Bulk acoustic wave resonator and method of manufacturing the same

A bulk acoustic wave resonator includes a substrate including a cavity groove, a membrane layer disposed above the substrate and including a convex portion. And a lower electrode including a portion thereof disposed on the convex portion. The bulk acoustic wave resonator also includes a piezoelectric layer configured so that a portion of the piezoelectric layer is disposed above the convex portion, and an upper electrode disposed on the piezoelectric layer. A first space formed by the cavity groove and a second space formed by the convex portion form a cavity, the cavity groove is disposed below an active region, and the convex portion comprises an inclined surface disposed outside of the cavity groove.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims benefit under 35 USC 119(a) of priority to Korean Patent Application No. 10-2017-0050608 filed on Apr. 19, 2017 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The following description relates to a bulk acoustic wave resonator and a method of manufacturing the same.

2. Description of Related Art

In general, a space, which may be secured for resonance in bulk acoustic resonators, is determined by thicknesses of sacrificial layers.

Also, as sacrificial layer thicknesses are further reduced, there is a high possibility that resonant portions and substrates may be stuck during manufacturing processes, increasing constraints on structures and process designs.

On the other hand, as the thicknesses of sacrificial layers increase, the possibility of occurrence of stiction between resonant portions and substrates may be reduced. However, increasing the thickness of a sacrificial layer unconditionally may not be feasible in terms of a manufacturing process.

For example, in order to fabricate a resonant structure for the generation of resonance, a plurality of thin films are deposited on a sacrificial layer. To this end, the sacrificial layer is inclined by slope etching. However, as the thickness of a sacrificial layer increases, the length of an inclined surface of the sacrificial layer also increases, which leads to an increase in the size of an overall filter device, as well as, a respective resonator. In addition, as the thickness of the sacrificial layer increases, characteristic deterioration may be easily caused due to an increase in a length of a connection portion between resonators.

Furthermore, because increasing the thickness of a sacrificial layer causes an increase in a size of a step to correspond to the increased thickness in a subsequent process, a problem of negative properties in terms of process accuracy may occur.

Thus, the development of a structure, in which the occurrence of stiction of a substrate may be reduced and a problem caused by the increase in a thickness of a sacrificial layer may also be solved, is needed.

SUMMARY

Examples provide a bulk acoustic wave resonator that prevents stiction between a substrate and a membrane layer, and a method of manufacturing the same.

In accordance with an example, there is provided a bulk acoustic wave resonator, including: a substrate comprising a cavity groove; a membrane layer disposed above the substrate and comprising a convex portion; a lower electrode comprising a portion thereof disposed on the convex portion; a piezoelectric layer configured so that a portion of the piezoelectric layer may be disposed above the convex portion; and an upper electrode disposed on the piezoelectric layer, wherein a first space formed by the cavity groove and a second space formed by the convex portion form a cavity, the cavity groove may be disposed below an active region, and the convex portion may include an inclined surface disposed outside of the cavity groove.

The cavity groove may be sized to be disposed in a central portion of the active region.

The cavity groove may be configured to have a size corresponding to the convex portion.

The convex portion may include a support layer formed therearound so that the lower electrode may be disposed on a flat surface.

The support layer may be formed of a material comprising silicon nitride (SiN) or silicon oxide (SiO2) or a material comprising relatively low reactivity to a halide-based etching gas.

The bulk acoustic wave resonator may also include: a metal pad configured to be connected to a portion of the lower electrode and a portion of the upper electrode; and a passivation layer disposed on the lower electrode excluding a region in which the metal pad may be formed.

The upper electrode may be provided with a frame portion formed thereon so that the frame portion may be disposed at an edge of the active region.

A volume of the first space may be greater than a volume of the second space.

The active region may include a region in which the lower electrode, the piezoelectric layer, and the upper electrode are laminated.

In accordance with an example, there is provided a method of manufacturing a bulk acoustic wave resonator, including: forming a cavity groove in a substrate; forming a substrate protective layer on the substrate; forming a sacrificial layer portion on the substrate protective layer; forming a sacrificial layer by removing a portion of the sacrificial layer portion; forming a membrane layer to cover the sacrificial layer; forming a resonant portion on the membrane layer; and forming a cavity by removing the sacrificial layer.

The forming a resonant portion may include: forming a lower electrode on the membrane layer so that a portion of the lower electrode may be disposed above the sacrificial layer; forming a piezoelectric layer above the sacrificial layer to cover a portion of the lower electrode; forming an upper electrode on the piezoelectric layer; forming a passivation layer to expose a portion of the lower electrode and a portion of the upper electrode; and forming a metal pad on the exposed portion of the lower electrode and the exposed portion of the upper electrode.

The forming a sacrificial layer may include: planarizing an upper surface of the sacrificial layer portion; and removing a portion of the sacrificial layer portion, excluding a region thereof remaining as the sacrificial layer.

The forming a sacrificial layer may include: planarizing an upper surface of the sacrificial layer portion; and forming a depression groove in the sacrificial layer portion and around the sacrificial layer.

The method may also include: forming a support layer in the depression groove.

The forming of the cavity may include forming a first space by the cavity groove and forming a second space by a convex portion of the membrane layer.

The cavity groove may be sized to be disposed in a central portion of an active region.

The cavity groove may be formed to have a size corresponding to a size of the convex portion.

The upper electrode may include a frame portion formed thereon so that the frame portion may be disposed at an edge of an active region.

The method may also include: forming an active region in a region in which the lower electrode, the piezoelectric layer, and the upper electrode are laminated.

Throughout the drawings and the detailed description, the same reference numerals refer to the same elements. The drawings may not be to scale, and the relative sizes, proportions, and depictions of elements in the drawings may be exaggerated for clarity, illustration, and convenience.

DETAILED DESCRIPTION

FIG. 1is a schematic cross-sectional view of a bulk acoustic wave resonator, according to an example.

With reference toFIG. 1, a bulk acoustic wave resonator100according to a first example is configured to include a substrate110, a membrane layer120, a lower electrode130, a piezoelectric layer140, an upper electrode150, a passivation layer160, and a metal pad170.

The substrate110is a silicon-accumulated substrate. For example, a silicon wafer may be used as the substrate. The substrate110is disposed or provided with a substrate protective layer112thereon, to prevent damage to the substrate110when a cavity C is formed. The substrate protective layer112prevents the substrate110from being etched during a process of removing a sacrificial layer180(seeFIGS. 6 to 13) to be described later. For purposes of description, the term disposed will be used to describe the formation and disposition of the various layers and elements described in the present description.

A cavity formation groove or a cavity groove114is formed in the substrate110. The cavity groove114prevents stiction between the membrane layer120and the substrate110during resonance of the membrane layer120to be later described.

For example, the stiction between the membrane layer120and the substrate110during the resonance of a resonant portion is prevented through the cavity groove114formed to be recessed from the substrate110.

The cavity groove114is disposed below an active region S to prevent stiction between the membrane layer120and the substrate110when a resonant portion vibrates.

In this case, the active region S refers to a region in which all three layers of the lower electrode130, the piezoelectric layer140, and the upper electrode150are laminated. The resonant portion refers to a region in which vibrations are generated, and refers to a region corresponding to the active region S.

Further, the cavity groove114is formed to be tapered. A first space C1is formed through the cavity groove114. As described above, because the first space C1forming the cavity C is formed through the cavity groove114, a problem occurring due to an increase in a thickness of a sacrificial layer180(seeFIG. 4) is resolved. For example, a length of an inclined surface of the sacrificial layer180is prevented from increasing due to the increase in a thickness of the sacrificial layer.

In addition, the cavity groove114has a size corresponding to a size of the active region S described above. As an example, the cavity groove114corresponds to a central portion of the convex portion122to be described later, but is not limited thereto. For example, the cavity groove114may have a size that varies from a size that corresponds to a central portion of the convex portion122to a size corresponding to a size of the convex portion122.

The membrane layer120is formed on the substrate110and has the convex portion122. The convex portion122, together with the substrate110, forms a second space C2. The cavity C includes the first space C1formed by the cavity groove114, and the second space C2formed by the convex portion122.

Further, an edge of the convex portion122is formed to have an inclined surface122a.

In addition, the membrane layer120is formed to cover the sacrificial layer180in a fabrication process, and then, the second space C2is formed below the membrane layer120by removing the sacrificial layer180.

The membrane layer120is formed of a material having relatively low reactivity with a halide-based etching gas such as fluorine (F), chlorine (Cl) or the like to remove the silicon-based sacrificial layer180.

In one example, a volume of the first space C1is formed to be greater than a volume of the second space C2. Thus, the resonant portion stably and simultaneously resonates, thus, preventing stiction between the membrane layer120and the substrate110during resonance of the resonant portion.

In one example, the inclined surface122aof the convex portion122is formed to be disposed outwardly of the cavity groove114.

The lower electrode130is formed on the membrane layer120, and at least a portion of the lower electrode130is located above the cavity C. As an example, the lower electrode130is formed using a conductive material, such as molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum, and the like, or alloys thereof.

The lower electrode130is used as either an input electrode or an output electrode, receiving or outputting an electrical signal, such as a radio frequency (RF) signal or the like. For example, when the lower electrode130is an input electrode, the upper electrode150is an output electrode, and when the lower electrode130is an output electrode, the upper electrode150is an input electrode.

The piezoelectric layer140is formed to cover at least a portion of the lower electrode130. The piezoelectric layer140converts a signal input through the lower electrode130or the upper electrode150into acoustic waves. For example, the piezoelectric layer140serves to convert electrical signals into acoustic waves through physical vibrations.

For example, the piezoelectric layer140is formed by depositing aluminum nitride, doped aluminum nitride, zinc oxide, or lead zirconate titanate.

In addition, when the piezoelectric layer140is formed of aluminum nitride (AlN), the piezoelectric layer140further includes a rare earth metal. For example, as the rare earth metal, at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La) may be used. In addition, when the piezoelectric layer140is formed of aluminum nitride (AlN), the piezoelectric layer140further includes a transition metal. For example, as the transition metal, at least one of zirconium (Zr), titanium (Ti), magnesium (Mg), and hafnium (Hf) may be used.

The upper electrode150may be formed to cover the piezoelectric layer140, and may be formed using a conductive material, such as molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), or the like, or alloys thereof, in a manner similar to the lower electrode130.

On the other hand, a frame portion152is provided on the upper electrode150. The frame portion152refers to a portion of the upper electrode150, having a thickness greater than a thickness of a remaining portion of the upper electrode150. The frame portion152is disposed on the upper electrode150, in such a manner that the frame portion is disposed in a region of the active region S, excluding a central portion of the active region S, that is, at an edge of the active region S.

The frame portion152serves to reflect lateral waves generated during resonance to an interior of the active region S, thus, confining resonance energy in the active region S. In other words, the frame portion152is formed to be disposed at an edge of the active region S, to prevent vibrations from escaping externally from the active region S.

A passivation layer160is formed at least on the piezoelectric layer140and the upper electrode150. For example, the passivation layer160is formed in a region except for portions of the lower electrode130and the upper electrode150on which the metal pad170is formed.

Furthermore, a thickness of the passivation layer160is adjusted by etching in an ultimate process to control a passing-frequency band.

The metal pad170is formed on portions of the lower electrode130and the upper electrode150, on which the passivation layer160is not formed. As an example, the metal pad170is formed of a material, such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), a copper-tin (Cu—Sn) alloy, or the like.

As described above, stiction between the substrate110and the membrane layer120is prevented through the cavity C of which a volume is increased compared to existing bulk acoustic wave resonators. For example, as the volume of the cavity C is increased through the cavity groove114formed in the substrate110, the membrane layer120is prevented from being stuck to the substrate110. In other words, stiction therebetween may be prevented.

In addition, even when the volume of the cavity C is increased, as described above, a problem occurring due to an increase in a thickness of the sacrificial layer180(seeFIG. 4) in a fabrication process is resolved. For example, a length of an inclined surface of the sacrificial layer180is prevented from increasing due to the increase in a thickness of the sacrificial layer as the volume of the cavity C increases.

As a result, an increase in a size of the bulk acoustic wave resonator100is reduced, thus, suppressing an increase in an overall size of a filter device. Furthermore, characteristics deterioration is prevented from occurring due to an increase in a length of a connection portion between the bulk acoustic wave resonators100.

FIGS. 2 to 13are process drawings illustrating a method of manufacturing a bulk acoustic wave resonator, according to an example.

First, as illustrated inFIG. 2, a cavity groove114is formed in a base part116of the substrate110. The cavity groove114is formed on the base part116as an indentation on an upper surface of the base part166. The cavity groove114may be formed to be tapered.

Also, as illustrated inFIG. 3, a substrate protective layer112is formed on the base part116of the substrate110. The substrate protective layer112serves to prevent the substrate110from being etched during a process of removing a sacrificial layer180(seeFIGS. 6 to 13) to be later described.

As illustrated inFIG. 4, a sacrificial layer portion or a sacrificial layer formation portion182is formed on the substrate protective layer112. The sacrificial layer portion182is also formed to be inserted into the cavity groove114.

As an example, the sacrificial layer portion182may be formed of a material containing polysilicon or silicon oxide.

Then, as illustrated inFIG. 5, the sacrificial layer portion182is planarized. The planarization process is performed by chemical mechanical polishing (CMP).

Subsequently, as illustrated inFIG. 6, a sacrificial layer180is formed through patterning of the sacrificial layer portion182. For example, a shape of the sacrificial layer180is formed by removing the sacrificial layer portion182in a region excluding a region of the sacrificial layer180.

Then, as illustrated inFIG. 7, a membrane layer120is formed. The membrane layer120is formed to cover the sacrificial layer180and; thus, a convex portion122is formed on the membrane layer120. Further, the convex portion122has an inclined surface122a.

As illustrated inFIG. 8, a lower electrode130is formed on the membrane layer120so that a portion of the lower electrode130is disposed above the sacrificial layer180. The lower electrode130is formed to extend outwardly of the sacrificial layer180.

Subsequently, as illustrated inFIG. 9, a piezoelectric layer140is formed. The piezoelectric layer140is formed such that a portion thereof is disposed above the sacrificial layer180. The portion of the piezoelectric layer140disposed above the sacrificial layer180is formed on at least a portion of the lower electrode130.

Then, as illustrated inFIG. 10, an upper electrode150is formed on the piezoelectric layer140. The upper electrode150is provided with a frame portion152formed thereon, and the frame portion152is formed to be disposed at an edge of an active region S.

Then, as illustrated inFIG. 11, a passivation layer160is formed such that a portion of the upper electrode150and a portion of the lower electrode130are externally exposed.

Subsequently, as illustrated inFIG. 12, a metal pad170is formed on the exposed portions of the lower electrode130and the upper electrode150.

Then, a cavity C is formed by removing the sacrificial layer180as illustrated inFIG. 13. The cavity C includes a first space C1formed by the cavity groove114, and a second space C2formed by the convex portion122of the membrane layer120.

As described above, stiction between the substrate110and the membrane layer120is prevented via the cavity C of which a volume is increased compared to existing bulk acoustic wave resonators. For example, as the volume of the cavity C is increased through the cavity groove114formed in the substrate110, the membrane layer120is prevented from being stuck to the substrate110. In other words, stiction between the membrane layer120and the substrate110is prevented.

In addition, even when the volume of the cavity C increases, the occurrence of a problem due to an increase in a thickness of the sacrificial layer180(seeFIG. 4) in a fabrication process may be prevented. For example, even when the volume of the cavity C increases, a length of an inclined surface of the sacrificial layer180is prevented from increasing due to the increase in a thickness of the sacrificial layer.

FIG. 14is a schematic cross-sectional view of a bulk acoustic wave resonator, according to an example.

Referring toFIG. 14, a bulk acoustic wave resonator200, according to an example, includes a substrate210, a membrane layer220, a support layer230, a lower electrode240, a piezoelectric layer250, an upper electrode260, a passivation layer270, and a metal pad280, by way of example.

The substrate210may be a silicon-accumulated substrate. For example, a silicon wafer may be used as the substrate. The substrate210is provided with a substrate protective layer212thereon to prevent damage to the substrate210when a cavity C is formed. The substrate protective layer212serves to prevent the substrate210from being etched during a process of removing a sacrificial layer290(seeFIGS. 16 to 22), to be later described.

A cavity formation groove or a cavity groove214is formed in the substrate210. The cavity groove214prevents stiction between a membrane layer220and the substrate210during resonance of the membrane layer220, to be later described.

For example, the stiction between the membrane layer220and the substrate210during the resonance of a resonant portion is prevented through the cavity groove214formed to be recessed from the substrate210.

The cavity groove214is disposed below an active region S to prevent stiction between the membrane layer220and the substrate210when the resonant portion vibrates.

In this case, the active region S refers to a region in which all three layers of the lower electrode240, the piezoelectric layer250, and the upper electrode260are laminated. The resonant portion refers to a region in which vibrations are generated, and refers to a region corresponding to the active region S.

Further, the cavity groove214is formed to be tapered. A first space C1is formed through the cavity groove214. As described above, because the first space C1forming the cavity C is formed through the cavity groove214, the occurrence of a problem due to an increase in a thickness of the sacrificial layer290during a fabrication process is prevented. For example, a length of an inclined surface of the sacrificial layer290is prevented from increasing due to the increase in a thickness of the sacrificial layer.

In addition, the cavity groove214has a size corresponding to a size of the active region S.

The membrane layer220is formed on the substrate210and has a convex portion222. The convex portion222and the substrate210form a second space C2. The cavity C includes the first space C1formed by the cavity groove214, and the second space C2formed by the convex portion222.

Further, an edge or a portion of the convex portion222is formed to have an inclined surface222a. In an example, the inclined surface222ais formed at both ends of the second space C2formed by the convex portion222.

In addition, the membrane layer220is formed to cover the sacrificial layer290in a fabrication process, and then, the second space C2is formed below the membrane layer220by removal of the sacrificial layer290.

The membrane layer220is formed of a material having low reactivity to a halide-based etching gas such as fluorine (F), chlorine (Cl) or the like to remove the silicon-based sacrificial layer180.

In one example, a volume of the first space C1is formed to be greater than a volume of the second space C2. Thus, the resonant portion may stably resonate, and simultaneously therewith, stiction between the membrane layer220and the substrate210is prevented during resonance of the resonant portion.

The support layer230is formed to be disposed around the convex portion222of the membrane layer220. The support layer230enables a lower electrode240, to be described later, to be formed on a flat surface.

For example, the bulk acoustic wave resonator200, according to an example, is a flat-type resonator.

The support layer230may be formed of a material including silicon nitride (SiN) or silicon oxide (SiO2) as an example, but a material of the support layer230is not limited thereto. Thus, the support layer230may be formed of a material which is not damaged when the sacrificial layer290(seeFIG. 16) to be described later is removed. In other words, the support layer230may be formed of a material that is not damaged by halide-based etching gas.

The lower electrode240is formed on the membrane layer220, and at least a portion of the lower electrode240is located above the cavity C. As an example, the lower electrode240is formed using a conductive material, such as molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum, and the like, or alloys thereof.

The lower electrode240is used as either an input electrode or an output electrode, receiving or providing an electrical signal, such as a radio frequency (RF) signal or the like. For example, when the lower electrode240is an input electrode, the upper electrode260is an output electrode, and when the lower electrode240is an output electrode, the upper electrode260is an input electrode.

The piezoelectric layer250is formed to cover at least a portion of the lower electrode240. The piezoelectric layer250converts a signal input through the lower electrode240or the upper electrode260into an acoustic wave. For example, the piezoelectric layer250converts electrical signals into acoustic waves through physical vibration.

As an example, the piezoelectric layer250is formed by depositing aluminum nitride, doped aluminum nitride, zinc oxide, or lead zirconate titanate.

In addition, when the piezoelectric layer250is formed of aluminum nitride (AlN), the piezoelectric layer250may further include a rare earth metal. For example, as the rare earth metal, at least one of scandium (Sc), erbium (Er), yttrium (Y), and lanthanum (La) is used. In addition, when the piezoelectric layer250is formed of aluminum nitride (AlN), the piezoelectric layer250may further include a transition metal. For example, as the transition metal, at least one of zirconium (Zr), titanium (Ti), magnesium (Mg), and hafnium (Hf) is used.

The upper electrode260is formed to cover the piezoelectric layer250, and is formed using a conductive material, such as molybdenum (Mo), ruthenium (Ru), tungsten (W), iridium (Ir), platinum (Pt), or the like, or alloys thereof, in a manner similar to the case of the lower electrode240.

On the other hand, a frame portion262is disposed on the upper electrode260. The frame portion262refers to a portion of the upper electrode260, having a thickness greater than a thickness of a remaining portion of the upper electrode260. The frame portion262is disposed on the upper electrode260, in such a manner that the frame portion is disposed in a region of the active region S excluding a central portion of the active region S, for instance, at an edge of the active region S.

The frame portion262serves to reflect lateral waves generated during resonance to an inside of the active region S, to confine resonance energy in the active region S. In other words, the frame portion262is disposed at an edge of the active region S, to prevent vibrations from escaping externally from the active region S.

A passivation layer270is formed at least on the piezoelectric layer250and the upper electrode260. For example, the passivation layer270is formed in a region on which the metal pad280is formed, except for portions of the lower electrode240and the upper electrode260.

In addition, a thickness of the passivation layer270is adjusted by etching performed in an ultimate process to control a passing-frequency band.

The metal pad280is formed on portions of the lower electrode240and the upper electrode260, on which the passivation layer270is not formed. As an example, the metal pad280is formed of a material, such as gold (Au), a gold-tin (Au—Sn) alloy, copper (Cu), a copper-tin (Cu—Sn) alloy, or the like.

As described above, stiction between the substrate210and the membrane layer220is prevented via the cavity C of which a volume is increased. For example, as the volume of the cavity C is increased through the cavity groove214formed in the substrate210, the membrane layer220is prevented from being stuck to the substrate210. In other words, stiction between the membrane layer220and the substrate210is prevented.

In addition, even when the volume of the cavity C increases, the occurrence of a problem due to an increase in a thickness of the sacrificial layer290(seeFIG. 4) in a fabrication process is prevented. For example, a length of an inclined surface of the sacrificial layer290is prevented from increasing due to the increase in a thickness of the sacrificial layer while increasing the volume of the cavity C.

As a result, an increase in the size of the bulk acoustic wave resonator200is reduced, thereby suppressing an increase in an overall size of a filter device. Furthermore, characteristic deterioration is prevented from occurring due to an increase in a length of a connection portion between the bulk acoustic wave resonators200.

FIGS. 15 to 23are process drawings illustrating a method of manufacturing a bulk acoustic wave resonator, according to an example.

As illustrated inFIG. 15, a sacrificial layer portion or a sacrificial layer formation portion292is formed on a substrate protective layer212. The sacrificial layer portion292is also formed to be inserted into a cavity groove214.

The sacrificial layer portion292is formed of, for example, a material containing polysilicon or silicon oxide.

A planarization process of the sacrificial layer portion292is performed. The planarization process is performed by chemical mechanical polishing (CMP).

Subsequently, as illustrated inFIG. 16, a sacrificial layer290is formed through patterning of the sacrificial layer portion292. For example, a depression groove292ais formed in the sacrificial layer portion292to form the sacrificial layer290.

Further, as illustrated inFIG. 17, a membrane layer220is formed. The membrane layer220is formed to cover the sacrificial layer290, and thus, a convex portion222is formed on the membrane layer220. The convex portion222has an inclined surface222a.

A support layer230is formed in the depression groove292aformed in the sacrificial layer portion292. Subsequently, a planarization process is performed via chemical mechanical polishing (CMP).

In addition, as illustrated inFIG. 18, a lower electrode240is formed on the membrane layer220so that a portion of the lower electrode240is disposed above the sacrificial layer290. The lower electrode240is formed to extend outwardly of the sacrificial layer290. Because a flat surface extending from an upper surface of the sacrificial layer290is formed by the support layer230, the lower electrode240is formed to have a flat shape.

Subsequently, as illustrated inFIG. 19, a piezoelectric layer250is formed. The piezoelectric layer250is formed such that a portion thereof is disposed above the sacrificial layer290. The portion of the piezoelectric layer250disposed above the sacrificial layer290is formed on the lower electrode240.

As illustrated inFIG. 20, an upper electrode260is formed on the piezoelectric layer250. The upper electrode260is provided with a frame portion262formed thereon, and the frame portion262is formed to be disposed at an edge of an active region S.

Then, as illustrated inFIG. 21, a passivation layer270is formed so that a portion of the upper electrode260and a portion of the lower electrode240are externally exposed.

Subsequently, as illustrated inFIG. 22, a metal pad280is formed on the exposed portions of the lower electrode240and the upper electrode260.

Then, a cavity C is formed by removing the sacrificial layer290as illustrated inFIG. 23. The cavity C includes a first space C1formed by the cavity groove214, and a second space C2formed by the convex portion222of the membrane layer220.

As described above, stiction between the substrate210and the membrane layer220is prevented via the cavity C of which a volume is increased compared to existing bulk acoustic resonators. For example, as the volume of the cavity C is increased through the cavity groove214formed in the substrate210, stiction between the membrane layer220and the substrate210is prevented.

In addition, even when the volume of the cavity C increases, the occurrence of a problem due to an increase in a thickness of the sacrificial layer290in a fabrication process is prevented. For example, a length of an inclined surface of the sacrificial layer290is prevented from increasing due to the increase in a thickness of the sacrificial layer while increasing the volume of the cavity C.

As set forth above, according to examples, stiction between a substrate and a membrane layer is prevented.