Toshiaki Nonaka

Effect of excimer laser annealing on a-InGaZnO thin-film transistors passivated by solution-processed hybrid passivation layers

We demonstrate the use of excimer laser annealing (ELA) as a low temperature annealing alternative to anneal amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) passivated by a solution-processed hybrid passivation layer. Usually, a-IGZO is annealed using thermal annealing at high temperatures of up to 400 °C. As an alternative to high temperature thermal annealing, two types of ELA, XeCl (308 nm) and KrF (248 nm) ELA, are introduced. Both ELA types enhanced the electrical characteristics of a-IGZO TFTs leading to a mobility improvement of ~13 cm2 V−1 s−1 and small threshold voltage which varied from ~0–3 V. Furthermore, two-dimensional heat simulation using COMSOL Multiphysics was used to identify possible degradation sites, analyse laser heat localization, and confirm that the substrate temperature is below 50 °C. The two-dimensional heat simulation showed that the substrate temperature remained at very low temperatures, less than 30 °C, during ELA. This implies that any flexible material can be used as the substrate. These results demonstrate the large potential of ELA as a low temperature annealing alternative for already-passivated a-IGZO TFTs.

Highly reliable photosensitive organic-inorganic hybrid passivation layers for a-InGaZnO thin-film transistors

We report the fabrication of a photosensitive hybrid passivation material on amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) that greatly enhance its stability and improve its electrical characteristics. The hybrid passivation based on polysilsesquioxane is transparent and fabricated using a simple solution process. Because the passivation is photosensitive, dry etching was never performed during TFT fabrication. TFTs passivated with this material had a small threshold voltage shift of 0.5 V during positive bias stress, 0.5 V during negative bias stress, and −2.5 V during negative bias illumination stress. Furthermore, TFTs passivated by this layer were stable after being subjected to high relative humidity stress — confirming the superb barrier ability of the passivation. Analysis of secondary ion mass spectrometry showed that a large amount of hydrogen, carbon, and fluorine can be found in the channel region. We show that both hydrogen and fluorine reduced oxygen vacancies and that fluorine stab...

Low temperature cured poly-siloxane passivation for highly reliable a-InGaZnO thin-film transistors

Low temperature processable passivation materials are necessary to fabricate highly reliable amorphous InGaZnO (a-IGZO) thin-film transistors (TFT) on organic substrates for flexible device applications. We investigated 3 types of poly-siloxane (Poly-SX) passivation layers fabricated by a solution process and cured at low temperatures (180 °C) for a-IGZO TFTs. This passivation layer greatly improves the stability of the a-IGZO device even after being subjected to positive (PBS) and negative bias stress (NBS). The field effect mobility (μ) of MePhQ504010 passivated on the TFT reached 8.34 cm2/Vs and had a small threshold voltage shift of 0.9 V after PBS, −0.8 V after NBS without the hump phenomenon. Furthermore, we analyzed the hydrogen and hydroxide states in the a-IGZO layer by secondary ion mass spectrometry and X-ray photoelectron spectroscopy to determine the cause of excellent electrical properties despite the curing performed at a low temperature. These results show the potential of the solution processed Poly-SX passivation layer for flexible devices.Low temperature processable passivation materials are necessary to fabricate highly reliable amorphous InGaZnO (a-IGZO) thin-film transistors (TFT) on organic substrates for flexible device applications. We investigated 3 types of poly-siloxane (Poly-SX) passivation layers fabricated by a solution process and cured at low temperatures (180 °C) for a-IGZO TFTs. This passivation layer greatly improves the stability of the a-IGZO device even after being subjected to positive (PBS) and negative bias stress (NBS). The field effect mobility (μ) of MePhQ504010 passivated on the TFT reached 8.34 cm2/Vs and had a small threshold voltage shift of 0.9 V after PBS, −0.8 V after NBS without the hump phenomenon. Furthermore, we analyzed the hydrogen and hydroxide states in the a-IGZO layer by secondary ion mass spectrometry and X-ray photoelectron spectroscopy to determine the cause of excellent electrical properties despite the curing performed at a low temperature. These results show the potential of the solution pro...

Reliability improvement in amorphous InGaZnO thin film transistors passivated by photosensitive polysilsesquioxane passivation layer

We report the fabrication of highly reliable amorphous InGaZnO (a-IGZO) passivated by a novel photosensitive polysilsesquioxane-based passivation layer using a simple solution process. Results show that the photosensitive passivation material is effective in improving the reliability of a-IGZO. a-IGZO thin film transistors (TFT) passivated by this photosensitive material exhibited a small threshold voltage (Vth) shift of ~ 0.4 V during positive bias stress (PBS), ~ -0.15 V during negative bias stress (NBS) and -2.3 V during negative bias illumination stress (NBIS). These results demonstrate the large potential of easy to fabricate photosensitive polysilsesquioxane passivation layers as effective passivation material.

Development of Photosensitive Silsesquioxane

We succeeded in development of SOG materials comprised of cage-type phenyl silsesquioxanes (PSQ) and their alkali soluble derivatives. The alkali soluble silsesquioxane (APSQ) can provide both positive and negative tone photosensitive SOG combination with diazo naphtoquinone (DNQ) and photo-base (acid) agent, respectively. Here we present feature of photolithography process and film properties for our SOG materials.