Fabrication and Electromechanical Properties of Conductive Polymer Microbridge Actuators
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Fabrication and Electromechanical Properties of Conductive Polymer Microbridge Actuators Guandong Zhang1, Joao Gaspar1, Virginia Chu1 and Joao Pedro Conde1,2 1 Instituto de Engenharia de Sistemas e Computadores - Microsistemas e Nanotecnologias (INESC-MN), Rua Alves Redol, 9, 1000-029 Lisbon, Portugal. 2 Department of Chemical Engineering, Instituto Superior Técnico (IST), Portugal, Av. Rovisco Pais, 1049-001 Lisbon, Portugal. ABSTRACT This paper reports on the fabrication of novel all-polymer microbridge electrostatic actuators based on conductive polymers and using surface micromachining on glass substrates. The electromechanical properties of the microbridges are studied using electrostatic actuation and optical and electrical detection. The pull-in phenomena and a dependence of the bridge deflection with the square of the applied voltage are observed. Compared to the silicon-based microbridges, the polymer structures present higher deflection amplitude for the same applied electrical force. The resonance frequency of the polymer bridges occurs in the MHz range and with quality factors of the order of 100 when measured in vacuum. The mechanical properties of the polymer device are affected by the residual stresses.
INTRODUCTION Microelectromechanical systems (MEMS) refer to a class of microsensors and actuators which, with a three dimensional structure, can sense its environment and have the ability to react to changes in that environment. Currently, the majority of MEMS are fabricated using siliconbased materials [1]. Recently, there has been intense interest in the development of polymeric materials for application in electronic devices [2] and MEMS [3] due to their relative low cost and simple processing. In addition, polymer materials are flexible, chemically and biologically compatible, available in many varieties, and can be fabricated in truly 3-D shapes. However, polymer microfabrication techniques are still not well developed and studies are just beginning to be made of the mechanical properties of polymeric microstructures [4]. In the past, polymer electrostatic actuators and resonators have used a metal layer on the polymer structure surface to increase its electrical conductivity [5,6] and the metal layer dominated the mechanical behavior of the devices. In this work, a conductive polymer is used to create all-polymer microbridges fabricated on glass substrates using surface micromachining. The electromechanical properties of these microbridges are presented.
EXPERIMENTAL PROCEDURES For an electrostatic resonator, both the bridge and the gate electrodes must be conductive enough to ensure that the charging/discharging frequency, 1/RC, of the formed capacitor is higher than the actuation frequency. The fabrication process described below is developed to minimize the degradation of the electrical properties of the polymer during processing and to
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allow the polymer microbridge to retain sufficient conductivity (resistance below 50 MΩ) to function as a resonator. A blended conductive
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