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333-eDRAM - 3T Embedded DRAM Leveraging Monolithic 3D Integration of 3 Transistor Types: IGZO, Carbon Nanotube and Silicon FETs

SessionShaping Tomorrow: Co-Designing Emerging Technologies for Computing and Beyond

DescriptionThe memory wall is a major bottleneck for continuing to improve the energy efficiency of computing systems. To overcome this challenge, various nanomaterials, devices, circuits, architectures, and three-dimensional (3D) integration techniques are under development for future memory solutions. However, major trade-offs must be made when designing memories to achieve high on-chip memory capacity, high retention time, high endurance, low access times, low access energy, and low static leakage power. We present an energy- and area-efficient embedded DRAM memory architecture (quantified by EADP: the product of total energy consumption, circuit area footprint and application execution time) that leverages monolithic 3D integration of three types of transistors: (i) Indium Gallium Zinc Oxide (IGZO) FETs for ultra-low off-state leakage currents enabling high retention time DRAM; (ii) Carbon Nanotube FETs (CNFETs) for high on-state drive currents leading to fast access times; and (iii) Silicon CMOS for its combined energy efficiency and low off-state leakage current (for memory peripheral circuits implemented on the bottom physical circuit layer). Our resulting 333-eDRAM achieves each of the following simultaneously, which we quantify and describe how to co-optimize in this paper: high density, high retention time, high endurance, low access times, low access energy, and low static leakage power. We show full physical layout designs detailing how to implement 333-eDRAM and quantify EDAP for an ARM Cortex-M0 processor + on-chip 333-eDRAM implemented at a 7 nm technology node, running applications from the Embench benchmark suite. Using cycle-accurate simulations, SPICE circuit simulations, compact models calibrated to experimental data, and detailed full physical layout designs of 333-eDRAM memories, we show that on average (across 16 Embench benchmarks), ARM Cortex-M0 + IGZO/CNT/Si 333-eDRAM offers 1.7× better EDP and 4.47× better EDAP than ARM Cortex-M0 + Silicon eDRAM.

Authors

Pragmatic Semiconductor