ACOUSTIC RESONATOR AND METHOD OF MANUFACTURING THE SAME

An acoustic resonator and a method of manufacturing the same are provided. An acoustic resonator includes a resonating part disposed on a substrate, a cap accommodating the resonating part and bonded to the substrate, and a bonded part bonding the cap and the substrate to each other, the bonding part including at least one block disposed between a bonding surface of the cap and a bonding surface of the substrate to block a leakage of a bonding material that forms the bonded part during a bonding operation.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 USC 119(a) of Korean Patent Application No. 10-2015-0181531, filed on Dec. 18, 2015, 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 an acoustic resonator and a method of manufacturing the same.

2. Description of Related Art

In accordance with the recent development of communications technology, a corresponding development of signal processing technology and radio frequency (RF) component technology have become desirable.

For example, in response to the recent demand to miniaturize wireless communications devices, the miniaturization of the radio frequency component technology has become desirable. An example of technology developed to miniaturize the radio frequency component technology includes a filter having a form of a bulk acoustic wave (BAW) resonator manufactured using a semiconductor thin film wafer.

The bulk acoustic wave (BAW) resonator refers to a resonator with an element having a thin film causing resonance by depositing a piezoelectric dielectric material on a silicon wafer, which is a semiconductor substrate, and using piezoelectric characteristics of the piezoelectric dielectric material implemented as the filter.

Applications of bulk acoustic wave (BAW) resonators include small and light weight filters such as mobile communications devices, chemical and biological devices, and the like, an oscillator, a resonance element, an acoustic resonance mass sensor, and the like.

SUMMARY

In one general aspect, an acoustic resonator includes a resonating part disposed on a substrate, a cap accommodating the resonating part and bonded to the substrate, and a bonded part bonding the cap and the substrate to each other, the bonding part including at least one block disposed between a bonding surface of the cap and a bonding surface the substrate to block a leakage of a bonding material that forms the bonded part during a bonding operation.

The bonded part may include a first metal layer disposed on the bonding surface of the cap, a second metal layer disposed on the bonding surface of the substrate, and a third metal layer interposed between the first metal layer and the second metal layer.

The third metal layer may include tin (Sn).

The first and second metal layers may include copper (Cu) or gold (Au).

The block may be spaced apart from the first and second metal layers by a predetermined distance.

The block may be disposed on at least one of the bonding surface of the cap and the bonding surface of the substrate.

The at least one block may include a first block disposed on the bonding surface of the cap and a second block disposed on the bonding surface of the substrate.

The first block and the second block may be disposed at positions that do not face each other.

The first block and the second block may be disposed not to contact each other.

In another general aspect, a method of manufacturing an acoustic resonator involves forming a resonating part on a substrate, and bonding a cap to the substrate, in which the bonding of the cap involves providing a block on at least one of a bonding surface of the cap and a bonding surface of the substrate.

The bonding of the cap may involve forming a first metal layer on the bonding surface of the cap and forming a second metal layer on the bonding surface of the substrate, and forming a third metal layer between the first metal layer and the second metal layer to bond the cap and the substrate to each other.

The block may include the same material as that of the first metal layer or the second metal layer, and may be formed during a same process with the first metal layer or the second metal layer.

The block may be formed at a position spaced apart from the first metal layer or the second metal layer by a predetermined distance.

The forming of the third metal layer may involve melting and curing the third metal layer, and the block may impede a leakage of the molten third metal layer.

The block may be formed along an edge of the bonding surface of the cap or the bonding surface of the substrate.

A material that forms the third metal layer may have a lower melting point than a material that forms the block.

In yet another general aspect, an acoustic resonator includes a cap disposed over a resonating part and bonded to a substrate, and a bonded part disposed between a bonding surface of the cap and the substrate. The bonded part includes a block disposed along an edge of a bonding surface of the cap and a bonding material disposed on the bonding surface and abutting an inner sidewall of the block.

The bonded part may include a first metal layer disposed on the bonding surface of the cap, the first metal layer being spaced apart from the block; and the bonding material may extend from a first area between from the first metal layer and the substrate to a second area between the first metal layer and the sidewall of the block.

The block and the first metal layer may be formed of a same material, and the bonding material may include a metal having a lower melting point than the material forming the block and the first metal layer.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present description will be described with reference to schematic views. In the drawings, for example, due to manufacturing techniques and/or tolerances, modifications of the shape shown may be estimated. Thus, embodiments should not be construed as being limited to the particular shapes of regions shown herein, for example, to include a change in shape results in manufacturing. The following embodiments may also be constituted by one or a combination thereof.

FIG. 1illustrates a cross-sectional view of an example of an acoustic resonator, andFIG. 2illustrates an enlarged cross-sectional view of part A of the acoustic resonator illustrated inFIG. 1.

First, referring toFIG. 1, an acoustic resonator100according to the illustrated example includes a substrate110, a resonating part120, and a cap140.

In this example, an air gap130is formed between the substrate110and the resonating part120, and the resonating part120is formed on a membrane layer150to be spaced apart from the substrate110by the air gap130.

The substrate110may be formed as a silicon substrate or a silicon-on-insulator (SOI) type substrate. However, the substrate110is not limited thereto.

The resonating part120includes a first electrode121, a piezoelectric layer123, and a second electrode125. The resonating part120may be formed by sequentially stacking the first electrode121, the piezoelectric layer123, and the second electrode125from the bottom up. In this example, the piezoelectric layer123is disposed between the first electrode121and the second electrode125.

Because the resonating part120is formed on a membrane layer150, the membrane layer150, the first electrode121, the piezoelectric layer123, and the second electrode125may be sequentially formed on the substrate110to obtain the structure illustrated inFIG. 1.

The resonating part120may make the piezoelectric layer123resonate in response to signals applied to the first electrode121and the second electrode125to generate a resonance frequency and an anti-resonance frequency.

The first electrode121and the second electrode125may be formed of a metal such as gold, molybdenum, ruthenium, aluminum, platinum, titanium, tungsten, palladium, chrome, nickel, or the like.

The resonating part120may use an acoustic wave of the piezoelectric layer123to generate resonance. For example, in response to signals being applied to the first electrode121and the second electrode125, mechanical vibration may occur in a thickness direction of the piezoelectric layer123to generate the acoustic wave.

The piezoelectric layer123may include zinc oxide (ZnO), aluminum nitride (AlN), quartz, and the like.

A resonance phenomenon of the piezoelectric layer123may occur in response to a half of a wavelength of the applied signal matching a thickness of the piezoelectric layer123. Because electrical impedance is changed sharply when the resonance phenomenon occurs, the acoustic resonator according to an example may be used as a filter capable of selecting a frequency.

The resonance frequency may be determined by the thickness of the piezoelectric layer123, the first electrode121, the second electrode125that surrounds the piezoelectric layer123, inherent acoustic wave velocity of the piezoelectric layer123, and the like.

For example, as the thickness of the piezoelectric layer123is reduced, the resonance frequency may be increased.

Referring toFIG. 1, the resonating part120further includes a protection layer127. In this example, the protection layer127is formed on the second electrode125to prevent the second electrode125from being exposed to an external environment.

The first electrode121and the second electrode125are formed on an outer surface of the piezoelectric layer123, and are connected to a first connection electrode180and a second connection electrode190, respectively.

The first connection electrode180and the second connection electrode190may be provided to confirm characteristics of the resonator and the filter, and to perform a required frequency trimming. However, the first connection electrode180and the second connection electrode190are not limited thereto.

In this example, the resonating part120is spaced apart from the substrate110by the air gap130in order to improve a quality factor.

For example, by forming the air gap130between the resonating part120and the substrate110, the acoustic wave generated from the piezoelectric layer123may not be affected by the substrate110.

Further, reflective characteristics of the acoustic wave generated from the resonating part120may be improved by the air gap130. Because the air gap130, which is an empty space, has an impedance that is close to infinity, the acoustic wave may not be lost by using the air gap130, and may remain in the resonating part120.

Therefore, by reducing loss in the acoustic wave in a longitudinal direction by the air gap130, a quality factor value of the resonating part120may be improved.

In this example, a plurality of via holes112penetrating through the substrate110is formed in a lower surface of the substrate110. In addition, connection conductors115aand115bmay be formed in the respective via holes112.

The connection conductors115aand115bare formed on inner surfaces of the via holes112, that is, overall inner walls of the via holes112, but are not limited thereto.

Further, one end of the connection conductors115aand115bare connected to external electrodes117formed on the lower surface of the substrate110, and the other end thereof are connected to the first electrode121or the second electrode125.

In this example, a first connection conductor115aelectrically connects the first electrode121and the external electrode117to each other, and a second connection conductor115belectrically connects the second electrode125and the external electrode117to each other.

Therefore, the first connection conductor115amay penetrate through the substrate110and the membrane layer150, and may be electrically connected to the first electrode121, and the second connection conductor115bmay penetrate through the substrate110, the membrane layer150, and the piezoelectric layer123, and may be electrically connected to the second electrode125.

Meanwhile, althoughFIG. 1illustrates and describes only two via holes112and two connection conductors115aand115b,the number of via holes and connection conductors is not limited to thereto. A great number of via holes112and connection conductors115aand115bmay be provided, as needed.

The cap140is provided to protect the resonating part120from an external environment.

The cap140is formed in a cover form including an internal space in which the resonating part120is accommodated. The cap140may hermetically seal the resonating part120. Thus, the cap140is bonded to the substrate so that a side wall141thereof surrounds the resonating part120.

Further, a lower surface of the side wall141may be used as a bonding surface141awith the substrate110.

In this example, the cap140is bonded to the substrate110by a solid liquid inter-diffusion (SLID) bonding, and a resultant bonded part175is formed between the bonding surface141aof the cap and the bonding surface110aof the substrate.

As the SLID bonding, a Cu—Sn bonding may be used. However, an Au—Sn bonding may also be used.

Referring toFIG. 2, the bonded part175includes a first metal layer171formed on the cap140, a second metal layer172formed on the substrate110, and a third metal layer173interposed between the first metal layer171and the second metal layer172.

The first metal layer171and the second metal layer172may be formed of a Cu material, and the third metal layer173may be formed of a Sn material.

In addition, the third metal layer173extends to outer sides of the first and second metal layers171and172.

The extended portions may be portions formed by the Sn bonding material that is melted during the SLID bonding process and leaks outside of the space between the first and second metal layers171and172before being cured.

Because the third metal layer173is formed by spreading the molten Sn bonding material between the first and second metal layers171and172, the third metal layer173protruding to the outer sides of the first and second metal layers171and172is likely to be separated from the third metal layer173and to be introduced into the resonating part120. Further, in the event that an excessive amount of the molten Sn flows out to the outer sides of the first and second metal layers171and172, an amount of Sn bonding the first and second metal layers171and172to each other may be decreased in the region between the first and second metal layers171and172, thereby deteriorating coupling reliability.

Thus, the acoustic resonator includes at least one blocking block177at the outer side of the first metal layer171or the second metal layer172.

Referring toFIG. 2, the blocking block177is disposed at a position spaced apart from the first metal layer171or the second metal layer172by a predetermined distance, and is disposed within the area corresponding to the bonding surface141aof the cap140.

The blocking block177has an elongated shape along the edges of the bonding surface141aof the cap140. The blocking block177may have a continuous ring shape along the bonding surface141ain a plan view, or another geometric shape along the bonding surface141a.However, the blocking block177is not limited thereto, and may also be formed in, for example, a dashed-lines shape under the bonding surface141a.

In this example, the blocking block177is formed to have a thickness substantially similar to that of the first metal layer171or the second metal layer172. However, the thickness of the blocking block177is not limited thereto. For example, as long as the blocking block177may block a flow of the molten Sn, the blocking block177may be formed to have various thicknesses.

FIG. 2illustrates an example in which the blocking blocks177are formed on both of the cap140and the substrate110. However, a configuration of the present description is not limited thereto, and the blocking block177may also be formed on only any one of the cap140and the substrate110.

Further, in the example in which the blocking blocks177are formed on both of the cap140and the substrate110, a blocking block177a(hereinafter referred to as a first blocking block) formed on the cap140and a blocking block177b(hereinafter referred to as a second blocking block) formed on the substrate110may be disposed not to face or coincide with each other.

For example, the first blocking block177ais disposed on an inner side of the second blocking block177b.However, the first blocking block177aand the second blocking block177bmay be variously modified. Conversely, for example, the second blocking block177bmay be disposed on an inner side of the first blocking block177a, and so forth.

This is a configuration to smoothly and externally discharge air within the bonded part175upon forming the bonded part175. In an example in which the first blocking block177aand the second blocking block177bare in contact with each other and are bonded to each other during a process of forming the bonded part175, an internal space of the blocking block177may be sealed by the first blocking block177aand the second blocking block177b.Thus, air in the blocking block177may not be externally discharged, and in an example in which the air in the blocking block177is expanded by heat, a bonding defect may result from air pressure.

However, in an example in which the first blocking block177aand the second blocking block177bare disposed not to coincide with each other as in the embodiment illustrated inFIG. 2, because a passage through which the air in the blocking block177may be discharged is provided, an occurrence of the above-mentioned bonding defect may be prevented.

The blocking block177illustrated inFIG. 2may be formed of the same material (e.g., copper (Cu)) as that of the first metal layer171or the second metal layer172. The reason is that the blocking block177may be formed together with the first metal layer171or the second metal layer172during a same process, but a configuration of the present disclosure is not limited thereto.

Meanwhile, althoughFIG. 2illustrates an example in which the entire first blocking block177aand the entire second blocking block177bare not in contact with each other, the blocking block177is not limited to the above-mentioned configuration, and may be variously modified.

FIG. 9illustrates a cross-sectional view of another example of a blocking block, similar toFIG. 2.

Referring toFIG. 9, a blocking block177disposed at an outer side of the bonded part175includes a first blocking block177aand a second blocking block177b.The first blocking block177ais disposed to be adjacent to the bonded part175as compared to the second blocking block177b.In addition, another blocking block177disposed at an inner side of the bonded part175includes a second blocking block177bis disposed to be adjacent to the bonded part175as compared to a first blocking block177a.

In this example, the first blocking block177aand the second blocking block177bhave a section in which at least portions thereof overlap each other. However, because the entire first blocking block177aand the entire second blocking block177bdo not overlap each other, the passage through which the air in the bonded part175may be discharged is still provided.

FIG. 10illustrates a plan view of an example of an acoustic resonator according toFIG. 1. Referring toFIG. 10, the acoustic resonator includes a cap140having a side wall141that forms a rectangular shape. The blocking blocks177are disposed along an inner edge and an outer edge of the side wall141to form a closed shape or a loop, such as a rectangular shape similar to that of the side wall141. While an acoustic resonator having a cap140and blocking blocks177with a rectangular shape is illustrated inFIG. 10, in another example, other geometric shapes, such as a ring shape, may be applied. In yet another example, the blocking blocks177may not form a closed shape. For instance, the blocking blocks177may be provided only under a portion of the side wall141, such as at least two opposing sides of the cap140, or in a dash line, to preventing the leakage of the bonding material. The resonating part120is accommodated between the substrate110and the cap140. Various features of the acoustic resonator are omitted inFIG. 10. For these features, the description of the acoustic resonator in reference toFIG. 1applies to the acoustic resonator ofFIG. 10.

Next, an example of a method of manufacturing an acoustic resonator will be described.

FIGS. 3 through 7are views illustrating an example of a method of manufacturing an acoustic resonator.

First, referring toFIG. 3, the resonating part120is formed on the substrate110. In this example, the resonating part120is obtained by forming a sacrificial layer (not illustrated) on the substrate110and sequentially laminating the membrane layer150, the first electrode121, the piezoelectric layer123, the second electrode125, and the protection layer127on the sacrificial layer and the substrate110. Further, after the membrane layer150is formed on the sacrificial layer, the air gap130is formed by afterward removing the sacrificial layer.

The first electrode121and the second electrode125are formed in a necessary pattern by forming a conductive layer, depositing a photoresist on the conductive layer, performing a patterning using a photolithography process, and then removing unnecessary portions using the patterned photoresist as a mask.

According to the illustrated embodiment, the first electrode121may be formed of a molybdenum (Mo) material, and the second electrode125may be formed of ruthenium (Ru). However, the materials of the first and second electrodes121and125are not limited thereto, and the first electrode121and the second electrode125may be formed of various metals such as gold, ruthenium, aluminum, platinum, titanium, tungsten, palladium, chrome, nickel, and the like, as needed.

Further, the piezoelectric layer may be formed of aluminum nitride AlN. However, the material of the piezoelectric layer123is not limited thereto, and the piezoelectric layer123may be formed of various piezoelectric materials such as zinc oxide (ZnO), quartz, and the like.

The protection layer170may be formed of an insulating material. The insulating material may include a silicon oxide based material, a silicon nitride based material, and an aluminum nitride based material.

Next, the connection electrodes180and190for a frequency trimming are formed on the first electrode121and the second electrode125. The connection electrodes180and190may be formed on the first and second electrodes121and125, and may penetrate through the protection layer127or the piezoelectric layer123to be bonded to the electrodes.

The first connection electrode180may be formed by partially removing the protection layer127and the piezoelectric layer123by the etching to externally expose the first electrode121, and then depositing gold (Au), copper (Cu), or the like on the first electrode121.

Similarly, the second connection electrode190may be formed by partially removing the protection layer127by the etching to externally expose the second electrode125, and then depositing gold (Au), copper (Cu), or the like on the second electrode125.

Thereafter, after confirming characteristics of the resonating part120or the filter and performing a necessary frequency trimming using the connection electrodes180and190, the air gap130may be formed.

As noted above, the air gap130is formed by removing the sacrificial layer. As a result, the resonating part120according toFIG. 3is completed.

Next, referring toFIG. 4, the cap140is formed to protect the resonating part120from an external environment. The cap140may be formed by wafer bonding at a wafer level. That is, a substrate wafer on which a plurality of unit substrates110are disposed, and a cap wafer on which a plurality of caps140are disposed may be bonded to each other to be integrally formed.

In this case, the substrate wafer and the cap wafer which are bonded to each other may be diced by a dicing process later to be divided into a plurality of individual acoustic resonators.

In the operation of bonding the cap140to the substrate, as illustrated inFIG. 5, an operation in which the first metal layer171is first formed on the bonding surface141aof the cap140and the second metal layer172is formed on the bonding surface110aof the substrate110are performed. In this example, the blocking block177is formed together with the first and second metal layers171and172. That is, the blocking block177and the first and second metal layers171and172are formed substantially concurrently in the same process.

The first and second metal layers171and172and the blocking block177are formed on the cap140or the substrate110by a deposition method, or the like, but are not limited thereto. Further, the first and second metal layers171and172and the blocking block177may be formed of the same copper (Cu) material. Thus, because the blocking block177may be formed together with the first and second metal layers171and172in the process of forming the first and second metal layers171and172, a separate process of manufacturing the blocking block177may not be required.

Next, referring toFIG. 6, bonding layers173ais formed on a surface of the first metal layer171and a surface of the second metal layer172, respectively. In this example, the bonding layers173aare finally formed to be the third metal layer173. The bonding layers173amay be formed of Sn, and may be formed on the surface of the first metal layer171and the surface of the second metal layer172by the depositing method, or the like.

Next, referring toFIG. 7, the cap140is seated on the substrate110. In addition, the bonding layer173aformed on the cap140and the bonding layer173aformed on the substrate110are bonded to each other by performing heating and pressing. In this process, the bonding layers173amay be melted and then cured to be bonded to each other, and may be formed to be the third metal layer173. As a result, the bonded part175illustrated inFIG. 2may be obtained.

In this example, portions of the molten bonding layers173athat flow outside of the first metal layer171and the second metal layer172are prevented from further leakage by the blocking block177. As a result, the molten bonding layers173amay be positioned only in an inner space of the blocking block177and may not flow to the outside of the blocking block177.

Next, referring toFIG. 8, after the via holes112are formed in the substrate110, the connection conductors115aand115bare formed in the via holes112.

The connection conductors115aand115bmay be manufactured by forming a conductive layer on the inner surfaces of the via holes112. For example, the connection conductors115aand115bmay be formed by depositing, coating, or providing a conductive metal (e.g., gold, copper, or the like) along the inner walls (112aand112b) of the via holes112.

Next, the acoustic resonator100illustrated inFIG. 1is completed by forming the external electrodes117on the lower surface of the substrate110.

The external electrode117is formed on the connection conductors115aand115bextended to the lower surface of the substrate110. As the external electrodes117, solder balls formed of a Sn material may be used, but the external electrodes117are not limited thereto.

In the method of manufacturing the acoustic resonator according to the example having the configuration as described above, because the blocking block may be formed together in the operation of forming the first and second metal layers, a separate process of forming the blocking block may not be required.

Further, the example in which the bonding layers melted in the process of forming the bonded part excessively flow to the outside of the first and second metal layers may be prevented by the blocking block.

Meanwhile, the acoustic resonator and the method of manufacturing the same are not limited to the above-mentioned embodiments, and may be variously modified.

For example, the above mentioned embodiment illustrates an example in which the cap is attached to the substrate and the connection conductors are then formed. However, the present disclosure is not limited thereto, and may be variously modified. For example, after the connection conductors are first formed, the cap may be attached to the substrate, and so forth.

In addition, the above-mentioned embodiment illustrates an example in which a cross section of the blocking block is formed in a quadrangular shape. However, the present disclosure is not limited thereto, and may be variously modified. For example, the cross section of the blocking block may be formed in a triangular shape or a trapezoidal shape, and so forth.

As set forth above, according to the examples described above, the acoustic resonator may include the blocking block blocking the flow of the bonding layer melted by the heat when the cap and the substrate are bonded. As a result, the blocking block may prevent the flow of the molten bonding layer to the outside of the bonded portion.

Further, in the example of a method of manufacturing the acoustic resonator described above, because the blocking block may be formed together in the operation of forming the first and second metal layers, the separate process of forming the blocking block may not be required. As a result, the acoustic resonator may be easily manufactured.