CN115250111A - Support structure of bulk acoustic wave resonator - Google Patents

Abstract

Bulk acoustic wave resonators and processes for making the same are described. A stacked structure formed over a substrate includes a piezoelectric thin film member, a first (e.g., bottom) electrode coupled to a first side of the piezoelectric thin film member, and a second (e.g., top) electrode coupled to a second side of the piezoelectric thin film member. A cavity is provided between the stack and the substrate. The resonator includes one or more planarization layers including a first planarization layer surrounding a cavity, wherein a first portion of the first electrode is adjacent the cavity and a second portion of the first electrode is adjacent the first planarization layer. The resonator optionally includes an air reflector around the perimeter of the piezoelectric film member. The stacked structure may resonate an electrical signal applied between the first electrode and the second electrode.

Description

Support structure of bulk acoustic wave resonator

RELATED APPLICATIONS

This application is a partial continuation of U.S. patent application No. 16/455,627, filed on 27.6.2019, which claims priority from U.S. provisional patent application No. 62/701,382 entitled "support structure for bulk acoustic wave resonator", filed on 20.7.2018, which is incorporated by reference in its entirety herein.

Technical Field

Embodiments of the present invention generally relate to bulk acoustic wave resonators, and more particularly, to thin film bulk acoustic resonators having improved manufacturability and reduced thermal resistance.

Background

A Bulk Acoustic Wave (BAW) resonator includes a stacked structure of a bottom electrode, a piezoelectric thin film layer, and a top electrode. (the bottom electrode, the piezoelectric thin film layer, and the top electrode are collectively referred to as a "stacked structure" in the present invention.) when an electrical signal is applied to the top and bottom electrodes, the piezoelectric thin film layer converts the electrical energy of the signal into mechanical energy (also referred to as acoustic energy in the present invention). An oscillating electrical signal applied across the piezoelectric thin film layers causes pressure and/or shear waves to propagate in the body of the BAW stack. The waves in the stacked structure are bulk acoustic waves. The main resonance frequency of the bulk acoustic wave in the stacked structure is determined by the thickness of the piezoelectric film and the electrode layer.

To achieve high performance operation, the resonator stack must be acoustically isolated from the substrate to reduce the leakage of acoustic energy generated by the resonator stack into surrounding structures. Acoustic isolation of the resonator stack is achieved by creating a cavity that separates the resonator stack from the substrate from which it is formed. For example, a resonator stack is fabricated on a silicon oxide sacrificial layer deposited on a silicon substrate. A via hole is provided in the silicon oxide layer, and a metal pillar is formed in the via hole. The silicon oxide layer is etched by a liquid etchant, thereby creating a cavity between the resonator stack and the substrate, leaving the resonator stack suspended on the metal posts. Resonator stack structures suspended over a cavity and supported only by metal posts are prone to stability problems. In addition, the use of a liquid etchant to remove the silicon oxide layer can compromise the circuit components, making these components susceptible to damage by the etchant.

Another prior approach to acoustically isolating resonator stack structures is to etch a cavity in a substrate, fill the cavity with a sacrificial material, form a resonator stack structure over the sacrificial material, remove the sacrificial material, and form a cavity under the resonator stack structure. With this approach, there is a lack of control over cavity depth and shape due to the lack of etch stop layers and the dependence of the etch profile on the crystal.

BAW resonators are typically designed to resonate (and thus act as filters) at a particular frequency. The frequency at which BAW resonators resonate is affected by temperature changes. When BAW resonators resonate, the movement of the resonators generates heat, causing temperature variations that can cause the pass and stop band frequencies of the filter to deviate from specification tolerances.

Disclosure of Invention

Without limiting the scope of the appended claims, after considering this disclosure, and particularly after considering the section "detailed description" one will understand how to use various aspects of the various embodiments to address the above-described issues (e.g., by improving the structural integrity of a BAW stacked structural support structure). For example, using a cavity frame and planarization materials to support the BAW stack structure over the cavity may improve the structural integrity of the resonator. In certain embodiments, one or more components of a BAW resonator described herein (e.g., the cavity frame and/or the heat sink) dissipate heat generated in the resonator stack.

In some embodiments, the bulk acoustic wave resonator includes a stacked structure formed over a substrate, the stacked structure including a piezoelectric thin-film member, a first electrode (e.g., bottom) coupled to a first side of the piezoelectric thin-film member, and a second electrode (e.g., top) coupled to a second side of the piezoelectric thin-film member. A cavity is provided between the stack and the substrate. The resonator further includes one or more planarization layers including a first planarization layer surrounding the cavity, wherein a first portion of the first electrode is adjacent the cavity and a second portion of the first electrode is adjacent the first planarization layer. The stacked structure may resonate for an electrical signal applied between the first electrode and the second electrode.

In some embodiments, the bulk acoustic wave resonator is prepared by a process of forming a layer of sacrificial material on a substrate. The process further comprises the following steps: forming a first planarization layer around the sacrificial material layer, such that the first planarization layer and the sacrificial material layer together form a first planar surface, and forming a stacked structure over the substrate. Forming a stacked structure over a substrate includes: forming a first electrode (e.g., a bottom electrode) over the first planar surface, wherein a first portion of the first electrode is formed on the sacrificial material layer and a second portion of the first electrode is formed on the first planarization layer; forming a piezoelectric thin film member over the first electrode; and forming a second electrode (e.g., a top electrode) over the piezoelectric thin film member. The process further comprises the steps of: at least a portion of the sacrificial material layer is removed to form a cavity between the stacked structure and the substrate. The resulting stacked structure of the bulk acoustic wave resonator may resonate an electric signal applied between the first electrode and the second electrode.

In certain embodiments, the cavity comprises one or more posts supporting the stacked structure, and/or one or more members of the stacked structure have a plurality of perforations that reduce stray wave resonance (e.g., as described in U.S. patent application No. 15/789,109 entitled "rigid acoustic wave resonator with stray resonance suppression" filed on 20/10/2017, which is incorporated by reference herein in its entirety).

Drawings

So that the disclosure can be understood in detail, a more particular description of the disclosure may be had by reference to features of various embodiments, some of which are illustrated in the appended drawings. The drawings, however, illustrate only relevant features of the invention and are therefore not to be considered limiting of the invention, as other effective features may be admitted to the description of the invention.

Figure 1 is a cross-sectional view of a bulk acoustic wave resonator according to some embodiments.

Figure 2 is a layout diagram showing a bulk acoustic wave resonator according to some embodiments.

Fig. 3 is a top view of a cavity frame of a bulk acoustic wave resonator according to some embodiments.

Figure 4 is a top view of a planarized material of a bulk acoustic wave resonator, in accordance with certain embodiments.

Figure 5 is a top view of a heat sink frame of a bulk acoustic wave resonator according to some embodiments.

Figures 6A-6I illustrate a method of forming a bulk acoustic wave resonator (involving etching of sacrificial material to form a cavity) according to some embodiments.

Figures 7A-7B illustrate a process flow diagram for forming a bulk acoustic wave resonator according to some embodiments.

Figure 8A is a cross-sectional view of a bulk acoustic wave resonator according to some embodiments.

Figures 8B-8E are layout diagrams illustrating planarization layers in bulk acoustic wave resonators according to some embodiments.

Figures 9A-9J illustrate a method of fabricating a bulk acoustic wave resonator, including forming one or more planarization layers, according to some embodiments.

Figure 9K illustrates a cross-sectional view of a bulk acoustic wave resonator (with an air reflector formed around the piezoelectric film member) according to some embodiments.

Figure 9L is a layout diagram illustrating various layers of a bulk acoustic wave resonator (with an air reflector formed around the piezoelectric film member) according to some embodiments.

Figures 9M-9N illustrate a method of fabricating a bulk acoustic wave resonator according to some embodiments, including forming one or more piezoelectric layers and an air reflector around a piezoelectric film member.

Figure 9O is a cross-sectional view of a bulk acoustic wave resonator (with an air reflector formed around the piezoelectric film member) according to some embodiments.

Figure 9P is a layout diagram illustrating various layers of a bulk acoustic wave resonator (with an air reflector formed around the piezoelectric film member) according to some embodiments.

Figures 9Q-9R illustrate a method of fabricating a bulk acoustic wave resonator according to some embodiments, including forming one or more planarization layers and an air reflector around a piezoelectric thin-film member.

Figures 10A-10D illustrate a process flow diagram for forming a bulk acoustic wave resonator according to some embodiments.

By convention, the various features shown in the drawings may not be drawn to scale. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. Moreover, some of the figures may fail to describe all of the components of a given system, method, or apparatus. Finally, like reference numerals may be used to denote like features throughout the specification and figures.

Detailed Description

Various embodiments described herein include systems, methods, and/or apparatus for improving BAW resonator performance, structural integrity, and thermal stability.

The present invention has been described in considerable detail to facilitate a thorough understanding of the exemplary embodiments illustrated in the drawings. However, certain embodiments may be practiced without many of these specific details, and the scope of the claims is limited only by the features and aspects specifically enumerated in the claims. In other instances, well-known processes, components, and materials have not been described in detail so as not to unnecessarily obscure aspects of the described embodiments of the invention.

Fig. 1 is a cross-sectional view of a BAW resonator 100 according to some embodiments. The BAW resonator 100 comprises a stacked structure comprising a top electrode 104 coupled to a first side of the piezoelectric layer 102 and a bottom electrode 106 coupled to a second side of the piezoelectric layer 102. The stacked structure resonates an electrical signal applied between the top electrode 104 and the bottom electrode 106.

In certain embodiments, the stacked structure of piezoelectric layer 102, top electrode 104, and bottom electrode 106 is supported relative to substrate 110 by chamber frame 108. The chamber frame 108 is formed by an opening (e.g., a rectangular opening) through the chamber frame 108 such that the chamber frame 108 forms a perimeter around the chamber 114 (as shown in fig. 3). In certain embodiments, the stacked structure is supported relative to the substrate 110 by the planarizing material 112. A top view of the planarization material 112 in the BAW resonator 100 is shown in figure 4. In certain embodiments, the stack is supported by the cavity frame 108 and the planarizing material 112.

The cavity 114 provides a space between the substrate 110 and the stacked structure. The open space under the stacked structure formed by the cavity 114 and the open space above the stacked structure (including the opening 202 in the heat sink 116 shown in fig. 2) allow the stacked structure to freely resonate for electrical signals. The inclusion of the cavity frame 108 and/or the planarization material 112 in the support structure provides a high degree of structural integrity for the portion of the BAW resonator 100 structure that supports the stacked structure suspended above the cavity 114.

In some embodiments, the BAW resonator includes a heat sink 116 coupled to the top electrode 104. Fig. 5 is a top view of the heat sink 116.

In certain embodiments, the chamber frame 108 and/or the heat sink 116 are formed from or include the following materials: high thermal conductivity (e.g., aluminum, gold, copper, silver, or diamond) and/or high electrical conductivity (e.g., aluminum, gold, copper, or silver). The cavity frame 108 and/or heat sink 116, which comprise a high thermal conductivity material, dissipates heat (e.g., the "self-heating" produced by the device when the BAW resonator resonates). This may reduce and/or avoid the temperature-induced frequency shift behavior of the BAW resonator 100. For example, a device that includes a heat sink 116, the heat sink 116 having a thickness greater than the top electrode 106, the heat sink 116 being more electrically conductive than the top electrode 106, provides better heat dissipation than a device that relies on the top electrode 106 to dissipate heat. The cavity frame 108 and/or the heat sink 116 are made of highly conductive materials that reduce the resistance of the device and increase the mass coefficient (Qs) of the device (e.g., increase the performance of the BAW resonator 100 in a filter).

In certain embodiments, the material of the cavity frame 108 may cause the cavity frame 108 to generate an acoustic impedance that is highly inconsistent with the acoustic impedance of the BAW stack structure (e.g., including the top electrode 104, the piezoelectric layer 102, and the bottom electrode 106). The resulting acoustic impedance mismatch between the cavity frame 108 and the BAW stack can reduce acoustic energy leakage at the device edges. In certain embodiments, the material of the heat spreading ring 116 may make the acoustic impedance of the heat spreading ring 116 highly inconsistent with the acoustic impedance of the BAW stack. The resulting acoustic impedance mismatch between the heat spreader ring 116 and the BAW stack can reduce acoustic energy leakage at the device edges.

Fig. 2 is a layout diagram of the BAW resonator 100. The planarization material 112 and piezoelectric layer 102 are omitted from fig. 2 for clarity. A top view of the planarization material 112 is shown in fig. 4.

Fig. 3 is a top view of the cavity frame 108 of the bulk acoustic wave resonator according to some embodiments. In certain embodiments, the cavity frame 108 has an intermediate opening (e.g., a rectangular opening in the cavity frame 108) that extends through the cavity frame layers (e.g., from an upper layer to a lower layer of the cavity frame layers). The sacrificial material deposited on the substrate 110 is removed, thereby forming a cavity 114 in a location corresponding to the cavity frame opening. In certain embodiments, the middle opening of the chamber frame 108 is substantially centered along one or more axes of the chamber frame 108.

Figure 4 is a top view of the planarized material 112 of the bulk acoustic wave resonator described in some embodiments. In some embodiments, planarization material 112 forms a perimeter around cavity frame 108 in planar-type layer 604 (see fig. 6D).

Fig. 5 is a top view of a heat sink 116 of a bulk acoustic wave resonator according to some embodiments. In some embodiments, the heat sink frame 116 has a central opening 202 (e.g., a rectangular opening in the heat sink frame 116) that extends through the heat sink frame 116 (e.g., from the top surface to the bottom surface of the heat sink frame layer). In some embodiments, the intermediate opening 202 is substantially centered along one or more axes of the heat sink 116.

Figures 6A-6I illustrate cross-sectional views of the bulk acoustic wave resonator during the formation of the bulk acoustic wave resonator 100, according to some embodiments, wherein the formation of the bulk acoustic wave resonator 100 involves etching a sacrificial layer material to form the cavity 114.

In fig. 6A, a layer of sacrificial material 602 (e.g., silicon dioxide) is formed (e.g., by chemical vapor deposition) on a substrate 110 (e.g., silicon, glass, ceramic, gallium arsenide, and/or silicon carbide). The sacrificial material is patterned (e.g., using a mask and chemical etching) such that the sacrificial material 602 occupies an area of the substrate 110 corresponding to the final position of the cavity 114.

In fig. 6B, the cavity frame 108 is formed around the sacrificial material 602 (e.g., by e-beam evaporation). The cavity frame 108 is patterned (e.g., using a mask during e-beam evaporation) to form a perimeter around the sacrificial material 602 (see fig. 1-3).

In fig. 6C, a planarization material 112 (e.g., polysilicon) is formed (e.g., by chemical vapor deposition) on the substrate 110, the cavity frame 108, and the sacrificial material 108.

In fig. 6D, planarization material 112 is planarized (e.g., by chemical mechanical polishing) to form a flat upper surface 606 of planar-type layer 604, planar-type layer 604 including planarization material 112, cavity frame 108, and sacrificial material 602. A planar layer 604 is formed on the substrate 110, on top of the substrate 110.

In fig. 6E, the bottom electrode layer 106 (e.g., molybdenum, aluminum, and/or tungsten) is formed (e.g., by physical vapor deposition) over the planar-type layer including the planarization material 112, the cavity frame 108, and the sacrificial material 602. In some embodiments, the bottom electrode layer 106 is patterned (e.g., using a mask during physical vapor deposition) such that the bottom electrode layer 106 occupies the area shown in fig. 2 for the bottom electrode layer 106.

In fig. 6F, a piezoelectric thin film layer 102 (e.g., aluminum nitride and/or zinc oxide) is formed (e.g., by physical vapor deposition) over the bottom electrode layer 106.

In fig. 6G, a top electrode layer 104 (e.g., molybdenum, aluminum, and/or tungsten) is formed over the piezoelectric thin film layer 102. In some embodiments, the top electrode layer 104 is patterned (e.g., using a mask during physical vapor deposition) such that the top electrode layer 104 occupies the area shown in fig. 2 as the top electrode layer 104.

In fig. 6H, a heat sink 116 is formed over the top electrode layer 104 (e.g., by electron beam evaporation). In some embodiments, the heat-sink shelf 116 is patterned (e.g., using a mask during e-beam evaporation) such that the heat-sink shelf 116 occupies the area shown in fig. 2.

In fig. 6I, the cavity 114 is formed by removing the sacrificial material 602 from the bottom of the bottom electrode 106 (e.g., by a vapor HF etch). Vapor HF etching can advantageously reduce the etching time (e.g., compared to liquid HF) and provide a clean surface for the bottom electrode. In certain embodiments, the cavity 114 has a depth and shape corresponding to the cavity frame 108 opening. Thus, forming the cavity frame 108 allows for the formation of a cavity having a predetermined depth and shape.

The bulk acoustic wave resonator 100 formation process 700 (shown below in figures 7A-7B) includes deposition, oxidation, photolithographic patterning, etching, lift-off, and/or chemical mechanical planarization processes (in the appropriate order), as described below. While these sequences of operations and the resulting bulk acoustic wave resonators are entirely new, the techniques required to perform each individual step or operation of these processes are well known in the art and thus the present invention does not detail the individual processing steps or operations. The dashed lines in process 700 illustrate optional operations.

Figures 7A-7B illustrate a flow diagram of a process 700 for forming the bulk acoustic wave resonator 100, according to some embodiments.

A layer of sacrificial material 602 (702) is formed on the substrate 110 (e.g., as shown in fig. 6A).

The cavity frame 108 is formed 704 within a perimeter around the sacrificial material 602 (e.g., as shown in fig. 6B).

A planarization material 112 is formed 706 over the sacrificial material 602 and the cavity frame 108 (e.g., as shown in figure 6C). The planarization material 112 forms a perimeter around the chamber body frame 108.

A portion of the planarization material 112 is removed 708 to form a planar-type layer 604 comprising the sacrificial material 602, the cavity frame 108, and the planarization material 112 (e.g., as shown in fig. 6D). For the upper surface 606 of the planar-type layer 604 opposite the lower planar-type layer surface 608 (coupled to the substrate 110), the upper sacrificial material surface 610 of the sacrificial material 602 is substantially planar with the upper cavity frame surface 612 of the cavity frame 108 and the upper planarization material surface 614 of the planarization material 112 (e.g., as shown in fig. 6D).

A first electrode (bottom electrode 106) is formed 710 over the planarization layer (e.g., as shown in fig. 6E).

A planarizing film member 102 is formed 712 over the first electrode (e.g., as shown in fig. 6F).

A second electrode (top electrode 104) is formed 714 over the planarizing film member 102 (e.g., as shown in figure 6G).

In some embodiments, a heat sink shelf 116 is formed 716 over the second electrode 104 (e.g., as shown in fig. 6H).

In certain embodiments, the heatsink frame 116 includes (718) a central opening 202 through the heatsink frame 116 (e.g., as shown in fig. 1-2).

In certain embodiments, the heat sink 116 includes (720) at least one of the following materials: aluminum, copper, silver, gold, and diamond. In some embodiments, the heat sink 116 is made of one or more materials having a thermal conductivity of at least 200W/(mK) at 20 ℃.

At least a portion of sacrificial material 602 is removed 722 to form cavity 114 (e.g., as shown in fig. 6I).

In certain embodiments, the cavity 114 is bounded 724 by the first electrode 106, the substrate 110, and the cavity frame 108 (e.g., as shown in fig. 2-3 and 6I).

In certain embodiments, the chamber frame 108 may dissipate (726) heat generated by the stacked structure. In certain embodiments, the chamber frame 108 is made of one or more materials having a thermal conductivity of at least 200W/(mK) at 20 ℃.

In certain embodiments, the cavity frame 108 includes (728) at least one of the following materials: aluminum, copper, silver, gold, and diamond.

Thus, according to some embodiments, the bulk acoustic wave resonator 100 may be formed using process 700. As described above, in order to prevent or reduce the formation of parasitic resonators and the loss of acoustic energy, the bottom electrode layer 106 in the BAW resonator 100 is patterned such that the bottom electrode layer 106 occupies the area shown in fig. 2 for the bottom electrode layer 106, e.g., the bottom electrode conductive material is removed from outside the area. The patterned bottom electrode 106 has a non-planarized surface 610, as shown in FIG. 6E, on which a piezoelectric film is deposited, as shown in FIG. 6F. Such a non-planar surface 610 may cause problems in the piezoelectric film 102 at the edge 107 of the bottom electrode 106, making the piezoelectric film 102 susceptible to cracking near the edge 107 of the bottom electrode 106 during subsequent processing and/or end product operations.

Therefore, a special etching method is proposed to form a small angle and smooth edges for the bottom electrode. However, this method is not only difficult to implement in an actual manufacturing process, but also results in the piezoelectric film having a crystal structure near the edge that is not aligned correctly in the vertical direction, thereby degrading the quality of the piezoelectric film near the edge and the performance of the BAW resonator.

In addition, a typical BAW resonator structure deposits a cover piezoelectric film over a substrate (on which a bottom electrode is formed) and leaves the cover piezoelectric film for subsequent processing. Thus, the portion of the piezoelectric film outside the active area of the BAW resonator (e.g., defined as the area where the top electrode, the piezoelectric film, and the bottom electrode overlap) can provide a medium for lateral acoustic waves generated in the resonator, which leaks out of the resonator, thereby causing acoustic energy loss.

Thus, in certain embodiments, after patterning the bottom electrode, a second planarization layer is formed around the patterned bottom electrode, providing a planarized surface thereon, resulting in a high quality and uniformly stressed PZ film. The second planar layer may include a fill material selected from the group of dielectric materials (e.g., polysilicon). In some embodiments, the piezoelectric film is patterned, the outer portion is removed, leaving only the piezoelectric film member in the active area. In certain embodiments, an air reflector is formed around the piezoelectric film member to further reduce acoustic energy leakage.

Figure 8A is a cross-sectional view of a BAW resonator 800 according to some embodiments. The BAW resonator 800 includes a stack structure formed over a substrate 801 and a cavity 810 located between the stack structure and the substrate 801. The stacked structure includes a piezoelectric thin film member 802, a first electrode (or bottom electrode) 806 coupled to a first side (side facing the substrate 801) of the piezoelectric thin film member 802, and a second electrode (top electrode) 804 coupled to a second side (side facing away from the substrate 801) of the piezoelectric thin film member 802. The bulk acoustic wave resonator 800 further includes one or more planarization layers, for example, a first planarization layer 812 surrounding the cavity 810, a second planarization layer 814 surrounding the first electrode 806, and a third planarization layer 816 surrounding the piezoelectric thin-film member 802. The bulk acoustic wave resonator 800 further includes one or more metal contacts 821 electrically coupled to the first electrode 806 and one or more metal contacts 822 electrically coupled to the second electrode 804.

In some embodiments, a first planarization layer 812 is included, providing a first planar surface over which the first electrode 806 is formed during fabrication of BAW resonator 800, and a sacrificial layer occupying the space of cavity 810. In some embodiments, a second planarization layer 814 is included, providing a second planar surface on which the piezoelectric thin-film member 802 is formed during fabrication of the BAW resonator 800. In some embodiments, a third planarization layer 816 is used to provide a third planar surface over which a second electrode is formed during fabrication of BAW resonator 800. In some embodiments, the first portion 806a of the bottom electrode is adjacent to the cavity and the second portion 806b of the bottom electrode is adjacent to the first planarizing layer 812. In certain embodiments, the first planarization layer 812, the second planarization layer 814, and/or the third planarization layer 816 include polysilicon.

In some embodiments, the stacked structure of the piezoelectric thin-film member 802, the top electrode 804, and the bottom electrode 806 is supported relative to the substrate 801 by a first planarization layer 812. A top view of the first planarization layer 812 in BAW resonator 800 is shown in fig. 8B. As shown, the first planarization layer 812 surrounds the cavity 810 and has an inner perimeter that surrounds the cavity 810. In some embodiments, a cavity frame (e.g., cavity frame 108) is also included and formed around the cavity, with a first planarization layer 812 formed around the cavity frame. The first planarizing layer 812 (and the cavity frame, if included) and the sacrificial material occupying the cavity space collectively form a first planar surface over which the first (bottom) electrode 806 is formed during fabrication of the BAW resonator 800, as discussed further below.

A top view of the second planarization layer 814 in the BAW resonator 800 is shown in fig. 8C. As shown, a second planarization layer 814 is formed around the first (bottom) electrode 806, having an inner periphery connected to the outer periphery of the first (bottom) electrode 806. The second planarizing layer 814 cooperates with the first (bottom) electrode 806 to form a second planar surface over which the piezoelectric thin film element 802 is formed, as discussed further below.

A top view of the third planarization layer 816 in the BAW resonator 800 is shown in fig. 8D. The plan view in FIG. 8D shows that the bottom electrode 806 and the second planarization layer 814 surrounding the bottom electrode 806 together provide a planar surface over which the piezoelectric thin-film element 802 is formed.

The plan view in fig. 8E shows that a third planarizing layer 816 is formed around the piezoelectric film member 802, having an inner periphery connected to the outer periphery of the piezoelectric film member 802. The piezoelectric thin-film member 802 and the third planarization layer 816 together provide a third planar surface on which the top electrode 804 is formed. Fig. 8E also illustrates a contact hole 817 for forming a contact 821 in the third planarization layer 816.

In certain embodiments, the stacked structure may resonate for an electrical signal applied between the first electrode 806 and the second electrode 804. The cavity 810 provides a space between the substrate 801 and the stacked structure, allowing the stacked structure to freely resonate for electrical signals. In certain embodiments, first planarization layer 812 (with or without a cavity frame) forms a support structure that provides a high degree of structural integrity for BAW resonator 800 structure to support the portion of the stacked structure suspended above cavity 810.

Figures 9A-9J illustrate cross-sectional views of various layers of the bulk acoustic wave resonator 800 during the formation of the bulk acoustic wave resonator 800, in accordance with certain embodiments.

In fig. 9A, a layer of sacrificial material 902 (e.g., silicon dioxide) is formed (e.g., by chemical vapor deposition) on a substrate 801 (e.g., silicon, glass, ceramic, gallium arsenide, and/or silicon carbide). The sacrificial material is patterned (e.g., using a mask and chemical etch) such that the layer of sacrificial material 602 occupies the cavity 810 space on the substrate 801.

In fig. 9B, a first planarization layer 812 is formed by depositing (e.g., using chemical vapor deposition) a dielectric material (e.g., polysilicon) over the substrate 110 and the sacrificial material 902, and then planarizing (e.g., by chemical mechanical polishing) the first planarization layer 812 to form a first planar surface 910 with the sacrificial material 902. A first planarization layer 812 is formed on the substrate 801, on top of the substrate 801.

In fig. 9C, the bottom electrode layer 806 is formed over the first planar surface 910 (e.g., by physical vapor deposition), wherein a first portion of the bottom electrode 806 is formed on the sacrificial material layer and a second portion of the bottom electrode 806 is formed on the first planarization layer. In some embodiments, the bottom electrode layer 806 is patterned (e.g., using a lift-off process) such that the bottom electrode 806 occupies the area shown in the bottom electrode layer 806 in FIG. 9C.

In fig. 9D, a second planarization layer 814 is formed by depositing (e.g., using chemical vapor deposition) a dielectric material (e.g., polysilicon) over the bottom electrode 806 and the first planarization layer 812, and then planarizing (e.g., by chemical mechanical polishing) the second planarization layer 814 to form a second planar surface 920 in cooperation with the bottom electrode 806.

In fig. 9E, a layer of piezoelectric material 902 (e.g., aluminum nitride and/or zinc oxide) is formed (e.g., by physical vapor deposition) over the second planar surface layer 920.

In fig. 9F, the piezoelectric material 902 layer is patterned (e.g., by anisotropic etching) to form the piezoelectric thin film member 802.

In fig. 9G, a third planarization layer 816 is formed by depositing (e.g., using chemical vapor deposition) a dielectric material (e.g., polysilicon) on the piezoelectric thin-film member 802 and the second planarization layer 814, and then planarizing (e.g., by chemical-mechanical polishing) the third planarization layer 816 to form a third planar-type surface 930 in cooperation with the piezoelectric thin-film member 802.

In fig. 9H, a top electrode layer 804 (e.g., molybdenum, aluminum, and/or tungsten) is formed over the piezoelectric thin film member 802. In some embodiments, the top electrode layer 804 is patterned (e.g., using a lift-off process) such that the top electrode layer 804 occupies the area shown in fig. 9H for the bottom electrode layer 804. As shown in fig. 9H, a first portion 816a of the third planarization layer 816 is adjacent to the first electrode 806 and not adjacent to the second electrode 804, and a second portion 816b of the third planarization layer 816 is adjacent to the second electrode 804 and not adjacent to the first electrode 806.

In FIG. 9I, one or more contact holes 817 are etched in the third planarization layer 816, exposing a portion of the bottom electrode 806 at the bottom of each contact hole 817.

In FIG. 9J, one or more metal contacts 821 electrically coupled to the first electrode 806 and one or more metal contacts 822 electrically coupled to the second electrode 804 are formed. The cavity 810 is then formed by removing the sacrificial material 902 (e.g., by vapor HF etching) from the bottom of the bottom electrode 806. Vapor HF etching can advantageously reduce the etching time (e.g., compared to liquid HF) and ensure that the bottom electrode surface facing the chamber is clean.

Thus, in BAW resonator 800, the layer of piezoelectric material 902 outside the active resonator is removed and a third planarized layer 816 of filler material (e.g., polysilicon) is used to provide a third planar surface 930, according to some embodiments. This filler material is chosen because it has a large difference in acoustic impedance from the piezoelectric material, and thus acts as an "acoustic mirror" that confines the acoustic energy within the active BAW resonator 800.

Figure 9K is a cross-sectional view of a BAW resonator 950 according to some embodiments. As shown in fig. 9K, the BAW resonator 950 corresponds to the BAW resonator 800 except that an inner portion of the third planarization layer 816 adjacent to the piezoelectric thin-film member 802 and/or an outer portion of the piezoelectric thin-film member 802 adjacent to the third planarization layer 816 are removed, thereby forming an air reflector 955 around the piezoelectric thin-film member 802. The air reflector 955 functions to eliminate or further reduce acoustic energy leakage from the edges of the piezoelectric film member 802.

Fig. 9L is a plan view showing a BAW resonator 950 in which an air reflector 955 is formed around the piezoelectric thin-film member 802.

Figures 9M-9N illustrate cross-sectional views of different layers of the bulk acoustic wave resonator 950 during air reflector formation according to some embodiments.

In fig. 9M, after forming the third planarization layer 816 (as shown in fig. 9G) and before forming the top electrode 804 (as shown in fig. 9H), an anisotropic etching process is used to remove the interior of the third planarization layer 816 adjacent to the piezoelectric thin film member 802 or the exterior of the piezoelectric thin film member 802 adjacent to the third planarization layer 816, resulting in a gap 951 between the piezoelectric thin film member 802 or the remaining portion thereof and the third planarization layer 816 or the remaining portion thereof.

In fig. 9N, the gap 951 (e.g., the same sacrificial material 902 that fills the space of the cavity 810) is filled with the sacrificial material 952 by chemical vapor deposition of the sacrificial material over the piezoelectric film member 802 and the third planarization layer 816, and then the sacrificial material on the top surfaces of the piezoelectric film member 802 and the third planarization layer 816 is removed by chemical mechanical polishing, leaving the sacrificial material 952 in the gap 951. The piezoelectric thin film member 802, the third planarizing layer 816, and the sacrificial material 952 collectively provide a third planar surface 930, and the top electrode 804 is formed over the third planar surface 930, as shown in FIG. 9H. Contacts 821, 822 can then be formed, as shown in fig. 9I-9J, and sacrificial material 952 can be removed using the same process as sacrificial material 902, thereby forming air reflectors 955 around piezoelectric film member 802, as shown in fig. 9O-9P.

Figure 9O is a cross-sectional view of a BAW resonator 960 according to some embodiments. As shown in fig. 9O, a BAW resonator 960 corresponds to the BAW resonator 950, except that the BAW resonator 960 does not include the third planarization layer 816, and an air reflector 965 is formed in the cover piezoelectric thin film layer, dividing the cover piezoelectric thin film layer into the piezoelectric thin film member 802 in the middle and the piezoelectric filler 903 surrounding the piezoelectric thin film member 802. The air reflector 965 may still function to eliminate or further reduce acoustic energy leakage from the edge of the piezoelectric film member 802.

Fig. 9P is a plan view showing a BAW resonator 960 forming an air reflector 965 around a piezoelectric film member 802 and separating the piezoelectric film member 802 from a piezoelectric filler 903 around the piezoelectric film member 802.

Figures 9Q-9R illustrate cross-sectional views of different layers of the bulk acoustic resonator 960 during the formation of the air reflector 965 in accordance with certain embodiments.

In fig. 9Q, after the piezoelectric material 902 layer is formed, as shown in fig. 9E, a gap 961 is etched in the piezoelectric material 902 layer using an anisotropic etching process, separating a middle portion of the piezoelectric material 902 layer (to become the piezoelectric thin film member 802) and an outer portion of the piezoelectric material 902 layer (to become the piezoelectric filler 903).

In fig. 9R, the gap 961 is filled with a sacrificial material 962 (e.g., the same sacrificial material 902 that fills the space of the cavity 810). The top electrode 804 and contacts 821, 822 can then be formed, as shown in FIGS. 9H-9J, and the sacrificial material 962 can be removed in the same process as the sacrificial material 902, thereby forming an air reflector 965 around the piezoelectric thin film member 802.

Figures 10A-10D illustrate a process 1000 for forming a BAW resonator (including one or more planarization layers) according to some embodiments. Process 1000 includes deposition, oxidation, lithographic patterning, etching, lift-off, and/or chemical mechanical planarization processes (in appropriate order), as described below. While these sequences of operations and the resulting bulk acoustic wave resonators are entirely new, the techniques required to perform each individual step or operation of these processes are well known in the art and thus the present invention does not detail the individual processing steps or operations. The dashed lines in process 1000 illustrate optional operations.

As shown in fig. 10A, the process 1000 includes forming 1002 a layer of sacrificial material 902 (e.g., as shown in fig. 9A) or 602 (e.g., as shown in fig. 6A) on the substrate 801, and optionally forming 1003 a cavity frame 108 (e.g., as shown in fig. 6B) in the perimeter around the sacrificial material 602.

The process 1000 further includes forming 1004 a first planarizing layer 812 around the layer of sacrificial material 902 (e.g., as shown in fig. 9B). In some embodiments, forming (1004) includes depositing (1006) a first layer of dielectric material (e.g., polysilicon) over the sacrificial material 902 and the exposed surface of the substrate 801 and planarizing (1008) the first layer of dielectric material to form a first planarizing layer 812. Thus, the first planarization layer 812 is formed to provide, in conjunction with the layer of sacrificial material 902, a first planar surface 910 (e.g., as shown in fig. 9B).

The process 1000 further includes forming 1010 a first electrode (bottom electrode 806) over the first planar surface 910 (e.g., as shown in fig. 9C).

The process 1000 further includes forming 1012 a second planarizing layer 814 around the first electrode 806 (e.g., as shown in fig. 9D). In some embodiments, forming (1012) includes depositing (1014) a second layer of dielectric material (e.g., polysilicon) over the bottom electrode 806 and the exposed portion of the first planar surface 910, and planarizing (1016) the second layer of dielectric material to form the second planarizing layer 814. Thus, the second planarization layer 814 is formed to provide a second planar surface 920 in cooperation with the bottom electrode 806 (e.g., as shown in FIG. 9D).

Process 1000 further includes depositing 1018 a layer of piezoelectric material 902 on the second planar surface 920 (e.g., as shown in fig. 9E).

As shown in fig. 10B, to form BAW resonator 800 or BAW resonator 950, process 1000 further includes forming a pattern on the layer of piezoelectric material 902 (1020), removing an outer portion of the layer of piezoelectric material 902, wherein a remaining portion of the layer of piezoelectric material 902 becomes the piezoelectric thin film member 802 over the bottom electrode 806, forming (1022) a third planarizing layer 816 around the piezoelectric thin film member 802 (e.g., as shown in fig. 9G). In certain embodiments, forming (1022) includes depositing (1024) a third layer of dielectric material over piezoelectric thin-film member 802 and second planar surface 920, and planarizing the third layer of dielectric material to form third planarized layer 816. Thus, the third planarization layer 816 is formed to provide, in conjunction with the piezoelectric film member 802, a third planar surface 930 (e.g., as shown in fig. 9G).

As shown in fig. 10B, an air reflector 955 can optionally be formed in the BAW resonator 950, and the process 1000 can further include forming (1028) a gap 951 around the piezoelectric thin film member by removing an interior portion of the third planarization layer or an exterior portion of the piezoelectric thin film member (e.g., as shown in fig. 9M), depositing (1030) a layer of sacrificial material over the third planar surface 930 to fill the gap 951, and removing (1032) portions of the sacrificial material outside the gap, leaving the sacrificial filler 952 in the gap 951 (e.g., as shown in fig. 9N).

The process 1000 further includes forming 1034 a second electrode (top electrode 804) over the piezoelectric thin film member 802 (e.g., as shown in fig. 9H), forming 1036 contact holes 817 in the third planarizing layer 816, exposing a portion of the bottom electrode 806 at the bottom of each contact hole 817 (e.g., as shown in fig. 9I), depositing 1038 (e.g., by physical vapor deposition) a metal layer over the second electrode 804 and exposed surfaces of the third planarizing layer 816 and the first electrode 806, the metal layer filling one or more of the contact holes 817, forming a pattern 1040 (e.g., by anisotropic etching) on the metal layer, thereby forming the first contact 821 and the second contact 822 (e.g., as shown in fig. 9J).

As shown in fig. 10C, to form the BAW resonator 960, the process 1000 further includes, after depositing 1018 a layer of piezoelectric material 902 on the second planar surface 920, etching 1042 the layer of piezoelectric material 902 to form the piezoelectric thin film member 802 and a gap around the piezoelectric thin film member 802, rather than removing an outer portion of the layer of piezoelectric material 902. The piezoelectric film member 802 is separated from the piezoelectric filler 903 forming the outside of the layer of piezoelectric material 902 by a gap 961 (e.g., as shown in fig. 9Q). Piezoelectric filler 903 serves as a third planarization layer for BAW resonator 960, similar to third planarization layer 816 of BAW resonator 950. The process 1000 further includes depositing (1044) a layer of sacrificial material on the layer of piezoelectric material 902 to fill the gaps 961 and removing (1032) portions of the sacrificial material outside the gaps using chemical mechanical polishing, leaving the sacrificial filler 962 in the gaps 961 of the third planarizing layer 816 (e.g., as described in fig. 9Q and 9R).

Process 1000 further includes forming 1048 a second electrode (top electrode 804) over piezoelectric film member 802 (e.g., as shown in fig. 9R), forming 1050 contact holes 817 in piezoelectric fill 903, exposing a portion of bottom electrode 806 at the bottom of each contact hole 817, depositing 1052 (e.g., by physical vapor deposition) a metal layer over second electrode 804 and the exposed surfaces of piezoelectric film member, piezoelectric fill 903, and first electrode 806, the metal layer filling one or more contact holes 817, forming a pattern 1054 (e.g., by anisotropic etching) over the metal layer, thereby forming first contact 821 and second contact 822 (e.g., as shown in fig. 9O).

As shown in fig. 10D, to form any of BAW resonators 800, 950, and 960, process 1000 further includes removing 1056 the sacrificial material to form cavities 810 (for BAW resonators 800, 950, and 960) and air reflectors 955 (for BAW resonator 950) or 965 (for BAW resonator 960).

At least a portion of the sacrificial material 902 is removed 1056 to form the cavity 810 (e.g., as shown in fig. 9J). In some embodiments, the cavity 810 is bounded by the first electrode 806, the substrate 801, and the first planarization layer 812 or the cavity frame 108 (if present) (e.g., as shown in FIGS. 8A-8E, 9J, 9K-9L, and 9O-9P).

Removing (1056) at least a portion of the sacrificial filler 952 or 962 forms an air reflector 955 or 965, respectively (e.g., as shown in fig. 9K or 9O).

It will be understood that, although the present invention may be described using the terms "first," "second," etc. to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the claims in any way. In the description of the embodiments and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. It is also to be understood that, as used herein, the term "and/or" refers to and includes any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

In the present invention, the term "if" can be interpreted as "when" or "via" or "corresponding determination" or "according to determination" or "corresponding detection" depending on the context and the prerequisite is true. Also, depending on the context and the prerequisite is true, the phrase "if [ the prerequisite is determined to be true ]" or "if [ the prerequisite is true ]" or "when [ the prerequisite is true ]" may be interpreted as "determined" or "corresponding determined" or "according to a determination" or "detected" or "corresponding detected".

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be exhaustive or to limit the claims to the precise forms disclosed. Many modifications and variations of the present invention are possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of operation and the practical application, thereby enabling others skilled in the art to best utilize the invention.

Claims (20)

1. A bulk acoustic wave resonator comprising:

a stack formed over a substrate, the stack comprising:

a piezoelectric thin film member;

a first electrode (bottom electrode) coupled to the first face of the piezoelectric thin-film member; and

a second electrode (top electrode) coupled to the second face of the piezoelectric thin-film member;

a cavity between the stack and the substrate; and

one or more planarization layers including a first planarization layer surrounding the cavity, wherein a first portion of the first electrode is adjacent the cavity and a second portion of the first electrode is adjacent the first planarization layer;

wherein the stacked structure may resonate an electrical signal applied between the first electrode and the second electrode.

2. The bulk acoustic wave resonator according to claim 1, wherein:

forming the first electrode on a first planar surface provided by a first planarization layer and a sacrificial layer; and

after the stacked structure is formed, the cavity is formed by removing the sacrificial layer, the cavity being bounded by the first electrode, the substrate and the first planarizing layer.

3. The bulk acoustic wave resonator according to claim 1, wherein the first planarization layer comprises polysilicon.

4. The bulk acoustic wave resonator according to claim 1, wherein:

the one or more planarization layers further include a second planarization layer surrounding the first electrode; and

the second planarization layer and the first electrode together provide a second planar surface over which the piezoelectric thin film member is formed.

5. The bulk acoustic wave resonator according to claim 1, further comprising an air reflector surrounding the piezoelectric film member.

6. The bulk acoustic wave resonator according to claim 4, wherein the second planarization layer comprises polysilicon.

7. The bulk acoustic wave resonator according to claim 4, further comprising a third planarization layer surrounding the piezoelectric thin film member, wherein the third planarization layer and the piezoelectric thin film member together provide a third planar surface over which the second electrode is formed.

8. The bulk acoustic wave resonator according to claim 7, wherein the first portion of the third planarization layer is adjacent to the first electrode and not adjacent to the second electrode, and the second portion of the third planarization layer is adjacent to the second electrode and not adjacent to the first electrode.

9. The bulk acoustic wave resonator according to claim 8, further comprising a contact hole through the first portion of the third planarization layer and a metal contact filling the contact hole and electrically coupled to the first electrode.

10. The bulk acoustic wave resonator according to claim 7, further comprising an air reflector located between at least a portion of the third planarization layer and the piezoelectric thin-film member.

11. A bulk acoustic wave resonator prepared by a process comprising the steps of:

forming a layer of sacrificial material on a substrate;

forming a first planarization layer around the sacrificial material layer, so that the first planarization layer and the sacrificial material layer form a first planar surface together;

forming a stacked structure over a substrate, comprising:

forming a first electrode (bottom electrode) over the first planar surface, wherein a first portion of the first electrode is formed on a sacrificial material layer and a second portion of the first electrode is formed on a first planarization layer;

forming a piezoelectric thin film member over the first electrode; and

forming a second electrode (top electrode) over the piezoelectric thin-film member; and

removing at least a part of the sacrificial material layer to form a cavity between the stacked structure and the substrate;

wherein the stacked structure may resonate an electric signal applied between the first electrode and the second electrode.

12. The bulk acoustic wave resonator according to claim 11, wherein forming the first planarization layer comprises:

depositing a first layer of dielectric material over the layer of sacrificial material and the exposed surface of the substrate; and

planarizing a first layer of dielectric material to form a first planarizing layer, wherein the first planarizing layer and the layer of sacrificial material together form a first planar surface; and

wherein the cavity formed after removal of the layer of sacrificial material is bounded by the first electrode, the substrate and the first planarizing layer.

13. The bulk acoustic wave resonator according to claim 11, wherein the first planarization layer comprises polysilicon.

14. The bulk acoustic wave resonator according to claim 11, wherein the process further comprises forming a second planarization layer around the first electrode after forming the first electrode and before forming the piezoelectric thin-film member, comprising the steps of:

depositing a second layer of dielectric material over the first electrode and the exposed portion of the first planar surface; and

planarizing the first layer of dielectric material to form a second planarizing layer, wherein the second planarizing layer and the first electrode form a second planar surface;

wherein the piezoelectric thin film member is formed on the second planar surface.

15. The bulk acoustic wave resonator according to claim 14, wherein forming the piezoelectric thin film member comprises:

depositing a layer of piezoelectric material on the second planar surface;

etching a recess in the piezoelectric material layer around a portion of the piezoelectric material layer, wherein a portion of the piezoelectric material layer forms the piezoelectric thin film member; and

filling the grooves with a sacrificial filler; and

wherein the sacrificial filler and at least a portion of the sacrificial material layer are removed to form an air reflector around the piezoelectric film member after the stacked structure is formed.

16. The bulk acoustic wave resonator according to claim 14, wherein the second planarization layer comprises polysilicon.

17. The bulk acoustic wave resonator according to claim 14, wherein forming the piezoelectric thin-film member comprises:

depositing a layer of piezoelectric material on the second planar surface;

removing the exterior of the piezoelectric material layer, wherein the remaining portion of the piezoelectric material forms a piezoelectric thin film member; and

wherein the process further comprises forming a third planarization layer around the piezoelectric thin film member, comprising the steps of:

depositing a third layer of dielectric material over the piezoelectric thin film member and the exposed portion of the second planar surface; and

planarizing the third layer of dielectric material, wherein remaining portions of the third layer of dielectric material and the piezoelectric film member collectively form a third planar surface.

18. The bulk acoustic wave resonator according to claim 17, wherein the first portion of the third planarization layer is adjacent to the first electrode and not adjacent to the second electrode, and the second portion of the third planarization layer is adjacent to the second electrode and not adjacent to the first electrode.

19. The bulk acoustic wave resonator according to claim 18, wherein the process further comprises, after forming the second electrode, forming a first metal contact coupled to the first electrode, forming a second metal contact coupled to the second electrode, comprising:

etching one or more contact holes through a first portion of the third planarization layer;

depositing a metal layer over the second electrode and exposed surfaces of the third planarization layer and first electrode, the metal layer filling one or more contact holes; and

the metal layer is patterned to form a first metal contact and a second metal contact.

20. The bulk acoustic wave resonator according to claim 19, wherein the process further comprises the steps of:

etching a remaining portion of the third planarization layer to form a gap between the piezoelectric thin film member and the third planarization layer; and

filling the gap with a sacrificial filler; and

wherein the sacrificial filler and at least a portion of the sacrificial material layer are removed to form an air reflector around the piezoelectric film member after the stacked structure is formed.

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