Method for carrying out surface treatment on n-type bismuth telluride

Abstract

The invention provides a method for carrying out surface treatment on n-type bismuth telluride. According to the method, anode electrolysis is carried out on n-type bismuth telluride under the action of an electric field of current, in an alkaline NaOH solution, part of Te and Bi in the n-type bismuth telluride are oxidized, an orange glass phase film is generated and attached to the surface of the n-type bismuth telluride, and the film can be cleaned away. According to the anode treatment process, the microstructure and roughness of the surface of the n-type bismuth telluride material can be changed, the preparation of the barrier layer is facilitated, the combination between bismuth telluride and the barrier layer is enhanced, the interface contact resistivity is reduced, and the reliability of a thermoelectric device is improved to a certain extent. According to the invention, the problems of high barrier layer preparation difficulty, poor interface contact, low reliability of the thermoelectric device, complex process flow, poor stability and the like caused by insufficient binding force between the barrier layer and n bismuth telluride in the bismuth telluride-based thermoelectric device can be solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bismuth telluride-based thermoelectric technology, and particularly relates to a method for surface treatment of n-type bismuth telluride. BACKGROUND

[0002] Thermoelectric technology is a technology capable of directly converting thermal energy and electrical energy into each other. With the rapid development of industrial society, the application value of thermoelectric technology becomes increasingly important. Meanwhile, with the improvement of industrial technology, electronic devices are continuously miniaturized, high-performance, and the requirement for energy utilization efficiency is continuously improved, and the application field of thermoelectric technology is also continuously expanding, such as in waste heat recovery power generation, refrigeration and heat dissipation of portable electronic devices, temperature control of biomedical detection equipment, etc., which plays a key role. Among many thermoelectric materials, bismuth telluride-based materials stand out due to their excellent properties and become one of the preferred materials for thermoelectric applications near room temperature, so they have been successfully commercialized.

[0003] In the manufacturing process of thermoelectric devices, a barrier layer needs to be prepared on the surface of bismuth telluride to achieve metallurgical bonding and inhibit element diffusion at the interface, thereby improving the thermal stability and reliability of the thermoelectric device. Before preparing the barrier layer, the bismuth telluride wafer usually needs to be surface treated to facilitate the preparation of the barrier layer. With the development of thermoelectric devices towards high performance, high reliability and miniaturization, the surface treatment technology of bismuth telluride materials is in urgent need. Traditional surface treatment methods (grinding, sandblasting, mechanical polishing, chemical etching) have many shortcomings in dealing with the demand of modern thermoelectric devices. For example, for bismuth telluride wafers with increasingly thin thickness (such as wafers with a thickness of less than 1 mm), traditional sandblasting or mechanical polishing treatment methods are easy to cause micro-cracks or even breakage of the wafer due to the mechanical impact force generated, which not only reduces the utilization rate of the material, but also increases the production cost and manufacturing cycle. After grinding and sandblasting treatment of bismuth telluride, the bonding between the barrier layer and bismuth telluride is not good, and the abrasive particles left on the wafer surface after grinding and sandblasting treatment will increase the interface contact resistivity, thereby reducing the reliability of the thermoelectric device. Chemical etching treatment of bismuth telluride will cause uneven etching or over-etching, and uneven etching will cause uneven bonding force between the plating layer and the substrate, increasing the risk of plating layer falling off. In addition, the etching solution usually has strong corrosive or volatile properties, which will cause serious pollution to the production environment, and a complex ventilation and treatment system needs to be provided, which increases the production cost and environmental management difficulty. SUMMARY

[0004] The present application aims to overcome the defects of the prior art, and provides a method for surface treatment of n-type bismuth telluride, which can obtain n-type bismuth telluride wafers with sufficient surface roughness and good surface chemical state, strengthen the combination of n-type bismuth telluride and the barrier layer, reduce the interface contact resistivity, and further improve the reliability of thermoelectric devices.

[0005] The present application provides the following technical solutions:

[0006] The present application provides a method for surface treatment of n-type bismuth telluride, which comprises: surface treatment of n-type bismuth telluride wafers by anodic electrolysis in an alkaline solution.

[0007] The present application utilizes the electric field effect of current to anodically electrolyze n-type bismuth telluride (BiSeTe) in an alkaline solution, and part of Te and Bi in n-type bismuth telluride (BiSeTe) is oxidized to generate an orange glass phase film attached to the surface of n-type bismuth telluride.

[0008] Further, the anodic electrolysis is: the n-type bismuth telluride wafer is used as an anode, a titanium plate is used as a cathode, an alkaline solution is used as an electrolyte, and the anodic electrolysis is carried out in a constant current mode.

[0009] Further, the titanium plate has two pieces, and the titanium plates are parallel to the n-type bismuth telluride wafer and are respectively arranged on both sides of the n-type bismuth telluride wafer.

[0010] Further, the alkaline solution is a NaOH solution, the concentration of the NaOH solution is 30-40 g / L, the current density is kept at 0.03-0.05 A / cm 2 , and the upper limit of the power supply voltage is set to 13-15 V.

[0011] Further, in the process of anodic electrolysis, the power supply voltage gradually rises, and after the voltage reaches the upper limit, the current value gradually decreases, and the electrolysis time is maintained at 90-120 s.

[0012] Further, the n-type bismuth telluride wafer is pretreated before anodic electrolysis, and the pretreatment comprises grinding and surface cleaning.

[0013] Further, the grinding is to grind the surface of the wafer through 2000-5000 mesh sandpaper; and the surface cleaning is to immerse the wafer in acetone and then immerse it in deionized water.

[0014] Further, after anodic electrolysis, the wafer is ultrasonically cleaned; the ultrasonic cleaning is: the wafer is immersed in a 10-30 v. % HCl solution for ultrasonic cleaning for 60-90 s, and then the wafer is taken out and immersed in deionized water for ultrasonic cleaning for 60-90 s.

[0015] Further, the anodic electrolysis and ultrasonic cleaning are repeated for 3-4 times.

[0016] The present application has the following advantages:

[0017] 1. The present application can significantly change the micro-morphology and surface roughness of the n-type bismuth telluride wafer, improve the surface activity, facilitate the deposition of metal ions in electroplating or chemical plating during the preparation of the barrier layer, strengthen the bonding between the barrier layer and the n-type bismuth telluride wafer, reduce the interface contact resistance, and is very beneficial to improving the reliability of thermoelectric devices.

[0018] 2. The present application only needs to prepare NaOH solution, which is simple, short in process and convenient to operate, and is beneficial to improving the production efficiency and suitable for large-scale production.

[0019] 3. The present application does not affect the thermoelectric performance because the atomic proportion of the n-type bismuth telluride wafer surface after treatment is close to that of the n-type bismuth telluride itself, and is beneficial to improving the product qualification rate.

[0020] 4. The present application can control the rate of n-type bismuth telluride wafer surface treatment, and the wafer surface roughening effect is uniform, and the product quality consistency is good.

[0021] 5. The present application avoids using a large amount of harmful chemical reagents, and reduces environmental pollution. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0023] Figure 1 is a photo of the n-type bismuth telluride wafer after anodic electrolysis treatment in example 1 of the present application;

[0024] Figure 2 is a photo of the n-type bismuth telluride wafer after anodic electrolysis treatment and ultrasonic cleaning in example 1 of the present application;

[0025] Figure 3 is a SEM picture of the n-type bismuth telluride wafer after anodic treatment and ultrasonic cleaning in example 1 of the present application;

[0026] Figure 4 is the XRD result of the n-type bismuth telluride wafer with an orange glass phase thin film attached to the surface after anodic treatment in example 1 of the present application;

[0027] Figure 5Figure 1 is a SEM picture of the surface of the n-type bismuth telluride wafer after anodic treatment in Example 1 of the present application, points 1 and 2 are EDS analysis positions;

[0028] Figure 6 Figure 2 is a SEM picture of the surface of the n-type bismuth telluride wafer after ultrasonic cleaning with HCl solution and deionized water in Example 1 of the present application, points 3 and 4 are EDS analysis positions;

[0029] Figure 7 Figure 3 is a comparison of the wafer surface roughness R a of the n-type bismuth telluride wafer before and after anodic treatment in Example 1 of the present application;

[0030] Figure 8 Figure 4 is a comparison of the wafer surface roughness R sm of the n-type bismuth telluride wafer before and after anodic treatment in Example 1 of the present application;

[0031] Figure 9 Figure 5 is a comparison of the thermoelectric leg shear strength of the n-type bismuth telluride wafer before and after anodic treatment in Example 1 of the present application;

[0032] Figure 10 Figure 6 is a comparison of the thermoelectric leg interface contact resistivity of the n-type bismuth telluride wafer before and after anodic treatment in Example 1 of the present application;

[0033] Figure 11 Figure 7 is a photo of the n-type bismuth telluride wafer after anodic electrolytic treatment in Example 2 of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0035] The embodiments of the present application provide a method for surface treatment of n-type bismuth telluride, which comprises: surface treatment of the n-type bismuth telluride wafer by anodic electrolysis in an alkaline solution.

[0036] Specifically, the method can comprise the following steps: the n-type bismuth telluride wafer is used as an anode material, two titanium plates are used as cathode materials, and the titanium plates are distributed on both sides parallel to the p-type bismuth telluride wafer;

[0037] 30-40 g / L of NaOH solution is configured as an electrolyte, and the temperature is maintained at room temperature;

[0038] The anode and cathode materials are respectively placed in the electrolyte of NaOH solution, the circuit is connected, the upper limit of the power voltage is set to 13-15v, and the anode electrolysis is carried out in the constant current mode.

[0039] As a preferred solution, the concentration of the NaOH solution is 30-40g / L, and the current density is kept at 0.03-0.05A / cm in the constant current mode. 2 .

[0040] As a preferred solution, during the anode electrolysis, the power voltage gradually rises, and after the voltage reaches the upper limit of 13v, the current value gradually decreases from the maximum current 0.2A to close to 0A, and the electrolysis time is maintained at 90-120s.

[0041] As a preferred solution, before the anode electrolysis, the n-type bismuth telluride wafer is pretreated, and the pretreatment includes grinding and surface cleaning, and the pretreatment is used to remove impurities on the wafer surface.

[0042] As a preferred solution, the method further comprises: after the anode electrolysis, ultrasonic cleaning the wafer; the ultrasonic cleaning is: placing the wafer in a 10-30vt.% HCl solution for ultrasonic cleaning for 1-5min, and then taking out the wafer and placing it in deionized water for ultrasonic cleaning for 1-5min.

[0043] As a preferred solution, the anode electrolysis and ultrasonic cleaning are repeated for 3-4 times.

[0044] The application will be further described below through specific examples.

[0045] Example 1

[0046] A surface treatment method for an n-type bismuth telluride wafer, comprising the following steps:

[0047] (1) Cutting the n-type crystal bar produced by zone melting into a wafer with a diameter of 30mm and a thickness of 1.5mm, then grinding the wafer with 2000-mesh and 5000-mesh sandpaper, then immersing the wafer in acetone for 3min, and then immersing it in deionized water for 3min;

[0048] (2) Preparing a 40g / L NaOH solution as an electrolyte, and preparing a 10vt.% hydrochloric acid solution for subsequent cleaning;

[0049] (3) Taking the above wafer as an anode, two titanium plates as cathodes, and placing the titanium plates parallel to the wafer on both sides of the wafer, connecting the circuit, and starting the anode electrolysis in the constant current mode at room temperature, the initial current is 0.4A, and the power-on time is 90s;

[0050] (4) In the power-on time, the power supply voltage is continuously increased to 13V, and then the current value is reduced, gradually reduced from the maximum current 0.2A to close to 0A, and stopped after 90s;

[0051] (5) The wafer after anodic electrolysis is placed in the prepared hydrochloric acid solution, ultrasonic cleaning for 90s, and then the wafer is placed in deionized water, ultrasonic cleaning for 90s;

[0052] (6) Repeat the anodic electrolysis operation and cleaning operation in (3) and (4) 3 times to complete the surface treatment of the n-type bismuth telluride wafer.

[0053] Referring to Figure 1 , after the anodic electrolysis treatment of step (4), the wafer surface appears reddish brown, because part of Te and Bi in the n-type bismuth telluride (BiSeTe) as the anode is oxidized by the action of the applied electric field, and a glass phase film is attached to the surface of the n-type bismuth telluride (appears reddish brown in appearance); referring to Figure 2 , after ultrasonic cleaning of step (5), the attached film on the surface is cleaned off, the reddish brown color of the wafer surface disappears, and the n-type bismuth telluride wafer is exposed.

[0054] Referring to Figure 3 , after the anodic electrolysis treatment of step (4), the electrolysis rate is well controlled, and from the SEM image it can be seen that the wafer surface is uneven, with obvious peak top and valley, and the roughening effect is uniform; referring to Figure 4 , it can be seen that after anodic electrolysis, the surface of the n-type bismuth telluride wafer as the anode does indeed undergo an oxidation reaction, generating a glass phase film.

[0055] Referring to Figure 5 , 6 , EDS analysis was performed on the wafer surface after anodic electrolysis of step (4) (analysis sites 1 and 2) and the wafer surface after ultrasonic cleaning of step (5) (analysis sites 3 and 4), respectively, and the results are shown in Table 1:

[0056] Table 1 EDS results (at. %)

[0057] O Na Se Te Bi 1 41.79 - 2.32 31.30 24.59 2 38.90 0.61 2.14 33.13 25.21 3 3.29 - 2.46 55.92 38.33 4 7.11 - 4.12 52.32 36.45

[0058] It can be seen that after anodic treatment, the orange film of the glass phase is attached to the surface of the n-type bismuth telluride wafer, causing the chemical composition of points 1 and 2 to change, with a large amount of O, i.e. Te and Bi in the n-type bismuth telluride are oxidized, and from the EDS results of points 3 and 4 it can be seen that after ultrasonic cleaning, the orange film is removed and the surface of the n-type bismuth telluride after surface treatment is exposed, with the atomic percentage of Te, Se and Bi very close to that of the n-type bismuth telluride (Bi2Sb 0.3 Te 2.7 ) itself.

[0059] The present application can achieve the purpose of roughening treatment by anodizing the wafer, and the Te and Bi in the n-type bismuth telluride (BiSeTe) are oxidized in the alkaline solution, and the surface of the material is locally oxidized, and the surface attached film can be quickly cleaned by acid treatment, and the atomic proportion of Te, Sb and Bi on the wafer surface is also very close to the n-type bismuth telluride (Bi2Sb 0.3 Te 2.7 ) itself, and will not affect the thermoelectric performance.

[0060] The wafer after repeating anodization and ultrasonic cleaning of step (6) is dried, and the surface roughness is measured, R a is the arithmetic mean of the absolute value of the profile deviation, R q is the root mean square value of the profile deviation, and R sm is the average distance of the profile. Referring to Figure 7 , it can be seen that the anode treatment can significantly improve the surface roughness of the wafer, R a increases to 1.623 μm; referring to Figure 8 , after anode treatment, R sm increases to 0.045 mm.

[0061] The wafer after repeating anodization and ultrasonic cleaning of step (6) is dried, and the surface roughness is measured, R

[0062] The plating solution for electroplating nickel is prepared, and the components are as follows: nickel sulfate hexahydrate 200 g / L, nickel chloride hexahydrate 15 g / L, boric acid 30 g / L, sodium hypophosphite 20 g / L, and sodium dodecyl sulfate 0.05 g / L;

[0063] The electroplating current is 0.2 A, the electroplating time is 20 min, and the temperature is 50℃.

[0064] The n-type bismuth telluride wafer with a prepared barrier layer is cut into a block with a length and width of 3 mm and a thickness of 1.5 mm, and then two Cu blocks are connected to the n-type bismuth telluride block by welding to prepare a simple thermoelectric leg.

[0065] The interface contact resistivity and shear strength of the simple thermoelectric leg are tested, referring to Figure 9 , the shear strength of the thermoelectric leg increases from 5.28 MPa to 13.05 MPa, referring to Figure 10 , the interface contact resistivity of the thermoelectric leg decreases from 13.52 μΩ·cm 2 to 3.44 μΩ·cm 2 .

[0066] From the above comparison results, it can be seen that the surface treatment method of the n-type bismuth telluride wafer can significantly improve the wafer surface roughness, microscopic morphology, surface chemical state, and enhance the bonding between the Ni layer and the n-type bismuth telluride, reduce the interface contact resistance, and improve the interface contact performance of the n-type bismuth telluride wafer treated by anode treatment, thereby improving the reliability of the thermoelectric device.

[0067] Example 2

[0068] A surface treatment method of an n-type bismuth telluride wafer, comprising the following steps:

[0069] (1) Cutting the extrusion-produced n-type crystal bar into a wafer with a diameter of 30 mm and a thickness of 0.4 mm, then polishing the wafer with 5000 mesh sandpaper, then soaking the wafer in acetone for 3 min, and then soaking the wafer in deionized water for 2 min;

[0070] (2) Preparing a 40 g / L NaOH solution as an electrolyte, and preparing a 10 vt.% hydrochloric acid solution for subsequent cleaning;

[0071] (3) Taking the above wafer as an anode, two titanium plates as cathodes, the titanium plates being parallel to the wafer and placed on both sides of the wafer, connecting the circuit, and starting anode electrolysis in a steady current mode at room temperature, with a current of 0.4 A and a power-on time of 90 s;

[0072] (4) Placing the wafer after anode electrolysis in the prepared hydrochloric acid solution, ultrasonic cleaning for 90 s, and then placing the wafer in deionized water, ultrasonic cleaning for 90 s;

[0073] (5) Repeating the anode electrolysis operation and cleaning operation in (3) and (4) 4 times to complete the surface treatment of the n-type extrusion-produced bismuth telluride wafer.

[0074] Referring to Figure 11 After anode electrolysis treatment in step (3), it can be seen from the SEM image that the wafer surface is very rough and has a stepped microscopic morphology, achieving the purpose of roughening treatment.

[0075] After anode electrolysis and ultrasonic cleaning in step (5), the wafer is dried and the surface roughness is measured. After anode electrolysis, the surface roughness Ra of the p-type extruded bismuth telluride wafer increases from 0.2422 μm to 1.6732 μm, and Rsm increases from 0.02514 to 0.04465 μm;

[0076] The wafer after repeating the anode electrolysis and ultrasonic cleaning of step (5) was prepared with a Ni barrier layer on the treated surface, and the operation was the same as in Example 1, except that the plating time was 15 min. The interface contact resistivity and shear strength of the simple thermoelectric leg were tested. After the anode electrolysis treatment of the p-type bismuth telluride wafer, the shear strength of the thermoelectric leg increased from 3.75 MPa to 11.07 MPa, and the interface contact resistivity of the thermoelectric leg decreased from 14.24 μΩ·cm 2 to 3.46 μΩ·cm 2 .

[0077] Based on the above, under the premise of not departing from the basic technical idea of the present application, according to the technical knowledge and means in the technical field, the content can be modified and replaced in various forms. For example, the preparation method of the n-type bismuth telluride wafer includes zone melting and extrusion, and the soaking time in the pretreatment of the n-type bismuth telluride wafer is adjusted.

[0078] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of surface treating n-type bismuth telluride, characterized by, The n-type bismuth telluride wafer is surface treated by anodic electrolysis in an alkaline solution.

2. The method of claim 1, wherein the n-type bismuth telluride is surface treated by: The anodic electrolysis is performed in a steady current mode with the n-type bismuth telluride wafer as an anode, a titanium plate as a cathode and an alkaline solution as an electrolyte.

3. The method of claim 2, wherein the n-type bismuth telluride is surface treated by: The titanium plate has two pieces, which are parallel to the n-type bismuth telluride wafer and are respectively arranged on the two sides of the n-type bismuth telluride wafer.

4. The method of claim 2, wherein the n-type bismuth telluride is surface treated by: The alkaline solution is NaOH solution, the concentration of the NaOH solution is 30-40g / L, the current density is kept at 0.03-0.05A / cm under the steady flow mode, and the upper limit of the power supply voltage is set at 13-15V. 2 , the upper limit of the power supply voltage is set at 13-15V.

5. The method of claim 4, wherein the n-type bismuth telluride is surface treated by: During the anodic electrolysis, the power voltage gradually increases, and after the voltage reaches an upper limit, the current value gradually decreases, and the electrolysis time is maintained at 90-120 s.

6. The method of claim 1, wherein the n-type bismuth telluride is surface treated by: The n-type bismuth telluride wafer is pretreated before the anodic electrolysis, and the pretreatment includes grinding and surface cleaning.

7. The method of claim 6, wherein the n-type bismuth telluride is surface treated by: The grinding is performed by grinding the wafer surface through 2000-5000 mesh sandpaper, and the surface cleaning is performed by immersing the wafer in acetone and then in deionized water.

8. The method of claim 1, wherein the n-type bismuth telluride is surface treated by, The method further includes: after the anodic electrolysis, ultrasonic cleaning the wafer; the ultrasonic cleaning is performed by immersing the wafer in a 10-30 vt.% HCl solution for 60-90 s, and then taking out the wafer and immersing it in deionized water for 60-90 s.

9. The method of claim 8, wherein the n-type bismuth telluride is surface treated by: The anodic electrolysis and the ultrasonic cleaning are repeated for 3-4 times.

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