KR20110001476A - Apparatus and method for measurement of transverse piezoelectric coefficient of piezoelectric thin films by measurement of quantity of electric charge - Google Patents

Abstract

PURPOSE: An apparatus and a method for the measurement of the transverse piezoelectric property of a piezoelectric thin film by the measurement of electric charge are provided to precisely and reliably measure the piezoelectric constant of a piezoelectric thin film by employing tension for a load application instead of bending. CONSTITUTION: An apparatus for the measurement of the transverse piezoelectric property of a piezoelectric thin film by the measurement of electric charge comprises a tension driving unit(120), a tensile load measuring unit(122), a strain measuring unit(132), an electric charge measuring unit(142) and a piezoelectric constant output unit(151). The tension driving unit applies a tensile load to a specimen(20) including a piezoelectric thin film. The tensile load measuring unit is connected to the tension driving unit and measures the tensile load exerted on the specimen. The strain measuring unit measures the strain of the specimen. The electric charge measuring unit measures the amount of electric charge created in the piezoelectric thin film. The piezoelectric constant output unit computes the traverse piezoelectric constant from the strain measured by the strain measuring unit.

Description

Apparatus and method for measuring lateral piezoelectric properties of piezoelectric thin film by measuring charge amount TECHNICAL OF ELECTRIC CHARGE

The present invention relates to an apparatus and method for measuring the piezoelectric properties of a piezoelectric thin film by measuring the amount of charge, and more specifically, through a tensile test on a piezoelectric thin film specimen used for manufacturing a micro sensor or an actuator. The present invention relates to an apparatus and a method for measuring displacement, strain, charge amount, and the like, and measuring a lateral piezoelectric constant of a piezoelectric thin film therefrom.

Conventionally, when grasping deformation characteristics of microstructures, pattern recognition is used to measure strains of microstructures due to mechanical or thermal loads. However, the grasp of deformation characteristics by the mechanical measurand has been limited in the precision of the microstructure. In this regard ("Piezoelectric thin films: Evaluation of electrical and electromechanical characteristics for MEMS devices", IEEE Trans. Ultrason., Ferroelect., Freq. Contr., Vol. 54, No. 1, Jan. 2007), A method of obtaining a piezoelectric constant by measuring the amount of charge during deformation of a piezoelectric thin film has been proposed. According to the method for measuring the longitudinal and transverse piezoelectric constants using the four-point bending test, the piezoelectric constant is calculated through data analysis while measuring the electric charge generated during the bending test. However, in order to obtain the piezoelectric constant by measuring the electric charge generated during the bending test, there is an assumption that the amount of deflection generated during bending should be significantly lower than the length of the specimen. That is, there is a problem that it is difficult to measure the correct value when large bending is applied.

The present invention was devised to solve such a problem, and when measuring the lateral piezoelectric constant of a thin film piezoelectric body composed of piezoelectric materials, a tensile load is applied, not bending, and the strain and the amount of charge accumulated in the process are measured. This enables accurate and reliable measurement of piezoelectric constants of piezoelectric thin films, thereby enabling various studies on the lateral piezoelectric properties of thin film piezoelectric materials, thereby matured research on the performance of products using thin film piezoelectric materials. Not only that, but also to enable stable reliability evaluation of piezoelectric products.

In order to achieve the above object, the device for measuring the amount of charge generated during the transverse deformation of the piezoelectric thin film according to the present invention and measuring the transverse piezoelectric properties of the piezoelectric thin film from the tensile load is applied to the specimen including the piezoelectric thin film. Tensile drive; A tensile load measuring unit connected to the tensile driving unit to measure a tensile load applied to the specimen; A strain measuring unit measuring a strain of the specimen; A charge amount measuring unit measuring a charge amount generated in the piezoelectric thin film; And a piezoelectric constant calculating unit calculating a lateral piezoelectric constant from the strain measured by the strain measuring unit and the amount of charge measured by the charge amount measuring unit.

The piezoelectric thin film included in the specimen may be attached to a region having a constant strain due to tensile strain on the specimen substrate.

The tensile drive unit, a fixed grip mounted and fixed to one side of the specimen; And a driving grip mounted on the other side of the specimen to cause displacement in accordance with the tensile load applied by the tensile drive.

An apparatus for measuring lateral piezoelectric properties of the piezoelectric thin film by measuring the charge amount may further include a displacement measuring unit configured to measure a displacement due to tensile deformation of the specimen by using the displacement of the driving grip.

The displacement measuring unit may measure the displacement using a laser displacement sensor.

Preferably, the specimen is mounted to the drive grip and the fixed grip using an adhesive (adhesive).

The strain measuring unit may measure the strain by an image pattern matching method through two dual microscopes.

The lateral piezoelectric property measuring apparatus of the piezoelectric thin film by the charge amount measurement may further include a charge amount amplifier which amplifies the amount of charge measured by the charge amount measuring unit and provides it to the piezoelectric constant calculation unit.

According to another aspect of the present invention, the method of measuring the lateral piezoelectric properties of the piezoelectric thin film by measuring the amount of charge generated when the transverse piezoelectric physical properties measuring device in the transverse deformation of the piezoelectric thin film, (a) Applying a tensile load to a grip equipped with a specimen; (b) measuring the strain of the specimen according to the tensile load; (c) measuring the amount of charge generated in the piezoelectric thin film according to the tensile strain; And (d) calculating a transverse piezoelectric constant from the measured data.

The piezoelectric thin film included in the specimen may be attached to a region having a constant strain due to tensile strain on the specimen substrate.

After the step (a), (a1) may further include the step of measuring the displacement caused by the tensile deformation of the driving grip mounted on the other side of the specimen, one side of the specimen is mounted on a fixed grip .

The displacement measurement of step (a1) is preferably performed by measuring a change in the distance between the plate and the laser displacement sensor through the reflected signal after irradiating the laser to the plate connected to the driving grip.

The specimen may be mounted to the drive grip and the stationary grip using an adhesive.

Step (b) may include: (b11) obtaining images of two points of the object to be measured by two objective lenses; (b12) acquiring an image by passing the image obtained in the step (b11) through a zoom lens for each of the cameras; And (b13) recognizing a pattern in the image acquired in step (b12), and tracking the recognized pattern to calculate a displacement at each position.

Between step (c) and step (d), (c1) preferably further comprises amplifying the amount of charge measured in step (c).

According to the present invention, when measuring the lateral piezoelectric constant of a thin piezoelectric material composed of piezoelectric material, a piezoelectric thin film is precisely and reliably applied by applying a tensile load rather than bending, and measuring strain and accumulated charge in the process. It is possible to measure the piezoelectric constants of, which enables various studies on the lateral piezoelectric properties of thin-film piezoelectric materials, which not only matures the performance of products using thin-film piezoelectric materials but also makes them stable for piezoelectric products. It has the effect of enabling reliability evaluation.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms or words used in this specification and claims should not be construed as having a conventional or dictionary meaning, and the inventors will appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that it can. Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

1 is a functional block diagram of a lateral piezoelectric physical property measuring apparatus 100 of a piezoelectric thin film by measuring the amount of charge of the present invention, Figure 2 is a transverse piezoelectric physical property measuring apparatus 100 of a piezoelectric thin film by measuring the amount of charge of the present invention (100) It is a figure which shows the structure of). Hereinafter, the function and structure of the lateral piezoelectric property measuring apparatus 100 of the piezoelectric thin film will be described with reference to FIGS. 1 and 2.

The tension driver 120 includes an actuator 121 for generating a tensile load and a tension load measuring unit for measuring the applied tensile load, that is, a load cell 122. As the actuator 121 for applying the tensile load, a DC motor actuator may be used, and in other embodiments, a piezoelectric actuator may be used. The DC motor actuator or piezoelectric actuator is directly connected to the specimen 20 to apply a tensile load. The magnitude of the applied tensile load is measured in the load cell 122 between the specimen and the actuator.

The piezoelectric thin film 22 (see FIG. 3) included in the specimen 20 is preferably attached to the region 30 having a constant strain within the specimen gauge distance.

The grips 161 and 162 for mounting the specimen 20 are mounted on one side of the specimen 20 and fixed to the fixed end 10 and attached to the other side of the specimen 20 and the tensile drive. It may include a drive grip 162 causing a displacement according to the tensile load applied by the.

Displacement and strain measurement unit 130, image pattern matching through a dual microscope and a displacement measuring unit 131 for measuring the displacement of the specimen using a laser displacement sensor (laser displacement sensor) It includes a strain measuring unit 132 for measuring the strain of the specimen gage length through.

The charge amount measuring unit 141 measures the amount of charge generated in the upper and lower electrodes of the piezoelectric thin film of the specimen, and further includes a charge amount amplifying unit 142 for amplifying the measured charge amount and transferring it to the piezoelectric constant calculating unit 151. can do.

The measurement data processor 150 may include a piezoelectric constant calculator 151, a screen provider 152, and a measurement data database 153.

The piezoelectric constant calculating unit 151 calculates the lateral piezoelectric constant from the charge amount of the piezoelectric thin film measured by the strain and charge amount measuring unit 141 measured by the displacement and strain measuring unit 130.

The screen providing unit 152 provides the screen with various data according to the tensile strain, including the measured strain and charge amount. One embodiment of the provided screen is shown in FIG. 4.

The measurement data database 153 stores various data according to the tensile strain, and is used to calculate the transverse piezoelectric constant or provide various data according to the tensile strain on the screen.

3 is a plan view 310 and a front view 320 showing the configuration of the piezoelectric thin film specimen.

The piezoelectric thin film specimen 20 includes a substrate 21, a piezoelectric thin film 22, an upper electrode 23, and a lower electrode 24. In particular, the piezoelectric thin film 22 is deposited at the gauge distance on the substrate 21. This figure shows how the substrate 21 deforms when a tensile load is applied, which is well illustrated in plan view 310. The piezoelectric thin film 22 is constrained to the substrate and deformed together.

FIG. 4 is a diagram 402 showing a strain distribution of a portion 401 of the specimen 20 by using the finite element method when the specimen 20 is tensioned. It is a figure which shows the stress in each element and the displacement in each node which comprise the test piece restrained by.

This figure is a case where the stress concentration factor is designed to be 1.1 or less, and it can be seen that the strain is uniformly distributed within the specimen gauge distance (403). The substrate 21 most frequently used as the substrate of the piezoelectric thin film 22 is a silicon (Si) material and has a brittle characteristic, so stress concentration occurs when a pin hole is used to mount the specimen. This can cause destruction around the hall. Therefore, it is desirable to adopt a method of adhering the specimen using an adhesive. Through the adhesive, the specimen 20 is mounted to the driving grip 162 connected to the tension driving unit 120 and the fixed grip 161 fixed to the fixed end 10.

The displacement of the specimen 20 due to the tensile load can be measured using the displacement measuring unit 131 by a laser displacement sensor. As shown in FIG. 2, the laser is directed toward the plate 40 connected to the driving grip, and measures the change in distance between the sensor 131 and the plate 40 in real time through the reflected signal 50. In addition, the strain within the gauge distance of interest in the specimen 20 is measured through image pattern matching through a dual microscope. Since both ends of the specimen are adhered to the fixed grip and the driving grip, the difference in the moving distance of the area reflected by the two microscopes causes the strain to be calculated through Equation 1 using the displacement difference between the two points.

The microstructure strain measurement method will be described in detail with reference to FIG. 5.

5 is a view showing an embodiment of a microstructure strain measurement method.

Two independent objective lenses 511 and 512 are included to acquire images of two points 501 and 502 spaced apart from each other on the specimen 20 as a measurement target. The images obtained by the objective lenses 511 and 512 are adjusted by the zoom lenses 521 and 522, respectively, to acquire images from the cameras 531 and 532, to recognize patterns in the acquired images, and to track the recognized patterns to detect displacements at each position. Strain measurement is enabled by calculating.

6 is a plan view 610 and a front view 620 illustrating a method of measuring the amount of charge generated in the piezoelectric thin film 22 of the specimen 20.

As shown in FIG. 6, a micro probe, that is, a charge measurement probe 615, is used to measure the charge and is connected to the upper electrode 23 and the lower electrode 24, respectively, in the piezoelectric thin film 22. The charge generated is measured. In addition, the amount of charge measured at the electrodes 23 and 24 is amplified by the charge amplifier 142 and then sent to the piezoelectric constant calculation unit 151, and this data is used to obtain data according to tensile strain. It is sent to the screen providing unit 152 for providing a screen, it can be visually displayed to the user through the screen. In Figure 4 its embodiment is shown. The piezoelectric constant calculator 151 calculates the lateral piezoelectric constant e ₃₁ of the piezoelectric thin film using the strain and the charge value. The piezoelectric equations used to measure the transverse piezoelectric constants are described in detail below.

For piezoelectric materials polarized in the longitudinal direction, the piezoelectric equation of piezoelectric ceramic is

는 유전상수 행렬을 나타낸다.It is expressed as Where S _i represents mechanical strain and T _j represents stress. In addition, E _k represents the electric field ( D _m ), D _m represents the dielectric displacement (dielectric displacement). s _ij denotes the mechanical compliance matrix, d _jk denotes the piezoelectric constant matrix,

Denotes the dielectric constant matrix.

When the tensile load is applied to the specimen in the same structure as in the present invention, the stress in the longitudinal direction within the gauge distance of the specimen can be ignored (traction-free),

It can be thought of as an electrical field, and the electrical field is measured when the charge generated between the electrodes is measured by the virtual ground method.

It can be assumed that the piezoelectric equation can be summarized simply by applying the equations (6) and (7). When Equation 2 and Equation 3 are added together

Can be expressed as

By substituting Equation 9 into Equation 5 using

는 실리콘의 프와송비이다. 압전 박막은 실리콘 기판에 접착되어 기판의 변형을 따르므로, 프와송비로서 실리콘의 프와송비를 사용한다.It can be represented as

Is the Poisson's ratio of silicon. Since the piezoelectric thin film adheres to the silicon substrate and follows the deformation of the substrate, the Poisson's ratio of silicon is used as the Poisson's ratio.

Therefore, the lateral piezoelectric constant e of the piezoelectric thin film₃₁ Can be calculated as

From above, the longitudinal dielectric displacement D ₃ represents the generated charge Q divided by the area A of the electrode where the charge is integrated. Therefore, the transverse piezoelectric constant can be obtained by measuring the charge Q generated during the tensile test of the piezoelectric thin film specimen and the strain S ₁ within the specimen gauge distance.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a functional block diagram of a lateral piezoelectric property measuring apparatus of a piezoelectric thin film by measuring the amount of charge of the present invention.

2 is a view showing the structure of a lateral piezoelectric property measuring apparatus of a piezoelectric thin film by measuring the amount of charge of the present invention.

3 is a plan view and a front view showing the configuration of the piezoelectric thin film specimen.

4 is a diagram showing a strain distribution of a specimen when the specimen is subjected to tension by using the finite element method.

5 is a view showing an embodiment of a microstructure strain measurement method.

6 is a plan view and a front view showing a method of measuring the charge generated in the piezoelectric thin film.

Claims (15)

A device for measuring the amount of charge generated during transverse deformation of a piezoelectric thin film and measuring the transverse piezoelectric properties of the piezoelectric thin film therefrom, A tension drive unit for applying a tensile load to a specimen including a piezoelectric thin film; A tensile load measuring unit connected to the tensile driving unit to measure a tensile load applied to the specimen; A strain measuring unit measuring a strain of the specimen; A charge amount measuring unit measuring a charge amount generated in the piezoelectric thin film; And A piezoelectric constant calculating unit that calculates a lateral piezoelectric constant from the strain measured by the strain measuring unit and the amount of charge measured by the charge amount measuring unit. Transverse piezoelectric property measurement apparatus of a piezoelectric thin film by measuring the amount of charge comprising a. The method according to claim 1, The piezoelectric thin film included in the specimen is attached to a region of a constant strain due to tensile strain on the specimen substrate Transverse piezoelectric physical property measuring apparatus of a piezoelectric thin film by measuring the amount of charge. The method according to claim 1, The tensile drive unit, A fixed grip mounted and fixed to one side of the specimen; And A driving grip mounted on the other side of the specimen to cause displacement in accordance with the tensile load exerted by the tensile drive Transverse piezoelectric properties measuring apparatus of the piezoelectric thin film by measuring the amount of charge, characterized in that it comprises a. The method according to claim 3, Displacement measuring unit for measuring the displacement caused by the tensile deformation of the specimen using the displacement of the drive grip Horizontal piezoelectric properties measuring apparatus of the piezoelectric thin film by measuring the amount of charge, characterized in that it further comprises. The method according to claim 4, The displacement measuring unit, Measuring displacement using laser displacement sensors Transverse piezoelectric physical property measuring apparatus of a piezoelectric thin film by measuring the amount of charge. The method according to claim 3, The specimen is Mounted to the drive and stationary grips using an adhesive Transverse piezoelectric physical property measuring apparatus of a piezoelectric thin film by measuring the amount of charge. The method according to claim 1, The strain measuring unit, Measuring strain by means of image pattern matching through two dual microscopes Transverse piezoelectric physical property measuring apparatus of a piezoelectric thin film by measuring the amount of charge. The method according to claim 1, Charge amount amplifier for amplifying the amount of charge measured by the charge amount measuring unit to provide the piezoelectric constant calculation unit Horizontal piezoelectric properties measuring apparatus of the piezoelectric thin film by measuring the amount of charge, characterized in that it further comprises. As a method of measuring the lateral piezoelectric properties of a piezoelectric thin film, the transverse piezoelectric physical property measuring device measures the amount of charge generated when the piezoelectric thin film is transversely deformed. (a) applying a tensile load to a grip equipped with a specimen comprising a piezoelectric thin film; (b) measuring the strain of the specimen according to the tensile load; (c) measuring the amount of charge generated in the piezoelectric thin film according to the tensile strain; And (d) calculating a transverse piezoelectric constant from the measured data Transverse piezoelectric physical property measurement method of the piezoelectric thin film by measuring the amount of charge comprising a. The method according to claim 9, The piezoelectric thin film included in the specimen is attached to a region of a constant strain due to tensile strain on the specimen substrate The lateral piezoelectric property measurement method of the piezoelectric thin film by measuring the amount of charge. The method according to claim 9, After step (a), (a1) measuring a displacement due to tensile deformation of a driving grip mounted on the other side of the specimen, with one side of the specimen mounted on a fixed grip; Transverse piezoelectric physical property measurement method of the piezoelectric thin film by measuring the amount of charge, characterized in that it further comprises. The method of claim 11, The displacement measurement of the step (a1), By irradiating a laser to a plate connected to a drive grip and then measuring the change in the distance between the plate and the laser displacement sensor through the reflected signal The lateral piezoelectric property measurement method of the piezoelectric thin film by measuring the amount of charge. The method according to claim 9, The specimen is Mounted with an adhesive on a fixed fixed grip and a drive grip causing displacement due to tensile deformation The lateral piezoelectric property measurement method of the piezoelectric thin film by measuring the amount of charge. The method according to claim 9, Step (b) is, (b11) obtaining images of two points of the object to be measured by two objective lenses; (b12) acquiring an image by passing the image obtained in the step (b11) through a zoom lens for each of the cameras; And (b13) calculating a displacement at each position by recognizing a pattern in the image acquired in step (b12) and tracking the recognized pattern; Transverse piezoelectric property measurement method of the piezoelectric thin film by measuring the amount of charge, characterized in that it comprises a. The method according to claim 9, Between step (c) and step (d), (c1) amplifying the amount of charge measured in step (c) Transverse piezoelectric physical property measurement method of the piezoelectric thin film by measuring the amount of charge, characterized in that it further comprises.

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