Quasi-static RAM design for high performance operation at liquid nitrogen temperature

Abstract

The leakage currents which cause information loss in dynamic random access memories (DRAMs) at room temperature disappear at liquid nitrogen temperature, permitting operation of the circuits without the need for refresh (quasi-static operation). The current drive characteristics of the MOS transistor also improve significantly at liquid nitrogen temperatures. Combining these factors leads to an exploration of high speed dynamic RAM design based upon cells with non-destructive readout. This paper describes an experimental high speed RAM based upon a new two-transistor (2T) memory cell designed to exploit the unique advantages of operation at low temperature. Non-destructive readout coupled with a large d.c. sensible output current yields a high speed RAM with low power consumption. An experimental 4 kbit memory, fabricated using a 2 μm CMOS technology, exhibits an access time of 7 nS at 77 K.