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

Abstract

Ferroelectric nanoparticles have attracted much attention for numerous electronic applications owing to their nanoscale structure and size-dependent behavior. 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 paraelectric phase of BTO with different nanoparticle dimensions was evaluated through variable-temperature X-ray diffraction measurement accompanied by electrical analysis using capacitor structures. A symmetric single 200 peak was constantly detected at different measurement temperatures for the 20 nm BTO sample, marking a stable cubic crystal structure. 100 nm BTO on the other hand shows splitting of 200/002 peaks correlating to a tetragonal crystal form which further merged, thus forming a single 200 peak at higher temperatures. Smaller BTO dimension exhibits clockwise hysteresis in capacitance–voltage measurement and correlates to a cubic crystal structure which possesses paraelectric properties. Bigger BTO dimension in contrast, demonstrates counterclockwise hysteresis owing to their tetragonal crystal form. Through further Rietveld refinement analysis, we found that the tetragonality (c/a) of 100 nm BTO decreases at a higher temperature which narrows the hysteresis window. A wider hysteresis window was observed when utilizing 100 nm BTO compared to 20 nm BTO even at a lower loading ratio. The present findings imply different hysteresis mechanisms for BTO nanoparticles with varying dimensions which is crucial in understanding the role of how the BTO size tunes the crystal structures for integration in thin-film transistor devices.

Effect of Average Grain Size on the Uniformity and Ferroelectricity of BTO/PSX Thin Films Processed by Low-Temperature Solution Method

“…The polarization intensity of the film increases as the electric field strength increases, while the width of the hysteresis window remains relatively constant, as shown in Figure . Compared to the polarization intensity of 100 nm BTO nanoparticles around 1.2 μC/cm 2 measured in the prior research, 50 nm BTO nanoparticles exhibited a smaller polarization intensity of 0.03 μC/cm 2 with a narrower hysteresis window.…”

“…The phase transition of two BTO nanoparticles with distinct sizes in response to a change in temperature was verified using variable temperature X-ray diffraction (VTXRD), as illustrated in Figure . Upon comparison of the peak changes at 2θ = 45° position for both samples as they rose from room temperature to 300 °C, it becomes evident that all experimental samples underwent a phase transition due to the increase in temperature.…”

“…(d) 50 nm particle size BTO/PSX films. Figure 2a is reproduced from ref []. Copyright [2023] American Chemical Society.…”

“…Differences in phase transition temperatures for (a) wide range of 50 nm BTO, (b) wide range of 100 nm BTO, (c) 44−46 degree of 50 nm BTO, and (d) 44−46 degree of 100 nm BTO. Figure b, d is reproduced from ref []. Copyright [2023] American Chemical Society.…”

“…As a result, ferroelectricity was found only in the 100 nm diameter BTO/PSX film. However, because the surface of the film is too rough, it is not favorable for the subsequent preparation of TFT devices …”