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.
This CBM mainly consists of cation s-orbitals that are large enough to overlap the adjacent cations. Therefore, the effective mass of electrons is relatively small and less affected by the disorder of non-directional s-orbitals than the directional sp3 orbital in Si, allowing the AOS to make relatively high mobility even in the amorphous phase. [3,4] The fabrication process of AOS is not as complicated as that of low-temperature poly-Si (LTPS). [5] AOS can be fabricated by both vacuum and low-cost solution processes. The conventional AOS processing methods are sputtering, atomic layer deposition (ALD), metal-organic chemical vapor deposition (MOCVD), spin coating, ink-jet printing, spray pyrolysis, and so on. [6][7][8][9][10] Among these methods, spray pyrolysis is one of the most promising technology due to its simplicity, cost-efficiency, and vacuum-free deposition capability. Compared to the other solution methods, spray pyrolysis can produce uniform films over large areas. [11] However, the main challenges of the spray pyrolysis technique are to make dense and bubbles free films at low temperature. The rapid evaporation of the solvent during spray coating often results in bubbles or coffee rings throughout the film. In previous work, we developed high-density and bubbles-free metal oxide films using precursor solution modification. [12a] The zinc (Zn) based thin-films grown at 350 °C have shown high density with bubbles-free smooth surface morphology. [12a] These materials are applied to obtain high-performance zinc oxide (ZnO) based TFTs, exhibiting mobility over 70 cm 2 V −1 s −1 and excellent stability. [13][14][15][16][17] The device structure is one of the crucial technology to fabricate TFTs backplane for an active-matrix organic light-emitting diode (AMOLED) display. The self-aligned (SA) coplanar TFTs offer a large area, fast frame rate, and high-resolution AMOLED display compared to the bottom-gated (BG) structure. Therefore, the SA coplanar TFTs are being used for the manufacturing of AMOLED television (TV). To the best of our knowledge, there is only one report on SA coplanar TFT with a metal oxide semiconductor (MOS) using spray pyrolysis. [18] Most reports on spray-pyrolyzed MOS devices have focused on the BG TFTs with the inverted staggered structure such as etch stopper (ES) or back channel etched (BCE). [19] This structure has high parasitic capacitance (C par ) due to the overlap between the gate and source/drain (S/D) electrodes. [20] On the High-performance, spray-pyrolyzed amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistor (TFT) with self-aligned (SA) coplanar structure is demonstrated. The spray-pyrolyzed a-IGZO film exhibits bubbles-free smooth surface roughness (0.81 nm) and low oxygen-related defects (22.5%). The fluorine-doped a-IGZO film shows a low resistivity of 1.18 × 10 −3 Ω-cm by NF 3 plasma treatment. This is sufficient to obtain ohmic contact with the source/ drain electrodes and doped IGZO in the offset region of the SA coplanar TFT. The spray-pyrolyzed a-IGZ...
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