NTC thermosensitive film, preparation method and application thereof

Abstract

This invention provides an NTC thermistor thin film, its preparation method, and its application. The preparation method includes the following steps: MnO2, Co3O4, and Ni2O3 are weighed according to a stoichiometric ratio, and subjected to a first ball milling, pre-calcination, second ball milling, granulation, sintering, and backplate welding to obtain a target material; the substrate is sequentially ultrasonically cleaned with anhydrous ethanol, pure water, and a mixture of pure water and anhydrous ethanol, and then dried with nitrogen; a silver paste electrode is prepared on the cleaned substrate surface using a screen printing process; the target material and the treated substrate are placed in a magnetron sputtering deposition apparatus, using argon as the working gas and a sputtering power of 170-190W, to sputter and deposit a thin film on the substrate; the deposited film is annealed; and the annealed film is aged to obtain the NTC thermistor thin film. The NTC thermistor thin film prepared by this invention exhibits excellent crystallinity, excellent resistance characteristics, stable thermistor sensitivity, and outstanding long-term aging stability.

Description

Technical Field

[0001] This invention relates to the field of functional ceramic thin film materials and microelectronic devices, and particularly to an NTC thermistor thin film, its preparation method and application. Background Technology

[0002] As a key electronic component, NTC thermistors are widely used in temperature measurement, industrial control, and thermal protection of electronic equipment. Among them, Mn-Co-Ni-O thin films have become the core material system for integrated NTC thermistors in the medium and low temperature range (-50℃ to 300℃) due to their excellent thermistor sensitivity, good chemical stability, and moderate B constant.

[0003] In existing technologies, the preparation methods of Mn-Co-Ni-O NTC thermistor films mainly include radio frequency magnetron sputtering, chemical solution deposition, and electron beam deposition. Among them, radio frequency magnetron sputtering has become the mainstream preparation technology due to its advantages such as good film uniformity, strong composition controllability, and compatibility with silicon-based processes.

[0004] However, existing technologies still have the following key shortcomings: (1) Sputtering power is the core parameter of the deposition stage, which directly determines the sputtering yield of the target material, the kinetic energy of the deposited particles and the microstructure of the thin film. However, the existing research has not clarified the synergistic regulation law of its effect on the crystallinity, density and long-term stability of the thin film, resulting in poor crystal quality, uneven grain distribution, high room temperature resistance (usually >6MΩ), and resistivity >700Ω·cm, which makes it difficult to meet the low power consumption requirements of integrated devices. (2) During high-temperature service or long-term aging, existing NTC thermistor films are prone to runaway grain boundary defects and disordered migration of oxygen vacancies, resulting in a resistance aging rate >2%, a drastic fluctuation in the rate of change of B value (peak value >2.5%), poor thermistor stability, and seriously affecting the service life and measurement accuracy of the device. (3) In the existing technology, the process parameters (such as sputtering power, annealing temperature, and working pressure) have not formed a quantitative combination scheme, resulting in large performance dispersion of different batches of NTC thermistor films, which makes it difficult to meet the needs of mass production.

[0005] In summary, existing NTC thermistor films cannot simultaneously achieve a balance of low resistance, high crystallinity, and high aging stability, and their poor process repeatability limits their application in high-precision integrated devices. Therefore, developing a process-controllable, performance-balanced NTC thermistor film preparation technology that combines low resistance, high crystallinity, and excellent long-term stability has become an urgent technical problem to be solved in this field. Summary of the Invention

[0006] The main objective of this invention is to provide an NTC thermistor film, its preparation method, and its application, aiming to solve the problems of poor performance uniformity, insufficient long-term stability, and poor process repeatability of current NTC thermistor films.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing an NTC thermistor thin film, comprising the following steps: (1) Weigh out MnO2, Co3O4, and Ni2O3 with a purity ≥ 99.99% according to the stoichiometric ratio n(MnO2): n(Co3O4): n(Ni2O3) = 1.56: 0.32: 0.24. Then, process them by ball milling, pre-calcination, ball milling, granulation, sintering, and backplate welding to obtain MnO2. 1.56 Co 0.96 Ni 0.48 O4 ceramic target material; (2) The substrate was ultrasonically cleaned sequentially with anhydrous ethanol, pure water, and a mixture of pure water and anhydrous ethanol, and then dried with nitrogen gas. (3) Silver paste electrodes are prepared on the cleaned substrate surface by screen printing process; (4) Mn 1.56 Co 0.96 Ni 0.48 The O4 ceramic target and the treated substrate are loaded into a magnetron sputtering coating equipment, with argon as the working gas, a sputtering power of 170~190W, and a sputtering time of 70~90min, to sputter and deposit a thin film on the substrate. (5) The deposited film is placed in a box-type high-temperature resistance sintering furnace and annealed in an air atmosphere. (6) The annealed film is placed in a high and low temperature humidity alternating chamber for aging treatment to obtain an NTC thermistor film.

[0008] The inventors discovered that by precisely controlling the stoichiometry of the target material components, optimizing the sputtering power range, and the annealing process, a single spinel-type solid solution phase can be formed without the formation of other impurity phases, thereby improving the density and crystallinity of the NTC thermistor film. The single spinel-type solid solution phase ensures the stability and consistency of the thermistor properties and also facilitates the orderly distribution of transition metal ions (Mn, Co, Ni) in the octahedral and tetrahedral interstices, optimizing electron transition efficiency and thus reducing the resistivity of the material. Furthermore, the spinel-type solid solution phase exhibits strong structural stability, which can suppress the runaway of grain boundary defects and the disordered migration of oxygen vacancies during high-temperature aging, improving long-term aging stability.

[0009] Preferably, in step (1), the ball-to-material ratio of the first ball mill is 10:1, the rotation speed is 230 rpm, the ball milling time is 24 h, and the dispersion medium is pure water; the ball-to-material ratio of the second ball mill is 10:1, the rotation speed is 230 rpm, the ball milling time is 72 h, and the dispersion medium is pure water.

[0010] Preferably, in step (1), the specific process of pre-firing is as follows: under an air atmosphere, the temperature is increased from room temperature to 350°C at 2.75°C / min, held for 2.5h, then increased to 1000°C at 2.7°C / min, held for 5h, and then cooled down with the furnace.

[0011] Preferably, in step (1), the specific sintering process is as follows: under an air atmosphere, the temperature is raised from 25°C to 100°C within 0.6 hours, held for 3 hours, then raised to 130°C within 1 hour, held for 3 hours, then raised to 350°C within 2 hours, held for 2.5 hours, then raised to 950°C within 3 hours, held for 5 hours, then raised to 1180°C within 5 hours, held for 20 hours, and finally cooled to room temperature.

[0012] Preferably, in step (2), the substrate is ultrasonically cleaned for 15 minutes each with anhydrous ethanol, pure water, and a mixture of pure water and anhydrous ethanol, with a power of 50 kHz, and then dried with nitrogen gas at a pressure of 0.3 MPa.

[0013] Preferably, in step (2), an alumina substrate is selected for electrical performance testing, or a Si(100) substrate is selected for structural characterization.

[0014] Preferably, in step (3), the specific parameters of the screen printing process are as follows: the mesh number of the screen is 300 mesh, the screen tension is 23±1N / cm, the tension difference is ≤1N / cm; the squeegee pressure is 0.1MPa, the electrode spacing is 0.12cm, the drying temperature is 80℃, and the drying time is 30min.

[0015] Preferably, in step (4), the sputtering power is 180W and the sputtering time is 80min.

[0016] Preferably, in step (4), the working gas pressure of the magnetron sputtering coating equipment is 0.4~0.6 Pa, the substrate temperature is 140~160℃, the target-substrate distance is 55~65 mm, the argon flow rate is 45~55 sccm, and the furnace pressure before sputtering is <1.5×10 −3 More preferably, the working gas pressure of the magnetron sputtering coating equipment is 0.5 Pa, the substrate temperature is 150 °C, the target-substrate distance is 60 mm, and the argon flow rate is 50 sccm.

[0017] Preferably, in step (5), the annealing temperature is 680~720℃, the holding time is 0.8~1.2h, the heating rate is 6~8℃ / min, and the cooling rate is 0.8~1.2℃ / min. More preferably, the annealing temperature is 700℃, the holding time is 1h, the heating rate is 7℃ / min, and the cooling rate is 1℃ / min.

[0018] Preferably, in step (6), the aging treatment specifically involves holding the film at 150°C for 240 hours. The NTC thermistor film of the present invention is used in integrated NTC thermistor devices. These devices have industrial-grade requirements for long-term stability. As a preparation step, the aging treatment can allow the grain boundaries and oxygen vacancies of the NTC thermistor film to reach a stable state in advance, avoiding performance drift due to structural relaxation during actual service. This is a necessary process guarantee for the NTC thermistor film to adapt to industrial applications.

[0019] Secondly, this invention proposes an NTC thermistor film prepared by the aforementioned method.

[0020] Thirdly, this invention proposes the application of the aforementioned NTC thermistor film in integrated NTC thermistor devices.

[0021] Compared to existing technologies, this invention has at least the following beneficial effects: First, by precisely controlling the stoichiometric ratio of the target material, this invention ensures that the NTC thermistor film is a single spinel-type solid solution phase, with no impurity phases generated. Second, by limiting the RF magnetron sputtering power to 170~190W and coordinating parameters such as working pressure and substrate temperature, this invention achieves synergistic optimization of the crystallinity and density of the NTC thermistor film. Finally, by employing a suitable annealing temperature and slow heating and cooling, this invention alleviates the internal stress of the NTC thermistor film, improving lattice order and structural stability. In summary, by optimizing the combination of core parameters such as sputtering and annealing processes, this invention prepares an NTC thermistor film with high crystallinity and a dense and uniform microstructure, reducing room temperature resistance and resistivity, improving the long-term aging stability of the film, and achieving a performance breakthrough for NTC thermistor films. In other words, the NTC thermistor film prepared by this invention exhibits excellent crystallinity, excellent resistance characteristics, stable thermistor sensitivity, and outstanding long-term aging stability. Furthermore, all process parameters of this invention are quantified into clearly defined ranges, ensuring strong process repeatability and consistent performance across different batches of NTC thermistor films. In addition, the NTC thermistor films prepared by this invention can be directly used in the fabrication of microelectronic integrated devices requiring high consistency in thermistor properties and long-term stability. This allows for a wide range of applications, including integrated temperature sensors, temperature compensation modules for electronic devices, and surge current suppression devices in power supply circuits, filling a gap in existing technologies for high-performance integrated NTC devices. Attached Figure Description

[0022] Figure 1 This is a flowchart of the NTC thermistor film preparation process in this invention; Figure 2 Mn in this invention 1.56 Co 0.96 Ni 0.48 Flowchart of the preparation process of O4 ceramic target material; Figure 3 Mn in this invention 1.56 Co 0.96 Ni 0.48 Schematic diagram of the pre-firing curve of O4 ceramic target; Figure 4 Mn in this invention 1.56 Co 0.96 Ni 0.48 Schematic diagram of the sintering curve of O4 ceramic target; Figure 5 This is a schematic diagram of the NTC thermistor thin-film planar device structure; Figure 6 These are the XRD patterns of NTC thermistor films under different sputtering powers; Figure 7 These are the Raman spectra of NTC thermistor films under different sputtering powers; Figure 8 These are SEM images of the surface morphology of NTC thermistor films under different sputtering powers; Figure 9 The RT curves of NTC thermistor films under different sputtering powers are shown. Figure 10 This is a graph of ln(R)-1000 / T for NTC thermistor films under different sputtering powers; Figure 11 The room temperature resistance value R of the NTC thermistor film. 25 and thermistor constant B 25 / 50 Curve showing the variation of sputtering power; Figure 12 This is a graph showing the change in resistivity aging rate of NTC thermistor films over time under different sputtering powers; Figure 13 This is a graph showing the rate of change of the B value of NTC thermistor films over time under different sputtering powers. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0025] Example like Figure 1 As shown, a method for preparing an NTC thermistor thin film includes the following steps: (1) such as Figure 2 As shown, MnO2, Co3O4, and Ni2O3 with a purity ≥99.99% were weighed according to the stoichiometric ratio n(MnO2): n(Co3O4): n(Ni2O3) = 1.56: 0.32: 0.24. The resulting MnO2 was produced through a process of ball milling, pre-calcination, secondary ball milling, granulation, sintering, and backplate welding. 1.56 Co 0.96 Ni 0.48 O4 ceramic target material; single ball milling: ball-to-material ratio 10:1, rotation speed 230 rpm, time 24 h, dispersion medium pure water; pre-firing: as follows Figure 3 As shown, under air atmosphere, the temperature was increased from room temperature to 350℃ at 2.75℃ / min and held for 2.5h, then increased to 1000℃ at 2.7℃ / min and held for 5h, followed by furnace cooling; secondary ball milling: ball-to-material ratio was 10:1, rotation speed was 230rpm, time was 72h, and the dispersion medium was pure water; sintering: as... Figure 4 As shown, in an air atmosphere, the temperature is raised from 25℃ to 100℃ in 0.6h, held for 3h, then raised to 130℃ in 1h, held for 3h, then raised to 350℃ in 2h, held for 2.5h, then raised to 950℃ in 3h, held for 5h, then raised to 1180℃ in 5h, held for 20h, and finally cooled to room temperature. (2) The substrate was ultrasonically cleaned for 15 minutes each with anhydrous ethanol, pure water, and a mixture of pure water and anhydrous ethanol, with a power of 50 kHz, and then dried with nitrogen gas at a pressure of 0.3 MPa. (3) such as Figure 5 As shown, silver paste electrodes were prepared on the cleaned substrate surface by screen printing. The specific parameters of the screen printing process were: screen mesh size of 300 mesh, screen tension of 23±1N / cm, tension difference ≤1N / cm; squeegee pressure of 0.1MPa, electrode spacing of 0.12cm, drying temperature of 80℃, and drying time of 30min. (4) Mn 1.56 Co 0.96 Ni 0.48The O4 ceramic target and the treated substrate were loaded into a magnetron sputtering coating apparatus. Argon was used as the working gas, the sputtering power was 180W, the sputtering time was 80min, the working gas pressure was 0.5Pa, the substrate temperature was 150℃, the target-substrate distance was 60mm, the argon flow rate was 50sccm, and the pre-sputtering furnace pressure was <1.5×10⁻⁶. −3 Pa, a thin film is formed by sputtering deposition on the substrate; (5) The deposited film was placed in a box-type high-temperature resistance sintering furnace and annealed in air atmosphere. The annealing temperature was 700℃, the holding time was 1h, the heating rate was 7℃ / min, and the cooling rate was 1℃ / min. (6) The annealed film was placed in a high and low temperature humidity alternating chamber and kept at 150°C for 240 hours to obtain an NTC thermistor film.

[0026] The NTC film prepared in this embodiment is a single spinel phase with a thickness of 163 nm, a deposition rate of 2.038 nm / min, an average grain size of 38.617 nm, a grain size standard deviation of 8.228 nm, a room temperature resistivity of 4.45 MΩ, and a resistivity of 513.78 Ω·cm. 25 / 50 The resistance value is 3451.91K; after aging for 240 hours, the resistance aging rate is 0.112%, and the change rate of the B value is 0.840%.

[0027] Comparative Example 1 The difference from the embodiments is that the sputtering power in this comparative example is 120W. The rest is the same as in the embodiments and will not be repeated here.

[0028] The NTC thermistor film prepared in this comparative example has low crystallinity and loose structure. The film thickness is 98 nm, the deposition rate is 1.225 nm / min, the average grain size is 33.289 nm, the standard deviation of the grain size is 7.807 nm, the room temperature resistance is 9.166 MΩ, and the resistivity is 1058.24 Ω·cm. After aging for 240 h, the resistance aging rate is 1.32%, and the peak change rate of B value is 2.172%.

[0029] Comparative Example 2 The difference from the embodiments is that the sputtering power in this comparative example is 210W. The rest is the same as in the embodiments and will not be repeated here.

[0030] The NTC thermistor film prepared in this comparative example exhibits grain boundary distortion and grain agglomeration. The film thickness is 213 nm, the deposition rate is 2.6625 nm / min, the average grain size is 40.511 nm, and the standard deviation of the grain size is 10.123 nm. The room temperature resistance is 6.51 MΩ, the resistivity is 751.63 Ω·cm, and the resistance aging rate is 2.673% after aging for 240 h.

[0031] Comparative Example 3 The difference from the embodiments is that the sputtering power in this comparative example is 150W. The rest is the same as in the embodiments and will not be repeated here.

[0032] The NTC thermistor film prepared in this comparative example has an unsatisfactory grain boundary structure, a film thickness of 105 nm, a deposition rate of 1.3125 nm / min, an average grain size of 36.007 nm, and a grain size standard deviation of 8.923 nm; its room temperature resistivity is 5.886 MΩ, and its resistivity is 679.63 Ω·cm. 25 / 50 The resistance value is 3457.61K; after aging for 240 hours, the resistance aging rate is 3.827%, and the change rate of the B value is 1.326%.

[0033] Performance testing (1) Mn prepared in Examples 1-3 and Comparative Examples 1-3 respectively 1.56 Co 0.96 Ni 0.48 XRD tests were performed on the O4NTC thermistor film, and the test results are as follows: Figure 6 As shown; (2) Mn prepared in Examples 1-3 and Comparative Examples 1-3 respectively 1.56 Co 0.96 Ni 0.48 Raman spectroscopy was performed on the O4NTC thermistor film, and the results are as follows: Figure 7 As shown; (3) Mn prepared in Examples 1-3 and Comparative Examples 1-3 respectively 1.56 Co 0.96 Ni 0.48 The O4NTC thermistor film was tested using scanning electron microscopy, and the results are as follows: Figure 8 As shown, (a) is Comparative Example 1, (b) is Comparative Example 3, (c) is an Example 2, and (d) is Comparative Example 2. (4) The Mn prepared in Examples 1-3 and Comparative Examples 1-3 were measured respectively. 1.56 Co 0.96 Ni 0.48 The resistance of the O4NTC thermistor film at different temperatures is shown in the plotted RT curves. Figure 9 As shown, the ln(R)-1000 / T curve is as follows: Figure 10 As shown; (5) The Mn prepared in Examples 1-3 and Comparative Examples 1-3 were measured respectively. 1.56 Co 0.96 Ni 0.48 The room temperature resistivity R of the O4NTC thermistor film 25 and thermistor constant B 25 / 50 The plotted change curve is as follows Figure 11 As shown; (6) The Mn prepared in Examples 1-3 and Comparative Examples 1-3 were measured respectively. 1.56 Co0.96 Ni 0.48 The aging rate of O4NTC thermistor film after different aging times is shown in the plotted curves. Figure 12 As shown; (7) The Mn prepared in Examples 1-3 and Comparative Examples 1-3 were measured respectively. 1.56 Co 0.96 Ni 0.48 The rate of change of B value of O4NTC thermistor film after different aging times is shown in the plotted curve. Figure 13 As shown.

[0034] Analysis of test results: Through the analysis of... Figure 6 The calibration and analysis of XRD diffraction peaks confirmed that all films prepared at all power levels were crystallized, with characteristic diffraction peaks concentrated in the range of 2θ = 30.6°, 33°, 36°, 43.8°, 56.4°, 61.8°, and 63.5°. No impurity phase diffraction peaks were observed at any power level, and all diffraction peaks could be attributed to characteristic crystal planes of three types of spinel oxides: MnCo2O4, CoMn2O4, and NiMn2O4. This demonstrates that the NTC thermistor films prepared at sputtering powers from 120W to 210W are all single spinel ternary solid solutions. With changes in sputtering power, the intensity of the diffraction peaks in the NTC thermistor films exhibited a clear evolutionary pattern: when the sputtering power was 120W, the intensity of diffraction peaks on each crystal plane was relatively weak, with only the 2θ = 33° crystal plane showing a slight signal advantage; overall, there was no obvious preferred orientation. This is because when the sputtering power is low, the energy of the deposited particles generated by argon ions bombarding the target is insufficient, making it difficult for them to migrate to low-energy lattice positions, resulting in poor crystallinity of the NTC thermistor film. As the sputtering power increases to 180W, the intensity of the diffraction peaks at 30.6°, 33°, 61.8°, and 63.5° increases and shows a preferred orientation along the 30.6° crystal plane. This is because the surface free energy corresponding to this crystal plane is low. As the sputtering power increases, the energy of the deposited particles increases, and atoms are more likely to migrate to this low-energy crystal plane to complete ordered arrangement, thus forming preferred growth. Based on the diffraction peak intensity and half-width at half-maximum, it can be determined that the film crystal quality is better when the sputtering power is 180W. However, when the sputtering power is increased to 210W, the diffraction peak intensity of several crystal planes is slightly weakened. This phenomenon can be attributed to the excessively fast deposition rate under high power, which causes an excessive amount of high-energy particles to accumulate rapidly on the substrate surface. The atoms do not have enough time to fully relax before the deposition is completed, resulting in an increase in the disorder of the crystal structure, which in turn causes a slight decline in the crystal quality of the NTC thermistor film.

[0035] Depend on Figure 7The Ramman spectra show that no vibrational signals of non-spinel phases were observed in the NTC thermistor films at any power, consistent with the XRD findings, confirming the single spinel solid solution nature of the NTC thermistor films. The intensity patterns of the vibrational peaks closely match those of the XRD diffraction peaks, with the peak intensity gradually increasing from 120 W to 180 W and slightly decreasing at 210 W, further supporting the conclusion that the NTC thermistor films have optimal crystallinity near 180 W. Furthermore, no additional impurity peaks (such as vibrational signals of non-spinel phases) were observed in the NTC thermistor films at any power. Only in the Raman spectrum of the NTC thermistor film sample prepared with a sputtering power of 120 W was a slight baseline fluctuation observed. This is related to the lower crystallinity and slightly more lattice defects in the low-power sample, but no obvious structural distortion peaks were observed, further demonstrating the purity of the single spinel solid solution phase in the NTC thermistor films.

[0036] Depend on Figure 8 The SEM images show that the NTC thermistor film sample prepared with a sputtering power of 120W exhibits a relatively uniform fine-particle accumulation, but the particle size is small and the boundaries are blurred, resulting in a relatively smooth overall texture. The NTC thermistor film sample prepared with a sputtering power of 150W shows a slightly larger particle size, clearer particle boundaries, and a more pronounced texture layering compared to 120W, but local particle agglomeration still exists. At this point, the deposition energy is increased, and the grains initially meet the growth conditions, but have not yet reached the optimal accumulation state. The sample prepared with a sputtering power of 180W… The NTC thermistor thin film sample surface exhibits a uniform and dense granular structure with significantly increased grain size and sharp, clear boundaries, distinct texture layers, and no obvious pores or defects. This corresponds to the conclusion in XRD that 180W yields the best crystal quality, as the particle energy and deposition rate are optimally matched at this power, allowing atoms to migrate fully and complete ordered stacking, forming a highly dense and clear microstructure. The NTC thermistor thin film sample prepared with a sputtering power of 210W shows a further increase in surface particle size, but the uniformity of particle distribution decreases, and localized areas of grain agglomeration lead to blurred texture.

[0037] Depend on Figure 9 It can be seen that as the temperature rises from 0℃ to 90℃, the resistance of all samples shows a monotonically decreasing trend, and the higher the temperature, the more gradual the rate of resistance decrease, which is consistent with the core characteristic of NTC thermistors that "resistance decreases as temperature increases".

[0038] Depend on Figure 10 It can be seen that the linear correlation coefficient of all samples is greater than 0.999, indicating that the resistance change of the NTC thermistor film strictly follows the intrinsic law of NTC thermistor. This result confirms that the prepared NTC thermistor film has excellent NTC thermistor characteristics in the sputtering power range of 120~210W and does not lose the thermistor function due to power change.

[0039] Depend on Figure 11 It can be seen that the room temperature resistance exhibits a non-monotonic trend of first decreasing and then increasing with sputtering power: when the sputtering power increases from 120W to 180W, R... 25 The resistance decreased from 9.166 MΩ to 4.45 MΩ; when the sputtering power increased from 180 W to 210 W, R... 25 The rise to 6.51 MΩ is essentially due to the effect of sputtering power on the film density and grain boundary structure: at a low power of 120 W, the film has low crystallinity, a loose microstructure, a high grain boundary barrier, and high electron transport resistance, therefore R... 25 At a high level; at a medium power of 180W, the highly crystalline, dense, and uniform microstructure lowers the grain boundary barrier, facilitating electron transport. Simultaneously, the lattice order ensures stable transport of oxygen vacancies, corresponding to R... 25 Reaching the minimum value; at a high power of 210W, excessively high particle energy induces a deoxidation effect in the target material. Although this increases the oxygen vacancy content in the film, particle bombardment leads to grain boundary distortion, causing a slight increase in the grain boundary barrier, ultimately manifesting as R 25 The material constant B is the core parameter for measuring the thermistivity of NTC films; the higher the value, the higher the thermistivity. The change of B value with sputtering power is relatively gradual, generally remaining within the range of 3410~3460K. This result indicates that sputtering power mainly regulates the resistance level of the thin film and has a weak effect on the thermistivity. The intrinsic thermistivity of NTC thermistor films is determined by composition, while sputtering power affects the absolute value of resistance by changing the grain boundary structure, but does not significantly change the rate of resistance change with temperature. This suggests that the thermistor sensitivity of this system has good process stability.

[0040] Depend on Figure 12 It can be seen that the NTC thermistor thin film sample prepared with a sputtering power of 180W exhibits the best aging stability. Its aging rate shows a characteristic of narrowing negative bias, slight positive drift, and then stabilizing. It is -0.51% at 24h, crosses 0 into the positive range at 72h, reaches a peak positive drift of only 0.431% at 168h, and falls back to 0.112% at 240h, with an absolute drift value of ≤0.51% over the entire cycle. The aging rate of the NTC thermistor thin film sample prepared with a sputtering power of 120W shows a trend of slight decrease in the early stage, increase in the middle stage, and decrease in the later stage, with a final value of 1.320% at 240h. The aging rate of the NTC thermistor thin film sample prepared with a sputtering power of 210W increases steadily and positively throughout the entire process, reaching 2.673% at 240h. The NTC thermistor thin film sample prepared with a sputtering power of 150W shows the lowest stability at the full power level, with a sharp increase in the aging rate in the later stage, and a final value of 3.827% at 240h.

[0041] Depend on Figure 13It can be seen that the rate of change of B value for all four power thin films is much smaller than that of resistance aging, indicating that the B value, as an intrinsic thermistor parameter of the material lattice, is significantly less affected by grain boundary aging than room temperature resistance. The NTC thermistor thin film sample prepared with sputtering power of 180W has the lowest rate of change of B value at all power levels, showing a continuous and gradual decrease in the early stage and a slight rebound in the later stage without drastic fluctuations, reflecting its highly stable lattice structure and minimal impact from aging. The NTC thermistor thin film sample prepared with sputtering power of 210W shows a linear and gradual decrease in the rate of change of B value, gradually decreasing from 0.982% at 24h to 0.502% at 168h, and slightly rebounding to 0.559% at 240h, matching its intrinsically intact lattice structure. The NTC thermistor thin film sample prepared with sputtering power of 150W shows a gradual decrease in the rate of change of B value in the early stage and a continuous increase in the later stage, consistent with the sharp increase in resistance aging in the later stage, reflecting the slight influence of uncontrolled grain boundary defects on the lattice thermistor properties. The NTC thermistor film sample prepared by sputtering power of 120W exhibited a trend of slight decrease, rising to a peak value, and then falling back significantly due to its low crystallinity and loose porous structure. The peak value reached 2.172% at full power after 168h and then dropped to 1.004% after 240h. This is the result of the structural evolution of disordered rearrangement of oxygen vacancies in the middle stage of aging and self-equilibrium of pore oxygen adsorption in the later stage.

[0042] Combination Figure 12 and Figure 13 Analysis shows that sputtering power has a significant non-monotonic regulatory effect on the aging rate of NTC thermistor resistance and the rate of change of B value. 180W is the optimal process parameter, and the NTC thermistor prepared by it achieves high stability of both resistance and B value due to its high crystallinity and dense and uniform grain boundary structure. On the other hand, the NTC thermistor prepared by sputtering power of 120W has a loose structure, the NTC thermistor prepared by sputtering power of 150W has uncontrolled grain boundary defects, and the NTC thermistor prepared by sputtering power of 210W has grain boundary distortion. All of these lead to a decrease in the aging stability of the NTC thermistor. Moreover, the influence of grain boundary structure evolution on resistance is much greater than its influence on the intrinsic B value of the crystal lattice.

[0043] In summary, the NTC thermistor film of Example 1 (180W, the optimal range of this invention) achieves the best balance in crystallinity, room temperature resistivity, and long-term stability, with all performance characteristics significantly superior to Comparative Examples 1-3. Comparative Example 1 (120W) suffers from a loose structure due to excessively low power, Comparative Example 2 (210W) suffers from grain boundary distortion due to excessively high power, and Comparative Example 3 (150W) suffers from the worst stability due to uncontrolled grain boundary defects. All three deviate from the power range of 170-190W specified in this invention, and their performance fails to meet the requirements. The comparative results fully demonstrate that the sputtering power of 170-190W and the annealing process combination of 700℃ and 1h specified in this invention are key to achieving low resistivity, high crystallinity, and high stability of the film, and are not simply a matter of parameter superposition, but rather have a significant synergistic effect.

[0044] Application Examples Using the NTC thermistor film prepared in the examples as the core sensing element, and combining it with silicon-based packaging technology, an integrated temperature sensor is fabricated. The specific steps are as follows: (1) Sensitive chip cutting: The NTC thermistor film (alumina substrate) prepared by 180W power is cut into 1mm×1mm size to obtain the thermistor sensitive chip. The original screen-printed silver electrodes (0.12cm spacing) are retained on the chip surface. (2) Wire bonding: Gold wire bonding process is used to connect the silver electrode of the sensitive chip to the pad of the printed circuit board (PCB) substrate. The wire diameter is 25μm and the bonding temperature is 180℃ to ensure reliable electrical connection. (3) Packaging: The sensitive chip and leads are packaged with epoxy molding compound. The package size is 3mm×3mm×1mm, and the pins are reserved for external circuit connection. The temperature is controlled at ≤200℃ during the packaging process to avoid high temperature affecting the thermal properties of the film. (4) Circuit matching: The signal amplification circuit (operational amplifier LM324) and temperature compensation resistor are integrated on the PCB substrate to make the sensor output signal linear with temperature, and the measurement range is -50℃~300℃ (typical application scenario in the medium and low temperature range).

[0045] The integrated temperature sensor was tested according to the industrial temperature sensor standard (GB / T 26140-2010) "Performance Evaluation Method for Industrial Temperature Sensors", and the results are as follows: (1) Temperature measurement accuracy: The temperature measurement error is ≤ ±0.3℃ in the range of -50℃ to 300℃, which is far better than the industry standard error (±0.5℃), proving that the film has excellent consistency in thermosensitive properties; (2) Response speed: When the ambient temperature changes abruptly from 25℃ to 100℃, the sensor output stabilization time is ≤50ms, which meets the requirements for rapid temperature measurement (due to the improved thermal conductivity brought about by the dense structure of the thin film). (3) Long-term reliability: After 1000h of damp heat aging test at 85℃ and 85% relative humidity (85%RH), the temperature measurement error change is ≤±0.05℃, the corresponding film resistance aging rate is ≤0.2%, and the B value change rate is ≤0.9%, which proves that the sensor has industrial-grade long-term stability. (4) Power consumption: Operating current ≤100μA (3.3V power supply), which is much lower than that of traditional bulk NTC sensors (≥500μA), and is suitable for the low power consumption requirements of integrated microelectronic systems.

[0046] The integrated temperature sensor fabricated in this application example can be directly used in the following industrial scenarios: (1) Consumer electronics: Temperature monitoring of the core processor (CPU) of smartphones and laptops; (2) Industrial control: Temperature acquisition in the low-temperature zone (-50℃~300℃) of the chemical reactor; (3) Automotive electronics: Power battery pack temperature monitoring module; (4) Medical equipment: thermometer, temperature control unit of constant temperature incubator / incubator.

[0047] The sensor's core performance (accuracy, response speed, stability, and power consumption) all meet industrial-grade standards, and its fabrication process is compatible with silicon-based microelectronics processes, enabling mass production. This fully demonstrates the industrial application value of the thin film of this invention.

[0048] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the present invention specification under the concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing an NTC thermistor thin film, characterized in that, Includes the following steps: (1) Weigh out MnO2, Co3O4, and Ni2O3 with a purity ≥ 99.99% according to the stoichiometric ratio n(MnO2): n(Co3O4): n(Ni2O3) = 1.56: 0.32: 0.

24. Then, process them by ball milling, pre-calcination, ball milling, granulation, sintering, and backplate welding to obtain MnO2. 1.56 Co 0.96 Ni 0.48 O4 ceramic target material; (2) The substrate was ultrasonically cleaned sequentially with anhydrous ethanol, pure water, and a mixture of pure water and anhydrous ethanol, and then dried with nitrogen gas. (3) Silver paste electrodes are prepared on the cleaned substrate surface by screen printing process; (4) Mn 1.56 Co 0.96 Ni 0.48 The O4 ceramic target and the treated substrate are loaded into a magnetron sputtering coating equipment, with argon as the working gas, a sputtering power of 170~190W, and a sputtering time of 70~90min, to sputter and deposit a thin film on the substrate. (5) The deposited film is placed in a box-type high-temperature resistance sintering furnace and annealed in an air atmosphere; (6) The annealed film is placed in a high and low temperature humidity alternating chamber for aging treatment to obtain an NTC thermistor film.

2. The method for preparing the NTC thermistor film as described in claim 1, characterized in that, In step (1), the ball-to-material ratio of the first ball mill is 10:1, the rotation speed is 230 rpm, the ball milling time is 24 h, and the dispersion medium is pure water; the ball-to-material ratio of the second ball mill is 10:1, the rotation speed is 230 rpm, the ball milling time is 72 h, and the dispersion medium is pure water.

3. The method for preparing the NTC thermistor film as described in claim 1, characterized in that, In step (1), the specific process of pre-firing is as follows: under an air atmosphere, the temperature is increased from room temperature to 350℃ at 2.75℃ / min, held for 2.5h, then increased to 1000℃ at 2.7℃ / min, held for 5h, and then cooled down with the furnace.

4. The method for preparing the NTC thermistor film as described in claim 1, characterized in that, In step (1), the specific sintering process is as follows: under an air atmosphere, the temperature is raised from 25°C to 100°C within 0.6 hours and held for 3 hours, then raised to 130°C within 1 hour and held for 3 hours, then raised to 350°C within 2 hours and held for 2.5 hours, then raised to 950°C within 3 hours and held for 5 hours, then raised to 1180°C within 5 hours and held for 20 hours, and finally cooled to room temperature.

5. The method for preparing the NTC thermistor film as described in claim 1, characterized in that, In step (2), the substrate is ultrasonically cleaned for 15 minutes each with anhydrous ethanol, pure water, and a mixture of pure water and anhydrous ethanol, with a power of 50 kHz, and then dried with nitrogen gas at a pressure of 0.3 MPa.

6. The method for preparing the NTC thermistor film as described in claim 1, characterized in that, In step (4), the working gas pressure of the magnetron sputtering coating equipment is 0.4~0.6 Pa, the substrate temperature is 140~160℃, the target-substrate distance is 55~65 mm, the argon flow rate is 45~55 sccm, and the furnace pressure before sputtering is <1.5×10 −3 Pa.

7. The method for preparing the NTC thermistor film as described in claim 1, characterized in that, In step (5), the annealing temperature is 680~720℃, the holding time is 0.8~1.2h, the heating rate is 6~8℃ / min, and the cooling rate is 0.8~1.2℃ / min.

8. The method for preparing the NTC thermistor film as described in claim 1, characterized in that, In step (6), the aging treatment specifically involves keeping the temperature at 150℃ for 240 hours.

9. An NTC thermistor film prepared by the method of any one of claims 1 to 8.

10. The application of the NTC thermistor film as described in claim 9 in integrated NTC thermistor devices.

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