Large area semi-permeable encapsulation membranes using carbon nanotube composites

Abstract

A batch-fabrication methodology to create large area vacuum-sealed cavities on top of silicon substrates is reported. This process uses a semi-permeable membrane made of carbon nanotubes (CNTs) and polysilicon. The dense forest of CNTs, conformally coated with polysilicon by low pressure chemical vapor deposition (LPCVD), functions as the semi-permeable membrane. When the top surface is opened via plasma etching of polysilicon, the membrane is penetrable to liquid and vapor. Hydrofluoric acid (HF) vapor is used to etch the underlying oxide before sealing the film with another LPCVD of polysilicon, rendering it impermeable. Sealed areas of more than 1x1 mm2 have been fabricated.