Invited Paper: LCOS microdisplay technology for advanced applications Dieter Cuypers Herbert De Smet André Van Calster Abstract — 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 V com drift inside the asymmetrical LCOS cells are presented. Keywords — LCOS, VAN, V com , fringe field. 1 Introduction 1.1 LCOS The liquid-crystal–on–silicon technology has in the recent past conquered its place as an established display technol- ogy. It offers a clear path to the fabrication of high-resolution miniature displays, which can be employed in a plethora of applications. From the very beginning, it has been pointed out that the key advantage of the LCOS approach is the fact that it is actually a combination of two thoroughly known technolo- gies: on the one hand, the CMOS processing and, on the other hand, the LCD manufacturing. Although the expected benefits from this synergy were not always so obvious during the initial development and the maturing phase of the technology, nowadays the potential of the approach is beginning to pay off. A typical example is the possibility to design and pro- duce LCOS displays using the so-called fabless model, where the LCOS company obtains the silicon backplanes at any suitable foundry and has them assembled into imagers at another suitable LC assembly house. This results in a relatively low initial level of invest- ment for a production facility. Quite a number of companies actually work in this way. LCOS microdisplays are being used in various appli- cations, largely to be divided in two categories: near-to-eye and projection. The first category contains systems such as camera viewfinders, virtual-reality goggles, and personal viewers. The projection category comprises applications such as head-up displays systems, presentation beamers of all sizes and resolutions, and of course rear-projection TV sets. Although there are still some exceptions, the liquid- crystal mode of choice for projection devices seems now to have consolidated around the vertically aligned nematic mode. The reasons behind this choice are by now quite well known: the VAN mode offers a very attractive combination of characteristics featuring a high contrast ratio together with moderate driving voltages, fast switching, and high efficiency. On the architectural side, there are quite some differ- ences in the approach between the contenders. For the driv- ing electronics, the battle between digital versus analog production of gray scales is still ongoing. To a certain extent, this architectural choice is entangled with the choice for the color management, i.e., whether a single-panel or a three- panel optical engine is used. Roughly speaking, the low end generally features sin- gle panel all-digital solutions, while at the high end of the spectrum a strong preference for analog-driven three-panel systems is found. 1–3 1.2 Current status The tendency in the television market for ever-growing screen dimensions has been regarded as an ideal opportu- nity for LCOS technology to become mature in a high-vol- ume business. The technology allows for the production of rear-projection TV sets with high resolution and large screen diagonals while maintaining a slim form factor for the cabinet. In the beginning, the focus was on XGA, SXGA, and derived wide-screen resolutions. The rapid paced introduc- tion of the HDTV standard, however, caused the demand for these types to drop quickly. The deployment of HDTV itself is of course in itself another real opportunity for the LCOS technology to prove its merits. Because of the scalability, the higher resolution does not alter anything substantial in the cost structure of the LCOS panel, giving the technology an advantage over the others. Despite these considerations, if one looks at the mar- ket today, it is clear that the direct-view LCD sets and the D. Cuypers is with IMEC vzw, TFCG Microsystems, Technologiepark B914, B-9052 Zwijnaarde, Belgium; telephone +32-9-264-5353, fax -5374 e-mail: dcuypers@elis.ugent.be. H. De Smet and A. Van Calster are with Ghent University, ELIS – TFCG Microsystems, Technologiepark B914, B-9052, Zwijnaarde, Belgium. © Copyright 2007 Society for Information Display 1071-0922/07/1510-0775$1.00 Journal of the SID 15/10, 2007 775