# Patent

## Title
Spacers for maintaining display apparatus alignment

## Abstract

The invention relates to methods and apparatus for forming a display apparatus. According to one aspect of the invention, the display apparatus includes a first substrate having an aperture layer formed thereon, a light guide for guiding light towards the aperture layer, a plurality of MEMS light modulators for modulating light passing through the aperture layer from the light guide, and a spacer substantially surrounding the light guide for keeping the light guide and the first substrate a predetermined distance apart from one another, thereby forming a gap between the first substrate and the light guide. Alternatively or in addition, the first substrate may have a control matrix formed thereon.

## Background
FIELD OF THE INVENTION
In general, the invention relates to the field of imaging displays, in particular, the invention relates to packaging of displays.
BACKGROUND OF THE INVENTION
Displays built from mechanical light modulators are an attractive alternative to displays based on liquid crystal technology. Mechanical light modulators are fast enough to display video content with good viewing angles and with a wide range of color and grey scale. Mechanical light modulators have been successful in projection display applications. Direct-view displays using mechanical light modulators have not yet demonstrated sufficiently attractive combinations of brightness and low power. There is a need in the art for fast, bright, low-powered mechanically actuated direct-view displays. Specifically there is a need for direct-view displays that can be driven at high speeds and at low voltages for improved image quality and reduced power consumption.
Direct view displays built with MEMS-based light modulators are often packaged together with a lamp or lamps and a light guide. There is a need in the art to provide a packaging technology that is rugged, that economizes on space, and that provides for correct mechanical alignment between various components including light guide, lamp or lamps, electrical interconnections, and the display assembly.
SUMMARY OF THE INVENTION
The invention relates to display apparatuses having an array of pixels, a substrate, and a control matrix formed on the substrate. The array may include light modulators that each correspond to pixels in the array. The substrate may be transparent. The control matrix may have at least one switch or cascode corresponding to each pixel in the array.
According to one aspect of the invention, a display apparatus includes a first substrate having an aperture layer formed thereon, a light guide for guiding light towards the aperture layer, a plurality of MEMS light modulators for modulating light passing through the aperture layer from the light guide, and a spacer substantially surrounding a periphery of the light guide for keeping the light guide and the first substrate a predetermined distance apart from one another, thereby forming a gap between the first substrate and the light guide. The aperture layer may include a reflective aperture layer.
In one embodiment, the spacer includes a structural feature having a geometrical shape selected to maintain alignment between different components of the display apparatus, such as between the light guide and at least one of the first substrate, a lamp for providing light to the light guide, an electrical connection for controlling a MEMS light modulator of the plurality of MEMS light modulators, and a reflective layer for reflecting light towards the light guide. In another embodiment, the spacer includes a structural feature having a geometrical shape selected to restrict translational motion of at least one of the light guide and the first substrate. A structural feature may include a shelf on which one of the light guide and the first substrate rests. An adhesive may be disposed on the structural feature for adhering to at least one of the light guide and the first substrate.
The spacer may include a reflective surface for reflecting light into the light guide. The spacer may include a rigid material, such as polycarbonate, polyethylene, polypropylene, polyacrylate, a metal, or a metal and plastic composite. The plurality of MEMS light modulators may include shutter-based light modulators or electrowetting light modulators and may be formed on the first substrate or on a second substrate.
According to another aspect of the invention, a display apparatus includes a first substrate having a control matrix formed thereon, a light guide for guiding light towards the control matrix, a plurality of MEMS light modulators for modulating light from the light guide, and a spacer substantially surrounding a periphery of the light guide for keeping the light guide and the first substrate a predetermined distance apart from one another, thereby forming a gap between the first substrate and the light guide.



BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing discussion will be understood more readily from the following detailed description of the invention with reference to the following drawings:
FIG. 1A is an isometric view of display apparatus, according to an illustrative embodiment of the invention;
FIG. 1B is a block diagram of the display apparatus of FIG. 1A, according to an illustrative embodiment of the invention;
FIG. 2A is a perspective view of an illustrative shutter-based light modulator suitable for incorporation into the MEMS-based display of FIG. 1A, according to an illustrative embodiment of the invention;
FIG. 2B is a cross-sectional view of a rollershade-based light modulator suitable for incorporation into the MEMS-based display of FIG. 1A, according to an illustrative embodiment of the invention;
FIG. 2C is a cross sectional view of a light-tap-based light modulator suitable for incorporation into an alternative embodiment of the MEMS-based display of FIG. 1A, according to an illustrative embodiment of the invention;
FIG. 2D is a cross sectional view of an electrowetting-based light modulator suitable for incorporation into an alternative embodiment of the MEMS-based display of FIG. 1A, according to an illustrative embodiment of the invention;
FIG. 3A is a schematic diagram of a control matrix suitable for controlling the light modulators incorporated into the MEMS-based display of FIG. 1A, according to an illustrative embodiment of the invention;
FIG. 3B is a perspective view of an array of shutter-based light modulators connected to the control matrix of FIG. 3A, according to an illustrative embodiment of the invention;
FIGS. 4A and 4B are plan views of a dual-actuated shutter assembly in the open and closed states respectively, according to an illustrative embodiment of the invention.
FIG. 5 is a cross-sectional view of a shutter-based display apparatus, according to an illustrative embodiment of the invention;
FIG. 6 is a cross-sectional view of a liquid crystal display apparatus, according to an illustrative embodiment of the invention;
FIG. 7A is a cross-sectional view of a display module, according to an illustrative embodiment of the invention;
FIG. 7B is an isometric and exploded view of a display module, according to an illustrative embodiment of the invention;
FIG. 8 is a cross-sectional view of a display module, according to an illustrative embodiment of the invention; and
FIG. 9 is a cross-sectional view of a display module, according to an illustrative embodiment of the invention.



DESCRIPTION OF CERTAIN ILLUSTRATIVE EMBODIMENTS
To provide an overall understanding of the invention, certain illustrative embodiments will now be described, including apparatus and methods for displaying images. However, it will be understood by one of ordinary skill in the art that the systems and methods described herein may be adapted and modified as is appropriate for the application being addressed and that the systems and methods described herein may be employed in other suitable applications, and that such other additions and modifications will not depart from the scope hereof.
FIG. 1A is a schematic diagram of a direct-view MEMS-based display apparatus 100, according to an illustrative embodiment of the invention. The display apparatus 100 includes a plurality of light modulators 102a-102d (generally “light modulators 102”) arranged in rows and columns. In the display apparatus 100, light modulators 102a and 102d are in the open state, allowing light to pass. Light modulators 102b and 102c are in the closed state, obstructing the passage of light. By selectively setting the states of the light modulators 102a-102d, the display apparatus 100 can be utilized to form an image 104 for a backlit display, if illuminated by a lamp or lamps 105. In another implementation, the apparatus 100 may form an image by reflection of ambient light originating from the front of the apparatus. In another implementation, the apparatus 100 may form an image by reflection of light from a lamp or lamps positioned in the front of the display, i.e. by use of a frontlight. In one of the closed or open states, the light modulators 102 interfere with light in an optical path by, for example, and without limitation, blocking, reflecting, absorbing, filtering, polarizing, diffracting, or otherwise altering a property or path of the light.
In the display apparatus 100, each light modulator 102 corresponds to a pixel 106 in the image 104. In other implementations, the display apparatus 100 may utilize a plurality of light modulators to form a pixel 106 in the image 104. For example, the display apparatus 100 may include three color-specific light modulators 102. By selectively opening one or more of the color-specific light modulators 102 corresponding to a particular pixel 106, the display apparatus 100 can generate a color pixel 106 in the image 104. In another example, the display apparatus 100 includes two or more light modulators 102 per pixel 106 to provide grayscale in an image 104. With respect to an image, a “pixel” corresponds to the smallest picture element defined by the resolution of the image. With respect to structural components of the display apparatus 100, the term “pixel” refers to the combined mechanical and electrical components utilized to modulate the light that forms a single pixel of the image.
Display apparatus 100 is a direct-view display in that it does not require imaging optics. The user sees an image by looking directly at the display apparatus 100. In alternate embodiments the display apparatus 100 is incorporated into a projection display. In such embodiments, the display forms an image by projecting light onto a screen or onto a wall. In projection applications the display apparatus 100 is substantially smaller than the projected image 104.
Direct-view displays may operate in either a transmissive or reflective mode. In a transmissive display, the light modulators filter or selectively block light which originates from a lamp or lamps positioned behind the display. The light from the lamps is optionally injected into a light guide or “backlight”. Transmissive direct-view display embodiments are often built onto transparent or glass substrates to facilitate a sandwich assembly arrangement where one substrate, containing the light modulators, is positioned directly on top of the backlight. In some transmissive display embodiments, a color-specific light modulator is created by associating a color filter material with each modulator 102. In other transmissive display embodiments colors can be generated, as described below, using a field sequential color method by alternating illumination of lamps with different primary colors.
Each light modulator 102 includes a shutter 108 and an aperture 109. To illuminate a pixel 106 in the image 104, the shutter 108 is positioned such that it allows light to pass through the aperture 109 towards a viewer. To keep a pixel 106 unlit, the shutter 108 is positioned such that it obstructs the passage of light through the aperture 109. The aperture 109 is defined by an opening patterned through a reflective or light-absorbing material.
The display apparatus also includes a control matrix connected to the substrate and to the light modulators for controlling the movement of the shutters. The control matrix includes a series of electrical interconnects (e.g., interconnects 110, 112, and 114), including at least one write-enable interconnect 110 (also referred to as a “scan-line interconnect”) per row of pixels, one data interconnect 112 for each column of pixels, and one common interconnect 114 providing a common voltage to all pixels, or at least to pixels from both multiple columns and multiples rows in the display apparatus 100. In response to the application of an appropriate voltage (the “write-enabling voltage, Vwe”), the write-enable interconnect 110 for a given row of pixels prepares the pixels in the row to accept new shutter movement instructions. The data interconnects 112 communicate the new movement instructions in the form of data voltage pulses. The data voltage pulses applied to the data interconnects 112, in some implementations, directly contribute to an electrostatic movement of the shutters. In other implementations, the data voltage pulses control switches, e.g., transistors or other non-linear circuit elements that control the application of separate actuation voltages, which are typically higher in magnitude than the data voltages, to the light modulators 102. The application of these actuation voltages then results in the electrostatic driven movement of the shutters 108.
FIG. 1B is a block diagram 150 of the display apparatus 100. Referring to FIGS. 1A and 1B, in addition to the elements of the display apparatus 100 described above, as depicted in the block diagram 150, the display apparatus 100 includes a plurality of scan drivers 152 (also referred to as “write enabling voltage sources”) and a plurality of data drivers 154 (also referred to as “data voltage sources”). The scan drivers 152 apply write enabling voltages to scan-line interconnects 110. The data drivers 154 apply data voltages to the data interconnects 112. In some embodiments of the display apparatus, the data drivers 154 are configured to provide analog data voltages to the light modulators, especially where the gray scale of the image 104 is to be derived in analog fashion. In analog operation the light modulators 102 are designed such that when a range of intermediate voltages is applied through the data interconnects 112 there results a range of intermediate open states in the shutters 108 and therefore a range of intermediate illumination states or gray scales in the image 104.
In other cases the data drivers 154 are configured to apply only a reduced set of 2, 3, or 4 digital voltage levels to the control matrix. These voltage levels are designed to set, in digital fashion, either an open state or a closed state to each of the shutters 108.
The scan drivers 152 and the data drivers 154 are connected to digital controller circuit 156 (also referred to as the “controller 156”). The controller 156 includes an input processing module 158, which processes an incoming image signal 157 into a digital image format appropriate to the spatial addressing and the gray scale capabilities of the display 100. The pixel location and gray scale data of each image is stored in a frame buffer 159 so that the data can be fed out as needed to the data drivers 154. The data is sent to the data drivers 154 in mostly serial fashion, organized in predetermined sequences grouped by rows and by image frames. The data drivers 154 can include series to parallel data converters, level shifting, and for some applications digital to analog voltage converters.
The display 100 apparatus optionally includes a set of common drivers 153, also referred to as common voltage sources. In some embodiments the common drivers 153 provide a DC common potential to all light modulators within the array of light modulators 103, for instance by supplying voltage to a series of common interconnects 114. In other embodiments the common drivers 153, following commands from the controller 156, issue voltage pulses or signals to the array of light modulators 103, for instance global actuation pulses which are capable of driving and/or initiating simultaneous actuation of all light modulators in multiple rows and columns of the array 103.
All of the drivers (e.g., scan drivers 152, data drivers 154, and common drivers 153) for different display functions are time-synchronized by a timing-control module 160 in the controller 156. Timing commands from the module 160 coordinate the illumination of red, green and blue and white lamps (162, 164, 166, and 167 respectively) via lamp drivers 168, the write-enabling and sequencing of specific rows within the array of pixels 103, the output of voltages from the data drivers 154, and the output of voltages that provide for light modulator actuation.
The controller 156 determines the sequencing or addressing scheme by which each of the shutters 108 in the array 103 can be re-set to the illumination levels appropriate to a new image 104. Details of suitable addressing, image formation, and gray scale techniques can be found in U.S. patent application Ser. Nos. 11/326,696 and 11/643,042, incorporated herein by reference. New images 104 can be set at periodic intervals. For instance, for video displays, the color images 104 or frames of video are refreshed at frequencies ranging from 10 to 300 Hertz. In some embodiments the setting of an image frame to the array 103 is synchronized with the illumination of the lamps 162, 164, and 166 such that alternate image frames are illuminated with an alternating series of colors, such as red, green, and blue. The image frames for each respective color is referred to as a color sub-frame. In this method, referred to as the field sequential color method, if the color sub-frames are alternated at frequencies in excess of 20 Hz, the human brain will average the alternating frame images into the perception of an image having a broad and continuous range of colors. In alternate implementations, four or more lamps with primary colors can be employed in display apparatus 100, employing primaries other than red, green, and blue.
In some implementations, where the display apparatus 100 is designed for the digital switching of shutters 108 between open and closed states, the controller 156 determines the addressing sequence and/or the time intervals between image frames to produce images 104 with appropriate gray scale. The process of generating varying levels of grayscale by controlling the amount of time a shutter 108 is open in a particular frame is referred to as time division gray scale. In one embodiment of time division gray scale, the controller 156 determines the time period or the fraction of time within each frame that a shutter 108 is allowed to remain in the open state, according to the illumination level or gray scale desired of that pixel. In other implementations, for each image frame, the controller 156 sets a plurality of sub-frame images in multiple rows and columns of the array 103, and the controller alters the duration over which each sub-frame image is illuminated in proportion to a gray scale value or significance value employed within a coded word for gray scale. For instance, the illumination times for a series of sub-frame images can be varied in proportion to the binary coding series 1, 2, 4, 8 . . . The shutters 108 for each pixel in the array 103 are then set to either the open or closed state within a sub-frame image according to the value at a corresponding position within the pixel's binary coded word for gray level.
In other implementations, the controller alters the intensity of light from the lamps 162, 164, and 166 in proportion to the gray scale value desired for a particular sub-frame image. A number of hybrid techniques are also available for forming colors and gray scale from an array of shutters 108. For instance, the time division techniques described above can be combined with the use of multiple shutters 108 per pixel, or the gray scale value for a particular sub-frame image can be established through a combination of both sub-frame timing and lamp intensity. Details of these and other embodiments can be found in U.S. patent application Ser. No. 11/643,042, referenced above.
In some implementations the data for an image state 104 is loaded by the controller 156 to the modulator array 103 by a sequential addressing of individual rows, also referred to as scan lines. For each row or scan line in the sequence, the scan driver 152 applies a write-enable voltage to the write enable interconnect 110 for that row of the array 103, and subsequently the data driver 154 supplies data voltages, corresponding to desired shutter states, for each column in the selected row. This process repeats until data has been loaded for all rows in the array. In some implementations the sequence of selected rows for data loading is linear, proceeding from top to bottom in the array. In other implementations the sequence of selected rows is pseudo-randomized, in order to minimize visual artifacts. And in other implementations the sequencing is organized by blocks, where, for a block, the data for only a certain fraction of the image state 104 is loaded to the array, for instance by addressing only every 5th row of the array in sequence.
In some implementations, the process for loading image data to the array 103 is separated in time from the process of actuating the shutters 108. In these implementations, the modulator array 103 may include data memory elements for each pixel in the array 103 and the control matrix may include a global actuation interconnect for carrying trigger signals, from common driver 153, to initiate simultaneous actuation of shutters 108 according to data stored in the memory elements. Various addressing sequences, many of which are described in U.S. patent application Ser. No. 11/643,042, can be coordinated by means of the timing control module 160.
In alternative embodiments, the array of pixels 103 and the control matrix that controls the pixels may be arranged in configurations other than rectangular rows and columns. For example, the pixels can be arranged in hexagonal arrays or curvilinear rows and columns. In general, as used herein, the term scan-line shall refer to any plurality of pixels that share a write-enabling interconnect.
The display 100 is comprised of a plurality of functional blocks including the timing control module 160, the frame buffer 159, scan drivers 152, data drivers 154, and drivers 153 and 168. Each block can be understood to represent either a distinguishable hardware circuit and/or a module of executable code. In some implementations the functional blocks are provided as distinct chips or circuits connected together by means of circuit boards and/or cables. Alternately, many of these circuits can be fabricated along with the pixel array 103 on the same substrate of glass or plastic. In other implementations, multiple circuits, drivers, processors, and/or control functions from block diagram 150 may be integrated together within a single silicon chip, which is then bonded directly to the transparent substrate holding pixel array 103.
The controller 156 includes a programming link 180 by which the addressing, color, and/or gray scale algorithms, which are implemented within controller 156, can be altered according to the needs of particular applications. In some embodiments, the programming link 180 conveys information from environmental sensors, such as ambient light or temperature sensors, so that the controller 156 can adjust imaging modes or backlight power in correspondence with environmental conditions. The controller 156 also comprises a power supply input 182 which provides the power needed for lamps as well as light modulator actuation. Where necessary, the drivers 152 153, 154, and/or 168 may include or be associated with DC-DC converters for transforming an input voltage at 182 into various voltages sufficient for the actuation of shutters 108 or illumination of the lamps, such as lamps 162, 164, 166, and 167.
MEMS Light Modulators
FIG. 2A is a perspective view of an illustrative shutter-based light modulator 200 suitable for incorporation into the MEMS-based display apparatus 100 of FIG. 1A, according to an illustrative embodiment of the invention. The shutter-based light modulator 200 (also referred to as shutter assembly 200) includes a shutter 202 coupled to an actuator 204. The actuator 204 is formed from two separate compliant electrode beam actuators 205 (the “actuators 205”), as described in U.S. patent application Ser. No. 11/251,035, filed on Oct. 14, 2005. The shutter 202 couples on one side to the actuators 205. The actuators 205 move the shutter 202 transversely over a surface 203 in a plane of motion which is substantially parallel to the surface 203. The opposite side of the shutter 202 couples to a spring 207 which provides a restoring force opposing the forces exerted by the actuator 204.
Each actuator 205 includes a compliant load beam 206 connecting the shutter 202 to a load anchor 208. The load anchors 208 along with the compliant load beams 206 serve as mechanical supports, keeping the shutter 202 suspended proximate to the surface 203. The load anchors 208 physically connect the compliant load beams 206 and the shutter 202 to the surface 203 and electrically connect the load beams 206 to a bias voltage, in some instances, ground.
Each actuator 205 also includes a compliant drive beam 216 positioned adjacent to each load beam 206. The drive beams 216 couple at one end to a drive beam anchor 218 shared between the drive beams 216. The other end of each drive beam 216 is free to move. Each drive beam 216 is curved such that it is closest to the load beam 206 near the free end of the drive beam 216 and the anchored end of the load beam 206.
The surface 203 includes one or more apertures 211 for admitting the passage of light. If the shutter assembly 200 is formed on an opaque substrate, made for example from silicon, then the surface 203 is a surface of the substrate, and the apertures 211 are formed by etching an array of holes through the substrate. If the shutter assembly 200 is formed on a transparent substrate, made for example of glass or plastic, then the surface 203 is a surface of a light blocking layer deposited on the substrate, and the apertures are formed by etching the surface 203 into an array of holes 211. The apertures 211 can be generally circular, elliptical, polygonal, serpentine, or irregular in shape.
In operation, a display apparatus incorporating the light modulator 200 applies an electric potential to the drive beams 216 via the drive beam anchor 218. A second electric potential may be applied to the load beams 206. The resulting potential difference between the drive beams 216 and the load beams 206 pulls the free ends of the drive beams 216 towards the anchored ends of the load beams 206, and pulls the shutter ends of the load beams 206 toward the anchored ends of the drive beams 216, thereby driving the shutter 202 transversely towards the drive anchor 218. The compliant members 206 act as springs, such that when the voltage across the beams 206 and 216 is removed, the load beams 206 push the shutter 202 back into its initial position, releasing the stress stored in the load beams 206.
The shutter assembly 200, also referred to as an elastic shutter assembly, incorporates a passive restoring force, such as a spring, for returning a shutter to its rest or relaxed position after voltages have been removed. A number of elastic restore mechanisms and various electrostatic couplings can be designed into or in conjunction with electrostatic actuators, the compliant beams illustrated in shutter assembly 200 being just one example. Other examples are described in U.S. patent applications Ser. Nos. 11/251,035 and 11/326,696, incorporated herein by reference. For instance, a highly non-linear voltage-displacement response can be provided which favors an abrupt transition between “open” vs “closed” states of operation, and which, in many cases, provides a bi-stable or hysteretic operating characteristic for the shutter assembly. Other electrostatic actuators can be designed with more incremental voltage-displacement responses and with considerably reduced hysteresis, as may be preferred for analog gray scale operation.
The actuator 205 within the elastic shutter assembly is said to operate between a closed or actuated position and a relaxed position. The designer, however, can choose to place apertures 211 such that shutter assembly 200 is in either the “open” state, i.e. passing light, or in the “closed” state, i.e. blocking light, whenever actuator 205 is in its relaxed position. For illustrative purposes, it is assumed below that elastic shutter assemblies described herein are designed to be open in their relaxed state.
In many cases it is preferable to provide a dual set of “open” and “closed” actuators as part of a shutter assembly so that the control electronics are capable of electrostatically driving the shutters into each of the open and closed states.
Display apparatus 100, in alternative embodiments, includes light modulators other than transverse shutter-based light modulators, such as the shutter assembly 200 described above. For example, FIG. 2B is a cross-sectional view of a rolling actuator shutter-based light modulator 220 suitable for incorporation into an alternative embodiment of the MEMS-based display apparatus 100 of FIG. 1A, according to an illustrative embodiment of the invention. As described further in U.S. Pat. No. 5,233,459, entitled “Electric Display Device,” and U.S. Pat. No. 5,784,189, entitled “Spatial Light Modulator,” the entireties of which are incorporated herein by reference, a rolling actuator-based light modulator includes a moveable electrode disposed opposite a fixed electrode and biased to move in a preferred direction to produce a shutter upon application of an electric field. In one embodiment, the light modulator 220 includes a planar electrode 226 disposed between a substrate 228 and an insulating layer 224 and a moveable electrode 222 having a fixed end 230 attached to the insulating layer 224. In the absence of any applied voltage, a moveable end 232 of the moveable electrode 222 is free to roll towards the fixed end 230 to produce a rolled state. Application of a voltage between the electrodes 222 and 226 causes the moveable electrode 222 to unroll and lie flat against the insulating layer 224, whereby it acts as a shutter that blocks light traveling through the substrate 228. The moveable electrode 222 returns to the rolled state by means of an elastic restoring force after the voltage is removed. The bias towards a rolled state may be achieved by manufacturing the moveable electrode 222 to include an anisotropic stress state.
FIG. 2C is a cross-sectional view of an illustrative non shutter-based MEMS light modulator 250. The light tap modulator 250 is suitable for incorporation into an alternative embodiment of the MEMS-based display apparatus 100 of FIG. 1A, according to an illustrative embodiment of the invention. As described further in U.S. Pat. No. 5,771,321, entitled “Micromechanical Optical Switch and Flat Panel Display,” the entirety of which is incorporated herein by reference, a light tap works according to a principle of frustrated total internal reflection. That is, light 252 is introduced into a light guide 254, in which, without interference, light 252 is for the most part unable to escape the light guide 254 through its front or rear surfaces due to total internal reflection. The light tap 250 includes a tap element 256 that has a sufficiently high index of refraction that, in response to the tap element 256 contacting the light guide 254, light 252 impinging on the surface of the light guide 254 adjacent the tap element 256 escapes the light guide 254 through the tap element 256 towards a viewer, thereby contributing to the formation of an image.
In one embodiment, the tap element 256 is formed as part of beam 258 of flexible, transparent material. Electrodes 260 coat portions of one side of the beam 258. Opposing electrodes 260 are disposed on the light guide 254. By applying a voltage across the electrodes 260, the position of the tap element 256 relative to the light guide 254 can be controlled to selectively extract light 252 from the light guide 254.
FIG. 2D is a cross sectional view of a second illustrative non-shutter-based MEMS light modulator suitable for inclusion in various embodiments of the invention. Specifically, FIG. 2D is a cross sectional view of an electrowetting-based light modulation array 270. The electrowetting-based light modulator array 270 is suitable for incorporation into an alternative embodiment of the MEMS-based display apparatus 100 of FIG. 1A, according to an illustrative embodiment of the invention. The light modulation array 270 includes a plurality of electrowetting-based light modulation cells 272a-272d (generally “cells 272”) formed on an optical cavity 274. The light modulation array 270 also includes a set of color filters 276 corresponding to the cells 272.
Each cell 272 includes a layer of water (or other transparent conductive or polar fluid) 278, a layer of light absorbing oil 280, a transparent electrode 282 (made, for example, from indium-tin oxide) and an insulating layer 284 positioned between the layer of light absorbing oil 280 and the transparent electrode 282. Illustrative implementations of such cells are described further in U.S. Patent Application Publication No. 2005/0104804, published May 19, 2005 and entitled “Display Device.” In the embodiment described herein, the electrode takes up a portion of a rear surface of a cell 272.
The light modulation array 270 also includes a light guide 288 and one or more light sources 292 which inject light 294 into the light guide 288. A series of light redirectors 291 are formed on the rear surface of the light guide, proximate a front facing reflective layer 290. The light redirectors 291 may be either diffuse or specular reflectors. The modulation array 270 includes an aperture layer 286 which is patterned into a series of apertures, one aperture for each of the cells 272, to allow light rays 294 to pass through the cells 272 and toward the viewer.
In one embodiment the aperture layer 286 is comprised of a light absorbing material to block the passage of light except through the patterned apertures. In another embodiment the aperture layer 286 is comprised of a reflective material which reflects light not passing through the surface apertures back towards the rear of the light guide 288. After returning to the light guide, the reflected light can be further recycled by the front facing reflective layer 290.
In operation, application of a voltage to the electrode 282 of a cell causes the light absorbing oil 280 in the cell to move into or collect in one portion of the cell 272. As a result, the light absorbing oil 280 no longer obstructs the passage of light through the aperture formed in the reflective aperture layer 286 (see, for example, cells 272b and 272c). Light escaping the light guide 288 at the aperture is then able to escape through the cell and through a corresponding color (for example, red, green, or blue) filter in the set of color filters 276 to form a color pixel in an image. When the electrode 282 is grounded, the light absorbing oil 280 returns to its previous position (as in cell 272a) and covers the aperture in the reflective aperture layer 286, absorbing any light 294 attempting to pass through it.
The roller-based light modulator 220, light tap 250, and electrowetting-based light modulation array 270 are not the only examples of MEMS light modulators suitable for inclusion in various embodiments of the invention. It will be understood that other MEMS light modulators can exist and can be usefully incorporated into the invention.
U.S. patent applications Ser. Nos. 11/251,035 and 11/326,696 have described a variety of methods by which an array of shutters can be controlled via a control matrix to produce images, in many cases moving images, with appropriate gray scale. In some cases, control is accomplished by means of a passive matrix array of row and column interconnects connected to driver circuits on the periphery of the display. In other cases it is appropriate to include switching and/or data storage elements within each pixel of the array (the so-called active matrix) to improve either the speed, the gray scale and/or the power dissipation performance of the display.
FIG. 3A is a schematic diagram of a control matrix 300 suitable for controlling the light modulators incorporated into the MEMS-based display apparatus 100 of FIG. 1A, according to an illustrative embodiment of the invention. FIG. 3B is a perspective view of an array 320 of shutter-based light modulators connected to the control matrix 300 of FIG. 3A, according to an illustrative embodiment of the invention. The control matrix 300 may address an array of pixels 320 (the “array 320”). Each pixel 301 includes an elastic shutter assembly 302, such as the shutter assembly 200 of FIG. 2A, controlled by an actuator 303. Each pixel also includes an aperture layer 322 that includes apertures 324. Further electrical and mechanical descriptions of shutter assemblies such as shutter assembly 302, and variations thereon, can be found in U.S. patent applications Ser. Nos. 11/251,035 and 11/326,696. Descriptions of alternate control matrices can also be found in U.S. patent application Ser. No. 11/607,715.
The control matrix 300 is fabricated as a diffused or thin-film-deposited electrical circuit on the surface of a substrate 304 on which the shutter assemblies 302 are formed. The control matrix 300 includes a scan-line interconnect 306 for each row of pixels 301 in the control matrix 300 and a data-interconnect 308 for each column of pixels 301 in the control matrix 300. Each scan-line interconnect 306 electrically connects a write-enabling voltage source 307 to the pixels 301 in a corresponding row of pixels 301. Each data interconnect 308 electrically connects a data voltage source, (“Vd source”) 309 to the pixels 301 in a corresponding column of pixels 301. In control matrix 300, the data voltage Vd provides the majority of the energy necessary for actuation of the shutter assemblies 302. Thus, the data voltage source 309 also serves as an actuation voltage source.
Referring to FIGS. 3A and 3B, for each pixel 301 or for each shutter assembly 302 in the array of pixels 320, the control matrix 300 includes a transistor 310 and a capacitor 312. The gate of each transistor 310 is electrically connected to the scan-line interconnect 306 of the row in the array 320 in which the pixel 301 is located. The source of each transistor 310 is electrically connected to its corresponding data interconnect 308. The actuators 303 of each shutter assembly 302 include two electrodes. The drain of each transistor 310 is electrically connected in parallel to one electrode of the corresponding capacitor 312 and to one of the electrodes of the corresponding actuator 303. The other electrode of the capacitor 312 and the other electrode of the actuator 303 in shutter assembly 302 are connected to a common or ground potential. In alternate implementations, the transistors 310 can be replaced with semiconductor diodes and or metal-insulator-metal sandwich type switching elements.
In operation, to form an image, the control matrix 300 write-enables each row in the array 320 in a sequence by applying Vwe to each scan-line interconnect 306 in turn. For a write-enabled row, the application of Vwe to the gates of the transistors 310 of the pixels 301 in the row allows the flow of current through the data interconnects 308 through the transistors 310 to apply a potential to the actuator 303 of the shutter assembly 302. While the row is write-enabled, data voltages Vd are selectively applied to the data interconnects 308. In implementations providing analog gray scale, the data voltage applied to each data interconnect 308 is varied in relation to the desired brightness of the pixel 301 located at the intersection of the write-enabled scan-line interconnect 306 and the data interconnect 308. In implementations providing digital control schemes, the data voltage is selected to be either a relatively low magnitude voltage (i.e., a voltage near ground) or to meet or exceed Vat (the actuation threshold voltage). In response to the application of Vat to a data interconnect 308, the actuator 303 in the corresponding shutter assembly 302 actuates, opening the shutter in that shutter assembly 302. The voltage applied to the data interconnect 308 remains stored in the capacitor 312 of the pixel 301 even after the control matrix 300 ceases to apply Vwe to a row. It is not necessary, therefore, to wait and hold the voltage Vwe on a row for times long enough for the shutter assembly 302 to actuate; such actuation can proceed after the write-enabling voltage has been removed from the row. The capacitors 312 also function as memory elements within the array 320, storing actuation instructions for periods as long as is necessary for the illumination of an image frame.
The pixels 301 as well as the control matrix 300 of the array 320 are formed on a substrate 304. The array includes an aperture layer 322, disposed on the substrate 304, which includes a set of apertures 324 for respective pixels 301 in the array 320. The apertures 324 are aligned with the shutter assemblies 302 in each pixel. In one implementation the substrate 304 is made of a transparent material, such as glass or plastic. In another implementation the substrate 304 is made of an opaque material, but in which holes are etched to form the apertures 324.
Components of shutter assemblies 302 are processed either at the same time as the control matrix 300 or in subsequent processing steps on the same substrate. The electrical components in control matrix 300 are fabricated using many thin film techniques in common with the manufacture of thin film transistor arrays for liquid crystal displays. Available techniques are described in Den Boer, Active Matrix Liquid Crystal Displays (Elsevier, Amsterdam, 2005), incorporated herein by reference. The shutter assemblies are fabricated using techniques similar to the art of micromachining or from the manufacture of micromechanical (i.e., MEMS) devices. Many applicable thin film MEMS techniques are described in Rai-Choudhury, ed., Handbook of Microlithography, Micromachining & Microfabrication (SPIE Optical Engineering Press, Bellingham, Wash. 1997), incorporated herein by reference. Fabrication techniques specific to MEMS light modulators formed on glass substrates can be found in U.S. patent application Ser. Nos. 11/361,785 and 11/731,628, incorporated herein by reference. For instance, as described in those applications, the shutter assembly 302 can be formed from thin films of amorphous silicon, deposited by a chemical vapor deposition process.
The shutter assembly 302 together with the actuator 303 can be made bi-stable. That is, the shutters can exist in at least two equilibrium positions (e.g. open or closed) with little or no power required to hold them in either position. More particularly, the shutter assembly 302 can be mechanically bi-stable. Once the shutter of the shutter assembly 302 is set in position, no electrical energy or holding voltage is required to maintain that position. The mechanical stresses on the physical elements of the shutter assembly 302 can hold the shutter in place.
The shutter assembly 302 together with the actuator 303 can also be made electrically bi-stable. In an electrically bi-stable shutter assembly, there exists a range of voltages below the actuation voltage of the shutter assembly, which if applied to a closed actuator (with the shutter being either open or closed), holds the actuator closed and the shutter in position, even if an opposing force is exerted on the shutter. The opposing force may be exerted by a spring such as spring 207 in shutter-based light modulator 200, or the opposing force may be exerted by an opposing actuator, such as an “open” or “closed” actuator.
The light modulator array 320 is depicted as having a single MEMS light modulator per pixel. Other embodiments are possible in which multiple MEMS light modulators are provided in each pixel, thereby providing the possibility of more than just binary “on” or “off” optical states in each pixel. Certain forms of coded area division gray scale are possible where multiple MEMS light modulators in the pixel are provided, and where apertures 324, which are associated with each of the light modulators, have unequal areas.
In other embodiments the roller-based light modulator 220, the light tap 250, or the electrowetting-based light modulation array 270, as well as other MEMS-based light modulators, can be substituted for the shutter assembly 302 within the light modulator array 320.
FIGS. 4A and 4B illustrate an alternative shutter-based light modulator (shutter assembly) 400 suitable for inclusion in various embodiments of the invention. The light modulator 400 is an example of a dual actuator shutter assembly, and is shown in FIG. 4A in an open state. FIG. 4B is a view of the dual actuator shutter assembly 400 in a closed state. Shutter assembly 400 is described in further detail in U.S. patent application Ser. No. 11/251,035, referenced above. In contrast to the shutter assembly 200, shutter assembly 400 includes actuators 402 and 404 on either side of a shutter 406. Each actuator 402 and 404 is independently controlled. A first actuator, a shutter-open actuator 402, serves to open the shutter 406. A second opposing actuator, the shutter-close actuator 404, serves to close the shutter 406. Both actuators 402 and 404 are compliant beam electrode actuators. The actuators 402 and 404 open and close the shutter 406 by driving the shutter 406 substantially in a plane parallel to an aperture layer 407 over which the shutter is suspended. The shutter 406 is suspended a short distance over the aperture layer 407 by anchors 408 attached to the actuators 402 and 404. The inclusion of supports attached to both ends of the shutter 406 along its axis of movement reduces out of plane motion of the shutter 406 and confines the motion substantially to a plane parallel to the substrate. By analogy to the control matrix 300 of FIG. 3A, a control matrix suitable for use with shutter assembly 400 might include one transistor and one capacitor for each of the opposing shutter-open and shutter-close actuators 402 and 404.
The shutter 406 includes two shutter apertures 412 through which light can pass. The aperture layer 407 includes a set of three apertures 409. In FIG. 4A, the shutter assembly 400 is in the open state and, as such, the shutter-open actuator 402 has been actuated, the shutter-close actuator 404 is in its relaxed position, and the centerlines of apertures 412 and 409 coincide. In FIG. 4B the shutter assembly 400 has been moved to the closed state and, as such, the shutter-open actuator 402 is in its relaxed position, the shutter-close actuator 404 has been actuated, and the light blocking portions of shutter 406 are now in position to block transmission of light through the apertures 409 (shown as dotted lines).
Each aperture has at least one edge around its periphery. For example, the rectangular apertures 409 have four edges. In alternative implementations in which circular, elliptical, oval, or other curved apertures are formed in the aperture layer 407, each aperture may have only a single edge. In other implementations the apertures need not be separated or disjoint in the mathematical sense, but instead can be connected. That is to say, while portions or shaped sections of the aperture may maintain a correspondence to each shutter, several of these sections may be connected such that a single continuous perimeter of the aperture is shared by multiple shutters.
In order to allow light with a variety of exit angles to pass through apertures 412 and 409 in the open state, it is advantageous to provide a width or size for shutter apertures 412 which is larger than a corresponding width or size of apertures 409 in the aperture layer 407. In order to effectively block light from escaping in the closed state, it is preferable that the light blocking portions of the shutter 406 overlap the apertures 409. FIG. 4B shows a predefined overlap 416 between the edge of light blocking portions in the shutter 406 and one edge of the aperture 409 formed in aperture layer 407.
The electrostatic actuators 402 and 404 are designed so that their voltage—displacement behavior provides a bi-stable characteristic to the shutter assembly 400. For each of the shutter-open and shutter-close actuators there exists a range of voltages below the actuation voltage, which if applied while that actuator is in the closed state (with the shutter being either open or closed), will hold the actuator closed and the shutter in position, even after an actuation voltage is applied to the opposing actuator. The minimum voltage needed to maintain a shutter's position against such an opposing force is referred to as a maintenance voltage Vm. A number of control matrices which take advantage of the bi-stable operation characteristic are described in U.S. patent application Ser. No. 11/607,715, referenced above.
FIG. 5 is a cross sectional view of a display apparatus 500 incorporating shutter-based light modulators (shutter assemblies) 502, according to an illustrative embodiment of the invention. Each shutter assembly incorporates a shutter 503 and an anchor 505. Not shown are the compliant beam actuators which, when connected between the anchors 505 and the shutters 503, help to suspend the shutters a short distance above the surface. The shutter assemblies 502 are disposed on a transparent substrate 504, preferably made of plastic or glass. A rear-facing reflective layer, reflective film 506, disposed on the substrate 504 defines a plurality of surface apertures 508 located beneath the closed positions of the shutters 503 of the shutter assemblies 502. The reflective film 506 reflects light not passing through the surface apertures 508 back towards the rear of the display apparatus 500. The reflective aperture layer 506 can be a fine-grained metal film without inclusions formed in thin film fashion by a number of vapor deposition techniques including sputtering, evaporation, ion plating, laser ablation, or chemical vapor deposition. In another implementation, the rear-facing reflective layer 506 can be formed from a mirror, such as a dielectric mirror. A dielectric mirror is fabricated as a stack of dielectric thin films which alternate between materials of high and low refractive index. The vertical gap which separates the shutters 503 from the reflective film 506, within which the shutter is free to move, is in the range of 0.5 to 10 microns. The magnitude of the vertical gap is preferably less than the lateral overlap between the edge of shutters 503 and the edge of apertures 508 in the closed state, such as the overlap 416 shown in FIG. 4B.
The display apparatus 500 includes an optional diffuser 512 and/or an optional brightness enhancing film 514 which separate the substrate 504 from a planar light guide 516. The light guide is comprised of a transparent, i.e. glass or plastic material. The light guide 516 is illuminated by one or more light sources 518, forming a backlight. The light sources 518 can be, for example, and without limitation, incandescent lamps, fluorescent lamps, lasers, or light emitting diodes (LEDs). A reflector 519 helps direct light from lamp 518 towards the light guide 516. A front-facing reflective film 520 is disposed behind the backlight 516, reflecting light towards the shutter assemblies 502. Light rays such as ray 521 from the backlight that do not pass through one of the shutter assemblies 502 will be returned to the backlight and reflected again from the film 520. In this fashion light that fails to leave the display to form an image on the first pass can be recycled and made available for transmission through other open apertures in the array of shutter assemblies 502. Such light recycling has been shown to increase the illumination efficiency of the display.
The light guide 516 includes a set of geometric light redirectors or prisms 517 which re-direct light from the lamps 518 towards the apertures 508 and hence toward the front of the display. The light re-directors can be molded into the plastic body of light guide 516 with shapes that can be alternately triangular, trapezoidal, or curved in cross section. The density of the prisms 517 generally increases with distance from the lamp 518.
In alternate embodiments the aperture layer 506 can be made of a light absorbing material, and in alternate embodiments the surfaces of shutter 503 can be coated with either a light absorbing or a light reflecting material. In alternate embodiments the aperture layer 506 can be deposited directly on the surface of the light guide 516. In alternate embodiments the aperture layer 506 need not be disposed on the same substrate as the shutters 503 and anchors 505 (see the MEMS-down configuration described below). These and other embodiments for a display illumination system are described in detail in the U.S. patent application Ser. Nos. 11/218,690 and 11/528,191, incorporated herein by reference.
In one implementation the light sources 518 can include lamps of different colors, for instance, the colors red, green, and blue. A color image can be formed by sequentially illuminating images with lamps of different colors at a rate sufficient for the human brain to average the different colored images into a single multi-color image. The various color-specific images are formed using the array of shutter assemblies 502. In another implementation, the light source 518 includes lamps having more than three different colors. For example, the light source 518 may have red, green, blue and white lamps or red, green, blue, and yellow lamps.
A cover plate 522 forms the front of the display apparatus 500. The rear side of the cover plate 522 can be covered with a black matrix 524 to increase contrast. In alternate implementations the cover plate includes color filters, for instance distinct red, green, and blue filters corresponding to different ones of the shutter assemblies 502. The cover plate 522 is supported a predetermined distance away from the shutter assemblies 502 forming a gap 526. The gap 526 is maintained by mechanical supports or spacers 527 and/or by an adhesive seal 528 attaching the cover plate 522 to the substrate 504.
The adhesive seal 528 seals in a working fluid 530. The working fluid 530 is engineered with viscosities preferably below about 10 centipoise and with relative dielectric constant preferably above about 2.0, and dielectric breakdown strengths above about 104 V/cm. The working fluid 530 can also serve as a lubricant. In one implementation, the working fluid 530 is a hydrophobic liquid with a high surface wetting capability. In alternate implementations the working fluid 530 has a refractive index that is either greater than or less than that of the substrate 504.
A sheet metal or molded plastic assembly bracket 532 holds the cover plate 522, the substrate 504, the backlight 516 and the other component parts together around the edges. The assembly bracket 532 is fastened with screws or indent tabs to add rigidity to the combined display apparatus 500. In some implementations, the light source 518 is molded in place by an epoxy potting compound. Reflectors 536 help return light escaping from the edges of light guide 516 back into the light guide. Not shown in FIG. 5 are electrical interconnects which provide control signals as well as power to the shutter assemblies 502 and the lamps 518.
Further details and alternate configurations for the display apparatus 500, including manufacturing methods therefore, can be found in the U.S. patent application Ser. Nos. 11/361,785 and 11/731,628, incorporated herein by reference
Display apparatus 500 is referred to as the MEMS-up configuration, wherein the MEMS based light modulators are formed on a front surface of substrate 504, i.e. the surface that faces toward the viewer. The shutter assemblies 502 are built directly on top of the reflective aperture layer 506. In an alternate embodiment of the invention, referred to as the MEMS-down configuration, the shutter assemblies are disposed on a substrate separate from the substrate on which the reflective aperture layer is formed. The substrate on which the reflective aperture layer is formed, defining a plurality of apertures, is referred to herein as the aperture plate. In the MEMS-down configuration, the substrate that carries the MEMS-based light modulators takes the place of the cover plate 522 in display apparatus 500 and is oriented such that the MEMS-based light modulators are positioned on the rear surface of the top substrate, i.e. the surface that faces away from the viewer and toward the back light 516. The MEMS-based light modulators are thereby positioned directly opposite to and across a gap from the reflective aperture layer. The gap can be maintained by a series of spacer posts connecting the aperture plate and the substrate on which the MEMS modulators are formed. In some implementations the spacers are disposed within or between each pixel in the array. The gap or distance that separates the MEMS light modulators from their corresponding apertures is preferably less than 10 microns, or a distance that is less than the overlap between shutters and apertures, such as overlap 416. Further details and alternate embodiments for the MEMS-down display configuration can be found in the U.S. patent applications Ser. Nos. 11/361,785, 11/528,191, and 11/731,628 referenced above.
In other embodiments, the roller-based light modulator 220, the light tap 250, or the electrowetting-based light modulation array 270, as well as other MEMS-based light modulators, can be substituted for the shutter assemblies 502 within the display assembly 500.
FIG. 6 is a cross sectional view of a display apparatus 600 incorporating liquid crystal light modulators 602, according to an illustrative embodiment of the invention. The display apparatus includes a liquid crystal material 604 interposed between two transparent substrates 606 and 608. An array of electrodes 610 and 612 are formed on each of the two substrates for controlling voltages imposed across the liquid crystal material. The display apparatus 600 modulates light by altering the polarization properties of the light passing through liquid crystal material 604, depending on the voltages selected at the electrodes 610 and 612.
A rear-facing reflective layer, reflective film 614, disposed on the substrate 606, defines a plurality of surface apertures 616 located beneath the liquid crystal light modulators 602. The reflective film 614 reflects light not passing through the surface apertures 616 back towards the rear of the display apparatus 600. The reflective aperture layer 614 can be a fine-grained metal film without inclusions formed in thin film fashion by a number of vapor deposition techniques including sputtering, evaporation, ion plating, laser ablation, or chemical vapor deposition. In another implementation, the rear-facing reflective layer 614 can be formed from a mirror, such as a dielectric mirror. A dielectric mirror is fabricated as a stack of dielectric thin films which alternate between materials of high and low refractive index.
The liquid crystal display apparatus 600 includes an optional diffuser 622 and/or an optional brightness enhancing film 624 which separates the substrate 606 from a planar light guide 616. The light guide is comprised of a transparent, i.e. glass or plastic material. The light guide 616 is illuminated by one or more light sources 618, forming a backlight. A reflector 619 helps direct light from lamp 618 towards the light guide 616. A front-facing reflective film 620 is disposed behind the light guide 616, reflecting light towards the liquid crystal modulators 602. Light rays from the backlight that do not pass through one of the shutter liquid crystal modulators 602 will be returned to the backlight and reflected again from the film 620. In this fashion light that fails to leave the display to form an image on the first pass can be recycled and made available for transmission through other open apertures in the array of liquid crystal modulators 602.
The light guide 616 includes a set of geometric light redirectors or prisms 617 which re-direct light from the lamps 618 towards the apertures 616 and hence toward the front of the display. The light re-directors can be molded into the plastic body of light guide 616 with shapes that can be alternately triangular, trapezoidal, or curved in cross section. The density of the prisms 617 generally increases with distance from the lamp 618.
A sheet metal or molded plastic assembly bracket 632 holds the cover plate 608, the substrate 606, the backlight 616 and the other component parts together around the edges. The assembly bracket 632 is fastened with screws or indent tabs to add rigidity to the combined display apparatus 600. Reflectors 636 help return light escaping from the edges of light guide 616 back into the light guide.
FIG. 7A provides a cross-sectional view of a display module assembly 700, in the MEMS-up configuration, according to an illustrative embodiment of the invention. FIG. 7B provides an exploded and isometric view of the display assembly 700. The module assembly includes a lamp or lamps 702, a light guide 704, a MEMS modulator substrate 706, a cover plate 708, a driver circuit 710, a module spacer 712, assembly brackets 713 and 714, and flexible electrical interconnects 716 and 718. In a fashion similar to that illustrated for display apparatus 500, the module assembly 700 also includes a working fluid 720, cell spacers (not shown in FIG. 6), and a seal material 722. The module assembly also includes an electrical connection 724 between the substrates 706 and 708. The assembly includes a front-facing reflector film 728.
The combination of MEMS modulator substrate 706, cover plate 708, cell spacers, working fluid 720, and seal 722 is often referred to as cell assembly 705. Techniques for alignment, fluid filling, and sealing of the cell assembly have been previously described in U.S. patent application Ser. No. 11/731,628 and 60/930,872, the entireties of which are incorporated herein by reference.
After the components of the cell assembly are brought together, the steps for assembling the module 700 proceed as follows. First the driver circuits 710 are attached to the cell assembly 705. The driver circuits 710 can be silicon chips which comprise any or all of the functional blocks illustrated as part of block diagram 150, including timing control circuits, buffer memory, scan drivers, data drivers and common drivers. Electrical connections are made between the driver circuits 710 and interconnect wiring on the substrate 706 by means of an anisotropic conductive adhesive 726. In a second step of module assembly the flexible electrical interconnects 716 are also attached to cell assembly 705, also by means of an anisotropic conductive adhesive. In an optional third step of module assembly the lamp or lamps 702 are attached to the light guide 704. The lamps are also attached to the flexible electrical interconnect 718. In an optional fourth step of assembly the front facing reflector 728 is attached to bottom surfaces of the module spacer 712. In a fifth step of assembly the module spacer 712 is inserted into the assembly bracket 714. And in a sixth step of assembly all of the remaining components, starting with the light guide, are fitted into their places on or within the module spacer 712. In a final step of assembly, the assembly bracket 713 is fitted in place over the cell assembly 705. The assembly bracket 713 includes indent tabs that rigidly connect the bracket 713 to bracket 714, thereby completing an enclosure of the display module.
The module spacer 712 includes several features to facilitate and maintain the mechanical alignment between components of the module. For instance, the locating surfaces 730 and 732 help to restrict motion of the lamps 702 after assembly. Such surfaces in spacer 712 help to maintain proper x-y alignment between the lamps 702 and the light guide 704. By appropriate design of such locating surfaces in module spacer 712, sometimes referred to as receiving pockets, a high degree of alignment can be maintained between components even when components are to be assembled by hand. In a similar feature, the x-y alignment between the light guide 704 and the MEMS modulator substrate 706 is in part ensured by the locating surfaces 734 and 736, respectively.
Vertical alignment between the components of assembly 700 is also maintained by locating surfaces designed into the module spacer 712. The MEMS modulator substrate 706, for instance, rests on a shelf formed by the locating surface 740. The substrate 706 is supported by locating surfaces 740 at several points around the periphery of the substrate 706. Similarly, the light guide 704 rests on a locating surface 742. An air gap 744 has been established between the light guide 704 and the MEMS modulator substrate 706. This air gap is maintained because the vertical distance between the locating surfaces 740 and 742 has intentionally been made greater than the thickness of the light guide 704. The air gap 744 performs a useful function, as it enables the use of total internal reflection at the top surface of light guide 704 for distributing light within the light guide. Additionally, the air gap does not impede light rays, such as light ray 521 in display 500, from bouncing between the two reflective surfaces of the optical cavity in the display (formed for instance between the reflective film 506 and the front-facing reflector film 520).
In module assembly 700 the locating surface 742 supports the light guide 704 only along the periphery of the light guide. An open area is left in the module spacer 712 underneath the light guide 704 in the viewing area of the display. The module spacer 712 also includes a locating surface 746 along the periphery at a surface opposite to surface 742. The front-facing reflector 728 is attached with an adhesive to the locating surface 746. In this fashion, an air gap is also be provided between the front-facing reflector 728 and the light guide 704. In alternate embodiments the front-facing reflector 728 is adhered directly to the assembly bracket 714.
The module spacer 712 can be manufactured from either plastic or metal materials. Polished metal materials are useful as their surfaces reflect light escaping from the light guide 704 back into the optical cavity. In the particular embodiment of module 700, the spacer 712 is fabricated from the injection molding of polycarbonate. The polycarbonate is dyed to a white color and the edges are smooth to enhance reflection of light back into the optical cavity. Other plastic materials applicable for this component include, without limitation, polyethylene, polypropylene, acrylic, or epoxy materials. The materials can be molded through use of either thermoplastic or thermosetting characteristics. In some embodiments, the module spacer can be formed of conductive polymers or polymer composites to provide protection from electromagnetic interference.
The module spacer 712 generally supports the light guide 704 and the MEMS modulator substrate 706 only along the periphery of those substrates. The assembly brackets 713 and 714, however, are designed to completely enclose the module along the bottom, the sides, and also along non-viewing portions of the top surface. Gaps are left in sides of the assembly bracket leaving for the admission of flexible electrical interconnects 716 and 718. The assembly brackets 713 and 714, when connected by means of their indent tabs, provide mechanical rigidity to the display module. When formed from sheet metal, the assembly brackets also provide electronic shielding for the display and protection from electromagnetic interference.
In some embodiments, the functions of the module spacer 712 and the assembly bracket 714 can be combined in a composite structure. For such a composite structure, the plastic components are molded onto or around and permanently adhered to a base made of sheet metal. After plastic molding is complete, any sheet metal protrusions can be further bent or folded to form a part of an interlocking enclosure.
In some embodiments adhesives are applied along the periphery of the cell assembly and/or the light guide 704 to prevent movement of the components along their respective locating surfaces on the module spacer 712. In other embodiments elastic materials (either synthetic sponges or rubber materials) are inserted between the components, for instance between the light guide 704 and the modulator substrate 706 and/or between the cover plate 708 and the assembly bracket 714. The elastic materials can be compressed after enclosure of the assembly brackets 713 and 714, thereby preventing further movement of the components. The elastic materials also protect the display components from mechanical shock. In some embodiments protrusions are provided in the spacer 712 which align to indents or tabs in the assembly brackets 713 or 714. These locator protrusions prevent motion of the spacer 712 within the assembly bracket 714.
Although in a preferred embodiment the MEMS modulator substrate 706 comprises an array of shutter-based MEMS modulators, such as light modulators 200 and 220, substrates comprising non-shutter based MEMS light modulators can be usefully employed in the invention. Applicable non-shutter based modulators that can be arrayed on substrate 706 include the light tap 250 and the electrowetting-based light modulator 270.
In an alternate embodiment the cell components of display apparatus 600 can be substituted for the MEMS light modulators in display apparatus 700. For instance the substrate 606 can be substituted for the MEMS modulator substrate 706 and the substrate 608 can be substituted for the cover plate 708. In the liquid crystal embodiment of this invention the fluid 720 is replaced by the liquid crystal material 604. The same advantages offered by the design of module spacer 712 apply when adopted to the liquid crystal display apparatus 600.
FIG. 8 provides a detailed view of a display module assembly 800, in the MEMS-up configuration, according to an illustrative embodiment of the invention. The module assembly includes a lamp or lamps 802, a light guide 804, an modulator substrate 806, a cover plate 808, a driver circuit 810, a module spacer 812, a front facing reflector 828, assembly brackets 813 and 814, and a flexible electrical interconnects 816 and 818.
Vertical alignment between the components of assembly 800 is also maintained by locating surfaces designed into the module spacer 812. The MEMS modulator substrate 806, for instance, rests on a shelf formed by the locating surface 840. The substrate 806 is supported by locating surfaces 840 at several points around the periphery of the substrate 806. Similarly, the light guide 804 rests on a locating surface 842, which is located directly opposite the locating surface 840 on module spacer 812. An air gap 844 has been established between the light guide 804 and the MEMS modulator substrate 806 by the insertion of the module spacer 812 between the substrates along the periphery of the display. The shape of the module spacer 812 has been designed so that at several points along the periphery of the substrates 804 and 806 the spacer material is disposed between the two substrates.
The module assembly 800 also includes elastic inserts 850 and 852. The elastic insert 850 is placed between the cover plate and the assembly bracket 813. The elastic inserts 852 are placed between the light guide 804 and the assembly bracket 814. The elastic inserts are comprised of elastic materials (either synthetic sponges or rubber materials) so that they can be compressed during enclosure of the brackets 813 and 814. The elastic inserts ensure that the light guide 804 and the modulator substrate 806 are pressed directly against the locator surfaces 842 and 840, respectively. The elastic materials also protect the display components from mechanical shock. In some embodiments the front facing reflector 828 is adhered directly to the light guide 804, such that the elastic insert 852 is positioned between the assembly bracket 814 and the reflector 828.
FIG. 9 provides a detailed view of a display module assembly 900, in the MEMS-down configuration, according to an illustrative embodiment of the invention. The module assembly includes a lamp or lamps 902, a light guide 904, an aperture plate 906, a modulator substrate 908, a driver circuit 910, a module spacer 912, a front facing reflector 928, assembly brackets 913 and 914, and flexible electrical interconnects 916 and 918.
The combination of MEMS modulator substrate 908, aperture plate 906, cell spacers, working fluid 920 and seal 922 is referred to as cell assembly 905. For the MEMS-down configuration, however, the array of MEMS shutter assemblies is fabricated on the side of substrate 908 which is directed toward the light guide 904 and away from the viewer. As a consequence, the driver circuits 910 are also mounted on the bottom surface of modulator substrate 908.
The module spacer 912 includes several features to facilitate and maintain the mechanical alignment between components of the module. For instance, the spacer 912 includes locating surfaces 930 and 932 to help ensure the proper positioning of the lamps 902. In a similar feature, the x-y alignment between the light guide 904 and the MEMS aperture plate 906 is in part ensured by the locating surfaces 934 and 936, respectively.
Vertical alignment between the components of assembly 900 is also maintained by locating surfaces designed into the module spacer 912. The aperture plate 906, for instance, rests on a shelf formed by the locating surface 940. The substrate 906 is supported by locating surfaces 940 at several points around the periphery of the substrate 906. Similarly, the light guide 904 rests on a locating surface 942. An air gap 944 has been established between the light guide 904 and the aperture plate 906. This air gap is maintained because the vertical distance between the locating surfaces 940 and 942 has intentionally been made greater than the thickness of the light guide 904. The air gap 944 performs a useful function, as it enables the use of total internal reflection at the top surface of light guide 904 for distributing light within the light guide. Additionally, the air gap does not impede light rays, such as light ray 521 in display 500, from bouncing between the two reflective surfaces of the optical cavity in the display (formed for instance between the reflective film 506 and the front-facing reflector film 520).
In module assembly 900 the locating surface 942 supports the light guide 904 only along the periphery of the light guide. An open area is left in the module spacer 912 underneath the light guide 904 in the viewing area of the display. The module spacer 912 also includes a locating surface 946 along the periphery at a surface opposite to surface 942. The front-facing reflector 928 is attached with an adhesive to the locating surface 946. In this fashion, an air gap is also be provided between the front-facing reflector 928 and the light guide 904. In alternate embodiments the front-facing reflector 928 is adhered directly to the assembly bracket 914.

## Claims

1. A display apparatus, comprising:
a first substrate having an aperture layer formed thereon,
a light guide for guiding light towards the aperture layer,
a plurality of MEMS light modulators for modulating light passing through the aperture layer from the light guide, and
a spacer substantially surrounding a periphery of the light guide for keeping the light guide and the first substrate a predetermined distance apart from one another, thereby forming a gap between the first substrate and the light guide, wherein the spacer comprises a shelf on which one of the light guide and the first substrate rests.

2. The display apparatus of claim 1, wherein the spacer comprises a reflective surface for reflecting light into the light guide.

3. The display apparatus of claim 1, wherein the spacer comprises a structural feature having a geometrical shape selected to maintain alignment between the light guide and a lamp for providing light to the light guide.

4. The display apparatus of claim 1, wherein the spacer comprises a structural feature having a geometrical shape selected to maintain alignment between the light guide and an electrical connection for controlling a MEMS light modulator of the plurality of MEMS light modulators.

5. The display apparatus of claim 1, wherein the spacer comprises a structural feature having a geometrical shape selected to maintain alignment between the light guide and the first substrate.

6. The display apparatus of claim 1, wherein the spacer comprises a structural feature having a geometrical shape selected to restrict translational motion of at least one of the light guide and the first substrate.

7. The display apparatus of claim 1, comprising an adhesive disposed on the spacer for adhering to at least one of the light guide and the first substrate.

8. The display apparatus of claim 1, wherein the spacer is disposed between the light guide and the first substrate.

9. The display apparatus of claim 1, wherein the spacer comprises a rigid material.

10. The display apparatus of claim 9, wherein the spacer comprises at least one of polycarbonate, polyethylene, polypropylene, and polyacrylate.

11. The display apparatus of claim 9, wherein the spacer comprises a metal.

12. The display apparatus of claim 9, wherein the spacer comprises a metal and plastic composite.

13. The display apparatus of claim 1, wherein the MEMS light modulators comprise shutter-based light modulators.

14. The display apparatus of claim 1, wherein the MEMS light modulators comprise electrowetting light modulators.

15. The display apparatus of claim 1, wherein the spacer comprises a structural feature having a geometrical shape selected to maintain alignment between the light guide and a reflective layer for reflecting light towards the light guide.

16. The display apparatus of claim 1, wherein the aperture layer comprises a reflective aperture layer.

17. The display apparatus of claim 1, wherein the plurality of MEMS light modulators are disposed on the first substrate.

18. The display apparatus of claim 1, wherein the plurality of MEMS light modulators are disposed on a second substrate.

19. A display apparatus, comprising:
a plurality of MEMS light modulators;
a first substrate having a control matrix formed thereon for controlling the plurality of MEMS light modulators,
a light guide for guiding light towards the first substrate, and
a spacer substantially surrounding a periphery of the light guide for keeping the light guide and the first substrate a predetermined distance apart from one another, thereby forming a gap between the first substrate and the light guide, wherein the spacer comprises a structural feature having a geometrical shape selected to maintain alignment between the light guide and the first substrate.

20. The display apparatus of claim 19, wherein the spacer comprises a structural feature having a geometrical shape selected to maintain alignment between the light guide and a lamp for providing light to the light guide.

21. The display apparatus of claim 19, wherein the spacer comprises a reflective surface for reflecting light into the light guide.

22. The display apparatus of claim 19, wherein the spacer comprises a structural feature having a geometrical shape selected to restrict translational motion of at least one of the light guide and the first substrate.

23. The display apparatus of claim 19, wherein the spacer comprises a shelf on which one of the light guide and the first substrate rests.