Spray‐Pyrolyzed High‐k Zirconium‐Aluminum‐Oxide Dielectric for High Performance Metal‐Oxide Thin‐Film Transistors for Low Power Displays

Abstract

A high‐k, zirconium‐aluminum‐oxide (ZAO) gate insulator (GI) using low‐cost spray pyrolysis technique for large area and low power electronics is demonstrated. The high‐quality spray‐pyrolyzed ZAO GI is obtained with subsequent oxidation by eco‐friendly Ar/O2 plasma treatment. Analyses reveal that only one cycle Ar/O2 plasma treatment significantly enhances the thin‐film and dielectric properties of ZAO, exhibiting improved mass density (4.16 g cm−3), smooth surface roughness (0.32 nm), low leakage current density (2.26 × 10−6 A cm−2), high breakdown electric field (5.15 MV cm−1), and negligible frequency‐dependent capacitance. Hysteresis free, amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistors (TFTs) with ZAO GI exhibit a field‐effect mobility of 15.04 cm2 V−1 s−1, threshold voltage of 1.46 V, subthreshold swing of 115 mV dec−1, ION/IOFF ratio of 7.54 × 108, and negligible positive bias stress. The highly reliable a‐IGZO TFTs performances are achieved due to the significant reduction of oxygen‐related defects at the dielectric/semiconductor interface. The TFT inverter and an eleven‐stage ring oscillator have been demonstrated with ZAO/a‐IGZO TFTs, exhibiting a high voltage gain of 58, oscillation frequency of 2.43 MHz, and signal propagation delay of 18.7 ns at a supply voltage of 6 V, confirming the benefit of spray‐pyrolyzed high‐k ZAO dielectric for low power displays.

Improvement of Thermal and Environmental Stabilities of Short Channel Coplanar Amorphous InGaZnO Thin‐Film Transistors by Introducing Amorphous ZrAlOx Interlayer

“…The ZAO deposited by spray pyrolysis at the substrate temperature of 350 °C has no bubbles and no coffee rings and shows a smooth, uniform film surface and amorphous structure. [ 18,22,23 ] The mass density of ZAO film is found to be 4.03 g cm −2 . [ 22 ] A coplanar a‐IGZO TFT has an offset between channel and source/drain electrodes with an offset length of 3 μm each.…”

“…[ 18,22,23 ] The mass density of ZAO film is found to be 4.03 g cm −2 . [ 22 ] A coplanar a‐IGZO TFT has an offset between channel and source/drain electrodes with an offset length of 3 μm each. The high‐resolution transmission electron microscope (HR‐TEM) images show that the channel length is 0.87 μm, as shown in Figure 1c.…”

“…[ 18 ] We have reported the high‐quality ZrAlO x (ZAO) film by spray coating as a high‐ к gate insulator, which is used in this work for gas barrier. [ 22 ]…”

“…[17] The deposition parameters by spray pyrolysis such as substrate temperature, flow rate, nozzle speed, and distance between substrate and nozzle should be optimized to produce uniform, coffee ring-free, high-quality thin films over large areas. [18][19][20][21][22][23] Note that adding a stabilizer (ammonium acetate) in solution for spray coating increases the solubility of the solution and enhances the film quality by reducing the defects. [18] We have reported the high-quality ZrAlO x (ZAO) film by spray coating as a high-к gate insulator, which is used in this work for gas barrier.…”

“…[18] We have reported the high-quality ZrAlO x (ZAO) film by spray coating as a high-к gate insulator, which is used in this work for gas barrier. [22] The performances of a-IGZO TFTs are very sensitive to hydrogen and oxygen diffusions, where the former is commonly considered as a donor and the latter can compensate oxygen vacancy. [24,25] To overcome the diffusion of hydrogen/oxygen into the active a-IGZO, a passivation layer is required to protect the TFT channel from external diffusion.…”