Bulk acoustic wave structure with heat dissipation structure and method of making same

Abstract

A bulk acoustic wave (BAW) device includes a transducer die (103, 205), a heat dissipation layer (206), and a molding layer (210). The transducer die includes a BAW transducer (112, 222) and is mounted on a circuit (118) on a first surface of the transducer die. The heat dissipation layer (206) is thermally coupled to the transducer die on a second surface of the transducer die, optionally through an adhesive layer (204). The molding layer encapsulates the transducer die and the heat dissipation layer.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 488,928, filed on March 7, 2023, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to bulk acoustic wave (BAW) structures. In particular, the present disclosure relates to BAW structures having a heat dissipation structure stacked above a BAW (eg, transducer) die and methods for forming the BAW structures. Background Art

[0004] Acoustic filters, such as, in particular, bulk acoustic wave (BAW) resonators or BAW filters, are used in high-frequency communication applications, such as third-generation (3G), fourth-generation (4G), and fifth-generation (5G) wireless devices. In particular, BAW filters are typically used to provide a flat passband, a steep filter skirt, and square shoulders at the upper and lower ends of the passband, and provide excellent rejection outside the passband in the filter network. BAW filters also have relatively low insertion loss, tend to decrease in magnitude with increasing operating frequency, and are relatively stable over a wide temperature range. These wireless devices typically support various communication methods, such as cellular, wireless fidelity (Wi-Fi), Bluetooth, and / or near-field communication, and therefore require the high performance of BAW filters.

[0005] For example, the electrical performance of radio frequency (RF) BAW filters is sensitive to temperature. Specifically, the electrical performance of BAW filters can vary with frequency and can typically degrade in loss / resonator Q factor as temperature increases. When BAW filters operate at high RF power, inherent power dissipation and the resulting self-heating become major limiting factors in the electrical design of BAW filters. Furthermore, the effective thermal resistance from the BAW filter to the corresponding ambient background (e.g., a heat sink) can be a key design parameter to minimize.

[0006] Therefore, there is a need to provide better thermal control in BAW structures. Summary of the Invention

[0007] Aspects of the present disclosure include a BAW device. The BAW device includes a transducer die having a BAW transducer, the transducer die mounted on a circuit on a first surface of the transducer die. The BAW device also includes a heat dissipation layer thermally coupled to the transducer die on a second surface of the transducer die. The BAW device further includes a molding layer that encapsulates the transducer die and the heat dissipation layer.

[0008] In some embodiments, the thermal conductivity of the heat dissipation layer is equal to or greater than 10 W / (m·K), and the resistivity of the heat dissipation layer is equal to or greater than 1000 Ω·cm.

[0009] In some embodiments, the resistivity of the heat dissipation layer is greater than 5000 Ω·cm.

[0010] In some embodiments, the heat dissipation layer comprises silicon.

[0011] In some embodiments, the BAW device further includes an adhesive layer in contact with the transducer die and the heat dissipation layer. The heat dissipation layer can be thermally coupled to the transducer die through the adhesive layer.

[0012] In some embodiments, the adhesive layer has a thermal conductivity equal to or greater than 0.5 W / (m·K) and a resistivity equal to or greater than 1 Ω·cm.

[0013] In some embodiments, the adhesive layer is non-conductive.

[0014] In some embodiments, the adhesive layer comprises an epoxy resin.

[0015] In some embodiments, the BAW device further includes a second transducer die mounted on the circuit on the first surface of the second transducer die. The heat dissipation layer may be thermally coupled to the second transducer die on the second surface of the second transducer die through the adhesive layer. The molding layer may encapsulate the second transducer die.

[0016] In some embodiments, the second transducer die is directly adjacent to the transducer die.

[0017] In some embodiments, the second transducer die and the transducer die operate at different audio frequencies.

[0018] In some embodiments, the BAW device further includes a cover layer in contact with the heat dissipation layer and the molding layer. The thermal conductivity of the cover layer is equal to or greater than 50 W / (m·K), and the resistivity of the cover layer is equal to or lower than 1.0 -6 Ω·m.

[0019] In some embodiments, the cover layer comprises metal.

[0020] Aspects of the present disclosure provide a method for forming a BAW device. The method may include attaching an adhesive layer to a first surface of a transducer die. The transducer die includes a BAW transducer. The method may also include: bonding the transducer die to circuitry on a second surface of the transducer die; attaching a heat dissipation layer to the adhesive layer such that the heat dissipation layer is thermally coupled to the transducer die; and forming a molding layer that encapsulates the transducer die and the heat dissipation layer.

[0021] In some embodiments, attaching the adhesive layer to the first surface of the transducer die comprises attaching an adhesive material layer to a transducer die layer. The transducer die layer comprises the BAW transducer. Attaching the adhesive layer further comprises cutting the adhesive material layer and the transducer die layer together to form the transducer die having the BAW transducer and the adhesive layer.

[0022] In some embodiments, the bonding of the transducer die comprises flip-chip bonding.

[0023] In some embodiments, the method further includes grinding the mold layer so that the surface of the heat dissipation layer is coplanar with the surface of the mold layer. In some embodiments, the method further includes attaching a second transducer die to the adhesive layer on the first surface of the second transducer die. The second transducer die includes a second BAW transducer. The method may also include bonding the second transducer die to the circuit on the second surface of the second transducer die in the same process as bonding the transducer die to the circuit.

[0024] In some embodiments, forming the transducer die, the second transducer die, and the bonding layer includes cutting the transducer die layer having the BAW transducer and the second BAW transducer to form the transducer die and the second transducer die, and attaching the transducer die and the second transducer die to the bonding layer.

[0025] In some embodiments, the method further includes plating a metal layer covering the transducer die and the molding layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 An exemplary BAW structure according to an embodiment of the present disclosure is described.

[0027] Figure 2 Another exemplary BAW structure according to an embodiment of the present disclosure is described.

[0028] Figure 3A flow chart illustrating an exemplary fabrication process for forming a BAW structure according to an embodiment of the present disclosure.

[0029] Figures 4A to 4C Illustrated are cross-sectional views of a BAW structure at different stages of an exemplary fabrication process according to an embodiment of the present disclosure.

[0030] Figure 5 A cross-sectional view illustrating another BAW structure at one stage of an exemplary fabrication process according to an embodiment of the present disclosure.

[0031] Figure 6 Simulation results showing temperature distribution in various BAW structures according to embodiments of the present disclosure are described. DETAILED DESCRIPTION

[0032] The following specific embodiments are illustrative in nature and are not intended to limit the scope, applicability or configuration of the embodiments of the invention disclosed herein in any way. On the contrary, the following embodiments provide actual examples, and those skilled in the art will recognize that some of the examples may have suitable alternatives. The following embodiments will be described in conjunction with the accompanying drawings, which are not drawn to scale (unless otherwise indicated), in which the same numbers / letters represent the same elements. However, it should be understood that the use of numbers to refer to components in a given figure is not intended to limit the components marked with the same numbers in another figure. In addition, the use of different numbers to refer to components in different figures is not intended to indicate that different numbered components cannot be the same or similar to other numbered components. Examples of construction, materials, dimensions and manufacturing processes are provided for selected elements, and all other elements adopt construction, materials, dimensions and manufacturing processes known to those skilled in the art.

[0033] As used herein, the term "approximately" refers to a value of a given amount that may vary based on a particular technology node associated with a semiconductor device. Based on the particular technology node, the term "approximately" may refer to a value of a given amount that varies within, for example, 10-30% of the value (e.g., ±10%, ±20%, or ±20%, or ±30% of the value).

[0034] Reference will now be made in detail to various embodiments of the presently disclosed subject matter, some of which are illustrated in the accompanying drawings.

[0035] BAW filters, especially in flip-chip technology, are subject to two competing design requirements: 1) the design requirement of small size; and 2) the design requirement of thermal control. In such BAW filters, the BAW filter chip is typically bonded (e.g., in a face-down configuration) to the filter circuit via bonding contacts (or laminate bump connections). The main interface of the electrical connection, i.e., the bonding contacts, is also required for heat dissipation functions. In addition, the bonding contacts usually implement sensitive off-chip inductors, which limits the ability to provide high heat transfer in the vertical direction to sink heat from the BAW filter chip through the bonding contacts to a substrate (e.g., a motherboard or the like) connected to a background heat sink. One option to overcome this problem is to enlarge the size of the BAW filter to increase the area of ​​the bonding contacts in order to increase the area of ​​the thermal and electrical connections. However, this approach has a huge penalty in cost and is not a desired solution for size and cost sensitive products (such as mobile applications).

[0036] Embodiments of the present disclosure provide BAW structures with heat dissipation structures. The BAW structures each include a BAW die having a transducer. The heat dissipation structure provides an additional heat dissipation path parallel to the bonding contacts, thereby improving the thermal and electrical performance of the BAW structure. Components in the heat dissipation structure can connect the BAW die to a global / ambient background, which has an ideal low thermal resistance. An additional heat dissipation path can be created. The BAW die is bonded to a filter circuit on one surface by flip-chip bonding. A heat dissipation structure comprising an adhesive layer, a heat dissipation layer, and an optional cover layer is stacked above the BAW die on another surface. The adhesive layer and the heat dissipation layer each include a material with high thermal conductivity and high resistivity, while the cover layer includes a material with high thermal conductivity and high electrical conductivity. The materials of the adhesive layer, the heat dissipation layer, and the cover layer can improve the heat dissipation from the BAW die while maintaining the ideal low electrical losses of the BAW structure. In some embodiments, the heat dissipation layer is thermally coupled to the BAW die via the adhesive layer and is in contact with the cover layer. The heat generated in the BAW die can be conducted away through the heat dissipation path formed by the adhesive layer, heat dissipation layer and cover layer.

[0037] In some embodiments, in addition to the BAW die, the heat dissipation structure also includes one or more other devices. In addition to the BAW die, the adhesive layer may be thermally coupled to one or more other devices so that the heat dissipation is thermally coupled to one or more other devices including the BAW die. The one or more other devices may include any suitable device having a temperature lower than that of the BAW die when the BAW die is in operation. The one or more other devices and the adhesive layer may provide another heat dissipation path so that the heat generated by the BAW die can be conducted to the filter circuit through the bonding contacts of the one or more other devices. In some embodiments, the one or more other devices include another BAW die adjacent to the BAW die. For example, the other BAW die may operate at a different frequency from the BAW die, so that the other BAW die and the BAW die are driven by electricity at different times. Therefore, when the BAW die is in operation (for example, driven by electricity), the other BAW die may have a lower temperature than the BAW die. In some embodiments, the heat dissipation layer also spans to cover one or more devices to improve the heat dissipation of the BAW die. In various embodiments, a structure / device (eg, a heat dissipation layer, a cover layer, and / or one or more other devices) thermally coupled to the BAW die via an adhesive layer may serve as an additional heat sink for the BAW die.

[0038] The BAW structure can be formed by attaching an adhesive layer to the BAW die (and one or more other devices) and bonding the BAW die (and one or more other devices) to the filter circuit via flip-chip bonding. A heat dissipation layer is then mounted on the adhesive layer. A mold layer is formed to encapsulate the BAW die, adhesive layer, and heat dissipation layer (and one or more other devices). The mold layer is then machined so that the top surfaces of the mold layer and the heat dissipation layer are coplanar. A cover layer is then formed to cover the heat dissipation layer and the mold layer. The cover layer can be formed by a suitable process, such as plating and / or sputtering.

[0039] Figure 1 A BAW structure 100 having a heat dissipation structure according to some embodiments is illustrated. The BAW structure 100 may include a transducer die 103, circuitry 118 bonded to the transducer die 103 on a first surface of the transducer die 103, and a heat dissipation structure 109 thermally coupled to the transducer die 103 on a second surface of the transducer die 103. The BAW structure 100 may also include a mold layer 110 that encapsulates at least a portion of the transducer die 103 and the heat dissipation structure 109. Arrows indicate the direction of heat dissipation or heat sink paths.

[0040] The transducer die 103 may include a transducer layer 112 and a base layer 102 on the transducer layer 112. The base layer 102 may include any suitable material that provides a base and support for forming the transducer layer 112. In some embodiments, the base layer 102 includes one or more of silicon, glass, plastic, and / or carbon. For example, the base layer 102 may include silicon and may be a thinned silicon substrate. The transducer layer 112 may have a multilayer structure and may include a BAW transducer, such as a BAW resonator / filter. The BAW resonator may include a first electrode, a second electrode, and a piezoelectric layer between the first and second electrodes. In some embodiments, the piezoelectric layer includes a suitable piezoelectric material, such as aluminum nitride (AlN), zinc oxide (ZnO), aluminum scandium nitride (AlScN), and / or other suitable materials. The first and second electrodes may each include one or more suitable conductive materials and may have a single layer or multilayer structure. For example, the first and second electrodes may each include one or more of copper (Cu), tungsten (W), aluminum copper (AlCu), molybdenum (Mo), and / or platinum (Pt). In some embodiments, the transducer layer 112 also includes other structures / layers that provide electrical connections between the transducer die 103 and the circuit 118. For example, the transducer layer 112 may include one or more conductive vias and / or a bonding layer (not shown) having a plurality of first bonding contacts (e.g., laminate bumps). The bonding layer may include an insulating layer such as silicon oxide, silicon dioxide, silicon oxynitride, epoxy, etc. The first bonding contacts (not shown) may extend within the insulating layer and may be exposed by the bonding layer on the first surface of the transducer layer 112 facing the circuit 118. The first bonding contacts may include a suitable conductive material such as copper (Cu), aluminum (Al), silver (Ag), cobalt (Co), or an alloy. In some embodiments, the first bonding contacts include solder joints such as tin (Sn), silver (Ag), lead (Pb), nickel (Ni), copper, and / or SnAgCu. In some embodiments, the transducer die 103 is flip-chip bonded to the circuitry 118 such that the transducer die 103 is in a “face-down” configuration with the transducer layer facing the circuitry 118 and the base layer 102 facing away from the circuitry 118 .

[0041] Circuit 118 may include any suitable circuitry (e.g., filter circuitry) for transmitting and processing electrical signals from transducer layer 112. Circuit 118 may be disposed on substrate 116. Substrate 116 may include any suitable material and / or structure that provides a base for forming circuit 118. For example, substrate 116 may include a substrate comprising a suitable material such as silicon, carbon, glass, plastic, or a combination thereof. Circuit 118 includes various structures and / or devices to ensure operation (e.g., signal transmission and / or processing). For example, circuit 118 may include transistors, resistors, inductors, multiple metallization layers, and / or multiple dielectric layers. Circuit 118 may include semiconductor materials such as silicon; dielectric materials such as silicon oxide, glass, and / or epoxy; and conductive materials such as copper, titanium nitride, aluminum, and / or aluminum copper. In some embodiments, circuit 118 includes a plurality of second bonding contacts 114 (e.g., laminate bumps). The second bonding contacts 114 can be conductively connected to the I / O of the circuit 118 and can be located on a surface of the circuit 118 that faces the transducer die 103. The second bonding contacts 114 can each be bonded to (or soldered to) a corresponding first bonding contact, allowing electrical signals to be transmitted between the transducer die 103 and the circuit 118. The second bonding contacts 114 can include a suitable conductive material, such as copper (Cu), aluminum (Al), silver (Ag), cobalt (Co), or an alloy. In some embodiments, the second bonding contacts 114 include solder balls, such as tin (Sn), silver (Ag), lead (Pb), nickel (Ni), copper, and / or SnAgCu. As previously described, the circuit 118 can serve as a heat sink for the transducer die 103. When the transducer die 103 (e.g., the transducer layer 112) is powered and in operation, heat generated by the transducer layer 112 can be dissipated through the bonded bonding contacts (e.g., the first and second bonding contacts 114) to the circuit 118. In other words, the bonded bonding contacts provide a heat dissipation path for the transducer die 103.

[0042] The heat dissipation structure 109 may include an adhesive layer 104 positioned / attached to the transducer die 103. In some embodiments, the adhesive layer 104 may cover a second surface of the transducer die 103 facing away from the circuitry 118, maximizing the interface between the adhesive layer 104 and the transducer die 103 to increase heat dissipation from the transducer layer 112. The adhesive layer 104 may include a suitable material that provides sufficient adhesion between the heat dissipation layer (described below) and the transducer die 103. The adhesive layer 104 may also have a desirable high thermal conductivity to improve heat dissipation and a desirable low electrical conductivity to suppress electrical losses. In some embodiments, the adhesive layer 104 has a thermal conductivity equal to or greater than 0.5 W / (m·K) and a resistivity equal to or greater than 1 Ω·cm. In some embodiments, the adhesive layer 104 is non-conductive. In some embodiments, the adhesive layer 104 comprises glue and / or a resin, such as an epoxy resin. In some embodiments, the adhesive layer 104 comprises adhesive tape. In some embodiments, the adhesive layer 104 has a thickness in the z-direction ranging between about 1 μm and about 100 μm. In some embodiments, the thickness of the adhesive is in a range between about 10 μm and 30 μm.

[0043] The heat dissipation structure 109 may also include a heat dissipation layer 106 disposed on the bonding layer 104. In some embodiments, the heat dissipation layer 106 may serve as another heat sink for the transducer die 103 (or transducer layer 112). A first surface of the heat dissipation layer 106 may be attached to the bonding layer 104, such that the heat dissipation layer 106 is thermally coupled to the transducer die 103 through the bonding layer 104. In some embodiments, the heat dissipation layer 106 covers the bonding layer 104 on a side facing away from the circuit 118, maximizing the interface between the bonding layer 104 and the heat dissipation layer 106 to increase heat dissipation from the transducer layer 112. The heat dissipation layer 106 may include a suitable material having desired heat dissipation properties without increasing electrical / RF losses in the BAW structure 100. For example, the heat dissipation layer 106 may have a desirably low electrical conductivity. In some embodiments, when the transducer die 103 is in operation (e.g., driven by electricity), the heat dissipation layer 106 has a temperature lower than the temperature of the transducer die 103. In some embodiments, the thermal conductivity of the heat dissipation layer 106 is equal to or greater than 10 W / (m·K), and the resistivity of the heat dissipation layer is equal to or greater than 2000 Ω·cm. In some embodiments, the resistivity of the heat dissipation layer is equal to or greater than 1000 Ω·cm. In some embodiments, the heat dissipation layer 106 includes silicon, such as high-resistivity silicon. In some embodiments, the resistivity of the heat dissipation layer 106 is greater than 5000 Ω·cm. Figure 1As shown in FIG, heat generated in the transducer layer 112 (or transducer die 103) can be dissipated to the heat dissipation layer 106 through the bonding layer 104. In some embodiments, in the BAW structure 100, the bonding layer 104 and the heat dissipation layer 106 are disposed on a single transducer die (e.g., the transducer die 103). In some embodiments, the heat dissipation layer 106 has a thickness in the z-direction ranging from about 50 μm to about 300 μm. In some embodiments, the thickness of the heat dissipation layer 106 can vary depending on the application (e.g., for various transducer dies 103). For example, in some embodiments, the thickness of the heat dissipation layer 106 can be up to 1 mm.

[0044] The BAW structure 100 may include a mold layer 110 that contacts and encapsulates the circuit 118, the transducer die 103, the bonding layer 104, and the heat dissipation layer 106. The mold layer 110 may provide insulation and support for the transducer die 103. The mold layer 110 may also form an underfill between the transducer die 103 and the circuit 118 for support and heat redistribution / dissipation. In some embodiments, the mold layer 110 includes a filler material with a desirable high thermal conductivity, such as a resin and / or aluminum oxide. For example, the mold layer 110 may include a molded epoxy, a nitride such as silicon nitride, an oxide such as silicon oxide, phosphosilicate glass (PSG), borosilicate glass (BSG), boron-doped phosphosilicate glass (BPSG), a phenolic hardener, silicon dioxide, a pigment, and / or combinations thereof. The top surface of the mold layer 110 (e.g., away from the circuit 118) can be coplanar with or higher than the second surface of the heat dissipation layer 106 (e.g., away from the circuit 118). In other words, the distance between the top surface of the mold layer 110 and the circuit 118 can be the same as or greater than the distance between the second surface of the heat dissipation layer 106 and the circuit 118. In some embodiments, as Figure 1 , the top surface of the mold layer 110 is coplanar with the second surface of the heat dissipation layer 106. In some other embodiments, the mold layer 110 may cover the heat dissipation layer 106 such that the mold layer 110 is disposed on the second surface of the heat dissipation layer 106.

[0045] In some embodiments, heat dissipation structure 109 includes a cover layer 108 positioned above mold layer 110 and heat dissipation layer 106. Cover layer 108 may be positioned above the second surface of heat dissipation layer 106 and the top surface of mold layer 110. In some embodiments, cover layer 108 includes a horizontal portion (e.g., extending in the x- and y-directions) and at least one (e.g., two) vertical portions (e.g., extending in the z-direction) in contact with the horizontal portion. The horizontal portion may be positioned above heat dissipation layer 106 and mold layer 110. One or more vertical portions may contact mold layer 110 and portions of circuitry 118. In some embodiments, the top surface of mold layer 110 is coplanar with the second surface of heat dissipation layer 106, and the horizontal portion of cover layer 108 contacts each of the top surface of mold layer 110 and the second surface of heat dissipation layer 106. In some embodiments, the mold layer 110 covers the second surface of the heat dissipation layer 106, and the horizontal portion of the cover layer 108 is in contact with the mold layer 110 and is not in contact with the heat dissipation layer 106. The cover layer 108 may include a material having a desired high thermal conductivity and a desired high electrical conductivity. In some embodiments, the cover layer 108 has a thermal conductivity equal to or greater than 50 W / (m·K) and a conductivity equal to or less than 1.0 -6 In some embodiments, the cover layer 108 comprises a metal such as copper, aluminum, copper-aluminum, or the like. In some embodiments, the cover layer 108 has a thickness in the z-direction ranging from about 1 μm to about 500 μm. In some embodiments, the cover layer 108 has a thickness between about 1 μm and about 100 μm, for example, between about 1 μm and about 50 μm.

[0046] When the cover layer 108 is in contact with the heat dissipation layer 106, the cover layer 108 may provide an additional heat dissipation / heat sink path from the transducer die 103 through the adhesive layer 104 and the heat dissipation layer 106 to the cover layer 108. Figure 1 , heat generated in the transducer die 103 can be dissipated to the cover layer 108 on the opposite side of the heat dissipation layer 106. The heat flux in the cover layer 108 can be further conducted by the vertical portions of the cover layer 108, for example, to the circuit 118. In some embodiments, when the mold layer 110 covers the heat dissipation layer 106 and the cover layer 108 is in contact with the mold layer 110, the mold layer 110 can also assist in heat dissipation by conducting heat from the portion of the cover layer 108 between the heat dissipation layer 106 and the cover layer 108.

[0047] Figure 2Another BAW structure 200 having a heat dissipation structure according to some embodiments is illustrated. The BAW structure 200 may include a substrate 116, circuitry 118, a transducer die 103, a molding layer 210, and a heat dissipation structure 209. The heat dissipation structure 209 may include an adhesive layer 204, a heat dissipation layer 206, and, in some embodiments, a cover layer 208.

[0048] Unlike BAW structure 100, adhesive layer 204 and heat dissipation layer 206 may each be located above at least one other device / structure 205 in addition to transducer die 103. Heat dissipation structure 209 may also include at least one other device / structure 205. Adhesive layer 204 and heat dissipation layer 206 may each span transducer die 103 and at least one other device / structure 205, such that at least one other device / structure 205 is thermally coupled to heat dissipation layer 206 via adhesive layer 204. In some embodiments, adhesive layer 204 and heat dissipation layer 206 completely cover transducer die 103 and at least one other device / structure 205. A first surface of adhesive layer 204 may contact transducer die 103 and at least one other device / structure 205, and a second surface of adhesive layer 204 may contact a first surface of heat dissipation layer 206. A second surface of heat dissipation layer 206 may contact cover layer 208 or molding layer 210. The mold layer 210 can serve as an underfill for the transducer die 103 and the at least one other device / structure 205 and can encapsulate the transducer die 103, the at least one other device / structure 205, the adhesive layer 204, and the heat dissipation layer 206. In some embodiments, the top surface of the mold layer 210 is coplanar with the second surface of the heat dissipation layer 206, and the heat dissipation layer 206 is in contact with the cover layer 208. In some embodiments, the top surface of the mold layer 210 is higher than the second surface of the heat dissipation layer 206, and the cover layer 208 is in contact with the mold layer 210 (e.g., not with the heat dissipation layer 206). The cover layer 208 can cover the heat dissipation layer 206, the transducer die 103, the at least one other device / structure 205, and the mold layer 210 horizontally (e.g., in the x- and y-directions) and vertically (e.g., in the z-direction). The materials of the adhesive layer 204 , the heat dissipation layer 206 , the cover layer 208 , and the mold layer 210 may be similar or identical to their counterparts in the BAW structure 100 , and detailed descriptions are not repeated herein.

[0049] In some embodiments, the at least one other device / structure 205 can be thermally and / or electrically coupled to the circuit 118 by any suitable means (e.g., bonding, welding, and / or gluing), and can include any suitable active and / or passive components. In some other embodiments, the at least one other device / structure 205 is thermally and / or electrically coupled to another heat sink (e.g., not shown) rather than the circuit 118, and has a lower temperature than the transducer die 103 when the transducer die 103 is in operation. In some embodiments, the other device / structure is positioned directly adjacent to the transducer die 103, such that no other objects are located therebetween. For example, the at least one other device / structure 205 can include another chip or die, or the like.

[0050] like Figure 2 , in some embodiments, at least one other device / structure includes another transducer die 205a that includes a transducer layer 222 on a base layer 220. For example, the heat dissipation structure 209 may include an adhesive layer 204, a heat dissipation layer 206, the transducer die 205a, and in some embodiments, a cover layer 208. Figure 2 , the transducer die 205a can be thermally coupled to the circuit 118 (e.g., via bonding contacts such as bonding contacts 224) and the adhesive layer 204. In some embodiments, the transducer layer 222 includes a BAW resonator / filter. Similar to the transducer die 103, the transducer die 205a can be bonded to the circuit 118 via flip-chip bonding. For example, the transducer die 205a can be bonded to the circuit 118 via multiple bonding contacts such as bonding contacts 224. The transducer die 205a and the bonding contacts (e.g., bonding contacts 224) can be similar to the transducer die 103 and the second bonding contacts 114, respectively, and a detailed description is not repeated herein.

[0051] When the transducer die 103 is in operation (eg, driven by power), the transducer die 205a may have a lower temperature than the transducer die 103. The transducer die 205a and the adhesive layer 204 may provide an additional heat dissipation path for heat generated by the transducer die 103. Figure 2, when the transducer die 103 is in operation, heat generated in the transducer die 103 can be conducted through the transducer die 205a (e.g., and the bonding layer 204 and the bonding contacts) to the circuit 118. In addition, the bonding layer 204 and the portion of the heat dissipation layer 206 located above the transducer die 205a (e.g., beyond the boundary of the transducer die 103) can serve as an additional heat sink or provide an additional heat dissipation path for the heat generated by the transducer die 103 to the cover layer 208. In some embodiments, when the transducer die 103 is in operation, the transducer die 205a is not in operation (e.g., being driven by power). For example, the transducer layer 222 can include a BAW resonator that operates at an acoustic frequency different from the acoustic frequency of the transducer layer 112, so that the transducer dies 205a and 103 (or the BAW resonators in the transducer dies 205a and 103) are not driven by power at the same time. In some embodiments, transducer dies 103 and 205a may or may not operate at different audio frequencies. In some embodiments, circuitry 118 includes control circuitry that controls the operation of transducer dies 103 and 205a. For example, when transducer die 103 is powered, the control circuitry may shut down transducer die 205a, and vice versa. In some embodiments, transducer dies 103 and 205a are identical (e.g., operate at the same audio frequency), and only one is powered at a given time.

[0052] Figure 3 Flowchart of method 300 for forming a BAW structure according to some embodiments of the present disclosure. Method 300 is merely an example and is not intended to limit the present disclosure beyond what is explicitly recited in the claims. Additional operations may be provided before, during, and after method 300, and some of the operations described may be replaced, removed, or moved around for additional embodiments of method 300. Method 300 is described in more detail below. Figures 4A to 4C The structure of a BAW structure at different stages of an alternative fabrication process is illustrated. In some embodiments, the BAW structure may be an example of BAW structure 100 .

[0053] At step 302 , an adhesive layer is attached to a first surface of a transducer die having a BAW transducer. Figure 4A Describe the corresponding structure.

[0054] like Figure 4A, an adhesive layer 402 may be attached to a first surface of a transducer die 403. The transducer die 403 may include a transducer layer 406 on a second surface and a base layer 404 over the transducer layer 406. The transducer layer 406 may be disposed on the base layer 404 and may include a BAW transducer (e.g., a BAW resonator). The transducer layer 406 may be exposed on the second surface of the transducer die 403. In some embodiments, the transducer layer 406 may also include a plurality of bonding contacts for flip-chip bonding.

[0055] Figure 4A The structure in can be formed by attaching an adhesive material layer to a transducer die layer. In some embodiments, the adhesive material layer is attached to a surface of the transducer die layer away from the BAW transducer (e.g., a surface not used to form a bond with the circuit). The adhesive material layer and the transducer die layer can each be formed prior to attaching the adhesive material layer. The transducer die layer may include a BAW transducer, a base material layer on which the BAW transducer is mounted, and may include other devices / structures, such as bonding contacts, a dielectric layer, electrodes, one or more piezoelectric layers, conductive vias, etc. In some embodiments, the fabrication of the transducer die layer includes photolithography, dry etching, wet etching, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), electroplating, electroless plating, welding, grinding, chemical mechanical polishing (CMP), or a combination thereof. In some embodiments, the adhesive material layer includes epoxy resin and can be formed by spin-on coating (e.g., followed by a curing process). In some embodiments, the adhesive material layer includes an adhesive tape that can be directly bonded to the transducer die layer. In some embodiments, the attachment of the adhesive material layer includes applying heat and / or pressure to the adhesive material layer and the transducer die layer.The attached adhesive material layer and transducer die layer may be cut to form transducer die 403 and adhesive layer 402.

[0056] At step 304 , the transducer die is bonded to the circuitry on the second surface of the transducer die. Figure 4B Describe the corresponding structure.

[0057] like Figure 4B , the transducer die 403 can be flip-chip bonded to the circuit 412 on the second surface of the transducer die 403. The second surface of the transducer die 403 can expose the transducer layer 406 and can face the circuit 412. In some embodiments, the flip-chip bonding process includes aligning bonding contacts on the transducer layer 406 with bonding contacts 416 on the circuit 412 such that each bonding contact 416 is aligned with a corresponding bonding contact in the transducer layer 406. The flip-chip bonding process can also include applying heat and / or pressure to the transducer die 403 and / or the circuit 412 so that the bonding contacts are bonded together in the z-direction.

[0058] In some embodiments, circuit 412 is formed prior to flip-chip bonding. Circuit 412 may include various components required for the normal operation of transducer die 403 and may be formed on substrate 414. Substrate 414 may be a substrate. For example, circuit 412 may include signal processing circuitry. Circuit 412 may include a plurality of active and / or passive devices, one or more conductive vias, a plurality of dielectric layers, a plurality of metallization layers, and the like. In some embodiments, fabrication of circuit 412 includes photolithography, dry etching, wet etching, chemical vapor deposition (CVD), physical vapor deposition (PVD), atomic layer deposition (ALD), electroplating, electroless plating, soldering, grinding, chemical mechanical polishing (CMP), or a combination thereof.

[0059] At step 306 , a heat dissipation layer is attached to the adhesive layer such that the heat dissipation layer is thermally coupled to the transducer die. Figure 4B Describe the corresponding structure.

[0060] like Figure 4B , a heat dissipation layer 408 is attached to the adhesive layer 402 such that the heat dissipation layer 408 is thermally coupled to the transducer die 403. In some embodiments, a first surface of the heat dissipation layer 408 is in contact with the adhesive layer 402, and a second surface of the heat dissipation layer 408 faces away from the adhesive layer 402. In some embodiments, the heat dissipation layer 408 is cut (e.g., pre-cut) to a suitable shape / size before being attached to the adhesive layer 402 after flip-chip bonding. In some embodiments, attaching includes aligning the heat dissipation layer 408 with the adhesive layer 402 and applying heat and / or pressure to the heat dissipation layer 408.

[0061] In some other embodiments, heat dissipation layer 408 is formed by attaching a thermal material layer to an adhesive material layer and cutting the thermal material layer, adhesive material layer, and transducer die layer before attaching the transducer die layer. The thermal material layer and the transducer die layer are attached to the adhesive material layer on opposite sides of the adhesive material layer. Heat dissipation layer 408 can then be formed on adhesive layer 402. The stacked structure including heat dissipation layer 408, adhesive layer 402, and transducer die 403 can then be bonded to circuit 412 via flip-chip bonding.

[0062] At step 308 , a molding layer is formed that encapsulates the transducer die and the heat dissipation layer. Figure 4B Describe the corresponding structure.

[0063] like Figure 4BAs shown in FIG, a mold layer 410 is formed that encapsulates the transducer die 403, the bonding layer 402, and the heat dissipation layer 408. The mold layer 410 can be formed by depositing (e.g., spin coating) a layer of molding material, which can then be cured to harden. In some embodiments, depending on the design, the molding material may cover or expose the heat dissipation layer 408. A grinding process and / or a planarization process, such as CMP and / or recess etching, can be performed to remove excess material from the mold layer 410. In some embodiments, depending on the design, the molding material can be ground to expose the heat dissipation layer 408. In some embodiments, the grinding process can cause the second surface of the heat dissipation layer 408 to be coplanar with the top surface of the mold layer 410. In some embodiments, the mold layer 410 forms an underfill between the transducer die 403 and the circuit 412. In some embodiments, to form the underfill, a portion of the molding material can be deposited on the circuit 412 before flip-chip bonding. After flip chip bonding, the remainder of the molding material may be deposited to surround the transducer die 403 , the adhesive layer 402 , and the heat dissipation layer 408 .

[0064] like Figure 4C As shown in FIG. , a cover layer 418 is formed over the heat dissipation layer 408 and the molding layer 410. The cover layer 418 may contact the circuit 412. In some embodiments, the cover layer 418 contacts the second surface of the heat dissipation layer 408 and horizontally and vertically covers the molding layer 410. The cover layer 418 may be formed using a suitable deposition process, such as plating, for example, electroplating and / or electroless plating. The cover layer 418 may also be formed using sputtering, electron beam evaporation, ALD, CVD, or a combination thereof.

[0065] Figure 5 1 illustrates portions of a method for forming a BAW structure similar to BAW structure 200 according to some embodiments. Figure 5 , an adhesive layer 502 and a heat dissipation layer 508 may be mounted on the transducer die 403 and another structure / device 503. In some embodiments, the adhesive layer 502 may be in contact with the structure / device 503 and may cover both the transducer die 403 and the structure / device 503 on a first side of the adhesive layer 502. In some embodiments, the heat dissipation layer 508 may be attached to a second side of the adhesive layer 502 and may cover both the transducer die 403 and the structure / device 503. In some embodiments, the structure / device 503 includes a transducer die having a transducer layer 506 mounted on a base layer 504. Figure 5 , the adhesive layer 502 can be attached to the base layer 504 on a side facing away from the transducer layer 506, such that the transducer layer 506 faces away from the adhesive layer 502 similar to the transducer layer 406. The detailed description of the transducer layer 506 and the base layer 504 can refer to the detailed description of the transducer layer 406 and the base layer 404 and is not repeated herein.

[0066] Figure 5 The structure shown in FIG. 4 can be formed in various suitable ways. In some embodiments, transducer dies 403 and 503 can be cut, for example, from the same transducer die layer or from different transducer die layers. In some embodiments, transducer dies 403 and 503 can be attached to adhesive layer 502 (e.g., pre-cut) adjacent to each other before being flip-chip bonded to the circuit. In some other embodiments, transducer dies 403 and 503 are each flip-chip bonded to a circuit (e.g., similar to circuit 118 ) with the respective transducer layers facing the circuit, and then adhesive layer 502 (e.g., cut from an adhesive material layer) is attached to transducer dies 403 and 503. A heat dissipation layer 508 can then be attached to adhesive layer 502. In some other embodiments, transducer dies 403 and 503 can be attached to adhesive layers, each located on a surface distal from the respective transducer layer. The adhesive layer can then be cut to cover transducer die 403 or 503. Transducer dies 403 and 503 can then be flip-chip bonded to a circuit (e.g., similar to circuit 118), with the respective transducer layers facing the circuit. Heat dissipation layer 508 can then be attached to adhesive layer 502. In yet other embodiments, adhesive layer 502 is attached to heat dissipation layer 508 and then to transducer dies 403 and 503. For example, a stack including heat dissipation layer 508, adhesive layer 502, and transducer dies 403 and 503 can then be flip-chip bonded to a circuit (e.g., similar to circuit 118).

[0067] After heat dissipation layer 508, adhesive layer 502, and transducer dies 403 and 503 are formed over the circuit (e.g., similar to circuit 118), a mold layer (e.g., similar to mold layer 410) and a cover layer (e.g., similar to cover layer 418) may be formed over the circuit. The formation of the mold layer and the cover layer may refer to the description of mold layer 410 and cover layer 418, and a detailed description will not be repeated herein.

[0068] It should be noted that, although not shown, the adhesive layer and the heat dissipation layer may each span (e.g., cover) one or more other devices / structures in addition to transducer die 403 and transducer die 503. In some embodiments, the one or more other devices / structures may be directly adjacent to transducer die 403. In the present disclosure, the adhesive layer and the heat dissipation layer may have any suitable shape and size in the xy plane, such as square, rectangular, irregular, etc. In various embodiments, the adhesive layer and the heat dissipation layer may or may not be completely aligned with each other in the xy plane. For example, the heat dissipation layer may or may not completely cover the adhesive layer, and vice versa. The number of devices / structures covered by the adhesive layer and the specific configuration of the adhesive layer and the heat dissipation layer in the xy plane should not be limited by the embodiments of the present disclosure.

[0069] Figure 6 The simulated temperature distribution in various BAW structures in the xz plane according to some embodiments is illustrated. "Reference" refers to a BAW structure provided by the present disclosure without a heat dissipation structure, "single-chip" refers to a BAW structure with a heat dissipation structure above a single transducer die (e.g., similar to BAW structure 100), and "multi-chip" refers to a BAW structure with a heat dissipation structure above more than one transducer die (e.g., similar to BAW structure 200). In each BAW structure, the rectangle in the center represents the transducer die that requires heat dissipation (e.g., similar to transducer die 103). The transducer die includes a base layer (e.g., similar to base layer 102) and a transducer layer (e.g., similar to transducer layer 112). As shown Figure 6 As shown in FIG, when the transducer layer is in operation (e.g., driven by electricity), the "reference" layer exhibits the highest temperature. The "single chip" layer exhibits a lower temperature than the "reference" layer but a higher temperature than the "multi-chip" layer. The "multi-chip" layer exhibits the lowest temperature. The simulated temperature distribution shows that the disclosed heat dissipation structure can effectively reduce the temperature of the transducer die during operation.

[0070] Those skilled in the art will appreciate improvements and modifications to the preferred embodiments of the present disclosure, and all such improvements and modifications are considered to be within the scope of the concepts disclosed herein and the following claims.

Claims

1. A bulk acoustic wave (BAW) device comprising: a transducer die including a BAW transducer, the transducer die mounted on circuitry on a first surface of the transducer die; a heat dissipation layer thermally coupled to the transducer die on a second surface of the transducer die; and A molding layer encapsulates the transducer die and the heat dissipation layer. 2 . The BAW device according to claim 1 , wherein a thermal conductivity of the heat dissipation layer is equal to or greater than 10 W / (m·K), and a resistivity of the heat dissipation layer is equal to or greater than 1000 Ω·cm. The BAW device according to claim 1 , wherein the resistivity of the heat dissipation layer is greater than 5000 Ω·cm. The BAW device of claim 1 , wherein the heat dissipation layer comprises silicon. 5 . The BAW device of claim 1 , further comprising an adhesive layer in contact with the transducer die and the heat dissipation layer, wherein the heat dissipation layer is thermally coupled to the transducer die through the adhesive layer. 6 . The BAW device according to claim 5 , wherein the adhesive layer has a thermal conductivity equal to or greater than 0.5 W / (m·K) and a resistivity equal to or greater than 1 Ω·cm.

7. The BAW device of claim 1, wherein the transducer die is mounted in a face-down configuration such that the BAW transducer faces the circuit. The BAW device of claim 7 , wherein the adhesive layer comprises an epoxy resin.

9. The BAW device of claim 6, further comprising a second transducer die mounted on the circuit on the first surface of the second transducer die, wherein: The heat dissipation layer is thermally coupled to the second transducer die on a second surface of the second transducer die through the adhesive layer, and The molding layer encapsulates the second transducer die.

10. The BAW device of claim 9, wherein the second transducer die is directly adjacent to the transducer die.

11. The BAW device of claim 9, wherein the second transducer die and the transducer die operate at different audio frequencies.

12. The BAW device of claim 1 , further comprising a cover layer over the heat dissipation layer and the molding layer, wherein: The thermal conductivity of the cover layer is equal to or greater than 50 W / (m·K); and The resistivity of the covering layer is equal to or lower than 1.0 -6 Ω·m. The BAW device of claim 12 , wherein the capping layer comprises a metal.

14. A method for forming a bulk acoustic wave (BAW) device, comprising: attaching an adhesive layer to a first surface of a transducer die, the transducer die including a BAW transducer; bonding the transducer die to circuitry on a second surface of the transducer die; attaching a heat dissipation layer on the adhesive layer such that the heat dissipation layer is thermally coupled to the transducer die; and A molding layer is formed that encapsulates the transducer die and the heat dissipation layer.

15. The method of claim 14, wherein the attaching of the adhesive layer on the first surface of the transducer die comprises: attaching a layer of adhesive material to a transducer die layer, the transducer die layer including the BAW transducer; and The bonding material layer and the transducer die layer are cut together to form the transducer die having the BAW transducer and the bonding layer.

16. The method of claim 14, wherein the bonding of the transducer die comprises flip-chip bonding. 17 . The method of claim 14 , further comprising grinding the mold layer so that a surface of the heat dissipation layer is coplanar with a surface of the mold layer.

18. The method of claim 14, further comprising: attaching a second transducer die to the adhesive layer on the first surface of the second transducer die, the second transducer die including a second BAW transducer; and The second transducer die is bonded to the circuit on the second surface of the second transducer die in the same process in which the transducer die is bonded to the circuit.

19. The method of claim 18, wherein forming the transducer die, the second transducer die, and the adhesive layer comprises: cutting a transducer die layer including the BAW transducer and the second BAW transducer to form the transducer die and the second transducer die; and The transducer die and the second transducer die are attached to the adhesive layer.

20. The method of claim 14, further comprising plating a metal layer covering the transducer die and the molding layer.

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