Biology Reference
In-Depth Information
6.2.1
Field-Effect Transistor Technologies
One of the major advantages of employing FETs in sensor
applications is their mature manufacturing technology. Due to the
development of the microelectronics industry, the microfabrication
process has been well established allowing FETs to be mass-
produced with extremely high yield. Thin layers of materials can be
deposited on large areas of substrates and patterns of the device
can be created by lithography, through customized masks which
can be reused. The cost of each device is mainly determined by
the substrate area and production volume, making it possible to
fabricatecomplexsensorarraysataffordablecosts.Thisisespecially
attractive for biosensor applications, as disposability is a highly
emphasized feature to avoidcontaminations.
6.2.1.1 Single crystalline silicon and CMOS
Traditional FET transistors are fabricated on a single crystalline
silicon wafer of a few hundred micrometer thickness. The silicon
crystallineframeworkishomogenousandcontinuouswithverylow
levels of defects. The electron mobility,
μ
,isthereforeatahighlevel,
rangingfromfewhundredstooverathousandcm
2
V
−
1
s
−
1
,enabling
high performance devices to be fabricated. In addition with the
abundance of material, cost-e
ciency, and well-understood device
physics, single crystalline silicon has been the most widely used
substrate material in themicroelectronics industry.
Complementary metal-oxide-semiconductor (CMOS) is a sin-
gle crystalline silicon-based semiconductor fabrication technology,
which distinguishes itself from other types of fabrication technolo-
gies by providing both n-type (as shown in Fig. 6.2a) and p-type
MOSFETs on the same substrate. It has been used predominantly in
microprocessors, memories, and other digital logic circuits due to
its low power consumption and unmatched production yield. CMOS
technology is also used for a wide variety of analog circuits such as
image sensors, data converters, and transceivers.
Driven by the microelectronics industry, the CMOS fabrication
process has been continuously refined to make smaller MOSFETs,
which are both faster and more cost-e
cient. The state-of-the-art
