Buried oxide leakage current as a function of total dose

Summary form only given. A study of the properties of implanted oxide as a function of total dose is discussed. As a comparison, thermally grown top oxide was also studied. Mesa-isolated individual MOS transistors with body contacts were chosen. The measured leakage current through the buried oxide and top oxide as a function of bias at pre-radiation is shown. The back gate bias voltage was increased from -20 V to 20 V and back to -20 V in 0.5 V steps and held at each voltage for 0.5 sec delay time before making the current measurements. A peak in the leakage current is exhibited in the second quadrant. The peak is very large when the delay time is reduced or eliminated. The peak completely vanishes when the delay time is increased to 4 sec. Peak current is therefore identified as current due to mobile carriers in the buried oxide. The peak effect is greatly enhanced when the measurement is made at an elevated temperature. A similar plot for top oxide is also shown. The leakage currents through the buried oxide and top oxide at a total dose of 1 Mrad (Si) are shown. The peak magnitude increases for both oxide cases. The front channel characteristics of n-channel devices which had these oxide layers showed no shift or distortion in their subthreshold characteristics when irradiated to 1 Mrad (Si)