In this brief, we investigate device variability in advanced fin field effect transistor (FinFET) static random access memory (SRAM) devices (12 and 7 nm) as a function of drain-to-source (Vds) bias. Drain-induced barrier lowering (DIBL) and the variation in DIBL are found to exhibit a logarithmic dependence with drain bias in the advanced node FinFET devices. Correctly capturing the DIBL and device variation as a function of drain bias is required, as the SRAM operation voltage range is expanded. We show the improved hardware correlation in Vmin yield and the improved slow corner read performance when the Vds-dependent variation is considered.

A previously unrecognized vertical-extrinsic device in advanced 7-nm FinFET SRAM structures is identified and characterized for the first time. The ON-current for this vertical-extrinsic device is modulated by gate bias and exhibits a process-dependent threshold behavior. The ON-state of this parasitic device can exceed several nanoamperes and become the dominant mechanism in the static power of an SRAM array. Aggressively pushed ground rules used to achieve competitive SRAM density can result in exposure in FinFET-based SRAMs to this parasitic leakage path; n-Well and p-well dopant profiles, alignments, and dimensions must be carefully controlled to avoid this leakage mechanism in high-density FinFET SRAM arrays.

A numerical method for the determination of isotropic band models has been developed and applied to silicon. The resulting model accurately approximates both density of states and group velocity of the corresponding anisotropic band structure, thus providing an excellent agreement with both the collision and nonhomogeneous terms of the Boltzmann transport equation. The model, represented by a simple set of energy-wave vector tables, has been implemented in a Monte Carlo device simulator, but can also be extended to alternative methods for solving the Boltzmann equation. Simulation of homogeneous silicon shows a very good agreement with available experimental data. Comparison with results obtained using the complete anisotropic band structure, both in homogeneous and nonhomogeneous silicon devices, confirms the validity of the model.>