Major contributors to the mottling defect in micro electromechanical projection displays



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For 75 years, Texas Instruments has repeatedly pioneered the semiconductor industry, from the invention of the integrated circuit to the design and production of the digital micromirror device. Texas Instruments’ DLP® Products division, established in 1993, creates world-class digital technology that enables breakthrough development in light-steering applications. One scientist's vision for an all-digital optical device has led to applications ranging from digital cinema and home entertainment to optical networking and DNA synthesis. Device layers require a shortlist of electrical engineers, mechanical engineers, and physicists to cohesively design and produce a product that is more than adequate to market demands while remaining at least one-step ahead of competitors. Over the last several years optical performance engineers, IC manufacturing engineers, and design engineers have evolved the DMDTM into what it is today to meet the market’s demands.
Semiconductor DLP® must factor in future trends in quality, performance, reliability, and cost requirements in design and the fabrication process. There are conflicting requirements forcing all the facets that produce the DMDTM to balance the trade-offs. Conventional IC manufacturing wisdom would suggest smaller pixel, but the optical performance suggests larger pixel. The compromise between customer demands and production costs leads to smaller pixels because the optical performance can be balanced by minimizing the gaps between the mirrors within limits, which taps into design constraints. The gaps between each pixel are sources of stray light that downgrade the image quality. The smaller pixel trend comes with negative benefit larger diffraction angles which leads to contrast ratio and mottling concerns. Since Larry Hornbeck and Ed Nelson invented the DMDTM, the architecture has advanced by maximizing mirrored surface reflectivity to increase the contrast ratio and reduce wasted energy. Reducing the amount of stray light reflected off surfaces beneath the micromirror that are exposed to the light source increases the contrast ratio by reducing off-state light. As the pixel size decreases, the fabrication process accommodates new design constraints, DLP® will need to update Production Test Systems to prepare for new defects. This paper will introduce a flexible quantitative/analytical projector test that substantially improves DLP® projector testing. This paper also explores the Digital Micromirror DeviceTM’s root physical parameter(s) contributing to the recently discovered amorphous mottling defect in micro-electromechanical projection systems.