KR20070108487A - Fabrication of bst-pb based pyroclore composite dielectric films for tunability - Google Patents

Abstract

A fabrication of tunable BST-Pb based pyrochlore composite dielectric films is provided to obtain dielectric films having about 20-70% of total tunability at the electric field of 1000kV/cm having high dielectric constant and low dielectric loss as well as excellent tunability. A fabrication of composite dielectric films comprises steps of: preparing a calcinated body target represented by Pb-X-Nb-O (wherein, X is selected from a group consisting of Zn, Ni, Cu and Mg), and a calcinated body target represented by Ba-Sr-Ti-O, respectively; heating a substrate; and forming Ba1-xSrxTiO3 thin films comprising Pb-X-Nb-O thin films on the substrate by sputtering the target materials coincidently. The temperature of the substrate is maintained to 350-600deg.C during heating step. For sputtering, the ratio of oxygen to argon for mixing is maintained to 10%, and the deposition pressure is maintained to 10mTorr. The step for forming composite dielectric thin films optionally comprises post-heating step at the temperature of at least 500deg.C. The composite dielectric films of Ba-Sr-Ti-O based pyrochlore composite dielectric films comprising Pb-X-Nb-O(wherein, X is one element selected from a group consisting of Zn, Ni, Cu and Mg) based pyrochlore phase have tunability of about 20-75%, and the tunability is defined by tunability(%)=[(Co-Cv)/Co]x100 (wherein, Co is the electrostatic capacity when no electric field is applied, and Cv is the electrostatic capacity when electric field of 1000kV/cm is applied). The dielectric constant of the composite dielectric film is at least 100, and the tan delta of the composite dielectric film is less than 0.03. The thickness of the composite dielectric film is less than 3000Å.

Description

Field Variable Type VTS-PJ Based Pyroclaw Composite Dielectric Thin Film and Manufacturing Method {FABRICATION OF BST-PB BASED PYROCLORE COMPOSITE DIELECTRIC FILMS FOR TUNABILITY}

The present invention relates to a composite dielectric thin film and a method for manufacturing the same, and more particularly, to a field-variable Ba1-x SrxTiO3 thin film including a Pb-based Pyrochlore structure dielectric and a method of manufacturing the same.

In general, the electric field variable characteristic of a dielectric thin film refers to a characteristic in which capacitance and dielectric constant change according to a change in an applied electric field, and this characteristic is defined as a ratio of the change in permittivity at the time of electric field application to the dielectric constant without an electric field. Can be evaluated by electric field tunability.

Until now, examples of applying the field-variable thin film as a capacitor have been limited to a single thin film of Ba1-xSrxTiO3 (hereinafter referred to as 'BST'), which is a solid solution of BaTiO3 and SrTiO3. Curie temperature (Tc) changes according to the composition of the BST thin film, and it is known that a composition around x = 0.3 to 0.5 where the Curie temperature is near room temperature is suitable as an electric field variable element. BST thin films generally have an electric field variable rate of 0.5 or more, and use an oxide single crystal substrate as a substrate or exhibit an electric field variable rate of about 0.7 under other special deposition conditions. However, the BST thin film has a problem in that practical application is difficult due to a large dielectric loss exceeding 0.03 in spite of excellent electric field variation characteristics.

In order to solve this problem, efforts have been made to reduce the dielectric loss of BST thin films. For example, a method such as epitaxial growth of a BST thin film on an oxide single crystal substrate or addition of a cation such as Mg2 + to a BST thin film. Although some methods have reported that the BST thin film having a dielectric loss lower than 0.03 can be produced by this method, it is not a fundamental solution to the high dielectric loss of the BST thin film.

As a result, much effort has been devoted to the development of new materials with lower dielectric losses, and a lot of research has been made especially on Bi-Zn-Nb-O based films (hereinafter referred to as 'BZN'). Among them, the BZZN thin film having a (Bi1.5Zn0.5) (Zn0.5Nb1.5) O7 (hereinafter referred to as 'BZZN') composition having a cubic crystal structure has a dielectric constant of 150, a dielectric loss of 0.005, and an electric field of 830 kV / cm. An electric field variable rate of about 0.1 is shown. Of course, in case of BZZN thin film, if the applied electric field is increased, the electric field variability is expected to increase slightly.However, the relatively low permittivity and electric field variability characteristics of the BZZN thin film do not replace the existing BST thin film. to be.

Accordingly, there is a demand for the development of a dielectric thin film having a composition having a larger dielectric constant and excellent electric field variable characteristics while maintaining a low dielectric loss.

Accordingly, the present invention provides a dielectric thin film having a new composition having a high dielectric constant and low dielectric loss and having excellent electric field variable characteristics, and a method of manufacturing the same.

The present invention described above is a Ba1-xSrxTiO3 dielectric thin film comprising a Pb-X-Nb-O (where X is one element selected from the group consisting of Zn, Ni, Cu, and Mg) pyrochlore-based dielectrics, It provides a dielectric thin film, characterized in that the electric field variable rate is defined by the following formula is about 20 to 75%.

(Where C0 is the capacitance at the time of electroless field, Cv is the capacitance at the time of 1000 kV / cm field applied)

The present invention provides a Ba1-xSrxTiO3 composite dielectric thin film including a Pb-based dielectric on a pyroclaw. The composite dielectric thin film of the present invention exhibits low dielectric loss characteristics while maintaining a high dielectric constant of Ba1-xSrxTiO3. In addition, the composite dielectric thin film of the present invention exhibits a high electric field variable rate of up to 75% or more, which is suitable for use as an electric field variable capacitor of a phase converter, a flat antenna, a filter, and the like.

In addition, the method of manufacturing a composite dielectric thin film of the present invention has an advantage of controlling the dielectric properties of the thin film, that is, the dielectric constant and the electric field variable rate, in a wide range according to the substrate temperature and the post-heat treatment temperature. Furthermore, the composite dielectric thin film of the present invention has the advantage of producing a thin film having low loss while maintaining a high electric field variable rate because the composite dielectric thin film is made of a mixture of ferroelectric Ba1-xSrxTiO3 and Pb-based pyroclaw dielectric. As a result, a dielectric thin film having a very high profit index can be manufactured.

Hereinafter, with reference to the accompanying drawings will be described in detail the operating principle of the present invention. In the following description of the present invention, when it is determined that a detailed description of a known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

Looking at the specific core technical gist of the present invention, it is easy to achieve the present invention through the technology to provide a Ba1-xSrxTiO3 composite dielectric thin film including a Pb-based dielectric on the Pyroclaw.

In the thin film of the present invention, the electric field variable rate is preferably 30 to 60%, the dielectric constant is preferably 100 or more, and the dielectric loss tan δ is 0.03 or less, preferably 0.01 or less. It is preferable that the said thin film of this invention is 3000 Pa or less in thickness.

The present invention also provides a Ba1-xSrxTiO3 thin film comprising a cubic pyrochlore phase represented by Pb6X1Nb6O22, where X is one element selected from the group consisting of Zn, Ni, Cu and Mg.

The composite thin film has an electric field variable rate of 20 to 75%, preferably 40, which is defined as a percentage of the dielectric constant of the thin film when the electric field is applied to the dielectric constant of the thin film when no electric field is applied in an electric field application range of 1000 kV / cm. To 65%. The dielectric constant of the thin film is preferably 200 or more and the dielectric loss tan δ is 0.03, preferably 0.01 or less.

In another aspect, the present invention provides a sintered compact represented by Pb-X-Nb-O (where X includes at least one selected from the group consisting of Zn, Ni, Cu and Mg) and Ba-Sr-Ti-O sintered target step; Heating the substrate; And simultaneously sputtering the two sintered body targets to form a Pb-X-Nb-O and Ba-Sr-Ti-O composite thin film on the substrate. In the above method, the composite thin film is preferably a pyrochlore phase and a Ba1-xSrxTiO3 composite phase represented by the composition formula Pb6X1Nb6O22. In addition, the substrate temperature in the substrate heating step in the method is preferably maintained at 350 ~ 600 ℃.

In addition, in the method of the present invention, the forming of the composite dielectric thin film may further include post-heat treatment at a temperature of 500 ° C. or more. At this time, the post-heat treatment step is preferably performed at a temperature of 800 ℃ or less.

In addition to the Zn, Mg, Cu and Ni listed as the element X on the Pb-X-Nb-O-based pyroclaw phase and Ba-Sr-Ti-O of the present invention described above, other divalent metals having similar ion radiuses to these It may be used by those skilled in the art to which the present invention pertains.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart illustrating a thin film manufacturing process of the present invention. Referring to FIG. 1, first, a target is manufactured by a solid phase synthesis method (S110), and then a Pb-X-Nb-O and Ba-Sr-Ti-O composite dielectric thin film is formed on a substrate using the prepared target (S120). . At this time, the substrate is maintained at a temperature of about 300 to 600 ° C. The upper limit of the holding temperature of the substrate depends on the heating conditions of the stuffer device, and may be maintained at a high temperature such as, for example, a sintering temperature suitable for the manufacture of the sputter target, if the sputter device permits. Subsequently, the obtained thin film is post-heated at a temperature of about 500 to 800 ° C. (S130). The post heat treatment is for increasing the dielectric properties and crystallization of the obtained thin film in the amorphous phase. Hereinafter, the above-described thin film manufacturing process and the characteristics of the obtained thin film through the preferred embodiment of the present invention will be described in more detail.

Preparation of Sputter Target

PbO, ZnO, MgO, NiO, and Nb2O5 with a purity of 99.9% or higher of Kojundo Chemical Lab Co., Ltd., Japan, were weighed with anhydrous ratios according to the stoichiometry of Pb6ZnNb6O22, Pb6ZnNb6O22, and Pb6ZnNb6O22, respectively. Mix using zirconia balls. In addition, BaCO3, SrCO3 and TiO2 with a purity of 99.9% or higher of Kojundo Chemical Lab Co., Ltd., respectively, were weighed according to the stoichiometric ratio of Ba0.5Sr0.5TiO3 and Ba0.6Sr0.4TiO3. And mixed using anhydrous ethanol and zirconia balls.

The mixed powder was calcined at about 900-950 ° C. and then ground using zirconia balls. After pulverization, polyvinyl alcohol was added as a binder to granulate the particles, and then a uniaxial pressure and hydrostatic pressure (Cold Isostatic Pressure) were manufactured at a pressure of about 1000 kg / cm < 2 > Next, the molded body was sintered at a temperature range of 1150 ° C to 1250 ° C. The sintered body was processed into a disk shape having a diameter of 2 inches and a thickness of 7 mm, and burned out at a temperature of about 800 ° C. to prepare a sputter target.

Table 1 below is a table summarizing the physical properties and manufacturing conditions of each manufactured target.

TABLE 1

Furtherance sign Calcination temperature (degrees) Sintering Temperature (degrees) Pb6ZnNb6O22 PZN 900 1150 Ba0.5Sr0.5TiO3 B5S5T 950 1200 Ba0.6Sr0.4TiO3 B6S4T 950 1200 Pb6ZnNb6O22 PMN 950 1250

Fabrication of Dielectric Thin Films

Composite dielectric thin films were prepared by sputtering simultaneously with two targets of Table 1 using a reactive RF magnetron sputtering system having off-axis geometry. Pt (111) / TiO 2 / SiO 2 / Si was used as the substrate material, and the thickness of each substrate was 1500 μs / 200 μs / 3000 μs / 550 μm. The chamber was initially maintained in a vacuum at a pressure of about 3 × 10 −6 Torr, and argon gas having a purity of 99.99% as a sputter gas and oxygen gas having a purity of 99.99% as a reactive gas were introduced into the chamber.

As the plasma source, the RF power of 150 W was used for the BST target side, and the target side of the Pb system was adjusted to 50 to 150 W. The flow rate controller maintained the flow rate of argon gas at 20 sccm and the flow rate of oxygen gas at 2 sccm, thereby maintaining the O 2 / Ar ratio at about 10%. Working pressure was maintained at 10 mTorr.

During deposition, the temperature of the substrate was set as the main process variable, and deposition was performed at a temperature range of 350 to 550 ° C. for each target composition. During deposition, the distance between the target and the substrate was maintained at 13 cm. The thickness of the deposited thin film was maintained to be about 3000 mm 3.

As-deposited thin films may exist in the amorphous phase at low temperature and in the crystalline phase at high temperature according to the substrate temperature at the time of manufacture. Heat treatment.

Dielectric Thin Film Characteristics

Using a shadow mask for measuring dielectric properties of the composite dielectric thin film, Ag dots having a diameter of 250 μm and a thickness of 5 μm were formed on the thin film by thermal evaporation, and the capacitance between the Pt layer and the Ag dot of the substrate was measured. . 2 schematically shows a laminated structure of a thin film sample for measuring dielectric properties.

Capacitance and dissipation factor (tan δ) were measured at an effective voltage of 500 mV oscillating at a frequency of 40 Hz to 10 MHz using an Agilent 4249A impedance analyzer.

The dielectric constant was calculated from Equation 1 below from the measured capacitance.

(Where C is the capacitance, d is the film thickness, A is the upper electrode area, and 8.8542 ㅧ 10-12)

In addition, the electric field variable rate defined by the change in the dielectric constant of the thin film when the electric field is applied to the dielectric constant of the thin film when no electric field is applied was measured according to the following [Equation 2]. The electric field variable rate was measured at a frequency of 1 MHz, and the applied electric field range was ㅁ 1000 kV / cm.

(Where C0 is the capacitance at the time of electrostatic field, Cv is the capacitance at the time of electric field application)

3A and 3B are graphs showing changes in dielectric constants according to deposition conditions and post-heating temperatures of a Ba1-xSrxTiO3-PMN composite dielectric thin film formed at a substrate temperature of 500 ° C. It can be seen from this graph that the dielectric constant increases as the postheating temperature increases. In the case of a composite dielectric thin film deposited at a substrate temperature of 500 ° C., the dielectric constant is about 260 after the post-heat treatment of 600 ° C.

5A and 5B are graphs showing dielectric loss characteristics of a Ba1-xSrxTiO3-PMN thin film formed at a substrate temperature of 500 ° C. according to deposition conditions and post-heating temperatures.

As shown, it can be seen that the dielectric loss of the obtained thin film is at most 0.03 or less, and in the case of a thin film formed at a substrate temperature of 500 ° C. and an RF source of Pb-based target at 150 W, the dielectric loss is less than 0.01 and decreases up to 0.004. Able to know.

4A and 4B are graphs showing changes in dielectric constants according to deposition conditions and post-heating temperatures of a Ba1-xSrxTiO3-PZN composite dielectric thin film formed at a substrate temperature of 500 ° C. It can be seen from this graph that the dielectric constant of the thin film increases as the substrate temperature and the post-heating temperature increase. A thin film deposited at a substrate temperature of 500 ° C. has a dielectric constant of 100 or more, and the dielectric constant is about 260 when subjected to post-heat treatment at 600 ° C.

6A and 6B are graphs showing dielectric loss characteristics of a Ba1-xSrxTiO3-PZN thin film formed at a substrate temperature of 500 ° C. according to deposition conditions and post-heat treatment temperatures. As shown, it can be seen that the dielectric loss of the obtained thin film is at most 0.033 or less, and in the case of the thin film formed at 150W of the target RF source of PZN, the dielectric loss is reduced to about 0.0005.

7A and 7B are graphs showing electric field variable rate characteristics of a Ba1-xSrxTiO3-PMN thin film formed at a substrate temperature of 500 ° C. Here, the electric field variable rate is a value calculated at 1000 kV / cm.

Referring to FIG. 7A, the electric field variable rate increases with increase in post-heat treatment temperature, but the increase is not large. When the RF source toward the Pb target is small, the electric field variable rate has the maximum value, and when the source is 50 W, it has the lowest value. In the case of the thin film formed at the substrate temperature of 500 ° C., the name of the thin film may be about 20% to about 65% depending on the post-heat treatment temperature.

8A and 8B are graphs showing electric field variable rate characteristics of a Ba1-xSrxTiO3-PZN thin film formed at a substrate temperature of 500 ° C. Referring to FIG. 8A, the electric field variable rate increases with increasing post-heating temperature, but the increase is not large. In addition, depending on the post-heating temperature, the electric field variable rate can be known up to about 75%.

Dielectric properties (dielectric constant, dielectric loss) and electric field variable rate characteristics of PZN and PMN thin films calculated with reference to the above graphs are summarized in Tables 2 to 5 below.

[Table 2] Characteristics of Ba0.5Sr0.5TiO3-PMN Composite Thin Film

[Table 3] Characteristic table of Ba0.6Sr0.4TiO3-PMN Composite thin film

[Table 4] Characteristics of Ba0.5Sr0.5TiO3-PZN Composite Thin Films

[Table 5] Characteristics of Ba0.6Sr0.4TiO3-PZN Composite Thin Films

Meanwhile, in the above description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the invention should be determined by the claims rather than by the described embodiments.

1 is a flowchart illustrating a thin film manufacturing process of the present invention.

2 is a diagram schematically illustrating a laminated structure of a thin film sample for measuring dielectric properties of the dielectric thin film of the present invention.

3A to 3B are graphs showing changes in dielectric constants according to deposition states and post-heating temperatures of Ba0.5Sr0.5TiO3-PMN and Ba0.6Sr0.4TiO3-PMN thin films formed by various RF sources, respectively.

4A to 4B are graphs showing changes in dielectric constants according to deposition states and post-heating temperatures of Ba0.5Sr0.5TiO3-PZN and Ba0.6Sr0.4TiO3-PZN thin films formed by various RF sources, respectively.

5A to 5B are graphs showing changes in dielectric loss according to deposition states and post-heating temperatures of Ba0.5Sr0.5TiO3-PMN and Ba0.6Sr0.4TiO3-PMN thin films formed by various RF sources, respectively.

6A to 6B are graphs showing changes in dielectric loss according to deposition states and post-heating temperatures of Ba0.5Sr0.5TiO3-PZN and Ba0.6Sr0.4TiO3-PZN thin films formed by various RF sources, respectively.

7A to 7B are graphs showing electric field variable rate characteristics of Ba0.5Sr0.5TiO3-PMN and Ba0.6Sr0.4TiO3-PMN thin films formed by various RF sources, respectively.

8A to 8B are graphs showing electric field variable rate characteristics of Ba0.5Sr0.5TiO3-PZN and Ba0.6Sr0.4TiO3-PZN thin films formed by various RF sources, respectively.

Claims (21)

A composite dielectric thin film of Ba-Sr-Ti-O comprising a Pb-X-Nb-O (where X is one element selected from the group consisting of Zn, Ni, Cu and Mg) based pyrochlore phases, Dielectric thin film, characterized in that the electric field variable rate is defined by the formula of about 20 to 75%

(Where C0 is the capacitance at the field, Cv is the capacitance at 1000 kV / cm). The method of claim 1, The electric field variable rate is a dielectric thin film, characterized in that 20 to 70%. The method of claim 1, The dielectric thin film, characterized in that the dielectric constant is 100 or more. The method of claim 1, The dielectric loss tan δ is less than 0.03. The method of claim 1, The thickness of the thin film is a dielectric thin film, characterized in that less than 3000Å. Ba1-xSrxTiO3 composite dielectric thin film comprising a pyrochlore phase represented by Pb6Zn1Nb6O22. The method of claim 6, The thin film composite dielectric thin film, characterized in that the electric field variable rate is defined by the following formula 50 ~ 75%

(Where C0 is the capacitance at the field, Cv is the capacitance at 1000 kV / cm). The method of claim 6, The dielectric constant is a composite dielectric thin film, characterized in that 50 to 260 or less.  The method of claim 6, Wherein said dielectric loss tan δ is less than 0.03. The method of claim 6, The composite dielectric thin film, characterized in that the thickness of the thin film is less than 3000Å. A composite dielectric thin film of Ba1-xSrxTiO3 comprising a pyrochlore phase represented by Pb6Mg1Nb6O22. The method of claim 11, The thin film has an electric field variable rate of 20 to 70% defined by the following equation.

Composite dielectric thin film  (Where C0 is the capacitance at the field, Cv is the capacitance at 1000 kV / cm). The method of claim 11, Composite dielectric thin film, characterized in that the dielectric constant is 45 or more and 260 or less. The method of claim 11, The dielectric loss tan δ is less than 0.025. The method of claim 11, The composite dielectric thin film, characterized in that the thickness of the thin film is less than 3000Å. Providing a sintered compact target represented by Pb-X-Nb-O (where X includes at least one selected from the group consisting of Zn, Ni, Cu and Mg) and a sintered compact target represented by Ba-Sr-Ti-O step; Heating the substrate; And Simultaneously sputtering the target material to form a Ba1-xSrxTiO3 thin film including a Pb-X-Nb-O thin film on the substrate. The method of claim 16, The Pb-X-Nb-O thin film is a pyrochlore phase and Ba1-xSrxTiO3 ferroelectric represented by the composition formula Pb6X1Nb6O22, characterized in that the composite dielectric thin film formation method. The method of claim 16, In the substrate heating step, the substrate temperature is maintained at 350 ~ 600 ℃ characterized in that the dielectric thin film forming method. The method of claim 16, And the mixing ratio of oxygen gas to argon is maintained at 10% in the sputtering of the composite dielectric thin film. The method of claim 16, And depositing pressure is maintained at 10 mTorr in the step of simultaneously sputtering the composite dielectric thin film. The method of claim 16, The composite dielectric thin film forming step further comprises the step of post-heat treatment at a temperature of 500 ℃ or more.

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