Freeze-out characterization of radiation-hardened N+ polysilicon-gate CMOS transistors

Freeze-out characteristics of radiation hardened N+ polysilicon-gate CMOS devices was studied at liquid-nitrogen temperature before and after irradiation. Characterization was performed at room temperature, 77 K, and at 77 K with total dose up to 200 Krads(Si), with a gate bias from -4.5V to +6V. explanations are given for the threshold variations and freeze-out effects both before and after irradiation. The degree of freeze-out of the counterdope implant is controlled by temperature, applied gate potential, and applied body potential. A kink appears in the transfer characteristics at 77 K pre-rad, and appears to be reduced with increasing total dose. Experimental results indicate that the reduction of the freeze-out kink with total dose is not due to changes in freeze-out with dose or gate bias, but to smearing of the transfer curves as a result of transconductance degradation with total dose