Chih-Tsung Tsai

Influence of electrode material on the resistive memory switching property of indium gallium zinc oxide thin films

The InGaZnO taken as switching layer in resistive nonvolatile memory is proposed in this paper. The memory cells composed of Ti/InGaZnO/TiN reveal the bipolar switching behavior that keeps stable resistance ratio of 102 with switching responses over 100 cycles. The resistance switching is ascribed to the formation/disruption of conducting filaments upon electrochemical reaction near/at the bias-applied electrode. The influence of electrode material on resistance switching is investigated through Pt/InGaZnO/TiN devices, which perform the unipolar and bipolar behavior as applying bias on Pt and TiN electrode, respectively. Experimental results demonstrate that the switching behavior is selective by the electrode.

Influence of positive bias stress on N2O plasma improved InGaZnO thin film transistor

A post-treatment using N2O-plasma is applied to enhance the electrical characteristics of amorphous indium gallium zinc oxide thin film transistors. Improvements in the field-effect mobility and the subthreshold swing demonstrate that interface states were passivated after N2O-plasma treatment, and a better stability under positive gate-bias stress was obtained in addition. The degradation of mobility, resulted from bias stress, reduces from 6.1% (untreated devices) to 2.6% (N2O-plasma treated devices). Nevertheless, a strange hump characteristic occurs in transfer curve during bias stress, inferring that a parasitic transistor had been caused by the gate-induced electrical field.

Behaviors of InGaZnO thin film transistor under illuminated positive gate-bias stress

In this letter, we investigate the impact of the light illumination on the stability of indium–gallium– zinc oxide thin film transistors under positive gate-bias stress. The noticeable decrease in threshold voltage Vt shift more than 5.5 V under illuminated positive gate-bias stress indicates a superior reliability in contrast with the dark stress. The accelerated Vt recovery characteristic compared with dark recovery demonstrates that the charge detrapping effect was enhanced under illumination. Furthermore, the average effective energy barrier of charge trapping and detrapping was derived to verify that illumination can excite the trapped charges and accelerate the charge detrapping process.

Investigating the degradation behavior caused by charge trapping effect under DC and AC gate-bias stress for InGaZnO thin film transistor

This letter investigates the degradation mechanism of amorphous indium-gallium-zinc oxide thin-film transistors under gate-bias stress. The larger Vt shift under positive AC gate-bias stress when compared to DC operation indicates that an extra electron trapping mechanism occurs during rising/falling time during the AC pulse period. In contrast, the degradation behavior under illuminated negative gate-bias stress exhibits the opposite degradation tendency. Since electron and hole trapping are the dominant degradation mechanisms under positive and illuminated negative gate-bias stress, respectively, the different degradation tendencies under AC/DC operation can be attributed to the different trapping efficiency of electrons and holes.

Light-induced instability of an InGaZnO thin film transistor with and without SiOx passivation layer formed by plasma-enhanced-chemical-vapor-deposition

This paper investigates the illuminated behaviors of InGaZnO thin film transistors with and without a SiOx passivation. For the passivated device, more interface states were generated during SiOx passivation layer deposition by plasma-enhanced-chemical-vapor-deposition. The enhanced trap-assisted photoexcited hole generation induces source side barrier lowering and causes an apparent subthreshold stretch-out phenomenon. However, for the unpassivated device, the fact that the threshold voltage shift in ambient oxygen is lower than in vacuum under light illumination suggests oxygen desorption and readsorption occurs simultaneously, which is consistent with the accelerated recovery rate in oxygen ambiance.

Bipolar Resistive Switching Characteristics of Transparent Indium Gallium Zinc Oxide Resistive Random Access Memory

This study investigates a sputtered InGaZnO (IGZO) thin film to apply into a resistive random access memory device. After the formation of an indium tin oxide (ITO)/IGZO/ITO structure at room temperature, the device exhibits a repeatable bipolar resistance switching behavior without an electroforming process and an excellent transmittance in the visible region. The conduction mechanisms for low and high resistance states are dominated by Ohms law and space-charge-limited current behavior, respectively. In retention and endurance tests, a resistance ratio of more than 1 order remains after 10 4 s at 90°C and after 100 dc voltage sweeping cycles.

Effects of Ambient Atmosphere on Electrical Characteristics of Al2O3 Passivated InGaZnO Thin Film Transistors during Positive-Bias-Temperature-Stress Operation

This study investigates the effects of ambient atmosphere on electrical characteristics of Al2O3 passivated InGaZnO thin film transistors during positive bias temperature stress. Under H2O vapor environment, the Al2O3 passivated device exhibited stable electrical behaviors (ΔV th < 0.5 V), while the unpassivated device showed an apparent hump effect in the transfer curves under bias stress. The hump phenomenon was attributed to the absorption of the H2O molecule which can serve as a donor to develop a conductive back channel. The experiment results suggest that Al2O3 is an effective passivation layer to suppress water vapor absorption in the InGaZnO back channel.

Low-temperature method for enhancing sputter-deposited HfO2 films with complete oxidization

A low-temperature method, supercritical CO2 fluid (SCF) technology, is proposed to improve the dielectric properties of ultrathin hafnium oxide (HfO2) film at 150°C without significant formation of parasitic oxide at the interface between HfO2 and Si substrate. In this research, the HfO2 films were deposited by dc sputter at room temperature and post-treated by SCF which is mixed with 5vol% propyl alcohol and 5vol% H2O. From high-resolution transmission electron microscopy image, the interfacial oxide of SCF-treated HfO2 film is only 5A thick. Additionally, the enhancements in the qualities of sputter-deposited HfO2 film after SCF process are exhibited by x-ray photoelectron spectroscopy and capacitance-voltage (C-V) measurement.

A low temperature fabrication of HfO2 films with supercritical CO2 fluid treatment

To improve the dielectric properties of sputter-deposited hafnium oxide (HfO2) films, the supercritical CO2 (SCCO2) fluid technology is introduced as a low temperature treatment. The ultrathin HfO2 films were deposited on p-type (100) silicon wafer by dc sputtering at room temperature and subsequently treated with SCCO2 fluids at 150°C to diminish the traps in the HfO2 films. After SCCO2 treatment, the interfacial parasitic oxide between the Si substrate and HfO2 layer is only about 5A, and the oxygen content of the HfO2 films apparently increased. From current-voltage (I-V) and capacitance-voltage (C-V) measurements, the leakage current density of the SCCO2-treated HfO2 films is repressed from 10−2to10−7A∕cm2 at electric field=3MV∕cm due to the reduction of traps in the HfO2 films. The equivalent oxide thickness also obviously decreased. Besides, the efficiency of terminating traps is relative to the pressure of the SCCO2 fluids.

Low-Temperature Passivation of Amorphous-Silicon Thin-Film Transistors With Supercritical Fluids

In this letter, supercritical CO2 (SCCO2) fluids technology is employed for the first time to effectively passivate the defect states in hydrogenated amorphous-silicon thin-film transistors (a-Si:H TFTs) at low temperature (150degC ). With the high transport and diffusion properties of fluids, it is proposed to act as a transporter in delivering the molecules into the amorphous-silicon film and repairing defect states by the molecules. In addition, the propyl alcohol is used as the surfactant between nonpolar-SCCO2 fluids and polar-H2O molecules for mingling H2O molecules uniformly with the SCCO2 fluids. After the treatment of SCCO2 fluids mixed with water and propyl alcohol, the a-Si:H TFT exhibited superior transfer characteristics and lower threshold voltage. The improvement in electrical characteristics could be verified by the significant reduction of density of states in the mobility gap of amorphous-silicon.