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MEMS in biomedical applications

Abstract
Micromachining and MEMS
technologies can be used to produce complex
electrical, mechanical, fluidic, thermal, optical,
and magnetic structures, devices, and systems
on a scale ranging from organs to subcellular
organelles. This miniaturization ability has
enabled MEMS to be applied in many areas of
biology, medicine, and biomedical engineering –
a field generally referred to as BioMEMS. The
future looks bright for BioMEMS to realize (1)
microsensor arrays that act as an electronic
nose or tongue, (2) microfabricated neural
systems capable of controlling motor or sensory
prosthetic devices, (3) painless microsurgical
tools, and (4) complete microfluidic systems for
total chemical or genetic analyses.

INTRODUCTION

Microelectromechanical systems (MEMS) is a
technology of miniaturization that has been largely
adopted from the integrated circuit (IC) industry and
applied to the miniaturization of all systems (i.e., not
only electrical systems but also mechanical, optical,
fluidic, magnetic, etc). Miniaturization is
accomplished with microfabrication processes, such
as micromachining, that typically use lithography,
although other non-lithographic precision
microfabrication techniques exist (FIB, EDM, laser
machining). Due to the enormous breadth and
diversity of the field of MEMS, the acronym is not a
particularly apt one. However, it is used almost
universally to refer to the entire field (i.e., all devices
produced by micromachining). Other names for this
general field include “microsystems”, popular in
Europe, and “micromachines”, popular in Asia.

For a discussion of the early work in MEMS,
including many of the seminal papers, the interested
reader is directed to reference [1]. For a
comprehensive discussion of micromachining
processes and MEMS devices, the interested reader
is directed to the texts by Kovacs [2] and Madou [3].
MICROFABRICATION
Although many of the microfabrication techniques
and materials used to produce MEMS have been
borrowed from the IC industry, the field of MEMS has
also driven the development and refinement of other
microfabrication processes and non-traditional
materials.
Conventional IC Processes and Materials:
- photolithography; thermal oxidation; dopant
diffusion; ion implantation; LPCVD; PECVD;
evaporation; sputtering; wet etching; plasma
etching; reactive-ion etching; ion milling
- silicon; silicon dioxide; silicon nitride; aluminum
Additional Processes and Materials used in MEMS:
- anisotropic wet etching of single-crystal silicon;
deep reactive-ion etching or DRIE; x-ray
lithography; electroplating; low-stress LPCVD
films; thick-film resist (SU-8); spin casting;
micromolding; batch microassembly
- piezoelectric films such as PZT; magnetic films
such as Ni, Fe, Co, and rare earth alloys; high
temperature materials such as SiC and ceramics;
mechanically robust aluminum alloys; stainless
steel; platinum; gold; sheet glass; plastics such as
PVC and PDMS

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