阅读说明：本技术 一种利用纳米压痕提高压电材料压电系数的方法 (Method for improving piezoelectric coefficient of piezoelectric material by using nano indentation ) 是由 刘铎 颜为山 罗雯耀 赵超鹏 张汪阳 韩素芹 于 2021-04-30 设计创作，主要内容包括：本发明涉及一种利用纳米压痕提高压电材料压电系数的方法,该方法对压电晶体施加载荷外力,使压电晶体表面获得周期性纳米级图形化压痕结构,大大提高了压电晶体的压电系数,由17pC/N提高到44pC/N,采用的用纳米压痕技术直接在压电晶体表面制备大面积周期性纳米压痕结构,成本低,操作简便,并且无需昂贵的设备。(The invention relates to a method for improving piezoelectric coefficient of piezoelectric material by using nano indentation, which applies load external force to a piezoelectric crystal to enable the surface of the piezoelectric crystal to obtain a periodic nano-scale patterned indentation structure, greatly improves the piezoelectric coefficient of the piezoelectric crystal from 17pC/N to 44pC/N, adopts a nano-indentation technology to directly prepare a large-area periodic nano-indentation structure on the surface of the piezoelectric crystal, and has the advantages of low cost, simple and convenient operation and no need of expensive equipment.)

1. A method for improving piezoelectric coefficient of piezoelectric crystal by using nano indentation, said method comprising the steps of:

and applying a load external force to the piezoelectric crystal to enable the surface of the piezoelectric crystal to obtain a periodic nanoscale patterned indentation structure so as to improve the piezoelectric coefficient of the piezoelectric crystal.

2. The method of claim 1, wherein the piezoelectric crystal is LiNbO₃Crystal and ZnO crystalBody or BaTiO₃And (4) crystals.

3. The method of claim 1, wherein the periodic nanoscale patterned indentation structure is obtained in one of the following ways:

a. using the raised patterned substrate as a template, applying a load external force through the raised patterned substrate and the piezoelectric crystal in a hydraulic tablet press, and pressing the raised pattern on the raised patterned substrate into the surface of the piezoelectric crystal as a pressure head, so as to obtain a periodic nanoscale patterned indentation structure on the surface of the piezoelectric crystal;

b. pressing pins of the nanoindentor are pressed into the piezoelectric crystal with a certain external load force, loaded for a certain time, then unloaded to obtain holes with plastic deformation, and the loading and unloading are repeated continuously to arrange the pressed holes at intervals, so that a periodic nanoscale patterned indentation structure is finally obtained.

4. The method of claim 3, wherein in the method a, the raised patterned substrate is a nano-scale patterned sapphire substrate.

5. The method of claim 3, wherein in the method a, the external load is applied at 0.5-1MPa for 8-12 s.

6. The method according to claim 3, wherein the specific process of the method a is as follows:

(1) sequentially ultrasonically cleaning the piezoelectric single crystal and the raised patterned substrate for 10-15 min by using acetone, absolute ethyl alcohol and deionized water, and then performing N treatment₂Drying to obtain a pretreated piezoelectric single crystal and a raised patterned substrate;

(2) clinging the pattern surface of the raised patterned substrate to the polished surface of the piezoelectric crystal, placing the pattern surface and the polished surface into a die, and placing the die into a hydraulic tablet press together for pressing, wherein the load is 0.5-1MPa, and the loading time is 8-12 s;

(3) after loading, unloading pressure, and obtaining an indentation structure with nanoscale patterning on the surface of the piezoelectric single crystal; the pressing depth is 10-20% of the length of the substrate structure.

7. The method as claimed in claim 3, wherein in the method b, the loading external force of the pressing pin of the nanoindenter is 5-8gf, the depth of the pressing pin pressed into the piezoelectric crystal is 300-450nm, and the retention time is 0.5-1.5 s.

8. The method of claim 3, wherein in method b, the spacing between the holes is 3-10 μm.

9. The method according to claim 3, wherein the specific process of the method b is as follows:

1) sequentially ultrasonically cleaning the piezoelectric single crystal for 10-15 min by using acetone, absolute ethyl alcohol and deionized water, and then performing N treatment₂Drying to obtain pretreated piezoelectric single crystals;

2) putting the pretreated piezoelectric single crystal into a nano indenter, wherein a pressing needle of the nano indenter is close to the surface of the piezoelectric single crystal, pressing points are carried out on the surface of the piezoelectric single crystal by a load external force of 5-8gf, the depth of pressing the pressing needle into the piezoelectric single crystal is 300-450nm, and the load retention time is 0.5-1.5 s;

3) and unloading the pressure after the load is kept, completing indentation of one hole, pressing the next hole after one indentation is pressed, and repeating continuously, and finally processing a periodic indentation array on the surface of the piezoelectric crystal, wherein the interval of the indentations is 4-8 mu m.

Technical Field

The invention relates to a method for improving piezoelectric coefficient of a piezoelectric material by utilizing nano indentation, belonging to the field of piezoelectric material processing.

Background

Since piezoelectricity was formally discovered in 1880 by curie brother of france on alpha-quartz crystals, the research on the piezoelectric effect has grown to maturity and formed a complete set of theoretical systems. Meanwhile, the piezoelectric coefficient reflecting the piezoelectric effect of the piezoelectric crystal is also improved year by year along with the improvement of the growth quality of the piezoelectric crystal. Generally, the performance of a material is changed by changing the external temperature and pressure, but when the material is integrated into a sensor, a driver, a transducer, a Micro Electro Mechanical System (MEMS) and other devices which are finer and have higher integration level, the method is not applicable because the device itself cannot bear the drastic change of temperature and pressure, so how to obtain a higher piezoelectric coefficient from the nature of the piezoelectric material and to apply the piezoelectric material to various devices better, and the communication technology, the sensor technology and the like in the information age are pushed to become a hot problem of scientific and extensive research at present.

The existing methods for improving the piezoelectric coefficient of the piezoelectric material include the following 4 methods:

1. doping method

The doping method is a main method for modifying the material, and the crystal lattice and the energy band structure of the material are adjusted by adding other atoms, so that certain characteristic of the material is obviously improved. In 2007, Pan et al propose to dope 2.5% vanadium (V) into a ZnO piezoelectric film on Applied Physics Letters, so that the piezoelectric coefficient of the ZnO film is increased from 12pC/N to 110 pC/N. The main action principle is that V doping and high dielectricity thereof cause steerable spontaneous polarization and have obvious electric field-strain butterfly curve, so that ZnO piezoelectric crystal has the characteristics of ferroelectric crystal, in addition, V with valence of +5 has higher charge than Zn with valence of +2, V-O bond has stronger polarity than Zn-O bond, and V-O bond has stronger polarity than Zn-O bond⁵⁺Ionic radius ratio of (Zn)²⁺Small, more favorable to the displacement of ions, and the easy turning of the V-O bond which is not collinear with the c axis under the electric field is also one of the reasons for the remarkable improvement of the piezoelectric coefficient. However, the doping method requires the use of direct current reactive magnetron sputtering to prepare the thin film material, and then the plasma emission spectrometer is used to control the content of the doped atoms, which is more complicated and complex and has higher requirements for equipment.

2. Epitaxial strain method

This method is usually by Molecular Beam Epitaxy (MBE) or pulsingLaser beam deposition (PLD) epitaxially grows single crystal material on other substrates. If the lattice constant of the base material does not match that of the single crystal material to be grown, the single crystal material is subjected to tensile or tensile stress from the base while being grown, and finally grows into a single crystal material with a portion of strain remaining therein. Choi et al, 2004 Science, propose to grow BaTiO in this way₃Thin film and significantly enhance its ferroelectricity, ultimately this epitaxially strained BaTiO₃Film Curie point ratio single crystal block BaTiO₃The temperature is increased by 500 ℃, and the polarization strength is increased by 2.5 times, but the method also has the disadvantages of expensive equipment and long preparation and processing time.

3. Size effect method

The size effect refers to the limitation of the size of the material to the nanometer level, and some properties of the material are obviously enhanced and even some new properties appear. For piezoelectric materials, the dimensional effect is to prepare the piezoelectric material as a two-dimensional domain-limited thin film whose thickness direction is much smaller than its length and width directions. The piezoelectric film prepared and processed by the material not only can inherit and retain the performance of the body block, but also is more beneficial to being applied to more fine and wider application. Buhlmann et al utilizes magnetron sputtering of Nb-doped SrTiO₃Overgrowth of 200nm thick Pb (Zr)_0.40Ti_0.60)O₃(PZT) thin films were found to have a significant increase in their piezoelectric response, and they speculate that the enhancement of the piezoelectric effect results from a reduction in the number of a-domains at lateral dimensions of the film of less than 300 nm. The disadvantage of the magnetron epitaxy for preparing the film is that a substrate material is needed, and the manufacturing equipment is expensive.

4. Method for eliminating in-plane binding

Eliminating in-plane confinement refers to processing a piezoelectric material using a Focused Ion Beam (FIB) or other means to reduce in-plane confinement. The FIB focuses ion beams to submicron or even nanometer level under the action of an electric field and a magnetic field, and controls the scanning motion of the ion beams through a deflection system and an acceleration system, so that the detection and analysis of micro-nano patterns and the maskless processing of micro-nano structures are realized. The high-energy ions can collide with the atoms on the surface of the solid to form the solidAtom sputtering stripping, so the FIB technology is directly used for a tool for processing a micro-nano structure. In 2002, R.Ramesh et al proposed in Nature Materials to FIB piezoelectric PZT thin films from a continuous film structure to discrete 1um²The piezoelectric coefficient of the island-shaped structure is improved by 3 times through testing. The reason for the improvement of the piezoelectric coefficient is that the piezoelectric film is grown on the substrate material, the FIB processing weakens the mechanical binding effect of the substrate on the PZT film, and the island-shaped structure weakening the binding of the substrate obviously facilitates the movement of the 90-degree domain, so that the 90-degree domain also greatly contributes to the piezoelectric response. However, the FIB milling technology has disadvantages in that the milling speed is low and the milling area is small, and in addition, ion implantation is inevitably introduced during the milling process, contaminating the original crystal, and causing partial amorphization.

Therefore, in order to overcome the defects of the existing method, such as complexity, high requirement on equipment, long processing time and high cost, a method for improving the piezoelectric coefficient of the piezoelectric crystal, which is low in cost, simple and convenient to operate and high in efficiency, needs to be developed urgently.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for improving the piezoelectric coefficient of a piezoelectric crystal by using nano-indentation.

The invention is realized by the following technical scheme:

a method for improving piezoelectric coefficient of piezoelectric crystal by using nano indentation, said method comprising the steps of:

and applying a load external force to the piezoelectric crystal to enable the surface of the piezoelectric crystal to obtain a periodic nanoscale patterned indentation structure so as to improve the piezoelectric coefficient of the piezoelectric crystal.

According to the invention, the piezoelectric crystal is LiNbO₃Crystals, ZnO crystals or BaTiO₃And (4) crystals.

The ZnO crystal and BaTiO of the invention₃Crystal and LiNbO₃Like the crystal, the piezoelectric crystal also has the enhancement effect after applying load external force.

Preferably, according to the present invention, the periodic nanoscale patterned indentation structure is obtained in one of the following ways:

a. using the raised patterned substrate as a template, applying a load external force through the raised patterned substrate and the piezoelectric crystal in a hydraulic tablet press, and pressing the raised pattern on the raised patterned substrate into the surface of the piezoelectric crystal as a pressure head, so as to obtain a periodic nanoscale patterned indentation structure on the surface of the piezoelectric crystal;

b. pressing pins of the nanoindentor are pressed into the piezoelectric crystal with a certain external load force, loaded for a certain time, then unloaded to obtain holes with plastic deformation, and the loading and unloading are repeated continuously to arrange the pressed holes at intervals, so that a periodic nanoscale patterned indentation structure is finally obtained.

According to a preferred embodiment of the present invention, in the method a, the patterned substrate for the protrusions is a nano-scale patterned sapphire substrate.

According to the invention, in the method a, the applied load external force load is 0.5-1MPa, and the loading time is 8-12 s.

Further preferably, the specific process of the method a is as follows:

(1) sequentially ultrasonically cleaning the piezoelectric single crystal and the raised patterned substrate for 10-15 min by using acetone, absolute ethyl alcohol and deionized water, and then performing N treatment₂Drying to obtain a pretreated piezoelectric single crystal and a raised patterned substrate;

(2) clinging the pattern surface of the raised patterned substrate to the polished surface of the piezoelectric crystal, placing the pattern surface and the polished surface into a die, and placing the die into a hydraulic tablet press together for pressing, wherein the load is 0.5-1MPa, and the loading time is 8-12 s;

(3) after loading, unloading pressure, and obtaining an indentation structure with nanoscale patterning on the surface of the piezoelectric single crystal; the pressing depth is 10-20% of the length of the substrate structure.

The hydraulic tablet press adopted by the invention is a hydraulic powder tablet press and the existing equipment.

According to the invention, in the method b, the loading external force of the pressing needle of the nano indenter is 5-8gf, the depth of the pressing needle pressed into the piezoelectric crystal is 300-450nm, and the holding time is 0.5-1.5 s.

According to a preferred embodiment of the invention, in method b, the spacing between the holes is 3 to 10 μm.

Further preferably, the specific process of the method b is as follows:

1) sequentially ultrasonically cleaning the piezoelectric single crystal for 10-15 min by using acetone, absolute ethyl alcohol and deionized water, and then performing N treatment₂Drying to obtain pretreated piezoelectric single crystals;

2) putting the pretreated piezoelectric single crystal into a nano indenter, wherein a pressing needle of the nano indenter is close to the surface of the piezoelectric single crystal, pressing points are carried out on the surface of the piezoelectric single crystal by a load external force of 5-8gf, the depth of pressing the pressing needle into the piezoelectric single crystal is 300-450nm, and the load retention time is 0.5-1.5 s;

3) and unloading the pressure after the load is kept, completing indentation of one hole, pressing the next hole after one indentation is pressed, and repeating continuously, and finally processing a periodic indentation array on the surface of the piezoelectric crystal, wherein the interval of the indentations is 4-8 mu m.

Nanoindenters are existing devices.

The invention has the technical characteristics and advantages that:

1. the invention applies load external force to the piezoelectric crystal to ensure that the surface of the piezoelectric crystal obtains a periodic nanometer patterned indentation structure, thereby greatly improving the piezoelectric coefficient of the piezoelectric crystal. The method is improved from 17pC/N to 44pC/N, has low cost and simple and convenient operation, and does not need expensive equipment.

2. The method for preparing the large-area periodic nano-indentation structure directly on the surface of the piezoelectric crystal by using the nano-indentation technology has the advantages of low cost, simple operation, no need of an optical mask, no need of chemical doping, no need of complicated or expensive preparation processes such as focused ion beams and the like, and the method for preparing the nano-indentation by using the sapphire substrate as the template has the advantages of simple operation and no need of complex or expensive preparation processes such as focused ion beams and the like.

3. The method of the invention is easy to control, wherein the method of using the nano-indenter can adjust the indentation depth and period, and a structure with tunable piezoelectric coefficients is easy to obtain.

4. The method of the invention has strong practicability and can be used in LiNbO₃Crystals, ZnO crystals or BaTiO₃The preparation of nano-indentation is realized on the surfaces of various piezoelectric crystals such as crystals.

Drawings

FIG. 1 example 1 Using a nanoscale patterned sapphire substrate in LiNbO₃Preparing a schematic diagram of nano-indentation on the surface of a wafer;

FIG. 2 is a scanning electron micrograph of a nano-scale patterned sapphire substrate in example 1;

FIG. 3 is LiNbO with nanoindentation obtained by patterning a sapphire substrate on the nanometer scale in example 1₃Scanning electron microscope pictures of the wafer surface;

FIG. 4 is LiNbO with nanoindentation obtained by using a nanoindenter in example 2₃Optical photograph of the wafer surface.

FIG. 5 LiNbO with nanoindentation prepared by the method₃Wafer contrast with non-indentation treated LiNbO₃The piezoelectric coefficient obtained for the wafer was improved by about 2.7 times as seen from the graph.

Detailed Description

The invention is further defined in the following, but not limited to, the figures and examples in the description.

Example 1

A method for improving piezoelectric coefficient of piezoelectric crystal by nano indentation uses LiNbO₃Taking a piece of (0001) plane LiNbO as an example of a piezoelectric single crystal₃Piezoelectric single crystal of 5X 0.5mm size³Polishing one side, and mixing one piece with LiNbO₃The piezoelectric single crystal is a nano patterned sapphire substrate with the same length and width dimensions, and the raised pattern period on the surface of the piezoelectric single crystal is 3 mu m;

the method comprises the following specific steps:

(1) LiNbO is reacted with₃Sequentially ultrasonically cleaning a piezoelectric monocrystal and a patterned sapphire substrate for 10-15 min by using acetone, absolute ethyl alcohol and deionized water, and then performing N treatment₂Drying;

(2) the pattern surface of the patterned sapphire substrate and LiNbO₃The polished surface of the piezoelectric single crystal is tightly attached and placed into a die, the die is placed into a hydraulic tablet press together for pressing, the load is 1MPa, and the loading time is 10 s;

(3) after loading, unloading pressure, and obtaining an indentation structure with nanoscale patterning on the surface of the piezoelectric single crystal; the pressing depth is 10-20% of the length of the substrate structure.

Example 2

A method for improving piezoelectric coefficient of piezoelectric crystal by nano indentation uses LiNbO₃Piezoelectric single crystals are an example. Selecting LiNbO of (0001) face₃Piezoelectric single crystal of 5X 0.5mm size³And (4) polishing the single surface.

The method comprises the following specific steps:

(1) LiNbO is reacted with₃Cleaning the piezoelectric single crystal, specifically, ultrasonically cleaning the piezoelectric single crystal for 10-15 min by using acetone, absolute ethyl alcohol and deionized water in sequence, and then performing N treatment₂And drying by blowing to obtain the piezoelectric crystal sample with a clean and dry surface.

(2) LiNbO is reacted with₃The piezoelectric single crystal is put into a nano-indentation instrument for nano-indentation processing, which specifically comprises the following steps: the indenter of the nanoindenter was brought close to the sample surface at 1000nm/s and at LiNbO at a maximum load of 7gf₃And (3) pressing points are formed on the surface of the piezoelectric crystal, the pressing depth is about 400nm, and the holding time is 1 s.

(3) And after the load is kept, unloading the pressure, thus completing the indentation of one hole. And after pressing one indentation, continuously pressing the next indentation, and repeating continuously, and finally processing a 300X 300 periodic indentation array on the surface of the piezoelectric crystal, wherein the indentation interval is 5 mu m.

As can be seen from FIG. 5, the invention compares LiNbO of the same size without nanoindentation treatment₃The piezoelectric coefficient of the wafer under the same conditions is improved by about 2.7 times.