Hermetically sealed micro-device package with window

Details Hermetically sealed micro-device package with window Hermetically sealed micro-device package with window

2002-03-22

2003-09-30

Ngo, Hung V. (Department: 2831)

Electricity: conductors and insulators

Boxes and housings

Hermetic sealed envelope type

C174S050510, C257S680000, C029S592100

Reexamination Certificate

active

06627814

ABSTRACT:

TECHNICAL FIELD OF THE INVENTION
The current invention relates to packages for photonic devices,optical devices, micro-mechanical devices, micro-electromechanical systems (MEMS) devices or micro-optoelectromechanical systems (MOEMS) devices, and more particularly, to packages having a hermetically sealed chamber covered by a transparent window.
BACKGROUND OF THE INVENTION
Photonic, optical and micro-mechanical devices are typically packaged such that the active elements (i.e., the emitters, receivers, micro-mirrors, etc.) are disposed within a sealed chamber to protect them from handling and other environmental hazards. In many cases, it is preferred that the chamber be hermetically sealed to prevent the influx, egress or exchange of gasses between the chamber and the environment. Of course, a window must be provided to allow light or other electromagnetic energy of the desired wavelength to enter and/or leave the package. In some cases, the window will be visibly transparent, e.g. if visible light is involved, but in other cases the window may be visibly opaque while still being “optically” transparent to electromagnetic energy of the desired wavelengths. In many cases, the window is given certain optical properties to enhance the performance of the device. For example, a glass window may be ground and polished to achieve certain flatness specifications in order to avoid distorting the light passing therethrough. In other cases, anti-reflective or anti-refractive coatings may be applied to the window to improve light transmission therethrough.
Hermetically sealed micro-device packages with windows have heretofore been produced using cover assemblies with metal frames and glass window panes. To achieve the required hermetic seal, the glass window pane has heretofore been fused to its metallic frame by heating it in a furnace at a temperature exceeding the glass transition temperature, T
G
(typically at or above 900° C.). However, because the fusing temperature is above T
G
, the original surface finish of the glass pane is typically ruined, making it necessary to finish or re-finish (e.g., grinding and polishing) both surfaces of the window pane after fusing in order to obtain the necessary optical characteristics. This polishing of the window panes requires additional process steps during manufacture of the cover assemblies, which steps tend to be relatively time and labor intensive, thus adding significantly to the cost of the cover assembly, and hence to the cost of the overall package. In addition, the need to polish both sides of the glass after fusing requires the glass to project both above and below the attached frame. This restricts the design options for the cover assembly with respect to glass thickness, dimensions, etc., which can also result in increased material costs.
Once a cover assembly with a hermetically sealed window is prepared, it is typically seam welded to the device base (i.e., substrate) in order to produce the finished hermetically sealed package. Seam welding uses a precisely applied AC current to produce localized temperatures of about 1,100° C. at the frame/base junction, thereby welding the metallic cover assembly to the package base and forming a hermetic seal. To prevent distortion of the glass windowpane or package, the metal frame of the cover assembly should be fabricated from Kovar alloy or another alloy having a CTE (i.e., coefficient of thermal expansion) which is similar to that of the transparent window material and to the CTE of the package base.
While the methods described above have heretofore produced useable window assemblies for hermetically sealed micro-device packages, the relatively high cost of these window assemblies is a significant obstacle to their widespread application. A need therefore exists, for package and component designs and assembly methods which reduce the labor costs associated with producing each package.
A need still further exists for package and component designs and assembly methods which will minimize the manufacturing cycle time required to produce a completed package.
A need still further exists for package and component designs and assembly methods which reduce the number of process steps required for the production of each package. It will be appreciated that reducing the number of process steps will reduce the overhead/floorspace required in the production facility, the amount of capital equipment necessary for manufacturing, and handling costs associated with transferring the work pieces between various steps in the process. A reduction in the cost of labor may also result. Such reductions would, of course, further reduce the cost of producing these hermetic packages.
A need still further exists for package and component designs and assembly methods which will reduce the overall materials costs associated with each package, either by reducing the initial material cost, by reducing the amount of wastage or loss during production, or both.
SUMMARY OF THE INVENTION
The present invention disclosed and claimed herein comprises, in one aspect thereof, a method for manufacturing a cover assembly including a transparent window portion and a frame that can be joined to a micro-device's package base to form a hermetically sealed micro-device package. First, a frame is provided having a continuous sidewall defining a frame aperture therethrough. The sidewall includes a frame seal-ring area circumscribing the frame aperture. The frame seal-ring area has a metallic surface. A sheet of a transparent material is provided having a window portion defined thereupon. The window portion has finished top and bottom surfaces. Next, a sheet seal-ring area on the sheet is prepared, the sheet seal-ring area circumscribing the window portion. Next, the prepared sheet seal-ring area of the sheet is metallized. Next, the frame is positioned against the sheet such that at least a portion of the frame seal-ring area and at least a portion of the sheet seal-ring area contact one another along a continuous junction region that circumscribes the window portion. Next, the junction region is heated until a metal-to-metal joint is formed between the frame and sheet all along the junction region, whereby a hermetic seal circumscribing the window portion is formed.
The present invention disclosed and claimed herein comprises, in another aspect thereof, a cover assembly including a transparent window portion and a frame that can be joined to a micro-device package base to form a hermetically sealed micro-device package.
The present invention disclosed and claimed herein comprises, in yet another aspect thereof, a micro-device module including a package base, micro-device mounted on the package base, and a cover assembly having a transparent window portion and a frame, the cover assembly being welded to the package base to hermetically seal the micro-device within a cavity formed therebetween.


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Doron Teomim, Avner Badhi, Gil Zilber; “An innovative approach to wafer-level MEMS packaging”; Solid State Technology (Magazine); Jan. 2002; Penwell (Publ.); Nashua, NH USA.
Carpenter Specialty Alloys: Controlled-Expansion Alloys (Catalog/Brochure); Dec. 1999; pp. 1-24 (esp. 5-8); Carpenter Technology Corporation (Publ.); Wyomissing, PA USA.
JPL Technology Reporting Office; “Hermetic Wafer Bonding By Use of Microwave Heating”; NASA Tech Brief, vol. 25, No. 5, from JPL New Technology Report NPO-20608 (NASA Contract No. NAS-7-918); May 1, 2001; Jet Propulsion Laboratory, California Institute of Technology (Publ.); Pasadena, CA, USA; including therein.
NTR Inventors Report by Henry W Jackson, John D Mai, Martin B Barmatz, Nasser K Budraa, William T Pike; NASA Case No. 0205 20608; Mar. 1997 (?) (Best Available Copy); Including therein: (same authors) “Low Pressure and Low Temperature Hermetic Wafer Bonding Using Microwave Heating”; Jet Propulsion Laboratory, California Institute of Technology; Pasadena,

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