Write-Verify Scheme for IGZO DRAM in Analog in-Memory Computing

Abstract

Large weight variations cause significant degradation in Deep Neural Networks (DNNs) accuracy in machine learning (ML) context. Indium-Gallium-Zinc-Oxide (IGZO) DRAM compute cell is a promising option for Analog in-Memory Computing (AiMC) accelerators, but its applicability requires the compensation of large variations affecting the voltage threshold of the readout device. This paper proposes a write-verify scheme for IGZO-based AiMC accelerator, designed in 22-nm technology, based on a compensation loop operating on the analog weight value stored in the IGZO DRAM cell. After the compensation routine, the IGZO ION normalized variation drops from +/- 27% to +/- 3% in simulation. With sufficiently large weight reuse, the additional energy spent for the compensation of the entire arrays becomes negligible, recovering the 2000 TOPS/W baseline performance of an ideal IGZO array without the write-verify.