Hybrid Nonvolatile Memory Devices with Ferroelectric Copolymers Based on ZnO Nanowire Field Effect Transistors

Zinc Oxide (ZnO) nanowire (NW) field effect transistors (FETs) have been increasingly popular recently as promising circuitry building blocks. ZnO NWs have a relatively good ohmic contact between the metal electrodes and semiconductor materials, which results in a high device performance and fabrication yield.  At the same time, organic thin film transistors (OTFTs) with ferroelectric materials have been researched extensively owing to their nonvolatile memory effect, nondestructive readout and applications to flexible electronics [1, 2].  However, research works on ferroelectric memory devices based NW FETs are still limited [3, 4], while that on their thin film counterparts are relatively widespread [5].

We will first introduce the nonvolatile memory device arrangement based on a ZnO NW FET. Single NW and network NW FET configurations are compared in terms of their associated ferroelectric memory properties.  We will show our previous work on the ZnO NWs grown by a chemical vapor transport method on glass substrates [6] together with that by a hydrothermal method on flexible substrates, with the dimensions ranging from 100-300 nm in diameter and up to 5-10 um in length. Our ZnO NW FETs grown on flexible substrates directly shows a high current on/off ratio of up to 10⁵-10⁷with an anticlockwise hysteresis loop present on the transfer curve. The top-gate and bottom-gate structures have been prepared by spin coating a 5 wt% solution of ferroelectric PDVF-TrFE powders in cyclohexane. After spin coating, the ZnO NW FETs with PVDF-TrFE thin films have been thermally cured in a vacuum oven at 150°C for 5 hours. The device showed a memory window of at least 10-20 volts depending on the type of the substrates, which can be tuned by varying the sweep range of the gate voltages.

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[2] S.K. Hwang et al., Adv. Mater. 24, 5910 (2012).

[3] D. Yeom et al., Nanotechnology 19, 395204 (2008).

[4] Y.T. Lee et al., Adv. Mater. 24, 3020 (2012).

[5] K.H. Lee et al., Adv. Mater. 21, 4287 (2009).

[6] S. Nedic, et al., Appl. Phys. Letts. 104, 033101 (2014).