KR100416397B1 - Measuring Method for Piezoelectric Characterization of Thin Film Type Materials and Apparatus the Same - Google Patents

Abstract

The present invention relates to an apparatus for evaluating piezoelectric properties of thin film materials, and more particularly, in evaluating the piezoelectric properties of thin piezoelectric materials formed on a substrate, only the longitudinal piezoelectric constant (d ₃₃ ) has been measured. In order to simultaneously measure the directional piezoelectric constant d ₃₁ , a compressor for step 1 and a vacuum pump for step 2 are simultaneously provided to effectively apply mechanical energy of positive pressure and negative pressure to the piezoelectric thin film. In this case, the charge generated from the piezoelectric material is measured through a charge amplifier and the data is processed using a computer to determine the longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₁ ) of the thin piezoelectric material formed on the substrate. A device that can measure at the same time.

The present invention is a core technology essential for the application of various sensors or MEMS (Micro-Electro Mechanical System), which is a very important technology in consideration of future growth. It is to provide an essential technology essential for the application of various sensors or MEMS, etc., which are manufactured by using. In addition, the present invention can measure up to a small area of the specimen and can easily measure the piezoelectric constant by controlling the experimental conditions such as temperature.

Description

Method for evaluating piezoelectric properties of thin film materials and its apparatus {Measuring Method for Piezoelectric Characterization of Thin Film Type Materials and Apparatus the Same}

The present invention does not cause short circuit or plastic deformation of the piezoelectric thin film and can measure the piezoelectric constant of the thin film accurately and reliably by applying uniform stress to the entire surface of the thin film regardless of the topology of the thin film. The present invention relates to an apparatus capable of measuring the piezoelectric constant of a thin film type piezoelectric body which can be manufactured at low cost by having a simple configuration.

The piezoelectric constant measuring device of a conventional thin film type piezoelectric body has a structure in which only one of a compressor and a vacuum pump is used during stress loading, thereby evaluating the piezoelectric properties of a thin piezoelectric material formed on a substrate. Since only the longitudinal piezoelectric constant d ₃₃ is measured, there is a problem that a separate device must be introduced to measure the lateral piezoelectric constant d ₃₁ .

Therefore, the present invention relates to an apparatus for evaluating piezoelectric properties of thin film materials, and more particularly, to provide a positive pressure and a negative pressure by simultaneously providing a compressor for step 1 and a vacuum pump for step 2. Mechanical energy is effectively applied to the piezoelectric thin film (Sample). In this case, the charge generated from the piezoelectric material is measured through a charge amplifier, and then the data is processed using a computer. The longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₁ ) of the thin piezoelectric material formed on the substrate are processed. It relates to a device capable of measuring at the same time.

Until now, miniaturization of electronic devices such as microprocessors or memory devices has significantly reduced the manufacturing cost, and the performance has been greatly improved. For this reason, miniaturization is also required for mechanical parts such as actuators, and there is a need for microactuators for future applications such as medical or biochemical applications. On the other hand, electronic components such as sensors are also being developed to meet the trend of becoming smaller and lighter. In general, micromechanical devices operate according to electrostatic, piezoelectric, thermal or electromagnetic principles.

Piezoelectric devices (piezoelectric device) is a device that converts electrical energy into mechanical energy according to the piezoelectric effect (piezoelectric effect), or mechanical energy to electrical energy by the inverse piezoelectric effect (inverse piezoelectric effect). The piezoelectric actuator is capable of converting electrical energy into mechanical energy by contracting or expanding in accordance with the direction of the polarization and the electric field to which the piezoelectric material is applied. The expansion or contraction of the piezoelectric material is not determined by the size of the piezoelectric material but by the magnitude and direction of the voltage applied to the piezoelectric material. Therefore, a piezoelectric thin film may be used in manufacturing the micro actuator. The maximum expansion length of the piezoelectric thin film is limited by its breakdown voltage, or maximum stress, and the micro-actuator including the piezoelectric thin film is generally operated in proportion to the voltage.

Piezoelectric components can be mass-produced at low cost using a semiconductor manufacturing process, and various applications of piezoelectric thin films manufactured using such semiconductor manufacturing processes are already known.

In the present invention, when measuring the piezoelectric constant of a thin film piezoelectric body, the compressor for step 1 and the vacuum pump for step 2 are simultaneously provided to effectively apply the positive and negative pressure mechanical energy to the piezoelectric thin film so that the longitudinal piezoelectric constant of the piezoelectric material ( d _33), and an object thereof is to provide a transverse piezoelectric constant (d ₃₁₎ at the same time measured by, simple, precise and reliable so the thin-film piezoelectric element to measure the piezoelectric constant of the thin film piezoelectric constant measuring apparatus and method.

1 is a block diagram of an apparatus for evaluating piezoelectric properties of a thin film material of the present invention.

2 shows the effect of the falling voltage on the piezoelectric constant of Pb (Zr _0.5 Ti _0.5 ) O ₃ piezoelectric thin film material.

3 shows the situation when the positive pressure of Step 1 and the negative pressure of Step 2 are applied, respectively.

Fig. 4 (a) shows the stress distribution at the time of applying the positive pressure in step 1 by using the finite element method.

4 (b) shows the stress distribution at the time of applying the negative pressure in Step 2 by using the finite element method.

Figure 5 shows the induced voltage measured from each state of positive and negative pressure.

<Explanation of symbols for the main parts of the drawings>

100: Compressor 200: Main valve

320: vacuum pump 400: pressure gauge

500 ： release valve 510 ： shield box

600: computer 700: pressure probe

800 ： charge meter 900 ： piezoelectric thin film

XXX: Venturi Valve

The piezoelectric constant measuring apparatus of the thin film type piezoelectric body of the present invention includes a compressor for step 1 and a vacuum pump for step 2 to effectively transfer the mechanical energy of positive and negative pressure to the piezoelectric thin film, and the longitudinal piezoelectric constant (d ₃₃ ), the transverse An apparatus for allowing simultaneous measurement of the directional piezoelectric constant d ₃₁ is configured as follows.

Compressor 100 for applying a predetermined positive pressure to the thin film type piezoelectric body 900 at the bottom,

A vacuum pump 320 for applying a predetermined negative pressure to the thin film type piezoelectric body 900;

A pressure gauge 400 for visualizing and measuring the pressure exerted on the thin film piezoelectric body in combination with the pressure probe 700 is coupled to the main valve 200 and the release valve 500 connected to the computer 600 to control the applied pressure. ),

A pressure probe 700 adjacent to the thin film piezoelectric body to form a predetermined pressure on the thin film piezoelectric body and to be electrically connected while maintaining the pressure constant;

A tube extending from one side thereof is connected between the pressure probe and the pressure gauge, and a tube extending from the other side thereof is connected between the main valve 200 and the thin film type piezoelectric body to change the pressure applied to the thin film type piezoelectric body to change the pressure. A release valve 500 to allow measurement of the piezoelectric constant of

One terminal is connected to the lower electrode of the thin film piezoelectric body, the other terminal is connected to the upper electrode to measure a small amount of charge generated from the thin film type piezoelectric body, and one side thereof is connected to the pressure gauge, The other side is connected to the charge amount measuring means to control the members, and provides a piezoelectric constant measuring apparatus of a thin film type piezoelectric body including a computer 600 for calculating the piezoelectric constant of the thin film type piezoelectric body.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

<Example 1>

The measuring principle of providing the measuring method of the present invention is derived from the piezoelectric state equation showing the following positive piezoelectric effect.

D ₃ = d ₃₃ σ ₃ + d ₃₁ (σ ₁ + σ ₂ )

Here, D ₃ is the amount of charge per unit area in the triaxial direction, that is, electrical displacement, and σ ₁ , σ ₂ , σ ₃ are stress components in each direction.

The measuring method adjusts each stress element (σ ₁ , σ ₂ , σ ₃ ) through a stress application process consisting of steps 1 and ₂ , and the information related to the longitudinal piezoelectric constant d ₃₃ and the transverse piezoelectric constant d ₃₁ . To extract it. In step 1, positive pressure is applied to obtain the longitudinal piezoelectric constant d ₃₃ , and in step 2, sound pressure is applied to derive the transverse piezoelectric constant d ₃₁ . 3 schematically shows the situation of each step. As can be seen in the figure, when positive pressure is applied only the vertical stress component, σ _3, is applied. On the other hand, bending occurs when a negative pressure is applied, and σ ₁ , σ ₂ , and σ ₃ components contribute to charge generation. In general, the charge generated in the case of negative pressure is larger than in the case of positive pressure, and the difference between these two stages is important information to derive d ₃₁ . 4 (a) and (b) verify the validity of the assumption as a result calculated by the finite element method.

The crystal structure of the titanium oxide salt (perovskite) such as PZT works with three independent piezoelectric constants of d ₃₃ , d ₃₁ and d ₁₅ , respectively. The piezoelectric constant of the conventional PZT thin film has been mainly studied to measure the longitudinal piezoelectric d-coefficient of d _33. However, since the PZT thin film has a larger transverse direction than the longitudinal thickness, d There are many cases where the transverse piezoelectric d-coefficient of ₃₁ is important. Therefore, the present invention provides a new method for measuring the transverse piezoelectric constant (d ₃₁ ) by applying the same equipment.

Conventionally, two different types of equipment are required to measure the longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₁ ), but the present invention uses the same equipment to measure the longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₃ ). A method for measuring the direction piezoelectric constant (d ₃₁ ) has been developed. The present invention derives the difference between the result of applying a negative pressure to the result of applying a positive pressure to the thin film. When a positive pressure is applied, only the vertical stress component (σ ₃ ) acts. On the other hand, bending occurs when a negative pressure is applied, and stress components σ ₁ , σ ₂ , and σ ₃ contribute to charge generation. Therefore, in general, it is found that the charge generated in the case of negative pressure is larger than that of positive pressure, and the information of the transverse piezoelectric constant d ₃₁ can be obtained from the difference between these two processes.

Figure 5 shows the actual measurement results of the positive and negative pressure from the voltage applied to the 1000pF range capacitor. This result was in the case of the negative pressure is larger than the measurement of the positive pressure to 55.6pC 98.8pC was confirmed that the difference between the two results may be the clue to obtain the transverse piezoelectric constant (d _31).

From the state equation describing the positive piezoelectric effect, the equations for the two steps of positive and negative pressures are derived for the standard specimen and the thin-film specimen to the standard constant of the longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₁ ). Developed. The first step (step 1) and the step 2 (step 2) is obtained, the result of a piezoelectric property measured and compared against a standard sample and the thin film sample in order to perform accurate measurements. The first step is to obtain the d ₃₃ Positive pressure is applied and the second step applies negative pressure to derive d ₃₁ .

In the first step (step 1), the state equation of the positive piezoelectric effect expressed only as σ ₃ can be expressed as follows.

(5-1)

; Electric displacement when positive pressure is applied to standard specimen

(5-2)

; Electrical displacement when positive pressure is applied to the thin film specimen, where (SI) represents one stage of the standard specimen, d ^s ₃₃ represents the longitudinal piezoelectric constant of the standard specimen, and (FI) represents one stage of the thin specimen, d ^F ₃₃ is the longitudinal piezoelectric constant of the thin film specimen and α is the proportionality constant. From the above two equations, d ^F ₃₃ of the thin film can be calculated from the known bulk d ^s ₃₃ . At the same pressure, the thin film can be obtained from equations (5-1) and (5-2). Is as follows.

(5-3)

In the second step (step 2), the state equation describing the positive piezoelectric effect can be described in terms of σ ₁ , σ ₂ , and σ ₃ .

(5-4)

Electrical displacement when negative pressure is applied to the standard specimen

(5-5)

Electrical displacement when negative pressure is applied to the thin film specimen, where (SII) denotes the second stage of the standard specimen, d^S ₃₁Is the lateral piezoelectric constant of the standard specimen, d^F ₃₁ Is the lateral piezoelectric constant of the thin film specimen, and β is the proportionality constant, where the first term on the right side of Eqs. (5-4) and (5-5) is Eq. (5-1) and (5-2), respectively. Substitution is possible. Therefore, equations (5-4) and (5-5) are summarized as follows.(5-6)

(5-7)

Divide the equation (5-7) by the equation (5-6) To sum up

(5-8)

Becomes Equations (5-1 to 8) above are the lateral piezoelectric constants of the thin film specimens when applied to the thin film specimens and the reference specimens. Longitudinal Piezoelectric Constant of Thin Film Specimens Describes the process of simultaneously obtaining.

It can be seen from FIG. 4 that the total amount of charges generated in the first step is 23.5 pC and that the total amount of charges generated in the second step is 51.6 pC. In general, a reference specimen is used to set up a virtual specimen by using the finite element method and input an arbitrary piezoelectric constant. At this time, Wow Were 140pC / N and 60pC / N, respectively.

If the set standard specimen and the measured value of Fig. 5 are applied to equations (5-1) to (5-8),

,

Becomes

<Test Example>

Longitudinal piezoelectric piezoelectric specimens of the thin film specimens measured by using the above formulas (5-1 to 5-8) in the same manner as in the examples of the thin film specimen and the standard specimen by the piezoelectric constant measuring apparatus of the thin film type piezoelectric body of the present invention. a constant( ) Is 331 pC / N, and the lateral piezoelectric constant ( ) Were -92.2pC / N and these piezoelectric constants were measured simultaneously.

<Example 2>

As another embodiment of the present invention, the venturi valve (XXX) illustrated in FIG. 2 is installed, and a vacuum of about 0.5 atm can be formed only by the compressor, and when the degree of vacuum is low, the vacuum pump for step 2 Without it, the longitudinal piezoelectric constant and the transverse piezoelectric constant were simultaneously measured.

The piezoelectric constant measuring device of a conventional thin film type piezoelectric body has a structure in which only one of a compressor and a vacuum pump is used during stress loading, thereby evaluating the piezoelectric properties of a thin piezoelectric material formed on a substrate. Since only the longitudinal piezoelectric constant d ₃₃ is measured, there is a problem that a separate device must be introduced to measure the lateral piezoelectric constant d ₃₁ . The present invention is to evaluate the piezoelectric properties of the thin film material represented by the piezoelectric constant system and a method for measuring the longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₁ ) simultaneously in a single device and a measuring method thereof It will provide the standardization of the next generation piezoelectric characterization as a foundation technology for future industrial development in this field.

Claims (5)

A main valve 200 connected to the compressor 100 and the vacuum pump 300 to selectively output a positive pressure or a negative pressure; A release valve 500 connected to the main valve 200 to adjust to a predetermined pressure; A thin film type piezoelectric body 900 which is pressurized by a pressure probe 700 connected to the release valve 500; A charge amount measuring device (800) electrically connected to the thin film piezoelectric body (900) to measure a minute amount of charge generated from the thin film piezoelectric body (900); And The computer 600 which controls the release valve 500 and calculates and outputs the longitudinal piezoelectric constant d ₃₃ and the transverse piezoelectric constant d ₃₁ of the thin film type piezoelectric body through the measured value of the charge amount measuring instrument 800. Piezoelectric constant measuring device of a thin film type piezoelectric body comprising a. Applying a positive pressure of step 1 from the compressor using a piezoelectric constant measuring device equipped with a compressor and a vacuum pump at the same time, and then applying a negative pressure of step 2 from the vacuum pump, Transferring the mechanical energy of each stress to the piezoelectric thin film, Measuring the charge generated from the piezoelectric body through a charge amplifier, And measuring the longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₁ ) of the piezoelectric material at the same time by processing data using a computer. The state equation of claim 2, which describes the positive piezoelectric effect of the electrical displacement upon application of the positive pressure in step 1. (Eq. 5-1), Equation 5-2 and state equation describing the positive piezoelectric effect of electrical displacement when applying negative pressure in Step 2 (Eq. 5-4) Inducing piezoelectric constants of the standard specimen and the thin film specimen from the equation (5-5) to the standard constant; From these state equations, the longitudinal piezoelectric constants of the standard and ) (Eq. 5-3), The standard specimens are described in steps 1 and 2 above. (Eq. 5-4) From (Equation 5-1) (5-6) and describe thin film specimens (Eq. 5-5) and From (Equation 5-2) (Eq. 5-7) (Eq. 5-7) From (Eq. 5-6) Transverse piezoelectric constant of thin film specimen satisfying (Equation 5-8) The piezoelectric constant measuring method of a thin film type piezoelectric body characterized by simultaneously measuring the longitudinal piezoelectric constant (d ₃₃ ) and the transverse piezoelectric constant (d ₃₁ ) The method of claim 3, wherein the positive piezoelectric effect expressed by σ ₃ in step 1 is a state equation of electrical displacement when positive pressure is applied to a standard specimen. (5-1), the state equation of electrical displacement when positive pressure is applied to the thin film specimen Where α is the proportionality constant, and the standard specimen is the same as the longitudinal pressure constant of the thin film specimen from equation (5-1) and equation (5-2) under the same pressure. ) Is a piezoelectric constant measuring method of a thin film type piezoelectric body, which satisfies Equation (5-3) (Eq. 5-3) The method of claim 3, wherein the positive piezoelectric effect represented by σ ₁ , σ ₂ , σ ₃ in step 2 is a state equation of electrical displacement when negative pressure is applied to the standard specimen. (5-4), the state equation of electrical displacement when negative pressure is applied to the thin film specimen (5-5), and β is a proportional constant, from equations (5-4) and (5-1) describing standard specimens under the assumption that σ ₃ in step 1 and step 2 are the same. From equation (5-5) and equation (5-2) describing (5-5) and describing thin film specimens Obtain the lateral piezoelectric constants of the thin film specimens from equations (5-7) and (5-6). ) Piezoelectric constant measuring method of a thin film type piezoelectric body characterized by satisfying formula (5-8)