MEMSTECH’2007, May 23-26, 2007, Lviv-Polyana, UKRAINE

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An Analysis of Material Choices for Capacitive Microaccelerometers

Yu. Kushnir, V. Teslyuk, P. Turchenko

Abstract – in this paper, a reaction of deformations and stresses upon admixtures variation in an accelerometer is analyzed. Keywords – MEMS, CAD, accelerometer, material.

I. INTRODUCTION Recent scientific activity has been performed actively in the

field of microsystems. Being now a brand new trend, they seem to penetrate most life issues. Microelectromechanical systems are becoming yet more popular and even move aside a lot of common macro scale devices. The rapid evolution of the branch stimulates great numbers of theoretical and applied works striving towards improvement of different MEMS development and utilization parameters. While performing theoretical investigations, bare formulae are often enough. In the case of MEMS this is not confirmed in practice. Usually, thorough applied research is needed in order to ensure reliable and adequate performance of micro scale systems. However, it is worth mentioning here that practical realization and testing of MEMS devices is relatively hard, long, and expensive work, especially in case of reengineering [1]. The helping hand is a large amount of CAD systems allowing relatively reliable investigation of different parameters important for MEMS development. In this paper, the work done in the field of microaccelerometers [2] is continued.

II. INFLUENCE OF MATERIAL CHOICE UPON ACCELEROMETER FUNCTIONALITY

The microaccelerometer considered in this work is presented in Fig. 1. Its construction includes a seismic mass exposed to acceleration and a number of parallel beams functioning as shifting capacitors [2].

Fig.1. Capacitive microaccelerometer.

The performance principle of the device is based upon deformation of the construction under the influence of outer force, which causes capacitance shifts. The shifts are detected by sensing schemes attached to the device. A decision making intelligent device reacts to the shift through certain kinds of

actuation. The key problem appearing while developing the device is to calculate capacitance shifts [2] and to test how

these shifts depend upon the material used while device development. To provide approximate previous calculations of this reaction, the integrated CAD system ANSYS v.8.0 has been used. Below a table is presented, showing the maximal deformation and stress values for a number of materials applied in MEMS (the gravity applied is constant and equal to 100000g).

TABLE 1

Material Displacement (μm) Stress (MPa)

Si 0.0266 3.07

poly Si 0.0186 2.91

SiC 0.0176 4.15

SiO2 0.0437 3.15

Si3N4 0.0190 4.60

The results presented in the chart show that different admixtures provide silicon with different parameter deviations. Thus, it is predicted to be possible to find an optimal material combination with maximal deformation (in allowed rates) and minimized stress values allowing higher reliability of the device. The optimal deformation itself can vary in certain frames allowing the developer set the device according to the sensitivity requirements.

III. CONCLUSIONS In this paper, microaccelerometer sensitivity upon material

admixtures has been considered. The ANSYS aided analysis allows proclamation of tuning possibilities for accelerometer development on stages before manufacturing.

REFERENCES

[1] T. Sviridova, Y. Kushnir, D. Korpyljov “An overview of MEMS testing technologies” [2] V. Teslyuk, Yu. Kushnir, R. Zaharyuk, M. Pereyma “A computer aided analysis of a capacitive accelerometer parameters” Yuri Kushnir – CAD/CAM Department, Lviv Polytechnic National University, 12, S. Bandery Str., Lviv, 79013, UKRAINE, E-mail: ravnen@rambler.ru Vasyl Teslyuk – CAD/CAM Department, Lviv Polytechnic National University, 12, S. Bandery Str., Lviv, 79013, UKRAINE Pavlo Turchenko – CAD/CAM Department, Lviv Polytechnic National University, 12, S. Bandery Str., Lviv, 79013, UKRAINE