Jim-Long Her

Electrical and Reliability Characteristics of High-

In this letter, we investigated the electrical and reliability characteristics of high- κ HoTiO₃ amorphous indium-gallium-zinc oxide ( α-IGZO) thin-film transistor (TFT) devices. The α-IGZO TFT device incorporating an HoTiO₃ dielectric exhibited excellent electrical characteristics in terms of a low threshold voltage of 0.12 V, a high field-effect mobility of 21.4 cm²/V_s, a small subthreshold swing of 160 mV/decade, and a high I_ON/I_OFF current ratio of 1.3 ×10⁸. These results are attributed to the incorporation of TiO_x into the Ho₂O₃ film forming the smooth surface roughness and thus reducing the oxygen vacancies. Furthermore, the threshold voltage stability of HoTiO₃ α-IGZO TFT was studied under both positive and negative bias stress conditions.

\kappa~{\rm HoTiO}_{3}~\alpha

We investigate the resistive memory switching behaviors of Yb2O3 thin films for different Ti-dopant concentrations. A higher doping concentration of 9.4% of Ti atom into Yb2O3 thin film causes the switching mechanism to change from bipolar to unipolar behavior. This is ascribed to different chemical compositions of the filament through the oxide film. The reset mechanism is associated with the annihilation of oxygen vacancies and other ionic and electronic defects within or near the interface area of oxide film for bipolar switching, while it is believed to be due to rupture of the conducting filament by local Joule heating effect for unipolar resistive switching. Furthermore, the incorporation of Ti atom into the Yb2O3 memory device exhibits improved electrical performances including low set/reset voltages and good endurance and retention characteristics.

-InGaZnO Thin-Film Transistors

In this letter, we investigated the structural and electrical characteristics of high-κ Er2O3 and Er2TiO5 gate dielectrics on the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices. Compared with the Er2O3 dielectric, the a-IGZO TFT device incorporating an Er2TiO5 gate dielectric exhibited a low threshold voltage of 0.39 V, a high field-effect mobility of 8.8 cm2/Vs, a small subthreshold swing of 143 mV/decade, and a high Ion/Ioff current ratio of 4.23 × 107, presumably because of the reduction in the oxygen vacancies and the formation of the smooth surface roughness as a result of the incorporation of Ti into the Er2TiO5 film. Furthermore, the reliability of voltage stress can be improved using an Er2TiO5 gate dielectric.

Effect of Ti doping concentration on resistive switching behaviors of Yb2O3 memory cell

We investigated the impact of Ti doping in the Sm2O3 dielectric on the electrical stress-induced instability in amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). With increasing stress time in a-IGZO TFT devices, a small initial positive shift followed by a negative shift of threshold voltage is characterized in the Sm2O3 dielectric, whereas only positive shift of threshold voltage is observed for Ti-doped Sm2O3 dielectric. The positive shift of the threshold voltage can be explained by charge trapping in the Sm2O3 film and/or the Sm2O3/IGZO interfaces, while the negative shift of threshold voltage is probably due to the extra charges from the IGZO channel by self-heating effect.

Structural and electrical characteristics of high-κ Er2O3 and Er2TiO5 gate dielectrics for a-IGZO thin-film transistors.

A conventional approach of doping to control the bistable resistance switching in Yb₂O₃ was investigated for nonvolatile memory applications. With the help of Ti doping into oxide films during the process, better cycle-to-cycle resistance distribution and switching voltage uniformity were found due to modulation of current conduction mechanism from space-charge-limited current in Yb₂O₃ to Schottky type in YbTiO_x. The program/erase cycles with successive readout operation over 10⁵ cycles can be achieved without any degradation. No data loss was found upon continuous readout process at both room temperature and 85°C. The Ni/YbTiO_x/TaN memory is a promising candidate to be integrated into future memory processes.

Impact of Ti doping in Sm2O3 dielectric on electrical characteristics of a-InGaZnO thin-film transistors

In this paper, we compared the structural and electrical properties of high- κ Gd₂O₃ and GdTiO₃ gate dielectrics for an amorphous indium-gallium-zinc oxide ( α-IGZO) thin-film transistor (TFT) application. In comparison with the Gd₂O₃ dielectric, the α-IGZO TFT featuring the GdTiO₃ dielectric exhibited better electrical characteristics in terms of a large field effect mobility of 26.9 cm²/Vs, a low threshold voltage of 0.04 V, a high ION/IOFF ratio of 1.2×10⁸, and a low subthreshold swing of 200 mV/decade. We attribute these results to the incorporation of Ti into the Gd₂O₃ film, forming a smooth surface and thus reducing density of interface states at the oxide/channel interface. In addition, the stability of threshold voltage on high- κ Gd₂O₃ and GdTiO₃ a-IGZO TFTs was studied under positive gate bias stress.

Improved Resistance Switching Characteristics in Ti-Doped

The valence state of Ce in a canonical heavy fermion compound CeRu2Si2 has been investigated by synchrotron X-ray absorption spectroscopy at 1.8 K in high magnetic fields of up to 40 T. The valence was slightly larger than for the pure trivalent state (Ce3+: f1), as expected in heavy fermion compounds, and it decreased toward the trivalent state as the magnetic field was increased. The field-induced valence reduction indicates that the itinerant character of the 4f electrons in CeRu2Si2 was suppressed by a strong magnetic field. The suppression was gradual and showed characteristic magnetic field dependence, which reflects the metamagnetism around Hm \sim 8 T. The itinerant character persisted, even at 40 T (\sim 5Hm), suggesting that the Kondo bound state is continuously broken by magnetic fields and that it should completely collapse at fields exceeding 200 T.

\hbox{Yb}_{2}\hbox{O}_{3}

In this study, we report the structural and electrical characteristics of high-κ Sm2O3 and SmTiO3 charge trapping layers on an indium–gallium–zinc oxide (IGZO) thin-film transistor (TFT) for non-volatile memory device applications. The IGZO TFT non-volatile memory featuring a SmTiO3 charge trapping layer exhibited better characteristics, including a larger memory window (2.7 V), long charge retention time (105 s with charge loss <15%) and better endurance performance for program/erase cycles (104), compared with a Sm2O3 charge trapping layer. These results can be attributed to the SmTiO3 film possessing a high dielectric constant and deep trapping level. The high-κ SmTiO3 is an excellent candidate for use as the trapping layer in IGZO TFT non-volatile memories.

for Resistive Nonvolatile Memory Devices

The electric resistivity of single crystalline Fe-based superconductors FeSe and FeSeTe was measured in pulsed magnetic fields up to 55 T. Te-doped iron selenide, FeSeTe, shows rather isotropic behavior in both magnetoresistance (MR) and upper critical fields ((0)/(0) = 48 T/ 42 T ~ 1.14), when an external magnetic field is applied parallel and perpendicular to the crystallographic c-axis. These isotropic behaviors are frequently observed in an iron-based superconductor, and the isotropy in Hc2 can likely be described by the Pauli effect. In contrast, our measurements elucidate that the undoped iron selenide, FeSe, exhibits a clear anisotropy in both MR and Hc2 ((0)/(0) = 27 T/ 15 T ~ 1.8). This behavior occurs because the clean in-plane conduction (RRR = 35) allows to form a closed electron orbit within the two-dimensional Fermi sheets only for the magnetic field parallel to the c-axis, which results in an appearance of an intrinsic (orbital-effect limited) upper critical field for the undoped FeSe. Doping of Te breaks the clean in-plane conduction and leads to a crossover from an orbital limit dominating behavior to a Pauli limit dominating one.

Comparison of High-

The X-ray absorption and magnetic circular dichroism (XMCD) spectra at the L 3 edge of Yb have been studied experimentally as well as theoretically in the mixed-valent heavy fermion compound YbAgCu...