CN217116044U

CN217116044U - Broadband film bulk acoustic resonator

Info

Publication number: CN217116044U
Application number: CN202123421151.9U
Authority: CN
Inventors: 李国强
Original assignee: Aifotong Technology Co ltd
Current assignee: Aifotong Technology Co ltd
Priority date: 2021-12-31
Filing date: 2021-12-31
Publication date: 2022-08-02
Anticipated expiration: 2031-12-31

Abstract

The utility model provides a broadband film bulk acoustic resonator, which comprises a top electrode, a composite piezoelectric film, a bottom electrode and a substrate in sequence from top to bottom; the top electrode, the composite piezoelectric film and the bottom electrode form a sandwich structure; an air gap is formed between the bottom electrode and the substrate; the composite piezoelectric film is formed by stacking a plurality of piezoelectric layers. The utility model discloses a structure and the special air gap's of compound piezoelectric film combination design obtain a broadband film bulk acoustic resonator with low loss.

Description

Broadband film bulk acoustic resonator

Technical Field

The utility model relates to a film bulk acoustic resonator, concretely relates to broadband film bulk acoustic resonator

Background

The fifth generation mobile communication (5G) technology has made an urgent need for a thin film bulk acoustic resonator Filter (FBAR) with small volume, high frequency, broadband, and high performance. FBAR technology combines acoustic, radio frequency and MEMS processes. At present, the research difficulties of no special design platform, high requirement on film materials, complex process and the like exist. Meanwhile, the FBAR filter is a typical narrow-band device, and how to increase the working bandwidth of the FBAR filter and meet the requirement of broadband signal processing is also a research hotspot in recent years. The conventional FBAR device usually adopts an AlN film as a piezoelectric film, but the electromechanical coupling coefficient of the AlN film is only 6.5%, and the prepared FBAR device is often low in bandwidth. Furthermore, FBAR devices using ZnO thin films as piezoelectric thin films have been developed, ZnO is a piezoelectric material with higher piezoelectric coupling coefficient, but FBAR devices prepared only using ZnO thin films have large loss, which is a difficult problem in the industry.

Disclosure of Invention

Problem to prior art existence, the utility model provides a broadband film bulk acoustic resonator, this FBAR simple structure, stable performance. The technical scheme of the utility model is that:

a broadband film bulk acoustic resonator comprises a top electrode, a composite piezoelectric film, a bottom electrode and a substrate in sequence from top to bottom; the top electrode, the composite piezoelectric film and the bottom electrode form a sandwich structure; an air gap is formed between the bottom electrode and the substrate; the composite piezoelectric film is formed by stacking a plurality of piezoelectric layers.

Preferably, the substrate is high-resistance monocrystalline silicon.

Further, the depth of the air gap is 800 nm-5 μm.

Furthermore, the composite piezoelectric film is formed by stacking 2-8 piezoelectric layers, wherein the piezoelectric layer is made of AlN or ZnO, and the thickness of each piezoelectric layer is 100 nm-3 mu m.

Preferably, the composite piezoelectric film is formed by alternately stacking AlN piezoelectric layers and ZnO piezoelectric layers.

Preferably, the deposition thickness of the top electrode and the bottom electrode is 40 nm-450 nm, and the material is one of Al, Pt, Mo, W, Ti and Au.

Compared with the prior art, the beneficial effects of the utility model reside in that:

the utility model discloses a structure and the special air gap's of compound piezoelectric film combination design obtain a broadband film bulk acoustic resonator with low loss.

Drawings

Fig. 1 is a schematic structural diagram of a resonator manufacturing process according to an embodiment of the present invention after a groove is etched on a substrate and a sacrificial layer is used for filling.

Fig. 2 is a schematic structural diagram of the resonator according to the embodiment of the present invention after the bottom electrode is deposited.

Fig. 3 is a schematic structural diagram of the composite piezoelectric film deposited in the process of manufacturing the resonator according to the embodiment of the present invention.

Fig. 4 is a schematic structural diagram of the resonator according to the embodiment of the present invention after the top electrode is deposited.

Fig. 5 is a schematic structural diagram of resonators prepared in embodiments 1 and 2 of the present invention.

Fig. 6 is a schematic structural diagram of an FBAR device according to comparative example 1 of the present invention.

In fig. 1 to 6, the specific marks are: the piezoelectric element comprises a first substrate 101, a sacrificial layer 102, a first bottom electrode 103, a first piezoelectric film 104, a second piezoelectric film 105, a third piezoelectric film 106, a fourth piezoelectric film 107, a first top electrode 108, a second substrate 201, a second bottom electrode 203, a piezoelectric layer 204 and a second top electrode 205.

Detailed Description

In the description of the present invention, it should be noted that the specific conditions are not specified in the examples, and the description is made according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

The present invention will be described in further detail with reference to the following embodiments to help those skilled in the art to understand the concept and technical solutions of the present invention more completely, accurately and deeply, and the protection scope of the present invention includes but is not limited to the following embodiments, and any modifications made to the details and forms of the technical solutions of the present invention are within the protection scope of the present invention without departing from the spirit and scope of the present invention.

Example 1

The embodiment provides a broadband film bulk acoustic resonator, the structure of which is shown in fig. 5, and the resonator includes a first substrate 101, a first bottom electrode 103, a composite piezoelectric film, and a first top electrode 108, which are sequentially distributed from bottom to top; an air gap is formed between the first bottom electrode 103 and the first substrate 101; the composite piezoelectric film is composed of a first piezoelectric film 104, a second piezoelectric film 105, a third piezoelectric film 106 and a fourth piezoelectric film 107, wherein the upper surface and the lower surface of the composite piezoelectric film are respectively and oppositely connected with a first top electrode 108 and a first bottom electrode 103, the first bottom electrode 103 is directly contacted with an air gap, and the first top electrode 108, the composite piezoelectric film and the first bottom electrode 103 form a sandwich structure.

The substrate 101 is high-resistance monocrystalline silicon; the first bottom electrode 103 is metal Mo with the thickness of 160 nm; the top electrode I108 is metal Mo with the thickness of 160 nm; the first piezoelectric film 104 is an AlN film 200nm thick; the second piezoelectric film is a ZnO film with the thickness of 105 nm; the third piezoelectric film 106 is an AlN film 200nm thick; the fourth piezoelectric film was a ZnO film 107 with a thickness of 200 nm. The air gap has a depth of 2 μm and a width greater than the top electrode.

The preparation method of the resonator comprises the following steps:

(1) selecting high-resistance monocrystalline silicon as an epitaxial substrate, coating glue, exposing and cleaning, and etching a groove on the upper surface of the epitaxial substrate by using ICP-RIE equipment, wherein the depth and the width of the groove are the same as those of an air gap;

(2) filling the groove by using the PSG as a sacrificial layer, and then removing all the PSG outside the groove by using a CMP (chemical mechanical polishing) process; as shown in fig. 1;

(3) depositing a bottom electrode above the groove by using a magnetron sputtering PVD method, photoetching and etching the pattern and reserving a release hole; as shown in fig. 2;

(4) depositing 4 layers of piezoelectric films layer by layer above the bottom electrode by using a PLD (programmable logic device) method to form a composite piezoelectric film, and photoetching patterns; as shown in fig. 3;

(5) depositing a top electrode above the composite piezoelectric film by using PVD (physical vapor deposition), and photoetching and etching a pattern; as shown in fig. 4;

(6) and removing the sacrificial layer through wet etching of the release hole to form a complete device structure.

The series resonance frequency of the resonator is 2643MHz, the parallel resonance frequency is 2739MHz, and the bandwidth is 96 MHz.

Example 2

This embodiment provides a broadband film bulk acoustic resonator having a structure substantially the same as that of embodiment 1, except for the following details: the first bottom electrode 103 is 140nm thick metal Mo; the top electrode one 108 is metal Mo with the thickness of 140 nm; the first piezoelectric film 104 is an AlN film 180nm thick; the second piezoelectric film is a ZnO film 105 with the thickness of 250 nm; the third piezoelectric film 106 is an AlN film 180nm thick; the fourth piezoelectric film was a ZnO film 107 a 250nm thick.

The obtained resonator has a series resonance frequency of 2646MHz, a parallel resonance frequency of 2746MHz and a bandwidth of 100 MHz.

Example 3

This embodiment provides a broadband film bulk acoustic resonator having a structure substantially the same as that of embodiment 1, except for the following details: the first bottom electrode 103 is metal Mo with the thickness of 140 nm; the top electrode I108 is 140nm thick metal Mo, the 1-7 piezoelectric layers are AlN, ZnO and AlN respectively, the AlN thickness is 80nm, and the ZnO thickness is 180 nm.

The obtained resonator has a series resonance frequency of 2624MHz, a parallel resonance frequency of 2724MHz, and a bandwidth of 100 MHz.

Example 4

This example provides a method for manufacturing a broadband film bulk acoustic resonator, which has a structure substantially the same as that of example 1, and the details are different from each other in that: the first bottom electrode 103 is metal Mo with the thickness of 140 nm; the top electrode I108 is metal Mo with the thickness of 140nm, the 1-9 piezoelectric layers are AlN, ZnO, AlN, ZnO and AlN respectively, the AlN thickness is 60nm, and the ZnO thickness is 140 nm.

The obtained resonator has a series resonance frequency of 2602MHz, a parallel resonance frequency of 2702MHz and a bandwidth of 100 MHz.

Comparative example 1

The resonator comprises a second substrate 201, a second bottom electrode 203, a piezoelectric layer 204, a second top electrode 205, a second bottom electrode 203 and an air gap surrounded by the second substrate 201, wherein the second substrate, the second bottom electrode 203, the piezoelectric layer 204, the second top electrode 205, the second bottom electrode 203 and the second substrate 201 are sequentially distributed from bottom to top, the second top electrode 205 and the second bottom electrode 203 are respectively and oppositely connected to the upper surface and the lower surface of the piezoelectric layer, the second bottom electrode 203 is directly contacted with the air gap, and the second top electrode 205, the piezoelectric layer 204 and the second bottom electrode 203 form a sandwich structure.

The second substrate 201 is single crystal high-resistance silicon; the second bottom electrode 203 is metal Mo with the thickness of 200 nm; the top electrode II 205 is metal Mo with the thickness of 200 nm; the piezoelectric layer 204 is a 1 μm thick layer of AlN film. The depth of the air gap was 2 μm. The preparation method is the same as example 1.

The preparation method of the resonator comprises the following steps:

(2) filling the groove by using the PSG as a sacrificial layer, and then removing all the PSG outside the groove by using a CMP (chemical mechanical polishing) process;

(3) depositing a bottom electrode above the groove by using a magnetron sputtering PVD method, photoetching and etching the pattern and reserving a release hole;

(4) depositing a piezoelectric layer above the bottom electrode layer by layer, and photoetching and etching the pattern;

(5) depositing a top electrode over the piezoelectric layer using PVD and lithographically etching the pattern;

(6) and removing the sacrificial layer through the release hole of the photoetching and wet etching to form a complete device structure.

The series resonance frequency of the resonator is 2648MHz, the parallel resonance frequency is 2738MHz, and the bandwidth is 90 MHz.

In summary, by comparing the examples with the comparative examples, it can be seen that the series resonance frequency of example 1 is 2643MHz, the parallel resonance frequency is 2739MHz, and the bandwidth is 96 MHz; the series resonance frequency of the embodiment 2 is 2646MHz, the parallel resonance frequency is 2746MHz, and the bandwidth is 100 MHz; the series resonance frequency of embodiment 3 is 2624MHz, the parallel resonance frequency is 2724MHz, and the bandwidth is 100 MHz; the series resonance frequency of embodiment 4 is 2602MHz, the parallel resonance frequency is 2702MHz, and the bandwidth is 100 MHz; the series resonance frequency of comparative example 1 was 2648MHz, the parallel resonance frequency was 2738MHz, and the bandwidth was 90 MHz. Therefore, the utility model discloses a control ZnO/AlN's proportion, can adjust the bandwidth, under the same resonant frequency, embodiment 1's bandwidth has promoted 6.7% compared with comparative example 1, embodiment 2's bandwidth has promoted 11.1% compared with comparative example 1, embodiment 3's bandwidth has promoted 11.8% compared with comparative example 1, embodiment 4's bandwidth has promoted 12.8% compared with comparative example 1. The effect of embodiment 1 ~ 4 all is superior to comparative example 1, demonstrates the utility model discloses a low-loss broadband film bulk acoustic resonator has been obtained.

The above-mentioned embodiments only represent some embodiments of the present invention, and the description thereof is specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for those skilled in the art, without departing from the spirit of the present invention, several variations and modifications can be made, which are within the scope of the present invention. Therefore, the protection scope of the present invention should be subject to the appended claims.

Claims

1. A broadband thin film bulk acoustic resonator, characterized by: the resonator sequentially comprises a top electrode, a composite piezoelectric film, a bottom electrode and a substrate from top to bottom; the top electrode, the composite piezoelectric film and the bottom electrode form a sandwich structure; an air gap is formed between the bottom electrode and the substrate; the composite piezoelectric film is formed by stacking a plurality of piezoelectric layers.

2. The broadband thin film bulk acoustic resonator according to claim 1, wherein: the substrate is high-resistance monocrystalline silicon.

3. The broadband thin film bulk acoustic resonator according to claim 1, wherein: the depth of the air gap is 800 nm-5 μm.

4. The broadband thin film bulk acoustic resonator according to claim 1, wherein: the composite piezoelectric film is formed by superposing 2-8 piezoelectric layers, wherein each piezoelectric layer is made of AlN or ZnO, and the thickness of each piezoelectric layer is 100 nm-3 mu m.

5. The broadband thin film bulk acoustic resonator according to claim 4, wherein: the composite piezoelectric film is formed by alternately superposing AlN piezoelectric layers and ZnO piezoelectric layers.

6. The broadband thin film bulk acoustic resonator according to claim 1, wherein: the deposition thickness of the top electrode and the bottom electrode is 40 nm-450 nm, and the material is one of Al, Pt, Mo, W, Ti and Au.