Ashok K. Sharma, NASA GSFC
Ashok.k.Sharma.1@gsfc.nasa.gov

Alexander Teverovsky, QSS Group Inc./NASA Goddard Operations
Alexander.Teverovsky@gsfc.nasa.gov

Terry W. Dowdy, NAVSEA Crane
dowdy_t@crane.navy.mil

Abstract

A major reliability issue for all advanced nonvolatile memory (NVM) technology devices including FRAMs is the data retention characteristics over an extended period of time, under environmental stresses and exposure to total ionizing dose (TID) radiation effects. These advanced memories are mostly available as commercial-off-the-shelf (COTS) devices and often use the latest submicron technologies, new dielectric materials, multi-layer interconnect processes, and advanced plastic packaging. In the NVMTS 2001, data retention and fatigue characteristics of 64 Kb PZT-based FRAMs from Ramtron Corp., tested over a temperature range from -85 °C to +310 °C for ceramic packaged parts and from -85° C to +175 °C for plastic parts, during retention periods of up to several thousand hours, were reported. The observed data retention failures were divided into three categories: (1) random failures that were not related to stress conditions, (2) weak cell failures, which were also not related to a particular stress condition but were reproducible from test to test, and (3) intrinsic failures that were caused by thermal degradation (or wearout) of the ferroelectric cell material. A conclusion was that additional testing should be performed on higher density 256 Kb FRAMs.

For this additional testing, 256 Kb FRAMs in 28-pin plastic DIPs, rated for an industrial grade temperature range of -40 °C to +85 °C, were procured. These are two-transistor, two-capacitor (2T-2C) design FRAMs. In addition to data retention characteristics, the parts were also evaluated for imprint failures, which are defined as the failure of cells to change states (e.g., from 1 to 0, or 0 to 1) and are somewhat similar to hysteresis effect.

These 256 K FRAMs were subjected to scanning acoustic microscopy (C-SAM); 1,000 temperature cycles from -65 °C to +150 °C; high temperature aging at 150 °C, 175 °C, and 200 °C for 1,000 hours; highly accelerated stress test (HAST) for 500 hours; 1,000 hours of operational life test at 125 °C; and total ionizing dose radiation testing. As a preconditioning, 10 K read/write cycles were performed on all devices. Interim electrical measurements were performed throughout this characterization, including special imprint testing.

Failures were observed during high temperature aging testing at 200 °C, during HAST testing, and during 1,000 hours of operational life at 125 °C. The parts passed 20 Krad exposure, but there were failures during post-30 Krad electrical measurements. Test results and failures analysis will be presented at the Non-Volatile Memory Technology Symposium, NVMT’02 and posted on the NEPP Web site when they have been completed.