Chip-scale optical interconnects using micro light emitting diodes (microleds)

Abstract

Intra-package, intra-chip and / or inter-chip optical communication is provided using micro-LEDs and photodetectors mounted to and / or associated with an integrated circuit (IC) chip and a transceiver die. Light from the LEDs can be through a waveguide on or in a substrate to or coupled with the IC chip.

Description

Background Technology

[0001] This application generally relates to high-speed electronic packaging with short-range connections using optical links.

[0002] Over time, optical interconnects have replaced electrical connections. The low optical loss of fiber optics, the inherent high bandwidth of light, the absence of interference, and the absence of parasitic inductance and capacitance are all characteristics that facilitate optical modulation for interconnects. Starting with long distances, the advantages of optics have been proven over time at shorter distance scales. Today, the highest-speed links exceeding a few meters are almost always optical. The growth of data centers and the large-scale deployment of optical components connecting switches and servers over the past decade have generated a large number of optical components and led to significant innovations and investments in manufacturing infrastructure, which have reduced the cost of optics, thereby further enabling their deployment.

[0003] However, at lengths less than one meter, interconnects remain an electrical and performance barrier. Integrated circuits, such as CPUs and GPUs, are large, and the transmission of data and clock signals across silicon chips can be limited by the RC time constant of the interconnect metals. Retrieving information from the chip to the co-packaged memory and connecting to peripherals consumes significant power because electrical interconnects are lossy, distort signals, and have capacitors that require power to recharge. Clock and data recovery circuitry is typically used to periodically clean up signals, which requires considerable power. In servers, less than 5% of power consumption is used for actual computation within gates, while more than 95% is used for transferring data across ICs and from packages and communicating with peripherals.

[0004] In addition to RC and loss issues with electrical wiring, these interconnects are often confined to a 2D plane, for example, on the surface of a chip, ceramic package, silicon interposer, or circuit board.

[0005] As Moore's Law slows, electrical interconnects at short-range scales have become a critical barrier. Greater computing power is now increasingly achieved through parallelization, which emphasizes communication between processor blocks. The growing importance of artificial intelligence circuits and graphics processing units is entirely limited by this communication barrier at shorter distances. Difficulties in on-chip clock synchronization, limited memory bandwidth, and long latency in data access all hinder high-speed computing.

[0006] As an example, GPUs (Graphics Processing Units) and microprocessors tend to have high-speed access to large amounts of memory. The amount of available memory and the latency of accessing data from memory are severely limited by electrical interconnect limitations. The lowest latency memory is an onboard cache directly integrated into the same chip as the processor. However, there are limitations on how much cache can be integrated. To access more memory, advanced packaging techniques (such as using silicon interposers or silicon bridges) are used to co-package high-bandwidth memory (HBM) with the processor. Figure 1 This diagram illustrates the co-package between the processor and memory. Figure 1 The image shows a semiconductor package 111 in which a graphics processing unit (GPU) chip 113 is centrally located. HBM chips 115a to 115f surround the GPU chip. To access more memory, the processor can communicate with memory located further away via a slower bus (PCIe / CXL / or GenZ). However, this comes at the cost of higher latency and slower transfer rates.

[0007] The HBM modules can be implemented as a DRAM stack within a memory stack 121, mounted on top of a controller chip electrically connected to the GPU 113 via a silicon interposer 123. The stack can be eight layers high and can contain 128 channels connected to each die to form a 1024-line-width bus. The transfer rate is 0.5 GT / s, potentially moving to 2 GT / s or higher in the future, providing a total transfer rate of 500 Gb / s to 2 Tb / s per HBM. GPUs typically have four such HBM modules, providing a total transfer rate of up to 10 Tb / s and approximately 150 GB of total accessible memory.

[0008] Of course, more DDR memory is available further away from the processor, typically ranging from about 256GB to 2TB in capacity, with a slower transfer rate of about 250GB / s. The use of the PCIe bus allows access to even larger amounts of storage, but at a slower rate of about 64GB / s per x16 PCIe.

[0009]

[0010] Fundamentally, the barrier for optical devices to penetrate these smaller links lies in both generating light and transmitting it through the appropriate medium.

[0011] On the transmission side, lasers are generally unsuitable for mass production of short-distance interconnects. Edge-emitting lasers are typically relatively large, with lengths of several hundred micrometers. They are usually grown on group III to V materials incompatible with silicon, resulting in yields far lower than those of silicon-based electronics. Semiconductor lasers are highly temperature-sensitive, with their power and reliability rapidly declining at normal operating temperatures for processor ICs. Lasers also have a threshold current of approximately several milliamps, which wastes power. Vertical-cavity lasers are considered more suitable than waveguide edge-emitting lasers because they are smaller and have lower threshold currents, but they are more temperature-sensitive. The use of external lasers and on-chip modulators has been investigated, but waveguide modulators are lossy, consume significant amounts of power, and are typically the same size as edge-emitting lasers. Vertical-cavity modulators are temperature-sensitive and difficult to use.

[0012] Recent advancements in silicon photonics and the heterogeneous integration of group III to V materials with silicon have led to progress in optical transceivers and hold promise for breakthroughs in bringing optical links to shorter distances. However, silicon photonics also suffers from losses and consumes the same amount of power as group III to V components.

[0013] The medium is also an issue. Coupled fiber to a silicon chip and integrated with the co-packaged laser and electronics are complex and expensive. Furthermore, it doesn't break the 2D limitation of signals in a plane. Using optics in free space, on-chip, and off-chip with VCSELs or vertical-cavity modulators is one possibility, but all the issues discussed regarding lasers will still apply. Summary of the Invention

[0014] Some embodiments leverage advancements in unrelated fields of optics for displays and waveguide structures to jointly control three-dimensional (3D) beams, breaking down technological barriers in short-range data communication and providing implementations of devices capable of forming potentially fast, low-power, and low-cost data connections over short distances. This can help synchronize clock signals on chips, transfer data across chips, connect ICs to memory, and connect to other peripheral devices.

[0015] In some embodiments, optical communication is provided between two semiconductor chips using an LED as a light source. In some embodiments, the two semiconductor chips are within the same package or coupled to the same package substrate. In some embodiments, at least one of the semiconductor chips is configured to provide a data signal to the LED, while the other semiconductor chip has a detector, either as part of the chip or coupled to the chip, to detect light from the LED. In some embodiments, the LED and the detector are optically coupled using waveguides. In some embodiments, the two semiconductor chips are configured to provide a data signal to the LED and both semiconductor chips have detectors for detecting light from the LED of the other chip. In various embodiments, the LED is a microLED.

[0016] Some embodiments provide a multi-chip module with chip-to-chip optical communication capability, comprising: a semiconductor package; a substrate within the semiconductor package; a first semiconductor chip containing logic circuitry within the semiconductor package, the first semiconductor chip being electrically coupled to the substrate; a second semiconductor chip containing logic circuitry within the semiconductor package, the second semiconductor chip being electrically coupled to the substrate; a first microLED coupled to the first semiconductor chip within the semiconductor package; a circuit within the semiconductor package for driving the first microLED with signals based on the logic circuitry of the first semiconductor chip; at least one waveguide; and a first photodetector within the semiconductor package and optically coupled to the first microLED via the at least one waveguide, the first photodetector being electrically coupled to the logic circuitry of the second semiconductor chip.

[0017] In some embodiments, a first microLED is mounted to a first semiconductor chip. In some embodiments, the first microLED is bonded to the first semiconductor chip. In some embodiments, a first microLED wafer is bonded to the first semiconductor chip. In some embodiments, a first photodetector is mounted to a second semiconductor chip. In some embodiments, the first microLED is part of a transceiver separate from the first semiconductor chip. In some embodiments, the first photodetector is part of a transceiver separate from the second semiconductor chip. In some embodiments, a waveguide is on the surface of a substrate. In some embodiments, a waveguide is within a substrate. In some embodiments, a waveguide is on the surface of another substrate. In some embodiments, a waveguide is within another substrate.

[0018] In some embodiments, the substrate includes an interposer. In some embodiments, the first semiconductor chip includes a processor and the second semiconductor chip includes a memory.

[0019] In some embodiments, the microLED is approximately 2µm × 2µm or smaller. In some embodiments, at least one waveguide is in a planar optical wave circuit. In some embodiments, at least one waveguide includes a mirrored or angle-polished edge. In some embodiments, at least one waveguide is a three-dimensional (3D) waveguide. In some embodiments, the 3D waveguide is in glass. In some embodiments, at least one waveguide is a multimode waveguide.

[0020] In some embodiments, at least one waveguide is a single-mode waveguide.

[0021] Some embodiments further include: a second microLED coupled to the second semiconductor chip within the semiconductor package; a circuit within the semiconductor package for signal driving of the second microLED based on the logic circuit of the second semiconductor chip; and a second photodetector within the semiconductor package and optically coupled to the second microLED and electrically coupled to the logic circuit of the first semiconductor chip.

[0022] In some such embodiments, the second microLED is mounted to a second semiconductor chip. In some such embodiments, the second photodetector is mounted to a first semiconductor chip. In some such embodiments, the first microLED and the second photodetector are part of a first transceiver separate from the first semiconductor chip, and the second microLED and the first photodetector are part of a second transceiver separate from the second semiconductor chip. In some such embodiments, the first microLED is bonded to the first semiconductor chip and the second microLED is bonded to the second semiconductor chip. In some such embodiments, the first microLED and the second microLED are approximately 2 μm × 2 μm. Some embodiments further include a lens for coupling light from the first microLED to at least one waveguide.

[0023] Some embodiments provide an optical communication system for semiconductor chips on a common substrate, comprising: a plurality of first microLEDs associated with a first semiconductor chip electrically coupled to the substrate; a plurality of first photodetectors associated with a second semiconductor chip electrically coupled to the substrate; and a plurality of waveguides, each of the plurality of waveguides coupling different first microLEDs of the plurality of first microLEDs to different first photodetectors of the plurality of first photodetectors.

[0024] In some embodiments, multiple waveguides include silicon dioxide waveguides. In some embodiments, the silicon dioxide waveguides are in a glass substrate. Some embodiments further include an etched mirror in the glass substrate. In some embodiments, at least some waveguides are combined by a beam splitter. In some embodiments, a first semiconductor chip includes a processor and a second semiconductor chip includes memory. In some embodiments, the waveguides include 2D waveguides. In some embodiments, the waveguides include 3D waveguides. Some embodiments further include a base having at least some waveguides, the base including an electrical interface for at least one of the first and second semiconductor chips.

[0025] Some embodiments provide an optical communication system for a semiconductor chip, comprising: an integrated circuit (IC) chip; at least one LED on the IC chip; at least one photodetector on the IC chip; and a substrate having an electrical coupling to the IC chip, the substrate having at least one waveguide for optically coupling the at least one LED and the at least one photodetector.

[0026] In some embodiments, at least one waveguide includes a mirror for deflecting light received from at least one LED and directing the light to at least one photodetector. In some embodiments, the IC chip includes a processor. In some embodiments, the substrate includes a base. In some embodiments, the substrate includes an interposer. In some embodiments, the electrical coupling includes solder microbumps. In some embodiments, the substrate includes through-chip vias.

[0027] These and other aspects of the invention will be more fully understood upon review of this disclosure. Attached Figure Description

[0028] Figure 1 This demonstrates how processor chips are currently packaged together with high-bandwidth memory (HBM) (previous technology).

[0029] Figure 2 The exhibit showcases an electronic IC featuring a miniature LED and a detector that interfaces with an optical waveguide chip.

[0030] Figure 3 This demonstrates how a 3D waveguide chip can connect multiple ICs on different facets.

[0031] Figure 4 This demonstrates how waveguide chips can also be metallized and have vias to provide electrical connections to silicon processor chips.

[0032] Figure 5A E describes an integrated circuit chip coupled to a substrate, which has LED-based optical communication for transmitting information between integrated circuit chips.

[0033] Figure 6 This demonstrates how microlenses can increase the brightness of a light beam and improve coupling with optical waveguides. Detailed Implementation

[0034] According to embodiments of the invention, LEDs (micro-LEDs in various embodiments) are used for chip-to-chip communication, wherein in some embodiments, the communicating chips are within a common package or on a common package substrate. Some embodiments use arrays of micro-LEDs, for example, each approximately 2µm × 2µm of blue LEDs. In some embodiments, micro-LEDs are distinguished from semiconductor lasers (SLs) as follows: (1) micro-LEDs do not have an optical resonator structure; (2) the optical output from micro-LEDs is almost entirely spontaneous emission, while the output from SLs is primarily stimulated emission; (3) the optical output from micro-LEDs is temporally and spatially incoherent, while the output from SLs is significantly temporally and spatially coherent; (4) micro-LEDs are designed to be driven down to a minimum current of zero, while SLs are designed to be driven down to a minimum threshold current, typically at least 1mA. In some embodiments, microLEDs differ from standard LEDs in that (1) they have an emission area smaller than 25µm × 25µm in some embodiments, smaller than 10µm × 10µm in some embodiments, and smaller than 5µm × 5µm in some embodiments; (2) they often have positive and negative contacts on the top and bottom surfaces, while standard LEDs typically have both positive and negative contacts on a single surface; and (3) they are typically used in large arrays for display and interconnect applications. In some embodiments, microLEDs are bonded to chips, and in some embodiments, wafers are bonded to chips. For example, in some embodiments, microLEDs are bonded to GPUs and memory stacks. Blue light generated by the microLEDs carries data received by detectors (e.g., GaN detectors or silicon photodetectors / phototransistors). Memory modules with similarly bonded microLEDs are connected to the GPU via 3D waveguides.

[0035] Very high pixel-per-inch (PPI) microLEDs, with sizes as small as 1µm reported in the literature, have recently been developed for various display applications. At this size, LEDs possess some properties similar to lasers. The devices have high external quantum efficiencies that match those of lasers. Given their very small size, they have a small span, meaning they can be coupled into small waveguides, much like lasers. Although stimulated emission is absent, modulation speeds of several GHz are possible, limited only by the LED's RC time constant and carrier lifetime. Like carrier-induced waveguide modulators, faster responses can be obtained by reversing the bias voltage during non-periodic periods. Faster responses can also be obtained by driving the LED at high current densities. Drive currents can be as low as 50 nA, with good external efficiency, and will practically be limited by the receiver's bit error rate (BER) at a given power.

[0036] A bonding technique for attaching approximately one million microLEDs to silicon ICs has also been developed. Low capacitance can be achieved through oxide-oxide bonding with vias. A high-temperature step causes the metal in the vias to expand and fuse them together. Using commercially available equipment, alignment between the source LED wafer and the target wafer (which is typically a silicon wafer containing LED driver circuitry) can be achieved at the submicron level.

[0037] Blue GaN microLEDs typically have an emission peak at around 430 nm, a wavelength where silicon is highly absorbent and allows for very fast photodetectors with small absorption lengths. Avalanche photodiode (APD) structures can be used to achieve lower noise operation.

[0038] Of course, LEDs lack the coherence of lasers and emit light over a relatively broad spectrum. This can be a serious problem over long distances because any medium is dispersive and the wide spectral bandwidth will cause the pulse to spread over time with distance. However, this is not a problem because applications typically travel several centimeters at speeds of approximately 1 to 5 Gb / s. To put it in perspective, the full width at half maximum (FWHM) of the spectrum of a blue micro-LED centered at 430 nm is likely to be around 20 nm, and the dispersion (dn / dλ) of fused silica is approximately 0.08 / µm, so broadening would occur on a scale of many meters.

[0039] The remaining issue is the optical interconnection between chips. The simplest implementation would be a planar optical wave circuit (PLC) on silicon dioxide with mirrored or even angle-polished edges, a well-established technology. In some embodiments, SiO2, SiN, or SiON waveguide arrays can be used. In some embodiments, polymer waveguides can be used. SiO2, SiN, or SiON waveguide arrays can be fabricated on rigid planar substrates (e.g., silicon or glass). Polymer waveguides can be fabricated on one of the aforementioned rigid planar substrates, or on a flexible substrate such as a polyester film, supporting flexible waveguide arrays that are not limited to being located in a plane. These waveguide arrays are typically fabricated using planar semiconductor techniques such as photolithography, planar deposition, etching, and diffusion. In some embodiments, light is guided between chips via waveguides in the PLC, where 45-degree mirrored or angle-polished edges are used to couple vertically emitted light into horizontal waveguides. Simple optical devices, such as beam splitters, can be incorporated into the PLC chip. Multilayer waveguides can be formed on top of each other, having mirrors and vertical waveguides. A more robust implementation is the use of 3D waveguides that can be fabricated in glass using several techniques. A common approach is to focus a high-power laser into a block of glass to create defects that act as material or microlenses with a higher exponent. Arbitrary 3D waveguides can be formed in this way. These defects act as waveguides to carry energy from the transmitter to the receiver. Alternative methods, such as 3D printing, can also be used to fabricate dense optical waveguides. Even without waveguides, microlenses and mirrors can deflect thousands of beams simultaneously.

[0040] These aspects are discussed using diagrams.

[0041] Figure 2 A simplified embodiment incorporating aspects of the invention is shown. In this case, two chips are shown as optically interconnected with an optical waveguide. The leftmost chip is, for example, a CPU 211, and the rightmost chip is a memory 213. The chips are electrically connected from below to a substrate or package using standard solder bumps or microbumps 215.

[0042] The two chips contain micro-LEDs 217 and a photodetector 219. While only a few micro-LEDs are shown, typical applications will involve tens of thousands or even millions of micro-LEDs. The micro-LEDs are grown on suitable “source” substrates 221, such as sapphire, GaN, or silicon, and then peeled off and bonded to a “target” substrate or chip. This process is commercially available, and a photograph of micro-LEDs on silicon is actually shown on the left. This technology is primarily developed for micro-LED displays, where the silicon chip serves as the backplane for addressing the micro-LEDs. Typically, solder is used to bond the micro-LEDs to the target substrate or chip, and subsequent processing steps (such as planarization and metallization) are usually present to electrically connect the micro-LEDs to the CMOS silicon chip. The micro-LEDs will typically have a size of 2 micrometers × 2 micrometers.

[0043] Silicon chips will also have photodetectors fabricated on their surfaces. These can be easily fabricated in silicon using pin or APD architectures. Silicon is highly absorbent at wavelengths close to 430 nm, with an absorption coefficient of approximately 5 × 10^4 / cm, and therefore an absorption length of 1 micrometer is sufficient to provide very high quantum efficiency. Alternatively, detectors can be fabricated in GaN or other materials and bonded to silicon in the same manner as microLEDs.

[0044] Waveguide structure 223 is aligned and attached to the assembly. The simplest implementation of this waveguide wafer is achieved using proven silicon-on-silicon dioxide (SOC) technology, via PECVD or FHD deposition. These waveguides are typically formed on a silicon wafer by first growing a thermal oxide layer 225 approximately 10 or 20 (or 2 to 5) micrometers thick, followed by depositing a high-index germanium-doped core 227, typically 4 (or 2) micrometers thick. This core is then laterally patterned using photolithography, followed by a top cladding 229 formed from silicon dioxide. In the figure, the silicon substrate is not shown, and the waveguide dimensions are greatly magnified. Other materials besides SOC can be used, such as silicon oxynitride waveguides, polymer waveguides, or other dielectrics. The waveguide structure can be a simple interconnect or may contain beam splitters or possess other functionalities. The waveguide can be single-mode or multimode in the lateral direction. Given the very short interconnect distances, modal dispersion from multimode waveguides will not limit the useful data rate of the optical signal in many cases.

[0045] Various methods can be used to couple light into and out of these waveguides. The simplest is to polish the end face of the waveguide wafer at approximately 45 degrees. In this case, light is reflected into the waveguide through the angled edge 231. This is shown on the far left of the figure. Alternatively, a 45-degree mirror 233 can be etched into the waveguide. These are schematically shown in the figure, and a photograph of an actual mirror etched into silicon is shown on the right side of the main figure. Note that this mirror has several designs. The core can be angled at 45 degrees, or light can exit the waveguide at a normal facet and then strike a second facet at 45 degrees. Light can also enter the waveguide using a grating. Instead of a mirror, a waveguide oriented normal to the bottom of the chip and then turning 90 degrees can also be used.

[0046] In this way, light is coupled from the micro-LED into the waveguide, crosses (several) chips, and is reflected downwards onto the photodetector. The connection can span a single chip or many chips.

[0047] Small 2µm × 2µm LEDs can be operated at a variety of current densities, depending on the optical losses between the LED and the photodetector, the receiver sensitivity, and the required LED modulation speed. Current densities in the range of 5 A / cm² to 10000 A / cm² are typically useful, corresponding to drive currents of 200 nA to 400 μA.

[0048] Figure 2 The waveguide structure shown is a 2D waveguide, where light is largely confined to a plane. However, waveguide structures containing more than a single waveguide plane can be realized. Waveguides can be formed on top of each other to create multiple planes. Perhaps more interestingly, recent progress has been made in fabricating 3D waveguide structures. Figure 3 The illustration shows an example where multiple waveguides 311 alter their vertical orientation via a single piece of glass 313. These can be fabricated using 3D printing, where layers are formed on top of each other. Alternatively, a high-power beam is focused into the glass and pulsed, permanently altering the material's optical properties at the location of the beam waist's minimum. Multiple altered regions are connected to form waveguides. These structures can then be used to connect ICs to different facets of the glass. The image in the upper right corner is a schematic diagram of a commercial product using 3D waveguides formed in glass for connection to fiber optic arrays. The two lower figures illustrate how these 3D waveguides can connect multiple ICs. For example, in… Figure 3 In the left-hand image, GPU 315 is located at one end of a glass plate 317, while memory chips 319a to 319d are connected to other facets, and 3D waveguides 321 connect different chips. In some embodiments, the GPU may include up to one million optical inputs and outputs, with hundreds of memory chips optically connected to the GPU, each having tens of thousands of optical connections.

[0049] By attaching the optical waveguide layer to the IC, we may have removed the surface that could be used for cooling. Figure 4 This illustration shows an embodiment where the optical waveguide chip 411 can also provide an electrical interface, leaving the other surface 415 of the chip for cooling. In this way, the optical waveguide chip becomes an interposer or substrate. The CPU / GPU chip 419 is now inverted so that the LED 421 and photodetector 423 face downwards. The optical waveguide layer has a mirror 425 that receives light from the LEDs and guides it horizontally back to the detector, as previously described. However, this time, the chip undergoes deep reactive ion etching (DRIE) to form through-chip vias 427 that can be electrically connected to the CPU using standard solder bumps or microbumps. Even without vias, electrical signals 429 can still be guided to peripheral devices of the chip and connected in this manner. Adding metallization to the optical waveguide chip and adding solder bumps or microbumps is straightforward. The other side of the chip can now be easily cooled within a standard geometry. The waveguide can also be connected to other ICs.

[0050] Figure 5A The section to E illustrates an integrated circuit (IC) chip coupled to a substrate, which has LED-based optical communication for transmitting information between IC chips. In most embodiments, the LED is a micro-LED. For convenience, in... Figure 5A In each of E, only a single LED is shown; in most embodiments, multiple LEDs are present. In all Figure 5A In E, the first IC chip 511a and the second IC chip 511b are both in Figure 5A The substrate is mounted to substrate 513 on the same side of the substrate in E. In some embodiments, the substrate may be a portion of an integrated circuit package. In some embodiments, the substrate may be an interposer. In some embodiments, the substrate may be a bridge, wherein, for example, only a portion of each of the first IC chips and only a portion of the second IC chip are mounted to the bridge. In some embodiments, the first IC chip and the second IC chip are portions of a multi-chip module. The IC chips are shown to have electrical connections to the substrate through through-holes via solder bumps or microbumps 515. Figure 5A The via is shown as a through-substrate via (TSV) 517 in embodiment E, but in various embodiments, the via may lead to a redistribution layer (RDL) or other signal routing components in the substrate, and in some embodiments, the substrate may not provide electrical connections for the IC chip. An optical waveguide 519 is on the substrate, on the same side as the first IC chip and the second IC chip. In some embodiments, the optical waveguide is within the substrate, and in some embodiments, the optical waveguide is on the side of the substrate opposite to the first IC chip and the second IC chip.

[0051] exist Figure 5AIn this design, LED 521 is mounted on a first IC chip 511a. Light from the LED propagates through an optical waveguide 519 to a photodetector (not shown) on a second IC chip 511b. In some embodiments, and as illustrated in FIG. 5a, the LED has a height less than the height of the solder bumps and / or microbumps, and the height of the space between the first IC chip and the substrate is determined by the size and / or properties of the solder bumps / microbumps. A driver circuit for operating the LED and imposing a data signal on the light emitted through the LED is part of the first IC chip. A receiving circuit for processing the signal generated by the photodetector is part of the second IC chip. In many embodiments, the photodetector is part of the receiving circuit. In some embodiments, the photodetector is a discrete device mounted to the second IC chip, wherein the photodetector is electrically coupled to the receiving circuit. In many embodiments, the optical waveguide also transmits light from the LED (not shown) on the second IC chip to a photodetector (not shown) on the first IC chip, which has a driver circuit for the LED on a second chip portion of the second IC chip and a receiving circuit associated with the photodetector portion of the first IC chip. Since the combination of driver circuit and receiver circuit is usually referred to as a transceiver circuit, for convenience... Figure 5A The transceiver circuits 523a and 523b are simply shown in section E. For Figure 5A The first IC chip includes transceiver circuitry 523a and the second IC chip includes transceiver circuitry 523b. An LED is shown on a portion of the first IC chip having transceiver circuitry 523a, but in some embodiments, the LED may be positioned differently.

[0052] for Figure 5B In step E, the LED is not shown as being on the first IC chip. Figure 5B In this configuration, LED 521 is alternatively mounted on substrate 513, and transceiver circuits 523a (and 523b) are embedded within the substrate. Figure 5B In this embodiment, the transceiver circuitry is shown within the substrate and surrounding a side of the substrate facing and partially overlapping the first IC chip. However, in various embodiments, the transceiver circuitry may be positioned within the substrate in other ways. The transceiver circuitry may be electrically coupled to the first IC chip via electrical connections to the substrate and / or solder bumps / microbumps. LED 521 in Figure 5B The LED is shown on the side of the substrate facing the first IC chip, at the location of transceiver circuit 523a. However, in some embodiments, the LED may be positioned differently. Transceiver circuit 523b is correspondingly positioned and electrically coupled relative to the substrate and the second IC chip.

[0053] Figure 5C Implementation examples and Figure 5BThe difference in the embodiments is that the transceiver circuits 523a and 523b are in a semiconductor die mounted in a cavity within the substrate. The LED can be mounted to the substrate, or as... Figure 5C As explained in the document, it is installed onto the transceiver semiconductor die.

[0054] exist Figure 5D In one embodiment, the transceiver semiconductor die is mounted to a substrate, wherein the LED is on the transceiver semiconductor die. Figure 5E In this configuration, the transceiver semiconductor die is coupled to the substrate via one or more solder bumps or microbumps, wherein the LED on the transceiver die is located between the die and the substrate.

[0055] Unlike lasers, which typically emit light upwards, the emission mode from LEDs is usually Lambertian. Adding optics (such as microlenses) can greatly improve beam coupling to the waveguide. Figure 6 This paper demonstrates an implementation scheme of this method, along with some simulation results for the far-field angle with and without microlenses. Figure 6 In this embodiment, a microLED 611 is mounted on a CPU / GPU 613. A microlens 615 focuses at least some of the light emitted by the microLED onto a steering mirror 617. The steering mirror deflects the light 90 degrees into an optical waveguide 619. The microlens may be part of a microlens assembly 621. In some embodiments, the microlens assembly may include 1.5µm lenses with a 3.6µm pitch. Utilizing a 23-degree FWHM, as indicated by analog, this provides tight mode matching with single-mode fiber and efficient coupling. However, in some embodiments, the lens is significantly larger than the LED; for example, the lens may have a diameter at least twice the size of the LED in some embodiments and at least eight times the size of the LED in other embodiments.

[0056] Compared to CMOS electronics, blue micro-LEDs are considered to require relatively large drive voltages, and suitable circuitry can be formed in a VLSI to apply a forward bias to the LED. For faster response, a reverse bias voltage can be used to sweep carriers out of the quantum well in the LED. In some embodiments, a higher voltage line is provided to and / or provided in a CMOS IC for the driver. Alternatively, GaN is an excellent electronic material, and the driver can be monolithically integrated with the LED. On the receiver side, detectors made of Si or GaN can have very high bandwidth and very high quantum efficiency when used in conjunction with GaN LEDs emitting at short wavelengths. Therefore, various embodiments will have very good receiver signal-to-noise ratios without requiring special receiver circuitry.

[0057] Although the invention has been discussed with respect to various embodiments, it should be recognized that the invention includes the novel and non-obvious claims supported by this disclosure.

Claims

1. A multi-chip module having inter-chip optical communication capability, comprising: a semiconductor package; a substrate within the semiconductor package; a first semiconductor chip including logic circuitry within the semiconductor package, the first semiconductor chip electrically coupled to the substrate; a second semiconductor chip including logic circuitry within the semiconductor package, the second semiconductor chip electrically coupled to the substrate; a first micro-LED coupled to the first semiconductor chip within the semiconductor package; circuitry within the semiconductor package for driving the first micro-LED based on a signal of the logic circuitry of the first semiconductor chip; at least one waveguide; a first light detector within the semiconductor package and optically coupled to the first micro-LED through the at least one waveguide, the first light detector electrically coupled to the logic circuitry of the second semiconductor chip; and a lens coupling light from the first micro-LED into the at least one waveguide.

2. The multi-chip module of claim 1, wherein the first micro-LED is mounted to the first semiconductor chip.

3. The multi-chip module of claim 2, wherein the first micro-LED is bonded to the first semiconductor chip.

4. The multi-chip module of claim 2, wherein the first micro-LED is wafer bonded to the first semiconductor chip.

5. The multi-chip module of claim 1, wherein the first light detector is mounted to the second semiconductor chip.

6. The multi-chip module of claim 1, wherein the first micro-LED is part of a transceiver separate from the first semiconductor chip.

7. The multi-chip module of claim 1, wherein the first light detector is part of a transceiver separate from the second semiconductor chip.

8. The multi-chip module of claim 1, wherein the waveguide is on a surface of the substrate.

9. The multi-chip module of claim 1, wherein the waveguide is within the substrate.

10. The multi-chip module of claim 1, wherein the waveguide is on a surface of another substrate.

11. The multi-chip module of claim 1, wherein the waveguide is within another substrate.

12. The multi-chip module of claim 1, wherein the substrate comprises an interposer.

13. The multi-chip module of claim 1, wherein the first semiconductor chip comprises a processor and the second semiconductor chip comprises a memory.

14. The multi-chip module of claim 1, wherein the micro-LED is approximately 2 um x 2 um or less.

15. The multi-chip module of claim 1, further comprising: a second micro-LED coupled to the second semiconductor chip within the semiconductor package; circuitry within the semiconductor package for driving the second micro-LED based on a signal of the logic circuitry of the second semiconductor chip; ​ a second photodetector within the semiconductor package and optically coupled to the second micro-LED and electrically coupled to the logic circuit of the first semiconductor chip.

16. The multi-chip module of claim 15, wherein the second micro-LED is mounted to the second semiconductor chip.

17. The multi-chip module of claim 15, wherein the second photodetector is mounted to the first semiconductor chip.

18. The multi-chip module of claim 15, wherein the first micro-LED and the second photodetector are part of a first transceiver separate from the first semiconductor chip, and wherein the second micro-LED and the first photodetector are part of a second transceiver separate from the second semiconductor chip.

19. The multi-chip module of claim 15, wherein the first micro-LED is bonded to the first semiconductor chip and the second micro-LED is bonded to the second semiconductor chip.

20. The multi-chip module of claim 15, wherein the first micro-LED and the second micro-LED are approximately 2 pm x 2 pm.

21. The multi-chip module of claim 1, wherein the at least one waveguide is in a planar lightwave circuit.

22. The multi-chip module of claim 1, wherein the at least one waveguide includes a mirror or an angle-polished edge.

23. The multi-chip module of claim 1, wherein the at least one waveguide is a three- dimensional (3D) waveguide.

24. The multi-chip module of claim 23, wherein the 3D waveguide is in glass.

25. The multi-chip module of claim 1, wherein the at least one waveguide is a multi-mode waveguide.

26. The multi-chip module of claim 1, wherein the at least one waveguide is a single-mode waveguide.

27. An optical communication system for semiconductor chips on a common substrate, comprising: a plurality of first micro-LEDs associated with a first semiconductor chip, the first semiconductor chip electrically coupled to a substrate; a plurality of first photodetectors associated with a second semiconductor chip, the second semiconductor chip electrically coupled to the substrate; and a plurality of waveguides, each of the plurality of waveguides coupling a different first micro-LED of the plurality of first micro-LEDs with a different first photodetector of the plurality of first photodetectors; and a plurality of lenses coupling light from the plurality of first micro-LEDs into the plurality of waveguides.

28. The optical communication system of claim 27, wherein the plurality of waveguides comprises silica waveguides.

29. The optical communication system of claim 28, wherein the silica waveguides are in a glass substrate.

30. The optical communication system of claim 29, further comprising etched mirrors in the glass substrate.

31. The optical communication system of claim 27, wherein at least some of the waveguides are joined by a splitter.

32. The optical communication system of claim 27, wherein the first semiconductor chip comprises a processor and the second semiconductor chip comprises a memory.

33. The optical communication system of claim 27, wherein the waveguide comprises a 2- dimensional waveguide.

34. The optical communication system of claim 27, wherein the waveguide comprises a 3- dimensional waveguide.

35. The optical communication system of claim 27, further comprising a base having at least some of the waveguide, the base comprising an electrical interface for at least one of the first semiconductor chip and the second semiconductor chip.

36. An optical communication system for semiconductor chips, comprising: an integrated circuit (IC) chip; at least one LED on the IC chip; at least one photodetector on the IC chip; a substrate having electrical couplings to the IC chip, the substrate having at least one waveguide for optically coupling the at least one LED and the at least one photodetector; and at least one lens coupling light from the at least one LED into the at least one waveguide.

37. The optical communication system of claim 36, wherein the at least one waveguide comprises a mirror that turns light received from the at least one LED and directs the light to the at least one photodetector.

38. The optical communication system of claim 36, wherein the IC chip comprises a processor.

39. The optical communication system of claim 36, wherein the substrate comprises a base.

40. The optical communication system of claim 36, wherein the substrate comprises an interposer.

41. The optical communication system of claim 36, wherein the electrical couplings comprise solder micro-bumps.

42. The optical communication system of claim 37, wherein the substrate comprises through- chip vias. ​

Images