Showing papers by "Yang Liu published in 2013"

Magnetron Sputtered Ni‐rich Nickel Oxide Nano‐Films for Resistive Switching Memory Applications

Abstract: Radio-frequency magnetron sputtering has been used to deposit Ni-rich nickel oxide nano-films to form a metal-insulator-metal structure, which exhibits resistive switching behavior. Memory characteristics of the structure have been investigated. The ratio of the current of the structure at the reading voltage of 0.05 V between a low-resistance state (LRS) and a high-resistance state (HRS) was observed to be >103, showing a large memory window at a very low reading voltage. The memory window was well maintained within the time limit of the experiment (5 × 104 s), exhibiting good memory retention. The current transport at both the LRS and HRS has been studied, and the result suggests that the formation and annihilation of a conductive filament are responsible for the resistive switching.

Volume-change-free GeTeN films for high-performance phase-change memory

Abstract: N-doping into GeTe is investigated with the aim of reducing the volume change upon crystallization, which usually induces a huge internal stress in phase-change memory devices. It is demonstrated that the thickness change upon crystallization of a N-doped GeTe (GeTeN) film is almost zero when N is doped in an appropriate amount. Cracks resulting from the stress caused by volume change disappear and the mean crystal size decreases by more than 50% upon N-doping into GeTe. It is thought that the volume-change-free behaviour is due to the formation of low-density nitride and grain refinement.

Current density enhancement nano-contact phase-change memory for low writing current

Abstract: In this work, a phase-change memory (PCM) with self-assembled nanostructures and an oxidized thin phase-change layer is proposed and intensively investigated for low writing reset current by finite element analysis. Current density is significantly enhanced in our nano-contact memory because of the existence of nanostructures and oxidized phase-change layer. The writing current of our proposed memory is about 1/10-3/10 that of conventional cell, which is in good agreement with our experimental results. The heat efficiency in the nano-contact PCM cell is greatly improved and its power consumption can be as low as about 1/10 that of the conventional cell.

Self‐calibrated SAR ADC based on split capacitor DAC without the use of fractional‐value capacitor

Abstract: A successive approximation register analog-to-digital converter (SAR ADC) based on a split-capacitor digital-to-analog converter (CDAC) with a split binary weighted capacitor array and C-2C ladder is proposed. In present design, a unit split capacitor is used in the CDAC instead of the fractional-value capacitor in the conventional configuration. The preset error induced by the unit split capacitor and the mismatch error of the upper bit CDAC are self-calibrated. The calibration range and the impact of calibration DAC resolution on circuit linearity are studied to provide an optimum design guideline. Behavior simulation and post-layout simulation are performed to verify the proposed calibration method. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

A novel hydrogen sensor based on Pt/WO 3 /Si MIS Schottky diode

Abstract: In this work, we investigate the static and dynamic gas response of Schottky diode based hydrogen sensor employing a Pt/WO3/n-type Si configuration The role and importance of tungsten trioxide as an insulating layer within the device is discussed with respect to the measured electronic properties The WO3 thin films were deposited using RF reactive magnetron sputtering The surface morphology was studied by an atomic force microscopy (AFM) and the scan results indicated a smooth film with a roughness of 018 Å From the X-ray photoelectron spectroscopy (XPS) characterization, it can be confirmed that the films were stoichiometric WO3 with a thickness of about 4 nm (as measured by an ellipsometer) The I-V characteristics and dynamic response with respect to H2 gas were measured at elevated temperatures from 50°C to 150°C and the results indicate that the H2 sensitivity of this device can exceed approximately 1000 % with an average response time of less than 10 seconds We discuss and explain these observations in terms of current transportation mechanisms using the thermionic emission model and the change in the Schottky barrier height

Vco-based continuous-time sigma delta adc based on a dual-vco-quantizer-loop structure

Abstract: This paper explores a continuous time (CT) sigma delta (ΣΔ) analog-to-digital converter (ADC) based on a dual-voltage-controlled oscillator (VCO)-quantizer-loop structure. A third-order filter is adopted to reduce quantization noise and VCO nonlinearity. Even-order harmonics of VCO are significantly reduced by the proposed dual-VCO-quantizer-loop structure. The prototype with 10 MHz bandwidth and 400 MHz clock rate is designed using a 0.18 μm RF CMOS process. Simulation results show that the signal-to-noise ratio and signal-to-noise distortion ratio (SNDR) are 76.9 and 76 dB, respectively, consuming 37 mA at 1.8 V. The key module of the ADC, which is a 4-bit VCO-based quantizer, can convert the voltage signal into a frequency signal and quantize the corresponding frequency to thermometer codes at 400 MS/s.