Page 17 - Principles and Applications of NanoMEMS Physics

1. NANOELECTROMECHANICAL SYSTEMS 3

and pressure sensors, on the one hand, and a number of emerging devices,
such as, gyroscopes, flow sensors, micromotors, switches, and resonators, on
the other. Coinciding, as they do, with the dimensional features germane to
ICs, i.e., microns, these mechanical devices whose behavior was controlled
by electrical means, exemplified what has come to be known as the field of
microelectromechanical systems (MEMS).
Three events might be construed as conspiring to unite nanoelectronics
and MEMS, namely, the invention of a number of scanning probe
microscopies, in particular, scanning tunneling microscopy (STM) and
atomic force microscopy (AFM), the discovery of carbon nanotubes (CNTs),
and the application of MEMS technology to enable superior RF/Microwave
systems (RF MEMS) [16-18]. STM and AFM, by enabling our ability to
manipulate and measure individual atoms, became crucial agents in the
imaging of CNTs and other 3-D nanoscale objects so we could both “see”
what is built and utilize manipulation as a construction technique. CNTs,
conceptually, two-dimensional graphite sheets rolled-up into cylinders, are
quintessential nanoelectromechanical (NEMS) devices, as their close to 1-
nm diameter makes them intrinsically quantum mechanical 1-D electronic
systems while, at the same time, exhibiting superb mechanical properties.
MEMS, on the other hand, due to their internal mechanical structure, display
motional behavior that may invade the domain of the Casimir effect, a
quantum electrodynamical phenomenon elicited by a local change in the
distribution of the modes in the zero-point fluctuations of the vacuum field
permeating space [19-21]. This effect which, in its most fundamental
manifestation, appears as an attractive force between neutral metallic
surfaces, may both pose a limit on the packing density of NEMS devices, as
well as on the performance of RF MEMS devices [22].
In the balance of this chapter, we present the fundamentals of the
fabrication techniques which form the core of NanoMEMS devices, circuits
and systems.

1. 2 NanoMEMS Fabrication Technologies

NanoMEMS fabrication technologies extend the capabilities of
conventional integrated circuit (IC) processes, which are predicated upon the
operations of forming precise patterns of metallization and doping (the
controlled introduction of atomic impurities) onto and within the surface and
bulk regions of a semiconductor wafer, respectively, with the performance of
the resulting devices depending on the fidelity with which these operations
are effected. Excellent books on IC fabrication, giving in-depth coverage of
the topic, already exist [23] and the reader interested in process development