Page 177 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

158 Chapter Fourteen

This leads to the concept of an equivalent gate, whereby each type of logic
function is assigned an equivalent gate value, and the relative complexity of an
integrated circuit is judged by summing its equivalent gates. Unfortunately, the
definition of an equivalent gate can vary, depending on whom one is talking to.
A reasonably common convention is for a 2-input NAND to represent one
equivalent gate. A more esoteric convention defines an ECL equivalent gate as
being “one-eleventh the minimum logic required to implement a single-bit full-udder , ”
while some vendors define an equivalent gate as being equal to an arbitrary
number of transistors based on their own particular technology. The best policy
is to establish a common frame of reference before releasing a firm grip on your
hard-earned lucre.
The acronyms SSI, MSI, LSI, VLSI, and ULSI represent Small-, Medium-,
Large-, Very-Large- , and Ultra-Large-Scale Integration, respectively. By one
convention, the number of gates represented by these terms are: SSI (1-12),
MSI (13-99), LSI (100-999), VLSI (1,000-999,999), and ULSI (1,000,000
or more).

Device Geometries
Integrated circuits are also categorized by their geometries, meaning the size
of the structures created on the substrate. For example, a 1 pmI3 CMOS device
has structures that measure one-millionth of a meter. The structures typically
embraced by this description are the width of the tracks and the length of the
channel between the source and drain diffusion regions; the dimensions of
other features are derived as ratios of these structures.
Geometries are continuously shrinking as fabrication processes improve.
In 1990, devices with 1 pm geometries were considered to be state of the art,
and many observers feared that the industry was approaching the limits of
manufacturing technology, but geometries continued to shrink regardless:
Anything below 0.5 pm is referred to as deep-submicron (DSM), and
at some point that isn’t particularly well defined (or is defined differently by
different people) we move into the realm of ultra-deep-submicron (UDSM) .

13 The p symbol stands for “micro” from the Greek micros, meaning “small” (hence the use of
pl’ as an abbreviation for microprocessor). In the metric system, p stands for “one millionth
part of,” so 1 pm means one millionth of a meter.