Non-quasi-static Effects Research Articles

Extraction of Gate Resistance in Sub-100-nm MOSFETs With Statistical Verification

This paper presents an improved z-parameter based approach to extract the gate resistance at low frequencies. The effectiveness of this approach, compared with other y-parameter based approaches, is verified using 430 samples fabricated in 40-, 55-, 90-, and 110-nm CMOS technology nodes. The influence of the nonquasi-static (NQS) effect, resulting from the distributed channel resistance, on the gate resistance extraction is studied, and the optimum processes are suggested to reduce the NQS effect. Finally, the extraction of the channel resistance in the lightly doped drain region is also presented.

Implementation of Delay-Time-Based Nonquasi-Static Bipolar Transistor Models in Circuit Simulators

We found that for a correct simulation of nonquasi-static (NQS) effect in compact bipolar transistor models, a dynamic or small-signal transit time must be used instead of the classical dc transit time. It is shown that the dynamic transit time is slowed down compared with the dc transit time of the intrinsic device owing to the bias-dependence of the latter. Since the instance value of the dynamic transit time is needed at the operating point, a formerly proposed scaling technique is used. The model shows perfect agreement with a widely accepted theoretical approach as well as with numerical device simulation.

Analyzing distortion contributions in a complex device model

Purpose – The purpose of this paper is to propose a method to reduce the non-linear distortion of a transistor to its input and output ports to aid distortion contribution analysis (DCA). This is especially needed when the internal structure of a device model is complex. Design/methodology/approach – The non-linear distortion generated by all non-linear sources inside a device model are reduced to transistor i/o ports by LMSE fitting techniques. Simulations of an LDMOS power transistor are used to compare the reduced distortion results with the actual non-linear sources. Findings – It is shown, that device models where the current sources are split by intermediate nodes cause superficial results, when distortion contributions are calculated as a superposition of contributions from individual non-linear sources. The proposed iterative fitting technique works. Research limitations/implications – Some non-quasistatic effects and the transfer functions from external terminals to internal controlling nodes are not covered. Practical implications – The analysis is a step toward a generic non-linear distortion contribution simulation tool that would aid the designers to develop more linear analog circuits. Originality/value – The concept of DCA itself is fairly new. This paper makes a step to represent the distortion sources in a canonical way.

A new approach to extracting the RF parameters of asymmetric DG MOSFETs with the NQS effect

In analog circuit design an important parameter, from the perspective of superior device performance, is linearity. The DG MOSFET in asymmetric mode operation has been found to present a better linearity. In addition to that it provides, at the discretion of analog circuit designer, an additional degree of freedom, by providing independent bias control for the front and the back gates. Here a non-quasi-static (NQS) small signal model for DGMOSFET with asymmetric gate bias is proposed for extracting the parameters of the device using TCAD simulations. The parameters extracted here for analysis are the intrinsic front and back gate to drain capacitance, Cgd1 and Cgd2, the intrinsic front and back distributed channel resistance, Rgd1 and Rgd2 respectively, the transport delay, τm, and the inductance, Lsd. The parameter extraction model for an asymmetric DG MOSFET is validated with pre-established extracted parameter data, for symmetric DG MOSFET devices, from the available literature. The device simulation is performed with respect to frequency up to 100 GHz.

Lumped Models for Assessment and Optimization of Bipolar Device RF Noise Performance

We present a method for simulation of RF noise characteristics of both intrinsic and complete Si(Ge) heterojunction bipolar transistors (HBT's), aiming at support for device design and optimization. RF noise at the intrinsic device level is addressed through an equivalent circuit based on a discretization of partial differential equations describing the transport of minority carriers in quasi-neutral regions. Effects of nonuniform impurity/bandgap distribution and finite velocity recombination at the polysilicon emitter contact are accounted for. Accuracy is verified against analytical results at intrinsic device level. Assessment of noise characteristics of a complete industrial SiGe HBT demonstrates the practical relevance of nonquasi-static effects on noise characteristics. Exploration of the impact of intrinsic base doping profiles on noise performance demonstrates the potential for device optimization.

Design and Analysis of CMOS-Based Terahertz Integrated Circuits by Causal Fractional-Order RLGC Transmission Line Model

A causal and compact fractional-order model is developed for complementary metal-oxide-semiconductor (CMOS) on-chip transmission line (T-line) at Terahertz (THz) frequencies. With consideration of the loss from frequency-dependent dispersion and nonquasi-static effects at THz, good agreement of characteristic impedance is observed between the proposed fractional-order model and the measurement up to 110 GHz, while traditional integer-order model can only match up to 10 GHz. The developed fractional-order model is further deployed in the design and analysis of CMOS-based THz integrated circuits that utilize T-line, such as standing-wave oscillator, which has significantly improved accuracy with causality.

Modeling the input non-quasi-static effect in small signal equivalent circuit based on charge partitioning for bipolar transistors and its impact on RF noise modeling

This paper models the input non-quasi-static (NQS) effect of bipolar transistors using charge partitioning. The input NQS effect associated with the base minority carrier transport is modeled with a RC network, while the input NQS effect associated with the base-collector space charge region (CB SCR) carrier transport is modeled with a RLC network. With the proposed input NQS equivalent circuit model, Y-parameters and RF noise parameters using the van Vliet model are successfully modeled for frequencies up to f T . The transport noise model is extended to represent the van Vliet model by using two noise related time constants, which eliminates the need of Y-parameter in the description of the noise source. The input NQS effect for such model is verified to be important only for frequencies above f T /3. Analytical Y-parameter and noise solutions of a 1-D bipolar transistor at low injection level are used for validation.

Modeling Nonquasi-Static Effects in SiGe HBTs

The shortcomings of quasi-static and partitioned charge-based models are quantitatively demonstrated for 1-D SiGe heterojunction bipolar transistors. This points out the need to include higher order frequency-dependent terms, i.e., nonquasi-static effects in the model. Three different implementation-suitable modeling approaches are presented with associated formulations. Detailed comparison with the original theory is carried out to show the different levels of achievable accuracy of the formulated models. Circuit simulator implementations, parameter extractions, and validations of the models with device simulation results are also carried out. Frequency- and time-domain small-signal modeling results are found to be consistent and provide a high level of accuracy. For two selected cases among the various modeling approaches, results of large-signal transient switching are presented, showing excellent agreement with device simulation.

Nonquasi-Static Effects and the Role of Kinetic Inductance in Ballistic Carbon-Nanotube Transistors

Nonquasi-static effects in ballistic carbon-nanotube (CN) FETs (CNFETs) are examined by solving the Boltzmann transport equation self-consistently with the Poisson equation. We begin by specifying the proper boundary conditions that should be employed in time-dependent simulations at high speeds; these are the proper boundary conditions for a characterization of the so-called intrinsic transistor, i.e., the internal portion of the device that is unaffected by the source and drain contacts. A transmission-line model that includes both the kinetic inductance (LK) and quantum capacitance (CQ) is then analytically developed from the Boltzmann and Poisson equations, and it is shown to represent the intrinsic transistor's behavior at high frequencies, including a correct prediction of resonances in the transistor's y-parameters. Finally, we show how to represent LK using lumped elements in the transistor's traditional quasi-static equivalent circuit, and we demonstrate that the resulting circuit is capable of modeling the intrinsic behavior of a ballistic CNFET, including the observed resonances, to frequencies beyond the unity-current-gain frequency fT. External parasitics can be easily added for an overall compact model of ballistic CNFET operation.

Purely analytical extraction of an improved nonlinear FinFET model including non-quasi-static effects

An analytical procedure is proposed for extracting a new nonlinear FinFET model, which accounts for non-quasi static effects. The accuracy and the robustness of the obtained nonlinear model are completely validated through the comparison between simulated and measured device behaviour in both linear and nonlinear cases. This study clearly shows that the inclusion of the non-quasi-static phenomena leads to significant model simulation improvements, which become more pronounced at higher frequency.

Degraded Frequency-Tuning Range and Oscillation Amplitude of LC-VCOs due to the Nonquasi-Static Effect in MOS Varactors

Frequency dependent properties of accumulation-mode MOS varactors, which are key elements in many RF circuits, are dominated by Non-Quasi-Static (NQS) effects in the carrier transport. The circuit performances containing MOS varactors can hardly be reproduced without considering the NQS effect in MOS-varactor models. For the LC-VCO circuit as an example it is verified that frequency-tuning range and oscillation amplitude can be overestimated by over 20% and more than a factor 2, respectively, without inclusion of the NQS effect.

Nonquasi-static large-signal model of GaN FETs through an equivalent voltage approach

A new empirical nonlinear model of GaN-based electron devices is presented in the article. The model takes into account low-frequency dispersion due to self-heating and charge-trapping phenomena and provides accurate predictions at frequencies where nonquasi-static effects are important. The model is based on the application of a recently proposed equivalent-voltage approach and is identified by using pulsed measurements of drain current characteristics and pulsed S-parameter sets. Full experimental validation on a GaN on SiC PHEMT is provided at both small- and large-signal operating conditions. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.

A scalable advanced RF IC design-oriented MOSFET model

This article presents a validation of the EKV3 MOSFET compact model dedicated to the design of analogue/RF ICs using advanced CMOS technology. The EKV3 model is compared with DC, CV and RF measurements up to 20 GHz of a 110 nm CMOS technology. The scaling behaviour over a large range of channel lengths and bias conditions is presented. Long-channel devices show significant non-quasi static effects while in short-channel devices the parasitics modelling is critical. This is illustrated with Y-parameters and ft vs. ID in NMOS and PMOS devices, showing good overall RF modelling abilities of the EKV3 MOSFET model. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2008.

Time-dependent quantum transport and nonquasistatic effects in carbon nanotube transistors

Nonquasistatic effects in ac characteristics of carbon nanotube field-effect transistors are examined by solving a full time-dependent, open-boundary Schrödinger equation. The nonquasistatic characteristics, such as the finite channel charging time, and the dependence of small signal transconductance and gate capacitance on the frequency, are explored. The validity of the widely used quasistatic approximation is examined. The results show that the quasistatic approximation overestimates the transconductance and gate capacitance at high frequencies, but gives a more accurate value for the intrinsic cutoff frequency over a wide range of bias conditions.

Modeling of anomalous frequency and bias dependences of effective gate resistance in RF CMOS

This paper explains the frequency and bias dependences of the effective gate resistance (real part of h/sub 11/) by considering the effect of the gate-to-body capacitance, gate-to-source/drain overlap capacitances, fringing capacitances, and nonquasi-static (NQS) effect. A new method of separating the physical gate resistance and the NQS channel resistance is proposed. Separating the gate-to-source parasitic capacitances from the gate-to-source inversion capacitance is found to be necessary for an accurate modeling of all the Y-parameters.

Impact of technology scaling and process variations on RF CMOS devices

Inspired by the huge improvement in the RF properties of CMOS devices, RF designers are invading the wireless market with all-CMOS RF transceivers and system-on-chip implementations. In this work, the impact of technology scaling on the RF properties of CMOS; frequency properties, noise performance, linearity, stability, and non-quasi static effects is investigated to provide RF designers with an insight to the capabilities of future CMOS technologies. Moreover, the RF frequency performance of CMOS is investigated under the influence of process variations for different CMOS generations. Using the BSIM4 model, it is found that future CMOS technologies have high prospects in the RF industry and will continue challenging other technologies in the RF domain to be the dominant technology for RF transceivers and system-on-chip implementations.

A new approach to model nonquasi-static (NQS) effects for mosfets-part II: small-signal analysis

We present a new approach to model nonquasi-static (NQS) effects in a MOSFET in a small-signal situation. The model derived here is based on the large-signal NQS model previously proposed. The derivation of the small-signal model is presented. The small-signal parameters obtained with this model prove to be accurate up to very high frequencies. An excellent match between the new model and device simulation results has been observed even when the frequency is many times larger than the cutoff frequency.

A new approach to model nonquasi-static (NQS) effects for mosfets-part I: large-signal analysis

We present a new approach to model nonquasi-static (NQS) effects in a MOSFET in a small-signal situation. The model derived here is based on the large-signal NQS model previously proposed. The derivation of the small-signal model is presented. The small-signal parameters obtained with this model prove to be accurate up to very high frequencies. An excellent match between the new model and device simulation results has been observed even when the frequency is many times larger than the cutoff frequency.

Implementation of nonquasi-static effects in compact bipolar transistor models

Large-signal implementation of nonquasi-static (NQS) effects in bipolar transistors is reviewed. An approach is proposed to introduce first-order NQS correction to typical quasi-static phenomenological models. Both charge- and noncharge-conserving implementations are considered. The resulted large-signal equivalent-circuit model compares well with the two-dimensional physical model in simulating HBT transient response under high-current operations. The present approach advances the state-of-the-art by allowing arbitrary bias dependence of transit times in large-signal NQS models.

A Self-Consistent Non-Quasi-Static MOSFET Model for Circuit Simulation Based on Transient Carrier Response

We have developed a basic concept for a non-quasi-static (NQS) metal-oxide-semiconductor field-effect transistor (MOSFET) model for circuit simulation. The model is based on a carrier-response delay, and incorporates the time and position dependence of the carrier density along the channel. This is the exact origin of the NQS effect. By comparing model results with 2D device simulation results, solving the continuity equation explicitly, we found that the carrier-response delay consisted of a conductive delay and a charging delay. The developed model was successfully applied to test transient behavior of the drain current.