A packaging method for GaAs-based high-power laser chips to improve heat dissipation efficiency

Abstract

This invention relates to a packaging method for GaAs-based high-power laser chips to improve heat dissipation efficiency. The method includes the following steps: adhering a graphene film to the p-side of the GaAs-based high-power laser chip, and then using a graphene-In52Sn48 alloy hybrid solder to package it onto a base heat sink via low-temperature soldering. This invention, by covering the p-side of the chip with a graphene film and then soldering it to the base heat sink with the graphene-In52Sn48 alloy hybrid solder, increases the contact area between the chip and the heat sink. The high thermal conductivity of graphene allows for rapid transfer of waste heat generated in the active region to the heat sink, reducing the thermal gradient of the chip and significantly enhancing the heat dissipation effect of the packaged module. Compared to traditional methods, the reliability, stability, and heat dissipation effect of GaAs-based high-power lasers packaged using this method are significantly improved, while also extending the laser's lifespan.

Description

Technical Field

[0001] This invention relates to a packaging method for GaAs-based high-power laser chips that improves heat dissipation efficiency, belonging to the field of optoelectronic technology. Background Technology

[0002] Semiconductor lasers have developed rapidly in recent years. Among them, GaAs-based high-power lasers have stood out due to their advantages such as simple fabrication process, small size, high power density, and high electro-conversion efficiency, and have been applied in many industrial fields. With industrial development, the requirements for power, beam quality, and conversion efficiency of GaAs-based high-power lasers are becoming increasingly stringent. Since the photoelectric conversion efficiency of semiconductor lasers is around 40%-60%, the increase in laser power is accompanied by an increase in waste heat generation. The waste heat generated during laser operation can cause uneven stress distribution, leading to a redshift in the output wavelength, reduced output power, decreased photoelectric conversion efficiency, and increased threshold current, resulting in reduced reliability. Therefore, solving the problems of packaging stress and heat dissipation in semiconductor lasers, and improving their reliability and stability, is of practical significance.

[0003] High-power laser packaging can be categorized into top-mount and bottom-mount types based on chip orientation. Bottom-mount avoids the high thermal resistance issues associated with the substrate, offering better heat dissipation and becoming the more commonly used packaging method. However, the mismatch in the coefficients of thermal expansion (CTE) between the chip and the heat sink in bottom-mount leads to significant stress during solder cooling to room temperature. Graphene, a two-dimensional crystal with six polar phonons, possesses excellent optical, electrical, and mechanical properties, as well as high thermal conductivity. Phonon transport is the process of heat conduction within graphene, and the thermal conductivity of a single layer of graphene can reach 5300 W / m². -1 K -1 With its superior thermal conductivity compared to currently used thermal conductive materials, more and more researchers are beginning to study the application of graphene materials in heat dissipation.

[0004] Currently, there are two main methods for encapsulating lasers using graphene: One is to bond the laser chip to a heat sink using graphene. However, graphene lacks strong adhesion, making the direct connection between graphene and the chip / heat sink unreliable. Furthermore, while graphene's porous structure facilitates heat dissipation, it can also introduce voids at the chip / heat sink interface, leading to chip burn-out and reduced lifespan. The second method involves soldering with traditional solders such as In-type solder and gold-tin solder. However, graphene begins to oxidize at 350°C in an oxygen-rich environment, and traditional solders generate high temperatures during the soldering process or are used in high-temperature environments. This makes graphene highly susceptible to oxidation and failure during soldering, resulting in a reduced laser lifespan.

[0005] To address the above issues, a new laser packaging method is needed. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a GaAs-based high-power laser chip packaging method that improves heat dissipation efficiency.

[0007] The technical solution of the present invention is as follows:

[0008] A method for packaging GaAs-based high-power laser chips to improve heat dissipation efficiency includes the following steps:

[0009] A graphene film is adhered to the P-side of a GaAs-based high-power laser chip, and then encapsulated onto a base heat sink using a graphene-In52Sn48 alloy hybrid solder via low-temperature welding.

[0010] According to a preferred embodiment of the present invention, the GaAs-based high-power laser chip comprises, from bottom to top, an N-side metal electrode contact layer, a GaAs substrate, an N-side confinement layer, a first waveguide layer, an active layer of a quantum well structure, a second waveguide layer, a P-side confinement layer, a surface layer, a SiO2 current injection barrier layer, and a P-side metal electrode contact layer.

[0011] According to a preferred embodiment of the present invention, the thickness of the graphene film is 0.5 to 1.5 μm.

[0012] According to a preferred embodiment of the present invention, the graphene-In52Sn48 alloy hybrid solder is prepared according to the following method:

[0013] Graphene nanosheets and In52Sn48 alloy were mixed at a volume ratio of (5-10):(90-95), and then ball-milled for 48 hours under N2 protection using a planetary ball mill, with a 0.5-hour stop every 1 hour. The ball-to-material ratio was 107:1. After ball milling, the mixture of graphene nanosheets and In52Sn48 alloy was pressed into a solder sheet using a high-pressure molding machine to obtain graphene-In52Sn48 alloy mixed solder.

[0014] According to a preferred embodiment of the present invention, the temperature of the low-temperature welding is 135–145°C.

[0015] According to a preferred embodiment of the present invention, the base heat sink is a Cu heat sink.

[0016] According to a preferred embodiment of the present invention, the GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency specifically includes the following steps:

[0017] (1) Provide an epitaxial wafer, wherein the epitaxial wafer comprises, from bottom to top, a GaAs substrate, an N-confinement layer, a first waveguide layer, an active layer of a quantum well structure, a second waveguide layer, a P-confinement layer, and a surface layer;

[0018] (2) The epitaxial wafer is etched by photolithography to form two trenches on the epitaxial wafer, with the light-emitting gain region in the middle of the two trenches;

[0019] (3) A SiO2 current injection barrier layer is covered in the light-emitting gain region by PECVD process, and then the P-side metal electrode contact layer is deposited.

[0020] (4) Thin the epitaxial wafer obtained in step (3) and then deposit an N-side metal electrode contact layer on the back side of the substrate, keeping the trench in a hollow state, to obtain a GaAs-based high-power laser chip with high heat dissipation.

[0021] (5) A graphene film is adhered to the metal electrode contact layer on the P side of the chip obtained in step (4), and then the chip is placed with the P side facing down. The graphene-In52Sn48 alloy mixed solder is used to weld and encapsulate it onto the Cu heat sink at 140°C.

[0022] According to a preferred embodiment of the present invention, in step (2), the etching is etching to the second waveguide layer.

[0023] According to a preferred embodiment of the present invention, in step (5), the thickness of the solder layer formed by the graphene-In52Sn48 alloy mixed solder is 5 to 10 μm.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. This invention involves coating the P-side of a chip with a graphene film, and then soldering the chip to a base heat sink using a graphene-In52Sn48 alloy mixed solder at a low temperature of 135-145°C. The solder connects the graphene film to the base heat sink, increasing the contact area between the chip and the heat sink. The high thermal conductivity of graphene can quickly transfer the waste heat generated in the active region to the heat sink, reducing the thermal gradient of the chip and greatly enhancing the heat dissipation effect of the packaging module. Compared with GaAs-based high-power lasers packaged by traditional methods, the reliability, stability, and heat dissipation effect are significantly enhanced.

[0026] 2. The solder used in this invention is a mixture of graphene nanosheets and In52Sn48 alloy. It fully utilizes the low melting point of the indium tin solder (120°C eutectic temperature) to achieve the coexistence of the solder and the graphene film. Traditional In solder and gold tin solder require very high welding temperatures. However, excessively high welding temperatures can lead to the oxidation and decomposition of the graphene film. During the oxidation and decomposition process, gas is generated, which can cause the chip and heat sink to not be tightly connected, resulting in defects such as voids and reduced chip life. Furthermore, In52Sn48 alloy is a soft metal with cold-pressing properties, making it susceptible to corrosion in humid environments and exhibiting poor high-temperature thermal fatigue performance. However, by mixing graphene nanosheets with In52Sn48 alloy, the excellent optical, electrical, and mechanical properties of graphene can be utilized to fully leverage the low-temperature ductility of In52Sn48 alloy solder while mitigating the impact of its inherent problems. The increased surface area provided by graphene nanosheets can absorb stress caused by the mismatch of thermal expansion coefficients between different materials. The addition of graphene nanosheets also improves the welding effect between the solder and the graphene film, reducing the likelihood of defects such as voids.

[0027] 3. The structure of the package in this invention is chip-graphene film-solder layer-base heat sink, so that the heat sink and chip do not directly contact each other. The stress caused by the inconsistency of CTE between chip and heat sink will not be introduced into the active area of ​​chip. This avoids problems such as redshift of package wavelength, reduced output power, reduced photoelectric conversion efficiency, and increased threshold current caused by heat dissipation and stress, which lead to reduced reliability. This effectively improves the stability of GaAs-based high-power laser.

[0028] 4. This invention controls the thickness of the solder layer formed by the graphene-In52Sn48 alloy hybrid solder to 5-10 μm, enabling the laser to achieve optimal performance. When the solder thickness is less than 5 μm, the use of low-temperature soldering can lead to insufficient soldering, introducing defects such as voids at the chip-solder interface, affecting the lifespan and heat dissipation of the device. When the solder thickness is greater than 10 μm, the solder may cover the light-emitting surface of the chip due to excessive thickness, affecting the light emission qualification rate. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the chip structure after graphene is adhered to it according to the present invention.

[0030] Figure 2 This is a schematic diagram of the laser structure after encapsulation according to the present invention.

[0031] In the figure: 1. N-confinement layer, 2. First waveguide layer, 3. Active layer of quantum well structure, 4. Second waveguide layer, 5. P-confinement layer, 6. Surface layer, 7. SiO2 current injection barrier layer, 8. P-side metal electrode contact layer, 9. N-side metal electrode contact layer, 10. Graphene film, 11. GaAs substrate, 12. Trench. Detailed Implementation

[0032] The present invention will be further described below with reference to the embodiments and accompanying drawings, but is not limited thereto.

[0033] Example 1

[0034] A method for packaging GaAs-based high-power laser chips to improve heat dissipation efficiency includes the following steps:

[0035] (1) Provide an epitaxial wafer, wherein the epitaxial wafer comprises, from bottom to top, a GaAs substrate, an N-confinement layer, a first waveguide layer, an active layer of a quantum well structure, a second waveguide layer, a P-confinement layer, and a surface layer;

[0036] (2) The epitaxial wafer is etched to the second waveguide layer by photolithography, forming two trenches on the epitaxial wafer, with the light-emitting gain region in the middle of the two trenches;

[0037] (3) A SiO2 current injection barrier layer is covered in the light-emitting gain region by PECVD process, and then the P-side metal electrode contact layer is deposited.

[0038] (4) Thin the epitaxial wafer obtained in step (3) and then deposit an N-side metal electrode contact layer on the back side of the substrate, keeping the trench in a hollow state, to obtain a GaAs-based high-power laser chip with high heat dissipation.

[0039] (5) A graphene film with a thickness of 1 μm is adhered to the metal electrode contact layer on the P side of the chip obtained in step (4). Then, with the P side of the chip facing down, a graphene-In52Sn48 alloy mixed solder is used to weld and encapsulate it onto the Cu heat sink at 140°C.

[0040] In step (5), the graphene-In52Sn48 alloy hybrid solder is prepared as follows: graphene nanosheets and In52Sn48 alloy are mixed at a volume ratio of 8:92, and then ball-milled for 48 hours under N2 protection using a planetary ball mill, with a 0.5-hour stop every 1 hour. The ball-to-material ratio is 107:1. After ball milling, the graphene nanosheets and In52Sn48 alloy hybrid solder are pressed into solder sheets using a high-pressure molding machine to obtain the graphene-In52Sn48 alloy hybrid solder. The solder layer thickness formed by the graphene-In52Sn48 alloy hybrid solder is 7 μm.

[0041] A schematic diagram of the chip structure after graphene adhesion in this embodiment is shown below. Figure 1 As shown in the diagram, the packaged chip structure is as follows: Figure 2 As shown, no solder covered the light-emitting surface of the chip during the fabrication process, and the light emission pass rate was 100%.

[0042] Example 2

[0043] A method for packaging GaAs-based high-power laser chips to improve heat dissipation efficiency, the specific steps are the same as those described in Example 1, except that in step (5), the thickness of the graphene film is 0.5 μm, the welding temperature is 135℃, and the thickness of the solder layer formed by the graphene-In52Sn48 alloy mixed solder is 5 μm.

[0044] Example 3

[0045] A method for packaging GaAs-based high-power laser chips to improve heat dissipation efficiency, the specific steps are the same as those described in Example 1, except that in step (5), the thickness of the graphene film is 1.5 μm, the welding temperature is 145 °C, and the thickness of the solder layer formed by the graphene-In52Sn48 alloy mixed solder is 10 μm.

[0046] Example 4

[0047] A method for packaging GaAs-based high-power laser chips to improve heat dissipation efficiency, the specific steps are the same as those described in Example 1, except that in step (5), the graphene-In52Sn48 alloy mixed solder has a volume ratio of graphene nanosheets and In52Sn48 alloy of 10:90.

[0048] Comparative Example 1

[0049] A GaAs-based high-power laser chip packaging method, the specific steps are the same as those described in Example 1, the difference being that after the chip is fabricated in step (5), no graphene film is adhered to the metal electrode on the P side of the chip, the chip is directly placed with the P side facing down, and graphene-In52Sn48 alloy mixed solder is used to weld and package it onto the Cu heat sink at 140°C.

[0050] Comparative Example 2

[0051] A GaAs-based high-power laser chip packaging method, the specific steps are the same as those described in Example 1, the difference being that in step (5), solder is not used for welding, but high temperature and high pressure bonding is used to package the chip onto the heat sink.

[0052] Comparative Example 3

[0053] A GaAs-based high-power laser chip packaging method, the specific steps are the same as those described in Example 1, except that in step (5), the solder used is In solder or gold-tin solder, which is soldered to Cu heat sink at 480°C.

[0054] Comparative Example 4

[0055] A GaAs-based high-power laser chip packaging method, the specific steps are the same as those described in Example 1, except that in step (5), the thickness of the solder layer formed by the graphene-In52Sn48 alloy mixed solder is 1μm.

[0056] Comparative Example 5

[0057] A GaAs-based high-power laser chip packaging method, the specific steps are the same as those described in Example 1, except that in step (5), the thickness of the solder layer formed by the graphene-In52Sn48 alloy mixed solder is 17μm.

[0058] In this comparison, 70% of the chips had solder covering the light-emitting surface due to excessive solder thickness, affecting the light emission pass rate.

[0059] Test case

[0060] The heat dissipation effect of the laser packaged in Example 1 and the lasers packaged in Comparative Examples 1 to 4 was tested.

[0061] The specific method is as follows: the laser is used at 200A for 12 hours, the temperature is recorded, then it is cooled under natural conditions, the time is recorded, and an aging test is performed by pulse. The results are shown in Table 1.

[0062] Table 1

[0063]

[0064]

[0065] As shown in Table 1, firstly, the addition of a graphene film between the heat sink and the chip in this invention significantly improves the heat dissipation performance of the packaged laser. The laser packaged in Example 1 reached a temperature of 60°C after 12 hours of use at 200A, and only required 10 minutes to cool back to room temperature. In contrast, Comparative Example 1 reached a temperature of 75°C under the same conditions, requiring 25 minutes to cool back to room temperature. Secondly, this invention uses a graphene-In52Sn48 alloy mixed solder for low-temperature welding, which significantly extends the lifespan of the packaged laser and further enhances its heat dissipation capacity. The laser packaged in Example 1 did not fail after 1000 hours of use, while Comparative Example 2 reached a temperature of 85°C under the same conditions, requiring 60 minutes to cool back to room temperature and failing after 100 hours. Comparative Example 3 reached a temperature of 78°C under the same conditions, requiring 27 minutes to cool back to room temperature and failing after 700 hours. Finally, this invention controls the thickness of the solder layer formed by the graphene-In52Sn48 alloy hybrid solder to 5-10 μm, so that the laser can achieve the best performance. In contrast, under the same conditions, the temperature of Comparative Example 4 is 70°C, and it takes 20 minutes to cool down to room temperature and fails after 800 hours of use.

Claims

1. A method for packaging GaAs-based high-power laser chips to improve heat dissipation efficiency, characterized in that, The steps include the following: A graphene film is adhered to the P-side of a GaAs-based high-power laser chip, and then encapsulated onto a base heat sink using a graphene-In52Sn48 alloy mixed solder via a low-temperature soldering method. The graphene-In52Sn48 alloy hybrid solder is prepared according to the following method: Graphene nanosheets and In52Sn48 alloy were mixed at a volume ratio of (5~10):(90~95), and then ball-milled for 48 hours under N2 protection using a planetary ball mill, with a 0.5-hour stop every 1 hour. The ball-to-material ratio was 107:

1. After ball milling, the mixture of graphene nanosheets and In52Sn48 alloy was pressed into a solder sheet using a high-pressure molding machine to obtain graphene-In52Sn48 alloy mixed solder.

2. The GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency as described in claim 1, characterized in that, The GaAs-based high-power laser chip comprises, from bottom to top, an N-side metal electrode contact layer, a GaAs substrate, an N-side confinement layer, a first waveguide layer, an active layer with a quantum well structure, a second waveguide layer, a P-side confinement layer, a surface layer, a SiO2 current injection barrier layer, and a P-side metal electrode contact layer.

3. The GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency as described in claim 1, characterized in that, The thickness of the graphene film is 0.5~1.5μm.

4. The GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency as described in claim 1, characterized in that, The temperature for the low-temperature welding is 135~145℃.

5. The GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency as described in claim 1, characterized in that, The base heat sink is a Cu heat sink.

6. The GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency as described in claim 1, characterized in that, The specific steps are as follows: (1) Provide an epitaxial wafer, wherein the epitaxial wafer comprises, from bottom to top, a GaAs substrate, an N-confinement layer, a first waveguide layer, an active layer of a quantum well structure, a second waveguide layer, a P-confinement layer, and a surface layer; (2) The epitaxial wafer is etched by photolithography to form two trenches on the epitaxial wafer, with the light-emitting gain region in the middle of the two trenches; (3) A SiO2 current injection barrier layer is covered in the light-emitting gain region by PECVD process, and then the P-side metal electrode contact layer is deposited. (4) Thin the epitaxial wafer obtained in step (3) and then deposit an N-side metal electrode contact layer on the back side of the substrate, keeping the trench in a hollow state, to obtain a GaAs-based high-power laser chip with high heat dissipation. (5) Adhere a graphene film to the metal electrode contact layer on the P side of the chip obtained in step (4), and then, with the P side of the chip facing down, use graphene-In52Sn48 alloy mixed solder to weld and encapsulate it onto the Cu heat sink at 140°C.

7. The GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency as described in claim 6, characterized in that, In step (2), the etching is etching to the second waveguide layer.

8. The GaAs-based high-power laser chip packaging method for improving heat dissipation efficiency as described in claim 6, characterized in that, In step (5), the thickness of the solder layer formed by the graphene-In52Sn48 alloy mixed solder is 5~10μm.

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