Chemical composition and temperature dependent performance of ZnO-thin film transistors deposited by pulsed and continuous spray pyrolysis

Abstract

Zinc oxide thin film transistors (TFTs) deposited by continuous and pulsed spray pyrolysis were investigated to analyze process kinetics which make reduction of process temperature possible. Thus, fluid mechanics, chemical composition, electrical performance, and deposition and annealing temperature were systematically analyzed. It was found that ZnO layers continuously deposited at 360 °C contained zinc oxynitrides, CO3, and hydro carbonate groups from pyrolysis of basic zinc acetate. Statistically, every second wurtzite ZnO unit cell contained an impurity atom. The purity and performance of the ZnO-TFTs increased systematically with increasing deposition temperature due to an improved oxidation processes. At 500 °C the zinc to oxygen ratio exceeded a high value of 0.96. Additionally, the ZnO film was not found to be in a stabilized state after deposition even at high temperatures. Introducing additional subsequent annealing steps stabilizes the film and allows the reduction of the overall thermal stress to the substrate. Further improvement of device characteristics was obtained by pulsed deposition which allowed a more effective transport of the by-products and oxygen. A significant reduction of the deposition temperature by 140 °C was achieved compared to the same performance as in continuous deposition mode. The trap density close to the Fermi energy could be reduced by a factor of two to 4 × 1017 eV−1 cm−3 due to the optimized combustion process on the surface. The optimization of the deposition processes made the fabrication of TFTs with excellent performance possible. The mobility was high and exceeded 12 cm2/V s, the subthreshold slope was 0.3 V dec−1, and an on-set close to the ideal value of 0 V was achieved.

Significant improvement of spray pyrolyzed ZnO thin film by precursor optimization for high mobility thin film transistors

“…Whereas, Fig. 4(d-f) www.nature.com/scientificreports www.nature.com/scientificreports/ and -OH groups are related to the improvement of the film quality [28][29][30][31][32][33][34][35] , The ZnO film without AA shows a higher percentage of the hydroxide group (12%) compared to the ZnO film with AA (6%). Oxygen vacancies are related to point defects in the crystalline ZnO film.…”

Sub-second photonic processing of solution-deposited single layer and heterojunction metal oxide thin-film transistors using a high-power xenon flash lamp

“…The VTH on the other hand remains unchanged due to the shallow slope of the transfer characteristic in the subthreshold regime which might indicate the presence of electron trap states in the bulk of the active area and/or at the interface with the gate dielectric. 27,28 Increasing the number of pulses to 20 results to a significant increase in the electron mobility to a value of 36 cm 2 /Vs accompanied by shifts in VON and VTH towards negative voltages, both denoting a higher concentration of mobile electrons. We attribute this to the transfer of electrons from the conduction band (CB) of ZnO to that of the In2O3 driven by the significant difference in their work functions and CB energies.…”

Influence of annealing temperature on photoluminescence properties and optical constants of N-doped ZnO thin films grown on muscovite mica substrates

“…In addition, it has chemical and thermal stability, high radiation resistance, high transparency, and good conductivity [2]. It thus has been in increasing demand for various potential applications in sensors [3], thin-film transistors (TFTs) [4], solar cells [5], and photo-catalysts [6] etc. However, it is difficult to achieve reliable and reproducible p-type ZnO for developing ZnO-based devices because ZnO exhibits natural n-type conductivity.…”