A 7000-gate microprocessor on SOS—PULCE

An n-channel MOS LSI microprocessor integrating 20 000 transistors on a chip has been realized on a sapphire substrate utilizing the Coplanar-II process. It contains ALU, shifters, and 44 registers which are combined to three 16-bit buses. By utilizing three types of threshold voltage for load transistors, 28-percent reduction in power dissipation is achieved. The minimum cycle time is 200 ns. By using the Coplanar-II process, anomalous leakage currents due to parasitic transistors at the sides of island are suppressed. It is found that the silicon-on-sapphire (SOS) version operates 2.3 times faster than the bulk-silicon version, which is mainly explained by the parasitic capacitance ratio. Parallel-plate approximation in calculating a wiring capacitance results in an underestimate by a factor of 60 compared with taking the two-dimensional effect into account. It is verified that a) the observed yield of a very large SOS chip is higher than the value predicted from a randomly distributed defects model, and b) the yield-sensitive active area of an SOS is so small that it can compensate for the yield degradation due to the very large defects density on an SOS wafer.