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.