Fabrication of a high-aspect-ratio structure (HARS) and a 3D feed-horn-shaped structure array for a 3D MEMS antenna array by using a novel UV lithography apparatus

This paper reports a novel UV lithography technique for fabricating a 3-dimensional (3D) feed-horn-shaped structure mold array, and obtaining parallel light by using a mirror-reflected parallel-beam illuminator (MRPBI) system. A 3D feed-horn-shaped micro-electro-mechanical systems (MEMS) antenna has some attractive features for array applications, which can be used to improve microbolometer performance and to enhance the optical efficency for thin film transistor-liquid crystal display (TFT-LCD) and other display devices. Since MEMS technology has faced many difficulties in the fabrication of a 3D feed-horn-shaped MEMS antenna array itself, The purpose of this paper is to propose a new fabrication method to realize a 3D feed-horn-shaped MEMS antenna array by using a mirror-reflected parallel-beam illuminator (MRPBI) System with an very slowly rotated, inclined x-y-z stage [1-5]. With a conventional UV lithography apparatus, it is very difficult to fabricate high-aspect-ratio structures (HARS) because a typical UV lithography apparatus cannot produce perfectly parallel light. From a theorectical anlysis, a columnar illuminator over 6 m in height is required to achieve parallel light, but generally a laboratory height is not 6 m. An essential idea of this research is to make a light ray with long propagation by using a reflective mirror and a conventional UV-lithography apparatus for creating parallel light in a small lab space. Also, a novel method of lithography was tried to make a 3D structure array by exposing a planar wafer to the generated parallel light and rotating an inclined x-y-z stage at an ultra-slow rate. An optimization of the 3D structure array can be achieved by simulating a 3D feed-horn MEMS antenna. By using a high-frequency structure simulator (HFSS), a vertical sidewall array and 30° tilted sidewall array, we achieved a 300-μm-high structure array using a MRPBI system, which was confirmed using scanning electron microscopy. A high-aspect-ratio, 300-μm, thick sturucture with 30° tilted sidewalls was fabricated using a SU-8 negative photoresist, and a 100-μm vertical sidewall structure array was fabricated using a PMER negative photoresist. The feasibility of fabricating both a 3D feed horn MEMS antenna and a mold array was demonstrated. In order to study the effect of this new technique, we simulated the 3D feed-horn-shaped MEMS antenna array had been simulated with high frequency structure simulator (HFSS) and then compared the results with those from traditional 3D theoretical antenna models. As a result, it seems possible to use a 3D feed-horn-shaped MEMS antenna in the tera-hertz range to improve microbolometer performance and to fabricate several optical MEMS devices.