Ultrafast (50 ns) ID–VG Analysis on Oxide Thin-Film Transistors With Morphotropic Phase Boundary State High-κ Gate Insulator

The advancement of oxide thin-film transistors (TFTs) with high-performance is crucial for high-resolution, high-framerate displays as they serve as switching and driving elements. To ensure high mobility characteristics and withstand relatively high supply voltage (5 V), a TFT panel must have a high- $\kappa $ gate dielectric (DE) with comparatively thick thickness and good interfacial quality. Maintaining a high- $\kappa $ gate insulator in a moderately thick regime and preventing charge-trapping from deteriorating electrical properties are still difficult tasks. In this study, we employed an oxide TFT with a morphotropic phase boundary (MPB) Hf-Zr-O (HZO) film as a high- $\kappa $ gate insulator. MPB is a combination of two crystalline phases between the orthorhombic phase of the ferroelectric (FE) phase and the tetragonal phase of the anti-FE (AFE) phase, which exhibits the maximum DE constant ( $\kappa \sim {64}$ ) of the HZO film. A 30 nm-thick film of MPB HZO (Hf:Zr = 1:5) was used as the high-gate insulator in TFT. Also, by inserting 1 nm-thick AlO between the oxide channel and the HZO gate insulator, we mitigated the impact of charge trapping on the electrical properties. Ultimately, we used a pulse with a rise duration of 50 ns for ultrafast ${I}_{D}$ – ${V}_{G}$ to estimate intrinsic mobility. The intrinsic mobility of the MPB HZO + AlO device was found to be 20.9 cm2/ $\text{V}\cdot \text{s}$ , which is equivalent to the mobility of a SiO2 gate insulator in the same device. The findings of this research are noteworthy as we assessed the electrical characteristics of oxide TFT using MPB HZO as a gate insulator for the first time.

I. Introduction

For the next-generation devices, it is required to develop large-area, high-resolution, high-framerate displays [1], [2], [3]. Thus, the oxide thin-film transistor (TFT) used as the switching and driving elements of the display should exhibit a high ON-current at the supply bias voltage of 5 V [4]. Since the Ion of the device is proportional to the mobility of the electronically active oxide semiconductor channel, various research has been conducted to increase its mobility in oxide semiconductor TFT by employing metal doping, [5] heterostructure stack, [6] and changing the atomic ratio of the oxide channel [7]. However, it is difficult to resolve issues regarding reliability degradation such as negative threshold voltage () shifts and instabilities [8]. As an alternative, high- gate insulators can be used for developing high- devices, provided that the reliability and quality of the interfacial layer are guaranteed. Particularly, in the past ten years, hafnia-based oxide film has attracted a lot of interest as a potential technique for high- gate insulators [9], [10], [11], [12]. Benefits of hafnia-based oxide film include a wide bandgap, low equivalent oxide thickness (EOT), facile atomic layer deposition (ALD) deposition, high dielectric (DE) constant ( 20), and excellent compatibility with the CMOS process [13], [14].