Nano-imprinting lithography of P(VDF–TrFE–CFE) for flexible freestanding MEMS devices

Abstract

Thermoplastic nano-imprinting lithography (T-NIL) has been used for the first time as a method of creating freestanding smooth and patterned membranes of micron scale thickness using poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) [P(VDF-TrFE-CFE)]. PVDF and its copolymers and terpolymers cannot be processed using classical lithography techniques because it is incompatible with most solvents and photoresist developers. In this work, patterning at micron scale resolution and creating freestanding layers is facilitated by means of a hydrophobic dodecyltrichlorosilane layer deposited on the silicon (Si) prior to imprinting. This surface treatment reduces the adhesion between the polymer and Si substrate or stamp, aiding with mould release. A sacrificial layer beneath a spin-coated layer of P(VDF-TrFE-CFE) is presented as an alternative method of creating freestanding membranes. The latter method was used in conjunction with exploiting the thermoplastic properties of P(VDF-TrFE-CFE) during T-NIL to improve the quality of the patterned freestanding layers. The cured membrane thicknesses ranged from 0.4-5.8@mm with diameters of centimeters order of magnitude. The processes presented here comprise a basis for integrating P(VDF-TrFE-CFE) as an active material in three dimensional electro-active polymeric microelectromechanical system (MEMS) devices.