KR100953200B1 - Dielectric film employing PST heterolayered thin films, method of fabricating the same and tunable capacitor including the same - Google Patents

Abstract

A dielectric film employing PST heterolayer thin films, a method of manufacturing the same, and a variable capacitor including the dielectric film are provided. The dielectric film includes a first dielectric film containing (Pb _x Sr _{1 -x} ) TiO ₃ (0 <x <1) having a cubic structure. A second dielectric film containing (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) having a tetragonal structure is provided on the first dielectric film. The first and second dielectric layers are repeatedly stacked alternately with each other. Also provided is a method of producing the dielectric film. In addition, a variable capacitor including the dielectric film is provided.

Ferroelectric Film, Dielectric Loss, Voltage Variability

Description

Dielectric film employing PST heterolayered thin films, method of fabricating the same and tunable capacitor including the same

1 is a cross-sectional view of a variable capacitor according to an embodiment of the present invention.

2 and 3 are cross-sectional views illustrating a method of manufacturing a dielectric film according to an embodiment of the present invention.

4 is a cross-sectional view of the variable capacitor used in the experimental examples.

5 is a graph illustrating an X-ray diffraction pattern (XRD) of dielectric films manufactured according to an embodiment of the present invention.

6 is a graph illustrating lattice constants and lattice distortion of dielectric films fabricated according to an embodiment of the present invention.

7 is a graph showing dielectric constant and dielectric loss of dielectric films fabricated according to an embodiment of the present invention.

8 is a graph illustrating dielectric constant-voltage characteristics of dielectric films manufactured according to an embodiment of the present invention.

FIG. 9 is a graph illustrating voltage tunability and device characteristic index (FOM) of dielectric films fabricated according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric film, a method of manufacturing the same, and an ultra-high frequency variable device including the same, and more particularly, to a dielectric film employing PST heterolayer thin films, a method of manufacturing the same, and a variable capacitor including the dielectric film.

In general, the dielectric film may be classified into a ferroelectric film and a paraelectric film. The ferroelectric film has a dielectric constant of hundreds to thousands at room temperature and has a residual polarization (Pr) state. The residual polarization exhibits a phase transition phenomenon in which polarization reversal is caused by an electric field. Furthermore, the ferroelectric film exhibits a phase transition phenomenon below the Curie temperature and loses residual polarization above the Curie temperature due to thermal fluctuations. Herein, when the residual polarization is lost, this is called a dielectric dielectric film.

The ferroelectric film has various applications due to various properties of the material itself. The ferroelectric films are widely applied to nonvolatile memory devices using two stable residual polarizations, capacitors in memory devices using large dielectric constants, uncooled infrared sensors using pyroelectricity, micro-driven devices using piezoelectric properties, and optical devices using electro-optic effects. It is becoming. In addition, the ultra-high frequency tunable device including the ferroelectric film uses a difference in dielectric constant due to a change in the microstructure of the material when an electric field is applied to the ferroelectric film. For example, as an example of the ultra-high frequency variable element, a frequency variable filter using a phase shifter, which is a key part of an active antenna system, which is electrically controlled without mechanically adjusting the direction of an antenna, and a change in dielectric constant of the ferroelectric film that varies depending on an applied electric field. Or tunable capacitors, voltage controlled resonators, oscillators and voltage controlled dividers.

In the field of the ultra-high frequency variable element, ferroelectric films having a Curie temperature close to room temperature, for example, BST films (Ba, Sr) TiO3), PZT films (Pb (Zr, Ti) O3), and PCT films ((Pb, Research on titanium oxides (CaTiO 3), PST films ((Pb, Sr) TiO 3), and similar structures is continuing. In order to be optimally implemented in the ultra-high frequency variable device, the ferroelectric film is required to have characteristics such as low dielectric constant, low dielectric loss, low leakage current, and voltage variability indicating a change in the dielectric constant according to an applied bias field at ultra-high frequency. Among the above-described ferroelectric films, the PST film has a lower crystallization temperature and a higher dielectric constant than the BST film widely used in the microwave variable device according to the composition ratio of Pb and Sr. B. Dibenedetto and C. J. Cronan, J. Am. Ceram. Soc., 51, 364 (1968)] However, research on the PST film is continuously required in view of dielectric loss characteristics and voltage variability.

The ultra-high frequency variable element is disclosed in Korean Patent No. 10-355380. According to the Korean patent, the BST film and the electrodes are sequentially disposed on a substrate. The SrRuO ₃ buffer layer interposed between the SrTiO ₃ buffer layer and the BST layer and the electrode is interposed between the substrate and the BST film is provided. However, the BST film has poor dielectric properties due to the high crystallization temperature.

SUMMARY OF THE INVENTION The present invention provides a dielectric film that improves dielectric loss characteristics and voltage variability.

Another object of the present invention is to provide a method of manufacturing a dielectric film that improves dielectric loss characteristics and voltage variability.

Another technical object of the present invention is to provide a method of manufacturing a variable capacitor to improve the dielectric loss characteristics and voltage variability.

According to one aspect of the present invention for achieving the above technical problem, a dielectric film is provided. The dielectric film includes a first dielectric film containing (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) having a cubic structure. A second dielectric film containing (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) having a tetragonal structure is provided on the first dielectric film. The first and second dielectric layers are repeatedly stacked alternately with each other.

In some embodiments of the present invention, the (Pb _x Sr _1-x ) TiO ₃ has a composition ratio of 0.1 ≦ _x ≦ 0.4, and the (Pb _y Sr _1-y ) TiO ₃ has a ratio of 0.6 ≦ _y ≦ 0.9. It may have a composition ratio.

In other embodiments, the first and second dielectric layers may have a perovskite crystal phase.

According to another aspect of the present invention for achieving the above technical problem, a method for producing a dielectric film is provided. The method for producing a dielectric film includes forming a first dielectric film containing (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) having a cubic structure on a substrate. A second dielectric layer containing (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) having a tetragonal structure is formed on the first dielectric layer. The first and second dielectric layers are formed to be repeatedly stacked alternately with each other.

In some embodiments of the present disclosure, forming the first dielectric layer may include forming a (Pb _x Sr _1-x ) TiO ₃ film having a cubic structure on the substrate. The (Pb _x Sr _1-x ) TiO ₃ film may be heat-treated to crystallize the (Pb _x Sr _1-x ) TiO ₃ film.

In other embodiments, forming the second dielectric layer may include forming a (Pb _y Sr _1-y ) TiO ₃ layer having a tetragonal structure on the first dielectric layer. The (Pb _y Sr _1-y ) TiO ₃ film may be heat-treated to crystallize the (Pb _y Sr _1-y ) TiO ₃ film.

In another embodiment, the substrate is selected from the group consisting of lanthanum aluminum oxide (LaAl ₂ O ₃ ), magnesium oxide (MgO ₂ ), cesium oxide (CeO ₂ ), aluminum oxide (Al ₂ O ₃ ), and silicon film. It can be formed of either.

According to another aspect of the present invention for achieving the above technical problem, a variable capacitor is provided. The variable capacitor has a substrate. One or a plurality of electrodes are provided disposed on the substrate. A dielectric film interposed between the substrate and the electrode is provided. The dielectric film is a _first dielectric film containing (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) having a cubic structure and (Pb _y Sr _1-y ) having a tetragonal structure on the first dielectric film. A second dielectric film containing TiO ₃ (0 <y <1) is provided, and the first and second dielectric films are alternately stacked alternately with each other.

In some embodiments of the present invention, the electrodes may be a metal film or a metal oxide film.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments disclosed herein are being provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. Like numbers refer to like elements throughout. Also, an element or layer is referred to as "on" or "on" of another element or layer by interposing another layer or other element in the middle as well as directly above the other element or layer. Include all cases.

First, a variable capacitor according to an embodiment of the present invention will be described with reference to FIG. 1. 1 is a cross-sectional view of a variable capacitor according to an embodiment of the present invention.

Referring to FIG. 1, a dielectric film 130 is provided on a substrate 100. The substrate 100 may be any one selected from the group consisting of a lanthanum aluminum oxide layer (LaAl ₂ O ₃ ), a magnesium oxide layer (MgO ₂ ), a cesium oxide layer (CeO ₂ ), an aluminum oxide layer (Al ₂ O ₃ ), and a silicon layer. The above films may be made of single crystal. The dielectric film 130 is provided as a combination film of the first and second dielectric films 110 and 120, and the first and second dielectric films 110 and 120 are formed in a cubic system, respectively. (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) and (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) of tetragonal structure. The (Pb _x Sr _1-x ) TiO ₃ may have a composition ratio of 0.1 ≦ _x ≦ 0.4 to have the cubic structure, and the (Pb _y Sr _1-y ) TiO ₃ may have the tetragonal structure. It may have a composition ratio of 6 ≦ y ≦ 0.9. In addition, the first and second dielectric layers 110 and 120 may be formed of a polycrystal phase to have a high dielectric constant, and specifically, may be formed of a perovskite crystal phase. The first and second dielectric layers 110 and 120 are alternately and repeatedly stacked alternately. In other words, the first and second dielectric layers 110 and 120 may be repeatedly stacked alternately at least one or more times, and the top layer repeatedly stacked may be stacked as the first dielectric layer 110. .

One or a plurality of electrodes 140 and 142 may be provided on the dielectric layer 130. The electrodes 140 and 142 may be metal layers or metal oxide layers as noble metals. The metal film may be a platinum film (Pt), a ruthenium film (Ru), or an iridium film (Ir), and the metal oxide film may be a ruthenium oxide film (RuO ₂ ) and an iridium oxide film (IrO ₂ ).

According to the present invention described above, the first dielectric film 110 containing (Pb _x Sr _1-x ) TiO ₃ of the cubic structure has the (Pb _y Sr _1-y ) TiO ₃ of the tetragonal structure Unlike the second dielectric layer 120, it has a paraelectric property. The first dielectric layer 110 having the dielectric constant has a lower dielectric loss than the second dielectric layer 120. As a result, the dielectric film 130 may exhibit better dielectric loss characteristics than a conventional dielectric film composed entirely of the second dielectric film 120. In addition, the dielectric layer 130 may exhibit good dielectric loss characteristics, and thus may exhibit improved voltage tunability than the conventional dielectric layer.

Hereinafter, a method of manufacturing a variable capacitor according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3. 2 and 3 are cross-sectional views illustrating a method of manufacturing a dielectric film according to an embodiment of the present invention.

Referring to FIG. 2, a first dielectric layer 110 containing (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) having a cubic structure is stacked on the substrate 100. The substrate 100 is formed of any one selected from the group consisting of a lanthanum aluminum oxide film (LaAl ₂ O ₃ ), a magnesium oxide film (MgO ₂ ), a cesium oxide film (CeO ₂ ), an aluminum oxide film (Al ₂ O ₃ ), and a silicon film. The above-described films may be formed of a single crystal. The (Pb _x Sr _1-x ) TiO ₃ may have a composition ratio of 0.1 ≦ _x ≦ 0.4 to have the cubic structure.

The first dielectric layer 110 may be formed using a sol-gel technique, a sputtering technique, and a pulsed laser ablation technique. Lead acetate trihydrate (Pb (CH ₃ COO) ₂ / 3H ₂ O; lead acetate trihydrate), strontium acetate and titanium isopropoxide (Ti [OCH (CH ₃ ) _{2] 4;} and a first spin-coating (spin coating) using the precursor solution on the substrate 100 containing the titanium isopropoxide). The compositions of the first precursor solution may have a molar ratio corresponding to the range of the composition ratio of the first dielectric layer 110. The first precursor solution may be formed to 0.1M to 0.6M, the rotation speed of the substrate 100 during the spin coating may be 2000RPM (Revolutions per Minute) to 5000RPM. After the spin coating, the first dielectric layer 110 is dried. The drying temperature may be 300 ℃ to 400 ℃. Subsequently, a first heat treatment (H1) is performed on the first dielectric layer 110. The first heat treatment H1 may be performed at a temperature of 600 ° C to 700 ° C. As a result, the first dielectric layer 110 is formed to have a perovskite crystal phase.

Referring to FIG. 3, a second dielectric layer 120 containing (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) having a tetragonal structure is formed on the first dielectric layer 110. The (Pb _y Sr _1-y ) TiO ₃ may have a composition ratio of 0.6 ≦ _y ≦ 0.9 to have the tetragonal structure, and the second dielectric layer 120 is the same as the method of forming the first dielectric layer 110. And sol-gel technique, sputtering technique and pulsed laser ablation technique. In the case of the sol-gel technique, spin coating is performed on the first dielectric layer 110 using a second precursor solution containing the compositions constituting the first precursor solution. The composition of the second precursor solution may have a molar ratio corresponding to the range of the composition ratio of the second dielectric layer 120. The rotation speed of the spin coating may be the same as the rotation speed mentioned in the method of forming the first dielectric layer described above. After the spin coating, the second dielectric layer 120 is dried. Subsequently, a second heat treatment (H2) is performed on the second dielectric layer 120. The second heat treatment H2 may be performed at the same temperature as that performed in the first heat treatment H1. As a result, the second dielectric layer 120 is formed to have a pebble crystalline phase.

When the second dielectric layer 120 is stacked on the first dielectric layer 110, the cubic structure of the first dielectric layer 110 affects crystal growth of the second dielectric layer 120. In other words, the first dielectric layer 110 may act as a seed layer to cause deformation of the crystal structure of the second dielectric layer 120. As a result, the laminated dielectric film, which is a combination film of the first and second dielectric films, may have better lattice distortion characteristics than the prior art having a single-layer dielectric film composed of the second dielectric film. In conclusion, the multilayer dielectric film may exhibit improved dielectric loss characteristics because the lattice distortion is reduced.

Referring back to FIG. 1, the first and second dielectric layers 110 and 120 may be alternately stacked alternately. In other words, the first and second dielectric layers 110 and 120 may be repeatedly stacked alternately at least one or more times, or the top layer repeatedly stacked may be formed to be stacked on the first dielectric layer 110. Can be. As a result, a laminated dielectric film formed of the first and second dielectric layers 110 and 120 that are alternately stacked is formed. The first and second dielectric layers 110 and 120 stacked on the second dielectric layer 120 illustrated in FIG. 3 may be formed using the methods described with reference to FIGS. 2 and 3, respectively. Subsequently, the multilayer dielectric film is patterned to form a dielectric film 130. Subsequently, an electrode film may be deposited on the dielectric film 130. The electrode film may be formed of a metal film or a metal oxide film as a noble metal film. The metal film may be formed of a platinum film (Pt), a ruthenium film (Ru), or an iridium film (Ir), and the metal oxide film may be formed of a ruthenium oxide film (RuO ₂ ) and an iridium oxide film (IrO ₂ ). have. The electrode layer may be patterned to form one or a plurality of electrodes 140 and 142 on the dielectric layer 130.

<Examples>

FIG. 5 is a graph illustrating an X-ray diffraction pattern (XRD) of dielectric films manufactured according to an embodiment of the present invention. In FIG. 5, the horizontal axis represents an angle (2θ) between an X-ray light source and a detector centered on a specimen (here, a variable capacitor used as an experimental specimen) in an X-ray diffraction analyzer, and the vertical axis represents the intensity of light diffracted and emitted into the dielectric film. That is, it represents intensity (Int). The variable capacitor used for the illustrated experiments of FIGS. 5 to 9 was formed in the structure shown in FIG. 4. 4 is a cross-sectional view of the variable capacitor used in the experimental examples. Referring to FIG. 4, the silicon oxide film 210, the titanium film 212, and the platinum film 214 are sequentially stacked on the silicon substrate 200. The platinum film 214 was used as a lower electrode film. The first lower dielectric layer 220a containing (Pb _0.2 Sr _0.8 ) TiO ₃ having the cubic structure was stacked on the platinum layer 214 by applying the sol-gel technique. Specifically, spin coating was performed on the platinum film 214 using a first precursor solution containing lead acetate trihydrate, strontium acetic acid, and titanium isopropoxide. The molar ratio of lead acetate trihydrate, strontium acetate, and titanium isopropoxide was 0.2: 0.8: 1. The spin coating was performed for 30 seconds at a rotation speed of 4000 RPM. Solvents used in the spin coating were acetic acid and 2-methositol (C ₃ H ₈ O; 2-methoxyethol). Subsequently, the first lower dielectric layer 220a was dried at a temperature of 400 ° C. for 30 seconds to remove organic substances remaining after the reaction of the composition constituting the first precursor solution. Subsequently, the first lower dielectric layer 220a was heat treated at a temperature of 650 ° C. for 1 hour to sinter the first lower dielectric layer 220a. Subsequently, the second lower dielectric layer 230a containing (Pb _0.8 Sr _0.2 ) TiO ₃ having the tetragonal structure was stacked on the first lower dielectric layer 220a by using the sol-gel technique. Specifically, spin coating was performed on the first lower dielectric layer 220a using a second precursor solution containing lead acetate trihydrate, strontium acetate, and titanium isopropoxide. The molar ratio of lead acetate trihydrate, strontium acetate and titanium isopropoxide was set to 0.8: 0.2: 1. In addition, the spin coating, drying, and heat treatment processes of the second lower dielectric layer 230a were performed under the same conditions as the method of forming the first lower dielectric layer 220a.

The first intermediate dielectric layer 220b, the second intermediate dielectric layer 230b, the first upper dielectric layer 220c and the second upper dielectric layer 230c may be formed on the second lower dielectric layer 230a according to the number of dielectric layers constituting the dielectric layer. ) Were formed by laminating them in sequence. The first intermediate and upper dielectric layers 220b and 230c are formed using the same method as the method of forming the first lower dielectric layer 220a, and the second intermediate and upper dielectric layers 230b and 230c are formed of the first and second dielectric layers 220b and 230c. 2 was formed using the same method as the method of forming the lower dielectric layer 230a. Each of the first and second dielectric layers 220a, 220b, 220c, 230a, 230b, and 230c is formed to have a thickness of 45 nm.

On the other hand, in the experiment of the X-ray diffraction pattern in FIG. 5, the target metal used as the X-ray light source was copper (Cu), and the wavelength of the light source was 1.542 kHz as the wavelength of Cukα. In addition, the scan range of 2θ is set to 20 degrees to 60 degrees, the step pitch is 0.01 degrees, and the scan speed is set to 4 degrees / min. Proceeded.

Referring to FIG. 5, the first graph 510 corresponds to the measurement result of the dielectric film having three stacked numbers. Here, the dielectric film having the number of n stacked layers means the total number of first and second dielectric films constituting the dielectric film. For example, when the number of stacked layers n is 4, the dielectric layers are the first lower and middle dielectric layers 220a and 220b and the second lower and intermediate dielectric layers 230a and 230c and four dielectric layers. It consists of. The second graph 520 corresponds to the measurement result of the dielectric film having four stacked numbers. The third graph 530 corresponds to the measurement result of the dielectric film having five stacked numbers. The fourth graph 540 corresponds to the measurement result of the dielectric film having six stacked numbers.

In the measurement results shown in FIG. 5, the first to fourth dielectric films showed a typical polycrystalline phase. Furthermore, as the number of stacked layers of the first and second dielectric layers 220a, 220b, 220c, 230a, 230b, and 230c increases, the peak of the intensity of each plane increases. gave. Therefore, it can be seen that the size of the grains increases as the number of stacked layers increases.

6 is a graph illustrating lattice constants and lattice distortion of dielectric films fabricated according to an embodiment of the present invention. In Fig. 6, the horizontal axis is the number n of stacked dielectric films. The stacked number n means the stacked number described with reference to FIG. 5. The vertical axis on the left represents the lattice constants (C) 610 and 620 of the dielectric films. The graph 610 shown below is the lattice constant C of the dielectric films measured along the in-plane direction, and the graph 620 shown above is the normal direction of the in-plane plane. is the lattice constant C of the dielectric films measured along the normal direction. The vertical axis on the right represents lattice distortion (D) of the dielectric films. The lattice distortion D is defined as the ratio of the lattice constant in the normal direction to the lattice constant in the in-plane direction. The graph 630 shows the lattice distortion D of the dielectric films according to the stacked number n.

On the other hand, the measurement of the lattice constants (C) was performed using the X-ray diffraction pattern machine, it was carried out by applying the experimental conditions mentioned in FIG.

Referring to FIG. 6, the lattice constants C in the in-plane direction of the dielectric films have a substantially constant value even when the number n of layers is increased, whereas the lattice constants in the normal direction are shown. (C) has been shown to decrease. As a result, it was shown that the lattice distortion D of the dielectric films is reduced even if the number of stacked layers n increases. The reduction of the lattice distortion D means that the dielectric film composed of the first and second dielectric films has a structure similar to a cubic structure.

7 is a graph showing dielectric constant and dielectric loss of dielectric films fabricated according to an embodiment of the present invention. The horizontal axis is the same as the stacking number described with reference to FIG. 5. The vertical axis on the left is the dielectric constant ε ₀ of the dielectric films, and the graph 710 shows the dielectric constant ε ₀ of the dielectric films according to the number of stacked layers of the dielectric films. The vertical axis on the right is the dielectric loss L of the dielectric films, and the graph 720 shows the dielectric loss L of the dielectric films according to the number of stacked layers of the dielectric films. The dielectric constant and the dielectric loss were measured by applying a voltage of 0V and a frequency of 100 kHZ to the dielectric films.

In the graph of FIG. 7, the dielectric constant ε ₀ increases as the number of stacked layers n increases, while the dielectric loss L decreases. This is because the size of the crystal grains increases and the lattice distortion D decreases as the number of stacked layers n described in FIGS. 5 and 6 increases. In addition, although not shown in the graph of Figure 7, it can be seen that the dielectric loss of the conventional dielectric film has a larger value than the dielectric films according to the present invention. In conclusion, it can be seen that the dielectric films according to the present invention have improved leakage current characteristics compared to the conventional dielectric films.

8 is a graph illustrating dielectric constant-voltage characteristics of dielectric films manufactured according to an embodiment of the present invention. The horizontal axis is the voltage V _d applied to the dielectric films. The vertical axis is the dielectric constant ε of the dielectric films. Range of the voltage (V _d) applied to the dielectric film was a gap in a 5V -5V, it is applied a voltage (V _d) is 0.5V. In addition, the frequency applied to the dielectric films was 100 kHz. The first, second, third and fourth curves 810, 820, 830, and 840 have the applied voltage V _d when the number of stacks 3, 4, 5, and 6, respectively, described in FIG. Are the measurement results of the dielectric constant?

In the graph of FIG. 8, in contrast to the dielectric constants ε when the applied voltage V _d is 0 V, the dielectric constant ε is 6 compared to other dielectric films when the stacking number is 6. Had the highest value. In addition, the dielectric constants ε of the dielectric layers did not have a difference when the applied voltage V _d was 5V, but when the applied voltage V _d was 0V, The dielectric constants ε had a large difference. That is, the maximum / minimum difference of the dielectric constants ε was also found to be the highest when the number of stacks was six. This is due to the decrease in stress between the first and second dielectric layers as the number of stacked layers increases.

9 is a graph illustrating voltage tunability and device characteristic index (FOM) of dielectric films fabricated according to an embodiment of the present invention. The horizontal axis is the stacking number n of the dielectric films described with reference to FIG. 5. The vertical axis on the left is the voltage variability (T) of the dielectric films, and the voltage variability (T) is obtained by using the dielectric constant ε of FIG. 8 [(maximum dielectric constant-minimum dielectric constant) / maximum dielectric constant] to be. The vertical axis on the right is a figure of merit (FOM) of the dielectric films. The device characteristic index FOM is the voltage variability T / tan δ (dielectric loss angle).

Referring to FIG. 9, it was shown that the voltage variability T increased as the number of stacked layers n increased, and the device characteristic index FOM also increased. As can be seen in the graph of FIG. 8, since the maximum / minimum difference of the dielectric constants ε increases as the number of stacked layers n increases, the voltage variability T increases accordingly. As shown in the graph of FIG. 7, it can be seen that the device characteristic index FOM increases correspondingly as the number of stacked layers n increases due to the decrease in the dielectric loss L. FIG. Although not shown in the graph of FIG. 9, it can be seen that the conventional dielectric film has the low device characteristic index as well as the low voltage variability. Accordingly, the dielectric films according to the present invention have characteristics of improved voltage variability and device characteristic index as compared with the prior art.

According to the invention as described above, of the alternately repeatedly laminated in the cubic structure _{(Pb x Sr 1-x)} TiO 3 of the first dielectric layer and a tetragonal structure containing (0 <x <1) ( Pb y Sr A dielectric film is formed including a second dielectric film containing _1-y ) TiO ₃ (0 <y <1). In addition, during the formation of the dielectric layer, the first dielectric layer may affect the crystal structure of the second dielectric layer, thereby improving lattice distortion characteristics of the dielectric layer. As a result, the dielectric film has improved dielectric loss characteristics and voltage variability characteristics compared with the conventional dielectric film having only a tetragonal structure.

Claims (13)

A first dielectric film containing (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) having a cubic structure; And And a second dielectric layer containing (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) having a tetragonal structure on the first dielectric layer, wherein the first and second dielectric layers are artificially alternated with each other. A dielectric film that is repeatedly stacked while going. According to claim 1, The (Pb _x Sr _1-x ) TiO ₃ has a composition ratio of 0.1 ≦ _x ≦ 0.4 and the (Pb _y Sr _1-y ) TiO ₃ has a composition ratio of 0.6 ≦ _y ≦ 0.9. According to claim 1, The first and second dielectric layers have a perovskite crystal phase. Forming a first dielectric film containing (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) having a cubic structure on the substrate, Forming a second dielectric layer containing (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) having a tetragonal structure on the first dielectric layer, wherein the first and second dielectric layers are artificial The dielectric film manufacturing method is formed so as to be repeatedly stacked alternately with each other. The method of claim 4, wherein The (Pb _x Sr _1-x ) TiO ₃ has a composition ratio of 0.1 ≦ _x ≦ 0.4 and the (Pb _y Sr _1-y ) TiO ₃ has a composition ratio of 0.6 ≦ _y ≦ 0.9. The method of claim 4, wherein Forming the first dielectric film is a (Pb _x Sr _1-x ) TiO ₃ film having a cubic structure on the substrate is laminated, It said dielectric film production method comprising heat treatment the crystallized film _{(Pb x Sr 1-x)} TiO 3 with respect to the _{(Pb x Sr 1-x)} TiO 3 film. The method of claim 4, wherein Forming the second dielectric film is a (Pb _y Sr _1-y ) TiO ₃ film having a tetragonal structure on the first dielectric film, It said dielectric film production method which comprises heat-treating to crystallize the _{(Pb y Sr 1-y)} TiO 3 film to the _{(Pb y Sr 1-y)} TiO 3 film. The method of claim 4, wherein The substrate may be a dielectric film formed of any one selected from the group consisting of a lanthanum aluminum oxide film (LaAl ₂ O ₃ ), a magnesium oxide film (MgO ₂ ), a cesium oxide film (CeO ₂ ), an aluminum oxide film (Al ₂ O ₃ ), and a silicon film. Way. Board; One or more electrodes disposed on the substrate; And A dielectric film interposed between the substrate and the electrode, wherein the dielectric film includes a first dielectric film containing (Pb _x Sr _1-x ) TiO ₃ (0 <x <1) having a cubic structure and on the first dielectric film And a second dielectric film containing (Pb _y Sr _1-y ) TiO ₃ (0 <y <1) having a tetragonal structure, wherein the first and second dielectric films are repeatedly stacked alternately with each other artificially. Tunable capacitor. The method of claim 9, The (Pb _x Sr _{1 -x} ) TiO ₃ has a composition ratio of 0.1 ≦ x ≦ 0.4, and the (Pb _y Sr _{1 -y} ) TiO ₃ has a composition ratio of 0.6 ≦ _y ≦ 0.9. The method of claim 9, And the first and second dielectric layers have a perovskite crystal phase. The method of claim 9, The substrate is any one selected from the group consisting of lanthanum aluminum oxide (LaAl ₂ O ₃ ), magnesium oxide (MgO ₂ ), cesium oxide (CeO ₂ ), aluminum oxide (Al ₂ O ₃ ) and silicon film. delete

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