1. Technical Field of the Invention
The present invention relates generally to spatial light modulators, and more particularly to a spatial light modulator having its array of micro-mirrors manufactured in two sets.
2. Background Art
FIG. 1 illustrates a top view of a simplified spatial light modulator (SLM) 10 such as is known in the art. The SLM includes an array of reflective micro-mirrors 12 each of which constitutes an electrode of a respective display pixel. The other electrode of the display pixels is formed as a transparent electrode layer (not shown, on top of an area of liquid crystal (not shown).
Due to limitations in existing fabrication techniques, the array of micro-mirrors is arranged such that there is a space or gap 14 between adjacent micro-mirrors. Currently, this space accounts for upward of 10% of the surface area of the pixel array. This means that upward of 10% of the light striking the array is lost, and is not reflected back through the liquid crystal. This lost light is actually of absorbed by the SLM, causing heating and other problems. Furthermore, the spacing places limitations on the scalability of the micro-mirror array, making it increasingly difficult to effectively decrease the micro-mirror size and increase the resolution of the device.
FIG. 2 illustrates a cross-sectional view of a portion of the SLM 10. The device is built upon a substrate 18, such as silicon. Conductive vias 16 or other interconnecting structures are built into the substrate. The micro-mirrors 12 are fabricated in electrical contact with the vias, with spacing 14 between adjacent neighbors. The micro-mirrors are encased in one or more insulative, antireflective layers. These layers can include a first layer 20, such as SiO2, and a second layer 22, such as Si3N4, which is fabricated over the first layer. A layer of liquid crystal material 24 is sandwiched between these layers and a glass layer 26 which holds the transparent electrode layer 28. When an electrical potential is applied between a micro-mirror and the transparent electrode layer, the region of liquid crystal between them becomes transparent. The degree of transparency can be adjusted, such as by altering the electrical potential or by phase width modulating its signal, to give plural levels of transparency, and thus plural levels of reflected light. A typical SLM offers 256 levels of color resolution.