High sensitivity organic inorganic hybrid X-ray detectors with direct transduction and broadband response

X-ray detectors are critical to healthcare diagnostics, cancer therapy and homeland security, with many potential uses limited by system cost and/or detector dimensions. Current X-ray detector sensitivities are limited by the bulk X-ray attenuation of the materials and consequently necessitate thick crystals (~1 mm-1 cm), resulting in rigid structures, high operational voltages and high cost. Here we present a disruptive, flexible, low cost, broadband, and high sensitivity direct X-ray transduction technology produced by embedding high atomic number bismuth oxide nanoparticles in an organic bulk heterojunction. These hybrid detectors demonstrate sensitivities of 1712 µC mGy-1 cm-3 for "soft" X-rays and ~30 and 58 µC mGy-1 cm-3 under 6 and 15 MV "hard" X-rays generated from a medical linear accelerator; strongly competing with the current solid state detectors, all achieved at low bias voltages (-10 V) and low power, enabling detector operation powered by coin cell batteries

Universal three-dimensional crosslinker for all-photopatterned electronics

All-solution processing of large-area organic electronics requires multiple steps of patterning and stacking of various device components. Here, we report the fabrication of highly integrated arrays of polymer thin-film transistors and logic gates entirely through a series of solution processes. The fabrication is done using a three-dimensional crosslinker in tetrahedral geometry containing four photocrosslinkable azide moieties, referred to as 4Bx. 4Bx can be mixed with a variety of solution-processable electronic materials (polymer semiconductors, polymer insulators, and metal nanoparticles) and generate crosslinked network under exposure to UV. Fully crosslinked network film can be formed even at an unprecedentedly small loading, which enables preserving the inherent electrical and structural characteristics of host material. Because the crosslinked electronic component layers are strongly resistant to chemical solvents, micropatterning the layers at high resolution as well as stacking the layers on top of each other by series of solution processing steps is possible

Charge trapping in organic transistor memories: On the role of electrons and holes

In this work, we study charge trapping in organic transistor memories with a polymeric insulator as gate dielectric. We found that the mechanism of charge trapping is tunneling from the semiconductor channel into the gate dielectric. Depending on the semiconductor and its processing, charge trapping can result in large bi-directional threshold voltage shifts, in case the semiconductor is ambipolar, or in shifts in only one direction (unipolar semiconductor). These results indicate that optimal memory performance requires charge carriers of both polarities, because the most efficient method to lower the programming field is by overwriting a trapped charge by an injected charge of opposite polarity. (C) 2009 Elsevier B.V. All rights reserved.status: publishe

An organic field-effect transistor with programmable polarity

Selective ambipolar transport in solution-processed polymer ferroelectric field-effect transistors (FeFETs) is reported. Depending on the polarization state of the ferroelectric, either remanent hole or electron accumulation is achieved in the transistor, as illustrated by a butterfly-shaped current-voltage (I-V) transfer curve (see Figure). For memory purposes, the polarity of the channel can be easily read using the change in drain current in response to a small gate voltage

Optimized circuit design for flexible 8-bit RFID transponders with active layer of ink-jet printed small molecule semiconductors

We ink-jet print a blend of 6,13-bis(triisopropyl-silylethynyl)pentacene and polystyrene as the active layer for flexible circuits. The discrete ink-jet printed transistors exhibit a saturation mobility of 0.5 cm2 V−1 s−1. The relative spread in transistor characteristics can be very large. This spread is due to the morphology of the TIPS-PEN crystals, and is difficult to control using inkjet printing. Here we apply a novel circuitry design to minimize the probability of differences between the transistors. We include up to four transistors under the same ink-jet printed deposit. With the new design, we demonstrate unipolar circuitry building blocks such as inverters, NANDs and 19-stage ring-oscillators. Additionally, we integrate almost 300 TFTs, on a surface area of 34 mm2 of plastic foil, for 8-bit RFID transponder circuits.status: publishe

Interlayer processing in active matrix OLED displays

status: publishe

High-performance solution-processed polymer ferroelectric field-effect transistors

We demonstrate a rewritable, non-volatile memory device with flexible plastic active layers deposited from solution. The memory device is a ferroelectric field-effect transistor (FeFET) made with a ferroelectric fluoropolymer and a bisalkoxy-substituted poly(p-phenylene vinylene) semiconductor material. The on- and off-state drain currents differ by several orders of magnitude, and have a long retention time, a high programming cycle endurance and short programming time. The remanent semiconductor surface charge density in the on- state has a high value of 18 mC m(-2), which explains the large on/off ratio. Application of a moderate gate field raises the surface charge to 26 mC m(-2), which is of a magnitude that is very difficult to obtain with conventional FETs because they are limited by dielectric breakdown of the gate insulator. In this way, the present ferroelectric-semiconductor interface extends the attainable field-effect band bending in organic semiconductors