Doped Transistors Research Articles

Analysis of Mismatching on the Analog Characteristics of GC SOI MOSFETs

This paper presents an evaluation of mismatching impact on the analog characteristics of fully-depleted graded-channel (GC) SOI MOSFET. This study is carried out by means of electrical measurements and two-dimensional numerical simulations, comparing GC to uniformly doped transistors. Important basic parameters such as threshold voltage and subthreshold slope were analyzed as well as analog parameters, namely transconductance, output conductance, Early voltage and intrinsic voltage gain.

Anomalous Transconductance in Long Channel Halo Implanted MOSFETs: Analysis and Modeling

In this paper, we report anomalous behavior of transconductance ( ${g}_{m}$ ) in halo implanted MOSFET for linear and saturation regions across both gate and body biases. The ${g}_{m}$ characteristics undergo sharp change of slope in saturation which cannot be modeled by conventional compact models. The cause of such behavior is identified and explained using the TCAD simulations of source side halo, drain side halo (DH), both side halos, and uniformly doped transistors. An analytical model, based on the equivalent conductance of the halo device, is developed to understand the ${g}_{m}$ behavior. It is shown that the commonly used approach where only the DH region is considered in saturation, is insufficient to model the atypical ${g}_{m}$ behavior. The effect of oxide thickness ( ${T}_{\text {ox}}$ ) variation on ${g}_{m}$ is also studied, which demonstrates a deviation from the conventional $g_{m}$ behavior for halo implanted devices with thicker ${T}_{\text {ox}}$ . A computationally efficient SPICE model is proposed to model ${g}_{m}$ characteristics which shows excellent matching with the measured data.

Design of Novel Pixel with Non-Uniform Doped Transistor Channel and Triangle-Tooth Shape Pinned Photodiode for High Speed CMOS Image Sensors

Design of Novel Pixel with Non-Uniform Doped Transistor Channel and Triangle-Tooth Shape Pinned Photodiode for High Speed CMOS Image Sensors

Improved operation of graded-channel SOI nMOSFETs down to liquid helium temperature

This paper presents the operation of Graded-Channel (GC) Silicon-On-Insulator (SOI) nMOSFETs at low temperatures down to liquid helium temperature in comparison to standard uniformly doped transistors. Devices from two different technologies have been measured and show that the mobility increase rate with temperature for GC SOI transistors is similar to uniformly doped devices for temperatures down to 90 K. However, at liquid helium temperature the rate of mobility increase is larger in GC SOI than in standard devices because of the different mobility scattering mechanisms. The analog properties of GC SOI devices have been investigated down to 4.16 K and show that because of its better transconductance and output conductance, an intrinsic voltage gain improvement with temperature is also obtained for devices in the whole studied temperature range. GC devices are also capable of reducing the impact ionization due to the high electric field in the drain region, increasing the drain breakdown voltage of fully-depleted SOI MOSFETs at any studied temperature and the kink voltage at 4.16 K.

Experimental and simulation analysis of electrical characteristics of common‐source current mirrors implemented with asymmetric self‐cascode silicon‐on‐insulator n‐channel metal–oxide–semiconductor field‐effect transistors

In this paper, the performance of asymmetric self-cascode (A-SC) fully depleted silicon-on-insulator n-channel metal–oxide–semiconductor field-effect transistors configuration applied to common-source current mirrors (CMs) have been analysed through experimental measurements, comparing with symmetric self-cascode configuration as well as with standard uniformly doped transistor. The mirroring precision, output resistance and output swing have been used as figures of merit to evaluate the improvements achieved with the use of A-SC transistors. Two-dimensional numerical simulations have been also performed in order to further explore the advantages of A-SC transistor in common-source CMs. The obtained results have shown that the best mirroring precision has been obtained with larger channel lengths of the transistor near the source. Despite the worsened intrinsic mismatching presented by common-source CMs implemented with A-SC transistors in comparison with single transistor CM, the A-SC structure has allowed larger output resistance, breakdown voltage and better mirroring precision.

Finite-Difference Time-Domain (FDTD) Simulation of Novel Terahertz Structures

Previous work on compact, variable, efficient, high brightness radiation sources is extended by calculating the radiated power and angular distributions for different configurations and drive sources. Figures of merit are defined in terms of efficiencies or effective impedances such as the radiation coupling impedance Zr .Characteristics of representative cases are discussed in terms of a few basic parameters. Conditions for interference are discussed and demonstrated. Finally, we discuss some further possibilities together with various impediments to realizing such devices. The differences between bound and free electrons are studied from the standpoint of the frequencies that are practicably achievable. With the ansatz that the transport physics with Maxwell’s Equations are valid but modified by the material properties, a number of analogs exist between these two basic sources of radiation. In many cases, the differences are between macro and micro implementations e.g. between klystrons and klystrinos (micro or nano)  or solid state and semiconductor lasers or rare-earth doped transistors. Cases with no apparent analogs are ones due to unique quantum effects e.g. radiation at 3kTc in superconductors. This is well above magnetic resonance imaging MRI around 0.4 eV but well below room temperature at 25 meV. Bound and free possibilities for planar, micro undulators over this range are studied using FDTD techniques. To our knowledge, there have been no implementations of either possibility.

Simulation of OTA's with Double-Gate Graded-Channel MOSFETS using the Symmetric Doped Double-Gate Model

In this paper, Operational Transconductance Amplifiers (OTA's) were simulated in SPICE using the Symmetric Doped Double-Gate Model which includes the capacitances of Double-Gate (DG) transistors. In this work, all the transistors have been simulated using just one model for lightly doped transistors (TLD), high doped transistors (THd) N-channel devices and P-channel devices. These OTA's show an improvement in the high open-loop voltage gain which is related mainly to the reduction of the drain output conductance which gives higher Early voltages for DG GC transistors.

Analytical Modeling of Output Conductance in Long-Channel Halo-Doped MOSFETs

In this paper, a detailed physical analysis and an analytical derivation of the degradation of the output resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> ) observed in relatively long-channel laterally nonuniformly doped devices with halo implants are presented. Two-dimensional device simulations were performed, and the simulations show that the channel can be split into two uniformly doped transistors in series for the purpose of analysis. The lower doped bulk transistor is on the source side, while the higher doped halo transistor is toward the drain end. Based on this two-transistor analysis, a simple R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> degradation model is derived for implementation in a MOSFET compact model

Ion implantation of rare earth ions for light emitters

We discuss the excitation and deexcitation processes for solid state optical emitters. At present, there is considerable interest in depositing a material system, which is compatible to silicon microelectronics processing and which emits electroluminescence (EL). We will compare the EL results of rare earth doped transistors in silicon with doped insulators and doped wide bandgap semiconductors, especially Er in Si (a source for 1.5 μm) as well as Er and Tb in SiO 2, Si 3N 4 and AIN, which are sources for infrared and visible light. The most impressive results are achieved by RE doped GaN film devices, which cover the entire visible spectrum.

Two dimensional electron gases induced by spontaneous and piezoelectric polarization in undoped and doped AlGaN/GaN heterostructures

Two dimensional electron gases in AlxGa1−xN/GaN based heterostructures, suitable for high electron mobility transistors, are induced by strong polarization effects. The sheet carrier concentration and the confinement of the two dimensional electron gases located close to the AlGaN/GaN interface are sensitive to a large number of different physical properties such as polarity, alloy composition, strain, thickness, and doping of the AlGaN barrier. We have investigated these physical properties for undoped and silicon doped transistor structures by a combination of high resolution x-ray diffraction, atomic force microscopy, Hall effect, and capacitance–voltage profiling measurements. The polarization induced sheet charge bound at the AlGaN/GaN interfaces was calculated from different sets of piezoelectric constants available in the literature. The sheet carrier concentration induced by polarization charges was determined self-consistently from a coupled Schrödinger and Poisson equation solver for pseudomorphically and partially relaxed barriers with different alloy compositions. By comparison of theoretical and experimental results, we demonstrate that the formation of two dimensional electron gases in undoped and doped AlGaN/GaN structures rely both on piezoelectric and spontaneous polarization induced effects. In addition, mechanisms reducing the sheet carrier concentrations like nonabrupt interfaces, dislocations, and the possible influence of surface states on the two dimensional electron gases will be discussed briefly.

Current gain of the bipolar transistor

A generalized expression of current gain for nonuniformly doped bipolar transistor considering the effects of energy-gap narrowing, doping-dependent diffusivity, contact-surface and bulk recombinations, is derived by using generalized current flow equations and continuity equations. Based on the derived expression, the generalized expressions of current gain and transit times across the neutral base and emitter regions in the case of uniformly doped transistor structure are calculated in detail. Numerical results have shown that the recombination in heavily doped emitter may not be neglected and the conventional charge control expression of current gain does give erroneous predictions. Moreover, the current gain and transit time for a transparent emitter bipolar transistor have been studied, which are shown to be quite sensitive to the contact-surface recombination velocity, and are found to be useful in the study of microwave bipolar transistor.