4.6 Conclusion This study presented a viable alternative to wet HNA or vapor XeF2 bulk isotropic etching, which each pose significantly more complications in processing. Furthermore, HNA polishing was found to be an effective method for alleviating the commonly encountered problems of undercutting, surface roughness, and anisotropy. Additionally, the development of the closed-loop photolithography process leverages the capabilities of existing cleanroom devices to perform sophisticated wafer alignment and patterning processes capable of drastically improving process throughputs. Acknowledgments The authors would like to thank Tom Stephenson and Rich Johnston for their assistance in the AFIT cleanroom, as well as Andy Browning’s assistance with the Plasma-Therm DSE. References 1. Lee Y, Bang S, Lee I, Kim Y, Kim G, Ghaed MH, Pannuto P, Dutta P, Sylvester D, Blaauw D (2013) A modular 1 mm3 die-stacked sensing platform with low power I2C inter-die communication and multi-modal energy harvesting. IEEE J Solid-State Circuits 48:229–243 2. Richards Grayson AC, Shawgo RS, Johnson AM, Flynn NT, Li Y, Cima MJ, Langer R (2004) A BioMEMS review: MEMS technology for physiologically integrated devices. Proc IEEE 92(1):6–21 3. Donald BR, Levey CG, McGray CD, Paprotny I, Rus D (2006) An untethered, electrostatic, globally controllable MEMS micro-robot. J Microelectromech Syst 15(1):1–15 Fig. 4.11 (a) Example of three laterally displaced images being stitched, (b) three laterally stitched images were combined using vertical stitching to produce a 3 3 array, (c) the same 33 3 array is shown as an L-Edit mask layer Fig. 4.10 (a) SF11 photoresist patterned over the edge of a hemispherical cavity, exhibiting pull back from the sharp cavity edge. (b) Successful lift-off of Ti/Au layers on the wafer surface. (c) Unsuccessful lift-off within an etch cavity 4 Bonded Hemishell Approach to Encapsulate Microdevices in Spheroidal Packages 33
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