A multi-layer aluminum nitride integrated laser power probe and a manufacturing method thereof

Abstract

A multilayer aluminum nitride integrated laser power probe is disclosed. An insulating porous silicon laser absorption layer is located at the top front of the probe. Each unit layer includes a thick-film thermopile layer, an aluminum nitride insulating and thermally conductive layer, and an LTCC (low-temperature co-fired) ceramic layer. The thick-film thermopile layer is located in the center of the top surface of the aluminum nitride insulating and thermally conductive layer. The LTCC ceramic layer surrounds the thick-film thermopile layer and covers the gaps around the top surface of the aluminum nitride insulating and thermally conductive layer. Adjacent unit layers are stacked vertically. The thick-film thermopile layer of the uppermost unit layer is located on the bottom surface of the insulating porous silicon laser absorption layer. The bottom surface of the aluminum nitride insulating and thermally conductive layer of the lowermost unit layer is connected to the bottom thermopile. Leads are extended from the uppermost unit layer and the bottom thermopile. A method for manufacturing the multilayer aluminum nitride integrated laser power probe is also provided. This invention improves the response speed of the thermopile laser power probe.

Description

Technical Field

[0001] This invention belongs to the field of laser power probes and relates to an integrated laser power probe of multilayer aluminum nitride and its manufacturing method, which is used to improve the sensitivity and response speed of thermopile. Background Technology

[0002] Lasers have broad application prospects, especially in high-end manufacturing. High-power laser processing has entered the field of electronic devices, with processing precision reaching the micron level. Therefore, precise feedback control of laser power has become a major factor limiting the development of the laser processing industry towards high-precision and cutting-edge technologies. The demand for real-time monitoring and rapid detection of high-power lasers is becoming increasingly urgent.

[0003] The probe is the key component of a laser power detector. Mainstream high-power laser detectors use thermopile to sense the laser power signal. One mainstream configuration (1) places the laser absorption layer on the front of an aluminum alloy substrate and the thin-film thermopile on the back (CN202020227804). This allows the thermopile to be as close as possible to the heat dissipation substrate to prevent overheating, enabling the probe's power threshold to reach approximately 350W. However, because the thermopile is far from the laser heat source, the temperature difference between its high and low temperature ends is insufficient (often less than 2°C), resulting in a long heat transfer time (around 7-10 seconds). Therefore, the sensitivity of this type of probe is generally only 0.1W / mV, with a response time of 6-7 seconds. To shorten the response time, another mainstream configuration (2) places the thermopile between the laser absorption layer and the heat dissipation substrate (CN202011578264), bringing it closer to the heat source, which can shorten the response time to 2 seconds. However, the laser absorption layer of this type of probe is generally placed on a high-temperature resistant PCB board, often limiting its measurement threshold to below 50W. The aforementioned two mainstream probe configurations are used by international manufacturers Gentech of Canada and Greentech of Switzerland, respectively. In recent years, probes with non-metallic heat-dissipating substrates have become a key research focus for experts in the field. For example, by utilizing the high temperature resistance, high thermal conductivity (400 W / K / m), and stable infrared light absorption characteristics of silicon carbide single crystals, a thermoelectric photodetector based on black silicon carbide ceramics (CN202010366053) has been developed, combining the laser absorption layer and the heat-dissipating substrate, achieving a power threshold of 30 kW. However, the thermal conductivity of single-crystal silicon carbide is twice that of traditional aluminum substrates, but its price is 10 times higher (including the silicon laser absorption layer). Therefore, practical probes often use ceramic silicon carbide, which has a similar price to traditional aluminum alloy substrates but slightly lower thermal conductivity (120 W / K / m). Since the current preparation of ceramic silicon carbide relies heavily on boron flux, its porosity is relatively high and its insulation is insufficient, severely affecting the probe's sensitivity; its response time still requires 3-5 seconds. On the other hand, with current technology, ceramic aluminum nitride is an insulating and heat-dissipating substrate with better thermal conductivity (200 W / K / m) and insulation than ceramic silicon carbide, but at a lower price. Therefore, aluminum nitride is often used as an HTCC substrate for photodetector bases (CN202610193030).

[0004] like Figure 1 The image shows the spatial distribution of isotherms after a laser beam strikes the center of the upper surface of a substrate with a thermal conductivity of 200 W / K / m and reaches a steady state. It can be seen that a high temperature gradient exists only within 4 mm of the laser heat source, resulting in a faster response and a higher temperature difference. However, the higher temperature also affects the lifespan of the thermoelectric material. Therefore, traditional probes using thin-film thermopile as the sensing core often place the high-temperature end of the thermopile at a distance of more than 10 mm from the center. This leads to a longer response time for traditional probes, affecting their application in real-time monitoring. Summary of the Invention

[0005] To overcome the problem that current high-power laser probes cannot be used for real-time monitoring of laser processing due to their excessively long response time (longer than 1s), this invention provides an integrated laser power probe based on multilayer aluminum nitride and its manufacturing method. Using multilayer aluminum nitride as a substrate, a high-power laser probe with a sensitivity higher than 1.2W / mV and a response time lower than 0.5s is developed.

[0006] The technical solution adopted by this invention to solve its technical problem is: A multilayer aluminum nitride integrated laser power probe includes an insulating porous silicon laser absorption layer, at least two unit layers, and a bottom thermopile. The insulating porous silicon laser absorption layer is located at the top front of the probe. Each unit layer includes a thick-film thermopile layer, an LTCC (low-temperature co-fired ceramic) layer, and an aluminum nitride insulating and thermally conductive layer. The LTCC and thick-film thermopile layers are located on the same layer, with the thick-film thermopile layer non-contactly surrounding the aluminum nitride insulating and thermally conductive layer. The layer and the surrounding thick film thermopile layer have the same thickness and cover the remaining space around the top surface of the aluminum nitride insulating thermally conductive layer; the upper and lower adjacent unit layers are stacked vertically, and the positive and negative electrode materials of the upper and lower adjacent unit layers have opposite chirality. The uppermost unit layer's thick film thermopile layer is located on the bottom surface of the insulating porous silicon laser absorption layer, and the bottom surface of the lowermost unit layer's aluminum nitride insulating thermally conductive layer is connected to the bottom layer thermopile. Leads are led out from the uppermost unit layer's thick film thermopile layer and the bottom layer thermopile, respectively.

[0007] Furthermore, the porous silicon laser absorption layer is made of silicon wafers that have undergone anti-reflection treatment, with a thickness of 100-500 micrometers.

[0008] The porous silicon laser absorption layer is sintered together with the thick film thermopile layer through the LTCC low-temperature co-fired ceramic layer of the uppermost unit layer to form a good thermal contact. In the uppermost unit layer, the thick film thermopile layer, the LTCC low-temperature co-fired ceramic layer and the aluminum nitride insulating and thermally conductive layer form a good thermal contact through sintering.

[0009] Preferably, the unit layer has 2 to 8 layers, and the 2 to 8 unit layers are stacked together longitudinally to form a periodic multi-layer structure.

[0010] The number of series pairs of thick film thermopile in the unit layer is 8-16.

[0011] Both the thick film thermopile layer and the bottom thermopile use nickel-chromium and silver-palladium as positive and negative electrode materials, forming a radial pattern. On each layer, the positive and negative electrode materials are periodically connected in series and form a disc-shaped thermopile in a circular radial pattern.

[0012] The rear film thermopile layers of adjacent unit layers are connected by connecting pillars, and the connecting pillars are made of good conductors such as Cu and Ag.

[0013] A method for manufacturing a multilayer aluminum nitride integrated laser power probe includes the following steps: Step 1: A porous antireflection structure is prepared on the surface of a single-crystal silicon wafer by acid etching using chemical etching to obtain an insulating porous silicon laser absorption layer with a reflectivity of less than 10% in the visible light band. Step 2: Use screen printing to pre-form a radial pattern of the positive and negative electrode pastes of the thick film thermopile onto the aluminum nitride insulating and thermally conductive layer; Step 3: Use laser drilling technology to pre-drill small holes for the connecting posts on the aluminum nitride insulating thermally conductive layer; then fill the small holes with the connecting posts to make the upper and lower back film thermopiles conductive; Step 4: Use screen printing to cover the periphery of the thermopile with LTCC (Low Temperature Co-fired Ceramic) layers, ensuring the LTCC and thick-film thermopile are not in contact, forming unit layers. Stack these unit layers longitudinally according to the required number of layers. Each thick-film thermopile and LTCC layer is sandwiched between adjacent aluminum nitride insulating and thermally conductive layers, forming a periodic multilayer structure in the longitudinal direction. Place an anti-reflection treated insulating porous silicon laser absorption layer on the topmost unit layer of the thick-film thermopile. The bottom surface of the bottommost unit layer of the aluminum nitride insulating and thermally conductive layer is in contact with the bottom thermopile, forming a preliminary multilayer aluminum nitride integrated laser power probe. Step 5: Place the initial sample of the multilayer aluminum nitride integrated laser power probe into a vacuum or reducing atmosphere at 850~900℃ for sintering for 60-120 minutes in one step, and then use lead wires to lead out the electrodes of the uppermost unit layer thick film thermopile and the bottom thermopile.

[0014] In step 1, the resistivity of the monocrystalline silicon wafer is 2000-20000 Ω·cm, the thickness is 100-500 micrometers, and the diameter is 3-4 millimeters; in step 2, the outer diameter of the thick film thermopile is 2-4 mm, the inner diameter is 1-2 mm, the width of each foot of the thick film thermopile is 100 to 180 micrometers, and the film thickness is 50-100 micrometers.

[0015] In step 3, the thickness of the aluminum nitride insulating and thermally conductive layer is 100-200 micrometers, and a small hole with a diameter of 100-180 micrometers is pre-drilled on the aluminum nitride insulating and thermally conductive layer for the connecting post using laser drilling technology; then, Cu or Ag wire of appropriate diameter is used to fill the small hole so that the upper and lower thermopile can be connected through the conductor wire connecting post.

[0016] This invention uses screen printing to fabricate a thick-film thermopile within a 2-4 mm range of the probe center, thereby achieving a rapid response. Simultaneously, since the small area of ​​the central region limits the number of thermocouples that can be connected in series on a plane, this invention employs a method of longitudinally stacking and connecting multiple thermopiles in series to increase the number of thermocouple pairs and achieve higher sensitivity.

[0017] The beneficial effect of this invention is that it improves the response speed of the thermopile laser power probe to as short as 0.5s. Attached Figure Description

[0018] Figure 1 This is an isotherm distribution diagram when a laser irradiates a traditional probe.

[0019] Figure 2 This is a structural diagram of the multi-layer periodic structure probe of the present invention.

[0020] Figure 3 This is a schematic diagram of the multilayer thermopile in the laser power probe of the present invention.

[0021] Figure 4 This is a schematic diagram showing the positions of the thermopile and LTCC paste printing on the aluminum nitride layer in the laser power probe of the present invention.

[0022] Figure 5 This is the power response curve of the three-layer periodic structure laser power probe of the present invention.

[0023] Figure 6 This is the temperature-time curve of the hot and cold ends of the thermopile on the 3-layer periodic structure laser power probe of the present invention.

[0024] The attached figures are labeled as follows: 1 Insulating porous silicon laser absorption layer; 2 Aluminum nitride insulating thermally conductive layer; 3 LTCC low-temperature co-fired ceramic layer; 4 Bottom thermopile; 5 Lead wire; 6 Connecting post; 7 Laser incident direction. Detailed Implementation

[0025] The invention will now be further described with reference to the accompanying drawings.

[0026] Reference Figures 1-6A multilayer aluminum nitride integrated laser power probe includes an insulating porous silicon laser absorption layer 1, at least two unit layers, and a bottom thermopile 4. The insulating porous silicon laser absorption layer 1 is located on the topmost side of the probe's front surface. The unit layers include a thick-film thermopile layer, an LTCC low-temperature co-fired ceramic layer 3, and an aluminum nitride insulating and thermally conductive layer 2. The LTCC low-temperature co-fired ceramic layer 3 and the thick film thermopile layer are located in the same layer. The thick film thermopile layer is surrounded in a non-contact manner on top of the aluminum nitride insulating and thermally conductive layer 2. The LTCC low-temperature co-fired ceramic layer 3 and the thick film thermopile layer surrounded by it have the same thickness and cover the remaining space around the top surface of the aluminum nitride insulating and thermally conductive layer 2. The vertically adjacent unit layers are stacked, and the positive and negative electrode materials of the thick film thermopile of the vertically adjacent unit layers have opposite chirality. The thick film thermopile layer of the uppermost unit layer is located on the bottom surface of the insulating porous silicon laser absorption layer 1, and the bottom surface of the aluminum nitride insulating and thermally conductive layer 2 of the lowermost unit layer is connected to the bottom thermopile 4. Lead wires 5 are led out from the uppermost unit layer thick film thermopile layer and the bottom thermopile 4, respectively.

[0027] The insulating porous silicon laser absorption layer 1 is formed by copper ion-assisted chemical etching. On an insulating single-crystal silicon wafer with a resistivity of 2000 Ω·cm, a etching solution consisting of 6 mol / L hydrofluoric acid, 2 mol / L hydrogen peroxide, 0.08 mol / L copper nitrate and deionized water is used to etch a porous columnar surface with a thickness of nearly 10 μm to form a porous silicon laser absorption layer.

[0028] To achieve a multilayer thermopile structure, each unit layer of the thick-film thermopile and the same layer of LTCC low-temperature co-fired ceramic layer 3, together with the underlying aluminum nitride insulating and thermally conductive layer 2, form a unit layer structure. In this embodiment, three cycles of the above unit layers are longitudinally stacked to form a periodic multilayer structure, such as... Figure 3 As shown, the thick film thermopile layers of adjacent unit layers are connected by connecting posts 6.

[0029] The aluminum nitride insulating and thermally conductive layer 2 has a thickness of 100 micrometers. First, a pattern of a thick-film thermopile is positioned on the aluminum nitride insulating and thermally conductive layer 2. This embodiment uses, as shown in the example... Figure 3 The radial pattern shown has 8 pairs of thermocouples connected in series. A 0.18mm diameter hole is pre-drilled for the connecting posts using laser drilling technology, and then the hole is filled with Ag wire of 0.15mm diameter.

[0030] Both the thick-film thermopile layer and the bottom thermopile 4 use nickel-chromium and silver-palladium as the positive and negative electrode materials. On each layer's pattern, the positive and negative electrode materials are periodically connected in series and arranged in a radial pattern to form a disk-shaped thermopile. To achieve direct vertical connection between adjacent thermopile layers, the positive and negative electrode materials of adjacent layers are prepared with opposite chirality, according to... Figure 4Regarding the configuration of layers A and B, this embodiment uses ABA to form the main structure of the probe.

[0031] like Figure 4 The diagram shows that the positive and negative electrode pastes of the thick film thermopile are pre-formed into a radial pattern on the aluminum nitride insulating and thermally conductive layer using screen printing. The outer diameter is 4 mm, the inner diameter is 2 mm, each leg of the thermopile thick film is 180 micrometers wide, and the film thickness is 80 micrometers.

[0032] A method for manufacturing a multilayer aluminum nitride integrated laser power probe includes the following steps: Step 1: A porous antireflection structure is prepared on the surface of a single-crystal silicon wafer by acid etching using chemical etching to obtain an insulating porous silicon laser absorption layer with a reflectivity of less than 10% in the visible light band. Step 2: Use screen printing to pre-form a radial pattern of the positive and negative electrode pastes of the thick film thermopile onto the aluminum nitride insulating and thermally conductive layer; Step 3: Use laser drilling technology to pre-drill small holes for the connecting posts on the aluminum nitride insulating thermally conductive layer; then fill the small holes with the connecting posts to make the upper and lower back film thermopiles conductive; Step 4: The periphery of the thick-film thermopile is covered with an LTCC (Low Temperature Co-fired Ceramic) layer 3 using screen printing. However, the LTCC layer 3 and the thick-film thermopile do not contact each other; the LTCC layer 3 is primarily used for bonding and heat conduction between unit layers. The thickness of the LTCC layer 3 is the same as that of the thick-film thermopile, 80 micrometers. These pastes and the aluminum nitride insulating and thermally conductive layer 2 form a unit layer structure. Three such unit layer structures are stacked longitudinally, with each thick-film thermopile and the corresponding LTCC layer 3 positioned between adjacent aluminum nitride insulating and thermally conductive layers 2. An anti-reflection treated insulating porous silicon laser absorption layer 1 is placed on the topmost unit layer of the thick-film thermopile; the bottom surface of the bottommost unit layer's aluminum nitride insulating and thermally conductive layer is in contact with the bottom thermopile, forming a preliminary multilayer aluminum nitride integrated laser power probe. Step 5: The initial sample of the multilayer aluminum nitride integrated laser power probe is sintered in a reducing atmosphere at 850℃ for 100 minutes in a single process. Then, the uppermost and lowermost thermopile electrodes 5 are led out using low-temperature silver paste and wires.

[0033] Figure 5 The laser power response curve of the probe in this embodiment is shown. Using a 600W laser as the incident light, the stable value of the thermoelectric signal is 726mV, indicating that the sensitivity of this probe reaches 1.2mV / W. The thermoelectric signal reaches 95% of its stable value in 0.38s; this time is the probe's response time, which is less than 0.5s. Therefore, the probe designed and manufactured using the method proposed in this invention significantly improves both response speed and sensitivity, meeting the requirements for real-time monitoring of high-power laser processing.

[0034] It should be noted that when the laser input power is 600W, the thermopile needs to withstand relatively high temperatures. Although the temperature difference reaches a constant level within 0.5 seconds, the temperatures at the high and low temperature ends continue to rise, reaching 400℃ at 50 seconds and exceeding 600℃ after 150 seconds. Because this probe uses high-temperature resistant ceramic aluminum nitride, it can operate at high power for more than 2 minutes, which is impossible with traditional probes based on aluminum alloys.

[0035] The embodiments described in this specification are merely examples of implementations of the inventive concept and are for illustrative purposes only. The scope of protection of this invention should not be considered limited to the specific forms described in these embodiments; rather, it extends to equivalent technical means conceived by those skilled in the art based on the inventive concept.

Claims

1. A multilayer aluminum nitride integrated laser power probe, characterized in that, The probe comprises an insulating porous silicon laser absorption layer, at least two unit layers, and a bottom thermopile. The insulating porous silicon laser absorption layer is located at the top front of the probe. Each unit layer includes a thick-film thermopile layer, an LTCC (low-temperature co-fired) ceramic layer, and an aluminum nitride insulating and thermally conductive layer. The LTCC ceramic layer and the thick-film thermopile layer are located on the same layer. The thick-film thermopile layer is non-contactly surrounded on top of the aluminum nitride insulating and thermally conductive layer. The LTCC ceramic layer and the surrounding thick-film thermopile layer have the same thickness and cover the remaining space around the top surface of the aluminum nitride insulating and thermally conductive layer. The unit layers are vertically stacked, and the positive and negative electrode materials of the thick-film thermopile in the adjacent unit layers have opposite chirality. The thick-film thermopile layer of the uppermost unit layer is located on the bottom surface of the insulating porous silicon laser absorption layer, and the bottom surface of the aluminum nitride insulating and thermally conductive layer of the lowermost unit layer is in contact with the bottom thermopile. Leads are led out from the thick-film thermopile layer of the uppermost unit layer and the bottom thermopile, respectively.

2. The multilayer aluminum nitride integrated laser power probe as described in claim 1, characterized in that, The porous silicon laser absorption layer is made of silicon wafers that have undergone anti-reflection treatment and has a thickness of 100-500 micrometers.

3. A multilayer aluminum nitride integrated laser power probe as described in claim 1 or 2, characterized in that, The porous silicon laser absorption layer is sintered together with the thick film thermopile layer through the LTCC low-temperature co-fired ceramic layer of the uppermost unit layer to form a good thermal contact. In the uppermost unit layer, the thick film thermopile layer, the LTCC low-temperature co-fired ceramic layer and the aluminum nitride insulating and thermally conductive layer form a good thermal contact through sintering.

4. A multilayer aluminum nitride integrated laser power probe as described in claim 1 or 2, characterized in that, The unit layer has 2 to 8 layers, and the 2 to 8 unit layers are stacked together longitudinally to form a periodic multi-layer structure.

5. A multilayer aluminum nitride integrated laser power probe as described in claim 1 or 2, characterized in that, The number of series pairs of thermopile in the unit layer is 8-16.

6. A multilayer aluminum nitride integrated laser power probe as described in claim 1 or 2, characterized in that, Both the thick film thermopile layer and the bottom thermopile use nickel-chromium and silver-palladium as positive and negative electrode materials, forming a radial pattern. On each layer, the positive and negative electrode materials are periodically connected in series and form a disc-shaped thermopile in a circular radial pattern.

7. A multilayer aluminum nitride integrated laser power probe as described in claim 1 or 2, characterized in that, The thick film thermopile layers of adjacent unit layers are connected by connecting pillars, and the connecting pillars are made of a good conductor.

8. A method for manufacturing a multilayer aluminum nitride integrated laser power probe as described in claim 1, characterized in that, The method includes the following steps: Step 1: A porous antireflection structure is prepared on the surface of a single-crystal silicon wafer by acid etching using chemical etching to obtain an insulating porous silicon laser absorption layer with a reflectivity of less than 10% in the visible light band. Step 2: Use screen printing to pre-form a radial pattern of the positive and negative electrode pastes of the thick film thermopile onto the aluminum nitride insulating and thermally conductive layer; Step 3: Use laser drilling technology to pre-drill small holes for the connecting posts on the aluminum nitride insulating and thermally conductive layer; then fill the holes with the connecting posts to make the thick film thermopile of the upper and lower layers conductive; Step 4: Use screen printing to cover the periphery of the thermopile with LTCC (Low Temperature Co-fired Ceramic) layers, ensuring the LTCC and thick-film thermopile are not in contact, forming unit layers. Stack these unit layers longitudinally according to the required number of layers, with each thick-film thermopile and LTCC layer sandwiched between adjacent LTCC layers, forming a periodic multilayer structure in the longitudinal direction. Place an anti-reflection treated insulating porous silicon laser absorption layer on the thick-film thermopile of the top unit layer. The bottom surface of the aluminum nitride insulating thermally conductive layer of the bottom unit layer is in contact with the bottom thermopile, forming a preliminary multilayer aluminum nitride integrated laser power probe. Step 5: Place the initial sample of the multilayer aluminum nitride integrated laser power probe into a vacuum or reducing atmosphere at 850~900℃ for sintering for 60-120 minutes in one step, and then use lead wires to lead out the electrodes of the uppermost unit layer thick film thermopile and the bottom thermopile.

9. The manufacturing method as described in claim 8, characterized in that, In step 1, the resistivity of the monocrystalline silicon wafer is 2000-20000 Ω·cm, the thickness is 100-500 micrometers, and the diameter is 3-4 millimeters; in step 2, the outer diameter of the thick film thermopile is 2-4 mm, the inner diameter is 1-2 mm, the width of each foot of the thick film thermopile is 100 to 180 micrometers, and the film thickness is 50-100 micrometers.

10. The manufacturing method as described in claim 8 or 9, characterized in that, In step 3, the thickness of the aluminum nitride insulating and thermally conductive layer is 100-200 micrometers, and a small hole with a diameter of 100-180 micrometers is pre-drilled on the aluminum nitride insulating and thermally conductive layer for the connecting post using laser drilling technology; then, Cu or Ag wire is used to fill the small hole so that the upper and lower thermopiles are connected through the conductor wire connecting post.

Images