High fill-ratio mirror-based spatial light modulator

A spatial light modulator includes a two-dimensional array of hexagonal mirror plates disposed in a honeycomb pattern over a substrate. Each of the hexagonal mirror plates is supported by one or more structural members. There is a gap between adjacent hexagonal mirror plates. The structural members are not located in the gap.

BACKGROUND

The present disclosure relates to micro-mirror based spatial light modulators.

A spatial light modulator can include an array of tiltable micro mirrors. A micro mirror built on a substrate can include a tiltable mirror plate that can be tilted by electrostatic forces. The mirror plate tilts to an “on” position, wherein the micro mirror plate directs incident light to a display device, and to an “off” position, wherein the micro mirror plate directs incident light away from the display device. The mirror plate can be stopped by mechanical stops at the “on” or the “off” positions so that the orientation of the mirror plate can be precisely defined at these two positions. For the micro mirror to properly function, the mirror plate must be able to promptly change between the “on” or the “off” positions without any delay. The mirror plates in a spatial light modulator can be selectively tilted to “on” or “off” positions to form a display image. A desirable performance for the spatial light modulator in a display application is to provide bright and high contrast display images.

SUMMARY

In one general aspect, the present invention relates to a spatial light modulator, including a two-dimensional array of hexagonal mirror plates disposed in a honeycomb pattern over a substrate, wherein each of the hexagonal mirror plates is supported by one or more structural members, there is a gap between adjacent hexagonal mirror plates and the structural members are not located in the gap.

In another general aspect, a spatial light modulator is described that includes a two-dimensional array of hexagonal mirror plates disposed in a honeycomb pattern over a substrate, wherein each of the hexagonal mirror plates is supported by one or more structural members, there is a gap between adjacent hexagonal mirror plates, the structural members are not located in the gap and the distance between a structural member of a mirror plate and the upper surface of the mirror plate is less than 1 micron.

In yet another aspect, a spatial light modulator is described having a two-dimensional array of hexagonal mirror plates disposed in a honeycomb pattern over a substrate, wherein each of the hexagonal mirror plates is supported by a structure, wherein the structure is located between two corners of the hexagonal mirror plate and the structure is at least partially under the hexagonal mirror plate.

In another general aspect, a spatial light modulator is described having a two-dimensional array of hexagonal mirror plates disposed in a honeycomb pattern over a substrate, wherein adjacent hexagonal mirror plates in the two-dimensional array are separated by gaps less than 2 micron.

In another general aspect, a spatial light modulator is described having a two-dimensional array of hexagonal mirror plates disposed in a honeycomb pattern over a substrate, wherein each of the hexagonal mirror plates is supported by one or more structural members, wherein at least one of the structural members is located in the vicinity of the middle of an edge of the hexagonal mirror plate and the structural member is at least partially under the hexagonal mirror plate.

Implementations of the system may include one or more of the following. The one or more structural members can each be supported by a support post in connection with the substrate. The support post can be hidden under the hexagonal mirror plate At least one of the hexagonal mirror plates can configured to tilt around the one or more structural members supporting the hexagonal mirror plate. At least one of the hexagonal mirror plates can include a cavity having an opening on the lower surface and at least one of the structural members associated with the hexagonal mirror plate extends into the cavity. At least one of the mirror plates does not include a hole in its upper surface. The spatial light modulator can further include a mechanical stop over the substrate, wherein the mechanical stop is configured to contact one of the hexagonal mirror plates to stop the movement of the hexagonal mirror plate when the hexagonal mirror plate tilts around the one or more structural members supporting the hexagonal mirror plate. Adjacent hexagonal mirror plates in the two-dimensional array can be separated by gaps less than 2 micron. Adjacent hexagonal mirror plates in the two-dimensional array can be separated by gaps less than 1 micron. Adjacent hexagonal mirror plates in the two-dimensional array can be separated by gaps less than 0.5 micron. The upper surfaces of the hexagonal mirror plates can occupy at least 85% of the area of the two-dimensional array. The upper surfaces of the hexagonal mirror plates can occupy at least 90% of the area of the two-dimensional array.

The upper surfaces of the hexagonal mirror plates can occupy at least 95% of the area of the two-dimensional array. The distance between a structural member and the upper surface of the associated hexagonal mirror plate can be less than 1 micron. The distance between a structural member and the upper surface of the associated hexagonal mirror plate can be less than 0.5 micron.

Implementations may include one or more of the following advantages. The disclosed methods and systems provide a micro-mirror based spatial light modulator that can produce bright and high contrast display images. The spatial light modulator can include an array of tiltable hexagonal mirrors that are distributed in honey-comb shaped cells. The disclosed hexagonal mirrors include reflective upper surfaces that have no holes, which in some instances may be an improvement over some of the conventional mirror designs that include holes in the mirror plates. Holes in the mirror plates are known to scatter light and reduce the contrast and sharpness of the display images. The elimination of holes in the disclosed hexagonal mirrors may therefore improve the contrast and sharpness in the display image as compared to conventional mirror based display systems.

The disclosed methods and systems provide an array of tiltable hexagonal mirrors with high fill-in ratios, which may more fully utilizes incident light and reduce light loss, producing brighter display images. Unlike some conventional mirror-based spatial light modulators that include flexure hinges exposed in the gaps between adjacent mirror plates, the disclosed hexagonal mirrors do not require structural members on the substrate between adjacent mirror plates. Several features of the structures of the hexagonal mirrors can enable small gaps between adjacent hexagonal mirrors and thus denser packing of the hexagonal mirrors. The hexagonal mirrors can include hinge components that extend into cavities having opening at the lower surfaces of the mirror plates. The hinge components can be completely hidden to an observer of the top of the mirror plates, because the hinge components are under the hexagonal mirror plates. The disclosed hexagonal mirror plate can tilt about a rotation axis defined by the one or more hinge components associated with the mirror plate. The positions of the hinge components can allow the rotation axis to be located in the mirror plate, which minimizes the lateral movement at the edges of the hexagonal mirror plate during the tilt movement of the hexagonal mirror. Moreover, the adjacent micro mirrors do not have to be spaced apart to leave room for any structures that are required in some conventional micro-mirror systems. These advantageous features may allow the disclosed hexagonal mirror plates to be closely disposed with small gaps between adjacent mirror plates while still providing enough clearance for the tilt movement of the adjacent hexagonal mirror plates.

Although the invention has been particularly shown and described with reference to multiple embodiments, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope of the invention.

DETAILED DESCRIPTION

FIG. 1is a top view of an array100that is compatible with a spatial light modulator. The array100includes a plurality of hexagonal mirrors110distributed in a honey-comb pattern. The array100is bounded by a boundary120, which can form a simple polygonal or circular shape, such as a rectangle, as shown, or a circle, hexagon, triangle, square, or other polygon. Adjacent hexagonal mirrors150-152are separated by gaps751and752(shown inFIG. 6). Each mirror plate and half the gap area between a mirror plate and its neighboring plates defines a cell. Inactive areas130can exist between the array100and the boundary120.

The upper surfaces of the hexagonal mirrors110are reflective. The reflective surfaces enable the hexagonal mirrors110to reflect light. The mirrors are tiltable, which controls where the reflected light is directed. The total active area for the array100is the sum of the reflective upper surface areas of all the hexagonal mirrors110in the array100. The inactive areas within the boundary120include the inactive areas130and gaps within the boundary. Although only a few dozen mirrors are shown, the array100can include hundreds to thousands of micro mirrors110along each dimension. For example, the array100can include 1024 micro mirrors110along one dimension and 1536 micro mirrors along the other dimension.

A “fill-in” ratio can be defined as the percentage of the active area within a cell in a mirror array. In the example illustrated inFIG. 1, the fill-in ratio is the sum of the total area of the reflective upper surfaces of all the hexagonal mirrors110divided by the total areas for all the cells in the array100. In other words, the fill-in ratio is approximately the ratio of the total reflective area in the array100divided by the difference between the area within the rectangular boundary120and the inactive areas130. The fill-in ratio can indicate the reflective efficiency for an array of micro mirrors. A mirror array having large gaps between adjacent mirror plates loses more incident light in the gaps than a mirror array having smaller gaps between adjacent mirrors. The former therefore has a lower fill-in ratio than the latter.

Referring toFIGS. 2-5, a single hexagonal mirror150includes a hexagonal mirror plate200. In some embodiments, the mirror plate200includes a reflective upper layer201, a middle layer202, and a lower layer203. The reflective upper layer201can be made of a metallic material such as aluminum, gold, or one of their alloys. The middle layer202provides mechanical strength to the mirror plate. The middle layer202also includes a portion of a cavity205. The middle layer202can include silicon, polysilicon, amorphous silicon, aluminum, titanium, tantalum, tungsten, molybdenum, and silicides or alloys of aluminum, titanium, tantalum, tungsten, or molybdenum. The lower layer203can be made of an electrically conductive material such as aluminum, doped silicon, polysilicon, amorphous silicon, aluminum-silicon alloys, titanium, tantalum, tungsten, molybdenum, and silicides or alloys of aluminum, titanium, tantalum, tungsten or molybdenum. The lower layer203includes a portion of the cavity205that has an opening at the lower surface of the lower layer203.

The hexagonal mirror150also includes a hinge component210that extends into the cavity205. The hinge component210is connected with the lower layer203through a connection portion and with an upper portion215of a hinge support post217. The hinge component210, upper portion215and the hinge support post217are under the hexagonal mirror plate200and can be hidden from above the hexagonal mirror plate200. That is, the hinge component210, upper portion215and hinge support post217do not extend beyond the footprint of the hexagonal mirror150. The hinge component210and the hinge support post215are located in the vicinity of the middle of an edge of the hexagonal mirror plate200, between two corners of the mirror150.

The upper portion215of the hinge support post217is connected with an electrode220via a lower portion216of the hinge support post217. The hinge component210, the upper portion215of the hinge support post217, and the lower portion216of the hinge support post217are made of electrically conductive materials, which allow the electric potential of the lower layer203to be controlled by a voltage signal applied to the electrode220. The electrically conductive materials can include silicon, polysilicon, amorphous silicon, aluminum, titanium, tantalum, tungsten, molybdenum, and silicides or alloys of aluminum, titanium, tantalum, tungsten, or molybdenum. One or more step electrodes230aand230bare also disposed over the substrate (not shown for illustration clarity) under the mirror plate200. Each of the step electrodes230aand230bincludes a lower layer and an upper layer. Each of the step electrodes230aand230bcan receive voltage signals to establish electrostatic potential differences between the lower layer203and the step electrodes230aor230b. As a result, an electrostatic force can be produced over the mirror plate200. The voltage signals applied to the electrode220and the step electrodes230sand230bcan be designed to produce an electrostatic torque to tilt the mirror plate200. The typical diagonal dimension for the hexagonal mirror plate200is in the range of 1 to 100 microns.

One or more landing stops260can be provided over the substrate. The tilt movement of the mirror plate200can be stopped when the mirror plate200comes to contact with one of the landing stops260. The landing stops260can be made of electrically conductive materials. The electric potential of the landing stops260can be controlled by electrodes261. The electrodes261can be connected with the electrode220such that landing stops260are at the same voltage as the lower layer203of the mirror plate200. The equal potential between the lower layer203and the landing stops260assures that the voltage of the lower plate203is maintained when it comes to contact with one of the landing stops260.

The lower layer203can further include one or more cavities each having an opening in its lower surface. A deflectable cantilever265in connection with the lower layer203extends into the cavity205. The tilt movement of the mirror plate200can be stopped when a landing stop260contacts the corresponding cantilever265on the mirror plate200. The cantilever is deflectable and slightly bent by the pressure applied by the landing stop260. The elastic energy stored in the distorted cantilever265can be released to cause the mirror plate200to snap back during the separation of the mirror plate200from the landing stop260. The release of the elastic distortion energy can help overcome stiction between the landing stop260and the mirror plate200. Details about the structures and the fabrication of the cantilever in the mirror plate are disclosed in the commonly assigned U.S. patent application Ser. No. 11/366,195, entitled “Spatial Light Modulator Having a Cantilever Anti-Stiction Mechanism”, filed Mar. 1, 2006.

The lateral dimensions of the mirror plate200extend beyond the lateral dimensions of the hinge component210, and the upper portion215and the lower portion216of the hinge support post217. In other words, the hinge component210, the upper portion215of a hinge support post217, and the lower portion216of a hinge support post217are completely hidden under the mirror plate200when viewed from above the mirror plate200. The step electrodes230a,230band the landing stop260can also be hidden under the mirror plate200. No support structures are needed outside the lateral dimensions of the mirror plate200(i.e., in the gaps751and752) over the substrate. This is one reason that the adjacent mirror pates150-152can be closely positioned and separated by only small gaps751and752. The above disclosed mirror design is also an improvement over some conventional micro mirror systems that include structures on the substrate between adjacent mirrors. These conventional mirror systems require much larger gaps between adjacent mirrors to accommodate these structures.

Details about fabricating the tiltable micro mirrors are disclosed in the commonly assigned U.S. patent application Ser. No. 10/974,468, tilted “High contrast spatial light modulator and method”, filed Oct. 27, 2004, and the commonly assigned provisional U.S. patent application Ser. No. 60/750,506, tilted “System and Method for Making a Micro-Mirror Array Device”, filed Dec. 14, 2005.

Referring toFIG. 6, the mirror plates of the hexagonal mirrors150-152are separated by gaps751and752. Referring toFIG. 7, the upper portions215of the two hinge support posts217support two hinge components210(not visible inFIG. 6) that extend into the cavities205in the lower layer203in the hexagonal mirror plate200. The two hinge components210can define a rotational axis about which the hexagonal mirror plate200can tilt. An advantageous feature of the disclosed hexagonal mirror is that the hinge components210extend into the cavity205in the lower layer of the mirror plate200. Referring back toFIG. 7, the rotational axis for the tilt movement of the hexagonal mirror plate200is therefore within the lower layer of the mirror plate200. As a result, the edges of the mirror plates730,731,732in the hexagonal mirrors150-152experience mostly vertical displacement during the tilting of the mirror plates730,731,732. The mirror plates730,731,732can therefore be closely spaced without interfering with one another's tilting. In some embodiments, the gaps751and752can be smaller than 2 microns, such as less than 1 micron or less than 0.5 micron.

Due to the above described advantageous features of the hexagonal mirrors150-152, the gaps751and752can be kept very small. In some implementations, the fill-in ratio of the array100hexagonal mirrors110can be over 85%, 90%, 93% or 95%.

Another advantageous feature of the disclosed hexagonal mirror is that the upper layer201does not include a hole in its reflective upper surface. Holes in the mirror plates in some conventional micro-mirror based display systems are known to scatter light, and reduce the contrast and sharpness of the display images. The elimination of holes in the disclosed hexagonal mirrors can provide improved contrast and sharpness in the display image as compared to these conventional micro-mirror based display systems.

Still another advantageous feature of the disclosed array of hexagonal mirrors is that the gaps between the hexagonal mirrors are not distributed in a set of periodic straight lines across the whole array as in an array of rectangular mirrors. Moreover, the corners of a hexagonal mirror are more obtuse than the right angles in a rectangular mirror. These advantageous features allow the disclosed array of hexagonal mirrors to produce less stray light caused by unwanted diffractions and scatterings.

Although multiple embodiments have been shown and described, it will be understood by persons skilled in the relevant art that various changes in form and details can be made therein without departing from the spirit and scope. For example, the exact design of the electrodes for producing electrostatic forces on the hexagonal mirror plates can vary. Furthermore, the substrates compatible with the disclosed system can include electronic circuits for controlling the hexagonal mirror plates. Moreover, the boundaries of the array of the hexagonal mirrors can take many shapes such as rectangular, hexagonal, or round.

The content of all patents and publications described herein are incorporated by reference for all purposes.