Vacuum thermal isolation packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer

Abstract

The invention discloses a vacuum thermal isolation packaging structure for a high-precision two-dimensional photonic crystal cavity optical force accelerometer, which comprises a tube shell base, a thermoelectric cooler TEC, an insulating heat sink with a thermal insulation groove, an insulating cushion block, a semiconductor laser chip LD, an SOI substrate, a tube shell enclosure frame and a tube shell cover plate, an accelerometer sensor and an on-chip photoelectric detector (PD) are integrated on an SOI substrate. And the tube shell base is made of a copper-tungsten alloy material. The tube shell enclosure frame and the cover plate are made of kovar alloy materials. The insulation heat sink is placed on the cold end surface of the thermoelectric cooler TEC, a transverse through heat insulation groove is formed in the upper surface of the insulation heat sink, a transverse heat conduction path is physically cut off through the heat insulation groove, and the surface of the insulation heat sink is physically divided into a heat source area and a cold source area. The semiconductor laser chip LD is installed in a heat source area through a cushion block, the SOI substrate is directly installed in a cold source area, and longitudinal thermal resistance is increased through the cushion block.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic device packaging technology, specifically relating to a vacuum thermal isolation packaging structure for a high-precision two-dimensional photonic crystal cavity optical accelerometer. Background Technology

[0002] Cavity optical force sensors utilize high-quality optical microcavities to detect minute mechanical displacements (such as acceleration and angular velocity). They are extremely sensitive and often need to operate in a vacuum and constant-temperature environment to reduce the influence of air damping on the mechanical oscillator.

[0003] However, the vacuum environment presents significant challenges for thermal design. In conventional packaging, the pump light source (LD) and the sensing chip typically share a heat sink for integration and optical alignment. However, the LD generates continuous Joule heat during operation, and in a vacuum environment, due to the lack of convection cooling, the heat can only be conducted through the solid. If the LD and the temperature-sensitive Si chip are directly mounted on the same heat sink, the heat generated by the LD will be laterally conducted to the Si chip, causing the Si chip's temperature to rise, its refractive index to shift, and ultimately disrupting the resonant state of the optical microcavity, leading to sensor failure.

[0004] Existing technologies typically address this by increasing the size of the heat sink or adding a separate TEC, but this significantly increases package size, power consumption, and vacuum venting source, which is detrimental to device miniaturization and long-term reliability. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems and provide a vacuum thermal isolation packaging structure for a high-precision two-dimensional photonic crystal cavity optical accelerometer that achieves effective thermal decoupling between the LD heat source and the high-precision two-dimensional photonic crystal cavity optical accelerometer in a compact single TEC architecture.

[0006] To solve the above-mentioned technical problems, the technical solution of the present invention is: a vacuum thermal isolation packaging structure for a high-precision two-dimensional photonic crystal cavity optical accelerometer, comprising a tube base, a thermoelectric cooler (TEC), an insulating heat sink with a heat insulation groove, insulating pads, a semiconductor laser chip (LD), an SOI substrate, a tube frame, and a tube cover plate. An accelerometer sensor and an on-chip photodetector (PD) are integrated on the SOI substrate. The tube base is made of copper-tungsten alloy; the tube frame and cover plate are made of Kovar alloy; the insulating heat sink is placed on the cold end surface of the thermoelectric cooler (TEC), and the upper surface of the insulating heat sink has a transversely penetrating heat insulation groove, which physically cuts off the transverse heat conduction path, physically dividing the surface of the insulating heat sink into a heat source area and a cold source area; the semiconductor laser chip (LD) is mounted in the heat source area via the pads, and the SOI substrate is directly mounted in the cold source area, using the pads to increase longitudinal thermal resistance.

[0007] Preferably, the insulating heat sink is made of aluminum nitride (AlN) with a volume of 9 mm × 6 mm × 1 mm, and the insulating pad is also made of aluminum nitride (AlN) with a volume of 1.2 mm × 0.6 mm × 0.38 mm. The thickness of the insulating pad is configured such that the light emission height of the semiconductor laser chip LD is aligned with the waveguide coupling height of the SOI substrate in the Z-axis direction.

[0008] Preferably, the width of the heat insulation groove is 0.3 mm, the depth is 80% of the thickness of the insulating heat sink, i.e., 0.8 mm, and the length is the same as the width of the heat sink, which is 6 mm; the heat insulation groove is a vacuum environment.

[0009] Preferably, the tube base is made of copper-tungsten alloy (CuW) with a volume of 14 mm × 10 mm × 2 mm, wherein the copper content is 10%-20%, which can quickly guide the waste heat generated by the thermoelectric cooler (TEC) to the external environment, and the thermal conductivity is not less than 160 W / (m·K).

[0010] Preferably, the length and width of the casing frame and casing cover are the same as those of the casing base. The casing frame is 1mm thick and 7mm high, and the casing cover is 0.4mm thick. The casing frame and casing cover are made of Kovar alloy. The thermal expansion coefficient of Kovar alloy is approximately 5.9×10-6 / K, which is relatively compatible with high-resistivity silicon (2.6×10-6 / K) and germanium (5.8×10-6 / K) as well as commonly used TEC ceramic plates (alumina). Good airtightness can be achieved through glass-metal sintering. The inner wall of the casing is polished or gold-plated to reduce thermal emissivity.

[0011] Preferably, the miniature thermoelectric cooler TEC has a volume of 8 mm × 6 mm × 2 mm, its surface is metallized, and the cold end area is smaller than the bottom area of ​​the insulating heat sink; the edge of the insulating heat sink covers or extends beyond the cold end edge of the miniature thermoelectric cooler TEC in the horizontal direction to shield the radiant heat from the inner wall of the tube shell to the cold end of the TEC in a vacuum environment.

[0012] Preferably, the connection material between the SOI substrate and the insulating heat sink is nano-silver paste (Nano-Ag), which is connected by a low-temperature sintering process to reduce the mechanical stress on the MEMS structure; the insulating heat sink and the micro thermoelectric cooler TEC are welded using indium silver solder (InAg); the welding material between the semiconductor laser chip LD and the insulating pad, the insulating pad and the insulating heat sink, and the thermoelectric cooler TEC and the housing base is gold-tin solder (AuSn).

[0013] Preferably, the encapsulation structure is placed inside an airtight metal tube, the inside of which is kept under vacuum, and a non-evaporable getter (NEG) is provided inside to maintain the vacuum level.

[0014] The beneficial effects of this invention are:

[0015] 1. The vacuum thermal isolation packaging structure for a high-precision two-dimensional photonic crystal cavity optical accelerometer provided by the present invention physically cuts off the shortest heat conduction path on the AlN heat sink surface through the heat insulation groove, forcing the heat of the LD to reach the TEC by passing downward through the pad and then through the thickness direction of the main heat sink, and cannot be directly transferred laterally to the SOI substrate, thus having a significant thermal isolation effect.

[0016] 2. This invention uses copper-tungsten alloy (CuW) material with high thermal conductivity as the tube shell base, which enables the waste heat generated by TEC to be quickly directed to the external environment, thereby improving the temperature stability inside the package.

[0017] 3. This invention, through optimized matching of TEC and heat sink dimensions (heat sink covering TEC), eliminates the radiation heat absorption effect caused by the exposed cold end of TEC under vacuum, improves the cooling efficiency (COP) of TEC, and effectively suppresses parasitic radiation.

[0018] 4. This invention uses a CuW base to match the coefficient of thermal expansion (CTE) of ceramics and employs a nano-silver sintering process on the SOI substrate side, which effectively absorbs thermal mismatch stress and protects the fragile nano-photonic crystal structure, exhibiting the characteristics of low stress and high reliability.

[0019] 5. By selecting Kovar alloy as the casing frame and cover plate, the present invention can achieve good airtightness through glass-metal sintering, so that the inside of the casing maintains a vacuum state, and the inside is equipped with a non-evaporable getter (NEG) to effectively maintain a high vacuum degree. Attached Figure Description

[0020] Figure 1 This is an exploded view of the internal three-dimensional structure of the vacuum tube shell of a vacuum thermal isolation packaging structure for a high-precision two-dimensional photonic crystal cavity optical accelerometer according to the present invention;

[0021] Figure 2 This is a side cross-sectional view of the present invention.

[0022] Explanation of reference numerals in the attached drawings: 1. Tube shell base; 2. Thermoelectric cooler (TEC); 3. Insulating heat sink with heat insulation groove; 4. Insulating pad; 5. Semiconductor laser chip (LD); 6. SOI substrate; 7. Tube shell frame; 8. Tube shell cover plate; 9. Nano silver paste solder layer; 10. Gold-tin solder layer; 11. Indium silver solder layer. Detailed Implementation

[0023] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0024] like Figure 1 and Figure 2 As shown, the present invention provides a vacuum thermal isolation packaging structure for a high-precision two-dimensional photonic crystal cavity optical accelerometer, including a tube base 1, a thermoelectric cooler TEC2, an insulating heat sink 3 with a heat insulation groove, an insulating pad 4, a semiconductor laser chip LD5, an SOI substrate 6, a tube frame 7, and a tube cover plate 8. An accelerometer sensor and an on-chip photodetector PD are integrated on the SOI substrate 6.

[0025] The casing frame 7 is located on the casing base 1. The thermoelectric cooler TEC2, the insulating heat sink 3, the insulating pad 4, the semiconductor laser chip LD5, and the SOI substrate 6 are all located on the casing base 1 and inside the casing frame 7. The casing cover plate 8 is located on top of the casing frame 7.

[0026] The thermoelectric cooler TEC2, the insulating heat sink 3, and the SOI substrate 6 are stacked sequentially from bottom to top. The insulating pad 4 and the semiconductor laser chip LD5 are located on the insulating heat sink 3 and are respectively connected to the SOI substrate 6. A gold-tin solder layer 10 is provided between the thermoelectric cooler TEC2 and the tube base 1, an indium silver solder layer 11 is provided between the thermoelectric cooler TEC2 and the insulating heat sink 3, a nano-silver paste solder layer 9 is provided between the insulating heat sink 3 and the SOI substrate 6, and a gold-tin solder layer 10 is also provided between the insulating heat sink 3 and the insulating pad 4.

[0027] The tube base 1 is made of copper-tungsten alloy. The tube frame 7 and cover plate 8 are made of Kovar alloy. The insulating heat sink 3 is placed on the cold end surface of the thermoelectric cooler TEC2, and the upper surface of the insulating heat sink 3 is provided with a transversely penetrating heat insulation groove. The heat insulation groove physically cuts off the transverse heat conduction path, physically dividing the surface of the insulating heat sink 3 into a heat source area and a cold source area. The semiconductor laser chip LD5 is mounted in the heat source area through a pad 4, and the SOI substrate 6 is directly mounted in the cold source area. The pad 4 is used to increase the longitudinal thermal resistance. This effectively solves the problem of thermal crosstalk between the waste heat of the semiconductor laser chip and the high-precision accelerometer chip in a vacuum environment. At the same time, the nano-silver sintering process reduces the packaging stress, significantly improving the temperature stability and optical coupling efficiency of the sensor in a vacuum environment.

[0028] The insulating heat sink 3 is made of aluminum nitride (AlN) and has a volume of 9 mm × 6 mm × 1 mm. The insulating pad 4 is also made of aluminum nitride (AlN) and has a volume of 1.2 mm × 0.6 mm × 0.38 mm. The thickness of the insulating pad 4 is configured such that the light emission height of the semiconductor laser chip LD5 is aligned with the waveguide coupling height of the SOI substrate 6 along the Z-axis. The "Z-axis" direction refers to the Z-axis direction in a three-dimensional coordinate system based on the right-hand rule.

[0029] The insulation groove is 0.3 mm wide, 0.8 mm deep (80% of the thickness of the insulating heat sink 3), and 6 mm long (the same as the width of the heat sink). The insulation groove is a vacuum environment.

[0030] The base 1 of the tube shell is made of copper-tungsten alloy (CuW), with dimensions of 14 mm × 10 mm × 2 mm. It contains 10%-20% copper and can quickly dissipate waste heat generated by the thermoelectric cooler TEC2 to the external environment, with a thermal conductivity of not less than 160 W / (m·K). The selection of CuW aims to match the coefficient of thermal expansion of the ceramic and semiconductor materials above, reducing thermal stress, while simultaneously providing an efficient heat dissipation channel for rapidly dissipating waste heat generated by the TEC.

[0031] The tube casing frame 7 and the tube casing cover plate 8 have the same length and width as the tube casing base 1. The tube casing frame 7 is 1mm thick and 7mm high, and the tube casing cover plate 8 is 0.4mm thick. The tube casing frame 7 and the tube casing cover plate 8 are made of Kovar alloy. The thermal expansion coefficient of Kovar alloy is about 5.9×10-6 / K, which is relatively compatible with high-resistivity silicon (2.6×10-6 / K) and germanium (5.8×10-6 / K) as well as commonly used TEC ceramic plates (alumina). Good airtightness can be achieved through glass-metal sintering. The inner wall of the tube casing is polished or gold-plated to reduce the thermal emissivity.

[0032] The miniature thermoelectric cooler TEC2 has a volume of 8 mm × 6 mm × 2 mm and its surface is metallized. The cold end area is smaller than the bottom area of ​​the insulating heat sink 3. The edge of the insulating heat sink 3 covers or extends beyond the edge of the cold end of the miniature thermoelectric cooler TEC2 in the horizontal direction to shield the radiant heat from the inner wall of the tube shell to the cold end of the TEC in a vacuum environment.

[0033] The "cantilever" shielding structure is formed, which blocks the heat radiation from the tube base 1 and the surrounding environment from directly hitting the cold end ceramic surface of TEC2.

[0034] The connection material between the SOI substrate 6 and the insulating heat sink 3 is nano-silver paste (Nano-Ag), and the connection is achieved through a sintered layer. This low-temperature sintering process reduces mechanical stress on the MEMS structure. The nano-silver sintered layer has a porous structure and low elastic modulus, which absorbs thermal mismatch stress between AlN and Si, protecting the deformation-sensitive photonic crystal microcavity structure inside the SOI substrate 6. The insulating heat sink 3 is soldered to the micro thermoelectric cooler TEC2 using indium silver solder (InAg). The soldering material between the semiconductor laser chip LD5 and the insulating pad 4, the insulating pad 4 and the insulating heat sink 3, and the thermoelectric cooler TEC2 and the housing base 1 is gold-tin solder (AuSn). Eutectic bonding is used to ensure connection rigidity and long-term optical path stability.

[0035] The encapsulation structure is placed inside an airtight metal tube, which maintains a vacuum state inside and contains a non-evaporable getter (NEG) to maintain the vacuum level.

[0036] This invention utilizes the physical characteristic that heat transfer in a vacuum environment primarily relies on solid conduction. Through structural design, it achieves decoupling between the heat source and the sensitive source: When the semiconductor laser chip LD5 generates Joule heat during operation, the heat is first conducted to the insulating pad 4, and then to the first mounting area of ​​the insulating heat sink 3. At this point, due to the presence of the heat insulation groove, the shortest path for lateral heat conduction to the second mounting area, i.e., the SOI substrate 6, is cut off, thus thermally blocking the lateral flow. The obstructed lateral heat flow is forced to pass through the thickness of the insulating heat sink 3 vertically, and is actively extracted by the micro thermoelectric cooler TEC2 below and discharged to the tube base 1, where it is thermally guided longitudinally. The pad 5 not only serves to align the optical path along the Z-axis, but its thickness also increases the vertical thermal resistance from the semiconductor laser chip LD5 to the main heat sink, further limiting the heat diffusion range and separating the optical path from the thermal path. By combining the radiation shielding effect of the insulating heat sink 3 on the miniature thermoelectric cooler TEC2, this structure significantly reduces ineffective radiation power consumption in a vacuum environment, ensuring the temperature stability of the SOI substrate 6 under continuous operation of the semiconductor laser chip LD5 and external temperature fluctuations, thereby guaranteeing the measurement accuracy of the cavity optical force sensor and exhibiting extremely high environmental adaptability.

[0037] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A vacuum thermally isolated packaging structure for a high-precision two-dimensional photonic-crystal-cavity optical-force accelerometer, characterized by: The application relates to a micro-thermoelectric cooler TEC (2) and a semiconductor laser module, which comprises a tube shell base (1), the micro-thermoelectric cooler TEC (2), an insulating heat sink (3) with a heat insulation groove, an insulating cushion block (4), a semiconductor laser chip LD (5), an SOI substrate (6), a tube shell frame (7) and a tube shell cover plate (8), wherein an accelerometer sensor and an on-chip photodetector PD are integrated on the SOI substrate (6); the tube shell base (1) is made of copper-tungsten alloy material; the tube shell frame (7) and the cover plate (8) are made of Kovar alloy material; the insulating heat sink (3) is arranged on the cold end surface of the micro-thermoelectric cooler TEC (2), and the upper surface of the insulating heat sink (3) is provided with a transversely penetrating heat insulation groove; the heat insulation groove physically cuts off the transverse heat conduction path, and the surface of the insulating heat sink (3) is physically divided into a heat source area and a cold source area; the semiconductor laser chip LD (5) is installed on the heat source area through the cushion block (4), and the SOI substrate (6) is directly installed on the cold source area; the cushion block (4) is used for increasing the longitudinal thermal resistance.

2. The vacuum thermally isolated packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer according to claim 1, characterized in that: The material of the insulating heat sink (3) is aluminum nitride (AlN), the volume is 9 mm*6 mm*1 mm, the material of the insulating cushion block (4) is also aluminum nitride (AlN), and the volume is 1.2 mm*0.6 mm*0.38 mm; the thickness of the insulating cushion block (4) is configured so that the light emitting height of the semiconductor laser chip LD (5) and the waveguide coupling height of the SOI substrate (6) are aligned in the Z-axis direction.

3. The vacuum thermally isolated packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer according to claim 1, characterized in that: The width of the heat insulation groove is 0.3 mm, the depth is 80% of the thickness of the insulating heat sink (3), that is, 0.8 mm, and the length is the same as the width of the heat sink, that is, 6 mm; the heat insulation groove is in a vacuum environment.

4. The vacuum thermally isolated packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer according to claim 1, characterized in that: The material of the tube shell base (1) is copper-tungsten alloy (CuW), the volume is 14 mm*10 mm*2 mm, the copper content is 10%-20%, the waste heat generated by the micro-thermoelectric cooler TEC (2) can be quickly guided to the external environment, and the thermal conductivity is not less than 160 W / (m*K).

5. The vacuum thermally isolated packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer according to claim 1, characterized in that: The length and width of the tube shell frame (7) and the tube shell cover plate (8) are the same as those of the tube shell base (1), the tube shell frame (7) is 1 mm thick and 7 mm high, the tube shell cover plate (8) is 0.4 mm thick, the material of the tube shell frame (7) and the tube shell cover plate (8) is Kovar alloy (Kovar), the thermal expansion coefficient of the Kovar alloy is about 5.9*10-6 / K, which is relatively matched with high-resistance silicon (2.6*10-6 / K) and germanium (5.8*10-6 / K) and commonly used TEC ceramic plates (alumina), good air tightness can be realized through glass-metal sintering, the inner wall of the tube shell is polished or plated with gold to reduce the thermal emissivity.

6. The vacuum thermally isolated packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer according to claim 1, characterized in that: The volume of the micro-thermoelectric cooler TEC (2) is 8 mm*6 mm*2 mm, the surface is metallized, and the cold end area is smaller than the bottom area of the insulating heat sink (3); the edge of the insulating heat sink (3) covers or exceeds the cold end edge of the micro-thermoelectric cooler TEC (2) in the horizontal direction, so as to shield the radiation heat of the inner wall of the tube shell in the vacuum environment to the TEC cold end.

7. The vacuum thermally isolated packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer according to claim 1, characterized in that: The connecting material between the SOI substrate (6) and the insulating heat sink (3) is nano-silver paste (Nano-Ag), which is connected through a low-temperature sintering process to reduce the mechanical stress on the MEMS structure; the insulating heat sink (3) and the micro thermoelectric cooler TEC (2) are welded using indium-silver solder (InAg); the soldering material between the semiconductor laser chip LD (5) and the insulating pad (4), the insulating pad (4) and the insulating heat sink (3), the thermoelectric cooler TEC (2) and the tube shell base (1) is gold-tin (AuSn) solder.

8. The vacuum thermally isolated packaging structure for high-precision two-dimensional photonic crystal cavity optical force accelerometer according to claim 1, characterized in that: The packaging structure is placed in a gas-tight metal tube shell, the inside of the tube shell is maintained in a vacuum state, and a non-evaporable getter (NEG) is arranged inside to maintain the vacuum degree.

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