Fabrication of cracking-free CeO2 thin film using UV/O3 and plasma treatment and their applications in wearable devices

Abstract

Recent development of wearable devices in healthcare, wearable and soft robotics has generated increasing demand for memory devices which are more compact with higher data storage capacity and mechanical flexibility, as well as lower fabrication costs. Resistive random access memory (RRAM), which is an emerging technology, has unique advantage of high response speed, low power consumption, and 3D stack architecture. In this research, a sandwich structure (Au/CeO2/Au/Si) based RRAM device has been developed. Scanning electron microscope (SEM), transmission electron microscopy (TEM) were applied to analyze the phase and microstructure for both inks and the thin films. The electrical properties including current-voltage (I-V) response were systematically tested by auto-lab and source meter. A stretching test also was done with a thermoplastic polyurethane (TPU) based device. A suspension ink with controlled shape of CeO2 nanocrystals was prepared. A series of samples have been prepared with solvent, toluene or hexane, by using CeO2 as core material for the ink. The thin film was deposited by spin coating or drop-coating following with plasma treatment. Both silicon and TPU based device have been used as substrates for comparison. Shape controlled CeO2 nanocrystals and printable inks have been successfully fabricated. Different solvent was used to vary the properties of the ink and improve the cracking-free films. A large area cracking-free CeO2 thin film was obtained by plasma processing. Ink jet printing method was also involved as one method of film fabrication. The memory behaviour could be more clearly demonstrated with obvious characteristic from the I-V curve both at silicon and TPU elastic substrates. Thus, the plasma treatment with different treatment time and power could help improve the thin film performance. A simple flexible device had been manufactured with a basic memory behaviour. In summary, the project provided a systematic study on developing metal oxide based nanocrystals towards crack-free thin film and memory devices applications, which may have potential applications in future printed, flexible data storage devices.