TWI766476B - Bulk acoustic wave device - Google Patents

Abstract

A bulk acoustic wave (BAW) device includes a BAW structure, bumps, a carrier, and a package. The BAW structure includes a layer of single crystal piezoelectric material, a first electrode, a second electrode, and an acoustic reflector. The first and the second electrodes are respectively disposed on a first surface and a second surface of the layer of single crystal piezoelectric material. The acoustic reflector is disposed on a surface of the first electrode. The bumps are disposed below the BAW structure and electrically connected the first and the second electrodes respectively. The carrier is electrically connected the first and the second electrodes respectively via the bumps, and a spacing is formed between the carrier and the BAW structure. The package is disposed on the carrier to encapsulate the BAW structure and the package fills up the spacing.

Description

Bulk acoustic wave device

The present invention relates to a bulk acoustic wave (BAW) device, and more particularly, to a bulk acoustic wave device comprising a bulk acoustic wave structure having a layer of a single crystal piezoelectric material.

The BAW structure basically consists of two metal electrodes sandwiching a piezoelectric material layer. When an electric field is applied to the metal electrode, the piezoelectric material layer will excite sound waves due to vibration, and the sound waves will oscillate in the piezoelectric material layer to form standing waves to reduce energy loss.

Since the acoustic signal of the BAW structure is transmitted inside the medium, its volume can be small, and it is suitable for application in various portable electronic products, such as band-pass filters for mobile communication products.

However, in the application as a band-pass filter, there are quite strict requirements for the frequency specification of the bulk acoustic wave structure. For example, the piezoelectric material layer may not easily grow into a single crystal material due to the process, resulting in the Q value of the bulk acoustic wave filter. (or quality factor) decreases, which in turn affects the reliability of the product.

The bulk acoustic wave device of the present invention includes a bulk acoustic wave structure, a bump, a carrier and a package body. The bulk acoustic wave structure includes a single crystal piezoelectric material layer, a first electrode, a second electrode and an acoustic wave reflector. The first and second electrodes are respectively located on the first and second surfaces of the single crystal piezoelectric material layer, and the area of the second electrode is greater than or equal to the area of the second surface of the single crystal piezoelectric material layer, and the single crystal piezoelectric material The contact area of the layer with the second electrode is equal to the area of the second surface of the single crystal piezoelectric material layer. The acoustic wave reflector is disposed on the surface of the first electrode. The bumps are arranged under the BAW structure and are respectively electrically connected to the first and second electrodes, and the carrier is electrically connected to the first and second electrodes respectively through the bumps, wherein the carrier is connected to the first and second electrodes respectively. There are gaps between the substrate-less bulk acoustic wave structures. The encapsulation system is located on the carrier and encapsulates the bulk acoustic wave structure, and the encapsulation body fills the gap.

In order to make the above-mentioned features of the present invention more obvious and easy to understand, the following specific embodiments are given and described in detail as follows in conjunction with the accompanying drawings.

Some embodiments are listed below and described in more detail with the accompanying drawings, but the provided embodiments are not intended to limit the scope of the present invention. In addition, the drawings are for illustrative purposes only and are not drawn in full scale. In order to facilitate understanding, the same elements in the following description will be denoted by the same symbols. In addition, the terms such as "comprising", "including", "having", etc. used in the text are all open-ended terms; that is, including but not limited to. Moreover, the directional terms mentioned in the text, such as "up", "down", etc., are only used to refer to the direction of the drawings. Accordingly, the directional terms used are intended to illustrate rather than limit the present invention.

FIG. 1 is a schematic diagram of a bulk acoustic wave structure according to a first embodiment of the present invention.

Referring to FIG. 1 , the bulk acoustic wave structure 100 of the first embodiment includes a single crystal piezoelectric material layer 102 , a first electrode 104 , a second electrode 106 and a first acoustic wave reflector 108 , wherein the material of the single crystal piezoelectric material layer 102 is For example aluminium nitride, LiTaO ₃ , LiNbO ₃ , quartz or diamond. In one embodiment, the thickness of the single crystal piezoelectric material layer 102 is, for example, between 100 nm and 200 nm. The first electrode 104 and the second electrode 106 are respectively located on the first surface 102 a and the second surface 102 b of the single crystal piezoelectric material layer 102 , wherein the materials of the first electrode 104 and the second electrode 106 independently include molybdenum (Mo), Tungsten (W), Ruthenium (Ru), Tantalum (Ta), Platinum (Pt), Titanium (Ti), Gold (Au) or Aluminum (Al). The first acoustic wave reflector 108 is disposed on the surface 104 a of the first electrode 104 . The first acoustic wave reflector 108 includes a first sub-layer 110a and a second sub-layer 110b stacked alternately, such as a Bragg reflector, wherein the first sub-layer 110a and the second sub-layer 110b are respectively different in impedance (Z) Material. In addition, metal materials, dielectric materials or semiconductor materials with different impedances can be applied to the first sub-layer 110 a and the second sub-layer 110 b of the first acoustic wave reflector 108 . In another embodiment, different kinds of materials can also be mixed and used as the first sub-layer 110a and the second sub-layer 110b of the first acoustic wave reflector 108 , such as: alternately stacked metal materials/dielectric materials, alternately stacked of metal materials/semiconductor materials, alternately stacked dielectric materials/semiconductor materials, etc. For example, taking the alternately stacked metal material/dielectric material as an example, the material of the first sub-layer 110a is such as silicon oxide (SiO ₂ ), and the material of the second sub-layer 110b is such as molybdenum (Mo).

Please continue to refer to FIG. 1 , the bulk acoustic wave structure 100 of this embodiment has no substrate, so the contact area between the single crystal piezoelectric material layer 102 and the second electrode 106 is equal to the area of the second surface 102 b of the single crystal piezoelectric material layer 102 , And the area of the second electrode 106 should be greater than or equal to the area of the second surface 102b of the single crystal piezoelectric material layer 102 to facilitate circuit design; taking FIG. 1 as an example, the area of the second electrode 106 is equal to the area of the single crystal piezoelectric material layer 102 The area of the second surface 102b of the material layer 102, but in fact the second electrode 106 may extend beyond the edge of the single crystal piezoelectric material layer 102.

FIG. 2 is a schematic diagram of another bulk acoustic wave structure of the first embodiment, wherein the same components are represented by the reference numerals of FIG. 1 .

In FIG. 2 , in addition to the single crystal piezoelectric material layer 102 , the first electrode 104 , the second electrode 106 and the first acoustic wave reflector 108 , a second acoustic wave reflector 200 is also disposed on the surface 106 a of the second electrode 106 . The second acoustic wave reflector 200 includes the first sub-layer 202a and the second sub-layer 202b stacked alternately, wherein the material selection of the first sub-layer 202a and the second sub-layer 202b can refer to the first sub-layer 202b in the first acoustic wave reflector 108 The layer 110a and the second layer 110b are not repeated here. In addition, the first sub-layers 110a, 202a and the second sub-layers 110b, 202b in which the second acoustic wave reflector 200 and the first acoustic wave reflector 108 are alternately stacked may be of the same or different materials; The good thing is that both materials are selected the same.

3 is a schematic diagram of a bulk acoustic wave device according to a second embodiment of the present invention.

Referring to FIG. 3 , the BAW device 300 of the second embodiment includes a BAW structure 302 , a bump 304 , a carrier 306 and a package body 308 . The BAW structure 302 may be the BAW structure of the first embodiment, the bumps 304 are disposed under the BAW structure 302 , and the bumps 304 are respectively electrically connected to the first electrodes (not shown) in the BAW structure 302 . shown) and a second electrode (not shown). Although the first and second electrodes are not shown in FIG. 3 , it should be known that the first and second electrodes can be pulled to the same surface of the BAW structure 302 through the prior art, and then flip chip technology (Flip Chip) can be used. Perform packaging; for example, a contact pad 310 may be formed first, then a bump 304 may be formed on the contact pad 310, and then the bump 304 may face the contact pad 312 of a carrier 306, Then, the bumps 304 are remelted (eg, using hot air reflow), so that the contact pads 312 of the carrier 306 are electrically connected to the first and second electrodes respectively through the bumps 304 . The carrier 306 is, for example, a lead frame, a substrate, or a printed circuit board. The package body 308 is located on the carrier 306 and covers the bulk acoustic wave structure 302 . Generally speaking, there is a gap 314 between the carrier 306 and the BAW structure 302, so the package body 308 does not fill the gap 314; alternatively, as shown in FIG. 4, the package body 308 in the BAW device 400 can be filled Gap 314 . If the package body 308 does not fill the gap 314, the BAW structure of FIG. 1 or FIG. 2 can be used, and it is more suitable to use the BAW structure of FIG. 1 having only a single surface with an acoustic wave reflector. If the package body 308 fills the gap 314, since there is no space for reflection, it is more suitable to use the bulk acoustic wave structure of FIG. 2 with acoustic wave reflectors on both sides. In addition, a passivation layer 316 may be provided on the bulk acoustic wave structure 302 as a protective layer, and the material thereof is, for example, silicon oxide (SiO ₂ ) or a corrosion-resistant polymer material (polymer).

5A to 5F are schematic cross-sectional views of a manufacturing process of a bulk acoustic wave structure according to a third embodiment of the present invention.

Referring first to FIG. 5A , the manufacturing method of the third embodiment first provides a single crystal substrate 500 , which is made of a material such as zinc oxide, silicon carbide or silicon. The single crystal piezoelectric material layer 502 is formed on the single crystal substrate 500 by a method such as single crystal epitaxy. Due to the structural properties of the single crystal substrate 500 itself, it can be ensured that the grown piezoelectric material is also a single crystal, thereby improving the Q value of the subsequently formed bulk acoustic wave structure. The single crystal piezoelectric material layer 502 has a first surface 502 a and a second surface 502 b opposite to each other, and the second surface 502 b is in direct contact with the single crystal substrate 500 .

Please continue to refer to FIG. 5A , the material of the single crystal piezoelectric material layer 502 is, for example, aluminum nitride, LiTaO ₃ , LiNbO ₃ , quartz or diamond. From the viewpoint of process control, there should be a high etching selectivity ratio between the single crystal substrate 500 and the single crystal piezoelectric material layer 502, for example, the etching selectivity ratio between the single crystal substrate 500 and the single crystal piezoelectric material layer 502 is greater than 10:1, preferably greater than 20:1. For example, if the material of the single crystal substrate 500 is zinc oxide, the material of the single crystal piezoelectric material layer 502 may be aluminum nitride, but the invention is not limited thereto.

Then, referring to FIG. 5B , a first electrode 504 is formed on the first surface 502 a of the single crystal piezoelectric material layer 502 . A method of forming the first electrode 504 is, for example, sputtering or other suitable methods. The material selection of the first electrode 504 can refer to the first electrode 104 in the first embodiment, so it is not repeated here.

5C, the first acoustic wave reflector 506 is formed on the surface 504a of the first electrode 504, and the first acoustic wave reflector 506 is formed by alternately depositing the first sub-layer 508a and the second sub-layer 508b, wherein the first sub-layer 508a and the second sub-layer 508b are alternately deposited. For the material selection of the primary layer 508a and the second sublayer 508b, reference may be made to the first sublayer 110a and the second sublayer 110b in the first acoustic wave reflector 108 in the first embodiment, and details are not described herein again.

Next, the single crystal substrate 500 is removed to obtain the structure shown in FIG. 5D . A method of removing the single crystal substrate 500 is, for example, wet etching. If zinc oxide is used as the material of the single crystal substrate 500, sulfur hexafluoride (SF ₆ ) or citric acid can be used as an etchant. Moreover, in order to protect the first acoustic wave reflector 506, a passivation layer 510 may be formed on the first acoustic wave reflector 506 before removing the single crystal substrate 500, and the material selection can refer to the passivation layer 316 in the second embodiment , so it is not repeated here.

Then, referring to FIG. 5E, the structure of FIG. 5D is reversed, and a second electrode 512 is formed on the second surface 502b of the single crystal piezoelectric material layer 502, wherein the area of the second electrode 512 is greater than or equal to the single crystal piezoelectric material layer The area of the second surface 502b of the single crystal piezoelectric material layer 502 is equal to the area of the second surface 502b of the single crystal piezoelectric material layer 502. The method of forming the second electrode 512 can refer to the method of forming the first electrode 504 ; the material selection of the second electrode 512 can refer to the second electrode 106 in the first embodiment, so it is not repeated here.

Basically, FIG. 5A to FIG. 5E can complete the fabrication of a single-surface BAW structure with an acoustic wave reflector. If it is necessary to manufacture a bulk acoustic wave structure with acoustic wave reflectors on both sides, the steps of FIG. 5F can be continued to form a second acoustic wave reflector 514 on the surface 512a of the second electrode 512, wherein the method of forming the second acoustic wave reflector 514 The method of forming the first acoustic wave reflector 506 can be referred to, and the material selection of the first sub-layer 516a and the second sub-layer 516b in the second acoustic wave reflector 514 can be referred to in the first acoustic wave reflector 108 in the first embodiment. The first sub-layer 110a and the second sub-layer 110b are not repeated here. Finally, another passivation layer 518 can also be formed on the second acoustic wave reflector 514 , and the material of which can be referred to as the passivation layer 510 , so it is not repeated here.

6A to 6D are schematic cross-sectional views of a manufacturing process of a bulk acoustic wave device according to a fourth embodiment of the present invention.

Referring to FIG. 6A first, at least a one-piece acoustic wave structure 600 is formed, and the manufacturing method of the bulk acoustic wave structure 600 can be referred to the third embodiment, so it will not be repeated. Then, contact pads 602 can be formed under the BAW structure 600 first, and then a plurality of bumps 604 are formed on the contact pads 602 , and the bumps 604 can be electrically connected through the contact pads 602 respectively. to the first and second electrodes (not shown) of the BAW structure 600 . Although the first and second electrodes are not shown in FIG. 6A , it should be known that the first and second electrodes can be pulled to the same surface of the BAW structure 600 through the prior art, and then the contact pads 602 can be formed on this surface. with bump 604. In addition, before forming the contact pads 602 , a passivation layer 606 may be formed on the surface of the bulk acoustic wave structure 600 as a protective layer, and the material selection can refer to the passivation layer 316 in the second embodiment, so it will not be repeated.

Then, referring to FIG. 6B , the BAW structure 600 is flip-chip bonded to a carrier 608 through bumps 604 , and the carrier 608 has contact pads 610 on the surface of the carrier 608 opposite to the bumps 604 . After bonding, the carrier 608 and the BAW Gaps 612 are formed between the structures 600 . The flip-chip bonding method, for example, first aligns the bumps 604 with the contact pads 610 of the carrier 608 , and then remelts the bumps 604 (eg, using hot air reflow), so that the carrier 608 is bonded to the bumps 604 , and The bumps 604 are electrically connected to the first and second electrodes, respectively. The above-mentioned carrier 608 can be referred to the carrier 306 of the second embodiment, so it will not be repeated.

Next, referring to FIG. 6C , for encapsulation, the solid encapsulation body 614 may be pressed against the bulk acoustic wave structure 600 by means of heating and pressing for encapsulation.

6D , in the packaged bulk acoustic wave device, since the package body 614 is originally solid, the gap 612 is not filled, and a cavity that can be used for sound wave reflection is formed. Therefore, the manufacturing method of the bulk acoustic wave device of this embodiment is more suitable for using a bulk acoustic wave structure having only a single surface with an acoustic wave reflector (as shown in FIG. 5E ).

7A to 7C are schematic cross-sectional views of a manufacturing process of a bulk acoustic wave device according to a fifth embodiment of the present invention.

Referring to FIG. 7A first, at least a one-piece acoustic wave structure 700 is formed, and the manufacturing method of the bulk acoustic wave structure 700 can be referred to the third embodiment, so it will not be repeated. Subsequently, several contact pads 702 are formed under the BAW structure 700 , and then bumps 704 are formed on the contact pads 702 to electrically connect the first and second electrodes of the BAW structure 700 ( not shown). In addition, before forming the contact pads 702 , a passivation layer 706 may be formed on the surface of the bulk acoustic wave structure 700 as a protective layer, and the material selection can refer to the passivation layer 316 in the second embodiment, so it will not be repeated.

Then, referring to FIG. 7B , the BAW structure 700 is flip-chip bonded to the contact pads 710 of a carrier 708 through the bumps 704 , and a gap 712 is formed between the carrier 708 and the BAW structure 700 . The method of flip-chip bonding can refer to the fourth embodiment, so it is not repeated here. The above-mentioned carrier 708 can be referred to the carrier 306 of the second embodiment, so it will not be repeated.

Next, referring to FIG. 7C , a colloidal packaging material may be used for encapsulation by means of injection and potting, so as to form an encapsulation body 714 on the carrier 708 and make the encapsulation body 714 cover the bulk acoustic wave structure 700 . Since a colloidal packaging material is used, the packaging body 714 will fill the gap 712 . Therefore, the manufacturing method of the bulk acoustic wave device of this embodiment is more suitable for using a bulk acoustic wave structure having acoustic wave reflectors on both sides (as shown in FIG. 5F ).

FIG. 8 is a schematic diagram of a bulk acoustic wave device according to a sixth embodiment of the present invention.

Referring to FIG. 8 , the BAW device of the sixth embodiment at least includes a plurality of BAW structures 800 a - c connected in series with each other, a bump 802 , a carrier 804 and a package body 808 . Basically, the bumps 802 , the carrier 804 and the package body 808 can all refer to the second embodiment, so they will not be repeated here. In addition, the bulk acoustic wave structures 800a-c may further have contact pads 810 and a passivation layer 812, and the carrier 804 may further have contact pads 814. As for the BAW structures 800a-c, the filtering effects of different frequency bands (frequency) can be achieved, so the BAW device of this embodiment can be applied in different frequency bands. Although FIG. 8 shows three BAW structures 800a-c, the present invention is not limited thereto, and the number of BAW structures can be increased or decreased as required.

Furthermore, by using the method of the fourth embodiment or the fifth embodiment, the bulk acoustic wave device as shown in FIG. 8 can also be manufactured. For example, in the flip chip bonding step of FIG. 6B or FIG. 7B , the BAW structures 800a-c can be bonded to the carrier 804, and the BAW structures 800a, 800b and the BAW structures 800a, 800b can be electrically connected through the bumps 802, respectively. The first and second electrodes (not shown) of 800c. Wherein, the second electrodes of the respective bulk acoustic wave structures 800a, 800b and 800c can be connected in series with each other through the wire design in the carrier 804 to form a common electrode (not shown), and the second electrodes of the respective bulk acoustic wave structures 800a, 800b and 800c are connected in series with each other. Different voltages are applied to one electrode to achieve the purpose of application in different bands. In addition, although FIG. 8 shows the case where the package body 808 fills the gap 806 , the package body 808 may be the case where the gap 806 is not filled.

To sum up, the present invention uses a single crystal substrate to form a single crystal piezoelectric material layer thereon, so that the Q value of the bulk acoustic wave structure can be effectively improved, and the prepared bulk acoustic wave structure has no substrate, so the The structure size (thickness) can meet the development of miniaturized products. And with a specific package structure, it can be used as a bulk acoustic wave device (such as a filter). In addition, if BAW structures with different filter frequencies are installed in the same BAW device, applications in different bands can also be performed.

Although the present invention has been disclosed as above with examples, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field can make some changes and modifications without departing from the spirit and scope of the present invention. The protection scope of the present invention shall be determined by the scope of the appended patent application.

100, 302, 600, 700, 800a, 800b, 800c: Bulk Acoustic Wave Structures 102, 502: single crystal piezoelectric material layer 102a, 502a: first surface 102b, 502b: second surface 104, 504: the first electrode 104a, 106a, 504a: Surface 106, 512: the second electrode 108, 506: First acoustic reflector 110a, 202a, 508a, 516a: first layer 110b, 202b, 508b, 516b: Second layer 200, 514: Second acoustic reflector 300, 400: Bulk acoustic wave device 304, 604, 704, 802: bumps 306, 608, 708, 804: Carrier 308, 614, 714, 808: Package 310, 312, 602, 610, 702, 710, 810, 814: Contact pads 314, 612, 712, 806: Clearance 316, 510, 518, 606, 706, 812: Passivation layer 500: single crystal substrate

FIG. 1 is a schematic diagram of a bulk acoustic wave structure according to a first embodiment of the present invention. FIG. 2 is a schematic diagram of another bulk acoustic wave structure of the first embodiment. 3 is a schematic diagram of a bulk acoustic wave device according to a second embodiment of the present invention. FIG. 4 is a schematic diagram of another bulk acoustic wave device of the second embodiment. 5A to 5F are schematic cross-sectional views of a manufacturing process of a bulk acoustic wave structure according to a third embodiment of the present invention. 6A to 6D are schematic cross-sectional views of a manufacturing process of a bulk acoustic wave device according to a fourth embodiment of the present invention. 7A to 7C are schematic cross-sectional views of a manufacturing process of a bulk acoustic wave device according to a fifth embodiment of the present invention. FIG. 8 is a schematic diagram of a bulk acoustic wave device according to a sixth embodiment of the present invention.

302: Bulk Acoustic Wave Structures

304: bump

306: Carrier

308: Package body

310, 312: Contact pads

314: Clearance

316: Passivation layer

400: Bulk Acoustic Wave Device

Claims (6)

A bulk acoustic wave device, comprising: at least one bulk acoustic wave (BAW) structure without a substrate, the bulk acoustic wave structure without a substrate is composed of the following structures: a single crystal piezoelectric material layer, having opposite first surfaces and a second surface; a first electrode, disposed on the first surface of the single crystal piezoelectric material layer; a second electrode, disposed on the second surface of the single crystal piezoelectric material layer, wherein the The area of the second electrode is greater than or equal to the area of the second surface of the single crystal piezoelectric material layer, and the contact area between the single crystal piezoelectric material layer and the second electrode is equal to the single crystal piezoelectric material layer the area of the second surface of the material layer; the first acoustic wave reflector, disposed on the surface of the first electrode; the second acoustic wave reflector, disposed on the surface of the second electrode; the first passivation layer, on the surface of the first acoustic wave reflector, wherein the material of the first passivation layer is silicon oxide; and a second passivation layer on the surface of the second acoustic wave reflector, wherein the material of the second passivation layer is silicon oxide; a plurality of bumps are arranged under the bulk acoustic wave structure without substrate, and are respectively electrically connected to the first electrode and the second electrode of the bulk acoustic wave structure without substrate; carrier , respectively electrically connected to the first electrode and the second electrode through the bump, wherein there is a space between the carrier and the bulk acoustic wave structure without substrate a gap; and a package body located on the carrier and covering the substrateless bulk acoustic wave structure, and the package body fills the gap. The BAW device of claim 1, wherein the first passivation layer is located on a surface of the substrate-less BAW structure facing the carrier. The BAW device according to claim 1, wherein the substrateless BAW structure is a plurality of substrateless BAW structures connected in series with each other. The bulk acoustic wave device of claim 1, wherein each of the first acoustic wave reflector and the second acoustic wave reflector comprises a plurality of first sub-layers and a plurality of second sub-layers that are alternately stacked, the first acoustic wave reflector The sub-layer and the second sub-layer are materials with different impedances (Z). The bulk acoustic wave device of claim 1, wherein the material of the single crystal piezoelectric material layer comprises aluminum nitride, LiTaO ₃ , LiNbO ₃ , quartz or diamond. The bulk acoustic wave device of claim 1, wherein the carrier comprises a lead frame, a substrate, or a printed circuit board.

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