Yadong Tao

Analytic Carrier-Based Charge and Capacitance Model for Long-Channel Undoped Surrounding-Gate MOSFETs

Three terminal charges and nine intrinsic capacitances associated to the gate, source, and drain terminals of long-channel undoped surrounding-gate (SRG) MOSFETs are derived physically from an exact analytical solution of the channel current-continuity principle and channel charge-partition scheme in this paper. Although requiring lengthy and complex mathematical expressions, all explicit solutions for the capacitances can be obtained analytically. The validity of the analytical solutions is confirmed by comparing model predictions with simulation data obtained using the 3-D numerical solvers. The explicit expressions to the terminal charges and transcapacitance not only lead to a clearer understanding of SRG MOSFET device physics but also provide a better infrastructure to develop a complete carrier-based model for the SRG-MOSFET-based circuit simulation

An Analytic Potential-Based Model for Undoped Nanoscale Surrounding-Gate MOSFETs

An analytic potential-based model for the undoped surrounding-gate MOSFETs is derived in the paper. The model is obtained from rigorously solving Poisson equation together with the drain-current formulation equivalent to Pao-Sahs double integral that is previously proposed for long-channel bulk MOSFETs. The model consists of an analytic drain-current equation that accounts for both drift and diffusion current components in terms of the potential at the oxide silicon interface and the silicon center of device body evaluated at the source and drain terminals. The model gives a fully self-consistent physical description for the channel potential, charge, and current that is valid for the subthreshold, linear, and saturation regions. The validity of the proposed model has been verified by extensive comparison with the exact numerical integrations and 2-D numerical simulation, which demonstrates model accuracy and prediction capability.

Electrical, spectral and optical performance of yellow?green and amber micro-pixelated InGaN light-emitting diodes

Micro-pixelated InGaN LED arrays operating at 560 and 600 nm, respectively, are demonstrated for what the authors believe to be the first time. Such devices offer applications in areas including bioinstrumentation, visible light communications and optoelectronic tweezers. The devices reported are based on new epitaxial structures, retaining conventional (0 0 0 1) orientation, but incorporating electron reservoir layers which enhance the efficiency of radiative combination in the active regions. A measured output optical power density up to 8 W cm−2 (4.4 W cm−2) has been achieved from a representative pixel of the yellow–green (amber) LED array, substantially higher than that from conventional broad-area reference LEDs fabricated from the same wafer material. Furthermore, these micro-LEDs can sustain a high current density, up to 4.5 kA cm−2, before thermal rollover. A significant blueshift of the emission wavelength with increasing injection current is observed, however. This blueshift saturates at 45 nm (50 nm) for the yellow–green (amber) LED array, and numerical simulations have been used to gain insight into the responsible mechanisms in this microstructured format of device. In the relatively low-current-density regime (<3.5 kA cm−2) the blueshift is attributable to both the screening of the piezoelectric field by the injected carriers and the band-filling effect, whereas in the high-current regime, it is mainly due to band-filling. Further development of the epitaxial wafer material is expected to improve the current-dependent spectral stability.

Linear Cofactor Difference Extrema of MOSFET's Drain–Current and Application to Parameter Extraction

The linear cofactor difference extrema due to the nonlinearity of the MOSFET drain-current and their application to extract MOSFET parameters are presented in this brief. The extrema of drain-current are obtained by applying the linear cofactor difference operator to the drain-current versus gate voltage curve in the linear region. These extrema are directly used to find the threshold voltage and the mobility of a MOSFET. This method has been tested using data from experimentally fabricated MOSFETs and by simulating results through the device simulator DESSIS-ISE. The results agree well with those obtained by the standard second-derivative approach, which demonstrates the validity of the method presented. The advantages and disadvantages of this method are also discussed

Carrier-based compact modeling of charge and capacitance of long channel undoped symmetric double-gate MOSFETs

Carrier-based compact modeling of terminal charges and intrinsic trans-capacitances of a long channel undoped symmetric double-gate MOSFET is presented in this paper. The explicit expressions for the terminal charges are obtained from a simplified carrier-based drain current model and the current continuity principle. Then analytic trans-capacitances are derived in terms of the charges at the source and drain ends. The validity of the analytic terminal charges and trans-capacitances is also verified by 2D numerical analysis proving the accuracy of the compact model presented here.

Full-band quantum transport based simulation for carbon nanotube field effect transistor from chirality to device performance

Carbon nanotube field effect transistor (CNFET) may be one of the most promising alternatives to silicon complementary metal-oxide-semiconductor (CMOS) due to its unique advantages. The predicted dependences of band structure and device performance on chirality of carbon nanotube (CNT) and device structure have been studied in this paper by the means of a full-band based quantum transport simulator, ALTRAS-CNFET. Including the modification of curvature effect, the band structure of CNT is obtained by the tight-binding approach. The self-consistent solution of Schrödinger–Poisson equation groups is employed to calculate the direct tunneling gate current in the coaxial CNFET radial direction under cylindrical coordinates. The electrical characteristic in the coaxial CNFET channel direction is also computed based on the ballistic transport mechanism.

Yellow-green and amber InGaN micro-pixellated light-emitting diode arrays

Micro-pixel InGaN LED arrays operating at 560nm and 600nm, respectively, are demonstrated, based on new epitaxial structures. Such devices have applications in areas including bioinstrumentation, visible light communications and micro-displays.

An analytic potential-based model for undoped nanoscale surrounding-gate MOSFETs

An analytic potential-based model for the undoped surrounding-gate MOSFETs is derived in the paper. The model is obtained from solving Poisson equation rigorously together with the drain current formulation equivalent to Pao-Sahpsilas double integral previously proposed for long-charnel bulk MOSFETs. The model gives a fully self-consistent physical description for the channel potential, charge and current that is valid for the sub threshold, linear and saturation regions. The validity of the proposed model has been verified by extensive comparison with the exact numerical integrations and 3-D numerical simulation , demonstrating the modelpsilas accuracy and prediction capability.

Analog/RF performance analysis of coaxial carbon nanotube MOS field effect transistor from non-equilibrium Green’s function simulation

Based on the non-equilibrium Greenpsilas function simulation, the analog/RF performance of Coaxial Carbon Nanotube Field Effect Transistor (CNTFET) including the trans-conductance efficiency gm/Id, cutoff frequency ft, and maximum oscillation frequency fmax are analyzed in details. The analysis method is described and the CNTFET analog/RF performance dependence on the operation bias, device chirality, and gate oxide thickness are demonstrated. These results will be useful for the device scientists and circuit engineers to optimize the CNTFET structure and improve its circuit performance for the potential analog/RF application in near future.

Tests on Symmetry and Continuity between BSIM4 and BSIM5

This paper presents the test results on the CMOS model symmetry and continuity characteristics between BSIM4 and BSIM5 from University of California at Berkeley. It is shown that the industry standard model BSIM4 has a series of the shortcomings of the continuity and symmetry, such as the charge, high-order current derivatives, and the trans-capacitances while new generation BSIM MOSFET compact model, BSIM5, demonstrates all necessary continuity and symmetry characteristics, which are very important for analog and RF circuit design