Recovery of Gamma Dose Military Specification Failures during Low and High Power Life Testing of Silicon Transistors

A statistical investigation was conducted to determine recovery of and long term reliability of silicon transistors degraded by total gamma dose. This work was sponsored by the U. S. Naval Radiological Defense Laboratory under contract N0022867-C-0292. This program was performed in three phases. Phase I. Over 1,400 transistors were electrically "burned-in" prior to irradiation to secure Joint Army and Navy TX (text extra) devices per MIL-S-19500 for control and test groups. Culling of devices was performed on the basis of PDS (parameter drift screening) and mil. spec. parameter limits. Parameters measured included common emitter current gains, hFE; breakdown and saturation voltages; and leakage currents, ICBO and IEBO. Control and test groups were maintained under electrical operation before, during, and for a total of 1,000 hours following exposure without disconnecting the biasing. Serious degradation of current gain was observed during irradiation. Following exposure, partial recovery of both current gain degradation and leakage current increases were monitored while the transistors remained under continuous operation. Phase II. After 1,000 hours of post exposure continuous operation the transistors were disconnected periodically for the monitoring of transistor parameters during an additional 2,700 hours of low power lifetesting. Although significant recovery was observed during the 1,000 hours of Phase I continuous operation, only slight recovery was noted in the remaining Phase II 2,700 hours of testing. Phase III. Following the low power lifetesting transistors were then subjected to electrical stressing at various biasing levels at, below, and above maximum rated power.