nm or less.

13. A process for preparing an aluminum oxide single crystal substrate or an yttria-stabilized zirconia single crystal substrate; and depositing a water-soluble film of CaO and a water-soluble film of BaO on the substrate. １－ｘ Sr ｘ TiO ３ (0≦x≦0.5) or PLTZ, forming a protective film made of an amorphous oxide on the dielectric film to produce an as-grown film made of a substrate, a water-soluble film, a dielectric film, and a protective film, and immersing the as-grown film in a solution to dissolve the water-soluble film, and separating an oxide ferroelectric sheet made of the dielectric film and protective film from the substrate.

14. The method according to claim 13, further comprising a step of depositing a conductive electrode layer between the dielectric film and the protective film, and a step of dissolving the water-soluble film to separate the oxide ferroelectric sheet consisting of the dielectric film, the electrode layer and the protective film from the substrate.

15. Ba １－ｘ Sr ｘ TiO ３ (0≦x≦0.5) is BaTiO ３ The method according to claim 14 or 13,