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Devices and structures

Devices and structures

Nonvolatile charge memory device shows excellent room-temperature performance

28 Dec 2019
Nonvolatile charge memory

Qinliang Li, Cailei Yuan and Ting Yu from Jiangxi Normal University, along with Qisheng Wang and Jingbo Li from South China Normal University, are developing nonvolatile charge memory devices with simple structures. Wang explains how the optically controllable devices combine the functions of light sensing and electrical storage.

The research is reported in full in Journal of Physics D: Applied Physics, published by IOP Publishing – which also publishes Physics World.

What was the motivation for the research and what problem were you trying to solve?

Nonvolatile memory devices are central to modern communication and information technology. Among various material systems, emerging two dimensional (2D) materials offer a promising platform for next-generation data-storage devices due to their unique planar structure and brilliant electronic properties. However, 2D materials-based nonvolatile memory devices have complicated architectures with multilayer stacking of 2D materials, metals, organics or oxides. This limits the capacity for device miniaturization, scalability and integration functionality.

In this work, we are trying to design a nonvolatile charge memory with simple device architecture. We also expect to explore a new type of optical control on the charge storage devices, which may bring us smart operation on data deposition and communication.

What did you do in this work?  

We discovered the novel optical-tunable charge memory behaviour in In2Se3 nanosheets. We grew the single-crystalline In2Se3 nanosheets in a tube furnace with chemical vapour deposition methods, and used standard photolithography to depict the device contacts by depositing Ti (3 nm)/Au (50 nm) as electrodes. We recorded electrical signals using an Agilent B1500 semiconductor characterization system equipped with a probe station, at temperatures from 30 to 300 K. In order to observe the effect of laser irradiation on the charge memory, we used a 532 nm laser to irradiate the device.

What was the most interesting and/or important finding?

The devices showed superb memory properties at room temperature, with a large memory window, long retention time and robust endurance. Furthermore, we demonstrated optical manipulation of charge storage, with laser powered control of the numbers of stored charges and the on/off ratio. Supported by a theoretical model, we found that the nonvolatile charge storage originated from the surficial/interfacial trapped electrons, which are removed via photo-generated holes.

Why is this research significant?

Our photo-tunable nonvolatile charge memory devices combine the functions of light sensing and electrical storage. In comparison with multilayer heterostructures of 2D materials, our work facilitates device manufacture, reduces the circuit complexity, and is of benefit for the miniaturization and large-scale integration of functional devices.

At room temperature, the devices showed comparable memory properties to memory devices of 2D material heterostructures with floating gate mode. Together with the simple device structure, the photo-tunable nonvolatile charge memory devices will pave the way towards large-scale integration and high-speed intelligent electronics, such as ultrafast remote operation on data coding, artificial synapse and neurons.

What is the next stage for the research?

In the future, we plan to optimize the memory performance of α-In2Se3 nanosheets via surface chemical modification. Meanwhile, we will develop the wafer-scale growth of α-In2Se3 nanosheets, which would be useful for industrial application. The large-area growth will allow us to explore an artificial visual system based on optical-controllable data memory properties of α-In2Se3 nanosheets.

The full results of the study are reported in Journal of Physics D: Applied Physics.

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