8 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
testing as well as 3D imaging. However, there are several drawbacks in the
optics-based time domain THz spectroscopy and imaging system. Firstly, the
optics-based THz system is us ually bulky, expensive and lacks portability.
For example, a Ti:Sapphire laser source is usually required for femtosecond
pulse generation, and lots of mirrors and lenses are needed for optical path
adjustment. Secondly, the detection resolution and efficiency a re limited. The
absorption and reflection properties of tissues are usually spectral specific. As
such, low spectrum res olution in frequency domain results.
1.2 CMOS THz Electronics
The THz imaging system can be potentially implemented by elec tronic ap-
proaches. With the rapid scaling of CMOS technology, it has become feasible
to realize integrated circuits with standard CMOS process in THz regime to-
wards a low-cost, portable and large-arrayed THz imaging system on a chip.
Recently, several CMOS-based tr ansmitting and receiving components have
been developed in THz [31, 32, 33, 34, 35]. As shown in Fig. 1.4(a) from [6],
when the size of transistors is scaling down, the gap between CMOS transis-
tors and three five-group transisto rs is getting smaller and smaller. The ITRS
(Internatio nal Technology Roadmap for Semiconductors) projected roadmap
of f
t
and f
max
for NMOS transistors is shown in Figure 1.4(b). By the year
2020, the f
max
of CMOS transistors will be higher than 1THz. Compared to
the other semiconductor fabrication processes like SiGe, InP or GaAs, stan-
10010
1
10
100
1,000
1,000
Record graphene FET
Record CNT FET
FET C
FET B
2,000
Gate length (nm)
InP HEMT, GaAs mHEMT
Si MOSFET
GaAs pHEMT
CNT FET
Graphene FET
FET A
(a)
(b)
Figure 1.4: (a) Comparing cut-off frequencies for different FETs [6];
(b) ITRS projected f
max
and f
t
of NMOS transistors.
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