Thermoelectric material / metal interface performance optimization method based on ultrafast laser

Abstract

The invention discloses a thermoelectric material / metal interface performance optimization method based on ultrafast laser. The method comprises the following steps: pretreating a bismuth telluride-based thermoelectric material; ultrafast laser surface irradiation treatment is conducted on the pretreated bismuth telluride-based thermoelectric material, the pulse width of ultrafast laser ranges from 200 fs to 500 ps, the center wavelength of the laser ranges from 343 nm to 1064 nm, the single pulse energy density (F) ranges from 200 mJ cm <-2 > to 1200 mJ cm <-2 >, and the light spot overlapping rate (EL = 10%-90%); and cleaning and drying the obtained bismuth telluride-based thermoelectric material, and then forming a metal electrode layer on the surface subjected to ultrafast laser irradiation treatment to obtain the thermoelectric material / metal interface material. The method can strengthen the electrical property and the mechanical property of the gold-half interface.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric conversion technology, specifically relating to a method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers. Background Technology

[0002] With the rapid development of the social information technology industry, the Internet of Things (IoT) and intelligentization led by ultra-high-speed communication technology place increasingly stringent requirements on the performance, power consumption, size, and heat dissipation of the key electronic components it relies on. Reliable and easily integrated energy conversion technologies are a critical requirement. Thermoelectric devices, based on the Seebeck and Peltier effects, can realize the mutual conversion of electrical and thermal energy. They also feature small solid-state size, no noise, high stability, long service life, and environmental friendliness, making them an important technical solution for wearable energy harvesting, sensor node power supply, thermal management of high-power electronic devices, and multifunctional sensors.

[0003] The conventional structure of thermoelectric devices mainly consists of three key materials: a thermally conductive substrate, a metal electrode, and a thermoelectric material. In the process of miniaturization and high integration of thermoelectric devices, the number of interfaces formed between thermoelectric materials and metal electrodes has increased rapidly. The contact resistance generated by the metal-semiconductor interface accounts for an increased proportion of the device's internal resistance, and the mechanical properties of the interface have become a key factor in the device's operational stability.

[0004] Chinese patent application CN103413889A discloses a bismuth telluride-based thermoelectric device and its fabrication method. The bismuth telluride-based thermoelectric device comprises: a bismuth telluride matrix layer; a drag-reducing layer formed on the bismuth telluride matrix layer by arc spraying, plasma spraying, electroplating, or chemical plating; and a barrier layer, a stress buffer layer, and an electrode layer sequentially formed on the drag-reducing layer by arc spraying. The bismuth telluride-based thermoelectric device provided by this invention features low interfacial contact resistivity, high interfacial stability, and a simple and stable manufacturing process.

[0005] Patent application CN120680078A discloses a method for connecting SiGe high-temperature thermoelectric material and a metal electrode, relating to the field of welding technology. The method includes: preparing a carbon layer on the surface of SiGe to obtain carbon-coated SiGe; assembling the carbon-coated SiGe, multi-principal element alloy brazing filler metal, and metal electrode material sequentially from top to bottom to obtain an assembly; heating the assembly to a preset temperature at a preset heating rate under vacuum conditions, holding it at that temperature for a preset time, and then cooling it to room temperature to obtain a connecting joint. Using the method provided by this invention to connect SiGe thermoelectric material and a metal electrode not only avoids cracking of the connecting joint but also prevents significant diffusion of Si and Ge elements from the SiGe thermoelectric material into the weld, thereby avoiding the degradation of thermoelectric material performance and the continuous deterioration of the heterogeneous interface bonding performance.

[0006] The aforementioned patent applications and existing methods for controlling the interface between thermoelectric materials and metal electrodes primarily focus on the regulation of thermoelectric materials before the formation of a heterogeneous interface. These methods include controlling the crystal structure of the thermoelectric material during growth, near-surface doping, chemical etching, and plasma cleaning. However, controlling the crystal structure during the thermoelectric material growth process is difficult; near-surface doping may cause damage and performance degradation; chemical etching is difficult to control in terms of depth and is environmentally unfriendly; and plasma cleaning is prone to material damage and is unsuitable for thin-film thermoelectric materials. These existing surface treatment methods for thermoelectric materials typically aim to optimize the interface's electrical or mechanical properties. Their processes are complex, have specific requirements regarding the type and morphology of the material, and thus have certain limitations. Summary of the Invention

[0007] This invention provides a method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers, which can enhance the electrical and mechanical properties of metal-metal interfaces.

[0008] This invention provides a method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers, comprising: (1) Pretreatment of bismuth telluride-based thermoelectric materials; (2) The pretreated bismuth telluride-based thermoelectric material was subjected to ultrafast laser surface irradiation treatment. The ultrafast laser had a pulse width of 200 fs-500 ps, ​​a laser center wavelength of 343 nm-1064 nm, and a single pulse energy density (F) of 200 mJ / cm². -2 -1200mJ cm -2 The overlap rate of the light spots is (OL=10%-90%). (3) The bismuth telluride-based thermoelectric material obtained in step (2) is cleaned and dried, and then a metal barrier layer and a metal electrode layer are formed sequentially on the surface after ultrafast laser irradiation treatment to obtain thermoelectric material / metal interface material.

[0009] Preferably, the bismuth telluride-based thermoelectric material is Bi2Te3 or Bi2Te4. 2.7 Se 0.3 Sb 1.5 Bi 0.5 Te3 or Sb2Te3.

[0010] Preferably, the specific steps of step (1) include: rinsing the surface of the bismuth telluride-based thermoelectric material with nitrogen gas.

[0011] More preferably, if the bismuth telluride-based thermoelectric material is a bulk material, it is first ultrasonically cleaned with acetone, ethanol and deionized water in sequence, and then purged and dried with nitrogen.

[0012] Preferably, before subjecting the pretreated bismuth telluride-based thermoelectric material to ultrafast laser surface irradiation, a laser processing path is first set, wherein the laser processing path is filled with straight lines with a spacing of 1 µm-100 µm.

[0013] Preferably, in step (3), if the bismuth telluride-based thermoelectric material is a thin film material, it is directly purged with nitrogen gas; if the bismuth telluride-based thermoelectric material is a bulk material, it is first ultrasonically cleaned in an ethanol solution and then purged with nitrogen gas.

[0014] Preferably, a metal electrode layer is formed on the surface after ultrafast laser irradiation using magnetron sputtering, thermal evaporation, electron beam evaporation, electrochemical deposition, or laser pulse deposition.

[0015] Preferably, the material of the metal barrier layer is any one of Ni, Cu, Ti, Fe, Ag, and Au, and the material of the metal electrode layer is Cu.

[0016] If only a copper layer is used, copper will diffuse into the thermoelectric material during long-term service, leading to a decrease in the thermoelectric material's functionality. Therefore, a more stable metal material such as Ni or Ti is usually added as a barrier layer to ensure the reliability of the interface under temperature and electric fields. Copper is generally chosen as the electrode layer with high thermal and electrical conductivity, while the barrier layer can be made of various materials such as Ni, Ti, Co, Mo, Fe, and Au.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves significant surface planarization and wettability control of bismuth telluride-based thermoelectric materials through ultrafast laser irradiation. The treated surface has low undulation and high surface energy, which helps to form a high-quality gold-semi-heteromeric interface.

[0018] This invention enables precise control of the surface modification depth, allowing for surface treatment of bismuth telluride-based thermoelectric materials at the submicron scale without affecting the composition and structure of the substrate material. It is applicable to thermoelectric materials of various sizes and forms, including thin films, thick films, and bulk materials.

[0019] A dense metal layer can be grown on the surface of the bismuth telluride-based thermoelectric material with surface treatment provided by this invention, and the resulting gold-semiconductor interface has a significantly reduced contact resistivity to 10. -6 Ω cm 2 The increase in interface bonding strength is orders of magnitude greater, demonstrating the feasibility of this technology in synergistically optimizing the electrical and mechanical properties of gold semiconductor interfaces. This invention synergistically enhances the electrical and mechanical properties of gold semiconductor interfaces, significantly reducing the power generation and cooling capacity degradation caused by interface resistance, and improving the operational stability of devices, thus meeting the basic requirements for the fabrication of current micro-thermoelectric devices. Attached Figure Description

[0020] Figure 1 The processing pattern used for ultrafast laser surface treatment provided in Embodiment 1 of the present invention; Figure 2 The images provided in Embodiment 1 of this invention show the surface morphology of bismuth telluride films before and after laser treatment as observed by a scanning electron microscope. Figure 3 The surface roughness test images of bismuth telluride thin film samples before and after laser treatment provided in Embodiment 1 of the present invention are shown. Figure 4 The image shows the surface energy test results of the bismuth telluride thin film before and after laser treatment provided in Embodiment 1 of the present invention; Figure 5 This is a cross-sectional morphology diagram of the interface between the bismuth telluride thin film and the metal electrode before and after laser treatment, provided in Embodiment 1 of the present invention. Figure 6 This is a graph showing the contact resistivity of the gold semiconductor interface before and after laser treatment, as provided in Embodiment 1 of the present invention. Figure 7 The image shows the nano-scratch test results of the metal electrode fabricated in Example 1 of this invention on the surface of different bismuth telluride samples. Figure 8 The laser energy density provided for Comparative Example 1 of this invention is 1800 mJ / cm². -2 The surface morphology of the bismuth telluride thin film after time treatment and the interface morphology after the preparation of the metal layer are shown. Figure 8 (a) shows the surface morphology of the bismuth telluride thin film. Figure 8 (b) is an image of the interface morphology after the metal layer has been prepared; Figure 9 The laser processing energy density provided for Comparative Example 1 of this invention is 1800 mJ / cm². -2 The image shows the results of the nano-scratch test on the sample. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0022] Example 1 One embodiment of the present invention provides a method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers, comprising the following steps: (1) Pretreatment of thermoelectric materials: Nitrogen gas is used to blow through the bismuth telluride thin film material to ensure that the surface is clean and dry; (2) Laser processing drawing: Laser parameters with a center wavelength of 343 nm, a pulse width of 290 fs, and a spot diameter of 15 µm were used. Based on the sample size, a processing drawing with a fill line spacing of 10 µm was drawn within a 15 mm * 15 mm range, as shown below. Figure 1As shown.

[0023] (3) Ultrafast laser surface treatment: Using the above laser processing parameters, with F=330 mJ / cm², respectively... -2 680 mJcm -2 1200 mJ cm -2 The bismuth telluride thin film sample was processed with OL=50% to obtain the surface morphology, roughness and surface energy before and after the processing. Figure 2 As can be seen, compared with the initial sample (for laser scanning), the surface grain edge morphology of the sample after ultrafast laser treatment begins to blur and the grain gaps are significantly reduced. This is mainly due to the material being melted or vaporized by the laser undergoing a phase transition back to solid state, forming a cladding layer. Accompanying the grain interconnection, the gap size gradually decreases and becomes more circular, significantly improving surface smoothness. Its surface roughness decreases from 258 nm to 108 nm, and then slowly increases again to 133 nm with increasing laser energy density (e.g., ...). Figure 3 Meanwhile, the sample surface energy increased from 21.6 mN / m. -1 Significantly improved by more than 26%, the maximum surface energy can be increased to 29.9 mN m⁻¹ (e.g. Figure 4 Compared to the absence of laser application, the surface energy is significantly improved and the roughness is significantly reduced, confirming that the present invention can significantly control the surface morphology and wettability of bismuth telluride-based thermoelectric materials using ultrafast lasers.

[0024] (4) Surface cleaning of thermoelectric materials: The bismuth telluride film after laser surface treatment is cleaned under a nitrogen gas flow. (5) Preparation of metal electrodes: Using the common magnetron sputtering method, a 200 nm Ni layer and a 2.8 µm Cu layer were sequentially deposited on the surfaces of the laser-treated and untreated bismuth telluride thin film samples as metal electrodes, forming a gold-silicon interface. The cross-sectional morphology is as follows. Figure 5 As shown, a thermoelectric material layer is formed on a ceramic substrate. A nanoscale Ni layer is located between the thermoelectric material layer and the copper layer; it is not labeled in the figure due to its small size. The un-laser-irradiated sample has a low surface energy, and the metal film on top grows in an island-like pattern. The microstructure shows a loose arrangement of large-sized equiaxed crystals with obvious porosity at the interface with the thermoelectric material. However, after laser irradiation, the surface energy of the bismuth telluride is significantly increased. The metal deposition atoms grow in a two-dimensional layered manner, resulting in a very tight bond between the electrode layer metal atoms and the thermoelectric material. The decrease in the surface roughness of bismuth telluride also makes the columnar growth direction of the electrode layer more consistent. The contact resistivity of the gold-semiconductor interface before treatment, measured using a linear transmission line model, is 1.16 × 10⁻⁶. -4 Ω cm 2 Then, with laser processing, the value rapidly decreased to 6.41 × 10⁻⁶. -5 Ωcm2 By further increasing the laser energy density, the specific contact resistivity can be reduced to as low as 5.29 × 10⁻⁶. -6 Ω cm 2 Then, as the energy continued to increase, the specific contact resistivity rose slightly to 1.47 × 10⁻⁶. -5 Ω cm 2 This result indicates that laser surface treatment can improve the contact electrical properties of the interface by two orders of magnitude (e.g., Figure 6 Meanwhile, the critical peel load measured using the nano-scratching method gradually increased with increasing laser energy, rising from 55.7 mN to 94.8 mN (e.g., Figure 7 This indicates that the thermoelectric material laser surface treatment technology used in this invention can effectively synergistically improve the electrical and mechanical properties of the gold semiconductor interface.

[0025] Comparative Example 1 Comparative Example 1 provided by this invention describes the surface treatment of a bismuth telluride thermoelectric thin film sample using an ultrafast laser exceeding the optimal parameter range, increasing the laser energy to 1800 mJ / cm². -2 The surface morphology of the sample obtained after processing is as follows: Figure 8 As shown in (a), obvious ablation and pores appear on the surface, and the surface roughness increases to 456 nm. A metal electrode layer is fabricated on its surface, and the cross-sectional morphology is as follows. Figure 8 As shown in (b), there are obvious pores at the interface, and the specific contact resistivity drops rapidly to 4.32 × 10⁻⁶. -4 Ω cm2, the critical peel load in the scratch test results decreased to 52.8 mN (e.g. Figure 9 (As shown in the figure). The above results indicate that there is a process window for ultrafast laser processing of thermoelectric material surfaces, and appropriate process parameters need to be selected for surface treatment to optimize the interfacial electrical and mechanical properties.

[0026] Example 2 Unlike Example 1, the cleaning process involved sequential ultrasonic cleaning with acetone, ethanol, and deionized water, followed by nitrogen purging and drying. The single-pulse energy density (F) was 680 mJ / cm³. -2 A 200 nm Ni layer and a 2.8 µm Cu layer were sequentially deposited on the surfaces of laser-treated and untreated bismuth telluride bulk materials as metal electrodes, forming a gold-semiconductor interface. The specific contact resistivity of the gold-semiconductor interface before and after treatment, measured using a linear transmission line model, was 4.32 × 10⁻⁶. -4 Ω cm 2 and 3.20×10 -5 Ω cm 2The results show that ultrafast laser irradiation of bulk bismuth telluride samples also has the ability to effectively control the electrical transport properties of the gold semiconductor interface by changing the surface characteristics. That is, this method is applicable to thermoelectric materials of various sizes and shapes, such as thin films, thick films and bulk materials.

Claims

1. A method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers, characterized in that, include: (1) Pretreatment of bismuth telluride-based thermoelectric materials; (2) The pretreated bismuth telluride-based thermoelectric material is subjected to ultrafast laser surface irradiation treatment. The ultrafast laser has a pulse width of 200 fs-500 ps, ​​a laser center wavelength of 343 nm-1064 nm, and a single pulse energy density of 200 mJ / cm². -2 -1200mJ cm -2 The overlap rate of light spots is 10%-90%; (3) The bismuth telluride-based thermoelectric material obtained in step (2) is cleaned and dried, and then a metal barrier layer and a metal electrode layer are formed sequentially on the surface after ultrafast laser irradiation treatment to obtain thermoelectric material / metal interface material.

2. The method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers according to claim 1, characterized in that, The bismuth telluride-based thermoelectric material is Bi2Te3 or Bi2Te. 2.7 Se 0.3 Sb 1.5 Bi 0.5 Te3 or Sb2Te3.

3. The method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers according to claim 1, characterized in that, The specific steps of step (1) include: rinsing the surface of the bismuth telluride-based thermoelectric material with nitrogen gas.

4. The method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers according to claim 3, characterized in that, If the bismuth telluride-based thermoelectric material is a bulk material, it should first be ultrasonically cleaned with acetone, ethanol and deionized water in sequence, and then purged and dried with nitrogen.

5. The method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers according to claim 1, characterized in that, Before subjecting the pretreated bismuth telluride-based thermoelectric material to ultrafast laser surface irradiation, a laser processing path is first set. The laser processing path is filled with straight lines with a spacing of 1 µm-100 µm.

6. The method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers according to claim 1, characterized in that, In step (3), if the bismuth telluride-based thermoelectric material is a thin film material, it is directly purged with nitrogen gas. If the bismuth telluride-based thermoelectric material is a bulk material, it is first ultrasonically cleaned in an ethanol solution and then purged with nitrogen gas.

7. The method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers according to claim 1, characterized in that, Metal electrode layers are formed on surfaces treated with ultrafast laser irradiation using magnetron sputtering, thermal evaporation, electron beam evaporation, electrochemical deposition, or laser pulse deposition methods.

8. The method for optimizing the performance of thermoelectric materials / metal interfaces based on ultrafast lasers according to claim 1, characterized in that, The metal barrier layer is made of any one of Ni, Cu, Ti, Fe, Ag, and Au, and the metal electrode layer is made of Cu.

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