Optical chassis, camera having an optical chassis, and associated methods

[0001] This is a continuation-in-part application based on pending application Ser. No. 11/783,530, filed on Apr. 10, 2007, which in turn claims priority under 35 U.S.C. §120 as a continuation to Ser. No. 10/809,914, filed Mar. 26, 2004, now U.S. Pat. No. 7,224,856, which in turn claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 60/457,664 filed on Mar. 26, 2003, entitled “Wafer Based Optical Chassis” and under 35 U.S.C. §120 as a continuation-in-part to U.S. Application Ser. No. 09/983,278 filed Oct. 23, 2001, now U.S. Pat. No. 6,798,931 B2, entitled “Separating of Optical Integrated Modules and Structures Formed Thereby,” the entire contents of all of which are hereby incorporated by reference for all purposes.

[0002] 1. Field of the Invention

[0003] The present invention is directed to a wafer based optical chassis and associated methods. More particularly, the present invention is directed to protecting active elements in an optical system and realizing electrical input/output without requiring separate packaging.

[0004] 2. Description of Related Art

[0005] Active elements, such as optoelectronic chips, e.g., light sources for transmitters and detectors for receivers, are typically housed in a transistor outline (TO) can. Such a TO can is typically made of metal, has a large form factor, involves an expensive serial manufacturing process and requires active alignment with external passive optical elements. This large form factor separates the active element from an external passive optic along the optical axis, resulting in the passive optic needing to handle a more divergent beam, rendering the optic bigger, thereby further increasing the size of the system. Additionally, the TO can has electrical termination concerns, limiting the speed of the active elements.

[0006] Current trends towards miniaturization have spurred numerous small form factor designs. Most of these designs are directed to integrating the passive optical element with some connector, separate from the TO can. While this may reduce the length of the system and simplify the manufacturing of the passive optical portion of the system, the TO can, and the problems attendant therewith, are still present.

[0007] The present invention is therefore directed to a optical chassis, camera having the same, and associated methods that substantially overcome one or more of the problems due to the limitations and disadvantages of the related art.

[0008] It is a feature of the present invention to protect an active element with an assembly including passive optical elements.

[0009] It is another feature of the present invention to provide efficient electrical coupling to and from the protected active elements.

[0010] It is yet another feature of the present invention to provide packaging of an active element that can at least partially be created in parallel.

[0011] It is yet another feature of the present invention to provide alignment that compensates for variations arising in the manufacturing process.

[0012] At least one of the above and other features may be realized by providing a camera, including a mount substrate, a detector on a first surface of the mount substrate, a spacer on the mount substrate, the spacer including a hole exposing the detector, a cover on the spacer, the cover covering the hole, the mount substrate, the spacer and the cover together sealing the detector, the cover having a planar surface facing the detector, and an external electrical interconnection for the detector provided outside the sealing, the external electrical interconnection being on a first surface and a second surface, different from the first surface, of the mount substrate, the external electrical interconnection adapted to connect the detector to an electrical contact pad.

[0013] The camera may include a passive optical element on a surface of the cover opposite the planar surface.

[0014] The camera may include a via extending through a bottom surface of the mount substrate, the electrical interconnection going through the via and connecting the detector on the first surface of the mount substrate to the electrical contact pad on a bottom surface of the mount substrate. The mount substrate may be a detector chip and an active area of the detector chip may be integrated in the first surface of the mount substrate.

[0015] The first surface may or may not be parallel with the second surface. The camera may include an optical element on a substrate, substantially planar regions of the substrate being secured to the cover.

[0016] The camera may include an upper substrate, a lower substrate, and a spacer between the upper and lower substrates, wherein a substantially planar region of the lower substrate, on a surface of the lower substrate opposite the second spacer, being secured to the cover. The camera may include an optical element on at least one of the upper and lower substrates. The optical element may be on a surface adjacent the spacer. The spacer may be an adhesive, e.g., a punched adhesive. The spacer may include an aperture.

[0017] At least one of the above and other features may be realized by providing a camera, including an upper substrate, a middle substrate, a first spacer between the upper and middle substrates, the middle and upper substrates and the first spacer defining a first interior space, a lower substrate, a second spacer between the middle and lower substrates, the middle and lower substrates and the second spacer defining a second interior space, a first optical element on the upper substrate, a second optical element on the lower substrate, at least one of the first and second optical elements being in the first interior space, a detector on the lower substrate in the second interior space, and an electrical contact coupled to the detector on the lower substrate outside the second interior space.

[0018] The first and second spacers may be an adhesive, e.g., a punched adhesive.

[0019] At least one of the above and other features may be realized by providing a method of making a camera, including providing an upper substrate, providing a middle substrate, providing a first spacer between the upper and middle substrates, the middle and upper substrates and the first spacer defining a first interior space, providing a lower substrate, providing a second spacer between the middle and lower substrates, the middle and lower substrates and the second spacer defining a second interior space, providing a first optical element on the upper substrate, providing a second optical element on the lower substrate, at least one of the first and second optical elements being in the first interior space, providing a detector on the lower substrate in the second interior space, and providing an electrical contact coupled to the detector on the lower substrate outside the second interior space.

[0020] At least three of the upper substrate, the first spacer, the middle substrate, the second spacer and the lower substrate may be provided on a wafer level.

[0021] At least one of providing the first and second spacers may include simultaneously providing an adhesive.

[0042] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thickness of layers and regions are exaggerated for clarity. It will also be understood that when a layer is referred to as being “on” another layer or substrate, it may be directly on the other layer or substrate, or intervening layers may also be present. Further, it will be understood that when a layer is referred to as being “under” another layer, it may be directly under, or one or more intervening layers may also be present. In addition, it will also be understood that when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or one or more intervening layers may also be present. Like numbers refer to like elements throughout.

[0043] As used herein, the term “wafer” is to mean any substrate on which a plurality of components are formed on a planar surface which are to be separated through the planar surface prior to final use. Further, as used herein, the term “camera” is to mean any system including an optical imaging system relaying optical signals to a detector system, e.g. an image capture system, which outputs information, e.g., an image.

[0044] FIG. 1 shows an embodiment of an optical chassis 5 of the present invention having four substrates. These four substrates include a mount substrate 10, a spacer substrate 20, a sealer substrate 30 and an optional optics substrate 40. The mount substrate 10 serves as a mount for optoelectronic devices, here a light source 12 and a power monitor 14, and provides the electrical interconnections, here including a wire bond 16, conductive patterns 17 and metalized trenches 18. The conductive patterns 17 each include a pad for the wire bond 16 and connect the pad to the trench 18 for external communication. The conductive patterns 17 may be created by patterning conductive material on the mount substrate 10 in a known manner. The trenches 18 may be created by removing a portion of the mount substrate 10 in a conventional manner and filling this portion with conductive material. The conductive material for the trenches 18 may be provided at the same time the conductive patterns 17 are formed. The details of the mount substrate 10 can be seen more clearly in FIG. 2.

[0045] The spacer substrate 20 provides room for the beam output from the light source 12 to expand. If the optoelectronic device 12 does not have its active area on its top face, e.g., an edge emitting laser, an appropriate portion of a sidewall 22 of the spacer substrate 20 may be angled and coated with a reflective coating to appropriately direct the beam in the optical chassis 5. A hole 24 in the spacer wafer 20 may be formed by etching a silicon wafer, producing the characteristic angled sidewall 22 from such an etch. The spacer substrate 20, in conjunction with the sealer substrate 30, hermetically seals and protects the optoelectronic devices 12, 14 from the environment. The sealer substrate 30 may also include an optical element on either surface thereof, e.g., an optical element which reduces the divergence of the beam output from the light source 12.

[0046] The optional optics substrate 40 includes at least one optical element. Here, a diffractive optical element 44 on a first surface of the optics substrate 40 directs some of the light from the light source 12 to the power monitor 14, as disclosed, for example, in commonly assigned U.S. Pat. No. 6,314,223 entitled “Diffractive Vertical Cavity Surface Emitting Laser Power Monitor and System.” A coupling element 42 on a second surface of the optics substrate 40 may couple the light between the optoelectronic device, here the light source 12, and further applications, e.g., a fiber. Of course, more than one functionality may be incorporated into each optical element.

[0047] If an optical element is to be provided on one or both of the surfaces of the optional optical substrate 40 or the sealer substrate 30 adjacent to one another, a separation feature 32, e.g., an indentation or stand off, may be provided on either the sealer substrate 30 or the optional optics substrate 40 to insure proper functioning of the optical element. The sealer substrate 30 is transparent. The sealer substrate 30 may be glass or may be some other transparent material that closely matches the coefficient of thermal expansion of the spacer substrate 20, e.g., Pyrex when the spacer substrate is silicon. The smaller size of the chassis 5, e.g., roughly 2 mm by 2 mm in x and y, also helps with any thermal mismatch, since there is not a lot of strain placed in the securing joints between the substrates.

[0048] Finally, when the optical chassis 5 is to be joined with another device, mating features may be provided on a terminal surface thereof. For example, if the optical chassis is to be mated with a fiber optic ferule, a standoff 43 encircling the optical element 42 may be provided. The standoff 43 may be SU-8 and provides both alignment of the optical chassis 5 with additional devices and provides separation of the optical element 42.

[0049] As can be seen from the profile of the optical chassis 5, a plurality of each of these substrates may be created on a wafer level, secured together with other substrates in a vertical stack, and then vertically separated to form a plurality of individual optical chassis 5. As shown in FIG. 3, a mount wafer 10′, a spacer wafer 20′, a sealer wafer 30′ and an optional optics wafer 40′ are to be aligned and secured together on a wafer level. Each of these wafers includes a plurality of the respective mount substrates 10, spacer substrates 20, sealer substrates 30 and optional optical substrates 40. The top three wafers 40′, 30′ and 20′ may be created completely on a wafer level in known fashions. These wafers may then be secured together as shown in FIG. 4 forming a secured stack wafer 50′. These wafers may be aligned and secured as set forth, for example, in U.S. Pat. No. 6,096,155 entitled “Method of Dicing Wafer Level Integrated Optical Elements.”

[0050] For the mount wafer 10′, a plurality of metalized trenches 18 for providing the electrical interconnections may be formed on the wafer level. The optoelectronic elements 12, 14 may then be positioned on the mount wafer 10′, e.g., using pick-and-place techniques, and then wire bonded 16 to the metalized trenches 18. The metalized trenches 18 may extend along the mount wafer 10′, so the separation of the mount wafer 10′ will expose the metal on the edge of the mount substrate, as can be seen in FIGS. 1 and 2. The secured stack wafer 50′ is then secured to the mount wafer 10′ and then vertically separated to form a plurality of optical chassis 5 as shown in FIG. 1. Alternatively, the secured stack wafer may be vertically separated to form secured stack substrates, which are then bonded to the mount wafer 10′.

[0051] An alternative optical chassis 55 is shown in FIGS. 6 and 7. Here, the optional optical substrate 40 is not included. Only a diffractive optical element 34 for power monitoring and/or efficient coupling is provided on the sealer substrate 30. The spacer substrate 20 is the same as in FIG. 1. The mount substrate 60 provides different electrical connections as in FIG. 1 for the light source 12 and the power monitor 14. Here, the optoelectronic devices are again wire bonded, here to conductive pads 65. Then, on the bottom of the mount substrate 60, conductive, e.g., metalized, through holes or vias 64 and conductive structures 62, e.g., solder balls, are used to provide the electrical interconnections to the electrooptical elements on the top surface of the mount substrate 60. These conductive structures may be large enough to obscure the hole in the mount substrate to insure the seal, to avoid creating a thermal gradient and to avoid extra oxidation. This solution may be particularly useful if the mount substrate is a ceramic, since it is expensive to put solder on ceramic. The seal may be hermetic.

[0052] Another alternative for providing electrical interconnections to the optoelectronic element on a wafer level is shown in FIGS. 8A-8D. As shown in FIG. 8A, a saw or other etching device is used to produce V-shaped groove 81 in a wafer 80. Then, the groove 81 and the wafer 80 are coated with an electrically conductive coating 82, e.g., metal, as shown in FIG. 8B. Then, the wafer 80 is separated at the V-groove 81 and at another portion to form a mount substrate 83, as shown in FIG. 8C. The groove 81 needs to be wide enough so that an angle remains after separation. For example, if dicing is used as the separation technique, the groove will need to be wider than the blade width of the dicing saw.

[0053] As shown in FIG. 8D, an optoelectronic device 86 is mounted on the conductive coating 82 of the mount substrate 83. A solder ball 84 or other conductive structure may then used to connect the conductive coating 82 to an electrical connection on a board 88. The other substrates 20, 30 and optionally 40 may be stacked over the mount substrate 83 as shown in the other configurations.

[0054] Electrical input/output may also be realized as shown in FIG. 9, in which the substrates forming the optical chassis do not have the same width, thereby forming a ledge 15, with the electrical connection being realized on a portion of the chassis 5 providing the ledge 15. As shown in FIG. 9, the ledge 15 may be formed by having the mount substrate 10 extend further in at least one direction than the adjacent spacer substrate 20. The electrical contacts may be formed on the surface of the ledge or a portion of the ledge 15 may be removed to form the trenches 18 therein to increase the surface for electrical contact.

[0055] Such a ledge may be formed by die bonding a secured stacked substrate having the spacer substrate 20 and the sealer substrate 30 to the mount substrate 10. Forming such a ledge on wafer level may be realized in a number of manners, including using dicing saws of different thicknesses and dicing through opposite surfaces, e.g., flipping the wafer after partial dicing, of the secured stacked wafer, including the mount wafer 10′. Details of forming such a ledge on a wafer level are set forth in the commonly assigned, co-pending application entitled “Separating of Optical Integrated Modules and Structures Formed Thereby,” filed Oct. 23, 2001, which is hereby incorporated by reference in its entirety.

[0056] If customized performance of the optical chassis is known, optional optical substrate(s) may be incorporated to provide the desired performance. Otherwise, the optical chassis of the present invention may be used to simply replace the conventional TO-can element and can have the conventional optics aligned thereto, as is currently done for the TO-can optoelectronics. Two manners of achieving this are shown in shown in FIGS. 10 and 11. As shown in FIG. 10, the vertically integrated optical chassis 55 of the present invention may have an optical element 90, including optical elements larger in the x- and/or y-direction than the optical chassis 55, die-bonded thereto. As shown in FIG. 11, the optical element 90 may be separate from but aligned with the optical chassis 55, here shown in a common housing 92. This separation reduces the alignment tolerances for the optical element 90. The sealer substrate 30 may still include optics thereon for improving the light from the light source 12, e.g., collimating or at least reducing the divergence of the light.

[0057] A specific configuration of an optical chassis in accordance with the present invention is shown in FIGS. 12A-12B. As can be seen therein, an optical chassis 100 is attached to a flex lead 150, inserted into a magnet 160, on which a fiber stop 170 and then a fiber sleeve 180 is secured. This structure may be provided on a heat sink.

[0058] The optical chassis 100 includes a mount substrate 110 having a ledge 115, a spacer substrate 120 and a sealer substrate 130. An optoelectronic device 112 and wire bonds 116 are on the mount substrate 110. The sealer substrate 130 includes a lens 132 and an angled, reflective sidewall 122. The angled, reflective sidewall 122 serves as a mirror to direct light between the optoelectronic device 112 and the fiber in the fiber sleeve 180. If the active area or facet of the optoelectronic device is not on an edge thereof, this angled, reflective sidewall 122 is not needed.

[0059] An additional spacer substrate 136, which may include additional spacing structures 138, separates the lens 132 from an isolator stack 140. The spacing structures 138 are used when a passive optical element is on one or more opposing surfaces in the stack and the surfaces would otherwise contact the passive optical element. The spacing structures may be integral with the surface or may be provided on the surface. Alternatively, these spacing structures may be on the sealer substrate 130. The electrical connection of the optoelectronic device 116 is realized using the ledge 115, as discussed in connection with FIG. 9.

[0060] The isolator stack 140 includes a first polarizer 142, a Faraday rotator 144 and a second polarizer 146. The magnet 170, which may be a ring magnet, surrounds the isolator stack 140 when the optical chassis 100 is inserted as shown in FIG. 12A, thereby completing the isolator. If the Faraday rotator 144 is a latching type, then the separate magnet 170 is not needed.

[0061] In any of the above configurations, the active elements are secured to the mount substrate such that they remain secured and withstand subsequent processing, e.g., the securing of the substrate. The construction of the optical chassis of the present invention needs to be determined in an appropriate order, with the least robust technique being performed last. The materials used for the securing of the active elements, realizing the electrical connections and the securing of the substrates must be selected in accordance with the required order. For example, the active elements may be secured on the mount substrate using a gold-tin (AuSn) solder and the substrates may then be secured using a material with a lower melting point, e.g., silver-tin (AgSn) solder.

[0062] Techniques for realizing alignment of the optical elements in the optical chassis are shown in FIGS. 13A-14B. In making micro-optical elements, there are inevitable variations in characteristics, e.g., lens thickness, radius of curvature (ROC), of individual elements. By classifying these lenses by their ROC into different groups within a range, e.g., ±1%, the variation in ROC may be compensated for with the placement of the angled surface 122 of the spacer substrate 120, as shown in FIG. 13A-13B. Once a lens is selected for a particular optoelectronic device 112 on the mount substrate 110, the separation d between the optoelectronic device 112 and a back edge of the angled surface 122 is determined in accordance with the ROC of the lens to be used. If the angled surface 122 has an angle of approximately 45°, this distance d will be roughly equal to the height of the spacer substrate 120. Thus, this aligning of the optoelectronic device 112 with the angled surface 122 compensates for any variations in the thickness of the spacer substrate 120, as well as taking the ROC of the lens into account.

[0063] The aligning of the lens to the optoelectronic device 112 is shown in FIGS. 14A-14B. Here, the image of the active area of the optoelectronic device 112 in the reflective angled surface 122 may be used to align the lens. A bottom surface of the substrate having the lens thereon, which may be the sealer substrate 130 as shown in FIGS. 12A-12B, includes alignment features 134, here in the form of a crosshair centered on the lens on the top surface of the substrate. The alignment features 134 are then centered with the image of the active area of the optoelectronic device 112 as reflected by the angled surface 122 to insure proper alignment there between. Since the height of the optoelectronic element changes its location on the angled surface 122, by aligning the lens to the reflection from the angled surface 122, variations in the height of the optoelectronic element may be compensated for as well.

[0064] If the active area of the optoelectronic device 112 is not on a side thereof, the lens may be aligned by directly viewing the active area using alignment features 134. The variation in height of such optoelectronic devices, i.e., in the z-direction, do not significantly affect the performance. If there are no optical elements on the sealer substrate 130, the alignment thereof is not critical. Since the sealer substrate 130 is transparent, alignment features do not need to be provided thereon, as alignment features on surfaces below the sealer substrate may be viewed through it. If there are optical elements on other substrates, and the sealer substrate 130 is transparent, the same alignment techniques may be employed.

[0065] Another embodiment of an optical chassis 200 is illustrated in FIG. 15. As can be seen therein, the optical chassis may include a sealer substrate 230, a spacer substrate 220, and a mount substrate 260. The sealer substrate 230, the spacer substrate 220 and the mount substrate 260 may form an enclosure 240.

[0066] While the mount substrate 260 is illustrated in FIG. 15 as being larger in the x-y plane than the sealer substrate 230 and the spacer substrate 220, the mount substrate may be the same size in the x-y plane as the remaining substrates. The spacer substrate 220 may be formed from a wafer, e.g., a silicon wafer, etc. or may be an adhesive, e.g., a punched adhesive, or simultaneously provided, as set forth, for example, in U.S. Pat. No. 6,669,803, which is hereby incorporated by reference in its entirety.

[0067] The sealer substrate 230 may include an optical element 232 on one or both surfaces in the x-y plane. When the optical chassis 200 is to serve as a camera, the optical element(s) may provide an image onto the detector array 262.

[0068] Alternatively or additionally, by vertical stacking, i.e., in the z direction, of n/2 substrates on the sealer substrate 230 may provide up to n parallel surfaces on which optical elements may be created. An example of such an optics stack 270 is illustrated in the schematic cross-sectional perspective view of FIG. 16. The optics stack 270 may have a same dimension in the x-y plane as the sealer substrate 230 or may be smaller or larger in the x-y plane than the sealer substrate 230.

[0069] The optics stack 270 may include a first substrate 280, a spacer 285, and a second substrate 290, thereby providing four parallel surfaces on which optical elements may be formed. The first substrate 280, the spacer 285 and the second substrate 290 may form interior space 295. In the particular example illustrated, a first optical element 282 is on an upper surface of first substrate 280 and a second optical element 292 is on an upper surface of the second substrate 290, i.e., within the interior space 295.

[0070] As can be seen therein, and as is evident in the previous embodiments, even when optical elements are formed on these parallel surfaces, opposing substantially planar regions remain at which adjacent substrates may be readily secured, e.g., on a wafer level. The spacer 285 may be integrated with one or both of the adjacent substrates, formed from a wafer, e.g., a silicon wafer, etc. or may be an adhesive, e.g., a punched adhesive, or simultaneously provided, as set forth, for example, in U.S. Pat. No. 6,669,803, which is hereby incorporated by reference in its entirety.

[0071] The mount substrate 260 may be a sensor substrate, and may include detector array 262. The detector array 262 may be in the enclosure 240. The detector array 262 may be a CMOS photodiode array, i.e., may be monolithically integrated in the mount substrate 260, which may be a CMOS IC substrate. The detector array 262 may receive an image output from the optical element 232. The mount substrate may further include an array of microlenses (not shown) on the detector array 262.

[0072] Then, on the bottom of the mount substrate 260, conductive, e.g., metalized, through holes or vias (not seen in this view) and conductive structures 266, e.g., solder balls, may be used to provide the electrical interconnections to the detector array 262 on the top surface of the mount substrate 260. These through holes may have any appropriate cross section.

[0073] As shown in FIG. 15, the sealer substrate 230 and the spacer substrate 220 may be secured and singulated on the wafer level, with or without the optics stack 270 of FIG. 16. Then, a plurality of resultant structure may be secured to a corresponding plurality of detector arrays mount substrates on the wafer level. The mount substrate may then be singulated to form the optical chassis 200.

[0074] Alternatively, any of the two adjacent substrates in the z direction may be secured on a wafer level, with resultant structures secured to remaining substrate(s) on wafer level. For example, the optics stack 270 may be secured on a wafer level, and singulated, then the substrates forming the optical chassis 200 may be secured on a wafer level, a plurality of optics stacks 270 may be secured to the wafer level optical chassis, and then the optical chassis may be singulated to form individual optical chassis with the optics stacks 270 thereon. Further, even when the mount substrate 260 is larger in the x-y plane than the sealer substrate 230 and the spacer substrate 220, illustrated in FIG. 15, these may still be secured on a wafer level. For example, after securing the three substrates on a wafer level, a first singulation step may be used to expose an upper surface of the mount substrate 260, then a second singulation step, which may be the same process or a different process as the first singulation step, may be used to form the individual optical chassis 200.

[0075] Thus, in accordance with the present invention, an optical chassis having a small form factor may be created at least partially on a wafer level, including electrical interconnections. The optical chassis of the present invention also provides a seal without requiring a TO can or other separate housing. Further, since substrates of the optical chassis are secured to one another, rather than to a carrier as in a TO can, better alignment can be maintained for longer.

[0076] While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the present invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the invention would be of significant utility without undue experimentation. For example, any of the electrical interconnections shown may be used with any optical chassis embodiments. Further, additional optical substrates or elements as needed may be secured to the optical chassis. Additionally, the optics stack may be secured to any of the optics chassis. Finally, any of the configurations of the optical chassis may be created at least partially on a wafer level as discussed regarding FIGS. 3-5.