Are There Limits?
What are the limits to integration? Time after time, as the so-called limits
approach, they are exceeded. A quick look at the technical literature today
shows engineers writing and presenting papers that describe the design,
fabrication, and characterization of 0.1-micron-channel CMOS devices with
polysilicon gates on 35-angstrom-thick gate oxides, at a power supply voltage
of 1.5 volts or less. An angstrom is about one-millionth the width of a human
hair. Thirty-five of them are equal to approximately eight atomic layers.
We know from the work of many researchers that, at dimensions only slightly
less than this (25 angstroms), electrons can tunnel directly through the
dielectric into the depletion regions of the device, severely degrading the
operation of the transistor. Also at these dimensions, the number of impurity
atoms becomes so small that statistical fluctuations in their number can have a
serious effect on the electric field of the device. The problem is compounded
by Dennard's scaling theory, which suggests that the number of atoms in a
significant region of the semiconductor decreases as the square of the
dimension.
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