Michael G. Kane

Organic thin-film transistor-driven polymer-dispersed liquid crystal displays on flexible polymeric substrates

We have fabricated organic thin-film transistor (OTFT)-driven active matrix liquid crystal displays on flexible polymeric substrates. These small displays have 16×16 pixel polymer-dispersed liquid crystal arrays addressed by pentacene active layer OTFTs. The displays were fabricated using a low-temperature process (<110 °C) on flexible polyethylene naphthalate film and are operated as reflective active matrix displays.

Electron traps and hysteresis in pentacene-based organic thin-film transistors

In the absence of charge storage or slow polarization in the gate dielectric, the hysteresis in the current-voltage (I−V) characteristics of pentacene-based organic thin-film transistors (OTFTs) is dominated by trapped electrons in the semiconductor. The immobile previously stored negative charge requires extra holes to balance it, resulting in the early establishment of the channel and extra drain current. Inferred from I−V characteristics, this simple electrostatic model qualitatively explains memory effects in pentacene-based OTFTs, and was verified by a time domain measurement.

Field effect in epitaxial graphene on a silicon carbide substrate

The authors report a strong field effect observed at room temperature in epitaxially synthesized, as opposed to exfoliated, graphene. The graphene formed on the silicon face of a 4H silicon carbide substrate was photolithographically patterned into isolated active regions for the semimetal graphene-based transistors. Gold electrodes and a polymer dielectric were used in the top-gate transistors. The demonstration of a field effect mobility of 535cm2∕Vs was attributed to the transistor geometry that maximizes conductance modulation, although the mobility is lower than observed in exfoliated graphene possibly due to grain boundaries caused by the rough morphology of the substrate surface.

Moisture induced electron traps and hysteresis in pentacene-based organic thin-film transistors

Previous work revealed that electron traps in pentacene formed in air cause hysteresis in thin-film transistor characteristics. Here, we experimentally showed that water vapor, rather than oxygen, is responsible for these hysteresis-causing trap states. Photogenerated and injected electrons are trapped at the pentacene-dielectric interface under positive gate bias, and induce extra holes, resulting in the observed extra drain current. The electron detrapping causes the decay of the extra hole population with time under negative gate bias and, therefore, that of the drain current.

Reversible memory effects and acceptor states in pentacene-based organic thin-film transistors

Hysteresis is commonly seen in the current-voltage characteristics of organic thin-film transistors (OTFTs). In the absence of memory effects associated with the gate dielectric, the hysteresis in p-channel pentacene-based OTFTs, as measured in air and under illumination, was found to be dominated by trapped electrons in the semiconductor. The responsible acceptor-type traps have very long lifetimes. The immobile, previously stored negative charge requires extra holes to balance it, resulting in early establishment of the channel and extra drain current. This model is unique in that it explains the memory effect in terms of the electrostatic effect on the majority carrier population of trapped charge, opposite in sign to the majority carriers. The model is supported by drain current transient decay data. By studying the presence or absence of this effect and repeatedly measuring same devices on one substrate under various ambient and illumination conditions, we found that the responsible acceptor states a...

Fast organic circuits on flexible polymeric substrates

We have fabricated the fastest organic circuits on flexible substrates yet reported. These circuits use the small-molecule hydrocarbon pentacene as the active semiconductor material and 75 /spl mu/m thick flexible, transparent, colorless, polyethylene naphthalate (PEN) film as the substrate. Transistor arrays, inverters, ring oscillators, and other circuits with good electrical performance, yield, and uniformity were obtained. A field-effect mobility of 1 cm/sup 2// V-s was extracted from OTFT saturation characteristics, and ring oscillators had minimum propagation delay <40 /spl mu/sec per stage and <50 /spl mu/sec per stage at bias levels below 8 V.

6.5L: Late-News Paper: AMLCDs using Organic Thin-Film Transistors on Polyester Substrates

We have fabricated and demonstrated active-matrix liquid-crystal displays using organic thin-film transistors (OTFTs) on polyester substrates. This is the first reported demonstration of an OTFT active-matrix liquid-crystal display, and also the first demonstration of a TFT active-matrix liquid-crystal display of any type fabricated on a polyester substrate.

35.2: Sub-Notebook a-Si Color SVGA Display with integrated Drivers

We have successfully designed and fabricated a SASID SVGA 8.4V AMLCD display. This is the largest Self-scanned Amorphous Silicon Integrated Display (SASID) built to date for use in laptop computers and PDAs. New circuits have been added for threshold drift cancellation to extend lifetime and special bussing techniques were used to reduce power dissipation.

Hysteresis in pentacene-based organic thin-film transistors

Memory effects are commonly seen in organic thin-film transistor (OTFT) characteristics. In the absence of memory effects associated with the gate dielectric, the hysteresis in p-channel pentacene-based OTFTs, as measured in air and under illumination, was found to be dominated by trapped electrons, rather than trapped holes, in the semiconductor. The responsible acceptor type traps have very long lifetime. The immobile, previously stored negative charge requires extra holes to balance it, resulting in early establishment of the channel and extra drain current. This model is unique in that it discusses the majority carrier population influenced by trapped charge opposite in sign to the majority carriers in a simple electrostatic manner, to explain history dependence. The model was supported by drain current transient decay data. This memory effect is ambient and illumination sensitive. We studied the presence or absence of this effect under various ambient and illumination conditions, and found the responsible acceptor type traps mostly extrinsic and their formation reversible. Efforts were taken in the quantitative analysis to exclude the bias stress effect from the memory effect due to the charged acceptors.

An organic thin film transistor backplane for flexible liquid crystal displays

Organic thin film transistors (OTFTs) have made impressive progress over the past decade, and it appears increasingly likely that OTFTs will find use in a number of low-cost, large-area electronic applications, such as active-matrix displays, smart cards, price and inventory tags, and large-area sensor arrays. OTFTs provide two principal advantages over TFTs based on inorganic semiconductors: they can be fabricated at lower temperature and, potentially, at significantly lower cost. Low processing temperatures allow OTFT device and circuit fabrication on polymeric or other inexpensive substrates, rather than glass. The prospect of a flexible, rugged, lightweight active-matrix display at relatively low cost has spurred a number of manufacturers and government agencies to consider plastic displays for a variety of military, medical, industrial, and consumer applications. We report here on the design and fabrication of a flexible active-matrix OTFT backplane suitable for use in flexible polymer-dispersed liquid crystal displays. 75 /spl mu/m thick flexible polyethylene naphthalate (PEN) film was used as the substrate, and OTFT and pixel arrays with good electrical performance, yield, and uniformity were obtained.