A generic analytical model for the current-voltage characteristics of organic thin-film transistors (OTFTs) is derived. Based on this generic model, a TFT compact dc model that meets the requirements ...for compact modeling, including for computer circuit simulators, is proposed. The models are fully symmetrical, and the TFT compact dc model covers all regimes of TFT operation-linear and saturation above threshold, subthreshold, and reverse biasing. The empirical fitting parameters are mostly eliminated from the characteristic equations. The developed models are also in close correspondence to several physical, parametric, and limiting models for current-voltage and mobility characteristics. An essential practical feature of the TFT compact dc model is that the model is both upgradable and reducible, allowing for easier implementation and modifications and also simultaneously allowing for separation of characterization techniques. This allows for systematic fitting of experimental data with large scattering in the values, but at the same time, preserving consistently the OTFT behavior in the model.
A parameter extraction methodology and a verification of a generic analytical model and a thin-film transistor (TFT) compact dc model for the current-voltage characteristics of organic TFTs are ...presented. The verification shows that the proposed models meet the requirements for compact modeling and for computer circuit simulators. The models are fully symmetrical, and the TFT compact dc model is validated in all regimes of operation-linear and saturation above threshold, subthreshold, and reverse biasing. Suitable characterization techniques for parameter extraction of mobility, threshold voltage, and contact resistance are provided. Approaches are elaborated for the essential practical feature of upgradability and reducibility of the TFT compact dc model, allowing for easier implementation and modification, as well as separation of characterization techniques.
Organic solar cells (OSCs) are promising photovoltaic devices to convert solar energy into electrical energy. Their many advantages such as lightweight, flexibility and low manufacturing costs are ...intrinsic to the organic/polymeric technology. However, because the performance of OSCs is still not competitive with inorganic solar cells, there is urgent need to improve the device performance using better designs, technologies and models. In this work, we focus on developing an accurate physics-based model that relates the charge carrier density at the metal-organic boundaries to the current density in OSCs. This analysis is based on our previous studies on single-carrier and bipolar diodes. The model for the boundary condition of the charge carrier density at the interfaces of OSCs follows a power-law function with the current density, both in dark and under illumination. Simulated current-voltage characteristics are verified with experimental results. The numerical simulations of the current-voltage characteristics of OSCs consider well-established models for the main physical and optical processes that take place in the device: light absorption and generation of excitons, dissociation of excitons into free charge carriers, charge transport, recombination and injection-extraction of free carriers. Our analysis provides important insights on the influence of the metal-organic interfaces on the overall performance of OSCs. The model is also used to explain the anomalous S-shape current-voltage curves found in some experimental data.
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•Boundary conditions for simulation in organic solar cells (OSCs).•Influence of the metal-organic interfaces on the overall performance of OSCs.•Interface charge density follows a power-law function with the current density.•Reproduction of experimental current-voltage curves in dark and under illumination.•Prediction of anomalous S-shape current-voltage curves.
Fluorescence-based spectroscopy and imaging techniques provide qualitative and quantitative diagnostic information on biological systems. In this paper, we report on the design, fabrication, and ...testing of a miniaturized wireless fluorescence imaging device for noninvasive clinical diagnosis and screening of diseases in the gastrointestinal tract. The system includes three submodules: optical imaging, electronics control and image acquisition, and information processing and transmission. These modules were individually developed and tested before being integrated into a battery-powered wireless device. The final integrated system is mounted in a customized, compact cylindrical housing. The performance of each individual module and the overall integrated system has been evaluated using fluorescent phantoms. It has been demonstrated that the miniaturized device can acquire spectrally resolved fluorescence images and transmit the image stream wirelessly. An important outcome of this feasibility study is the identification of important technological issues and pathways for future prototype development.
The effects of hot carrier stress on a fully integrated negative resistance LC-tank CMOS oscillator are investigated. The major effect is the decrease of the amplitude of the oscillation due to ...degradation in the I-V characteristics of the MOSFETs. The oscillator phase noise increases with stress duration since the amplitude of the oscillation decreases. A change in the biasing of the circuit due to the stress affects the parasitic capacitances in the circuit which in turn cause a slight change in the oscillation frequency.
The low-frequency noise in asymmetric MOS transistors with graded channel doping from the source to the drain can be partitioned by assuming a series connection of two or more transistors along the ...device's channel length. The partition explains the noise overshoot at gate biases around the threshold voltage of the composite device. Expressions for the input-referred gate noise voltage are obtained and verified.
The (100) surface of MgAl
2
O
4
is evaluated as a substrate for the thin film deposition of the relaxor ferroelectric PbMg
1/3
Nb
2/3
O
3
(65%)–PbTiO
3
(35%). With a lattice mismatch of less than ...0.5%, this film-substrate combination presents a geometrical template for growth that is far superior to that formed with other commercially available oxide substrates. Films were deposited using the pulsed laser deposition technique and were characterized in terms of their crystallographic, microstructural, and dielectric properties. From a crystallographic perspective the films show excellent cube-on-cube epitaxy, are highly oriented, and show no evidence of the frequently observed parasitic pyrochlore phase. With the exception of a few faceted surface structures, the film’s microstructure is single-crystal-like, exhibiting a sharp film-substrate interface, a smooth top surface, and no discernable granularity. The dielectric response shows the frequency-dependent diffuse phase transition characteristic of a relaxor material, but with less frequency dispersion and a smaller maximum in the dielectric constant. Taken together, the results suggest that the (100) MgAl
2
O
4
substrate could prove to be an effective substrate material, not only for the PbMg
1/3
Nb
2/3
O
3
(65%)–PbTiO
3
(35%) system, but also for a number of other important lattice-matched ferroelectric, relaxor, and ferroelectric superlattice systems.
Forward body biasing improves the low-frequency noise performance of p-channel metal-oxide semiconductor (PMOS) transistors by about 8 dB/V. Therefore, for analog design, forward body biasing may be ...preferred if noise is a concern. This is in agreement with the improvement of other MOSFET parameters such as the decrease of the threshold voltage (V/sub T/) or the increase of unity current-gain frequency (f/sub T/) on forward substrate- (or body)-source biasing (V/sub BS/). Also, forward V/sub BS/ is very attractive for low voltage supply (V/sub DD/<0.6 V) and low-power, low-noise circuits. A detailed analysis of the dependence of the noise level on VBS and on the gate-source (V/sub GS/) biasing showed that the dependence on V/sub BS/ seems to be smaller in weak inversion, and it increases in strong inversion. The dependence on V/sub GS/ has a turning point at V/sub GS//spl ap/0.8 V, independent of body bias, which it seems is due to the activation of oxide traps, as the noise waveform showed a random telegraph signal (RTS) component at V/sub GS/>0.8 V. Generally, it is confirmed that the spectral density S/sub I/ of the total low-frequency noise of the drain current I/sub D/ is proportional to the square of I/sub D/, i.e., S/sub I//spl prop/I/sub D//sup 2/, but it cannot be clearly ascribed to either number fluctuation or mobility fluctuation models. In addition, both models cannot accurately describe the dependence of the noise level on the body bias.
Metal-polymer-oxide-silicon (MPOS) structures with poly(3,3'''-dialkyl-quaterthiophene) as an active semiconductor layer have been characterized by means of capacitance-voltage (C-V) methods at ...different ramping rates (dV/dt) for the voltage sweep in the quasi-static capacitance-voltage method (QCV), and at different frequencies (f) for the dynamic or high-frequency method (DCV or HCV). The observed dependency of the capacitance on ramping rate and frequency are explained with a frequency dependent carrier enhancement and a long relaxation time constant in the polymer. The surface modification of gate oxide is found to improve the carrier enhancement in the active polymer layer of MPOS.
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