The formation of Cu2O nanoparticles in polyimide using Cu electrodes via chemical curing, and their application in flexible polymer memory devices

Abstract

Flexible polymer memory devices were fabricated based on 4,4′-(hexafluoroisopropylidene)diphthalic anhydride-4,4′-oxydianiline (6FDA-ODA) polyimide (PI)/Cu2O nanocomposite via chemical curing, heat treatment, and post-heat treatment at low temperature (<200 °C). Following the deposition of a Cu bottom electrode on a commercial PI film substrate, a PI precursor, polyamic acid (PAA) was spin-coated onto the Cu bottom electrode, and Cu was dissolved into the PAA, providing Cu ions for particle formation. The 6FDA-ODA PAA–Cu complex was imidized via chemical curing using acetic anhydride and triethylamine at 50 °C, and thermal treatment was performed at 200 °C in a reducing atmosphere to remove the solvent completely and precipitate Cu nanoparticles. Post-heat treatment was sequentially carried out at 150 °C in an oxidizing atmosphere to oxidize Cu to Cu2O. The Al top electrode was deposited onto the 6FDA-ODA PI/Cu2O nanocomposite film, and the flexible memory device with a crossbar array showed an ON/OFF ratio of ∼104, endurance of 60 cycles, retention time of 104 s, and device yield of 86% (31 cells out of total 36 cells) under flat and bending conditions (bending radius ∼1.5 mm) when the electrical measurements were performed in air at room temperature.