High-k Solution-Processed Barium Titanate/Polysiloxane Nanocomposite for Low-Temperature Ferroelectric Thin-Film Transistors

Ferroelectric nanoparticles have attracted much attentionfor numerouselectronic applications owing to their nanoscale structure and size-dependentbehavior. Barium titanate (BTO) nanoparticles with two different sizes(20 and 100 nm) were synthesized and mixed with a polysiloxane (PSX)polymer forming a nanocomposite solution for high-k nanodielectric films. Transition from the ferroelectric to paraelectricphase of BTO with different nanoparticle dimensions was evaluatedthrough variable-temperature X-ray diffraction measurement accompaniedby electrical analysis using capacitor structures. A symmetric single200 peak was constantly detected at different measurement temperaturesfor the 20 nm BTO sample, marking a stable cubic crystal structure.100 nm BTO on the other hand shows splitting of 200/002 peaks correlatingto a tetragonal crystal form which further merged, thus forming asingle 200 peak at higher temperatures. Smaller BTO dimension exhibitsclockwise hysteresis in capacitance-voltage measurement andcorrelates to a cubic crystal structure which possesses paraelectricproperties. Bigger BTO dimension in contrast, demonstrates counterclockwisehysteresis owing to their tetragonal crystal form. Through furtherRietveld refinement analysis, we found that the tetragonality (c/a) of 100 nm BTO decreases at a highertemperature which narrows the hysteresis window. A wider hysteresiswindow was observed when utilizing 100 nm BTO compared to 20 nm BTOeven at a lower loading ratio. The present findings imply differenthysteresis mechanisms for BTO nanoparticles with varying dimensionswhich is crucial in understanding the role of how the BTO size tunesthe crystal structures for integration in thin-film transistor devices.