Solution-Processed Gallium–Tin-Based Oxide Semiconductors for Thin-Film Transistors

Abstract

We investigated the effects of gallium (Ga) and tin (Sn) compositions on the structural and chemical properties of Ga–Sn-mixed (Ga:Sn) oxide films and the electrical properties of Ga:Sn oxide thin-film transistors (TFTs). The thermogravimetric analysis results indicate that solution-processed oxide films can be produced via thermal annealing at 500 °C. The oxygen deficiency ratio in the Ga:Sn oxide film increased from 0.18 (Ga oxide) and 0.30 (Sn oxide) to 0.36, while the X-ray diffraction peaks corresponding to Sn oxide significantly reduced. The Ga:Sn oxide film exhibited smaller grains compared to the nanocrystalline Sn oxide film, while the Ga oxide film exhibited an amorphous morphology. We found that the electrical properties of TFTs significantly improve by mixing Ga and Sn. Here, the optimum weight ratio of the constituents in the mixture of Ga and Sn precursor sols was determined to be 1.0:0.9 (Ga precursor sol:Sn precursor sol) for application in the solution-processed Ga:Sn oxide TFTs. In addition, when the Ga(1.0):Sn(0.9) oxide film was thermally annealed at 900 °C, the field-effect mobility of the TFT was notably enhanced from 0.02 to 1.03 cm2/Vs. Therefore, the mixing concentration ratio and annealing temperature are crucial for the chemical and morphological properties of solution-processed Ga:Sn oxide films and for the TFT performance.

Solution-processed amorphous gallium-tin oxide thin film for low-voltage, high-performance transistors

“…From Fig. 2c, Ga 3d peaks are located at 20.2 eV [20]. The Ga and Sn orbital peaks in the full spectra ( Fig.…”

“…Consequently, the excess electrons in the conductive SnO 2 thin film must be inhibited to achieve the enhancement-mode TFT device. The Sn 3d peaks at 486.4 (Sn 3d 5/2 ) and 494.8 eV (Sn 3d 3/2 ) [20] do not obviously shift after Ga incorporation, indicating the oxidation state of Sn element is not affected evidently, as shown in Fig. 2b.…”

“…Recently, Matsuda et al [19] reported RF magnetron sputtered a-GaSnO (GTO)-TFTs with high mobility of 25.6 cm 2 V −1 s −1 at 350°C. Zhang et al [20] reported nanocrystalline Ga-rich GTO-TFTs with mobility of 1.03 cm 2 V −1 s −1 at 900°C. The high annealing temperature is not compatible with high-k dielectric and flexible substrates.…”

Memristive characteristic of an amorphous Ga-Sn-O thin-film device

“…3c. It is found that the Ga 2p and Sn 3d peaks are observed, which means that the α-GTO thin-film layer is composed of GaO x and SnO x , and the Sn 3d 5/2 peak is the sum of the large Sn 4+ peak and small Sn 2+ peak, which means that SnO 2 is more than SnO, although they are mixed, which is also similar to GTO thin films made under different conditions 13 . Because it was reported that SnO 2 is n-type semiconductor and SnO is p-type semiconductor 23,24 , the α-GTO thin-film layer is overall n-type semiconductor, which is also confirmed by the facts that α-GTO thin-film transistors show n-type transistor characteristics 12 and α-GTO thin-film thermoelectric devices show negative Seebeck coefficients 14 .…”

“…They can be fabricated at low temperature and produced on large area with low cost. Particularly, the research on α-GTO thin-film devices is focused for not only thin-film conductors 5–10 but also thin-film transistors 11–13 and other applications 14,15 . They do not include rare metals such as In, and industrial issues on resource depletion and supply anxiety can be solved.…”