0741-3106 (c) 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/LED.2017.2758349, IEEE Electron Device Letters > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract— This letter reports the fabrication of p-channel tin monoxide (SnO) thin-film transistors (TFTs) with a high-permittivity zirconium oxide (ZrO2) gate insulator film, which were prepared by a low-cost spin-cast method. The spin-cast ZrO2 dielectrics exhibit a low leakage current density of 4.5  10 -8 A/cm 2 at 1 MV/cm. Introducing the ZrO2 dielectric into p-type SnO TFTs allows for a reduction in the driving gate voltage range from 80 V to 10 V, as compared to devices with a thermal SiO2 gate insulator. Additionally, a high field-effect mobility of 2.5 cm 2 /Vs and an ION/OFF of 3 x 10 3 were preserved. Index Terms— ZrO2 gate dielectric, spin cast, tin monoxide, p-type semiconductor, thin-film transistors. I. INTRODUCTION ECENTLY, p-type oxide semiconductors (OSs) have received much attention because highly-efficient transparent circuits and electronics can be realized via the simultaneous implementation of p-type oxide semiconductors (OSs) and commercially-available n-type IGZO semiconductors. Tin monoxide (SnO), as a p-type OS, exhibits a promising performance due to its relatively large optical band gap of 2.7 eV and the effective intercalation of the 5s orbital of Sn 2+ into its valence band. [1] Device performance has been improved by optimizing the stoichiometry, valence state of tin cations, and microstructure of the SnO channel. [2] So far, a typical field-effect mobility (FE) of ~2 cm 2 /Vs and drain current modulation (ION/OFF) of ~10 4 have been achieved for SnO TFTs. Gate dielectric films also play an important role in determining the device performance because the transporting properties of hole carriers along the channel layer are strongly affected via scattering and trapping of charge carriers near the channel/gate dielectric interface. For this purpose, high- dielectrics, such as HfO 2 , Al 2 O 3 , and AlTiO, have been studied for p-channel SnO TFTs. [3-5] However, most high- dielectrics have been prepared using vacuum-based technologies, including atomic layer deposition and pulsed laser deposition methods. [3-5] Although solution-based processes have the This work was supported by Samsung Research Funding Center for Future Technology through Samsung Electronics. Azida Azmi and Rino Choi are with the Department of Materials Science and Engineering, Inha University, Incheon 22212, Republic of Korea. Jiwon Lee, Tae Jung Gim, and Jae Kyeong Jeong are with the Department of Electronic Engineering, Hanyang University, Seoul 04763, Republic of Korea (e-mail: jkjeong1@hanyang.ac.kr). advantages of utilizing relatively simple and low-cost fabrication methods, compared to vacuum-based processes, [6] there have been no reports investigating p-channel SnO TFTs with a solution-processed gate dielectric (to the best of our knowledge). In this letter, the suitability of a spin-cast ZrO2 film was examined for p-channel SnO TFTs. The high- ZrO2 dielectric was chosen because it has high permittivity, good thermal stability, and a wide energy bandgap. It was found that spin-cast ZrO 2 had a low leakage current density (J g ) of 4.5 x 10 -8 A/cm 2 at an electric field of 1 MV/cm and a high dielectric constant of 17. The p-channel SnO TFTs with a ZrO2 dielectric exhibited a low voltage drivability (< 5 V), high FE of 2.5 cm 2 /Vs, and I ON/OFF of 3 x 10 3 . II. EXPERIMENTAL PROCEDURE A 0.1 M ZrO2 precursor solution was prepared by dissolving zirconium oxynitrate hydrate (ZrO(NO 3 ) 2 , Sigma Aldrich) in 2-methoxyethanol (C3H8O2, Sigma Aldrich), which was then stirred vigorously for 3 h at 50  C until the solute was dissolved completely. The heavily-doped p-type bare Si substrate was cleaned with acetone, isopropyl alcohol, and deionized water for 10 min each prior to deposition of the gate dielectric. The prepared ZrO2 solution was filtered through a 0.2-m syringe filter and spin-coated at 3000 rpm for 30 s. Samples were then pre-baked on a hotplate at 100  C for 10 min to remove residual solvent. The deposited layers were annealed at 400  C and 450  C for 1 h under an ambient atmosphere in an electric furnace. Metal-insulator-metal (MIM) capacitors were fabricated by sputtering ITO (as the gate electrodes) through a patterned shadow mask with 100-m-diameter holes onto ZrO 2 /Si substrates. The working pressure and DC power during ITO deposition were 5 mTorr and 50 W under Ar atmosphere, respectively. The frequency-dependent capacitance was measured using an HP 4284A impedance analyzer over a frequency range of 1 – 10 3 kHz. The dielectric leakage current density (J g ) was measured using an HP 4140B Picoammeter/DC voltage source. The bottom gate p-type TFTs were fabricated by depositing SnO as a channel layer on the ZrO 2 /Si substrates using a DC sputtering system. A 3” diameter metallic Sn target was used and the sputtering was performed at the room temperature. DC power, working pressure, and O 2 /(Ar+O 2 ) ratio were 50 W, 3 mTorr, and 3.8%, respectively. The gas flow rate for Ar and O2 were fixed to 30 Performance Improvement of p-Channel Tin Monoxide Transistors with a Solution-Processed Zirconium Oxide Gate Dielectric Azida Azmi, Jiwon Lee, Tae Jung Gim, Rino Choi and Jae Kyeong Jeong R