Photoalignment of LCoS LCDs

Because the pixel area of liquid‐crystal‐on‐silicon (LCoS) microdisplays is about 100 times smaller than that of direct‐view liquid‐crystal displays (LCDs), the limitations of the conventional alignment by brushing are obvious: Scratches and particle contamination caused by brushing become visible due to the strong optical magnification required for LCoS LCDs both in front or rear projection. As an alternative, photoalignment with the linear photo‐polymerization (LPP) technology avoids the generation of defects, thus increasing production yields considerably. For application in LCoS LCDs, alignment layer materials must match the high‐voltage holding ratio (VHR) specifications of TFT‐LCDs. The VHR performance of the newly developed second‐generation LPP materials is shown to be similar to standard TFT polyimides used for conventional brushed alignment. We report investigations of pretilt‐angle generation by photoalignment on reflective CMOS substrates. UV light reflected from the CMOS surface during LPP exposure affects the resulting pretilt angle. Compared to pretilt angles on transmissive substrates, the reflected UV light can induce lower, higher, or identical pretilt angles, depending on LPP material properties. In any case, the pretilt angles are well defined, which results in perfect LCD alignment.     

Contrast improvements for scrolling‐color LCoS

Abstract— A scrolling‐color LCoS (liquid‐crystal‐on‐silicon) display must exhibit both fast speed and high contrast. These requirements drive design choices for the liquid crystal and optics of the image kernel. The input director was aligned to the incoming polarization and a compensated 45TN0 effect was choosen. Contrast demands place tight requirements on interfacial reflections. A wire‐grid PBS can achieve high contrast and can simplify the system construction. With attention to the above, we report a sequential contrast of 800:1 at the viewing screen. With a 90TN0 effect, the contrast can be increased even further, but with some penalty in light efficiency. With this effect, sequential contrast of 2000:1 was measured.     

General methodology for LCoS panel compensation

Abstract— A general three‐step methodology is presented to optimize contrast when compensating LCoS panels. The first step acts to compensate the in‐plane residual retardation, while the second one improves the field of view (FOV) using either MacNeille‐type or wire‐grid polarizing beamsplitters (PBS). The orientation of the LCoS panel and compensator, relative to the MacNeille PBS, are very critical to achieve good system contrast. The final step is to account for reflections from anisotropic material, which appear as on‐state light, limiting contrast.     

Measurement methods for LCoS displays

Abstract— Two measurement methods to characterize uniformity and the absolute cell gap of LCoS images will be reviewed. These are simple to use in a production environment and have allowed major improvements in manufacture to be achieved. For the purpose of this paper, the liquid‐crystal mode used is the 45° normally black mode.     

Nematic liquid‐crystal technology for Si wafer‐based reflective spatial light modulators

Various nematic LC modes are reviewed and compared in terms optical throughput, driving voltage, response time, contrast ratio, and spectral responses for LCoS applications. The effects of fringe‐field‐induced disclination on display performance and the mechanism of slow response of the disclination line between two topologically non‐equivalent LC states will be discussed. Issues involving flicker and photo‐instability of LCoS displays will be addressed as well.     

Curved OLED microdisplays

Technical background for CMOS substrate thinning of CEA‐LETI (historically developed for through silicon via technology as well as for more recent activity to provide curved image sensors, for IR as well as for visible spectra) has been applied to realize curved OLED‐based microdisplays. It will be shown that test OLEDs made onto silicon wafers as well as 873 × 500 WVGA, 0.38″ diagonal, and an innovative 1920 × 1200 WUXGA, 1″diagonal, CMOS‐based microdisplays can be curved at R = 45 mm radius of curvature (1D) with no negative impact onto the circuit electrical characteristics. This feature can allow significant innovation on the system and application because it can help to redesign simpler and lighter optical engine systems, in the same manner as for curved image sensors. These results can be obtained owing to the integration of a new protective hard coat layer that has been used in conjunction with a robust thin‐film encapsulation to protect OLEDs from mechanical ingress (from process steps and handling) and oxidizing gas of the atmosphere, respectively. Results have been produced within the framework of the EU‐funded, H2020 project, called L arge cost‐effective O LED MI cro D isplays (LOMID and their applications).     

Fully digital LCoS device for consumer applications

Abstract— This paper presents a new display device, which combines a digital backplane and a vertically aligned nematic liquid‐crystal layer. The device has 1280 × 720 pixels in a 0.7‐in.‐diagonal display area. In this paper, we present the concept of the new device and overview the performance of the device for a rear‐projection television application.     

A single‐panel LCoS engine based on light guides

Abstract— By using light‐guide components, a new scrolling‐color engine for single‐panel LCoS projection has been developed. Light guides allow for loss‐less delivery of light leading to a simpler and more‐compact system. Engine design and construction based on a single 0.88‐in.‐diagonal LCoS panel is described. Separate results with a multilayer optical film Cartesian PBS show that a significant improvement in system efficiency is possible.     

LCoS microdisplay throughput measurements

Abstract— We propose a straightforward method to measure the absolute throughput of an LCoS microdisplay. The method requires two measurements. The first measurement is of the lumens delivered from a testbed, which includes the microdisplay under test, with a folded light path. The second measurement is of the lumens delivered by the unfolded testbed with the microdisplay removed. This second measurement is used to normalize the first to obtain a fractional transmission that a designer can use to make a meaningful prediction of the system brightness of a LCoS‐based projection system.     

A new class of bookshelf bistable siloxane modified ferroelectric LC materials with electrical repairability in an LCoS configuration

Abstract— Investigation of siloxane‐based ferroelectric liquid crystals (Si‐FLCs) has revealed chevron‐free long‐term bistable behavior and, unusually, an easy regeneration of bistable performance after damage (e.g., by mechanical shock). The properties are intrinsically related to the chemical structure of the oligosiloxane materials. The phenomena result from the coupling of siloxane and organic moieties that causes nano‐phase segregation, which essentially reduces the correlation of tilting from adjacent layers and also generates weak anchoring by decoupling the bulk structure from the strong surface anchoring. A method of regenerating a condition with bistable performance by an electric field (without mechanical and heat treatment) is established. An in‐house Si‐FLC over a silicon (Si‐FLCoS) device is demonstrated, which exhibits good memory effects without chevron defects and a repair function for regenerating bistability in case of damage.     

Front‐projection optical‐system design for reflective LCoS technology

Abstract— Optical designs for three‐panel LCoS projection systems are reviewed. The impact of polarization aberrations in prism‐based systems is discussed and a simple model to analyze the sensitivity of contrast to thermal gradients in prisms is presented. To eliminate stress birefringence in LCoS projection systems, we have developed a projection optical system that does not require the use of polarizing prisms. An improved off‐axis design has been designed that simplifies manufacture and reduces cost. The performance of systems based on this architecture will be discussed.     

Advances in contrast enhancement for DLP projection displays

Abstract— Increased contrast ratios are essential to the continued success of DLP? products in the marketplace, from rear‐projection televisions and home‐theatre systems to large venue displays and DLP Cinema?. The contrast of DLP projection systems has increased steadily over the past 5 years due to improvements in illumination and projection optics, as well as changes to the DMD itself. The authors will present an overview of the contrast performance of DLP projectors over time as well as describe illumination and projection techniques that optimize the performance of the DMD.     

Microdisplay wafer‐flatness metrology by optical interferometry

Abstract— We report a microdisplay wafer‐flatness metrology technique based on digital high‐pass filtering of topography data obtained from a commercial optical interferometer. This technique discriminates against both wafer‐scale bow/warp and pixel‐scale roughness to reveal die‐scale flatness variations that are the most relevant to microdisplay gap uniformity. We report flatness measurements of a variety of live and test silicon wafers supporting VLSI microdisplay circuitry, and show how these measurements correlate with the performance of liquid‐crystal microdisplays assembled from similar wafers. The technique is sensitive to cross‐die flatness variations as small as 25 nm in the presence of wafer bow of tens of microns. The wafer flatness variations that make the greatest contribution to liquid‐crystal cell‐gap non‐uniformity arise from interactions between the chemical mechanical planarization (CMP) process and the VLSI circuit layout. Our metrology technique can help the VLSI designer optimize microdisplay layout, and provides an objective flatness specification for wafers purchased from third‐party foundries.     

Post-processing and assembly of reflective microdisplays

Abstract— The performance and manufacturability of reflective displays can be enhanced by planarization, post-processing, and integrated assembly. Simplified methods for planarization and assembly of liquid-crystal-on-silicon (LCOS) microdisplays using polymeric resins are presented. Spin-cast benzocyclobutene (BCB) resin shows a six-fold reduction in step height on the surface of a typical LCOS backplane, at a cost significantly less than chemical mechanical polishing. Methods for dry-etching low-resistance contacts to the underlying circuitry and depositing high-reflectivity mirrors have been developed. In addition, photo-definable BCB resin has been utilized as both a spacer and adhesive technology in miniature-display assembly. Cell-gap thicknesses of 0.9–2.4 μm with 50–100-nm cell-gap variation and bonding shear strengths of 3200 ± 460 psi have been demonstrated, leading to wafer-scale assembly of LCOS cells. The photo-BCB spacer and adhesive technology is compatible with common liquid-crystal-alignment techniques. In this paper, the methods and results of LCOS backplane planarization, post-processing, and integrated display assembly are described.     

适用于性能测量的设计模式研究

针对应用系统性能指标难于测量的现状，提出一种以测量性能指标为目的的设计模式。通过应用本模式，软件开发人员可以使设计出的软件系统本身具有测量性能的功能，从而为定位系统瓶颈提供依据。     

A digitally driven pixel circuit with current compensation for AMOLED microdisplays

A novel digitally driven pixel circuit for active‐matrix organic light‐emitting diode (OLED) microdisplays is proposed and evaluated. This circuit supports both pulse width modulation and pulse density modulation digital drive approaches. Only three transistors and one capacitor are required per pixel for the proposed circuit. A current mirror is used to compensate for the pixel current changes that occur because of the degradation of the OLEDs over time. The compensation current depends on the potential of the common cathode, the properties of the current mirror, and the Width/Length (W/L) ratio of the drive transistor. The proposed digital pixel circuit also has advantages in circuit layout compared with analog pixel circuits.     

Application‐specific integrated filters for color‐sequential microdisplay‐based projection applications

Abstract— Application‐specific integrated filters (ASIFs), based on a unique holographic polymer‐dispersed liquid‐crystal (H‐PDLC) material system offering high efficiency, fast switching, and low switching voltage, are being developed for microdisplay‐based projection applications. The basic properties and key benefits of ASIFs in projection displays are reviewed.     

Development of a touch probe based on five-dimensional force/torque transducer for coordinate measuring machine (CMM)

Systematic errors due to the pre-travel variation and the probe tip shape are irreducible to the traditional touch trigger probing systems. This paper describes the development of a probing system based on five-dimensional force/torque transducer for coordinate measuring machines. The compensation for pre-travel variation is accomplished through the five-dimensional force/torque information acquired by the integrated transducer and the stiffness matrix of the stylus. From the relationship between the obtained force/torque information and the geometrical shape equation, coordinates of the exact contact point immune from the contact error are acquired. After calibration, the combined measurement uncertainty is estimated to be less than ±0.3 μm.     

Development of a knowledge-based self-assessment system for measuring organisational performance

Effective performance measurement is an important task in the discipline of engineering management. With the support of City University of Hong Kong, a research project was initiated to develop a knowledge-based expert self-assessment (KES) training toolkit on measuring and assessing organisational performance based on the evaluation criteria of a renowned Business Excellence Model—the Malcolm Baldrige National Quality Award (MBNQA). This paper explains the development of and elaborates the system framework, requirements, design and validation of the toolkit. The project results shows that the toolkit could facilitate the teaching of students of engineering management courses by providing a stimulating learning environment and practical experiences in measuring and assessing enterprise performance. Incorporating the KES model and toolkit into the engineering management curriculum can provide students and industrial users with hands-on experience and insights of organisational PM.     

A Web-Service based framework for analyzing and measuring business performance

The web services paradigm provides organizations with an environment to enhance B2B communications. The aim is to create modularized services supporting the business processes within their organization and also those external entities participating in these same business processes. Current web service frameworks do not include the functionality required for web service execution performance measurement from an organization perspective. As such, a shift to this paradigm is at the expense of the organizations performance knowledge, as this knowledge will become buried within the internal processing of the web service platform. This research introduces an approach to reclaim and improve this knowledge for the organization establishing a framework that enables the definition of web services from a performance measurement perspective, together with the logging and analysis of the enactment of web services. This framework utilizes web service concepts, DSS principles, and agent technologies, to enable feedback on the organizations performance measures through the analysis of the web services. A key benefit of this work is that the data is stored once but provides information both to the customer and the supplier of a web service, removing the need for development of internal web service performance monitoring.