CN105897211A - Film bulk acoustic resonator having multiple resonance modes and preparation method thereof and filter - Google Patents

Abstract

The invention discloses a thin film bulk acoustic resonator with multi-resonant modes, which sequentially includes a silicon substrate and a piezoelectric stack structure, and the cavity between the piezoelectric stack structures forms a resonant cavity of the thin film bulk acoustic resonator; the piezoelectric The stacked structure includes a bottom electrode, more than two layers of piezoelectric films, and a top electrode in order from bottom to top. The film bulk acoustic resonator of the present invention has multiple resonance points, and multi-passband filters can be designed through cascading, bridging, etc., greatly reducing the number of FBAR filters on the wireless terminal.

Description

Thin film bulk acoustic resonator with multi-resonant modes, its preparation method and filter

technical field

The invention relates to a bulk acoustic wave resonator, in particular to a multi-resonance mode film bulk acoustic wave resonator, a preparation method thereof and a filter.

Background technique

Miniaturization, integration, and high performance are the requirements of wireless terminals for frequency devices. The solutions for traditional RF/microwave frequency devices are dielectric filters and surface acoustic wave filters. The former has better performance, but the size is too large. Although the latter is small in size, it has the disadvantages of low operating frequency, large insertion loss, and low power capacity. Film bulk acoustic resonator (FBAR) technology is currently the only RF filter technology that is expected to be integrated. It combines the superior performance of dielectric filters and the small size of surface acoustic wave (SAW) filters. At the same time Overcome the shortcomings of both. It has the advantages of high operating frequency, large power capacity, low loss, small size, good temperature stability, and can be integrated with radio frequency integrated circuit (RFIC) or microwave monolithic integrated circuit (MMIC).

The film bulk acoustic resonator adopts the sandwich structure of metal electrode-piezoelectric film-metal electrode. Its working principle is: when an alternating voltage is applied to the two electrodes, an alternating electric field will be formed in the piezoelectric film, and the piezoelectric film will Mechanically deformed due to the inverse piezoelectric effect, the piezoelectric film expands or contracts in response to changes in the applied electric field, creating oscillations that convert electrical signals into acoustic signals. At this time, the bulk acoustic wave propagating along the thickness direction of the film will be excited in the film and reflected back and forth between the two electrodes. When the propagation distance of the bulk acoustic wave in the piezoelectric film is exactly an odd multiple of the half wavelength, resonance will occur. Among them, the acoustic wave loss at the resonant frequency is the smallest, so that the acoustic signal at this frequency can pass through the piezoelectric film layer, while other acoustic signals that do not meet the resonance conditions will attenuate, and the farther the difference from the resonant frequency, the faster the attenuation of the acoustic signal. A single thin-film bulk acoustic resonator only resonates at a certain frequency point and cannot be called a filter. By cascading, bridging or coupling multiple thin film bulk acoustic resonators together in a certain way, a bandpass filter meeting certain requirements can be formed, among which the cascading method is the most commonly used.

Today's wireless mobile products not only have higher and higher requirements for volume and power saving, but also develop in the direction of multi-function, multi-band, multi-system, and multi-protocol fusion and integration. Typically, each filter has a specific passband frequency response characteristic. Sometimes a system may need to process signals in two or more different frequency ranges simultaneously. The current method needs to connect multiple filters in parallel to realize multiple frequency passband filtering functions. In theory, multiple filters can be connected in parallel to obtain the multi-passband synthesis characteristics of the sum of the characteristics of a single filter. In the case of using an FBAR filter, because the index of the FBAR filter is related to the impedance characteristics of the external circuit, the parallel connection of multiple filters increases the complexity of the external impedance of the filter, making the overall characteristics worse and making it difficult to debug the whole machine. In addition, multiple FBAR bandpass filters are required to realize multiple frequency passband filtering functions, which is bound to be detrimental to the development of the RF front-end in the direction of miniaturization and integration.

Contents of the invention

In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, one of the purposes of the present invention is to provide a multi-resonant mode film bulk acoustic resonator, which has multiple resonance points and can be designed with multiple passbands by cascading, bridging, etc. filter, greatly reducing the number of FBAR filters on the wireless terminal.

The second object of the present invention is to provide a method for preparing the above multi-resonance mode film bulk acoustic resonator.

The third object of the present invention is to provide a filter.

The object of the present invention is achieved through the following technical solutions:

The thin film bulk acoustic resonator of multi-resonance mode comprises a silicon substrate and a piezoelectric stack structure in turn, and the cavity between the piezoelectric stack structures forms a resonant cavity of the thin film bulk acoustic resonator; the piezoelectric stack structure consists of the following The top includes bottom electrodes, more than two layers of piezoelectric films, and top electrodes in sequence; the areas of the piezoelectric films of each layer are different.

The cavity is convex or concave.

When the cavity is an upwardly convex cavity, the piezoelectric stack structure further includes a support layer located under the bottom electrode, and the cavity between the support layer and the silicon substrate forms a bulk acoustic wave resonator. resonant cavity.

The piezoelectric thin film is an AlN piezoelectric thin film with C-axis preferential orientation.

The preparation method of the thin film bulk acoustic resonator of described multi-resonant mode, comprises the following steps:

(1) Utilize etching technique to prepare a groove on the top surface of silicon substrate;

(2) filling the sacrificial layer material in the groove;

(3) Depositing a layer of metal bottom electrode on the sacrificial layer material and patterning it;

(4) Deposit a layer of piezoelectric film by radio frequency magnetron sputtering, and carry out photolithography and ICP etching to the piezoelectric film to obtain a multilayer piezoelectric film, the area of each layer of piezoelectric film is different;

(5) Deposit a layer of metal top electrode on the piezoelectric film and image it; the bottom electrode, multi-layer piezoelectric film and top electrode form a piezoelectric stack structure;

(6) A sacrificial layer release via hole is etched on the piezoelectric stack structure, and the sacrificial layer is released through the sacrificial layer release via hole to obtain a thin film bulk acoustic resonator with multiple resonant modes.

The preparation method of the thin film bulk acoustic resonator of described multi-resonant mode, comprises the following steps:

(1) Deposit a sacrificial layer on the silicon substrate, and etch to form sacrificial layer protrusions;

(2) preparing a support layer on the sacrificial layer;

(3) Depositing a layer of metal bottom electrode on the support layer and patterning it;

(4) A layer of piezoelectric film is deposited by radio frequency magnetron sputtering, and a multilayer piezoelectric film is etched by photolithography and ICP;

(5) Deposit a layer of metal top electrode on the piezoelectric film and image it; the support layer, bottom electrode, multilayer piezoelectric film and top electrode form a piezoelectric stack structure;

(6) A sacrificial layer release via hole is etched on the piezoelectric stack structure, and the sacrificial layer is released through the sacrificial layer release via hole to obtain a thin film bulk acoustic resonator with multiple resonant modes.

The filter includes the film bulk acoustic wave resonator with multiple resonance modes.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

(1) In the thin film bulk acoustic resonator of the present invention, a single thin film bulk acoustic resonator can have multiple resonance points, thereby greatly reducing the number of thin film bulk acoustic resonators required for preparing a multi-passband filter, which is beneficial to the radio frequency front-end miniature development of culture.

(2) The preparation method of the thin film bulk acoustic resonator of the present invention is compatible with the conventional CMOS production process, reduces the difficulty of actual production, and is beneficial to the integration of the radio frequency front end.

(3) When using the thin film bulk acoustic resonator proposed by the present invention to design a filter, the complexity of the external impedance can be reduced and the debugging of the whole machine can be facilitated.

Description of drawings

FIG. 1 is a cross-sectional view of a multi-resonance mode thin-film bulk acoustic resonator according to Embodiment 1 of the present invention.

FIG. 2 is a diagram of the electrical impedance amplitude-frequency characteristics of the multi-resonance mode thin-film bulk acoustic resonator according to Embodiment 1 of the present invention.

3 is a cross-sectional view of the multi-resonance mode thin-film bulk acoustic resonator according to Embodiment 2 of the present invention after photolithography and sacrificial layer etching.

4 is a cross-sectional view of a multi-resonance mode thin-film bulk acoustic resonator according to Example 2 of the present invention.

FIG. 5 is a diagram of amplitude-frequency characteristics of electrical impedance of the multi-resonance mode thin-film bulk acoustic resonator of Embodiment 2 of the present invention.

detailed description

The present invention will be described in further detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto.

Example 1

The thin film bulk acoustic resonator of the multi-resonance mode of this embodiment is prepared by the following preparation method:

1. Etching a groove on the surface of the silicon substrate 1 with a depth of 30 μm, and then depositing a Si ₃ N ₄ substrate protective layer 2 with a thickness of 200 nm by PECVD to protect the silicon substrate. As shown in Figure 1.

2. A layer of PSG (phosphorus quartz glass) is deposited by PECVD on Si ₃ N ₄ as a sacrificial layer.

3. The surface of the sacrificial layer is polished by a CMP process.

4. A layer of Mo bottom electrode 4 with a thickness of 200 nm is deposited on the polished surface by DC magnetron sputtering, and patterned by photolithography.

5. Using radio frequency magnetron sputtering to deposit C-axis preferred orientation AlN piezoelectric film. And a multi-layer structure is etched by photolithography and ICP. This embodiment is a 3-layer AlN piezoelectric film, and the area size of the AlN piezoelectric film decreases sequentially from bottom to top; the thickness of each layer is 1 μm, 0.5 μm, and 0.3 μm from bottom to top.

6. Pattern a layer of Mo top electrode 6 with a thickness of 100 nm by photolithography and electron beam evaporation; the bottom electrode 4 , multi-layer piezoelectric film 5 and top electrode 6 form a piezoelectric stack structure.

7. Etch a sacrificial layer release hole on the piezoelectric stack structure, and use XeF ₂ (xenon fluoride) gas to pass through the sacrificial layer release hole to obtain a cavity 3 . Finally, a film bulk acoustic resonator with multiple resonance modes is obtained, as shown in Fig. 1 .

FIG. 2 is a diagram of the amplitude-frequency characteristics of the electrical impedance of the thin film bulk acoustic resonator prepared in this embodiment. It can be seen from the figure that the resonator resonates around 1.9GHz, 2.2GHz, and 2.8GHz.

The filter of this embodiment includes the thin film bulk acoustic resonator of this embodiment. Two serial thin film bulk acoustic resonators and one parallel thin film bulk acoustic resonator are cascaded into a trapezoidal topology. Wherein, the thickness of the top electrode of the parallel thin film bulk acoustic resonator is 10nm thicker than that of the series thin film bulk acoustic resonator. Thus forming a three-pass band filter.

Example 2

1. A layer of PSG (phosphorus quartz glass) is deposited by PECVD on the surface of the silicon substrate 1 as the sacrificial layer 7, and a pattern of the sacrificial layer is photoetched. As shown in Figure 3.

2. A layer of Si ₃ N ₄ supporting layer 8 is deposited by PECVD with a thickness of 300 nm.

3. A layer of Mo bottom electrode 4 with a thickness of 150 nm is patterned by photolithography and magnetron sputtering.

4. Using radio frequency magnetron sputtering to deposit C-axis preferred orientation AlN piezoelectric film. And a multi-layer structure is etched by photolithography and ICP. This embodiment is a three-layer AlN piezoelectric film, and the area size of the AlN piezoelectric film decreases successively from bottom to top; the thickness of each layer is 2 μm, 0.8 μm, and 0.5 μm from bottom to top.

5. A layer of Mo top electrode 6 with a thickness of 150 nm is patterned by photolithography and electron beam evaporation. The support layer 8 , the bottom electrode 4 , the multilayer piezoelectric film 5 and the top electrode 6 form a piezoelectric stack structure.

6. Etch the sacrificial layer release via hole, and use XeF ₂ (xenon fluoride) gas to pass through the sacrificial layer release via hole to obtain the cavity 3 . Finally, a film bulk acoustic resonator with multiple resonance modes is obtained, as shown in Fig. 4 .

As shown in FIG. 5 , the electrical impedance amplitude-frequency characteristic diagram of the film bulk acoustic resonator prepared in this embodiment. It can be seen from the figure that the resonator resonates around 1.12GHz, 1.25GHz, and 1.55GHz.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions and combinations made without departing from the spirit and principle of the present invention , simplification, all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims (7)

1. the FBAR of multi-resonant pattern, it is characterised in that include silicon substrate and piezoelectricity successively Stacked structure, the cavity between described piezo-electric stack structure forms the resonator cavity of FBAR；Institute State piezo-electric stack structure and include the piezoelectric membrane of more than hearth electrode, two-layer, top electrode the most successively；Respectively The area of lamination conductive film is different.

The FBAR of multi-resonant pattern the most according to claim 1, it is characterised in that Described cavity is epirelief or recessed cavity.

The FBAR of multi-resonant pattern the most according to claim 1, it is characterised in that When the cavity that described cavity is epirelief, described piezo-electric stack structure also includes the support being positioned under hearth electrode Layer, the cavity between described supporting layer and silicon substrate forms the resonator cavity of FBAR.

The FBAR of multi-resonant pattern the most according to claim 1, it is characterised in that Described piezoelectric membrane is the AlN piezoelectric membrane of C axle preferrel orientation.

5. the preparation method of the FBAR of the multi-resonant pattern described in claim 1, its feature It is, comprises the following steps:

(1) lithographic technique is utilized to prepare a groove at the top surface of silicon substrate；

(2) sacrificial layer material is filled up in a groove；

(3) on sacrificial layer material, deposit layer of metal hearth electrode, and be patterned；

(4) use r. f. magnetron sputtering one to be laminated electrolemma, piezoelectric film carried out photoetching, ICP etching, Obtaining multi-layer piezoelectric thin film, the area being often laminated conductive film is different；

(5) on piezoelectric membrane, deposit layer of metal top electrode, and carry out image conversion；Described hearth electrode, Multi-layer piezoelectric thin film, top electrode form piezo-electric stack structure；

(6) in piezo-electric stack structure, etch sacrifice layer release through hole, discharged by sacrifice layer release through hole Sacrifice layer, obtains the FBAR of multi-resonant pattern.

6. the preparation method of the FBAR of the multi-resonant pattern described in claim 1, its feature It is, comprises the following steps:

(1) deposit one layer of sacrifice layer at silicon substrate, and it is protruding to etch formation sacrifice layer；

(2) on sacrifice layer, one layer of supporting layer is prepared；

(3) on supporting layer, deposit layer of metal hearth electrode, and be patterned；

(4) use r. f. magnetron sputtering one to be laminated electrolemma, etch multi-layer piezoelectric by photoetching, ICP Thin film；

(5) on piezoelectric membrane, deposit layer of metal top electrode, and carry out image conversion；Described supporting layer, Hearth electrode, multi-layer piezoelectric thin film, top electrode form piezo-electric stack structure；

(6) in piezo-electric stack structure, etch sacrifice layer release through hole, discharged by sacrifice layer release through hole Sacrifice layer, obtains the FBAR of multi-resonant pattern.

7. wave filter, the film bulk acoustic comprising multi-resonant pattern described in any one of Claims 1 to 4 is humorous Shake device.