Nanometer Field Effect Transistors Research Articles

Spin contribution to the instability of THz plasma waves

When the boundary conditions of the source and drain are asymmetric, the plasma waves may become unstable in the channel of a field effect transistor (FET). We use the quantum magnetohydrodynamic model to study the influence of the quantum Bohm potential, Fermi statistical pressure, and electron spin effects on the stability of THz plasma waves propagating perpendicular to the magnetic field in the FET. A dispersion equation governing the THz plasma oscillation is obtained. Numerical results have shown that the presence of spin effects has enlarged the instable range of β, enhanced the instability increment, and made the frequency of THz plasma waves larger. The research shows that nanometer FETs with spin effects have advantages in realizing practical terahertz radiation.

Energy Consumption, Conversion, and Transfer in Nanometric Field-Effect Transistors (FET) Used in Readout Electronics at Cryogenic Temperatures

The energy consumed by electron devices such as field-effect-transistors (FET) in an integrated circuit is mostly used to process different electrical signals. However, a fraction of that energy is also converted into heat that gets transferred throughout the integrated circuit and modifies the local temperature. The modification of the local temperature, which is interpreted as a self-heating mechanism, is a function of different charge carrier scattering mechanisms, the characteristic energy relaxation times for charge carriers, the heat carrier mechanisms, the geometry of the FET, the volume of the integrated circuit, and the composed thermal properties of the integrated circuit and the system package. Besides all those dependencies, the charge and heat transport properties are temperature dependent. All these features make the electrothermodynamic analysis and modeling of low-power cryogenic electron devices a compulsory need. In this work, we introduce an analysis based on experimental results obtained from characterizing FET test structures in the temperature range between 300 K and down to 3.1 K.

Linear conduction in N-type organic field effect transistors with nanometric channel lengths and graphene as electrodes

In this work, we test graphene electrodes in nanometric channel n-type Organic Field Effect Transistors (OFETs) based on thermally evaporated thin films of the perylene-3,4,9,10-tetracarboxylic acid diimide derivative. By a thorough comparison with short channel transistors made with reference gold electrodes, we found that the output characteristics of the graphene-based devices respond linearly to the applied bias, in contrast with the supralinear trend of gold-based transistors. Moreover, short channel effects are considerably suppressed in graphene electrode devices. More specifically, current on/off ratios independent of the channel length (L) and enhanced response for high longitudinal biases are demonstrated for L down to ∼140 nm. These results are rationalized taking into account the morphological and electronic characteristics of graphene, showing that the use of graphene electrodes may help to overcome the problem of Space Charge Limited Current in short channel OFETs.

Imaging and Gas Spectroscopy for Health Protection in Sub-THz Frequency Range

An overview of main results concerning THz detection related to plasma nonlinearities in nanometer field effect transistors is presented. In particular the physical limits of the responsivity, speed and the dynamic range of these detectors are discussed. As a conclusion, we will present applications of the FET THz detectors for construction of focal plane arrays. These arrays, together with in purpose developed diffractive 3D printed optics lead to construction of the demonstrators of the fast postal security imagers and nondestructive industrial quality control systems. We will show also first results of FET based imaging that uses for contrast not only usual THz radiation amplitude, but also the degree of its circular polarization. Sub-THz high resolution gas spectroscopy is shown to be a powerful means to diagnose various diseases via exhaled breath analysis.

The Instability of Terahertz Plasma Waves in Two Dimensional Gated and Ungated Quantum Electron Gas**supported by National Natural Science Foundation of China (No. 10975114)

The instability of terahertz (THz) plasma waves in two-dimensional (2D) quantum electron gas in a nanometer field effect transistor (FET) with asymmetrical boundary conditions has been investigated. We analyze THz plasma waves of two parts of the 2D quantum electron gas: gated and ungated regions. The results show that the radiation frequency and the increment (radiation power) in 2D ungated quantum electron gas are much higher than that in 2D gated quantum electron gas. The quantum effects always enhance the radiation power and enlarge the region of instability in both cases. This allows us to conclude that 2D quantum electron gas in the transistor channel is important for the emission and detection process and both gated and ungated parts take part in that process.

Terahertz Plasma Waves in Two Dimensional Quantum Electron Gas with Electron Scattering**supported by National Natural Science Foundation of China (No. 10975114)

We investigate the Terahertz (THz) plasma waves in a two-dimensional (2D) electron gas in a nanometer field effect transistor (FET) with quantum effects, the electron scattering, the thermal motion of electrons and electron exchange-correlation. We find that, while the electron scattering, the wave number along y direction and the electron exchange-correlation suppress the radiation power, but the thermal motion of electrons and the quantum effects can amplify the radiation power. The radiation frequency decreases with electron exchange-correlation contributions, but increases with quantum effects, the wave number along y direction and thermal motion of electrons. It is worth mentioning that the electron scattering has scarce influence on the radiation frequency. These properties could be of great help to the realization of practical THz plasma oscillations in nanometer FET.

Effect of gate-length shortening on the terahertz small-signal and self-oscillations characteristics of field-effect transistors

We investigate the shortening of the gate-length in submicrometric and nanometric field-effect transistors as a powerful tool to improve their self-oscillations performances in the terahertz frequency region due to the appearance of the Dyakonov–Shur instability. The theoretical model is based on the numerical solution of hydrodynamic equations for the electron transport in FETs/HEMTs channels. We show that a decrease of the gate length allows, on the one hand, to increase the intrinsic resonant frequencies near 1THz and, on the other hand, to improve the conditions for the onset of the Dyakonov–Shur instability and related phenomena. The small-signal characteristics calculated under constant drain-voltage operation are compared with the drain-voltage self-oscillations calculated under constant drain-current operation.

Hybrid plasma modes in transistors: linear and non-linear responses

We present an analytical model based on hydrodynamic equations and a pseudo-two-dimensional Poisson equation to study the response of a nanometric field-effect transistor channel in the THz domain. This model allows to study different kinds of external excitations of plasma modes and different geometries. We calculate the two first-order responses of the drain voltage or current, which are of peculiar interest in the perspective of THz wave generation and detection and THz electronics. Even at room temperature, each responses present resonances at the eigenfrequencies of the hybrid plasma modes sustained in the channel.

Terahertz Small-Signal Response of Field-Effect Transistor Channels

In this paper, we present an analytical approach for the study of the small-signal response of nanometric field-effect transistor at terahertz frequencies. One-dimensional hydrodynamic equations coupled with a pseudo-two-dimensional Poisson equation are derived at first-order to obtain the small-signal admittance matrix describing the transistor. This matrix is then used to model the loaded device and establish its voltage amplification. The admittances and voltage amplification spectra exhibit sharp resonances associated with the plasma modes of the channel. The influences of the device geometry, operating temperature and connected load are investigated.

The THz Instability in a Two Dimensional Quantum Gated Electron Gas with Scattering of Carriers

Plasma wave generation is a result of the wave amplification due to the reflection from the device boundaries, and typical plasma frequencies lie in the terahertz (THz) range in nanometer field effect transistors (FETs). In this paper, the influence of the scattering of carriers on the instability of plasma waves in nanometer FETs is reported with quantum effects. The quantum effects enhance this instability considerably, as the imaginary part of the wave increases with quantum effects, but the external friction associated with electron scattering reduces the instability. Accordingly, the quantum effects can be used to compensate or overcome the stabilizing role of the friction due to the scattering of carriers on plasma wave generation. These properties could make the nanometer FETs advantageous for the design of terahertz plasmonic sources.

Plasma wave instability in a quantum field effect transistor with magnetic field effect

The current-carrying state of a nanometer Field Effect Transistor (FET) may become unstable against the generation of high-frequency plasma waves and lead to generation of terahertz radiation. In this paper, the influences of magnetic field, quantum effects, electron exchange-correlation, and thermal motion of electrons on the instability of the plasma waves in a nanometer FET are reported. We find that, while the electron exchange-correlation suppresses the radiation power, the magnetic field, the quantum effects, and the thermal motion of electrons can enhance the radiation power. The radiation frequency increases with quantum effects and thermal motion of electrons, but decreases with electron exchange-correlation effect. Interestingly, we find that magnetic field can suppress the quantum effects and the thermal motion of electrons and the radiation frequency changes non-monotonely with the magnetic field. These properties could make the nanometer FET advantageous for realization of practical terahertz oscillations.

Quantum simulation of an ultrathin body field-effect transistor with channel imperfections

An efficient program for the all-quantum simulation of nanometer field-effect transistors is elaborated. The model is based on the Landauer–Buttiker approach. Our calculation of transmission coefficients employs a transfer-matrix technique involving the arbitrary precision (multiprecision) arithmetic to cope with evanescent modes. Modified in such way, the transfer-matrix technique turns out to be much faster in practical simulations than that of scattering-matrix. Results of the simulation demonstrate the impact of realistic channel imperfections (random charged centers and wall roughness) on transistor characteristics. The Landauer–Buttiker approach is developed to incorporate calculation of the noise at an arbitrary temperature. We also validate the ballistic Landauer–Buttiker approach for the usual situation when heavily doped contacts are indispensably included into the simulation region.

Impact of carrier heating on backscattering in inversion layers

In this work, Monte Carlo simulations and analytical modeling are used to investigate quasi-ballistic transport in nanometric metal oxide semiconductor field effect transistors (MOSFETs). In particular, we examine how the thermal nature of the distribution functions, which is implicitly assumed in the most common expression for the backscattering coefficient, leads to an underestimation of the backscattering coefficient in high field conditions and erroneous velocity distribution along the channel. An improved analytical model is proposed, which better captures the nonequilibrium nature of the distribution function and its impact on backscattering and by allowing velocity profiles to exceed the thermal limit. The improved model provides additional insights on the impact of several assumptions on backscattering and could serve as the basis for the development of physically based compact models of quasi-ballistic MOSFETs.

Terahertz instability of field effect transistor in quantum regime

The current-carrying state of a field effect transistor (FET) with asymmetric source and drain boundary conditions may become unstable and lead to generation of terahertz radiation. While previous studies of this instability are limited to the classical case, we extend this analysis to the nanometer FET with quantum effects. We find that quantum effects broaden the instability range of the drift velocity and enhance the radiation frequencies and the output power. These properties could make the nanometer FET advantageous for realization of practical terahertz oscillations.

Adiabatic charge control in a single donor atom transistor

We charge an individual donor quantum dot with an electron originally stored in another quantum dot in its proximity. The single arsenic donor quantum dot and the electrostatic quantum dot in parallel are contained in a silicon nanometric field effect transistor. Their different coupling capacitances with the control and back gates determine a honeycomb pattern at high control gate voltage. It is therefore possible to control the exchange coupling of an electron of the quantum dot with the electrons bound to the donor quantum dot toward the realization of a physical qubit for quantum information processing applications.

Transconductance characteristics and plasma oscillations in nanometric InGaAs field effect transistors

AbstractBy Monte Carlo simulations we investigate the plasma spectrum in n-type InGaAs field effect transistors at 300K in the whole region of operating conditions from ohmic to saturation regime of the transconductance characteristics. The presence of a two dimensional (2D) plasma peak predicted within the gradual channel approximation is confirmed by the microscopic model and its properties are analyzed systematically. At the highest gate voltages the 2D peak is found to become practically independent of the channel width.

Room temperature imaging at 1.63 and 2.54 THz with field effect transistor detectors

GaAs nanometric field effect-transistors are used for room temperature single-pixel imaging using radiation frequencies above 1 THz. Images obtained in transmission mode at 1.63 THz are recorded using transistors operating in a photovoltaic mode with spatial resolution of 300 μm and voltage sensitivity of about 8 mV/W. A reduction in response with increasing frequency was observed and mitigated by the application of a source-drain current, leading to the demonstration of imaging at up to 2.54 THz.

Hydrodynamic modeling of optically excited terahertz plasma oscillations in nanometric field effect transistors

We present a hydrodynamic model to simulate the excitation by optical beating of plasma waves in nanometric field effect transistors. The biasing conditions are whatever possible from Ohmic to saturation conditions. The model provides a direct calculation of the time-dependent voltage response of the transistors, which can be separated into an average and a harmonic component. These quantities are interpreted by generalizing the concepts of plasma transit time and wave increment to the case of nonuniform channels. The possibilities to tune and to optimize the plasma resonance at room temperature by varying the drain voltage are demonstrated.

Plasma wave oscillations in nanometer field effect transistors for terahertz detection andemission

The channel of a field effect transistor can act as a resonator for plasma waves propagatingin a two-dimensional electron gas. The plasma frequency increases with reduction of thechannel length and can reach the terahertz (THz) range for nanometer size transistors.Recent experimental results show these transistors can be potential candidatesfor a new class of THz detectors and emitters. This work gives an overview ofour recent relevant experimental results. We also outline unresolved problemsand questions concerning THz detection and emission by nanometer transistors.

Quantum mechanical effects in nanometer field effect transistors

The atomistic pseudopotential quantum mechanical calculations for million atom nanosized metal-oxide-semiconductor field-effect transistors (MOSFETs) are presented. When compared with semiclassical Thomas-Fermi simulation results, there are significant differences in I-V curve, electron threshold voltage, and gate capacitance. In many aspects, the quantum mechanical effects exacerbate the problems encountered during device minimization, and it also presents different mechanisms in controlling the behaviors of a nanometer device than the classical one.