We prepared indium zinc oxide ͑IZO͒ semiconductors for low temperature solution-processed thin-film transistors ͑TFTs͒. The sol-gel derived IZO films, annealed at 300°C, are uniform and have smooth surface morphology ͑root-mean-square roughness of 0.27 nm͒. Both the composition and the film thickness need to be optimized for high performance TFTs. With the composition of In/Zn equal to 50/50 in mol percent, the IZO TFTs with a thickness of 10 nm exhibited the best performance for a clear switching behavior ͑on/off current ratio of 1.2 ϫ 10 7 ͒ and output characteristics ͑drain current of 3.7 ϫ 10 −4 A͒, with a relatively high field-effect mobility ͑0.54 cm 2 V −1 s −1 ͒ and a low threshold voltage ͑1.9 V͒. The nonpassivated IZO-TFT stably operates over a two-month period without any significant change in the on/off current ratio and the mobility.Zinc oxide ͑ZnO͒-based thin film transistors ͑TFTs͒ have drawn significant attention due to their high performance and optical transparency in the visible region. 1-4 However, despite their superior performance, most fabrication methods for the production of ZnObased thin films involve high cost vacuum processes such as sputtering and pulsed laser deposition. 2-5 For mass-producible and cost-effective flexible electronics, TFTs need to be processed on plastic substrates by low cost, solution-based techniques at lower temperatures. 6-9 Recent years have witnessed a growing interest in solution-processed ZnO-related oxide TFTs. [8][9][10][11][12] Various solution deposition methods such as chemical bath deposition, hydrothermal growth, and spin-coating of either colloidal dispersion or sol-gel solution have been extensively researched. 8-17 Chemical bath deposition and hydrothermal growth techniques allow the formation of high quality films at lower temperatures, approximately 100°C, but the entire device must be submerged in a solution to produce the films. 11,13-15 The nanoparticulate derived deposition is suitable for obtaining high purity crystalline films at low temperatures, but it adversely affects a TFT's performance due to grain boundary scattering and surface roughness issues. 16 The sol-gel precursor solution is appropriate for various coating and printing techniques such as spin-coating and inkjet printing. Several groups have also studied the sol-gel derived oxide semiconductor transistors based on ZnO, 6,18 In 2 O 3 , 19 InZnO, 7 InZnSnO, 20 ZnSnO,21,22 GaZnO, 23 and InGaZnO. 8,9 It was demonstrated that the sol-gel derived oxide TFTs show high mobility ͑approximately 30 cm 2 /V s͒ and an on/off current ratio ͑10 6 ͒ comparable to vacuum deposited counterparts. 20 However, high annealing temperatures ͑400°C or more͒ are required to decompose the organic additives as well as the crystallization of the semiconducting oxides. A postannealing process may also be necessary to generate the charge carriers to enhance the TFT performance. Recently, Meyers et al. reported low temperature ͑less than 300°C͒ processed, high performance ZnO-TFTs in which an aqueous Zn͑OH͒ ...

We investigated the influence of the chemical compositions of gallium and indium cations on the performance of sol-gel-derived amorphous gallium indium zinc oxide (a-GIZO)-based thin film transistors (TFTs). A systematic compositional study allowed us to understand the solution-processed a-GIZO TFTs. We generated a compositional ternary diagram from which we could predict electrical parameters such as saturation mobility, threshold voltage, and the on/off current ratio as the constituent compositions varied. This diagram can be utilized for tailoring solution-processed amorphous oxide TFTs for specific applications.

Highly stable and high performance solution-processed amorphous oxide semiconductor thin film transistors (TFTs) were produced using a Li and Zr co-doped ZnO-based aqueous solution. Li and Zr co-doping at the appropriate amounts enhanced the oxide film quality in terms of enhanced oxygen bonding and reduced defect sites. The 0.5 mol% Li and 1.0 mol% Zr co-doped ZnO TFTs annealed at 320 C exhibited noticeably lower threshold voltage shifts of 3.54 V under positive bias stress and À2.07 V under negative bias temperature stress than the non-doped ZnO TFTs. The transistors revealed a good device mobility performance of 5.39 cm 2 V À1 s À1 and an on/off current ratio of 10 8 when annealed at 320 C, compared to a mobility performance of 2.86 cm 2 V À1 s À1 and an on/off current ratio of $10 7 when annealed at 270 C. Our results suggest that Li and Zr co-doping can be a useful technique to produce more reliable and low temperature solution-processed oxide semiconductor TFTs.

The effects of bias stress on spin-coated zinc tin oxide ͑ZTO͒ transistors are investigated. Applying a positive bias stress results in the displacement of the transfer curves in the positive direction without changing the field-effect mobility or the subthreshold behavior, while a negative stress has no effect on the threshold voltage shift. Device instability appears to be a consequence of the charging and discharging of the temporal trap states at the interface and in the ZTO channel region. All the stressed devices recover their original characteristics after 10 min at room temperature. Furthermore, the inkjet-printed transistor yields similar bias stress effects as those observed in their spin-coated counterparts but has a greater shift in the threshold voltage. Microstructural evidence in conjunction with Rutherford backscattering spectroscopy confirms that severe instability is attributed to the presence of nanopores in the inkjet-printed channel layer.ZnO-based oxide semiconductor thin-film transistors ͑TFTs͒ have become attractive for its use in switching devices of large electronics, such as active matrix liquid crystal displays and active matrix light emitting diode displays, due to their good uniformity and better device performance as compared with conventional Sibased TFTs. 1 The transparency of ZnO-based materials can support the next generation of applications, including "see-through" displays. 2 They have been generally fabricated by vacuum deposition methods such as radio-frequency magnetron sputtering and pulsed laser deposition. However, their high manufacturing costs pose an obstacle for modern, mass-produced, large electronics.In contrast, solution-processed deposition, such as spin coating and inkjet printing, offers many advantages such as simplicity, low cost, and high throughput, thus enabling the fabrication of low cost printed electronics. Solution-processable organic semiconductors such as poly͑3-hexylthiophene͒ have therefore been extensively researched, but they suffer low mobility ͑below 0.1 cm 2 V −1 s −1 ͒ and poor stability against humidity during long-term operations. 3,4 For this reason, ZnO-based oxide semiconductors that are stable in air and suitable for solution processes in the form of colloidal dispersions or sol-gel solutions have drawn research interest. Recent years have seen a growing number of reports on solution-processed high performance TFTs with oxide semiconductors based on ZnO, 5 InZnO, 6 and ZnSnO. 7 For practical use, the stability of ZnO-based TFT devices has remained the most important and critical issue to overcome. The application of a prolonged gate bias results in the deterioration of the current-voltage characteristics. This effect could be demonstrated as a change in the field-effect mobility, a change in the subthreshold slope, or as a shift in the threshold voltage. 8-10 In particular, the shift in the threshold voltage of organic light emitting diodedriving transistors leads to a change in the individual pixel brightness. Though several groups hav...