Magali Estrada

An efficient and accurate procedure to evaluate distortion in SOI FD MOSFET

The total harmonic distortion (THD) and the third harmonic distortion (HD3) of the output current-voltage characteristics of SOI FD MOSFET is calculated using a new integral method. The method is based on the calculation of two functions, which we call D and D3 and are based on a specific integration of the DC current-voltage characteristic of the device. We demonstrate that function D can be related with the THD and function D3 with the HD3, so that both THD and HD3 can be determined in a much simpler way, with no need to use derivatives, Fourier coefficients or Fast Fourier Transforms. The new method is applied to calculate the harmonic distortion of a SOI FD MOS transistor in the triode regime, when used as an active resistor at the input of an operational amplifier in a MOSFET-C filter configuration. It is also demonstrated that the values of THD and HD3 obtained in a very simple and straightforward way by our new method have an excellent coincidence with values obtained by calculating Fourier coefficients for experimental, simulated or calculated I/sub DS/-V/sub DS/ characteristics and with AC measured values.

Analysis of the Performance of an Inverter Circuit: Varying the Thickness of the Active Layer in Polymer Thin Film Transistors with Circuit Simulation

In this paper, we study, through simulation, the effects on the behavior of an inverter circuit when the active layer thickness of the polymer thin film transistor design is modified. A previously developed compact model for polymer transistors was implemented in standardized hardware description language. We validate results with measured characteristics of transistors fabricated with a poly(methyl methacrylate) layer on top of a poly(3-hexylthiophene-2,5-diyl). This analysis indicates that decreasing the thickness of the active layer can increase the output voltage swing and hence the noise margin in digital circuits. Higher noise margin and larger gain were found for inverters with active layer thicknesses less than 40 nm.

Optimised design of an organic thin-film transistor amplifier using the gm/ID methodology

Most of the applications of circuits that are currently in existence use mainly digital circuits. However, interfacing with the external world is a task that can be only accomplished by analog circuits. Thus, to obtain a functional system, some attention must be paid to them, especially when using organic thin-film transistors. In this case, some new issues arise that are very different from those in the digital world. Analog circuits pose a special problem to analog designers. Owing to their low mobilities, they present very low gains, and biasing them in the right point becomes a critical point. Another critical aspect is the high parameter dispersion, which makes analog designs quite complex. In this study, we will try to present a similar strategy, adapted to the specific case of organic TFTs.

Effects of impurity concentration, hydrogen plasma process and crystallization temperature on poly-crystalline films obtained from PECVD a-Si:H layers

Abstract In this work we report the effects of impurity concentration and crystallization temperature on the crystalline orientation and final layer resistivity of poly-crystalline films obtained from a-Si:H layers deposited by PECVD at 225 °C followed by a hydrogen plasma process in the same PECVD equipment in which they are deposited. Films were characterized electrically, by X-ray diffractometry and by transmission electron microscopy. Crystallized films were used to fabricate poly-Si TFTs.

Impact of inkjet printed ZnO electron transport layer on the characteristics of polymer solar cells

In this paper, we demonstrate that zinc oxide (ZnO) layers deposited by inkjet printing (IJP) can be successfully applied to the low-temperature fabrication of efficient inverted polymer solar cells (i-PSCs). The effects of ZnO layers deposited by IJP as electron transport layer (ETL) on the performance of i-PSCs based on PTB7-Th:PC70BM active layers are investigated. The morphology of the ZnO-IJP layers was analysed by AFM, and compared to that of ZnO layers deposited by different techniques. The study shows that the morphology of the ZnO underlayer has a dramatic effect on the band structure and non-geminate recombination kinetics of the active layer deposited on top of it. Charge carrier and transient photovoltage measurements show that non-geminate recombination is governed by deep trap states in devices made from ZnO-IJP while trapping is less significant for other types of ZnO. The power conversion efficiency of the devices made from ZnO-IJP is mostly limited by their slightly lower JSC, resulting from non-optimum photon conversion efficiency in the visible part of the solar spectrum. Despite these minor limitations their J–V characteristics compare very favourably with that of devices made from ZnO layer deposited using different techniques.

High-efficiency organic solar cells based on a halide salt and polyfluorene polymer with a high alignment-level of the cathode selective contact

Advances in organic photovoltaic technology for improving the power conversion efficiency (PCE) towards the theoretical maximum require efficient light-absorbing polymers, a high alignment-level of selective contacts, and an easy manufacturing process with low cost to reach them. The halide salts constitute a highly promising class of materials that can produce better selective contacts in solar cells for improving the PCE. In this article, we demonstrate and report the use of a haloid salt in organic solar cells utilized as an interlayer. The haloid salt is deposited on top or below of polyfluorene polymer (PFN) layer and after it is placed on a transparent conductive oxide (TCO). Thermal evaporation of LiF layers is carried out to deposit ultrathin films of 0.5 nm to 0.8 nm thickness. As a photoactive layer we use the low-bandgap PBDTTT-EFT:PC70BM bulk-heterojunction. Among the different architectures analyzed we obtained a PCE of 11.00%, with an outstanding fill factor of FF = 73.5%, which is among the best reported for solar cells. This new stacking of a halide salt with polyfluorene materials could find use in fully exploiting the potential of various halide systems, and also opens up new opportunities to improve OSCs with a view to achieving record efficiencies.