[paper] ULTRARAM Memory on Silicon

Peter D. Hodgson, Dominic Lane, Peter J. Carrington, Evangelia Delli, 

Richard Beanland and Manus Hayne

ULTRARAM: A Low-Energy, High-Endurance, Compound-Semiconductor Memory 

on Silicon

First published: 05 January 2022

Adv. Electron. Mater. 2022, 8, 2101103

DOI: 10.1002/aelm.202101103

Abstract: ULTRARAM is a nonvolatile memory with the potential to achieve fast, ultralow-energy electron storage in a floating gate accessed through a triple-barrier resonant tunneling heterostructure. Here its implementation is reported on a Si substrate; a vital step toward cost-effective mass production. Sample growth using molecular beam epitaxy commences with deposition of an AlSb nucleation layer to seed the growth of a GaSb buffer layer, followed by the III–V memory epilayers. Fabricated single-cell memories show clear 0/1 logic-state contrast after ≤10ms duration program/erase pulses of ≈2.5V, a remarkably fast switching speed for 10 and 20µm devices. Furthermore, the combination of low voltage and small device capacitance per unit area results in a switching energy that is orders of magnitude lower than dynamic random access memory and flash, for a given cell size. Extended testing of devices reveals retention in excess of 1000 years and degradation-free endurance of over 107 program/erase cycles, surpassing very recent results for similar devices on GaAs substrates.

FIG: a) Schematic cross-section of ULTRARAM device concept with corresponding material layers. The floating gate (1: FG), triple-barrier resonant-tunneling structure (2: TBRT), and readout channel (3) are highlighted. Arrows indicate the direction of electron flow during program/erase operations; b) Scanning electron micrograph of a fabricated device of 10 µm gate length. 

Acknowledgements: P.D.H. and D.L. contributed equally to this work. This work was supported by the Engineering and Physical Sciences Research Council, UK, via the 2017–2020 Impact Acceleration Account funding allocation to Lancaster University under grant EP/R511560/1, a scholarship under grant EP/N509504/1, equipment funding under grant EP/T023260/1, and the Future Compound Semiconductor Manufacturing Hub grant EP/P006973/1, by the ATTRACT project funded by the EC under Grant Agreement 777222 and by the Joy Welch Educational Charitable Trust.