 before and after irradiation [Briss-96]. III-91 Bird's beak region 100 krad 50 krad 40 krad 30 krad Gate oxide Field oxide X (um) Figure 85. Evolution of IDo(x) (IDS(X) at VGS = V and VDS = 5 V) along the interface after irradiation [ibidem]. 9.1.5. TRENDS OF SUPPLY VOLTAGE DURING IRRADIATION The use of simulation can also be exploited to understand the influence of the decrease of supply voltage on dose hardness. For this analysis, the modeling exposed above is calibrated at 5 V and applied at decreasing gate voltages: Simulation : V =1V 10-10 V =0V 10-11 Experiment : 10-12 V =5V 10-13 Dose (krad) Figure 86. Simulated IDO VS dose for VGS=0 V to 5 V during irradiation. Experimental results are also plotted, with open symbols [Bris-96]. At a given dose, the VGS bias during irradiation has an important effect on IDO. Since the electric field in the oxide decreases when VGs decreases, the probability of initial recombination 1 - Y(E) of the generated electron-hole pairs increases. Consequently, a lower density of holes is trapped in the oxide during irradiation. The leakage current appears at a higher dose when VGS is lower. The hardening for low voltage, low power technologies should be easier to optimize than for 5- volt technologies thanks to the lower supply voltage. III-92 This can be compared to data originating from global leakage of commercial parts, i.e. 54AC series of National Semiconductors fabricated using the FACT™ JAN process [Mahe-94]. The trend is verified between 5V and 3.3V. Icc (Standby) vs Total Dose Icc (Standby) vs Total Dose 54AC161-Synchronous 54AC14-Hex Inverter with Presetable Binery Counter Schmitt Trigger Input 'cc (MA) bc (HA) 'cc (5.5 VDC) 'cc (5.5 VDC) cc (3.6 VDC) 'cc (3.6 VDC) Total Dose [krads($i)] Total Dose [krads(Si)] Figure 87. Supply stand-by current of 54AC circuits in FACT™ technology [Mahe-94]. 9.1.6. OTHER TYPES OF EDGE OXIDES A part of the commercial semiconductor market is driven by need of best electrical performances, obtained for always lower power supply consumption,