The Relationship Between the Intrinsic Reliability and Radiation Susceptibility of IGFETS

The susceptibility of Insulated Gate Field Effect Transistors (IGFETS) to ionizing radiation (neutron and gamma) has been exhaustively studied in the past few years1-3. Furthermore, it has been established that most of the damage, and hence degradation, is due to positive charge generation and accumulation in the insulating region. It has also been determined that the thermal stability and intrinsic reliability of an IGFET is strongly dependent on the physical characteristics of the insulating layer. The purpose of this paper is to report on the results of an effort which successfully established and demonstrated a correlation between the intrinsic reliability and radiation susceptibility of IGFETS. Both commercially available units and specially fabricated devices were tested. The commercial units included General Instrument´s 2N4353 p-channel MOS FETS, Fairchild´s FI-100 and 2N4067 dual p-channel MOS FETS, Motorola´s 2N4351 and 2N4352 n- and p-channel MNOS respectively, and Hughes´ HRN1030 p-channel, low threshold, MNOS. The custom fabricated units were supplied by Hughes and were electrically similar to HRN1030 units but differed in oxide thickness and the absence of a nitride layer. Each ensemble of units was divided into two subassemblies. One-half the units were irradiated and the remaining devices were temperature cycled. Irradiation was carried out using a Van de Graaff accelerator with a peak electron energy of 1.7 MeV. In the gamma mode, a bremsstrahlung spectra was obtained with a mean energy of 1 MeV. The dose rate varied from 300 to 3000 rad/sec, and the maximum total dose per irradiation was 106 rads.