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Micron- and Submicron-thick Parylene Substrates for Transfer Printing and Solar Applications

• Authors: A. I. Wang, A. Murarka, F. Niroui, J. Jean, J. H. Lang, V. Bulović
• Sponsorship: NSF

Transfer printing of thin metal films enables the fabrication of both planar and suspended membrane electrodes for microelectromechanical (MEMS) sensors and actuators in an additive process. In addition, transfer-printed metal films can be used to form abrupt junctions between organic and metal layers. In contrast, conventional deposition processes such as evaporation or sputtering can cause the metal atoms to penetrate into underlying organic layers.

We have developed a solvent-free transfer printing method using micron- or submicron-thick films of a robust, flexible polymer, parylene-C, as a carrier membrane. The transparent parylene films are initially deposited by chemical vapor deposition onto a rigid or semi-rigid handle substrate for ease of handling during fabrication. Metal and/or organic layers are subsequently deposited and patterned on top. The entire stack is then peeled away from the handle in a continuous sheet and transferred to the receiving substrate. After transfer, the ultrathin parylene carrier may be left in place or removed by oxygen plasma.

Using this method, we have demonstrated electrostatically-actuated gold membrane-covered cavity arrays for microspeakers with larger areas (>1cm²) than previously possible using a solvent-assisted contact transfer printing method^[1]. The solvent-free method has also been employed to deposit metal electrodes on top of solvent-sensitive organic layers in metal-molecule-metal structures for tunneling nanoelectromechanical switches^[2].

Parylene films can also serve as ultrathin, lightweight substrates for organic photovoltaics (OPVs). Their chemically inert and insoluble nature enables the use of common vapor- and solution-phase methods for thin-film deposition, including thermal evaporation and layer-by-layer spin-casting. Since the full active layer stack in an OPV is itself less than a micron thick, moving to thinner, lighter substrates could significantly reduce total weight and cost^[3]. Although our current devices absorb strongly in the visible wavelength range, further materials and architecture engineering could yield a fully transparent solar cell on parylene with exceptional flexibility and versatility for optoelectronic applications.

1. A. Murarka, S. Paydavosi, T. Andrew, A. Wang, J. Lang, and V. Bulović, “Printed MEMS membranes on silicon,” in Proc. IEEE 25th Int. Conf. Micro Electro Mechanical Systems (MEMS), Paris, France, 2012, pp. 309-312. [↩]
2. F. Niroui, A. I. Wang, E. M. Sletten, T. M. Swager, J. H. Lang, and V. Bulović, “Tunneling Nanoelectromechanical Switches Based on Organic Thin Films,” MTL Annual Report, 2013. [↩]
3. M. Kaltenbrunner, M. S. White, E. D. Glowacki, T. Sekitani, T. Someya, N. S. Sariciftci, and S. Bauer. “Ultrathin and lightweight organic solar cells with high flexibility,” Nat. Comm., 3:770 doi: 10.1038/ncomms1772 (2012). [↩]