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Title: Techniques to improve the optical quality of liquid crystal over silicon spatial light modulators
Author: Seunarine, Krishna
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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Systems using Ferroelectric (F) Liquid Crystal over Silicon (LCoS) Spatial Light Modulators (SLMs) have been limited, in the past, by the poor optical performance of the devices. The high degree of backplane flatness and hence LC layer thickness uniformity required have been very difficult to achieve due to stresses induced in the silicon wafer as a consequence of CMOS processing. Mirror quality and LC alignment are also major factors in determining the (F)LCoS SLM optical efficiency and contrast ratio. A process of forming "thin" high-quality mirrors was developed, using an intermediate metal chemical mechanical polishing process (CMP). An associated process was also developed in which the thin mirrors were fabricated flush with the surrounding oxide, using a novel interpixel gap fill process (flat at 2.5nm) which allowed a major improvement to be made in the liquid crystal flow front, during cell filling. We have successfully demonstrated a technique for reducing the backplane warpage from 3.0λ down to λ/8, over a die, thus improving the LC layer thickness uniformity. The robust silicon dioxide spacers used in the die flattening experiments, above, were fully characterized and the deposition and patterning process optimized to consistently provide spacer layer thickness uniformities of <1% over a 75mm wafer. Issues relating to the transparent ITO layer were addressed. We have shown that the surface roughness of the granular "in-house" deposited ITO can be reduced by ~40% (on a submicrometer scale) using a slight variant of the oxide CMP process. The optical performance of LC devices was also found to be improved by optimizing the ITO and SiO layer thickness. Reflections from the ITO coated glass have been reduced by approximately 10% by optimizing the ITO layer thickness for a particular wavelength.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available