U. Glaeser

FIGURE 2.92 Steep subthreshold slope in FD device.
FIGURE 2.93 No need for body contacts in FD device.
depletion layer capacitance in the bulk Si device, C dep, is a series connection of the body depletion layer
capacitance, C Si, and the buried oxide layer capacitance, C BOX, and the controllability of the gate voltage
with respect to the channel surface potential is improved.
Furthermore, from the viewpoint of circuit design, the superiority of the FD-SOI device relative to
the PD-SOI device is that the kink phenomenon does not appear in the drain voltage current characteristic
(Fig. 2.89), and, further, that dynamic instabilities such as changes in V th caused by the floating body
effect during circuit operation are small [23]. As a result, there is an advantage in terms of the layout
area, because there is no need for body contacts including for analog circuits, and it is also possible for
the layoutss and other such design assets that have been used for bulk Si to be used as they are (Fig. 2.93).
An example of a prototype FD-SOI device LSI that takes advantage of the features described above that
was newly announced at the ISSCC is shown in Table 2.6.
Low-Power, Mixed-Signal LSI Application
Further advancement of portable systems in the form of wearable information equipment with a wireless
interface will enable us to enjoy various multimedia applications anywhere and anytime. The realization
of wearable communication devices requires lower power consumption, ultra-compactness, reduced
© 2002 by CRC Press LLC
SiO 2
n + p
Si Substrate
S = (kT/q) ln (10)
(1 + C dep /C ox )
~ (kT/q) In(10)
~ 60 mV/dec
n +
C Si
n +
C BOX
Cdep 1/CSi + 1/CBOX in SOI
Cdep /Cox