Improvement of InGaZnO<sub>4</sub>Thin Film Transistors Characteristics Utilizing Excimer Laser Annealing

Nakata, Masaya; Takechi, Kazushige; Azuma, Kazufumi; Tokumitsu, Eisuke; Yamaguchi, Hirotaka; Kaneko, Shigeo

doi:10.1143/apex.2.021102

Cited by 46 publications

(37 citation statements)

References 10 publications

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“…A drastic variation from low conductivity to high conductivity occurs at a critical laser energy density ͑10.7 mJ/cm 2 ͒ or at a critical UV irradiation time. The influence of laser energy density on IGZO conductivity was also reported by Nakata et al 5 when they used a XeCl excimer laser to treat an IGZO film. In their article, increasing laser energy density also significantly increases IGZO conductivity, and a critical laser energy density such as 90 mJ/cm 2 is observed.…”

Section: Resultssupporting

confidence: 67%

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Low Temperature Annealing with Solid-State Laser or UV Lamp Irradiation on Amorphous IGZO Thin-Film Transistors

Zan

Chen

Chou

et al. 2010

Electrochem. Solid-State Lett.

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Instead of the conventional furnace annealing process with a temperature higher than 300°C, two low temperature annealing methods are successfully demonstrated to suppress the instability problem of amorphous indium gallium zinc oxide ͑IGZO͒ thin film transistors ͑TFTs͒. With adequate Nd:yttrium aluminum garnet laser ͑266 nm͒ annealing energy density or Xe excimer UV lamp ͑172 nm͒ irradiation time, the on voltage shift is greatly suppressed from over 10 to 0.1 V. The influence of laser energy density and UV lamp irradiation time on the performance of IGZO TFTs is also investigated and explained. The proposed methods are promising for the development of amorphous IGZO TFTs on flexible substrates.Recently, transparent amorphous InGaZnO 4 ͑IGZO͒ thin-film transistors ͑TFTs͒ have become promising candidates to realize flexible display on plastic substrates because they can be deposited at a temperature lower than 150°C. 1 Compared to amorphous silicon TFT, IGZO TFT exhibits a higher mobility ͑3-30 cm 2 /V s͒ even in the amorphous phase. 2 However, in many articles, low temperature deposited IGZO TFT suffers from significant instability problems. 3,4 Its current-voltage ͑I-V͒ characteristics shift during electrical measurement. To suppress the characteristics' shift, furnace annealing higher than 300°C is usually used. It was reported that the annealing process reduces the tail state defects, rearranges the amorphous structure, and improves oxygen compensation in the nonstoichiometric film. 3,4 However, an annealing temperature higher than 300°C makes the process unsuitable for flexible substrates. A low temperature annealing process is essential for the development of stable IGZO TFTs on flexible substrates.One method utilizing excimer laser annealing ͑ELA͒ to improve IGZO TFT characteristics was proposed recently. 5 Although the authors did not mention stability issues, they successfully demonstrated the feasibility of using ELA on IGZO TFTs. In our study, two low temperature annealing methods are proposed to effectively solve the stability problem. One method is the solid-state Nd:yttrium aluminum garnet ͑YAG͒ laser annealing method; the other method is a simple UV lamp irradiation method. The Nd:YAG solid-state laser operates at a wavelength of 266 nm, annealing the IGZO TFT at a low laser energy density of 10.7 mJ/cm 2 . This low energy density enables the future design of a large laser beam size with a low production cost. To further reduce the production cost, another annealing process is proposed. This annealing process uses a low power ͑50 mW/cm 2 ͒ Xe excimer lamp with a wavelength of 172 nm ͑UV light͒. The UV lamp irradiation effectively anneals the devices. The proposed method is a promising candidate to realize large-area, low cost UV lamp annealing for IGZO TFTs. In this article, the influences of laser energy density and UV lamp irradiation time on the performance and stability of IGZO TFTs are investigated. The bias-stress effects of an unannealed device, a laserannealed device, and a UV-annealed devic...

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Section: Resultssupporting

confidence: 67%

“…5 Although the authors did not mention stability issues, they successfully demonstrated the feasibility of using ELA on IGZO TFTs. In our study, two low temperature annealing methods are proposed to effectively solve the stability problem.…”

mentioning

confidence: 99%

Low Temperature Annealing with Solid-State Laser or UV Lamp Irradiation on Amorphous IGZO Thin-Film Transistors

Zan

Chen

Chou

et al. 2010

Electrochem. Solid-State Lett.

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“…In this study, we focused on an IZO TFT with a higher field-effect mobility than an a-IGZO TFT. We assumed that an ELA process crystallizes IZO with nanograins easily since this material has a lower crystallization temperature than a-IGZO 12,13 and that an IZO film composed of nanograins has better characteristics than a noncrystallized IZO TFT since carrier scattering is suppressed in the disordered film. We considered it is necessary to use a laser with a wavelength shorter than 400 nm, for the laser to be absorbed by the IZO film since IZO has a wide band gap (higher than 3 eV).…”

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confidence: 99%

Low temperature high-mobility InZnO thin-film transistors fabricated by excimer laser annealing

Fujii

Ishikawa

Ishihara

et al. 2013

Applied Physics Letters

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In this study, we successfully achieved a relatively high field-effect mobility of 37.7 cm 2 /Vs in an InZnO thin-film transistor (TFT) fabricated by excimer layer annealing (ELA). The ELA process allowed us to fabricate such a high-performance InZnO TFT at the substrate temperature less than 50 C according to thermal calculation. Our analysis revealed that high-energy irradiation in ELA produced a mixed phase of InZnO and SiO 2 , leading to the deterioration of TFT characteristics. Oxide semiconductor films deposited by sputtering have recently attracted considerable attention in the fields of transparent and flexible electronics for next-generation displays, in comparison with conventional amorphous silicon-based materials. In particular, an In 2 O 3 -doped ZnO (IZO) thin film is widely recognized as a suitable oxide semiconductor since thin-films transistors (TFTs) with that material in the channel layer yield a higher field-effect mobility than amorphous InGaZnO (a-IGZO) TFTs. [1][2][3] In the case of the IZO film, the amorphous phase generally provides a high conductivity of about 400 X À1 cm À1 , which is much higher than the conductivity suitable for the TFT's channel layer. 4,5 The conductivity of this material can possibly be reduced by a thermal annealing process. 6,7 In previous reports, thermal annealing with a relatively high temperature of about 300 C has been proposed to produce operative IZO TFTs. 8,9 However, such a high-temperature process in postannealing limits the choice for plastic flexible substrates. The excimer laser annealing (ELA) process with short pulses has been widely utilized to achieve a low processing temperature to produce a polycrystalline silicon thin film on a glass substrate. 10 This technique has also been utilized for oxide-semiconductor materials. Nakata et al. reported the fabrication of a-IGZO TFTs by ELA process, which acted as a postannealing process, and the improvement of the TFTs characteristics by ELA, 11 suggesting that the ELA process is also a promising technique for improving the characteristics of oxide-semiconductor devices. In this study, we focused on an IZO TFT with a higher field-effect mobility than an a-IGZO TFT. We assumed that an ELA process crystallizes IZO with nanograins easily since this material has a lower crystallization temperature than a-IGZO 12,13 and that an IZO film composed of nanograins has better characteristics than a noncrystallized IZO TFT since carrier scattering is suppressed in the disordered film. We considered it is necessary to use a laser with a wavelength shorter than 400 nm, for the laser to be absorbed by the IZO film since IZO has a wide band gap (higher than 3 eV). 14 We used an XeCl excimer laser with a sufficiently short wavelength of 308 nm (photon energy: 4.02 eV) 15,16 and investigated the effects of the ELA process on the IZO TFT characteristics and film properties.A thermally oxidized SiO 2 film of 100 nm thickness was formed on a highly doped p-type silicon wafer (<0.002 X cm) as a gate insulator. IZO films with...

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“…In general, furnace annealing above 300 • C is effective for obtaining good transfer characteristics and stable IGZO-TFTs [9]- [11], but processing temperatures above 150 • C are not compatible with most flexible polymer substrates. To address the low temperature integration issue, excimer laser annealing (ELA) has been explored [12], [13]. However, the small laser beam size is a major limitation to meet the high throughput and low-cost demands of large area roll-to-roll manufacturing.…”

Section: Introductionmentioning

confidence: 99%

Pulse Thermal Processing for Low Thermal Budget Integration of IGZO Thin Film Transistors

Noh

Joshi

Kuruganti

et al. 2015

IEEE J. Electron Devices Soc.

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Pulse thermal processing (PTP) has been explored for low thermal budget integration of indium gallium zinc oxide (IGZO) thin film transistors (TFTs). The IGZO TFTs are exposed to a broadband (0.2-1.4 µm) arc lamp radiation spectrum with 100 pulses of 1 m pulse width. With power density of 3.95 kW/cm 2 and 0.1 s total irradiation time, the PTP treated IGZO TFTs showed comparable or improved switching and bias stability properties, at significantly lower thermal budget, to furnace annealed IGZO TFT. The typical field effect mobility µFE, threshold voltage VT, and sub-threshold gate swing S.S were calculated to be 7.8 cm 2 /V·s, 8.1 V, and 0.22 V/decade, respectively. The observed performance shows promise for low thermal budget TFT integration on flexible substrates exploiting the large-area, scalable PTP technology.INDEX TERMS Thin film transistors, thin film, pulse thermal annealing.

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Improvement of InGaZnO₄Thin Film Transistors Characteristics Utilizing Excimer Laser Annealing

Cited by 46 publications

References 10 publications

Low Temperature Annealing with Solid-State Laser or UV Lamp Irradiation on Amorphous IGZO Thin-Film Transistors

Low Temperature Annealing with Solid-State Laser or UV Lamp Irradiation on Amorphous IGZO Thin-Film Transistors

Low temperature high-mobility InZnO thin-film transistors fabricated by excimer laser annealing

Pulse Thermal Processing for Low Thermal Budget Integration of IGZO Thin Film Transistors

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Improvement of InGaZnO4Thin Film Transistors Characteristics Utilizing Excimer Laser Annealing

Cited by 46 publications

References 10 publications

Low Temperature Annealing with Solid-State Laser or UV Lamp Irradiation on Amorphous IGZO Thin-Film Transistors

Low Temperature Annealing with Solid-State Laser or UV Lamp Irradiation on Amorphous IGZO Thin-Film Transistors

Low temperature high-mobility InZnO thin-film transistors fabricated by excimer laser annealing

Pulse Thermal Processing for Low Thermal Budget Integration of IGZO Thin Film Transistors

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Improvement of InGaZnO₄Thin Film Transistors Characteristics Utilizing Excimer Laser Annealing