Lead-free piezoelectric film with high electromechanical response, piezoelectric device and preparation method thereof

Abstract

The invention discloses a lead-free piezoelectric film with high electromechanical response, a piezoelectric device and a preparation method thereof, and belongs to the field of lead-free piezoelectric film materials, the chemical general formula of the lead-free piezoelectric film is Nb1-yMnyOx, y represents the doping amount and is equal to 0-0.05, x represents the molar ratio of O atoms to Nb atoms, and 2.3 < = xlt; 2.5); comprising an NbOx-based binary lead-free piezoelectric film and a doping element, and the doping element is an Mn element. According to the lead-free piezoelectric film with high electromechanical response, the piezoelectric device and the preparation method of the piezoelectric device, the NbOx matrix is subjected to cation doping modification through the Mn element, and the structure of the lead-free piezoelectric film containing at least two crystal phases at room temperature is prepared in a magnetron sputtering mode; the coexisting phase structure can effectively activate interaction between crystal lattices and an external electric field, so that enhanced electromechanical response is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of lead-free piezoelectric film materials, and in particular to a lead-free piezoelectric film with high electromechanical response, a piezoelectric device and a preparation method thereof. Background Art

[0002] In the field of advanced functional materials, smart materials with significant electromechanical coupling effects (such as piezoelectric and ferroelectric materials) have become core components of modern sensing technology and energy conversion systems due to their unique mechanical energy-electrical energy bidirectional conversion characteristics. Such materials are widely used in key fields such as high-precision sensors (such as MEMS accelerometers), ultrasonic medical imaging probes, and sonar transducers, and their performance directly determines the sensitivity and energy conversion efficiency of the device.

[0003] Lead-based piezoelectric ceramic systems, represented by lead zirconate titanate (Pb(Zr,Ti)O3, PZT), have excellent piezoelectric coefficients (d 33 ≈500pC / N-600pC / N) and Curie temperature (Tc≈350℃), thus dominating the market for more than 60 years. However, the lead content in this material system is as high as 60% (in the form of PbO), which is prone to soluble lead pollution during preparation, use and disposal, causing irreversible damage to soil and groundwater systems.

[0004] To address this technical dilemma, academia and industry are accelerating the development of lead-free alternative materials. The most promising solutions currently include:

[0005] 1. Alkali metal niobate system: lead-free piezoelectric ceramics based on (K,Na)NbO3 (KNN) are controlled by adjusting the ratio of alkali metal ions at the A site (K + / Na + ≈50 / 50), achieved 33 =450pC / N-490pC / N high voltage electrical activity, its Curie temperature can reach 420℃ (better than traditional PZT);

[0006] 2. Defective niobate materials: such as Li / Ta co-doped (Na,K)(Nb,Sb)O3 system, by constructing local structural distortion, while maintaining d 33 ≈400pC / N, while increasing the electromechanical coupling coefficient to 62%;

[0007] However, the alkali metal elements (such as K + 、Na +) During the high-temperature sintering process, there is significant volatilization (K2O volatilization rate > 15% at 1000℃), which leads to a shift in the stoichiometric ratio; at the same time, the low activation energy of ion migration (about 0.8eV) easily causes grain boundary segregation, resulting in material microstructure inhomogeneity. Experiments show that a sintering process fluctuation of ±10℃ can cause the piezoelectric performance dispersion of KNN ceramics to reach ±12%, which poses a severe challenge to industrial-grade mass production. Summary of the invention

[0008] The purpose of the present invention is to provide a lead-free piezoelectric film with high electromechanical response, a piezoelectric device and a preparation method thereof, so as to solve the above-mentioned technical problems.

[0009] To achieve the above object, the present invention provides a lead-free piezoelectric film with high electromechanical response, the chemical formula of the lead-free piezoelectric film is: Nb 1-y Mn y O x , and the atomic ratios of Nb element, Mn element and O element are 0.95-1, 0-0.05, 2.3-2.5, wherein y represents the doping amount, and y=0-0.05, x represents the molar ratio of O atoms to Nb atoms, and 2.3≤x<2.5; including NbO x The invention relates to a binary lead-free piezoelectric film and a doping element, wherein the doping element is a Mn element.

[0010] A piezoelectric device comprises a substrate, a bottom electrode, a lead-free piezoelectric film with high electromechanical response and a top electrode which are arranged in sequence from bottom to top.

[0011] A method for preparing a piezoelectric device comprises the following steps:

[0012] S1. Select Nb2O5 and MnO as raw materials according to molar percentage, use anhydrous ethanol as ball milling medium, and roll ball mill to obtain uniform powder;

[0013] S2, drying the powder obtained in step S1 to obtain a uniformly mixed dry powder;

[0014] S3, adding the dry powder obtained in step S2 into a polyvinyl alcohol aqueous solution, and sequentially performing granulation, pressing and debinding to obtain a ceramic target material body;

[0015] S4, sintering the ceramic target material blank obtained in step S3 to obtain a ceramic target material;

[0016] S5, after growing a bottom electrode on the substrate, depositing the ceramic target material obtained in step S4 on the bottom electrode by magnetron sputtering to form a lead-free piezoelectric film;

[0017] S6. Growing a top electrode on the lead-free film obtained in step S5 by magnetron sputtering to obtain a piezoelectric device with a sandwich structure.

[0018] Preferably, in step S1, a nylon jar is used as the ball mill jar and a zirconium ball is used as the milling ball.

[0019] Preferably, the mass percentage of the polyvinyl alcohol aqueous solution in step S3 is 3wt%-8wt%;

[0020] The pressing step described in step S3 is: placing the dry powder in a mold with a cavity, and pressing the dry powder into a sheet using a hand-cranked tablet press or an electric tablet press, wherein the pressure of the electric tablet press is 10MPa-20MPa.

[0021] Preferably, the sintering temperature in step S4 is 1300° C. and the sintering time is 10 hours.

[0022] Preferably, the substrate material in step S5 is one of Si, glass, Al2O3, SrTiO3, LaAlO3, SrLaAlO4, MgO and any combination thereof;

[0023] The bottom electrode is one of a conductive metal and a conductive oxide, or a combination thereof;

[0024] In step S5, the process parameters of magnetron sputtering are adjusted so that the molar ratio x of O atoms to Nb atoms is in the range of 2.3-2.5.

[0025] Preferably, the bottom electrode is one of Pt, SrRuO3, LaNiO3, (La, Sr)MnO3, Au, Mo, Nb-doped SrTiO3 and any combination thereof.

[0026] Preferably, in the magnetron sputtering described in step S6, the sputtering power is set to 120W-200W, the temperature is set to 600°C-750°C, the sputtering time is set to 60min-240min, and a mixed gas of argon and oxygen is introduced at a pressure of 10mTorr-25mTorr during the whole process.

[0027] Preferably, the material of the top electrode in step S6 is one of Pt, Au, Ag, Al, Cu, TiN, ITO and any combination thereof.

[0028] Therefore, the present invention adopts the above-mentioned lead-free piezoelectric film with high electromechanical response, piezoelectric device and preparation method thereof, which has the following beneficial effects:

[0029] 1. Doping NbO with Mn x substrate, and obtain NbO with at least two kinds of NbO at room temperature by magnetron sputtering xThe structure of the piezoelectric film with a crystalline phase (orthorhombic T-monoclinic B phase, or pseudo-hexagonal TT-orthogonal T-monoclinic B phase, or orthorhombic T-monoclinic B-monoclinic H phase), the above multi-phase coexistence structure can effectively modulate the defect concentration of the intrinsic structure of the film material, so that the lattice can produce a more active strain response under the action of an external electric field; on this basis, by optimizing the process parameters, the defect concentration of the film can be further controlled, so that the prepared NbO x The lattice activation of the base piezoelectric film material makes it easier to respond to external electric fields, thereby obtaining enhanced electromechanical response;

[0030] 2. The AC conductivity of the prepared piezoelectric film material is 8×10 -9 S / cm, effective piezoelectric strain coefficient d under an applied AC unipolar voltage of 3V 33,f At a test frequency of 1kHz, it is about 631pm / V. The piezoelectric film material does not contain lead elements and is an environmentally friendly material. It is in line with the sustainable development strategy of the current international community and has a very wide range of applications.

[0031] 3. The preparation method is simple and stable, easy to operate, and convenient for industrial production.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of a method for preparing a piezoelectric device of the present invention;

[0034] Figure 2 is an X-ray diffraction pattern of the lead-free piezoelectric film described in Examples 1-5 of the present invention;

[0035] Figure 3 1 is a test result diagram of the electro-induced strain generated by the lead-free piezoelectric film described in Example 2 of the present invention when an alternating current (AC) unipolar voltage with an amplitude of 3V and a frequency of 1kHz is applied;

[0036] Figure 4 3 is a test result diagram of the electro-induced strain generated by the lead-free piezoelectric film described in Example 3 of the present invention when an alternating current (AC) unipolar voltage with an amplitude of 3V and a frequency of 1kHz is applied;

[0037] Figure 5 is an XPS analysis chart of the lead-free piezoelectric film described in Examples 1-5 of the present invention;

[0038] Figure 6 is the electrodisplacement δ and the effective piezoelectric coefficient d of the lead-free piezoelectric film described in Examples 1-5 of the present invention 33,f Comparison chart with changes in components x and y;

[0039] Figure 7 is a comparison diagram of the conductivity of the lead-free piezoelectric film described in Examples 1-5 of the present invention as a function of components x and y;

[0040] Figure 8 is the effective piezoelectric coefficient d generated by the lead-free piezoelectric film described in Example 2 of the present invention when an alternating current (AC) unipolar voltage of different amplitudes and a frequency of 1 kHz is applied. 33,f Plot of test results as a function of amplitude;

[0041] Fig. 9 is the effective piezoelectric coefficient d generated by the lead-free piezoelectric film described in Example 3 of the present invention when an alternating current (AC) unipolar voltage of different amplitudes and a frequency of 1 kHz is applied. 33,f Plot of test results as a function of amplitude. DETAILED DESCRIPTION

[0042] In order to make the purpose, technical scheme and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail in combination with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not used to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions.

[0043] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or inherent to these processes, methods, products or devices.

[0044] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0045] A lead-free piezoelectric film with high electromechanical response, the chemical formula of the lead-free piezoelectric film is: Nb 1- y Mn y O x, and the atomic ratios of Nb, Mn and O are 0.95-1, 0-0.05 and 2.3-2.5, otherwise, when the ratio changes, the phase structure will change, resulting in a decrease in its electromechanical response performance. In particular, when the atomic ratio of O is less than 2.3, the conductivity will increase significantly, making the sample unable to carry the test voltage, resulting in a decrease in its electromechanical response performance, where y represents the doping amount, and y = 0-0.05, x represents the molar ratio of O atoms to Nb atoms, and 2.3 ≤ x < 2.5; including NbO x The invention relates to a binary lead-free piezoelectric film and a doping element, wherein the doping element is a Mn element.

[0046] A piezoelectric device comprises a substrate, a bottom electrode, a lead-free piezoelectric film with high electromechanical response and a top electrode which are arranged in sequence from bottom to top.

[0047] like Figure 1 As shown, the method for preparing a piezoelectric device comprises the following steps:

[0048] S1. Select Nb2O5 and MnO as raw materials according to molar percentage, use anhydrous ethanol as ball milling medium, and roll ball mill to obtain uniform powder;

[0049] In step S1, a nylon jar is used as a ball mill jar and a zirconium ball is used as a milling ball.

[0050] S2, drying the powder obtained in step S1 to obtain a uniformly mixed dry powder;

[0051] S3, adding the dry powder obtained in step S2 into a polyvinyl alcohol aqueous solution, and sequentially performing granulation, pressing and debinding to obtain a ceramic target material body;

[0052] The mass percentage of the polyvinyl alcohol aqueous solution in step S3 is 3wt%-8wt%;

[0053] The pressing step described in step S3 is: placing the dry powder in a mold with a cavity, and pressing the dry powder into a sheet using a hand-cranked tablet press or an electric tablet press, wherein the pressure of the electric tablet press is 10MPa-20MPa.

[0054] S4, sintering the ceramic target material blank obtained in step S3 to obtain a ceramic target material;

[0055] The sintering temperature in step S4 is 1300° C. and the sintering time is 10 hours.

[0056] S5, after growing a bottom electrode on the substrate, depositing the ceramic target material obtained in step S4 on the bottom electrode by magnetron sputtering to form a lead-free piezoelectric film;

[0057] The substrate material in step S5 is one of Si, glass, Al2O3, SrTiO3, LaAlO3, SrLaAlO4, MgO and any combination thereof;

[0058] The bottom electrode is one of a conductive metal and a conductive oxide, or a combination thereof;

[0059] In step S5, the process parameters of magnetron sputtering are adjusted so that the molar ratio x of O atoms to Nb atoms is in the range of 2.3-2.5.

[0060] The bottom electrode is one of Pt, SrRuO3, LaNiO3, (La, Sr)MnO3, Au, Mo, Nb-doped SrTiO3 and any combination thereof.

[0061] S6. Growing a top electrode on the lead-free film obtained in step S5 by magnetron sputtering to obtain a piezoelectric device with a sandwich structure.

[0062] In the magnetron sputtering described in step S6, the sputtering power is set to 120W-200W, the temperature is set to 600°C-750°C, the sputtering time is set to 60min-240min, and a mixed gas of argon and oxygen is introduced at a pressure of 10mTorr-25mTorr during the whole process.

[0063] The material of the top electrode in step S6 is one of Pt, Au, Ag, Al, Cu, TiN, ITO and any combination thereof.

[0064] Example 1

[0065] In this embodiment, x=2.45, y=0, and the chemical formula of the lead-free piezoelectric film is NbO 2.45 .

[0066] A method for preparing a piezoelectric device comprises the following steps:

[0067] S1. Select Nb2O5 and MnO as raw materials according to molar percentage, use anhydrous ethanol as ball milling medium, and roll ball mill to obtain uniform powder;

[0068] S2, drying the powder obtained in S1 to obtain a uniformly mixed dry powder;

[0069] S3, adding polyvinyl alcohol aqueous solution to the dry powder obtained in S2, and sequentially performing granulation, pressing and debinding to obtain a ceramic target material body;

[0070] S4, sintering the ceramic target material blank obtained in S3 at 1300° C. for 10 hours to obtain a ceramic target material;

[0071] S5, using the ceramic target material obtained in S4 to deposit a lead-free piezoelectric film on a polycrystalline silicon substrate with a Pt bottom electrode by magnetron sputtering, and on the lead-free piezoelectric film obtained in S5, by adjusting the process parameters of magnetron sputtering, such as sputtering power and oxygen partial pressure, the defect concentration inside the film is adjusted to make x=2.45;

[0072] S6. On the lead-free piezoelectric film obtained in S5, a layer of Pt top electrode is grown by magnetron sputtering to obtain a lead-free piezoelectric device with a sandwich structure.

[0073] Example 2

[0074] Different from Example 1, in Example 2, x=2.37, y=0, and the chemical formula of the lead-free piezoelectric film is NbO 2.37 In the preparation method, the sputtering power and the oxygen partial pressure are adjusted so that the molar percentages of Nb and O in step S5 reach the ratio in the above chemical formula.

[0075] Example 3

[0076] Different from Example 1, in Example 3, x=2.37, y=0.02, and the chemical formula of the lead-free piezoelectric film is Nb 0.98 Mn 0.02 O 2.37 In step S1 of the preparation method, Nb2O5 and MnO are weighed according to the above chemical formula, and in step S5, the sputtering power and oxygen partial pressure are adjusted so that the molar percentages of Nb and O reach the ratio in the above chemical formula.

[0077] Example 4

[0078] Different from Example 1, in Example 4, x=2.33, y=0, and the chemical formula of the lead-free piezoelectric film is NbO 2.33 In step 5 of the preparation method, the sputtering power and the oxygen partial pressure are adjusted so that the molar percentages of Nb and O reach the ratio in the above chemical formula.

[0079] Example 5

[0080] Different from Example 1, in Example 5, x=2.26, y=0, and the chemical formula of the lead-free piezoelectric film is NbO 2.26 In step 5 of the preparation method, the sputtering power and the oxygen partial pressure are adjusted so that the molar percentages of Nb and O reach the ratio in the above chemical formula.

[0081] like Figure 2As shown, the lead-free piezoelectric films in Examples 1-5 all exhibit a multi-phase coexistence structure; among them, Examples 1-4 exhibit a "T+B" phase coexistence structure, and Example 5 exhibits a "T+M" phase coexistence structure.

[0082] like Figure 8 and Fig. 9 As shown, the effective piezoelectric coefficient of the lead-free piezoelectric film materials with electromechanical response of Examples 1-5 is tested. The test principle is: on the lead-free piezoelectric film sample, an alternating current (AC) unipolar voltage with an amplitude of 3V and a frequency of 1kHz is applied to excite the film to undergo periodic deformation, which is manifested as periodic displacement on the film surface. The laser beam of the laser vibrometer is tested through the Doppler effect to obtain the displacement size δ on the lead-free piezoelectric film sample, and then the size d of the effective piezoelectric coefficient is calculated according to the amplitude U of the input excitation voltage. 33,f =δ / U. Figure 3 As shown, the displacement of the lead-free piezoelectric film under an applied AC voltage was measured by a laser vibrometer. The electro-induced displacement value of Example 2 was 2172 pm, and the effective piezoelectric coefficient d was calculated. 33,f It is 724pm / V.

[0083] like Figure 4 As shown, the displacement of the lead-free piezoelectric film under an applied AC voltage was measured by a laser vibrometer. The electro-induced displacement value of Example 3 was 1893 pm, and the effective piezoelectric coefficient d was calculated. 33,f It is 631pm / V.

[0084] like Figure 5 As shown, in the lead-free piezoelectric film, when the x content is in the range of 2.33-2.37, the main profiles of the XRD diagram of the lead-free piezoelectric film shown in Example 2-4 remain basically consistent, indicating that the phase structure of the lead-free piezoelectric film shown in Example 2-4 is relatively stable, which is a multi-phase coexistence structure close to the "T+B" type.

[0085] like Figure 6 As shown, as x decreases, the d 33,f First increase and then decrease, in the range of x = 2.35-2.37, a higher d 33,f , up to 631pm / V-724pm / V.

[0086] like Figure 7 As shown, as x decreases, the conductivity of the samples of Examples 1-2, 4-5 gradually increases; as y increases, the conductivity of the samples of Examples 2-3 effectively decreases.

[0087] Table 1 Effective piezoelectric performance data of the lead-free piezoelectric film materials described in Examples 1-5

[0088]

[0089] It can be seen from Table 1 that when the molar ratio x of O atoms to Nb atoms is adjusted to 2.37, the effective piezoelectric coefficient of the prepared lead-free piezoelectric film can reach 724pm / V, which is much higher than 2.5pm / V of a higher x value (x=2.45) and much higher than 7.5pm / V of a lower x value (x=2.26).

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A lead-free piezoelectric film with high electromechanical response, characterized in that: The chemical formula of the lead-free piezoelectric film is: Nb 1-y Mn y O x , and the atomic ratios of Nb element, Mn element and O element are 0.95-1, 0-0.05, 2.3-2.5, wherein y represents the doping amount, and y=0-0.05, x represents the molar ratio of O atoms to Nb atoms, and 2.3≤x<2.5; including NbO x The invention relates to a binary lead-free piezoelectric film and a doping element, wherein the doping element is a Mn element.

2. A piezoelectric device, characterized in that: The invention comprises a substrate, a bottom electrode, the lead-free piezoelectric film with high electromechanical response as claimed in claim 1 and a top electrode which are arranged in sequence from bottom to top.

3. The method for preparing a piezoelectric device according to claim 2, characterized in that: The following steps are involved: S1. Select Nb2O5 and MnO as raw materials according to molar percentage, use anhydrous ethanol as ball milling medium, and roll ball mill to obtain uniform powder; S2, drying the powder obtained in step S1 to obtain a uniformly mixed dry powder; S3, adding the dry powder obtained in step S2 into a polyvinyl alcohol aqueous solution, and sequentially performing granulation, pressing and debinding to obtain a ceramic target material body; S4, sintering the ceramic target material blank obtained in step S3 to obtain a ceramic target material; S5, after growing a bottom electrode on the substrate, depositing the ceramic target material obtained in step S4 on the bottom electrode by magnetron sputtering to form a lead-free piezoelectric film; S6. Growing a top electrode on the lead-free film obtained in step S5 by magnetron sputtering to obtain a piezoelectric device with a sandwich structure.

4. The method for preparing a piezoelectric device according to claim 3, characterized in that: In step S1, a nylon jar is used as a ball mill jar and a zirconium ball is used as a milling ball.

5. The method for preparing a piezoelectric device according to claim 3, characterized in that: The mass percentage of the polyvinyl alcohol aqueous solution in step S3 is 3wt%-8wt%; The pressing step described in step S3 is: placing the dry powder in a mold with a cavity, and pressing the dry powder into a sheet using a hand-cranked tablet press or an electric tablet press, wherein the pressure of the electric tablet press is 10MPa-20MPa.

6. The method for preparing a piezoelectric device according to claim 3, characterized in that: The sintering temperature in step S4 is 1300° C. and the sintering time is 10 hours.

7. The method for preparing a piezoelectric device according to claim 3, characterized in that: The substrate material in step S5 is one of Si, glass, Al2O3, SrTiO3, LaAlO3, SrLaAlO4, MgO and any combination thereof; The bottom electrode is one of a conductive metal and a conductive oxide, or a combination thereof; In step S5, the process parameters of magnetron sputtering are adjusted so that the molar ratio x of O atoms to Nb atoms is in the range of 2.3-2.

5.

8. The method for preparing a piezoelectric device according to claim 7, characterized in that: The bottom electrode is one of Pt, SrRuO3, LaNiO3, (La, Sr)MnO3, Au, Mo, Nb-doped SrTiO3 and any combination thereof.

9. The method for preparing a piezoelectric device according to claim 3, characterized in that: In the magnetron sputtering described in step S6, the sputtering power is set to 120W-200W, the temperature is set to 600°C-750°C, the sputtering time is set to 60min-240min, and a mixed gas of argon and oxygen is introduced at a pressure of 10mTorr-25mTorr during the whole process.

10. The method for preparing a piezoelectric device according to claim 3, characterized in that: The material of the top electrode in step S6 is one of Pt, Au, Ag, Al, Cu, TiN, ITO and any combination thereof.

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