Air-gap Film Bulk Acoustic Resonator

Abstract

An air-gap film bulk acoustic resonator (FBAR) is provided. The air-gap FBAR includes: a substrate including an air-gap portion having a substrate cavity formed in a top surface; a lower electrode formed on the substrate; a piezoelectric layer formed on the lower electrode and having one side thereof forming an edge portion near a virtual edge according to a vertical projection of the air-gap portion; an upper electrode formed on the piezoelectric layer; a first electrode frame including an open-loop structure in a plane surrounding a portion of an outer periphery of the piezoelectric layer on the lower electrode; and a second electrode frame positioned on the upper electrode and adjacent to an opening portion of the open-loop structure.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2019-0134779 filed in the Korean Intellectual Property Office on October 28, 2019, the entire disclosure of which is incorporated herein by reference for all purposes. Technical Field

[0003] The present invention relates to resonators for communication in a radio frequency (RF) 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 send information in a limited frequency band. In particular, filters in RF components are necessary for use in mobile telecommunication technology, which enables high-quality communication by selecting the signal required by the user in multiple frequency bands or by filtering the signal to be sent.

[0005] At present, the most widely used RF filters for wireless communication are dielectric filters and surface acoustic wave (SAW) filters. The advantages of dielectric filters are that they provide high dielectric permittivity, low insertion loss, stability at high temperatures, and are robust to vibration and shock. However, dielectric filters are limited in miniaturization and application to monolithic microwave integrated circuits (MMICs), which are the latest trends in technological development. In contrast, the advantages of SAW filters are that they provide small size, are easy to process signals, have simplified circuits, and can be mass-produced using semiconductor processes. In addition, compared with dielectric filters, SAW filters provide high-side suppression in the passband, allowing them to send and receive high-quality information. However, the disadvantage of SAW filters is that the interdigital transducer (IDT) line width is limited to about 0.5 μm because the process for manufacturing SAW filters includes exposure to ultraviolet (UV) light. Therefore, SAW filters cannot cover high-frequency bands, such as those exceeding 5 GHz. In addition, it is still difficult to integrate SAW filters with MMIC structures as a single chip on a semiconductor substrate.

[0006] In order to overcome the above limitations and problems, a film bulk acoustic resonator (FBAR) filter has been proposed, in which a frequency control circuit can be completely constructed in the form of an MMIC together with other active devices integrated on an existing Si or GaAs semiconductor substrate.

[0007] FBAR is a low-cost, small-size thin-film device and can be designed to have a high Q factor. Therefore, FBAR filters can be used in wireless communication devices and military radars in various frequency bands ranging from 900 MHz to 10 GHz, for example. In addition, FBAR can be made one order of magnitude smaller than dielectric filters or lumped constant (LC) filters and has very low insertion loss compared to SAW filters. Therefore, FBAR can be the most suitable device that can be integrated with MMICs that require high stability and high quality factor (Q factor).

[0008] The FBAR filter is formed by depositing zinc oxide (ZnO), aluminum nitride (AlN), etc., which are piezoelectric dielectric materials, on a Si or GaAs semiconductor substrate by RF sputtering. The resonance of the FBAR filter is caused by the piezoelectric properties of the piezoelectric material used therein. More specifically, the FBAR filter includes a piezoelectric film disposed between two electrodes, and generates a bulk acoustic wave to cause resonance.

[0009] So far, various FBAR structures have been studied. In a membrane type FBAR, a silicon oxide (SiO2) layer is deposited on a substrate, and a membrane layer is formed using a cavity formed by isotropically etching opposite sides of the substrate. Then, a lower electrode is formed on the SiO2 layer, a piezoelectric material is deposited on the lower electrode using an RF magnetron sputtering method to form a piezoelectric layer, and an upper electrode is formed on the piezoelectric layer.

[0010] The above-mentioned film-based FBAR provides low dielectric loss of the substrate and less power loss due to the cavity. However, the film-based FBAR occupies a large area due to the orientation of the silicon substrate and is easily damaged due to low structural stability in the subsequent packaging process, resulting in low yield. Therefore, recently, air gap type and Bragg reflector type FBAR have been created to reduce the loss due to the film and simplify the device manufacturing process.

[0011] The Bragg reflector type FBAR is formed by stacking a reflective layer, a lower electrode, a piezoelectric layer, and an upper electrode in order, wherein the reflective layer is formed by depositing a material having a large elastic impedance difference on a substrate in an alternating manner. The Bragg reflector type FBAR element of this structure can effectively generate resonance because all the elastic acoustic wave energy passing through the piezoelectric layer is not transferred to the substrate but is reflected at the reflective layer. The Bragg reflector type FBAR is structurally strong and does not exhibit stress when bent, but it has the following disadvantages: it is difficult to accurately form more than four reflective layers for total reflection, and its manufacture requires a lot of time and cost.

[0012] On the other hand, a conventional air-gap type FBAR having a structure in which an air gap is used instead of a reflective layer to separate a substrate from a resonant portion realizes the FBAR by isotropically etching a surface of a silicon substrate to form a sacrificial layer, polishing the surface using chemical mechanical planarization (CMP), and then sequentially depositing an insulating layer, a lower electrode, a piezoelectric layer, and an upper electrode, and removing the sacrificial layer through a through hole to form an air gap.

[0013] In the prior art, a piezoelectric layer is sandwiched between an upper electrode and a lower electrode in a FBAR structure, and installing the upper electrode and the lower electrode in a region where such a piezoelectric layer is required enables the piezoelectric effect. Therefore, the conventional FBAR structure has a high mechanical anchor loss, which results in a decrease in mechanical energy.

[0014] The upper electrode or the lower electrode may be formed of a material such as Mo, Ru, W, etc. to increase the acoustic impedance. The skin depth of the electrode material depends on the frequency of the filter. Generally, the electrode layer has a thickness much thinner than the skin depth, so the charge charged at the resonance point of the piezoelectric layer cannot be fully transferred through the lead, which causes a reduction in the quality factor.

[0015] Patent Literature

[0016] Korean Patent Publication No. 10-2004-0102390 (published on December 8, 2004) Summary of the invention

[0017] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0018] The following description relates to an air-gap film bulk acoustic resonator (FBAR) capable of reducing anchor loss (mechanical loss) while improving quality factor, wherein a piezoelectric layer is formed to coincide with an edge of the resonator, a first electrode frame is formed on a lower electrode and the piezoelectric layer, and a second electrode frame is formed on an upper electrode.

[0019] According to one aspect of the present invention, an air-gap type FBAR includes: a substrate including an air-gap portion having a substrate cavity formed in a top surface; a lower electrode formed on the substrate; a piezoelectric layer formed on the lower electrode and having one side thereof forming an edge portion near a virtual edge according to a vertical projection of the air-gap portion; an upper electrode formed on the piezoelectric layer; a first electrode frame including an open-loop structure in a plane surrounding a portion of an outer circumference of the piezoelectric layer on the lower electrode; and a second electrode frame positioned on the upper electrode and adjacent to an opening portion of the open-loop structure.

[0020] The open loop structure may surround a portion of the virtual edge according to the vertical projection of the air gap portion, and the second electrode frame may be spaced apart from the first electrode frame by a predetermined distance and surround a remaining portion of the virtual edge.

[0021] The first electrode frame may include the open loop structure formed on the lower electrode and spaced apart from an edge portion of the upper electrode and surrounding the virtual edge.

[0022] The first electrode frame may include the open loop structure having the edge portion located along the virtual edge.

[0023] The open loop structure may include two hook portions bent at both ends thereof to face each other, and an edge portion of the second electrode frame may be located between the hook portions.

[0024] The first electrode frame may include a first frame extension portion formed on the lower electrode extension portion of the lower electrode and extending for connection with the outside.

[0025] An edge portion of the second electrode frame may be located along the virtual edge.

[0026] The second electrode frame may include a second frame extending portion formed on the upper electrode extending portion of the upper electrode and extending for connection with the outside.

[0027] The first electrode frame may be formed on the lower electrode, and when the piezoelectric layer extends beyond the virtual edge and completely surrounds the air gap portion, an edge portion of the first electrode frame may be spaced apart from the edge portion of the piezoelectric layer by a predetermined distance.

[0028] The piezoelectric layer may further include a cavity portion including a piezoelectric cavity formed between the lower electrode and the upper electrode, and the cavity portion may be formed on a lower portion of an edge portion of the upper electrode.

[0029] The cavity portion may be a first cavity portion including a first piezoelectric cavity having an exposed upper surface formed to expose a portion of a lower portion of the edge portion of the upper electrode and a closed lower surface formed not to expose an upper portion of the lower electrode.

[0030] The piezoelectric layer may further include a second cavity portion including a second piezoelectric cavity formed to be spaced apart from the first cavity portion by a predetermined distance.

[0031] The second piezoelectric cavity may have a closed lower surface formed not to expose an upper portion of the lower electrode and an exposed upper surface formed to allow an entire upper portion to be opened.

[0032] The first electrode frame may include an edge portion that coincides with a boundary wall of one side of the second piezoelectric cavity when the piezoelectric layer extends beyond the virtual edge and completely surrounds the air gap portion.

[0033] The air-gap type FBAR may further include an air bridge including an air cavity formed on one side of the virtual edge according to the virtual projection of the air gap portion.

[0034] The piezoelectric layer may include the edge portion formed near the virtual edge according to the virtual projection of the air gap portion, and also include an extended piezoelectric layer that is spaced apart from the edge portion by more than a predetermined distance and extends, and the first electrode frame may be formed on the extended piezoelectric layer as well as on the piezoelectric layer and the lower electrode.

[0035] Other features and aspects will be apparent from the following detailed description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a cross-sectional view of a first embodiment of an air-gap film bulk acoustic resonator (FBAR) according to the present invention.

[0037] Figure 2 yes Figure 1 Top view of the air-gap FBAR shown in FIG.

[0038] Figure 3 yes Figure 1 Vertical cross-sectional views of each side of the air-gap FBAR shown in FIG.

[0039] Figure 4 is a reference diagram for illustrating a distance between an edge portion of the second electrode frame and an end portion of any one hook portion of the first electrode frame.

[0040] Figure 5 is a graph according to one embodiment of characteristics of a spacing distance between a first electrode frame and a second electrode frame.

[0041] Figure 6 is a graph showing the quality factor characteristics of the air-gap type FBAR according to the present invention.

[0042] Figure 7 is a cross-sectional view of a second embodiment of an air-gap type FBAR according to the present invention.

[0043] Figure 8is a cross-sectional view of a third embodiment of an air-gap type FBAR according to the present invention.

[0044] Fig. 9 is a cross-sectional view of a fourth embodiment of an air-gap type FBAR according to the present invention.

[0045] Fig.10 is a cross-sectional view of a fifth embodiment of an air-gap type FBAR according to the present invention.

[0046] Fig.11 is a cross-sectional view of a sixth embodiment of an air-gap type FBAR according to the present invention.

[0047] Throughout the drawings and detailed description, unless otherwise described, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. DETAILED DESCRIPTION

[0048] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0049] The embodiments of the present invention are provided to explain the present invention more comprehensively to those of ordinary skill in the art. The following embodiments may be modified into various forms, and the scope of the present invention is not limited thereto. These embodiments are provided to make the present disclosure more substantial and complete, and to fully convey the concept of the present invention to those skilled in the art.

[0050] The terms used herein are used to explain specific embodiments and are not intended to limit the present invention. As used herein, unless the context otherwise defines, the singular may include the plural. Moreover, as used herein, the term "and / or" includes any and all combinations or one of a plurality of related listed items. Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, which schematically illustrate embodiments.

[0051] Figure 1 is a cross-sectional view of a first embodiment of an air-gap film bulk acoustic resonator (FBAR) 100 according to the present invention, Figure 2 yes Figure 1 A top view of the air-gap FBAR 100 is shown in FIG. Figure 3 yes Figure 1 1 and 2. A vertical cross-sectional view of each side of the air-gap FBAR 100 is shown in FIG.

[0052] Reference Figures 1 to 3 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 , an upper electrode 140 , a first electrode frame 150 , and a second electrode frame 160 .

[0053] In the air-gap FBAR 100, if an external signal is applied between the lower electrode 120 and the upper electrode 140, a portion of the electrical energy transferred between the two electrodes is converted into mechanical energy due to the piezoelectric effect. In the process of converting this mechanical energy back into electrical energy, resonance occurs about an appropriate vibration frequency depending on the thickness of the piezoelectric layer 130.

[0054] The substrate 110 is a semiconductor substrate, which may be a common silicon wafer, and is preferably a high resistivity silicon (HRS) substrate. An insulating layer (not shown) may be formed on the top surface of the substrate 100. The insulating layer may include a thermal oxide film that can be easily grown on the substrate 100, or may alternatively include an oxide film or a nitride film formed using a general deposition process such as chemical vapor deposition.

[0055] The air gap portion 110-1 is formed as follows. A substrate cavity is formed in the substrate 110, and then an insulating layer is formed in the substrate cavity. A sacrificial layer is deposited on the insulating layer and then planarized by etching, and then finally removed to form an air gap. Here, for the sacrificial layer, a material having a high surface roughness and that can be easily formed and removed, such as tetraethyl orthosilicate (TEOS), phosphosilicate glass (PSG), etc., is used. For example, polycrystalline silicon can be used as a sacrificial layer. Such polycrystalline silicon can have excellent surface roughness and enables the sacrificial layer to be easily formed and removed, and in particular, can be removed by applying dry etching in subsequent processes.

[0056] The lower electrode 120 is formed on the air gap portion 110-1, wherein the sacrificial layer exists in the substrate cavity. The lower electrode 120 is formed by depositing and patterning a predetermined material on the substrate 110. For the lower electrode 120, a general conductive material such as a metal is used, and preferably one of aluminum (Al), tungsten (W), gold (Au), platinum (Pt), nickel (Ni), chromium (Cr), titanium (Ti), palladium (Pd), ruthenium (Ru), rhenium (Re) and molybdenum (Mo) is used. The thickness of the lower electrode 120 can be from 10 to 1000nm.

[0057] The piezoelectric layer 130 is formed on the lower electrode 120. The piezoelectric layer 130 may be formed by depositing and patterning a piezoelectric material on the lower electrode 120. For the piezoelectric material, AlN or ZnO may be used. The deposition method may include an RF magnetron sputtering method, an evaporation method, etc. The thickness of the piezoelectric layer 130 may be 5 to 500 nm.

[0058] Unlike the prior art, the piezoelectric layer 130 is formed on the lower electrode 120, and at this time, the edge portion 130-1 of the piezoelectric layer 130 is formed only to the vicinity of the virtual edge VE according to the vertical projection of the air gap portion 110-1. The edge portion 130-1 of the piezoelectric layer 130 may have an inclined shape, and its inclination angle may be about 30 degrees.

[0059] The piezoelectric layer 130 may include a cavity portion in which a piezoelectric cavity is formed between the lower electrode 120 and the upper electrode 140. Here, the cavity portion may be formed under an edge portion corresponding to an end portion of the upper electrode 140. Details of the cavity portion will be described below.

[0060] An upper electrode 140 is formed on the piezoelectric layer 130. If a cavity portion is formed in the piezoelectric layer 130 and a sacrificial layer is formed therein, the upper electrode 140 may also be formed on a portion of the sacrificial layer. The upper electrode 140 may be formed by depositing and patterning a metal film for the upper electrode on a predetermined region of the piezoelectric layer 130. The upper electrode 140 and the lower electrode 120 may be formed of the same material by using the same deposition method and patterning method. The thickness of the upper electrode 400 may be 5 to 1000 nm.

[0061] The edge portion 140-1 is formed at one end of the upper electrode 140. The edge portion 140-1 may be an electrode structure having a relatively thick electrode thickness compared to other portions of the electrode structure constituting the upper electrode 140. The edge portion 140-1 corresponds to an edge frame of the upper electrode 140 for preventing energy from escaping through the side.

[0062] Meanwhile, a cushion layer to be applied to respective portions of the above-described lower electrode 120, piezoelectric layer 130, and upper electrode 140 may be formed. The cushion layer serves as a cover layer for protecting the lower electrode 120, piezoelectric layer 130, and upper electrode 140.

[0063] The first electrode frame 150 corresponds to the electrode frame formed on the lower electrode 120, which has an open loop structure in a plane. The first electrode frame 150 for reinforcing the electrode is formed on the lower electrode Mo or Ru exposed by removing the piezoelectric layer 130 from the upper portion of the lower electrode extending beyond the air gap portion 110-1. The metal used to form the first electrode frame 150 is Cu, Au, AlCu, Mo, etc., and the first electrode frame 150 is formed to have a height and width that are sufficiently greater than the skin depth, and is formed around the periphery of the lower electrode 120 and the piezoelectric layer 130. As a metal for the first electrode frame 150, a material having a conductivity less than that of the electrode material Mo or RU and having an acoustic impedance significantly different from the AIN of the piezoelectric layer 130 used can be selected. Before the first electrode frame 150 is formed on the lower electrode 120, chromium (Cr) and nickel chromium (NiCr) are first formed as a metal barrier layer.

[0064] Reference Figure 2 The first electrode frame 150 is formed in a planar shape to surround the outer circumference of the piezoelectric layer 130 on the lower electrode 120. To this end, the first electrode frame 150 has a ring structure with one side partially opened, that is, an open ring structure (or hook structure) 150-1.

[0065] The open loop structure 150 - 1 includes two hook portions 150 - 11 and 150 - 12 bent at both ends thereof to face each other.

[0066] The hooks 150-11 and 150-12 are bent and extended at both ends of the open loop structure 150-1, and they are bent in directions facing each other to form a shape surrounding the upper electrode 140. In this case, the hooks 150-11 and 150-12 may extend in a straight line or a bent shape.

[0067] The first electrode frame 150 includes a first frame extending portion which is located above the lower electrode extending portion of the lower electrode 120 and which extends to be connected to the outside.

[0068] Reference Figure 3 In the side cross-sectional view along the AA' direction shown in , the first frame extension portion 150-2 of the first electrode frame 150 is formed on the lower electrode extension portion 120-1 of the lower electrode 120, which is extended to be connected to the outside. The first frame extension portion 150-2 may surround the lower electrode extension portion 120-1 in a manner covering the entire lower electrode extension portion 120-1, or may surround only a portion of the lower electrode extension portion 120-1.

[0069] The open loop structure 150 - 1 of the first electrode frame 150 surrounds a portion of a virtual edge according to a vertical projection of the air gap portion 110 - 1 .

[0070] Reference Figure 3 In the side cross-sectional view of the first electrode frame 150 in each direction (A-A' and BB') shown in FIG, an open-loop structure 150-1 of the first electrode frame 150 is formed on the lower electrode 120, is spaced apart from an edge portion 140-1 of the upper electrode 140 formed on the air gap portion 110-1, and surrounds a virtual edge VE according to a vertical projection of the air gap portion 110-1.

[0071] At this time, referring to the side cross-sectional view in the BB' direction, the edge portion 150-13 of the open loop structure 150-1 is located at a position corresponding to the virtual edge VE of the air gap portion 110-1. In addition, referring to the side cross-sectional view along the AA' direction, the edge portion 150-21 of the first frame extension portion 150-2 is located at a position corresponding to the virtual edge VE of the air gap portion 110-1. Here, the edge portions 150-13 and 150-21 of the open loop structure 150-1 may each be formed as a vertical boundary wall.

[0072] The open loop structure 150-1 and the first frame extension portion 150-2 of the first electrode frame 150 are spaced apart from the edge portion 140-1 of the upper electrode 140 by a predetermined distance and are positioned along a virtual edge VE of the air gap portion 110-1. Figure 3 It can be seen that in the BB' side cross-sectional view, the edge portion 150-13 of the open-loop structure 150-1 is spaced apart from the edge portion 140-1 of the upper electrode 140, and in the AA' side cross-sectional view, the edge portion 150-21 of the first frame extension portion 150-2 is spaced apart from the edge portion 140-1 of the upper electrode 140.

[0073] The second electrode frame 160 is positioned on the upper electrode 140 and adjacent to the opening portion of the open loop structure 150-1 forming the first electrode frame 150. Here, the second electrode frame 160 includes an edge portion surrounding a portion of a virtual edge VE of the air gap portion 110-1, and the other portion is surrounded by the edge portions 150-13 and 150-21 of the first electrode frame 150.

[0074] The metal used to form the second electrode frame 160 is Cu, Au, AlCu, Mo, etc., and the second electrode frame 160 is formed to have a height and a width sufficiently larger than the skin depth, and is formed on the upper electrode 140. Before the second electrode frame 160 is formed on the upper electrode 140, Cr and NiCr are first formed as a metal barrier.

[0075] Reference Figure 3 In the side cross-sectional view along the CC′ direction shown in FIG. 1 , the edge portion 160 - 1 of the second electrode frame 160 is located at a point corresponding to the virtual edge VE of the air gap portion 110 - 1 .

[0076] The edge portion 160-1 of the second electrode frame 160 is spaced apart from each end of the hooks 150-11 and 150-12 constituting the first electrode frame 150 by a predetermined distance D and surrounds a virtual edge VE of the air gap portion 110-1. Here, the edge portion 160-1 of the second electrode frame 160 may be formed as a vertical edge barrier.

[0077] Figure 41 is a reference diagram for illustrating a distance between one side of the edge portion 160 - 1 of the second electrode frame 160 and any one of the hook portions 150 - 11 of the first electrode frame 150 . Figure 4 , one side of the edge portion 160 - 1 of the second electrode frame 160 is spaced apart from the end of the hook 150 - 11 by a predetermined distance D.

[0078] Figure 5 is a graph according to one embodiment of characteristics of a spacing distance between the first electrode frame 150 and the second electrode frame 160 .

[0079] Reference Figure 5 As the distance between the first electrode frame 150 and the second electrode frame 160 increases, the quality factor (Qs) decreases but K 2 eff Increase, as shown in the chart.

[0080] Qs and K 2 eff are important, but when Qs increases, K 2 eff decreases, and when Qs decreases, K 2 eff Therefore, figure of merit (FOM) = Qs × K 2 eff Sometimes used as a performance indicator. Figure 5 As shown in the graph, comparing the distance of 2μm and 5μm, Qs decreases by 1.68%, K 2 eff增 The value is 0.64% greater, so it can be seen that the influence of Qs is greater and the distance of 2 μm is better. Therefore, preferably, the distance between the first electrode frame 150 and the second electrode frame 160 is designed to be 1 to 2 μm.

[0081] The second electrode frame 160 includes a second frame extending portion located above the upper electrode extending portion of the upper electrode 140 , which extends to be connected to the outside.

[0082] Reference Figure 3 In the side cross-sectional view shown in FIG, the second frame extension portion 160-2 of the second electrode frame 160 is formed on the upper electrode extension portion 140-2 of the upper electrode 140, which is extended to be connected to the outside. The second frame extension portion 160-2 may surround the upper electrode extension portion 140-2 in a manner covering the entire upper electrode extension portion 140-2, or may surround only a portion of the upper electrode extension portion 140-2.

[0083] Figure 6 is a graph showing the quality factor characteristics of the air-gap type FBAR according to the present invention.

[0084] Reference Figure 6 , it can be seen that the quality factor characteristics of the air-gap FBAR (C3R_frame width 2.6 μm) according to the present invention are improved compared with the conventional air-gap FBAR (AFO_frame width 6 μm). In particular, the value of the quality factor of the resonance can be increased. The filter incorporating such a resonator can improve the insertion loss and edge characteristics of the filter.

[0085] Figure 7 is a cross-sectional view of a second embodiment of an air-gap type FBAR 200 according to the present invention.

[0086] Reference Figure 7 The air-gap type FBAR 200 of the second embodiment includes a substrate 210 , an air-gap portion 210 - 1 , a lower electrode 220 , a piezoelectric layer 230 , an upper electrode 240 , a first electrode frame 250 , a second electrode frame 260 , and an air bridge 270 .

[0087] Here, the functional characteristics of the substrate 210, the air gap portion 210-1, the lower electrode 220, the piezoelectric layer 230, the upper electrode 240, the first electrode frame 250 and the second electrode frame 260 are the same as those described above with reference to Figure 1 The functional characteristics of the described substrate 110, the air gap portion 110-1, the lower electrode 120, the piezoelectric layer 130, the upper electrode 140, the first electrode frame 150, and the second electrode frame 260 are substantially the same or similar. However, the second embodiment is different from the first embodiment in that the edge portion 260-1 of the second electrode frame 260 is not located on the virtual edge VE of the air gap portion 210-1, but is arranged to be a predetermined distance backward from the virtual edge VE. At the same time, the second embodiment 200 also includes an air bridge 270.

[0088] Therefore, descriptions of components performing common or similar functions will be omitted, and the air bridge 270 will be described below.

[0089] The air bridge 270 is an air cavity formed on one side of a virtual edge VE according to a vertical projection of the air gap portion 1. The air cavity of the air gap portion 210-1 may be formed in any one of the piezoelectric layer 230 and the upper electrode 240, or may be formed to span both the piezoelectric layer 230 and the upper electrode 240.

[0090] Reference Figure 7 , the air cavity may have an inclined step as shown in the vertical cross-sectional view, or a horizontal air cavity without a step may be formed. The air bridge 270 is preferably formed on an upper portion of a virtual edge VE of the air gap portion 210-1.

[0091] Figure 8 is a cross-sectional view of a third embodiment of an air-gap type FBAR 300 according to the present invention.

[0092] Reference Figure 8 The air-gap type FBAR 300 of the third embodiment includes a substrate 310, an air-gap portion 310-1, a lower electrode 320, a piezoelectric layer 330, an upper electrode 340, a first electrode frame 350, and a second electrode frame 260 (not shown).

[0093] Here, the functional characteristics of the substrate 310, the air gap portion 310-1, the lower electrode 320, the upper electrode 340, and the second electrode frame are respectively the same as those in the above reference Figure 1 The functional characteristics of the described substrate 110 , the air gap portion 110 - 1 , the lower electrode 120 , the upper electrode 140 , and the second electrode frame 260 are substantially the same or similar.

[0094] Meanwhile, the piezoelectric layer 330 is formed beyond the virtual edge VE to completely surround the air gap portion 310 - 1 . Here, the piezoelectric layer 330 may include a cavity portion formed at a position below the edge portion 340 - 1 of the upper electrode 340 .

[0095] Reference Figure 8 , the piezoelectric layer 330 may include an air space between the lower electrode 320 and the upper electrode 340 , that is, a first cavity portion 330 - 1 having a first piezoelectric cavity.

[0096] The first cavity portion 330-1 is formed by etching a portion of the upper portion of the piezoelectric layer 330 to form a first piezoelectric cavity, depositing and flattening a sacrificial layer on the first piezoelectric cavity, stacking an upper electrode 340 on the piezoelectric layer 330 including the sacrificial layer, and then removing the sacrificial layer. Here, for the sacrificial layer, a material having a high surface roughness and that can be easily formed and removed, such as TEOS, PSG, etc., is used.

[0097] The first cavity portion 330-1 may have a first piezoelectric cavity which is a partial air space in which a portion of the lower portion of the upper electrode 340 is exposed and an upper portion of the lower electrode 320 is not exposed. That is, the first cavity portion 330-1 may include a first piezoelectric cavity having an exposed upper surface formed to expose a portion of the lower portion of the edge portion 340-1 and a closed lower surface formed to not expose the upper portion of the lower electrode 320.

[0098] The first cavity portion 330-1 is formed below the edge portion 340-1 corresponding to the end of the upper electrode 340. Here, the edge portion 340-1 of the upper electrode 340 does not surround the entire upper surface of the first piezoelectric cavity in the first cavity portion 330-1, but surrounds only a portion of the first piezoelectric cavity (for example, may surround only about 1 / 2 of the first piezoelectric cavity), so that the first cavity portion 330-1 may open a portion of the upper portion of the first piezoelectric cavity.

[0099] The thickness of the first cavity portion 330-1 may be less than or equal to half the thickness of the piezoelectric layer 130. When the first cavity portion 330-1 is formed, the thickness of each region of the piezoelectric layer 330 varies. By designing the height of the first cavity portion 330-1 to be less than or equal to half the thickness of the piezoelectric layer 330, the minimum thickness that allows the heat generated inside to escape easily can be ensured. In addition, the length of the horizontal width of the first cavity portion 330-1 may be greater than or equal to 1 / 4 of the wavelength of the energy flowing out through the piezoelectric layer 330.

[0100] The first electrode frame 350 has the same or similar structure as the first electrode frame 150 described above, wherein the first electrode frame 350 corresponds to an electrode frame formed on the lower electrode 320 and has an open loop structure on a plane. Figure 8 As shown, the edge portion 350 - 1 of the first electrode frame 350 in the third embodiment is not located on the virtual edge VE of the air gap portion 310 - 1 , but is disposed a predetermined distance backward from the virtual edge VE and located on the lower electrode 320 .

[0101] Fig. 9 is a cross-sectional view of a fourth embodiment of an air-gap type FBAR 400 according to the present invention.

[0102] Reference Fig. 9 The air-gap type FBAR 400 of the fourth embodiment includes a substrate 410, an air-gap portion 410-1, a lower electrode 420, a piezoelectric layer 430, an upper electrode 440, a first electrode frame 450 and a second electrode frame 260 (not shown).

[0103] Here, the functional characteristics of the substrate 410, the air gap portion 410-1, the lower electrode 420, the upper electrode 440 and the second electrode frame are respectively the same as those in the above reference Figure 8 The functional characteristics of the described substrate 310 , the air gap portion 310 - 1 , the lower electrode 320 , the upper electrode 340 , and the second electrode frame are substantially the same or similar.

[0104] Meanwhile, the piezoelectric layer 430 is formed beyond the virtual edge VE to completely surround the air gap portion 410-1. Here, the piezoelectric layer 430 may include a first cavity portion 430-1 having a first piezoelectric cavity formed at a position below the edge portion 440-1 of the upper electrode 440. The functional characteristics of the first cavity portion 430-1 are the same as those of the above reference Figure 8The functional characteristics of the first cavity portion 330-1 described are the same. However, the piezoelectric layer 430 extends beyond the virtual edge VE, and an edge portion 430-2 of the piezoelectric layer 430 corresponding to the end of the extended portion forms a right-angle boundary wall. The edge portion 430-2 of the piezoelectric layer 430 is separated from the edge portion 450-1 of the first electrode frame 450 by a predetermined distance d. The predetermined distance d can vary according to the design.

[0105] The first electrode frame 450 has the same or similar structure as the first electrode frame 150 described above, wherein the first electrode frame 450 corresponds to an electrode frame formed on the lower electrode 420 and has an open loop structure on a plane. Fig. 9 As shown, the edge portion 450 - 1 of the first electrode frame 450 in the fourth embodiment is not located on the virtual edge VE of the air gap portion 410 - 1 , but is disposed a predetermined distance backward from the virtual edge VE and located on the lower electrode 420 .

[0106] Fig.10 is a cross-sectional view of a fifth embodiment of an air-gap type FBAR 500 according to the present invention.

[0107] Reference Fig.10 The air-gap type FBAR 500 of the fifth embodiment includes a substrate 510, an air-gap portion 510-1, a lower electrode 520, a piezoelectric layer 530, an upper electrode 540, a first electrode frame 550 and a second electrode frame 260 (not shown).

[0108] Here, the functional characteristics of the substrate 510, the air gap portion 510-1, the lower electrode 520, the upper electrode 540, and the second electrode frame are respectively the same as those described above. Figure 8 The functional characteristics of the described substrate 310 , the air gap portion 310 - 1 , the lower electrode 320 , the upper electrode 340 , and the second electrode frame are substantially the same or similar.

[0109] Meanwhile, the piezoelectric layer 530 is formed beyond the virtual edge VE to completely surround the air gap portion 510-1. Here, the piezoelectric layer 530 may include a first cavity portion 530-1 having a first piezoelectric cavity formed at a position below the edge portion 540-1 of the upper electrode 540. The functional characteristics of the first cavity portion 530-1 are the same as those of the above reference Figure 8 The functional characteristics of the first chamber portion 330-1 described above are the same. Fig.10 As shown, the piezoelectric layer 530 includes a second cavity portion 530 - 2 in addition to the first cavity portion 530 - 1 .

[0110] The second piezoelectric cavity of the second cavity portion 530-2 may include a closed lower surface formed not to expose the upper portion of the lower electrode 520 and an exposed upper surface formed to allow the entire upper portion to be opened.

[0111] The boundary wall 530 - 3 located at one side of the second piezoelectric cavity of the second cavity part 530 - 2 is located at a point coincident with the edge part 550 - 1 of the first electrode frame 550 and the virtual edge VE of the air gap part 510 - 1 .

[0112] Similar to the first cavity portion 530-1, the thickness of the second cavity portion 530-2 may be less than or equal to half the thickness of the piezoelectric layer 530. Since the first cavity portion 530-1 and the second cavity portion 530-2 are formed on the piezoelectric layer 530, the thickness of each region of the piezoelectric layer 530 varies. In addition, the length of the horizontal width of the first cavity portion 530-1 or the second cavity portion 530-2 may be greater than or equal to 1 / 4 of the wavelength of the energy flowing out through the piezoelectric layer 530. The difference in acoustic impedance due to the thickness variation of the piezoelectric layer 530 can prevent the leakage of energy escaping from the piezoelectric layer 530 in the lateral direction.

[0113] The first electrode frame 550 has the same or similar structure as the first electrode frame 150 described above, wherein the first electrode frame 550 corresponds to an electrode frame formed on the lower electrode 520 and the piezoelectric layer 530 and has an open loop structure on a plane. Fig.10 As shown, the edge portion 550 - 1 of the first electrode frame 550 in the fifth embodiment is located on the virtual edge VE of the air gap portion 510 - 1 and the boundary wall 530 - 3 on one side of the second cavity portion 530 - 2 .

[0114] Fig.11 is a cross-sectional view of a sixth embodiment of an air-gap type FBAR 600 according to the present invention.

[0115] Reference Fig.11 The air-gap type FBAR 600 of the sixth embodiment includes a substrate 610, an air-gap portion 610-1, a lower electrode 620, a piezoelectric layer 630, an upper electrode 640, a first electrode frame 650 and a second electrode frame 260 (not shown).

[0116] Here, the functional characteristics of the substrate 610, the air gap portion 610-1, the lower electrode 620, the upper electrode 640 and the second electrode frame are respectively the same as those in the above reference Figure 1 The functional characteristics of the described substrate 110 , the air gap portion 110 - 1 , the lower electrode 120 , the upper electrode 140 , and the second electrode frame are substantially the same or similar.

[0117] Meanwhile, the piezoelectric layer 630 is formed beyond the virtual edge VE to completely surround the air gap portion 610-1. Here, the piezoelectric layer 630 may include a first cavity portion 630-1 having a first piezoelectric cavity formed at a position below the edge portion 640-1 of the upper electrode 640. The functional characteristics of the first cavity portion 630-1 are the same as those of the above reference Figure 8 The functional characteristics of the first cavity portion 330-1 described are the same.

[0118] The piezoelectric layer 630 is formed on the lower electrode 620, and at this time, the edge portion of the piezoelectric layer 630 is formed to be inclined near the virtual edge VE according to the vertical projection of the air gap portion 610-1. In addition, after cutting off the end of a portion of the piezoelectric layer 630 extending beyond the virtual edge VE, an extended piezoelectric layer 630-2 is additionally formed on the substrate 610 on which the lower electrode 620 is not stacked. The extended piezoelectric layer 630-2 is a piezoelectric layer that restarts at a point spaced a predetermined distance from the edge portion of the piezoelectric layer 130 and extends therefrom. In this way, since the extended piezoelectric layer 630-2 is additionally formed on the substrate 610 on which the lower electrode 620 is not stacked, the upper portion (seed layer) of the substrate 610 is prevented from being exposed to the release solution used to form the air gap portion 610-1.

[0119] The first electrode frame 650 has a structure that is the same as or similar to the first electrode frame 150 described above, wherein the first electrode frame 650 corresponds to an electrode frame formed on the lower electrode 620 and has an open loop structure on a plane. An edge portion 650-1 of the first electrode frame 650 is located at a point corresponding to a virtual edge VE of the air gap portion 110-1. However, the first electrode frame 650 is Figure 1 The first electrode frame 650 stacked on the lower electrode 620 and the substrate 110 in FIG. 1 is different in that the first electrode frame 650 is stacked on the piezoelectric layer 630 and the lower electrode 620 and the piezoelectric layer 630 is also stacked on the additionally stacked extended piezoelectric layer 630 - 2 .

[0120] According to the present invention, in the resonator structure, the piezoelectric layer is formed to conform to the edge of the resonator, wherein the first electrode frame is formed on the lower electrode, and the piezoelectric layer and the second electrode frame are formed on the upper electrode. Therefore, the current of the lower electrode and the upper electrode gathers and flows to the first electrode frame and the second electrode frame having low resistance, so that the resistance can be significantly reduced, and in addition to this electrical benefit, the heat generated at high power driving can be easily dissipated in the piezoelectric layer. Therefore, the electrode resistance occurring at the lower electrode and the upper electrode is minimized, thereby improving the quality factor.

[0121] Furthermore, the first electrode frame and the second electrode frame cover the electrodes and thus may serve as a passivation to protect the electrodes.

[0122] Many examples have been described above. However, it should be understood that various modifications may be made. For example, suitable results may be achieved if the described techniques and / or if components in the described systems, architectures, devices, or circuits are combined in different ways and / or replaced or supplemented by other components or their equivalents. Therefore, other implementations are within the scope of the appended claims.

[0123] Reference numerals

[0124] 100, 200, 300, 400, 500, 600: Air-gap FBAR

[0125] 110, 210, 310, 410, 510, 610: substrate

[0126] 110-1, 210-1, 310-1, 410-1, 510-1, 510-1, 610-1: air gap part

[0127] 120, 220, 320, 420, 520, 620: lower electrode

[0128] 130, 230, 330, 430, 530, 630: piezoelectric layer

[0129] 140, 240, 340, 440, 540, 640: upper electrode

[0130] 150, 250, 350, 450, 550, 650: First electrode frame

[0131] 160, 260: second electrode frame.

Claims

1. An air-gap film bulk acoustic resonator, comprising: a substrate including an air gap portion having a substrate cavity formed in a top surface; a lower electrode formed on the substrate; a piezoelectric layer formed on the lower electrode and having one side thereof forming an edge portion near a virtual edge according to a vertical projection of the air gap portion; an upper electrode formed on the piezoelectric layer; a first electrode frame including an open-loop structure in a plane, the open-loop structure surrounding a portion of an outer periphery of the piezoelectric layer on the lower electrode; as well as a second electrode frame positioned on the upper electrode and adjacent to an opening portion of the open-loop structure, wherein the piezoelectric layer further includes a cavity portion, the cavity portion includes a piezoelectric cavity formed between the lower electrode and the upper electrode, and the cavity portion is formed on a lower portion of an edge portion of the upper electrode, wherein the cavity portion is a first cavity portion including a first piezoelectric cavity having an exposed upper surface formed to expose a portion of a lower portion of the edge portion of the upper electrode and a closed lower surface formed not to expose an upper portion of the lower electrode, The piezoelectric layer further includes a second cavity portion, wherein the second cavity portion includes a second piezoelectric cavity formed to be spaced apart from the first cavity portion by a predetermined distance.

2. The air-gap film bulk acoustic resonator according to claim 1, wherein: The open loop structure surrounds a portion of the virtual edge according to the vertical projection of the air gap portion, and the second electrode frame is spaced a predetermined distance from the first electrode frame and surrounds a remaining portion of the virtual edge.

3. The air-gap film bulk acoustic resonator according to claim 2, wherein: The first electrode frame includes the open loop structure formed on the lower electrode and spaced apart from an edge portion of the upper electrode and surrounding the virtual edge.

4. The air-gap film bulk acoustic resonator according to claim 2, wherein: The first electrode frame includes the open loop structure having the edge portion located along the virtual edge.

5. The air-gap film bulk acoustic resonator according to claim 2, wherein: The open loop structure includes two hooks bent at both ends thereof to face each other, and an edge portion of the second electrode frame is located between the hooks.

6. The air-gap film bulk acoustic resonator according to claim 2, wherein: The first electrode frame includes a first frame extension portion, which is formed on the lower electrode extension portion of the lower electrode and extends for connection with the outside.

7. The air-gap film bulk acoustic resonator according to claim 2, wherein: An edge portion of the second electrode frame is positioned along the virtual edge.

8. The air-gap film bulk acoustic resonator according to claim 2, wherein: The second electrode frame includes a second frame extension portion, which is formed on the upper electrode extension portion of the upper electrode and extends for connection with the outside.

9. The air-gap film bulk acoustic resonator according to claim 2, wherein: The first electrode frame is formed on the lower electrode, and when the piezoelectric layer extends beyond the virtual edge and completely surrounds the air gap portion, an edge portion of the first electrode frame is spaced apart from the edge portion of the piezoelectric layer by a predetermined distance.

10. The air-gap film bulk acoustic resonator according to claim 1, wherein: The second piezoelectric cavity has a closed lower surface formed so as not to expose an upper portion of the lower electrode and an exposed upper surface formed so as to allow the entire upper portion to be opened.

11. The air-gap film bulk acoustic resonator according to claim 10, wherein: The first electrode frame includes an edge portion that coincides with a boundary wall of one side of the second piezoelectric cavity when the piezoelectric layer extends beyond the virtual edge and completely surrounds the air gap portion. 12 . The air-gap type film bulk acoustic resonator of claim 1 , further comprising an air bridge including an air cavity formed on one side of the virtual edge according to the vertical projection of the air gap portion.

13. The air-gap film bulk acoustic resonator according to claim 1, wherein: The piezoelectric layer includes the edge portion formed near the virtual edge according to the vertical projection of the air gap portion, and also includes an extended piezoelectric layer, which is spaced apart from the edge portion by more than a predetermined distance and extends, and the first electrode frame is formed on the extended piezoelectric layer as well as on the piezoelectric layer and the lower electrode.

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