The influences of model parameters on the characteristics of memristors

As the fourth passive circuit component, a memristor is a nonlinear resistor that can ＂remember＂ the amount of charge passing through it. The characteristic of ＂remembering＂ the charge and non-volatility makes memristors great potential candidates in many fields. Nowadays, only a few groups have the ability to fabricate memristors, and most researchers study them by theoretic analysis and simulation. In this paper, we first analyse the theoretical base and characteristics of memristors, then use a simulation program with integrated circuit emphasis as our tool to simulate the theoretical model of memristors and change the parameters in the model to see the influence of each parameter on the characteristics. Our work supplies researchers engaged in memristor-based circuits with advice on how to choose the proper parameters.

Improved performance of near UV light-emitting diodes with a composition-graded p-AlGaN irregular sawtooth electron-blocking layer

We investigate the performances of the near-ultraviolet（about 350 nm-360 nm） light-emitting diodes（LEDs） each with specifically designed irregular sawtooth electron blocking layer（EBL） by using the APSYS simulation program.The internal quantum efficiencies（IQEs）,light output powers,carrier concentrations in the quantum wells,energy-band diagrams,and electrostatic fields are analyzed carefully.The results indicate that the LEDs with composition-graded pAlxGa1-xN irregular sawtooth EBLs have better performances than their counterparts with stationary component p-AlGaN EBLs.The improvements can be attributed to the improved polarization field in EBL and active region as well as the alleviation of band bending in the EBL/p-AlGaN interface,which results in less electron leakage and better hole injection efficiency,thus reducing efficiency droop and enhancing the radiative recombination rate.

基于表面势的增强型p-GaN HEMT器件模型

为了满足功率电路及系统设计对p-GaN HEMT(High Electron Mobility Transistor)器件模型的需求,本文建立了一套基于表面势计算方法的增强型p-GaN HEMT器件SPICE(Simulation Program with Integrated Circuit Emphasis)模型.根据耗尽型GaN HEMT器件和增强型p-GaN HEMT器件结构的对比,推导出p-GaN栅结构电压解析公式.考虑到p-GaN栅掺杂效应和物理机理,推导出栅电容和栅电流解析公式.同时,与基于表面势的高电子迁移率晶体管高级SPICE模型内核相结合,建立完整的增强型p-GaN HEMT功率器件的SPICE模型.将所建立的SPICE模型与实测结果进行对比验证.结果表明,所建立的模型准确实现了包括转移特性、输出特性、栅电容以及栅电流在内的p-GaN HEMT器件的电学特性.模型仿真数据与实测数据拟合度误差均小于5%.本文所提出的增强型p-GaN HEMT器件模型在进行电路设计时具有重要的应用价值.

Advanced SPICE-Modeling of 4H-SiC MESFETs

A modified drain source current suitable for simulation program with integrated circuit emphasis （SPICE） simulations of SiC MESFETS is presented in this paper. Accurate modeling of SiC MESFET is achieved by introducing three parameters in Triquint＇s own model （TOM）. The model, which is single piece and continuously differentiable, is verified by measured direct current （DC） I-V curves and scattering parameters （up to 20 GHz）.

Characteristics of titanium oxide memristor with coexistence of dopant drift and a tunnel barrier

The recent published experimental data of titanium oxide memristor devices which are tested under the same experi- mental conditions exhibit the strange instability and complexity of these devices. Such undesired characteristics preclude the understanding of the device conductive processes and the memristor-based practical applications. The possibility of the coexistence of dopant drift and tunnel barrier conduction in a memristor provides preliminary explanations for the undesired characteristics. However, current research lacks detailed discussion about the coexistence case. In this paper, dopant drift and tunnel barrier-based theories are first analyzed for studying the relations between parameters and physical variables which affect characteristics of mernristors, and then the influences of each parameter change on the conductive behaviors in the single and coexistence cases of the two mechanisms are simulated and discussed respectively. The simulation results provide further explanations of the complex device conduction. Theoretical methods of eliminating or reducing the coex- istence of the two mechanisms are proposed, in order to increase the stability of the device conduction. This work also provides the support for optimizing the fabrications of memristor devices with excellent performance.

Design of Multi-Valued Logic Circuit Using Carbon Nano Tube Field Transistors

The design of a three-input logic circuit using carbon nanotube field effect transistors(CNTFETs)is presented.Ternary logic must be an exact replacement for dual logic since it performs straightforwardly in digital devices,which is why this design is so popular,and it also reduces chip area,both of which are examples of circuit overheads.The proposed module we have investigated is a triple-logic-based one,based on advanced technology CNTFETs and an emphasis on minimizing delay times at various values,as well as comparisons of the design working with various load capacitances.Comparing the proposed design with the existing design,the delay times was reduced from 66.32 to 16.41 ps,i.e.,a 75.26%reduction.However,the power dissipation was not optimized,and increased by 1.44%compared to the existing adder.The number of transistors was also reduced,and the product of power and delay(P∗D)achieved a value of 0.0498053 fJ.An improvement at 1 V was also achieved.A load capacitance(fF)was measured at different values,and the average delay measured for different values of capacitance had a maximum of 83.60 ps and a minimum of 22.54 ps,with a range of 61.06 ps.The power dissipations ranged from a minimum of 3.38μW to a maximum of 6.49μW.Based on these results,the use of this CNTFET half-adder design in multiple Boolean circuits will be a useful addition to circuit design.

Numerical simulation and analysis for collapse responses of RC frame structures under earthquake

In this paper,a discrete element model for collapse simulation of RC frame structure is constructed by discretizing the structure into a few elements and spring groups.This model introduces special hysteretic models of connected springs for arbitrary loading path and also takes into account reasonable failure criteria for springs considering coupling effect of shear and axial force.Based on the discrete element model,a computer program is developed to simulate the whole process of RC frame structures from initial state to collapse under earthquakes.Particularly,the contact-impact problem between discrete elements has been treated with effective measures.Then,the program is employed to study the collapse mechanism of a real building in Wenchuan earthquake-hit area;the result of which shows that the simulation program developed based on the new model can realistically simulate the seismic collapse process of RC frame structures.

Integration of USEPA WASP model in a GIS platform

The integration of water quality analysis simulation program (WASP) with a geographical information system (GIS) is presented.This integration was undertaken to enhance the data analysis and management ability of the widely used water quality model.Different types of data involved in WASP modeling were converted and integrated into GIS using a database method.The spatial data modeling and analysis capability of GIS were used in the operation of the model.The WASP water quality model was coupled with the environmental fluid dynamics code (EFDC) hydrodynamic model.A case study of the Lower Charles River Basin (Massachusetts,USA) water quality model system was conducted to demonstrate the integration process.The results showed that high efficiency of the data process and powerful function of data analysis could be achieved in the integrated model,which would significantly improve the application of WASP model in water quality management.