Kazuma Kurihara

Microoptical Two-Dimensional Devices for the Optical Memory Head of an Ultrahigh Data Transfer Rate and Density Sytem Using a Vertical Cavity Surface Emitting Laser (VCSEL) Array

The parallel optical memory system has important advantages for realizing both a fast data transfer rate and high memory capacity since it is based on multibeam recording and a smaller spot size using the vertical cavity surface emitting laser (VCSEL) and a nanoprobe array. The concept, theoretical analysis and fabrication process for the integrated VCSEL nanoprobe array head are discussed with emphasis on the micro-optical issues such as the improvement of optical efficiency by microlens focusing. The flat-tip nanoprobe structure was successfully prepared with the small metal aperture of 150 nm and 1.25% optical throughput using metal aperture Si or GaP semiconductor nano-probes. To realize better optical throughput in the integrated VCSEL, a special nanoprobe array and a microlens array were developed. The microlens array was prepared using a thermal reflow process of the photoresist and lens shape pattern transfering to the semiconductor nanoprobe bottom face by dry etching. Since this two-dimensional array system requires three-dimensional micro-optical adjustment to focus a very small spot on the recording media, this research can provide guidelines for new micro-optical components in future technology.

Fabrication of Micro-Pyramidal Probe Array with Aperture for Near-Field Optical Memory Applications

A new optical memory system is urgently required to realize high memory capacity and fast data transfer rates in the coming multimedia era. To overcome the current capacity barrier of far-field techniques, a novel near-field optical memory of evanescent wave has been proposed using a vertical cavity surface emitting laser (VCSEL) probe array, consisting of the VCSEL array as a light source and the micro-pyramidal probe array as an evanescent wave exit. The design and fabrication for the aperture probe array were developed in this research. An array of up to 10,000 pieces was prepared successfully using microfabrication processes, including photolithography, silicon wet etching, thermal oxidation and thin film deposition. The pyramidal probes in the array show little variation in size and are sufficiently sharp to apply to the near-field recording head. The probe tip has a small size of 100 nm and the aperture has a diameter of around 150 nm. A smaller aperture can be fabricated with more careful control of the experimental procedures, including the etching process and thermal wet oxidation.

High-speed optical nanofabrication by platinum oxide nano-explosion

We propose a new thermal lithography technique that utilizes the thermal decomposition of platinum oxide. This technique enables lithography characterized by high resolution, high speed and large writing area (96?cm2). The smallest reproduced feature was 110?nm in diameter, using an optical system consisting of a 405?nm laser beam and an objective lens with numerical aperture (NA) of 0.65. This feature is six times smaller than is achievable by conventional photolithographic techniques. High-speed writing of over 3?m?s?1 was achieved, with 1.5?million nanodots fabricated per second. Furthermore, a high-aspect-ratio structure, with holes with a diameter of 100?nm and depth 500?nm, was realized.

Characteristics of nanostructured Ag films by the reduction of sputtered AgOx thin films

The fabrication process and the optical properties of nanostructured silver?(Ag) films made from silver oxide (AgOx) thin films have been studied in detail. The formation of Ag nanoparticles with a diameter of about 50?nm during the reduction of AgOx films was clearly demonstrated by scanning electron microscopy?(SEM) and cross-sectional transmission electron microscopy?(TEM) observations. The reflectance spectra of the nanostructured Ag films exhibited an intensive localized surface plasmon resonance (LSPR). The transformation in the reflectance spectra with reduction time was in good agreement with computer simulations based on Mie theory. The composition ratio of AgOx films during the reduction was analysed by the Ag LIII edge x-ray absorption near-edge structure?(XANES) measurements.

Optical Disc Simulation Program Unified by Electromagnetic and Thermal Distributions

We developed a novel simulation program unified by electromagnetic and thermal distributions for a rotating optical disc on the basis of the three-dimensional finite-difference time-domain (FDTD) method. We applied this simulation to super-resolution near-field structure (super-RENS) read-only-memory (ROM) discs and elucidated that the temperature distribution is not only dependent on disc structure and pit shape, but also on incident laser light polarization. We obtained the result that the temperature at the pit became higher than the surrounding temperature for the first time using our simulation program. We believe that our program will aid our understanding of the phenomena behind the super-resolution readout of super-RENS discs.

The size control of silver nano-particles in SiO2 matrix film

We provide a fabrication method for silver nano-particles with a uniform particle size using vacuum deposition. The size uniformity was controlled by a small amount of neodymium?copper (Nd?Cu) as a co-sputtered material. Particles with a size of 20 ? 7?nm dispersed in a SiO2 matrix have been obtained. The full width at half maximum of the plasmon resonance in the optical spectrum by the silver?neodymium?copper (Ag?Nd?Cu) nano-particles was only half of the size compared with the spectral width of a pure Ag nano-particle system. The effect is attributed to an increased uniformity in the particle size.

High-speed fabrication of super-resolution near-field structure read-only memory master disc using PtOx thermal decomposition lithography

We propose a new lithography technique using thermal decomposition of platinum oxide (PtOx) for high-throughput master disc fabrication. The smallest pit size was evaluated to be 50 nm using a laser wavelength of 405 nm and a numerical aperture (NA) of 0.65; hence, it is one-twelfth the optical spot size. In addition, fabrication of pits with different shapes was examined, and its effects on super-resolution near-field structure (super-RENS) disc properties were studied. The readout signal characteristic evaluated on the basis of carrier-to-noise ratio (CNR) with an elliptical pit was 7 dB larger than that of the round one. The results demonstrated that this high-throughput fabrication technique is also useful for controling the pit shape for CNR improvement of super-resolution readout.

Carrier-to-noise ratio enhancement of super-resolution near-field structure disks by Ag nanostructure

The recording and retrieval characteristics of super-resolution near-field structure disks have been evaluated before and after the fabrication of a Ag-nanostructured film on the top dielectric layer, using a 405nm wavelength laser and a 0.65 numerical aperture lens system. The carrier-to-noise ratio for 100nm mark signals is significantly improved by applying the Ag-nanostructured film. The underlying mechanism for the enhancement depends on the top dielectric layer thickness. A simulation based on Mie theory shows good agreement with the measured reflectance spectrum for the Ag-nanostructured film.

Super-Resolution Readout of 50 nm Read-Only-Memory Pits Using Optics Based on High-Definition Digital Versatile Disc

A super-resolution near-field structure (super-RENS; ZnS–SiO2/Sb75Te25/ZnS–SiO2) and a read-only-memory (ROM) substrate with its pit wide in the radial direction (200 nm) are combined. The readout of 50-nm-long pits was examined, and the pit length is less than one third the resolution limit of the optics (laser wavelength: 405 nm, numerical aperture: 0.65) used. The carrier-to-noise ratio obtained was 39 dB, and it was possible to observe the reproduced waveform clearly. The results indicate that the capacity along the tangential direction can be increased by a factor of 4.

Fine and high-aspect-ratio screen printing combined with an imprinting technique

The development of screen-printing techniques in order to obtain fine patterns with a high aspect ratio is an important task in the advancement of printed electronics. To this end, we propose a new printing concept in this study that consists of a combination of the screen-printing process with an imprinting technique. We show that fine and high-aspect-ratio patterns are realized by the capillary force of parallel-walled structures (PWSs) on the material to be printed. The PWS is fabricated by an imprinting method using an ultra-violet curable resin. In order to obtain finer patterns with a higher aspect ratio, printed patterns according to the pitch and the height of the PWSs were assessed. A printed pattern with a line width of 6.3 μm was obtained at a PWS, with a pitch of 20 μm and at a height of 110 μm, when a screen mask with a 100 μm-wide resist opening was used. The line width of the printed patterns was well controlled by the pitch of the PWSs. Moreover, an aspect ratio of up to 7.4 was achieved. Furthermore, we expect this screen-printing process to implement submicron patterns as well as more complex patterns, including curves and rings, through well-designed microstructures.