Advanced Materials Research Vols. 403-408 (2012) pp 3769-3774 Online available since 2011/Nov/29 at www.scientific.net © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.403-408.3769
Design, Modeling and Simulation of CMOS-MEMS Piezoresistive Cantilever Based Carbon Dioxide Gas Sensor for Capnometry Asif Mirza1,a, Nor Hisham Hamid1, Mohd Haris Md Khir1, Khalid Ashraf1, *M.T.Jan1,, Kashif Riaz 2 1
Department of Electrical and Electronic Engineering,
Universiti Teknologi PETRONAS (UTP), Bandar Seri Iskandar¸ 31750, Tronoh, Perak, Malaysia. 2
Faculty of Electronic Engineering, GIK Institute of Engineering Sciences and Technology, Pakistan a
[email protected]
Key Words: Carbon dioxide, CMOS, Resonator, MEMS, Piezoresistive
Abstract. This paper reports design, modeling and simulation of MEMS based sensor working in dynamic mode with fully differential piezoresistive sensing for monitoring the concentration of exhaled carbon dioxide (CO2) gas in human breath called capnometer. CO2 being a very important biomarker, it is desirable to extend the scope of its monitoring beyond clinical use to home and ambulatory services. Currently the scope of capnometers and its adaption is limited by high cost, large size and high power consumption of conventional capnometers . In recent years, MEMS based micro resonant sensors have received considerable attention due to their potential as a platform for the development of many novel physical, chemical, and biological sensors with small size, low cost and low power requirements. The sensor is designed using 0.35 micron CMOS technology. CoventorWare and MATLAB have been used as simulation software. According to the developed model and simulation results the resonator has resonant frequency 57393 Hz and mass sensitivity of 3.2 Hz/ng. The results show that the longitudinal relative change of resistance is 0.24%/µm while the transverse relative change of resistance is -0.03%/µm. Introduction Capnometry deals with the monitoring of concentration of CO2 in exhaled breath and has a wide range of applications including monitoring of correct positioning of endotracheal tubes, accidental extubation and suppressed breathing conditions under the influence of anesthetic agents [1]. Patients breath monitoring during treatment of cardiac arrest, asthma and pediatric trauma etc. are other reported applications of capnometry. Medical organizations such as the American Society of Anesthesiologists (ASA), the American Association for Respiratory Care (AARC), and the American Hospital Association (AHA) have all adopted standards and guidelines for CO2 monitoring. In many states of US such as Florida and New York, laws have been enforced that every ambulance be equipped with a CO2 measurement device. CO2 monitoring has been adopted in different countries Europe as a result of either societal standards or individual country law. Infra-red analyzers and mass spectrometers are used as current measurement systems for CO2 gas monitoring. Mass spectrometers are popular due to fast response time, ability to measure dry gases, accuracy, stability of measures and measuring multiple gases simultaneously [2]. However higher cost, large size and preventive maintenance are some factors limiting the use of spectrometers. When cost and space are not an issue, they remain the premier system for respiratory gas analysis. The most common approach for CO2 detection is the use of simplest spectroscopic sensors which includes non-dispersive infrared (NDIR) sensors [3-5]. Key components of NDIR sensors are an infrared source, a light tube, an interference filter and an infrared detector. Limitations of this technology are due to physical size and power consumption. To overcome above mentioned limitations, an alternate technology is needed to fabricate low cost, low power consuming, easy to calibrate and a portable CO2 sensor for capnometric uses in ambulatory services and home. In recent years, MEMS based micro resonant sensors are capturing market and becoming popular due to their involvement in many novel physical, chemical, and biological sensors with small sizes, low cost and low power requirements [6]. Cantilever based sensors have been also proven to be very sensitive, recent developments have reported sensing of gases in parts per billion and even attogram-level mass measurements. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 121.52.144.99-30/11/11,08:09:17)
