A novel MOS PROM using a highly resistive poly-Si resistor

A novel MOS electrically programmable read-only memory (PROM) using a highly resistive polycrystalline silicon (poly-Si) resistor as a memory element is proposed. In a highly resistive poly-Si, a new memory effect of an irreversible resistivity transition, from an initial highly resistive value to a low resistive one, is observed. The dependencies of the transition voltage and current, which cause the transition, on the poly-Si deposition conditions, are studied, and the deposition conditions suitable for MOS PROM fabrication are obtained. The transition voltage Vtcan be reduced down to 10 V by decreasing the poly-Si film thickness to 0.4 µm. The transition current is less than 10 mA. A 36-bit MOS PROM, using the poly-Si resistor as a memory element, is fabricated. The programming voltage used in this work is 25 V and the programming time per bit is less than 10 µs. The read access time is less than 300 ns. The programming voltage, however, can be reduced down to 15 V by decreasing the poly-Si film thickness and the series resistance in the circuit. The novel PROM has another advantage in that the poly-Si resistor is compatible with a conventional silicon-gate process.