Measurements of Resonance Frequency of Parylene Microspring Arrays Using Atomic Force Microscopy
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Measurements of Resonance Frequency of Parylene Microspring Arrays Using Atomic Force Microscopy
C. Gaire1, M. He1, A. Zandiatashbar2, P.-I. Wang1, R. C. Picu2, G.-C. Wang1 and T.-M. Lu1 1 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY, 12180, U. S. A. 2 Department of Mechanical, Aeronautical and Nuclear Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, NY, 12180, U. S. A. ABSTRACT A mechanical vibration system was made by sandwiching an array of parylene-C microsprings between two flat plates of Si. This system was driven mechanically in forced oscillation using a piezo transducer attached to the bottom Si plate. An atomic force microscope was used to record the displacement of the top plate in both the contact and non-contact modes. At the resonance, the system was observed to give large vertical displacement amplitude of up to 100 nm with a Q-factor of up to 900. INTRODUCTION Recent advents of micro- or nanospring arrays for optical interferometry [1], pressure sensing [2] and electromechanical actuation [3,4] have generated a significant interest in the use of such structures as elements of micro- and nanoelectromechanical systems (MEMS and NEMS). Most of the current MEMS or NEMS elements are made of Si microstructures that inherit the advantages of fabrication by planar processing techniques used in silicon microelectronic technology [5-7]. The use of microstructures made of polymers such as parylene as elements of MEMS or NEMS is less developed to date [8,9]. Due to its low elastic modulus, high structural flexibility, chemical robustness and ease of fabrication, parylene microstructures could play an important role in future MEMS or NEMS devices.The ability of an accurate measurement of natural frequency of such structures is required to gain control over the desired precision in the mechanical motion. Hence, resonance frequency measurement is one of the most important prerequisite of MEMS or NEMS elements. In this article, we present the results of resonance frequency measurement of a mechanical vibration system composed of an array of parylene-C microsprings using an atomic force microscope (AFM). The system contains several millions microsprings sandwiched between two Si plates. A piezoelectric transducer is used to drive the system from the bottom plate and the AFM is used to record the displacement of the top plate. EXPERIMENT Parylene spring growth The growth of parylene-C microsprings was carried out by oblique angle deposition [10]. We have employed a substrate swing rotation scheme during deposition to control the size and uniformity of the springs [11,12]. In short, the parylene vapor sublimated at 190 oC was passed
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through a pyrolysis furnace at 680 oC to convert to parylene-C monomers. This monomer flux was guided by a nozzle [10] and was deposited on Si(001) wafer at an angle of ~ 85o with respect to the substrate normal. The parylene-C monomers polymerize upon deposition onto the substrate [13]. Due to
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