Patent Publication Number: US-2021181510-A1

Title: Bonded optical devices

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 62/949,312, filed Dec. 17, 2019, the entire contents of which are hereby incorporated by reference in their entirety and for all purposes. 
    
    
     BACKGROUND 
     Field of the Invention 
     The field relates to bonded optical devices and, in particular, to bonded optical devices for use in wearable electronics. 
     Description of the Related Art 
     In some types of display devices, a very small and extremely high resolution device is desirable. Examples include directly viewed display screens, such as smart watches and cell phone displays, as well as applications with projected images from small screens, such as heads-up displays (HUDs) and smart glasses. For example, in wearable smart glasses, such as augmented reality (AR) glasses, or other eyewear that includes electronic circuitry and a display, the image may be positioned less than 1-2 cm (e.g., 1-1.2 cm) from the user&#39;s eye. In such devices, it can be desirable to utilize a pitch for the display pixels that are as small as possible (e.g., less than 5-6 μm), for example, in order to provide a desired quality of image. Some technologies, such as liquid crystal-on-silicon (LCoS) may be able to provide pixels with low pitches, but are inefficient in that an insignificant amount of optical energy (e.g., light) is lost, may have low manufacturing yield, lower resolution and may be expensive. 
     Other technologies such as micro light emitting diodes (microLED) are capable of providing very bright images for AR/MR (Mixed Reality) applications because they can provide a sufficient amount of optical energy (e.g., brightness) to provide, e.g., a clear image visible in well-lit ambiance. Light Emitting Diode (LED) wafers can be processed for one wavelength of light at a time (red “R”, green “G” or blue “B”), and making a multi-colored display still poses a challenge against providing a desired level of image quality in the aforementioned applications. 
     Accordingly, there remains a continuing need for improved optical devices, for example to create a colored image from monochromatic LED displays and integrate these monochromatic microLED displays for applications such as AR smart glasses, projection systems, car HUDs, smart watch displays, cell phone displays, etc. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Specific implementations will now be described with reference to the following drawings, which are provided by way of example, and not limitation. 
         FIG. 1  is a diagram showing an illustration of relative distances between a display device and a user&#39;s eye. 
         FIG. 2  is a schematic side sectional view of directly bonded optical devices, according to an embodiment. 
         FIG. 3  is a schematic side sectional view of directly bonded optical devices, according to another embodiment. 
         FIG. 4  is a schematic side sectional view of an optical assembly, according to an embodiment. 
         FIG. 5  is a schematic side sectional view of an optical assembly, according to another embodiment. 
         FIG. 6  is a diagram showing an illustration of physical separation between pixels within an optical device, according to an embodiment. 
         FIG. 7A  is a diagram showing an illustration of physical separation between individual pixels of an optical device, according to an embodiment. 
         FIG. 7B  is a diagram showing an illustration of physical separation only in an A×A matrix of pixels within an optical device, according to an embodiment. 
         FIG. 8  is a diagram showing an optical system that can incorporate the optical assemblies described herein, according to an embodiment. 
         FIG. 9  is a diagram showing optical devices directly bonded to a waveguide with input and output couplings, according to an embodiment. 
         FIG. 10  is a diagram showing optical devices configured to direct light to a waveguide with input and output couplings, according to another embodiment. 
         FIG. 11  is a diagram showing an illustration of superposition of three color pixels. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagram showing an illustration  100  of the relative display distances between various display devices  104 ,  106 ,  108  and a user&#39;s eye  102 . The most sensitive part of the eye, fovea, contains the most cones (which help us identify colors), and has a resolution of ˜1 arc-minute, which is 60 pixels-per-degree (PPD). PPD identifies the pixel pitch needed in a display based on a distance of the display device from the user&#39;s eye  102 . For an AR smart glass display  104  with working distance of ˜1 cm from the user&#39;s eye  102 , a pixel pitch of ˜5 μm produces what is perceived as a “clear image.” For a cell phone display  106  with a working distance of ˜20 cm from the user&#39;s eye  102 , a pixel pitch of ˜50 μm produces a clear image. For a computer display  108  with a working distance of ˜50 cm from the user&#39;s eye  102 , a pixel pitch of ˜300 μm produces a clear image. Digital Light Processing (DLP) and liquid crystal-on-silicon (LCoS) based technologies are not sufficient for several reasons, including, e.g., low brightness, pixel size, pitch, display size, etc. Accordingly, microLED devices may be beneficial in some applications, such as AR display applications. 
     Various embodiments disclosed herein relate to bonded optical devices  200 ,  300   a - c  (shown in, e.g.,  FIGS. 2 and 3 ). As explained herein, some types of optical elements  202   a - c ,  302   a - c  (shown in, e.g.,  FIGS. 2 and 3 ), particularly light emitting elements (e.g., light emitting diodes, or LEDs), may be fabricated in wafers having devices configured to emit light of a single color (e.g., red, green, or blue), which can make fabrication of multi-colored displays comprised of several hundred thousand or millions of LEDs from these separate wafers, challenging. In various embodiments, the optical elements  202   a - c ,  302   a - c  can be formed of a semiconductor material. For example, optical wafers (such as LED wafers) can be formed from a Group III-V compound semiconductor material(s), such as InP, GaN, AlGaAs, InGaN, AlGaInP, etc. In various embodiments, direct bonding procedures can enable such compound semiconductor materials to be bonded to a different type of semiconductor processor element (e.g., a Si or CMOS processor die), creating a heterogenous system. Furthermore, it can be challenging to provide optical elements  202   a - c ,  302   a - c  (shown in, e.g.,  FIGS. 2 and 3 ) that have pixels  602   a - c  (shown in, e.g.,  FIG. 6 ) (or display regions) having a sufficiently small pitch (e.g., space between pixels) for displaying high quality and high brightness images to be directly viewed or projected on displays (such as small displays or displays configured to be positioned close to the user). In various embodiments, a pitch of the optical emitters of an array can be less than 50 microns, e.g., less than 10 microns. 
     In some microLED displays, each pixel  704  (shown in, e.g.,  FIG. 7A ) can utilize individual LED chips (e.g., optical elements) as a pixel  704  (shown in, e.g.,  FIG. 7A ) or sub-pixel. For example, microLED chips (e.g., optical elements including array(s) of emitters) can be separately manufactured and positioned with pick-and-place techniques. Transfer and placement techniques and color conversion schemes can also be used but these techniques may not be economical or may be very lossy. Accordingly, there remains a continuing need for improved optical devices. 
     Embodiments disclosed herein can enable displays having a fine pixel pitch by bonding (e.g., directly bonding or hybrid bonding) an optical element  202   a - c ,  302   a - c  (shown in, e.g.,  FIGS. 2 and 3 ) (particularly a light emitting element such as an LED device including a plurality of LEDs) to at least one carrier  204 ,  304   a - c  (shown in, e.g.,  FIGS. 2 and 3 ), such as a processor, e.g., an image processor element that can include active circuitry (e.g., one or more transistors) configured to control the operation of the optical element  202   a - c ,  302   a - c  (shown in, e.g.,  FIGS. 2 and 3 ). In various embodiments, the optical emitters of the emitter arrays can be independently controllable. Beneficially, in some embodiments, direct bonding or hybrid bonding can be used to physically and electrically connect the optical element  202   a - c ,  302   a - c  (shown in, e.g.,  FIGS. 2 and 3 ) to the carrier  204 ,  304   a - c  (shown in, e.g.,  FIGS. 2 and 3 ) (e.g., processor element) without an adhesive. The use of direct bonding can enable pixel pitches of less than 5 microns, or less than 1 micron. The at least one carrier  204 ,  304   a - c  has a coefficient of thermal expansion (CTE) less than 7 ppm. 
       FIG. 2  is a schematic side sectional view of a bonded optical device  200  in which a plurality of optical elements  202   a - c  are bonded (e.g., directly bonded) to a common carrier  204  according to one embodiment. In some embodiments, the common carrier  204  can comprise an integrated device die, such as a processor die having circuitry that controls operation of the optical elements  202   a - 202   c .  FIG. 3  is a schematic side sectional view of a plurality of bonded optical devices  300   a - c  in which a plurality of optical elements  302   a - c  are bonded (e.g., directly bonded) to a corresponding plurality of carriers  304   a - c . The optical elements can be manufactured in wafer form and singulated to define the optical elements  202   a - c ,  302   a - c  shown in  FIGS. 2-3 . As shown in  FIG. 2 , the optical elements  202   a - c  (which can comprise emitter dies, such as LEDs) can be directly bonded to a common carrier  204  without an intervening adhesive, in for example a die-to-wafer (D2W) process. In some embodiments (see, e.g.,  FIG. 11 ), the optical elements  202   a - c ,  302   a - c  and carrier  204 ,  304   a - c  can be integrated into a larger optical system. For example, the bonded optical device  200  (including, e.g., the optical elements  202   a - c  and the common carrier  204  directly bonded thereto) can be mounted to a waveguide or other structure. 
     In other embodiments, the carrier  304   a - c  can be singulated to form a plurality of bonded optical devices  300   a - c , as shown in  FIG. 3 . In other embodiments, the singulated optical elements  302   a - c  can be bonded to the singulated carriers  304   a - c  in a die-to-die (D2D) process to obtain the bonded optical devices  300   a - c  shown in  FIG. 3 . In still other embodiments, the optical elements in wafer form (not shown) can be bonded (e.g., directly bonded) to the carrier in wafer form (not shown) (e.g., processor wafer) in a wafer-to-wafer (W2W) process (not shown). The bonded wafers can then be singulated to form a plurality of bonded optical devices  300   a - c.    
     The optical element(s)  202   a - c ,  302   a - c  can be directly bonded (e.g., using dielectric-to-dielectric bonding techniques, such as the ZiBond®, DBI or DBI Ultra techniques used by Xperi Corporation of San Jose, Calif.) to the at least one carrier  204 ,  304   a - c  (such as a processor element) without an adhesive. For example, the dielectric-to-dielectric bonds may be formed without an adhesive using the direct bonding techniques disclosed at least in U.S. Pat. Nos. 9,391,143 and 10,434,749, the entire contents of each of which are incorporated by reference herein in their entirety and for all purposes. 
     In various embodiments, the direct bonds can be formed without an intervening adhesive. For example, dielectric bonding surfaces  206 ,  306   a - c  can be polished to a high degree of smoothness. The bonding surfaces  206 ,  306   a - c  can be cleaned and exposed to a plasma and/or etchants to activate the surfaces. In some embodiments, the surfaces can be terminated with a species after activation or during activation (e.g., during the plasma and/or etch processes). In various embodiments, the terminating species can comprise nitrogen. Further, in some embodiments, the bonding surfaces can be exposed to fluorine. For example, there may be one or multiple fluorine peaks near layer and/or bonding interfaces. Without being limited by theory, in some embodiments, the activation process can be performed to break chemical bonds at the bonding surface, and the termination process can provide additional chemical species at the bonding surface that improves the bonding energy during direct bonding. Thus, in the directly bonded structures, the bonding interface between two dielectric materials can comprise a very smooth interface with higher nitrogen content and/or fluorine peaks at the bonding interface. 
     In various embodiments, conductive contact pads  208   a - c ,  308   a - c  of the optical element  202   a - c ,  302   a - c  or LED element can be directly bonded to corresponding conductive contact pads  210   a - c ,  310   a - c  of the carrier  204 ,  304   a - c  (e.g., a processor element). One LED pixel within an LED chip may have two contact pads or electrodes (positive electrode and negative electrode) in various embodiments. In various embodiments, the carrier  204 ,  304   a - c  (e.g., processor element) can create identical images on the optical corresponding elements  302   a - c . As explained herein, each optical element  302   a - 302   c  can comprise a monochromatic light emitting element, and can create identical images, such that, when the images are superimposed, a multi-colored image can be viewed. For example, a hybrid bonding technique can be used to provide conductor-to-conductor direct bonds along a bond interface  206 ,  306   a - c  that includes covalently direct bonded dielectric-to-dielectric surfaces. In various embodiments, the conductor-to-conductor (e.g., contact pad to contact pad) direct bonds and the dielectric-to-dielectric bonds can be formed using the direct bonding techniques disclosed at least in U.S. Pat. Nos. 9,716,033 and 9,852,988, the entire contents of each of which are incorporated by reference herein in their entirety and for all purposes. 
     For example, dielectric bonding surfaces  206 ,  306   a - c  can be prepared and directly bonded to one another without an intervening adhesive. Conductive contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  (which may be surrounded by nonconductive dielectric field regions) may also directly bond to one another without an intervening adhesive. In some embodiments, the respective contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  can be recessed below the dielectric field regions, for example, recessed by less than 20 nm, less than 15 nm, or less than 10 nm, for example, recessed in a range of 2 nm to 20 nm, or in a range of 4 nm to 10 nm. The dielectric field regions can be directly bonded to one another without an adhesive at room temperature in some embodiments and, subsequently, the bonded structure can be annealed. Upon annealing, the contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  can expand and contact one another to form a metal-to-metal direct bond. Beneficially, the use of Direct Bond Interconnect, or DBI®, and/or ZiBond techniques can enable fine pixel pitches as explained above. In some embodiments, the pitch of the bonding pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  may be less than 300 microns, less than 40 microns or less than 10 microns, or even less than 2 microns. For some applications the ratio of the pitch of the bonding pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  to one of the dimensions of the bonding pad  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  is less than 5, or less than 3 and sometimes desirably less than 2. In various embodiments, the contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  can comprise copper, although other metals may be suitable. 
     The embodiments disclosed herein can also be used in combination with the devices and methods disclosed throughout U.S. patent application Ser. No. 15/919,570 (which issued as U.S. Pat. No. 10,629,577 on Apr. 21, 2020); Ser. No. 16/219,693; and Ser. No. 16/176,191, the entire contents of each of which are incorporated by reference herein in their entirety and for all purposes. U.S. patent application Ser. No. 15/919,570, for example, teaches methods for direct hybrid bonding of CMOS logic wafers or dies to LED wafers or dies for direct control of the emitters (active matrix driving). U.S. application Ser. No. 16/176,191 teaches direct bonding of optically transparent substrates. 
     The embodiments disclosed herein can further be used in combination with the devices and methods (which describe how an optical element can be bonded to a processor die) disclosed throughout U.S. Pat. No. 10,629,577, the entire contents of which are incorporated by reference herein in their entirety and for all purposes. U.S. Pat. No. 10,629,577 teaches direct-bonded arrays of optical elements such as for example direct-bonded LED arrays. 
     Thus, in direct bonding processes, a first element (e.g., an optical element  202   a - c ,  302   a - c ) can be directly bonded to a second element (e.g., a carrier  204 ,  304   a - c  such as a processor die) without an intervening adhesive. In some arrangements, the first element can comprise a singulated element, such as a singulated optical device die. In other arrangements, the first element can comprise a carrier or substrate (e.g., a wafer) that includes a plurality (e.g., tens, hundreds, or more) of device regions that, when singulated, form a plurality of integrated device dies. Similarly, the second element can comprise a singulated element, such as a singulated integrated device die (e.g., a processor die). In other arrangements, the second element can comprise a substrate (e.g., a wafer). 
     As explained herein, the first and second elements (e.g., the optical element  202   a - c ,  302   a - c  and the carrier  204 ,  304   a - c  or processor die) can be directly bonded to one another without an adhesive, which is different from a deposition process. The first and second elements can accordingly comprise non-deposited elements. Further, directly bonded structures, unlike deposited layers, can include a defect region (not shown) along the bond interface  206 ,  306   a - c  in which nanovoids are present. The nanovoids may be formed due to activation of the bonding surfaces (e.g., exposure to a plasma). As explained above, the bond interface  206 ,  306   a - c  can include concentration of materials from the activation and/or last chemical treatment processes. For example, in embodiments that utilize a nitrogen plasma for activation, a nitrogen peak can be formed at the bond interface  206 ,  306   a - c . In embodiments that utilize an oxygen plasma for activation, an oxygen peak can be formed at the bond interface  206 ,  306   a - c . In some embodiments, the bond interface  206 ,  306   a - c  can comprise silicon oxide, silicon nitride, silicon oxynitride, silicon oxycarbonitride, or silicon carbonitride. As explained herein, the direct bond can comprise a covalent bond, which is stronger than van Der Waals bonds. The bonding layers can also comprise polished surfaces that are planarized to a high degree of smoothness. 
     In various embodiments, the metal-to-metal bonds between the contact pads  208   a - c ,  210   a - c  or  308   a - c ,  310   a - c  can be joined such that copper grains grow into each other across the bond interface  206 ,  306   a - c . In some embodiments, the copper can have grains oriented along the crystal plane for improved copper diffusion across the bond interface  206 ,  306   a - c . The bond interface  206 ,  306   a - c  can extend substantially entirely to at least a portion of the bonded contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c , such that there is substantially no gap between the nonconductive bonding regions at or near the bonded contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c . In some embodiments, a barrier layer (not shown) may be provided under the contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c  (e.g., which may include copper). In other embodiments, however, there may be no barrier layer under the contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c , for example, as described in U.S. Patent Application Publication No. US 2019/0096741, which is incorporated by reference herein in its entirety and for all purposes. 
     Although the illustrated embodiments show directly bonded optical elements, in other embodiments, the optical devices can be attached to the carrier(s) with an adhesive, e.g., a transparent adhesive. 
     As illustrated and described herein, in some embodiments, the bonded optical device  200 ,  300   a - c  can comprise an optical element  202   a - c ,  302   a - c  that includes a plurality of image regions or display regions (e.g., pixels  602   a - c  as shown in  FIG. 6 ). Each image region can comprise a monochromatic image region that includes an optical emitter  614  configured to emit light of a single color. The optical emitter  614  can comprise a light emitting diode, which can emit light from the region or surface in the optical element in which the LED is formed. The optical element  202   a - c ,  302   a - c  may comprise a LED wafer comprising Group III-V materials, e.g. GaAs, GaN, GaP, InGaN, AlGaInP, AlGaAs, etc. For example, the optical element  202   a - c ,  302   a - c  can comprise monochromatic LED chips in various embodiments. The LED chips can each be configured to emit light of a single color. The LED chips can be configured to emit different colors from one another. For example, a first LED chip (such as the optical element  202   a ) can be configured to emit red light, a second LED chip (such as the optical element  202   b ) can be configured to emit green light, and a third LED chip (such as the optical element  202   c ) can be configured to emit blue light. It should be appreciated that the LED chips can emit any suitable colors. 
     The optical element  202   a - c ,  302   a - c  can be bonded, e.g., directly bonded without an intervening adhesive, to at least one carrier  204 ,  304   a - c  (for example, at least one processor element) that has active circuitry for controlling operation of pixels of the optical element  202   a - c ,  302   a - c . The at least one carrier  204 ,  304   a - c  can comprise a semiconductor element, such as silicon, in various arrangements. For example, the carrier  204 ,  304   a - c  can serve as a silicon-based backplane in some embodiments. The carrier  204 ,  304   a - c  can comprise a processor die having driver circuitry electrically connected to the optical emitters by way of the contact pads  208   a - c ,  210   a - c ,  308   a - c ,  310   a - c . The driver circuitry can control the emission of light from the plurality of optical emitters of the optical element  202   a - c ,  302   a - c.    
     As explained herein, the plurality of image regions (such as the pixels  602   a - c  shown in  FIG. 6 ) can be arranged relative to one another and to a common optical pathway (such as an optical waveguide  804  shown in  FIG. 8 ) such that monochromatic light from each image region is coupled into the optical pathway. In some embodiments, a plurality of such bonded optical devices  200 ,  300   a - c  can be coupled with the common optical pathway. The plurality of bonded optical devices  200 ,  300   a - c  can be configured to emit light of different colors (e.g., a red bonded optical device, a green bonded optical device, a blue bonded optical device). A superimposed light beam from the plurality of bonded optical devices can be transferred along the optical pathway to an optical output to be viewed by a user. A plurality of monochromatic images can be superimposed into a polychromatic image in the waveguide representative of the combined contribution of the pixels each of the plurality of bonded optical devices. 
     In various embodiments, the superposition of light from multiple monochromatic image regions can provide redundancy in case one image region is damaged or unused. In such cases, light from the other pixels can compensate for the color of light in the damaged image region. 
     Beneficially, the embodiments disclosed herein can utilize bonded optical elements  202   a - c ,  302   a - c  that include an array or pixels of multiple LEDs, without separately singulating and repopulating the singulated LEDs on a substrate. The array of LED chips can be directly bonded to an array of processing elements configured to control operation of the LEDs. By contrast, in other methods, each LED pixel can be singulated and stacked on a substrate at higher pitches, which can complicate assembly processes. The use of directly bonded optical elements including an array of LEDs can accordingly improve manufacturability of display devices. In one example the array of red (R), Green (G) and Blue (B) LED wafers are each separately direct or hybrid bonded to silicon (Si) backplane or imager wafers. These stacks can then be singulated to form red, green and blue monochromatic imagers, which could be combined to form a multi-colored image. In another example, red, green, and blue LED wafers can be separately singulated to form R, G, B LED chips and can be direct bonded to one silicon backplane or imager. Elements in a silicon backplane can be electrically connected to LED pixels within R, G, B chips to achieve pixel level control. Although LED wafers can be direct or hybrid bonded to a silicon backplane, any other suitable backplane (e.g., a Thin Film Transistor, or TFT) backplane may also be used. In some embodiments, as explained herein, an optical assembly can comprise at least one red LED chip, at least one green LED chip, and at least one blue LED chip. In some embodiments, an optical system can comprise a plurality or an array of multiple such optical assemblies to direct image data to the user. 
     In some embodiments, the monochromatic image regions can be oriented parallel to one another. For example, in some embodiments, the image regions can be positioned laterally side-by-side on a waveguide. Light from the image regions can be coupled into the waveguide, and the waveguide can transmit a superimposed image of multiple colors to the user. In other embodiments, the image regions can be positioned non-parallel to one another (e.g., perpendicular to one another), and combiner optics can be provided to transmit a superimposed image of multiple colors to the user. 
       FIG. 4  is a schematic side sectional view of an optical assembly of combined optical devices (e.g., monochromatic emitter chips), according to one embodiment. The optical assembly  400  includes a plurality of optical devices  400   a - c  formed by a plurality of optical elements  402   a - c  (such as, e.g., monochromatic LED chips) directly bonded to a corresponding plurality of carrier elements  404   a - c  (such as, e.g., silicon-based backplane). The optical assembly  400  can include as a redirection element or mirroring apparatus  406   a - b  (e.g., a mirror, beamsplitter or other suitable optical redirection device) and an optical combiner apparatus  408  (e.g., a lens). 
     In one embodiment, the optical devices  400   a - c  (including the optical elements  402   a - c  (e.g., monochromatic LED chips, for example, for R, G, B, respectively) with corresponding carrier elements  404   a - c  (e.g., silicon backplane) can be combined to form a colored image or portion of a colored image. That is, instead of for example RGB microLED displays, separate monochromatic LED chips can be combined as shown in  FIG. 4 . With three (3) displays used, issues such as gang bonding of millions of pixels are not a concern. Multiple optical assemblies  400  may be incorporated in an array in various optical systems. 
     In one implementation, the bonded optical devices  400   a - c  can be oriented at an angle relative to one another. For example, the optical elements  402   a - c  can be approximately perpendicular to one another. In another implementation, the optical elements  402   a - c  can form a prescribed angle that is greater or less than 90° relative to one another. The optical devices  400   a - c  can each be mounted on a frame or other structure (not shown) and aligned relative to one or more mirroring apparatus  406   a - b  (which can be for example beam splitters for redirecting light). As shown in  FIG. 4 , the mirroring apparatus  406   a - b  can redirect the light from the optical elements  402   a - c  along a common channel so as to superimpose the colored light from each optical element  402   a - c . The light from each optical element  402   a - c  can be varied, based on for example control via the circuitry of the carrier elements  404   a - c , so as to generate a superimposed light of various colors. The image data of the light from each optical element  402   a - c  can pass through an optical combiner apparatus  408  (e.g., a lens) to collect the light and transfer it to the user. 
     In one implementation, hybrid direct bonding (such as DBI®) can be implemented to bond the carrier elements  404   a - c  (e.g., CMOS circuit) to control each pixel/diode at ˜5 μm pitch with the optical elements  402   a - c  such as large R, G and B chips based on the size of the display. 
     In another implementation, the colors as produced by the optical elements  402   a - c  as driven by the carrier elements  404   a - c  can be used to deliver an image or portion of an image to the user&#39;s eye by the optical combiner apparatus  408  (such as via curved combiners or waveguides). 
     In other implementations, D2D, W2W or D2W bonding can be used, based on the application. 
       FIG. 5  is a schematic side sectional view of an optical assembly including combined optical devices, according to another embodiment. The optical assembly  500  includes individual optical elements  502   a - c  (e.g., optical wafers, etc.) and carrier elements  504   a - c , as well as mirroring apparatus  506   a - c  and optical combiner apparatus  508 . 
     As shown, the individual optical elements (such as for example R, G, B wafers)  502   a - c  can be stacked on carrier elements  504   a - c  and singulated to form three (3) large optical devices such as monochromatic display chips with for example size of 5 mm×8 mm. 
     In one embodiment, the optical elements  502   a - c  can be placed side-by-side. In some embodiments, the optical elements  502   a - c  can be mounted on a common carrier (not shown). In other embodiments, the optical elements  502   a - 502   c  can be mounted on separate carrier elements  504   a - c  to form the optical devices  500   a - c.    
     In one implementation, the optical devices  500   a - c  can be arranged (e.g., mounted on a frame or structure) so as to be laterally offset by a predetermined amount. In such arrangement, the optical elements  502   a - c  are laterally offset from one another by a predetermined distance, along a direction that is parallel to a major surface of at least one carrier element  504   a - c . Here, the emission surfaces can also be parallel to one another. In another implementation, the emission surfaces may not be parallel to one another, but may instead be angled relative to one another. 
     As shown, the light from each optical element  502   a - c  can be redirected by the corresponding mirroring apparatus  506   a - c , so as to superimpose the image data, which can be collected via the optical combiner apparatus  508  (e.g., combiner optics such as a lens) to produce various colors. The light from each optical element  502   a - c  can be varied based on the control via the carrier elements  504   a - c , so as to produce different colors based on how much of each color from each optical element  502   a - c  is emitted and then combined. 
       FIG. 6  is a diagram showing an illustration of physical separation between pixels within an optical device. It includes a plurality of pixels  602   a - c , a plurality of light guides  604 , a plurality of physical separations  606 , a carrier element  608 , an optical element  610 , a bond interface  612  between the carrier element  608  and optical element  610 , a plurality of emitters  614  (light emitting regions), and a plurality of contact pads  616  of the carrier element  608  and the optical element  610 . Light can be emitted from the light emitting surface of the emitters  614 , and can propagate through the pixel regions as shown. 
     In various embodiments, each pixel  602   a - c  (e.g., monochromatic image region) can comprise one or a plurality of optical physical isolation or pixel isolation structures configured to limit crosstalk between neighboring regions of the optical element  610 . For example, the isolation structures can comprise trenches formed through at least a portion of the optical element  610 . The isolation structures may be similar to the deep trench isolation structures implemented in back side illuminated image sensors. 
     As shown, in one embodiment, the physical separation  606  between pixels  602   a - c  within an optical element  610 , such as a chip, can comprise deep trench isolation features for integrated microLED arrays. Such deep trench isolation features can prevent light received by one pixel from going into another, microLEDs can also be fabricated such that light  604  generated by one diode/pixel is not scattered internally to the neighboring pixel/diode, based for example on the physical separation  606 . Based on such individually controllable pixel  602   a - c , light emitted via the emitter  614  (which can be configured to emit light of a single prescribed color, and make up or define at least a part of the pixel  602   a - c ) from for example one pixel  602   c  is physically isolated from the adjacent pixel  602   b  by the physical separation  606 . 
       FIGS. 7A and 7B  are diagrams showing different embodiments with different physical separations.  FIG. 7A  is a diagram showing an illustration of physical separation  702  between every pixel  704 , and  FIG. 7B  is a diagram showing an illustration of physical separation  706  only in A×A matrix (for example, 2×2, 3×3, etc.)  708  of pixels  710 . The embodiment of  FIG. 7B  can produce a high yield because one (1) malfunctioning pixel may not be a concern for, e.g., the light emitted, since the physical separation is between the A×A matrices  708  rather than individual pixels  710 . Such embodiment can also enable improved control of, e.g., brightness of the light emitted. The processor element(s) (e.g., a CMOS or Si back plane) can control a selected number of pixels from the matrix  708  to turn ON or OFF to control brightness, such that the matrix  708  can serve as one large pixel of a display comprising several smaller pixels  710 . Thus, in various embodiments, the processor element(s) can independently control the pixels  710  as part of the matrix  708  to create desired image data, in which the matrix  708  can serve as a larger pixel and the pixels  710  can serve as sub-pixels. The pixels  710  in an optical element can accordingly be divided into matrices of pixels, and the processor element(s) can accordingly be configured to selectively control the brightness of pixels within each matrix. In various embodiments, the isolation features can be configured to optically separate (e.g., prevent crosstalk) between adjacent matrices  708  of pixels  710 . In some embodiments, adjacent pixels  710  within a matrix  708  may not be separated by isolation features. In other embodiments, adjacent pixels  710  may be separated by isolation features. 
       FIG. 8  is a diagram showing an optical system  800  configured to direct light to a waveguide. It includes input coupling  802 , a waveguide  804 , and output coupling  806 . 
     In one embodiment, the optical assemblies  400  and/or  500  such as with the optical assemblies of combined LED-CMOS structure (including monochromatic microLED display) described herein can be attached as separate units or mounted directly (for example via a plurality of input couplings  802 ) on the waveguide  804  in direct, side or angular configuration. In one or more implementations, this can be implemented in for example projectors (projection systems), car HUDs, smart watch displays, and cell phone displays, which include a plurality of output couplings  806 , used to transmit the image data to the user&#39;s eye  102 . 
       FIGS. 9 and 10  are diagrams showing optical devices such as microLEDs directly bonded to a waveguide  906 ,  1006  with input and output couplings. The devices each include optical assembly  902 ,  1002  (described in detail herein with respect to for examples  FIGS. 2-3 ) configured to couple light to the waveguide  906 ,  1006 , with input coupling ( 904  and  1004 , respectively) and to the user with output coupling ( 908  and  1008 , respectively). In some embodiments (e.g.,  FIG. 9 ), the bonded optical devices (e.g., the assembly  902 ) can be directly bonded to the waveguide  906  without an intervening adhesive to mechanically and optically couple the optical devices to the waveguide  906 . In other embodiments, the optical assembly can be mounted to a frame or other structure that connects to the waveguides. 
     The input coupling  904 ,  1004  allows the image data from the optical assembly  902 ,  1002  to enter the waveguide  906 ,  1006  (for example made of dielectric material), which is used to transfer the image data via light (including superimposed light emitted from the optical assembly  902 ,  1002  via for example a corresponding array of emitters) travelling through the waveguide  906 ,  1006  by for example total internal reflection (TIR) and to the user&#39;s eye  102  via the output coupling  908 ,  1008 . 
     In one embodiment, as shown in  FIG. 10 , an optical apparatus  1010  (such as for example a prism) can be used to redirect the light transmitted from the optical assembly  1002 , so as to enable the light to travel through the waveguide  1006 . In some embodiments, the optical assembly  1002  can be mounted to another structure that is angled relative to the waveguide  1006 , and light can be redirected to the optical apparatus  1010  by way of mirrors and combiner optics as shown. 
       FIG. 11  is a diagram showing an illustration of superposition of three color pixels. It includes a plurality of optical elements (e.g., LED die (R, G, B))  1102   a - c  including a plurality of pixels  1106 , a carrier element  1104 , a plurality of optical combining elements  1108  (e.g., lenses), a plurality of connecting waveguides  1110 , a plurality of mirroring apparatus  1112   a - c , an optical combiner apparatus  1114 , and a waveguide  1116 . 
     In one embodiment, the plurality of optical elements  1102   a - c  can emit, via a plurality of emitters (not shown) monochromatic light, which can travel through the corresponding optical combining element  1108  and connecting waveguide  1110 , to be reflected by the corresponding mirroring apparatus  1112   a - c . As shown, the plurality of optical elements  1102   a - c  can be disposed between the carrier element  1104  and the waveguide  1116 . The optical elements  1102   a - c  can be directly bonded to the carrier element  1104  without an intervening adhesive. Furthermore, the mirroring apparatus  1112   a - c  can be arranged at an angle relative to connecting waveguides  1110 , so as to direct the incoming lights through the optical combiner apparatus  1114  and the waveguide  1116  to the user&#39;s eye (not shown). 
     In one embodiment, the carrier element  1104  is a silicon/glass carrier, or an active silicon die driving the pixels  1106  and the optical elements (such as for example LED die)  1102   a - c  in another embodiment. In some embodiments, the optical elements can be directly bonded to the waveguide, e.g., to the connecting waveguide  1110 , without an intervening adhesive. In other embodiments, the optical elements can be attached to the waveguide with a transparent adhesive. 
     Thus, in various embodiments, a bonded optical device is disclosed. The bonded optical device can include a first optical element having a first array of optical emitters configured to emit light of a first color. The first optical element can be bonded to at least one processor element, the at least one processor element comprising active circuitry configured to control operation of the first optical element. The bonded optical device can include a second optical element having a second array of optical emitters configured to emit light of a second color different from the first color. The second optical element can be bonded to the at least one processor element. The at least one processor element can comprise active circuitry configured to control operation of the second optical element. The bonded optical device can include an optical pathway optically coupled with the first and second optical elements, the optical pathway configured to transmit a superposition of light from the first and second optical emitters to an optical output to be viewed by a user. 
     In some embodiments, the first optical element is directly bonded to the at least one processor element without an intervening adhesive, and the second optical element is directly bonded to the at least one processor element without an intervening adhesive. Respective dielectric bonding surfaces of the first optical element and the at least one processor element can be directly bonded to one another without an intervening adhesive. Respective conductive contact pads of the first optical element and the at least one processor element can be directly bonded to one another without an intervening adhesive. Each optical emitter of the first and second arrays of optical emitters can be electrically connected to a corresponding driver circuit on the at least one processor element. 
     In some embodiments, a first optical emitter of the first array of optical emitters and a second optical emitter of the second array of optical emitters at least partially define a pixel, and the optical pathway can be configured to transmit a superposition of the light from the first and second optical emitters of the pixel. The at least one processor element can comprise a first processor element and a second processor element separate from the first processor element. The first optical element can be bonded to the first processor element and the second optical element can be bonded to the second processor element. In some embodiments, the at least one processor element comprises a common carrier. 
     In various embodiments, the optical pathway comprises an optical waveguide. The first optical element can be disposed between the optical waveguide and the first processor element. The second optical element can be disposed between the optical waveguide and the second processor element. In some embodiments, the first and second optical elements are directly bonded to the optical waveguide without an intervening adhesive. In some embodiments, the first and second optical elements are bonded with one or more adhesives transparent to the respective first and second colors of light. 
     In some embodiments, the first and second optical elements can be laterally offset from one another along a direction parallel to a major surface of the at least one processor element. In some embodiments, respective emission surfaces of the first and second optical elements can be generally parallel to one another. In some embodiments, respective emission surfaces of the first and second optical elements can be disposed non-parallel to one another. 
     The bonded optical device can include one or a plurality of optical isolation structures in the first optical element. The optical isolation structures can be configured to limit crosstalk between adjacent optical emitters. 
     In some embodiments, the first color has a first peak at a first wavelength, the second color has a second peak at a second wavelength. A difference between the first and second wavelengths can be at least 25 nm. Thus, in various embodiments, the wavelengths can be separated by a sufficient amount such that the colors emitted by the optical elements can be distinguishable from one another. In some embodiments, the optical pathway can include one or more redirection elements (e.g., mirrors, beamsplitters, etc.) to redirect light from the first and second image regions. In some embodiments, the optical pathway comprises a lens configured to act upon the superimposed light. 
     The bonded optical device can include a third optical element optically coupled with the optical pathway and bonded to the at least one processor element. The third optical element can be configured to emit light of a third color that is different from the first and second colors. The first, second, and third colors can comprise red, green, and blue, respectively. In various embodiments, the optical emitters of the first array are independently controllable. The first and second arrays of optical emitters can comprise respective arrays of light emitting diodes (LEDs). A pitch of the optical emitters of the first array can be less than 50 microns. A pitch of the optical emitters of the first array can be less than 10 microns. 
     In another embodiment, a bonded optical device is disclosed. The bonded optical device can include a first optical element directly bonded to at least one carrier without an adhesive, the first optical element configured to emit light of a first color. The bonded optical device can include a second optical element directly bonded to the at least one carrier without an adhesive. The second optical element can be configured to emit light of a second color different from the first color. The first and second optical elements can be laterally offset from one another along a direction parallel to a major surface of the at least one carrier. The bonded optical device can include an optical pathway optically coupled with the first and second optical elements, the optical pathway configured to transmit a superposition of light from the first and second optical elements to an optical output to be viewed by a user. 
     In some embodiments, the at least one carrier comprises a first carrier and a second carrier separate from the first carrier. In some embodiments, the at least one carrier comprises at least one processor element comprising active circuitry configured to control operation of at least one of the first and second optical elements. In some embodiments, the first optical element can be directly bonded to the at least one carrier without an intervening adhesive, and the second optical element can be directly bonded to the at least one carrier without an intervening adhesive. In some embodiments, respective dielectric bonding surfaces of the first optical element and the at least one carrier are directly bonded to one another without an intervening adhesive. In some embodiments, respective conductive contact pads of the first optical element and the at least one carrier are directly bonded to one another without an intervening adhesive. In various embodiments, the at least one carrier comprises at least one of silicon or glass. In some embodiments, the at least one carrier can have a coefficient of thermal expansion (CTE) less than 7 ppm. 
     In some embodiments, the optical pathway can comprise an optical waveguide. In some embodiments, a third optical element can be optically coupled with the optical pathway. The third optical element can be directly bonded to the at least one carrier without an adhesive. The third optical element can be configured to emit light of a third color that is different from the first and second colors. 
     In some embodiments, the first, second, and third colors comprise red, green, and blue, respectively. The first and second optical elements can comprise respective arrays of optical emitters. The optical emitters can be independently controllable. The optical emitters can comprise light emitting diodes (LEDs). 
     In another embodiment, a method of bonding at least one optical element with at least one processor element is disclosed. The method can include bonding a first optical element with to at least one processor element, wherein the first optical element comprises a first array of optical emitters configured to emit light of a first color, and the at least one processor element comprises active circuitry configured to control operation of the first optical element; bonding a second optical element with to the at least one processor element, wherein the second optical element comprises a second array of optical emitters configured to emit light of a second color different from the first color, and the at least one processor element comprises active circuitry further configured to control operation of the second optical element; and coupling the first and second optical elements with an optical pathway, the optical pathway configured to transmit a superposition of light from the first and second optical emitters to an optical output to be viewed by a user. In some embodiments, the at least one carrier comprises a processor die. 
     Although disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and obvious modifications and equivalents thereof. Further, unless otherwise noted, the components of an illustration may be the same as or generally similar to like-numbered components of one or more different illustrations. In addition, while several variations have been shown and described in detail, other modifications, which are within the scope of this disclosure, will be readily apparent to those of skill in the art based upon this disclosure. It is also contemplated that various combinations or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the present disclosure. It should be understood that various features and aspects of the disclosed embodiments can be combined with, or substituted for, one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the aspects that follow.