D. W. Calton

Techniques to improve the flatness of reflective micro-optical arrays

Abstract Liquid crystal over silicon is an established technology for reflective spatial light modulators and microdisplays. In this paper, we describe progress in improving two key performance criteria. The first is backplane flatness; we describe recent developments in the use of chemical mechanical polishing to produce optically flat pixel mirrors on top of existing circuit topography; we further describe the use of an assembly technique that reduces chip bow caused by the microfabrication induced stresses in the silicon backplane. The second is liquid crystal layer thickness; we describe the use of a lithographically patterned spacer layer microfabricated on the surface of the silicon backplane to minimize layer thickness variations. Each of the techniques produces improvements in the performance of the final device.

Review of the history and technology of micromachined miniature displays using foundry-produced silicon backplanes

Liquid-crystal over silicon is an established technology for reflective spatial light modulators and microdisplays. This paper reviews their development to date, highlighting in particular the micromachining of the mirror array and the associated packaging issues.

26.3: Investigation of the Bow of Silicon Backplanes for Microdisplay Applications

The optical performance of ferroelectric liquid crystal over silicon (FLCOS) microdisplay devices can be greatly improved by ensuring that the silicon backplane that forms the core of the display engine is both smooth and flat. In this paper we investigate the effect of the circuit design and manufacturing process on the bow of the silicon CMOS drive circuitry.

Microdisplay Packaging Challenge

The packaging of ferro-electric liquid crystal over silicon (FLCOS) microdisplays presents itself as a formidable challenge to the package designer. The overall assembly should be lightweight, rugged, and incorporate the display engine, the illumination unit and the viewing optics. Good optical performance of the displays depends on many variables that need to be optimised. The silicon chip acts as part of an optical device and so standard packaging procedures are not readily applicable. In particular, the silicon chip requires significant post-processing to ensure it is both smooth and flat even after assembly. Selection of a suitable packaging strategy is key to success. In this paper we evaluate various methods of first level packaging of the silicon display engine.

Alignment of ferroelectric liquid crystals over CMOS-based microdisplay backplanes

Defect free homogeneous alignment of ferroelectric liquid crystals in the surface stabilized configuration remains challenging to obtain even over the relatively small area of liquid crystal on silicon microdisplays. The limitations of the conventional rubbed polymer alignment technique are discussed and the benefits brought by recent advances in backplane post-processing are demonstrated in realistic conditions. The potential of the linearly photopolymerized photoalignment technique are highlighted in terms of alignment quality, susceptibility to zigzag defects, and electro-optical performances.

Manufacture of aluminium micromirror arrays using a dual damascene process

Liquid crystal over silicon (LCoS) is an established technology for reflective spatial light modulators (SLMs) and microdisplays. While most of the manufacturing methods used are mature, there exist a number of unresolved issues associated with the mass production of high quality devices. Existing manufacturing technology leaves the final mirror elements raised from the surface of the surrounding dielectric causing problems with the filling of the liquid crystal (LC). The flow front during filling is influential on the final alignment qualities, so it is essential that this flow front follows the ideal linear shape. We report on a method to remove this mirror step height by the use of an aluminum dual damascene technique. This process produces mirrors which are embedded within the dielectric insulating layer thereby removing most of the LC flow front aberrations, caused by the surface topography, during LC filling. We discuss the novel methods developed to overcome the damascene induced problems of dishing and erosion. The results will be discussed with particular bias towards their use in the manufacture of reflective micro-displays.