Chalcogenide memory arrays: characterization and radiation effects

Abstract

The chalcogenide material used for phase-change applications in rewritable optical storage (Ge/sub 2/Sb/sub 2/Te/sub 5/) has been integrated with a 0.5-/spl mu/m radiation-hardened CMOS process to produce 64-Kbit memory arrays. On selected arrays, electrical testing demonstrated up to 100% memory cell yield, 100-ns programming and read speeds, and write currents as low as 1 mA/bit. Devices functioned normally from -55/spl deg/C to 125/spl deg/C. Write/read endurance has been demonstrated to 1/spl times/10/sup 8/ before first bit failure. Total ionizing dose (TID) testing to 2 Mrad(Si) showed no degradation of chalcogenide memory element, but it identified a write current generator circuit degradation specific to the test chip, which can be easily corrected in the next generation of array and product. Static single-event effects (SEE) testing showed no effect to an effective linear energy transfer (LET/sub EFF/) of 98 MeV/mg/cm/sup 2/. Dynamic SEE testing showed no latchup or single-event gate rupture (SEGR) to an LET/sub EFF/ of 123 MeV/mg/cm/sup 2/. Two sensitive circuits, neither containing chalcogenide elements, and both with small error cross sections, were identified. The sense amp appears sensitive to transients when reading the high-resistance state. The write driver circuit may be falsely activated during a read cycle, resulting in a reprogrammed bit. Radiation results show no degradation to the hardened CMOS or effects that can be attributed to the phase-change material.