In this paper, new processes have been developed to fabricate micromechanical components and systems that utilize two different photoresists (Shipley S1813 and Hoechst AZ P4620) as sacrificial layers in conjunction with SU-8 photoresist used as an electroplating mould. The use of photoresists as sacrificial layers offers several advantages including reduction in processing steps and hence processing cost. However, the normal sacrificial layer photoresist processing cycle fails when used in conjunction with SU-8 photoresist. The latter is often used as an electroplating mould, especially for high-aspect ratio or tall microstructures in MEMS fabrication. In this paper, problems arising in the use of a photoresist sacrificial layer are discussed and new sacrificial layer processes are developed. New curing temperatures for photoresist sacrificial layers are determined, which prevent damage that otherwise occurs from the use of SU-8 as an electroplating mould. New hard baking temperatures determined are 175 °C and 200 °C for S1813 and AZ P4620 photoresist processes, respectively. A comb drive structure is utilized to demonstrate these new fabrication processes.
This paper presents a new sidewall smoothing process for Si micro-optical components using focused ion beam (FIB) milling. First, the deep reactive ion etching (DRIE) Bosch process is employed to form a microstructure on a Si substrate. However, scalloping which is induced on the sidewall by the repetition of etching and passivation steps is a major source of light scattering, reducing surface reflectivity in optical applications. In this research, FIB is used to smooth the rough sidewall surface and obtain polished mirror surface. After the DRIE Bosch process, the values of sidewall roughness as measured by atomic force microscopy were 153.0 ± 13.5 nm with an rms value of 28.1 ± 6.4 nm. The FIB smoothing process tremendously improved the surface roughness of etched sidewalls resulting in a maximum peak-to-valley roughness and an rms roughness of 5.7 ± 1.8 nm and 1.6 ± 0.7 nm, respectively. In this paper, the DRIE Bosch process and the FIB smoothing process are described in detail and applications using this technique are discussed.
Background: Switchable glasses allow the control of light transmission-an attractive property for applications such as car sunroofs, aircraft windows, building windows, augmented reality, imaging, and displays. Commercialized switchable glasses have severe limitations, such as speed, cost, and operating conditions, among others. Microshutters, a type of switchable glass with very distinctive properties, are reviewed, as they are a technology that could significantly improve some or all of the shortcomings mentioned above. Aim: We will summarize the various types of microshutters and tentatively identify various critical designs, fabrication schemes, and performance criteria by the many research groups implementing them and investigating their properties. Approach: We will describe the various approaches used to control light transmission through microelectromechanical systems. It will compare their performances and comment on fabrication and implementation challenges. Conclusions: Microshutters have performance levels that could make them good candidates for switchable glasses. Many research groups have investigated various approaches to fabricate microshutters and have shown that they can be implemented reliably on a small scale, with fast actuation, low power, and high contrast and are relatively easy to manufacture. Work is needed to demonstrate that they can be scaled-up and still be economical to produce.
A novel thermoplastic fusion bonding method using a pressure-assisted boiling point (PABP) control system was developed to apply precise temperatures and pressures during bonding. Hot embossed polymethyl methacrylate (PMMA) components containing microchannels were sealed using the PABP system. Very low aspect ratio structures (AR = 1/100, 10 μm in depth and 1000 μm in width) were successfully sealed without collapse or deformation. The integrity and strength of the bonds on the sealed PMMA devices were evaluated using leakage and rupture tests; no leaks were detected and failure during the rupture tests occurred at pressures greater than 496 kPa. The PABP system was used to seal 3D shaped flexible PMMA devices successfully.
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