In this paper, the resistive switching characteristics in a Cu/HfO(2):Cu/Pt sandwiched structure is investigated for multilevel non-volatile memory applications. The device shows excellent resistive switching performance, including good endurance, long retention time, fast operation speed and a large storage window (R(OFF)/R(ON)>10(7)). Based on the temperature-dependent test results, the formation of Cu conducting filaments is believed to be the reason for the resistance switching from the OFF state to the ON state. By integrating the resistive switching mechanism study and the device fabrication, different resistance values are achieved using different compliance currents in the program process. These resistance values can be easily distinguished in a large temperature range, and can be maintained over 10 years by extrapolating retention data at room temperature. The integrated experiment and mechanism studies set up the foundation for the development of high-performance multilevel RRAM.

We report the direct electrical measurement of multiple resistance steps in the ZrO2-based solid electrolyte nonvolatile memory device using the refined dc I-V method with a very small voltage increasing rate. The results demonstrate that multiple conductive filaments are formed successively between the bottom and top metal electrodes through the insulating layer while increasing the bias voltage, which are consistent with the electrical field simulation results based on the solid electrolyte theory. The inverse relationship between resistance steps and the filament formation sequence are obtained, which helps understand the switching mechanism of the multiple conductive filaments.

A high-κ based charge trap flash (CTF) memory structure using bandgap engineered trapping layer HfO2/Al2O3/HfO2 (HAH) has been demonstrated for multilevel cell applications. Compared to a single HfO2 trapping layer, a CTF memory device based on the HAH trapping layer exhibits a larger memory window of 9.2 V, faster program/erase speed, and significantly improved data retention. Enhancements of memory performance and reliability are attributed to the modulation of charge distribution by bandgap engineering in trapping layer. The findings provide a guide for future design of CTF.

No abstract

Herbal drugs have been used for thousands of years in the east and have had a recent resurgence in popularity among consumers in the west. However, most of herbal drug are poorly soluble and have hydrophobic properties and poor distribution, leading to reduced bioavailability and hence decreased treatment efficacy, requiring repeated administration or increased dose. In the past few decades, considerable attention has been focused on the development of self-emulsifying drug delivery system (SEDDS) for herbal drugs. SEDDS is isotropic and thermodynamically stable solutions consisting of oil, surfactant, co-surfactant and drug that can spontaneously form oil-in-water micro/nanoemulsion when mixed with water under gentle stirring. The formulation can be a viable alternative to classical formulations to take advantage of their lipophilic nature and to solve their problems of poor solubility, poor bioavailability, low oral absorption and instability. The mechanism of self-emulsification, solubility studies, construction of phase diagram, optimization and characterization of herbal drugs-loaded SEDDS formulation and in situ absorption evaluation of herbal drugs in rat intestine are presented in our article.

There are three basic multiphonon trap-assisted tunneling (TAT) mechanisms in the gate leakage current of a metal-oxide-semiconductor (MOS) structure: the short-ranged trap potential, nonadiabatic interaction and electric field induced trap-band transitions. In this paper, a comparison of these three mechanisms is made for the first time in a single (Schenk’s model) MOS structure. A properly box-normalized electron wave function in the SiO2 conduction band in an electric field is used to calculate the field ionization rate of a deep neutral trap. It is found that capture and emission rates of a deep neutral trap are almost the same in the short-ranged trap potential and nonadiabatic interaction induced TAT processes, so the two mechanisms give a similar contribution to the total TAT current. The calculated TAT current and the average relaxation energy (∼1.5 eV) due to these two mechanisms are in good agreement with the experimental results. In contrast, capture and emission rates in Schenk’s model are several orders smaller. The TAT current induced by this mechanism is also much smaller and can be ignored.

No abstract

In this letter, the authors present the capacitance-voltage and current-voltage characteristics of TaN∕HfO2∕n-GaAs metal-oxide-semiconductor capacitors with thin silicon and germanium interfacial passivation layers (IPLs). Physical vapor deposition high-k dielectric films and silicon/germanium IPLs were deposited on GaAs substrate which has been cleaned with HCl and (NH4)2S solutions. Equivalent oxide thickness (EOT) of 12.5Å and dielectric leakage current density of 2.0×10−4A∕cm2 at ∣VG−VFB∣=1V with low capacitance-voltage frequency dispersion have been obtained. The results indicate that the use of a thin silicon/germanium IPL assists in scaling EOT below 13Å, while improving the quality of the interface.