Water‐Induced Scandium Oxide Dielectric for Low‐Operating Voltage n‐ and p‐Type Metal‐Oxide Thin‐Film Transistors

Abstract

7180 wileyonlinelibrary.com IntroductionIn the past decade amorphous metaloxide thin-fi lm transistors (TFTs) have been studied in depth for applications in active-matrix organic light-emitting diodes (AMOLEDs), solar cells, biosensor arrays, and photodetectors. [ 1 ] Along with the rapid developments in display technology, highresolution and high-speed displays have become one of the growing trends. In this regard, energy consumption has turned out to be an inevitable issue especially for mobile, battery-powered applications. As a low-voltage operation of the oxide TFTs is demanded for practical applications, it is necessary to develop novel gate dielectrics for producing a large areal capacitance. [ 2 ] The achievements of low-voltage oxide TFTs have been extensively reported in recent works, including the use of inorganic high-k dielectrics, [ 3 ] organic self-assembled-monolayer dielectrics, [ 4 ] and electrolyte dielectrics. [ 5 ] Among these, the use of inorganic high-k dielectrics is the most attractive option as it simultaneously enables a low leakage current, through the use of a thicker fi lm, as well as a low-voltage operation. The high-k dielectrics can be prepared by various methods such as metal anodic oxidation method, [ 6 ] vacuum-based deposition, [ 7 ] and low-cost solution-based techniques. [ 8 ] [ 12 ] silicates, [ 13 ] etc.) that could potentially replace conventional dielectrics, such as SiO 2 and SiN x . To the best of our knowledge, there are few reports on the demonstration of scandium oxide (Sc 2 O 3 ) as the gate dielectric in TFT devices.As a high-k material Sc 2 O 3 has a dielectric constant of 14, a bandgap of 6.3 eV and an excellent thermal stability with Si. [ 14 ] In addition, Sc 2 O 3 has been found to possess a negative fi xed charge. This is benefi cial to obtain a positive threshold or turnon voltage for n-type TFTs that operate in the enhancement mode. [ 15 ] Concerning the CMOS architecture development based on solution processing, a wet step is inevitably involved. In this regard, the resistance to moisture absorption is another important , a large current ratio ( I on / I off ) of 2.7 × 10 7 and high stability. Moreover, as far as we know it is the fi rst time that solution-processed p-type oxide TFTs based on a high-k dielectric are achieved. The as-fabricated p-type CuO/ScO x TFTs exhibit a large I on / I off of around 10 5 and a hole mobility of 0.8 cm 2 V −1 at an operating voltage of 3 V. To the best of our knowledge, these electrical parameters are among the highest performances for solution-processed p-type TFTs, which represents a great step towards the achievement of low-cost, all-oxide, and low-power consumption CMOS logics.

Fully Solution‐Processed Low‐Voltage Driven Transparent Oxide Thin Film Transistors

“…The increase of gate capacitance with high k dielectric may lower the activation energy of electron transition and lead to the filling of the tail state up to higher energy levels. Thus, the electron can easily jump to the transport bands in the percolation path, as demonstrated by the noticeably high mobility in our ZnO TFTs.…”

Solution‐Processed High‐Performance p‐Type Perovskite NdAlO3 Thin Films for Transparent Electronics

“…It is found that all the NdAlO 3 thin films exhibit high transparency (over 90%) in the visible region, indicating their potential application in transparent electronics. The transmittance of NdAlO 3 thin film is decreased with the temperature, which is ascribed to the annihilation of the interstitial oxygen at high temperatures 36,37. Based on the transmittance spectra, the band gap ( E g ) of the NdAlO 3 thin films were calculated from the Tauc plot (Figure S1, Supporting Information) and summarized in the inset of Figure 3.…”

“…For the NdAlO 3 thin films annealed at the elevated temperatures, oxygen vacancies and defects are decreased. Both of the light absorption and the localized states in the forbidden gap are reduced accordingly, giving rise to the increase of the E g 36,37…”

“…The transmittance of NdAlO 3 thin film is decreased with the temperature, which is ascribed to the annihilation of the interstitial oxygen at high temperatures. [36,37] Based on the transmittance spectra, the band gap (E g ) of the NdAlO 3 thin films were calculated from the Tauc plot ( Figure S1, Supporting Information) and summarized in the inset of Figure 3. The E g values are estimated to be 5.40, 5.48, 5.54, 5.58, and 5.61 eV for the NdAlO 3 thin films annealed at 400, 500, 600, 700, and 800 °C, respectively.…”

“…Both of the light absorption and the localized states in the forbidden gap are reduced accordingly, giving rise to the increase of the E g . [36,37] Figure 4a-e exhibits the surface morphologies of the NdAlO 3 thin films annealed at various annealing conditions. The rootmean square (RMS) roughnesses of the NdAlO 3 thin films annealed at 400, 500, 600, 700, and 800 °C are 0.493, 0.376, 0.322, 0.288, and 0.263 nm, respectively.…”