J.R. Huang

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.

Analog and digital circuits using organic thin-film transistors on polyester substrates

We have fabricated and characterized analog and digital circuits using organic thin-film transistors on polyester film substrates. These are the first reported dynamic results for organic circuits fabricated on polyester substrates. The high-performance pentacene transistors yield circuits with the highest reported clock frequencies for organic circuits.

Ion-beam-deposited ultrathin transparent metal contacts

Using ion-beam sputtering we have prepared ultrathin transparent metal contacts with large broad-band optical transmittance and low electrical sheet resistance. Metal films deposited by ion-beam sputtering have exceptionally small surface roughness, and films as thin as about 20 A are continuous and conductive, and provide optical transmittance as large as 80%. Ultrathin transparent metal contacts provide a number of advantages over more commonly used conductive transparent metal oxides such as indium tin oxide. Unlike indium tin oxide, ultrathin metal contacts can be deposited at room temperature and require no post-deposition anneal, allowing thin film optoelectronic devices such as organic light-emitting diodes and photovoltaic cells to be fabricated on low-cost, lightweight, flexible polymeric substrates. Transparent metal contacts may also eliminate the oxygen-related degradation of organic thin film devices associated with indium tin oxide contacts. Using 30-A thick ion-beam-deposited transparent palladium contacts we have fabricated organic light-emitting diodes on inexpensive, flexible plastic substrates and obtained devices with good injection and emission characteristics. Finally, unlike indium tin oxide, ultrathin metal contacts provide large optical transmittance in the ultraviolet part of the spectrum, making them useful for ultraviolet photodetectors and providing the potential for increased conversion efficiency for photovoltaic cells, especially for space applications.

High-mobility, low voltage organic thin film transistors

We have fabricated photolithographically defined organic thin film transistors (TFTs) on glass or plastic substrates with carrier field-effect mobility larger than 1 cm/sup 2//V-s, using the organic semiconductor pentacene as the active layer. In addition to high carrier mobility, devices on glass substrates have subthreshold slope as low as 0.4V/decade. TFT performance for devices on both substrate types was extracted at low bias (less than -30 V). These results are the best reported to date for organic TFTs on polymeric and glass substrates.

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.

Tri-layer a-Si:H integrated circuits on polymeric substrates

Using a thermal mountant, we have fabricated hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) and integrated circuits on both colored and nearly colorless polyimide substrates with performance very similar to devices fabricated on glass substrates. Delay and power dissipation were measured with ring oscillators; minimum stage delay was less than 10 /spl mu/sec, and minimum power dissipation was less than 10 /spl mu/W per stage. These results indicate that with suitable thermal engineering, a-Si:H devices and circuits can be fabricated on polymeric substrates using nearly standard processing.

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.

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.

Imaging microwell detectors for x-ray and gamma-ray applications

Gas proportional counter arrays based on the micro-well are an example of a new generation of detectors that exploit narrow anode-cathode gaps, rather than fine anodes, to create gas gain. These are inherently imaging pixel detectors that can be made very large for reasonable costs. Because of their intrinsic gain and room-temperature operation, they can be instrumented at very low power per unit area, making them valuable for a variety of space-flight applications where large-area X-ray imaging or particle tracking is required. We discuss micro-well detectors as focal plane imager for Lobster-ISS, a proposed soft X-ray all-sky monitor, and as electron trackers for the Next Generation High-Energy Gamma Ray mission. We have developed a fabrication technique using a masked UV laser that allows us both to machine micro-wells in polymer substrates and to pattern metal electrodes. We have used this technique to fabricate detectors which image X-rays by simultaneously reading out orthogonal anode and cathode strips. We present imaging results from these detectors, as well as gain and energy resolution measurements that agree well with results from other groups.

Tri-layer a-Si:H TFTs on polymeric substrates

Large area electronic applications such as active matrix flat panel displays currently use glass as substrate material. Glass substrates are available with large area, low cost, and with flat and smooth surfaces that simplify device processing. Glass is also heavy and fragile, however, and alternatives are of interest. Using a mountant technique, we have fabricated hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) on both colored and nearly colorless polyimide substrates with performance nearly identical to devices fabricated on glass substrates. These results indicate that with suitable thermal engineering, a-Si:H devices and circuits can be fabricated on polymeric substrates using nearly standard processing.