Po-Yung Liao

Characterization of IrO2 thin films by Raman spectroscopy

Abstract Raman scattering has been used as a technique for characterization of the sputtered IrO 2 thin films (SIROF) deposited on different substrates under various conditions. Compared with the spectrum of single crystal IrO 2 , red shift and broadening of the linewidth of the Raman peaks of SIROF are observed. X-ray diffraction measurements of SIROF were also carried out to assist the identification of the factor that influences the linewidth broadening of the Raman features. The results indicate that amorphous–crystalline transition for IrO 2 phase can be achieved at substrate temperature of 200–300 °C. The line-shape and position of the Raman features vary for films deposited on different substrates under the same conditions. These differences can be due to the existence of stress between IrO 2 and the substrates.

Application of in-cell touch sensor using photo-leakage current in dual gate a-InGaZnO thin-film transistors

In-cell touch sensor that can be integrated with display pixel circuit using dual gate InGaZnO thin-film transistor is proposed. Under bottom gate operation, device characteristics are not sensitive to light illumination. On the contrary, light can lead to evident subthreshold leakage when operated with top gate. This behavior allows touch sensor to be realized by sensing the ambient light using top gate operation, without affecting normal bottom gate operated devices in display pixel. Further, the proposed operation method of touch sensor needs no additional fabrication and cost, and even black matrix is not required either.

Impact of repeated uniaxial mechanical strain on p-type flexible polycrystalline thin film transistors

This letter investigates the effect of repeated bending of flexible p-channel low-temperature polycrystalline–silicon thin-film transistors employing an ultra-low-temperature process (<673 K). Experimental results reveal that interface state density (Nit) and grain boundary trap density (Ntrap) after 10 000 width-axis tensile strain bending iterations are more pronounced than after equivalent width-axis compressive strain bending. Extracted interface and grain boundary traps both increase, which elevate trap assisted leakage. Furthermore, the bending distorts the Si–Si bonds in the polycrystalline silicon (Poly-Si) film, which causes more significant negative bias temperature instability (NBTI) degradation because strain-induced weak Si–Si bonds can react with dissociated H during NBTI stress.

Hot-Carrier Effect on Amorphous In-Ga-Zn-O Thin-Film Transistors With a Via-Contact Structure

The effect of hot carriers on the characteristics of via-contact-type amorphous In-Ga-Zn-O thin-film transistors is investigated. After hot-carrier stress, the gate-to-source capacitance curve shows a two-stage rise while the gate-to-drain capacitance curve exhibits parallel shifts. It is found that hot electrons are injected into the etch-stop layer or trapped at the InGaZnO/etch-stop layer interface below redundant drain electrode. This is further verified by measuring the characteristic capacitance curve with a positive top gate bias.

Effect of mechanical-strain-induced defect generation on the performance of flexible amorphous In-Ga-Zn-O thin-film transistors

In this study, we investigate the effect of mechanical strain on the performance of flexible amorphous In–Ga–Zn–O (a-InGaZnO) thin-film transistors. Drain current–gate voltage (I D–V G) and capacitance–voltage (C–V) transfer curves are measured to analyze the degradation behavior. The I D–V G characteristic exhibits a clear negative shift under mechanical strain regardless of the tension or compression state. In addition, the C–V characteristic curves show a leftward shift with extra distortion or stretching out under mechanical strain. This indicates that InGaZnO generates additional defects under this mechanical strain, a phenomenon that can be attributed to the generation of mechanical-strain-induced oxygen vacancies on the flexible a-InGaZnO TFTs.

Effects of Repetitive Mechanical Bending Strain on Various Dimensions of Foldable Low Temperature Polysilicon TFTs Fabricated on Polyimide

This letter investigates the effect of repeated uniaxial mechanical stress on bias-induced degradation behavior in polycrystalline thin-film transistors (TFTs). After 100 000 iterations of channel-width-direction mechanical compression, serious threshold voltage degradation and an abnormal hump are observed. Simulation indicates that the strongest mechanical stress occurs at both sides of the channel edge, between the polycrystalline silicon and gate insulator. Since these stress points produce oxide traps in the gate insulator, the degradation of threshold voltage shift and parasitic current path can be attributed to electron trapping at these intense mechanical stress points. In addition, the degradation becomes serious with diminishing TFT size.

Investigation of carrier transport behavior in amorphous indium–gallium–zinc oxide thin film transistors

Behaviors of carrier transport in amorphous indium–gallium–zinc oxide (a-IGZO) thin film transistors are investigated. It is found that the electron mobility is higher at elevated temperatures, which is contrary to that in crystalline Si devices. Drain current enhancement with regard to temperature at corresponding gate voltage follows the Arrhenius equation. This implies that carrier transport is limited by the potential barrier heights induced by trap states within IGZO, and therefore current conduction is heat-activated to overcome those barriers. In addition, the extracted activation energy decreases with increasing gate voltage, indicating the effective potential barrier height is lowered when abundant electrons are injected into the channel. Furthermore, the relationship between carrier mobility and carrier concentration is also investigated, with the carrier mobility monotonically increasing with carrier concentration. Such behavior can be ascribed to a lowered effective barrier above the conduction band when the Fermi-level rises.

Characterization and Investigation of a Hot-Carrier Effect in Via-Contact Type a-InGaZnO Thin-Film Transistors

Electrical characteristics and the effect of hotcarriers are investigated in via-contact-type a-InGaZnO thinfilm transistors. Current-voltage as well as capacitance-voltage measurements are utilized to investigate the impact of top gate bias on device characteristics as well as degradation behaviors caused by a hot-carrier stress. It is found that the redundant source/drain electrodes in via-contact type devices can screen the electric field established by a top gate bias and have significant influence on the device characteristics. Hot-carrier stress brings about electron trapping in the etch stop layer below the redundant electrodes, and this is further verified through modulating the energy band structure by applying a top gate bias during the capacitance-voltage measurement.

Investigation of a Hump Phenomenon in Back-Channel-Etched Amorphous In-Ga-Zn-O Thin-Film Transistors Under Negative Bias Stress

The hump phenomenon along with a negative shift of threshold voltage emerging in the transfer characteristics of amorphous InGaZnO thin-film transistors under negative bias stress was investigated. Higher measurement temperature and larger bias voltage can induce more and faster hole injection, thus leading to the increased parasitic ON-state current and more negative shift of the threshold voltage. Nevertheless, the parasitic current is independent of the channel width, illustrating that the parasitic channel originates from the hole trapping near the IGZO edges along the channel length. Integrated Systems Engineering Technology Computer-aided Design simulation confirms that the electric field near the IGZO edge is relatively dense, and the direction is more conducive for the holes in IGZO to inject into passivation (PV), to gate insulator (GI), or at PV/GI interface.

Localized tail state distribution and hopping transport in ultrathin zinc-tin-oxide thin film transistor

Carrier transport properties of solution processed ultra thin (4 nm) zinc-tin oxide (ZTO) thin film transistor are investigated based on its transfer characteristics measured at the temperature ranging from 310 K to 77 K. As temperature decreases, the transfer curves show a parellel shift toward more postive voltages. The conduction mechanism of ultra-thin ZTO film and its connection to the density of band tail states have been substantiated by two approaches, including fitting logarithm drain current (log ID) to T−1/3 at 310 K to 77 K according to the two-dimensional Mott variable range hopping theory and the extraction of density of localized tail states through the energy distribution of trapped carrier density. The linear dependency of log ID vs. T−1/3 indicates that the dominant carrier transport mechanism in ZTO is the variable range hopping. The extracted value of density of tail states at the conduction band minimum is 4.75 × 1020 cm−3 eV−1 through the energy distribution of trapped carrier densit...