AVS 49th International Symposium
    Microelectromechanical Systems (MEMS) Wednesday Sessions
       Session MM+NS-WeM

Paper MM+NS-WeM7
Fabrication of Submicron-Scale Metallic Comb-Drive Actuators

Wednesday, November 6, 2002, 10:20 am, Room C-210

Session: Nanotechnology and Nanofabrication in NEMS
Presenter: S.W. Park, The University of Texas at Dallas
Authors: S.W. Park, The University of Texas at Dallas
N.A. Kumar, The University of Texas at Dallas
J.B. Lee, The University of Texas at Dallas
Correspondent: Click to Email
Comb-drive actuators have been widely used for more than a decade in many applications including resonators, accelerometers, and tunable capacitors with the advance of micromachining technologies. While single crystal or poly Si have been preferred materials for comb-drive actuators, metallic high aspect ratio comb-drive actuators were also of interest due to its electrical property such as lower resistivity in some applications. In this paper, we report the development of fabrication of a sub-micron scale (sub-micron gap and width) all metallic comb-drive actuator with small overall foot-print. All metallic comb-drive actuators with sub-micron gap/width and small foot-print have many advantages over traditional silicon-based micron scale comb-drive actuators. Such advantages include large increase of capacitance per unit area (good for sensing applications) and higher quality factor due to low equivalent series resistance of the metallic comb-finger structures (good for tunable capacitor application). The comb-drive actuator was designed as a tunable capacitor and intensive modeling of such tunable capacitor was carried out. Fabrication of such comb-drive actuators was started with a multiple spin-coatings of polymethyl methacrylate (PMMA) or SU-8 on an oxidized silicon substrate. PMMA was investigated for low aspect ratio and SU-8 was investigated as a potential electron beam photoresist for high aspect ratio comb-drive actuator fabrication. Numerous experimental runs were performed to find optimum exposure doses, developing conditions, etc. Different metals such as Cu, Cr, Ti/Cu, and Cr/Cu were investigated as candidate materials for comb-drive actuators. Optimum fabrication process based on PMMA was developed for 1:1 aspect ratio all metallic 500-nm width/gap comb-drive actuator. Preliminary results on negative tone SU-8 resist based comb-drive actuator with a goal of achieving high aspect ratio (up to 5:1 aspect ratio) structure will also be reported.