DAVE LAMMERS, Contributing Editor
Not too many years ago, the emerging memory category at conferences such as the International Electron Devices Meeting (IEDM) or the Symposium on VLSI Technology mainly featured resistive RAMs (RRAMs), phase-change memories (PCMs), and evolving forms of magneto resistive RAMs (MRAMs).
At IEDM 2021, held in San Francisco in mid-December and in virtual mode afterwards, the new star of the emerging memory firmament was ferroelectric memories, either in 1T/1C (FeRAM) or 1T (FeFET) structures. While FeRAMs are aimed at last-level cache, FeFETs can be used either in compute-in-memory or in a conventional near-memory hierarchy (FIGURE 1). To be sure, MRAM and other memory types are still being hotly pursued, and at IEDM IBM described a fast (2 ns access time) MRAM for cache applications.
However, the high write currents of the former Big Three emerging memory candidates — all current-driven devices — raise questions about their potential as last-level cache (LLC) memories (MRAM is also being pursued as a NOR flash replacement in MCUs). By contrast, FeRAMs and FeFETs store information by switching the polarization of the doped hafnium-based crystals (FIGURE 2). It was only a decade ago that researchers (T.S. Böscke et al., Appl. Phys. Letters, 2011) realized that hafnium-based insulators could be doped and turned into FE Hafnia with switchable dipoles.
At IEDM 2021 progress was seen in endurance, speed, and reducing the voltage required to induce the polarization effects.