Charge Control Model Research Articles

On the gm/ID-based approaches for threshold voltage extraction in advanced MOSFETs and their application to ultra-thin body SOI MOSFETs

In this paper, we investigate the transconductance-to-current ratio (gm/ID) methods for the threshold voltage extraction using two popular threshold voltage criteria applicable to advanced bulk and SOI MOSFETs, namely: the condition of the maximum of the second derivative of the inversion charge and of the equality of the drift and diffusion drain current components. Using analytical modeling, we derive the first-order electrical parameters matching these two physical conditions and show that in the ideal MOSFET they do not coincide. The first corresponds to the point on the gm/ID versus gate voltage (Vg) curve where d(gm/ID)/dVG exhibits a minimum and where the ratio of gm/ID to its maximum value is equal to 2/3, whereas the second is met at the point where this ratio equals 1/2. The gm/ID methods for the VTH extraction using the above two criteria and their correlation with other methods are discussed. Since our modeling is based on the unified charge control model, its predictions are expected to be valid for both bulk and SOI MOSFETs. Experimental and simulation results for advanced SOI MOSFETs are used to validate modeling derivations and clarify practical applicability and limitations of the gm/ID methods.

Theory and measurement of plasmonic terahertz detector response to large signals

Electron gas in the conduction channel of a Field Effect Transistor (FET) can support collective plasma oscillations tunable by the gate voltage. In the Dyakonov-Shur terahertz (THz) detector, nonlinearities in the plasma wave propagation in the gated channel of a FET lead to a constant source-to-drain voltage providing the detector output. We present the detector theory in the frame of the hydrodynamic model using the electron plasma Navier-Stokes and thermal transport equations, thus fully accounting for the hydrodynamic non-linearity, the viscosity, and pressure gradients in the detector response. Both resonant and broadband operations of the high electron mobility transistor (HEMT) based plasmonic detectors are described by this model. The relation between the electron channel density and gate voltage was modeled by the unified charge control model applicable both above and below the threshold voltage. The theoretical results are compared with the response measured in the short channel InGaAs HEMT and the analytical approximation. The THz source was operating at 1.63 THz, and the response was measured at varying signal intensities. The response of the detector operated in the open drain mode was measured above and below the threshold, and the theoretical and experimental results are shown to be in good agreement.

Compact Charge-Based Physical Models for Current and Capacitances in AlGaN/GaN HEMTs

This paper presents physics-based compact models for the C-V and I-V characteristics of AlGaN/GaN HEMT devices. The contribution of only the first energy level in the triangular quantum well at the AlGaN/GaN interface (where most of the charge carriers of the 2-DEG channel reside) is considered, which resulted in an accurate and simple unified charge control model. Based on this, analytical models of the drain current, the gate charge, and the gate capacitances have been developed. The models cover all the different operating regimes of a device. The excellent agreements between the model and measured C-V and I-V characteristics of devices with different gate lengths have demonstrated the validity of the model.

The Transistor Laser: Theory and Experiment

The quantum-well (QW) heterojunction bipolar transistor (HBT) laser [the transistor laser (TL)], inherently a fast switching device, operates by transporting small minority base charge densities <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sim\!\! {\hbox {10}}^{16}\ {\hbox {cm}}^{-3}$</tex></formula> over nanoscale base thickness ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt;$</tex></formula> 900 A) in picoseconds. The base QW acts as an optical “collector,” in addition to the usual electrical collector, that selects out “fast” recombining carriers, resulting in a short lifetime ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\sim$</tex></formula> 29 ps) and higher differential laser gains. Charge and current continuity, together with the boundary conditions imposed by both collectors of the TL lead to a new charge control model, “unpinning” of population inversion beyond lasing threshold, quasi-Fermi level discontinuity across base QW, and a new equivalent circuit model requiring an extension to Kirchhoff's law. With the TL, the HBT becomes more than just a charge control device, but also a photon storage and switching device. The TL, owing to fast recombination speed, its unique three-terminal configuration, and the complementary nature of its optical and electrical collector output signals, enables resonance-free base current and collector voltage modulations, and compact realization of electro–optical applications such as nonlinear signal mixing, frequency multiplication, negative feedback, and optoelectronic logic gates.

Physically based analytical model of the blocking I–V curve of Trench IGBTs

In this paper a physical model for the evaluation of the I–V curve in avalanche condition of the vertical PNP of an IGBT is presented. A two-zone linear approximation for the electric field in the depletion region is adopted and the slope of the two regions is defined from the total current and the ratio between the electrons and holes fluxes. The ratio between the electrons and holes which flow into the depletion region is evaluated by means of an accurate charge control model which provides the β of the PNP up to high injection current levels.

RF characterization of 100‐nm separate gate InAlAs/InGaAs DG‐HEMT

ABSTRACTThis article presents a three port analysis for separate gate In0.52Al0.48As/In0.53Ga0.47As DG‐HEMT and a small signal equivalent circuit is developed using charge control model. The various intrinsic short circuit admittance parameters (Y‐parameters) are evaluated to extract scattering parameters, to determine the maximum transducer power gain of the device. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:2796–2803, 2013

Analog memristive memory with applications in audio signal processing

Since the development of the HP memristor, much attention has been paid to studies of memristive devices and applications, particularly memristor-based nonvolatile semiconductor memory. Owing to its unique properties, theoretically, one could restart a memristor-based computer immediately without the need for reloading the data. Further, current memories are mainly binary and can store only ones and zeros, whereas memristors have multilevel states, which means a single memristor unit can replace many binary transistors and realize higher-density memory. It is believed that memristors can also implement analog storage besides binary and multilevel information memory. In this paper, an implementation scheme for analog memristive memory is considered. A charge-controlled memristor model is derived and the corresponding SPICE model is constructed. Special write and read operations are demonstrated through numerical analysis and circuit simulations. In addition, an audio analog record/play system using a memristor crossbar array is designed. This system can provide great storage capacity (long recording time) and high audio quality with a simple small circuit structure. A series of computer simulations and analyses verify the effectiveness of the proposed scheme.

A Closed-Form Charge Control Model for the Threshold Voltage of Depletion- and Enhancement-Mode AlGaN/GaN Devices

A closed-form charge control model (CCM) for threshold voltage (Vth) of single-heterojunction (AlGaN/GaN) devices is developed. The CCM reveals the mechanisms of how the space charges across the barrier of a heterojunction deplete or enhance 2-D electron gas. The V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> of both depletion- and enhancement-mode heterostructure field-effect transistors may be calculated through this model. Considering the strained and relaxed states, and surface states, the calculated results for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> are in good agreement with simulation results. The generalized form for CCM may have wide applications for theoretical-based design for V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> of AlGaN/GaN devices.

Direct-current and radio-frequency characteristics of passivated AlGaN/GaN/Si high electron mobility transistors

AlGaN/GaN/Si HEMTs grown by molecular beam epitaxy have been investigated using spectroscopy capacitance, direct and pulse current–voltage and small-signal microwave measurements. Passivation of the HEMT devices by SiO2/SiN with NH3 and N2O pretreatments is made in order to reduce the trapping effects. As has been found from DLTS data, some of electron traps are eliminated after passivation. This has led to an improvement in the drain current. To describe the electron transport, we have developed a charge-control model by including the deep traps observed from DLTS experiments. The thermal and trapping effects have been, on the other hand, studied from a comparison between direct-current and pulsed conditions. As a result, a gate-lag and a drain-lag were revealed indicating the presence of deep lying centers in the gate-drain spacing. Finally, small-signal microwave results have shown that the radio-frequency parameters of the AlGaN/GaN/Si transistors are improved by SiO2/SiN passivation and more increasingly with N2O pretreatment.

Analysis of Switching Circuits Through Incorporation of a Generalized Diode Reverse Recovery Model Into State Plane Analysis

A new switching circuit analysis technique is proposed in which the reverse recovery and junction capacitance non-idealities of diode-based switches are incorporated into a state plane analysis of the circuit. Accurate state plane modeling of the reverse recovery process is based on the development of new generalizations of the classic charge control model. Using as an example a zero-voltage switching dc transformer possessing high sensitivity to diode characteristics, these generalizations are shown to be necessary to achieve accurate results across all operating modes. The proposed circuit analysis technique produces excellent modeling agreement with results measured on a hardware prototype of the dc transformer circuit.

Equivalent circuit analysis model of charge-controlled memristor and its circuit characteristics

Memristor realized physically is recently a basic two-terminal circuit element with memory property. Based on Taylor series form of φ-q relationship, a charge-controlled memristor equivalent circuit analysis model is built. A charge-controlled memristor model with cubic nonlinearity is taken, as an example, to make a theoretical analysis of circuit characteristics, such as voltage-current relationship, active-passive property, and so on, of the charge-controlled memristor with different parameters. Results indicate that the voltage-current relationship of the charge-controlled memristor has an italic “8” shaped hysteresis loop characteristic, and the charge-controlled memristor shows passivity and activity accompanied with the variations of parameter symbols, resulting in the occurrence of the corresponding variations of circuit characteristics; compared with the passive memristor, the active memristor is more suitable for use as a second harmonic signal generation circuit. An experiment circuit is built based on the equivalent circuit of the charge-controlled memristor characteristic analysis, and the experimental results well verify the theoretical analysis.

Perhydropolysilazane spin-on-dielectric passivation buffer layers for AlGaN/GaN high-electron mobility transistors

Perhydropolysilazane spin-on-dielectric (SOD) is examined as a SiOx buffer for the plasma-enhanced CVD (PECVD) Si3N4 passivation of AlGaN/GaN high-electron-mobility transistors (HEMTs). Compared to HEMTs passivated by the conventional PECVD Si3N4, the SOD-buffered structure shows about two times greater saturation drain current. From the modified charge control model and Silvaco device simulation, it is proposed that this ehancement is due to the minimised plasma-induced surface states in the SOD-buffered structure compared to a high density (∼5×1012/cm2) of negatively charged states in the PECVD Si3N4 passivation structure.

An automatic gain control circuit with TiO2 memristor variable gain amplifier

An automatic gain control (AGC) topology with a variable gain amplifier utilizing a titanium dioxide (TiO2) memristor is described. A system analysis technique is developed based on the published physical charge-controlled memristor models and unique properties of this passive device. A linearized feedback loop amplitude model is used to design the AGC, and a design tradeoff analysis based on distortion performance is developed. The analysis results are verified with SPICE simulation including a TiO2 memristor SPICE model.

InxGa1−xAsyP1−y–InzGa1−zAs optical transistor

In this paper, we proposed, modeled and evaluated by numerical simulation of an InGaAsP–InGaAs optical transistor operating at optical communication wavelength of 1.55μm. We numerically simulated the proposed structure and investigated the transient and steady-state characteristics by calculating the required microscopic parameters and solving the rate equations within the charge control model. The frequency response and bandwidth modulation of the proposed device are also calculated.

2-D Theoretical Model for Current–Voltage Characteristics in AlGaN/GaN HEMT’s

A threshold-voltage-based 2-D theoretical model for the Current–Voltage characteristics of the AlGaN/GaN high electron mobility transistors (HEMT’s) is developed. The present work proposes an improved charge-control model by employing the Robin boundary condition when introduced the solution of the 2-D Poisson’s equation in the density of charge depleted in the AlGaN layer. The dependence of 2-DEG sheet carrier concentration on the aluminum composition and AlGaN layer thickness has been investigated in detail. Current–voltage characteristics developed from the 2-DEG model in order to take into account the impact of gate lengths. The relation between the kink effect and existing deep centers has also been confirmed by using an electrical approach, which can allow to adjust some of electron transport parameters in order to optimize the output current.

Analysis and improvement of optical frequency response in a long wavelength transistor laser

Charge control model and rate equations have been exploited for the first time in order to glean the optical frequency response of a long-wavelength heterojunction bipolar transistor laser. For a 1.56 μm N-InP/p-InAlGaAs/N-InP fabricated transistor laser with a single quantum well, the optical bandwidth is estimated using this model. All parameters of the mentioned model have been computed for this new type of long wavelength transistor laser. It has been found that frequency response of this optoelectronic device has a 29 dB resonance peak which is not very desirable and is so higher than traditional GaAs transistor lasers. Furthermore, we have illustrated that the resonance peak will decrease and the optical bandwidth will increase, if we increase the width of the quantum well. Finally, we have analyzed that how base width affects on the optical bandwidth and resonance peak of frequency response. It has been proved that, there is a trade-off between larger bandwidth and lower resonance peak for base width effect.

CHARGE BEHAVIOR IN ORGANIC THIN FILM TRANSISTORS

In this work, we review the physical properties of organic materials and transistors, discussing especially the charge transport mechanisms. Finally, we present an analytical and continuous charge model for Organic Thin Film Transistors (OTFTs) from which analytical expressions of all the total capacitances are obtained. They are developed and finally written as continuous explicit functions of the applied voltage, resulting in a complete charge-based small-signal model composed by a unified charge control model derived from Poisson equation assuming an exponential density of localized states. This charge model was developed from a previously proposed analytical DC current model assuming a hopping based transport. Therefore our complete small signal model has the potential to be successfully used in circuit simulators for the design of OTFTs.

Transport Properties of Insulated Gate AlInN/InN Heterojunction Field Effect Transistor

As a promising candidate for future high speed devices InN-based heterojunction field effect transistor (HFET) has gained a lot of attention in recent years. However, InN-based devices are still a less studied compared with other III-nitride based devices. This work investigates theoretically, the electron transport properties of insulated gate AlInN/InN Heterojunction Field Effect Transistor. A self-consistent charge control model based on one-dimensional Schrodinger-Poisson equations is developed. The transport properties of the device are calculated using an ensemble Monte Carlo simulation. The device model incorporates an analytical 3-valley band structure with non-parabolicity for all nitride materials. The scattering mechanisms considered are dislocations scattering, impurity scattering, interface roughness, alloy disorder scattering and phonon scattering. The model also takes into account the highly dominant spontaneous and piezoelectric polarization effects to predict the 2DEG sheet charge density more accurately at the heterointerface. The results obtained are agreed well with the literature.

An accurate polynomial-based analytical charge control model for AlGaN/GaN HEMT

A new nonlinear expression of Fermi-level variation with two-dimensional electron gas density in a high electron mobility has been proposed. It was found that our expression has a better fit with the numerical results. And, an analytical expression for ns in terms of the applied gate voltage is developed. Comparing with other previous approximations, the solutions of our expression has a better agreement with the exact numerical results over the entire range of interest. Besides, the solutions of our expression of ns versus VG are compared with the experimental data and shown to be in good agreement over a wide range of bias conditions.

Modeling of the Output and Transfer Characteristics of Graphene Field-Effect Transistors

We obtain the output and transfer characteristics of graphene field-effect transistors by using the charge-control model for the current, based on the solution of the Boltzmann equation in the field-dependent relaxation time approximation. Closed expressions for the conductance, transconductance, and saturation voltage are derived. We found good agreement with the experimental data of Meric et al. [Nat. Nanotechnol. vol. 3, p. 684, 2008] without assuming carrier density-dependent velocity saturation.