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2

Materials for

Microelectro-

mechanical Systems

2.1 Introduction ......................................................................2-1
2.2 Single-Crystal Silicon ........................................................2-2
2.3 Polysilicon ..........................................................................2-3
2.4 Silicon Dioxide ..................................................................2-9
2.5 Silicon Nitride ..................................................................2-11
2.6 Germanium-Based Materials ..........................................2-14
2.7 Metals ..............................................................................2-16
2.8 Silicon Carbide ................................................................2-17
2.9 Diamond ..........................................................................2-20
2.10 III–V Materials ................................................................2-22
Christian A. Zorman and
Mehran Mehregany 2.11 Piezoelectric Materials ....................................................2-22
Case Western Reserve University 2.12 Conclusions ......................................................................2-23

2.1 Introduction

Without question, one of the most exciting technological developments during the last decade of the 20th
century was the field of microelectromechanical systems (MEMS). MEMS consists of microfabricated
mechanical and electrical structures working in concert for perception and control of the local environ-
ment. It was no accident that the development of MEMS accelerated rapidly during the 1990s, as the field
was able to take advantage of innovations created during the integrated circuit revolution of the 1960s–80s
in terms of processes, equipment, and materials. A well-rounded understanding of MEMS requires a
mature knowledge of the materials used to construct the devices, as the material properties of each com-
ponent can influence device performance. Because the fabrication of MEMS structures often depends on
the use of structural, sacrificial, and masking materials on a common substrate, issues related to etch
selectivity, adhesion, microstructure, and a host of other properties are important design considerations.
A discussion of the materials used in MEMS is really a discussion of the material systems used in MEMS,
as the fabrication technologies rarely utilize a single material but rather a collection of materials, each

2-1

© 2006 by Taylor & Francis Group, LLC