298 Design of CMOS Millimeter-Wave and Terahertz Integrated Circuits
Figure 14.1: The layout and E-ﬁe ld distribution o f the on -chip
SPP/conventional T-line in lossy substrate environment, d, h, a, w
denotes the periodic pitch, groove depth, groove width and line width
oﬀ SPP T-line, respectively. The magnetic ﬁeld of SPP T-li ne is di-
rected to the x direction while the electrical ﬁeld is guided by the
grooves in the y-z plane.
[291, 292, 293]. By introducing sub-wavelength periodic corrugation structure
onto the T-line, SPPs can be established to propagate signals with strongly
localized surface-wave in the metal/dielectric interface at frequency up to
THz. Such a surface-wave can be supported with propagation adapted to the
curvature or holes of the surface [294, 169, 295, 296, 297, 298, 299, 30 0, 301].
Previous works have demonstrated GHz SPP T-lines on board level with bulky
size and loss [294, 169, 295, 296, 297, 298]. In this work, SPP T-line is inves-
tigated at the THz region in the standard CMOS process that shows great
potential for system-on-chip integration with other components in CMOS for
on-chip THz communication.
The physical layout of the proposed structure is illustrated in Figure 14.1.
Two on-chip SPP T-lines are placed back-to-back to form a broadband low-
loss, low-cr osstalk coupler. Such a plasmonic metamaterial consists of a metal
strip with thin ﬁlm thickness, in which a 1D periodical a rray of grooves is
drilled. The propagatio n of surface-conﬁned mode is adapted to the curva-
ture of the surface, and the resulting cr osstalk between the two back-to-back
placed SPP T-lines will be reduced signiﬁcantly. For comparison, two tradi-
tional quasi-TEM T-lines are also realized to form an on-chip coupler with
line space of 2.4 µm in standard 65 nm CMOS process, which shows la rge loss
and strong crosstalk at THz. Measurement results show that the SPP T-lines
achieve wide-band reﬂection coeﬃcient lower than -14 dB and the crosstalk
ratio better than -24 dB, which is 19 dB lower on average than the traditional
T-lines from 220 GHz to 325 GHz. The compact and wide -band SPP T-lines
have shown great potential for on-chip THz communication.