Current–voltage characteristic

Summary

A current–voltage characteristic or I–V curve (current–voltage curve) is a relationship, typically represented as a chart or graph, between the electric current through a circuit, device, or material, and the corresponding voltage, or potential difference, across it. In electronics In electronics, the relationship between the direct current (DC) through an electronic device and the DC voltage across its terminals is called a current–voltage characteristic of the device. Electronic engineers use these charts to determine basic parameters of a device and to model its behavior in an electrical circuit. These characteristics are also known as I–V curves, referring to the standard symbols for current and voltage. In electronic components with more than two terminals, such as vacuum tubes and transistors, the current–voltage relationship at one pair of terminals may depend on the current or voltage on a third terminal. This is usually displayed on a more complex current–vo

Official source

https://en.wikipedia.org/wiki/Current%E2%80%93voltage_characteristic

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Though models describing the operating mechanism of organic electrochemical transistors (OECTs) have been developed, these models are unable to accurately reproduce OECT electrical characteristics. Here, the authors report a thermodynamic-based framework that accurately models OECT operation. Despite their increasing usefulness in a wide variety of applications, organic electrochemical transistors still lack a comprehensive and unifying physical framework able to describe the current-voltage characteristics and the polymer/electrolyte interactions simultaneously. Building upon thermodynamic axioms, we present a quantitative analysis of the operation of organic electrochemical transistors. We reveal that the entropy of mixing is the main driving force behind the redox mechanism that rules the transfer properties of such devices in electrolytic environments. In the light of these findings, we show that traditional models used for organic electrochemical transistors, based on the theory of field-effect transistors, fall short as they treat the active material as a simple capacitor while ignoring the material properties and energetic interactions. Finally, by analyzing a large spectrum of solvents and device regimes, we quantify the entropic and enthalpic contributions and put forward an approach for targeted material design and device applications.

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Contact resistance effects in organic n-channel thin-film transistors

Reinhold Rödel

Organic thin-film transistors (TFTs) have undergone tremendous progress in the past few years. Their great potential in terms of mechanical flexibility, light weight, low-cost and large-area fabrication makes them promising candidates for novel electronic products, such as sensor arrays, radio-frequency identification tags and flexible displays. For the realization of these applications and to improve their performance it is necessary to miniaturize organic TFTs to dimensions of a few micrometers or even less. However, with such aggressive scaling, the device physics becomes more and more important. Especially the contact resistance at and close to the interface between the organic semiconductor and the source/drain metal limits the performance of the organic TFTs at miniaturized dimensions. In this thesis, the contact properties of bottom-gate, top-contact n-channel organic transistors are investigated using the gated four-probe (GFP) technique. The TFTs employ the small-molecule semiconductor N,N'-bis-(1H,1H-heptafluorobutyl)-1,7-dicyano-perylene-3,4:9,10-tetracarboxylic diimide (PDI-FCN2) and are fabricated on flexible plastic substrates. The transistors are air-stable and can be operated at low voltages of about 3 V, owing to a thin hybrid gate dielectric composed of aluminum oxide and a self-assembled molecular monolayer. The GFP method enabled a detailed investigation of the influence of a multitude of factors, including the gate-source and drain-source voltages, the contact length, the temperature and the contact metal, on the contact resistance. The contact properties are found to be very sensitive to the thickness of the organic semiconductor layer. In transistors in which this layer is relatively thin, ohmic contact resistances as small as about 0.6 Ohm cm were measured. In transistors with a relatively thick organic semiconductor layer, device physics becomes more complex and the current-voltage characteristics of the contact become nonlinear. Space-charge limited currents are identified as the probable origin of this nonlinear behavior. The good performance of the PDI-FCN2 transistors allows the realization of simple integrated circuits. Flexible organic complementary ring oscillators are fabricated and signal propagation delays per stage as short as 6 µs are demonstrated at a supply voltage of 3.6 V.

EPFL2016

Deep defects in InGaN LEDs: modeling the impact on the electrical characteristics

Jean-François Carlin, Nicolas Grandjean, Camille Haller

Deep defects have a fundamental role in determining the electro-optical characteristics and in the efficiency of InGaN light-emitting diodes (LEDs). However, modeling their effect on the electrical characteristics of the LED is not straightforward. In this paper we analyze the impact of the defects on the electrical characteristics of LEDs: we analyze three single-quantum-well (SQW) InGaN/GaN LED wafers, which differ in the density of defects. Through steady-state photocapacitance (SSPC) and light-capacitance-voltage measurements, the energy levels of these deep defects and their concentrations have been estimated. By means of a simulation campaign, we show that these defects have a fundamental impact on the current voltage characteristic of LEDs, especially in the sub turn-on region. The model adopted takes into consideration trap assisted tunneling as the main mechanism responsible for current leakage in forward bias. For the first time, we use in simulations the defect parameters (concentration, energy) extracted from SSPC. In this way, we can reproduce with great accuracy the current-voltage characteristics of InGaN LEDs in a wide current range (from pA to mA). In addition, based on SSPC measurements, we demonstrate that the defect density in the active region scales with the QW thickness. This supports the hypothesis that defects are incorporated in In-containing layers, consistently with recent publications.

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Contact resistance effects in organic n-channel thin-film transistors

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