Tang Ting-Ao

Polarity-Free Resistive Switching Characteristics of CuxO Films for Non-volatile Memory Applications

Resistive switching characteristics of CuxO films grown by plasma oxidation process at room temperature are investigated. Both bipolar and unipolar stable resistive switching behaviours are observed and confirmed by repeated current–voltage measurements. It is found that the RESET current is dependent on SET compliance current. The mechanism behind this new phenomenon can be understood in terms of conductive filaments formation/rupture with the contribution of Joule heating.

Multiple-State Storage Capability of Stacked Chalcogenide Films (Si16Sb33Te51/Si4Sb45Te51/Si11Sb39Te50) for Phase Change Memory

The multiple-state storage capability of phase change memory (PCM) is confirmed by using stacked chalcogenide films as the storage medium. The current–voltage characteristics and the resistance–current characteristics of the PCM clearly indicate that four states can be stored in this stacked film structure. Qualitative analysis indicates that the multiple-state storage capability of this stacked film structure is due to successive crystallizations in different Si–Sb–Te layers triggered by different amplitude currents.

Quantum-Mechanical Study on Surrounding-Gate Metal-Oxide-Semiconductor Field-Effect Transistors

As the channel length of metal-oxide-semiconductor field-effect transistors (MOSFETs) scales into the nanometer regime, quantum mechanical effects are becoming more and more significant. In this work, a model for the surrounding-gate (SG) nMOSFET is developed. The Schrodinger equation is solved analytically. Some of the solutions are verified via results obtained from simulations. It is found that the percentage of the electrons with lighter conductivity mass increases as the silicon body radius decreases, or as the gate voltage reduces, or as the temperature decreases. The centroid of inversion-layer is driven away from the silicon-oxide interface towards the silicon body, therefore the carriers will suffer less scattering from the interface and the electrons effective mobility of the SG nMOSFETs will be enhanced.

Nitrogen and Silicon Co-Doping of Ge2Sb2Te5 Thin Films for Improving Phase Change Memory Performance

Electrical properties and phase structures of (Si+N)-codoped Ge2Sb2Te5 (GST) for phase change memory are investigated to improve the memory performance. Compared to the films with N or Si dopants only in previous reports, the (Si+N)-doped GST has a remarkable improvement of crystalline resistivity of about 104mΩcm. The Fourier-transform infrared spectroscopy spectrum reveals the Si–N bonds formation in the film. X-ray diffraction patterns show that the grain size is reduced due to the crystallization inhibition of the amorphous GST by SiNx, which results in higher crystalline resistivity. This is very useful to reduce writing current for phase change memory applications.

Reactive Ion Etching of Sol-Gel derived PZT thin film and Pt/Ti bottom electrode for FRAM

Abstract To obtain a AL/PZT/Pt/Ti ferroelectric capacitor, Reactive Ion Etching (RIE) of Pb(Zr,Ti)O3 ferroelectric thin films and Pt bottom electrode with SF6/Ar plasmas is described in this work. The etch rate of PZT and Pt under different power, SF6/Ar gas flow ratio and gas pressure were studied. Its shown that there exists an optimum power, SF6/Ar gas flow ratio and pressure to etch PZT and Pt, respectively. Etch rates of the order of 2–7 nm/min were obtained under different conditions.

Thermal Stability of Reliable Polycrystalline Zirconium Oxide for Nonvolatile Memory Application

Thermal stability of resistive switching of stoichiometric zirconium oxide thin films is investigated for high yielding nonvolatile memory application. The Al/ZrO2/Al cell fabricated in the conventional device process shows highly reliable switching behaviour between two distinct stable resistance states. The retention capabilities are also tested under various conditions and temperatures. The excellent performance of Al/ZrO2/Al cell can be explained by assuming that anode/ ZrO2 interface exists and by conducting filament forming/rupture mechanism. The device failure is illustrated in terms of permanent conducting filaments formation.

Improvement of Electrical Properties of the Ge2Sb2Te5 Film by Doping Si for Phase-Change Random Access Memory

Si-doped Ge2Sb2Te5 films have been prepared by dc magnetron co-sputtering with Ge2Sb2Te5 and Si targets. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phase-transition temperature from face-centred-cubic (fcc) phase to hexagonal (hex) phase. The resistivity of the Ge2Sb2Te5 film shows a significant increase with the Si doping. When doping 11.8 at.% of Si in the film, the resistivity after 460°C annealing increases from 1 to 11 mΩ.cm and dynamic resistance increase from 64 to 99Ω compared to the undoped Ge2Sb2Te5 film. This is very helpful to writing current reduction of phase-change random access memory.

A C-V model of ferroelectric thin film capacitor

Abstract A ferroelectric thin film capacitor C-V model for nonvolatile memory is proposed based on the local hysteresis loop theory. The result of numerical simulation is verified with experimental data within a fixed scope.

Effects of Unintended Dopants on I-V Characteristics of the Double-Gate MOSFETs, a Simulation Study

In this paper, we study the effects of an unintended dopant in the channel on the current-voltage characteristics of a Double-Gate (DG) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). Non-Equilibrium Greens Function (NEGF) approach is used. A quantum transport model to calculate the drain current is presented and subthreshold swing and drain induced barrier lowering (DIBL) effect are studied.

Correlation between Imprint and Long-Time Polarization Reversal under Low Fields in Ferroelectric Thin Films

Time interval of slow polarization reversal in ferroelectric thin films is broadened over more than two decades to disobey the classical Kolmogorov–Avrami–Ishibashi (KAI) equation as the applied field approaches the coercive field of domain switching. The assumption of a Lorentzian distribution of logarithmic waiting times of reversed domain nucleation in this equation can resolve this dilemma. In our work, we explain this equation from the coercive-voltage distribution in thin films, and derive a similar function to describe slow polarization reversal from the consideration of a long-time imprint effect rather than the KAI model.