A modified exponential energy gap law for nonradiative decay has been derived for 4f–4f transitions where only a few phonons participate in the transition. Its preexponential factor varies by only a factor of 10 for different host materials and is purely electronic in nature. The modified law is the usual law (giving a factor of 105 variation) modified by using an energy gap which is effectively two (maximum) phonon energies smaller than the energy difference between the initial and the final electronic state. A general relation between the radiative and nonradiative decay rates has been constructed. For 4f–4f transitions this relation enables one to predict the nonradiative decay rate from a knowledge of the radiative decay rate to within one order of magnitude accuracy.

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Subnanosecond gate delays (0.8 n) have been measured on complex logic gates (e.g., sum functions of a full adder) designed in the differential split-level (DSL) CMOS circuit technique. This fdgh speed has been achieved by reducing the logic swing (2.4 V) on interconnect lines between logic gates, by using current controlled caseoded cross-coupled NMOS-PMOS loads, by using combhsed open NMOS drains as outputs, and by employiug shorter channel lengths (Leff= 1ym) for the NMOS devices in the logic trees with reduced maximum drain-source voltages to avoid reliability problems. Extra ion implantation protects these transistors from punchthrough.

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