Synthesized processing techniques for monolithic integration of nanometer-scale hole type photonic band gap crystal with micrometer-scale microelectromechanical structures

This article reports the synthesized fabrication process design and module development that enabled the monolithic integration of deep submicrometer size, two dimensional hole-type photonic band gap crystals (PhCs) with microelectromechanical system (MEMS) actuators and optical testing structures (OTS). Techniques enabling sublithographic wavelength patterning using only conventional chrome-on-glass binary photomasks without phase shift features were achieved through the manipulation of mask bias designs and the partial coherence control of the lithographic exposure system. Together with the development of time multiplexed reactive ion etching and focus ion beam milling techniques, such design of the process allows the realization of highly dense PhC and MEMS actuators physically released from the buried oxide layer. Here, disparate pattern dimensions [with PhC critical dimensions (CDs) of only 175 nm, MEMS typical dimensions of 2 μm, and OTS openings more than 400 μm wide], varied etch depth (3 μm for the PhC and MEMS, 61 μm for the OTS), and the requirement of a sufficient process latitude for exposure and etch processes are some of the key challenges that were overcome for a successful integration of air-bridge-type PhC CDs with movable MEMS actuators. Hence, the works described in this article enable MEMS tunable PhC properties with potential application in next generation dynamic optical communication networks and photonic integrated circuits.