CN218217328U

CN218217328U - Air gap film bulk acoustic wave filter

Info

Publication number: CN218217328U
Application number: CN202221524754.3U
Authority: CN
Inventors: 张志民; 张树民; 宋磊; 杨伟欣
Original assignee: Hangzhou Sappland Microelectronics Technology Co ltd
Current assignee: Hangzhou Sappland Microelectronics Technology Co ltd
Priority date: 2022-06-17
Filing date: 2022-06-17
Publication date: 2023-01-03
Anticipated expiration: 2032-06-17

Abstract

The utility model discloses an air gap film bulk acoustic wave filter, include: the device comprises a substrate, a first electrode and a second electrode, wherein the upper surface of the substrate is provided with a cavity; the sacrificial layer is deposited in the cavity, and the upper surface of the sacrificial layer is flush with the upper surfaces of the substrate and the cavity; a seed layer deposited on the substrate and the sacrificial layer; a lower electrode deposited on the seed layer; a piezoelectric layer deposited on the lower electrode; an upper electrode deposited on the piezoelectric layer. The beneficial effects of the utility model include: simple structure easily realizes, deposits the sacrificial layer in the cavity of substrate to make piezoelectric layer become the factor that directly influences resonant frequency among the overall structure, consequently no longer need the mass loading layer, can adjust required resonant frequency through changing piezoelectric layer thickness, thereby reduce the frequency modulation technology degree of difficulty, the large-scale production of being convenient for possesses good filter performance simultaneously.

Description

Air gap film bulk acoustic wave filter

Technical Field

The utility model relates to a wave filter technical field, in particular to air gap film body acoustic wave filter.

Background

With the increasing popularity of 5G technology, the radio frequency communication technology faces the challenges of higher frequency, larger relative bandwidth and higher power; this places increasingly higher demands on the performance of the filter.

In order to obtain the required resonant frequencies of different resonators, a mass loading layer needs to be additionally deposited on a specific resonator. The thickness of the mass loading layer and the number of the required mass loading layers are different according to different designs. The patterning process of the mass loading layer comprises the following steps: coating, photoetching, etching, photoresist removing, or photoetching, coating and stripping. The deposited mass load layer is usually small in thickness (about tens of nanometers or even smaller), the requirement on coating is high, the process difficulty is increased, and meanwhile, the accurate measurement of the mass load is also a great test. The step profiler or the resistance method cannot accurately measure the nanometer level, and expensive sound velocity measurement equipment such as Rudolph is needed.

Therefore, the air gap film bulk acoustic wave filter in the prior art has high production cost and difficult performance improvement due to the structural characteristics of the air gap film bulk acoustic wave filter.

SUMMERY OF THE UTILITY MODEL

Air gap film bulk acoustic wave filter manufacturing cost to prior art is higher, the relatively poor problem of performance, the utility model provides an air gap film bulk acoustic wave filter deposits sacrificial layer in the cavity of substrate to make the piezoelectric layer become the factor that directly influences resonant frequency among the overall structure, consequently no longer need the quality load layer, can adjust required resonant frequency through changing piezoelectric layer thickness, therefore can reduce the requirement to production technology, thereby reduction in production cost, and the performance is higher.

The technical proposal of the utility model is as follows.

An air gap thin film bulk acoustic wave filter comprising:

the device comprises a substrate, a first electrode and a second electrode, wherein the upper surface of the substrate is provided with a cavity;

the sacrificial layer is deposited in the cavity, and the upper surface of the sacrificial layer is flush with the upper surfaces of the substrate and the cavity;

a seed layer deposited on the substrate and the sacrificial layer;

a lower electrode deposited on the seed layer;

a piezoelectric layer deposited on the lower electrode;

an upper electrode deposited on the piezoelectric layer.

The utility model discloses a structural feature of sacrificial layer makes the thickness of piezoelectric layer can show and influences resonant frequency, consequently no longer need additionally redeposit one deck mass loading layer, also need not use expensive apparatus and material for the mass loading layer, only needs to set up corresponding piezoelectric layer thickness according to required resonant frequency, consequently this filter structure can be under the condition that does not influence the performance, reduce cost. The setting of the layer thicknesses is well known to those skilled in the art, and is typically adjusted in a subtractive manner after deposition is completed to achieve the desired resonant frequency, for example, and the invention is not limited thereto.

Preferably, the substrate material is: silicon or silicon carbide or gallium nitride or alumina or diamond.

Preferably, the piezoelectric material of the piezoelectric layer is aluminum nitride.

In the existing structure, a mass load layer is needed to adjust the resonance frequency, and the general mass load layer adopts molybdenum (Mo), and the sound velocity of aluminum nitride (ALN) is much higher than that of Mo, so that the sensitivity of the frequency to the variation of ALN under the same thickness is small (the variation of frequency caused by the ALN with a WiFi frequency band of 1nm is larger than that of 2 nm). When the required mass load is small, the frequency modulation by depositing Mo has extremely high requirements on the coating process, and the stability of the coating is unreliable; therefore, compared with the existing structure needing a mass load layer, the cost and the process difficulty of the scheme can be greatly reduced, and the performance is unchanged.

Preferably, the electrode materials of the upper electrode and the lower electrode are: aluminum or molybdenum or tungsten.

Preferably, the device further comprises a protective layer deposited on the upper electrode.

Preferably, the material of the protective layer is: aluminum nitride or silicon dioxide.

The thickness of the protective layer is set according to the desired resonance frequency. After the protective layer is additionally added, the thickness of the protective layer also influences the resonant frequency, so that the protective layer with the corresponding thickness can be arranged according to the required resonant frequency.

Preferably, the lower surface of the cavity is smaller than the upper surface. Such a structure facilitates the deposition of the sacrificial layer.

The beneficial effects of the utility model include:

the structure is simple, the realization is easy, the filter structure is obtained through the specific combination of different layers, and the thickness of the piezoelectric layer can obviously influence the resonant frequency due to the existence of the sacrificial layer, so the adjusting range of the resonant frequency can be improved;

the thickness of the piezoelectric layer can be adjusted according to the required resonance frequency, and compared with the method that the thickness is adjusted by additionally depositing a mass load layer, the frequency modulation process difficulty can be reduced, and the large-scale production is facilitated;

meanwhile, the additional protective layer can further increase the adjustment space of the resonant frequency and improve the performance of the resonator.

Drawings

FIG. 1 is a schematic structural diagram of an embodiment of the present invention;

fig. 2 is another schematic structural diagram of the embodiment of the present invention;

the drawing comprises the following steps: 1-substrate, 2-cavity, 3-sacrificial layer, 4-seed layer, 5-lower electrode, 6-piezoelectric layer, 7-upper electrode, 8-protective layer.

Detailed Description

The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. Furthermore, in the following detailed description, numerous specific details are set forth in order to provide a better understanding of the present invention. It will be understood by those skilled in the art that the present invention may be practiced without some of these specific details. In some instances, methods, means, elements and circuits that are well known to those skilled in the art have not been described in detail so as not to obscure the present invention.

In the description of the embodiments herein, "/" means "or" unless otherwise specified, for example, a/B may mean a or B; "and/or" herein is merely an association describing an associated object, and means that there may be three relationships, e.g., a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone. In the description of the present embodiment, the meaning of "a plurality" is two or more unless otherwise specified.

Example 1:

an air gap film bulk acoustic wave filter, as shown in fig. 1, since the filter usually includes a plurality of resonators, this embodiment only selects three resonators to be connected as a representative, and specifically includes: the structure comprises a substrate 1, a cavity 2, a sacrificial layer 3, a seed layer 4, a lower electrode 5, a piezoelectric layer 6 and an upper electrode 7. Wherein the cavity is arranged on the upper surface of the substrate; the sacrificial layer is deposited in the cavity, and the upper surface of the sacrificial layer is flush with the substrate and the upper surface of the cavity; a seed layer is deposited on the substrate and the sacrificial layer; a lower electrode is deposited on the seed layer; a piezoelectric layer deposited on the lower electrode; an upper electrode is deposited on the piezoelectric layer.

In this embodiment, the piezoelectric material of the piezoelectric layer is aluminum nitride, and the thickness of the piezoelectric layer is set according to the required resonant frequency.

Wherein the substrate material can be selected from: silicon or silicon carbide or gallium nitride or alumina or diamond, with silicon carbide being used in this embodiment.

The electrode material of the upper electrode and the lower electrode can be selected as follows: aluminum, molybdenum or tungsten, and the embodiment adopts molybdenum material.

The structural characteristics of the sacrificial layer of the embodiment enable the thickness of the piezoelectric layer to significantly influence the resonant frequency, so that an additional mass loading layer is not required, expensive instruments and materials are not required to be used for the mass loading layer, and the corresponding thickness of the piezoelectric layer is only required to be set according to the required resonant frequency, so that the cost of the filter structure can be reduced without influencing the performance.

In the prior art, molybdenum (Mo) generally used as a mass load layer is opaque, and cannot be accurately measured in a nanometer level when a step profiler and a resistance method are used for measuring the film thickness, so expensive acoustic thickness measuring equipment such as Rudolph is required. Since aluminum nitride (ALN) as the piezoelectric layer is transparent, frequency modulation is performed by aluminum nitride trimming, and the film thickness before and after trimming can be measured by an ellipsometer. Thereby reducing the early investment and the later maintenance cost of the production line.

Furthermore, the sound velocity of ALN is much higher than that of Mo, so that the sensitivity of frequency to the variation of ALN is small in the case of the same thickness (the variation of frequency due to ALN > 2nm in the WiFi band of 1nm in frequency). When the required mass load is small, the frequency modulation by depositing Mo has extremely high requirements on the coating process, and the stability of the coating is unreliable; frequency modulation by means of the reduction of the piezoelectric layer is much more reliable at this time.

The structural design of this embodiment for it can be in the technology manufacturing process, after the deposit piezoelectric layer, the photoetching goes out the resonator region that needs to cut down the same thickness, and reuse ion bombardment equipment cuts down corresponding piezoelectric layer thickness, gets rid of the photoresist at last again, and deposit the electrode on the graphical piezoelectric layer, consequently compares in the current structure that needs the quality load layer, and the cost and the technology degree of difficulty of this scheme can reduce by a wide margin and the performance is unchangeable. In this way, the error can be controlled within 1nm by selecting the output power and setting the scanning parameters to reduce the functional area of the resonator, the cost of the frequency modulation process is greatly reduced, and the precision is higher.

Example 2:

as shown in fig. 2, the overall structure of this embodiment is identical to that of embodiment 1 except that a protective layer 8 is further included, which is deposited on the upper electrode. The protective layer is made of the following materials: aluminum nitride or silicon dioxide. This example uses silicon dioxide.

Example 3:

this embodiment is generally identical to embodiment 2, except that the lower surface of the cavity is smaller than the upper surface. Such a structure facilitates the deposition of the sacrificial layer.

The beneficial effects of the utility model include: the piezoelectric layer thickness adjusting device is simple in structure and easy to achieve, the piezoelectric layer thickness can be adjusted according to the required resonance frequency, the frequency modulation process difficulty is reduced, large-scale production is facilitated, and meanwhile the piezoelectric layer thickness adjusting device has good filter performance.

Through the description of the foregoing embodiments, those skilled in the art will understand that, for convenience and simplicity of description, only the division of the functional modules is used for illustration, and in practical applications, the above function distribution may be completed by different functional modules according to needs, that is, the internal structure of the apparatus may be divided into different functional modules, so as to complete all or part of the functions described above.

Units described as separate parts may or may not be physically separate, and parts displayed as units may be one physical unit or a plurality of physical units, may be located in one place, or may be distributed to a plurality of different places. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

The above description is only for the specific embodiments of the present application, but the scope of the present application is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present application, and shall be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An air gap thin film bulk acoustic wave filter comprising:

the device comprises a substrate, a first electrode and a second electrode, wherein a cavity is formed in the upper surface of the substrate;

a seed layer deposited on the substrate and the sacrificial layer;

a lower electrode deposited on the seed layer;

a piezoelectric layer deposited on the lower electrode;

an upper electrode deposited on the piezoelectric layer.

2. The air gap thin film bulk acoustic wave filter of claim 1, wherein the substrate material is: silicon or silicon carbide or gallium nitride or alumina or diamond.

3. The air gap thin film bulk acoustic wave filter of claim 1, wherein the piezoelectric material of the piezoelectric layer is aluminum nitride.

4. The air gap thin film bulk acoustic wave filter of claim 1, wherein the electrode materials of the upper electrode and the lower electrode are: aluminum or molybdenum or tungsten.

5. The air gap thin film bulk acoustic wave filter of claim 1, further comprising a protective layer deposited on the upper electrode.

6. The air gap thin film bulk acoustic wave filter of claim 5, wherein the material of the protective layer is: aluminum nitride or silicon dioxide.

7. The air gap thin film bulk acoustic wave filter of claim 1, wherein the lower surface of the cavity is smaller than the upper surface.