Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2003-10-22
2004-10-12
Thompson, Tim (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S290000, C359S292000, C359S297000
Reexamination Certificate
active
06804039
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is related generally to spatial light modulators, and, more particularly, to hinge structures of the spatial light modulators and methods for making the same.
BACKGROUND OF THE INVENTION
Spatial Light Modulators (SLMs) are transducers that spatially modulate incident light beams according to optical or electrical input signals. A type of SLM is the microelectromechanical system (MEMS)-based SLM, which often consists of an array of micro-mirrors. The micromirrors of the array can be individually addressed and independently deflected by electrostatic forces.
Currently, a variety of MEMS-based SLMs for use in display systems has been developed. Regardless of the differences, a common basic configuration of the MEMS-based SLMs comprises a hinge and a micro-mirror plate that is attached to the hinge. In the display operation, the mirror plate rotates relative to a substrate of the micromirror so as to reflect incident light beams onto or away from a display target. In this regard, mechanical properties of the hinge and the micro-mirror plate and the attachment of the two are critical factors to the overall performance of the micro-mirrors and the quality of the displayed images.
In particular, since the hinges are often electrically conductive, they consist of metals, metal alloys, metal nitrides or metal silicides. While these materials may have the requisite conductivity, they are often poor mechanical elements, especially when compared to ceramic materials used in MEMS (e.g. silicon, silicon nitride, or silicon dioxide). The mechanical reliability problems arising from poor mechanical properties could include fracture, fatigue, plasticity, dislocation motion and creep. Because the reliability of a torsion hinge depends upon the amount of residual twist, which is caused by the rotation of the mirror plate, in the hinge as a function of the actuation time, it is necessary then to minimize the amount of residual twist at fixed torsion stiffness and fixed rate of plastic deformation in the mechanically undesirable element.
Therefore, what is needed is a spatial light modulator having micro-mirrors with robust mechanical properties for use in display systems.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention provides an improved multilayer hinge structure for use in a micro-mirror device for a spatial light modulator that has improved mechanical performance and robustness due do its geometrically optimized hinge structure.
In an embodiment of the invention, a spatial light modulator is provided. The spatial light modulator comprises: an array of micro-mirrors on a substrate, each micro-mirror of the array comprising a reflective mirror plate held by a hinge on the substrate, wherein the mirror plate and hinge extend substantially parallel to the substrate when the mirror plate is in an undetected position, wherein the hinge is a multilayer hinge having a first and second layer wherein the first layer is more electrically conductive than the second layer, and wherein the first layer is more narrow than the second layer in a direction substantially parallel to the substrate.
In yet another embodiment of the invention, a spatial light modulator is provided. The spatial light modulator comprises: an array of micro-mirrors on a substrate, each micro-mirror of the array comprising a reflective mirror plate held by a hinge on the substrate at the contact, wherein the mirror plate and hinge extend substantially parallel to the substrate when the mirror plate is in an undeflected position, wherein the hinge is a multilayer hinge having a first and second layer wherein the first layer has a creep rate higher than that of the second layer at the operating temperature of the spatial light modulator, and wherein the first layer is more narrow than the second layer in a direction substantially parallel to the substrate.
In yet another embodiment of the invention, a method of making a micro-mirror device, the device comprising a hinge and a micro-mirror plate attached to the hinge such that the micro-mirror plate can rotate relative to the substrate by the hinge, is disclosed. The method comprises: providing a substrate; depositing a first sacrificial layer on the substrate; forming either a hinge or a micro-mirror plate on the first sacrificial layer; depositing a second sacrificial layer; forming a micro-mirror plate or hinge on the second sacrificial; wherein the forming of the hinge on either the first or second sacrificial layer comprises: depositing a second layer comprised of a material with a creep rate lower than that of the first layer; depositing a first layer that comprises a material with a creep rate higher than that of the second layer, patterning the first layer so as to have a width that is 50% or less of the width of the second layer; and forming a hinge support to connect the hinge directly or indirectly to the substrate; and removing the first and second sacrificial layers so as to release the micro-mirror device.
In yet another embodiment of the invention, a method of making a micro-mirror device, the device comprising a hinge and a micro-mirror plate attached to the hinge such that the micro-mirror plate can rotate relative to the substrate by the hinge, is disclosed. The method comprises: providing a substrate; depositing a first sacrificial layer on the substrate; forming either a hinge or a micro-mirror plate on the first sacrificial layer; depositing a second sacrificial layer; forming a micro-mirror plate or hinge on the second sacrificial; wherein the forming of the hinge on either the first or second sacrificial layer comprises: depositing a second layer comprised of a material with a resistivity higher than 10
12
&mgr;&OHgr;·cm at the operating temperature of the device; depositing a first layer that comprises a material with a resistivity less than that of the second layer; patterning the first layer so as to have a width that is 50% or less of the width of the second layer; and forming a hinge support to connect the hinge directly or indirectly to the substrate; and removing the first and second sacrificial layers so as to release the micro-mirror device.
In yet another embodiment of the invention, a method of making a micro-mirror device, the device comprising a hinge and a micro-mirror plate attached to the hinge such that the micro-mirror plate can rotate relative to a substrate by the hinge, is disclosed. The method comprises: providing the substrate; depositing a first sacrificial layer on the substrate; forming the micro-mirror plate on the first sacrificial layer, depositing a second sacrificial layer on the micro-mirror plate; patterning the second sacrificial layer according to a structure of the hinge; forming the hinge on the patterned second sacrificial layer, further comprising: depositing a bottom layer that comprises a material with resistivity higher than 10
12
&mgr;&OHgr;·cm at the operating temperature of the device; depositing a top layer that comprises a material with resistivity lower than 100,000 &mgr;&OHgr;·cm at the operating temperature of the device; narrowing the topmost layer to cover at least 50% of the bottom layer surface by means of patterning and/or etching; and providing a means to connect the bottom and top layers directly or indirectly to the substrate; and removing the first and second sacrificial layers so that the bottom and top layers are free to move relative to the substrate.
In yet another embodiment of the invention, a method of making a micro-mirror device, the device comprising a hinge and a micro-mirror plate attached to the hinge such that the micro-mirror plate can rotate relative to a substrate by the hinge, is disclosed. The method comprises: providing the substrate; depositing a first sacrificial layer on the substrate; forming the micro-mirror plate on the first sacrificial layer, depositing a second sacrificial layer on the micro-mirror plate; patterning the second sacrificial layer, forming the hinge on the patterned second sacrifici
Doan Jonathan C.
Patel Satyadev R.
Muir Gregory R
Reflectivity, Inc.
Thompson Tim
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