Electro-mechanical investigation of polycrystalline silicon microcantilever

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Supervisor:
Dr. Szabó Péter Gábor
Department of Electron Devices

Abstract

Electro-mechanical analysis of Poly-crystalline Si micro-cantilever

Introduction

Significant numbers of the environmental or clinical analytic tests are aimed to quantitatively or qualitatively analyse the presence of different molecules in air or liquid samples. The micro and nanotechnology based sensing principles enable the development and realisation robust, user-friendly and cost-effective analytic platforms. Besides the sensing applications of the nanostructure based devices the mechanical principles have notable importance. Due to the scaling down the mechanical sensors has been reaching the range of 10pNs sensitivity, and the zeptogram resolution in molecular recognition. The basic element of several biosensor applications is the suspended microcantilever utilizing the surface stress monitoring or the dynamic mode sensing as detection principle. The surface stress monitoring is based on the measurement of the cantilever deflection caused by the molecular adsorption on the surface of the mechanical structure. The dynamic mode sensing is analysing the characteristic frequency shift of the actively oscillating (actuated) system.

Experimental results

The aim of the experimental work was to characterise the electro-mechanical behaviour of micro- and nanofabricated polycrystalline silicon cantilever structures, utilizing theoretical, numerical and experimental methods. These suspended mechanical structures allow us achieving adequately high parameter response as the function of the environmental changes due to their extremely high sensitivity.

Poly-crystalline silicon based suspended micro-cantilever structures were designed and fabricated by using the micromachining technology of MTA EK MFA MEMS Laboratory providing precise 3D microsctructuring of thin films. Considering the significant process parameter dependence of the thin films’ properties, our goal was to determine their material parameters (specific resistivity, piezorezistive components and mechanical coefficients) and to compare against the literature. Accordingly, the electro-mechanical behaviour of the structures was analysed by the comparison of the results of finite element modelling (FEM) and experiments. The fabricated microsystems were characterised by optical (laser position sensitive detection) and electrical (piezoresistive) methods. I developed a dedicated electromagnetic and mechanical based methods to achieve controlled actuation of the structures. Considering the proposed analytical application I aimed to analyse mostly the mechanical parameters (deformation, Eigenfrequency, quality factor).

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