Radiation-Hardened Structure to Reduce Sensitive Range of a Stacked Structure for FDSOI

Abstract

Flip-flops (FFs) with stacked transistors have high radiation tolerance in a fully depleted silicon on insulator (FDSOI) process. However, the FFs are weak against a radioactive particle hit with high linear energy transfer (LET) and from high incident angles. In this paper, we used heavy-ion irradiation tests to evaluate the soft-error tolerance of a stacked structure and a radiation-hardened structure in an attempt to reduce sensitive range (RSR). We propose a novel FF with the RSR structure. We fabricate a chip in a 65-nm FDSOI process with three latches, each with different distances between stacked transistors. Experimental results reveal that the stacked structures are weak against a heavy-ion hit that exceeds a LET of 60 MeV $\cdot $ cm2/mg even though the distance between stacked transistors was increased from 250 to 350 nm. We evaluated the RSR structure by TCAD simulations and measured the radiation hardness of the proposed FF by heavy-ion irradiation on the fabricated chips. Measurement by heavy ions with LET of 67.2 MeV $\cdot $ cm2/mg at all angles show no detectable errors in the proposed FF.