Alejandra Castro-Carranza

A Compact Model for Organic Field-Effect Transistors With Improved Output Asymptotic Behaviors

Here, we propose an advanced compact analytical current-voltage model for organic field-effect transistors (OFETs), which can be incorporated into SPICE-type circuit simulators. We improved the output saturation behavior by introducing a new asymptotic function that also enables more precise low-voltage current and conductance fitting. A new expression for the subthreshold current was suggested to cover all operation regimes of OFETs. All model parameters were extracted by a systematic method, and the comparison of the modeled current with the experimental data on pentacene-based OFETs confirmed the validity of the model over a wide operation range.

Effect of Density of States on Mobility in Small-Molecule n-Type Organic Thin-Film Transistors Based on a Perylene Diimide

Bottom-contact organic thin-film transistors with active layers made of n-type small-molecule perylene diimide Polyera ActivinkTM N1400 were fabricated and were compared with those of 6,13-bis (triisopropylsilylethinyl)pentacene and poly(triarylamine) (PTAA). For the three devices, the mobility values and the distribution of the density of states (DOS) were estimated from current-voltage measurements. The mobility value of the N1400 samples increases up to four orders of magnitude within the measured voltage range, reaching the PTAA mobility values at high gate voltages. Finally, we analyze the effect of the distribution of the DOS on the mobility by studying the free-charge sheet concentration.

Organic thin-film transistor bias-dependent capacitance compact model in accumulation regime

The authors present an analytical and continuous model for the total charges at the gate, drain and source electrodes for organic thin-film transistors (OTFTs), from which analytical expressions of the total capacitances are obtained. Under the quasi-static approximation, the model parameters are extracted using the previously developed unified model and parameter extraction method (UMEM). The capacitance model is valid above threshold voltage. It guarantees continuity of the expressions for the capacitance at the transition between linear and saturation regimes, as well as takes into account the overlap capacitance. Comparisons between modelled and experimental C GG values are shown.

Compact modeling of organic thin-film transistors

This paper explains the development of a compact model for organic thin film transistors (OTFTs), analyzing some of their features. The model, based on hopping transport between localized states, includes a mobility expression that depends explicitly on both the characteristic temperature and density of states of the distribution of localized states. Temperature dependences are also taken into account. A unified parameter extraction method is also described in detail. The model shows a very good agreement with experimental data from OTFTs of different organic and polymeric materials.

Study of frequency dispersion effects to consider in a capacitance model for OTFTs

This work presents a study of the frequency dispersion effects of the capacitance-voltage characteristics of organic PMMA on P3HT Thin Film Transistors (TFT) using simulated curves. For validation, simulated CV characteristics at 1 MHz are compared with experimental curves, measured at the same frequency.

Compact Capacitance Model for OTFTs at Low and Medium Frequencies

We present a compact capacitance model for organic thin-film transistors (OTFTs), which is valid not only in the accumulation regime but also in the partial and total depletion regimes. The parameters applied in the model are analytically extracted from the current-voltage characteristics of the devices, using a previously developed unified model and the parameter extraction method. The overlap capacitance effect is taken into account, and the frequency dependence is considered empirically by means of the insulator permittivity. Comparisons between modeled and experimental gate-to-channel capacitances of staggered upper contact p-channel OTFTs based on P3HT-PMMA and PCDTBT-PMMA show the validity of the model at low and medium frequencies.

OTFT modeling: Development and implementation in EDA tools

In this work we present the process entailed to implement a model for organic thin-film transistors (OTFTs): from the development of the complete model, to its validation and use in a circuit simulator. For this purpose the current-voltage model (UMEM) and its related charge and capacitance model for OTFTs (UBCM) were applied. The complete model is valid in the sub- and above-threshold regimes, and it is continuous in the transition from linear to saturation conditions. UMEM and UBCCM in Verilog-A are used with the SMASH circuit simulator for the analysis of the DC, small signal and transient behavior of OTFT circuits, and are compared with experimental data showing a good agreement.

Analytical energy-barrier-dependent Voc model for amorphous silicon solar cells

We show that the open circuit voltage (Voc) in hydrogenated amorphous silicon (a-Si:H) solar cells can be described by an analytical energy-barrier-dependent equation, considering thermionic emission as the physical mechanism determining the recombination current. For this purpose, the current-voltage characteristics of two device structures, i.e., a-Si:H(n)/a-Si:H(i)/a-Si:H(p)/AZO p-i-n solar cells with different p-doping concentrations and a-Si:H(n)/a-Si:H(i)/AZO Schottky structures with different intrinsic layer thicknesses, were analyzed in dark and under illumination, respectively. The calculated barrier in the p-i-n devices is consistent with the difference between the work function of the p-layer and the conduction band edge of the i-layer at the interface in thermal equilibrium.

Considerations on I DDQ test on OTFT circuits

In this paper we will analyze the feasibility of applying the well known IDDQ test technique to OTFT circuits. Specifically, we will analyze the implications of the leakage current, the Ion/Ioff ratio, and the S/N ratio on the applicability of IDDQ. It will be shown that, even if the IDDQ is applicable, some adaptation must be made, to allow detecting the possible faults over the background level. These adaptations may probably take the form of partitioning strategies, which must be adapted to the actual technology.

Study of the interface area effect on the density of states in PTAA-Cytop® OTFTs

In this paper we show that the mobility reduces for OTFTs with similar channel length when the channel width is increased. The effect is shown in staggered bottom contact organic thin film transitors (OTFTs) made of the P-Type semiconductor Poly(Triarylamine) PTAA and Cytop® as insulator. It can also be seen from experiment, that this mobility reduction is associated to an increase in the density of localized traps present in the active layer material. An interpretation of this effect is presented.