In a recent paper published in Nanomaterials, researchers investigated the effects of laser treatment on terbium-doped indium oxide (Tb: In₂O₃) thin films and transistors.
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Their primary objective was to explore how varying laser energy densities influence the physical, optical, and electrical properties of Tb: In₂O₃ thin films and understand how these changes impact the performance and stability of Tb: In₂O₃-based metal oxide thin film transistors (MOTFTs).
These transistors are essential in modern electronic devices, making this research significant for advancing technology.
Background
Indium gallium zinc oxide (IGZO) thin film transistors (TFTs) are widely utilized in display technologies due to their high mobility and transparency. However, IGZO-TFTs suffer from poor stability under negative bias illumination stress (NBIS), limiting their practical applications.
To address this issue, the researchers investigated Tb: In₂O₃ as a material. Tb is a rare-earth element that, when doped into In₂O₃, can modify its properties. They hypothesized that the f-f transition of Tb³⁺ ions and the charge-transfer (C-T) transition of Tb⁴⁺ions during laser treatment could reduce the peak of the laser thermal effect and prolong the action time, potentially improving the material and device performance.
Research Overview
The researchers focused on examining the effects of Tb doping and laser treatment on In₂O₃ thin films and MOTFTs. Tb-doped In₂O₃ thin films were prepared using a simple, low-cost method called spin-coating. Post-processing was performed using a krypton fluoride (KrF) excimer laser with a wavelength of 248 nm at different laser energy densities.
The choice of this laser system was based on the premise that the f-f jump of Tb³⁺ ions and the C-T jump of Tb⁴⁺ ions during laser treatment could reduce the peak of the laser thermal effect and extend the action time, thereby enhancing the material's properties and device performance.
Various characterization techniques, including X-Ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-Vis spectroscopy, and Hall effect measurement, were employed. The researchers fabricated Tb: In₂O₃-TFTs and measured their electrical properties, such as current-voltage characteristics, switching current ratio, and bias stress stability. These properties were then compared with those of pure In₂O₃-TFTs and IGZO-TFTs prepared using the same methods.
Research Findings
The study revealed that laser treatment significantly affected the Tb: In₂O₃ films and devices. As the laser energy density increased, the film density increased, film thickness decreased, carrier concentration rose, and the optical band gap widened. These changes indicated that laser treatment induced structural and compositional modifications in the Tb: In₂O₃ films, such as grain growth, oxygen desorption, and Tb valence states.
XPS analysis confirmed the presence of both Tb³⁺and Tb⁴⁺ ions in the films, with the Tb³⁺/Tb⁴⁺ratio increasing with higher laser energy densities. The Tb³⁺/Tb⁴⁺ ions acted as shallow donors and deep acceptors, respectively, enhancing carrier concentration and mobility.
The Tb₂O₃ films did not exhibit significant crystallization, even when subjected to laser energy density treatments up to 250 mJ/cm². This was attributed to terbium's low electronegativity (1.1 eV) and high Tb-O dissociation energy (707 kJ/mol), which caused large lattice distortions and hindered the material's crystallization.
Laser treatment improved the performance and stability of Tb: In₂O₃-TFTs. Compared to pure In₂O₃-TFTs, Tb: In₂O₃-TFTs showed lower off-state current, higher switching current ratio, and improved bias stress stability.
The researchers also found that Tb: In₂O₃-TFTs had superior NBIS stability compared to IGZO-TFTs and comparable positive bias illumination stress (PBIS) stability. These advancements were attributed to Tb doping and laser-induced defects, which decreased trap density and improved carrier transport.
Applications
The authors suggested that Tb doping and laser treatment are effective methods for enhancing the properties and performance of In₂O₃thin films and MOTFTs.
Tb: In₂O₃-TFTs show great potential for applications requiring high-performance, transparent, and stable electronic devices, such as displays, sensors, and memory devices.
Additionally, these transistors can be integrated with other functional materials and devices, such as organic light-emitting diodes (OLEDs), photodetectors, and solar cells, to create novel optoelectronic systems.
Conclusion
The research showed that Tb doping and laser treatment induced advantageous structural and compositional changes in Tb: In₂O₃ films, improving carrier concentration, mobility, and the optical band gap.
Tb: In₂O₃-TFTs exhibited superior electrical properties and stability compared to pure In₂O₃-TFTs and IGZO-TFTs, making them promising candidates for high-performance, transparent, and stable electronic devices and systems.
For future research, the researchers recommended optimizing the Tb doping concentration and laser energy density to further enhance the performance of Tb: In₂O₃-TFTs. They also proposed investigating the effects of Tb doping and laser treatment on other metal oxide materials and devices.
This future work could lead to further advancements in electronic materials and devices, potentially expanding the applications and improving the performance of various optoelectronic systems.
Journal Reference
Yao, R., et al. (2024). Effects of Laser Treatment of Terbium-Doped Indium Oxide Thin Films and Transistors. Nanomaterials.. doi.org/10.3390/nano14110908
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