A self-biased piezoelectric thin film and its preparation method and application

Abstract

The present invention relates to a self - biased piezoelectric thin film, a preparation method thereof and an application thereof. The self - biased piezoelectric thin film includes a conductive part, a piezoelectric thin film layer and a top electrode which are arranged along the thickness direction of the self - biased piezoelectric thin film; the conductive part includes an oxide layer, or a bottom electrode and an oxide layer which are stacked; the oxide layer is arranged on the side close to the piezoelectric thin film layer; the material of the oxide layer includes LaNi 1+x O3, MgO or any one or a combination of at least two of SrRuO3. By selecting a specific material for the oxide layer, a potential difference is generated between the conductive part and the top electrode, so that a built - in electric field is generated inside the self - biased piezoelectric thin film, and a self - biased piezoelectric thin film is obtained. Due to the existence of the self - bias voltage, no pre - polarization treatment is required during use, and an ideal displacement can be obtained at a low voltage, which helps to further reduce the size and power consumption of electronic devices, and no depolarization phenomenon will occur during the use of electronic devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of piezoelectric materials, and relates to a piezoelectric thin film and its preparation method and application, and particularly relates to a self-biased piezoelectric ceramic thin film and its preparation method and application. Background Art

[0002] Ferroelectric materials have excellent ferroelectricity, piezoelectricity, pyroelectricity, dielectricity and optoelectronic properties, and ferroelectric thin films are one of the important functional device raw materials in the electronics industry. It can utilize the piezoelectric effect to realize the mutual conversion between external mechanical stimuli and electric energy, or can utilize electric energy to achieve mechanical response. Perovskite ferroelectric thin films have unique structural and performance advantages and have become the most widely studied and applied ferroelectric thin films.

[0003] Lead zirconate titanate (PZT) is a representative material of perovskite ferroelectric thin films, with excellent piezoelectric properties and good stability, and is a widely used ferroelectric thin film material. However, the high preparation temperature and the complex structural state of multiple phases and domains lead to a series of problems in its actual application process.

[0004] CN112928200A discloses a lead zirconate titanate piezoelectric thin film and its preparation method and application. It uses perovskite oxide lanthanum nickelate as a buffer layer to prepare a lead zirconate titanate piezoelectric thin film, and obtains a piezoelectric thin film with excellent performance through two-step annealing. However, when preparing the buffer layer, it needs to use radio frequency magnetron sputtering and also needs high-temperature annealing to obtain a piezoelectric thin film with excellent crystal orientation, which seriously increases the production cycle of the piezoelectric thin film.

[0005] CN108511112A discloses a lanthanum nickelate conductive thin film and its preparation method and application. This method uses pulsed laser deposition to prepare a LaNi 1+δ O 3 conductive thin film, and with a high oxygen pressure annealing process, the resistivity of the prepared LNO conductive thin film is not affected by stress. However, this method uses a single crystal strontium titanate substrate, resulting in a high preparation cost; in addition, the lattice compatibility between Si and LNO is poor, resulting in difficulty in forming texture for LNO. Moreover, this method requires long-time high-temperature annealing, which also increases the preparation cost.

[0006] Therefore, there is a need to provide a self-biased piezoelectric thin film with low cost and guaranteed quality, and its preparation method and application. Summary of the Invention

[0007] The object of the present invention is to provide a self - biased piezoelectric thin film, a preparation method and an application thereof. By selecting a specific material for the oxide layer, a potential difference is generated between the conductive part and the top electrode, thereby generating a built - in electric field inside the self - biased piezoelectric thin film, and a self - biased piezoelectric thin film is obtained. Due to the existence of the self - bias voltage, no pre - polarization treatment is required during use, an ideal displacement can be obtained at a low voltage, which helps to further reduce the size and power consumption of electronic devices, and depolarization does not occur during the use of electronic devices.

[0008] To achieve the object of the present invention, the following technical solutions are adopted:

[0009] In a first aspect, the present invention provides a self - biased piezoelectric thin film, which includes a conductive part, a piezoelectric thin film layer and a top electrode arranged along the thickness direction of the self - biased piezoelectric thin film;

[0010] The conductive part includes an oxide layer, or a bottom electrode and an oxide layer arranged in a stacked manner;

[0011] The oxide layer is arranged on the side close to the piezoelectric thin film layer;

[0012] The material of the oxide layer includes LaNi 1+x O 3 、MgO or SrRuO 3 Any one or a combination of at least two of them, where the value range of x is from 0.05 to 0.15. For example, it can be 0.05, 0.08, 0.1, 0.12 or 0.15, but is not limited to the listed values, and the remaining unlisted values within the value range are equally applicable.

[0013] For the piezoelectric material in the piezoelectric thin film layer, its intrinsic contribution to piezoelectric performance comes from the displacement of the central ions. When an external electric field is applied, the displacement of the central ions inside the crystal will cause the lattice to deform, and macroscopic deformation occurs to generate the piezoelectric effect. The present invention generates a potential difference between the conductive part and the top electrode by specifically selecting the material of the oxide layer, thereby generating a built - in electric field inside the self - biased piezoelectric thin film, and a self - biased piezoelectric thin film is obtained. Due to the existence of the self - bias voltage, no pre - polarization treatment is required during use, an ideal displacement can be obtained at a low voltage, which helps to further reduce the size and power consumption of electronic devices, and depolarization does not occur during the use of electronic devices.

[0014] In addition, for specific application scenarios, such as piezoelectric MEMS (Micro - Electro - Mechanical System) speakers, due to the self - polarization of the self - biased piezoelectric thin film, its transverse piezoelectric coefficient shows high linearity under different external electric fields, avoiding distortion during the use of MEMS speakers.

[0015] Preferably, the material of the top electrode includes any one or a combination of at least two of titanium (Ti), platinum (Pt), gold (Au), chromium (Cr), or aluminum (Al). Typical but non-limiting combinations include the combination of Ti and Pt, the combination of Au and Cr, the combination of Pt and Al, the combination of Ti, Pt, and Au, the combination of Au, Cr, and Al, or the combination of Ti, Pt, Au, Cr, and Al.

[0016] When the material of the top electrode is a combination of at least two elements, it includes sequential individual deposition of each element or simultaneous deposition of each element.

[0017] Preferably, the material of the bottom electrode includes any one or a combination of at least two of titanium (Ti), platinum (Pt), gold (Au), chromium (Cr), or aluminum (Al). Typical but non-limiting combinations include the combination of Ti and Pt, the combination of Au and Cr, the combination of Pt and Al, the combination of Ti, Pt, and Au, the combination of Au, Cr, and Al, or the combination of Ti, Pt, Au, Cr, and Al.

[0018] When the material of the bottom electrode is a combination of at least two elements, it includes sequential individual deposition of each element or simultaneous deposition of each element.

[0019] Preferably, the material of the piezoelectric thin film layer includes lead zirconate titanate (Pb a Zr 1-a TiO 3 , 0 < a < 1).

[0020] Preferably, the self - biased piezoelectric thin film further includes a substrate disposed on the side of the conductive portion away from the piezoelectric thin film layer.

[0021] Preferably, the material of the substrate includes any one or a combination of at least two of silicon, quartz, silicon - on - insulator, or 316 stainless steel.

[0022] Preferably, in order to enhance the adhesion between the substrate and the conductive portion, an adhesion layer is provided between the substrate and the conductive portion.

[0023] Preferably, the thickness of the adhesion layer is 18 - 22 nm. For example, it can be 18 nm, 19 nm, 20 nm, 21 nm, or 22 nm, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0024] Preferably, when the material of the oxide layer is LaNi 1+x O 3 the oxide layer is prepared by magnetron sputtering of a lanthanum nickelate (LNO) target.

[0025] Preferably, in the lanthanum nickelate target, the molar ratio of La, Ni, and O is 1:(1.05 - 1.15):(2.65 - 2.75).

[0026] In the lanthanum nickelate target, the molar ratio of La to Ni is 1:(1.05 - 1.15). For example, it can be 1:1.05, 1:1.08, 1:1.1, 1:1.12, or 1:1.15, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0027] In the lanthanum nickelate target, the molar ratio of La to O is 1:(2.65 - 2.75). For example, it can be 1:2.65, 1:2.68, 1:2.7, 1:2.72, or 1:2.75, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0028] The conductivity of the oxide layer is affected by the orientation and composition. For an oxide layer with a perovskite oxide composition, when using the magnetron sputtering method for preparation, only radio frequency magnetron sputtering can be used, and direct current magnetron sputtering cannot be used, which greatly limits its mass production prospects. The present invention controls the molar ratio of La, Ni, and O in the lanthanum nickelate target to form a lanthanum nickelate target with oxygen deficiency, which has excellent electrical conductivity and can use direct current magnetron sputtering for the preparation of the oxide layer.

[0029] Moreover, by controlling the molar ratio of La, Ni, and O in the lanthanum nickelate target, when using the lanthanum nickelate target for the preparation of the oxide layer, oxide layers with different work functions can be obtained.

[0030] Preferably, the preparation method of the lanthanum nickelate target includes the following steps:

[0031] Wet ball-mill and mix La 2 O 3 with Ni 2 O 3 According to the formula amount. After drying the ball-milled material, sinter it in an atmosphere with an oxygen content ≤ 21 vol%, and cool it naturally to obtain a sintered material; the sintered material is made into a green body by cold isostatic pressing, and then heat-treated in an atmosphere with an oxygen content ≤ 21 vol% to obtain the lanthanum nickelate target.

[0032] Wet ball-mill and mix La 2 O 3 with Ni 2 O 3 means that in the obtained lanthanum nickelate target, the molar ratio of La to Ni is 1:(1.05 - 1.15).

[0033] Atmospheric pressure sintering and heat treatment are carried out in an atmosphere with an oxygen content ≤ 21 vol%, and by adjusting the oxygen content, a molar ratio of La to O of 1:(2.65 - 2.75) can be achieved.

[0034] During sintering and heat treatment, the lower the oxygen content in the atmosphere, the lower the content of element O in the obtained lanthanum nickelate target; the higher the oxygen content in the atmosphere, the higher the content of element O in the obtained lanthanum nickelate target. In order to make the molar ratio of La to O in the lanthanum nickelate target 1:(2.65 - 2.75), during sintering and heat treatment, the oxygen content ≤ 21 vol%, for example, it can be 5 vol%, 10 vol%, 15 vol%, 20 vol% or 21 vol%, but not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0035] Preferably, zirconia is used as the ball milling medium and absolute ethanol is used as the grinding aid in the wet ball milling.

[0036] Preferably, the sintering temperature is 880 - 920 °C, for example, it can be 880 °C, 890 °C, 900 °C, 910 °C or 920 °C, but not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0037] Preferably, the heat treatment temperature is 960 - 1000 °C, for example, it can be 960 °C, 970 °C, 980 °C, 990 °C or 1000 °C, but not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0038] In a second aspect, the present invention provides a method for preparing the self - biased piezoelectric thin film described in the first aspect, characterized in that the preparation method includes the following steps:

[0039] The conductive part, the piezoelectric thin film layer and the top electrode are sequentially deposited by magnetron sputtering to obtain the self - biased piezoelectric thin film;

[0040] The conductive part includes an oxide layer, or a bottom electrode and an oxide layer arranged in a stacked manner;

[0041] The oxide layer is arranged on the side close to the piezoelectric thin film layer.

[0042] Preferably, the magnetron sputtering method for the bottom electrode includes DC magnetron sputtering.

[0043] The magnetron sputtering temperature of the bottom electrode is 25 - 100 °C, for example, it can be 25 °C, 40 °C, 50 °C, 60 °C, 80 °C or 100 °C, but not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0044] Exemplarily, the process parameters for preparing the bottom electrode by DC magnetron sputtering include: the heating rate is ≤ 12 °C / min, under the conditions of a magnetron sputtering temperature of 25 - 100 °C and an absolute pressure of 0.3 - 0.5 Pa, the target-substrate distance is controlled to be 40 - 50 mm, and magnetron sputtering is carried out under the condition of a power density of 1.5 - 2.5 W / cm 2 to complete the preparation of the bottom electrode with a thickness of 90 - 110 nm; the sputtering atmosphere is argon.

[0045] Preferably, the magnetron sputtering method for the oxide layer includes DC magnetron sputtering or RF magnetron sputtering.

[0046] Preferably, the magnetron sputtering temperature of the oxide layer is 300 - 600 °C. For example, it can be 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C or 600 °C, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0047] Exemplarily, taking the material of the oxide layer as LaNi 1+x O 3 (0.05 ≤ x ≤ 0.15) as an example, the process parameters for preparing the oxide layer by DC magnetron sputtering include: the heating rate is ≤ 15 °C / min, under the conditions of a magnetron sputtering temperature of 300 - 500 °C and an absolute pressure of 0.3 - 0.5 Pa, the target-substrate distance is controlled to be 35 - 45 mm, and magnetron sputtering is carried out under the condition of a power density of 2.2 - 2.5 W / cm 2 to complete the preparation of the oxide layer with a thickness of 90 - 110 nm; the sputtering atmosphere is argon and oxygen with a volume ratio of 40:15.

[0048] Preferably, the magnetron sputtering method for the piezoelectric thin film layer includes RF magnetron sputtering.

[0049] Preferably, the magnetron sputtering temperature of the piezoelectric thin film layer is 400 - 650 °C. For example, it can be 400 °C, 450 °C, 500 °C, 550 °C, 600 °C or 650 °C, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0050] Exemplarily, the process parameters for preparing the piezoelectric thin film layer by RF magnetron sputtering include: the heating rate is ≤ 15 °C / min, under the conditions of a magnetron sputtering temperature of 550 - 650 °C and an absolute pressure of 0.3 - 0.5 Pa, the target-substrate distance is controlled to be 45 - 55 mm, and magnetron sputtering is carried out under the condition of a power density of 1.8 - 2.2 W / cm 2 to complete the preparation of the piezoelectric thin film layer with a thickness of 1.8 - 2.2 μm; the sputtering atmosphere is argon and oxygen with a volume ratio of 32:8.

[0051] Preferably, the magnetron sputtering method for the top electrode includes DC magnetron sputtering.

[0052] Preferably, the magnetron sputtering temperature of the top electrode is 25 - 100 °C. For example, it can be 25 °C, 40 °C, 50 °C, 60 °C, 80 °C or 100 °C, but is not limited to the listed values, and the other unlisted values within the numerical range are equally applicable.

[0053] Exemplarily, the process parameters for preparing the top electrode by DC magnetron sputtering include: the heating rate ≤ 12 °C / min, under the conditions of a magnetron sputtering temperature of 25 - 100 °C and an absolute pressure of 0.3 - 0.5 Pa, controlling the target-substrate distance to be 40 - 50 mm, and magnetron sputtering under the condition of a power density of 1.5 - 2.5 W / cm 2 , and keeping warm for 10 - 20 min to complete the preparation of the top electrode; the sputtering atmosphere is argon.

[0054] In a third aspect, the present invention provides an electronic device, and the electronic device includes the self-biased piezoelectric thin film described in the second aspect.

[0055] Compared with the prior art, the present invention has the following beneficial effects:

[0056] Through the specific selection of the oxide layer material, the present invention generates a potential difference between the conductive part and the top electrode, thereby generating a built-in electric field inside the self-biased piezoelectric thin film and obtaining a self-biased piezoelectric thin film. Due to the existence of the self-bias voltage, pre-polarization treatment is no longer required during use, and an ideal displacement can be obtained at a low voltage, which helps to further reduce the size and power consumption of the electronic device, and depolarization will not occur during the use of the electronic device. Description of the Drawings

[0057] Figure 1 Schematic structural diagram of the self-biased piezoelectric thin film provided for Example 1;

[0058] Figure 2 Transverse piezoelectric coefficients of the self-biased piezoelectric thin films obtained in Examples 1 - 6 and Comparative Examples 1 - 2;

[0059] Figure 3 Electric hysteresis loop of the self-biased piezoelectric thin film obtained in Example 1.

[0060] Wherein: 101, silicon substrate; 102, bottom electrode; 103, oxide layer; 104, piezoelectric thin film layer; 105, top electrode. Detailed Embodiments

[0061] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0062] To clearly illustrate the technical solution of the present invention, in the specific embodiment, the material of the piezoelectric thin film layer is Pb 0.52 Zr 0.48 TiO 3 , and this description is not regarded as a further limitation to the present invention.

[0063] Example 1

[0064] This embodiment provides a self - biasing piezoelectric thin film as Figure 1 shown, and the self - biasing piezoelectric thin film includes a conductive part, a piezoelectric thin film layer 104 and a top electrode 105 arranged along the thickness direction of the self - biasing piezoelectric thin film;

[0065] The conductive part includes a bottom electrode 102 and an oxide layer 103 arranged in a stacked manner;

[0066] The oxide layer 103 is arranged on the side close to the piezoelectric thin film layer 104;

[0067] The material of the bottom electrode 102 is Pt, the material of the oxide layer 103 is LaNi 1.1 O 3 , and the material of the top electrode 105 is Pt.

[0068] The oxide layer 103 is prepared by using a lanthanum nickelate target, and in the lanthanum nickelate target, the molar ratio of La, Ni, and O is 1:1.1:2.7;

[0069] The preparation method of the lanthanum nickelate target includes the following steps:

[0070] Using zirconia as the ball - milling medium and absolute ethanol as the grinding aid, wet - ball - mill and mix La 2 O 3 and Ni 2 O 3 according to the formula amount. After drying the ball - milled material, sinter it in an air atmosphere at 900 °C for 12 h and cool it naturally to obtain the sintered material; the sintered material is made into a green body by cold isostatic pressing, and then heat - treated in an air atmosphere at 980 °C to obtain the lanthanum nickelate target;

[0071] The preparation method of the self - biasing piezoelectric thin film includes the following steps:

[0072] (1) Select a single - polished 3 - inch silicon substrate 101 with a thickness of 625 μm, and grow a 300 - nm - thick silicon dioxide layer on the polished surface by PECVD;

[0073] (2) To increase the adhesion between the silicon substrate 101 and the bottom electrode 102, a Ti adhesion layer with a thickness of 20 nm is deposited by DC magnetron sputtering: heated to 100 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, controlling the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; after the magnetron sputtering is completed, keep the temperature for 15 min;

[0074] (3) The bottom electrode 102 with a thickness of 100 nm is prepared by DC magnetron sputtering: heated to 100 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, controlling the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; after the magnetron sputtering is completed, keep the temperature for 15 min;

[0075] (4) The oxide layer 103 with a thickness of 100 nm is prepared by DC magnetron sputtering: heated to 400 °C at a rate of 15 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon-oxygen atmosphere with a volume ratio of 40:15, controlling the target-substrate distance to 40 mm, and performing magnetron sputtering under the condition of a power density of 2.4 W / cm 2 ;

[0076] (5) The piezoelectric thin film layer 104 with a thickness of 2 μm is prepared by RF magnetron sputtering: under the conditions of a temperature of 600 °C, an absolute pressure of 0.5 Pa, and an argon-oxygen atmosphere with a volume ratio of 32:8, controlling the target-substrate distance to 50 mm, and performing magnetron sputtering under the condition of a power density of 2 W / cm 2 ;

[0077] (6) The top electrode 105 with a thickness of 100 nm is prepared by DC magnetron sputtering: set the mask plate, heated to 100 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, controlling the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; after the magnetron sputtering is completed, keep the temperature for 15 min.

[0078] The transverse piezoelectric coefficient of the self-biased piezoelectric thin film obtained in this example is as Figure 2 shown, and the polarization hysteresis loop is as Figure 3 shown.

[0079] Example 2

[0080] This example provides a self-biased piezoelectric thin film, which includes a conductive part, a piezoelectric thin film layer, and a top electrode arranged along the thickness direction of the self-biased piezoelectric thin film;

[0081] The conductive part includes a bottom electrode and an oxide layer arranged in a stacked manner;

[0082] The oxide layer is disposed on one side close to the piezoelectric thin film layer;

[0083] The bottom electrode is made of Pt, the oxide layer is made of MgO, and the top electrode is made of Pt.

[0084] The preparation method of the self - biased piezoelectric thin film includes the following steps:

[0085] (1) Select a single - polished 3 - inch silicon substrate with a thickness of 625 μm, and use PECVD to grow a silicon dioxide layer with a thickness of 300 nm on the polished surface;

[0086] (2) To increase the adhesion between the silicon substrate and the bottom electrode, deposit a Ti adhesion layer with a thickness of 20 nm by DC magnetron sputtering: heat it to 100 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 45 mm, and the power density to 2 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min;

[0087] (3) Prepare a bottom electrode with a thickness of 100 nm by DC magnetron sputtering: heat it to 100 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 45 mm, and the power density to 2 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min;

[0088] (4) Prepare an oxide layer with a thickness of 100 nm by RF magnetron sputtering: heat it to 300 °C at a rate of 15 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 40 mm, and magnetron sputter under the condition of a power density of 2 W / cm 2 ;

[0089] (5) Prepare a piezoelectric thin film layer with a thickness of 2 μm by RF magnetron sputtering: under the conditions of a temperature of 600 °C, an absolute pressure of 0.5 Pa, and an argon - oxygen atmosphere with a volume ratio of 32:8, control the target - substrate distance to 50 mm, and magnetron sputter under the condition of a power density of 2 W / cm 2 ;

[0090] (6) Prepare a top electrode with a thickness of 100 nm by DC magnetron sputtering: set a mask plate, heat it to 100 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 45 mm, and the power density to 2 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min.

[0091] The transverse piezoelectric coefficient of the self - biased piezoelectric thin film obtained in this embodiment is as Figure 2 shown.

[0092] Example 3

[0093] This example provides a self - biased piezoelectric thin film, which includes a conductive part, a piezoelectric thin film layer, and a top electrode arranged along the thickness direction of the self - biased piezoelectric thin film;

[0094] The conductive part includes an oxide layer;

[0095] The material of the oxide layer is LaNi 1.12 O 3 , and the material of the top electrode is Pt;

[0096] The oxide layer is prepared by using a lanthanum nickelate target, in which the molar ratio of La, Ni, and O is 1:1.12:2.72;

[0097] The preparation method of the lanthanum nickelate target includes the following steps:

[0098] Using zirconia as the ball - milling medium and anhydrous ethanol as the grinding aid, wet - ball - mill and mix La 2 O 3 and Ni 2 O 3 according to the formula amount. After drying the ball - milled material, sinter it in an air atmosphere at 900 °C for 12 h and cool it naturally to obtain a sintered material; the sintered material is made into a green body by cold isostatic pressing, and then heat - treated in an air atmosphere at 980 °C to obtain the lanthanum nickelate target;

[0099] The preparation method of the self - biased piezoelectric thin film includes the following steps:

[0100] (1) Select a single - polished 3 - inch silicon substrate with a thickness of 625 μm, and use PECVD to grow a 300 - nm - thick silicon dioxide layer on the polished surface;

[0101] (2) Prepare an oxide layer with a thickness of 100 nm by DC magnetron sputtering: heat it to 400 °C at a rate of 15 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an atmosphere of argon and oxygen with a volume ratio of 40:15, control the target - substrate distance to be 40 mm, and magnetron sputter under the condition of a power density of 2.4 W / cm 2 ;

[0102] (3) Prepare a piezoelectric thin film layer with a thickness of 2 μm by RF magnetron sputtering: under the conditions of a temperature of 600 °C, an absolute pressure of 0.5 Pa, and an atmosphere of argon and oxygen with a volume ratio of 32:8, control the target - substrate distance to be 50 mm, and magnetron sputter under the condition of a power density of 2 W / cm 2 ;

[0103] (4) Preparation of the top electrode with a thickness of 100 nm by DC magnetron sputtering: Set the mask plate, heat it to 100 °C at a rate of 12 °C / min, and under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; After the magnetron sputtering is completed, keep the temperature for 15 min.

[0104] The transverse piezoelectric coefficient of the self-biased piezoelectric thin film obtained in this example is as Figure 2 shown.

[0105] Example 4

[0106] This example provides a self-biased piezoelectric thin film, except that the material of the conductive oxide layer is SrRuO 3 other than that, the rest are the same as in Example 1.

[0107] The transverse piezoelectric coefficient of the self-biased piezoelectric thin film obtained in this example is as Figure 2 shown.

[0108] Example 5

[0109] This example provides a self-biased piezoelectric thin film, and the self-biased piezoelectric thin film includes a conductive part, a piezoelectric thin film layer, and a top electrode arranged along the thickness direction of the self-biased piezoelectric thin film;

[0110] The conductive part includes a bottom electrode and an oxide layer arranged in a stacked manner;

[0111] The oxide layer is arranged on the side close to the piezoelectric thin film layer;

[0112] The material of the bottom electrode is Pt, the material of the oxide layer is LaNi 1.05 O 3 , and the material of the top electrode is Pt.

[0113] The oxide layer is prepared by using a lanthanum nickelate target, and in the lanthanum nickelate target, the molar ratio of La, Ni, and O is 1:1.05:2.65;

[0114] The preparation method of the lanthanum nickelate target includes the following steps:

[0115] Using zirconia as the ball-milling medium and absolute ethanol as the grinding aid, wet ball-mill and mix La 2 O 3 and Ni 2 O 3 according to the formula amount. After drying the ball-milled material, sinter it at 880 °C for 12 h in an air atmosphere, and cool it naturally to obtain the sintered material; the sintered material is made into a green body by cold isostatic pressing, and then heat-treated at 960 °C in an air atmosphere to obtain the lanthanum nickelate target;

[0116] The preparation method of the self - biased piezoelectric thin film includes the following steps:

[0117] (1) Select a single - polished 3 - inch silicon substrate with a thickness of 625 μm, and grow a silicon dioxide layer with a thickness of 300 nm on the polished surface by PECVD;

[0118] (2) To increase the adhesion between the silicon substrate and the bottom electrode, deposit a Ti adhesion layer with a thickness of 20 nm by DC magnetron sputtering: heat up to 50 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 40 mm and the power density to 1.5 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min;

[0119] (3) Prepare a bottom electrode with a thickness of 100 nm by DC magnetron sputtering: heat up to 50 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 40 mm and the power density to 1.5 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min;

[0120] (4) Prepare an oxide layer with a thickness of 100 nm by DC magnetron sputtering: heat up to 300 °C at a rate of 15 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon - oxygen atmosphere with a volume ratio of 40:15, control the target - substrate distance to 35 mm, and magnetron sputter under the condition of a power density of 2.2 W / cm 2 ;

[0121] (5) Prepare a piezoelectric thin - film layer with a thickness of 2 μm by RF magnetron sputtering: under the conditions of a temperature of 550 °C, an absolute pressure of 0.5 Pa, and an argon - oxygen atmosphere with a volume ratio of 32:8, control the target - substrate distance to 45 mm, and magnetron sputter under the condition of a power density of 1.8 W / cm 2 ;

[0122] (6) Prepare a top electrode with a thickness of 100 nm by DC magnetron sputtering: set the mask plate, heat up to 50 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 40 mm and the power density to 1.5 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min.

[0123] The transverse piezoelectric coefficient of the self - biased piezoelectric thin film obtained in this example is as Figure 2 shown.

[0124] Example 6

[0125] This embodiment provides a self - biased piezoelectric thin film, which includes a conductive part, a piezoelectric thin film layer, and a top electrode arranged along the thickness direction of the self - biased piezoelectric thin film;

[0126] The conductive part includes a bottom electrode and an oxide layer arranged in a stacked manner;

[0127] The oxide layer is arranged on the side close to the piezoelectric thin film layer;

[0128] The material of the bottom electrode is Pt, and the material of the oxide layer is LaNi 1.15 O 3 , and the material of the top electrode is Pt.

[0129] The oxide layer is prepared by using a lanthanum nickelate target, and in the lanthanum nickelate target, the molar ratio of La, Ni, and O is 1:1.15:2.75;

[0130] The preparation method of the lanthanum nickelate target includes the following steps:

[0131] Using zirconia as the ball - milling medium and anhydrous ethanol as the grinding aid, wet - ball - mill and mix La 2 O 3 and Ni 2 O 3 according to the formula amount. After drying the ball - milled material, sinter it at 920 °C for 12 h in an air atmosphere, and cool it naturally to obtain the sintered material; the sintered material is made into a green body by cold isostatic pressing, and then heat - treated at 1000 °C in an air atmosphere to obtain the lanthanum nickelate target;

[0132] The preparation method of the self - biased piezoelectric thin film includes the following steps:

[0133] (1) Select a single - polished 3 - inch silicon substrate with a thickness of 625 μm, and use PECVD to grow a silicon dioxide layer with a thickness of 300 nm on the polished surface;

[0134] (2) To increase the adhesion between the silicon substrate and the bottom electrode, deposit a Ti adhesion layer with a thickness of 20 nm by DC magnetron sputtering: heat it to 25 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 50 mm and the power density to 2.5 W / cm 2 ; after magnetron sputtering, keep it warm for 15 min;

[0135] (3) Prepare a bottom electrode with a thickness of 100 nm by DC magnetron sputtering: heat it to 25 °C at a rate of 12 °C / min, under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target - substrate distance to 50 mm and the power density to 2.5 W / cm 2 ; after magnetron sputtering, keep it warm for 15 min;

[0136] (4) Preparation of an oxide layer with a thickness of 100 nm by DC magnetron sputtering: Heat up to 500 °C at a rate of 15 °C / min. Under the conditions of an absolute pressure of 0.5 Pa and an atmosphere of argon and oxygen with a volume ratio of 40:15, control the target-substrate distance to be 45 mm, and perform magnetron sputtering under the condition of a power density of 2.5 W / cm 2 ;

[0137] (5) Preparation of a piezoelectric thin film layer with a thickness of 2 μm by RF magnetron sputtering: Under the conditions of a temperature of 650 °C, an absolute pressure of 0.5 Pa, and an atmosphere of argon and oxygen with a volume ratio of 32:8, control the target-substrate distance to be 55 mm, and perform magnetron sputtering under the condition of a power density of 2.2 W / cm 2 ;

[0138] (6) Preparation of a top electrode with a thickness of 100 nm by DC magnetron sputtering: Set up a mask plate, heat up to 25 °C at a rate of 12 °C / min. Under the conditions of an absolute pressure of 0.5 Pa and an atmosphere of argon, control the target-substrate distance to be 50 mm and the power density to be 2.5 W / cm 2 ; After magnetron sputtering, keep the temperature for 15 min.

[0139] The transverse piezoelectric coefficient of the self-biased piezoelectric thin film obtained in this example is as Figure 2 shown.

[0140] Comparative Example 1

[0141] This comparative example provides a self-biased piezoelectric thin film, which includes a conductive part, a piezoelectric thin film layer, and a top electrode arranged along the thickness direction of the self-biased piezoelectric thin film;

[0142] The conductive part includes a bottom electrode;

[0143] The material of the bottom electrode is Pt, and the material of the top electrode is Pt.

[0144] The preparation method of the self-biased piezoelectric thin film includes the following steps:

[0145] (1) Select a single-polished 3-inch silicon substrate with a thickness of 625 μm, and grow a silicon dioxide layer with a thickness of 300 nm on the polished surface using PECVD;

[0146] (2) To increase the adhesion between the silicon substrate and the bottom electrode, deposit a Ti adhesion layer with a thickness of 20 nm by DC magnetron sputtering: Heat up to 100 °C at a rate of 12 °C / min. Under the conditions of an absolute pressure of 0.5 Pa and an atmosphere of argon, control the target-substrate distance to be 45 mm and the power density to be 2 W / cm 2 ; After magnetron sputtering, keep the temperature for 15 min;

[0147] (3) Preparation of the bottom electrode with a thickness of 100 nm by DC magnetron sputtering: Heat up to 100 °C at a rate of 12 °C / min, and under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; After the magnetron sputtering is completed, keep the temperature for 15 min;

[0148] (4) Preparation of the piezoelectric thin film layer with a thickness of 2 μm by RF magnetron sputtering: Under the conditions of a temperature of 600 °C, an absolute pressure of 0.5 Pa, and an atmosphere of argon and oxygen with a volume ratio of 32:8, control the target-substrate distance to 50 mm, and perform magnetron sputtering under the condition of a power density of 2 W / cm 2 ;

[0149] (5) Preparation of the top electrode with a thickness of 100 nm by DC magnetron sputtering: Set the mask plate, heat up to 100 °C at a rate of 12 °C / min, and under the conditions of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; After the magnetron sputtering is completed, keep the temperature for 15 min.

[0150] The transverse piezoelectric coefficient of the self-biased piezoelectric thin film obtained in this comparative example is as Figure 2 shown.

[0151] Comparative Example 2

[0152] This comparative example provides a self-biased piezoelectric thin film, which includes a conductive part, a piezoelectric thin film layer, and a top electrode arranged along the thickness direction of the self-biased piezoelectric thin film;

[0153] The conductive part includes a bottom electrode and an oxide layer arranged in a stacked manner;

[0154] The oxide layer is arranged on the side close to the piezoelectric thin film layer;

[0155] The material of the bottom electrode is Pt, the material of the oxide layer is LaNiO 3 , and the material of the top electrode is Pt.

[0156] The oxide layer is prepared by using a lanthanum nickelate target, and in the lanthanum nickelate target, the molar ratio of La, Ni, and O is 1:1:3;

[0157] The preparation method of the lanthanum nickelate target includes the following steps:

[0158] Using zirconia as the ball milling medium and absolute ethanol as the grinding aid, wet ball mill and mix La 2 O 3 and Ni 2 O 3, after drying the ball abrasive, sinter it at 900 °C for 12 h in an oxygen atmosphere, and cool it naturally to obtain a sintered material; the sintered material is made into a green body by cold isostatic pressing, and then heat-treated at 980 °C in an oxygen atmosphere to obtain a lanthanum nickelate target;

[0159] The preparation method of the self-biased piezoelectric thin film includes the following steps:

[0160] (1) Select a single-polished 3-inch silicon substrate with a thickness of 625 μm, and use PECVD to grow a silicon dioxide layer with a thickness of 300 nm on the polished surface;

[0161] (2) In order to increase the adhesion between the silicon substrate and the bottom electrode, deposit a Ti adhesion layer with a thickness of 20 nm by DC magnetron sputtering: heat it to 100 °C at a rate of 12 °C / min, and under the condition of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min;

[0162] (3) Prepare a bottom electrode with a thickness of 100 nm by DC magnetron sputtering: heat it to 100 °C at a rate of 12 °C / min, and under the condition of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min;

[0163] (4) Prepare an oxide layer with a thickness of 100 nm by RF magnetron sputtering: heat it to 400 °C at a rate of 15 °C / min, and under the condition of an absolute pressure of 0.5 Pa and an argon-oxygen atmosphere with a volume ratio of 40:10, control the target-substrate distance to 40 mm, and magnetron sputter under the condition of a power density of 2.4 W / cm 2 ;

[0164] (5) Prepare a piezoelectric thin film layer with a thickness of 2 μm by RF magnetron sputtering: under the conditions of a temperature of 600 °C, an absolute pressure of 0.5 Pa, and an argon-oxygen atmosphere with a volume ratio of 32:8, control the target-substrate distance to 50 mm, and magnetron sputter under the condition of a power density of 2 W / cm 2 ;

[0165] (6) Prepare a top electrode with a thickness of 100 nm by DC magnetron sputtering: set a mask plate, heat it to 100 °C at a rate of 12 °C / min, and under the condition of an absolute pressure of 0.5 Pa and an argon atmosphere, control the target-substrate distance to 45 mm and the power density to 2 W / cm 2 ; after magnetron sputtering, keep the temperature for 15 min.

[0166] The transverse piezoelectric coefficient of the self-biased piezoelectric thin film obtained in this comparative example is as Figure 2 shown.

[0167] Performance characterization

[0168] The work function of the conductive oxide layers obtained in Examples 1-6 and Comparative Examples 1-2, the transverse piezoelectric coefficient of the self-biased piezoelectric thin film, and the difference in coercive voltage were measured. The difference in coercive voltage was the self-polarization driving electric field. The obtained results are shown in Tables 1 and 2.

[0169] Table 1

[0170]

[0171] Table 2

[0172]

[0173]

[0174] In summary, through the specific selection of the oxide layer material, the present invention generates a potential difference between the conductive part and the top electrode, thereby generating a built-in electric field inside the self-biased piezoelectric thin film, and obtaining a self-biased piezoelectric thin film. Due to the existence of the self-bias voltage, pre-polarization treatment is no longer required during use, and an ideal displacement can be obtained at a low voltage, which helps to further reduce the size and power consumption of electronic devices, and depolarization will not occur during the use of electronic devices.

[0175] The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A self-biased piezoelectric film, characterized in that: The self-biased piezoelectric film comprises a conductive portion, a piezoelectric film layer and a top electrode arranged along the thickness direction of the self-biased piezoelectric film; The conductive part includes an oxide layer, or a bottom electrode and an oxide layer stacked together; The oxide layer is arranged on a side close to the piezoelectric film layer; The material of the oxide layer is LaNi 1+x O3, where x ranges from 0.05 to 0.15; The material of the oxide layer is LaNi 1+x When O3, the oxide layer is prepared by DC magnetron sputtering of a lanthanum nickelate target; in the lanthanum nickelate target, the molar ratio of La, Ni and O is 1:(1.05-1.15):(2.65-2.75).

2. The self-biased piezoelectric film according to claim 1, characterized in that The material of the top electrode includes any one of titanium, platinum, gold, chromium or aluminum, or a combination of at least two thereof.

3. The self-biased piezoelectric film according to claim 1, characterized in that The material of the bottom electrode includes any one of titanium, platinum, gold, chromium or aluminum, or a combination of at least two thereof.

4. The self-biased piezoelectric film according to claim 1, characterized in that The material of the piezoelectric film layer includes lead zirconate titanate.

5. The self-biased piezoelectric film according to claim 1, characterized in that: The preparation method of the lanthanum nickelate target comprises the following steps: La2O3 and Ni2O3 are mixed by wet ball milling according to the formula, and the ball mill is dried, sintered in an atmosphere with an oxygen content of ≤21vol%, and naturally cooled to obtain a sintered material; the sintered material is formed into a green body by cold isostatic pressing, and then heat treated in an atmosphere with an oxygen content of ≤21vol% to obtain a lanthanum nickelate target.

6. The self-biased piezoelectric film according to claim 5, characterized in that: The sintering temperature is 880-920°C.

7. The self-biased piezoelectric film according to claim 5, characterized in that The temperature of the heat treatment is 960-1000°C.

8. A method for preparing a self-biased piezoelectric film according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: Using magnetron sputtering to sequentially deposit a conductive portion, a piezoelectric film layer, and a top electrode to obtain the self-biased piezoelectric film; The conductive part includes an oxide layer, or a bottom electrode and an oxide layer stacked together; The oxide layer is arranged on a side close to the piezoelectric film layer, and the magnetron sputtering method of the oxide layer includes direct current magnetron sputtering.

9. The preparation method according to claim 8, characterized in that: The magnetron sputtering method of the bottom electrode includes DC magnetron sputtering.

10. The preparation method according to claim 8, characterized in that: The magnetron sputtering method of the piezoelectric film layer includes radio frequency magnetron sputtering.

11. The preparation method according to claim 8, characterized in that: The magnetron sputtering method of the top electrode includes direct current magnetron sputtering.

12. The preparation method according to claim 8, characterized in that: The magnetron sputtering temperature of the bottom electrode is 25-100°C.

13. The preparation method according to claim 8, characterized in that: The magnetron sputtering temperature of the oxide layer is 300-600°C.

14. The preparation method according to claim 8, characterized in that: The magnetron sputtering temperature of the piezoelectric film layer is 400-650°C.

15. The preparation method according to claim 8, characterized in that: The magnetron sputtering temperature of the top electrode is 25-100°C.

16. An electronic device, characterized in that: The electronic device comprises the self-biased piezoelectric film according to any one of claims 1-7.

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