A bulk acoustic wave resonator includes: a substrate; a first electrode disposed on the substrate; a piezoelectric layer at least partially disposed on the first electrode; and a second electrode disposed on the piezoelectric layer; wherein the first electrode includes an aluminum alloy layer containing scandium (Sc), and has a surface roughness of 2.4 nm or less, based on an arithmetic mean roughness.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application No. 10-2018-0164882 filed on Dec. 19, 2018 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes.

BACKGROUND

The following description relates to a bulk acoustic wave resonator.

2. Description of Related Art

Interest in 5G communications technology has been increasing, and technological developments have been undertaken in candidate bands.

On the other hand, a frequency band that may be implemented with a film bulk acoustic wave resonator (FBAR), is a frequency band of about 6 GHz or less. In the case of FBARs operating in frequency bands of 2 to 3 GHz, an electrode thickness and a piezoelectric layer thickness may be easily implemented. However, in the case of FBARs operating in a 5 GHz frequency band, significant manufacturing process difficulty and performance degradation are anticipated.

In detail, in the case of a FBAR operating in the 5 GHz frequency band, an ultrathin film electrode should be able to be implemented, and a piezoelectric layer thickness should also be relatively thin. However, in a case in which an electrode material having relatively high acoustic impedance, such as molybdenum (Mo), is used, an increase in electrical loss due to reduction in thickness is anticipated, and electrical loss of the resonator and a filter device including the resonator is expected to increase.

However, in a case in which an electrode material having low acoustic impedance properties, such as aluminum (Al), is used, mechanical properties of aluminum (Al) are degraded and, thus, are predicted to have great mechanical dynamic loss, and crystal orientation is deteriorated at the time of forming a piezoelectric layer.

SUMMARY

In one general aspect, a bulk acoustic wave resonator includes: a substrate; a first electrode disposed on the substrate; a piezoelectric layer at least partially disposed on the first electrode; and a second electrode disposed on the piezoelectric layer; wherein the first electrode includes an aluminum alloy layer containing scandium (Sc), and has a surface roughness of 2.4 nm or less, based on an arithmetic mean roughness.

A content of the scandium (Sc) in the aluminum alloy layer may be 0.1 at % to 5 at %.

A doping material of the piezoelectric layer may include any one or any combination of any two or more of scandium, erbium, yttrium, lanthanum, titanium, zirconium, and hafnium.

A content of the doping material in the piezoelectric layer may be 0.1 at % to 30 at %.

A full width at half maximum (FWHM), representing crystallinity, of the piezoelectric layer may be 1 degree or less.

The bulk acoustic wave resonator may further include a passivation layer disposed to cover either one or both of the first electrode and the second electrode.

The second electrode may include an aluminum alloy layer containing scandium (Sc).

The second electrode may be composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or may include a layer composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr.

The first electrode may include a first electrode layer composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr, and a second electrode layer disposed on the first electrode layer and including an aluminum alloy containing scandium (Sc).

The first electrode may include a first electrode layer including an aluminum alloy containing scandium (Sc), and a second electrode layer disposed on the first electrode layer, the second electrode layer being composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or being composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr.

The second electrode may include a first electrode layer composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr, and a second electrode layer disposed on the first electrode layer and including an aluminum alloy containing scandium (Sc).

The second electrode may include a third electrode layer composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr, and a fourth electrode layer disposed on the third electrode layer and including an aluminum alloy containing scandium (Sc).

The second electrode may include a third electrode layer composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr, and a fourth electrode layer disposed on the third electrode layer and including an aluminum alloy containing scandium (Sc).

The second electrode may include a first electrode layer including an aluminum alloy containing scandium (Sc), and a second electrode layer disposed on the first electrode layer, the second electrode layer being composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or being composed of an alloy including one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, or Cr.

The second electrode may include a third electrode layer including an aluminum alloy containing scandium (Sc), and a fourth electrode layer disposed on the third electrode layer, the fourth electrode layer being composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or being composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr.

The second electrode may include a third electrode layer including an aluminum alloy containing scandium (Sc), and a fourth electrode layer disposed on the third electrode layer, the fourth electrode layer being composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or being composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr.

The first electrode may include a first electrode layer composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni) and chromium (Cr), or composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr, and a second electrode layer disposed on the first electrode layer and including an aluminum alloy containing scandium (Sc).

The first electrode may include a first electrode layer including an aluminum alloy containing scandium (Sc), and a second electrode layer disposed on the first electrode layer, the second electrode layer being composed of any one of molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), and chromium (Cr), or being composed of an alloy including any one of Mo, Ru, W, Ir, Pt, Cu, Ti, Ta, Ni, and Cr.

In another general aspect, a bulk acoustic wave resonator includes: a substrate; a first electrode disposed on the substrate, and including an aluminum alloy layer containing scandium (Sc); a piezoelectric layer at least partially disposed on the first electrode; and a second electrode disposed on the piezoelectric layer, wherein a full width at half maximum (FWHM), representing crystallinity, of the piezoelectric layer is 1 degree or less.

DETAILED DESCRIPTION

FIG. 1is a schematic plan view illustrating a bulk acoustic wave resonator100, according to an embodiment.FIG. 2is a cross-sectional view taken along line I-I′ inFIG. 1.FIG. 3is a cross-sectional view taken along line II-II′ inFIG. 1.FIG. 4is a cross-sectional view taken along line III-III′ inFIG. 1.

Referring toFIGS. 1 to 4, the bulk acoustic wave resonator100may include a substrate110, a sacrificial layer120, an etch stop portion130, a membrane layer140, a first electrode150, a piezoelectric layer160, a second electrode170, an insertion layer180, a passivation layer190, and a metal pad195.

The substrate110may be a silicon substrate. For example, a silicon wafer may be used as the substrate110. Alternatively, a silicon on insulator (SOI)-type substrate may be used.

An insulating layer112may be formed on an upper surface of the substrate110, and may electrically isolate the substrate110from layers, components, and/or elements disposed on an upper portion thereof. In addition, the insulating layer112prevents the substrate110from being etched by etching gas in a case in which a cavity C is formed during a manufacturing process.

The insulating layer112may be formed of any one or any combination of any two or more of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O2), and aluminum nitride (AlN), and may be formed using chemical vapor deposition, RF magnetron sputtering, or evaporation.

The sacrificial layer120is formed on the insulating layer112, and the cavity C and the etch stop portion130may be disposed inside the sacrificial layer120. The cavity C is formed by removing a portion of the sacrificial layer120. As such, as the cavity C is formed inside the sacrificial layer120, the first electrode150and the like disposed on the sacrificial layer120may be formed to be flat.

The etch stop portion130is disposed along a boundary of the cavity C. The etch stop portion130prevents etching from progressing beyond a cavity area in the process of forming the cavity C.

The membrane layer140forms the cavity C together with the substrate110. In addition, the membrane layer140may be formed of a material having a low reactivity with the etching gas when the sacrificial layer120is removed. The etch stop portion130is inserted into a groove142formed by the membrane layer140. A dielectric layer including a material including any one of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the membrane layer140.

A seed layer (not illustrated) formed of aluminum nitride (AlN) may be formed on the membrane layer140. For example, the seed layer may be disposed between the membrane layer140and the first electrode150. The seed layer may be formed using a dielectric or metal having a hexagonal close packing (HCP) crystal structure in addition to aluminum nitride (AlN). For example, when the seed layer is a metal layer, the seed layer may be formed of titanium (Ti).

The first electrode150is formed on the membrane layer140, and a portion of the first electrode150is disposed on an upper portion of the cavity C. The first electrode150may be used as either an input electrode or an output electrode for inputting and outputting an electrical signal such as a radio frequency (RF) signal or the like.

The first electrode150may be formed of an aluminum alloy containing scandium (Sc), as an example. As described above, since the first electrode150is formed of an aluminum alloy containing scandium (Sc), mechanical strength of first electrode150may be increased and high power reactive sputtering may be performed. Surface roughness of the first electrode150may be prevented from increasing and high orientation growth of the piezoelectric layer160may be induced under such deposition conditions.

In addition, since the first electrode150contains scandium (Sc), chemical resistance of the first electrode150is increased, and a disadvantage that occurs in a case in which the first electrode is formed of pure aluminum may be mitigated. Further, stability of a process, such as dry etching or wet processing, may be provided in manufacturing. Further, in a case in which the first electrode is formed of pure aluminum, oxidation is easily caused. However, since the first electrode150is formed of an aluminum alloy containing scandium, chemical resistance to oxidation may be improved.

In an example, first, an electrode was formed of a molybdenum (Mo) material and an aluminum alloy (AlSc) material containing scandium to have a thickness of 1500 Å, and sheet resistance thereof was measured. In this example, when the electrode was formed of a molybdenum (Mo) material, the sheet resistance was 0.9685, while when the electrode was formed of an aluminum alloy (AlSc) containing 0.625 at % of scandium, the sheet resistance was 0.316. As described above, it can be appreciated that when the electrode was formed of an aluminum alloy (AlSc), the sheet resistance was reduced as compared with the case in which the electrode was formed of the molybdenum (Mo) material.

On the other hand, the content of scandium (Sc) may be 0.1 at % to 5 at %. For example, if the content of scandium (Sc) is less than 0.1 at %, mechanical property deterioration and hillock may be caused by aluminum (Al), and if the content of scandium (Sc) is 5 at % or more, it may be difficult to reduce electrical loss indicating sheet resistance. In addition, if the content of scandium (Sc) increases, the surface roughness may increase, which may adversely affect crystal orientation.

As illustrated above in Table 1, yield strength is increased and elongation is decreased in the case of the aluminum alloy containing scandium (AlSc, 0.625 at %), as compared with the case of pure aluminum (Al). In addition, as illustrated inFIG. 5, the pure aluminum (Al) material and the aluminum alloy (AlSc, 0.625 at %) containing scandium were deposited to have a thickness of 1500 Å to measure a sheet resistance change in a reliable environment. As a result, it can be appreciated that a rate of change of sheet resistance after 96 Hr is about 50% in the case of the aluminum alloy (AlSc, 0.625 at %) containing scandium, as compared with that in the pure aluminum (Al), thereby exhibiting excellent oxidation resistance.

Also, since the first electrode150has excellent galvanic corrosion resistance with the metal pad195, stability in a manufacturing process may be obtained. For example, a material of pure aluminum (Al) and an aluminum alloy containing scandium (AlSc, 0.625 at %) were deposited to have a thickness of 1500 Å and then contacted with gold (Au), which is mainly used as a material of the metal pad195, and the deposited material of pure aluminum (Al) and aluminum alloy containing scandium (AlSc, 0.625 at %) were then immersed in an electrolyte solution for 65 hours, to compare galvanic corrosion characteristics. As a comparison result, no change in a surface was observed for the aluminum alloy containing scandium (AlSc, 0.625 at %), but corrosion with gold (Au) was observed in the pure aluminum material. Therefore, when the first electrode150is formed of an aluminum alloy (AlSc) containing scandium, excellent galvanic corrosion resistance properties may also be provided.

Furthermore, the first electrode150may be formed of an aluminum alloy (AlSc) only containing scandium (Sc). For example, no additional metal except aluminum (Al) and scandium (Sc) is contained in the first electrode150. If additional metals other than scandium (Sc) are present with aluminum (Al), such an aluminum alloy forms a ternary phase diagram. In such a case, it is difficult to control a composition, and a complex phase system is generated, thereby causing the occurrence of compositional unevenness and undesired crystal phase.

Further, when the first electrode150is formed of an aluminum alloy having a ternary system, the surface roughness is increased due to uneven composition and undesired crystal phase formation, which may adversely affect crystal orientation when the piezoelectric layer160is formed.

Thus, since the first electrode150is formed of an aluminum alloy (AlSc) containing only scandium (Sc), the crystal orientation of the piezoelectric layer160disposed on the first electrode150may be improved.

On the other hand, the surface roughness of the first electrode150may be 2.4 nm or less, based on the arithmetic mean roughness Ra. In this case, the arithmetic mean roughness Ra is defined by the following equation.

As an example,FIGS. 6 to 8illustrate a case in which a surface roughness of pure aluminum imaged by an atomic force microscope is 3.64 nm based on the arithmetic mean roughness Ra, a case in which a surface roughness of a scandium-containing aluminum alloy imaged by an atomic force microscope is 1.90 nm based on the arithmetic mean roughness Ra, and a case in which a surface roughness of the scandium-containing aluminum alloy by the atomic force microscope is 10.68 nm based on the arithmetic mean roughness Ra.

In this case, as illustrated inFIG. 9, it can be seen that crystallinity of the piezoelectric layer160deteriorates when the surface roughness of the aluminum alloy (AlSc) containing scandium (Sc) deteriorates.

For example, it can be seen that: when the surface roughness of pure aluminum is 3.64 nm based on the arithmetic mean roughness Ra, a full width at half maximum (FWHM) representing the crystallinity of the piezoelectric layer160is 1.73 deg.; when the surface roughness of the scandium-containing aluminum alloy is 1.90 nm based on the arithmetic mean roughness Ra, FWHM representing the crystallinity of the piezoelectric layer160is 0.83 deg.; and when the surface roughness of the scandium-containing aluminum alloy is 10.68 nm based on the arithmetic mean roughness Ra, FWHM representing the crystallinity of the piezoelectric layer160is 4.37 deg.

In other words, it can be appreciated that even when the first electrode is formed of an aluminum alloy (AlSc) containing only scandium (Sc), if the surface roughness of the first electrode is poor, the piezoelectric layer160is deteriorated in crystallinity, even compared with the case in which the first electrode is formed of pure aluminum.

On the other hand, as illustrated inFIG. 10, it can be seen that when the surface roughness of the scandium-containing aluminum alloy is greater than 2.4 nm on the basis of the arithmetic mean roughness Ra, the FWHM indicating the crystallinity of the piezoelectric layer160increases sharply.

For example, when the surface roughness of the scandium-containing aluminum alloy is 1.9 nm based on the arithmetic mean roughness Ra, as in a first test piece (#1) ofFIGS. 9 and 10, FWHM indicating the crystallinity of the piezoelectric layer160is 0.83 deg. When the surface roughness of the scandium-containing aluminum alloy is 2.1 nm based on the arithmetic mean roughness Ra, as in a third test piece (#3) ofFIG. 10, the FWHM indicating the crystallinity of the piezoelectric layer160is 0.86 deg. When the surface roughness of the scandium-containing aluminum alloy is 2.4 nm based on the arithmetic mean roughness Ra, as in a fourth test piece (#4), the FWHM indicating the crystallinity of the piezoelectric layer160is 0.95 deg.

For example, when a difference between arithmetic mean roughnesses Ra of the first test piece #1and the third test piece #3is 0.2 nm, a difference in FWHM indicating the crystallinity of the piezoelectric layer160is 0.03 deg. When the difference between the arithmetic mean roughnesses Ra of the third test piece #3and the fourth test piece #4is 0.3 nm, the difference in FWHM indicating the crystallinity of the piezoelectric layer160is 0.09 deg. In other words, when the surface roughness of the scandium-containing aluminum alloy is 2.4 nm or less, based on the arithmetic mean roughness Ra, it can be seen that an increase in FWHM indicating the crystallinity of the piezoelectric layer160is relatively low.

On the other hand, when the surface roughness of the scandium-containing aluminum alloy as in a fifth test piece (#5) is 2.6 nm based on the arithmetic mean roughness Ra, the FWHM indicating the crystallinity of the piezoelectric layer160is 1.84 deg.

Surface roughnesses of the scandium-containing aluminum alloys of the fourth test piece (#4) and the fifth test piece (#5) have a difference of 0.2 nm, based on the arithmetic mean roughness Ra. In this case, it can be seen that the difference in FWHM representing the crystallinity of the piezoelectric layer160is approximately twofold (0.89 deg.). Thus, when the surface roughness of the scandium-containing aluminum alloy exceeds 2.4 nm based on the arithmetic mean roughness Ra, the crystallinity of the piezoelectric layer160drastically deteriorates. In detail, when the surface roughness of the scandium-containing aluminum alloy exceeds 2.4 nm based on the arithmetic mean roughness Ra, the FWHM indicating the crystallinity of the piezoelectric layer160increases sharply.

Further, as illustrated inFIGS. 9 and 10, in the case of a second test piece (#2), a surface roughness of the scandium-containing aluminum alloy is 10.7 nm based on the arithmetic mean roughness Ra, and the FWHM indicating the crystallinity of the piezoelectric layer160is 4.37 deg. As illustrated inFIG. 10, in the case of a sixth test piece (#6), a surface roughness of the scandium-containing aluminum alloy is 17.0 nm based on the arithmetic mean roughness Ra, and in this case, the FWHM indicating the crystallinity of the piezoelectric layer160is 7.33 deg.

As described above, in the case in which the surface roughness of the first electrode exceeds 2.4 nm based on the arithmetic mean roughness Ra, the FWHM indicating the crystallinity of the piezoelectric layer160sharply increases. Thus, the surface roughness of the first electrode150is set to 2.4 nm or less, based on the arithmetic mean roughness Ra.

The piezoelectric layer160is formed to cover at least a portion of the first electrode150disposed on an upper portion of the cavity C. The piezoelectric layer160is formed of any one of aluminum nitride (AlN), zinc oxide (ZnO), and lead zirconium titanium oxide (PZT:PbZrTiO), and is a part causing a piezoelectric effect to convert electrical energy into mechanical energy in the form of acoustic waves. In detail, for example, when the piezoelectric layer160is formed of aluminum nitride (AlN), the piezoelectric layer150may further include a rare earth metal. As an example, the rare earth metal may include any one or any combination of any two or more of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). Also, as an example, a transition metal may include any one or any combination of any two or more of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb), and may also include magnesium (Mg), which is a divalent metal.

The content of elements included in the aluminum nitride (AlN) to improve piezoelectric properties may be 0.1 to 30 at %. If the content of the elements included to improve piezoelectric properties is less than 0.1 at %, piezoelectric properties higher than that of aluminum nitride (AlN) may not be implemented. If the content of the elements included to improve piezoelectric properties exceeds 30 at %, it may be difficult to perform deposition and control a composition for deposition, and a nonuniform phase may be formed. In addition, if the element content exceeds 30 at %, the probability of occurrence of abnormal grain growth sharply increases, so that serious surface defects may occur on the piezoelectric layer.

The piezoelectric layer160includes a piezoelectric portion162disposed on a flat portion S of the bulk acoustic wave resonator100and a bent portion164disposed on an extended portion E of the bulk acoustic wave resonator100.

The piezoelectric portion162is a portion directly stacked on an upper surface of the first electrode150. Therefore, the piezoelectric portion162is interposed between the first electrode150and the second electrode170, and is formed as a flat shape together with the first electrode150and the second electrode170.

The bent portion164may be a region extending outwardly from the piezoelectric portion162and located in the extended portion E.

The bent portion164is disposed on the insertion layer180, to be described later, and is formed in a protruding shape along the shape of the insertion layer180. Thus, the piezoelectric layer160is bent at a boundary between the piezoelectric portion162and the bent portion164, and the bent portion164protrudes, corresponding to a thickness and a shape of the insertion layer180.

The bent portion164may include an inclined portion164aand an extended portion164b.

The inclined portion164ais a portion formed to be inclined along an inclined surface or plane L of the insertion layer180, to be described later. The extended portion164bis a portion extending outwardly from the inclined portion164a.

The inclined portion164ais formed parallel to the inclined surface L of the insertion layer180, and an inclination angle of the inclined portion164ais formed to be equal to an inclination angle of the inclined surface L.

The FWHM indicating the crystallinity of the piezoelectric layer160may be 1 degree or less. For example, as illustrated inFIG. 10, when the surface roughness of the first electrode150is 2.4 nm or less, based on the arithmetic mean roughness Ra, the FWHM indicating the crystallinity of the piezoelectric layer160is 1 degree or less. In more detail, as illustrated inFIG. 10, when the surface roughness of the scandium-containing aluminum alloy is 1.9 nm based on the arithmetic mean roughness Ra as in the first test piece (#1), FWHM indicating the crystallinity of the piezoelectric layer160is 0.83 deg. When the surface roughness of the scandium-containing aluminum alloy is 2.1 nm based on the arithmetic mean roughness Ra as in the third test piece (#3) ofFIG. 10, the FWHM indicating the crystallinity of the piezoelectric layer160is 0.86 deg. When the surface roughness of the scandium-containing aluminum alloy is 2.4 nm based on the arithmetic mean roughness Ra as in the fourth test piece (#4), the FWHM indicating the crystallinity of the piezoelectric layer160is 0.95 deg.

The second electrode170is formed to cover at least a portion of the piezoelectric layer160disposed on an upper portion of the cavity C. The second electrode170may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode150is used as an input electrode, the second electrode170may be used as an output electrode, and when the first electrode150is used as an output electrode, the second electrode170may be used as an input electrode.

The second electrode170may also be formed of an aluminum alloy containing scandium (Sc) as in the case of the first electrode150.

In addition, the second electrode170may be formed of an aluminum alloy (AlSc) containing only scandium (Sc). For example, no additional metal except scandium (Sc) is contained in the aluminum alloy. If additional metals other than scandium (Sc) are present with aluminum (Al), these aluminum alloys form a ternary phase diagram. In this case, it may be difficult to control a composition, and a complex phase system is caused, thereby causing compositional unevenness and formation of undesired crystal phase.

Further, when the second electrode is formed of an aluminum alloy having a ternary system, the surface roughness thereof is increased due to an uneven composition and undesired crystal phase formation, which may adversely affect crystal orientation when the passivation layer190is formed.

Therefore, the second electrode170is formed of an aluminum alloy (AlSc) containing only scandium (Sc), and thus, crystal orientation of the passivation layer190disposed on the second electrode170may be improved.

The insertion layer180is disposed between the first electrode150and the piezoelectric layer160. The insertion layer180may be formed of a dielectric material such as silicon oxide (SiO2), aluminum nitride (AlN), aluminum oxide (Al2O3), silicon nitride (Si3N4), manganese oxide (MgO), zirconium oxide (ZrO2), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), zinc oxide (ZnO), or the like, and is formed of a material different from that of the piezoelectric layer160. Further, a region in which the insertion layer180is provided may also be provided as air, as required, which may be implemented by removing the insertion layer180during a manufacturing process.

In this embodiment, a thickness of the insertion layer180may be less than that of the piezoelectric layer160. If the thickness of the insertion layer180were greater than that of the piezoelectric layer160, it may be difficult to form the bent portion164covering the insertion layer180. The insertion layer180should be formed to have a thickness of 100 Å or more such that the bent portion164may be easily formed, and sound waves in a horizontal direction of the bulk acoustic wave resonator100may be effectively prevented, thereby improving performance of the bulk acoustic wave resonator100.

The insertion layer180is disposed along a surface formed by the membrane layer140, the first electrode150and the etch stop portion130.

The insertion layer180is disposed around the flat portion S to support the bent portion164of the piezoelectric layer160. The bent portion164of the piezoelectric layer160may include the inclined portion164aand the extended portion164balong a shape of the insertion layer180.

The insertion layer180is disposed in an area excluding the flat portion S. For example, the insertion layer180may be disposed over the entire region except the flat portion S, or may be disposed over a portion of the area excluding the flat portion S.

At least a portion of the insertion layer180is disposed between the piezoelectric layer160and the first electrode150.

A side surface of the insertion layer180disposed along a boundary of the flat portion S is formed to have a thickness increased away from the flat portion S. Thus, the insertion layer180is formed to have the inclined surface L by which a side surface of the insertion layer adjacent to the flat portion S has a predetermined inclination angle (θ).

If the inclination angle (θ) of the side surface of the insertion layer180were formed to be less than 5 degrees, the insertion layer180would be difficult to implement, because a thickness of the insertion layer180would be significantly reduced, or an area of the inclined surface L would be excessively large.

If the inclination angle (θ) of the side surface of the insertion layer180were formed to be greater than 70 degrees, an inclination angle of the inclined portion164aof the piezoelectric layer160stacked on the insertion layer180would be formed to be greater than 70 degrees. In this case, since the piezoelectric layer160would be excessively bent, a crack may occur in the bent portion of the piezoelectric layer160.

Therefore, in the embodiment, the inclination angle (θ) of the inclined surface L is formed in a range of 5 degrees to 70 degrees.

The passivation layer190is formed in a region except for portions of the first electrode150and the second electrode170. The passivation layer190prevents damage to the second electrode170and the first electrode150during a manufacturing process.

Furthermore, the passivation layer190may be partially removed in a final process by etching for frequency control. For example, the thickness of the passivation layer190may be adjusted. In an example, a dielectric layer including any one of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the passivation layer190.

The metal pad195is formed on portions of the first electrode150and the second electrode170on which the passivation layer190is not formed. As an example, the metal pad195may be formed of a material such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), a copper-tin (Cu—Sn) alloy, aluminum (aluminum), an aluminum alloy, or the like. For example, the aluminum alloy may be an aluminum-germanium (Al—Ge) alloy.

As described above, since the surface roughness of the first electrode150is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystal orientation of the piezoelectric layer160may be improved.

FIG. 11is a schematic cross-sectional view illustrating a bulk acoustic wave resonator200, according to another embodiment.

Referring toFIG. 11, the bulk acoustic wave resonator200may include the substrate110, the sacrificial layer120, an etch stop portion130, the membrane layer140, the first electrode150, the piezoelectric layer160, a second electrode270, the insertion layer180, the passivation layer190, and the metal pad195.

The second electrode270is formed to cover at least a portion of the piezoelectric layer160disposed on an upper portion of a cavity C. The second electrode270may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode150is used as an input electrode, the second electrode270may be used as an output electrode, and when the first electrode150is used as an output electrode, the second electrode270may be used as an input electrode.

The second electrode270may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to this example. For example, the second electrode270may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like, or may be formed of a layer composed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

As described above, the first electrode150is formed of the aluminum alloy containing scandium (Sc), like in the first electrode150provided in the bulk acoustic wave resonator100according to the first embodiment. Furthermore, as described above, since the first electrode150is formed of an aluminum alloy containing scandium (Sc), mechanical strength may be increased and high power reactive sputtering may be performed. In this deposition condition, surface roughness of the first electrode150may be prevented from increasing and high orientation growth of the piezoelectric layer160may be induced.

In addition, since the scandium (Sc) is contained in the first electrode150, chemical resistance of the first electrode150is increased, and disadvantage that occurs in a case in which the first electrode is formed of pure aluminum may be mitigated. Further, stability of a process such as dry etching or wet processing may be provided in manufacturing. Further, in a case in which the first electrode is formed of pure aluminum, oxidation is easily caused. However, since the first electrode150is formed of an aluminum alloy containing scandium, chemical resistance to oxidation may be improved.

Further, a surface roughness of the first electrode150may be 2.4 nm or less, based on the arithmetic mean roughness Ra.

As described above, since the surface roughness of the first electrode150is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystal orientation of the piezoelectric layer160may be improved.

FIG. 12is a schematic cross-sectional view illustrating a bulk acoustic wave resonator300, according to another embodiment.

Referring toFIG. 12, the bulk acoustic wave resonator300may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode350, the piezoelectric layer160, the second electrode170, the insertion layer180, a passivation layer190, and a metal pad195, by way of example.

The first electrode350is formed on the membrane layer140, and a portion of the first electrode350is disposed on an upper portion of a cavity C. The first electrode350may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as an RF signal.

As an example, the first electrode350includes a first electrode layer352formed of an aluminum alloy containing scandium (Sc), and a second electrode layer354formed on the first electrode layer352.

A surface roughness of the first electrode layer352may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode layer352is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystal orientation of the piezoelectric layer160may be improved.

The second electrode layer354may be formed of a conductive material such as molybdenum (Mo) or an alloy thereof, but a material of the second electrode layer354is not limited to molybdenum (Mo). The second electrode layer354may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include an aluminum alloy layer including a layer composed of an alloy including any one thereof.

As described above, since the second electrode170and the first electrode layer352are formed of an aluminum alloy containing scandium (Sc), chemical resistance of the second electrode170and the first electrode layer352is increased, and disadvantages occurring in a case in which the first electrode and the second electrode are formed of pure aluminum may be mitigated. Further, stability of a process such as dry etching or wet processing may be provided in manufacturing. Further, in the case in which the first electrode and the second electrode are formed of pure aluminum, oxidation is easily caused. However, since the second electrode170and the first electrode layer352are formed of an aluminum alloy containing scandium, chemical resistance to oxidation may be improved.

Furthermore, since the surface roughness of the first electrode layer352is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystal orientation of the piezoelectric layer160may be improved.

FIG. 13is a schematic cross-sectional view illustrating a bulk acoustic wave resonator400, according to another embodiment.

Referring toFIG. 13, the bulk acoustic wave resonator400may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode450, the piezoelectric layer160, a second electrode470, the insertion layer180, a passivation layer190, and a metal pad195, by way of example.

The first electrode450is formed on the membrane layer140, and a portion of the first electrode450is disposed on an upper portion of a cavity C. In addition, the first electrode450may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

As an example, the first electrode450includes a first electrode layer452, and a second electrode layer454formed on the first electrode layer452and formed of an aluminum alloy containing scandium (Sc).

The first electrode layer452may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. For example, the first electrode layer452may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

Further, a surface roughness of the second electrode layer454may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the second electrode layer454is 2.4 nm or less, based on the arithmetic mean roughness Ra, the crystal orientation of the piezoelectric layer160may be improved.

The second electrode470is formed to cover at least a portion of the piezoelectric layer160disposed on the upper portion of the cavity C. The second electrode470may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode450is used as an input electrode, the second electrode470may be used as an output electrode, and when the first electrode450is used as an output electrode, the second electrode470may be used as an input electrode.

The second electrode470includes a third electrode layer472formed of an aluminum alloy containing scandium (Sc), and a fourth electrode layer474formed on the third electrode layer472.

The fourth electrode layer474may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. For example, the fourth electrode layer474may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

As described above, the second electrode layer454is formed of an aluminum alloy containing scandium (Sc). As described above, since the second electrode layer454is formed of an aluminum alloy containing scandium (Sc), high power reactive sputtering may be performed as mechanical strength is increased. In this deposition condition, the surface roughness of the second electrode layer454may be prevented from increasing and high orientation growth of the piezoelectric layer160may be induced.

Since the second electrode layer454and the third electrode layer472are formed of an aluminum alloy containing scandium (Sc), chemical resistance of the second electrode layer454and the third electrode layer472increases. Thus, disadvantages occurring in a case in which the first electrode and the second electrode are formed of pure aluminum may be mitigated. Further, stability of a process such as dry etching or wet processing may be provided in manufacturing. Further, oxidation occurs easily in a case in which the first electrode and the second electrode are formed of pure aluminum, but since the second and third electrode layers454and472formed of an aluminum alloy containing scandium are provided, chemical resistance to oxidation may be improved.

In addition, since the surface roughness of the second electrode layer454is 2.4 nm or less, based on the arithmetic mean roughness Ra, the crystallinity of the piezoelectric layer160may be improved.

FIG. 14is a schematic cross-sectional view illustrating a bulk acoustic wave resonator500, according to another embodiment.

Referring toFIG. 14, the bulk acoustic wave resonator500may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, the first electrode150, the piezoelectric layer160, a second electrode570, the insertion layer180, the passivation layer190, and the metal pad195, by way of example.

The second electrode570is formed to cover at least a portion of the piezoelectric layer160disposed on an upper portion of a cavity C. The second electrode570may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as an RF signal. For example, when the first electrode150is used as an input electrode, the second electrode570may be used as an output electrode, and when the first electrode150is used as an output electrode, the second electrode570may be used as an input electrode.

The second electrode570includes a first electrode layer572and a second electrode layer574disposed on the first electrode layer572and formed of an aluminum alloy containing scandium (Sc).

The first electrode layer572may be formed of a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. For example, the first electrode layer572may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

The first electrode150is formed of an aluminum alloy containing scandium (Sc). As described above, since the first electrode150is formed of an aluminum alloy containing scandium (Sc), mechanical strength may be increased and high power reactive sputtering may be performed. In this deposition condition, the surface roughness of the first electrode150may be prevented from being increased and high orientation growth of the piezoelectric layer160may be induced.

In addition, since the scandium (Sc) is contained in the first electrode150, chemical resistance of the first electrode150is increased, and a disadvantage that occurs in a case in which the first electrode is formed of pure aluminum may be mitigated. Further, stability of a process such as dry etching or wet processing may be provided in manufacturing. Further, in a case in which the first electrode is formed of pure aluminum, oxidation is easily caused. However, since the first electrode150is formed of an aluminum alloy containing scandium, the chemical resistance to oxidation may be improved.

Further, the surface roughness of the first electrode150may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode150is 2.4 nm or less, based on the arithmetic mean roughness Ra, the crystal orientation of the piezoelectric layer160may be improved.

FIG. 15is a schematic cross-sectional view illustrating a bulk acoustic wave resonator600, according to another embodiment.

Referring toFIG. 15, the bulk acoustic wave resonator600may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode650, the piezoelectric layer160, the second electrode170, the insertion layer180, the passivation layer190, and the metal pad195, by way of example.

The first electrode650is formed on the membrane layer140, and a portion of the first electrode650is disposed on an upper portion of a cavity C. In addition, the first electrode650may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

As an example, the first electrode650includes a first electrode layer652, and a second electrode layer654formed on the first electrode layer652and formed of an aluminum alloy containing scandium (Sc).

The first electrode layer652may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. For example, the first electrode layer652may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

A surface roughness of the second electrode layer654may be 2.4 nm or less, based on the arithmetic mean roughness Ra. Thus, crystallinity of the piezoelectric layer160may be improved since the surface roughness of the second electrode layer654is 2.4 nm or less, based on the arithmetic mean roughness Ra.

FIG. 16is a schematic cross-sectional view illustrating a bulk acoustic wave resonator700, according to another embodiment.

Referring toFIG. 16, the bulk acoustic wave resonator700may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode750, the piezoelectric layer160, a second electrode770, the insertion layer180, the passivation layer190, and the metal pad195, by way of example.

The first electrode750is formed on the membrane layer140, and a portion of the first electrode750is disposed on an upper portion of a cavity C. The first electrode750may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

As an example, the first electrode750includes a first electrode layer752formed of an aluminum alloy containing scandium (Sc), and a second electrode layer754formed on the first electrode layer752.

A surface roughness of the first electrode layer752may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode layer752is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystallinity of the piezoelectric layer160may be improved.

The second electrode layer754may be formed of a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. The second electrode layer754may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

The second electrode770is formed to cover at least a portion of the piezoelectric layer160disposed on the upper portion of the cavity C. The second electrode770may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode750is used as an input electrode, the second electrode770may be used as an output electrode, and when the first electrode750is used as an output electrode, the second electrode770may be used as an input electrode.

The second electrode770includes a third electrode layer772, and a fourth electrode layer774disposed on the third electrode layer772and formed of an aluminum alloy containing scandium (Sc).

The third electrode layer772may be formed of a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an embodiment. The third electrode layer772may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of.

FIG. 17is a schematic cross-sectional view illustrating a bulk acoustic wave resonator800, according to another embodiment.

Referring toFIG. 17, the bulk acoustic wave resonator800may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, the first electrode150, the piezoelectric layer160, a second electrode870, the insertion layer180, the passivation layer190, and the metal pad195, by way of example.

The second electrode870is formed to cover at least a portion of the piezoelectric layer160disposed on an upper portion of a cavity C. The second electrode870may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode150is used as an input electrode, the second electrode870may be used as an output electrode, and when the first electrode150is used as an output electrode, the second electrode870may be used as an input electrode.

The second electrode870includes a first electrode layer872formed of an aluminum alloy containing scandium (Sc), and a second electrode layer874formed on the first electrode layer872.

The second electrode layer874may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. The second electrode layer874may be formed of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

The first electrode150is formed of an aluminum alloy containing scandium (Sc). As described above, since the first electrode150is formed of an aluminum alloy containing scandium (Sc), mechanical strength may be increased and high power reactive sputtering may be performed. In this deposition condition, the surface roughness of the first electrode150may be prevented from increasing, and high orientation growth of the piezoelectric layer160may be induced.

In addition, since the scandium (Sc) is contained in the first electrode150, chemical resistance of the first electrode150is increased, and disadvantage that occurs in a case in which the first electrode is formed of pure aluminum may be mitigated. Further, stability of a process such as dry etching or wet processing may be provided in manufacturing. Further, in a case in which the first electrode is formed of pure aluminum, oxidation is easily caused. However, since the first electrode150is formed of an aluminum alloy containing scandium, chemical resistance to oxidation may be improved.

Further, the surface roughness of the first electrode150may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode150is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystal orientation of the piezoelectric layer160may be improved.

FIG. 18is a schematic cross-sectional view illustrating a bulk acoustic wave resonator900, according to another embodiment.

Referring toFIG. 18, the bulk acoustic wave resonator900may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode950, the piezoelectric layer160, a second electrode970, the insertion layer180, the passivation layer190, and the metal pad195, by way of example.

The first electrode950is formed on the membrane layer140, and a portion of the first electrode950is disposed on an upper portion of a cavity C. The first electrode950may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

As an example, the first electrode950includes a first electrode layer952formed of an aluminum alloy containing scandium (Sc), and a second electrode layer954formed on the first electrode layer952.

A surface roughness of the first electrode layer952may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode layer952is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystallinity of the piezoelectric layer160may be improved.

The second electrode layers954may be formed of a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. The second electrode layer954may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

The second electrode970is formed to cover at least a portion of the piezoelectric layer160disposed on the upper portion of the cavity C. The second electrode970may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode950is used as an input electrode, the second electrode970may be used as an output electrode, and when the first electrode950is used as an output electrode, the second electrode970may be used as an input electrode.

The second electrode970may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof as an example, but the disclosure is not limited to such an example. The second electrode970may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), and the like.

FIG. 19is a schematic cross-sectional view illustrating a bulk acoustic wave resonator1000, according to another embodiment.

Referring toFIG. 19, the bulk acoustic wave resonator1000may be include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode1050, the piezoelectric layer160, a second electrode1070, the insertion layer180, the passivation layer190, and the metal pad195.

The first electrode1050is formed on the membrane layer140, and a portion of the first electrode1050is disposed on an upper portion of a cavity C. The first electrode1050may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

As an example, the first electrode1050includes a first electrode layer1052formed of an aluminum alloy containing scandium (Sc), and a second electrode layer1054formed on the first electrode layer1052.

A surface roughness of the first electrode layer1052may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode layer1052is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystallinity of the piezoelectric layer160may be improved.

The second electrode layer1054may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. The second electrode layer1054may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of these elements.

The second electrode1070is formed to cover at least a portion of the piezoelectric layer160disposed on the upper portion of the cavity C. The second electrode1070may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode1050is used as an input electrode, the second electrode1070may be used as an output electrode, and when the first electrode1050is used as an output electrode, the second electrode1070may be used as an input electrode.

The second electrode1070includes a third electrode layer1072formed of an aluminum alloy containing scandium (Sc), and a fourth electrode layer1074formed on the third electrode layer1072.

The fourth electrode layer1074may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. For example, the fourth electrode layer1074may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of these elements.

FIG. 20is a schematic cross-sectional view illustrating a bulk acoustic wave resonator1100, according to another embodiment.

Referring toFIG. 20, the bulk acoustic wave resonator1100may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode1150, the piezoelectric layer160, a second electrode1170, the insertion layer180, the passivation layer190, and the metal pad195.

The first electrode1150is formed on the membrane layer140and a portion of the first electrode1150is disposed on an upper portion of the cavity C. The first electrode1150may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

As an example, the first electrode1150includes a first electrode layer1152, and a second electrode layer1154formed on an upper portion of the first electrode layer1152and formed of an aluminum alloy containing scandium (Sc).

The first electrode layer1152may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof. The first electrode layer1152may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of these elements.

The surface roughness of the second electrode layer1154may be 2.4 nm or less, based on the arithmetic mean roughness Ra. Thus, the crystallinity of the piezoelectric layer160may be improved since the surface roughness of the second electrode layer1154is 2.4 nm or less, based on the arithmetic mean roughness Ra.

The second electrode1170is formed to cover at least a portion of the piezoelectric layer160disposed on the upper portion of the cavity C. The second electrode1170may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode1150is used as an input electrode, the second electrode1170may be used as an output electrode, and when the first electrode1150is used as an output electrode, the second electrode1170may be used an input electrode.

The second electrode1170may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof as an example, but the disclosure is not limited to such an example. The second electrode1170may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of these elements.

FIG. 21is a schematic cross-sectional view illustrating a bulk acoustic wave resonator1200, according to another embodiment.

Referring toFIG. 21, the bulk acoustic wave resonator1200may include the substrate110, the sacrificial layer120, the etch stop portion130, the membrane layer140, a first electrode1250, the piezoelectric layer160, a second electrode1270, the insertion layer180, the passivation layer190, and the metal pad195.

The first electrode1250is formed on the membrane layer140and a portion of the first electrode1250is disposed on an upper portion of a cavity C. The first electrode1250may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal or the like.

As an example, the first electrode1250includes a first electrode layer1252, and a second electrode layer1254formed on the first electrode layer1252and formed of an aluminum alloy containing scandium (Sc).

The first electrode layer1252may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. The first electrode layer1552may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of these elements.

A surface roughness of the second electrode layer1254may be 2.4 nm or less, based on the arithmetic mean roughness Ra. Thus, the crystallinity of the piezoelectric layer160may be improved since the surface roughness of the second electrode layer1254is 2.4 nm or less, based on the arithmetic mean roughness Ra.

The second electrode1270is formed to cover at least a portion of the piezoelectric layer160disposed on the upper portion of the cavity C. The second electrode1270may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode1250is used as an input electrode, the second electrode1270may be used as an output electrode, and when the first electrode1250is used as an output electrode, the second electrode1270may be used as an input electrode.

The second electrode1270includes a third electrode layer1272, and a fourth electrode layer1274disposed on the third electrode layer1272and formed of an aluminum alloy and containing scandium (Sc).

The third electrode layer1272may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. The second electrode layer1272may be formed of a conductive material such as ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr), or the like, or may include a layer formed of an alloy including any one of these elements.

FIG. 22is a schematic cross-sectional view illustrating a bulk acoustic wave resonator1300, according to another embodiment.

Referring toFIG. 22, the bulk acoustic wave resonator1300may include a substrate1310, a membrane layer1320, a first electrode1330, a piezoelectric layer1340, a second electrode1350, a passivation layer1360, and a metal pad1370.

The substrate1310may be a substrate on which silicon is accumulated. For example, a silicon wafer may be used as the substrate. A substrate protective layer1312, which is disposed to face a cavity C, may be disposed on the substrate1310.

The substrate protective layer1312may prevent the substrate1310from being damaged when the cavity C is formed.

As an example, the substrate protective layer1312may be formed of any one or any combination of any two or more of silicon dioxide (SiO2), silicon nitride (Si3N4), aluminum oxide (Al2O2), and aluminum nitride (AlN), and may be formed using a process among chemical vapor deposition, RF magnetron sputtering, and evaporation.

The membrane layer1320is formed on an upper portion of a sacrificial layer (not illustrated) that is ultimately removed. The membrane layer1320forms the cavity C together with the substrate protective layer1312through removal of the sacrificial layer. For example, the cavity C may be formed by forming a sacrificial layer for formation of the cavity C on the substrate1310, and then removing the sacrificial layer. A dielectric layer including one of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the membrane layer1320.

A seed layer (not illustrated) formed of aluminum nitride (AlN) may be formed on the membrane layer1320. For example, the seed layer may be disposed between the membrane layer1320and the first electrode1330. The seed layer may be formed using a dielectric or a metal having an HCP crystal structure in addition to aluminum nitride (AlN). For example, when the seed layer is a metal layer, the seed layer may be formed of titanium (Ti).

The first electrode1330is formed on the membrane layer1320. The first electrode1330may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

As an example, the first electrode1330may be formed of an aluminum alloy containing scandium (Sc). As described above, since the first electrode1330is formed of an aluminum alloy containing scandium (Sc), mechanical strength may be increased and high power reactive sputtering may be performed. Surface roughness of the first electrode1330may be prevented from increasing, and high orientation growth of the piezoelectric layer1340may be induced under such deposition conditions.

Also, since scandium (Sc) is contained, chemical resistance of the first electrode1330is increased to compensate for disadvantage occurring in a case in which the first electrode is formed of pure aluminum. Further, stability of a process such as dry etching, wet processing or the like may be provided in manufacturing. Further, when the first electrode is formed of pure aluminum, oxidation is easily caused. However, since the first electrode1330is formed of an aluminum alloy containing scandium, chemical resistance to oxidation may be improved.

The surface roughness of the first electrode1330may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode1330is 2.4 nm or less, based on the arithmetic mean roughness Ra, the crystal orientation of the piezoelectric layer1340may be improved.

The piezoelectric layer1340is formed to cover at least a portion of the first electrode1330. The piezoelectric layer1340may cause a piezoelectric effect to convert electrical energy into mechanical energy in the form of acoustic waves, and may be formed of any one of aluminum nitride (AlN), zinc oxide (ZnO), and lead zirconium titanium oxide (PZT; PbZrTiO). In detail, for example, when the piezoelectric layer1340is formed of aluminum nitride (AlN), the piezoelectric layer1340may further include a rare earth metal. As an example, the rare earth metal may include any one or any combination of any two or more of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). Also, as an example, the transition metal may include any one or any combination of any two or more of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb). Magnesium (Mg), which is a divalent metal, may also be included.

The crystallinity (FWHM) of the piezoelectric layer1340may be 2 deg. or less.

The second electrode1350is formed to cover at least a portion of the piezoelectric layer1340disposed on the upper portion of the cavity C. The second electrode1350may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode1330is used as an input electrode, the second electrode1350may be used as an output electrode, and when the first electrode1330is used as an output electrode, the second electrode1350may be used as an input electrode.

The second electrode1350may be formed of an aluminum alloy containing scandium (Sc), as in the case of the first electrode1330.

The second electrode1350may include a frame portion1352disposed at an edge of an active region, for example, a region in which the first electrode1330, the piezoelectric layer1340, and the second electrode1350are overlapped. The frame portion1352has a thickness greater than that of a remaining portion of the second electrode1350. In an example, the frame portion1352reflects a lateral wave generated during resonance to an inside of the active region to confine resonance energy in the active region.

The passivation layer1360is formed in a region excluding portions of the first electrode1330and the second electrode1350. The passivation layer1360prevents the second electrode1350and the first electrode1330from being damaged during a manufacturing process.

Further, a thickness of the passivation layer1360may be adjusted by etching in a final process, to control a frequency. The passivation layer1360may be formed using the same material as that of the membrane layer1320. In an example, a dielectric layer including one of manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the passivation layer1360.

The metal pad1370is formed on portions of the first electrode1330and the second electrode1350in which the passivation layer1360is not formed. As an example, the metal pad1370may be formed of a material such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), a copper-tin (Cu—Sn) alloy, aluminum (Al), an aluminum alloy, or the like. For example, the aluminum alloy may be an aluminum-germanium (Al—Ge) alloy.

FIG. 23is a schematic cross-sectional view illustrating a bulk acoustic wave resonator1400, according to another embodiment.

Referring toFIG. 23, the acoustic wave resonator1400may include a substrate1410, a membrane layer1420, a first electrode1430, a piezoelectric layer1440, a second electrode1450, a passivation layer1460, and a metal pad1470.

The substrate1410may be a substrate on which silicon is accumulated. For example, a silicon wafer may be used as the substrate1410. The substrate1410may include a groove1421for formation of a cavity C.

The groove1421may be disposed in a central portion of the substrate1410, and may be disposed below an active region. In this case, the active region is a region in which the first electrode1430, the piezoelectric layer1440, and the second electrode1450overlap.

The membrane layer1420forms the cavity C together with the substrate1410. For example, the membrane layer1420may be formed to cover the groove1421of the substrate1410. A dielectric layer including any one of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the membrane layer1420.

A seed layer (not illustrated) formed of aluminum nitride (AlN) may be formed on the membrane layer1420. For example, the seed layer may be disposed between the membrane layer1420and the first electrode1430. The seed layer may be formed using a dielectric or metal having an HCP crystal structure in addition to aluminum nitride (AlN). As an example, when the seed layer is a metal layer, the seed layer may be formed of titanium (Ti).

The first electrode1430is formed on the membrane layer1420. The first electrode1430may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

The first electrode1430may be formed of an aluminum alloy containing scandium (Sc) as an example. As described above, since the first electrode1430is formed of an aluminum alloy containing scandium (Sc), mechanical strength may be increased and high power reactive sputtering may be performed. In this deposition condition, an increase in the surface roughness of the first electrode1430may be prevented and high orientation growth of the piezoelectric layer1440may be induced.

In addition, since the scandium (Sc) is contained in the first electrode1430, chemical resistance of the first electrode1430is increased, and a defect occurring in a case in which the first electrode is formed of pure aluminum may be mitigated. Further, stability of a process such as dry etching or wet processing may be secured in manufacturing. Further, in a case in which the first electrode is formed of pure aluminum, oxidation is easily caused. However, since the first electrode1430is formed of an aluminum alloy containing scandium, chemical resistance to oxidation may be improved.

A surface roughness of the first electrode1430may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode1430is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystal orientation of the piezoelectric layer1440may be improved.

The piezoelectric layer1440is formed to cover at least a portion of the first electrode1430. The piezoelectric layer1440is a part causing a piezoelectric effect to convert electrical energy into mechanical energy in the form of acoustic wave, and may be formed of any one of aluminum nitride (AlN), zinc oxide (ZnO) and lead zirconium titanium oxide (PZT; PbZrTiO). In addition, when the piezoelectric layer1440is formed of aluminum nitride (AlN), the piezoelectric layer1440may further include a rare earth metal. As an example, the rare earth metal may include at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). Also, as an example, the transition metal may include any one or any combination of any two or more of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb). Magnesium (Mg), which is a divalent metal, may also be included.

The crystallinity (FWHM) of the piezoelectric layer1440may be 2 degrees or less.

The second electrode1450is formed to cover at least a portion of the piezoelectric layer1440disposed on an upper portion of the cavity C. The second electrode1450may be used as one of an input electrode and an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode1430is used as an input electrode, the second electrode1450may be used as an output electrode, and when the first electrode1430is used as an output electrode, the second electrode1450may be used as an input electrode.

The second electrode1450may also be formed of an aluminum alloy including scandium (Sc) like the first electrode1430.

In addition, the second electrode1450may include a frame portion1452disposed at an edge of the active region. The frame portion1452has a thickness greater than that of a remaining portion of the second electrode1450. For example, the frame portion1452reflects a lateral wave generated during resonance to the inside of the active region to confine resonance energy in the active region.

The passivation layer1460is formed in a region excluding portions of the first electrode1430and the second electrode1450. The passivation layer1460prevents damage to the second electrode1450and the first electrode1430during a manufacturing process.

Further, a thickness of the passivation layer1460may be adjusted in a final process by etching to adjust a frequency. The passivation layer1460may be formed using the same material as that used for the membrane layer1420. For example, a dielectric layer including any one of manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the passivation layer1460.

The metal pad1470is formed on portions of the first electrode1430and the second electrode1450in which the passivation layer1460is not formed. As an example, the metal pad1470may be formed of a material such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), a copper-tin (Cu—Sn) alloy, aluminum (Al), an aluminum alloy, or the like. For example, the aluminum alloy may be an aluminum-germanium (Al—Ge) alloy.

FIG. 24is a schematic cross-sectional view illustrating a bulk acoustic wave resonator1500, according to another embodiment.

Referring toFIG. 24, the bulk acoustic wave resonator1500may include a substrate1510, a membrane layer1520, a first electrode1530, a piezoelectric layer1540, a second electrode1550, a passivation layer1560, and a metal pad1570.

The substrate1510may be a substrate on which silicon is accumulated. For example, a silicon wafer may be used as the substrate1510. The substrate1510may include a reflective layer1511.

The reflective layer1511may be formed at a central portion of the substrate1510, and may be disposed below the active region. In this case, the active region is a region in which the first electrode1530, the piezoelectric layer1540, and the second electrode1550are overlapped with each other.

The reflective layer1511may include first and second reflective members1512and1514disposed in a groove. The first and second reflective members1512and1514may be formed of different materials.

The first reflective member1512may be formed using a conductive material such as molybdenum (Mo) or an alloy thereof, but the disclosure is not limited to such an example. For example, ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), copper (Cu), aluminum (Al), titanium (Ti), tantalum (Ta), nickel (Ni), chromium (Cr) or the like may be used as a material of the first reflective member1512. A dielectric layer including any one of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenide (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2) and zinc oxide (ZnO) may be used as the second reflective member1514. Also, the first and second reflective members1512and1514may be formed as only one pair, or the first and second reflective members1512and1514may be repeatedly formed as a pair.

The membrane layer1520may be formed to cover the reflective layer1511. A dielectric layer including any one of silicon nitride (Si3N4), silicon oxide (SiO2), manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the membrane layer1520.

A seed layer (not illustrated) formed of aluminum nitride (AlN) may be formed on the membrane layer1520. For example, the seed layer may be disposed between the membrane layer1520and the lower electrode1530. The seed layer may be formed using a dielectric or metal having an HCP crystal structure in addition to aluminum nitride (AlN). For example, when the seed layer is a metal layer, the seed layer may be formed of titanium (Ti).

The first electrode1530is formed on the membrane layer1520. Also, the first electrode1530may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal.

The first electrode1530may be formed of an aluminum alloy containing scandium (Sc) as an example. As described above, since the first electrode1530is formed of an aluminum alloy containing scandium (Sc), mechanical strength may be increased and high power reactive sputtering may be performed. Under such deposition conditions, an increase in surface roughness of the first electrode1530may be prevented and high orientation growth of the piezoelectric layer1540may be induced.

In addition, since the scandium (Sc) is contained in the first electrode1530, chemical resistance of the first electrode1530is increased, and disadvantage that occurs in a case in which the first electrode is formed of pure aluminum may be mitigated. Further, stability of a process such as dry etching or wet processing may be provided in manufacturing. Further, in a case in which the first electrode is formed of pure aluminum, oxidation is easily caused. However, since the first electrode1530is formed of an aluminum alloy containing scandium, chemical resistance to oxidation may be improved.

The surface roughness of the first electrode1530may be 2.4 nm or less, based on the arithmetic mean roughness Ra. As described above, since the surface roughness of the first electrode1530is 2.4 nm or less, based on the arithmetic mean roughness Ra, crystal orientation of the piezoelectric layer1540may be improved.

The piezoelectric layer1540is formed to cover at least a portion of the first electrode1530. The piezoelectric layer1540may be a part causing a piezoelectric effect to convert electrical energy into mechanical energy in the form of acoustic waves, and may be formed of any one of aluminum nitride (AlN), zinc oxide (ZnO), and lead zirconium titanium oxide (PZT; PbZrTiO). For example, when the piezoelectric layer1540is formed of aluminum nitride (AlN), the piezoelectric layer1540may further include a rare earth metal. As an example, the rare earth metal may include any one or any combination of any two or more of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La). Also, as an example, the transition metal may include any one or any combination of any two or more of titanium (Ti), zirconium (Zr), hafnium (Hf), tantalum (Ta), and niobium (Nb). Further, the transition metal may also include magnesium (Mg), which is a divalent metal.

The crystallinity (FWHM) of the piezoelectric layer1540may be 2 degrees or less.

The second electrode1550is formed to cover at least a portion of the piezoelectric layer1540disposed on an upper portion of a cavity C. The second electrode1550may be used as either an input electrode or an output electrode for inputting or outputting, respectively, an electrical signal such as a radio frequency (RF) signal. For example, when the first electrode1530is used as an input electrode, the second electrode1550may be used as an output electrode, and when the first electrode1530is used as an output electrode, the second electrode1550may be used as an input electrode.

The second electrode1550may be formed of an aluminum alloy containing scandium (Sc), like the first electrode1530.

In addition, the second electrode1550may include a frame portion1552disposed at an edge of an active region. The frame portion1552has a thickness greater than that of a remaining portion of the second electrode1550. For example, the frame portion1552reflects a lateral wave generated during resonance to an inside of the active region to confine resonance energy in the active region.

The passivation layer1560is formed in a region excluding portions of the first electrode1530and the second electrode1550. The passivation layer1560prevents damage to the second electrode1550and the first electrode1530during a manufacturing process.

The passivation layer1560may be adjusted in thickness in a final process to control a frequency. The passivation layer1560may be formed using the same material as that used for the membrane layer1520. For example, a dielectric layer including one of manganese oxide (MgO), zirconium oxide (ZrO2), aluminum nitride (AlN), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), and zinc oxide (ZnO) may be used as the passivation layer1560.

The metal pad1570is formed on portions of the first electrode1530and the second electrode1550in which the passivation layer1560is not formed. As an example, the metal pad1570may be formed of a material such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), a copper-tin (Cu—Sn) alloy, aluminum (Al), an aluminum alloy, or the like. For example, the aluminum alloy may be an aluminum-germanium (Al—Ge) alloy.

FIG. 25is a schematic cross-sectional view illustrating a bulk acoustic wave resonator1600, according to another embodiment.

Referring toFIG. 25, the bulk acoustic wave resonator1600may include a substrate1610, a membrane layer1620, a first electrode1650, a piezoelectric layer1660, a second electrode1670, an insertion layer1680, a passivation layer1690, and a metal pad1695.

The substrate1610and the membrane layer1620have the same respective configurations as the substrate1510and the membrane layer1520included in the bulk acoustic wave resonator1500ofFIG. 24. Thus, a detailed description of the substrate1610and the membrane layer1620will be omitted.

In addition, the first electrode1650, the piezoelectric layer1660, the second electrode1670, the insertion layer1680, the passivation layer1690and the metal pad1695are the same components as the second electrode150, the piezoelectric layer160, the second electrode170and the insertion layer180, the passivation layer190and the metal pad195, respectively, provided in the bulk acoustic wave resonator100ofFIGS. 1-4. Thus, a detailed description of these components will be omitted.

The insertion layer1680is disposed between the first electrode1650and the piezoelectric layer1660. The insertion layer1680may be formed using a dielectric such as silicon oxide (SiO2), aluminum nitride (AlN), aluminum oxide (Al2O3), silicon nitride (Si3N4), manganese oxide (MgO), zirconium oxide (ZrO2), lead zirconate titanate (PZT), gallium arsenic (GaAs), hafnium oxide (HfO2), aluminum oxide (Al2O3), titanium oxide (TiO2), zinc oxide (ZnO) or the like, and may be formed of a material different from that of the piezoelectric layer1860. In addition, an area in which the insertion layer1680is provided may also be provided as air, as required, which may be implemented by removing the insertion layer1680during fabrication.

In this embodiment, a thickness of the insertion layer1680may be the same as or similar to that of the first electrode1650. The insertion layer1680may also be formed to have a thickness less than or similar to that of the piezoelectric layer1660. For example, the thickness of the insertion layer1680may be 100 Å or more while being less than that of the piezoelectric layer1660, but the configuration of the insertion layer1680is not limited to this example.

The insertion layer1680is the same as the insertion layer180provided in the bulk acoustic wave resonator100ofFIGS. 1-4. Thus, a detailed description of the insertion layer1680will be omitted.

As set forth above, according to example embodiments, crystalline properties of a piezoelectric layer may be improved.