Light-transmitting metal electrode, electronic apparatus and light emitting device

According to one embodiment, a light-transmitting metal electrode includes a metal layer. The metal layer is provided on a major surface of a member and includes a metal nanowire and a plurality of openings formed with the metal nanowire. The thin layer includes a plurality of first straight line parts along a first direction and a plurality of second straight line parts along a direction different from the first direction. A maximum length of the first line parts along the first direction and a maximum length of the second line parts along the direction different from the first direction are not more than a wave length of visible light. A ratio of an area of the metal layer viewed in a normal direction of the surface to an area of the metal layer viewed in the normal direction is more than 20% and not more than 80%.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2011-208746, filed on Sep. 26, 2011; the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a light-transmitting metal electrode, an electronic apparatus and a light emitting device.

BACKGROUND

In display devices represented by a liquid crystal display, light emitting devices, such as, a semiconductor light emitting element and an organic electroluminescence element, photoelectric conversion devices, such as, a solar cell and a photodetector, or the like, ITO (Indium Tin Oxide), which is one of conductive oxide materials, is widely used as a light-transmitting electrode. The transmittance in a visible light region of an electrode with an ITO film formed on a glass substrate, is about 80%. On the other hand, the resistivity of ITO is about 10−4Ω-cm, which is higher than the resistivity of a general metal material by about two orders of magnitude.

A light-transmitting metal electrode, in which an opening having a circumference length shorter than the wavelength of used light is provided in a metal thin film, is also considered. In this light-transmitting metal electrode, the reflectance loss in a metal part is reduced by making the rate of an area occupied by the metal part not more than 20%, preferably, not more than 10%. There is room for improvement in such a light-transmitting metal electrode, in order to obtain sufficient transparency in a broad wavelength range, while maintaining low electric resistance.

DETAILED DESCRIPTION

In general, according to one embodiment, a light-transmitting metal electrode includes a metal layer. The metal layer is provided on a major surface of a member. The metal layer includes a metal nanowire and a plurality of openings formed with the metal nanowire. The metal thin layer includes a plurality of first straight line parts along a first direction parallel to the major surface, and a plurality of second straight line parts along a direction parallel to the major surface, and different from and intersecting the first direction. A maximum length of the plurality of first straight line parts along the first direction and a maximum length of the plurality of second straight line parts along the direction different from the first direction are not more than a wave length of visible light. A ratio of an area of the metal nanowire viewed in a normal direction of the major surface to an area of the metal layer viewed in the normal direction is more than 20% and not more than 80%.

The drawings are schematic or conceptual; and the relationships between the thicknesses and widths of portions, the proportions of sizes among portions, etc., are not necessarily the same as the actual values thereof. Further, the dimensions and the proportions may be illustrated differently among the drawings, even for identical portions.

In the specification and the drawings of the application, components similar to those described in regard to a drawing therein above are marked with like reference numerals, and a detailed description is omitted as appropriate.

As a light-transmitting electric conductor of which resistivity can be made lower compared to a conventional transparent conductive oxide, there is a metal nano-structure obtained by periodically forming nano-meter order circular openings in a metal thin film. When light enters this metal nano-structure, an extraordinary light transmission phenomenon may occur. The phenomenon is derived from an event in which when light enters the metal thin film with nano-openings formed therein a localized electric field originating from surface electric charges is generated at the edges of the nano-openings, and since the localized electric field vibrates similarly to the incident electric field, light is re-emitted. Transmission of light with a specific wavelength is enhanced by interference between the light re-emitted from the respective nano-openings interferes with light from neighboring nano-openings. Therefore, the transmission spectrum of the metal nano-structure becomes a spectrum having peaks at specific wavelengths corresponding to a material of the metal thin film, periods and aperture diameters of the circular nano-openings, and permittivity of the circumference medium, and, depending on conditions, such as, the thickness of the metal film, it is possible to achieve transmittance not less than the aperture ratio. Since, usual metal materials can be used for the material of the metal nano-structure, the metal nano-structure can be used as a transparent electrode having a higher carrier density and lower resistivity than a conventional transparent conductive oxide. However, in the transmission spectrum of the metal nano-structure, after a peak at a specific wavelength, the reflectance increases remarkably at a longer wavelength side with respect to the peak wavelength. Therefore, if this metal nano-structure is used as a light-transmitting electrode, it is not possible to achieve high transparency throughout the operating wavelength range. Therefore, if the light-transmitting electrode is applied for devices, such as, a display device and an illuminating device, which are required to have high transparency throughout the entire visible light range, a problem of, such as, reduction of visibility due to wavelength dependence appearing in a luminescent color will occur.

On the other hand, as described in back ground arts, the light-transmitting electrode, in which openings having a circumference length shorter than the wavelength of used light are provided, is known. In the light-transmitting metal electrode, high transparency can be achieved in a broad wavelength range by making the rate of an area occupied by the metal part not more than 20%, preferably, not more than 10% to reduce the reflectance loss. However, in order to achieve high transparency in a broad wavelength range, it is required to make the rate of an area occupied by the metal part not more than 20%, and thus, resistivity of the electrode will be remarkably larger than the resistivity of a bulk metal material. As a result, the resistivity will be comparable to or not less than the resistivity of a conventional transparent conductive oxide. That is, the light-transmitting electrode has a problem to satisfy two characteristics of having the resistivity lower than the resistivity of a conventional transparent conductive oxide and having high transparency in a broad wavelength range.

First Embodiment

FIG. 1is a schematic perspective view illustrating the structure of a light-transmitting metal electrode according to a first embodiment.

FIGS. 2A and 2bare schematic plan views in which a part of a metal layer is enlarged.

As shown in theFIG. 1, a light-transmitting metal electrode according to an embodiment is a metal layer2provided on the major surface is of a member1. The metal layer2has a metal nanowire22and a plurality of openings21formed with the metal nanowire22. That is, the light-transmitting metal electrode is configured with the plurality of openings21and the metal nanowire22provided among the plurality of openings21.

As shown inFIG. 2A, the metal nanowire22has a plurality of straight line parts220along a direction parallel to the major surface is of the member1. The plurality of straight line parts220at least have a plurality of straight line parts221aalong a direction D1aparallel to the major surface1aand a plurality of straight line parts222aalong a direction D2aparallel to the major surface1aand intersecting the direction D1a.

In the embodiment, the plurality of straight line parts are collectively referred to as straight line parts220.

Further, in the embodiment, the direction D1ais defined as a first direction and the direction D2ais defined as a second direction. Straight line parts220along the first direction are defined as first straight line parts, and straight line parts220along the second direction are defined as second straight line parts. In addition, the direction D2amay be the first direction, and the direction D1amay be the second direction. When three or more directions along which the plurality of straight line parts20extend are present, any one of the directions is defined as the first direction, and any one of the directions other than the first directions is defined as the second direction.

In the light-transmitting metal electrode, the maximum length of the plurality of the first straight line parts along the first direction is not more than the wavelength of visible light. For example, the maximum length of the plurality of straight line parts221aalong the direction D1is not more than the wavelength of visible light.

Further, the maximum length of the plurality of the second straight line parts along the second direction is not more than the wavelength of visible light. For example, the maximum length of the plurality of straight line parts222aalong the direction D2is not more than the wavelength of visible light.

Furthermore, in the light-transmitting metal electrode, the ratio of the area of the metal nanowire22viewed in the normal direction V of the major surface is to the area of the metal layer2viewed in the normal direction V is more than 20% and not more than 80%.

In such a light-transmitting metal electrode, while maintaining low electric resistance, high transparency can be achieved in a broad wavelength range.

The member1holds the metal layer2which is a light-transmitting metal electrode. The material of the member1is not limited especially as long as it can support the metal layer2. For example, a transparent substrate, such as, a quartz substrate and a glass substrate; a semiconductor substrate, such as, a silicon substrate and a gallium arsenide substrate; and a plastic substrate, such as, a substrate of polyethylene terephthalate, are used for the member1. The member1may be a structure made by stacking semiconductor materials etc.

The thickness of the member1is not limited especially as long as it can support the metal layer2. In order to achieve sufficient strength, it is preferable for the thickness of the member1to be, for example, not less than 5 μm.

The metal layer2acts as an electrode. As a material of the metal layer2, it is preferable to use gold, silver, copper, aluminum, nickel, lead, zinc, platinum, cobalt, magnesium, chromium, tungsten, palladium, indium, antimony, tin, or an alloy material containing at least one or more of them. Such a material has resistivity sufficiently lower than the resistivity of a material for a transparent conductive oxide (for example, ITO). Further, such a material has negative permittivity in a visible light region, and exhibits metallic optical properties.

It is desirable for the thickness (thickness along the normal direction V) of the metal layer2to be not less than 10 nm and not more than 400 nm. It is not preferable for the thickness of the metal layer2to be less than 10 nm, because the resistivity of the metal electrode layer increases. On the other hand, it is not preferable for the thickness of the metal layer2to be more than 400 nm, because the transparency of the metal layer2decreases.

The shape of the plurality of openings21viewed in the normal direction V is made polygon by the plurality of straight line parts220.

Here, angle CP (seeFIG. 2B) of the polygon in the specification referred to as a portion where respective side walls220wof two straight line parts (for example, straight line parts221aand222a) each directing different directions intersect. As the angle CP of the polygon, one rounded a little in fabrication is also included.

The shape of the plurality of openings21is at least one of, for example, tetragon, hexagon, and octagon.

The metal layer2illustrated inFIG. 2Aincludes hexagonal openings21. In an example of the metal layer2shown inFIGS. 2A and 2B, straight line parts221a,222a, and223aalong three mutually different directions (directions D1a, D2a, and D3a), are provided along the major surface1a.

The metal nanowire22has a structure made by connecting the straight line parts221a,222aand223a. As shown inFIG. 2B, length L of the straight line parts220is the length of a straight line connecting points where the central lines of straight line parts220intersect each other. That is, the length L of the straight line parts220denotes the maximum length of a structure obtained by projecting the above structure on a plane parallel to directions in which the straight line parts220extend. Maximum length L of each of the straight line parts221a,222aand223ais not more than the wavelength of visible light.

In the embodiment, the wavelength of visible light is, for example, 780 nm.

Lengths of the plurality of straight line parts220may be equal to each other or different from each other.

Further, the length (width) of the metal nanowire22on the straight line CL connecting centroids of two neighboring openings (for example, openings21aand21bshown inFIG. 2A) of the plurality of openings21is not less than 20 nm and not more than 200 nm.

FIGS. 3A and 3Bare schematic plan views showing examples of other metal layers.

The width W2of the straight line parts220(straight line parts221b,222band223b) shown inFIG. 3Bis wider than the width W1of the straight line parts220(straight line parts221a,222aand223a) shown inFIG. 2B.

Here, width is referred to as a width along a direction orthogonal to directions parallel to the major surface1aalong which the straight line parts220extend. When pitches of the openings21are equal to each other, as the width of each straight line part220becomes wider, the occupancy of the metal nanowire22becomes higher. Where, when the metal layer2is viewed in the normal direction V, the occupancy of the metal nanowire22is referred to as the rate of an area occupied by the metal nanowire22to the area of the metal layer2(sum of the area of the metal nanowire22and the area of the plurality of openings21viewed in the normal direction V).

For the light-transmitting metal electrode according to the embodiment, it is preferable for the maximum length L to be not less than 20 nm and not more than 780 nm. From a viewpoint of the fabrication yield, it is not preferable for the length L to be less than 20 nm, because fabrication of the metal layer2will be difficult. Further, it is not preferable for the length L to be more than 780 nm, because the transparency in a visible light region will decrease.

The shape of the openings21is not limited especially as long as it is a polygon. Openings21having different polygonal shapes may be included in one metal layer2. Typical polygonal shapes include a tetragon, a hexagon, and an octagon, etc. It is not required for the shape of the openings21to be a regular polygon, and the length of each side may differ from each other. Further, the shape may be any of a convex polygon and a concave polygon.

FIG. 4is a schematic plan view illustrating another metal layer.

In the metal layer2shown inFIG. 4, octagonal openings211and tetragonal (square) openings212are combined by a plurality of straight line parts220along four different directions. Straight line parts221calong direction D1b, straight line parts222calong direction D2b, straight line parts223calong direction D3b, and straight line parts224calong direction D4b, are included by the plurality of straight line parts220.

The plurality of octagonal openings211are arranged in a zigzag manner along the major surface1a. Each of the plurality of tetragonal openings212is arranged among the plurality of octagonal openings211. Accordingly, the plurality of tetragonal openings212are also arranged in a zigzag manner along the major surface1a.

In the metal layer2shown inFIG. 4, lengths of the straight line parts221c,222c,223c, and224care not more than the wavelength of visible light. For example, the lengths of the straight line parts221c,222c,223c, and224care equal to each other.

FIG. 5is a schematic plan view illustrating another metal layer.

In the metal layer2illustrated inFIG. 5, dodecagonal openings213and tetragonal (square) openings214are combined by a plurality of straight line parts220along two different directions. Straight line parts221dand223dalong direction D1c, and straight line parts222dand224dalong direction D2b, are included by the plurality of straight line parts220.

The plurality of dodecagonal openings213are arranged in a matrix along the major surface1a. Each of the plurality of tetragonal openings214is arranged among the plurality of octagonal openings213. Accordingly the plurality of openings212are also arranged in a matrix along the major surface1a.

In the metal layer2shown inFIG. 5, lengths of the straight line parts221d,222d,223d, and224dare not more than the wavelength of visible light. For example, the lengths of the straight line parts221d,222d,223d, and224dare equal to each other.

FIG. 6is a schematic plan view illustrating another metal layer.

In the metal layer2illustrated inFIG. 6, dodecagonal openings215, tetragonal (rectangular) openings216and217, and tetragonal (square) openings218are combined by a plurality of straight line parts220along two different directions. Straight line parts221eand223ealong direction D1c, and straight line parts222eand224ealong direction D2b, are included by the plurality of straight line parts220.

The plurality of dodecagonal openings215are arranged in a matrix along the major surface1a. Each of the plurality of tetragonal openings216is arranged between two of the plurality of openings215, neighboring in direction D2c. The shape of the openings216is rectangular with longer side in direction D2c. The plurality of openings216are also arranged in a matrix along the major surface1a.

Each of the plurality of openings217is arranged between two of the plurality of openings215, neighboring in direction D2c. The shape of the openings217is rectangular with longer side in direction D2c. The plurality of openings217are also arranged in a matrix along the major surface1a.

Each of the plurality of openings218is arranged between two of the plurality of openings215neighboring in direction D1cand between two of the plurality of openings215neighboring in direction D2c. The plurality of openings218are also arranged in a matrix along the major surface1a.

In the metal layer2shown inFIG. 6, lengths of the straight line parts221e,222e,223e, and224eare not more than the wavelength of visible light.

As mentioned above, various kinds of forms can be considered for the metal layer2.

For the light-transmitting metal electrode according to the embodiment, the occupancy of the metal nanowire22is more than 20%, and not more than 80%. It is not preferable for the occupancy of the metal nanowire22to be not more than 20%, because the resistivity becomes comparable to the resistivity of a transparent conductive oxide. On the other hand, it is not preferable for the occupancy of the metal nanowire22to be more than 80%, because the metallic reflection increases to reduce the transparency.

In the light-transmitting metal electrode, plurality of polygonal openings21are formed by the plurality of straight line part220. Thus, for the light-transmitting metal electrode, high transparency can be achieved in a broad wavelength range. Furthermore, since, the occupancy of the metal nanowire22is more than 20% and not more than 80%, the light-transmitting metal electrode can be a transparent electrode with resistance lower than the resistance of an electrode made of a transparent conductive oxide.

FIG. 7is a view showing an example of the transmission spectrum of a straight line part.

InFIG. 7, the horizontal axis shows the wavelength of light and the vertical axis shows the transmittance of light.

InFIG. 7, transmission-spectrum TM1in a case that light in a polarization direction vertical to a direction along which the straight line parts220extend (vertically polarized light) enters and transmission-spectrum TM2in a case of entering polarized light horizontal to the direction (horizontally polarized light) are shown.

If light in a polarization direction vertical to the direction along which the straight line parts220extend enters, free electrons in the straight line parts220will oscillate while responding to the oscillating electric field of incident light. When the length of the straight line parts220is sufficiently longer than the wavelength, reflected light arises by oscillation of the free electrons. Thereby, the straight line parts220become opaque.

On the other hand, if the length of the straight line parts220becomes comparable to the wavelength, oscillation of the free electrons by the oscillating electric field will be interrupted by the potential barrier of an interface between metal and air. As a result, surface charges are generated at the interface between metal and air. The surface charges generate an electric field of which direction is opposite to the direction of the oscillating electric field (anti-electric field), thereby, resonance between the anti-electric field and the incident electric field (localized surface plasmon resonance) takes place at a specific wavelength.

The wavelength at which localized surface plasmon resonance takes place depends on the amount of surface charges appearing on the surface of the straight line parts220and the distance of the free electrons moving in the straight line parts220. Therefore, the wavelength at which localized surface plasmon resonance takes place, changes depending on the length of the straight line parts220along the polarization direction of incident light, the permittivity of the straight line parts220, and the permittivity of a medium surrounding the straight line parts220.

As shown inFIG. 7, large dips are observed in transmission-spectra TM1and TM2of the straight line part220, at a specific wavelength. This is because generation of localized surface plasmon resonance causes reflection and absorption of light to occur in the straight line part220. On the other hand, it can be seen that high transmittance is shown at a wavelength region where the wavelength is larger than the wavelength at which the dip takes place. This is because, as the wavelength of incident light becomes larger (the frequency of incident light becomes lower), oscillation of free electrons is structurally interrupted by the side wall of the straight line part220to suppress reflection and enable free electrons in the straight line part220to follow the incident electric field of light, and thereby, localized surface plasmon resonance is also not generated.

As a result, as shown inFIG. 7, in the transmission spectrum in case that light in a polarization direction vertical to a direction along which the straight line part220extends, large dip is generated by localized surface plasmon resonance at a short wavelength side, and the straight line part220will behave as a transparent material with high transmittance in a broad wavelength range at the longer wavelength side.

On the other hand, when light in a polarization direction horizontal to the direction along which the straight line part220extends, enters, free electrons will be oscillated horizontally by the incident electric field. As a result, surface charges are generated at the end of the straight line part220, and localized surface plasmon resonance takes place like the case of vertically polarized light.

For horizontally polarized light, since the length of the straight line part220along the polarization direction is longer than the case of vertically polarized light, the wavelength at which localized surface plasmon resonance takes place, becomes longer than the corresponding wavelength for the vertically polarized light. At the longer wavelength side than the wavelength at which localized surface plasmon resonance takes place, high transmittance is shown like the case of vertically polarized light. As a result, in the transmission spectrum of horizontally polarized light as well as the case of vertically polarized light, a dip is generated by localized plasmon resonance in a short wavelength side, and the straight line part220will behave as a transparent material at the longer wavelength side.

Inventors, by connecting the plurality of straight line parts220with such optical properties in two dimensional directions (at least two directions) to constitute a light-transmitting metal electrode with polygonal openings21, found that the light-transmitting metal electrode exhibits low resistance, and high transparency in a broad wavelength range.

The optical properties of a light-transmitting metal electrode are explained from the optical characteristics of the straight line part220. The light-transmitting metal electrode has polygonal openings21constituted by connecting the plurality of straight line parts220. For this reason, oscillation of free electrons in the straight line part220caused by an incident electric field is structurally interrupted for light polarized in any direction. As a result, in the transmission spectrum of the light-transmitting metal electrode, a loss generated by localized plasmon resonance due to vertical polarization to the straight line part220and a loss generated by localized plasmon resonance due to horizontal polarization to the straight line part220, and high transmittance is exhibited in a wavelength range at the longer wavelength range side with respect to the wavelengths at which these losses take place.

As such, the light-transmitting metal electrode according to the embodiment will exhibit high transparency in a broad wavelength range.

FIG. 8is a view showing an example of the transmission spectrum of the light-transmitting metal electrode according to the embodiment.

Like transmission-spectrum TM3shown inFIG. 8, in the transmission spectrum of the light-transmitting metal electrode, high transparency can be achieved at the side of a wavelength longer than the wavelengths at which localized plasmon resonance takes place. On the other hand, near the wavelength at which localized plasmon resonance takes place, losses due to reflection and absorption caused by the metal nanowire22are generated, and thereby, transmittance decreases.

The wavelength for the straight line part220, at which localized surface plasmon resonance takes place, depends on the length of the straight line part220. That is, if the length of the straight line part220becomes longer, the wavelength at which localized plasmon resonance takes place will be shifted to the longer wavelength side. In order to achieve high transparency in a broad wavelength range of the visible light region, it is preferable to shift further the wavelength at which localized plasmon resonance takes place to a short wavelength side.

Therefore, the maximum length of the straight line part220in the light-transmitting metal electrode is made not more than the wavelength of visible light. As such, in the light-transmitting metal electrode, high transmittance can be achieved in a broad range of visible light.

When the metal electrode having openings sufficiently larger than a wavelength, if the occupancy of the metal nanowire part is made larger, transmittance will be reduced relative to the occupancy. This is due to reflection of light occurring in the metal part. On the other hand, the light transmission principle of the light-transmitting metal electrode according to the embodiment is based on the structure including the polygonal openings21made by connecting the straight line parts220with a length shorter than the wavelength of visible light. Thus, oscillation of the free electrons in the metal nanowire part is structurally interrupted. Thereby, even if occupancy of the metal nanowire22becomes high, reduction in transmittance is suppressed.

Here, although it is possible to achieve high transparency even if the occupancy of the metal nanowire22becomes not more than 20%, if the occupancy of the metal nanowire22decreases, the resistivity will increase. On the other hand, if the occupancy of the metal nanowire22becomes not less than 80%, reflection caused by the metal nanowire22will be larger, thereby transparency will be reduced. Therefore, it is preferable for the occupancy of the metal part to be more than 20% and not more than 80%.

The method for manufacturing the light-transmitting metal electrode is not limited especially, as long as the structure required by the invention is satisfied. The maximum length L of the straight line part220in the metal layer2of the invention is not less than the wavelength of visible light, and the size of the opening21is also comparable to the wavelength.

FIGS. 9A to 9Dare schematic cross-sectional views showing an example of methods for manufacturing the light-transmitting metal electrode.

First, as shown inFIG. 9A, a metal material layer2A is formed on a member1. The metal material layer2A may be formed using widely generalized thin film deposition processes. For example, a resistive thermal evaporation method, an electron-beam evaporation method, a laser deposition method, a sputtering method, a CVD (Chemical Vapor Deposition) method, and an MBE (Molecular Beam Epitaxy) method, are included.

Next, as shown inFIG. 9B, a patterned layer5corresponding to the shape of the metal nanowire22is formed on the metal material layer2A. The patterned layer5is formed using methods, such as, an optical lithography method, an electron-beam lithography method, a nanoimprint method, a soft imprint method, a block polymer lithography method, a colloidal lithography method, a scanning probe method.

Next, as shown inFIG. 9C, a pattern is formed on the metal material layer2A using the patterned layer5as a mask. The pattern is formed using, for example, a dry etching method, an ion milling method, and a focused ion beam method. Openings21are formed in the metal layer2by etching the metal material layer2A from an opening of the patterned layer5. The metal nanowire22remains on parts masked with the patterned layer5.

Then, as shown inFIG. 9D, by removing the patterned layer5, the metal layer (light-transmitting metal electrode)2is completed.

In the embodiment, since the metal nanowire22is used as a component, when the metal layer2is fabricated by electron beam drawing, there is an effect to shorten drawing time.

In this case, although the metal material layer2A is formed on the member1at a first process, the light-transmitting metal electrode may be fabricated using a lift-off method or a plating method including processes of forming the patterned layer5on the member1, then, forming the metal material layer2A, and removing the patterned layer5and the metal on the patterned layer5.

The structure of the light-transmitting metal electrode obtained by such a method can be confirmed using a common scanning electron microscope. For example, an electron microscope image containing one to about ten openings21in a scanning area, is observed. The maximum length of the straight line part220can be measured from the obtained image. Fluctuation in a straight line of the side wall220wof the straight line part220and fluctuation in an intersection point of the straight line part220, can also measured from the image. Subsequently, an electron microscope image containing about 50 openings21is observed. The occupancy of the metal nanowire22can be obtained by analyzing the obtained image and binarizing it into the metal nanowire22and the openings21.

FIGS. 10A and 10Bare schematic views illustrating an observation image by an electron microscope.

FIG. 10Bis an enlarged view of section A shown inFIG. 10A. It can be seen that the side wall220wof the straight line part220does not form a perfect straight line. This is due to fluctuation from a designed value during micro-fabrication.

For example, when the patterned layer5is formed using optical lithography, as a material forming the patterned layer5, an organic polymer, such as, resist used in a usual semiconductor process, is used. In optical lithography, if pattern formation is carried out to the patterned layer5using a photomask, fluctuation originating from the dimension of the organic polymer will occur on the side wall of the patterned layer5. Due to the straight line fluctuation of the patterned layer, similar fluctuation will occur in the metal material layer2A. However, as a result of inventors' investigation, even if such fluctuation occurs, the action and the effect of the embodiment will not be vitiated as long as fluctuation from the designed value is within, for example, ±30%. The reason of this is in that although the fluctuation will expand the half band width of dip of a transmission spectrum, at the wavelength at which localized surface plasmon resonance takes place, the transparency at the longer wavelength side with respect to this wavelength range, will not be affected.

FIGS. 11A to 11Bare schematic views illustrating another observation image by the electron microscope.

FIG. 11Bis an enlarged view of section B shown inFIG. 11A. That is, inFIG. 11B, the observation image of the intersection portion (section B inFIG. 11A) where three straight line parts220are overlapped, is shown.

In the intersection portion shown inFIG. 11, it can be seen that angle CP where the side walls220wcrosses did not make a perfect angle, instead, it is roundish. Similarly to the former case, this case is also derived from fluctuation. The reason is in that when optical lithography is used, light is broadened by diffraction at the pattern edge of a photomask. However, as long as the fluctuation from a design value is within, for example, ±30%, the action and the effect of the embodiment will not be vitiated.

The light-transmitting metal electrode has a resistance lower than the resistance of the transparent electrode using an transparent conducting oxide, and has high transparency in a broad wavelength range. Therefore, it is applied for optical components, such as, a touch panel; photoelectric conversion elements, such as, a semiconductor light emitting element, a solar cell, and a photodetector; display elements, such as, a liquid crystal display, and organic electroluminescence element; and various kinds of other instruments.

Second Embodiment

Next, an electronic apparatus according to a second embodiment will be described.

The above described light-transmitting metal electrode is applied for various kinds of electronic apparatuses.

The electronic apparatus includes a structure body having a major surface. The light-transmitting metal electrode is provided on the major surface of the structure body. Electric charges are supplied to the structure body through a metal layer2which is a light-transmitting metal electrode.

An example of application for a specific electronic apparatus will now be described.

FIG. 12is a schematic cross-sectional view illustrating the configuration of an organic electroluminescence element.

InFIG. 12, the structure of a bottom-emission type element is shown. As shown inFIG. 12, the organic electroluminescence element (hereinafter, simply referred to as an “organic EL device”)210includes a substrate9, an electrode layer10provided on the substrate9, a light emitting layer11provided on the electrode layer10, and a counter electrode12provided on the light emitting layer11. The structure body includes a stacked structure of, for example, the substrate9, the electrode layer10, and the light emitting layer11. In the organic EL device210, for example, the light-transmitting metal electrode according to the embodiment is applied for as the electrode layer10.

The substrate9has, for example, transparency. The light emitting layer11is an example of an optical layer, and includes at least one or more layers of an organic luminescent material. The light emitting layer11emits light according to electric charges supplied from the metal layer2of the light-transmitting metal electrode which is the electrode layer10. That is, in an organic EL device210, electrons and positive holes injected in the light emitting layer11from the electrode layer10and the counter electrode12, recombine in the light emitting layer11and emit light. Emitted light permeates through the electrode layer10which is the light-transmitting metal electrode, and it is emitted outside.

Although the structure of the bottom-emission type element is shown inFIG. 12, the structure of a top-emission type element may be used. The light-transmitting metal electrode is provided at the side where emission light is emitted to the light emitting layer11of the organic EL device210. In the organic EL device210, the light-transmitting metal electrode may be used for the counter electrode120.

The organic EL device210is also applicable to devices, such as, a display device composed of an array of a plurality of basic elements by using the element structure shown inFIG. 12as the basic element, and an illuminating device composed of a large area basic element. When a generally used transparent conductive oxide is used for the electrode layer10, the fluctuation in luminescence intensity may occur due to voltage drop caused by the resistance of the electrode layer10. In particular, for a large area device like the illuminating device, this problem is remarkable. By using a light-transmitting metal electrode of which resistance is lower than the resistance of an transparent conductive oxide, the fluctuation in luminescence intensity is improved without vitiating transparency.

FIG. 13is a schematic cross-sectional view illustrating the configuration of a liquid crystal display device.

As shown inFIG. 13, the liquid crystal display device310includes a drive substrate31, a counter substrate32, a seal part33, a liquid crystal layer34, a pixel electrode35, and a counter electrode36. The structure body includes, for example, the drive substrate31, a seal part33, a liquid crystal layer34, and a pixel electrode35. In the liquid crystal display device310, the light-transmitting metal electrode according to the embodiment is applied for the counter electrode36.

In the drive substrate31, the pixel electrode35is provided to each pixel. Drive elements (not shown), such as TFT (Thin Film Transistor), are connected to the pixel electrode35. The pixel electrode35is controlled by a drive element. Electric charges are supplied into the pixel electrode35of the structure through the counter electrode36and the drive element. In the pixel electrode35, a voltage according to the charges is generated. The voltage between the pixel electrode35and the counter electrode36is applied to the liquid crystal layer34, thereby, optical properties of the liquid crystal layer34are controlled.

The drive substrate31is adhered to the counter substrate32through the seal part33. The counter electrode36is provided with the counter substrate32. The liquid crystal layer34is provided between the drive substrate31and the counter substrate32.

The liquid crystal layer34is an example of optical layers of which optical properties including at least any one of current-birefringence, optical activity, scattering property, diffractive property, and absorption property change depending on a voltage according to electric charges. According to the change of the optical properties of the liquid crystal layer34, light transmittance of the liquid crystal layer34changes for every pixel.

FIG. 14is a schematic cross-sectional view illustrating the configuration of a solar cell.

As shown inFIG. 14, the solar cell410includes a silicon substrate13on which at least not less than one p-n junction is formed, an electrode layer14provided at one side (light radiation surface side) of the silicon substrate13, and a counter electrode15provide at the other side (a side opposite to the light radiation surface) of the silicon substrate13. The light-transmitting metal electrode according to the embodiment is applied for the electrode layer14.

In the example of the solar cell410shown inFIG. 14, the silicon substrate13is provided with an n-layer13nand a p-layer13p. The silicon substrate13is an example of structure bodies and includes a photoelectric conversion layer (for example, a layer containing a p-n junction) converting incident light into electric signals. For the solar cell410, the side of the n-layer13nof the silicon substrate13is used as a light radiation surface.

The sunlight permeated through the electrode layer14(a light-transmitting metal electrode) reaches to the silicon substrate13. Carriers in the n-layer13nand the p-layer13pof the silicon substrate13excited by the sunlight permeated through the silicon substrate13are separated by an internal electric field, and collected by the electrode layer14and the counter electrode15. In the light-transmitting metal electrode (the electrode layer14), current containing electric signals converted in the photoelectric conversion layer of the silicon substrate13flows in the metal layer2.

When the carrier diffusion length is long, like the solar cell using crystalline silicon, a comb-shaped electrode is used as an electrode at the light radiation surface side (electrode layer14). At this time, light radiated on the comb-shaped electrode is shaded and becomes as a reflectance loss. Reduction of such a reflectance loss is achieved using the light-transmitting metal electrode according to the embodiment.

On the other hand, for a thin film silicon solar cell, an amorphous silicon thin film is used as a power generation layer. Since the carrier diffusion length of amorphous silicon is shorter than the carrier diffusion length of crystalline silicon, the comb-shaped electrode is difficult to be used. Therefore, an electrode of which entire radiation surface has optical transparency (for example, an transparent conductive oxide) is used.

Since resistivity of the transparent conductive oxide electrode is higher than the resistivity of a metal material, efficiency of the solar cell decreases due to the resistance loss in the transparent conductive oxide electrode. If the substrate size of the solar cell becomes larger, such decrease in efficiency will be remarkable. If the light-transmitting metal electrode according to the embodiment is used, the resistance loss will be reduced and the conversion efficiency will be improved.

FIG. 15is a schematic cross-sectional view illustrating the configuration of a semiconductor light emitting element.

InFIG. 15, the structure of a face-up type semiconductor light emitting element is illustrated.

As shown inFIG. 15, the semiconductor light emitting device510includes a substrate16, a semiconductor layer17provided on the substrate16, an n-side electrode18provided on the semiconductor layer17, a p-side electrode19provided on the semiconductor layer17, a first pad electrode20nprovided on the n-side electrode18, and a second pad electrode20pprovided on the p-side electrode19. The structure body includes, for example, the substrate16and the semiconductor layer17. The light-transmitting metal electrode according to the embodiment is applied for the n-side electrode18.

The semiconductor layer17contains, for example, a p-type semiconductor layer17p, an n-type semiconductor layer17n, and a light emitting layer17a. The light emitting layer17ais provided between the p-type semiconductor layer17pand the n-type semiconductor layer17n. The light emitting layer17aemits light according to electric charges supplied from the electrode layer2of the light-transmitting metal electrode (the n-side electrode18). That is, electrons and positive holes injected into the semiconductor layer17recombine to emit light, which permeates through the n-side electrode18(the light-transmitting metal electrode) and is emitted outside the device.

In order to increase luminescence intensity of the semiconductor light emitting element510, it is effective to increase injection current. However, the current-luminance property of the semiconductor light emitting element to which the transparent conductive oxide electrode is applied as the n-side electrode18has a peak at a certain current value, thereby, even if current larger than the value is flown in the semiconductor light emitting element, the luminance will decrease. The reason is in that since the resistivity of the transparent conductive oxide electrode is high, current injection is difficult to be uniformly carried out, leading to difficulty of uniform light emission. By using the light-transmitting metal electrode with resistivity lower than the resistivity of the transparent conductive oxide electrode as the n-side electrode18, reduction of the luminance due to current concentration is suppressed, enabling to provide a high luminance semiconductor light emitting element510. Further, even for a large area semiconductor light emitting element510, uniform light-emitting property can be achieved.

Third Embodiment

Next, an light emitting device according to a third embodiment will be described.

The light-transmitting metal electrode described above is applied to various light emitting devices.

An light emitting device includes an optical member having a light-transmitting portion and a major surface. The light-transmitting metal electrode is provided on the major surface of the optical member.

An example of application for the light emitting device will now be described.

FIG. 16is a schematic perspective view illustrating the configuration of a touch panel.

As shown inFIG. 16, the touch panel610includes a substrate6(an example of an optical member) and an electrode layer7provided on the substrate6. The light-transmitting metal electrode according to the embodiment is applied for the electrode layer7. In the touch panel610, the substrate6is an example of an optical member. A drive circuit8is formed in the substrate6. The touch panel610may include a counter electrode (not shown) facing to and separated from the electrode layer7. The mode of the touch panel610may be either resistance change type or electrostatic capacity type. In contrast to a case of using an transparent conductive oxide as the electrode layer7, by using the light-transmitting metal electrode as the electrode layer7, contact sensitivity is improved without vitiating transparency.

FIG. 17is a schematic cross-sectional view illustrating the configuration of a color filter.

The color filter710includes a color layer72in which light transmittance of a specific wavelength band is higher than the light transmittance of the other wavelength band. The color layer is one example of optical members. The color layer is formed on, for example, the major surface71aof a substrate71. The color layer72is provided with an electrode layer73. The light-transmitting metal electrode according to the embodiment is applied for the electrode layer73.

The color layer72includes, for example, a first region721transmitting light in a first wavelength band, a second region722apposed with the first region721in a plane parallel to the major surface71aand transmitting light in a second wavelength band different from the first wavelength band, and a third region723apposed with the first region721and the second region722in a plane parallel to the major surface71aand transmitting light in a third wavelength band different from the first wavelength band and the second wavelength band.

A color filter710is used as, for example, a counter side member of a liquid crystal display. For example, the substrate71of the color filter710is used as the counter substrate32shown inFIG. 13, and the electrode layer73is used as the counter electrode36shown inFIG. 13.

In the color filter710, a covering layer74made of material different from the metal layer2may be provided on the metal layer2of the light-transmitting metal electrode (the electrode layer73). When using the color filter710as the counter side member, the covering layer74is, for example, an oriented film in which orientation of liquid crystal of the liquid crystal layer34is aligned.

FIRST EXAMPLE

First example is a specific example of a light-transmitting metal electrode using silver (Ag) with hexagonal openings21.

On a cleaned quartz substrate (AQ, made by Asahi Glass Co., Ltd.), AgCu (Ag73%, Cu27%) was deposited at a thickness of 30 nm by a vacuum deposition method. After subjecting the substrate to heat treatment at 300° C. in a nitrogen atmosphere, SiO was vapor-deposited on the substrate at a thickness of 30 nm. Then, resist (THMR-ip3250 made by TOKYO OHKA KOGYO CO., LTD.) was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

The mold used for nanoimprint includes a recessed portion for forming straight line parts220, and a regular hexagonal protrusion part for forming openings21. A plurality of protrusion parts were periodically formed on a support substrate. Maximum length of the recessed part was 200 nm. The occupancy of the protrusion parts was 60%. A pattern of the mold was transferred to resist.

After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, a residual resist film was removed using a reactive ion etching apparatus, then, SiO was etched using the resist as a mask. Residual resist was dissolved with acetone.

Then, AgCu was etched by an ion milling apparatus using SiO as the mask. Residual SiO was dissolved by hydrofluoric acid. The surface of the resultant structure was observed by a scanning electron microscope. As a result, the maximum length of the straight line part220was 200 nm. Arrangement of the hexagonal openings21formed with the straight line parts220was periodic. The area ratio of the metal nanowire22was about 40%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1000 nm. As a result, a large dip is generated at a wavelength of 400 nm, and high transmittance of 85% to 75% was exhibited at the longer wavelength side with respect to the wavelength. Further, as a result of measuring sheet resistance, it was 0.8 Ω/□.

SECOND EXAMPLE

Second example is a specific example of a light-transmitting metal electrode using gold (Au) having hexagonal openings21.

On a cleaned quartz substrate (AQ, made by Asahi Glass Co., Ltd.), Cr was deposited at a thickness of 0.5 nm. Subsequently, Au was deposited at a thickness of 30 nm by a vacuum deposition method. After subjecting the substrate to heat treatment at 300° C. in a nitrogen atmosphere, SiO was vapor-deposited on the substrate at a thickness of 30 nm. Then, resist (THMR-ip3250, made by TOKYO OHKA KOGYO CO., LTD.) was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

The mold used for nanoimprint is the same one as used in the first example. A pattern of the mold was transferred to resist. After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, a residual resist film was removed using a reactive ion etching apparatus, then, SiO was etched using the resist as a mask. Residual resist was dissolved with acetone.

Then, Au was etched by an ion milling apparatus using SiO as the mask. Residual SiO was dissolved by hydrofluoric acid. The surface of the resultant structure was observed by a scanning electron microscope. As a result, the maximum length of the straight line part220was 200 nm. Arrangement of the hexagonal openings21formed with the straight line parts220was periodic. The area ratio of the metal nanowire22was about 40%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1500 nm. As a result, a large dip is generated at a wavelength of 650 nm, and high transmittance of 85% to 75% was exhibited at the longer wavelength side with respect to the wavelength. Further, as a result of measuring sheet resistance, it was 0.9 Ω/□.

THIRD EXAMPLE

Third example is a specific example of a light-transmitting metal electrode using aluminum (Al) having hexagonal openings21.

On a cleaned quartz substrate (AQ, made by Asahi Glass Co., Ltd.), Al was deposited at a thickness of 30 nm by a vacuum deposition method. The substrate was subjected to heat treatment at 300° C. in a nitrogen atmosphere. Then, resist (THMR-ip3250, made by TOKYO OHKA KOGYO CO., LTD.) was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

The mold used for nanoimprint is the same one as used in the first example. A pattern of the mold was transferred to resist. After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, a residual resist film was removed using a reactive ion etching apparatus, then, Al was etched using the resist as a mask. Residual resist was dissolved with acetone.

The surface of the resultant structure was observed by a scanning electron microscope. As a result, the maximum length of the straight line part220was 200 nm. Arrangement of the hexagonal openings21formed with the straight line parts220was periodic. The area ratio of the metal nanowire22was about 40%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1000 nm. As a result, a large dip is generated at a wavelength of 280 nm, and high transmittance of 80% to 70% was exhibited at the longer wavelength side with respect to the wavelength. Further, as a result of measuring sheet resistance, it was 1.1 Ω/□.

FOURTH EXAMPLE

Fourth example is a specific example of a light-transmitting metal electrode using Ag having tetragonal openings212and octagonal openings211.

In the same way as the first example, a substrate on which AgCu and SiO were deposited, was prepared. Then, resist (THMR-ip3250, made by TOKYO OHKA KOGYO CO., LTD.) was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

The mold used for nanoimprint includes a recessed portion for forming straight line parts220, a regular octagonal protrusion part for forming openings211and a square protrusion part for forming openings212. A plurality of square protrusion parts and a plurality of regular octagonal protrusion parts were periodically formed on a support substrate. Maximum length of the recessed part was 200 nm. The occupancy of the protrusion parts was 70%. A pattern of the mold was transferred to resist.

After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, AgCu was etched by the same way as the first example. The surface of the resultant structure was observed by a scanning electron microscope. As a result, the maximum length of the straight line part220was 200 nm. Arrangement of the tetragonal openings21and octagonal openings21formed with the straight line parts220was periodic. The area ratio of the metal nanowire22was about 30%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1000 nm. As a result, a large dip is generated at a wavelength of 390 nm, and high transmittance of 85% to 80% was exhibited at the longer wavelength side with respect to the wavelength. Further, as a result of measuring sheet resistance, it was 0.9 Ω/□.

FIFTH EXAMPLE

Fifth example is a specific example of a light-transmitting metal electrode using Ag having tetragonal openings and dodecagonal openings.

In the same way as the first example, a substrate on which AgCu and SiO were deposited, was prepared. Then, resist (THMR-ip3250, made by TOKYO OHKA KOGYO CO., LTD.) was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

The mold used for nanoimprint includes a recessed portion for forming straight line parts220, a dodecagonal protrusion part for forming openings211and a square protrusion part for forming openings212. A plurality of dodecagonal protrusion parts and a plurality of square protrusion parts were periodically formed on a support substrate. Maximum length of the recessed part was 200 nm. The occupancy of the protrusion parts was 60%. A pattern of the mold was transferred to resist.

After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, AgCu was etched by the same way as the first example. The surface of the resultant structure was observed by a scanning electron microscope. As a result, the maximum length of the straight line part220was 200 nm. Arrangement of the dodecagonal openings213and square openings212formed with the straight line parts220was periodic. The area ratio of the metal nanowire22was about 40%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1000 nm. As a result, a large dip is generated at a wavelength of 430 nm, and high transmittance of 85% to 75% was exhibited at the longer wavelength side with respect to the wavelength. Further, as a result of measuring sheet resistance, it was 0.8 Ω/□.

SIXTH EXAMPLE

Sixth example is a specific example of a light-transmitting metal electrode using Ag having rectangular openings and dodecagonal openings.

In the same way as the first example, a substrate on which AgCu and SiO were deposited, was prepared. Then, resist was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

The mold used for nanoimprint includes a recessed portion for forming straight line parts220, a dodecagonal protrusion part for forming openings211and a protrusion part for forming openings212. A plurality of dodecagonal protrusion parts and a plurality of rectangular protrusion parts were periodically formed on a support substrate. Maximum length of the recessed part extending in one direction was 200 nm. Maximum length of the recessed part extending in another direction was 150 nm. The occupancy of the protrusion parts was 55%. A pattern of the mold was transferred to resist.

After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, AgCu was etched by the same way as the first example. The surface of the resultant structure was observed by a scanning electron microscope. As a result, the maximum length of the straight line part220extending in one direction was 200 nm, and the maximum length of the straight line part220extending in another direction was 150 nm Arrangement of the dodecagonal openings and rectangular openings formed with the straight line parts220was periodic. The area ratio of the metal nanowire22was about 45%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1000 nm. As a result, a large dip is generated at a wavelength of 450 nm, and high transmittance of 80% to 70% was exhibited at the longer wavelength side with respect to the wavelength. Further, as a result of measuring sheet resistance, it was 0.8 Ω/□.

FIRST COMPARATIVE EXAMPLE

First comparative example is a specific example of a light-transmitting metal electrode with a structure having regular hexagonal openings21in the same way as the first example, of which occupancy is 90%.

In the same way as the first example, a substrate on which AgCu and SiO were deposited, was prepared. Then, resist was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

The mold used for nanoimprint includes a recessed portion for forming straight line parts220, and a regular hexagonal protrusion part for forming openings211. A plurality of regular hexagonal protrusion parts were periodically formed on a support substrate. Maximum length of the recessed part was 200 nm. The occupancy of the protrusion parts was 90%. A pattern of the mold was transferred to resist.

After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, a residual resist film was removed using a reactive ion etching apparatus, then, SiO was etched using the resist as a mask. Residual resist was dissolved with acetone.

Then, AgCu was etched by an ion milling apparatus using SiO as the mask. Residual SiO was dissolved by hydrofluoric acid. The surface of the resultant structure was observed by a scanning electron microscope. As a result, the maximum length of the straight line part220was 200 nm. Arrangement of the hexagonal openings21formed with the straight line parts220was periodic. The area ratio of the metal nanowire22was about 10%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1000 nm. As a result, a large dip is generated at a wavelength of 380 nm, and high transmittance of 85% to 75% was exhibited at the longer wavelength side with respect to the wavelength. Further, as a result of measuring sheet resistance, it was 2.5 Ω/□. For the light-transmitting metal electrode according to the first comparative example, resistance was exhibited to be higher than the resistance of the light-transmitting metal electrode according to the first example.

Second comparative example is a specific example of a light-transmitting metal electrode having circular openings21.

In the same way as the first example, a substrate on which AgCu and SiO were deposited, was prepared. Then, resist was applied on the substrate, and the substrate was subjected to thermal nanoimprint at 120° C.

In the mold used for nanoimprint, circular protrusion parts with a diameter of 180 nm are arranged in a triangular lattice. The occupancy of the protrusion parts was 45%. A pattern of the mold was transferred to resist.

After removing the mold, it was confirmed that a structure of the reverse pattern of the mold was formed in the resist. Then, AuCu was etched in the same way as the first embodiment. The surface of the resultant structure was observed by a scanning electron microscope. As a result, circular protrusion parts with a diameter of 180 nm were formed in a triangular lattice. The area ratio of the metal nanowire22was 55%.

By entering light vertically to the light-transmitting metal electrode, transmittance with respect to the wavelength of the incident light was measured. Specifically, the transmission spectrum at vertical incidence was measured in a wavelength range of 200 nm to 1000 nm. As a result, a large dip is generated at a wavelength of 490 nm, and transmittance peak of 82% was generated at a wavelength of 560 nm. Thereby, the transmittance decreased at the longer wavelength side with respect to these wavelengths, and it was 32% at a wavelength of 1000 nm. For the light-transmitting metal electrode according to the second reference example, transparency in a broad wavelength range like the transparency for the light-transmitting metal electrode according to the first embodiment could not be achieved. Further, as a result of measuring sheet resistance, it was 0.7 Ω/□.

SEVENTH EXAMPLE

Seventh example is a specific example in which a light-transmitting metal electrode according to the embodiment is applied for lighting of an organic EL element.

The light-transmitting metal electrode according to the third embodiment was formed on a glass substrate. By applying PEDOT:PSS aqueous solution on the light-transmitting metal electrode, a positive-hole injection layer was formed. By depositing α-NPD thereon in a vacuum, a positive-hole transport layer was formed. Next, a blue light emitting layer in which FIrpic, a blue luminescent material, doped with CBP, was formed thereon by a co-evaporation method. Next, a red light emitting layer in which Btp2Ir (acac), a red luminescent material, doped with CBP, was formed thereon by the co-evaporation method. Next, a yellow light emitting layer in which Bt2Ir (acac), a yellow luminescent material, doped with CBP, was formed thereon by the co-evaporation method. Then, BCP was deposited thereon by an evaporation method, an electron transport layer was formed. Finally, a cathode was formed by depositing LiF (1 nm thick)/Al (150 nm thick) thereon by the evaporation method, resulting in a white organic EL illuminating device.

When the unevenness of luminance was evaluated for the resultant organic EL illuminating device, the difference in luminance between the central part and the end part was not more than 10%. Since the sheet resistance of the light-transmitting metal electrode applied as the anode became not more than ⅓ of the sheet resistance of ITO, uniform light emission of the resultant device was confirmed.

EIGHTH EXAMPLE

An eighth example is a specific example in which the light-transmitting metal electrode according to the embodiment is applied for an amorphous-silicon solar cell.

The light-transmitting metal electrode according to the third example was formed on a glass substrate. Next, a p-type Si layer was formed with a mixture gas of PH3and SiH4thereon using a plasma CVD apparatus. By forming an i-type Si layer with a SiH4gas, and forming an n-type Si layer with a mixture gas of B2H6and SiH4, a pin photoelectric conversion layer was formed.

Current-voltage characteristics of the amorphous-silicon solar cell fabricated by the above-described procedure were evaluated. As a comparative example, a solar cell fabricated in the same way as the eighth example, except for forming ITO at a thickness of 100 nm instead of the light-transmitting metal electrode, was used. In this example, since the sheet resistance of the light-transmitting metal electrode reduced than the sheet resistance of ITO, the resistance loss decreased. As a result, the conversion efficiency has improved from 4.6% to 4.8%.

NINTH EXAMPLE

A ninth example is a specific example in which the light-transmitting metal electrode according to the embodiment is applied for a crystalline-silicon solar cell.

An oxide film on the surface of a crystalline-silicon solar cell substrate in which a p-n junction was formed, was removed by hydrofluoric acid, and then the light-transmitting metal electrode according to the first example was formed at the n-surface side (light radiation surface side). Subsequently, a counter electrode was formed on the p-surface side (rear surface side), by applying an aluminum paste on the entire surface then heating the substrate.

The conversion efficiency of the crystalline-silicon solar cell fabricated by the above-described procedure was evaluated. As a comparative example, a solar cell fabricated in the same way as the ninth example, except for forming a comb-shaped surface electrode instead of the light-transmitting metal electrode, was used. The conversion efficiency of the solar cell according to the comparative example was 6.5%, on the contrary, the conversion efficiency of the crystalline silicon solar cell according to the ninth example was 6.8%.

TENTH EXAMPLE

A tenth example is a specific example in which the light-transmitting metal electrode according to the embodiment is applied for a semiconductor light emitting element.

A semiconductor light emitting element substrate (emission wavelength; 440 nm) was prepared by depositing an n-GaN layer as a buffer layer on a sapphire substrate, and depositing an MQW (multi quantum well) layer composed of n-GaN and InGaN/GaN, a p-AlGaN layer, and a p-GaN layer on the substrate in this order. A p-electrode was formed by forming a 1 nm thick Ni film on the p-surface side, and then forming a film of Ag alloy added with palladium thereon. After that, the light-transmitting metal electrode according to the first example was formed using a nanoimprint method. Subsequently, a 35 nm thick SiN film was formed thereon as an antireflection film and a protection film by sputtering. After that, figuring of the n-GaN layer was carried out by patterning resist by optical lithography, then patterning SiN by fluorine dry etching and patterning Ag by ion milling, and then etching the p-GaN layer by chlorine dry etching. After that, an n-side electrode was formed by sputtering Ti/Al/Ti on the etched n-GaN surface at a thickness of 10 nm/100 nm/50 nm. An ohmic contact was formed between the electrode layer and the element by annealing the wafer at 650° C. for ten minutes in a nitrogen atmosphere. The semiconductor light emitting element according to the tenth example was fabricated by forming an Au pad electrode on the surfaces of the p-side electrode and the n-side electrode.

As a third comparative example, a semiconductor light emitting element was fabricated, for which, instead of the light-transmitting metal electrode, the light-transmitting metal electrode having circular openings formed therein according to the first comparative example was applied.

Further, as a fourth comparative example, a semiconductor light emitting element fabricated in the same way as the tenth example except for using a 100 nm thick ITO instead of the light-transmitting metal electrode was used.

The current-luminance properties of the semiconductor light emitting element according to the tenth example, and semiconductor light emitting elements according to the third comparative example and the fourth comparative example were evaluated. As a result, the luminance of the semiconductor light emitting element according to the tenth example was larger by 1.2 times than the luminances of the third and fourth comparative examples.

ELEVENTH EXAMPLE

An eleventh example is a specific example in which the light-transmitting metal electrode according to the embodiment is applied for a semiconductor light emitting element.

A semiconductor light emitting element substrate (emission wavelength; 630 nm) was prepared by depositing thereon an n-InGaAlP layer as a cladding layer, an InGaAlP layer as an active layer, a p-InGaAlP layer as a cladding layer, and a p-GaP layer as a current diffusion layer in this order. Next, a metal electrode film consisting of a 10 nm thick Au film and a 30 nm thick Au—Zn alloy film was formed on a current diffusion layer by a vacuum deposition method as a metal electrode layer was formed. Furthermore, a rear electrode was formed by depositing Au—Ge alloy on the rear surface of a GaAs substrate at a thickness of 150 nm using a vacuum deposition method. After that, by sintering the substrate at 650° C. for ten minutes in a nitrogen atmosphere, ohmic contacts were formed between the substrate and the rear electrode layer, and between the current diffusion layer and the metal electrode layer. A structure equivalent to the structure of the light-transmitting metal electrode according to the first example was fabricated using a nanoimprint method. Subsequently, by forming a round-shaped electrode composed of Au on a part of the metal electrode layer, the semiconductor light emitting element according to the eleventh example was fabricated.

As a comparative example, a semiconductor light emitting element was prepared, in which, instead of the metal electrode, a 250 nm thick ITO having an ohmic contact to the current diffusion layer was used. By dicing the element into a 1 mm×1 mm chip, the luminance of the bare chip was measured by a chip tester. As a result, the maximum luminance of the semiconductor light emitting element according to the eleventh example was larger by 1.2 times than the luminance of the comparative example.

TWELFTH EXAMPLE

A twelfth example is a specific example in which the light-transmitting metal electrode according to the embodiment is applied for a semiconductor light emitting element.

A semiconductor light emitting element substrate (emission wavelength; 440 nm) was prepared by depositing thereon an n-GaN layer as a buffer layer, an MQW (multi quantum well) layer composed of n-GaN and InGaN/GaN as a cladding layer, a p-AlGaN layer as a cladding layer, and a p-GaN layer as a contact layer in this order. Subsequently, a p-side electrode layer composed of Ni (1 nm thick)/Au (30 nm thick) was formed on the p-side electrode layer by a vacuum deposition method. Furthermore, an n-side electrode layer composed of Ti (10 nm thick)/Au (100 nm thick) was formed on the rear surface of the substrate, and processed in a desired form. Finally, by subjecting the substrate to heat treatment, ohmic contacts were formed on contact surfaces between the element and each electrode layers. Next, a structure equivalent to the structure of the light-transmitting metal electrode according to the first example was fabricated using a nanoimprint method. Further, by forming a round-shaped electrode composed of Ti/Au on a part of the metal electrode layer, the semiconductor light emitting element according to the twelfth example was fabricated.

As a comparative example, a semiconductor light emitting element was prepared, in which, instead of the metal electrode, a 200 nm thick ITO was formed. By dicing the element into a 300 μm×300 μm chip, the luminance of the bare chip was measured by a chip tester. As a result, the maximum luminance of the semiconductor light emitting element according to the twelfth example was larger by 1.3 times than the maximum luminance of the comparative example.

According to the light-transmitting metal electrode according to the embodiment, for light polarized in any direction, by making the maximum length of straight line part220not more than the wavelength of visible light and by providing a plurality of polygonal openings21using the plurality of straight line parts220, oscillation of free electrons occurring in the metal layer2can be structurally interrupted and reflection loss can be suppressed. As such, even if the occupancy of the metal nanowire22is more than 20% and not more than 80%, a light-transmitting metal electrode having little wavelength dependence and having a resistance lower than the resistance of a conventional transparent conductive oxide, can be provided without vitiating its high transparency.

Further, by applying the optical transparency metal electrode according to the embodiment to electronic apparatuses and light emitting devices, highly efficient devices can be provided.

As described above, according to the embodiments, it is possible to provide a light-transmitting metal electrode, electronic apparatuses and light emitting devices which can achieve sufficient transparency in a broad wavelength range.

Although the embodiments and their modifications have been described above, the invention is not limited to these examples. For example, an example made by a person skilled in the art by suitably adding or deleting constituents or adding design change to/from the above mentioned embodiments or their modifications, or an example made by suitably combining features of the embodiments, will also be included within the scope of the invention, as long as it has the gist of the invention.