Author Topic: Optimization of Capacitive MEMS Pressure Sensor for RF Telemetry  (Read 2377 times)

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Optimization of Capacitive MEMS Pressure Sensor for RF Telemetry
« on: November 23, 2011, 07:11:40 am »
Author : Prince Nagpal, Manish Mehta, Kamaljeet Rangra, Ravinder Aggarwal
International Journal of Scientific & Engineering Research Volume 2, Issue 10, October-2011
ISSN 2229-5518
Download Full Paper : PDF

Abstract — This paper describes the capacitive pressure sensor design for biomedical applications like blood pressure measurement. The described pressure sensors provide high sensitivity even at low pressure range suitable for biomedical applications. Effects of varying different parameters on the pressure sensor performance have been studied. From the results, the pressure sensors with compatible parameters can be selected for specific requirements. These compact pressure sensors are made up of biocompatible materials and can be implanted easily inside body to be used for RF telemetry purpose.

Key Words— MEMS, Capacitive, Diaphragm, Biocompatible, Biomedical

1   INTRODUCTION                                                                      
SENSORS are one of the most active applications of MEMS. With the achievements in miniaturization of MEMS devices, sensor’s applications have expanded not only for industry purpose but also for biomedical applications. Pressure sensors are one of the various types of sensors, where pressure is to be measured. One of the types of pressure sensor is capacitive pressure sensor. The capacitive pressure sensing technique’s performance in respect of sensitivity is better than rest all other microsensing techniques viz. piezoresistive microsensing, piezoelectric microsensing and resonant microsensing. And so is applicable to wide range of applications like automotive applications, industrial applications, biomedical applications and general & consumer applications. The capacitive microsensing technique utilizes the diaphragm-deformation-induced capacit-ance change to convert the information of pressure into electrical signals. The capacitance is computed in a 3D model using C = ε * ∫ (1/h) dA [1]
     As MEMS technology is promising to achieve com-pact sizes, here we have optimized the capacitive pres-sure sensor to be implanted inside the body for blood pressure measurement [2] like applications. MEMS technology offers the possibility to realize devices of hundreds of micrometers and diaphragms of thickness 1 micrometer only. Therefore these capacitive pressure sensors are required to respond very less changes in applied pressure. Some of the desired features to these capacitive pressure sensors include high sensitivity at low pressures, bio-compatibility and low profile. Using contamination insensitive [3] manufacturing process, smooth contacts [4] and additional touch points [1] sensitivity of capacitive pressure can be further improved.
     In this paper, effect of varying different paramaters of the capacitive pressure sensors for biomedical applications in pressure range from 0 to twice of atmospheric pressure has been studied.
     In this paper we demonstate three different possible geometries for capacitive pressure sensor are circular, square & rectangular. These pressure sensors are de-signed by having a silicon substrate, a silica bridge and a biocompatible diaphragm [5]. Details of the pressure sensors design and effect of varying geometry, surface area of diaphragm [6], diaphragm thickness, diaphragm dimensions and diaphragm material are described.


2.1 Design Specifications
The design of the circular capacitive pressure sensor analysed is shown in figure. On an silicon substrate of radius 283 µm and thickness 500 µm, a silica bridge has been mounted of thickness 300 µm on substrate perimeter of 30 µm width. A thin silicon diaphragm of 2 µm and 253.885 µm radius is than placed on mounted bridge to create a vaccum compartment be-neath it.
The pressure sensor’s performance with three different geometries is studied as shown in Fig. 2 in accordance with the following Table 1

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