KR20070110237A - Fabrication of bst-pb based pyroclore composite dielectric films for tunability - Google Patents

Abstract

A composite dielectric film comprising a dielectric based on pyroclore Pb is provided to realize a high dielectric constant and a low dielectric loss while showing a high filed alteration ratio, and to produce a field alterable capacitor including a phase converter, flat panel antenna or filter. A composite dielectric film is represented by the formula of Ba-Sr-Ti-O comprising a pyroclore phase based on Pb-X-Nb-O(wherein X is any one element selected from the group consisting of Zn, Ni, Cu and Mg), and has a filed alteration ratio of 20-75% as defined by the formula of [field alteration ratio={(Co-Cv)/Co}x100, wherein Co represents an electrostatic capacity in the absence of filed, and Cv represents an electrostatic capacity upon the application of a field of 1000 kV/cm. A dielectric rate of the composite dielectric film is 100 or more.

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, a field-variable Ba _1-x Sr _x TiO ₃ thin film including a Pb-based Pyrochlore structure dielectric and a method of manufacturing the same. It is about.

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 the change of an applied electric field, and this characteristic is defined as the 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 tunability.

Until now, examples of applying the field-variable thin film as a capacitor have been limited to a single thin film of Ba _1-x Sr _x TiO ₃ (hereinafter referred to as 'BST'), which is a solid solution of BaTiO ₃ and SrTiO ₃ . 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 its practical application is difficult due to the 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, a BZZN thin film having a (Bi _1.5 Zn _0.5 ) (Zn _0.5 Nb _1.5 ) O ₇ (hereinafter referred to as 'BZZN') composition having a cubic crystal structure has a dielectric constant of 150 and a dielectric loss of 0.005, and has an electric field of about 830 kV / cm. An electric field variable rate of 0.1 is shown. Of course, in case of BZZN thin film, if the applied electric field is increased, the electric field variable rate is expected to increase slightly.However, compared to the advantage of low dielectric loss, the relatively low permittivity and electric field variable characteristics cannot replace the existing BST thin film. There is a situation.

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 Pb-X-Nb-O (where X is one element selected from the group consisting of Zn, Ni, Cu and Mg) based on the pyrochlore structure of the Ba _1-x Sr _x TiO _{As the three} dielectric thin films, there is provided a dielectric thin film, wherein the electric field variable rate defined by the following equation is in the range of 20 to 75%.

The present invention provides a Ba _1-x Sr _x TiO ₃ 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 Ba _1-x Sr _x TiO ₃ . 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 is made of a mixture of ferroelectric Ba _1-x Sr _x TiO ₃ and Pb-based pyrochlore dielectric, so that a thin film having a low loss while maintaining a high electric field variable rate can be manufactured. Therefore, there is an advantage that 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 aspect of the present invention, by implementing a Ba _1-x Sr _x TiO ₃ composite dielectric thin film containing a Pb-based dielectric on the Pyroclaw, a thin film having a low loss while maintaining a high electric field variable rate It is possible to easily achieve the purpose of the present invention through the technique.

In the field-variable BST-Pb based pyroclaw composite dielectric 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 It is preferably formed to 0.01 or less, and the thickness of the composite dielectric thin film is preferably less than 3000 kPa.

The present invention also relates to Ba _1-x Sr comprising a cubic pyrochlore phase represented by Pb ₆ X ₁ Nb ₆ O ₂₂ , where X is one element selected from the group consisting of Zn, Ni, Cu and Mg. _x TiO ₃ thin film.

The composite thin film has an electric field variability defined as a percentage of the dielectric constant change 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, preferably 40 to 40%. 65%. In addition, 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.

The present invention also provides a Pb-X-Nb-O (where X is at least one selected from the group consisting of Zn, Ni, Cu and Mg in the field variable BST-Pb-based pyroclaw composite dielectric thin film manufacturing method) Providing a sintered compact and Ba-Sr-Ti-O sintered compact target represented by; 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 Ba _1-x Sr _x TiO ₃ composite phase represented by the composition formula Pb ₆ X ₁ Nb ₆ O ₂₂ . In addition, the substrate temperature in the substrate heating step in the method is preferably maintained at 350 ~ 600 ℃.

In addition, the method of manufacturing a composite dielectric thin film of the present invention may further include a post heat treatment after forming the composite thin film 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 process of manufacturing a composite dielectric thin film according to an exemplary embodiment of the present invention. Referring to FIG. 1, first, a target is manufactured by a solid phase synthesis method (S110), and then sputtered for the manufactured target, and then, Pb-X-Nb-O and Ba-Sr on a substrate positioned below the target. A Ti-O composite dielectric thin film is formed (S120). At this time, the substrate is maintained at a temperature of about 300 ~ 600 ℃. 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 process of manufacturing the composite dielectric thin film and the characteristics of the obtained thin film will be described in more detail with reference to preferred embodiments of the present invention.

Preparation of Sputter Target

PbO, ZnO, MgO, NiO, and Nb ₂ O ₅ with a purity of 99.9% or higher of Kojundo Chemical Lab Co., Ltd., Japan, were converted into Pb ₆ ZnNb ₆ O ₂₂ , Pb ₆ ZnNb ₆ O ₂₂ and Pb ₆ Each was weighed according to the stoichiometric ratio of ZnNb ₆ O ₂₂ and then mixed using anhydrous ethanol and zirconia ball. Furthermore, BaCO ₃ , SrCO ₃ and TiO ₂ with a purity of 99.9% or higher of Kojundo Chemical Lab Co., Ltd., Japan, were converted into stoichiometric ratios of Ba _0.5 Sr _0.5 TiO ₃ and Ba _0.6 Sr _0.4 TiO ₃ . Each was weighed and then 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 pressurized and hydrostatic pressure (Cold Isostatic Pressure) was 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) Pb ₆ ZnNb ₆ O ₂₂ PZN 900 1150 Ba _0.5 Sr _0.5 TiO ₃ B5S5T 950 1200 Ba _0.6 Sr _0.4 TiO ₃ B6S4T 950 1200 Pb ₆ ZnNb ₆ O ₂₂ PMN 950 1250

Fabrication of Dielectric Thin Films

Composite dielectric thin films were prepared by simultaneous sputtering using a reactive RF magnetron sputtering system with off-axis geometry as the two targets of Table 1 above. At this time, Pt (111) / TiO ₂ / SiO ₂ / Si was used as the substrate material, and the thickness of each substrate layer was set to 1500 mW / 200 mW / 3000 mW / 550 µm. In addition, the process chamber for sputtering initially maintained a vacuum at a pressure of about 3 × 10 ⁻⁶ Torr, and argon gas having a purity of 99.99% as a sputtering gas and oxygen gas having a purity of 99.99% as a reactive gas were introduced into the chamber.

As a plasma source, 150 W of RF power was used for the BST target side, and 50 to 150 W was used for the target side of the Pb system. The flow rate controller maintained the flow rate of argon gas at 20 sccm and the flow rate of oxygen gas at ₂ sccm, maintaining an O ₂ / Ar ratio of about 10% and a working pressure of 10 ⁻³ Torr.

During deposition, the temperature of the substrate was set as the main process variable, and deposition was carried out at a temperature range of 350 to 550 ° C. for each target composition. During deposition, the distance between the target and the substrate in the process chamber was maintained at 13 cm, and the thickness of the deposited thin film was maintained at about 3000 mm 3. At this time, the thin film in the as-deposited state may exist as an amorphous phase at a low temperature and a crystalline phase at a high temperature according to the substrate temperature at the time of manufacture, so that the manufactured thin film is at a temperature of about 500 ° C. or higher and 800 ° C. or lower in an air atmosphere. After heat treatment for 3 hours.

Dielectric Thin Film Characteristics

Using a shadow mask to measure the dielectric properties of the composite dielectric thin film, an Ag dot having a diameter of 250 μm and a thickness of 5 μm was formed on the thin film by thermal evaporation to measure the capacitance between the Pt layer and the Ag dot of the substrate. It was. 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 ε _o is 8.8542 × 10 ^-12 )

In addition, the electric field variable rate defined by the change in 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 Equation 2 below. At this time, the electric field variable rate was measured at a frequency of 1 MHz, the applied electric field range was ± 1000 kV / cm.

(Where C _o is the capacitance at the electrostatic field and C _v 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 Ba _1-x Sr _x TiO ₃ -PMN composite dielectric thin film formed at a substrate temperature (ST) of 500 ° C.

It can be seen from the graphs shown in FIGS. 3A and 3B 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 Ba _1-x Sr _x TiO ₃ -PMN thin film formed at a substrate temperature of 500 ° C. according to deposition conditions and post-heating temperatures.

As shown in FIG. 5A and FIG. 5B, 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 having an RF source of 150W at a substrate temperature of 500 ° C. and a Pb-based target, the dielectric loss is less than 0.01. It can be seen that the maximum decrease to 0.004.

4A and 4B are graphs showing changes in dielectric constants according to deposition conditions and post-heating temperatures of a Ba _1-x Sr _x TiO ₃ -PZN composite dielectric thin film formed at a substrate temperature of 500 ° C.

It can be seen from the graphs shown in FIGS. 4A and 4B that the dielectric constant of the thin film increases as the substrate temperature and the post-heat treatment temperature increase. The thin film deposited at the substrate temperature of 500 ℃ has a dielectric constant of more than 100, the dielectric constant is about 260 after the post-heat treatment of 600 ℃.

6A and 6B are graphs showing dielectric loss characteristics of a Ba _1-x Sr _x TiO ₃ -PZN thin film formed at a substrate temperature of 500 ° C. according to deposition conditions and post-heating temperatures.

6A and 6B, 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. have.

7A and 7B are graphs showing electric field variable rate characteristics of a Ba _1-x Sr _x TiO ₃ -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 50W, it has the lowest value. In the case of the thin film formed at a substrate temperature of 500 ° C., the name of the thin film may be about 20 to 65% depending on the post-heat treatment temperature.

8A and 8B are graphs showing electric field variable rate characteristics of a Ba _1-x Sr _x TiO ₃ -PZN thin film formed at a substrate temperature of 500 ° C.

Referring to FIG. 8A, although the electric field variable rate increases with increasing post-heat treatment temperature, 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] Characteristic table of Ba _0.5 Sr _0.5 TiO ₃ -PMN Composite thin film

[Table 3] Ba _{0 .6} Sr _{0 .4} properties of the TiO thin film Table ₃ Composite -PMN

[Table 4] Ba _{0 0 .5} Sr _.5 TiO ₃ Properties of Composite films -PZN Table

[Table 5] Ba _{0 .6} Sr _{0 .4} properties of the TiO thin film Table ₃ Composite -PZN

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 procedure showing a thin film manufacturing process according to an embodiment of the present invention,

2 is a schematic diagram of a laminated structure of a thin film sample for measuring dielectric properties of a dielectric thin film according to an embodiment of the present invention;

3A to 3B are graphs showing changes in dielectric constants of Ba _0.5 Sr _0.5 TiO ₃ -PMN, Ba _0.6 Sr _0.4 TiO ₃ -PMN thin films formed by various RF sources according to deposition conditions and post-treatment temperatures;

4A to 4B are graphs showing changes in dielectric constants according to deposition states and post-heating temperatures of Ba _0.5 Sr _0.5 TiO ₃ -PZN and Ba _0.6 Sr _0.4 TiO ₃ -PZN thin films formed by various RF sources;

5A to 5B are graphs showing changes in dielectric loss of Ba _0.5 Sr _0.5 TiO ₃ -PMN, Ba _0.6 Sr _0.4 TiO ₃ -PMN thin films formed by various RF sources according to deposition conditions and post-treatment temperatures;

6A to 6B are graphs showing changes in dielectric loss of Ba _0.5 Sr _0.5 TiO ₃ -PZN and Ba _0.6 Sr _0.4 TiO ₃ -PZN thin films formed by various RF sources according to deposition conditions and post-heating temperatures.

7A to 7B are graphs showing electric field variable rate characteristics of Ba _0.5 Sr _0.5 TiO ₃ -PMN, Ba _0.6 Sr _0.4 TiO ₃ -PMN thin films formed by various RF sources;

Figure 8a to Figure 8b is a graph of Ba _{0 .5} Sr _{0 .5} field variation ratio characteristics of the _{TiO 3 -PZN, Ba 0.6 Sr 0.4} TiO 3 -PZN thin film formed by a variety of RF source.

Claims (22)

Pb-X-Nb-O (where X is one element selected from the group consisting of Zn, Ni, Cu, and Mg), a dielectric thin film of Ba-Sr-Ti-O including a pyrochlore phase, Composite dielectric thin film, characterized in that the electric field variable rate defined by the equation is in the range of 20 to 75% [Equation]

C _o : electrostatic capacitance at the time of electroless field, C _v : capacitance at 1000 kV / cm electric field. The method of claim 1, Said electric field variable rate is 20 to 70%, The composite dielectric thin film characterized by the above-mentioned. The method of claim 1, The dielectric constant of the dielectric thin film is a composite dielectric thin film, characterized in that 100 or more. The method of claim 1, The dielectric loss tan δ of the dielectric thin film is less than 0.03, the composite dielectric thin film. The method of claim 1, The thickness of the dielectric thin film is a composite dielectric thin film, characterized in that less than 3000Å. The method of claim 1, The dielectric thin film is a composite dielectric thin film, characterized in that the thin film of Ba _1-x Sr _x TiO ₃ including a pyrochlore phase represented by Pb ₆ Zn ₁ Nb ₆ O ₂₂ . The method of claim 6, The dielectric thin film is a composite dielectric thin film, characterized in that the electric field variable rate is defined by the following equation within the range of 50 to 75% [Equation]

C _o : electrostatic capacitance at the time of electroless field, C _v : capacitance at 1000 kV / cm electric field. The method of claim 6, The dielectric constant of the said dielectric thin film is 50 or more and 260 or less, The composite dielectric thin film characterized by the above-mentioned.  The method of claim 6, The dielectric loss tan δ of the dielectric thin film is less than 0.03, the composite dielectric thin film. The method of claim 6, The thickness of the dielectric thin film is a composite dielectric thin film, characterized in that less than 3000Å. The method of claim 1, The dielectric thin film is a composite dielectric thin film of Ba _1-x Sr _x TiO ₃ 3 including a pyrochlore phase represented by Pb ₆ Mg ₁ Nb ₆ O ₂₂ . The method of claim 11, The dielectric thin film is a composite dielectric thin film, characterized in that the electric field variable rate is defined by the following equation in the range of 20 to 70% [Equation]

C _o : electrostatic capacitance at the time of electroless field, C _v : capacitance at 1000 kV / cm electric field. The method of claim 11, The dielectric constant of the said dielectric thin film is 45 or more and 260 or less, The composite dielectric thin film characterized by the above-mentioned. The method of claim 11, The dielectric loss tan δ of the dielectric thin film is less than 0.025, the composite dielectric thin film. The method of claim 11, The thickness of the dielectric thin film is a composite dielectric thin film, characterized in that 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 two sintered target materials to form a Pb-X-Nb-O and Ba-Sr-Ti-O composite thin film on the substrate Composite dielectric thin film formation method comprising a. The method of claim 16, The dielectric thin film is a composite dielectric thin film formation method, characterized in that the Ba _1-x Sr _x TiO ₃ ferroelectric including a Pyroclaw phase represented by the composition formula Pb ₆ X ₁ Nb ₆ O ₂₂ . The method of claim 16, In the substrate heating step, the substrate temperature is maintained at 350 ~ 600 ℃ composite dielectric thin film formation method, characterized in that. The method of claim 16, In the step of sputtering the composite dielectric thin film, a method of forming a composite dielectric thin film, characterized in that using the argon gas as the sputtering gas, oxygen gas as the reaction gas. The method of claim 19, And a mixing ratio of oxygen gas to argon gas is maintained at 10%. The method of claim 16, In the sputtering of the composite dielectric thin film, the deposition pressure is maintained at 10 mTorr. The method of claim 16, After the composite dielectric thin film forming step, further comprising the step of post-heat treatment at a temperature of 500 ℃ or more.

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