Organic Logic Circuits Research Articles

Structured-gate organic field-effect transistors

We report the fabrication and electrical characteristics of structured-gate organic field-effect transistors consisting of a gate electrode patterned with three-dimensional pillars. The pillar gate electrode was over-coated with a gate dielectric (SiO2) and solution processed organic semiconductors producing both unipolar p-type and bipolar behaviour. We show that this new structured-gate architecture delivers higher source–drain currents, higher gate capacitance per unit equivalent linear channel area, and enhanced charge injection (electrons and/or holes) versus the conventional planar structure in all modes of operation. For the bipolar field-effect transistor (FET) the maximum source–drain current enhancements in p- and n-channel mode were >600% and 28%, respectively, leading to p and n charge mobilities with the same order of magnitude. Thus, we have demonstrated that it is possible to use the FET architecture to manipulate and match carrier mobilities of material combinations where one charge carrier is normally dominant. Mobility matching is advantageous for creating organic logic circuit elements such as inverters and amplifiers. Hence, the method represents a facile and generic strategy for improving the performance of standard organic semiconductors as well as new materials and blends.

Control of the charge transport properties in a solution-processible ambipolar quinoidal oligothiophene derivative by direct laser writing

We investigate the effects of laser irradiation on the performance of organic field-effect transistors based on the solution-processible quinoidal oligothiophene [QQT(CN)4]. Whereas electron field-effect mobilities are not modified, hole transport can be selectively controlled and even suppressed depending on the laser irradiation conditions. Vertical p-n bipolar structures in QQT(CN)4 realized by direct laser writing are also studied. The results provide essential information for the effective laser patterning of complementary organic logic circuits and suggests the possibility to fabricate by direct laser writing complex three-dimensional bipolar p-n structures in a single QQT(CN)4 thin film.

Solution-Processed Organic Field-Effect Transistors and Unipolar Inverters Using Self-Assembled Interface Dipoles on Gate Dielectrics

Self-assembled monolayers (SAMs) of polarized and nonpolarized organosilane molecules on gate insulators induced tunable threshold voltage shifting and current modulation in organic field-effect transistors (OFETs) made from solution-deposited 5,5'-bis(4-hexylphenyl)-2,2'-bithiophene (6PTTP6), defining depletion-mode and enhancement-mode operation. p-Channel inverters were made from pairs of OFETs with an enhancement-mode driver and a depletion-mode load to implement full-swing and high-gain organic logic circuits. The experimental results indicate that the shift of the transfer characteristics is governed by the built-in electric field of the SAM. The effect of surface functional groups affixed to the dielectric substrate on the grain appearance and film mobility is also determined.

Electrical properties in vanadyl-phthalocyanine-based metal-insulator-semiconductor devices

We investigated electrical properties of vanadyl phthalocyanine (VOPc) metal-insulator-semiconductor (MIS) devices by the measurement of capacitance and conductance, which were fabricated on ordered para-sexiphenyl (p-6P) layer by weak epitaxy growth method. The VOPc∕p-6P MIS diodes showed a negligible hysteresis effect at a gate voltage of ±20V and small hysteresis effect at a gate voltage of ±40V due to the low interface trap state density of about 1×1010eV−1cm−2. Furthermore, a high transition frequency of about 10kHz was also observed under their accumulation mode. The results indicated that VOPc was a promising material and was suitable to be applied in active matrix liquid crystal displays and organic logic circuits.

Organic Field‐Effect Transistors and Unipolar Logic Gates on Charged Electrets from Spin‐On Organosilsesquioxane Resins

AbstractControllable shifting of threshold voltage and modulation of current in organic field‐effect transistors (OFETs) is demonstrated, resulting in the formation of unipolar inverters by making use of space‐charge electrets. Prior to the deposition of the organic semiconductor (OSC), negative corona charges are injected and trapped in the bulk of the organosilsesquioxane glass resin gate dielectrics. The effective surface potential is controlled by the corona‐charging and subsequent annealing process. It is found that the shift of the transfer characteristics is governed by the electrostatic induction effects of the charged gate electrets, and this observed shift can be related to the surface potential of the layer next to the transistor channel. The process control, efficiency, and long‐term stability of charge storage in spin‐on organosilsesquioxane glass resins are sufficient to enable the construction of simple unipolar inverters and to allow for circuit tuning. New OFET unipolar inverters with an enhancement‐mode driver and a depletion‐mode load are presented, composed of only two simple OFETs with the same channel dimensions and the same p‐type OSC on charged electrets. This design allows the implementation of full‐swing organic logic circuits and illustrates a potential process simplification for organic electronics.

Orientation of Metalphthalocyanine Molecule Deposited on Polycarbonate Thin Film

A polymer gate dielectric layer is important when making organic FET because all organic FETs require flexibility, the right weight, optical transparence and low cost. It has various applications such as organic LSI, organic logic circuits and new information tools. In this paper, copperphthalocyanine (CuPc), vanadylphthalocyanine (VOPc) and zincphthalocyanine (ZnPc), to represent the active layers of OFET, were deposited using vapor deposition on polycarbonate (PC) thin film and their morphologies and molecular orientations were investigated using X-ray Diffraction (XRD) spectrometer and UV/Vis spectrometer. Based on these results, the molecular orientations of CuPc, ZnPc and VOPc thin films deposited on PC thin film were shown to be perpendicular to the insulating thin film of the PC thin film.

Organic Field-Effect Transistors, Inverters, and Logic Circuits on Gate Electrets

ABSTRACTBy incorporating dielectrics with stored electric fields and organic semiconductors, new organic electronic components such as circuits with controlling voltages “restored” for transistor tuning can be developed. We have successfully used excellent electret materials including charged and surface-treated silicon dioxide (SiO2) and silsesquioxane (SSQ) polymers as the dielectric layer in organic field-effect transistors (OFETs). Charge injection and quasipermanent charge storage induce threshold voltage shifts and current modulation, which results from the built-in electric fields in the conduction channels. Static and dynamic characteristics of organic thin-film transistors (OTFTs) such as charging conditions and voltage/current retention were evaluated. In addition, self-assembled monolayers (SAMs) of dipolar molecules have been utilized in the dielectric layer, with different mechanisms but similar effects compared to charged dielectrics. We also present new OFET unipolar inverters, comprised of only two simple OTFTs with enhancement-mode driver and depletion-mode load to implement full-swing organic logic circuits for process simplification of electronic components in organic electronics.