CN109889173B - Connection structure of flexible substrate thin-film bulk acoustic wave filter - Google Patents

Abstract

The present invention provides a connection structure of a thin-film bulk acoustic wave filter with a flexible base, comprising: a first top electrode and a second top electrode with a gap therebetween; a piezoelectric layer under the first top electrode and the second top electrode layer; one or two bottom electrodes under the piezoelectric layer; a flexible substrate under the bottom electrode; wherein the piezoelectric layer is absent under the gap between the two top electrodes.

Description

Connection structure of flexible substrate thin-film bulk acoustic wave filter

technical field

The invention relates to the technical field of semiconductors, in particular to a connection structure of a flexible substrate thin film bulk acoustic wave filter.

Background technique

Filters are one of the most commonly used electrical components in modern communication systems. According to the function, the filters are divided into low-pass, high-pass, band-pass and band-stop filters. At the same time, flexible electronics are also developing rapidly. So far, flexible electronics have developed rapidly in the fields of display, sensing, and communication, and wearable flexible electronics consumption has attracted more and more interest. Flexible electronics are generally considered to be electronics or electronic systems built on flexible substrates, and the systems can be bent, stretched, and twisted. Compared with electronic systems on conventional hard substrates, flexible electronics need to retain a certain working ability when flexible deformation occurs. In high communication efficiency applications, building a flexible RF system can further expand the field of flexible applications.

There are many types of filters in the form of composition, among which the Ladder topology is a more common one. As shown in Figure 1, each stage of the Ladder structure consists of an equivalent series resonator (Series Resonator) Xi (i=1, 2, 3...) and an equivalent parallel resonator (Shunt Resonator) Yi (i =1,2,3...), the parallel resonance frequency is lower than the series resonance frequency. The filter can be regarded as a two-port network. In Figure 1, Port 1 and Port 2 are the signal input and output respectively. Usually, the two resonators include two resonance points: a series resonance point with a lower frequency and a parallel resonance point with a higher frequency. Taking a band-pass filter as an example, in a filter with a ladder structure, the parallel resonance point of the parallel resonator is often equal to the series resonance point of the series resonator to obtain a filter with better performance, as shown in Figure 2.

On the other hand, the development of flexible electronics has put forward higher requirements for the development of flexible electrical components. The radio frequency band for communication will play an important role in future flexible electronic systems. The realization of the flexible function depends to a certain extent on the flexible design of the device. In recent years, Bulk Acoustic Wave (BAW) resonators have gained rapid development. BAW resonators have become one of the important components for realizing flexible electronic systems due to their advantages of simple structure, high performance, low power consumption, and small size. Take a bulk acoustic wave resonator film bulk acoustic wave resonator (Film Bulk Acoustic Resonator, FBAR) as an example, this type of resonator has a sandwich structure, from top to bottom, the top electrode (Top Electrode, TE), piezoelectric layer ( Piezoelectric Layer, PZ) and bottom electrode (Bottom Electrode, BE) can generate electrical resonance under the applied RF voltage. In addition, in order to form an effective acoustic reflection layer, it is usually necessary to construct an air cavity or a Bragg reflection layer outside the two electrodes. The application of BAW resonators on hard substrates and their extended filters has become mature in commercialization, but if the process is directly applied to flexible filters, the device flexibility is still not ideal.

For example, a schematic circuit diagram of two adjacent resonators without electrical links is shown in Fig. 3a, and a cross-sectional view of a prior art device structure is shown in Fig. 3b, including a top electrode 310, a piezoelectric layer 311, a bottom electrode 312 and a flexible substrate 320, wherein The top surface of the flexible substrate 320 has a cavity 330 aligned with the top electrode. Since the piezoelectric layer 311 is usually a brittle material, the flexibility of the device is not ideal.

For another example, the schematic circuit diagram of the adjacent resonators of the top electrode isolation type series-parallel structure is shown in Fig. 4a, and the cross-sectional view of the prior art device structure is shown in Fig. 4b, including the top electrode 410, the piezoelectric layer 411, the bottom electrode 412 and the flexible substrate 420, wherein the top surface of the flexible substrate 420 has a cavity 430 aligned with the top electrode. Since the piezoelectric layer 411 is usually a brittle material, the flexibility of the device is not ideal.

SUMMARY OF THE INVENTION

In view of this, the present invention provides a connection structure of a flexible base thin-film bulk acoustic wave filter, which is beneficial to improve the flexibility of the device.

The connection structure of the flexible base thin-film bulk acoustic wave filter proposed by the present invention includes: a first top electrode and a second top electrode with a gap therebetween; a piezoelectric layer below the first top electrode and the second top electrode; One or two bottom electrodes under the piezoelectric layer; a flexible substrate under the bottom electrode; wherein the piezoelectric layer is not provided under the gap between the two top electrodes.

Optionally, the bottom electrodes are a first bottom electrode and a second bottom electrode, respectively corresponding to the first top electrode and the second top electrode; the first bottom electrode and the second top electrode are connected via a The conductive film is connected, and the conductive film is located in the gap and below the gap.

Optionally, the conductive film is filled with a flexible material.

Optionally, a position below the gap without the piezoelectric layer is filled with a flexible material.

Optionally, the gap and the position below the gap without the piezoelectric layer are filled with a flexible material, wherein the flexible material covers the edge of the top electrode.

Optionally, the flexible material is epoxy resin or parylene.

Optionally, the material of the flexible substrate includes: polyethylene terephthalate plastic, polyacetimide, polyethylene naphthalate or polyetherimide.

Optionally, the top surface of the flexible substrate has two cavities, and the two cavities are respectively aligned with the first top electrode and the second top electrode.

Optionally, there is a Bragg reflection layer between the flexible substrate and the bottom electrode.

Optionally, the Bragg reflection layer is separately prepared and then transferred onto the flexible substrate.

Optionally, the material of the piezoelectric layer includes: aluminum nitride, zinc oxide, lead zirconate titanate piezoelectric ceramics or polyvinylidene fluoride.

According to the technical solution of the present invention, since there is no brittle piezoelectric material under the gap between the two top electrodes, the device has the advantage of good flexibility.

Description of drawings

The accompanying drawings are used for better understanding of the present invention and do not constitute an improper limitation of the present invention. in:

Fig. 1 is the circuit diagram of the ladder (Ladder) topology structure of the filter;

Fig. 2 is the performance schematic diagram of resonance unit and filter;

3a is a schematic circuit diagram of two adjacent resonators without electrical links, and FIG. 3b is a cross-sectional view of the device structure of two adjacent resonators without electrical links in the prior art;

4a is a schematic circuit diagram of an adjacent resonator of a top electrode isolation type series-parallel structure, and FIG. 4b is a sectional view of a device structure of a top electrode isolation type resonator in the prior art;

5 is a cross-sectional view of the device structure of two adjacent resonators without electrical links according to an embodiment of the present invention;

6 is a cross-sectional view of a device structure of an adjacent resonator of a top electrode isolation type series-parallel structure according to an embodiment of the present invention;

7a is a circuit diagram of an adjacent resonator with a top electrode and bottom electrode series jumper type structure according to an embodiment of the present invention, FIG. 7b is a cross-sectional view of a device structure corresponding to FIG. 7a, and FIG. 7c is another device corresponding to FIG. 7a. Structural sectional drawing;

8 is a cross-sectional view of a device structure filled with a flexible material at a position below the gap between two top electrodes without the piezoelectric layer according to an embodiment of the present invention;

9 is a cross-sectional view of a device structure filled with a flexible material at a gap between two top electrodes and a position below the gap without the piezoelectric layer according to an embodiment of the present invention;

10 is a cross-sectional view of the device structure of two adjacent resonators with Bragg reflection layers according to an embodiment of the present invention.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", " Rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc. The relationship is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore It should not be construed as a limitation of the present invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature. In the description of the present invention, "plurality" means two or more, unless otherwise expressly and specifically defined.

In the present invention, unless otherwise expressly specified and limited, the terms "installed", "connected", "connected", "fixed" and other terms should be understood in a broad sense, for example, it may be a fixed connection or a detachable connection , or integrally connected; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or the internal communication between the two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

In the present invention, unless otherwise expressly specified and limited, a first feature "on" or "under" a second feature may include the first and second features in direct contact, or may include the first and second features Not directly but through additional features between them. Also, the first feature being "above", "over" and "above" the second feature includes the first feature being directly above and obliquely above the second feature, or simply means that the first feature is level higher than the second feature. The first feature is "below", "below" and "below" the second feature includes the first feature being directly below and diagonally below the second feature, or simply means that the first feature has a lower level than the second feature.

The connection structure of the flexible base thin-film bulk acoustic wave filter according to the embodiment of the present invention includes: a first top electrode and a second top electrode with a gap therebetween; a piezoelectric layer below the first top electrode and the second top electrode; One or two bottom electrodes under the piezoelectric layer; a flexible substrate under the bottom electrode; wherein there is no piezoelectric layer under the gap between the two top electrodes. Specifically, it can be described in conjunction with Example 1 and Example 2.

example 1

FIG. 5 is a structural cross-sectional view of two resonators without electrical connection according to an embodiment of the present invention (the circuit diagram thereof corresponds to FIG. 3 a ). As shown in FIG. 5, the structure includes a top electrode 510, a piezoelectric layer 511, a bottom electrode 512, and a flexible substrate 520, wherein the top surface of the flexible substrate 520 may have a cavity 530 aligned with the top electrode. There may be no piezoelectric layer at the gap between the two top electrodes 510 to reduce the stress at the place during bending, so as to obtain better flexible bending performance. It should be noted that the manufacturing process of the device shown in FIG. 5 is as follows: a filter without a substrate is first fabricated through a MEMS process, secondly, a cavity is etched on the flexible substrate, and then the device is transferred by a transfer method. Align with cavity and transfer fix to flexible substrate. The fabrication processes of other devices having flexible substrates with cavities in this paper are similar and will not be repeated here.

Example 2

6 is a structural cross-sectional view of a TE isolated series-parallel structure resonator according to an embodiment of the present invention (its circuit diagram corresponds to FIG. 4a ). As shown in FIG. 6, the structure includes a top electrode 610, a piezoelectric layer 611, a bottom electrode 612, and a flexible substrate 620, wherein the top surface of the flexible substrate 620 may have a cavity 630 aligned with the top electrode. There may be no piezoelectric layer in the gap between the two top electrodes 610 to reduce the stress at the place during bending, so as to obtain better flexible bending performance.

Optionally, in the connection structure of the flexible substrate thin-film bulk acoustic wave filter according to the embodiment of the present invention, the bottom electrodes are a first bottom electrode and a second bottom electrode, respectively corresponding to the first top electrode and the second top electrode; The electrode and the second top electrode are connected through a conductive film, and the conductive film is located in the gap and below the gap. It should be noted that the conductive film connecting the electrodes may also be filled with a flexible material. Specifically, it can be described in conjunction with Example 3.

Example 3

Fig. 7a is a circuit diagram of an adjacent resonator with a top electrode and a bottom electrode series bridge structure, and Fig. 7b is a cross-sectional view of a device structure corresponding to Fig. 7a. As shown in Figure 7b, the structure includes: a top electrode 710, a piezoelectric layer 720, a bottom electrode 730, a conductive film 740 and a flexible substrate 750, wherein the top surface of the flexible substrate 720 may have a cavity aligned with the top electrode 770. In this embodiment, the bottom electrode of the left resonator is bridged to the top electrode of the right resonator through a conductive film, and the predefined top and bottom electrodes of the right resonator are exchanged. The formation of the conductive thin film 740 can be achieved by existing processes, for example, combined with a process such as photolithography, and a method such as magnetron sputtering is used to deposit the material on the target area.

In addition, FIG. 7c is a cross-sectional view of another device structure corresponding to FIG. 7a. As shown in FIG. 7c, the void above the conductive film 740 is filled with a flexible material 760 to obtain higher mechanical stability. In this embodiment, the filled flexible material includes, but is not limited to, epoxy resin (eg, epoxy SU-8 resin-based photoresist) or parylene.

Optionally, in the connection structure of the flexible substrate thin-film bulk acoustic wave filter according to the embodiment of the present invention, the position below the gap without the piezoelectric layer is filled with a flexible material;

Example 4

8, the structure includes two adjacent top electrodes 810, a piezoelectric layer 811, a bottom electrode 812, and a flexible substrate 820, wherein the top surface of the flexible substrate 820 may have a cavity 830 aligned with the top electrodes. The gap between the two top electrodes 810 is filled with a flexible material 860 .

Optionally, in the connection structure of the flexible substrate thin-film bulk acoustic wave filter according to the embodiment of the present invention, the gap and the position below the gap without the piezoelectric layer are filled with a flexible material, wherein the flexible material covers the edge of the top electrode. , which can effectively prevent the top electrode from lifting. Specifically, it can be described in conjunction with Example 5.

Example 5

As shown in FIG. 9, the structure includes two adjacent top electrodes 910, a piezoelectric layer 911, a bottom electrode 912, and a flexible substrate 920, wherein the top surface of the flexible substrate 920 may have a cavity 930 aligned with the top electrodes. The gap between the two top electrodes 910 is filled with a flexible material 960 .

Optionally, in the connection structure of the flexible substrate thin-film bulk acoustic wave filter according to the embodiment of the present invention, a Bragg reflection layer is provided between the flexible substrate and the bottom electrode. Bragg reflectors and devices are first fabricated through the MEMS process. Second, the device is directly transferred and fixed onto the flexible substrate by a transfer method. The Bragg reflection layer is obtained by cross stacking multiple layers of materials with different acoustic impedances (low acoustic impedance material-high acoustic impedance material-low acoustic impedance material-high acoustic impedance material so cross-stacked), suppressing acoustic energy leakage through multiple effective reflections . The Bragg reflection structure generally has at least 4 layers, and the number of layers can also be more. Common low-acoustic impedance materials include silicon dioxide (SiO ₂ ), metal aluminum (Al), etc., and common high-acoustic impedance materials include metal molybdenum (Mo), tungsten (W), etc. In the same Bragg reflection layer, low / The high acoustic impedance material is not limited to one material, and a mixture of these materials may be used. Specifically, it can be described with reference to Example 6.

Example 6

10, the structure includes two adjacent top electrodes 1010, a piezoelectric layer 1011, a bottom electrode 1012, and a flexible substrate 1020, wherein the bottom electrode 1012 and the flexible substrate 1020 have two layers of low acoustic impedance materials 1030 and High acoustic impedance material 1031.

It should be noted that the flexible material in all embodiments of the present invention may be epoxy resin or parylene; the material of the flexible substrate includes but is not limited to polyethylene terephthalate (PET), polyacetimide (PI) ), polyethylene naphthalate (PEN), polyetherimide (PEI), etc.

The materials of the piezoelectric layer include but are not limited to aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate piezoelectric ceramics (PZT) and polyvinylidene fluoride (PVDF), etc., and can also be doped with other elements. of the above materials. The above-mentioned material is a piezoelectric film with a thickness of less than 10 microns. The aluminum nitride thin film is in a polycrystalline form or a single crystal form, and the growth method is thin film sputtering (sputtering) or organic metal chemical vapor deposition (MOCVD).

It can be seen from the above that the flexibility of the device is enhanced by reducing the brittle piezoelectric material between the two top electrode gaps through the connection structure of the flexible substrate thin film bulk acoustic wave filter of the embodiment of the present invention.

The above-mentioned specific embodiments do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions may occur depending on design requirements and other factors. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. a connection structure of a flexible base film bulk acoustic wave filter, is characterized in that, comprises: a first top electrode and a second top electrode with a gap therebetween; a piezoelectric layer under the first top electrode and the second top electrode; one or two bottom electrodes below the piezoelectric layer; a flexible substrate under the bottom electrode; The gap and the position below the gap without the piezoelectric layer are filled with a flexible material, wherein the flexible material covers the edge of the top electrode. 2 . The connection structure of the flexible base film bulk acoustic wave filter according to claim 1 , wherein the flexible material is epoxy resin or parylene. 3 . 3. The connection structure of the flexible substrate film bulk acoustic wave filter according to claim 1, wherein the material of the flexible substrate comprises: polyethylene terephthalate plastic, polyacetimide, polyethylene naphthalate Alcohol ester or polyetherimide. 4 . The connection structure of the flexible substrate thin-film bulk acoustic wave filter according to claim 1 , wherein the top surface of the flexible substrate has two cavities, and the two cavities are respectively connected to the first top surface. 5 . The electrodes are aligned with the second top electrode. 5 . The connection structure of the flexible substrate thin-film bulk acoustic wave filter according to claim 1 , wherein a Bragg reflection layer is provided between the flexible substrate and the bottom electrode. 6 . 6 . The connection structure of the flexible substrate thin-film bulk acoustic wave filter according to claim 5 , wherein the Bragg reflection layer is prepared separately and then transferred to the flexible substrate. 7 . 7 . The connection structure of the flexible base film bulk acoustic wave filter according to claim 1 , wherein the material of the piezoelectric layer comprises: aluminum nitride, zinc oxide, lead zirconate titanate piezoelectric ceramics or polyvinylidene fluoride. 8 . vinyl.

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