Empirical modeling of low-frequency dispersive effects due to traps and thermal phenomena in III-V FET's

The modeling of low-frequency dispersive effects due to surface state densities, deep level traps and thermal phenomena plays an important role in the large-signal performance prediction of III-V FET's. This paper describes an empirical modeling approach to accurately predict deviations between static and dynamic drain current characteristics caused by dispersive effects in III-V devices operating at microwave frequencies. It is based on reasonable assumptions and can easily be embedded in nonlinear FET models to be used in Harmonic-Balance tools for circuit analysis and design. Experimental and simulated results, for HEMT's and GaAs MESFET's of different manufacturers, that confirm the validity of the new approach, are presented and discussed together with the characterization procedures require

Nonlinear modeling of trapping and thermal effects on GaAs and GaN MESFET/HEMT devices

A novel nonlinear model for MESFET/HEMT devices is presented. The model can be applied to low power (GaAs) and high power (GaN) devices with equal success. The model provides accurate simulation of the static (DC) and dynamic (Pulsed) I-V characteristics of the device over a wide bias and ambient temperature range (from -70ºC to +70ºC) without the need of an additional electro-thermal sub-circuit. This is an important issue in high power GaN HEMT devices where self-heating and current collapse due to traps is a more serious problem. The parameter extraction strategy of the new model is simple to implement. The robustness of the model when performing harmonic balance simulation makes it suitable for RF and microwave designers. Experimental results presented demonstrate the accuracy of the model when simulating both the small-signal and large-signal behavior of the device over a wide range of frequency, bias and ambient temperature operating points. The model described has been implemented in the Advanced Design System (ADS) simulator to validate the proposed approach without convergence problems.The authors would like to thank the Spanish Ministry of Science and Innovation (MICINN) by the financial support provided through projects CSD2008-00068, TEC2008-06684-C03-01 and TEC2011-29126-C03-01

DC and Microwave Analysis of Gallium Arsenide Field-Effect Transistor-Based Nucleic Acid Biosensors

Sensitive high-frequency microwave devices hold great promise for biosensor design. These devices include GaAs field effect transistors (FETs), which can serve as transducers for biochemical reactions, providing a platform for label-free biosensing. In this study, a two-dimensional numerical model of a GaAs FET-based nucleic acid biosensor is proposed and simulated. The electronic band structure, space charge density, and current-voltage relationships of the biosensor device are calculated. The intrinsic small signal parameters for the device are derived from simulated DC characteristics and used to predict AC behavior at high frequencies. The biosensor model is based on GaAs field-effect device physics, semiconductor transport equations, and a DNA charge model. Immobilization of DNA molecules onto the GaAs sensor surface results in an increase in charge density at the gate region, resulting from negatively-charged DNA molecules. In modeling this charge effect on device electrical characteristics, we take into account the pre-existing surface charge, the orientation of DNA molecules on the sensor surface, and the distance of the negative molecular charges from the sensor surface. Hybridization with complementary molecules results in a further increase in charge density, which further impacts the electrical behavior of the device. This behavior is studied through simulation of the device current transport equations. In the simulations, numerical methods are used to calculate the band structure and self-consistent solutions for the coupled Schrodinger, Poisson, and current equations. The results suggest that immobilization and hybridization of DNA biomolecules at the biosensor device can lead to measurable changes in electronic band structure and current-voltage relationships. The high-frequency response of the biosensor device shows that GaAs FET devices can be fabricated as sensitive detectors of oligonucleotide binding, facilitating the development of inexpensive semiconductor-based molecular diagnostics suitable for rapid diagnosis of various disease states

Advanced digital modulation: Communication techniques and monolithic GaAs technology

Communications theory and practice are merged with state-of-the-art technology in IC fabrication, especially monolithic GaAs technology, to examine the general feasibility of a number of advanced technology digital transmission systems. Satellite-channel models with (1) superior throughput, perhaps 2 Gbps; (2) attractive weight and cost; and (3) high RF power and spectrum efficiency are discussed. Transmission techniques possessing reasonably simple architectures capable of monolithic fabrication at high speeds were surveyed. This included a review of amplitude/phase shift keying (APSK) techniques and the continuous-phase-modulation (CPM) methods, of which MSK represents the simplest case

'Backgating' model including self-heating for low-frequency dispersive effects in III-V FETs

A new approach is proposed which takes into account both traps and thermal phenomena for the modelling of deviations between static and dynamic drain current characteristics in III-V field effect transistors. The model is based on the well-known `backgating' concept and can easily be identified on the basis of conventional static drain current characteristics and small-signal, low-frequency S parameters. Experimental results confirm the accuracy of the proposed mode

An overview on recent developments in RF and microwave power H-terminated diamond MESFET technology

Thanks to its wide bandgap, exceptionally high thermal conductivity and relatively high carrier velocities, diamond exhibits attractive semiconductor properties that make it an interesting candidate for high power, high frequency and high temperature solid-state microelectronic devices, able to withstand harsh environmental conditions (in terms of temperature and/or radiation). The development of a diamond transistor technology has been restricted for many years due to the difficulty in implementing conventional acceptor or donor bulk doping strategies with satisfactory activation at room temperature. More recently, a breakthrough in diamond MESFET technology was represented by the introduction of surface diamond p-doping by means of H-termination, opening the way to interesting development in the microwave field. The paper presents an overview on recent developments in H-terminated diamond MESFETs for power RF and microwave applications. After an introduction to the diamond technology and device state-of-the-art performance, the physics-based and large-signal modeling of diamond MESFETs is discusse

A multi-dimensional model of passive MESFETS for use in non-linear microwave signal processing

A multi-dimensional model which accurately predicts device non-linearities over frequency and power has been developed for MESFETs used in a passive configuration in microwave signal processing applications. Historically, MESFETs have been used in linear control applications as passive microwave switches and attenuators. More recently, MESFETs operated as passive elements have been employed as power-sensitive non-linear transfer function generators to produce limiters, phase shifters, and linearizers. These devices offer simplicity, high performance, and the opportunity for application in MMIC technology. This thesis deals with a mapping of passive MESFET non-linear characteristics, and provides insight into the causes of non-linearity in MESFETs when operated as control elements at near zero drain voltage. Five unique operating modes are identified, and discussed in terms of their equivalent circuit models. This work also deals with computer aided model extraction and non-linear simulation of MESFET characteristics, and presents a multi-dimensional lumped element model which accurately predicts device non-linearity over a wide range of power (-35 to \u3e 10 dBm) and frequency (.1 to \u3e 18 GHz). The application of this model to the design of a traveling wave tube amplifier (TWTA) linearizer is demonstrated. The model allows linearized TWTA transfer characteristics and two-tone carrier-to-intermodulation (C/I) performance to be predicted using standard CAD software