Biomedical Engineering Reference
In-Depth Information
11.1
INTRODUCTION
Nanotechnology refers to the manipulation, precise placement, measurement, modeling or manu-
facture of sub-100-nm scale matter
[1]
. In other words, it has been described as the ability to work
at atomic, molecular, and supramolecular levels (on a scale of ~1-100 nm) to understand, create,
and use material structures, devices, and systems with fundamentally new properties and functions
resulting from their small structure
[2]
. The technology has been approached in two ways: from the
“top-down” or the “bottom-up” approach. The “top-down” approach is nothing but the utilization of
miniaturization techniques to construct micro/nanoscale structures from a macroscopic material or a
group of materials by utilizing machining or etching techniques. The best example of a “top-down”
approach is the photolithography technique used in the semiconductor industry to fabricate compo-
nents of an integrated circuit (IC) by etching micro/nanoscale patterns on a silicon wafer
[3]
. The
“bottom-up” approach refers to the construction of macromolecular structures from atoms or mol-
ecules that have the ability to self-organize or self-assemble to form a macroscopic structure
[4,5]
.
In other words, the “bottom-up” approach has been referred to as “molecular nanotechnology”
[6]
.
Nanotechnology has much more to offer than just simple miniaturization and building the molecular
structures from the atomic scale. By investigating and understanding the functionality of materials
at the micro/nanoscale level, the scientific community is working toward finding new techniques to
achieve maximum functional output from these materials with minimum energy and resource input.
In short, microfabrication techniques along with nanotechnology have offered us the ability to design
materials with totally new desirable characteristics. These micro/nanomaterials fabricated by “top-
down” or “bottom-up” approach has been effectively applied in many areas of science and engineer-
ing: physics, chemistry, material science, computer science, ultraprecision engineering, fabrication
processes, and equipment designing
[7]
. Microfabrication techniques are also utilized in interdiscipli-
nary research bridging physics-chemistry-material science with biomedical science, for example, in
the fabrication of microelectromechanical systems (MEMS) for biosensor applications (diagnostics,
sensing, and detection) and in the field of pharmacotherapeutics and medical health care toward novel
drug delivery techniques, gene therapy, hybrid devices, and 3D artificial organs, to mention a few
[8]
.
11.2
MICROFABRICATION
“Microfabrication” or “micromanufacturing” are the terms used to describe techniques to fabricate
miniature structures of microscale level and smaller. In other words, it is the “top-down” approach.
Historically the earliest microfabrication was used in IC fabrication for semiconductor devices.
Microfabrication technologies originate from the microelectronics industry and the devices were usu-
ally made on silicon wafers even though glass, plastics, and many other substrates are in use cur-
rently
[7,8]
. Micromachining, semiconductor processing, microelectronic fabrication, semiconductor
fabrication, MEMS fabrication, and IC technology are the terms used instead of microfabrication,
but microfabrication is the broad general term. Some of them have very old origins, not connected to
manufacturing, like lithography or etching. Polishing was borrowed from optics manufacturing, and
many of the vacuum techniques come from nineteenth century physics research. Electroplating is also
a nineteenth century technique adapted to produce micrometer scale structures, as are various stamp-
ing and embossing techniques
[9]
.
