Abstract:
An silicon-on-insulator (SOI)-based photonics platform is formed to including a venting structure for encapsulating the active and passive optical components formed on the SOI-based photonics platform. The venting structure is used to allow for the encapsulated components to “breathe” such that water vapor and gasses will pass through the package and not condensate on any of the encapsulated optical surfaces. The venting structure is configured to also to prevent dust, liquids and other particulate material from entering the package.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 61/359,489, filed Jun. 29, 2010 and herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to silicon-on-insulator (SOI)-based photonic arrangements and, more particularly, to a vented packaging arrangement for encapsulating components on an SOI-based photonics platform. 
     BACKGROUND OF THE INVENTION 
     For many photonic products based on a silicon-on-insulator (SOI) opto-electronics platform, photonic components such as lasers, active optical devices and passive optical devices are mounted on (or integrated within) the same SOI substrate as the associated optical waveguides. In some cases, the electrical integrated circuits (ICs) used to control the lasers and other active optical devices are also mounted on/integrated within the common SOI substrate. 
     For any component with an optical “surface” (e.g., lasers, lenses, waveguide endface, etc.), dust and water condensation collecting on the optical surface will degrade the performance of the component, causing the optical signal entering or exiting the surface to scatter and reduce the power remaining along the optical signal path. Additionally, some active components (such as laser diodes and detectors) require a stringent operating environment for long-term reliability. Dust and water condensation are known to degrade the performance of these devices, leading to premature failure. 
     In order to protect a laser (or other critical component(s)) from dust/condensation, one prior art approach is to house these devices in a sealed environment (such as a hermetic package). As a general practice, hermetic sealing is relatively expensive and is not considered as a preferred alternative for use in high volume, consumer applications. 
     One non-hermetic prior art arrangement for protecting components from dust and water condensation utilizes a “cap” that is attached to and sealed around the perimeter of the SOI substrate. The cap is generally formed of a polymer material and is usually attached to the SOI substrate using adhesives or solders.  FIG. 1  is a side view of an SOI photonics platform including this prior art type of cap.  FIG. 1  shows an SOI photonics platform  1  including a silicon substrate layer  2 , a buried oxide layer  3  and a relatively thin silicon surface layer  4  (hereinafter referred to as SOI layer  4 ). Optical waveguides are generally formed within SOI layer  4 . In this particular configuration, a laser diode  5  is disposed within an etched region formed through SOI layer  4  and buried oxide layer  3  so as to be placed upon silicon substrate  2 . An optical detector  6  is positioned behind laser diode  5  (used in this case as a backface monitor). A lensing arrangement  7  is positioned along the output signal path from laser diode  5  and is used to focus the propagating optical signal into an optical waveguide  8  formed within SOI layer  4 . A set of electrical contacts  9  to both laser diode  5  and detector  6  are wire bonded to bond pads  10  placed above the interlayer dielectric (ILD) layer  11  of SOI photonic platform  1 . 
     As shown in  FIG. 1 , a cap  20  is disposed to cover and encapsulate the optical and electrical components included within the SOI photonics platform  1 . An adhesive/epoxy  22  is used to attach cap  20  to the platform. Cap  20  is generally formed of a polymer material and is suitable for preventing dust, liquids and other particulate matter from entering the structure and interfering with the operation of the optical components. 
     While the arrangement of  FIG. 1  is considered an improvement in terms of protecting the sensitive optical devices to an extent, it is still possible for moisture to penetrate through the cap, allowing water to condense inside the enclosure. Thus, a need remains for an encapsulation arrangement of SOI-based photonic structures that does not require the use of a hermetic seal to prevent the build-up of condensation within the package. 
     SUMMARY OF THE INVENTION 
     The need remaining in the prior art is addressed by the present invention, which relates to silicon-on-insulator (SOI)-based photonic arrangements and, more particularly, to a vented packaging arrangement for encapsulating components on an SOI-based photonics platform. 
     In accordance with the present invention, a venting structure is used in conjunction with an SOI-based photonics platform to allow for the encapsulated components to “breathe” such that water vapor and gasses will pass through the venting structure and not condensate on any of the encapsulated optical surfaces. The venting structure is also configured to prevent dust, liquids and other particulate material from entering the package. 
     In one embodiment, a vented cap is formed and comprises a breathable membrane formed as part of a conventional polymer cap. Alternatively, a plurality of slots (microstructure dimensioned) are formed through a cap comprising silicon (or another material that can be processed to form microstructured openings). The slots are sized to allow for exchange of water vapor and gasses without permitting dust, liquids and particulate matter from entering the enclosure. 
     In yet another embodiment, a plurality of etched through-holes are formed in the SOI structure itself, creating a path from “inside” the package to the outside, creating vents within the structure itself to prevent condensation within the package; a conventional cap may then be utilized to prevent dust, liquids and particulate matter from entering the package. Alternatively, a vented cap may be used in conjunction with the plurality of etched through-holes to provide additional paths for the exchange of water vapor and gasses between the interior and exterior of the package. 
     Other and further embodiments of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Referring now to the drawings, where like numerals represent like parts in several views: 
         FIG. 1  shows a prior art encapsulation arrangement for an SOI-based photonics platform, using a cap to prevent dust from contaminating optical surfaces; 
         FIG. 2  illustrates an exemplary vented SOI-based photonics platform formed in accordance with the present invention, in this case including a breathable membrane incorporated with the cap; 
         FIG. 3  illustrates an alternative vented cap for use in accordance with the present invention; 
         FIG. 4  shows yet another embodiment of the present invention, including a vent structure formed within the SOI structure itself to prevent condensation, this embodiment also using a conventional cap to prevent dust contamination; 
         FIG. 5  is a cut-away top view of an embodiment utilizing a vent structure formed within the SOI structure, as with  FIG. 4 , in this top view showing three separate pluralities of vias used to vent the enclosed arrangement; and 
         FIG. 6  shows yet another embodiment of the present invention, utilizing the vented substrate as shown in  FIG. 4  in conjunction with the breathable membrane as shown in  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 2  illustrates an exemplary vented SOI-based photonics platform formed in accordance with the present invention. The exemplary optical and electrical components as described above are also shown in  FIG. 2  (and the following drawings), where the specific included components and their arrangement are not considered as relevant to the present invention and are shown merely for the sake of illustrating the application of the invention. 
     It is proposed to include a vent structure with the encapsulated optical components to allow for any moisture that may be present to escape during “turn-on” and operation of the photonic arrangement. At the same time, the vent structure prevents dust particles, liquids and other particulate matter from entering the enclosure at all times. Advantageously, the vent structure allows for equalization of pressure during changing environmental conditions. 
     In the embodiment shown in  FIG. 2 , the inventive venting arrangement takes the form of a vented cap structure  30  disposed over and attached to SOI-based photonics platform  1 . Vented cap structure  30  is shown as including a breathable membrane  32  formed of a polymer-based membrane material (one example being sold under the tradename GORE™ Protective Vents). Breathable membrane  32  allows for water vapor and gasses to pass through, in both directions, in an unimpeded fashion, as shown by the double-ended arrow in  FIG. 2 . At the same time, breathable membrane  32  prevents dust, liquids and other particulate matter from entering the package (depicted by the “X”-d out arrow in  FIG. 2 ). 
     In the particular embodiment shown in  FIG. 2 , breathable membrane  32  is used as the upper surface of cap structure  30  and is sealed to sidewall  34  of cap structure  30 , sidewall  34  comprising a conventional material used for a cap or housing, such as a polymer. Sidewall  34  is then attached to the top surface of SOI photonics platform  1  using adhesive/epoxy  22  in the manner of the prior art as shown in  FIG. 1 . The amount of actual surface area covered by breathable membrane  32  is considered to be a design choice. While shown as completely covering the top surface of cap structure  30  in the embodiment of  FIG. 2 , it is also possible for breathable membrane  32  to form only a portion of the top surface or, alternatively, a portion (or all) of the side surface, of vented cap structure  30 . 
       FIG. 3  illustrates another vented arrangement formed in accordance with the present invention. As with the embodiment of  FIG. 2 , the arrangement of  FIG. 3  comprises a vented cap structure. Referring to  FIG. 3 , a vented cap structure  40  is shown, where cap structure  40  is formed of silicon or a glass material. In this embodiment, vented cap structure  40  is formed to include a plurality of etched through-holes  42 . The size of the openings of through-holes  42  is exaggerated for the sake of illustration, where in implementation the holes comprise a diameter ranging from submicron to a few microns in size. 
     By using silicon (or any other suitable glass material), conventional IC processing can be used to form through-holes  42 , including the location, number and arrangement of the holes. As with breathable membrane  32 , through-holes  42  are sized to allow for vapor and gasses to pass in both directions through vented cap structure  40 , while preventing dust particles, liquids and other particulate matter from entering the encapsulated arrangement. Vented cap structure  40  is attached to the top surface of SOI photonics platform  1  using, for example, a wafer scale bonding process or other suitable adhesive/epoxy  22 . 
     As mentioned above, it is possible to provide venting in the SOI-based opto-electronics platform without the need to modify the cap structure as used in prior art encapsulation methods.  FIG. 4  illustrates an embodiment of the present invention including a venting arrangement  50  that is formed within and through the layers of SOI photonics platform  1 . A top view of this arrangement is shown in  FIG. 5 . A conventional cap  20  as associated with the prior art can be used with this embodiment to prevent dust, liquids and other particulate matter from entering encapsulated arrangement. 
     Referring to  FIG. 4 , venting arrangement  50  includes at least one slot (microtrench)  52  formed through a portion of ILD layer  11  of SOI photonics platform  1 . As shown, slot  52  is formed to extend from an area outside of the encapsulated arrangement to an interior region thereof (slot  52  being shown in phantom in the view of  FIG. 4 ). Slot  52  is formed to have a width ranging from submicron to a few microns, and exhibit a length at least sufficient to extend underneath the sidewall  20 -S of cap  20 . Slot  52  may be formed through one or more of the underlying layers including SOI layer  4 , buried oxide layer  3  and silicon substrate  2  (at least needing to be formed through a depth of ILD layer  11 ). The particular embodiment as shown in  FIG. 4  illustrates slot  52  as extending into the upper portion of the silicon substrate. 
     Preferably, the vented structure embodiment of the present invention as shown in  FIG. 4  utilizes a plurality of slots  52 .  FIG. 5  is a cut-away top view, taken along line  5 - 5  of  FIG. 4 , illustrating an exemplary arrangement using a plurality of slots  52 - 1  through  52 -N disposed in parallel. While the slots are shown in this particular location, it is to be understood that the slots may be formed at any suitable location (or locations) around the periphery of the encapsulated arrangement. 
     It is also possible to use the venting arrangement as shown in  FIG. 4  in conjunction with the vented cap arrangement as shown in  FIG. 2 or 3 , providing pathways for exchange of water vapor and gasses through both locations (SOI substrate and cap) in the enclosed arrangement.  FIG. 6  illustrates one exemplary embodiment using breathable membrane  32  in conjunction with venting slot  52 . 
     It is to be understood that the above-described arrangements are merely illustrative of the many possible specific embodiments that can be devised to represent application of the principles of the invention. Numerous and varied other arrangements can be conceived in accordance with these principles by those skilled in the art without departing from the spirit and scope of the present invention as defined by the claims appended hereto.