Information Technology Reference
In-Depth Information
21 nm technology node. If adiabatic techniques to recover the dynamic com-
ponent of the energy consumption are used in conjunction with CMOS, only
0.040 fJ are required to switch a NAND gate (VII in Table
3
), mainly due to
the presence of leakage currents. In both cases our solution shows a remarkable
advantage over state of the art CMOS transistors and other NML clock systems
in terms of energy consumption.
3 Experimental Fabrication
We are currently experimentally validate the proposed clock solution. Our aim
is the demonstration of the working principle but also the characterization of
the structure in terms of power consumption. To enrich the explanation we also
present here a brief discussion on piezoelectric and magnetic materials required
by this clock system.
3.1 Piezoelectric Materials
Due to the fundamental role played by piezoelectric material in this clock sys-
tem, here an in-depth analysis of their state-of-the-art is presented. Moreover an
insight on the fabrication techniques commonly employed and the problematics
related to the dimensions scaling is given.
With the advent of the micro and nanotechnologies the development of
MEMS based on piezoelectric materials has gained growing and growing impor-
tance in the world of scientific research and a lot of attention is currently devoted
to the study of such materials. The possibility of combining piezoelectric sensors
and actuators with silicon-based CMOS technology, and to integrate them into
smart structures, allowing the implementation of a new class of devices which
integrate sensors and operate autonomously, converting mechanical energy into
dielectric displacement [
52
,
53
].
Among all functional ceramics, lead zirconate titanate (Pb(Zr1-xTix)O3,
PZT) attracted considerable attention thanks to the presence of excellent ferro-
electric and piezoelectric properties, becoming one of the most studied materials
of the last decade. It consists of a solid solution of lead titanate and lead zir-
conate, which can be present in different relative quantities. Piezoelectricity and
ferroelectricity of PZT are strictly related to the presence of a perovskite crystal
structure. The symmetry of the perovskite phase depends on the stoichiometry
of PZT, which influences also its electrical, dielectric, piezoelectric and ferro-
electric properties. A titanium-rich phase is responsible for the presence of the
tetragonal cell while a zirconium-rich composition gives rise to the presence of
a rhombohedral phase. It has been shown that there exists a particular value
of the ratio Zr/Ti for which the piezoelectric and ferroelectric properties are
maximized [
53
-
56
].
This condition is known as the morphotrophic phase boundary (MPB). When
Zr/Ti is around 53/47 the MPB is present and the dielectric/piezoelectric
Search WWH ::
Custom Search