Pragmatic design of gated-diode FinFET DRAMs

Abstract

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 with an 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 toward an era of multi-gate devices, which makes it necessary to identify design issues and advantages of gated-diode DRAMs implemented in a multi-gate 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, i.e., 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 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.