Preparation method of room-temperature high-TCR perovskite manganite film

Abstract

The application discloses a preparation method of a room-temperature high-TCR perovskite manganese oxide film, and belongs to the field of non-refrigeration high-sensitivity infrared detection. 0.70 Ca 0.18 Sr 0.12 MnO3, and perovskite manganese oxide film is obtained through gel preparation, aging, spin coating, pyrolysis, pre-sintering and final sintering treatment; the film prepared by the application has high phase purity, high crystallinity, smooth surface, and a peak TCR temperature (T k ) at room temperature (293-303K) and a TCR of 10.82% / K; the film is smooth and has a short preparation period and low cost, and can be used as a detection material of a non-refrigeration high-sensitivity infrared thermal radiation detector.

Description

Technical Field

[0001] This invention relates to a method for preparing a room-temperature high TCR perovskite manganese oxide thin film, belonging to the field of uncooled high-sensitivity infrared detection. Background Technology

[0002] Perovskite manganese oxide La 1-x (Ca , Sr) x MnO3 possesses unique physical properties, particularly its metal-insulator phase transition. During this transition, the resistivity changes significantly. This characteristic has led to its high-temperature resistivity coefficient (TCR), making this material of considerable interest. The TCR value and the peak TCR temperature (T0) are important parameters. k TCR (Total Reflectance) is an important performance parameter of uncooled infrared thermal radiators. Generally speaking, the higher the TCR value, the more sensitive the device, and T... k A temperature range of room temperature (293-303K) is also more conducive to practical applications. For thermosensitive room-temperature infrared detectors, the more advanced materials include La. 0.7 Sr 0.3 MnO3 and La 1-x (Ca , Sr) x MnO3 film.

[0003] Among them, FTO / Glass-based La was prepared by spin coating. 0.7 Sr 0.3 MnO3 thin films are dense and exhibit good ferromagnetism. However, they suffer from the following drawbacks: unoriented growth and low crystal quality, which hinders the control and improvement of their electrical transport properties. The films were only pre-calcined at relatively low temperatures (350-620℃) and not subjected to final calcination at temperatures exceeding 1000℃. In general, La... 0.7 Sr 0.3 MnO3 has room temperature T k While it has advantages, the TCR is low; the high mismatch FTO / Glass substrate failed to provide good nucleation conditions, and the low temperature pre-calcination and lack of final calcination also failed to provide good growth conditions for the film.

[0004] Regarding the operating temperature range, La 1-x (Ca , Sr) x MnO3 is better than La 1-x Sr x MnO3 is closer to room temperature; in terms of device sensitivity, La 1-x (Ca , Sr) x MnO3 is better than La 1-x Sr xMnO3, α-Si or VO x More superior. Another method uses spin coating to prepare high purity silicon, mica, high purity quartz and sapphire-based La 1-x (Ca , Sr) x MnO3 film, the film has a high TCR value near room temperature. There is a final firing temperature of more than 1000℃ for the film, but the film is still only pre-fired at low temperature or not pre-fired. The appropriate pre-firing and high temperature final firing are not reasonably matched and used, which leads to the film not only deviating from room temperature, but also not high TCR. k In addition, the same problem is that the results obtained by the method are similar to the aforementioned FTO / Glass-based La 0.7 Sr 0.3 MnO3 film, the substrate is not suitable for La 1-x (Ca , Sr) x MnO3 film, the film has low film quality.

[0005] As a kind of strong correlation material, film components, crystallinity, crystalline orientation, crystalline quality, A-site disorder degree and internal stress and many other factors all affect the film electrical transport performance. Generally speaking, the final firing temperature, the final firing time, the sintering atmosphere, the pre-firing temperature and the pre-firing time and other preparation process parameters can directly affect the aforementioned many factors. This is from the crystallinity of the film, the internal stress and the oxygen vacancy to jointly control the performance of the film. Therefore, the film quality can be changed by selecting a suitable substrate and reasonably matching the pre-firing and final firing conditions, so as to obtain a La 1-x (Ca,Sr) x MnO3 film material. SUMMARY

[0006] The purpose of the present application is to provide a preparation method of a room temperature high TCR perovskite manganite film, to solve the problems of high cost, long cycle and small size of various physical and chemical deposition methods, and to provide a film with excellent performance for infrared detection;

[0007] The material of the present application is a perovskite manganite film, and its molecular formula is La 0.70 Ca 0.18 Sr 0.12 MnO3.

[0008] To solve the problems of the prior art, the present application is realized by the following technical scheme:

[0009] (1) According to the stoichiometric ratio, the nitrate, acetate or oxide of La, Ca, Sr and Mn is weighed, the raw materials are loaded into a reaction container, and a mixed liquid is poured; stirring for 6h at a certain temperature, and then aging at room temperature for a certain time to obtain La 0.70 Ca0.18 Sr 0.12 MnO3 precursor sol.

[0010] (2) LaAlO3 (00l) single crystal substrate is placed in acetone and ethanol respectively for ultrasonic oscillation for 5 minutes, washed with deionized water, and then baked in an oven, and then the substrate is naturally cooled.

[0011] (3) The precursor sol is coated on the surface of the treated LaAlO3 (00l) single crystal substrate by spin coating, the rotating speed is 4000 r / min, and the time is kept for 15 seconds, and then a wet film is obtained.

[0012] (4) The obtained wet film is placed in a drying oven for drying, and then transferred to a box furnace for heat preservation for a certain time.

[0013] (5) The dry film is rapidly heated to a certain temperature in a tube furnace and kept for 10 minutes.

[0014] (6) Steps (1)-(5) are cycled for 5 times, and then the sample is rapidly heated to 1300°C by a tube furnace and kept for 10 minutes, and finally a La 0.70 Ca 0.18 Sr 0.12 MnO3 finished film is obtained, and the selection of the final firing temperature is critical, if the temperature is not enough, the material crystallinity is low, and the performance is not good, if the temperature is too high, the material is significantly damaged by heat, and the overall performance is not good, and moreover, the temperature is too high, which significantly increases the material preparation cost and difficulty.

[0015] In the above scheme, when the cation source in step (1) is nitrate, the mixed liquid added in the subsequent step is a mixed liquid of ethylene glycol methyl ether and ethylene glycol, the volume ratio of the two is (4.5-5.7):1, and the stirring temperature is controlled between 10-30°C; In addition, an appropriate amount of citric acid needs to be added into the glue, and the molar ratio of citric acid to cation is (4-4.5):1; The aging time is 24h.

[0016] In the above scheme, when the cation source in step (1) is acetate, the mixed liquid added in the subsequent step is a mixed liquid of water and acetic acid, the volume ratio of water to acetic acid is 1:(1-2), and the stirring temperature is controlled between 80-100°C; The aging time is 0-12h.

[0017] In the above scheme, when the cation source in step (1) is metal oxide, the mixed liquid added in the subsequent step is an appropriate amount of nitric acid, ethylene glycol methyl ether and ethylene glycol, the amount of substance of nitrate added is 5-10 times of the amount of metal cation, and the volume ratio of ethylene glycol methyl ether to ethylene glycol is (4.5-5.5):1; In addition, an appropriate amount of citric acid needs to be added into the glue, and the molar ratio of citric acid to cation is (4-4.5):1; The aging time is 24h.

[0018] In the above scheme, the cation concentration in step (1) is 0.2-0.6 mol / L.

[0019] In the above scheme, the Mn(NO3)2.4H2O in step (1) is introduced by mixing nitric acid solution, so that the pH of the sol is less than 2; the manganese nitrate will undergo hydrolysis reaction with water molecules and disproportionation reaction with oxygen molecules in the solution to generate Mn(OH)2 or MnO(OH)2, both of which are insoluble in water and ethylene glycol methyl ether, and the colloidal stability cannot be achieved without mixing the manganese nitrate with the nitric acid solution.

[0020] In the above scheme, the temperature of the oven in step (2) is 350℃, and the time is 1-2h.

[0021] In the above scheme, the drying conditions in step (4) are: drying at 80℃ and 140℃ for 5 and 15min respectively, and the holding conditions are: keeping at 350℃ for 30-60min.

[0022] In the above scheme, the pre-sintering temperature in step (5) is 650-950℃.

[0023] In the above scheme, the heat treatment of step (5) and step (6) is carried out in air atmosphere.

[0024] The present application has the following innovative points and beneficial effects:

[0025] (1) The present application improves the source of metal cations, uses nitrate as the source of cations, and prepares the colloid with nitric acid, ethylene glycol methyl ether and ethylene glycol, which has high solubility, high stability, high oxidation resistance, high spin coating property, and simple preparation process; uses acetate as the source of cations, and prepares the colloid with water and acetic acid, which has high solubility, high wettability, excellent colloid coating effect, and low and safe non-toxic raw material cost; all the above methods produce thin films with high phase purity and no impurities; uses metal oxide as the source of cations, and prepares the colloid with nitric acid, ethylene glycol methyl ether and ethylene glycol, which can be stored properly for a long time without problems such as water absorption, oxidation and explosion, and can ensure the purity of the cations in the colloid; and the colloid also has high stability, high oxidation resistance, high spin coating property, high chemical uniformity and other advantages.

[0026] (2) The colloid prepared by the method of the present application has high dispersibility and good coating property, the metal cations can be uniformly spin-coated on the surface of the substrate, and the sample elements are still highly dispersed after subsequent process, so that the cations in the thin film can be uniformly distributed in the A site of the crystal lattice, the A site cation has low disorder degree, which effectively reduces the scattering effect of the mobile electrons and the electron spin of the A site cation on the e g In addition, the low disorder degree can also effectively reduce the scattering effect of the mobile electrons and the electron spin of the A site cation on the e gThe influence of the perambulatory electronic transition is eliminated; therefore, the preparation method of the high-dispersibility and stability colloid can effectively improve the film electric transport performance.

[0027] (3) The LaAlO3 (00l) single crystal is used as a substrate to grow the film, and the substrate cell parameter is The film cell parameter is The two have a low mismatch degree, about 2%, and belong to the same perovskite structure; the selection of the substrate can effectively reduce the difficulty of film nucleation and subsequent growth along the substrate; in addition, the La-O surface of the substrate surface is close in chemical composition to the film, has high affinity to the precursor liquid, is easy to spin-coat and fully perform, and the film nucleates during subsequent heat treatment.

[0028] (4) The (00l) crystal surface of the single crystal substrate is used as the film nucleation surface, and the two have the same crystal structure; therefore, the prepared film grows along the preferential orientation of the crystal surface; because the perovskite manganese oxide has anisotropy characteristics, the oriented growth of the film can make it exhibit a high TCR value (more than 10% / K) at room temperature (20-30℃).

[0029] (5) The film nucleation and preliminary growth are regulated by increasing the pre-sintering process and optimizing the pre-sintering temperature, which effectively enhances the film crystallinity and reduces various types of scattering in the film, thereby effectively improving the TCR

[0030] value of the film; at the same time, the internal stress of the film dominated by point defects, dislocations and stacking faults is regulated, the bond length and bond angle of the Mn-O-Mn bond are effectively controlled, and the double exchange effect and Jahn-Teller distortion of the film are regulated; these can effectively improve the TCR value of the film, and make the T k range be within the room temperature range.

[0031] (6) The combination of drying (at 80, 140℃), pyrolysis (at 350℃), pre-sintering (at 650-950℃) and final sintering (at 1300℃) provided by the application not only can obtain a film with a significant metal-insulator transition, but also can make the film surface smooth and flat, with a roughness less than 70nm; in addition, generally, ceramic materials need high-temperature and long-time sintering; however, because the film provided by the application has a low thickness, only 50nm, the application of long sintering time above 1000℃ will lead to a high micro-defect concentration and poor film quality, and a short sintering time is not enough to support the complete film organization growth and the improvement of crystallinity; both long and short final sintering times will enhance various types of electronic scattering in the material and reduce the semiconductor property of the material, thereby reducing the TCR of the film; the final sintering temperature of 10min is most beneficial to the growth of the film organization.

[0032] (7) The film preparation method provided by the application has simple process, short preparation time and low cost, and all processes do not require preparation atmosphere, temperature, humidity and other conditions, so that commercial production of the film is facilitated. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 SEM surface morphology of the film obtained in Example 1

[0034] Figure 2 EDS diagram of the film obtained in Example 1

[0035] Figure 3 Cross-sectional SEM diagram of the film obtained in Example 1

[0036] Figure 4 Atomic force microscope two-dimensional and three-dimensional diagrams of the film obtained in Example 1

[0037] Figure 5 ρ-T curve and TCR-T curve diagram of the film obtained in Example 1 DETAILED DESCRIPTION

[0038] The application will be further described in detail below in combination with specific embodiments, but the protection scope of the application is not limited to the content described.

[0039] Example 1

[0040] (1) La (NO3) 3·6H2O, Ca (NO3) 2·4H2O, Sr (NO3) 2, Mn (NO3) 2·4H2O and citric acid were weighed according to the stoichiometric ratio, poured into ethylene glycol methyl ether, and then an appropriate amount of ethylene glycol was added, and the volume ratio of ethylene glycol methyl ether to ethylene glycol was 17:3; stirring at room temperature for 6h, and then aging at room temperature for 24h to obtain La 0.70 Ca 0.18 Sr 0.12 MnO3 precursor sol.

[0041] (2) The LaAlO3 (00l) single crystal substrate was first placed in acetone and then in ethanol and ultrasonically vibrated for 5min, washed with deionized water, and then baked in an oven at a temperature of 350℃ for 1h, and then the substrate was naturally cooled.

[0042] (3) The precursor sol was coated on the surface of the treated LaAlO3 (00l) single crystal substrate by spin coating, the rotation speed was 4000r / min, and the time was kept for 15s, and then a wet film was obtained.

[0043] (4) The obtained wet film was placed in a drying oven and dried at 80℃ and 140℃ for 5 and 15min respectively, and then transferred to a box-type furnace and kept at 350℃ for 30min.

[0044] (5) The dry film is rapidly heated to 850°C using a tube furnace and kept for 10 min.

[0045] (6) Steps (1)-(5) are repeated 5 times, then the sample is rapidly heated to 1300°C using a tube furnace and kept for 10 min again, and finally the La 0.70 Ca 0.18 Sr 0.12 MnO3 finished film is obtained.

[0046] The perovskite manganese oxide film obtained in this example has a TCR value of 10.82% / K; T k reaches 302.03 K, which is in the room temperature range; the surface of the film is smooth and defect-free, and the average roughness is less than 19 nm.

[0047] Example 2

[0048] (1) La(C2H3O2)3·4H2O, Ca(C2H3O2)2, Sr(C2H3O2)2 and Mn(C2H3O2)2·4H2O are weighed according to the stoichiometric ratio, poured into a mixture of water and acetic acid, and stirred at 90°C for 5 h, and then aged at room temperature for 10 h to obtain La 0.70 Ca 0.18 Sr 0.12 MnO3 precursor sol.

[0049] (2) The LaAlO3(00l) single crystal substrate is first placed in acetone and then in ethanol and ultrasonically vibrated for 5 min, washed with deionized water, and then baked in an oven at a temperature of 350°C for 1 h, and then the substrate is naturally cooled.

[0050] (3) The precursor sol is coated on the surface of the treated LaAlO3(00l) single crystal substrate by spin coating at a speed of 4000 r / min for 15 s, and then a wet film is obtained.

[0051] (4) The obtained wet film is placed in a drying oven and dried at 80°C and 140°C for 5 and 15 min respectively, and then transferred to a box furnace and kept at 350°C for 30 min.

[0052] (5) The dry film is rapidly heated to 850°C using a tube furnace and kept for 10 min.

[0053] (6) Steps (1)-(5) are repeated 5 times, then the sample is rapidly heated to 1300°C using a tube furnace and kept for 10 min again, and finally the La 0.70 Ca 0.18 Sr 0.12 MnO3 finished film is obtained.

[0054] The sol obtained in this example has good spin-coating property, and the perovskite manganese oxide thin film has similar electric transport performance, crystallinity, film surface roughness and morphology to those of Example 1.

[0055] Example 3

[0056] (1) La2O3, CaO, SrO and MnO were weighed according to the stoichiometric ratio and put into a beaker, and then a proper amount of 15% nitric acid solution was slowly added dropwise while continuously stirring; then, concentrated nitric acid was added dropwise to make the pH value of the precursor solution equal to 1, and the precursor solution was concentrated to light red. Then, citric acid, ethylene glycol methyl ether and ethylene glycol were added, and the volume ratio of ethylene glycol methyl ether to ethylene glycol was 16:3; the mixture was magnetically stirred at room temperature for 6 h, and then aged at room temperature for 24 h to obtain a La 0.70 Ca 0.18 Sr 0.12 MnO3 precursor sol.

[0057] (2) The LaAlO3(00l) single crystal substrate was first placed in acetone and then in ethanol and ultrasonically vibrated for 5 min, washed with deionized water, and then baked in an oven at a temperature of 350°C for 1 h, and then the substrate was naturally cooled.

[0058] (3) The precursor sol was coated on the surface of the treated LaAlO3(00l) single crystal substrate by spin coating at a speed of 4000 r / min for 15 s to obtain a wet film.

[0059] (4) The wet film was placed in a drying oven and dried at 80°C and 140°C for 5 and 15 min, respectively, and then transferred to a box furnace and kept at 350°C for 30 min.

[0060] (5) The dry film was rapidly heated to 850°C by a tube furnace and kept for 10 min.

[0061] Steps (1)-(5) were repeated for 5 times, and then the sample was rapidly heated to 1300°C by the tube furnace and kept for 10 min, and finally the La 0.70 Ca 0.18 Sr 0.12 MnO3 finished thin film was obtained.

[0062] The perovskite manganese oxide thin film obtained in this example has similar electric transport performance, crystallinity, film surface roughness and morphology to those of Example 1.

[0063] Analysis of experimental results obtained in the examples described in Examples 1-3

[0064] Figure 1 and Figure 2 EDS diagram and SEM surface morphology of the thin film obtained in Example 1; through Figure 1EDS diagram of the film of Example 1 can be seen that La, Ca, Sr, Mn, O elements are uniformly distributed on the film surface, which proves that the film prepared by the preparation method provided by the application has uniform element distribution, which is beneficial to improve the electrical transport performance of the film; in addition, no characteristic peak of impurity element is obviously found in the EDS diagram; from the SEM morphology diagram of Figure 2 it can be seen that the film surface organization is flat, the growth is good, the size is uniform, the morphology is regular, the connectivity is good, no abnormal growth phenomenon is observed, and no second phase is observed.

[0065] Figure 3 the cross-sectional SEM diagram of the film of Example 1; from Figure 3 it can be seen that the film thickness is about 50 nm; it is well known that the thicker the film thickness, the greater the heat capacity, and the less obvious the thermal effect caused by the infrared light irradiating on the material surface, so that the thicker film has weaker detection ability to infrared light.

[0066] Figure 4 the atomic force microscope two-dimensional and three-dimensional diagrams of the film of Example 1; from Figure 4 it can be seen that the film grows regularly and is relatively dense, the surface is flat, and the root mean square roughness, average roughness and maximum roughness are 32.1, 18.2 and 297 nm respectively; the film has the lowest roughness and the smoothest surface, which can effectively reduce the scattering effect of the film on infrared light, thereby improving the infrared detection sensitivity of the device; the suitable pre-burning temperature can make the film nucleate on the substrate surface most ideally, and the crystal nucleus can grow more regularly, which becomes a cross-shaped organization under the macro, as shown in Figure 4 ; this can effectively reduce the defect concentration in the film and improve the crystallinity of the film, reduce the electron-electron, electron-phonon and electron-magnetic scattering in the material, thereby improving the TCR value of the film.

[0067] Figure 5 the ρ-T curve and TCR-T curve diagram of the film of Example 1; from Figure 5 it can be seen that the maximum resistivity of the film is less than 3×10 -3 Ω·cm, which is the effect brought by the improvement of crystallinity; at the same time, from the TCR-T curve diagram, the TCR of the film is 10.82% / K, and T k =302.03K; the increase of TCR of the film is mainly caused by the reduction of electron-electron scattering, electron-phonon scattering and electron-magnetic scattering, and this improvement is contributed by the increase of crystallinity of the film; and kThe increase of about 3K is caused by the increase of internal stress in the film: the increase of internal stress caused by the increase of pre-sintering temperature changes the bond length and bond angle of Mn-O-Mn, and then the wave function overlap of Mn 3d electron and O 2p electron and the spin angle are increased, and then the resistivity curve moves to the high temperature direction; all the above factors make the pre-sintering at 850℃ effectively improve the electrical transport properties of the film.

Claims

1. A room temperature high TCR A method for producing a perovskite manganite thin film, characterized by, Specifically comprising the following steps: (1) Take the acetate salts of La, Ca, Sr and Mn according to the stoichiometric ratio, put the raw materials into a reaction container, pour a mixed solution of water and acetic acid into the reaction container according to the volume ratio of water to acetic acid being 1:(1-2), stir at 80-100℃ for 6h, then age at room temperature for 0-12h to obtain a La0.70Ca0.18Sr0.12MnO3 precursor sol with a cation concentration of 0.2-0.6 mol / L; (2) Put the LaAlO3(001) single crystal substrate into acetone and ethanol respectively for ultrasonic oscillation for 5 min, wash with deionized water, and then bake in an oven, and then naturally cool the substrate; (3) Apply the precursor sol to the surface of the treated LaAlO3(001) single crystal substrate by spin coating at a speed of 4000r / min for 15s to obtain a wet film; (4) Dry the wet film in a drying oven, and then transfer it to a box furnace for a certain period of time; (5) Rapidly heat the dry film to a certain temperature in a tube furnace and keep for 10 min; (6) Repeat steps (1)-(5) for 5 times, and then rapidly heat the sample to 1300℃ in a tube furnace and keep for 10 min, to finally obtain a La0.70Ca0.18Sr0.12MnO3 finished film; The temperature of the oven in step (2) is 350℃, and the time is 1-2h; The drying conditions in step (4) are: drying at 80℃ and 140℃ for 5 and 15 min respectively, and the holding conditions are: keeping at 350℃ for 30-60 min; The pre-burning temperature in step (5) is 850℃.

2. The room temperature high TCR A method for preparing a perovskite manganite thin film, characterized by: The heat treatment of step (5) and step (6) is carried out in air atmosphere.

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