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

Abstract

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.

Keywords

• compound semiconductor on silicon
• molecular beam epitaxy
• nonvolatile memory
• triple‐barrier resonant tunneling heterostructure