PDMS-on-silicon microsystems: Integration of polymer micro/nanostructures for new MEMS device functions.

Abstract

Modern technologies found in military, space-craft, automotive, and telecommunications applications strongly demand reductions of the manufacturing cost, power consumption, size, and weight of integrated sensors and actuators. The research field of microelectromechanical systems (MEMS) has seen significant technological innovations and advancements to meet this demand in the last two decades. Historically, MEMS technology has been seen as an offspring of silicon-based integrated circuit (IC) technology. But recently, the roles that polymer materials play in MEMS have been more pronounced due to their cost effectiveness, manufacturability, and compatibility with micro/nanoscale biological and chemical systems. Among these polymers, an organic elastomer, Polydimethylsiloxane (PDMS), has become one of the most popular materials because of its unique material properties and moldability suited for low-cost rapid prototyping based on a fabrication technique called soft lithography. However, PDMS micro/nanostructures, not allowed to be integrated with other silicon-based devices, find their limited use in MEMS other than in passive microfluidic components. The lack of a technology bridging the gap between silicon and PDMS prohibits us to realize new MEMS devices potentially resulting from the simultaneous use of these two materials. This research explores a fully new technological concept of PDMS-on-silicon microsystems. PDMS-on-silicon microsystems refers to a class of novel MEMS devices integrating PDMS micro/nanostructures onto silicon actuators and/or sensors. The research aims to demonstrate a new type of MEMS devices taking advantage of benefits resulting from both of silicon and PDMS. To achieve this goal, this work develops a new MEMS fabrication technique called soft-lithographic lift-off and grafting (SLLOG). The SLLOG process starts with soft lithography-based molding and release of a three-dimensional (3D) PDMS microstructure. This is followed by grafting of the microstructure onto silicon MEMS devices with high accuracy. The SLLOG process is further extended to allow imprinting of nanoscale features on the surface of the 3D PDMS microstructure. Using SLLOG, this work fabricates two new MEMS devices: a PDMS-on-silicon hybrid actuator and a reconfigurable nanoimprinted PDMS optical grating device, and presents their performance. The developed devices have a simple structural design, yet exhibit very unique functions such as high-speed multi-axis actuation and dynamic optical wavelength tuning. These MEMS device functions originate from combining the high-strain elasticity and optical transparency of the PDMS micro/nanostructures and the fast dynamic response of silicon MEMS actuators. The results shown in this thesis successfully prove the presented technological concept. The concept and fabrication technique developed in this work are to be useful for development of a new type of MEMS devices with reduced manufacturing cost and complexity for future microsystems.