Air-gap Film Bulk Acoustic Resonator

Abstract

An air-gap film bulk acoustic resonator (FBAR) is disclosed, comprising: a substrate including an air-gap portion having a top surface, in which a substrate cavity is formed; a lower electrode formed above the substrate while surrounding the air-gap portion; a piezoelectric layer formed above the lower electrode; and an upper electrode formed above the piezoelectric layer corresponding to a virtual area formed according to a vertical projection of the air-gap portion. Here, the piezoelectric layer includes a gap portion having a piezoelectric cavity between the lower electrode and the upper electrode, and the gap portion is formed below an edge portion corresponding to an end of the upper electrode.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 2019-0101222, filed on August 19, 2019, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present invention relates to a resonator for communication in a radio frequency band, and more particularly to an air-gap film bulk acoustic resonator (FBAR). Background Art

[0004] Wireless mobile communication technology requires various radio frequency (RF) components that can effectively transmit information within a limited frequency band. In particular, among RF components, filters are one of the basic components used in mobile communication technology, and can achieve high-quality communication by selecting the signal required by the user in multiple frequency bands or filtering the signal to be transmitted.

[0005] At present, dielectric filters and surface acoustic wave (SAW) filters are most commonly used as RF filters for wireless communications. Dielectric filters have advantages such as high dielectric constant, low insertion loss, stability at high temperature, high vibration resistance and high impact resistance. However, dielectric filters have limitations in miniaturization and realization of monolithic microwave integrated circuits (MMIC), which are the latest trends in technological development. In addition, SAW filters have small sizes compared to dielectric filters, are easy to process signals, have simple circuits, and are manufactured using semiconductor processes to facilitate mass production. Moreover, SAW filters have the advantage of sending and receiving advanced information due to higher side suppression within the passband compared to dielectric filters. However, since the SAW filter process includes an exposure process using ultraviolet (UV), there is a disadvantage that the line width of the interdigital transducer (IDT) has a limit of about 0.5 μm. Therefore, there is a problem that the ultra-high frequency band above 5 GHz cannot be covered using SAW filters. Basically, it is difficult to form an MMIC structure and a single chip on a semiconductor substrate.

[0006] To overcome these limitations and problems, a film bulk acoustic resonator (FBAR) filter is proposed, which is integrated with other active devices on an existing semiconductor (Si or GaAs) substrate to fully realize a frequency control circuit as a MMIC.

[0007] FBAR is a low-cost, small-size, high-quality thin-film device that can be applied to wireless communication equipment and military radars in various frequency bands from 900MHz to 10GHz. In addition, FBAR is reduced in size to a few hundredths of dielectric filters and lumped constant (LC) filters, and has much smaller insertion loss than SAW filters. Therefore, it is obvious that FBAR is the most suitable device for MMICs that require high stability and high quality coefficient.

[0008] The FBAR filter is formed by depositing zinc oxide (ZnO), aluminum nitride (AlN), etc. as a piezoelectric dielectric material on silicon (Si) or gallium arsenide (GaAs) as a semiconductor substrate using an RF sputtering method, and causes resonance due to piezoelectric characteristics. That is, by depositing a piezoelectric film between two electrodes and causing a bulk acoustic wave, the FBAR generates resonance.

[0009] So far, various forms of FBAR structures have been studied. In the case of a membrane type FBAR, a silicon oxide film (SiO2) is deposited on a substrate, and a membrane layer is formed using a cavity formed by isotropic etching on opposite sides of the substrate. In addition, a lower electrode is formed over the silicon oxide film, a piezoelectric layer is formed by depositing a piezoelectric material over the lower electrode using RF magnetron sputtering, and an upper electrode is formed over the piezoelectric layer.

[0010] The above-mentioned film-type FBAR has the advantages of small dielectric loss and power loss due to the cavity. However, the film-type FBAR has the following problems: the area occupied by the device is large due to the directivity of the silicon substrate, and the yield is reduced due to damage caused by low structural stability in the subsequent packaging process. Therefore, recently, in order to reduce the loss caused by the film and simplify the device manufacturing process, air gap type FBAR and Bragg reflector type FBAR have appeared.

[0011] The Bragg reflector type FBAR has a structure in which a reflective layer is formed by depositing a material having a high elastic impedance difference on every other layer on a substrate, and a lower electrode, a piezoelectric layer, and an upper electrode are sequentially deposited. Here, the elastic wave energy that has passed through the piezoelectric layer is not transmitted to the substrate, but is all reflected by the reflective layer, thereby generating effective resonance. Although the Bragg reflector type FBAR is structurally strong and has no stress caused by bending, it is difficult to form four or more reflective layers with precise thickness for total reflection, and manufacturing requires a lot of time and cost.

[0012] In the existing air-gap FBAR having a structure in which an air gap is used instead of a reflective layer to isolate the substrate and the resonant part, a sacrificial layer is realized by performing isotropic etching on the surface of a silicon substrate, and the sacrificial layer is surface-polished by chemical mechanical polishing, and then an insulating layer, a lower electrode, a piezoelectric layer, and an upper electrode are sequentially deposited, and the sacrificial layer is removed through a through hole to form an air gap, thereby realizing FBAR.

[0013] Until now, the piezoelectric layer itself grown in a different direction than the Z-axis direction has been used as is, depending on the electrode gradient in a portion of the edge region of the lower electrode. As a problem caused by this, in addition to the acoustic wave component in the vertical direction as the desired thickness direction, an acoustic wave is also generated in the lateral direction.

[0014] Therefore, in the case of a general existing bulk acoustic wave (BAW) structure, a frame structure is used to prevent energy from being released in the lateral direction. Even if the frame structure is optimized, there is a limit in reducing the energy released in the lateral direction.

[0015] [Prior art literature]

[0016] [Patent Document]

[0017] Patent Document 1: Korean Patent Publication No. 10-2004-0102390 (published on December 8, 2004) Summary of the invention

[0018] The present invention is directed to providing an air-gap film bulk acoustic resonator (FBAR) capable of minimizing energy escaping from the FBAR through a side surface and improving the quality factor of the resonator.

[0019] According to one aspect of the present invention, an air-gap FBAR is provided, comprising: a substrate including an air-gap portion having a top surface, in which a substrate cavity is formed; a lower electrode formed above the substrate while surrounding the air-gap portion; a piezoelectric layer formed above the lower electrode; and an upper electrode formed above the piezoelectric layer corresponding to a virtual area formed according to a vertical projection of the air-gap portion. Here, the piezoelectric layer includes a gap portion having a piezoelectric cavity between the lower electrode and the upper electrode, and the gap portion is formed below an edge portion corresponding to an end of the upper electrode.

[0020] The gap portion may be a first gap portion including a first piezoelectric cavity in which an open top surface is formed to partially expose a bottom of the edge portion and a closed bottom surface is formed not to expose a top of the lower electrode.

[0021] In the first gap portion, a first one side virtual surface vertically extending from a one side boundary wall forming the first piezoelectric cavity may intersect with a lower inner region of the edge portion. Also, a first other side virtual surface vertically extending from another side boundary wall forming the first piezoelectric cavity may intersect with an upper inner region of the substrate cavity.

[0022] An end surface of the edge portion may be spaced apart from the first other-side virtual surface by a certain distance or more, so that a top of the first piezoelectric cavity may be partially opened.

[0023] The edge portion may be an electrode structure having a relatively greater electrode thickness than other electrode structures forming the upper electrode.

[0024] The piezoelectric layer may further include a second gap portion having a second piezoelectric cavity, the second gap portion being formed to be spaced apart from the first gap portion by a certain distance.

[0025] In the second piezoelectric cavity, a closed bottom surface may be formed so as not to expose the top of the lower electrode, and an open top surface may be formed so as to open the entire top thereof.

[0026] In the second gap portion, a second one side virtual surface vertically extending from a one side boundary wall forming the second piezoelectric cavity may intersect with an upper inner region of the substrate cavity. Also, a second other side virtual surface vertically extending from the other side boundary wall forming the second piezoelectric cavity may coincide with a one side boundary wall of the air gap portion.

[0027] A height of the first gap portion or the second gap portion may be less than or equal to half of a thickness of the piezoelectric layer.

[0028] A lateral width of the first gap portion or the second gap portion may be greater than or equal to one quarter of a wavelength of energy released through the piezoelectric layer.

[0029] In the piezoelectric layer, a piezoelectric region located below the first gap portion or the second gap portion may have a relatively high acoustic impedance compared with piezoelectric regions at other positions.

[0030] The gap portion may be a third gap portion including a third piezoelectric cavity in which a closed top surface is formed so as not to expose a bottom of the upper electrode and an open bottom surface is formed to expose a top of the lower electrode.

[0031] In the third gap portion, a first one side virtual surface extending vertically from a one side boundary wall forming the third piezoelectric cavity may overlap with an end of the edge portion, and a first other side virtual surface extending vertically from another side boundary wall forming the third piezoelectric cavity may intersect with an upper inner region of the substrate cavity.

[0032] The piezoelectric layer may further include a fourth gap portion having a fourth piezoelectric cavity, the fourth gap portion being formed to be spaced apart from the third gap portion by a certain distance.

[0033] In the fourth piezoelectric cavity, a closed top surface may be formed so as not to expose a bottom of the upper electrode, and an open bottom surface may be formed so as to expose a top of the lower electrode.

[0034] A height of the third gap portion or the fourth gap portion may be less than or equal to half of a thickness of the piezoelectric layer.

[0035] A lateral width of the third gap portion or the fourth gap portion may be greater than or equal to one quarter of a wavelength of energy released through the piezoelectric layer.

[0036] In the piezoelectric layer, a piezoelectric region located above the third gap portion or the fourth gap portion may have a relatively high acoustic impedance compared with piezoelectric regions at other positions. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and other objects, features and advantages of the present invention will become more apparent to those skilled in the art by describing in detail exemplary embodiments of the present invention with reference to the accompanying drawings, in which:

[0038] Figure 1 is a cross-sectional view of an air-gap film bulk acoustic resonator (FBAR) according to a first embodiment of the present invention;

[0039] Figure 2 It shows that according to Figure 1 0 is an enlarged cross-sectional view of a main portion of the air-gap type FBAR of the first embodiment shown in FIG.

[0040] Figure 3 is a cross-sectional view of an air-gap FBAR according to a second embodiment of the present invention;

[0041] Figure 4 It shows that according to Figure 3 An enlarged cross-sectional view of a main portion of an air-gap type FBAR of a second embodiment shown in FIG.

[0042] Figure 5 is a cross-sectional view of an air-gap FBAR according to a third embodiment of the present invention;

[0043] Figure 6 It shows that according to Figure 5 An enlarged cross-sectional view of a main portion of an air-gap FBAR of a third embodiment shown in FIG.

[0044] Figure 7 is a cross-sectional view of an air-gap FBAR according to a fourth embodiment of the present invention; and

[0045] Figure 8 It shows that according to Figure 7 0 is an enlarged cross-sectional view of a main portion of the air-gap type FBAR of the fourth embodiment shown in FIG. DETAILED DESCRIPTION

[0046] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0047] The embodiments of the present invention are provided to explain the present invention more comprehensively to those of ordinary skill in the art. The embodiments of the present invention may be varied in various forms, and the scope of the present invention is not limited to the following embodiments. These embodiments are provided to make the present disclosure more complete and perfect, and to fully convey the concept of the present invention to those skilled in the art.

[0048] Terms are used herein to explain specific embodiments, but are not intended to limit the present invention. As used herein, unless otherwise clearly defined in the context, singular expressions also include plural expressions. Moreover, as used herein, the term "and / or" includes any and all combinations or one of a plurality of related listed items. In addition, hereinafter, the present invention will be described with reference to the accompanying drawings, which schematically illustrate embodiments of the present invention.

[0049] Figure 1 is a cross-sectional view of an air-gap film bulk acoustic resonator (FBAR) 100 according to a first embodiment of the present invention.

[0050] Reference Figure 1 , the air-gap type FBAR 100 according to the first embodiment includes a substrate 110, an air-gap portion 110-1, a lower electrode 120, a piezoelectric layer 130, and an upper electrode 140. When a signal is applied between the lower electrode 120 and the upper electrode 140, the air-gap type FBAR 100 resonates at a natural oscillation frequency according to the thickness of the piezoelectric layer 130, and a portion of electric energy input and transferred between the two electrodes is converted into mechanical energy according to the piezoelectric effect and converted into electric energy again.

[0051] The substrate 110 is a semiconductor substrate, and a general silicon wafer can be used. Preferably, a high resistivity silicon substrate (HRS) can be used. An insulating layer (not shown) can be formed on the top surface of the substrate 100. As the insulating layer, a thermal oxide layer that is easy to grow on the substrate 100 can be used, or an oxide film or a nitride film formed using a general deposition process such as chemical vapor deposition can be selectively used.

[0052] The air gap portion 110-1 is formed by forming a substrate cavity in the substrate 110, forming an insulating layer on the substrate cavity, depositing a sacrificial layer on the insulating layer, flattening the sacrificial layer on the insulating layer by etching, and removing the sacrificial layer. Here, a sacrificial layer is formed using a material with a high surface roughness such as polysilicon, tetraethyl orthosilicate, phosphosilicate glass (PSG), and the sacrificial layer using these materials is easy to form or remove. As an example, the sacrificial layer can be made of polysilicon with a high surface roughness. A sacrificial layer using polysilicon is easy to form or remove. In particular, dry etching can be used in a subsequent process to remove the sacrificial layer.

[0053] The lower electrode 120 is formed above the air gap portion 110-1, wherein the sacrificial layer is present in the substrate cavity. The lower electrode 120 is formed by depositing a material above the substrate 110 and patterning the deposited material. The material for the lower electrode 120 includes a general conductive material such as a metal, and preferably, may include one of aluminum (Al), tungsten (W), gold (Au), platinum (Pt), nickel (Ni), titanium (Ti), chromium (Cr), palladium (Pd), ruthenium (Ru), rhenium (Re) and molybdenum (Mo). The thickness of the lower electrode 120 may be 10 to 1000 nm.

[0054] A piezoelectric layer 130 is formed above the lower electrode 120. The piezoelectric layer 130 may be formed by depositing a piezoelectric material above the lower electrode 120 and patterning the deposited piezoelectric material. As a general piezoelectric material, there is aluminum nitride (AlN) or zinc oxide (ZnO). Deposition methods include radio frequency magnetron sputtering methods, evaporation methods, etc. The thickness of the piezoelectric electrode 130 may be 5 to 500 nm.

[0055] The piezoelectric layer 130 may include a gap portion between the lower electrode 120 and the upper electrode 140 in which a piezoelectric cavity is formed. Here, the gap portion may be formed below an edge portion corresponding to an end of the upper electrode 140. The gap portion will be described in detail below.

[0056] An upper electrode 140 is formed above the piezoelectric layer 130. The upper electrode 140 may be formed above the piezoelectric layer 130 corresponding to a virtual area according to a vertical projection of the air gap portion 110-1. When a void portion is formed in the piezoelectric layer 130 and a sacrificial layer is formed therein, the upper electrode 140 may be formed above a portion of the sacrificial layer. The upper electrode 140 may be formed by depositing a metal film for the upper electrode in a specific region above the piezoelectric layer 130 and patterning the deposited metal film. The upper electrode 140 may be formed using the same material, the same deposition method, and the same patterning method as the lower electrode 120. The thickness of the upper electrode 140 may be 5 to 1000 nm.

[0057] The edge portion 140-1 is formed at an end portion of one side of the upper electrode 140. The edge portion 140-1 may be an electrode structure having a relatively greater electrode thickness than other electrode structures included in the upper electrode 140. The edge portion 140-1 corresponds to an edge frame of the upper electrode 140, and performs a function of blocking energy from escaping through a side surface portion.

[0058] Meanwhile, a pad layer applied to a portion of the above-described lower electrode 120, the piezoelectric layer 130, and the upper electrode 140 may be formed. The pad layer serves as a cover layer to protect the lower electrode 120, the piezoelectric layer 130, and the upper electrode 140.

[0059] Detailed features of the void portion formed in the piezoelectric layer 130 will be described below.

[0060] Figure 2 It shows that according to Figure 1 0 is an enlarged cross-sectional view of a main portion of the air-gap type FBAR 100 of the first embodiment shown in FIG.

[0061] Reference Figure 2 , the piezoelectric layer 130 may include an air space, ie, a first gap portion 130 - 1 having a first piezoelectric cavity between the lower electrode 120 and the upper electrode 140 .

[0062] The first void portion 130-1 is formed by forming a first piezoelectric cavity by etching some areas on the top of the piezoelectric layer 130, depositing and flattening a sacrificial layer over the first piezoelectric cavity, depositing an upper electrode 140 over the piezoelectric layer 130 including the sacrificial layer, and then removing the sacrificial layer. Here, the sacrificial layer is formed using a material having excellent surface roughness such as polysilicon, tetraethyl orthosilicate, phosphosilicate glass (PSG), and the like, and the sacrificial layer using these materials is easily formed or removed.

[0063] Here, the first void portion 130-1 may form a first piezoelectric cavity, which is a local air space through which the bottom of the upper electrode 140 is partially exposed and the top of the lower electrode 120 is not exposed. That is, the first void portion 130-1 may include a first piezoelectric cavity having an open top surface OS formed to partially expose the bottom of the edge portion 140-1 and a closed bottom surface CS formed not to expose the top of the lower electrode 120.

[0064] In the first gap portion 130-1, a first one side virtual surface VS1 extending vertically from a side boundary wall forming the first piezoelectric cavity may intersect with a lower inner area of ​​the edge portion 140-1, and a point P1 where the first one side virtual surface VS1 intersects with the lower inner area of ​​the edge portion 140 may be located on the inner side of the end of the edge portion 140-1.

[0065] In the first gap portion 130-1, a first other side virtual surface VS2 extending vertically from the other side boundary wall forming the first piezoelectric cavity may intersect with the upper inner area of ​​the substrate cavity, and a point P2 at which the first other side virtual surface VS2 intersects with the upper inner area of ​​the substrate cavity may be located on the upper virtual surface of the substrate cavity included in the air gap portion 110-1.

[0066] The end surface ES of the edge portion 140-1 may be spaced apart from the first other side virtual surface VS2 by a certain distance or more, so that the top of the first piezoelectric cavity may be partially opened. The first gap portion 130-1 is formed below the edge portion 140-1 corresponding to the end of the upper electrode 140. Here, since the edge portion 140-1 does not surround the entire top surface of the first piezoelectric cavity in the first gap portion 130-1, but partially surrounds the first piezoelectric cavity (for example, only half of the first piezoelectric cavity), the first gap portion 130-1 may partially open the top of the first piezoelectric cavity. Here, the distance between the end surface ES of the edge portion 140-1 and the first other side virtual surface VS2, i.e., the specific distance D, may vary according to the deposition area of ​​the upper electrode 140 above the first gap portion 130-1.

[0067] The height H of the first void portion 130-1 may be less than or equal to half of the thickness T of the piezoelectric layer 130. The first void portion 130-1 is formed so that the thickness is different in each region of the piezoelectric layer 130. That is, the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR2, and the third piezoelectric region AR3 of the piezoelectric layer 130 may be different from each other. In particular, the second region AR2 may have a thickness that is reduced by as much as the height of the first void portion 130-1. The height H of the first void portion 130-1 is formed to be less than or equal to half of the thickness T of the piezoelectric layer 130 to provide a minimum thickness that allows internally generated heat to be easily released.

[0068] In addition, the lateral width of the first gap portion 130-1 may be one quarter of the wavelength of energy released through the piezoelectric layer 130. When the energy wavelength is expressed as λ, the value of the lateral width of the first gap portion 130-1 may be λ*(2N+1) / 4 (where N is an integer greater than or equal to 0).

[0069] Meanwhile, in the piezoelectric layer 130, the piezoelectric region located below the first gap portion 130-1 has a relatively high acoustic impedance compared to the piezoelectric region located at a different position. Since the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR2, and the third piezoelectric region AR3 of the piezoelectric layer 130 are different from each other, the acoustic impedance is different in each piezoelectric region. That is, as the thickness of the piezoelectric layer 130 decreases, the acoustic impedance increases. As the thickness increases, the acoustic impedance decreases. Therefore, in the case where the acoustic impedances of the first piezoelectric region AR1, the second piezoelectric region AR2, and the third piezoelectric region AR3 of the piezoelectric layer 130 are respectively referred to as the first acoustic impedance I1, the second acoustic impedance I2, and the third acoustic impedance I3, the second acoustic impedance I2 of the second piezoelectric region AR2 where the first gap portion 130-1 is located has an impedance value relatively larger than the impedance value of the first acoustic impedance I1 or the third acoustic impedance I3. In addition, when the acoustic impedances of the first piezoelectric region AR1 and the third piezoelectric region AR3 are compared with each other, the first acoustic impedance I1 has an impedance value larger than the third acoustic impedance I3. When the relationship is expressed by an inequality sign, it can be seen that the order of acoustic impedance is I3 <I1<I2。

[0070] The difference in acoustic impedance caused by the thickness variation can prevent acoustic energy from being released by reflecting the pressure wave escaping from the piezoelectric layer 130 in the lateral direction. That is, due to the difference between the first acoustic impedance I1 of the first piezoelectric region AR1 and the second acoustic impedance I2 of the second piezoelectric region AR2, the energy existing in the first piezoelectric region AR1 can collide with the boundary of the second piezoelectric region AR2 and return to the first piezoelectric region AR1, thereby minimizing the energy escaping from the first piezoelectric region AR1 to the second piezoelectric region AR2. In addition, although some energy escapes from the first piezoelectric region AR1 to the second piezoelectric region AR2, due to the difference between the second acoustic impedance I2 of the second piezoelectric region AR2 and the third acoustic impedance I3 of the third piezoelectric region AR3, the energy existing in the second piezoelectric region AR2 can collide with the boundary of the third piezoelectric region AR3 and return to the second piezoelectric region AR2, thereby minimizing the energy escaping from the second piezoelectric region AR2 to the third piezoelectric region AR3.

[0071] Figure 3 is a cross-sectional view of an air-gap type FBAR 200 according to a second embodiment of the present invention.

[0072] Reference Figure 3 The air-gap type FBAR 200 according to the second embodiment includes a substrate 210, an air-gap portion 210-1, a lower electrode 220, a piezoelectric layer 230, and an upper electrode 240. When a signal is applied between the lower electrode 220 and the upper electrode 240 from the outside, the air-gap type FBAR 200 resonates at a natural oscillation frequency according to the thickness of the piezoelectric layer 230.

[0073] Here, since the features of the substrate 210, the air gap portion 210-1, the lower electrode 220, and the upper electrode 240 are the same as those described above with reference to Figure 1 The described features of the substrate 110 , the air gap portion 110 - 1 , the lower electrode 120 , and the upper electrode 140 are the same, and thus a detailed description thereof will be omitted. Hereinafter, the piezoelectric layer 230 will be mainly described.

[0074] The piezoelectric layer 230 is formed above the lower electrode 220. The piezoelectric layer 230 may be formed by depositing a piezoelectric material above the lower electrode 220 and patterning the deposited piezoelectric material. The piezoelectric layer 230 may include two gap portions between the lower electrode 220 and the upper electrode 140, in which a piezoelectric cavity is formed. Here, the two gap portions are referred to as a first gap portion 230-1 and a second gap portion 230-2.

[0075] Figure 4 It shows that according to Figure 3 2 is an enlarged cross-sectional view of a main portion of an air-gap type FBAR 200 of the second embodiment shown in FIG.

[0076] Reference Figure 4, the piezoelectric layer 230 may include two air spaces, ie, a first gap portion 230 - 1 having a first piezoelectric cavity and a second gap portion 230 - 2 having a second piezoelectric cavity, between the lower electrode 220 and the upper electrode 240 .

[0077] The first void portion 230-1 is formed by forming a first piezoelectric cavity by etching some areas on the top of the piezoelectric layer 230, depositing and flattening a sacrificial layer over the first piezoelectric cavity, depositing an upper electrode 240 over the piezoelectric layer 230 including the sacrificial layer, and then removing the sacrificial layer. Figure 2 The features of the first gap portion 130-1 shown in FIG. 1 are the same, so the detailed description thereof will be omitted, and the second gap portion 230-2 will be described in detail below.

[0078] The second void portion 230-1 includes a second piezoelectric cavity formed to be spaced a distance SD from the first void portion 230. The second piezoelectric cavity of the second void portion 230-2 may include a closed bottom surface CS not exposing the top of the lower electrode 220 and an open top surface OS exposing the entire top thereof.

[0079] Here, the second one side virtual surface VS3 extending vertically from the one side boundary wall forming the second piezoelectric cavity may intersect with the upper inner region of the substrate cavity forming the air gap portion 210-1. A point P3 at which the second one side virtual surface VS3 intersects with the upper inner region of the substrate cavity may be located on the upper virtual surface of the substrate cavity forming the air gap portion 210-1.

[0080] Moreover, the second other side virtual surface VS4 extending vertically from the other side boundary wall forming the second piezoelectric cavity may coincide with one side boundary wall of the air gap portion 210-1. A point P4 where the second other side virtual surface VS4 intersects with the upper virtual surface of the substrate cavity may be located on one side boundary wall of the air gap portion 210-1.

[0081] and Figure 2, the height H of the second void portion 230-2 may be less than or equal to half of the thickness T of the piezoelectric layer 230. The first void portion 230-1 and the second void portion 230-2 are formed in the piezoelectric layer 230 so that the thickness of the piezoelectric layer 230 is different in each region. That is, the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR2, the third piezoelectric region AR3, the fourth piezoelectric region AR4, and the fifth piezoelectric region AR5 of the piezoelectric layer 230 may be different from each other. In particular, the second piezoelectric region AR2 and the fourth piezoelectric region AR4 may have a thickness that is reduced by as much as the height of the first void portion 230-1 or the second void portion 230-2. The height H of the first void portion 230-1 or the second void portion 230-2 is formed to be less than or equal to half of the thickness T of the piezoelectric layer 230 to provide a minimum thickness that allows the heat generated inside to be easily released.

[0082] In addition, the lateral width of the first gap portion 230-1 or the second gap portion 230-2 may be one quarter of the wavelength of energy released through the piezoelectric layer 230. When the energy wavelength is expressed as λ, the value of the lateral width of the first gap portion 230-1 or the second gap portion 230-2 may be λ*(2N+1) / 4 (here, N is an integer greater than or equal to 0).

[0083] Meanwhile, in the piezoelectric layer 230, the piezoelectric region located below the first gap portion 230-1 or the second gap portion 230-2 has a relatively high acoustic impedance compared to the piezoelectric region located at a different position. Since the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR2, the third piezoelectric region AR3, the fourth piezoelectric region AR4, and the fifth piezoelectric region AR5 of the piezoelectric layer 230 are different from each other, the acoustic impedance is different in each piezoelectric region.

[0084] In the case where the acoustic impedances of the first piezoelectric region AR1, the second piezoelectric region AR2, the third piezoelectric region AR3, the fourth piezoelectric region AR4, and the fifth piezoelectric region AR5 of the piezoelectric layer 230 are respectively referred to as the first acoustic impedance I1, the second acoustic impedance I2, the third acoustic impedance I3, the fourth acoustic impedance I4, and the fifth acoustic impedance I5, the second acoustic impedance I2 corresponding to the second piezoelectric region AR2 and the fourth acoustic impedance I4 corresponding to the fourth piezoelectric region AR4 have impedance values ​​that are relatively larger than the impedance values ​​of the first acoustic impedance I1, the third acoustic impedance I3, or the fifth acoustic impedance I5. In addition, when the first acoustic impedance I1, the third acoustic impedance I3, and the fifth acoustic impedance I5 are compared with each other, the third acoustic impedance I3 has an impedance value that is relatively larger than the first acoustic impedance I1 or the fifth acoustic impedance I5, and the first acoustic impedance I1 has an impedance value that is relatively larger than the fifth acoustic impedance I5. When the relationship is expressed by an inequality sign, it can be seen that the order of magnitude of the acoustic impedances is I5 to I6. <I1<I3<I2=I4。

[0085] The difference in acoustic impedance caused by the thickness variation of the piezoelectric layer 230 may prevent energy from escaping from the piezoelectric layer 230 in the lateral direction.

[0086] That is, due to the difference between the first acoustic impedance I1 of the first piezoelectric region AR1 and the second acoustic impedance I2 of the second piezoelectric region AR2, the energy existing in the first piezoelectric region AR1 may collide with the boundary of the second piezoelectric region AR2 and return to the first piezoelectric region AR1, thereby minimizing the energy escaping from the first piezoelectric region AR1 to the second piezoelectric region AR2. In addition, although some energy escapes from the first piezoelectric region AR1 to the second piezoelectric region AR2, due to the difference between the second acoustic impedance I2 of the second piezoelectric region AR2 and the third acoustic impedance I3 of the third piezoelectric region AR3, the energy existing in the second piezoelectric region AR2 may collide with the boundary of the third piezoelectric region AR3 and return to the second piezoelectric region AR2, thereby minimizing the energy escaping from the second piezoelectric region AR2 to the third piezoelectric region AR3.

[0087] In addition, due to the difference between the third acoustic impedance I3 of the third piezoelectric region AR3 and the fourth acoustic impedance I4 of the fourth piezoelectric region AR4, energy existing in the third piezoelectric region AR3 may collide with the boundary of the fourth piezoelectric region AR4 and return to the third piezoelectric region AR3. Due to the difference between the fourth acoustic impedance I4 of the fourth piezoelectric region AR4 and the fifth acoustic impedance I5 of the fifth piezoelectric region AR5, energy existing in the fourth piezoelectric region AR4 may collide with the boundary of the fifth piezoelectric region AR5 and return to the fourth piezoelectric region AR4, thereby minimizing the energy escaping from the fourth piezoelectric region AR4 to the fifth piezoelectric region AR5.

[0088] Figure 5 is a cross-sectional view of an air-gap type FBAR 300 according to a third embodiment of the present invention.

[0089] Reference Figure 5 The air-gap type FBAR 300 according to the third embodiment includes a substrate 310, an air-gap portion 310-1, a lower electrode 320, a piezoelectric layer 330, and an upper electrode 340. When a signal is applied between the lower electrode 320 and the upper electrode 340 from the outside, the air-gap type FBAR 300 resonates at a natural oscillation frequency according to the thickness of the piezoelectric layer 330.

[0090] Here, since the features of the substrate 310, the air gap portion 310-1, the lower electrode 320, and the upper electrode 340 are the same as those described above with reference to Figure 1 The described features of the substrate 110 , the air gap portion 110 - 1 , the lower electrode 120 , and the upper electrode 140 are the same, and thus a detailed description thereof will be omitted. Hereinafter, the piezoelectric layer 330 will be mainly described.

[0091] The piezoelectric layer 330 is formed over the lower electrode 320. The piezoelectric layer 330 may be formed by depositing a piezoelectric material over the lower electrode 320 and patterning the deposited piezoelectric material. The piezoelectric layer 330 may include a gap portion between the lower electrode 320 and the upper electrode 340, in which a piezoelectric cavity is formed. Here, the gap portion will be referred to as a third gap portion 330-1.

[0092] Figure 6 It shows that according to Figure 5 2 is an enlarged cross-sectional view of a main portion of an air-gap type FBAR 300 of the third embodiment shown in FIG.

[0093] Reference Figure 6 , the piezoelectric layer 330 may include an air space, ie, a third gap portion 330 - 1 having a third piezoelectric cavity between the lower electrode 320 and the upper electrode 340 .

[0094] The third void portion 330-1 may be formed in a portion of the bottom of the piezoelectric layer 330. The third void portion 330-1 may be formed by depositing a sacrificial layer corresponding to the third piezoelectric cavity over the lower electrode 320, depositing the piezoelectric layer 330 over the deposited sacrificial layer, and then removing the sacrificial layer of the third piezoelectric cavity.

[0095] Here, the third void portion 330-1 may form a third piezoelectric cavity as a local air space through which the top of the lower electrode 320 is partially exposed and the bottom of the upper electrode 340 is not exposed. That is, the third void portion 330-1 may include a third piezoelectric cavity including a closed top surface formed not to expose the bottom of the upper electrode 340 and an open bottom surface formed to expose the top of the lower electrode 320.

[0096] In the third gap portion 330-1, a first one side virtual surface VS1 extending vertically from a one side boundary wall forming the third piezoelectric cavity may coincide with an end surface of the edge portion 340-1 of the upper electrode 340. A point P1 at which the first one side virtual surface VS1 intersects the end surface of the edge portion 340-1 may be located on the boundary wall of the edge portion 340-1.

[0097] In addition, in the third gap portion 330-1, the first other side virtual surface VS2 extending vertically from the other side boundary wall forming the third piezoelectric cavity may intersect with the upper inner area of ​​the substrate cavity, and the point P2 where the first other side virtual surface VS2 intersects with the upper inner area of ​​the substrate cavity may be located on the upper virtual surface of the substrate cavity included in the air gap portion 310-1.

[0098] The height H of the third void portion 330-1 may be less than or equal to half of the thickness T of the piezoelectric layer 330. The third void portion 330-1 is formed such that the thickness is different in each region of the piezoelectric layer 330. That is, the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR2, and the third piezoelectric region AR3 of the piezoelectric layer 330 may be different from each other. In particular, the second region AR2 may have a thickness reduced by as much as the height of the third void portion 330-1. The height H of the third void portion 330-1 is formed to be less than or equal to half of the thickness T of the piezoelectric layer 330 to provide a minimum thickness that allows heat generated inside to be easily released.

[0099] In addition, the lateral width of the third void portion 330-1 may be one-fourth of the wavelength of the energy released through the piezoelectric layer 330. When the energy wavelength is represented as λ, the value of the lateral width of the third void portion 330-1 is λ*(2N + 1) / 4 (where N is an integer greater than or equal to 0).

[0100] Meanwhile, in the piezoelectric layer 330, the piezoelectric region located above the third void portion 330-1 has a relatively high acoustic impedance compared to the piezoelectric regions located at different positions. Since the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR2, and the third piezoelectric region AR3 of the piezoelectric layer 330 are different from each other, the acoustic impedance is different in each region. Therefore, in the case where the acoustic impedances of the first piezoelectric region AR1, the second piezoelectric region AR2, and the third piezoelectric region AR3 of the piezoelectric layer 330 are referred to as the first acoustic impedance I1, the second acoustic impedance I2, and the third acoustic impedance I3, respectively, the second acoustic impedance I2 of the second piezoelectric region AR2 where the third void portion 330-1 is located has an impedance value relatively greater than the impedance value of the first acoustic impedance I1 or the third acoustic impedance I3. In addition, when the acoustic impedances of the first piezoelectric region AR1 and the third piezoelectric region AR3 are compared with each other, the first acoustic impedance I1 has a greater impedance value than the third acoustic impedance I3. When expressing their relationship with inequality signs, the magnitude order of the acoustic impedance is I3 < I1 < I2. The difference in acoustic impedance caused by the thickness change of the piezoelectric layer 330 can prevent energy from being released from the piezoelectric layer 330 in the lateral direction.

[0101] Figure 7 is a cross-sectional view of the air-gap type FBAR 400 according to the fourth embodiment of the present invention.

[0102] Referring to Figure 7 , the air-gap type FBAR 400 according to the fourth embodiment includes a substrate 410, an air-gap portion 410-1, a lower electrode 420, a piezoelectric layer 430, and an upper electrode 440. When a signal is applied from the outside between the lower electrode 420 and the upper electrode 440, the air-gap type FBAR 400 resonates at a natural oscillation frequency according to the thickness of the piezoelectric layer 430.

[0103] Here, since the features of the substrate 410, the air gap portion 410-1, the lower electrode 420, and the upper electrode 440 are the same as those described above with reference to Figure 1 The described features of the substrate 110 , the air gap portion 110 - 1 , the lower electrode 120 , and the upper electrode 140 are the same, and thus a detailed description thereof will be omitted. Hereinafter, the piezoelectric layer 430 will be mainly described.

[0104] The piezoelectric layer 430 is formed over the lower electrode 420. The piezoelectric layer 430 may be formed by depositing a piezoelectric material over the lower electrode 420 and patterning the deposited piezoelectric material. The piezoelectric layer 430 may include two gap portions between the lower electrode 420 and the upper electrode 140, in which a piezoelectric cavity is formed. Here, the two gap portions are referred to as a first gap portion 430-1 and a second gap portion 430-2.

[0105] Figure 8 It shows that according to Figure 7 0 is an enlarged cross-sectional view of a main portion of an air-gap type FBAR 400 of a fourth embodiment shown in FIG.

[0106] Reference Figure 8 , the piezoelectric layer 430 may include two air spaces, ie, a third gap portion 430 - 1 having a third piezoelectric cavity and a fourth gap portion 430 - 2 having a fourth piezoelectric cavity, between the lower electrode 420 and the upper electrode 440 .

[0107] The third void portion 430-1 may be formed in a portion of the bottom of the piezoelectric layer 430. The third void portion 430-1 may be formed by depositing a sacrificial layer corresponding to the third piezoelectric cavity over the lower electrode 420, depositing the piezoelectric layer 430 over the deposited sacrificial layer, and then removing the sacrificial layer of the third piezoelectric cavity.

[0108] Here, due to the characteristics of the third gap portion 430-1 and Figure 6 The third gap portion 330-1 shown in FIG. 1 is the same as that in FIG. 1 , and thus a detailed description thereof will be omitted, and the fourth gap portion 430-2 will be described in detail below.

[0109] The fourth void portion 430-2 includes a fourth piezoelectric cavity formed to be spaced a certain distance SD from the third void portion 430-1. The fourth piezoelectric cavity of the fourth void portion 430-2 may include a closed top surface CS that does not expose the bottom of the upper electrode 440 and an open bottom surface OS that partially exposes the top of the lower electrode 420.

[0110] Here, the second one side virtual surface VS3 extending vertically from the one side boundary wall forming the fourth piezoelectric cavity may intersect with the upper inner region of the substrate cavity forming the air gap portion 410-1. A point P3 at which the second one side virtual surface VS3 intersects with the upper inner region of the substrate cavity may be located on the upper virtual surface of the substrate cavity forming the air gap portion 410-1.

[0111] Moreover, the second other side virtual surface VS4 extending vertically from the other side boundary wall forming the fourth piezoelectric cavity may coincide with the one side boundary wall of the air gap portion 410-1. The point P4 where the second other side virtual surface VS4 intersects with the upper virtual surface of the substrate cavity may be located on the one side boundary wall of the air gap portion 410-1.

[0112] and Figure 6 330-1, the height H of the fourth void portion 430-2 may be less than or equal to half of the thickness T of the piezoelectric layer 430. The third void portion 430-1 and the fourth void portion 430-2 are formed in the piezoelectric layer 430 so that the thickness of the piezoelectric layer 430 is different in each region. That is, the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR3, the third piezoelectric region AR4, the fourth piezoelectric region AR5, and the fifth piezoelectric region AR5 of the piezoelectric layer 430 may be different from each other. In particular, the second piezoelectric region AR2 and the fourth piezoelectric region AR4 may have a thickness that is reduced by as much as the height of the third void portion 430-1 or the fourth void portion 430-2. The height H of the third void portion 430-1 or the fourth void portion 430-2 is formed to be less than or equal to half of the thickness T of the piezoelectric layer 430 to provide a minimum thickness that allows the heat generated inside to be easily released.

[0113] In addition, the lateral width of the third gap portion 430-1 or the fourth gap portion 430-2 may be one quarter of the wavelength of energy released through the piezoelectric layer 430. When the energy wavelength is expressed as λ, the value of the lateral width of the third gap portion 430-1 or the fourth gap portion 430-2 may be λ*(2N+1) / 4 (here, N is an integer greater than or equal to 0).

[0114] Meanwhile, in the piezoelectric layer 430, the piezoelectric region located above the third gap portion 430-1 or the fourth gap portion 430-2 has a relatively high acoustic impedance compared to the piezoelectric region located at a different position. Since the thicknesses of the first piezoelectric region AR1, the second piezoelectric region AR2, the third piezoelectric region AR3, the fourth piezoelectric region AR4, and the fifth piezoelectric region AR5 of the piezoelectric layer 430 are different from each other, the acoustic impedance is different in each region.

[0115] When the acoustic impedances of the first piezoelectric region AR1, the second piezoelectric region AR2, the third piezoelectric region AR3, the fourth piezoelectric region AR4, and the fifth piezoelectric region AR5 of the piezoelectric layer 430 are respectively referred to as the first acoustic impedance I1, the second acoustic impedance I2, the third acoustic impedance I3, the fourth acoustic impedance I4, and the fifth acoustic impedance I5, the second acoustic impedance I2 corresponding to the second piezoelectric region AR2 and the fourth acoustic impedance I4 corresponding to the fourth piezoelectric region AR4 have impedance values relatively greater than the impedance values of the first acoustic impedance I1, the third acoustic impedance I3, or the fifth acoustic impedance I5. Additionally, when the first acoustic impedance I1, the third acoustic impedance I3, and the fifth acoustic impedance I5 are compared with each other, the third acoustic impedance I3 has a relatively greater impedance value than the first acoustic impedance I1 or the fifth acoustic impedance I5, and the first acoustic impedance I1 has a relatively greater impedance value than the fifth acoustic impedance I5. When expressing their relationship with inequality signs, it can be seen that the magnitude order of the acoustic impedances is I5 < I1 < I3 < I2 = I4. The difference in acoustic impedance caused by the thickness variation of the piezoelectric layer 430 can prevent energy from being released from the piezoelectric layer 430 in the lateral direction.

[0116] As described above, the piezoelectric layer includes at least one void portion to cause a pitch state of the acoustic impedance and minimize the energy released through the side surface of the FBAR. Therefore, since the quality factor can be increased and the void portion reduces the area of the thick edge portion 140-1 in contact with the piezoelectric layer, the spurious occurrence caused by the edge portion 140 can be suppressed, and the decrease in the K 2 eff value can be compensated.

[0117] According to the present invention, by using the piezoelectric cavity formed in the piezoelectric layer to cause a pitch state of the acoustic impedance and minimize the energy released through the side surface of the FBAR, the quality factor can be increased.

[0118] In addition, by forming a piezoelectric cavity in the piezoelectric layer, the decrease in the K 2 eff value due to the increase in the thickness of the edge portion of the upper electrode can be prevented.

[0119] In addition, in the case of a communication filter using the resonator according to the present invention, the quality factor is increased, so that the insertion loss can be reduced and the skirt characteristics can be improved.

[0120] Exemplary embodiments of the present invention have been described above. Those of ordinary skill in the art should understand that modifications can be made without departing from the essential features of the present invention. Therefore, the disclosed embodiments should not be considered restrictive but rather descriptive. The scope of the present invention will be shown in the claims rather than in the above description, and all differences within the scope equivalent to the claims should be considered included in the present invention.

Claims

1. An air-gap film bulk acoustic resonator, comprising: a substrate including an air gap portion having a top surface, a substrate cavity formed in the air gap portion; a lower electrode formed over the substrate while surrounding the air gap portion; a piezoelectric layer formed above the lower electrode; as well as an upper electrode formed above the piezoelectric layer corresponding to a virtual area formed according to a vertical projection of the air gap portion, wherein the piezoelectric layer includes a gap portion having a piezoelectric cavity between the lower electrode and the upper electrode, and wherein the gap portion is formed below an edge portion corresponding to an end portion of the upper electrode, wherein the gap portion is a first gap portion including a first piezoelectric cavity, in which an open top surface is formed to partially expose the bottom of the edge portion, and a closed bottom surface is formed to not expose the top of the lower electrode, wherein the piezoelectric layer further comprises a second gap portion having a second piezoelectric cavity, the second gap portion being formed to be spaced a certain distance from the first gap portion, wherein in the second piezoelectric cavity, a closed bottom surface is formed so as not to expose the top of the lower electrode, and an open top surface is formed so as to open the entire top thereof, wherein in the second gap portion, a second one side virtual surface extending vertically from a one side boundary wall forming the second piezoelectric cavity intersects with an upper inner region of the substrate cavity, and A second other-side virtual surface extending perpendicularly from the other-side boundary wall forming the second piezoelectric cavity coincides with one-side boundary wall of the air gap portion.

2. The air-gap film bulk acoustic resonator according to claim 1 , wherein in the first gap portion, a first one side virtual surface vertically extending from a one side boundary wall forming the first piezoelectric cavity intersects with a lower inner region of the edge portion, and A first other-side virtual surface vertically extending from the other-side boundary wall forming the first piezoelectric cavity intersects with an upper inner region of the substrate cavity. 3 . The air-gap film bulk acoustic resonator according to claim 2 , wherein an end surface of the edge portion is spaced apart from the first other-side virtual surface by a certain distance or more so that a top of the first piezoelectric cavity is partially opened. 4 . The air-gap type film bulk acoustic resonator according to claim 1 , wherein the edge portion is an electrode structure having a relatively larger electrode thickness than other electrode structures forming the upper electrode. 5 . The air-gap film bulk acoustic resonator according to claim 1 , wherein a height of the first gap portion or the second gap portion is less than or equal to a half of a thickness of the piezoelectric layer. 6 . The air-gap film bulk acoustic resonator according to claim 1 , wherein a lateral width of the first gap portion or the second gap portion is greater than or equal to a quarter of a wavelength of energy released through the piezoelectric layer. 7 . The air-gap film bulk acoustic resonator according to claim 1 , wherein in the piezoelectric layer, a piezoelectric region located below the first gap portion or the second gap portion has a relatively high acoustic impedance compared with piezoelectric regions at other positions.

8. The air-gap film bulk acoustic resonator according to claim 1, wherein the gap portion is a third gap portion including a third piezoelectric cavity, in which a closed top surface is formed so as not to expose a bottom of an upper electrode, and an open bottom surface is formed so as to expose a top of the lower electrode.

9. The air-gap film bulk acoustic resonator according to claim 8, wherein in the third gap portion, a first one side virtual surface extending vertically from a one side boundary wall forming the third piezoelectric cavity coincides with an end of the edge portion, and A first other-side virtual surface extending vertically from the other-side boundary wall forming the third piezoelectric cavity intersects with an upper inner region of the substrate cavity. 10 . The air-gap type film bulk acoustic resonator of claim 8 , wherein the piezoelectric layer further includes a fourth gap portion having a fourth piezoelectric cavity, the fourth gap portion being formed to be spaced apart from the third gap portion by a certain distance. 11 . The air-gap type film bulk acoustic resonator according to claim 10 , wherein in the fourth piezoelectric cavity, a closed top surface is formed so as not to expose a bottom of the upper electrode, and an open bottom surface is formed so as to expose a top of the lower electrode. 12 . The air-gap type film bulk acoustic resonator according to claim 10 , wherein a height of the third gap portion or the fourth gap portion is less than or equal to a half of a thickness of the piezoelectric layer. 13 . The air-gap film bulk acoustic resonator according to claim 10 , wherein a lateral width of the third gap portion or the fourth gap portion is greater than or equal to a quarter of a wavelength of energy released through the piezoelectric layer. 14 . The air-gap film bulk acoustic resonator according to claim 10 , wherein in the piezoelectric layer, a piezoelectric region located above the third gap portion or the fourth gap portion has a relatively high acoustic impedance compared with piezoelectric regions at other positions.

Images