CN102431235B - Dielectric adjustable compound film for stress auxiliary modulation and preparation method thereof - Google Patents

Abstract

The invention discloses a dielectrically adjustable composite film with stress auxiliary modulation and a preparation method thereof. On the front surface of the substrate, an ITO conductive layer, a PT stress-inducing layer and a PST film are plated sequentially from bottom to top, and the PT stress-inducing layer has a perovskite phase crystal structure and is doped with impurities, and the impurities are A metal ion whose ion size is larger than that of Ti and whose valence is smaller than that of Ti. The preparation process of the invention is simple, and the dielectric adjustability of the obtained composite film has excellent composition stability and temperature stability, and is very suitable for the industrialized production of the dielectric adjustable film.

Description

A dielectrically tunable composite film with stress-assisted modulation and its preparation method

technical field

The invention belongs to the technical field of dielectric adjustable thin films, and relates to a stable dielectric adjustable thin film and a preparation method thereof.

Background technique

The phase shifter is an important device. The new generation of phase shifter is a dielectric phase shifter. The dielectric phase shifter has many advantages, such as simple structure, small size, light weight, low power consumption, fast response speed, and low insertion loss. It is small and cheap, and there are two ways of phase shifting: digital and analog, which can meet the needs of various occasions. The dielectric phase shifter, also known as the ceramic phase shifter, utilizes the characteristic that the dielectric constant of some low-loss nonlinear microwave dielectric ceramic materials changes with the strength of the applied electric field. The size is used to control the delay in the signal transmission process, so as to achieve the purpose of phase shifting. Under the action of an external DC electric field, the percentage of dielectric constant reduction is the dielectric tunability, and its calculation formula is: dielectric tunability = dielectric constant reduction ÷ dielectric constant. Lead strontium titanate ((Pb,Sr)TiO ₃ , PST) film is such a microwave dielectric ceramic material, which has excellent dielectric tunable properties and can be widely used as the key material of dielectric phase shifting devices. In addition to being used as a dielectric phase shifter, the multilayer structure formed by combining the nonlinear dielectric film and the high-temperature superconducting film can prepare a high-quality factor (high-Q) resonator, and its center frequency can be adjusted by an external bias electric field. Adjustment, so that a class of voltage-tunable microwave devices with frequency truncation can be developed, such as decoupling capacitors, filter tuners, phase array antennas, low-phase-noise tunable local oscillators for portable communications and satellite communications, etc., with promising application prospects.

Under the action of an external DC electric field, the dielectric constant changes, that is, the materials that exhibit nonlinear characteristics mainly include SrTiO ₃ , (Ba,Sr)TiO ₃ , (Pb,Sr)TiO ₃ , (Pb,Ca)TiO ₃ , Ba(Ti,Sn)O ₃ , Ba(Ti,Zr)O ₃ and KTaO ₃ . As far as tunable dielectric materials are concerned, barium strontium titanate (BST) and its doped series have been studied more in the early stage and have better performance. And Yoshitaka Somiya is equal to 2001 in International Journal of Inorganic Materials (Yoshitaka Somiya, Amar S.Bhalla, L.Eric Cross, International Journal of Inorganic Materials 3 (2001) 709-714) introduction has discovered lead strontium titanate (PST), it It has high adjustability and relatively low dielectric loss, and its Curie point temperature _Tc can be easily adjusted to near room temperature, and its dielectric temperature coefficient is large. It is a perovskite that is very suitable for electric field adjustment elements. ferroelectric material.

A large number of studies have shown that high dielectric tunability always appears near the Curie point, and the dielectric tunability will be greatly reduced if the temperature or composition deviates slightly from the Curie point. As reported by Yoshitaka Somiya et al. (YoshitakaSomiya, Amar S.Bhalla, L.Eric Cross, International Journal of Inorganic Materials 3(2001) 709–714), when the Pb content varies by 10%, the dielectric properties of PST can be adjusted Dielectric tunability drops rapidly from 70% to 5%, and when the temperature changes by 25-30°C, dielectric tunability drops rapidly from 70% to 20%. We know that the operating temperature of the device will always change, and in addition, the material may have defects during the preparation process, and the components may also deviate from the design, so it is difficult to guarantee the high dielectric tunability of the material. That is to say, it is difficult to obtain a high dielectric tunability material and related devices with high stability.

A common approach to address temperature stability is to design multilayer materials with compositional gradients. Take the multilayer BST film (S.Zhong, S.P.Alpay, M.W.Cole, E.Ngo, S.Hirsch, J.D.Demaree, Applied Physics Letters 90(2007) 092901) reported by S.Zhong et al. on Applied Physics Letters as an example , the specific composition of BST material is BST(60/40)/BST(75/25)/BST(90/10), when the temperature gradually increases from room temperature, although the dielectric of BST(60/40) can The contribution of tonality decreases rapidly, but the contribution of BST(75/25) and BST(90/10) to dielectric tunability increases rapidly. Overall, the multilayer film has better temperature stability. In addition, the research results of M.W.Cole et al. (M.W.Cole, E.Ngo, S.Hirsch, J.D.Demaree, S.Zhong, S.P.Alpay, Journal of Applied Physics, 102(2007) 034104) show that using a The composition gradient change multi-layer structure with different chemical compositions will improve the temperature stability of the dielectric tunability of the material, and the more layers, the better the temperature stability. However, this composition gradient design method greatly complicates the preparation process while solving temperature stability. Because this composition gradient method requires that the composition of each layer is different, that is, the film preparation is actually made by stacking many thinner layers, which will inevitably greatly increase the production cost from the perspective of industrial production, which is obviously not a good method. craft.

In fact, in addition to the above-mentioned temperature stability, industrial production also requires materials to have a certain compositional stability. For example, under the current conditions, PST40 ((Pb _0.40 Sr _0.60 )TiO ₃ ) has high dielectric tunability, and the composition can be designed as PST40 during preparation. However, composition deviations are likely to occur in the mass production process. The dielectric tunability of the material is sensitive to composition, and the material originally designed to have high dielectric tunability may not achieve the expected effect due to composition deviation.

Contents of the invention

The object of the present invention is to provide a stress-assisted modulated dielectrically adjustable composite film and its preparation method. The composite film has high stable dielectric tunability under the conditions of temperature and composition changes.

According to the viewpoint of materials science, the performance comes from the structure, and the influence of composition and temperature on the performance always originates from the influence on the structure. In PST materials, the specific performance is that the high dielectric tunability of the material is always at the tetragonal-cubic phase transition point. Changes in temperature and composition can make PST deviate from the phase transition point, so the dielectric tunability is sensitive to temperature and composition, which eventually leads to composition and temperature instability. In addition to temperature and composition, another report (Z.G.Ban, S.P.Alpay, Journal of Applied Physics, 93(2003) 504-511) stated that stress can also have a great impact on dielectric adjustability, which can be understood as follows: stress The structure of the material changes, so the performance also changes. For example, for a unit cell with a cubic structure, if tensile stress is applied in a certain direction, the result is that the cubic structure becomes a tetragonal structure. From a macroscopic point of view, the stress makes the unit cell cross the phase transition point, and the cubic phase changes into a tetragonal phase. Performance Naturally, qualitative changes should also take place. According to the reports in the existing literature (W.K.Simon, E.K.Akdogan, A.Safari, Applied Physics Letters, 89(2006) 022902), in the thin film material induced by the substrate growth, the stress always presents a gradient distribution along the thickness. It can be seen that if a stress is applied to the PST film, the stress may cause the phase structure of the PST film to present a gradient distribution, so that the phase transition temperature point of the film will be distributed in a large temperature range according to this continuously changing phase structure , that is, the film can exhibit the characteristics of the tetragonal/cubic phase transition point required for the corresponding dielectric tunability in a large temperature range, so it is expected to achieve temperature stability. Further, if the stress can be automatically matched with the current composition, that is, the magnitude of the stress can be automatically matched with the difference of the composition, so that the movement of the phase transition point caused by the composition change can be automatically matched by the stress and then the phase transition point Moving back, it is expected to simultaneously achieve compositional stability with high dielectric tunability through this so-called means of modulating the Curie point.

In order to achieve this goal, the present invention designs a dielectric layer with an isomorphic structure but a larger lattice constant as the stress-inducing layer of the PST film. The present invention preferably uses doped lead titanate (PbTiO ₃ , PT) as the stress-inducing layer. layer, the ion size of its impurity ions is larger than that of Ti ions, and its valence is smaller than that of Ti ions. On the one hand, the intrinsic lattice constant of PT is slightly larger than that of PST, and the doping of impurity ions with metal ions larger in size than Ti ions can further improve the lattice parameters of PT, thereby improving the lattice parameters of PT and PST. difference. The PST grown on the PT induction layer is subjected to the tensile stress of PT due to the difference in lattice parameters, and doping amplifies the difference in lattice parameters, making PT an induction layer with obvious "stress" effect. On the other hand, the valence of the dopant ions needs to be smaller than that of Ti, so that the dopant ions replace the Ti position to form negatively charged substitution defects, and due to the need for charge balance, positively charged oxygen vacancies will be generated. The defects with positive and negative charges attract each other and are arranged along the <001> direction and <100> direction of the perovskite structure. Under the action of the natural surface electrostatic field of the ITO layer, the doped PT stress-inducing layer is along the <001>/<100> direction growth, that is, the surface of the PT stress-inducing layer is (001)(100) plane. In this way, when the same perovskite structure PST film is prepared on it, the (100) plane of the PST is attached to the (001)(100) plane of the PT induction layer, which can ensure that the direction of the tensile stress on the PST film is the film plane The direction effectively controls the direction of stress application. For example, as a preferred embodiment of the present invention, by doping Zn ²⁺ , Fe ³⁺ or Co ²⁺ ions in PT, a PT stress-inducing layer with an isomorphic structure whose lattice constant is significantly larger than that of PST has been successfully obtained, making PST The film is subjected to the obvious tensile stress of the stress-inducing layer in the film plane direction. This tensile stress actually increases the lattice parameters of PST in the film plane direction and decreases the lattice parameters in the film thickness direction, thus increasing the tetragonality of the PST lattice. When the Pb content in the PST film is high, the film itself has a high Curie temperature and a relatively large lattice parameter, so the lattice mismatch with the PT stress-induced layer is small, and the tensile stress is also small The increase of tetragonality is not much; when the Pb content is low, the PST film has a relatively small lattice parameter, and the lattice mismatch degree with the PT stress-induced layer is relatively large, and the tetragonality of the tensile stress is relatively large. Increase. The tensile stress along the film direction always tends to elongate the PST lattice along the film direction, increasing the tetragonality. Even though the original PST film has a cubic structure, it becomes a tetragonal structure under the action of tensile stress. Since the increase of the tetragonality of the structure corresponds to the increase of the Curie temperature, and the PST film with a lower Pb content has a lower Curie temperature, compared with the larger tensile stress of PT at this time, the Curie temperature is greatly increased. . On the contrary, the original PST film with higher Pb content has a higher Curie temperature. Compared with the smaller tensile stress of PT at this time, the Curie temperature is only slightly increased, so this tensile stress can automatically affect the Curie temperature. role of regulation. Therefore, even if the composition of PST changes, under the automatic modulation of tensile stress, the macroscopic Curie temperature of the stress-assisted modulation composite film composed of PT stress-inducing layer and PST film basically does not change. It can be seen that the Curie temperature of the stress-regulated composite film has good compositional stability. Since the high dielectric tunability always appears near the Curie point, the stress regulation can make the high dielectric tunability have compositional stability by controlling the Curie temperature.

As previously mentioned, stressing the PST film through the PT stress-inducing layer enables dielectric tunability with compositional stability. If no stress is applied, the molar percentage of Pb in the PST film can only have high dielectric tunability when it is strictly limited to 40%. After the stress is applied through the PT stress-inducing layer, the molar percentage of Pb in the PST film can be widened to 35%-50%, and can achieve high adjustability, thereby achieving high adjustability and composition stability.

Furthermore, the stress is transmitted from the stress-inducing layer PT to the PST, and the transfer direction is the thickness direction of the film. The bottom film is subjected to the tensile stress of the PT stress-inducing layer, and at the same time, the tensile stress is applied to the crystal lattice of the upper layer. The tensile stress is layer by layer. Decrementally, the gradient distribution of tensile stress is realized in this way. Under the action of gradient tensile stress, the degree of deviation from the cubic phase of a certain component of the PST material also presents a gradient distribution, so that the Curie temperature of each thin layer of the stress-assisted modulation composite film composed of the PT stress-induced layer and the PST film is different. The same, that is, the tetragonal-cubic phase transition temperature presents a diffuse distribution, and the Curie peak of the composite film as a whole is broadened. Since better dielectric tunability occurs near the Curie point, the broadening of the Curie peak indicates that the Curie point is distributed over a wide temperature range, that is, the temperature variation does not "significantly deviate" from the Curie point, which ensures that the dielectric tunability of the composite film has good temperature stability.

The above stress design can realize the temperature and composition stability of the dielectric adjustability of the composite film, and special attention should be paid to the maintenance of stress in the design of the film preparation method. In this way, using magnetron sputtering method (Chinese patent CN100480437C), pulsed laser deposition method (Structure and dielectric properties of highly(100)-oriented PST thin films deposited on MgO substrates, X.T.Li et al., Thin SolidFilms, 516(2008), 5296-5299) and other similar vapor deposition methods are difficult to maintain the stress in the entire film, because the ions are directly attached to the substrate to form crystals during the deposition process, even if the substrate lattice mismatch makes the film with stress, the stress is only There is a thin layer with the initial formation of the film, which is difficult to continue throughout the film. When the film is prepared by the sol-gel method, the whole film crystallizes together. The crystallization process is at a high temperature of about 600°C, and the lattice deformation of the entire film is uniform. After cooling to room temperature, there is naturally a gradient distribution of stress throughout the thickness, which effectively Stress exists throughout the film.

For realizing above object of the invention, the technical scheme that the present invention takes is:

On the front surface of the substrate of the dielectrically adjustable composite film of the stress-assisted modulation of the present invention, an ITO conductive layer, a PT stress-inducing layer and a PST film are sequentially plated from bottom to top, and the PT stress-inducing layer is a perovskite phase Crystal structure and doped with impurities which are metal ions whose ion size is larger than that of Ti ⁴⁺ and whose valence is smaller than that of Ti ⁴⁺ . Doping makes the PT stress-inducing layer have larger lattice parameters. The lead titanate stress inducing layer can apply tensile stress to the crystal lattice of the strontium lead titanate film so that the tensile stress of the composite film presents a gradient distribution that decreases layer by layer.

Further, the PT stress-inducing layer of the present invention is lead titanate doped with impurities, and the impurities are Zn ²⁺ ions, Fe ³⁺ ions or Co ²⁺ ions.

Further, in the present invention, in the PT stress-inducing layer, the molar percentage of the impurity is 1%-3%.

Further, in the present invention, in the PST film, the mole percentage of Pb is 35%-50%.

The preparation method of the composite thin film of the present invention is as follows: a PT stress inducing layer and a PST thin film are plated sequentially from bottom to top on the front surface of a substrate coated with an ITO conductive layer by using a sol-gel method.

The composite film of the present invention can use commonly used glass coated with indium tin oxide (Indium Tin Oxide, ITO) conductive electrodes as the substrate.

Compared with the background technology, the present invention has the beneficial effect that: the high dielectric tunability of the composite film of the present invention has no strict requirements on the chemical composition of PST, and the chemical formula of PST film is Pb _x Sr _1-x TiO ₃ , wherein The molar percentage of Pb is 35%-50%, that is, 0.35≤x≤0.50. When the percentage of Pb in the PST film varies from 35% to 50%, the dielectric tunability of the composite film remains around 63% to 68%. Moreover, the dielectric adjustable performance of the composite thin film of the invention has excellent temperature stability. When the temperature increases from room temperature (20°C) to 200°C, its dielectric tunability only decreases from 40% of room temperature to 35%. It can be seen from the above that the high dielectric tunability of the stress-assisted modulation composite film of the present invention has excellent composition stability and temperature stability.

Description of drawings

Fig. 1 is a schematic structural view of the high dielectric tunable composite film of the present invention;

Figure 2 is the XRD pattern of the Co ²⁺ , Fe ³⁺ , Zn ²⁺ doped PT stress-inducing layer prepared on the ITO conductive layer;

Fig. 3 forms the XRD pattern of composite thin film of the present invention after preparing PST thin film on PT stress inducing layer;

Fig. 4 is the dielectric constant and the dielectric loss curve of composite thin film PST35 with temperature change;

Fig. 5 is the dielectric constant and the dielectric loss curve of composite thin film PST45 with temperature change;

Fig. 6 is the dielectric constant and the dielectric loss curve of composite thin film PST50 with temperature variation;

Figure 7 shows the dielectric tunability of the composite film at room temperature (20°C);

Figure 8 shows the dielectric tunability of the composite film at high temperature (200°C);

Fig. 9 is the dielectric adjustable curve of the composite film PST35 at room temperature;

Fig. 10 is the dielectric adjustable curve of the composite film PST45 at room temperature;

Fig. 11 is the dielectric adjustable curve of the composite film PST50 at room temperature;

In the figure, 1. glass substrate; 2. ITO conductive layer; 3. PT stress-inducing layer doped with impurities; 4. PST thin film; 5. metal upper electrode.

Detailed ways

In the preparation of composite film of the present invention, adopted general-purpose sol-gel method, specifically as follows:

1) Preparation of doped PT sol: heat the mixed solution of acetic acid and ethylene glycol methyl ether as a solvent (the volume percentage of acetic acid is 80%-90%) to 40-70°C, and then put in lead acetate powder, zinc acetate Powder (or ferric nitrate powder, cobalt chloride powder), liquid butyl titanate, stirring continuously for 12 to 24 hours to obtain doped PT sol. The molar ratio of Pb and Ti elements is 1:1, the Pb concentration is controlled at 0.03-0.1mol/L, and the molar ratio of Zn (or Fe, Co) to Pb elements is: 0.01-0.03:1.

2) Utilizing the sol prepared in step 1), plating a doped PT stress-inducing layer on the ITO glass substrate by dipping and pulling method. The substrate is immersed in the sol instantaneously, and after staying for 10-25 seconds, the substrate is pulled at a pulling speed of 2-6cm/min to release the sol, and the sample is placed horizontally to dry naturally to obtain a dry film; direct heat treatment in a furnace at 550-600°C for 4- After 8 minutes, it was quickly taken out and cooled naturally in air at room temperature to obtain a PT stress-inducing layer doped with impurities that has a significantly higher lattice constant than the subsequently prepared PST.

3) Preparation of PST sol: heat the mixed solution of acetic acid and ethylene glycol methyl ether as a solvent (wherein the volume percentage of acetic acid is 80% to 90%) to 40 to 70°C, and then put in lead acetate powder, strontium acetate powder, Liquid butyl titanate, continuously stirred for 24-72 hours to obtain PST sol. The molar concentration of Ti is 0.2-0.4 mol/L, and the molar ratio of Pb, Sr, and Ti elements is x:(1-x):1, where 0.35≤x≤0.50.

4) Utilize the PST sol prepared in step 3), dip and pull the PT stress-inducing layer obtained in step 2) to prepare a PST film, quickly immerse the substrate with the PT stress-inducing layer into the sol, stay for 10-25 seconds, and then use 2- Pull the substrate at a pulling speed of 6cm/min to release the sol, place the wet film prepared by dipping and pulling together with the substrate horizontally, and let it dry naturally to obtain a dry film; put the dry film directly into a furnace at 550-600°C for sintering for 40-80 minutes , and then slowly cooled with the furnace to obtain a perovskite crystal phase PST film grown on the PT stress-inducing layer.

The thickness of PST film can be controlled by repeatedly repeating step 4) as required.

As shown in Figure 1, use metals such as gold, copper or platinum as the metal upper electrode 5 on the upper surface (i.e. on the PST film 4) of the composite film of the present invention prepared, with the whole ITO conductive layer 2 as the lower electrode, the PT stress The composite layer of the induction layer 3 and the PST film 4 is a dielectric layer, thereby forming a metal/dielectric/ITO parallel plate capacitor, and its dielectric properties are tested through the upper and lower electrodes.

The present invention is further illustrated below with specific examples.

Example 1:

Heat the mixed solution of acetic acid and ethylene glycol methyl ether as a solvent (the volume percentage of acetic acid is 80%) to 40°C, add lead acetate powder, zinc acetate powder, and liquid butyl titanate in sequence, and continue stirring for 12 hours to obtain Doped with PT sol. The molar concentrations of Pb and Ti elements are both controlled at 0.03mol/L, and the molar ratio of Zn and Pb elements is 1:100, forming a Zn ²⁺ doped PT sol with a concentration of 0.03mol/L.

Apply the above-mentioned Zn-doped PT sol, immerse the ITO/glass substrate, pull the substrate at a pulling speed of 2cm/min after staying for 10 minutes, and place the sample horizontally to dry naturally to obtain a dry film; After heat treatment for 4 minutes, it was quickly taken out and cooled naturally in air at room temperature to obtain a Zn-doped PT stress-inducing layer. The XRD pattern of the Zn-doped PT stress-inducing layer is shown in Figure 2. In Figure 2, except for the diffraction peaks of the ITO conductive layer, only the (001)/(100) diffraction peaks and (002)/ The (200) diffraction peak indicates that the Zn-doped PT stress-inducing layer is a perovskite phase structure with preferential orientation growth.

Heat a mixed solution of acetic acid and ethylene glycol methyl ether as a solvent (the content of acetic acid is 80%) to 40°C, add lead acetate powder, strontium acetate powder, and liquid butyl titanate in sequence, and continue stirring for 24 hours to obtain PST35 sol. The molar concentration of Ti is 0.4mol/L, and the molar ratio of Pb, Sr, and Ti elements is 0.35:0.65:1.

Using the above PST35 sol, dip and pull the Zn-doped PT stress-inducing layer to prepare the PST35 film: quickly immerse the substrate with the PT stress-inducing layer into the PST sol, stay for 10 seconds, and pull the substrate at a pulling speed of 2cm/min Solve the sol; place the wet film prepared by dipping and pulling together with the substrate horizontally, and dry it naturally to obtain a dry film; directly sinter the dry film in a furnace at 550 ° C for 40 minutes, and slowly cool down with the furnace, repeat the "dipping and pulling- —drying—sintering—cooling” process 6 times to obtain a perovskite crystal phase PST film grown on the PT stress-inducing layer. The composite film formed by preparing the PST35 film on the doped PT stress-inducing layer is called the composite film PST35. The composite film PST35 presents a perovskite structure, as shown in Figure 3. A gold electrode with a diameter of 0.2 mm was plated on the composite film PST35 by vapor deposition, and the dielectric properties of the composite film were tested through the gold electrode and the ITO electrode. Under the effect of stress-assisted modulation, the composite film PST35 has a broadened Curie peak, as shown in Figure 4. It is precisely because the composite film PST35 has a broadened Curie peak, and its dielectric tunability has good temperature stability. As shown in Figure 7 and Figure 8, when the temperature changes from room temperature 20°C to 200°C, The dielectric tunability of the composite film PST35 changed from 31% to 32%, that is, the dielectric tunability of the composite film has good temperature stability.

Example 2:

Heat the mixed solution of acetic acid and ethylene glycol methyl ether as a solvent (the volume percentage of acetic acid is 85%) to 40°C, add lead acetate powder, iron nitrate powder, and liquid butyl titanate in sequence, and continue stirring for 18 hours to obtain Doped with PT sol. The molar concentrations of Pb and Ti elements are both controlled at 0.07mol/L, and the molar ratio of Fe and Pb elements is 2:100, forming a Fe ³⁺ doped PT sol with a concentration of 0.07mol/L.

Apply the above-mentioned Fe-doped PT sol, immerse the ITO/glass substrate, pull the substrate at a pulling speed of 4cm/min after staying for 20 seconds, and place the sample horizontally to dry naturally to obtain a dry film; directly in a furnace at 580°C After rapid heat treatment for 6 minutes, it was quickly taken out and cooled naturally in air at room temperature to obtain a Fe-doped PT stress-inducing layer. The XRD pattern of the Fe-doped PT stress-inducing layer is shown in Figure 2. In addition to the diffraction peaks of the ITO conductive layer in Figure 2, only the (001)/(100) diffraction peaks and (002)/(002)/ The (200) diffraction peak indicates that the Zn-doped PT stress-inducing layer is a perovskite phase structure with preferential orientation growth.

The mixed solution of acetic acid and ethylene glycol methyl ether is used as a solvent (the content of acetic acid is 85%) and heated to 60°C, followed by adding lead acetate powder, strontium acetate powder, and liquid butyl titanate, and continuously stirring for 36 hours to obtain PST45 sol, wherein The molar concentration of Ti is 0.3mol/L, and the molar ratio of Pb, Sr, and Ti elements is 0.45:0.55:1.

Using the above PST45 sol, dip and pull the Fe-doped PT stress-inducing layer to prepare the PST45 film: quickly immerse the substrate with the PT stress-inducing layer into the PST sol, and pull the substrate at a pulling speed of 4cm/min after staying for 20 seconds Solve the sol; place the wet film prepared by dipping and pulling together with the substrate horizontally, and let it dry naturally to obtain a dry film; directly sinter the dry film in a furnace at 580°C for 60 minutes, cool slowly with the furnace, and repeat the PST film "dipping and pulling—— Drying - sintering - cooling" process 9 times to obtain a perovskite crystal phase PST film grown on the PT stress-inducing layer. The composite film formed by preparing the PST45 film on the doped PT stress-inducing layer is called the composite film PST45, and the composite film PST45 presents a perovskite structure, as shown in FIG. 3 . Platinum electrodes with a diameter of 0.2 mm were plated on the composite film by magnetron sputtering, and the dielectric properties of the composite film were tested by platinum electrodes and ITO electrodes. Affected by the stress-assisted modulation of the Fe-doped PT stress-inducing layer, the composite film PST45 has a broadened Curie peak, as shown in Figure 5. In view of its broadened Curie peak, the dielectric tunability of the composite film PST45 has excellent temperature stability. The dielectric tunability of the composite film is changed from 40% to 39%, that is, the dielectric tunability of the composite film has good temperature stability.

Example 3:

Heat the mixed solution of acetic acid and ethylene glycol methyl ether as a solvent (the volume percentage of acetic acid is 90%) to 70°C, add lead acetate powder, cobalt chloride powder, and liquid butyl titanate in sequence, and continue stirring for 24 hours Obtain doped PT sol. The molar concentrations of Pb and Ti elements are both controlled at 0.1mol/L, and the molar ratio of Co and Pb elements is 3:100, forming a Co ²⁺ doped PT sol with a concentration of 0.1mol/L.

Apply the above-mentioned Co-doped PT sol, immerse the ITO/glass substrate, pull the substrate at a pulling speed of 6cm/min after staying for 25 seconds, and place the sample horizontally to dry naturally to obtain a dry film; directly in a furnace at 600°C After rapid heat treatment for 8 minutes, it was quickly taken out and cooled naturally in air at room temperature to obtain a Co-doped PT stress-inducing layer. The XRD pattern of the Co-doped PT stress-inducing layer is shown in Figure 2. In addition to the diffraction peaks of the ITO conductive layer in Figure 2, only the (001)/(100) diffraction peaks and (002)/(002)/ The (200) diffraction peak indicates that the Zn-doped PT stress-inducing layer is a perovskite phase structure with preferential orientation growth.

Heat the mixed solution of acetic acid and ethylene glycol methyl ether as a solvent (wherein the content of acetic acid is 90%) to 70° C., put in lead acetate powder, strontium acetate powder, and liquid butyl titanate in sequence, and continue stirring for 72 hours to obtain PST50 sol, wherein The molar concentration of Ti is 0.4mol/L, and the molar ratio of Pb, Sr, and Ti elements is 0.50:0.50:1.

Using the above PST50 sol, dipping and pulling on the Co-doped PT stress-inducing layer to prepare the PST50 film: quickly immerse the substrate with the PT stress-inducing layer into the PST sol, and pull the substrate at a pulling speed of 6cm/min after staying for 25 seconds Solve the sol; place the wet film prepared by dipping and pulling together with the substrate horizontally to air-dry to obtain a dry film; directly sinter the dry film in a furnace at 600°C for 80 minutes, and slowly cool down with the furnace, repeat the "dipping and pulling- —drying—sintering—cooling” process 8 times to obtain a perovskite crystal phase PST film grown on the PT stress-inducing layer. The composite film formed by preparing the PST50 film on the doped PT stress-inducing layer is called the composite film PST50. The composite film PST50 presents a perovskite structure, as shown in Figure 3. Copper electrodes with a diameter of 0.2mm were plated on the composite film by magnetron sputtering, and the dielectric properties of the composite film were tested through copper electrodes and ITO electrodes. Affected by the stress-assisted modulation of the Co-doped PT stress-inducing layer, the composite film PST50 has a broadened Curie peak, as shown in Figure 6. In view of its broadened Curie peak, the dielectric tunability of the composite film PST50 has excellent temperature stability. The dielectric tunability of the composite film is changed from 35% to 32%, that is, the dielectric tunability of the composite film has good temperature stability.

By comparing the XRD pattern of the PT stress-inducing layer as shown in Figure 2 with the XRD pattern of the composite film of the present invention as shown in Figure 3, it can be seen that the two have similar diffraction peaks, indicating that the PT stress-inducing layer and the PST film are the same It belongs to perovskite structure. According to the positions of the XRD diffraction peaks in Figure 2 and Figure 3, the lattice constants of the doped PT stress-inducing layer and PST can be calculated. The lattice parameters of the PT stress-inducing layer are a=0.3950nm, c=0.4051nm, and the lattice constants of PST35, PST45, and PST50 films prepared on the PT stress-inducing layer are 0.3917nm, 0.3921nm, and 0.3922nm, respectively. The lattice parameter of PST is obviously larger than that of PST, so it can be concluded that in the direction of the film plane, the PST film is affected by the tensile stress of the doped PT stress-inducing layer.

From Example 1 to Example 3, comparing the room temperature adjustability as shown in Figure 7 and the high temperature as shown in Figure 8, it can be found that when the temperature rises from room temperature (20°C) to 200°C, the temperature of the composite film of the present invention The dielectric tunability is only slightly decreased from about 40% to about 35%, which shows that the dielectric tunability of the composite film of the present invention has good temperature stability.

Comparing Examples 1 to 3, because they are all subjected to stress-assisted modulation, the Curie temperatures of the composite films are almost the same, and they are all around room temperature, as shown in FIGS. 4 to 6 . Therefore, the dielectric tunability of the composite film PST35, composite film PST45, and composite film PST50 with three different chemical compositions is relatively close. If the electric field is increased, the dielectric tunability of the composite thin film PST35, composite thin film PST45, and composite thin film PST50 can be even higher. As shown in Figure 9, Figure 10 and Figure 11, when the electric field is doubled, the dielectric tunability values of the composite film PST35, composite film PST45, and composite film PST50 are 63%, 68%, and 65%, respectively, which are very close to each other. It fully demonstrates that the dielectric tunability of the multi-phase thin film of the present invention has good composition stability.

Claims (5)

1. the laminated film that the dielectric of a stress assisted modulation is adjustable, it is characterized in that: on the front surface of substrate (1), be coated with indium tin oxide conductive layer (2), lead titanates stress inducing layer (3) and strontium lead titanate film (4) from bottom to top successively, described lead titanates stress inducing layer (3) is for Perovskite Phase crystal structure and doped with impurity, and described impurity compares Ti for its ion size ⁴⁺size large and its chemical valence compares Ti ⁴⁺the little metal ion of chemical valence, described lead titanates stress inducing layer can apply tension to the lattice of strontium lead titanate film and make the tension of described laminated film in the gradient distribution of successively successively decreasing.

2. laminated film according to claim 1, is characterized in that: described lead titanates stress inducing layer (3) is the lead titanates doped with impurity, and described impurity is Zn ²⁺ion, Fe ³⁺ion or Co ²⁺ion.

3. laminated film according to claim 1 and 2, is characterized in that: in described lead titanates stress inducing layer (3), and the molar content of described impurity is 1% ~ 3%.

4. laminated film according to claim 1, is characterized in that: in described strontium lead titanate film (4), and the molar content of Pb is 35% ~ 50%.

5. a preparation method for the laminated film of claim 1, is characterized in that: use sol-gal process to plate lead titanates stress inducing layer (3) and strontium lead titanate film (4) from bottom to top successively at the front surface of the substrate (1) being coated with indium tin oxide conductive layer (2).