Dieter Cuypers

Design, fabrication and evaluation of a high-performance XGA VAN-LCOS microdisplay

Abstract The design, fabrication and evaluation of a high-performance 0.9xa0in. diagonal XGA microdisplay is described. The DRAM type active matrix comprises square pixels with a 17.6xa0μm pitch. Bi-directional row and column drivers are integrated on-chip. A 4-metal 0.35xa0μm CMOS technology enabled the design of a very effective light shield. The peripheral interface electronics supports a programmable look-up table with 10-bit voltage values, as well as programmable threshold voltage and steepness settings, all accessible through a graphic user interface. A vertically aligned nematic liquid crystal mode with an inorganic SiO2 homeotropic alignment layer yields contrast ratios exceeding 1900:1 and video-compatible response times.

Design and Wrinkling Behavior of a Contact Lens With an Integrated Liquid Crystal Light Modulator

A new design of a spherically molded liquid crystal cell intended for embedding in a contact lens is proposed. Wrinkle formation in these cells was investigated and a correlation was found between the total thickness of the cell and its smoothness. Smooth cells with minimal thickness were obtained by using an asymmetric configuration with a thin layer at the convex side and a thicker but threshold dependent layer at the concave side. Active liquid crystal cells filled with a guest-host liquid crystal mixture exhibited uniform light modulation along their surface, paving the way towards a modulation-based contact lens display.

VAN LCOS Microdisplays: A Decade of Technological Evolution

Microdisplays of the liquid crystals on silicon (LCOS) type have gone through a rapid evolution during the last decade. We present an overview of how vertically aligned nematic (VAN) LCOS have evolved from an attractive, but notoriously difficult and even infamous technology, to the mainstream microdisplay technology that it is today. At the same time, we highlight a number of remaining issues and concerns, and present some ideas of how to remedy them.

35.3: Fringe Field Effects in Microdisplays

Two-dimensional simulations of the liquid crystal behaviour are used to predict the influence of fringe fields on the optical performance of current and upcoming fast LCoS microdisplays based on the vertically aligned nematic mode. Results are demonstrated on LCoS devices using inorganic alignment layers.

Measurement methodology for vertically aligned nematic reflective displays

We developed a measurement method for the characteristics of microdisplays specifically aimed at vertically aligned nematic reflective cells. It allows determination of contrast ratio and cell gap, and gives good estimates for the pretilt angle and the elastic surface-coupling constant. The set-up consists of a laser source, high quality polarisers, a beamsplitter mirror, a quarter-wave plate and a sensitive photodiode. A model for the polarization changes in the light caused by each component allows the extraction of the initial phase retardation induced by the cell and gives a first estimate of the thickness. Simulation of the director configuration in liquid crystals is then used to enhance the accuracy by taking into account the properties of a real LC cell. Matching of the simulation and the measurements yields the required values together with a calibrated simulation model.

Assembly technology for the manufacture of LCOS panels

— The technological issues related to the fabrication of high-performance LCOS displays are described. The considered devices use the vertically aligned nematic liquid-crystal mode because of its superior performance characteristics. The issues addressed mostly stem from this choice and the ensuing need for inorganic alignment layers. In particular, the compatibility of the inorganic alignment layers with the sealant material are treated in detail.

18.1: Electronic Compensation for Fringe‐Field Effects in VAN LCOS Microdisplays

Although fringe field effects in LCOS projection panels can be suppressed sufficiently not to interfere with the optical performance needed for consumer applications, precise greylevel reproduction in professional applications still requires a detailed knowledge of the occurrence of disclinations at all driving voltages and neighboring pixel configurations. Such a study is presented in this paper, allowing the implementation of an electronic compensation for the fringe field effects.

Invited Paper: LCOS microdisplay technology for advanced applications

— Some technology aspects of LCOS microdisplays that are important for their deployment in advanced projection applications are discussed. The selection of the liquid-crystal parameters of the vertically aligned system as a function of the requirements (response speed, contrast, etc.) is addressed; a three-dimensional simulation engine to evaluate fringe-field effects between pixels is described, allowing the fine-tuning of the LCOS design with respect to the optical output. Finally, some observations on the nature of the so-called Vcom drift inside the asymmetrical LCOS cells are presented.

Silicon-based reflective polymer-dispersed LC display for portable low-power applications

Recently LCOS microdisplays are becoming available for personal IT applications, despite some problems which are less critical in poly silicon or amorphous silicon based displays. The most common problems which must be encountered are the polarization of the pixels and the light shielding of the silicon substrate. In this paper a methods proposed which solves the light shielding and pixel flatness problem. A non-critical back-end processing which can be applied outside the silicon foundry has been developed. The effectiveness of the light shielding on a working demonstrator display is shown. To avoid light losses caused by a polarization filter, a polymer dispersed LC has been chosen. By decreasing the cell gap we made the PDLC voltage compatible with a standard 3 micrometers CMOS process and its response fast enough to be used for video applications. It is shown that this choice is very suited in direct view and portable applications. The realized prototype has 3 bit grey levels and is video compatible and can be used in a number of applications, such as personal viewers, PDAs and data displays.

Pre-tilt angle and cell-gap measurement of vertically aligned non-twisted liquid-crystal displays

— A measurement method for the determination of the cell parameters of vertically aligned nematic LCOS devices has been developed. It provides the values for the pre-tilt angle and the cell thickness in a reliable way, without the need for spectroscopic instruments. The method uses oblique incidence to separate the determination of pre-tilt angle and cell thickness from each other and thus enhance the measurement accuracy. As a bonus, the measurement system consists only of simple optical components and does not need costly instruments.