From Stanford NEMS
Stanford Nano Electro-Mechanical Systems
My research program falls within the general area of nano- and micro-electromechanical systems (N/MEMS, which is pronounced “NEMS”). Having been at Stanford for five years as of July 1, 2010 and having selected nems.stanford.edu as my group’s website (mems.stanford.edu having been already previously taken by my colleague Tom Kenny in Mechanical Engineering), I’ve finally gotten around to organizing a few thoughts on promising research directions in NEMS.
The decades-long push to develop reliable, cost-effective MEMS for inertial sensing, electronic timing, and displays has, in the last few years, led to a significant, growing industry. Further enhancements in performance will require the tight integration of MEMS and electronics – through co-fabrication or a wafer-scale assembly process. Two of my research projects are to this overall goal: back-end-of-line processes for nano-electromechanical switches (R. Parsa, W. S. Lee, and K. Yoo) and parallel wafer-scale assembly and interconnect of CMOS and MEMS (J.-W. P. Chen). J. R. Jain is exploring NEMS techniques for applying strain to modify the band structure of germanium, with the goal of high-performance, CMOS-compatible opto-electronics. Another emerging research area is vacuum microelectronics. Scaling analysis indicates that resonant-cavity vacuum microelectronic devices are far more efficient than solid-state sources at frequencies in the THz region; Tom Lee and I are collaborating to demonstrate a micro Barkhausen-Kurz oscillator (J. S. Snapp).
Much of my research group is current working outside the conventional focus on applications in information technology, which has served as the primary motivator for MEMS from its beginnings in the 1970s. Why? The breakthroughs in materials, low-cost manufacturing technology, micro- and nano-structure design, sophisticated electromechanical control of arrays of active elements, and encapsulation and packaging can be used for applications in new fields, such as energy conversion and health care.
Thermionic energy conversion is based on the emission of electrons from a very hot cathode and their collection on a cooler anode that can be made of a material with a different workfunction. The concept dates to the 19th century (T. A. Edison being one of the earliest proponents) and was demonstrated using vacuum tube technology for space applications in the 1960s – 1980s. In 2008, Nick Melosh from Materials Science and Engineering invented a new kind of thermionic converter in which a semiconductor photocathode allows for harvesting the above-bandgap photon energy as well as the broad-spectrum thermal energy. Applying NEMS technology to the new PETE converter, as well as conventional thermionic converters, is being explored by Dr. I. Bargatin, S. Chou, T. Gwinn, and J. H. Lee.
The applications of silicon microstructures to biomedicine and biotechnology date from the pioneering research in the late Jim Angell’s group in Electrical Engineering in the 1960s. My research group is collaborating with the Stanford Genome Technology Center (SGTC) in investigating magnetic nanoparticle-based approaches to cell separation (S. Crippen, J. Padovani, and recent Ph.D., K. L. Tsai). Dr. C. Gupta’s research is focused on demonstrating a new approach toward enabling the all-electronic spectroscopy of biomolecules. Polymers are the material of choice for microfluidic systems and N. Klejwa is exploring new fabrication processes that will allow rapid prototyping.
The second phase of the Center on Interfacial Engineering for MEMS (CIEMS) started in late June 2010 and provides research funding for the fundamental science and technology associated with several of these research thrusts. Dr. J Provine, the Research Associate for CIEMS at Stanford, is exploring nanophotonic structures for optical sensing, thermal lensing, and signal processing, in collaboration with Olav Solgaard’s group, as well as the applications of atomic-layer deposition (ALD) in NEMS. Dr. Provine collaborates with Roya Maboudian’s group at UC Berkeley in CIEMS-funded research on nano-tribology and graphene formation on silicon carbide layers. Selected slides from my talk at the recent N/MEMS 20/20 Workshop in Newport Beach, California, provide my perspective on some compelling opportunities for NEMS in this decade that are becoming feasible through CIEMS.