Gated-Diode FinFET DRAMs: Device and Circuit Design-Considerations
Scaling bulk CMOS SRAM technology for on-chip caches beyond the 22nm node is questionable, on account of high leakage power consumption, performance degradation, and instability due to process variations. Recently, two-three transistor one gated-diode (2T/3T1D) DRAMs were proposed as alternatives to address the SRAM variability problem, with an emphasis on high-activity embedded cache applications. They are highly competitive to SRAM in terms of performance, while having a smaller power and area footprint at lower technology nodes. The current evolutionary trend in transistor structures is moving toward an era of multigate devices, which makes it necessary to identify design issues and advantages of gated-diode DRAMs implemented in a multigate technology. In this work, we address gated-diode DRAM design in FinFET technology using mixed-mode 2D-device simulations. We revisit the model of internal voltage gain in bulk gated diodes and extend it to provide quantitative insight into designing Fin gated diodes, that is, gated diodes in FinFET technology. To this effect, we propose FinFET variants of the bulk gated-diode configuration and identify parameters that are critical to enhancing the retention time and read current in 2T/3T1D FinFET DRAMs. Additionally, we show the superiority of 2T1D FinFET DRAM over 6T FinFET SRAM having pass-gate feedback (6T PGFB) and 2T1D bulk DRAM under the effect of physical parameter process variations using a quasi-Monte Carlo method implemented in FinE, an environment we have developed for double-gate circuit design that integrates Sentaurus TCAD from Synopsys with the Spice3-UFDG double-gate compact model from University of Florida, under a single framework. Finally, we present a new tunable threshold gated diode FinFET amplifier which uses an n-type gated diode for voltage-boosting, along with a p-type gated diode for zero-suppression.
finfet dram design sram performance gated diode theory technology cad