Mitigating Total-Ionizing-Dose-Induced Threshold-Voltage Shifts Using Back-Gate Biasing in 22-nm FD-SOI Transistors

The effects of total ionizing dose (TID) on MOSFETs fabricated in a 22-nm fully depleted silicon-on-insulator (FD-SOI) technology are analyzed. TID causes positive-trapped charge to accumulate in transistor isolation regions [e.g., the buried oxide (BOX)], thereby generating negative TID-induced threshold-voltage shiftsΔ Vₜₕthat facilitate nMOSFET turn-on and inhibit pMOSFET turn-on. Back-gate biasing options in the technology can be used to offset the threshold-voltage shifts. Applying a bias to the back gates of MOSFETs in a conventional-well back-gate configuration mitigates TID-inducedΔ Vₜₕin nMOSFETs (where a negative bias is applied to the P-well back-gate), while enhancing the same in pMOSFETs (where a positive bias is applied to the N-well back-gate). To mitigate and potentially reverse TID-inducedΔ Vₜₕof both nMOSFETs and pMOSFETs simultaneously, a single back-gate bias can be applied to MOSFETs in a common isolated P-well back-gate configuration. 3-D technology computer-aided design (3-D TCAD) device simulation results of the 22-nm FD-SOI technology confirm the conventional-well circuit-level radiation response and support the effectiveness of using the common isolated P-well back-gate configuration for TID mitigation. These results justify the utility of dynamically tuning back-gate bias according to actively monitored TID-inducedΔ Vₜₕfeedback.