Analysis of TID Process, Geometry, and Bias Condition Dependence in 14-nm FinFETs and Implications for RF and SRAM Performance

Abstract

Total ionizing dose results are provided, showing the effects of different threshold adjust implant processes and irradiation bias conditions of 14-nm FinFETs. Minimal radiation-induced threshold voltage shift across a variety of transistor types is observed. Off-state leakage current of nMOSFET transistors exhibits a strong gate bias dependence, indicating electrostatic gate control of the sub-fin region and the corresponding parasitic conduction path are the largest concern for radiation hardness in FinFET technology. The high- $V_{\textit {th}}$ transistors exhibit the best irradiation performance across all bias conditions, showing a reasonably small change in off-state leakage current and $V_{\textit {th}}$ , while the low- $V_{\textit {th}}$ transistors exhibit a larger change in off-state leakage current. The “ worst-case” bias condition during irradiation for both pull-down and pass-gate nMOSFETs in static random access memory is determined to be the on-state ( $V_{\textit {gs}}=V_{\textit {dd}}$ ). We find the nMOSFET pull-down and pass-gate transistors of the SRAM bit-cell show less radiation-induced degradation due to transistor geometry and channel doping differences than the low- $V_{\textit {th}}$ transistor. Near-threshold operation is presented as a methodology for reducing radiation-induced increases in off-state device leakage current. In a 14-nm FinFET technology, the modeling indicates devices with high channel stop doping show the most robust response to TID allowing stable operation of ring oscillators and the SRAM bit-cell with minimal shift in critical operating characteristics.