Performance Evaluation of Embedded Strain Sensing Varying Thickness Polymer Micro-cantilever as Biosensor Platform
Abstract – High deflection sensitivity of micro-cantilever is one of the important criteria for cantilever being used as a sensor as well as an actuator. Also resonance frequency of these sensors needs to be higher for biosensing applications. Varying thickness cantilever satisfy these desired criteria as compared to constant thickness micro-cantilever of similar length and width. Deflection sensitivity of polymer based cantilever is further enhanced by its low value of Young’s Modulus. Among various techniques of detection, piezoresistive based technique is treated as the most suitable detection technique for micro-cantilever in bio-sensing applications. Taking all these aspects into consideration, this paper presents design of varying thickness micro-cantilever and its simulations.The proposed varying thickness cantilever consists of strain sensing embedded piezoresistive material. The study also presents the optimization of dimensions of multi-layer varying thickness micro-cantilever with objective of high sensitivity and resonance frequency. The paper also presents the fabrication methodology and materials for fabrication of varying thickness multilayer varying thickness micro-cantilever. The electromechanical and mechanical performance characterization of this micro-cantilever is further evaluated. This paper uses Finite Element Method (FEM) to obtain the performance of piezoresistive micro-cantilever sensor by optimizing the geometrical dimensions of both cantilever and piezoresistor. CoventorWare a commercial FEM tool for MEMS device design and simulation is used for this work. It is observed that the deflection sensitivity, change in resistance due to stress for this proposed micro-cantilever is quite higher than the normal rectangular micro-cantilever
Keywords—Polymer, FEM, Biosensing,Piezo, Bulklithography, Direct Laser Write
INTRODUCTION
Micro Electro Mechanical Systems (MEMS) technology which deals with the fabrication of devices in the micron scale using a silicon processing technology has generated a noteworthy amount of attention due to the enhanced performance and cost benefit and it also covers the wide range of sensors and actuators. Like other several MEMS sensors, micro-cantilever based biosensors have also fascinated substantial importance to monitor a particular substance in applications such as chemical analysis, environmental control and industrial processes [1]. In these applications, micro cantilever either works on the principle of surface stress, bulk stress or mass changes. In first two modes micro-cantilever bends due to molecules attaching on one side of the cantilever or changes in temperature or humidity. In third mode its resonance frequency shifts due to mass loading. Among various detection techniques, piezoresistive read out has several advantages [2]. This technique is characterized by Gauge factor of the piezoresitive material. Doped Polysilicon, Gold (Ag), SU8-CB mixture, SU8-Ag nano particles mixture and Indium Tin Oxide (ITO) are some of the piezoresitive materials [2] [3] [4] [5] [6].