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...

Thin-film transistor (TFT) is a essential device for future electronics driving the next level of digital transformation. The development of metal-oxide-semiconductor (MOS) TFTs is considered one of the most advantageous devices for next-generation, large-area flexible electronics. This study demonstrates the systematic study of the amorphous gallium oxide (a-Ga2O3) and its application to nanocrystalline ZnO TFTs. The TFT with a-Ga2O3/c-ZnO-stack channel exhibits a field-effect mobility of ∼41 cm2 V–1 s–1 and excellent stability under positive-bias-temperature stress. The a-Ga2O3/c-ZnO-stack TFT on polyimide (PI) substrate exhibits a negligible threshold voltage shift upon 100k bending cycles with a radius of 3 mm and is very stable under environmental test. The smooth morphology with tiny grains of ∼12 nm diameter with fewer grain boundary states improves the charge transport in Ga2O3/ZnO-stack TFT. The existence of amorphous a-Ga2O3 in between very thin ZnO layers helps to enhance the heterointerfaces and reduce the defect density in Ga2O3/ZnO interface. Therefore, integrating a-Ga2O3 in the ZnO channel in stacked TFT can increase mobility and enhance stability for next-generation flexible TFT electronics.

There is increasing interest in a ferroelectric transistor, mainly using vacuum processed hafnium oxide based materials. We report in this paper a solution processed ZnO thin-film transistor (TFT) with improved ferroelectric performance in Hf0.5Zr0.5O2 (HZO) using a triple layer of ZrOx/HZO/AlOx by spray pyrolysis. The performance enhancement is due to the difference in thermal expansion coefficient between the bottom/top dielectric and HZO layers. Grazing incident x-ray diffraction, current–voltage, capacitance–voltage, polarization–voltage, and anticlockwise hysteresis in transfer curve confirm the excellent ferroelectricity of the triple layer. A memory window as large as ∼3 V, the maximum on/off ratio of 3.5 × 109, the field-effect mobility of 125 cm2/V s, and the subthreshold slope of 0.18 V/decade were obtained from the ZnO TFT with the ZrOx/HZO/AlOx gate insulator, demonstrating the high performance ferroelectric ZnO TFT. This result can open opportunities for ferroelectric oxide TFT for large area electronics on glass, including display.

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The development of low-cost, high-mobility oxide thin-film transistors (TFTs) with excellent stability is of increasing interest. The coplanar oxide TFTs can be used for high-speed, large-area, and high-resolution displays. Here, we report highly oriented, as-grown crystalline InGaZnO (c-IGZO) with very low oxygen vacancy defects using spray pyrolysis at the substrate temperature of 425 °C. The c-IGZO exhibits a highly oriented, c-axis aligned crystal perpendicular to the substrate with a high mass density of 6.73 g cm −3 without any disordered incubation layer. Its resistivity can be decreased to 0.42 mΩ cm by NF 3 plasma doping, which is essential to achieving high-performance coplanar TFT. We have demonstrated the application of this material to highperformance flexible TFTs. The self-aligned, coplanar c-IGZO TFTs on the polyimide substrate exhibit an average field-effect mobility of 39.60 cm 2 V −1 s −1 , threshold voltage of −1.00 V, subthreshold swing of 0.21 V dec −1 , and on/off current ratio over 10 8 . The ring oscillator and gate driver made of the c-IGZO TFTs exhibit a propagation delay of 8.77 ns/stage and rising/falling times of 648/564 ns, respectively. Therefore, the as-grown c-IGZO by spray pyrolysis has the potential to be utilized as a new oxide semiconductor for the production of low-cost, flexible TFT electronics.

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A stack passivation by spray pyrolysis is demonstrated for high performance and stable amorphous indium‐gallium‐zinc‐oxide (a‐IGZO) thin‐film transistors (TFTs). The device performances and stabilities of a‐IGZO TFTs are compared with single zirconium‐aluminium‐oxide (ZAO), aluminium oxide (Al2O3), and stack ZAO/Al2O3 and Al2O3/ZAO passivation layers. The a‐IGZO TFTs with Al2O3/ZAO stack exhibit high performance and excellent stabilities under electrical, thermal, and environmental tests with negligible threshold voltage shift. The origin of the device performances and improved stabilities are analyzed using X‐ray photoelectron spectroscopy and high‐resolution transmission electron microscopy analyses. It is found that the Zr elements diffuse into the a‐IGZO channel when ZAO is directly deposited on the a‐IGZO, resulting in the deterioration of the device performance. It is also found that the Al2O3 single layer on top of the a‐IGZO cannot protect the back‐channel from moisture diffusion. But a thin Al2O3 layer on top of the TFTs can protect the diffusion of Zr elements from ZAO into the a‐IGZO channel and enhances the performance and stabilities. Therefore, the low cost, Al2O3/ZAO stack by spray pyrolysis on the sputtered a‐IGZO can be an excellent passivation for highly stable metal‐oxide TFTs.

We report a method for low-cost deposition of bubble-free, high-quality amorphous InGaZnO (a-IGZO) on polyimide (PI) substrate for foldable activematrix organic light emitting diode (AMOLED) display by spray pyrolysis. The coplanar thin-film transistor (TFT) with spray-pyrolyzed (SP) a-IGZO on PI substrate exhibits threshold voltage (VTH) of À0.8 V, saturation mobility of 40.95 cm2 V À1 s À1 , and subthreshold swing of 0.18 V per decade with on/off drain current ratio of $108. The high mobility TFT could be achieved using high substrate temperature (350 C) and low contact resistance by NF3 plasma on the SP a-IGZO. The TFT shows a ΔVTH of À0.4 V when it is bent on a cylinder of 1-mm radius. The TFT shows the ΔVTH of +0.05 V for positive bias temperature stress at +20 V at 60 C for 1 h. The ring oscillator made of a-IGZO TFTs exhibits an oscillation frequency of 2.38 MHz at VDD of 10 V with a propagation delay of 9.13 ns per stage. Therefore, the a-IGZO TFT by spray pyrolysis could be used for low-cost, high-performance, and flexible display TFT backplane.