Wafer-level packaging of optical receivers
View Patent ↗A sub-assembly or package for a die in the receiving section of an optical transceiver includes a semiconductor sub-mount that is electrically connected to the die and a cap that is bonded to the sub-mount to hermetically seal the die in a cavity. The die can be flip-chip bonded to the sub-mount and can include a diffractive optical element fabricated on a back side of the die. Active circuitry such as an amplifier for an output signal from a photosensor on the die can be integrated into the sub-mount. For an OSA, a post can be attached to the package along a path of an optical signal to the photosensor. The post facilitates alignment of an optical fiber. A flexible or rigid circuit can be soldered to external terminals of the sub-mount.
1. A method for fabricating a package containing a photosensor, comprising:
fabricating a wafer that includes a plurality of sub-mount areas;
attaching and electrically connecting a plurality of dice respectively to the sub-mount areas, wherein each of the dice contains a photosensor;
bonding a plurality of separated caps to the wafer, wherein the dice are enclosed in respective cavities between the wafer and the respective caps, and for each of the dice, the photosensor on the die is positioned to receive an optical signal; and
dividing the resulting structure to separate a plurality of packages containing the dice.
2. The method of claim 1 , wherein fabricating the wafer comprises forming an active circuit in each of the sub-mount areas.
3. The method of claim 2 , wherein the active circuit is an amplifier for an output signal of the photosensor connected to the sub-mount area.
4. The method of claim 1 , further comprising:
processing a substrate to form the photosensor including a photosensitive area in the substrate and at a front face of the substrate; and
forming a lens on a back face of the substrate to focus light onto the photosensitive area.
5. The method of claim 1 , further comprising attaching posts to the packages, wherein each post is along a path of an optical signal to the die in the package.
6. The method of claim 1 , further comprising affixing a post to one of the packages, wherein the post is along an optical path of the optical signal into the cavity.
7. The method of claim 1 , wherein:
attaching and electrically connecting a die from the plurality of the dice to the respective one of the sub-mount areas comprises connecting terminals of the die to internal bond pads in the sub-mount area, wherein circuitry of the wafer connects the internal terminals to external terminals on the wafer; and
bonding the cap attaches the caps to the wafer so that the external terminals are outside the caps.
8. The method of claim 1 , wherein attaching and electrically connecting the dice comprises flip-chip bonding the dice to the wafer.
9. The method of claim 8 , wherein the photosensor in each of the dice receives an optical signal that passes through a back face of the die to a photosensitive area on a front face of the die.
10. A method for fabricating a package containing a photosensor, comprising:
fabricating a first wafer that includes a plurality of sub-mount areas, wherein each sub-mount area include internal bond pads, external bond pads, and circuitry that connects the internal ho d pads to the external bond pads;
attaching and electrically connecting a plurality of dice respectively to the sub-mount areas, wherein each of the dice contains a photosensor and is electrically connected to the internal bond pad in the corresponding one of the sub-mount areas;
bonding a second wafer to the first wafer to form a set of first cavities and a set of second cavities between the first wafer and the second wafer, wherein the first cavities respectively enclose the dice, and the external terminals are within the second cavities; and
dividing the first wafer and the second wafer to separate a plurality of packages in which the first cavities are intact and enclose the dice, and the external terminals are exposed.
11. The method of claim 10 , wherein fabricating the first wafer comprises forming an active circuit in each of the sub-mount areas.
12. The method of claim 11 , wherein the active circuit is an amplifier for an output signal of the photosensor connected to the sub-mount area.
13. The method of claim 10 , wherein attaching and electrically connecting the dice comprises flip-chip bonding the dice to the first wafer.
14. The method of claim 13 , wherein the photosensor in each of the dice receives an optical signal that passes through a back face of the die to a photosensitive area on a front face of the die.
15. The method of claim 10 , wherein dividing the first wafer and the second wafer comprises:
dividing the first wafer to form first pieces; and
dividing the second wafer to form second pieces, wherein each second piece is attached to and smaller an a corresponding one of the first pieces.