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8

Micromechatronics

8.1 Modelling Micromechatronic Systems

8.1.1 Introduction

Micromechatronic or microelectromechanical systems (MEMS) represent a signif-
icant part of microsystem technologies. We will consider surface micromechanics
as an example here, because in this field it is often possible to design the process
steps for micromechanics to be compatible with those for microelectronics, which
permits an integration of electronics and mechanics on a die. The dynamic inter-
actions between electronics and mechanics often cannot be disregarded in such
systems. Rather, the desired functionality is often only achieved by the close cou-
pling between the domains. Furthermore, the natural frequencies of the mechanical
and electronic oscillations often lie in the same range. This tends to be rare for the
general case of an electro-mechanical system and is primarily associated with small
mechanical component dimensions in the range of a few tens to a few hundreds
of microns. With typical material parameters this yields mechanical resonance fre-
quencies in the megahertz range. Thus a coupled simulation is a crucial prerequisite
for the design of electro-mechanical microsystems.
A glance at the development of microelectronics over the last 20 years helps
to characterise the situation. The availability of efficient simulation tools was a
key factor for dynamic development of the integrated circuits. Precise and efficient
models of basic components were, and remain, vital prerequisites for this. In the
case of microelectronics only very few components, such as MOS transistors,
diodes, capacitors or resistors, have to be taken into account. The introduction
of micromechanics has changed matters. For MEMS a variety of nonelectrical
components, with a still much greater number of geometric variations, have to be
modelled, which leads to significant problems.
The modelling and simulation of MEMS can be considered on component or
system level. In the first case, the emphasis is placed upon the design and opti-
misation of micromechanics, the second case focuses on how a micromechanical
component behaves in the context of the system, i.e. within a circuit, for example,

Mechatronic Systems Georg Pelz
 2003 John Wiley & Sons, Ltd ISBN: 0-470-84979-7