International Journal of Computer Applications (0975 – 8887) International Conference on Microelectronics, Circuits and Systems (MICRO-2014) 12 A Study of Silicon based MEMS Capacitive Sensor for Absolute Pressure Measurement of a Specific Range Priya Singha Roy 1 , Deborshi Chakraborty 2 , 3 Madhurima Chattopadhyay 1 Dept. of Applied Electronics and Instrumentation Engineering Techno India College of Technology, Kolkata-700 156, India 2 Dept. of Instrumentation Science, Jadavpur University, Kolkata: 700 032, India 3 Dept. of Applied Electronics and Instrumentation Engineering Heritage Institute of Technology, Kolkata-700 007, India ABSTRACT In this paper two MEMS capacitive pressure sensor of two diffident geometries are designed for measurement of absolute pressure. Both of these sensors are designed as parallel plates where one is movable and the other is fixed. The only difference with common parallel plate structure is that one of the movable plates is supported by four anchors with respect to the fixed plate. Here we have considered two such structures, one having square shaped parallel plates whereas the other having circular shaped. The area of the diaphragms for both the sensors are equal and will perform to sense absolute pressure variations for a very specific range. This specified range of absolute pressure is 10 KPa to 100 KPa for 5 micron thick diaphragm with 3600 micrometer area. Here silicon and silicon compound (like PolySi and SiC) are chosen for diaphragm material. In this paper various factors which play a critical role for measuring absolute pressure in the performance of a MEMS capacitive pressure sensor are discussed. Factors like length, radius, thickness, distance between two plates and shape and more above the selection of diaphragm materials are taken into consideration for the efficiency of the sensor. Mechanical, electromechanical as well as material studies were performed in the Finite Element Method based Multiphysics simulation platform. In this paper two same area different shape micro sensors are designed and their comparative study is analyzed with different silicon compound. This type of absolute pressure measuring sensor can be used for pulse rate measurement. Keywords: Capacitive pressure sensor, MEMS, Finite Element Method (FEM), Si, PolySi, SiC, absolute pressure 1. INTRODUCTION Absolute pressure measurements are of great importance in almost all field of engineering and industrial application. Microelectronics has known very important development. Specific manufacturing techniques have been developed to reduce the cost of objects using this technology. In particular, Micro Electromechanical Systems, called by the acronym MEMS, which combine mechanical, optical, electromagnetic, thermal and fluidic in electronic semiconductor substrates drivers, have benefits widely of this development. Most absolute pressure sensors which are based on piezoresistive effect are the common type. However in the past years capacitive absolute pressure sensors have received attention due to several advantages in comparison to piezoresistive absolute pressure sensor. The main disadvantage of the piezoresistive absolute pressure sensor is the inherent temperature dependence of piezoresistive coefficients [1].Capacitive pressure sensor has lower power consumption than piezoresistive pressure sensor [2]. But piezoresistive pressure sensor most widely used than capacitive pressure sensor because of two reason. Capacitive structure is more complicated to fabricate and the capacitive sensing principle is sensitive to parasitic capacitances. The structure of the capacitive pressure sensor is more complicated, because it involves formation of a cavity that separates the two sensing electrodes from each other. Formation of such a cavity is done in two different ways. For first case multiple film depositions and etch of a buried sabscrificial layer [3–6] or in second case bonding after the cavity has been etched into one of the wafer. Wafer bonding is done by fusion bonding of two silicon wafers [7–9] or anodic bonding of a silicon wafer and a glass wafer [10, 11]. Capacitive absolute pressure sensors are required in applications including bio-medical systems, environmental monitoring and industrial process control. Capacitive absolute pressure sensors provide low noise, high sensitivity, have low temperature sensitivity and are preferred in many emerging high performance applications and can with stand a lot of vibration. Here we have considered two such geometries, one having square shaped parallel plates whereas the other having circular plates. Both of the sensors are designed in such a manner that their areas are equal and will perform to sense absolute pressure variations for a very specific range. This specified range of absolute pressure is 10 kpa to 100 Kpa for 5 micron thick diaphragm with 3600 micrometer area. Silicon and silicon compound like PolySi (polysilicon) and SiC(silicon carbide) are chosen for diaphragm materials and performance is analyzed. It is also analyzed the effect of length, radius, thickness, distance between two plates and shape. More above the selection of diaphragm materials are taken into consideration for the efficiency of the sensor Mechanical, electromechanical as well as material studies were performed in the Finite Element Method based Multiphysics simulation platform. This paper explores the design parameters of MEMS based diaphragm type capacitive pressure sensor with anchors using FEM (Finite Element Modeling) [12] based Multiphysics software. Mechanical and electromechanical studies are performed. Sensor designing is given on section II. The chosen materials properties are given in section III. The analyzed results are in the form of 2-D plots in section IV as results and discussion. The outcome of this designed sensors are discussed and compared against their efficiencies. Materials performance are given in section V. The concluding remarks from these analyses are described in section VI.