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27 April 2009 Sapphire direct bonding as a platform for pressure sensing at extreme high temperatures
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Direct bonding between two epitaxy-ready (EPI polished) sapphire wafers is demonstrated as the basis for an all-sapphire pressure sensor. Through chemical processing, hydrogen pre-bonding, and a final high-temperature bakeout, the two single-crystal wafers are directly bonded without the use of any adhesive or intermediate layer. Dicing across the edge of the structure and inspection of the diced pieces with a scanning electron microscope (SEM) indicates a successful direct bond. Control of the bonding wave generates an air bubble sealed between the two bonded sapphire wafers. Optical interference-based measurements of the bubble height and shape at pressures from 0 to 60psig prove that the bubble is sealed by the bonded wafers and demonstrate the potential for sapphire direct bonding as a means of constructing an all-sapphire pressure sensor. Since the structure contains no adhesives, such an all-sapphire sensor is ideal for pressure sensing in extremely harsh, high-temperature environments, potentially operating at temperatures over 1500°C.
© (2009) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Evan M. Lally, Yong Xu, and Anbo Wang "Sapphire direct bonding as a platform for pressure sensing at extreme high temperatures", Proc. SPIE 7316, Fiber Optic Sensors and Applications VI, 73160Y (27 April 2009);

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