ULTRARAM: A Low‐Energy, High‐Endurance, Compound‐Semiconductor Memory on Silicon

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 ≤10 ms duration program/erase pulses of ≈2.5 V, a remarkably fast switching speed for 10 and 20 µm 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.

Anomalous luminescence temperature dependence of (In,Ga)(As,Sb)/GaAs/GaP quantum dots overgrown by a thin GaSb capping layer for nanomemory applications

“…Importantly, we note that our results in this work also confirm the previous predictions that a type-II confinement obtained by adding Sb to the QD-layer (in this case via the GaSb overgrowth), leads to a major increase in the QD retention time [17,23]. Here, it is important to point out that such projected retention time is comparable to the one of other nanomemory device concepts currently en-route to commercialization [69]. Finally, since our QDs and nanomemory units can be fabricated using the industrially compatible large-scale MOVPE technique, they are promising candidates for a viable nanomemory device.…”

“…Thus, in our work we considered only thinner GaSb caps. However, experimentally obtainable thickness of 3 ML would be enough to reach thousand years storage time, a reasonable value also considered in other III-V nanomemory devices such as Ultraram [69].…”