A novel FBAR filter and its manufacturing method

Abstract

The present invention discloses a novel FBAR filter and a method for preparing the same. The method includes: etching a groove on a preparation substrate, preparing a piezoelectric material and a bottom electrode in the groove, first preparing a thin seed layer before preparing the bottom electrode, preparing an air cavity support layer, taking another support substrate, bonding the support substrate, the preparation substrate and the air cavity support layer together, removing the preparation substrate to expose the piezoelectric material, preparing a top electrode on the piezoelectric material, and leading out the bottom electrode to obtain a filter formed by cascading a plurality of resonators. By the method of first digging a groove on the preparation substrate and then growing the piezoelectric material, the present invention effectively avoids the problem of cracks caused by excessive stress generated by growing a whole layer of piezoelectric thin film, reduces the stress of the piezoelectric thin film, and at the same time, due to the discontinuity of the piezoelectric thin film of each resonator unit, effectively avoids the problem of energy loss caused by lateral transmission of energy, and can also effectively suppress clutter, improving the preparation yield and performance of the filter.

Description

Technical Field

[0001] The present invention belongs to the technical field of radio frequency filtering, and particularly relates to a novel FBAR filter and a preparation method thereof. Background Art

[0002] The multi-functional development of wireless communication terminals has put forward high-tech requirements such as miniaturization, high frequency, high performance, low power consumption, and low cost for radio frequency devices. Traditional surface acoustic wave filters (SAW) have large insertion losses in the high-frequency band above 2.4 GHz, and dielectric filters have good performance but are too large in volume. The thin film bulk acoustic resonator (FBAR) technology is a new radio frequency device technology that has emerged in recent years with the improvement of processing technology levels and the rapid development of modern wireless communication technologies, especially personal wireless communication technologies. It has the advantages of an extremely high quality factor Q value (above 1000) and can be integrated on an IC chip, and is compatible with the complementary metal oxide semiconductor (CMOS) process, effectively avoiding the disadvantages that surface acoustic wave resonators and dielectric resonators cannot be compatible with the CMOS process.

[0003] However, the air-gap type FBAR filter is currently monopolized by foreign patents and this technical route cannot be used. However, the performance of the FBAR filter with this structure still has room for improvement. As Figure 1 shown, it includes a substrate, an air cavity on the substrate, a bottom electrode, a piezoelectric layer, and a top electrode sequentially fabricated across the air cavity on the substrate. In the master's thesis "Research and Modeling of Thin Film Bulk Acoustic Resonators (FBAR)" by Chen Wei of Zhejiang University, pages 47-48, the preparation process of foreign Agilent resonators is mentioned: an air cavity is etched on the upper surface of the Si wafer, and then a sacrificial layer material PSG is filled in the pit. After the surface of the sacrificial layer is polished by CMP, a metal film is sputtered and grown, and a bottom electrode pattern is etched at a position corresponding to above the sacrificial layer. Then a piezoelectric film is deposited above the bottom electrode. After etching, the piezoelectric film covers the boundary of the pit on the substrate and exposes the lead-out end of the bottom electrode. Next, a metal film is deposited on the piezoelectric film, and a top electrode pattern is etched. Next, a release window is etched on the piezoelectric layer through dry etching to expose part of the sacrificial layer. Finally, the sacrificial layer is released from the etched release window, and the FBAR across the air cavity on the substrate is fabricated. However, this sacrificial layer release method will leave many release channel holes on the piezoelectric layer, causing great damage to the piezoelectric thin film, resulting in the cavity structure being prone to collapse, and having a low Q value, low electromechanical coupling coefficient, and large insertion loss, affecting the performance of the device. Summary of the Invention

[0004] In order to overcome the deficiencies of the existing technology, the purpose of the present invention is to provide a novel FBAR filter and a preparation method thereof. The novel FBAR filter provided by the present invention is a thin film bulk acoustic wave filter.

[0005] Based on this, the purpose of the present invention is to overcome the defects of the existing technology, and a novel FBAR filter and a preparation method thereof are proposed. By using this preparation method, during the preparation process, there is no need to use a sacrificial layer, which reduces the damage to the piezoelectric thin film, thereby overcoming the problem of adverse effects on the filter structure during the removal of the sacrificial layer. And this method of etching grooves on the preparation substrate and preparing the piezoelectric thin film in the grooves can effectively reduce the stress of the piezoelectric thin film, suppress clutter, reduce energy loss, can well improve the quality of the piezoelectric film, reduce the insertion loss of the thin film bulk acoustic wave resonator, improve the Q value and the electromechanical coupling coefficient, and will become a solution suitable for radio frequency filters in future high-frequency and high-power applications.

[0006] The purpose of the present invention is achieved by at least one of the following technical solutions.

[0007] The novel FBAR filter provided by the present invention is composed of n resonators connected in cascade, where n is an integer and n≥1; the resonator includes a support substrate, an air cavity support layer, a bottom electrode, a seed layer, a piezoelectric thin film structure layer, a top electrode and a bottom electrode lead; there are two air cavity support layers, which are respectively laminated on the support substrate, and the bottom electrodes are respectively connected to these two air cavity support layers. The bottom electrode, the air cavity support layer and the support substrate enclose a cavity; the seed layer is laminated on the bottom electrode and the air cavity support layer; the piezoelectric thin film structure layer and the top electrode are sequentially laminated on the seed layer; the bottom electrode lead is connected to the bottom electrode.

[0008] Further, the support substrate is one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, an aluminum nitride substrate, an AlxGa1-xN buffer layer substrate, a glass substrate, an organic polymer material flexible substrate, etc.

[0009] Further, the material of the air cavity support layer is an insulating material, and the insulating material is one or more of SiO2, AlN, and Si3N4; the thickness of the air cavity support layer is 0.3 - 3μm.

[0010] Preferably, the material of the support layer is an insulating material; the material of the support layer is a material with a relatively high dielectric constant such as silicon dioxide, silicon nitride, aluminum nitride, gallium nitride, etc.

[0011] Further, the materials of the bottom electrode and the top electrode are one or more of Al, Mo, W, Pt, Cu, Ag, Au, ZrN, etc.; the thicknesses of both the bottom electrode and the top electrode are 20 - 500nm.

[0012] Further, the seed layer is a sputtered polycrystalline piezoelectric material or a single-crystalline piezoelectric material; the material of the seed layer is one or more of AlN, ZnO, lithium niobate, lithium tantalate, etc.; the thickness of the seed layer is 5-100 nm.

[0013] Further, the piezoelectric thin film structure layer is one or more of an epitaxially grown high-quality single-crystalline piezoelectric thin film, a polycrystalline piezoelectric thin film with a high C-axis orientation grown by sputtering, and a thin film with piezoelectric properties; the material of the piezoelectric thin film structure layer is one or more of AlN, ZnO, PZT, lithium niobate, lithium tantalate, etc.; the thickness of the piezoelectric thin film structure layer is 0.02 μm - 10 μm.

[0014] The novel FBAR filter provided by the present invention has a filtering frequency of 10 MHz - 100 GHz.

[0015] The preparation method of the novel FBAR filter provided by the present invention includes: First, grooves are prepared on a preparation substrate by an etching method (the number of grooves can be multiple), then a piezoelectric material is prepared in the grooves, and then a bottom electrode is prepared. Before preparing the bottom electrode, a thin seed layer is first prepared, an air cavity support layer is prepared, and another support substrate is taken. The support substrate is bonded together with the preparation substrate and the above structures, and then the preparation substrate is removed to expose the piezoelectric material. A top electrode is prepared above the piezoelectric material, and the bottom electrode is led out, and finally a filter composed of multiple basic resonators connected in cascade is prepared.

[0016] The preparation method of the novel FBAR filter provided by the present invention includes the following steps:

[0017] (1) Etch n grooves (the number of grooves can be multiple) on a preparation substrate, where n is an integer and n≥1; then a piezoelectric thin film structure layer (piezoelectric material) is prepared in the grooves, a seed layer (thin bottom electrode seed layer) is prepared on the piezoelectric thin film structure layer by an epitaxial or sputtering method, and then a bottom electrode is prepared on the seed layer by sputtering or electron beam evaporation and patterned;

[0018] (2) Prepare two air cavity support layers on the bottom electrode and the seed layer (deposit an insulating material and pattern it as the air cavity support layer), and take another support substrate (this substrate can be a silicon wafer, sapphire, silicon, sapphire, LiGaO2, GaN, SiC, glass, organic polymer material, etc.). Bond the support substrate to the two air cavity support layers and the preparation substrate at the same time. The bottom electrode, the air cavity support layer, and the support substrate enclose a cavity. After the bonding is completed, the preparation substrate is removed, and the removal method is the commonly used mechanical thinning combined with wet etching or dry etching in the industry;

[0019] (3) After the preparation substrate is removed, the piezoelectric thin film structure layer is exposed. A top electrode is prepared on the piezoelectric thin film structure layer, and the bottom electrode is led out (etching a through-hole on the bottom electrode for the seed layer, and the method can be wet etching or dry etching). The bottom electrode can be led out by methods such as electroplating, evaporation, or sputtering to obtain the novel FBAR filter (a filter composed of multiple resonators connected in cascade).

[0020] Further, the preparation substrate in step (1) is one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, a LiGaO2 substrate, an aluminum nitride substrate, an AlxGa1-xN buffer layer substrate, a glass substrate, and a flexible organic polymer material substrate.

[0021] Further, a cavity is etched in the middle of the surface of the support substrate bonded to the air cavity support layer in step (2), and the depth of the cavity is 0.5 - 3 micrometers.

[0022] The preparation method provided by the present invention can prepare FBAR filters with arbitrary frequencies, including FBAR filters in the frequency range from 10 MHz to 10 GHz.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] In the preparation process of the preparation method provided by the present invention, there is no need to use a sacrificial layer, which reduces the damage to the piezoelectric thin film, thereby overcoming the problem of adverse effects on the filter structure during the removal of the sacrificial layer. Moreover, the method of etching a groove on the preparation substrate and preparing a piezoelectric thin film in the groove can effectively reduce the stress of the piezoelectric thin film, suppress clutter, reduce energy loss, can well improve the quality of the piezoelectric film, reduce the insertion loss of the thin film bulk acoustic wave resonator, increase the Q value and the electromechanical coupling coefficient, and will become a solution suitable for radio frequency filters in future high-frequency and high-power applications. Description of the Drawings

[0025] Figure 1 It is a cross-sectional view of an air-gap type FBAR in the prior art;

[0026] Figure 2 It is a cross-sectional view of the preparation substrate in the embodiment;

[0027] Figure 3 It is a schematic diagram of etching a groove on the preparation substrate in the embodiment;

[0028] Figure 4 It is a schematic diagram of preparing a piezoelectric thin film in the groove of the preparation substrate in the embodiment;

[0029] Figure 5 It is a schematic diagram of preparing a seed layer and a bottom electrode in the embodiment;

[0030] Figure 6 Schematic diagram of depositing and patterning an insulating dielectric support layer in the embodiment;

[0031] Figure 7 Schematic diagram of taking another support substrate and bonding it to the previous wafer in the embodiment;

[0032] Figure 8 Schematic diagram of removing the substrate and preparing the top electrode in the embodiment;

[0033] Figure 9 Schematic diagram of the novel FBAR filter obtained after leading up the bottom electrode in the embodiment;

[0034] Figure 10 Schematic diagram for demonstrating the principle of the resonator ladder cascade structure filter in the embodiment;

[0035] Figure 11 Effect diagram showing the low insertion loss and wide passband of the filter manufactured in the embodiment. Detailed implementation manners

[0036] The following further illustrates the specific implementation of the present invention in conjunction with examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can implement or understand them with reference to the prior art. The reagents or instruments used without indicating the manufacturer are regarded as conventional products that can be obtained through commercial purchase.

[0037] Example 1

[0038] A novel FBAR filter is formed by cascading n resonators, where n is a positive integer and n≥1; as Figure 9 shown, the resonator includes a support substrate 106, an air cavity support layer 105, a bottom electrode 104, a seed layer 103, a piezoelectric thin film structure layer 102, a top electrode 107, and a bottom electrode lead-up 108; there are two air cavity support layers 105, which are respectively stacked on the support substrate 106, and the bottom electrode 104 is respectively connected to these two air cavity support layers 105. The bottom electrode 104, the air cavity support layer 105, and the support substrate 106 enclose a cavity; the seed layer is stacked on the bottom electrode 104 and the air cavity support layer 105; the piezoelectric thin film structure layer 102 and the top electrode 107 are sequentially stacked on the seed layer 103; the bottom electrode lead-up 108 is connected to the bottom electrode 104.

[0039] The support substrate 106 is one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, an aluminum nitride substrate, an AlxGa1-xN buffer layer substrate, a glass substrate, and a flexible organic polymer material substrate.

[0040] The material of the air cavity support layer 105 is an insulating material, and the insulating material is one or more of SiO2, AlN, and Si3N4; the thickness of the air cavity support layer 105 is 0.3 - 3 μm.

[0041] The materials of the bottom electrode 104 and the top electrode 107 are one or more of Al, Mo, W, Pt, Cu, Ag, Au, and ZrN; the thicknesses of both the bottom electrode 104 and the top electrode 107 are 20 - 500 nm.

[0042] The seed layer 103 is a sputtered polycrystalline piezoelectric material or a single crystal piezoelectric material; the material of the seed layer 103 is one or more of AlN, ZnO, lithium niobate, and lithium tantalate; the thickness of the seed layer 103 is 5 - 100 nm.

[0043] The piezoelectric thin film structure layer 102 is one or more of an epitaxially grown single crystal piezoelectric thin film, a highly c-axis oriented polycrystalline piezoelectric thin film grown by sputtering, and a thin film with piezoelectric properties; the material of the piezoelectric thin film structure layer 102 is one or more of AlN, ZnO, PZT, lithium niobate, and lithium tantalate; the thickness of the piezoelectric thin film structure layer 102 is 0.02 μm - 10 μm.

[0044] Through the combination of different piezoelectric layer thicknesses and different electrode thicknesses, the resonant frequency of the resonator can range from 10 MHz to 10 GHz, and then a filter passband from 10 MHz to 10 GHz can be formed by cascading. Figure 10 It is a schematic diagram showing the principle of the resonator ladder cascade structure filter in the embodiment. As Figure 10 shown, the series resonator and the parallel resonator are ladder-cascaded to form the most basic filter unit, and a passband is formed through the correspondence of the resonant frequencies; in this way, the frequency of the resonator is affected by the piezoelectric layer thickness and the electrode thickness (as shown in Table 1 below), and filters with different frequency passbands can be formed. Table 1 is a data table showing different resonant points formed by different combinations of piezoelectric layer thicknesses and electrode thicknesses in the embodiment.

[0045] Table 1

[0046]

[0047] Example 2

[0048] A preparation method of a novel FBAR filter is as follows:

[0049] (1) As Figure 2 shown, take a preparation substrate 110, and the preparation substrate 110 can be a substrate material such as silicon, silicon carbide, sapphire, glass, metal, or organic polymer.

[0050] (2) As Figure 3As shown, a groove 101 is etched on a preparation substrate 110 by an etching method;

[0051] (3) As Figure 4 shown, a piezoelectric thin film structure layer 102 is prepared in the groove 101 by chemical vapor deposition or sputtering. The piezoelectric thin film structure layer 102 is made of single crystal or polycrystalline aluminum nitride material, or can also be materials with piezoelectric properties such as ZnO and PZT. The thickness of the piezoelectric thin film structure layer 102 is between 0.02 and 10 microns.

[0052] (4) As Figure 5 shown, a seed layer 103 and a bottom electrode 104 are prepared on the piezoelectric thin film structure layer 102 by chemical vapor deposition, sputtering or electron beam evaporation, and are patterned to obtain the required electrode pattern. The electrode material can be one or more of Al, Mo, W, Pt, Cu, Ag, Au, ZrN, and the electrode material can also be other materials with good electrical conductivity, such as non-metallic materials like graphene. The electrode thickness is in the range of 0.1 nanometer to 500 nanometers.

[0053] (5) As Figure 6 shown, an air cavity support layer (insulating layer) 105 is then deposited, with a thickness in the range of 0.2 - 4 microns, and then is polished flat and patterned by mechanical polishing to obtain Figure 6 the air cavity support layer 105 as shown;

[0054] (5) As Figure 7 shown, another support substrate 106 is taken and bonded to the wafer prepared previously. This figure is a schematic diagram after bonding;

[0055] (6) As Figure 8 shown, the preparation substrate 110 is removed by mechanical thinning combined with wet etching or dry etching and other methods, and a top electrode 107 is prepared;

[0056] (7) As Figure 9 shown, the seed layer 103 is etched and the bottom electrode is led out or interconnected with the next resonator unit by sputtering or electron beam evaporation to complete the preparation of the filter, and the novel FBAR filter is obtained.

[0057] Figure 11 is the effect diagram showing the low insertion loss and wide passband demonstrated by the filter manufactured in the embodiment. As Figure 11 shown, resonators with high Q values and large effective electromechanical coupling coefficients show small insertion losses in the performance of the cascaded filter, and can meet a relatively large passband bandwidth, verifying the embodiments of the present invention.

[0058] The specific embodiments described above only represent one embodiment of the present invention, which can be used to prepare FBAR filters with different frequency ranges. The description herein is relatively brief, but it should not be construed as a limitation on the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A novel FBAR filter, characterized in that, It is formed by cascading n resonators, where n is an integer and n≥1; the resonator includes a support substrate, an air cavity support layer, a bottom electrode, a seed layer, a piezoelectric thin film structure layer, a top electrode, and a bottom electrode lead-out. There are two air cavity support layers, which are respectively laminated on the support substrate, and the bottom electrodes are respectively connected to these two air cavity support layers. The bottom electrode, the air cavity support layer, and the support substrate enclose a cavity; the seed layer is a sputtered AlN or ZnO material with a thickness of 5 - 100 nm, and is laminated on the bottom electrode and the air cavity support layer. The piezoelectric thin film structure layer and the top electrode are sequentially laminated on the seed layer; the bottom electrode lead-out is connected to the bottom electrode; the piezoelectric thin film structure layer is formed by confined growth through etching a groove on the substrate; a cavity is etched in the middle of the surface of the support substrate where it is bonded to the air cavity support layer, and the depth of the cavity is 0.5 - 3 microns.

2. The novel FBAR filter according to claim 1, characterized in that, The support substrate is one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, an aluminum nitride substrate, an AlxGa1-xN buffer layer substrate, a glass substrate, and a flexible organic polymer material substrate.

3. The novel FBAR filter according to claim 1, wherein The material of the air cavity support layer is an insulating material, and the insulating material is one or more of SiO2, AlN, and Si3N4; the thickness of the air cavity support layer is 0.3 - 3 μm.

4. The novel FBAR filter according to claim 1, wherein The materials of the bottom electrode and the top electrode are both one or more of Al, Mo, W, Pt, Cu, Ag, Au, and ZrN; the thicknesses of the bottom electrode and the top electrode are both 20 - 500 nm.

5. The novel FBAR filter according to claim 1, characterized in that, The piezoelectric thin film structure layer is one or more of an epitaxially grown single crystal piezoelectric thin film, a polycrystalline piezoelectric thin film with a high C-axis orientation grown by sputtering, and a thin film with piezoelectric properties; the material of the piezoelectric thin film structure layer is one or more of AlN, ZnO, PZT, lithium niobate, and lithium tantalate; the thickness of the piezoelectric thin film structure layer is 0.02 μm - 10 μm.

6. The novel FBAR filter according to claim 1, characterized in that, The filtering frequency is 10 MHz - 100 GHz.

7. A method for preparing the novel FBAR filter according to any one of claims 1-6, characterized in that, It includes the following steps: (1) Etch n grooves on the preparation substrate, where n is an integer and n≥1, then respectively prepare a piezoelectric thin film structure layer in each groove, prepare a seed layer on the piezoelectric thin film structure layer, and then prepare a bottom electrode on the seed layer. (2) Prepare two air cavity support layers on the bottom electrode and the seed layer, take another support substrate, bond the support substrate to the two air cavity support layers simultaneously, and the bottom electrode, the air cavity support layer, and the support substrate enclose a cavity. (3) Remove the preparation substrate to expose the piezoelectric thin film structure layer, prepare a top electrode on the piezoelectric thin film structure layer, and lead out the bottom electrode to obtain the novel FBAR filter.

8. The preparation method of the novel FBAR filter according to claim 7, characterized in that, The preparation substrate in step (1) is one or more of a silicon substrate, a sapphire substrate, a silicon carbide substrate, a gallium nitride substrate, an aluminum nitride substrate, an AlxGa1-xN buffer layer substrate, a glass substrate, and a flexible organic polymer material substrate.

Images