KR102460752B1 - Film bulk acoustic resonator and filter including the same - Google Patents

Abstract

The present invention is a substrate; a first electrode disposed on the substrate; a piezoelectric body disposed on the first electrode and including a plurality of piezoelectric layers including aluminum nitride to which a doping element is added; and a second electrode disposed on the piezoelectric body and opposite to the first electrode with the piezoelectric body interposed therebetween, wherein at least one of the piezoelectric layers is a compression layer formed under compressive stress. will be.

Description

FILM BULK ACOUSTIC RESONATOR AND FILTER INCLUDING THE SAME

The present invention relates to a thin film bulk acoustic resonator and a filter comprising the same.

With the recent rapid development of mobile communication devices, chemical and bio devices, etc., the demand for small and lightweight filters, oscillators, resonant elements, acoustic resonant mass sensors, etc. used in these devices is increasing

A thin film bulk acoustic resonator (FBAR) is known as a means for implementing such a small and lightweight filter, an oscillator, a resonance element, an acoustic resonance mass sensor, and the like.

FBAR has the advantage that it can be mass-produced at a minimum cost and can be implemented in a very small size. In addition, it is possible to implement a high quality factor (Q) value, which is the main characteristic of the filter, and can be used in the micro frequency band, especially in the PCS (Personal Communication System) and DCS (Digital Cordless System) bands. There are advantages to being able to

In general, the FBAR has a structure including a resonance part implemented by sequentially stacking a first electrode, a piezoelectric body, and a second electrode on a substrate.

Looking at the operating principle of the FBAR, first, when electric energy is applied to the first and second electrodes to induce an electric field in the piezoelectric layer, the electric field induces a piezoelectric phenomenon in the piezoelectric layer so that the resonator vibrates in a predetermined direction. As a result, a bulk acoustic wave is generated in the same direction as the vibration direction to cause resonance.

That is, the FBAR is a device that uses a bulk acoustic wave (BAW), and as the effective electromechanical coupling coefficient (Kt2) of the piezoelectric body increases, the frequency characteristic of the acoustic wave device is improved and broadband is possible. .

Japanese Patent Laid-Open No. 2016-502363 Republic of Korea Patent Publication No. 10-1386754

One object of the present invention is to provide a thin film bulk acoustic resonator capable of improving the electromechanical coupling constant of a piezoelectric body and at the same time preventing abnormal growth of aluminum nitride to which a doping element contained in a piezoelectric layer constituting the piezoelectric body is added. do.

As a method for solving the above problems, the present invention is to propose a novel structure of a thin film bulk acoustic resonator through an example, specifically, a substrate; a first electrode disposed on the substrate; a piezoelectric body disposed on the first electrode and including a plurality of piezoelectric layers including aluminum nitride to which a doping element is added; and a second electrode disposed on the piezoelectric body and facing the first electrode with the piezoelectric body interposed therebetween, wherein at least one of the piezoelectric layers is a compression layer formed under compressive stress.

In addition, the present invention intends to propose a filter including a thin film bulk acoustic resonator having the above-described structure through another embodiment. Specifically, in a filter including a plurality of thin film bulk acoustic resonators, the plurality of thin film bulk acoustic resonators The resonator may include a substrate; a first electrode disposed on the substrate; a piezoelectric body disposed on the first electrode and including a plurality of piezoelectric layers including aluminum nitride to which a doping element is added; and a second electrode disposed on the piezoelectric body and facing the first electrode with the piezoelectric body interposed therebetween, wherein at least one of the piezoelectric layers is a compression layer formed under compressive stress.

In the case of the thin film bulk acoustic resonator according to an embodiment of the present invention, the piezoelectric body includes a plurality of piezoelectric layers, and at least one of the piezoelectric layers is a compressive layer grown under compressive stress. and can have a high electromechanical coupling constant at the same time.

1 schematically shows a cross-sectional view of a thin film bulk acoustic resonator according to an embodiment of the present invention.
FIG. 2 schematically shows an enlarged view of A of FIG. 1 .
3 is a graph showing the change in the electromechanical coupling constant (Kt2) value of the thin film bulk acoustic resonator according to the residual stress of the piezoelectric body.
4 is a photograph observed by SEM that abnormal growth of aluminum nitride doped with scandium occurs.
5 is a measurement of the XRD rocking curve (Rocking Curve) of the samples of Table 1.
6 is a measurement of the half maximum width (FWHM) of the XRD rocking curve of the samples of Table 1 and the number of occurrences per unit area of abnormal growth.
7 shows measurements of density and refractive index according to stress applied during growth of the piezoelectric layer.
8 is a graph showing the measurement of the full width at half maximum (FWHM) of the XRD locking curve of the piezoelectric body according to the growth conditions of the first electrode.
9 is a graph showing the measurement of the full width at half maximum (FWHM) of the XRD locking curve of the first electrode according to the growth conditions of the first electrode.
10 shows the number of abnormal growths per unit area of the piezoelectric body according to the growth conditions of the first electrode.
11A to 11C are photographs of the boundary between the first electrode and the piezoelectric body observed by TEM according to magnification when the first electrode and the piezoelectric body are grown under tensile stress.
12A to 12C are photographs observed by TEM according to magnifications of the boundary between the first electrode and the piezoelectric body when the first electrode is grown under tensile stress and a compressive layer of the piezoelectric body is disposed in contact with the first electrode.
13A to 13C are photographs observed by TEM according to magnifications of the boundary between the first electrode and the piezoelectric body when the first electrode is grown under compressive stress and the compressive layer of the piezoelectric body is placed in contact with the first electrode.
14 is a schematic diagram showing a lattice structure of a first electrode and a piezoelectric body matching each other.
15 is a graph illustrating measurements of the c-axis lattice constant of the piezoelectric body and the a-axis lattice constant of the first electrode through XRD theta-2theta scan according to the formation conditions of the first electrode and the formation conditions of the piezoelectric body.
16 is a graph showing the c lattice constant according to the residual stress of the piezoelectric body measured through XRD theta-2theta scan.
17 is a photograph of observing the piezoelectric layer adjacent to the first electrode using HR-TEM.
18 and 19 are schematic circuit diagrams of filters according to other embodiments of the present invention.
20 shows a schematic diagram of a sputtering process of an apparatus for growing a piezoelectric body and an electrode.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to specific embodiments and the accompanying drawings. However, the embodiment of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below. Further, the embodiments of the present invention are provided in order to more completely explain the present invention to those skilled in the art. Accordingly, the shapes and sizes of elements in the drawings may be exaggerated for a clearer description, and elements indicated by the same reference numerals in the drawings are the same elements.

And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and the thickness is enlarged to clearly express various layers and regions, and components having the same function within the scope of the same idea are referred to as the same. It is explained using symbols. Furthermore, throughout the specification, when a part "includes" a certain component, it means that other components may be further included, rather than excluding other components, unless otherwise stated.

1 schematically shows a cross-sectional view of a thin film bulk acoustic resonator according to an embodiment of the present invention.

Referring to FIG. 1 , the acoustic resonator of the present invention may be a thin film bulk acoustic resonator, and includes a substrate 110 , an insulating layer 120 , an air cavity 112 , and a resonator 135 . may include

The substrate 110 may be formed of a silicon substrate, and an insulating layer 120 may be provided on the upper surface of the substrate 110 to electrically isolate the substrate 110 from the resonator 135 .

The insulating layer 120 is formed by chemical vapor deposition of at least one of silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), aluminum oxide (Al ₂ O ₂ ), and aluminum nitride (AlN). , RF magnetron sputtering (RF Magnetron Sputtering), and may be manufactured by forming on the substrate 110 using one of the evaporation (Evaporation) process.

The air cavity 112 may be formed on the substrate 110 . The air cavity 112 is positioned below the resonator 135 so that the resonator 135 vibrates in a predetermined direction. The air cavity 112 is an etching process in which an air cavity sacrificial layer pattern is formed on the insulating layer 120, a membrane 130 is formed on the air cavity sacrificial layer pattern, and then the air cavity sacrificial layer pattern is etched to remove it. can be formed by The membrane 130 may function as an oxidation protective layer or as a protective layer to protect the substrate 110 . Although not shown in FIG. 1 , a seed layer made of aluminum nitride (AlN) may be formed on the membrane 130 . Specifically, the seed layer may be disposed between the membrane 130 and the first electrode 140 .

Although not shown in FIG. 1 , an etch stop layer may be additionally formed on the insulating layer 120 . The etch stop layer protects the substrate 110 and the insulating layer 120 from an etching process for removing the sacrificial layer pattern, and may serve as a base for depositing other various layers on the etch stop layer.

The resonator 135 may include a first electrode 140 , a piezoelectric body 150 , and a second electrode 160 . The first electrode 140 , the piezoelectric body 150 , and the second electrode 160 may be sequentially stacked.

The first electrode 140 is formed to extend from an upper portion of one region of the insulating layer 120 to the membrane 130 over the air cavity 112 , and the piezoelectric body 150 is a first electrode over the air cavity 112 . The second electrode 160 may be formed on the piezoelectric body 150 above the air cavity 112 from the top of the other region of the insulating layer 120 . A common region overlapping the first electrode 140 , the piezoelectric body 150 , and the second electrode 160 in the vertical direction may be located above the air cavity 112 .

The piezoelectric body 150 is a part that generates a piezoelectric effect that converts electrical energy into mechanical energy in the form of acoustic waves, and includes a piezoelectric layer including aluminum nitride (AlN) to which a doping element is added. The doping element may be a rare earth metal, for example, the rare earth metal may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). Alternatively, the doping element may be at least one of titanium (Ti), zirconium (Zr), and hafnium (Hf). The content of the doping material included in the piezoelectric layer may be 1 to 20 at%.

The resonator 135 may be divided into an active region and an inactive region. The active region of the resonator 135 vibrates in a predetermined direction by a piezoelectric phenomenon occurring in the piezoelectric body 150 when electric energy such as a radio frequency signal is applied to the first electrode 140 and the second electrode 160 . The resonance region corresponds to a region in which the first electrode 140 , the piezoelectric body 150 , and the second electrode 160 vertically overlap on the air cavity 112 . The inactive region of the resonator 135 is a region that does not resonate due to the piezoelectric phenomenon even when electric energy is applied to the first electrode 140 and the second electrode 160 , and corresponds to a region outside the active region.

The resonator 135 outputs a radio frequency signal having a specific frequency by using the piezoelectric phenomenon. Specifically, the resonator 135 is a radio frequency signal having a resonant frequency corresponding to the vibration caused by the piezoelectric phenomenon of the piezoelectric body 150 . can be printed out.

The protective layer 170 is disposed on the second electrode 160 of the resonance unit 135 to prevent the second electrode 160 from being exposed to the outside from being oxidized, and the first electrode exposed to the outside ( An electrode pad 180 for applying an electrical signal may be formed on the second electrode 140 and the second electrode 160 .

FIG. 2 schematically shows an enlarged view of A of FIG. 1 .

Referring to FIG. 2 , the resonator 135 of the thin film bulk acoustic resonator according to an embodiment of the present invention has a stacked structure of a first electrode 140 , a piezoelectric body 150 , and a second electrode 160 .

The first electrode 140 , the piezoelectric body 150 , and the second electrode 160 may be formed using the sputtering apparatus shown in FIG. 20 .

The sputtering apparatus includes a chamber 11 , a support member 12 , and a target 13 . A base member 14, which is the basis of a material to be grown, is disposed on the upper portion of the support member 12, and as the sputtering process proceeds, a material to be grown is deposited on the upper portion of the base member 14 to form a forming layer ( 15) is grown. Argon (Ar) and nitrogen (N2) are injected into the chamber 11 to control the atmosphere in the chamber 11 in the process of growing the first electrode 140 , the piezoelectric body 150 , and the second electrode 160 . have.

The support member 12 is connected to the RF bias power unit to adjust the stress of the material grown in the process of growing the first electrode 140 , the piezoelectric body 150 , and the second electrode 160 to compressive stress or tensile stress. can

The step of growing the first electrode 140 may be performed using molybdenum (Mo) as the target 13 . However, not limited thereto, for example, gold (Au), titanium (Ti), tantalum (Ta), molybdenum (Mo), ruthenium (Ru), platinum (Pt), tungsten (W), aluminum (Al) , nickel (Ni), and iridium (Ir), or an alloy thereof. At this time, the crystal orientation may be improved by using the stress of the grown first electrode 140 as a compressive stress.

After forming the first electrode 140 , the step of forming the piezoelectric body 150 on the first electrode 140 is performed.

3 illustrates a change in the electromechanical coupling constant (Kt2) value of the thin film bulk acoustic resonator according to the residual stress of the piezoelectric body 150 . As the electromechanical coupling constant (Kt2) of the piezoelectric body 150 increases, the frequency characteristics of the acoustic wave element are improved, and broadband is also possible.

Referring to FIG. 3 , it can be seen that the electromechanical coupling constant Kt2 of the piezoelectric body 150 increases in proportion thereto as the residual stress of the piezoelectric body 150 increases as the tensile stress increases. In addition, it can be seen that the electromechanical coupling constant is higher in the case of using aluminum nitride to which a doping material is added, compared to the case of using aluminum nitride (AlN) as the piezoelectric body 150 . For example, the doping material may be scandium, but is not limited thereto.

However, when a piezoelectric body including aluminum nitride to which a doping material is added is formed such that residual stress becomes tensile stress, there is a problem in that the number of abnormal growths 155 occurs in the piezoelectric body 150 as shown in FIG. 4 increases.

Such abnormal growth mainly occurs at a position where the surface energy can be lowered during crystal growth, and as the number of abnormal growths 155 on the piezoelectric body 150 increases, the longitudinal direction in the thin film bulk acoustic resonator And there is a problem in that the loss of the wave in the transverse direction increases.

Therefore, it is necessary to form the piezoelectric body 150 using aluminum nitride to which a doping material is added, thereby preventing abnormal growth while maintaining the overall residual stress of the piezoelectric body 150 as a tensile stress.

The thin film bulk acoustic resonator according to an embodiment of the present invention includes at least one of the plurality of piezoelectric layers 151 and 152 constituting the piezoelectric body 150 in the process of forming the piezoelectric body 150 with aluminum nitride to which a doping material is added. By forming under compressive stress, it is possible to prevent abnormal growth from occurring and at the same time have a high electromechanical coupling constant.

As such, in the process of forming the piezoelectric body, a piezoelectric layer formed under compressive stress in at least one of the plurality of piezoelectric layers constituting the piezoelectric body 150 may be referred to as a compression layer.

As will be described later, in the compression layer, the ratio of the lattice constant in the a-axis direction to the lattice constant in the c-axis direction becomes larger than that of the piezoelectric layer formed in a state where no compressive stress is applied, and the density of the compression layer is 3.4681 g/cm ³ . and the refractive index of the compressive layer exceeds 2.1135. Also, the compression layer has a larger c lattice constant than other piezoelectric layers.

In addition, the compression layer is disposed in contact with the first electrode 140 under the piezoelectric body 150 to minimize abnormal growth in the process of forming the piezoelectric body 150 with aluminum nitride to which a doping material is added, or growth can be prevented.

After the piezoelectric body 150 is formed, the second electrode 160 is formed on the piezoelectric body 150 .

The second electrode 160 is disposed to face the first electrode 140 with the piezoelectric body 150 interposed therebetween.

Like the first electrode 140 , the second electrode 160 may be formed of molybdenum, but is not limited thereto. For example, the second electrode 160 may include gold (Au), titanium (Ti), tantalum (Ta), molybdenum (Mo), ruthenium (Ru), platinum (Pt), tungsten (W), or aluminum (Al). , nickel (Ni), and iridium (Ir), or an alloy thereof.

Hereinafter, the present invention will be described in more detail through Examples and Comparative Examples, but these are intended to help a specific understanding of the present invention, and the scope of the present invention is not limited by the Examples.

As shown in Table 1 below, the step of forming the piezoelectric body was divided into the step of forming the piezoelectric layer of four layers. However, the number of layers of the piezoelectric layer is not limited thereto.

The step of forming each piezoelectric layer was performed by adjusting the RF bias power to the support member of the sputtering apparatus of FIG. 20 to grow the piezoelectric layer in a state where compressive stress or tensile stress was applied.

In Table 1, the piezoelectric body of each sample was grown on top of a silicon wafer.

#1-1 #1-2 #1-3 #1-4 #1-5 #1-6 4th floor ◇ ■ ■ ■ ◆ □ 3rd floor ◇ ■ ■ ◆ ■ □ 2nd floor ◇ ■ ◆ ■ ■ □ 1st floor ◇ ◆ ■ ■ ■ □ Target residual stress of piezoelectric body (MPa) -300 300 300 300 300 300

The first to fourth layers in Table 1 are sequentially defined in the stacking direction from the first electrode among the plurality of piezoelectric layers constituting the piezoelectric body. The target residual stress of the piezoelectric body is the overall residual stress of the piezoelectric body after the piezoelectric body is formed. means

In addition, ◇, ◆, □, and ■ in Table 1 mean the same conditions as in Table 2 below.

RF bias (W) Stress (MPa) ■ 68.75 600 □ 82.25 300 ○ 95.75 0 ◇ 109.25 - 300 ◆ 122.75 - 600

In Table 2, RF bias means a bias applied to the support member in the sputtering apparatus of FIG. 15, and stress means a stress applied to the piezoelectric layer growing according to the RF bias.

5 is a measurement of the XRD rocking curve of each sample in Table 1, and the measurement result of the locking cuff is shown in Table 3 below.

Sample FWHM centroid (FWHM / Intentsity) × 10 ⁵ #1-1 1.50950 18.07454 0.447 #1-2 1.41530 18.00245 0.380 #1-3 1.48765 17.93866 0.437 #1-4 1.50853 18.03569 0.498 #1-5 1.52965 18.01024 0.430 #1-6 1.50006 17.79971 0.430

Referring to Table 3, it can be seen that all samples showed excellent values of about 1.41 to 1.5 at half maximum width, indicating that they had high crystal orientation.

In particular, in the case of Sample #1-2, it can be confirmed that the half width is the lowest and has the highest crystal orientation.

In addition, in the case of Sample #1-2, it was confirmed that the half width was the lowest and showed the highest intensity.

When the first layer of the piezoelectric layers constituting the piezoelectric body, ie, the piezoelectric layer disposed to be in contact with the first electrode, is formed as a compression layer, it is possible to obtain the effect of having the highest crystal orientation due to the lowest half width.

This is considered to be because the arrangement of the remaining piezoelectric layers grown above the first layer is also improved when the first layer, which is the lowest layer, is densely formed when the piezoelectric body is formed.

That is, in the thin film bulk acoustic resonator according to an embodiment of the present invention, the performance of the thin film bulk acoustic resonator can be improved by increasing the crystal orientation by disposing or forming the compression layer to be in contact with the first electrode under the piezoelectric body.

6 is a measurement of the half maximum width (FWHM) of the XRD rocking curve of the samples of Table 1 and the number of occurrences per unit area of abnormal growth, and the results are shown in Table 4.

#1-1 #1-2 #1-3 #1-4 #1-5 #1-6 FWHM 1.5095 1.4153 1.48765 1.50853 1.52965 1.50006 number of abnormal growth 0 0 3.6 3.6 4.3 2.1

The number of abnormal growths is a measure of the number of abnormal growths in an area of 14 μm × 12 μm. Referring to FIG. 6 and Table 4, Sample #1-2, in which the first layer is formed as a compression layer, has the lowest half width and the most It can be seen that excellent crystal orientation was exhibited and, at the same time, abnormal growth was not found.

As described above, when the first layer, which is the lowest layer, which is the most basic, is densely formed when the piezoelectric body is formed, the arrangement of the remaining piezoelectric layers grown on the first layer is also improved, so that abnormal growth is minimized. do.

According to the results of FIGS. 6 and 4, when the deposition condition of the piezoelectric layer initially deposited during the formation of the piezoelectric body is a compressive stress condition in which the ion bombarding energy is increased by improving the output of the RF bias, the piezoelectric body It can be confirmed that excellent crystal orientation and abnormal growth can be suppressed despite the overall residual stress of the tensile stress.

Accordingly, the thin film bulk acoustic resonator according to an embodiment of the present invention uses scandium-doped aluminum nitride as a piezoelectric body, and has a very high electromechanical coupling constant because residual stress is tensile stress. At the same time, in the thin film bulk acoustic resonator according to an embodiment of the present invention, at least one of the plurality of piezoelectric layers constituting the piezoelectric body, preferably the piezoelectric layer in contact with the first electrode, is formed as a compression layer to achieve excellent crystal orientation and abnormal growth. may have a preventive effect.

FIG. 7 is a measurement of density and refractive index according to stress applied during growth of the piezoelectric layer, and Table 5 shows the measurement results of FIG. 7 .

With reference to FIG. 7 and Table 5, the compression layer included in the thin film bulk acoustic resonator according to an embodiment of the present invention will be described in detail.

#2-1 #2-2 #2-3 Density (g/cm ³ ) 3.4925 3.4681 3.408 Refractive index 2.115 2.1135 2.1106

Samples #2-1, #2-2, and #2-3 in Table 5 are obtained by forming scandium-doped aluminum nitride under -600 MPa (compressive stress), 0 MPa and 600 MPa (tensile stress), respectively. Density was measured using X-ray reflectometry (XRR), and the refractive index was measured using an ellipsometer.

Referring to FIG. 7 , it can be seen that the tendency of a change in density and a change in refractive index according to pressure applied during formation are the same.

A case in which aluminum nitride is formed under compressive stress in order to understand the tendency of the lattice constant change of the compressive layer formed under compressive stress is as follows.

Aluminum nitride has an HCP structure, and has a c-axis lattice constant of 4.986 Å and an a-axis lattice constant of 3.116 Å. That is, the ratio (c/a) of the a-axis lattice constant to the c-axis lattice constant of aluminum nitride becomes 1.6.

When aluminum nitride is formed under compressive stress, the ratio (c/a) of the lattice constant of the a-axis to the lattice constant of the c-axis becomes larger than 1.6. Conversely, when aluminum nitride is formed under tensile stress, the ratio (c/a) of the lattice constant of the a-axis to the lattice constant of the c-axis becomes smaller than 1.6.

In the aluminum nitride doped with scandium, a part of aluminum is substituted with scantium in the crystal structure, so that the lattice constant of aluminum nitride changes. However, the crystal structure of aluminum nitride doped with scandium is also HCP, and the ratio (c/a) of the a-axis lattice constant to the c-axis lattice constant of aluminum nitride (c/a) shows a similar tendency with respect to the pressure applied during formation.

Accordingly, the ratio of the lattice constant in the a-axis direction to the lattice constant in the c-axis direction of the compression layer according to an embodiment of the present invention is greater than that of the piezoelectric layer formed in a state in which no stress is applied.

In addition, as shown in FIGS. 7 and 5, the density of the compression layer exceeds 3.4681 g/cm ³ , and the refractive index of the compression layer exceeds 2.1135.

Table 6 below shows samples according to the formation conditions of the first electrode. A first electrode was formed using molybdenum according to the formation conditions of the first electrode shown in Table 6, and a piezoelectric body having four piezoelectric layers was formed using aluminum nitride including scandium on the upper portion of the first electrode.

Unlike Table 1, the piezoelectric body was formed on the first electrode instead of the silicon wafer.

◇, ◆, □, and ■ used in Table 6 mean the same conditions as in Table 2 above.

group 1 group 2 #3-0 #3-1 #3-2 #3-3 #3-4 #3-5 #3-6 piezoelectric 4th floor ◇ □ □ □ ■ ■ ■ 3rd floor ◇ □ □ □ ■ ■ ■ 2nd floor ◇ □ □ □ ■ ■ ■ 1st floor ◇ □ □ □ ◆ ◆ ◆ first electrode □ □ ◇ ◆ □ ◇ ◆

Table 7 below shows the measurements of the full width at half maximum of the piezoelectric body and the half maximum width of the first electrode of the samples of Table 6, respectively.

#3-0 #3-1 #3-2 #3-3 #3-4 #3-5 #3-6 FWHM of piezoelectric body 1.543 1.513 1.489 1.469 1.491 1.446 1.434 FWHM of the first electrode 1.968 2.052 1.965 1.869 2.039 1.898 1.873

8 is a measurement of the full width at half maximum (FWHM) of the XRD locking curve of the piezoelectric body according to the growth conditions of the first electrode, and FIG. measured, and FIG. 10 shows the number of abnormal growths per unit area of the piezoelectric body according to the growth conditions of the first electrode. Referring to FIGS. 8, 9 and Table 7, as the first electrode is formed under high compressive stress, the piezoelectric body It can be seen that the half width at half maximum of the first electrode is decreased, and thus the crystal orientation is improved.

Specifically, when the first electrode is molybdenum (Mo), crystal orientation of 110 planes is improved in the crystal structure of molybdenum, and when the piezoelectric body is aluminum nitride doped with scandium, 0002 in the crystal structure of aluminum nitride doped with scandium. It can be seen that the crystal orientation of the surface is improved.

Also, referring to FIG. 10 , in both groups 1 and 2, it can be seen that the number of abnormal growths decreases as the first electrode is formed under high compressive stress.

That is, before the piezoelectric body is formed, it can be seen that the underlying first electrode is densely formed, and the piezoelectric body that grows upward on the first electrode is also formed with high crystal orientation, and thus the number of abnormal growths is also reduced.

11A to 11C are photographs of the boundary between the first electrode and the piezoelectric body observed by TEM according to the magnification when the first electrode and the piezoelectric body are grown under tensile stress (Sample #3-1), FIGS. 12A to 12C is a photograph observed by TEM according to the magnification when the first electrode was grown under tensile stress and the compressive layer of the piezoelectric body was placed in contact with the first electrode (Sample #3-4). 13A to 13C show that when the first electrode is grown under compressive stress and the compressive layer of the piezoelectric body is placed in contact with the first electrode (Sample #3-6), the boundary between the first electrode and the piezoelectric body is shown in magnification. It is a photograph observed by TEM.

11 to 13 are images of the interface between the first electrode (Mo) and the piezoelectric body (ScAlN) with high-resolution TEM.

11A, 12A, and 13A , the first electrode is shown as a dark layer, and the piezoelectric body is shown as a relatively light colored thick layer.

Referring to FIG. 11B , it can be seen that black spots indicating defects in the piezoelectric part appear significantly more than FIGS. 12B and 13B , and it can be seen that the black spots are the smallest in FIG. 13B .

Also, referring to FIGS. 12B and 12C , it can be seen that the interface between the first electrode and the piezoelectric body has a curved shape. As described above, when the interface between the first electrode and the piezoelectric body has a curved shape, the performance of the film bulk acoustic resonator is reduced.

Alternatively, referring to FIGS. 13B and 13C , it can be seen that the interface between the first electrode and the piezoelectric body is flat.

14 is a schematic diagram showing a lattice structure of a first electrode and a piezoelectric body matched with each other. Referring to FIG. 14 , it will be described that aluminum nitride doped with scandium is grown on the first electrode made of molybdenum.

In the case of molybdenum, the crystal structure is BCC, and the areal density of 110 planes is the highest.

In contrast, aluminum nitride doped with scandium has a crystal structure of HCP.

When the piezoelectric body is formed on the first electrode, when the centers of the surrounding molybdenum elements are connected to each other around one of the 110 molybdenum elements among the molybdenum elements, a hexagon appears as shown in FIG. 13 .

The 0002 side of HCP of aluminum nitride doped with scandium is placed in this hexagon.

15 shows the c lattice constant according to the residual stress of the piezoelectric body was obtained through XRD theta-2theta scan. Referring to FIG. 15 , it can be seen that the c lattice constant increases as the compressive stress increases, and the c lattice constant decreases as the tensile stress increases.

16 illustrates measurements of the lattice constant of the c-axis of the piezoelectric body and the lattice constant of the a-axis of the first electrode according to the formation conditions of the first electrode and the formation conditions of the piezoelectric body.

Referring to FIG. 16 , it can be seen that the c lattice constant value of the aluminum nitride doped with scandium has a constant value because the total residual stress of the piezoelectric body is the tensile stress (300 MPa). However, in the case of the first electrode, it can be seen that the lattice constant a greatly increases as the residual stress is the compressive stress.

That is, the lattice constant of the first electrode in which the residual stress is the compressive stress may have a value greater than 3.12 Å.

FIG. 17 is an HR-TEM image of a layer of scandium aluminum nitride adjacent to the first electrode (see '151' in FIG. 2) (#3-1, #3-4, #3-6 in the order of the figure). Since it is difficult to measure the a lattice constant of scandium aluminum nitride by XRD theta-2theta scan, the a lattice constant was measured by HR-TEM.

Table 8 below shows the calculation of lattice mismatch between the lattice of the first electrode and the piezoelectric body by measuring the lattice constant along the a-axis.

a-axis lattice constant (Å) #3-1 #3-4 #3-6 Piezoelectric body (1st layer) 2.64 2.64. 2.842 first electrode 3.139 3.117 3.125 1 stool
Grid mismatch (%) 15.28 15.22 9.06 6 stools
Grid mismatch (%) 39.283 38.825 -1.902

15 to 17 and Table 8, it can be seen that the lattice mismatch is the lowest when the first electrode is formed under compressive stress and the piezoelectric layer in contact with the first electrode is a compressive layer formed under compressive stress. . That is, when the first electrode is formed under compressive stress and the piezoelectric layer in contact with the first electrode is a compressive layer formed under compressive stress, crystal orientation of the piezoelectric body is improved, thereby improving the performance of the thin film bulk acoustic resonator.

18 and 19 are schematic circuit diagrams of a filter according to embodiments of the present invention.

Each of the plurality of volumetric acoustic resonators employed in the filters of FIGS. 18 and 19 corresponds to the thin film bulk acoustic resonator shown in FIG. 1 .

Referring to FIG. 18 , the filter 1000 according to an embodiment of the present invention may be formed in a ladder type filter structure. Specifically, the filter 1000 includes a plurality of thin film bulk acoustic resonators 1100 and 1200 .

The first thin film bulk acoustic resonator 1100 may be connected in series between a signal input terminal to which the input signal RFin is input and a signal output terminal to which the output signal RFout is output, and the second thin film bulk acoustic resonator 1200 is the signal It is connected between the output terminal and ground.

Referring to FIG. 19 , the filter 2000 according to an embodiment of the present invention may be formed in a lattice type filter structure. Specifically, the filter 2000 includes a plurality of thin film bulk acoustic resonators 2100 , 2200 , 2300 , and 2400 , and filters balanced input signals RFin+ and RFin- to filter the balanced output signals RFout+, RFout- ) can be printed.

In the above, the present invention has been described with specific matters such as specific components and limited embodiments and drawings, but these are provided to help a more general understanding of the present invention, and the present invention is not limited to the above embodiments. , those of ordinary skill in the art to which the present invention pertains can devise various modifications and variations from these descriptions.

Therefore, the spirit of the present invention should not be limited to the above-described embodiments, and not only the claims described below, but also all modifications equivalently or equivalently to the claims described below belong to the scope of the spirit of the present invention. will do it

110: substrate
112: air cavity
120: insulating layer
130: membrane
135: resonance unit
140: first electrode
150: piezoelectric body
151, 152: piezoelectric layer
155: abnormal determination
160: second electrode
170: protective layer
180: electrode pad
1000, 2000: filter
1100, 1200, 2100, 2200, 2300, 2400: thin film bulk acoustic resonators

Claims (14)

Board;
a first electrode disposed on the substrate;
a piezoelectric body disposed on the first electrode and including aluminum nitride to which a doping material is added; and
a second electrode disposed on the piezoelectric body;
The piezoelectric body includes first and second regions, wherein the first region is closer to the first electrode than the second region;
The first and second regions include an HCP crystal structure, and the HPC crystal structure included in the first region has a lattice constant in the a-axis direction and a lattice constant in the c-axis direction compared to the HPC crystal structure included in the second region. A thin film bulk acoustic resonator with a large ratio (c/a) of
According to claim 1,
The thin film bulk acoustic resonator further comprising an air cavity disposed between the substrate and the first electrode.
According to claim 1,
The doping material is one or a combination thereof selected from the group consisting of scandium (Sc), erbium (Er), yttrium (Y), lanthanum (La), titanium (Ti), zirconium (Zr), and hafnium (Hf). A thin film bulk acoustic resonator comprising
According to claim 1,
The content of the doping material included in the piezoelectric material is 1 to 20 at% thin film bulk acoustic resonator.
According to claim 1,
wherein the first region has a larger c lattice constant than the second region.
According to claim 1,
The first electrode may include gold (Au), titanium (Ti), tantalum (Ta), molybdenum (Mo), ruthenium (Ru), platinum (Pt), tungsten (W), aluminum (Al), nickel (Ni), and a thin film bulk acoustic resonator comprising one of iridium (Ir) or an alloy thereof.
delete According to claim 1,
The first electrode is a thin film bulk acoustic resonator including a BCC crystal structure.
Board;
a first electrode disposed on the substrate;
a piezoelectric body disposed on the first electrode and including aluminum nitride to which a doping material is added; and
a second electrode disposed on the piezoelectric body;
The piezoelectric body includes first and second regions, wherein the first region is closer to the first electrode than the second region;
The first and second regions include an HCP crystal structure, and the HPC crystal structure included in the first region has a lattice constant in the a-axis direction and a lattice constant in the c-axis direction compared to the HPC crystal structure included in the second region. has a large ratio (c/a) of
The first electrode is a thin film bulk acoustic resonator having a lattice constant greater than 3.12 Å in the a-axis direction.
10. The method of claim 9,
Further comprising an air cavity disposed between the substrate and the first electrode
Thin-film bulk acoustic resonators.
10. The method of claim 9,
The first electrode may include gold (Au), titanium (Ti), tantalum (Ta), molybdenum (Mo), ruthenium (Ru), platinum (Pt), tungsten (W), aluminum (Al), nickel (Ni), and a thin film bulk acoustic resonator comprising one of iridium (Ir) or an alloy thereof.
delete 10. The method of claim 9,
The first electrode is a thin film bulk acoustic resonator including a BCC crystal structure.
A filter comprising a plurality of thin film bulk acoustic resonators, comprising:
At least one of the plurality of thin film bulk acoustic resonators is a thin film bulk acoustic resonator selected from any one of claims 1 to 6, 8 to 11, and 13.

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