Page 54 - A Practical Guide from Design Planning to Manufacturing

30 Chapter One

same frequency as the previous generation, which has been gradually
improving since its launch.
The motivation for the new compaction is not only the immediate
reduction in cost due to a smaller die size, but the potential that it will
be able to eventually scale to frequencies beyond what the previous gen-
eration could reach. As an example the 180-nm generation Intel Pentium ®
4 began at a maximum frequency of 1.5 GHz and scaled to 2.0 GHz.
The 130-nm Pentium 4 started at 2.0 GHz and scaled to 3.4 GHz. The
90-nm Pentium 4 started at 3.2 GHz. Each new technology generation
is planned to start when the previous generation can no longer be easily
improved.

The future of Moore’s law
In recent years, the exponential increase with time of almost any
aspect of the semiconductor industry has been referred to as Moore’s
law. Indeed, things like microprocessor frequency, computer perform-
ance, the cost of a semiconductor fabrication plant, or the size of a
microprocessor design team have all increased exponentially. No expo-
nential trend can continue forever, and this simple fact has led to pre-
dictions of the end of Moore’s law for decades. All these predictions have
turned out to be wrong. For 30 years, there have always been seem-
ingly insurmountable problems about 10 years in the future. Perhaps
one of the most important lessons of Moore’s law is that when billions
of dollars in profits are on the line, incredibly difficult problems can
be overcome.
Moore’s law is of course not a “law” but merely a trend that has been
true in the past. If it is to remain true in the future, it will be because
the industry finds it profitable to continue to solve “insurmountable”
problems and force Moore’s law to come true. There have already been
a number of new fabrication technologies proposed or put into use that
will help continue Moore’s law through 2015.

Multiple threshold voltages. Increasing the threshold voltage dramati-
cally reduces subthreshold leakage. Unfortunately this also reduces the
on current of the device and slows switching. By applying different
amounts of dopant to the channels of different transistors, devices with
different threshold voltages are made on the same die. When speed is
devices, which are fast but high power, are used. In cir-
required, low V T
cuits that do not limit the frequency of the processor, slower, more power-
efficient, high V devices are used to reduce overall leakage power. This
T
technique is already in use in the Intel 90-nm fabrication generation. 13

13
Ghani et al., “90nm Logic Technology.”