Norbert Fruehauf

High Performance and Long-Term Stability in Ambiently Fabricated Segmented Solid-State Polymer Electrochromic Displays

This work reports on the performance of a segmented polymer electrochromic display that was fabricated with solution-based processes in ambient atmosphere. An encapsulation process and the combination of structured wells for the polymer electrochrome and electrolyte layers as well as the use of a preoxidized counter polymer yields high contrasts and fast switching speeds. Asymmetric driving-with respect to time-of the display is investigated for the first time and the degradation effects in the electrochrome layer are analyzed and addressed to yield a stable device exceeding 100,000 switching cycles. A printed circuit board was integrated with the display, allowing the device to be run as a clock, where the segments only required short pulses to switch without the need for a constant current to maintain its state. Such an application pairs well with the advantages of electrochromic polymers, drawing on its high contrast, stability, and ability to maintain its colored or colorless state without the need for a constant power supply, to demonstrate the promise as well as the challenges of developing more sophisticated electrochromic devices.

Active Matrix Color-LCD on 75

We have demonstrated a full color 4-in quarter-VGA amorphous silicon active-matrix (AM) LCD (AM-LCD) with 75 μm thick flexible glass backplane and frontplane substrates. The device was built directly on the flexible glass without using a processing carrier or additional protective layers. The overall thickness of the LC cell is <; 170 μ m. Process modifications were made to accommodate the flexibility and reduced thickness of the substrate. These process changes were related to: thin film deposition, photolithography, cell assembly and filling, glass scribing, and driver bonding. The achieved results indicate that the incorporated flexible glass substrates are compatible with the fabrication of high quality color AM-LCDs.

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Cellular neural networks (CNNs) consist of analog, nonlinear, dynamic processing elements which are locally interconnected. Most applications in the areas of image processing, pattern recognition and robot control require interconnections between all elements which are space invariant. This suggests an optical CNN implementation because optical processors are perfectly suited for both space invariant signal processing and complete interconnections between all elements. The theoretical and practical aspects of a hardware realization are described. The results of an optical CNN performing feature extraction are presented. >

m Thick Flexible Glass Substrates

A complete process for an active-matrix (AM) organic thin-film transistor (OTFT) polymer dispersed liquid crystal (PDLC) display is presented. Evaporated pentacene is used as semiconductor. The display comprises 64 times 64 pixel, each with a pixel pitch of (312.5 times 312.5) mum2. The AM display is fabricated with standard photolithographic processes. Since all process temperatures are below 180degC the processes for the AM backplane can be easily transferred to plastic substrates like PEN or PET. Due to the thin anodically oxidized Al2O3 gate dielectric with a thickness of 60 nm and epsivr = 9, driving voltages between 10 and 12 V are sufficient. To protect the pentacene against the PDLC, it is encapsulated with sputtered Ta2O5 layer. After the passivation a field effect mobility of 0.2 cm2/V ldr s is obtained for the OTFTs.

Fourier optical realization of cellular neural networks

Abstract— The unique properties of carbon nanotubes (CNTs) promise innovative solutions for a variety of display applications. The CNTs can be deposited from suspension. These simple and low-cost techniques will replace time-consuming and costly vacuum processes and can be applied to large-area glass and flexible substrates. Single-walled carbon nanotubes (SWNTs) have been used as conducting and transparent layers, replacing the brittle ITO, and as the semiconducting layer in thin-film transistors (TFTs). There is no need for alignment because a CNT network is used instead of single CNTs. Both processes can be applied to glass and to flexible plastic substrates. The transparent and conductive nanotube layers can be produced with a sheet resistance of 400 Ω/□ at 80% transmittance. Such layers have been used to produce directly addressed liquid-crystal displays and organic light-emitting diodes (OLED). The CNT-TFTs reach on/off ratios of more than 105 and effective charge-carrier mobilities of 1 cm2/V-sec and above.

Active Matrix OTFT Display With Anodized Gate Dielectric

A highly accurate measurement technique has been developed and applied for characterization of the complex transmittance of liquid crystal light valves (LC-LV). The measurement setup is based on a two-beam interference with partially coherent light. An arc lamp light source enables measurements over a large range of wavelengths. We propose a new Fourier transform interference pattern evaluation technique with a high signal-to-noise ratio. Calculations are sped up by FFT algorithms. Measurement results of the complex transmittance are shown for a twisted nematic and a Freederickzs liquid crystal light valve, built in our laboratory.

Suspension-deposited carbon-nanotube networks for flexible active-matrix displays

— The necessary processes to use random carbon-nanotube networks as transparent conductors in twisted-nematic liquid-crystal displays have been developed, replacing indium tin oxide. Because the nanotubes are deposited vacuum-free from suspension, the potential advantages are lower costs for material, equipment, and production. Nanotube networks are also much better suited for flexible displays than the commonly used metal oxides. With the developed processes, the worlds first full-color active-matrix LCDs as well as directly addressed flexible displays on plastic substrates with carbon-nanotube pixel electrodes, have been realized.

Fast and accurate techniques for measuring the complex transmittance of liquid crystal light valves

A low temperature high quality gate dielectric process for bottom gate organic thin film transistors (OTFT) is introduced which is compatible to plastic substrates. The Al2O3 dielectric is grown from the aluminum gate electrode by anodic oxidation at room temperature and exhibits an exceptionally good electrical performance even for thin layers of 50nm. Finding an electrolyte which significantly reduces dielectric charges was instrumental for the desired OTFT application. The electrolyte and substrate dependent behaviour was characterized and compared to different dielectrics to point out the advantages of anodic oxidized aluminum. The characteristics of pentacene bottom contact OTFTs realized with anodized Al2O3 gate dielectric on glass and plastic substrates are presented.

Active‐matrix and flexible liquid‐crystal displays with carbon‐nanotube pixel electrodes

Abstract We have developed a CMOS LTPS process which requires only five photolithographic masks and only one ion doping step. Drain/Source areas of NMOS TFTs were formed by PECVD deposition of a highly doped precursor layer while PMOS contact areas were defined by ion implantation. Single TFTs, inverters, ring oscillators and shift registers were fabricated. Nand p‐channel devices reached field effect mobilities of 173cm2/Vs and 47cm2/Vs, respectively.

Pentacene organic thin film transistors with anodized gate dielectric

— A calcium measurement setup was built for testing encapsulation especially for OLED applications. This setup is able to measure both reflective and transmissive cells. For the characterization of sealants, a method to compare them with other sealing products will be described. This includes the use of spacers, a homogeneous surface energy, and the geometry of the sealant line. The effects of different geometries will be discussed. The setup was designed to achieve good accuracy at a very reasonable component cost, which will allow other facilities to replicate this setup. Therefore, the construction plan as well as the list of components can be downloaded from our website (Ref. 3).