High mobility (004) textured silver telluride thin film and method of making same

Abstract

This invention belongs to the field of thermoelectric thin film technology, specifically relating to a high-mobility (004) textured silver telluride thin film and its preparation method. The film exhibits a layered structure, a thickness of 0.3~2μm, a high (004) texture, and a mobility as high as 6000cm⁻¹. 2 The value of / Vs exceeds the reported value of silver telluride in the literature and is compatible with flexible substrates. This invention has for the first time prepared a silver telluride thin film with a high (004) texture by combining a hollow sample disk with magnetron dual-target co-sputtering. The preparation method is simple, low-cost, and has excellent performance. It can be prepared on a large scale and is expected to be applied in thermoelectric, optoelectronic and other fields.

Description

Technical Field

[0001] This invention belongs to the field of thermoelectric thin film technology, specifically relating to a high-mobility (004) textured silver telluride thin film and its preparation method. Background Technology

[0002] Human daily life and development have always revolved around energy, and the massive energy consumption has led to severe environmental pollution and an energy crisis. To address this issue, researchers have been exploring cost-effective and efficient green energy technologies. Thermoelectric materials can directly and efficiently convert low- and medium-temperature waste heat, such as industrial waste heat and vehicle exhaust, into electrical energy. They can also collect body heat to power wearable devices or be used directly for self-powered temperature sensing, making them one of the key technologies for solving energy and environmental problems.

[0003] Silver telluride, as a room-temperature thermoelectric material possessing both excellent thermoelectric properties and mechanical flexibility, has attracted considerable attention in recent years, meeting the development needs of flexible wearables and self-powered sensing. However, most research has focused on bulk silver telluride materials, with a significant lack of research on high-performance silver telluride thin film materials. Compared to bulk materials, thin film materials, due to their small size and excellent flexibility, are more suitable for applications such as flexible wearables, self-powered sensing, and waste heat collection in irregularly shaped structures. Existing silver telluride thin films are mostly prepared using hydrothermal synthesis of silver telluride nanowires and electrochemical deposition methods, resulting in low crystallinity and numerous impurities, leading to low Seebeck coefficients and carrier mobility, and poor thermoelectric performance. Therefore, there is an urgent need to develop a method for preparing flexible silver telluride thin films with high thermoelectric performance. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a high-mobility (004) textured silver telluride thin film and its preparation method, wherein the thin film has a high (004) texture and a mobility as high as 6000 cm⁻¹. 2 / Vs exceeds the reported value for silver telluride in the literature, providing a new approach for the preparation of high-performance silver telluride materials.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A high-mobility (004) textured silver telluride thin film, wherein the film grains extend and stack along a direction parallel to the substrate surface to form a lamellar structure, is a highly (004) textured silver telluride thin film, similar to (00l) textured bismuth telluride thin film, but silver telluride does not have van der Waals gaps and is not a layered material itself.

[0006] The high-mobility (004) textured silver telluride film has a thickness of 0.3~2μm.

[0007] The high-mobility (004) textured silver telluride thin film has an atomic ratio of Ag:Te = 65~69:35~31, and its composition is adjustable.

[0008] The aforementioned high-mobility (004) textured silver telluride thin film exhibits a carrier mobility as high as 6000 cm⁻¹. 2 / Vs, higher than the reported value of silver telluride in the literature, and Seebeck coefficient reached -118μV / K, and conductivity reached 800s / cm.

[0009] The aforementioned high-mobility (004) textured silver telluride thin film has a low preparation temperature, no substrate effect, and can be successfully prepared on flexible polyimide substrates, quartz wafers, and silicon wafers.

[0010] The high-mobility (004) textured silver telluride film is prepared using a stainless steel perforated sample tray, which includes a 1 mm thick substrate and a 0.3 mm thick mask, and is used with M3 hex screws.

[0011] The specific preparation steps of the high-mobility (004) textured silver telluride thin film are as follows: (1) Substrate cleaning Substrates such as polyimide, quartz wafers, and silicon wafers are ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water for 20-40 minutes, dried with nitrogen, and then stored for later use.

[0012] (2) Install the target material Clean the magnetron cavity, polish the 4-inch silver and tellurium targets to remove oxides and impurities, wipe them with alcohol and then install them into the cavity. Connect the silver target to the DC power supply and the tellurium target to the RF power supply.

[0013] (3) Pre-sputtering To further eliminate impurities on the target surface and in the cavity, pre-sputtering is then performed. A blank sample disk is placed in the cavity and heated to 600-700℃ at a rate of 10-15℃ / min. The actual temperature on the hollowed-out sample disk is 400-500℃. This temperature is maintained for 2 hours. The process continues until the vacuum reaches 1-5 × 10⁻⁵ °C. -5 After Pa, high-purity argon gas is introduced into the chamber to maintain the working pressure at 0.6~0.8 Pa. The sample disk rotation speed is set to 20 r / min. After stabilization, the dual-target power supply is turned on, and the target cover and sample baffle are opened. Sputtering is performed for a total of 20~40 min, with the silver target power at 35~45 W and the tellurium target power at 55~65 W.

[0014] (4) Formal Splashing After the furnace is cooled down, the blank sample tray is removed and the actual sputtering begins. The cleaned sample is placed in the hollow sample tray, fixed with screws, and then sent into the cavity. The subsequent steps are the same as the pre-sputtering process.

[0015] The high-mobility (004) textured silver telluride thin film is characterized in that: both the silver target and the telluride target are 4 inches in size and have a purity of 99.99%.

[0016] The high-mobility (004) textured silver telluride thin film is characterized by: a silver target DC sputtering power of 35~45W, a tellurium target RF sputtering power of 55~65W, a working gas pressure of 0.6~0.8Pa, and a sputtering time of 20~40min.

[0017] The high-mobility (004) textured silver telluride thin film is characterized by: the cavity heating temperature being 600~700℃, and the surface temperature of the hollow sample disk being 400~500℃.

[0018] The design concept of this invention is as follows: First, utilizing a perforated sample disk in a multi-target magnetron sputtering system with an infrared heating tube as the heat source improved the uniformity of sample heating (no need for fixation with thermally conductive silver paste, direct infrared heating). Simultaneously, as a continuous thin film formed on the sample surface during sputtering, the substrate began to reflect infrared radiation, reducing the sample surface temperature and improving the compatibility of the flexible substrate. Second, single-target sputtering of silver telluride alloy targets resulted in greater tellurium loss due to the higher saturated vapor pressure, leading to a shift in the stoichiometry. Therefore, using dual-target co-sputtering technology to prepare silver telluride offers greater adjustability and helps reduce costs. Based on the above analysis, we successfully prepared a high-mobility (004) textured silver telluride thin film by adjusting the working pressure, coating temperature, sputtering power supply, and sputtering power.

[0019] The thin film of this invention exhibits a layered structure with a thickness of 0.3~2μm, a high (004) texture, and a mobility as high as 6000cm. 2 The value of / Vs exceeds the reported value of silver telluride in the literature and is compatible with flexible substrates. This invention has for the first time prepared a silver telluride thin film with a high (004) texture by combining a hollow sample disk with magnetron dual-target co-sputtering. The preparation method is simple, low-cost, and has excellent performance. It can be prepared on a large scale and is expected to be applied in thermoelectric, optoelectronic and other fields.

[0020] The advantages and beneficial effects of this invention are as follows: 1. The hollow sample disk used in the preparation of the high-mobility (004) textured silver telluride thin film of the present invention improves the uniformity of sample heating (no need to rely on thermally conductive silver paste for fixation, direct infrared heating), and as a continuous thin film is formed on the sample surface during sputtering, the substrate begins to reflect infrared radiation, which reduces the temperature of the sample surface and improves the compatibility of the flexible substrate.

[0021] 2. The method for preparing high-mobility (004) textured silver telluride thin films of the present invention is simple, efficient, and highly repeatable. The composition can be adjusted by adjusting the power ratio of the two targets, and the cost is much lower than that of a single alloy target. It can be used in flexible wearable electronic devices.

[0022] 3. The high-mobility (004) textured silver telluride thin film of the present invention exhibits a layered structure, achieving a high (004) texture for the first time, with a carrier mobility of 6000 cm⁻¹. 2 / Vs, exceeding the reported value for silver telluride in the literature. Attached Figure Description

[0023] Figure 1 The XRD analysis results are those of the (004) textured silver telluride film prepared in this invention and the non-textured silver telluride film prepared in Example 5.

[0024] Figure 2 The results are the surface SEM analysis results of the (004) textured silver telluride thin film prepared in this invention.

[0025] Figure 3 The results are the cross-sectional SEM analysis results of the (004) textured silver telluride thin film prepared in this invention.

[0026] Figure 4 This is a structural diagram of the hollow sample disk used in the preparation of the (004) textured silver telluride thin film of the present invention.

[0027] Figure 5 The results are the surface SEM analysis results of the non-textured silver telluride thin film prepared in Example 5 of this invention. Detailed Implementation

[0028] In specific implementation, the present invention can adjust the composition of silver telluride thin films by adjusting parameters such as target power, sputtering time, and working gas pressure to obtain (004) textured silver telluride thin films with different stoichiometric ratios.

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0030] The thin film was prepared by magnetron sputtering using a stainless steel perforated sample disk. The perforated sample disk consists of a flat, 1 mm thick base plate and a 0.3 mm thick mask. The base plate and mask are stacked and fixed together by screws. Multiple through holes with cross-sectional shapes that are parallel to the surface of the base plate and match the shape and size of the substrate surface are formed on the base plate. Corresponding through holes are also formed on the mask at the same locations as the through holes on the base plate. The through holes on the mask have the same shape as the corresponding through holes on the base plate, but their size is smaller. The through hole, that is, the projection of the through hole opened on the mask onto the base plate is located in the through hole at the corresponding position on the base plate, and there is a gap between the edge of the projection and the edge of the through hole at the corresponding position on the base plate; the mask is located below the base plate with its surface parallel to the horizontal plane and located on the side away from the infrared heating tube, that is, the base plate is located between the mask and the infrared heating tube, and the base (12.2mm square) is placed into the through hole (12.2mm square through hole, corresponding to a 10.5mm square through hole on the mask) in the base plate and fixed by dimensional limit.

[0031] Example 1

[0032] This invention provides a method for preparing a high-mobility (004) textured silver telluride thin film with a silver-telluride atomic percentage of 67:33, such as... Figure 1 The XRD micro-area diffraction pattern shows that the diffraction peak positions of the prepared film are basically consistent with those of the standard silver telluride PDF card, and the intensity of the (004) diffraction peak is much higher than that of the standard card, indicating that the film has a high (004) texture. Further morphological characterization is as follows: Figure 1 As shown in the surface scanning electron microscope images, the thin film grains extend and stack along a direction parallel to the substrate surface, forming a lamellar structure (grain size 0.5 μm~2 μm, thickness 50~150 nm), and as... Figure 3 The cross-sectional scanning electron microscope image shows that the film thickness is approximately 700 nm. The specific steps include: (1) Substrate cleaning The quartz substrate was ultrasonically cleaned for 30 minutes each with acetone, anhydrous ethanol, and deionized water, then dried with nitrogen and stored for later use.

[0033] (2) Install the target material Clean the magnetron cavity, and use 500-grit sandpaper to polish the surfaces of the 4-inch diameter (3mm thick) silver and tellurium targets to remove oxides and impurities. After wiping with alcohol, install them into the cavity, connect the silver target to the DC power supply, and connect the tellurium target to the RF power supply.

[0034] (3) Pre-sputtering To further eliminate impurities on the target surface and in the cavity, pre-sputtering is then performed by placing a blank, flat, solid sample disk into the cavity. Pre-sputtering process: Heat to 650℃ (sputtering temperature) at 15℃ / min. The actual temperature on the perforated sample tray (base plate) is 460℃. Hold at the target temperature for 2 hours. Wait for the vacuum degree to reach 5×10⁻⁶. -5 After Pa, high-purity argon gas is introduced into the chamber to maintain the working pressure at 0.68 Pa. The sample disk rotation speed is set to 20 r / min. After stabilization, the dual-target power supply is turned on, and the target cover and sample baffle are opened. Sputtering is carried out for a total of 30 min, with the silver target power at 35 W and the tellurium target power at 60 W.

[0035] (4) Formal Splashing After the furnace cools to room temperature, remove the blank sample tray and begin the actual sputtering process, placing the cleaned substrate into the tray. Figure 4 After being secured with screws in the hollow sample tray shown, it is sent into the cavity, and then the sputtering operation is carried out in the same manner as the pre-sputtering process (process and conditions).

[0036] The silver-tellurium atomic percentage of the thin film is 67:33. The diffraction peak positions of the prepared thin film are basically consistent with those of the standard silver telluride PDF card, and the intensity of the (004) diffraction peak is much higher than that of the standard card, indicating that the thin film has a high (004) texture. The thin film grains extend and stack along a direction parallel to the substrate surface, forming a lamellar structure (grain size 0.5μm~2μm, thickness 50~150nm), and the film thickness is about 700nm.

[0037] The Seebeck coefficient of the sample prepared in this embodiment is -118 μV / K, and the carrier concentration is -0.749 × 10⁻⁶. 18 cm -3 The conductivity is 713 S cm. -1 The migration rate was 5947 cm. 2 / V s. All thin film properties were characterized by measuring the Seebeck coefficient of the thin films using a Seebeck coefficient tester, and measuring conductivity, mobility, and carrier concentration using a Hall effect testing system (van der Bauer method).

[0038] Example 2

[0039] The steps (processes and conditions) of this embodiment are the same as those of Example 1, except that a flexible polyimide substrate is used, the Seebeck coefficient of the prepared sample is -118 μV / K, and the carrier concentration is -0.76 × 10⁻⁶. 18 cm -3 The conductivity is 650 S / cm. -1 The migration rate was 5341 cm. 2 / V s.

[0040] The silver-tellurium atomic percentage of the thin film is 67:33. The diffraction peak positions of the prepared thin film are basically consistent with those of the standard silver telluride PDF card, and the intensity of the (004) diffraction peak is much higher than that of the standard card, indicating that the thin film has a high (004) texture. The thin film grains extend and stack along a direction parallel to the substrate surface, forming a lamellar structure (grain size 0.5μm~2μm, thickness 50~150nm), and the film thickness is about 700nm.

[0041] Example 3

[0042] In this embodiment, the silver-tellurium atomic percentage is 68:32, and the steps (process and conditions) are the same as in Example 1, except that the silver target power is 40W, the film thickness is 900nm, the Seebeck coefficient of the prepared sample is -116μV / K, and the carrier concentration is -0.675×10⁻⁶. 18 cm -3 The conductivity is 630 S / cm. -1 The migration rate is 5807 cm. 2 / V s.

[0043] The diffraction peak positions of the prepared film are basically consistent with those of the standard silver telluride PDF card, and the intensity of the (004) diffraction peak is much higher than that of the standard card, indicating that the film has a high (004) texture. The film grains extend and stack along the direction parallel to the substrate surface to form a lamellar structure (grain size 0.5μm~2μm, thickness 50~150nm).

[0044] Example 4

[0045] The steps (process and conditions) of this embodiment are the same as those of Example 3, except that a flexible polyimide substrate is used, the Seebeck coefficient of the prepared sample is -118 μV / K, and the carrier concentration is -0.68 × 10⁻⁶. 18 cm -3 The conductivity is 581 S / cm. -1 The migration rate is 5340 cm. 2 / V s.

[0046] The silver-tellurium atomic percentage of the thin film is 68:32. The diffraction peak positions of the prepared thin film are basically consistent with those of the standard silver telluride PDF card, and the intensity of the (004) diffraction peak is much higher than that of the standard card, indicating that the thin film has a high (004) texture. The thin film grains extend and stack along a direction parallel to the substrate surface, forming a lamellar structure (grain size 0.5μm~2μm, thickness 50~150nm), and the film thickness is about 900nm.

[0047] Example 5

[0048] The steps (process and conditions) of this embodiment are the same as those of Embodiment 4, except that the sputtering temperature is 500℃ (sputtering temperature), the actual temperature on the hollow sample disk (base plate) is 340℃, the Seebeck coefficient of the prepared sample is -100μv / k, and the carrier concentration is -0.563×10 18 cm -3 The conductivity is 215 S cm⁻¹ -1 The migration rate is 2385 cm. 2 / V s. The film thickness is approximately 750 nm, such as Figure 1 As shown, its XRD pattern is consistent with the silver telluride standard PDF card, with no significant (004) texture. Its surface SEM analysis is as follows: Figure 5 As shown, the grains are small (grain size 50~500nm), with more surface protrusions and pores, resulting in a lower mobility.

[0049] Example 6

[0050] The steps (process and conditions) of this embodiment are the same as those of Embodiment 2, except that a traditional solid sample tray is used. The polyimide substrate is adhered to the surface of the sample tray, and the polyimide substrate deforms and shrinks, resulting in no effective sample.

[0051] The results show that the high-mobility (004) textured silver telluride thin film of the present invention has ultra-high mobility and excellent thermoelectric properties, good repeatability, low cost, adjustable composition and performance, and compatibility with flexible substrates. It can be used in flexible wearables, self-powered sensing and other fields, and has high application value.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the ideas of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-mobility (004) textured silver telluride thin film, characterized in that: The film has a thickness of 0.3~2μm (preferably 0.6~0.8μm) and an atomic ratio of Ag:Te = 65~69:35~31 (preferably 66~68:34~32, more preferably 67:33); the film is a (004) textured silver telluride film.

2. The high-mobility (004) textured silver telluride thin film as described in claim 1, characterized in that: The thin film grains extend and stack along a direction parallel to the substrate surface, forming a lamellar structure, which is a highly (004) textured silver telluride thin film, similar to the (00l) textured bismuth telluride thin film.

3. The thin film as described in claim 1, characterized in that: The thin film has a carrier mobility as high as 6000 cm⁻¹. 2 / Vs, higher than the reported value of silver telluride in the literature, and Seebeck coefficient reached -118μV / K, and conductivity reached 800s / cm.

4. The thin film as described in claim 1, characterized in that: This film can be prepared at low temperatures, without substrate effects, and can be successfully fabricated on flexible polyimide, hard quartz, or hard silicon substrates.

5. A method for preparing the thin film according to any one of claims 1-4, characterized in that: The substrate can be a flexible substrate (such as polyimide) or a rigid substrate (such as a quartz wafer or silicon wafer); the thin film is prepared by magnetron sputtering using a stainless steel perforated sample disk. The perforated sample disk includes a flat base plate with a thickness of 0.8~3mm (preferably 1~2mm) and a mask plate with a thickness of 0.2~0.6mm (preferably 0.3~0.4mm). The base plate and the mask plate are stacked and fixed together by screws; one or more through holes with cross-sectional shapes that are parallel to the surface of the base plate and have the same or matching shape and size as the surface of the substrate are formed on the base plate. A through hole is also made at the corresponding position of the through hole. The through hole on the mask plate has the same shape as the through hole at the corresponding position on the base plate, but its size is smaller than that of the through hole at the corresponding position on the base plate. That is, the projection of the through hole on the mask plate onto the base plate is located in the through hole at the corresponding position on the base plate, and there is a gap between the edge of the projection and the edge of the through hole at the corresponding position on the base plate. The mask plate is located below the base plate with its surface parallel to the horizontal plane and located on the side away from the infrared heating tube. That is, the base plate is located between the mask plate and the infrared heating tube. The substrate is placed into the through hole in the base plate and fixed by dimensional limitation. Alternatively, if a flexible substrate (such as polyimide) is used, it can be fixed by clamping. The film is prepared using a stainless steel perforated sample tray, which includes a flat base plate with a thickness of 0.8~3mm and a mask plate with a thickness of 0.2~0.6mm. The base plate and the mask plate are stacked and fixed together by screws. One or more through holes are opened on the base plate, and through holes are also opened at the corresponding positions of the through holes on the base plate on the mask plate. The mask plate is located below the base plate with its surface parallel to the horizontal plane and located on the side away from the infrared heating tube. That is, the base plate is located between the mask plate and the infrared heating tube. The substrate is placed in the through holes between the base plate and the base plate. The edges of the through holes of the mask plate and the base plate are respectively located on the substrate. That is, the edges of the projections of the through holes of the mask plate and the base plate onto the substrate are respectively located on the substrate. That is, there is a gap between the projected edges and the edges of the substrate, which is fixed by dimensional constraints.

6. The preparation method according to claim 5, characterized in that: The specific preparation steps are as follows: (1) Substrate cleaning Clean the polyimide, quartz, or silicon substrate thoroughly; (2) Install the target material The silver target and the tellurium target are installed in the sputtering chamber of a multi-target (e.g., dual-target) magnetron sputtering instrument. The silver target is connected to a DC power supply, and the tellurium target is connected to an RF power supply. (3) Splashing The sample tray is placed into the cavity, and then the infrared heating tube above the sputtering cavity is turned on to heat to 550-700℃ (preferably 600-700℃, more preferably 640-680℃) at a rate of 10-15℃ / min. The actual temperature on the hollowed-out sample tray (base plate) is 350-500℃ (preferably 400-500℃, more preferably 440-480℃). The sample is held at the target temperature for 0.5-4 hours (preferably 1-3 hours, more preferably 2-2.5 hours). The sample is then held until the vacuum degree reaches 1-8×10⁻⁶. -5 Pa (preferably 2~6×10) -5 Pa, more preferably 3~5×10 Pa -5 After the pressure reaches 0.4~1Pa, high-purity argon gas is introduced into the chamber to maintain the working pressure at 0.4~1Pa (preferably 0.5~0.8Pa, more preferably 0.6~0.7Pa). The sample disk rotation speed is set to 5~40r / min (preferably 10~30r / min, more preferably 18~22r / min). After stabilization, the dual-target power supply is turned on, and the target cover and sample baffle are opened. Sputtering is performed for 10~80min (preferably 15~40min, more preferably 20~30min). The silver target power is 20~50W (preferably 30~50W, more preferably 35~40W), and the tellurium target power is 40~80W (preferably 50~70W, more preferably 55~65W).

7. The preparation method according to claim 6, characterized in that: Both the silver and tellurium targets are 4 inches in size and have a purity of 99.99%.

8. The preparation method according to claim 6, characterized in that: The specific preparation steps are as follows: (1) Substrate cleaning Substrates such as polyimide, quartz sheets or silicon wafers are ultrasonically cleaned sequentially with acetone, anhydrous ethanol and deionized water for 20-40 minutes, and then dried for later use. (2) Install the target material Clean the sputtering chamber of the multi-target magnetron sputtering instrument, sand the surfaces of the silver target and tellurium target to remove oxides and impurities, wipe them with alcohol and then install them into the sputtering chamber. Connect the silver target to the DC power supply and the tellurium target to the RF power supply. (3) Pre-sputtering To further eliminate impurities on the target surface and in the cavity, pre-sputtering is performed by placing a blank sample disk into the cavity; Subsequently, the infrared heating tube above the sputtering chamber heats the sample to 600-700°C at a rate of 10-15°C / min, while the actual temperature on the hollow sample disk is 400-500°C. The sample is then held at the target temperature for 0.5-4 hours (preferably 1-3 hours, more preferably 2-2.5 hours); until the vacuum degree reaches 1-5 × 10⁻⁵ °C. -5 After Pa, high-purity argon gas is introduced into the chamber to maintain the working pressure at 0.6~0.8 Pa. The sample disk rotation speed is set to 5~40 r / min (preferably 10~30 r / min, more preferably 18~22 r / min). After stabilization, the dual-target power supply is turned on, the target cover and sample baffle are opened, and sputtering is performed for a total of 20~40 min, with the silver target power at 35~45 W and the tellurium target power at 55~65 W. (4) Formal Splashing After the furnace cools to room temperature, the blank sample tray is removed and the formal sputtering begins. The cleaned substrate is placed in the hollow sample tray, fixed with screws, and then sent into the sputtering chamber. The sputtering operation is then carried out according to the pre-sputtering process and conditions in step (3).

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