Design of LCOS microdisplay backplanes for projection applications

De evolutie van licht emitterende diodes (LED) heeft ervoor gezorgd dat het op dit moment interessant wordt om deze componenten als lichtbron te gebruiken in projectiesystemen. LED’s hebben belangrijke voordelen vergeleken met klassieke booglampen. Ze zijn compact, ze hebben een veel grotere levensduur en ogenblikkelijke schakeltijden, ze werken op lage spanningen, etc. LED’s zijn smalbandig en kunnen een groterekleurenbereik realiseren. Ze hebben momenteel echter een beperkte helderheid. Naast de lichtbron is het type van de lichtklep ook bepalend voor de kwaliteit van een projectiesysteem. Er bestaan verschillende lichtkleptechnologieën waaronder die van de reflectieve LCOS-panelen. Deze lichtkleppen kunnen zeer hoge resoluties hebben en wordenvaak gebruikt in kwalitatieve, professionele projectiesystemen. LED’s zijn echter totaal verschillend van booglampen. Ze hebben een andere vorm, package, stralingspatroon, aansturing, fysische en thermische eigenschappen, etc. Hoewel er een twintigtal optische architecturen bekend zijn voor reflectieve beeldschermen (met een booglamp als lichtbron), zijn ze niet geschikt voor LED-projectoren en moeten nieuwe optische architecturen en een elektronische aansturing ontwikkeld worden. In dit doctoraat werd er hieromtrent onderzoek gedaan. Er werd uiteindelijk een driekleurenprojector (R, G, B) met een efficiënt LED-belichtingssysteem gebouwd met twee LCOS-lichtkleppen. Deze LEDprojector heeft superieure eigenschappen (zeer lange levensduur, beeldkwaliteit, etc.) en een matige lichtopbrengst

Compact modeling of thin-film silicon transistors fabricated on glass

The semiconductor industry, now entering its seventh decade, continues to innovate and evolve at a breakneck pace. E. O. Wilson, the famous Harvard biologist who is an expert on ants, estimates that there are 1017 ants on earth. The semiconductor industry is now shipping 100 transistors per ant every year. In addition, the pace of growth means we are building more electronics in a year than existed on January 1st of that year! A major driver for this growth in recent years is the portable consumer electronics market which includes cell phones, personal digital assistants, and tablets. The focus of this dissertation is centered on a new thin-film silicon technology on glass introduced by Corning Inc., and targeted to meet the needs of the portable product display market. The work presented in this dissertation revolves around a new technology developed by Corning Inc. known as Silicon on Glass or SiOG which permits the transfer of a thin single-crystal silicon film to a glass substrate. This technology coupled with a low-temperature CMOS process has the potential to create devices with performance characteristics rivaling those developed using conventional bulk CMOS processes. These higher performing devices permit an increased level of circuit integration directly on the glass substrate and have the potential to enable new display technologies such as OLED (Organic Light Emitting Diode). The SiOG CMOS devices are distinctly different from traditional thin-film, silicon-on-insulator, and bulk CMOS devices in that they rely on both surface and bulk conduction. Furthermore, their current-voltage characteristics are heavily influenced by fringing electric fields in the glass substrate. This dissertation presents an overview of display technology as well as a review of computer- aided design tools for integrated circuit development with a focus on compact modeling. In addition, some early work on developing advanced OLED display driver circuits using SiOG technology is presented.The bulk of this dissertation is focused on the development of compact models which properly describe the electrical characteristics of SiOG CMOS devices. For all but the most trivial cases, the set of coupled nonlinear partial differential equations that describe semiconductor device behavior has not been solved analytically. Even when the semiconductor equations that represent current flow, charge distribution, and potential distribution are decoupled and device-specific simplifications are applied, analytic solutions remain elusive. Two different methods for developing compact models for the SiOG CMOS devices are presented with distinct methods for developing approximate solutions. In addition, a model for the fringing electric field is developed using conformal mapping techniques, and its effect on drain current is explored. Finally, a new technique for solving the nonlinear semiconductor equations is explored. The application of a new mathematical technique known as the Homotopy Analysis Method (HAM) is presented as it relates to the general Poisson\u27s equation for semiconductor devices

Portable Computer Technology (PCT) Research and Development Program Phase 2

The subject of this project report, focused on: (1) Design and development of two Advanced Portable Workstation 2 (APW 2) units. These units incorporate advanced technology features such as a low power Pentium processor, a high resolution color display, National Television Standards Committee (NTSC) video handling capabilities, a Personal Computer Memory Card International Association (PCMCIA) interface, and Small Computer System Interface (SCSI) and ethernet interfaces. (2) Use these units to integrate and demonstrate advanced wireless network and portable video capabilities. (3) Qualification of the APW 2 systems for use in specific experiments aboard the Mir Space Station. A major objective of the PCT Phase 2 program was to help guide future choices in computing platforms and techniques for meeting National Aeronautics and Space Administration (NASA) mission objectives. The focus being on the development of optimal configurations of computing hardware, software applications, and network technologies for use on NASA missions

Defects, Flexoelectricity and RF communications: the ZBD story

The zenithal bistable display (ZBD) was the first liquid crystal device mode to be commercialised that uses nematic disclinations in a constructive fashion, to use the flexoelectric effect inherent to all liquid crystals but at the time was considered too weak an effect to be useful, and to transfer nano-replication methods to the LCD manufacturing environment. The genesis of the invention and spin-out company ZBD Displays Limited will be described, and the evolution of that company from licensing model, through fabless manufacturer to display provider and finally to a system provider for the retail sector. The story may be useful not just to those interested in the science behind a rather unusual LCD, but also those involved in taking technology from laboratory to manufacturing, from idea to commercial success

Pixel design and characterization of high-performance tandem OLED microdisplays

Organic Light-Emitting Diode (OLED) microdisplays - miniature Electronic Displays comprising a sandwich of organic light emitting diode over a substrate containing CMOS circuits designed to function as an active matrix backplane – were first reported in the 1990s and, since then, have advanced to the mainstream. The smaller dimensions and higher performance of CMOS circuit elements compared to that of equivalent thin film transistors implemented in technologies for large OLED display panels offer a distinct advantage for ultra-miniature display screens. Conventional OLED has suffered from lifetime degradation at high brightness and high current density. Recently, tandem-structure OLED devices have been developed using charge generation layers to implement two or more OLED units in a single stack. They can achieve higher brightness at a given current density. The combination of emissive-nature, fast response, medium to high luminance, low power consumption and appropriate lifetime makes OLED a favoured candidate for near-to-eye systems. However, it is also challenging to evaluate the pixel level optical response of OLED microdisplays as the pixel pitch is extremely small and relative low light output per pixel. Advanced CMOS Single Photon Avalanche Diode (SPAD) technology is progressing rapidly and is being deployed in a wide range of applications. It is also suggested as a replacement for photomultiplier tube (PMT) for photonic experiments that require high sensitivity. CMOS SPAD is a potential tool for better and cheaper display optical characterizations. In order to incorporate the novel tandem structure OLED within the computer aided design (CAD) flow of microdisplays, we have developed an equivalent circuit model that accurately describes the tandem OLED electrical characteristics. Specifically, new analogue pulse width modulation (PWM) pixel circuit designs have been implemented and fabricated in small arrays for test and characterization purposes. We report on the design and characterization of these novel pixel drive circuits for OLED microdisplays. Our drive circuits are designed to allow a state-of-the-art sub-pixel pitch of around 5 μm and implemented in 130 nm CMOS. A performance comparison with a previous published analogue PWM pixel is reported. Moreover, we have employed CMOS SPAD sensors to perform detailed optical measurements on the OLED microdisplay pixels at very high sampling rate (50 kHz, 10 μs exposure), very low light level (2×10-4 cd/m2) and over a very wide dynamic range (83 dB) of luminance. This offers a clear demonstration of the potential of the CMOS SPAD technology to reveal hitherto obscure details of the optical characteristics of individual and groups of OLED pixels and thereby in display metrology in general. In summary, there are three key contributions to knowledge reported in this thesis. The first is a new equivalent circuit model specifically for tandem structure OLED. The model is verified to provide accurately illustrate the electrical response of the tandem OLED with different materials. The second is the novel analogue PWM pixel achieve a 5μm sub-pixel pitch with 2.4 % pixel-to-pixel variation. The third is the new application and successful characterization experiment of OLED microdisplay pixels with SPAD sensors. It revealed the OLED pixel overshoot behaviour with a QIS SPAD sensor

Data systems elements technology assessment and system specifications, issue no. 2

The ability to satisfy the objectives of future NASA Office of Applications programs is dependent on technology advances in a number of areas of data systems. The hardware and software technology of end-to-end systems (data processing elements through ground processing, dissemination, and presentation) are examined in terms of state of the art, trends, and projected developments in the 1980 to 1985 timeframe. Capability is considered in terms of elements that are either commercially available or that can be implemented from commercially available components with minimal development

Electrostatic MEMS Actuators using Gray-scale Technology

The majority of fabrication techniques used in micro-electro-mechanical systems (MEMS) are planar technologies, which severely limits the structures available during device design. In contrast, the emerging gray-scale technology is an attractive option for batch fabricating 3-D structures in silicon using a single lithography and etching step. While gray-scale technology is extremely versatile, limited research has been done regarding the integration of this technology with other MEMS processes and devices. This work begins with the development of a fundamental empirical model for predicting and designing complex 3-D photoresist structures using a pixilated gray-scale technique. A characterization of the subsequent transfer of such 3-D structures into silicon using deep reactive ion etching (DRIE) is also provided. Two advanced gray-scale techniques are then introduced: First, a double exposure technique was developed to exponentially increase the number of available gray-levels; improving the vertical resolution in photoresist. Second, a design method dubbed compensated aspect ratio dependent etching (CARDE) was created to anticipate feature dependent etch rates observed during gray-scale pattern transfer using deep reactive ion etching (DRIE). The developed gray-scale techniques were used to integrate variable-height components into the actuation mechanism of electrostatic MEMS devices for the first time. In static comb-drives, devices with 3-D comb-fingers were able to demonstrate >34% improvement in displacement resolution by tailoring their force-engagement characteristics. Lower driving voltages were achieved by reducing suspension heights to decrease spring constants (from 7.7N/m to 2.3N/m) without effecting comb-drive force. Variable-height comb-fingers also enabled the development of compact, voltage-controlled electrostatic springs for tuning MEMS resonators. Devices in the low-kHz range demonstrated resonant frequency tuning >17.1% and electrostatic spring constants up to 1.19 N/m (@70V). This experience of integrating 3-D structures within electrostatic actuators culminated in the development of a novel 2-axis optical fiber alignment system using 3-D actuators. Coupled in-plane motion of electrostatic actuators with integrated 3-D wedges was used to deflect an optical fiber both horizontally and vertically. Devices demonstrated switching speeds <1ms, actuation ranges >35μm (in both directions), and alignment resolution <1.25μm. Auto-alignment to fixed indium-phosphide waveguides with <1.6μm resolution in <10 seconds was achieved by optimizing search algorithms

Multimodal Wearable Sensors for Human-Machine Interfaces

Certain areas of the body, such as the hands, eyes and organs of speech production, provide high-bandwidth information channels from the conscious mind to the outside world. The objective of this research was to develop an innovative wearable sensor device that records signals from these areas more conveniently than has previously been possible, so that they can be harnessed for communication. A novel bioelectrical and biomechanical sensing device, the wearable endogenous biosignal sensor (WEBS), was developed and tested in various communication and clinical measurement applications. One ground-breaking feature of the WEBS system is that it digitises biopotentials almost at the point of measurement. Its electrode connects directly to a high-resolution analog-to-digital converter. A second major advance is that, unlike previous active biopotential electrodes, the WEBS electrode connects to a shared data bus, allowing a large or small number of them to work together with relatively few physical interconnections. Another unique feature is its ability to switch dynamically between recording and signal source modes. An accelerometer within the device captures real-time information about its physical movement, not only facilitating the measurement of biomechanical signals of interest, but also allowing motion artefacts in the bioelectrical signal to be detected. Each of these innovative features has potentially far-reaching implications in biopotential measurement, both in clinical recording and in other applications. Weighing under 0.45 g and being remarkably low-cost, the WEBS is ideally suited for integration into disposable electrodes. Several such devices can be combined to form an inexpensive digital body sensor network, with shorter set-up time than conventional equipment, more flexible topology, and fewer physical interconnections. One phase of this study evaluated areas of the body as communication channels. The throat was selected for detailed study since it yields a range of voluntarily controllable signals, including laryngeal vibrations and gross movements associated with vocal tract articulation. A WEBS device recorded these signals and several novel methods of human-to-machine communication were demonstrated. To evaluate the performance of the WEBS system, recordings were validated against a high-end biopotential recording system for a number of biopotential signal types. To demonstrate an application for use by a clinician, the WEBS system was used to record 12‑lead electrocardiogram with augmented mechanical movement information

The feasibility of miniaturizing the versatile portable speech prosthesis: A market survey of commercial products

The feasibility of a miniature versatile portable speech prosthesis (VPSP) was analyzed and information on its potential users and on other similar devices was collected. The VPSP is a device that incorporates speech synthesis technology. The objective is to provide sufficient information to decide whether there is valuable technology to contribute to the miniaturization of the VPSP. The needs of potential users are identified, the development status of technologies similar or related to those used in the VPSP are evaluated. The VPSP, a computer based speech synthesis system fits on a wheelchair. The purpose was to produce a device that provides communication assistance in educational, vocational, and social situations to speech impaired individuals. It is expected that the VPSP can be a valuable aid for persons who are also motor impaired, which explains the placement of the system on a wheelchair