Shi-Jin Ding

Characterization of atomic-layer-deposited Al2O3∕GaAs interface improved by NH3 plasma pretreatment

Al2O3 thin films were deposited by atomic layer deposition on HF-cleaned and NH3 plasma-treated GaAs surfaces, respectively. The precursors used for Al2O3 films are trimethylaluminum and water. Effects of NH3 plasma pretreatment on the electrical and structural properties of Al2O3∕GaAs interface were investigated by C-V measurements, high-resolution transmission electron microscopy, and x-ray photoelectron spectroscopy measurements. The C-V measurements showed that the electrical property is improved after NH3 plasma pretreatment. X-ray photo electron spectroscopy analyses confirmed that GaAs oxides and elemental As are greatly decreased and the GaAs surface can be efficiently protected during NH3 plasma pretreatment and atomic layer deposition of Al2O3.

The mechanism of the asymmetric SET and RESET speed of graphene oxide based flexible resistive switching memories

Oxygen migration is reported as key factors of resistive switching in graphene oxide (GO) based memories by different groups. A flexible nonvolatile resistive switching memory based on GO was fabricated through a spin-coating process. The speed of the SET and RESET operations of the GO memories was found to be significant asymmetric. The RESET speed is in the order of 100 ns under a −5 V voltage while the SET speed is three orders of magnitude slower (100 μs) under a 5 V bias. The behavior of resistive switching speed difference is elucidated by voltage modulated oxygen diffusion barrier change.

Synthesis and memory characteristics of highly organo-soluble polyimides bearing a noncoplanar twisted biphenyl unit containing aromatic side-chain groups

Two novel 3′,4′,5′-trifluorobiphenyl-based aromatic polyimide monomers, 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′-biphenyl diamine (BTFBPD) and 2,2′-bis[4′-(3′′,4′′,5′′-trifluorophenyl)phenyl]-4,4′,5,5′-biphenyltetracarboxylic dianhydride (BTFBPDA) were synthesized. Two fluorinated polyimides (PIs), PI(BTFBPD-DPBPDA) and PI(BTFBPD-BTFBPDA) were prepared via a two-step procedure using BTFBPD reacting with 2,2′-diphenyl-4,4′,5,5′-biphenyltetracarboxylic dianhydride (DPBPDA) and BTFBPDA, respectively. BTFBPD was characterized with single crystal X-ray diffraction analysis and the geometric parameters showed the noncoplanar twisted character. PIs exhibited highly organo-solubility and thermal stability. The PI films sandwiched between an indium-tin oxide(ITO) bottom electrode and Al top electrode exhibited two accessible conductivity states and can be switched from the low-conductivity to the high-conductivity. The memory devices with the configuration of Al/PI(BTFBPD-DPBPDA)/ITO exhibited a flash type memory capability, whereas the Al/PI(BTFBPD-BTFBPDA)/ITO presented a write once read many times (WORM) memory capability. The fabricated devices showed low turn-on threshold voltages of −1.3 V (PI(BTFBPD-DPBPDA)) and −1.7 V (PI(BTFBPD-BTFBPDA)) and both ON/OFF current ratios on the order of 103 to 104.

Highly Uniform Bipolar Resistive Switching With

The bipolar resistive switching characteristics of atomic-layer-deposited NbAlO-based devices have been investigated for nonvolatile memory applications. With the help of a thin Al2O3 buffer layer, highly uniform and reproducible bipolar resistance switching cycles could be observed. Four typical multilevel operations, with resistances being at 1000, 350, 145, and 75 ¿, respectively, are also successfully demonstrated by varying the current compliance during the set process. The resistance ratios of high-resistance state to low-resistance state are more than 103 within 5000 cycles during the test without any degradation. Moreover, the estimated retention lifetime at room temperature is sufficiently long to fulfill the typical ten-year requirement. Considering its excellent memory switching behavior, a resistance switching device composed of a NbAlO film with a thin Al2O3 buffer layer is a possible candidate to be integrated into future memory processes.

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

The integration of ultra-thin gate oxide, especially at sub-10 nm region, is one of the principle problems in MoS2 based transistors. In this work, we demonstrate sub-10 nm uniform deposition of Al2O3 on MoS2 basal plane by applying ultra-low energy remote oxygen plasma pretreatment prior to atomic layer deposition. It is demonstrated that oxygen species in ultra-low energy plasma are physically adsorbed on MoS2 surfaces without making the flakes oxidized, and is capable of benefiting the mobility of MoS2 flake. Based on this method, top-gated MoS2 transistor with ultrathin Al2O3 dielectric is fabricated. With 6.6 nm Al2O3 as gate dielectric, the device shows gate leakage about 0.1 pA/μm2 at 4.5 MV/cm which is much lower than previous reports. Besides, the top-gated device shows great on/off ratio of over 108, subthreshold swing (SS) of 101 mV/dec and a mobility of 28 cm2/Vs. With further investigations and careful optimizations, this method can play an important role in future nanoelectronics.

Buffer Layer in Robust NbAlO-Based RRAM

Atomic-layer-deposited Al2O3–HfO2–Al2O3 dielectrics have been investigated to replace conventional silicon oxide and nitride for radio frequency and analog metal-insulator-metal capacitors applications. In the case of 1‐nm‐Al2O3, sufficiently good electrical performances are achieved, including a high dielectric constant of ∼17, a small dissipation factor of 0.018 at 100kHz, an extremely low leakage current of 7.8×10−9A∕cm2 at 1MV∕cm and 125°C, perfect voltage coefficients of capacitance (74ppm∕V2 and 10ppm∕V). The quadratic voltage coefficient of capacitance decreases with the applied frequency due to the change of relaxation time with different carrier mobility in insulator, and correlates with the dielectric composition and thickness, which is of intrinsic property owing to electric field polarization. Furthermore, the conduction mechanism of the AHA dielectrics is also discussed, indicating the Schottky emission dominated at room temperature.

The Integration of Sub-10 nm Gate Oxide on MoS2 with Ultra Low Leakage and Enhanced Mobility

It is demonstrated that the voltage coefficients of capacitance (VCC) in high-/spl kappa/ metal-insulator-metal (MIM) capacitors can be actively engineered and voltage linearity can be significantly improved maintaining high capacitance density, by using a stacked insulator structure of high-/spl kappa/ and SiO/sub 2/ dielectrics. A MIM capacitor with capacitance density of 6 fF/spl mu/m/sup 2/ and quadratic VCC of only 14 ppm/V/sup 2/ has been demonstrated together with excellent frequency and temperature dependence (temperature coefficients of capacitance of 54 ppm /spl deg/C) as well as low leakage current of less than 10 nA/cm/sup 2/ up to 4 V at 125 /spl deg/C.

Atomic-layer-deposited Al2O3–HfO2–Al2O3 dielectrics for metal-insulator-metal capacitor applications

Thin NiO films are grown at 300 ° C on Si (100) using atomic layer deposition. The dependence of annealing temperature on the optical properties of NiO films has been investigated using spectroscopic ellipsometry in the spectral region of 1.24 – 5.05 eV . It is found that the refractive index and thickness of NiO films are affected by high temperature annealing. The optical band gap of the as-deposited thin NiO film is determined to be 3.8 eV , which is almost independent of the annealing temperature. The indirect band gap of NiO film shifts toward lower photon energy with an increase in annealing temperature.

Improvement of voltage linearity in high-kappa MIM capacitors using HfO2-SiO2 stacked dielectric

The as-grown single crystalline Gd2O3 thin film on Si(100) substrate suffers from flatband voltage instability and large hysteresis which are possibly due to the intrinsic dangling bonds induced by the existing binding mismatch at the Gd2O3∕Si(100) interface. The instability of flatband voltage and hysteresis of Pt∕Gd2O3∕Si and W∕Gd2O3∕Si structures can be fully eliminated by the introduction of traditional forming gas annealing with proper process optimization. Both optimized metal-oxide-semiconductor structures show negligible hysteresis with the interface state at the magnitude order of 1011∕cm2eV at the midgap of silicon and can be considered for the future of complementary metal oxide semiconductor devices.

Spectroscopic ellipsometry study of thin NiO films grown on Si (100) by atomic layer deposition

Energy band alignment of ZnO/Si heterojunction with thin interlayers Al2O3 and HfO2 grown by atomic layer deposition has been studied using x-ray photoelectron spectroscopy. The valence band offsets of ZnO/Al2O3 and ZnO/HfO2 heterojunctions have been determined to be 0.43 and 0.22 eV, respectively. Accordingly, the band alignment ZnO/Si heterojunction is then modified to be 0.34 and 0.50 eV through inserting a thin Al2O3 and HfO2 layer, respectively. The feasibility to tune the band structure of ZnO/Si heterojunction by selecting a proper interlayer shows great advantage in improving the performance of the ZnO-based optoelectronic devices.