An Optically Gated Transistor Composed of Amorphous M + Ge2Se3 (M = Cu or Sn) for Accessing and Continuously Programming a Memristor

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We demonstrate that a device composed of sputtered amorphous chalcogenide Ge2Se3/M + Ge2Se3 (M = Sn or Cu) alternating layers functions as an optically gated transistor (OGT) and can be used as an access transistor for a memristor memory element. This transistor has only two electrically connected terminals (source and drain), with the gate being optically controlled, thus allowing the transistor to operate only in the presence of light (385-1200 nm). The switching speed of OGTs is < 15 μs. The OGT is demonstrated in series with the Ge2Se3 + W memristor, where we show that by alternating the light intensity on the OGT gate, the memristor can be programmed to a continuous range of nonvolatile memory states using the saturation current of the OGT as a programming compliance current. By having a continuous range of nonvolatile states, one memory cell can potentially achieve 2n levels. This high density, combined with optical programmability, enables hybrid electronic/photonic memory.