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High-Throughput GaP Microprobe Array having Uniform Aperture Size Distribution for Near-Field Optical Memory

The GaP metal-aperture microprobe array has been studied for application to the parallel near-field optical array head of high memory capacity and fast data transfer rate. The fabrication of such an array having uniform aperture size distribution was realized using a low-temperature etching solution of HF:HNO3 and the careful control of ion-milling parameters. After the flat-tip formation by the wet etching method and the aperture formation by the ion-milling process, GaP microprobes of more than 90% in the array show an acceptable size distribution in the range of 150±30 nm. It was observed from the near field scanning optical microscope (NSOM) observation that tiny apertures are formed on the top of the microprobes and light comes out only from the aperture. The light penetrated through the 200 nm aperture shows approximately 170 nm beam size in full width half maximum (FWHM). Due to the high refractive index, the cut-off diameter of GaP microprobes decreases to approximately 200 nm, resulting in improved optical throughput with more than 100 times increment compared with that of the conventional optical fiber probe. For the microprobe having 150 nm aperture, 1.25% optical throughput was realized in this research. The design concept for the semiconductor microprobe array having high optical throughput with uniform aperture size distribution has been proved experimentally.