JP2006220746A - Light controller and structural body used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light controller in which a transparent electrode is used as an electrode material. <P>SOLUTION: The light controller 8 is equipped with a plurality of pixels 10 arrayed in two dimensions. A first reflection layer 32 is formed on a substrate 30. An optical modulation film 34 is arranged on an upper surface of the first reflection layer 32. An electro-optic material, such as PLZT, whose refractive index varies according to an applied electric field, is selected as a material of the optical modulation film 34. A protective layer 50 is equipped on an upper surface of the optical modulation film 34. The transparent electrode 36 is equipped on the upper surface of the optical modulation film 34 with the protective layer 50 interposed in between. A second reflection layer 40 is formed on an upper surface of the transparent electrode 36. The second reflection layer 40 is formed of a dielectric multilayer film comprising a first dielectric film 42 and a second dielectric film 44 with mutually different refractive indexes alternately laminated. The first reflection layer 32, the optical modulation film 34, and the second reflection layer 40 construct a resonator. The transparent electrode 36 and the first reflection layer 32 form an electrode pair, and control reflectance of the light controller 8 with the electric field applied to the optical modulation film 34. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a light control device, and more particularly to an electrode forming technique thereof.

  In recent years, as a large-capacity recording method, a digital information recording system using the principle of a hologram is known (for example, Patent Document 1).

As a material for the spatial light modulator of the hologram recording apparatus, a material having an electro-optic effect such as lead lanthanum zirconate titanate (hereinafter referred to as PLZT) can be used. PLZT is a transparent ceramic having a composition of (Pb _1-y La _y ) (Zr _1-x Ti _x ) O ₃ . The electro-optic effect is a phenomenon in which when an electric field is applied to a substance, the substance is polarized and the refractive index changes. When the electro-optic effect is used, the phase of light can be switched by turning on and off the applied voltage. Therefore, a light modulation material having an electro-optic effect can be applied to an optical shutter such as a spatial light modulator.

  Conventionally, bulk PLZT has been widely used for such applications as optical shutters (Patent Document 2). However, it is difficult for optical shutters using bulk PLZT to meet demands for miniaturization and integration, as well as reductions in operating voltage and cost. In addition, since the bulk method includes a process of processing at a high temperature of 1000 ° C. or higher after mixing raw material metal oxides, when applied to an element formation process, there are many restrictions on material selection, element structure, and the like. Will join.

For this reason, attempts are being made to apply PLZT, which is a thin film formed on a substrate, to a light control element instead of bulk PLZT. Patent Document 3 describes a display device in which a PLZT film is formed on a transparent substrate such as glass and a comb-shaped electrode is provided thereon. This display device has a configuration in which polarizing plates are provided on both surfaces of a display substrate on which a PLZT film is formed. Here, by connecting the electrode terminal portion of each pixel to an external drive circuit, a desired pixel is driven, and a desired display can be performed by transmitted light from a light source provided on one surface side of the display substrate. It can be done.
JP 2002-297008 A JP-A-5-257103 Japanese Patent Laid-Open No. 7-146657

Here, a method of applying an electric field to the light control element using the thin film PLZT as described in Patent Document 3 will be considered. When an electrode is formed on the surface of PLZT using Au, IrO ₂ , Al, or the like as a material, light does not pass through the electrode portion, and thus the aperture ratio and light utilization efficiency are unavoidable. Therefore, the present inventor has tried to improve the electrode formed on the PLZT by using a transparent electrode in order to further improve the light utilization efficiency.

As a typical transparent electrode material, ITO (Indium Tin Oxide) or the like is known. The inventor formed an electrode on the PLZT film using this ITO as an electrode material, and measured the electrical characteristics. FIG. 7 is a diagram showing the relationship between applied electric field and polarization when an opaque electrode is formed using IrO ₂ and a transparent electrode is formed using ITO. For any material, electrodes are formed by sputtering.

As can be seen from FIG. 7, when the electrode is formed of ITO, the amount of polarization when the same electric field is applied is greatly reduced as compared with the case of forming the electrode with Ir / IrO ₂ .
Further, when the relative permittivity was measured, the relative permittivity when the electrode was formed with Ir / IrO ₂ was ε = 1270, whereas when formed with ITO, it decreased to ε = 820. It became clear.

  The present invention has been made in view of such a situation, and an object thereof is to provide a light control device in which electrical characteristics are not deteriorated even when a transparent electrode is used as an electrode material.

  One embodiment of the present invention relates to a light control apparatus. The light control device includes a substrate, a first reflection layer provided on the substrate, a light modulation film provided on the first reflection layer, the refractive index of which can be controlled by an applied electric field, and a light modulation film And a transparent electrode provided on the protective layer and applying an electric field to the light modulation film.

  According to this aspect, by forming the protective layer between the light modulation film and the transparent electrode, it is possible to prevent the electrical characteristics of the light modulation film from deteriorating, and the light control device having excellent electrical characteristics Can be configured.

Protective layer may be formed by iridium oxide IrO _2. Since iridium oxide has conductivity, the light modulation film can be suitably protected without affecting the electric field applied to the light modulation film by the transparent electrode.

  The thickness of the protective layer may be in the range of 1 nm to 50 nm. When the protective film is formed of iridium oxide, a significant effect is recognized in the range of 1 nm to 50 nm as a characteristic of the light control device, and a more significant effect can be obtained by setting the thickness to 3 nm to 25 nm more preferably. .

The protective layer may be formed of strontium ruthenate SrRuO ₃ or may be formed of lanthanum strontium cobalt oxide La _0.5 Sr _0.5 CoO ₃ .
Even when these conductive oxides are used instead of iridium oxide, they function suitably as a protective layer.

  The transparent electrode may be formed of indium tin oxide (ITO). The transparent electrode may be formed of zinc oxide (ZnO).

The light modulating film is composed of lead zirconate titanate PZT (Pb (Zr _1-x Ti _x ) O ₃ ) or lead lanthanum zirconate titanate PLZT ((Pb _1-y La _y ) (Zr _1-x Ti _x ) O. ₃ ) may be formed.

The light control device may further include a second reflective layer provided on the transparent electrode.
The transparent electrode and the first reflective layer may form an electrode pair. In this case, since an electric field is applied in the thickness direction of the light modulation film, the electric field generated inside the light modulation film can be made uniform.

  The second reflective layer may have a laminated structure including a plurality of dielectric films having different refractive indexes. By forming the second reflective layer with a dielectric multilayer film, the reflectance can be suitably controlled by selecting the material, number of layers, and thickness of the multilayer film. The reflectances of the first reflective layer and the second reflective layer may be substantially the same.

  Another aspect of the present invention relates to a structure. The structure includes a light modulation film formed using an electro-optic material, a protective layer provided on the light modulation film, a transparent electrode layer provided on the protective layer and applying an electric field to the light modulation film, . This structure is provided in a light control device that modulates light by applying an electric field to the light modulation film and using a change in the refractive index thereof.

  According to this aspect, it is possible to prevent the electrical characteristics of the light modulation film from deteriorating when forming a transparent electrode for applying an electric field to the light modulation film by the protective layer.

  As a material for the protective layer of the structure, a conductive oxide film can be preferably used, and it may be formed of iridium oxide, strontium ruthenate, lanthanum strontium cobalt oxide, or the like.

  The transparent electrode layer of the structure may be formed of indium tin oxide or zinc oxide.

  The light modulation film of the structure may be formed of lead zirconate titanate or lead lanthanum zirconate titanate.

  According to the light control device of the present invention, it is possible to improve the aperture ratio while suppressing deterioration of electrical characteristics.

An outline of the light control apparatus according to the present embodiment will be described. This light control device is used, for example, as a spatial light modulator in a hologram recording / reproducing device.
FIG. 1 is a diagram showing a hologram recording device when the light control device according to the present embodiment is used as a spatial light modulator. The hologram recording device 70 includes a spatial modulator SLM (light control device 8), a control unit 60, a laser light source 72, a beam expander 74, a Fourier transform lens 76, and a recording medium 78.

  In the hologram recording device 70, the laser light emitted from the laser light source 72 is split into two lights by a beam splitter (not shown). One of these lights is used as reference light and guided into the recording medium 78. The other light is expanded in beam diameter by the beam expander 74 and irradiated to the spatial modulator SLM (light control device 8) as parallel light.

  The light control device 8 has pixels arranged in a matrix, and is configured such that the reflectance changes for each pixel. The control unit 60 controls the reflectance of each pixel of the light control device 8 using the control signal CNT. The light applied to the spatial modulator SLM is reflected from the spatial modulator SLM as signal light having different intensities for each pixel. This signal light passes through the Fourier transform lens 76 and is Fourier transformed and collected in the recording medium 78. In the recording medium 78, the signal light including the hologram pattern and the optical path of the reference light intersect to form an optical interference pattern. The entire optical interference pattern is recorded on the recording medium 78 as a change in refractive index (refractive index grating).

Fig.2 (a) shows the top view of the light control apparatus 8 which concerns on this Embodiment. The light control device 8 includes a plurality of pixels 10 arranged in a two-dimensional form of 8 rows and 8 columns on a substrate 30. Each pixel 10 has a size of about 20 μm × 20 μm. A control signal CNT output from the control unit 60 in FIG. 1 is input to each pixel 10.
FIG. 2B is a cross-sectional view taken along the line AA ′ of the light control device shown in FIG. The light control device 8 includes a substrate 30, a first reflective layer 32, a light modulation film 34, a protective layer 50, a transparent electrode 36, a wiring 38, and a second reflective layer 40.

The light control device 8 according to the present embodiment is formed on the substrate 30. As a material for the substrate 30, glass, silicon, or the like having a flat surface can be suitably used.
A first reflective layer 32 is formed on the substrate 30. As a material of the first reflective layer 32, for example, a metal material such as Pt can be suitably used. The thickness of the first reflective layer 32 is about 200 nm. In the present embodiment, the first reflective layer 32 is made of Pt, and the first reflective layer 32 functions as an electrode for applying an electric field to the light modulation film 34 as will be described later.
When the first reflective layer 32 is formed of Pt, the reflectance of the first reflective layer 32 is about 60% to 80%.

A light modulation film 34 is provided on the upper surface of the first reflective layer 32. As the material of the light modulation film 34, a solid electro-optic material whose refractive index changes according to the applied electric field is selected. As such an electro-optic material, PLZT, PZT, LiNbO ₃ , GaA-MQW, SBN ((Sr, Ba) Nb ₂ O ₆ ) and the like can be used, and PLZT is particularly preferably used. The thickness t of the light modulation film 34 is determined according to the incident angle and wavelength of the incident light. For example, when the incident light is red light near 650 nm, it is preferably formed in the range of 500 nm to 1500 nm. As will be described later, since the electric field applied to the light modulation film 34 is applied in the thickness direction, it is difficult to apply an electric field for obtaining a sufficient refractive index change when the film thickness is 1500 nm or more. Become. Further, when the film thickness is 500 nm or less, it becomes difficult to obtain a sufficient optical film thickness change Δnt.

In the light control device 8 according to the present embodiment, the protective layer 50 is formed on the upper surface of the light modulation film 34. The protective layer 50 serves to prevent the electrical characteristics of the light modulation film 34 from being deteriorated by the transparent electrode 36 formed on the upper surface thereof.
As a material of the protective layer 50, iridium oxide IrO ₂ which is a conductive oxide film, strontium ruthenate SrRuO ₃ , lanthanum strontium cobalt oxide La _0.5 Sr _0.5 CoO ₃ or the like can be preferably used. In this embodiment, the case of using iridium oxide IrO ₂ will be described.

The protective layer 50 can be formed by a sputtering method. A substrate 30 on which a PLZT film is formed and an iridium Ir target are placed in an oxygen atmosphere, and the iridium Ir target is irradiated with argon ions. As a result, the sputtered iridium combines with oxygen and is deposited on PLZT as iridium oxide IrO ₂ .
Although the film thickness tp of the protective layer 50 will be described later, it is preferably in the range of 1 nm to 50 nm, and more preferably in the range of 3 nm to 25 nm.

A transparent electrode 36 is formed on the protective layer 50 formed on the light modulation film 34. The transparent electrode 36 can be formed of, for example, ITO (Indium Tin Oxide), ZnO, or the like. When the transparent electrode 36 is formed of ITO or ZnO, the thickness is about 100 nm to 150 nm. Since the transparent electrode 36 has a trade-off relationship between the resistance value and the transmittance, the thickness thereof may be determined experimentally.
The transparent electrode 36 can be formed by sputtering as with the protective layer 50. The transparent electrode 36 is formed in a matrix for each pixel 10.

A second reflective layer 40 is formed on the upper surface of the transparent electrode 36. The second reflective layer 40 is formed of a dielectric multilayer film, and first dielectric films 42 and second dielectric films 44 having different refractive indexes are alternately stacked. As a combination of materials of the first dielectric film 42 and the second dielectric film 44, SiO ₂ (n = 1.48) and Si ₃ N ₄ (n = 2.0) can be used.

When the dielectric multilayer film is formed of a silicon oxide film and a silicon nitride film, the manufacturing process and manufacturing apparatus for the silicon semiconductor integrated circuit can be used as they are.
The dielectric multilayer film can be formed by a plasma CVD (Chemical Vapor Deposition) method. The SiO ₂ film can be grown in a TEOS, O ₂ atmosphere at a temperature of 200 ° C., and the Si ₃ N ₄ film can be preferably grown in a SiH ₄ , NH ₃ atmosphere at a temperature of 200 ° C.
The dielectric multilayer film may be formed by ion beam sputtering.

  The thicknesses t1 and t2 of the first dielectric film 42 and the second dielectric film 44 are designed to be ¼ of the wavelength of light incident on the light control device 8. That is, assuming that the wavelength of light incident on the light control device 8 is λ and the refractive index of the dielectric film is n, the thickness t of each dielectric film is t = λ / (n × 4). Adjust to.

For example, when a red laser beam having a wavelength λ = 633 nm is used for the light control device 8, the thickness t1 of the first dielectric film 42 is SiO ₂ (n = 1.48) as the material. t1 = 633 / (4 × 1.48) = about 106 nm. The thickness t2 of the second dielectric film 44 is about t2 = 633 / (4 × 2) = 79 nm when Si ₃ N ₄ (n = 2.0) is used as the material. The thicknesses t1 and t2 of the dielectric films constituting the second reflective layer 40 are not necessarily designed to be strictly λ / 4.

As a material of the dielectric film, TiO ₃ (n = 2.2) may be used instead of the silicon nitride film. In this case, the thickness t2 of the second dielectric film 44 is about t2 = 633 / (4 × 2.2) = 72 nm.

In FIG. 2B, the reflectance R2 of light incident on the second reflective layer 40 from the light modulation film 34 is equal to the reflectance R1 of light incident on the first reflective layer 32 from the light modulation film 34. design. The reflectance R1 is determined by the metal material used for the first reflective layer 32, and is 50 to 80% when Pt is selected.
Therefore, at this time, the reflectance R2 is designed to be 50 to 80%. The reflectance R2 of the second reflective layer 40 can be adjusted by the material and thickness of the first dielectric film 42 and the second dielectric film 44. In the present embodiment, as shown in FIG. 2, the second reflective layer 40 is formed by alternately laminating three first dielectric films 42 and two second dielectric films 44. In the second reflective layer 40, the order of stacking the first dielectric film 42 and the second dielectric film 44 may be reversed. In order to finely adjust the reflectance R2, a third dielectric film may be further laminated.

The second reflective layer 40 is opened, and the transparent electrode 36 is drawn out through the via and the wiring 38. As the material of the wiring 38, Al or the like is preferably used.
A protective layer may be further formed on the upper surface of the wiring 38.

  In the present embodiment, the transparent electrode 36 and the first reflective layer 32 form an electrode pair. The potential of the first reflective layer 32 is fixed, for example, to the ground potential, and the potential of the transparent electrode 36 of each pixel is controlled by a control signal CNT.

The operation of the light control device 8 configured as described above will be described.
FIG. 3 schematically shows an operation state of one pixel of the light control device 8. In the figure, the same components as those in FIG. 2 are denoted by the same reference numerals. For simplification, components such as the transparent electrode 36 are omitted.
Laser light having an intensity Iin is incident from above the light control device 8. The first reflection layer 32, the light modulation film 34, and the second reflection layer 40 of the light control device 8 constitute a Fabry-Perot resonator, in which part of the incident light is confined and part of it is reflected. The When the intensity of the incident laser beam is Iin and the intensity of the laser beam reflected by the light control device 8 is Iout, the reflectance R of the light control device 8 is defined by R = Iout / Iin.
FIG. 4 shows the relationship between the wavelength λ of light incident on the light control device 8 and the reflectance R.

  A Fabry-Perot resonator composed of the first reflective layer 32, the light modulation film 34, and the second reflective layer 40 has a resonance wavelength of λm = 2nt cos θ / m. Here, m represents the order, n represents the refractive index of the light modulation film 34, t represents the thickness of the light modulation film 34, and θ represents the incident angle of the laser light. As shown in FIG. 4, the reflectance R of the light control device 8 takes the minimum value at the resonance wavelength λm.

As described above, the refractive index n of the light modulation film 34 depends on the electric field applied to the electrode pair. Now, when the first reflective layer 32 is set to the ground potential and the control voltage Vcnt is applied to the transparent electrode 36 (not shown), an electric field E = Vcnt / t is applied to the light modulation film 34 in the thickness direction. The relationship Δn = 1/2 × n ³ × R × E ² is established between the change amount Δn of the refractive index n of the light modulation film 34 and the applied electric field E. Here, R is an electro-optic constant (Kerr constant).

FIG. 4I shows the reflection characteristic when the control voltage Vcnt is not applied.
Now, when the voltage V1 is applied as the control voltage Vcnt to the transparent electrode 36 of each pixel 10, the refractive index of the light modulation film 34 changes, and the resonance wavelength of the resonator shifts from λm1 to λm2. The reflection characteristic at this time is shown by (II) in FIG.
When the wavelength of the laser light incident on the light control device 8 is λm1, when the control voltage Vcnt is changed from the ground potential to a certain voltage value V1, the resonance wavelength is shifted, and thus the reflectance of the light control device 8 is Rm1. To Rm2.

Here, the ratio between the reflectance Ron when no voltage is applied and the reflectance Roff when a voltage is applied is defined as an on / off ratio. When the intensity Iin of the incident light is constant, the intensity Iout of the reflected light is proportional to the reflectance. Therefore, a larger on / off ratio means that the intensity Iout of the reflected light can be controlled more accurately.
The reflectance R of the light control device 8 at the resonance wavelength λm becomes lower as the reflectance R1 at the first reflective layer 32 and the reflectance R2 at the second reflective layer 40 are closer. Therefore, as described above, the number and material of the dielectric multilayer films of the second reflective layer 40 are adjusted, and the reflectance R1 in the first reflective layer 32 and the reflectance R2 in the second reflective layer 40 are designed to be equal. As a result, the off-time reflectance R1 can be set low, and the on / off ratio can be increased.

As described above, in the light control device 8 according to the present embodiment, an optical switch element that changes the reflectance and controls the intensity of the reflected light Iout by changing the electric field applied to the light modulation film 34 is realized. can do. In addition, since the phase of the reflected light can be controlled by changing the refractive index of the light modulation film 34, it can be suitably used for a hologram recording apparatus or the like.
Since the light control device 8 has a reflective configuration, it is not necessary to transmit the incident light Iin through the substrate 30. As a result, the light use efficiency can be improved as compared with the conventional transmission type light control device.

  In the light control device 8 according to the present embodiment, since the plurality of pixels 10 are arranged in a matrix and each pixel 10 has an electrode pair, the reflectance can be controlled for each pixel. It can be used as an optical modulator SLM.

  In the light control device 8 according to the present embodiment, since the electrode pair is formed by the first reflective layer 32 and the transparent electrode 36, an electric field can be applied uniformly in the thickness direction of the light modulation film 34, and the light modulation is performed. The refractive index inside the film 34 can be changed uniformly.

  Furthermore, according to the light control device 8 according to the present embodiment, an opaque material can be used as the substrate 30 in order to constitute a reflective modulator. For example, when silicon is used as the substrate 30, transistor elements and the like can be formed in the silicon, so that active matrix driving in which a control means for the control voltage Vcnt is provided for each pixel can also be performed.

  Further, by using the transparent electrode 36 as an upper electrode for applying an electric field to the light modulation film 34, the aperture ratio can be improved and diffraction can be minimized, so that the light utilization efficiency is improved. improves. The improvement of the light utilization efficiency means that the intensity Iin of the incident laser light can be lowered, and the power consumption can be reduced.

  Further, in the light control device 8 according to the present embodiment, the transparent electrode 36 is formed on the light modulation film 34 and the second reflective layer 40 is formed thereon. As a result, the distance between the upper electrode and the lower electrode can be shortened as compared with the case where the transparent electrode 36 is formed on the upper layer of the second reflective layer 40, so that the electric field E applied to the light modulation film 34 is increased. can do. From another point of view, this means that the voltage to be applied between the electrodes in order to apply the same electric field can be lowered, whereby the light control device 8 can be operated at a low voltage.

  Further, in the light control device 8 according to the present embodiment, since the intensity Iout of the reflected light is changed by controlling the reflectance R, there is an advantage that a deflecting plate and an analyzer are not required and the light use efficiency is high. Have

FIG. 5 is a diagram showing the relationship between the protective layer 50 thickness tp and the relative dielectric constant ε of PLZT. In this figure, the relative dielectric constant ε was measured using an IrO ₂ film thickness tp as a parameter when an IrO ₂ film was formed as a protective layer 50 on PLZT and the transparent electrode 36 was formed using ITO as an upper layer. Is.
When the thickness tp of the protective layer 50 is 0 nm, that is, when the ITO transparent electrode 36 is directly formed on the PLZT, the relative dielectric constant is about 800. Here, the relative dielectric constant increases as the thickness of the protective layer 50 is increased to 5 nm and 10 nm.

When the electrode on PLZT was formed using only IrO ₂ with a film thickness of about 50 nm and the electrode made of ITO was not formed on the upper surface, the relative dielectric constant of PLZT was about 1200. That is, by increasing the thickness tp of the protective layer 50, the relative permittivity of PLZT can be made closer to the relative permittivity when an electrode is formed only with IrO ₂ .
From this, it is considered that this IrO ₂ functions as a protective layer by forming a thin film of IrO ₂ between ITO and PLZT.

There are _two possible reasons why IrO ₂ functions as a protective layer. First, it is considered that when ITO is deposited on PLZT, the damage applied to the interface of PZLT is alleviated by providing an IrO ₂ protective layer. Another reason is that the formation of an IrO ₂ protective layer prevents the ITO from diffusing into the PLZT and deteriorating the electrical characteristics after the ITO electrode is formed.

When using PLZT as the light modulation film 34, it is preferable that the relative dielectric constant is high. On the other hand, since the light transmittance of IrO ₂ forming the protective layer 50 is not as high as that of ITO, increasing the thickness of the protective layer 50 decreases the light transmittance. Therefore, the thickness tp of the protective layer 50 needs to be determined from both the transmittance and the electrical characteristics of PLZT. As shown in FIG. 5, it can be seen that as the thickness tp of the protective layer 50 is increased, the relative dielectric constant is improved and takes a substantially constant value at a relative dielectric constant ε = 1200. Therefore, when the protective layer 50 is formed of IrO _{2, a} significant effect can be recognized if the thickness is 1 nm or more, and the relative dielectric constant can be improved by 100 or more by setting the thickness to 3 nm to 5 nm. When the film thickness is further increased to a range of 10 nm to 25 nm, a relative dielectric constant equivalent to that obtained when electrodes are formed using only IrO ₂ without using ITO can be obtained. As the thickness of the protective layer 50 is increased, the electrical characteristics of the PLZT are improved. However, in consideration of manufacturing cost and manufacturing time, it is desirable that the thickness is 50 nm or less.

  As shown in FIG. 4, the light control device 8 applies a voltage between the electrodes, so that the frequency characteristic of the reflectance shifts in wavelength. FIG. 6 is a diagram illustrating the relationship between the thickness tp of the protective layer 50 and the wavelength shift amount Δλm (= λm2−λm1) in the light control device 8. FIG. 6 shows the wavelength shift amount when the same electric field is applied, with the thickness of the protective layer as a parameter.

When the thickness of the protective layer 50 is 0 nm, that is, when the ITO transparent electrode 36 is directly formed on the PLZT, the wavelength shift amount Δλm is about 2.4 nm. As the thickness of the protective layer 50 is increased to 5 nm and 20 nm, the wavelength shift amount Δλm increases. The wavelength shift amount Δλm and the thickness of the protective layer show the same tendency as the relative dielectric constant of FIG. 5, and if the thickness is 1 nm or more, a significant effect can be recognized, and further 3 nm to 5 nm. The wavelength shift amount can be increased by about 1 nm. Furthermore, when the film thickness is increased to a range of 10 nm to 25 nm, it can be improved by about 1.5 nm.
As shown in FIG. 4, the larger the wavelength shift amount Δλm is, the higher the on / off ratio of the reflectance of the light control device 8 is. Therefore, the range of 3 nm to 25 nm is desirable.
By setting the thickness of the protective layer 50 within this range, it is possible to increase the light use efficiency as the light control device 8 while suppressing a decrease in light transmittance.

  As described above, by using the structure including the light modulation film 34, the protective layer 50, and the transparent electrode 36, the light control device 8 capable of good modulation while suppressing the decrease in light transmittance due to the electrode is realized. can do.

  The present invention has been described based on the embodiments. This embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible and that such modifications are also within the scope of the present invention.

In the embodiment, the case of using PLZT, IrO ₂ , and ITO as a combination of the light modulation film 34, the protective layer 50, and the transparent electrode 36 has been described, but the present invention is not limited to this. PZT may be used instead of PLZT, or ZnO may be used instead of ITO. Further, as the protective layer 50, SrRuO ₃ or La _0.5 Sr _0.5 CoO ₃ may be used. In these arbitrary combinations, the effects described in the embodiment can be obtained.

In the embodiment, the case where the electrode pair is formed by the transparent electrode 36 serving as the upper electrode and the first reflective layer 32 serving as the lower electrode has been described. However, the present invention is not limited to this. For example, an electric field is applied to the light modulation film 34. The electrode pair for application may be formed as a comb-shaped electrode on the upper surface of the protective layer 50. At this time, the electric field is applied laterally with respect to the light modulation film 34.
Even in this case, the comb-shaped electrode is preferably a transparent electrode made of ITO or the like, and a protective film is formed between the transparent electrode 36 and the PLZT film, which is the light modulation film 34, so that the optical Degradation of the electrical characteristics of the modulation film 34 can be suppressed.

  The second reflective layer 40 may be a half mirror formed of a metal thin film. In this case, the manufacturing process can be simplified as compared with the case where the dielectric multilayer film is formed. In addition, the protective layer 50 can be expected to reduce the influence of the metal thin film of the half mirror on the light modulation film 34.

  In the embodiment, the case where the light control device 8 is used as the spatial light modulator of the hologram recording device 70 has been described. However, the present invention is not limited thereto, and the display device, the optical communication switch, the optical communication modulator, and the optical arithmetic device are used. , And an encryption circuit.

  In the embodiment, the case where an electro-optic material is used as the light modulation film 34 and an electrode pair for applying an electric field to the light modulation film 34 is provided has been described. The present invention can also be used when a magneto-optical material is used for the light modulation film 34. In this case, the electrode pair for applying an electric field may be replaced with a magnetic field applying means for applying a magnetic field.

It is a figure which shows the hologram recording device at the time of using the light control apparatus in embodiment as a spatial light modulator. 2A and 2B are diagrams illustrating the structure of the light control device according to the embodiment. It is a figure which shows typically the operation state of the pixel of a light control apparatus. It is a figure which shows the relationship between wavelength (lambda) and the reflectance R of the light which injects into a light control apparatus. It is a figure which shows the relationship between thickness tp of the protective layer in light control apparatus, and the dielectric constant (epsilon) of PLZT. It is a figure which shows the relationship between thickness tp of the protective layer in light control apparatus, and wavelength shift amount (DELTA) (lambda) m. In the case of forming the electrodes of the non-transparent electrode using IrO _2, a diagram illustrating the relationship between polarization and an applied electric field in the case of forming a transparent electrode using ITO.

Explanation of symbols

  8 light control device, 30 substrate, 32 first reflection layer, 34 light modulation film, 36 transparent electrode, 38 wiring, 40 second reflection layer, 42 first dielectric film, 44 second dielectric film, 50 protective layer.

Claims (15)

A substrate,
A first reflective layer provided on the substrate;
A light modulation film provided on the first reflective layer, the refractive index of which can be controlled by an applied electric field;
A protective layer provided on the light modulation film;
A transparent electrode provided on the protective layer and applying an electric field to the light modulation film;
A light control device comprising:   The light control device according to claim 1, wherein the protective layer is made of iridium oxide.   The light control apparatus according to claim 2, wherein the protective layer has a thickness in a range of 1 nm to 50 nm.   The light control device according to claim 1, wherein the protective layer is made of strontium ruthenate.   The light control apparatus according to claim 1, wherein the protective layer is made of lanthanum strontium cobalt oxide.   The light control device according to claim 1, wherein the transparent electrode is made of indium tin oxide.   The light control device according to claim 1, wherein the transparent electrode is made of zinc oxide.   The light control device according to claim 1, wherein the light modulation film is made of lead zirconate titanate or lead lanthanum zirconate titanate.   The light control device according to claim 1, further comprising a second reflective layer provided on the transparent electrode, wherein the transparent electrode and the first reflective layer form the electrode pair. . A light modulation film formed using an electro-optic material;
A protective layer provided on the light modulation film;
A transparent electrode layer provided on the protective layer and applying an electric field to the light modulation film;
The structure is provided in a light control device that applies an electric field to the light modulation film and modulates light using a change in refractive index thereof.   The structure according to claim 10, wherein the protective layer is made of iridium oxide.   The structure according to claim 10, wherein the protective layer is made of strontium ruthenate.   The structure according to claim 10, wherein the protective layer is made of lanthanum strontium cobalt oxide.   The structure according to claim 10, wherein the transparent electrode layer is made of indium tin oxide.   The light control device according to claim 10, wherein the light modulation film is made of lead zirconate titanate or lead lanthanum zirconate titanate.

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