Masashi Miyakawa

Application of hydrogen injection and oxidation to low temperature solution-processed oxide semiconductors

Solution-processed oxide semiconductors are promising candidates for the low cost, large scale fabrication of oxide thin-film transistors (TFTs). In this work, a method using hydrogen injection and oxidation (HIO) that allows the low temperature solution processing of oxide semiconductors was demonstrated. We found that this method significantly decreases the concentration of residual species while improving the film densification. Additionally, enhanced TFT performance was confirmed following the use of processing temperatures as low as 300 °C. The proposed process is potentially applicable to the fabrication of a wide variety of solution-processed oxide semiconductors.

High-performance solution-processed thin-film transistors using fluorine-doped aqueous metal oxides

Simple and facile solution-processed oxide thin-film transistors (TFTs) using metal-oxide semiconductors are very promising for producing large-area electronics at a relatively low cost. This study aims to design and fabricate high-performance solution-processed TFTs using fluorine-doped aqueous metal oxides at a low temperature of 300°C. We investigated the effect of a simple method of doping the IGZO and IZO used for the active-channel layer with fluorine additives on the performance of the fabricated TFT. In addition, the hydrogen injection and oxidation method, which is considered effective for film densification, was tested and found to improve the electrical performance of the TFT. This simple, low-temperature fabrication technique will be useful for manufacturing large-area TFTs.

Simple and reliable direct patterning method for carbon-free solution-processed metal oxide TFTs

Metal oxide TFT fabrication based on a solution-processing method is considered a promising alternative to conventional vacuum processing and has a number of advantages such as low cost, large-area fabrication, and process simplicity. A simple and reliable, direct patterning method for obtaining a carbon-free aqueous metal oxide film is presented herein. Patterning, which is achieved by selective photoreaction of water molecules under ultraviolet irradiation and by a safe, environment-friendly chemical etching process using a non-toxic organic acid, is followed by an annealing process at a temperature of 350 °C to obtain carbon-free metal oxide TFTs. In–Ga–Zn oxide (IGZO), TFTs on SiO2 dielectrics that were fabricated with a direct patterning method exhibited an average mobility of 4.3 cm2/V·s with good uniformity, which is comparable to TFTs formed by conventional photolithography. The TFTs exhibited stable performance with small (within 0.5 V) shifts in switch-on voltage under positive and negative bias stress. Fabrication of flexible IGZO TFTs by direct patterning was also achieved.

Improvement in switching characteristics and long-term stability of Zn-O-N thin-film transistors by silicon doping

The effects of silicon doping on the properties of Zn-O-N (ZnON) films and on the device characteristics of ZnON thin-film transistors (TFTs) were investigated by co-sputtering silicon and zinc targets. Silicon doping was effective at decreasing the carrier concentration in ZnON films; therefore, the conductivity of the films can be controlled by the addition of a small amount of silicon. Doped silicon atoms also form bonds with nitrogen atoms, which suppresses nitrogen desorption from the films. Furthermore, Si-doped ZnON-TFTs are demonstrated to exhibit less negative threshold voltages, smaller subthreshold swings, and better long-term stability than non-doped ZnON-TFTs.