Patent Application
20130330033
1. Field
This disclosure is generally related to optoelectronic packaging. More specifically, this disclosure is related to an apparatus and a method for using a TSV substrate having a mirror facet in high-speed optoelectronic packaging.
2. Related Art
The increased demand for larger bandwidth in optical communications has driven the increased integration of optical and electrical devices in optoelectronic modules. These new modules require high-speed electrical interconnects and effective optical guiding. As the signal rate reaches 10 Gbps and beyond, traditional wire-bonding technology where metal wires are used to connect an integrated circuit (IC) chip or an optical chip (such as a laser diode or a light detector) to a printed circuit board (PCB) is no longer adequate.
One embodiment of the present invention provides a packaged optoelectronic module. The module includes a photonic chip having a top surface and a first substrate that includes a plurality of vias and a reflective surface. The photonic chip is flip-chip bonded to the first substrate with the top surface facing the first substrate. The vias facilitate electrical connections to the top surface, and the reflective surface forms an angle with the top surface, thereby enabling optical coupling between the top surface and an optical fiber placed in a direction that is substantially parallel to the top surface.
In a variation on this embodiment, the first substrate is a through silicon via (TSV) substrate.
In a variation on this embodiment, the photonic chip includes at least one of: a vertical-cavity surface-emitting laser (VCSEL), and a photo detector.
In a variation on this embodiment, the packaged optoelectronic module further comprises a second substrate situated below the first substrate. The first substrate is bonded to the second substrate.
In a further variation, the packaged optoelectronic module further comprises an electronic chip that is electrically coupled to the photonic chip using metal traces on the second substrate.
In a further variation, the electronic chip is flip-chip bonded to the second substrate.
In a further variation, the electronic chip is flip-chip bonded to the first substrate.
In a further variation, the second substrate includes one of: a ceramic substrate, and an organic substrate.
In a variation on this embodiment, the packaged optoelectronic module further comprises a focusing lens situated between the reflective surface and the optical fiber.
In a variation on this embodiment, the angle between the reflective surface and the top surface of the photonic chip is approximately 45°.
The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
Embodiments of the present invention provide an apparatus and a method for high-speed optoelectronic packaging. A flip-chip bonding method is used to bond a photonic die and an electronic die onto a common substrate. In addition, a through-silicon via (TSV) substrate with a mirror facet is used to guide light and enable electrical interconnection between the photonic die and the electronic die.
In this disclosure, the terms “chip” and “die” are used interchangeably to describe an integrated optical or electronic circuit on a diced semiconductor wafer. A packaged optoelectronic device or module may include multiple chips or dies enclosed inside a single housing.
Flip-chip bonding technology has been widely used in the packaging of high-speed IC chips. During packaging, the chips are flipped over to have their topsides facing down, and chip pads on the topside of the chips are aligned with matching connectors on the substrate. Previously deposited solder bumps/dots bond the chips to the PCB substrate, and transmission lines provide low-parasitic, high-speed electrical interconnects. Compared with traditional wire bonding technology, flip-chip bonding technology provides smaller package sizes, better heat conduction, and higher signal speeds. These advantages also make flip-chip bonding attractive for the packaging of photonic chips. However, there are challenges in applying flip-chip bonding to the packaging of photonic chips. More particularly, for photonic chips with a light-emitting or -receiving top surface, having their topsides facing down makes guiding light a challenge. For example, top-emitting vertical-cavity surface-emitting laser (VCSEL) chips often have their light-emitting surface on the same side of the electrodes, and the flip-chip packaging will result in the light-emitting surface facing the substrate. Similarly, flip-chip packaging of photo diodes generally results in the light-receiving surface facing the substrate.
Because the packaging of photonic chips often involves coupling light to or from an optical fiber (or a ribbon of fibers), the downward configuration of the light-emitting/receiving surface presents a challenge. For example, light emitted from the photonic chip is obstructed by the substrate. To solve this problem, embodiments of the present invention implement a TSV substrate with a mirror facet.
In
Photonic chip 102 can be a light-emitting device (such as a VCSEL), a light-receiving device (such as a photo detector), or other devices that interact with light. Reflecting mirror facet 110 forms an angle with a light-emitting/receiving surface 112 of photonic chip 102, thus changing the direction of the light emitted from photonic chip 102. In one embodiment, this angle is approximately 45°. Consequently, reflecting mirror facet 110 can change the direction of the light emitted from photonic chip 102 by 90°. More specifically, the downwardly directed light emitted from light-emitting/receiving surface 112 becomes horizontally oriented after it reflects off reflecting mirror facet 110. Reflecting mirror facet 110 can be a cleaved facet or an etched facet. The horizontally oriented light can be coupled to the core of an optical fiber 114 (which can be a single mode or multimode fiber) via a focusing lens 116. Similarly, if photonic chip 102 is a photo detector, light coming from optical fiber 114 can be coupled to light-emitting/receiving surface 112 via focusing lens 116 and reflecting mirror facet 110.
Note that angled reflecting mirror facet 110 on TSV substrate 104 and a focusing lens enable optical coupling between a flip-chip bonded photonic chip and an optical fiber. In addition to optical coupling to a fiber, it is also essential to provide electrical connections (either for supplying power or for extracting signals) to the photonic chip. In embodiments of the present invention, electrical connections from substrate 120 to photonic chip 102 are established using vias (such as via 108) within TSV substrate 104. More specifically, an electronic signal pad on top of photonic chip 102 can be connected to a corresponding metal trace on substrate 120 through a metal (such as Cu) pillar filled in a respective via within TSV substrate 104.
Today's high-speed optoelectronic modules often require electronic components and photonic components to be packaged together, sharing a common substrate. For example, inside the package of a typical high-speed laser, one can find a laser chip and its driver (which provides power and control to the laser chip), both of which are bonded to a common substrate, and metal traces deposited on the common substrate provide high-speed interconnects. Similarly, a packaged high-speed photo detector often includes a detector chip and a preamplifier, both are bonded to a common substrate. To reduce parasitics, in embodiments of the present invention, the electrical chips are flip-chip bonded to the common substrate.
TSV substrate 208 includes an angled facet, which causes light emitted from photonic chip 202 to change its direction. In one embodiment, the downwardly directed light reflects off the angled facet to become horizontally directed. The horizontally directed light is then coupled to a fiber pigtail 218 via a focusing lens 216. Similarly, light originating from fiber 218 can be coupled to photonic chip 202 via focusing lens 216 and the angled facet of TSV substrate 208.
Note that, compared with traditional wire-bonding technology, flip-chip bonding of the photonic dies and the electronic dies onto a common substrate not only reduces parasitics caused by wires, which improves the high-speed performance of the device, but also improves heat dissipation of the device.
In an alternative embodiment, the electronic chips, similarly to the photonic chips, are also flip-chip bonded to the TSV substrate, and are electrically coupled to the underlying substrate (such as a PCB) through metal pillars filled in the vias of the TSV substrate.
In
TSV substrate 306 includes an angled facet. Light emitted from the top surface of photonic chip 302 reflects off the angled facet and changes direction. In one embodiment, the downwardly directed light from photonic chip 302 becomes horizontally directed. The horizontally directed light is then coupled to a fiber pigtail 320 via a focusing lens 318. Similarly, light originating from fiber 320 can be coupled to photonic chip 302 via focusing lens 318 and the angled facet of TSV substrate 306.
In
In
Embodiments of the present invention provide a novel packaging solution for integrated optoelectronic devices. The flip-chip bonding of photonic and electronic components eliminates massive bonding wires used in conventional wire-bonding technologies, thus significantly improving the high-speed performance of the packaged device. Additional advantages include reduced size (thus reduced footprint) and better heat dissipation, thus making this packaging solution suitable for high-speed (10 GHz and beyond) parallel optical engines (POEs). Note that such high-speed POEs provide solutions such as rack-to-rack, board-to-board, and chip-to-chip optical interconnections in the field of data communication and telecommunication.
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The foregoing descriptions of various embodiments have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention.
