A surface treatment agent for bismuth telluride and method of using the same

Abstract

The present invention belongs to the field of thermoelectric devices. In order to solve the problem that the surface treatment of wafers with a thickness of less than 1 mm by a traditional method easily causes wafer breakage and damage, thereby reducing the utilization rate of materials and production efficiency, a surface treatment agent and method for bismuth telluride-based materials used in thermoelectric devices are provided. The surface treatment agent for bismuth telluride includes a roughening liquid and a deashing liquid. The treatment process is simple and the wafer will not be damaged. The surface treatment agent is particularly suitable for the surface treatment of bismuth telluride-based materials used in micro thermoelectric devices for large-scale processing.

Description

Technical Field

[0001] The invention belongs to the field of thermoelectric devices, and in particular relates to a surface treatment agent for bismuth telluride-based materials and a use method thereof. Background Art

[0002] At this stage, industrial technology is becoming more and more advanced, and more and more electronic devices are tending to be intelligent and wearable. As a new energy technology that can realize the direct conversion of heat energy and electrical energy, thermoelectric technology has attracted more and more attention in the current global energy crisis. Thermoelectric devices have the advantages of small mass, no noise, simple structure, high sensitivity, etc., and can realize the dual functions of cooling and heating. At present, thermoelectric devices are widely used in aerospace, electronic communications, biomedicine, automobile manufacturing and other fields. For example, temperature control of lasers, cycle temperature control on PCR equipment, temperature control of micro devices on wearable devices, etc.

[0003] Traditional bismuth telluride-based surface treatment is divided into two stages: pretreatment and electroplating. Pretreatment can also be called electroplating pretreatment. The traditional method is to perform sandblasting after the wafer is cut and then combine it with flame spraying or arc spraying to achieve the purpose of roughening the wafer surface and facilitate subsequent electroplating. This method will not cause any problems for wafers with a thickness of no more than 1 mm. However, as thermoelectric devices become more and more miniaturized, this traditional process is not applicable to wafers with a thickness of less than 1 mm. Traditional sandblasting and spraying processes will generate high temperature and high pressure during the production process. In this environment, it is easy to cause wafer breakage and damage, reducing material utilization and production efficiency. At the same time, it increases the production cycle and production cost. Therefore, a mild surface treatment method is needed to solve this problem. Summary of the invention

[0004] In order to solve the problem that the surface treatment of wafers with a thickness of less than 1 mm by traditional methods easily causes wafer breakage and damage, thereby reducing material utilization and production efficiency, a surface treatment agent and method for bismuth telluride-based materials used in thermoelectric devices are provided. The treatment process is simple and will not cause damage to the wafer. The surface treatment of bismuth telluride-based materials used in micro-thermoelectric devices is particularly suitable for large-scale processing.

[0005] The present invention is achieved through the following technical scheme: a surface treatment agent for bismuth telluride comprises a roughening liquid and a deashing liquid, wherein the roughening liquid is composed of the following components, calculated by mass fraction: 5%-60% ferric chloride, 0.1%-5% surfactant, 5%-10% hydrochloric acid, and the balance is water; the deashing liquid is composed of the following components, calculated by mass fraction: 0.5%-5% potassium permanganate, 5%-30% nitric acid, 0.1%-5% surfactant, and the balance is water.

[0006] Preferably, the hydrochloric acid includes dilute hydrochloric acid and concentrated hydrochloric acid. Since ferric chloride will generate +2-valent iron ions after coarsening, the divalent iron ions cannot exist stably in the solution, thereby increasing the service life of the solution, and the solution can be managed through regular analysis and testing, which is suitable for large-scale production.

[0007] As a priority, the nitric acid is concentrated nitric acid and dilute nitric acid, which can react with the dust produced by roughening without corroding the substrate, thereby achieving the effect of dust removal. Potassium permanganate can completely oxidize the intermediate valence oxides produced by roughening into the highest valence, making the surface uniform after dust removal.

[0008] Surfactants can reduce the surface tension of the oil-water interface. Preferably, the surfactant is selected from water-soluble surfactants. The surface treatment agent is simple to configure and easy to operate.

[0009] The surface treatment agent prepared by this formula will not produce a damage layer on the bismuth telluride-based wafer, but will improve the surface roughness and surface activity of the bismuth telluride substrate, which is beneficial to obtain a higher bonding strength with the coating, thereby optimizing the service life, number of cycles and performance of the thermoelectric device.

[0010] The method for treating the surface of bismuth telluride-based materials by using the bismuth telluride surface treatment agent is as follows: firstly immersing the cleaned bismuth telluride wafer into a roughening solution, then immersing it into a deashing solution, then performing ultrasonic cleaning, and then connecting other metals by electroplating or chemical plating.

[0011] Preferably, the roughening liquid temperature is 20-80° C., and the soaking time is 5s-600s.

[0012] Preferably, the deashing liquid temperature is 20-80° C., and the deashing time is 5s-600s.

[0013] Preferably, the bismuth telluride wafer obtained after the surface treatment is ultrasonically cleaned by ethanol and water in sequence. The ultrasonic cleaning conditions are: 20-40 kHz, time 180-360 s.

[0014] The method for surface treatment of bismuth telluride-based materials is applied to surface treatment of bismuth telluride-based materials of micro thermoelectric devices.

[0015] In thermoelectric devices, a damage layer will exist on the surface of the bismuth telluride substrate due to cutting. This damage layer will affect the interface bonding strength between the bismuth telluride base and the metal coating, resulting in a significant reduction in the service performance and reliability of the device. The present invention uses chemical roughening and ash removal to pretreat the surface of the bismuth telluride-based wafer, and then the coating can be directly prepared by electroplating or chemical plating, which improves the bonding strength between the coating and the bismuth telluride base and is beneficial to the preparation of thermoelectric devices.

[0016] Compared with the prior art, the beneficial effects of the present invention are: the surface treatment method does not cause any damage to the wafer, improves production efficiency, and can reduce the process of increasing the roughness of the wafer by sandblasting, thereby reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the SEM surface morphology of the P-type bismuth telluride-based wafer in Application Example 1;

[0018] Figure 2 This is a SEM surface morphology image of a P-type bismuth telluride-based wafer after chemical roughening treatment in Application Example 1;

[0019] Figure 3 This is a photo of a P-type bismuth telluride-based wafer after surface treatment in Application Example 1;

[0020] Figure 4 This is a photo of the P-type bismuth telluride-based wafer after nickel plating in Application Example 1;

[0021] Figure 5 This is the SEM surface morphology of the N-type bismuth telluride-based wafer in Application Example 2;

[0022] Figure 6 This is a SEM surface morphology image of an N-type bismuth telluride-based wafer after chemical roughening treatment in Application Example 2;

[0023] Figure 7 This is a photo of the N-type bismuth telluride-based wafer after surface treatment in Application Example 2;

[0024] Figure 8 This is a photo of the N-type bismuth telluride-based wafer after nickel plating in Application Example 2;

[0025] Fig. 9 This is a photo of the wafer after conventional surface treatment in Comparative Example 1;

[0026] Fig.10 This is a photo of the wafer after surface treatment in Comparative Example 2. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below by way of examples and drawings. The raw materials used in the examples are all commercially available or can be prepared by conventional methods.

[0028] The surfactant is commercially available sodium dodecylbenzene sulfonate.

[0029] Example 1

[0030] Preparation of roughening solution: 30% ferric chloride, 0.5% surfactant, 5% concentrated hydrochloric acid with a mass concentration of 37.5%, and the balance water, by weight percentage, and the above components are mixed evenly.

[0031] Preparation of deashing liquid: Calculated by mass percentage, 1% potassium permanganate, 20% nitric acid with a mass concentration of 20%, 0.5% surfactant, and the balance is water. Mix the above components evenly.

[0032] Application Example 1

[0033] (1) A circular P-type bismuth telluride-based wafer with a diameter of 30 mm and a thickness of 0.8 mm was taken from the zone melting material, and surface pollutants were removed by ultrasonic washing with alcohol. After drying, the wafer was immersed in the roughening solution prepared in Example 1 at a roughening temperature of 60° C. and a roughening time of 30 s. The roughened P-type bismuth telluride-based wafer was transferred into the deashing solution prepared in Example 1 for deashing treatment at a deashing temperature of 25° C. and a deashing time of 10 s.

[0034] (2) The P-type bismuth telluride-based wafer after the surface treatment in step (1) is placed in an ultrasonic device for cleaning; the ultrasonic frequency is 40 kHz and the time is 300 s. It is first cleaned with ethanol with a volume concentration of 95%, and then cleaned with pure water. Then, nickel is electroplated in the electroplating solution, followed by chemical nickel plating, and finally tin is electroplated.

[0035] The SEM surface morphology of P-type bismuth telluride-based wafer is as follows Figure 1 As shown, the SEM surface morphology of the P-type bismuth telluride-based wafer after chemical roughening treatment is as follows Figure 2 As shown, the photo of the P-type bismuth telluride-based wafer after surface treatment is as follows Figure 3 As shown, the photo of the P-type bismuth telluride-based wafer after nickel plating is as follows Figure 4 shown.

[0036] Application Example 2

[0037] (1) A circular N-type bismuth telluride-based wafer with a diameter of 30 mm and a thickness of 0.8 mm was taken from the zone melting material, and surface pollutants were removed by ultrasonic washing with alcohol, and then the wafer was dried and immersed in the roughening solution prepared in Example 1 at a roughening temperature of 60° C. for a roughening time of 30 s. The roughened N-type bismuth telluride-based wafer was transferred into the deashing solution prepared in Example 1 for deashing treatment at a deashing temperature of 25° C. for a deashing time of 10 s.

[0038] (2) The N-type bismuth telluride-based wafer after the surface treatment in step (1) is placed in an ultrasonic device for cleaning; the ultrasonic frequency is 40 kHz and the time is 300 s. It is first cleaned with ethanol with a volume concentration of 95%, and then cleaned with pure water. Then, nickel is electroplated in the electroplating solution, followed by chemical nickel plating, and finally tin is electroplated.

[0039] SEM surface morphology of N-type bismuth telluride wafer Figure 5 As shown in Figure 2, the SEM surface morphology of the N-type bismuth telluride-based wafer after chemical roughening treatment is as follows: Figure 6 As shown, the photo of the N-type bismuth telluride-based wafer after surface treatment is as follows Figure 7As shown, the photo of the N-type bismuth telluride-based wafer after nickel plating is as follows Figure 8 shown.

[0040] Example 2

[0041] Preparation of roughening solution: Calculated by mass percentage, ferric chloride 60%, surfactant 3%, concentrated hydrochloric acid 8% with a mass concentration of 20%, and the balance is water, and the above components are mixed evenly.

[0042] Preparation of deashing liquid: Calculated by mass percentage, 4% potassium permanganate, 10% nitric acid with a mass concentration of 40%, 3% surfactant, and the balance is water. Mix the above components evenly.

[0043] Application Example 3

[0044] (1) A circular P-type bismuth telluride-based wafer with a diameter of 30 mm and a thickness of 0.5 mm was taken from the zone melting material, and surface pollutants were removed by ultrasonic washing with alcohol, and then the wafer was dried and immersed in the roughening solution prepared in Example 2 at a roughening temperature of 25°C for a roughening time of 100 s. The roughened P-type bismuth telluride-based wafer was transferred into the deashing solution prepared in Example 2 for deashing treatment at a deashing temperature of 25°C for a deashing time of 100 s.

[0045] (2) The P-type bismuth telluride-based wafer after the surface treatment in step (1) is placed in an ultrasonic device for cleaning; the ultrasonic frequency is 28 kHz and the time is 360 s. It is first cleaned with ethanol with a volume concentration of 95%, and then cleaned with pure water. Then, nickel is electroplated in the electroplating solution, followed by chemical nickel plating, and finally tin is electroplated.

[0046] Example 3

[0047] Preparation of roughening solution: Calculated by mass percentage, 10% ferric chloride, 1% surfactant, 10% concentrated hydrochloric acid with a mass concentration of 20%, and the balance is water, and the above components are mixed evenly.

[0048] Preparation of deashing liquid: Calculated by mass percentage, 1% potassium permanganate, 30% nitric acid with a mass concentration of 40%, 5% surfactant, and the balance is water. Mix the above components evenly.

[0049] Application Example 4

[0050] (1) A circular N-type bismuth telluride-based wafer with a diameter of 30 mm and a thickness of 0.5 mm was taken from the zone melting material, and surface pollutants were removed by ultrasonic washing with alcohol, and then the wafer was dried and immersed in the roughening solution prepared in Example 3. The roughening temperature was 50° C. and the roughening time was 100 s. The roughened N-type bismuth telluride-based wafer was transferred to the deashing solution prepared in Example 3 for deashing treatment. The deashing temperature was 50° C. and the deashing time was 60 s.

[0051] (2) The N-type bismuth telluride-based wafer after the surface treatment in step (1) is placed in an ultrasonic device for cleaning; the ultrasonic frequency is 28 kHz and the time is 360 s. It is first cleaned with ethanol with a volume concentration of 95%, and then cleaned with pure water. Then, nickel is electroplated in the electroplating solution, followed by chemical nickel plating, and finally tin is electroplated.

[0052] Comparative Example 1

[0053] Surface treatment using conventional methods

[0054] A round N-type bismuth telluride-based wafer with a diameter of 30 mm and a thickness of 1 mm was subjected to high-pressure sandblasting and then flame sprayed with a Ni layer. The effect is as follows Fig. 9 , high pressure will cause many chips to break.

[0055] Comparative Example 2

[0056] A circular N-type bismuth telluride-based wafer with a diameter of 30 mm and a thickness of 1 mm was taken from the zone melting material, and surface pollutants were removed by ultrasonic washing with alcohol, and then immersed in the roughening solution prepared in Example 3 after drying. The roughening temperature was 50° C. and the roughening time was 100 s. No ash removal treatment was performed. Fig.10 As shown, the surface is covered with coarse ash and is uneven.

Claims

1. A surface treatment agent for bismuth telluride, characterized in that: The surface treatment agent includes a roughening liquid and a deashing liquid. The roughening liquid is composed of the following components, calculated by mass fraction: 5%-60% ferric chloride, 0.1%-5% surfactant, 5%-10% hydrochloric acid, and the balance is water; the deashing liquid is composed of the following components, calculated by mass fraction: 0.5%-5% potassium permanganate, 5%-30% nitric acid, 0.1%-5% surfactant, and the balance is water, wherein the hydrochloric acid is 37.5wt% concentrated hydrochloric acid, the nitric acid is 20wt% nitric acid, and the surfactant is soluble in water.

2. A method for surface treatment of bismuth telluride-based materials using the surface treatment agent for bismuth telluride according to claim 1, characterized in that: First, the cleaned bismuth telluride wafer is immersed in a roughening solution, then immersed in a deashing solution, and then ultrasonically cleaned, and then connected to other metals by electroplating or chemical plating, wherein the temperature of the roughening solution is 20~80°C, the roughening time is 5~600s; the temperature of the deashing solution is 20~80°C, and the deashing time is 5~600s.

3. The method for surface treatment of bismuth telluride-based materials according to claim 2, characterized in that: Ultrasonic cleaning was performed with ethanol and water in sequence.

4. The method for surface treatment of bismuth telluride-based materials according to claim 2 or 3, characterized in that: Ultrasonic cleaning conditions: 20-40kHz.

5. The method for surface treatment of bismuth telluride-based materials according to claim 4, characterized in that: The ultrasonic cleaning time is 180-360s.

6. The method for surface treatment of bismuth telluride-based materials according to claim 2, characterized in that: The roughening time is 30~100s.

7. The method for surface treatment of bismuth telluride-based materials according to claim 2, characterized in that: The dust removal time is 10~100s.

8. A method for surface treatment of bismuth telluride-based materials according to any one of claims 2 to 7, applied to surface treatment of bismuth telluride-based materials of micro thermoelectric devices.

Images