Plasmonic interface and method of manufacturing thereof

A method of manufacturing a layered material stack that includes a plasmonic interface between a plasmonic material and optical waveguide material is disclosed. The method includes providing a substrate layer, disposing a layer of plasmonic material on the substrate layer, depositing a metal constituent of an optical waveguide material directly onto the layer of plasmonic material, and anodizing the metal constituent of the optical waveguide material to form an optically transparent oxide of the metal constituent configured to couple light into the layer of plasmonic material, with the optically transparent oxide of the metal constituent forming an optical waveguide structure.

BACKGROUND OF THE INVENTION

The invention relates generally to plasmonic materials and, more particularly, to a plasmonic interface between a plasmonic material and optical waveguide material and method for providing such an interface.

Plasmonic materials are materials that exploit surface plasmons, which are produced from the interaction of light with the plasmonic material, which according to various designs can be a metal-dielectric metamaterial or suitable metallic material (e.g., gold (Au) or silver (Ag)). Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons (SPPs) or near-field light, which are much shorter in wavelength than the incident light.

One growing application of plasmonic materials is for use in plasmonic induced data storage. In plasmonic induced data storage, the near-field light generated by the plasmonic material—and the intense, localized optical fields of the near-field light—are focused and applied to a diffraction-limited spot over a small region of an optical disk containing metallic nano-structures to achieve high storage densities on the disk. One particular form of plasmonic induced data storage that continues to develop is heat assisted magnetic recording (HAMR), which is a technique that magnetically records data on high-stability media at a high storage density. In HAMR, a laser is used in conjunction with plasmonic materials to produce near-field light that momentarily heats the recording area of a recording medium to reduce its coercivity below that of a magnetic field applied from a recording head mechanism.

One known mechanism for generating near-field light is a near-field light generating device that includes a thin film optical light pipe or waveguide structure coupled to a thin film plasmonic material—with the thin film plasmonic material forming a structure that is commonly referred to as a near-field transducer (NFT). According to one embodiment, the optical light pipe/waveguide structure is formed of a waveguide material in combination with a buffer material—with one possible combination of the materials of the waveguide and the buffer layer being tantalum pentoxide (Ta2O5) as the material of the waveguide and aluminum oxide (Al2O3) as the material of the buffer layer. It is recognized, however, that the optical light pipe may be formed only of a waveguide material (e.g., Ta2O5) without the use of an accompanying buffer layer. Regarding the NFT, the plasmonic material of the NFT may be a noble metal such as Ag or Au.

A general construction of a material stack of a near-field light generating device as described above that includes a waveguide, a buffer layer, and a plasmonic material is shown inFIG. 1. As shown inFIG. 1, in the material stack1of the near-field light generating device, the construction is such that a thin film plasmonic material layer (forming an NFT)2is disposed on a thin film optical light pipe structure3, with the thin film optical light pipe structure3being adhered to a supporting substrate layer4by way of an adhesive5. The thin film optical light pipe structure3is formed of a waveguide layer6and a buffer layer7, with the plasmonic material layer2being applied to the buffer layer6of the light pipe3. In such a case, the material stack1is manufactured by forming the buffer layer7on the top surface of the waveguide layer6, and forming the plasmonic material layer2on the buffer layer7. It is recognized, however, that in the case of forming the plasmonic material layer2of a noble metal such as Ag or Au on the buffer layer7of Al2O3, there occurs the problem that the plasmonic material layer2may exfoliate in the process of manufacturing the material stack1, since noble metals such as Ag and Au are low in strength of adhesion to Al2O3. To cope with this, an adhesion layer8made of metal, such as titanium, may be formed as an interlayer between the buffer layer7and the plasmonic material layer2, with the adhesion layer8being deposited to adhere to the buffer layer7and promote the adhesion of the plasmonic material layer2.

While the inclusion of the adhesion layer8in the above described material stack1of near-field light generating device provides for a strong adhesion between the plasmonic material layer2and the buffer layer7of the optical light pipe3, the adhesion layer8can have a negative impact on the performance of the near-field light generating device in generating near-field light. That is, it is recognized that localized plasmon generation in the plasmonic material layer2and its efficiency in light energy conversion are both a function of the plasmonic material and the ability of applied light to efficiently couple into the plasmonic material. This efficiency in light energy conversion can be negatively affected by the presence of materials that reduce the ability of applied light to efficiently couple into the plasmonic material. With respect to the above described material stack1, the titanium adhesive layer8results in such a loss of efficiency in light energy conversion, since the titanium adhesive layer8is applied directly between the optical light pipe3and the plasmonic material layer2, and thus functions as a loss mechanism.

As an alternative method of forming a material stack of a near-field light generating device that includes a waveguide, a buffer layer, and a plasmonic material, it is recognized that a waveguide material could be sputtered onto a plasmonic layer to form the waveguide structure. However, it is recognized that such sputtering of the waveguide material will not provide a waveguide layer(s) that is stoichiometric, and thus a refractive index of the waveguide structure may not provide for optimal efficiency in the conversion of light energy into localized plasmon generation.

Therefore, it would be desirable to provide a material stack for a near-field light generating device that provides improved performance in generating near-field light, with the material stack providing optimal efficiency in the conversion of light energy into localized plasmon generation in the plasmonic material of the material stack. It would further be desirable for the material stack to maintain adequate adhesion between the thin film layers therein while providing this improved efficiency in light energy conversion, such that exfoliation of the plasmonic material from an optical waveguide is prevented.

BRIEF DESCRIPTION OF THE INVENTION

The invention is directed to a plasmonic interface between a plasmonic material and optical waveguide material and method for providing such an interface.

In accordance with one aspect of the invention, a method of manufacturing a layered material stack includes providing a substrate layer, disposing a layer of plasmonic material on the substrate layer, depositing a metal constituent of an optical waveguide material directly onto the layer of plasmonic material, and anodizing the metal constituent of the optical waveguide material to form an optically transparent oxide of the metal constituent configured to couple light into the layer of plasmonic material, the optically transparent oxide of the metal constituent forming an optical waveguide structure.

In accordance with another aspect of the invention, a layered material stack includes a substrate layer, a layer of plasmonic material disposed on the substrate layer, and an anodized optical waveguide structure affixed directly onto the layer of plasmonic material, the anodized optical waveguide structure comprising an optically transparent metal oxide. The optical waveguide structure is in direct atomic contact with the layer of plasmonic material, without an adhesion interlayer being applied between the optical waveguide structure and the layer of plasmonic material.

In accordance with yet another aspect of the invention, a method for fabricating a layered material stack for a near-field light generating device includes providing a substrate layer, applying an adhesion layer to the substrate layer, affixing a thin film plasmonic material to the substrate layer by way of the adhesion layer, and depositing a thin film metal layer directly on the thin film plasmonic material, the thin film metal layer comprising a metal constituent of an optical light pipe material. The method also includes anodizing the thin film metal layer to form an optically transparent oxide of the metal constituent, the optically transparent oxide of the metal constituent forming a thin film optical light pipe on the thin film plasmonic material, with the thin film optical light pipe being in direct contact with the thin film plasmonic material, without an adhesion interlayer being present between the thin film optical light pipe and the thin film plasmonic material.

DETAILED DESCRIPTION

Embodiments of the invention provide a material stack having plasmonic interface between a plasmonic material and optical waveguide material and method for providing such an interface. The material stack is formed such that the plasmonic material is placed in direct atomic contact with the optical material. Thin film anodization is employed to grow the optical material film(s) directly on the plasmonic material without the need for adhesion interlayers therebetween.

Referring toFIG. 2, a layered material stack10of thin film materials is shown according to an embodiment of the invention. According to one embodiment of the invention, it is envisioned that the material stack10is integrated as part of a near-field light generating device that is employed for performing a plasmonic induced data storage operation (e.g., HAMR). It is recognized, however, that material stack10may have applications outside that of plasmonic induced data storage applications.

As shown inFIG. 2, material stack10includes a thin film layer of plasmonic material12that is disposed on a substrate layer14, with a first surface16of the plasmonic material facing the substrate layer14and being secured thereto by way of an adhesive layer17. The thin film plasmonic layer12is formed of a plasmonic material such as gold (Au) or silver (Ag), or potentially of a metal-dielectric metamaterial, while the substrate layer14may be composed of any of a number of suitable electrically insulative or conductive materials that are capable of providing structural support during a build-up of the material stack10. According to one embodiment, the thin film plasmonic layer12may be form part of a near-field transducer (NFT).

Also included in the material stack is a thin film optical waveguide structure18(i.e., “light pipe structure”) that is disposed on a second surface20of the thin film plasmonic layer12. According to embodiments, the waveguide structure18is formed of one or more optical waveguide materials. In one embodiment, the waveguide structure18is formed of two optical waveguide materials, including what are generally referred to here as a waveguide layer22and a buffer layer24—with the buffer layer24comprising a waveguide material having a refractive index lower than that of the waveguide material of waveguide layer22. The buffer layer24is disposed on the thin film plasmonic layer12with the waveguide layer22being applied on the buffer layer24. In an exemplary embodiment, the waveguide layer22may be formed of tantalum pentoxide (Ta2O5), while the buffer layer24may be formed of aluminum oxide (Al2O3). The waveguide layer22and buffer layer24are formed as dense stoichiometric films with a refractive index that closely resembles the refractive index of crystalline Ta2O5and Al2O3.

According to an exemplary embodiment, the waveguide structure18is placed in direct atomic contact with the thin film plasmonic layer12without the presence of any adhesion interlayers therebetween. That is, the waveguide structure18is grown directly on the thin film plasmonic layer12by way of a thin film anodization process, such that no adhesion interlayers are required for adhering the layers12,18together therebetween. By placing the waveguide structure18in direct atomic contact with the thin film plasmonic layer12, light that is applied to the material stack10can be efficiently coupled into the thin film plasmonic layer12so as to minimize a loss of efficiency in light energy conversion in the plasmonic material of layer12.

Referring now toFIG. 3, a material stack26of thin film materials is shown according to another embodiment of the invention. The material stack26is similar to the material stack10ofFIG. 1, and thus like numbers are used to indicate identical elements. However, in material stack26, a thin film optical waveguide structure28(i.e., “light pipe structure”) is provided that is formed of only of a single waveguide material (e.g., Ta2O5) without the use of an accompanying buffer material.

Referring now toFIG. 4, and with continued reference back toFIG. 2, a technique30for performing a build-up of a material stack10, such as could be used a near-field light generating device, is shown according to an embodiment of the invention. The technique30begins at STEP32by providing a substrate layer14that is composed of any of a number of suitable electrically insulative or conductive materials that are capable of providing structural support for the build-up process. A thin film layer of plasmonic material12, such as gold or silver for example, is then disposed and adhered onto substrate layer14at STEP34, with an adhesive layer or material17being applied between the thin film plasmonic layer12and the substrate layer14to secure the layers together.

Upon securing of the thin film plasmonic layer12to the substrate layer14, the technique30continues by depositing the thin film optical waveguide structure18on the thin film plasmonic layer12at STEP36. More specifically, constituents of the wave guide materials are deposited on the thin film plasmonic layer12. Thus, according to one embodiment, where the waveguide structure18includes a waveguide layer22formed of tantalum pentoxide (Ta2O5) and a buffer layer24formed of aluminum oxide (Al2O3), tantalum (Ta) and aluminum (Al) are deposited on the thin film plasmonic layer12at STEP36. The tantalum and aluminum adhere well to the plasmonic material (i.e., gold/silver) of thin film plasmonic layer12, and thus no separate adhesion interlay is necessary for adhering the waveguide layer22and buffer layer24to the film plasmonic layer12.

While the tantalum and aluminum constituents of the wave guide materials adhere well to the thin film plasmonic layer12, it is recognized that they are not optically transparent in their metallic form. As such, the tantalum and aluminum are converted to their optically transparent oxides through an anodization process that is performed at STEP38. In performing the anodization of the tantalum and aluminum constituents of the waveguide layer22and buffer layer24, the electrically conductive thin film plasmonic layer12is used as an electrode in the anodization to supply current to the layers22,24. In one embodiment, where the substrate layer14is formed from an electrically insulating material, current is provided directly to the thin film plasmonic layer12. In another embodiment, where the substrate layer14is formed from an electrically conducting material, current is provided through the substrate layer14to thin film plasmonic layer12.

As a result of the anodization process at STEP38, the waveguide structure18is completely anodized to the thin film plasmonic layer12(i.e., is in direct atomic contact with the thin film plasmonic layer12), such that no interfacial adhesion layers are present at the interface of the waveguide structure18and thin film plasmonic layer12to act as a loss mechanism. The anodization process at STEP38produces a waveguide structure18in which a Ta2O5waveguide layer22and an Al2O3buffer layer24are formed as dense stoichiometric films with a refractive index that closely resembles the refractive index of crystalline Ta2O5and Al2O3. The stoichiometric waveguide layers22,24of waveguide structure18enable light that is applied to the material stack10to be efficiently coupled into the thin film plasmonic layer12so as to minimize a loss of efficiency in light energy conversion in the plasmonic material of layer12.

Beneficially, embodiments of the invention thus provide a material stack having a plasmonic interface between a plasmonic material and optical waveguide material that is free of an adhesive interlayer that can contribute to efficiency degradation. The material stack is formed using a technique/process that inverts the typical process order by which such a material stack is usually formed and—in doing so—enables the interface between the optical waveguide material and the plasmonic material to be free of such adhesion layers. In forming the material stack, an optical waveguide structure is anodized directly onto a plasmonic material supported by a substrate layer, with constituents of the wave guide materials (Ta and/or Al) being deposited on the plasmonic material and subsequently converted to their optically transparent oxides through anodization—with the plasmonic material being used as an electrode in the anodization. The waveguide structure is thus formed as a dense stoichiometric film having a refractive index that closely resembles the refractive index of crystalline Ta2O5and Al2O3so as to enable light that is applied to the material stack to be efficiently coupled into the plasmonic material so as to minimize a loss of efficiency in light energy conversion material stack. The anodized waveguide layers can be detected and determined different from other deposition techniques that could deposit similar quality waveguide films, such as sputtering, as the anodized film is denser than sputtered films.

Therefore, according to one embodiment of the invention, a method of manufacturing a layered material stack includes providing a substrate layer, disposing a layer of plasmonic material on the substrate layer, depositing a metal constituent of an optical waveguide material directly onto the layer of plasmonic material, and anodizing the metal constituent of the optical waveguide material to form an optically transparent oxide of the metal constituent configured to couple light into the layer of plasmonic material, the optically transparent oxide of the metal constituent forming an optical waveguide structure.

According to another embodiment of the invention, a layered material stack includes a substrate layer, a layer of plasmonic material disposed on the substrate layer, and an anodized optical waveguide structure affixed directly onto the layer of plasmonic material, the anodized optical waveguide structure comprising an optically transparent metal oxide. The optical waveguide structure is in direct atomic contact with the layer of plasmonic material, without an adhesion interlayer being applied between the optical waveguide structure and the layer of plasmonic material.

According to yet another embodiment of the invention, a method for fabricating a layered material stack for a near-field light generating device includes providing a substrate layer, applying an adhesion layer to the substrate layer, affixing a thin film plasmonic material to the substrate layer by way of the adhesion layer, and depositing a thin film metal layer directly on the thin film plasmonic material, the thin film metal layer comprising a metal constituent of an optical light pipe material. The method also includes anodizing the thin film metal layer to form an optically transparent oxide of the metal constituent, the optically transparent oxide of the metal constituent forming a thin film optical light pipe on the thin film plasmonic material, with the thin film optical light pipe being in direct contact with the thin film plasmonic material, without an adhesion interlayer being present between the thin film optical light pipe and the thin film plasmonic material.