Photonic crystal surface emitting laser and heat dissipation system thereof

Abstract

The invention provides a photonic crystal surface emitting laser and a heat dissipation system thereof. The photonic crystal surface emitting laser comprises a chip and a heat sink. Wherein the chip comprises a semiconductor substrate, an active layer and a photonic crystal layer which are stacked in sequence; the heat sink is provided with a cooling liquid flow channel used for conveying cooling liquid. A plurality of microstructure holes are formed in the photonic crystal layer, and the arrangement mode of the microstructure holes forms a photonic crystal structure for realizing laser emission; the chip is mounted on the heat sink in an inverted manner, and the openings of the plurality of microstructure holes are in fluid communication with the cooling liquid flow channel of the heat sink so as to allow the cooling liquid to directly flow into the plurality of microstructure holes, thereby forming a heat dissipation channel for taking away the heat of the active layer.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor optoelectronic technology, in particular to a photonic crystal surface emitting laser and a heat dissipation system thereof. Background Art

[0002] Photonic Crystal Surface Emitting Laser (PCSEL), a new type of semiconductor laser, has attracted considerable attention for its ability to achieve single-mode, high-power, and high-beam-quality coherent emission over a large area. It demonstrates enormous potential for applications in fields such as LiDAR, industrial processing, and optical communications. As applications demand higher power densities, the waste heat generated by PCSEL chips during operation has increased dramatically, and heat dissipation has become a key bottleneck restricting improvements in performance and reliability.

[0003] Currently, the mainstream packaging and heat dissipation solution for PCSEL devices is a bottom-mounted package structure. This solution first requires the use of precision micro-nanofabrication technology to create a complex microchannel cooling structure on a high-thermal conductivity substrate (commonly called a heat sink, such as copper or aluminum nitride). Subsequently, the active layer side of the PCSEL chip is bonded to the heat sink through eutectic welding, thermal compression welding, and other methods. Coolant flows through the microchannels inside the heat sink, removing the heat generated by the chip through the heat sink.

[0004] However, this traditional heat dissipation architecture is expensive to manufacture and has limited heat dissipation efficiency. For example, fabricating microchannels on a heat sink with micrometer-level widths and tens of micrometers deep requires a series of complex semiconductor processes, including photolithography, etching, bonding, and sealing. This requires high equipment requirements, has a narrow process window, and is difficult to control yield, directly driving up the cost of the entire laser module. Summary of the Invention

[0005] Based on this, it is necessary to provide a photonic crystal surface emitting laser and a heat dissipation system thereof to solve at least one of the above technical problems.

[0006] In a first aspect, the present application provides a photonic crystal surface emitting laser, comprising:

[0007] A chip comprising a semiconductor substrate, an active layer, and a photonic crystal layer stacked in sequence;

[0008] a heat sink having a coolant flow channel for conveying a coolant;

[0009] A plurality of microstructure holes are formed in the photonic crystal layer, and the arrangement of the plurality of microstructure holes constitutes a photonic crystal structure for realizing laser emission;

[0010] The chip is mounted on the heat sink in a flip-chip manner, and the openings of the multiple microstructure holes are fluidically connected to the coolant flow channel of the heat sink to allow the coolant to flow directly into the multiple microstructure holes, thereby forming a heat dissipation channel for removing heat from the active layer.

[0011] In this way, by combining the optical resonance structure and the heat dissipation channel inside the chip and adopting direct convection heat exchange, the bottleneck of the traditional solid-state heat conduction path is fundamentally eliminated, the ultimate heat dissipation efficiency is achieved, and the manufacturing process and cost of the heat sink are greatly simplified.

[0012] In a possible implementation, the plurality of microstructure holes penetrate the photonic crystal layer and extend to the vicinity of the interface between the active layer and the photonic crystal layer.

[0013] In this way, the coolant can be as close to the heat source (active layer) as possible, shortening the physical distance of heat transfer to the limit, thereby maximizing the heat exchange efficiency and achieving the strongest and most direct control of the chip junction temperature.

[0014] In a possible implementation, the plurality of microstructure holes extend and are closed in the photonic crystal layer.

[0015] In this way, while ensuring that the coolant effectively approaches the active layer, direct etching damage to the active layer or its adjacent sensitive layers (such as the cladding) is avoided, the electrical and optical integrity of the core area of ​​the chip is protected, and the manufacturing yield and long-term reliability of the device are improved.

[0016] In a possible implementation, the multiple microstructure holes penetrate the photonic crystal layer and extend into the active layer.

[0017] In this way, "zero-distance" contact between the coolant and the heat source is achieved, providing the theoretically most extreme heat dissipation capacity, suitable for dealing with extremely high heat flux density; at the same time, this structure may directly modulate carrier recombination and optical modes, providing the possibility of realizing new optoelectronic functions.

[0018] In a possible implementation, inner walls of the plurality of microstructured holes are coated with a dielectric passivation layer, and the dielectric passivation layer is used to achieve electrical and chemical isolation between the semiconductor material of the semiconductor chip and the coolant.

[0019] In this way, by constructing a dense insulating protective layer between the semiconductor etching surface and the coolant, surface leakage, electrochemical corrosion and material degradation caused by liquid contact are effectively prevented, which is a key technology to ensure the long-term stable and reliable operation of the laser.

[0020] In a possible implementation, the coolant flow channel of the heat sink is one or more macro-sized linear or U-shaped groove structures.

[0021] In this way, due to the use of an integrated metal solder layer, the four major functions of electrical connection, mechanical fixation, heat conduction (residual heat) and fluid sealing are solved at the same time, which simplifies the packaging structure, improves the compactness and reliability of the package, and ensures that the coolant does not leak at the interface between the chip and the heat sink.

[0022] In a possible implementation, the chip is bonded to the heat sink via a metal solder layer, and the metal solder layer serves as both an electrode and a sealing structure to prevent leakage of the coolant.

[0023] In this way, the complex microchannel processing requirements are completely removed from the heat sink, so that the heat sink can be manufactured only through conventional, low-cost mechanical processing technology, greatly reducing the manufacturing cost of the entire laser module and promoting the large-scale application of high-performance liquid-cooled lasers.

[0024] In a second aspect, the present application also provides a heat dissipation system for a photonic crystal surface emitting laser, comprising a photonic crystal surface emitting laser and a coolant as described in the first aspect or any possible implementation thereof; the coolant can be selectively injected from the inlet end of the coolant flow channel of the heat sink of the photonic crystal surface emitting laser, flows through the coolant flow channel, and then directly enters the multiple microstructure holes in the photonic crystal layer of the photonic crystal surface emitting laser, and the coolant is discharged from the outlet end of the coolant flow channel of the heat sink.

[0025] In this way, a complete and operational heat dissipation system and coolant flow path are formed. The system uses forced convection to efficiently and continuously remove the heat generated inside the chip, ensuring the thermal balance of the laser when it is in operation.

[0026] In a possible implementation, the cooling liquid is deionized water, an ethylene glycol aqueous solution, or a dielectric insulating liquid.

[0027] In this way, since a cooling medium with excellent thermophysical properties or electrical characteristics is provided, the heat dissipation effect and stability of the heat dissipation system are enhanced.

[0028] In a possible implementation, nanoparticles are added to the coolant to form a nanofluid with higher thermal conductivity, and the material of the nanoparticles is selected from at least one of aluminum oxide, copper oxide, carbon nanotubes, or graphene.

[0029] This further enhances heat dissipation by improving the thermophysical properties of the cooling medium itself. Without changing the system's hardware structure, the use of nanofluids can directly improve the convective heat transfer coefficient, providing an effective performance enhancement for handling higher heat flux densities or achieving lower junction temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are for illustrative purposes only and are not to be construed as limiting the present invention; identical reference numerals are used for components having identical structures and functions.

[0031] Figure 1 A schematic cross-sectional view of the overall structure of a photonic crystal surface emitting laser according to an embodiment of the present application;

[0032] Figure 2 This is a schematic diagram of the top view of the photonic crystal layer in Example 1 of the present application;

[0033] Figure 3 This is a schematic top view of the structure of the photonic crystal layer in Example 5 of the present application;

[0034] Figure 4 This is a schematic diagram of the top view of the photonic crystal layer in Example 2 of the present application;

[0035] Figure 5 This is a schematic diagram of the top view of the photonic crystal layer in Example 7 of the present application;

[0036] Figure 6 Schematic cross-sectional view of the bonding portion between the photonic crystal layer and the heat sink according to Example 4 of the present application;

[0037] Figure 7 Schematic cross-sectional view of the heat sink of Example 13 of the present application;

[0038] Explanation of the accompanying symbols: photonic crystal surface emitting laser - 100; semiconductor substrate - 1; carrier transport layer - 2; active layer - 3; photonic crystal layer - 4; microstructured holes - 5; heat sink - 6; inlet end - 7; outlet end - 8; cooling liquid flow channel - 9; laser emission direction - 10; dielectric passivation layer - 11; metal solder layer - 12; connecting structure - 13. DETAILED DESCRIPTION

[0039] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings in the embodiments of the present application. In the description of the embodiments of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B; "and / or" in this article is merely a description of the association relationship of associated objects, indicating that three relationships can exist, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the embodiments of the present application, "multiple" means two or more than two.

[0040] In the following, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the quantity of the technical features indicated. Therefore, features defined as "first" or "second" may explicitly or implicitly include one or more of the described features.

[0041] In the description of this embodiment, unless otherwise specified, “a plurality of” means two or more.

[0042] First, refer to Figure 1-7 This application provides a photonic crystal surface emitting laser 100 with integrated internal microfluidic cooling. This laser 100 is designed to stably output a high-quality, coherent laser beam under high-power drive. At the same time, through an internal cooling mechanism, it efficiently removes waste heat generated during operation, maintaining the chip at an ideal operating temperature.

[0043] The laser 100 mainly includes a semiconductor chip with a specially designed structure and a heat sink 6 with a simplified structure.

[0044] Chips are used to convert electrical energy into light energy. Figure 1 As shown in the figure, the chip is used to convert electrical energy into light energy. Figure 1 As shown, the chip is, for example, a photonic crystal surface emitting laser (PCSEL) epitaxial structure chip, and its material system can be selected according to the target wavelength. For example, the AlGaAs / GaAs system can be used for the 9XX nanometer band, and the InGaAsP / InP system can be used for the 1.3-1.55 micron communication band. The chip sequentially includes a semiconductor substrate 1 as a laser exit window and mechanical support, a lower cladding layer (not shown separately) for confining carriers and light fields, an active layer 3 as the photoelectric conversion core and main heat source, and an upper cladding layer (usually overlapping or adjacent to the functional regions of the carrier transport layer 2 and the photonic crystal layer 4).

[0045] In the photonic crystal layer 4, a large number of densely distributed microstructured holes 5 are etched through semiconductor micro-nano processing technology. These microstructured holes 5 have dual functions:

[0046] A. Optical Function: The periodic arrangement of these microstructured holes 5 forms a two-dimensional photonic crystal. This periodic structure diffracts and couples photons generated by the active layer 3, forming a two-dimensional optical resonant cavity with edge modes. This enables stimulated amplification of laser radiation and large-area coherent emission perpendicular to the chip surface, with laser light emitted along the laser emission direction 10.

[0047] B. Heat dissipation function: The internal hollow structures of these microstructured holes 5 are directly used as microfluidic channels for cooling liquid.

[0048] In this embodiment, the heat sink 6 has been redesigned. Rather than being a precision component primarily responsible for heat conduction and microchannel heat dissipation, it functions as a macroscopic fluid distribution system and mechanical support platform. A simple coolant channel 9 is machined into the heat sink 6, with an inlet 7 and an outlet 8. The coolant channel 9 has macroscopic dimensions, with widths and depths ranging from hundreds of microns to several millimeters, making it extremely easy to manufacture.

[0049] During assembly, the semiconductor chip is flip-chip mounted on the side with the microstructured holes 5 openings to the heat sink 6 using bonding techniques such as a metal solder layer 12. After mounting, the entrances of all microstructured holes 5 are fluidically connected to the coolant channels 9 on the heat sink 6.

[0050] Example 1:

[0051] In this embodiment, if Figure 2 As shown, the microstructured holes 5 have circular cross-sections, which exhibit isotropic scattering properties for light from different directions, easily forming a stable, unpolarized or weakly polarized circular light spot. In fluid mechanics, cylindrical channels offer the smallest circumference-to-area ratio, resulting in a relatively low pressure drop at a given flow rate.

[0052] In this embodiment, the microstructure holes 5 together constitute a triangular lattice structure. Since the triangular lattice structure has six-fold symmetry in reciprocal space, it can provide a large and complete photonic band gap, which is crucial for suppressing high-order modes and realizing single Γ-point lasing.

[0053] In this embodiment, the microstructured holes 5 can be formed by the following process: After the PCSEL epitaxial growth is completed, a circular dot pattern with a triangular lattice arrangement is defined on the photosensitive resin using electron beam lithography (EBL) or nanoimprint lithography (NIL). Subsequently, the pattern is transferred to the photonic crystal layer 4 using inductively coupled plasma (ICP) dry etching technology, forming cylindrical microstructured holes 5 with precisely controlled depth. The hole diameter can be designed between 100 nanometers and 2 microns, and the lattice constant (the center-to-center distance between adjacent holes) can be designed between 200 nanometers and 5 microns. The specific values ​​are optimized based on the target lasing wavelength and the material refractive index.

[0054] This embodiment achieves a good balance between optical and fluid performance. The triangular lattice ensures excellent laser mode selectivity, while tens of thousands of parallel cylindrical channels provide the coolant with a large heat exchange surface area and a low-resistance flow path, laying the foundation for efficient heat dissipation.

[0055] Example 2:

[0056] In this embodiment, if Figure 4 As shown, microstructured holes 5 are square holes. At the same lattice constant, square holes can achieve a higher duty cycle than circular holes, resulting in stronger modulation of the photon energy band. In fluid mechanics, the sharp corners of the square channel disrupt the laminar boundary layer, inducing localized micro-eddies at certain flow rates and enhancing heat transfer.

[0057] In this embodiment, the microstructure holes 5 together constitute a square lattice structure. Since the square lattice structure has a low symmetry (four-fold symmetry), it will lead to the removal of photon band degeneracy, which can be used to actively control the polarization state of the laser to output stable linearly polarized light, which is necessary in many applications.

[0058] In this embodiment, the process for forming the microstructured holes 5 differs from that in Example 1 in that the photolithography process is modified to define a square lattice. The etching process requires the use of a more anisotropic dry etching recipe, such as deep reactive ion etching (DRIE) based on the Bosch process, to ensure the formation of steep sidewalls with a near 90-degree angle.

[0059] In this way, by adjusting the side length and rotation angle of the square hole, the polarization characteristics of the laser can be finely controlled. A higher duty cycle means a larger heat exchange surface area. At the same coolant flow rate, the total heat exchange capacity is increased by about 15-20% compared with Example 1. The fluid disturbance at the sharp corners of the square channel increases its Nusselt number (characterizing the intensity of convective heat transfer) compared to a circular channel with the same hydraulic diameter, further enhancing the heat dissipation effect. This solution provides additional design freedom for the coordinated optimization of laser performance (such as polarization control) and heat dissipation performance.

[0060] Example 3:

[0061] The heat distribution of the PCSEL chip is not uniform, and the temperature in the center area is usually the highest. To achieve heat dissipation on demand, in this embodiment, all the microstructure holes 5 are designed to have uneven depths.

[0062] In this embodiment, the microstructured holes 5 can be formed by using two or more etching processes. In the first etching, a single mask is used to perform a shallow pre-etch at all hole locations. In the second etching, a new mask is used, exposing only the hole locations in the center of the chip, where a second, deeper etching is performed. This results in deeper holes in the center, closer to the active layer 3, while the holes in the edge regions are shallower.

[0063] This achieves "on-demand" cooling capacity. Deep channels in the center direct coolant to the hottest spots for maximum cooling, while shallow channels at the edges provide auxiliary cooling. This non-uniform design ensures adequate cooling in the center while avoiding excessively deep etching of the entire chip, reducing process risks and optimizing coolant utilization.

[0064] Example 4:

[0065] There are a large number of dangling bonds and surface states on the etched surface of semiconductor materials (such as GaAs, AlGaAs). Direct contact with coolant (especially deionized water) may cause surface leakage, material corrosion or performance degradation. Figure 6 As shown, a dense dielectric passivation layer 11 is grown on the inner wall of the microstructure hole 5 .

[0066] In this embodiment, the dielectric passivation layer 11 can be formed by the following process: after the etching of the microstructure holes 5 is completed, a layer of dielectric material such as silicon dioxide (SiO2), silicon nitride (SiN) with a thickness of 5 to 50 nanometers is uniformly deposited on the entire chip surface including the inner walls of all holes using atomic layer deposition (ALD) or plasma enhanced chemical vapor deposition (PECVD) technology. x) or aluminum oxide (Al2O3).

[0067] In this way, because the dielectric passivation layer 11 provides excellent electrical insulation, it completely eliminates the conductive path between the coolant and the semiconductor; at the same time, it is also a dense chemical protection layer to prevent the coolant from corroding the side walls of the hole. In addition, the presence of this film has little effect on the optical mode, but it can be accurately calculated and compensated, which is conducive to achieving long-term stable and reliable operation.

[0068] Example 5:

[0069] In order to more precisely control the flow field distribution inside the chip, in this embodiment, Figure 3 As shown, all microstructured holes 5 are designed with uneven diameters. In a parallel pipe network, the distribution of fluid flow is inversely proportional to the flow resistance of each branch. According to the Hagen-Poiseuille law, the flow resistance of a circular pipe is inversely proportional to the fourth power of the pipe diameter. Therefore, by fine-tuning the hole diameter, the flow resistance can be greatly varied, thereby precisely controlling the coolant flow distribution in each area.

[0070] In this embodiment, the microstructured holes 5 can be formed by directly designing hole patterns of different sizes on a photolithography mask. For example, larger diameter holes can be designed in the center of the chip, while smaller diameter holes can be designed in the peripheral area. These holes can be formed simultaneously through a single etching process.

[0071] This allows the large holes in the center to attract more coolant flow, thus matching the higher heat flux density in the center. This design eliminates the need for complex, multiple etching steps and allows spatial modulation of the internal flow field and heat dissipation intensity through mask design alone, making it a highly cost-effective optimization solution.

[0072] Example 6:

[0073] In microchannels, smooth sidewalls typically lead to laminar flow, and heat transfer efficiency is limited by the thickness of the boundary layer. Therefore, in this embodiment, by artificially creating micron- or nanometer-scale roughness on the hole sidewalls, the boundary layer can be effectively disturbed, and even microscopic turbulence can be stimulated at certain flow rates, significantly enhancing the convective heat transfer coefficient.

[0074] In this embodiment, the roughness structure can be formed by the following process: During the dry etching process, by adjusting the ICP etching parameters such as the gas ratio, bias voltage, and power, a sidewall with controlled roughness can be obtained, rather than a completely smooth sidewall. In some embodiments, after the main etching is completed, a brief, isotropic plasma or wet etching can be performed to form tiny pits on the sidewall.

[0075] This significantly improves the heat transfer coefficient. In applications with extremely stringent temperature control requirements, this active heat transfer enhancement strategy can control the chip junction temperature to a lower level.

[0076] Example 7:

[0077] In order to obtain unique optical properties, in this embodiment, as Figure 5 As shown, for certain crystal materials (such as GaAs), the chemical etching rates of different crystal planes are different, and a special-shaped microstructure hole 5 with a specific inclined sidewall, such as a V-shaped or inverted trapezoidal cross-section hole, is obtained by wet etching.

[0078] In this embodiment, the irregularly shaped microstructured holes 5 can be formed by the following process: a mask pattern (e.g., stripes or squares) is arranged along a specific crystal orientation on a (100)-oriented GaAs substrate, and then wet-etching is performed using a specific etchant (e.g., a citric acid / hydrogen peroxide solution). The etching automatically stops at a specific crystallographic plane (e.g., the {111} A plane), forming a V-shaped groove or inverted pyramid-shaped pit with a fixed tilt angle (approximately 54.7 degrees).

[0079] Because the shaped holes offer unique optical properties, they can be used to control the diffraction angle and polarization of light. In terms of heat dissipation, the inclined sidewalls have a larger surface area than vertical sidewalls, increasing the heat transfer area.

[0080] Example 8:

[0081] In this embodiment, the cooling medium may be deionized water. Deionized water has an extremely high specific heat capacity (about 4200 J / kg·K) and a very good thermal conductivity, and is a cooling medium with excellent performance and low cost.

[0082] In this embodiment, a closed-loop cooling system is constructed, including a water pump, a heat exchanger (for ultimately dissipating heat to the environment), a filter, and a liquid storage tank. The system uses strictly filtered and deionized pure water. When the laser is operating, the water pump drives the deionized water through the coolant flow channel 9 of the heat sink 6, into the microstructured pores 5 of the chip, and after completing the heat exchange, returns to the heat exchanger for cooling.

[0083] In this way, the excellent thermophysical properties of deionized water can be utilized to remove a large amount of heat at a relatively low flow rate. Combined with the inner wall passivation technology of Solution 4 of Example 1, it can perfectly solve the conductivity and corrosion problems and is the preferred solution for achieving efficient heat dissipation.

[0084] Example 9:

[0085] In this embodiment, in some scenarios where electrical reliability is required to be extremely high or perfect inner wall passivation cannot be achieved, a dielectric liquid that is non-conductive itself can be used as a coolant, such as 3M's Fluorinert or Novec series electronic engineering fluids.

[0086] In this embodiment, the cooling circulation system is constructed similarly to that of Option 1, but the sealing materials used for the piping and pump must be compatible with the selected dielectric fluid. Since the heat capacity and thermal conductivity of dielectric fluids are typically lower than those of water, this must be compensated for by increasing the flow rate or optimizing the heat exchange structure (e.g., using the roughened sidewalls of Option 6).

[0087] This virtually eliminates any risk of leakage or short circuits caused by the coolant, providing the highest possible electrical safety, which is essential for certain high-voltage or highly sensitive applications.

[0088] Example 10:

[0089] When a liquid absorbs heat near its boiling point and undergoes a phase change (boiling), the latent heat absorbed is far greater than the sensible heat absorbed through temperature rise alone. In this embodiment, by using a cooling medium with a specific boiling point to achieve controlled flow boiling within the microchannel, an equivalent heat transfer coefficient can be achieved that is several times, or even an order of magnitude, higher than that of single-phase countercurrent flow.

[0090] In this embodiment, the inlet temperature and pressure of the coolant entering the chip are precisely controlled to maintain it at or slightly below the saturation point. As the coolant flows through the microstructured pores 5 within the chip, where the heat is most intense, tiny bubbles form near the walls and quickly escape, dissipating a significant amount of heat. The entire system requires careful design to avoid instabilities such as dry-out (CHF, critical heat flux).

[0091] In this way, this extreme heat dissipation method can cope with extremely high heat flux density (>1kW / cm 2 It can "pin" the chip junction temperature near the boiling point of the coolant, achieving very uniform and stable temperature control, making it possible to achieve stable operation of ultra-high power PCSELs.

[0092] Example 11:

[0093] In this embodiment, the cooling medium may also be a nanofluid. By uniformly suspending a very small amount of high thermal conductivity nanoparticles (such as Al2O3, CuO, graphene) in a conventional coolant (such as deionized water), the equivalent thermal conductivity and convective heat transfer capacity of the base fluid can be significantly improved.

[0094] In this example, the nanofluid was prepared using a two-step process. First, commercial, surface-treated Al2O3 nanopowder (average particle size 20-50 nm) was purchased. This powder was then added to deionized water, a small amount of surfactant (such as SDS) was added, and ultrasonic dispersion was performed using a high-power ultrasonic probe for a long period of time (e.g., 1-2 hours) until a stable suspension with no noticeable precipitation was formed. The volume fraction was controlled between 0.1% and 0.5%.

[0095] In this embodiment, due to the presence of nanoparticles, the filter in the circulation system needs to have an appropriate pore size to filter impurities without trapping nanoparticles. The long-term abrasive effect of the pump impeller and seal also needs to be considered.

[0096] In this embodiment, using this nanofluid as the coolant, a more sophisticated filter may be required in the circulation system to prevent particle aggregation and clogging.

[0097] In this way, without changing the flow rate or channel geometry, nanofluids can directly improve heat transfer performance by approximately 10%-50%. This is an innovative approach to enhancing heat dissipation by targeting the cooling medium itself, providing a new path to further tap into the potential of heat dissipation.

[0098] Example 12:

[0099] Many PCSEL applications, such as lidar, operate in pulsed mode. The chip generates significant heat only during the duration of a pulse (e.g., nanosecond to microsecond timescales), while remaining essentially silent during the intervals between pulses. In this embodiment, this characteristic can be exploited to pulse the coolant flow.

[0100] In this embodiment, the coolant flow is pulsed as follows: a fast-response micropump (such as a piezoelectric pump) is used, and its operation is synchronized with the laser's power supply. At the moment of laser pulse emission and a short period thereafter, the pump operates at maximum power, driving the coolant through the chip at high speed. During the interpulse interval, the pump operates at very low power or even stops.

[0101] This significantly reduces the average power consumption of the cooling system and reduces pump wear. At the same time, the instantaneous high flow rate effectively suppresses temperature rise during peak heating periods. This intelligent cooling strategy is particularly suitable for power-constrained mobile platforms or portable devices.

[0102] Example 13:

[0103] In a standard straight flow channel, the cooling liquid will gradually heat up along the way, resulting in a cooling effect in the downstream area of ​​the chip that is worse than that in the upstream area. Figure 7 As shown, the coolant flow channel 9 adopts an anti-parallel flow channel.

[0104] In this embodiment, two parallel macroscopic grooves are machined on the heat sink 6 to serve as coolant flow channels 9, one serving as the main inlet and the other as the main outlet. The two grooves are connected by an internal connecting structure 13, and the design ensures that the chip coolant flows in opposite directions in the two channels.

[0105] In this way, because this design makes the flow path of the coolant on the heat sink 6 longer, a macro layout with hot and cold gradient changes is formed, which can effectively average the temperature of the entire chip, avoid the significant temperature difference caused by unidirectional flow, and is beneficial to the beam quality and wavelength consistency of large-area chips.

[0106] It is understandable that, in some embodiments, the flow path of the coolant on the heat sink 6 can be extended by increasing the number of macro grooves and planning the paths of the macro grooves.

[0107] Example 14:

[0108] Microchannel liquid cooling excels at removing large amounts of background heat, while thin-film thermoelectric coolers (micro-TECs) excel at precise and rapid temperature adjustment. This embodiment combines the two to achieve complementary advantages.

[0109] In this embodiment, a thin-film TEC (electrical rectifier) ​​is integrated between the semiconductor chip and heat sink 6. A microchannel liquid cooling system acts as a heat sink at the TEC's hot end, removing heat pumped from the TEC and removing most of the heat from the chip itself. The TEC, by controlling its operating current, quickly and precisely adjusts the chip temperature within a few degrees.

[0110] This approach combines powerful macro-level cooling with precise micro-level temperature control. This solution is particularly suitable for applications requiring extreme laser wavelength stability, such as dense wavelength division multiplexing (DWDM) optical communications and atomic clocks. Liquid cooling ensures essential operating conditions at high power, while the TEC ensures precise wavelength locking.

[0111] Example 15:

[0112] In this embodiment, the heat sink 6 is made of metal materials such as copper (Cu), copper tungsten (CuW), and copper molybdenum (CuMo), which have excellent thermal conductivity, mature processing technology, and relatively low cost.

[0113] In this embodiment, the heat sink 6 is formed as follows: a CuW alloy plate (its thermal expansion coefficient can be adjusted to match that of semiconductor materials such as GaAs to reduce thermal stress) is selected. A simple linear or U-shaped coolant flow channel 9 is machined onto its surface through conventional precision milling or laser cutting. Holes are then drilled at both ends of the channel and standard fluid connectors are installed, forming an inlet 7 and an outlet 8.

[0114] Thus, the manufacturing cost of the heat sink 6 is reduced by several times or even dozens of times compared to traditional microchannel heat sinks that require micromachining. The good thermal matching of CuW ensures the long-term reliability of the package.

[0115] Example 16:

[0116] In this embodiment, when electrical isolation between the chip and the heat sink 6 is required, high thermal conductivity ceramics such as aluminum nitride (AlN) or beryllium oxide (BeO, pay attention to its toxicity protection) can be used as the heat sink material.

[0117] In this embodiment, the heat sink 6 is formed as follows: an AlN ceramic substrate is used, and macroscopic coolant flow channels 9 are formed thereon by laser scribing or ultrasonic machining. AlN itself is an excellent insulator and can be directly used as a carrier substrate.

[0118] This eliminates the need for an additional insulating layer, simplifying the packaging structure. While AlN's thermal conductivity is lower than copper, it's much higher than semiconductor materials, and its coefficient of thermal expansion more closely matches that of the chip, providing excellent dimensional stability and electrical isolation.

[0119] Example 17:

[0120] In this embodiment, the bonding material may be AuSn solder, which has high thermal conductivity, high strength, excellent creep resistance and thermal fatigue resistance, and is the first choice for high-reliability packaging of optoelectronic devices.

[0121] In this embodiment, the bonding process is as follows: a layer of AuSn solder is pre-deposited by evaporation or sputtering on the bonding surface of the semiconductor chip (the surface where the photonic crystal layer 4 is located) and the corresponding area of ​​the heat sink 6. In the bonding machine, after the chip and heat sink 6 are aligned, they are heated to above the AuSn eutectic point (approximately 280°C). The solder melts and wets the two surfaces, forming a strong metallurgical bond upon cooling. This metal solder layer 12 not only achieves mechanical and electrical connection but also forms a dense sealing barrier surrounding the flow channel.

[0122] In this way, the electrical, thermal, mechanical and sealing functions are integrated. The AuSn solder joints have extremely low thermal and electrical resistance and excellent sealing, thus reliably preventing coolant leakage for a long time.

[0123] Example 18:

[0124] In this embodiment, for some chip structures that are sensitive to thermal stress or contain low-temperature materials, the bonding material may use indium (In) or its alloys with a lower melting point as solder.

[0125] In this embodiment, the bonding process is similar to that of Example 16, but the heating temperature only needs to be around 160°C.

[0126] In this way, the softness of indium can better absorb the stress caused by the mismatch of thermal expansion coefficients, thereby significantly reducing the thermal shock and residual stress in the packaging process, improving the yield and reliability of the device, and is particularly suitable for the packaging of large-area chips.

[0127] Example 19:

[0128] In this embodiment, for applications that are extremely cost-sensitive and do not require high airtightness, the heat sink 6 and the chip can be connected by bonding instead of bonding. Epoxy resin filled with high thermal conductivity particles (such as silver powder or boron nitride powder) can be used as the adhesive.

[0129] In this embodiment, the bonding process is as follows: a thermal conductive adhesive pattern is applied to the heat sink 6 by screen printing or a dispensing machine, and then the chip is mounted on it and cured at a certain temperature.

[0130] This process is simple, extremely low-cost, and eliminates the need for expensive bonding equipment. Although its thermal conductivity and sealing reliability are not as good as metal solder, it is an attractive alternative for low- to medium-power or consumer-grade applications.

[0131] In a second aspect, the present application also provides a heat dissipation system for a photonic crystal surface emitting laser, comprising a photonic crystal surface emitting laser 100 and a coolant as described in the first aspect or any possible implementation thereof; the coolant can be selectively injected from the inlet end 7 of the coolant flow channel 9 of the heat sink 6 of the photonic crystal surface emitting laser 100, and flows through the coolant flow channel 9, and then directly enters the multiple microstructure holes 5 in the photonic crystal layer 4 of the photonic crystal surface emitting laser 100, and the coolant is discharged from the outlet end 8 of the coolant flow channel 9 of the heat sink 6.

[0132] The coolant may be deionized water, ethylene glycol aqueous solution, or dielectric insulating liquid, but is not limited thereto.

[0133] Nanoparticles are added into the coolant to form a nanofluid with a higher thermal conductivity coefficient. The material of the nanoparticles is selected from at least one of aluminum oxide, copper oxide, carbon nanotubes or graphene.

[0134] The heat dissipation process of the heat dissipation system of this application is as follows:

[0135] Startup and coolant circulation: When the system is started, the micro pump starts working to pump the coolant from the inlet port 7 into the coolant channel 9 of the heat sink 6.

[0136] Fluid distribution and entry into the chip: After the coolant fills the macroscopic coolant flow channel 9, due to the pressure difference, it is evenly distributed and flows in parallel into the thousands of microstructure holes 5 in the photonic crystal layer 4 of the semiconductor chip.

[0137] In-chip convection heat transfer: The coolant flows at high speed within the microstructured holes 5, engaging in forced convection heat transfer with the inner walls of the holes. Because the holes are deep within the chip and very close to the active layer 3, which serves as the primary heat source, heat is transferred to the flowing coolant almost instantly.

[0138] Heat dissipation: The coolant that has absorbed a large amount of heat flows out from the microstructure holes 5, merges into the coolant flow channel 9 of the heat sink 6, and is finally discharged from the outlet end 8 and enters the external heat exchanger for cooling, completing a cycle.

[0139] Laser generation and emission: At the same time, the driving current is injected into the chip, generating photons in the active layer 3. The photons undergo resonant amplification in the photonic crystal structure composed of the microstructure holes 5, and eventually form a coherent laser beam, which is emitted vertically along the laser emission direction 10.

[0140] This application achieves multiple breakthrough technical effects by integrating photonic crystal structures with microfluidic heat dissipation channels at the chip level:

[0141] 1. Extreme heat dissipation efficiency: This technology fundamentally eliminates the solid-state heat conduction bottleneck caused by multiple layers of materials and interface thermal resistance in traditional packaging, enabling direct and efficient heat transfer from the source to the coolant. Compared to existing technologies, the overall thermal resistance can be reduced by more than an order of magnitude, enabling the junction temperature of high-power PCSELs to be controlled at extremely low levels.

[0142] 2. Significant performance improvement: Thanks to excellent temperature control, the PCSEL of this invention can operate at higher injection currents, thereby achieving higher output power and photoelectric conversion efficiency. At the same time, the stable low-temperature operating environment ensures the stability of the laser wavelength and excellent beam quality.

[0143] 3. Extended reliability and lifespan: Long-term operation in low-temperature zones greatly slows down the aging of semiconductor materials, the generation and expansion of defects, and other degradation processes, significantly extending the service life of the laser.

[0144] 4. Significantly Reduced Manufacturing Costs: This invention shifts complex microchannel processing from the heat sink to the chip itself. Chip manufacturing itself relies on wafer-level, batch micro-nanofabrication, resulting in a significantly lower cost per unit area than precision machining of a single heat sink. Furthermore, the heat sink structure is greatly simplified, dramatically reducing manufacturing costs. This makes the commercial application of high-performance liquid-cooled PCSELs possible.

[0145] 5. High degree of integration and design flexibility: The "structure as heat dissipation" design concept provides huge space for the multifunctional integration of devices. As shown in the embodiments, it can be highly integrated with electrical, optical, sensing and other functions, laying a solid foundation for the development of the next generation of compact, intelligent, and high-performance photonic integrated systems.

[0146] For those skilled in the art, it is obvious that the present application is not limited to the details of the above-mentioned exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or basic features of the present application. Therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive, and the scope of the present application is defined by the appended claims rather than the above description, and it is intended that all changes that fall within the meaning and scope of the equivalent elements of the claims are included in the present application. Any figure mark in the claims should not be regarded as limiting the claims involved. The above content is only a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto, and any changes or replacements within the technical scope disclosed in the present application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A photonic crystal surface emitting laser, characterized in that: include: A chip comprising a semiconductor substrate, an active layer, and a photonic crystal layer stacked in sequence; a heat sink having a coolant flow channel for conveying coolant; A plurality of microstructure holes are formed in the photonic crystal layer, and the arrangement of the plurality of microstructure holes constitutes a photonic crystal structure for realizing laser emission; The chip is mounted on the heat sink in a flip-chip manner, and the openings of the multiple microstructure holes are fluidically connected to the coolant flow channel of the heat sink to allow the coolant to flow directly into the multiple microstructure holes, thereby forming a heat dissipation channel for removing heat from the active layer.

2. The photonic crystal surface emitting laser according to claim 1, wherein The plurality of microstructure holes penetrate the photonic crystal layer and extend to the vicinity of the interface between the active layer and the photonic crystal layer.

3. The photonic crystal surface emitting laser according to claim 1, wherein The plurality of microstructure holes extend and are closed in the photonic crystal layer.

4. The photonic crystal surface emitting laser according to claim 1, wherein The plurality of microstructure holes penetrate the photonic crystal layer and extend into the active layer.

5. The photonic crystal surface emitting laser according to claim 1, wherein The inner walls of the plurality of microstructure holes are coated with a dielectric passivation layer to achieve electrical and chemical isolation between the semiconductor material of the chip and the coolant.

6. The photonic crystal surface emitting laser according to claim 1, wherein The coolant flow channel of the heat sink is one or more macro-sized linear or U-shaped groove structures.

7. The photonic crystal surface emitting laser according to claim 1, wherein: The chip is bonded to the heat sink via a metal solder layer, and the metal solder layer serves as both an electrode and a sealing structure to prevent leakage of the coolant.

8. A heat dissipation system for a photonic crystal surface emitting laser, characterized in that: The invention comprises a cooling liquid and a photonic crystal surface emitting laser according to any one of claims 1 to 7; the cooling liquid can be selectively injected from the inlet end of the cooling liquid flow channel of the heat sink of the photonic crystal surface emitting laser, flows through the cooling liquid flow channel, and then directly enters the multiple microstructure holes in the photonic crystal layer of the photonic crystal surface emitting laser, and the cooling liquid is discharged from the outlet end of the cooling liquid flow channel of the heat sink.

9. The heat dissipation system for a photonic crystal surface emitting laser according to claim 8, characterized in that: The cooling liquid is deionized water, ethylene glycol aqueous solution or dielectric insulating liquid.

10. The heat dissipation system for a photonic crystal surface emitting laser according to claim 8, characterized in that: Nanoparticles are added to the coolant to form a nanofluid with a higher thermal conductivity coefficient. The material of the nanoparticles is selected from at least one of aluminum oxide, copper oxide, carbon nanotubes or graphene.

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