Flexible altp thin film preparation method and transfer method

Abstract

The application relates to a flexible ALTP thin film preparation method and a transfer method, and relates to the technical field of electronic materials and devices.The flexible ALTP thin film preparation method comprises the following steps: (1) preparing a transition layer thin film on a single crystal substrate; (2) preparing an ALTP functional thin film in situ on the transition layer thin film to form a substrate / transition layer / ALTP functional thin film multilayer epitaxial structure; (3) attaching a flexible supporting layer to the surface of the ALTP functional thin film obtained in the step (2), then dissolving the transition layer, releasing the ALTP functional thin film from the substrate and transferring the ALTP functional thin film to the flexible supporting layer to obtain a flexible ALTP thin film.The application has the characteristics of large-area uniformity, high deposition rate, good expansibility and the like, and is more beneficial to industrialized production.

Description

Technical Field

[0001] This invention relates to the field of electronic materials and devices. Background Technology

[0002] Atomic layer thermopile (ALTP) thin films are heat flow sensitive materials based on the transverse thermoelectric effect. When a temperature gradient exists between the upper and lower surfaces of the film, a thermoelectric potential output is generated perpendicular to the temperature gradient direction due to the anisotropy of carrier transport in the material. Unlike traditional thermopile structures that require multiple layers, ALTP thin films can achieve heat flow detection with only a single layer of material. They have advantages such as simple structure, fast response speed (down to nanosecond levels), high sensitivity, and compatibility with semiconductor processes. They show broad application prospects in transient heat flow measurement, laser power detection, hypersonic wind tunnel testing, and engine blade heat flow monitoring.

[0003] The thermoelectric properties of ALTP thin films are closely related to their crystal orientation. Studies have shown that significant lateral thermoelectric effects can only be generated when the film has a highly textured tilted orientation. Specifically, the c-axis of the functional thin film needs to maintain a certain tilt angle relative to the substrate normal direction, and the film needs to have a high degree of biaxial texture, i.e., the in-plane and out-of-plane orientations are highly consistent. This special crystal structure makes the film anisotropic. When heat is conducted along the thickness direction, due to the anisotropy of the Seebeck coefficient, a lateral thermoelectric potential is generated in the film plane. Currently, the main method to obtain highly textured ALTP thin films is epitaxial growth on tilted single-crystal substrates, using the lattice template effect of the substrate to induce the orientation growth of the film. Commonly used substrate materials include tilted LaAlO3, SrTiO3, MgO, etc. By selecting a substrate that matches the lattice of the functional thin film, epitaxial films with high crystal quality and consistent orientation can be obtained, exhibiting excellent texture.

[0004] However, the fabrication of high-quality epitaxial ALTP thin films typically relies on rigid single-crystal substrates, which severely limits their application in flexible electronics, wearable devices, and curved integrated systems. To address this issue, researchers have developed methods for directly fabricating template layers on flexible amorphous substrates, attempting to obtain oriented ALTP thin films on flexible substrates. Chinese patent CN111334760A discloses a method for fabricating atomic-layer thermopile thin films on polycrystalline or amorphous substrates. This method uses ion beam assisted deposition (IBAD) to prepare a MgO template layer on a Hastelloy metal substrate, and then epitaxially grows a YBCO thin film on this layer, obtaining an ALTP thin film with a c-axis tilted structure. This method overcomes the limitations of single-crystal substrates, enabling thin film fabrication on flexible metal substrates. However, due to the amorphous nature of flexible substrates, the crystallinity of the template layer prepared by the IBAD method still differs from that of single-crystal substrates. Its X-ray rocking curve full width at half maximum (FWHM) is typically on the order of 4–10°, much larger than the 0.1–1° FWHM of epitaxial films on single-crystal substrates. Since the texture degree of the template layer directly affects the epitaxial quality of the upper functional thin film, the texture degree of ALTP films grown on this type of template layer is difficult to achieve the level of epitaxial growth on single-crystal substrates. In contrast, single-crystal substrates have atomically flat surfaces and highly ordered lattice periodic arrangements, which can provide excellent template effects for functional thin films, inducing them to achieve highly consistent orientation growth and obtain epitaxial films with excellent biaxial texture. Therefore, how to make ALTP films both flexible and highly textured has become a key technical challenge that needs to be solved. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing and transferring highly textured flexible atomic layer thermopile thin films, characterized by local high uniformity and high texture.

[0006] The technical solution adopted by the present invention to solve the aforementioned technical problem is a method for preparing flexible ALTP thin films, comprising the following steps: (1) Prepare a transition layer thin film on a single crystal substrate; (2) An ALTP functional film is prepared in situ on the transition layer film to form a substrate / transition layer / ALTP functional film multilayer epitaxial structure; (3) The flexible support layer is attached to the surface of the ALTP functional film obtained in step (2), and then the transition layer is dissolved to release the ALTP functional film from the substrate and transfer it to the flexible support layer to obtain a flexible ALTP film.

[0007] Furthermore, in step (1), a transition layer thin film is prepared on a tilted single-crystal substrate using metal-organic chemical vapor deposition.

[0008] In step (1), the thickness of the transition layer film is 100~400 nm; in step (2), the thickness of the ALTP functional film is 50 nm~1 µm.

[0009] The transition layer material is MgO, Sr3Al2O6, (Ca,Sr,Ba)3Al2O6, Sr4Al2O7, (Ca,Sr,Ba)4Al2O7, SrO or BaO, and the flexible support layer material is PDMS, PI or PMMA.

[0010] The single-crystal substrate material is LaAlO3, SrTiO3 or Al2O3 substrate, and the substrate tilt angle is 5~20°.

[0011] The material of the ALTP functional film is YBCO, LCMO or LSCO.

[0012] This invention also provides a method for transferring flexible ALTP thin films, comprising the following steps: (1) Prepare a transition layer thin film on a single crystal substrate; (2) An ALTP functional film is prepared in situ on the transition layer film to form a substrate / transition layer / ALTP functional film multilayer epitaxial structure; (3) The flexible support layer is attached to the surface of the ALTP functional film obtained in step (2), and then the transition layer is dissolved to release the ALTP functional film from the substrate and transfer it to the flexible support layer to obtain a flexible ALTP film. (4) Transfer the flexible support layer carrying the ALTP functional film to the target application location to obtain a highly textured flexible ALTP film.

[0013] In step (1), a transition layer film is prepared on a tilted single crystal substrate using metal-organic chemical vapor deposition. The thickness of the transition layer film is 100~400 nm, and the transition layer material is MgO, Sr3Al2O6, (Ca,Sr,Ba)3Al2O6, Sr4Al2O7, (Ca,Sr,Ba)4Al2O7, SrO, or BaO. In step (2), the thickness of the ALTP functional film is 50 nm~1 µm, and the material of the ALTP functional film is YBCO, LCMO, or LSCO. The material of the flexible support layer is PDMS, PI, or PMMA.

[0014] The ranges indicated by the "~" symbol in this invention include endpoint values, for example, "50 nm~1µm" includes 50 nm and 1 µm.

[0015] The present invention has the following advantages: This invention uses metal-organic chemical vapor deposition (MOCVD) to prepare transition layers and ALTP layers on single-crystal substrates. Compared with most other methods for preparing functional thin films, this method has the characteristics of large-area uniformity, high deposition rate, and good scalability, which is more conducive to industrial production. This invention does not require disruption of the vacuum environment during the preparation of a single-crystal substrate / transition layer / ALTP layer composite structure, thus avoiding interface contamination and facilitating the formation of high-quality, highly textured epitaxial heterostructures. The flexible ALTP film obtained by this invention has a highly textured characteristic similar to that of ALTP films epitaxially prepared on a single crystal substrate.

[0016] In summary, the method used in this invention can achieve the transfer of highly textured atomic layer thermopile thin films, thereby obtaining ALTP thin films with sensitivity properties close to those of epitaxially grown ALTP thin films on single crystal substrates, providing a new technical path for the large-scale preparation of high-performance flexible ALTP thin films. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the single-crystal substrate / transition layer / ALTP layer composite structure of the present invention; Figure 2 This is a flow chart of the preparation and transfer process of the present invention; Figure 3 The XRD characterization diagram of the sample in this invention is shown below. Figure 4 Example sample of the present invention ω Scan curve (left) and φ A graph of the scan curve (right); Figure 5 This is a transient thermal flow test diagram of an example sample of the present invention; Detailed Implementation

[0018] This invention employs metal-organic chemical vapor deposition (MOCVD) technology to prepare multiple transition layers on a tilted single-crystal substrate and grow atomic layer thermopile (ALTP) functional thin films in situ. Flexible transfer of the thin film is achieved by dissolving the transition layers, and finally the obtained highly textured, fast-response, and high-linearity ALTP thin film is transferred to the surface of the test scene.

[0019] Specifically, the following steps are included: (1) Select a tilted single crystal substrate of LaAlO3 (LAO) (001), or other tilted orientation single crystal substrates that can match the lattice of atomic layer thermopile functional thin films, such as SrTiO3 (STO) substrates or Al2O3 substrates. Preferably, the substrate tilt angle is 5~20°.

[0020] (2) A single-crystal transition layer is prepared on the tilted single-crystal substrate of step (1) using the MOCVD method. The transition layer material must be capable of highly textured epitaxial growth on the single-crystal substrate selected in step (1), such as MgO, Sr3Al2O6 (SAO). C ), (Ca,Sr,Ba)3Al2O6, Sr4Al2O7 (SAO T One or more transition layer materials selected from (Ca,Sr,Ba)4Al2O7, SrO, and BaO.

[0021] (3) An ALTP-sensitive thin film is prepared in situ on the single-crystal transition layer of step (2) to obtain a single-crystal substrate / transition layer / ALTP layer composite structure. Preferably, the ALTP functional thin film is YBa2Cu3O. 7-δ (YBCO), La 1-x Ca x MnO3 (LCMO), La 1-x Sr x CoO3 (LSCO) and other heat flow sensitive films.

[0022] LCMO and LSCO are both well-known materials, and the value of x can be determined according to the requirements. This is clear and understandable to ordinary technical personnel.

[0023] (4) The flexible support layer is attached to the single crystal substrate / transition layer / ALTP layer composite structure obtained in step (3), and then the transition layer is dissolved in a solution to obtain a flexible support layer carrying an ALTP film.

[0024] Preferably, the thickness of the transition layer is 100~400 nm. If the transition layer is too thin, its dissolution time will increase, which is not conducive to the release of the ALTP functional film; if the transition layer is too thick, the crystal quality of the epitaxially grown ALTP functional layer will be poor, which will lead to a decrease in performance. Example

[0025] Using LaAlO3 (LAO) with a 12° oblique cut (001) crystal plane as a single crystal substrate, Sr3Al2O6 (SAO) C YBa2Cu3O serves as a transition layer. 7-δ (YBCO) is an atomic layer thermopile thin film material used for the flexible transfer fabrication of highly textured atomic layer thermopile thin films.

[0026] Step 1: Prepare Sr3Al2O6 (SAO) on a slanted LaAlO3 single crystal substrate using metal-organic chemical vapor deposition (MOCVD). C Transition layer.

[0027] Step 2: YBCO thin films were prepared in situ on the SAO transition layer using metal-organic chemical vapor deposition (MOCVD) to obtain... Figure 1 The LAO substrate / SAO transition layer / YBCO composite structure is shown. Step 3: Lay a flexible polydimethylsiloxane (PDMS) support layer and dissolve the transition layer to obtain a PDMS support layer composite structure with a YBCO flexible film attached. Figure 2 This invention illustrates one bonding method in which the ALTP film is directly bonded to the surface of the target component with its face down. After being fixed by adhesion or van der Waals forces, the PDMS support layer is then removed. When using this bonding and fixing method, adhesive can be applied to the four corner edges of the ALTP film to assist in fixing the film to the surface of the target component.

[0028] Alternatively, depending on the actual application requirements, the composite structure can be flipped so that the composite structure is directly bonded with the PDMS support layer facing the surface of the target component, forming a stacked structure of target component surface - PDMS support layer - ALTP film. The double-layer composite film formed by the support layer and the ALTP film can be directly bonded to the surface of the workpiece and then fixed by heating with van der Waals forces, or it can be bonded by applying adhesive to the four corners of the double-layer composite film.

[0029] Step 4: Fabricate electrodes on the YBCO flexible thin film.

[0030] The process flow for steps 1-3 is as follows: Figure 2 As shown.

[0031] Detailed process of step 1: First, the precursor solution was prepared using Sr(TMHD)2 and Al(TMHD)3 as solutes and tetrahydrofuran as solvent. The concentration of Sr organic source was 0.09 mmol / 30 ml and the concentration of Al organic source was 0.06 mmol / 30 ml. Then, the solution was stirred with a magnetic stirrer for half an hour before use.

[0032] Then, the cleaned LaAlO3 (LAO) single crystal substrate was placed into the MOCVD deposition chamber, the chamber was evacuated to below 20 Pa, the substrate surface was heated to 830 ℃, and the flow rates of oxygen (O2), argon (Ar), and nitrous oxide (N2O) were set to 1.63:1.27:0.81 and introduced into the deposition chamber. The peristaltic pump was adjusted to a speed of 37.5 ml / h to pump the pre-prepared precursor solution into the chamber, and finally a SAO transition layer with a thickness of 200 nm was deposited.

[0033] Detailed process of step 2: First, the precursor solutions were prepared using Y(TMHD)3, Ba(TMHD)2(phen)2, and Cu(TMHD)2 as solutes and tetrahydrofuran as solvent. The concentrations of the Y organic source were 0.6036 mmol / 15 ml, the Ba organic source was 2.1551 mmol / 15 ml, and the Cu organic source was 2.6128 mmol / 15 ml. The solutions were then stirred with a magnetic stirrer for half an hour and filtered for later use to prevent undissolved organic source solutes from clogging the MOCVD inlet pipe.

[0034] After the SAO precursor solution has been fed into the cavity, without disrupting the vacuum environment, the substrate temperature is heated to 840 °C. While maintaining the gas flow rate and peristaltic pump speed, the prepared YBCO precursor solution is introduced into the cavity, and a YBCO film with a thickness of 150 nm is deposited, thus obtaining the LAO / SAO / YBCO composite structure.

[0035] Detailed process of step 3: First, a flexible polydimethylsiloxane (PDMS) support layer is smoothly bonded to the surface of the YBCO functional film of the multilayer epitaxial structure obtained in step 2, ensuring no bubbles or wrinkles. Then, the entire structure is slowly immersed in deionized water at room temperature. Due to the good water solubility of the SAO transition layer, water gradually penetrates from the edges to the interior, causing the SAO layer to dissolve layer by layer. After the SAO transition layer has completely dissolved (approximately several hours), the YBCO functional film adheres to the PDMS support layer and naturally peels off, yielding a directly transferable flexible YBCO film that can be transferred to the surface of the target component in subsequent processes.

[0036] Detailed process of step 4: A flexible PDMS support layer with an attached YBCO film is smoothly fixed onto the sample holder surface, ensuring the film is wrinkle-free. A precision mask is placed above the film to define the electrode pattern, with an electrode width of 2.5 mm and a spacing of 5 mm between the two electrodes. The sample holder is then placed into the magnetron sputtering chamber, the chamber door is closed, and vacuuming begins. The process continues until the background vacuum reaches 5 × 10⁻⁻⁻⁻⁶. 4 After the pressure drops below Pa, high-purity argon (Ar) is introduced as the sputtering gas, and the working pressure is adjusted to 0.5–1.0 Pa. A high-purity Ag target with a purity of 99.99% is selected, and a direct current (DC) sputtering mode is used, with the sputtering power set to 30–50 W. Before formal deposition, the sample baffle is closed, and the Ag target is pre-sputtered for 5–10 minutes to remove the oxide layer or contaminants on the target surface. Then, the baffle is opened to begin deposition, controlling the deposition rate between 0.2–0.5 nm / s. After deposition, atmospheric air is slowly introduced into the chamber, the sample is removed, and the mask is removed, resulting in an Ag electrode with a clear pattern and neat edges.

[0037] Electrodes were connected to the oscilloscope (model) of the data acquisition unit via copper wires for X-ray diffraction (XRD) characterization and thermal flux transient response testing. XRD characterization was performed using Cu... Kα Radiation source ( λ = 1.54 Å), operating at 30 kV and 15 mA, the crystal structure of the thin film was analyzed. The thermal flux transient response was measured using a single-pulse excimer laser (wavelength 248 nm, pulse width 28 ns) as the excitation source. The laser beam was incident perpendicularly on the film surface, generating a temperature gradient between the upper and lower surfaces. The voltage response signal was recorded using a data acquisition unit (such as an oscilloscope) connected to the electrodes, and the response time was calculated based on the thermoelectric effect principle of atomic layer thermopile (ALTP).

[0038] The XRD test results of the YBCO thin films prepared above are as follows: Figure 3 As shown: XRD tests were performed on the YBCO thin film before and after transfer. Comparison of the XRD patterns of YBCO before and after transfer revealed that only the characteristic diffraction peaks of YBCO were retained in the XRD pattern after exfoliation, while all characteristic peaks of the SAO transition layer and LAO substrate disappeared completely. The diffraction peak position of YBCO (00l) did not shift after transfer, indicating that its basic crystal structure was maintained.

[0039] The above-prepared YBCO thin film was subjected to... ω Scan and φ Scanning Figure 4 As shown, the YBCO thin film Δω Scan curve (left) and Δφ The values ​​are 0.549 and 1.295, respectively, which significantly improves the biaxial texture compared to YBCO films prepared on amorphous substrates.

[0040] The transient thermal flow test results of the transferred flexible YBCO thin film are as follows: Figure 5 As shown: The response time of the transferred YBCO flexible film is 76 ns, which is basically close to the response time of the YBCO film directly epitaxially prepared on the LAO single crystal substrate.

[0041] In summary, the transfer preparation method of the present invention is applicable to the flexible transfer preparation of highly textured ALTP heat flow sensitive films, solving the problem of how to make ALTP films both flexible and highly textured, and providing a new technical path for the large-scale preparation and application of high-performance flexible heat flow sensitive materials.

Claims

1. A method for preparing flexible ALTP thin films, characterized in that, Includes the following steps: (1) Prepare a transition layer thin film on a single crystal substrate; (2) An ALTP functional film is prepared in situ on the transition layer film to form a substrate / transition layer / ALTP functional film multilayer epitaxial structure; (3) The flexible support layer is attached to the surface of the ALTP functional film obtained in step (2), and then the transition layer is dissolved to release the ALTP functional film from the substrate and transfer it to the flexible support layer to obtain a flexible ALTP film.

2. The method for preparing flexible ALTP thin films as described in claim 1, characterized in that, In step (1), a transition layer thin film is prepared on a tilted single-crystal substrate using metal-organic chemical vapor deposition.

3. The method for preparing flexible ALTP thin films as described in claim 1, characterized in that, In step (1), the thickness of the transition layer film is 100~400 nm; in step (2), the thickness of the ALTP functional film is 50 nm~1 µm.

4. The method for preparing flexible ALTP thin films as described in claim 1, characterized in that, The transition layer material is MgO, Sr3Al2O6, (Ca,Sr,Ba)3Al2O6, Sr4Al2O7, (Ca,Sr,Ba)4Al2O7, SrO or BaO, and the flexible support layer material is PDMS, PI or PMMA.

5. The method for preparing flexible ALTP thin films as described in claim 1, characterized in that, The single-crystal substrate material is LaAlO3, SrTiO3 or Al2O3 substrate, and the substrate tilt angle is 5~20°.

6. The method for preparing flexible ALTP thin films as described in claim 1, characterized in that, The material of the ALTP functional film is YBCO, LCMO or LSCO.

7. A method for transferring flexible ALTP thin films, characterized in that, Includes the following steps: (1) Prepare a transition layer thin film on a single crystal substrate; (2) An ALTP functional film is prepared in situ on the transition layer film to form a substrate / transition layer / ALTP functional film multilayer epitaxial structure; (3) The flexible support layer is attached to the surface of the ALTP functional film obtained in step (2), and then the transition layer is dissolved to release the ALTP functional film from the substrate and transfer it to the flexible support layer to obtain a flexible ALTP film. (4) Transfer the flexible support layer carrying the ALTP functional film to the target application location to obtain a highly textured flexible ALTP film.

8. The flexible ALTP thin film transfer method as described in claim 6, characterized in that, In step (1), a transition layer film is prepared on a tilted single crystal substrate using metal-organic chemical vapor deposition. The thickness of the transition layer film is 100~400 nm, and the transition layer material is MgO, Sr3Al2O6, (Ca,Sr,Ba)3Al2O6, Sr4Al2O7, (Ca,Sr,Ba)4Al2O7, SrO, or BaO. In step (2), the thickness of the ALTP functional film is 50 nm~1 µm, and the material of the ALTP functional film is YBCO, LCMO, or LSCO. The material of the flexible support layer is PDMS, PI, or PMMA.

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