## 1 Introduction  
With the discovery of graphene, two-dimensional (2D) layered materials have been drawing intense research interest. Despite its excellent mechanical, optical, and electrical properties, however, graphene is considered unsuitable as an active component of field effect transistors due to its lack of a band gap [1; 2; 3]. In efforts to overcome this limitation, i.e., to produce a band gap in graphene, a great deal of research has been carried out, but the results thus far have only added to the complexity of the processes and reduced mobility [4; 5]. In this context, layered 2D transition metal dichalcogenides (TMDs)-based thin-film transistors (TFTs) are drawing considerable attention as promising candidates to lead the next-generation transistor technology. Among the 2D TMDs, molybdenum disulfide (MoS\({}_{2}\)) is at the center of attention, and relevant research is underway [6; 7; 8]. MoS\({}_{2}\) TFTs have excellent carrier mobility, a high on- and off-current ratio (\(I_{\text{on}}/I_{\text{off}}\)), mechanical flexibility, and a relatively large band gap [9; 10; 11; 12]. Despite these properties, when the MoS\({}_{2}\) channel is exposed to atmospheric environments, MoS\({}_{2}\) TFTs exhibit a hysteresis phenomenon in the transfer characteristic. Various research groups have already shown that this hysteresis phenomenon occurs in MoS\({}_{2}\) TFTs due to the effects of oxygen and water in the air [13; 14; 15]. To suppress this phenomenon, the surface of a semiconducting active channel must be isolated from the air by passivation layers, e.g., atomic-layer-deposited (ALD) aluminum oxide (Al\({}_{2}\)O\({}_{3}\)) or hafnium dioxide. It is known that the surface of pristine (i.e., without any surface modifications) MoS\({}_{2}\) does not react well with trimethylaluminum (TMA), which is used as a precursor to form Al\({}_{2}\)O\({}_{3}\) layers, due to the absence of dangling bonds [16; 17; 18; 19]. However, high-\(k\) dielectric layers without pinholesand/or cracks are indispensable for nano-electronic devices. To improve the wettability and reactivity between the MoS\({}_{2}\) surface and TMA and to ensure complete isolation of the surface from atmospheric environments, some strategies prior to deposition of the passivation layer were proposed, for example, oxygen plasma or ultraviolet-ozone (UV-ozone) treatment [18; 19; 20; 21; 22; 23]. Conventional MoS\({}_{2}\) TFTs without passivation layers exhibited different electrical properties at high temperatures with respect to the height of the Schottky barrier between the metal electrodes and MoS\({}_{2}\)[8; 24; 25]. For a relatively high Schottky barrier, charge carriers (i.e., electrons) were blocked by the barrier and thus could not pass at a low temperature. However, as the temperature increased, those carriers started to transport into the MoS\({}_{2}\) channels through thermionic emission [26]. This led to an increase in carrier mobility with respect to increased temperature. Unlike previous reports on MoS\({}_{2}\) TFTs, little research has been conducted on the transport mechanism at high temperatures in passivated MoS\({}_{2}\) TFTs. The present study investigated how passivated MoS\({}_{2}\) TFTs with a high Schottky barrier change in a high-temperature environment. First, cross-sectional transmission electron microscopy (TEM) was utilized to visualize the quality of Al\({}_{2}\)O\({}_{3}\) deposited on the MoS\({}_{2}\) surface through UV-ozone treatment. The surface morphology of the Al\({}_{2}\)O\({}_{3}\) on the MoS\({}_{2}\) channel was investigated by atomic force microscopy (AFM), depending on UV-ozone treatment. Also, the electrical properties of the devices were characterized to assess the effectiveness of Al\({}_{2}\)O\({}_{3}\) passivation. As a result, it was confirmed that carrier mobility improved and that the hysteresis effect decreased significantly; thus, the desired effect of passivation was achieved.