A crystal filter element

Abstract

The present invention discloses a crystal filter element, which includes a plurality of bulk resonators, a first input endpoint, a second input endpoint, a first output endpoint and a second output endpoint. The plurality of bulk resonators are divided into two types: a first bulk resonator having a series relationship with the two output endpoints and a second bulk resonator having a parallel relationship with the two output endpoints. Each bulk resonator includes a substrate, a first electrode and a second electrode. The substrate includes a growth substrate and a crystal thin film layer disposed on the growth substrate. The crystal thin film layer has an upper surface and a lower surface partially exposed outside the growth substrate. Each first electrode is disposed on the corresponding exposed lower surface of the crystal thin film layer, and the second electrode is disposed on the upper surface of the crystal thin film layer. There are at least two first bulk resonators, and each first bulk resonator is distributed on the same first arc, and the position thickness of the crystal thin film layer corresponding to the first arc is the same. A preparation method of the above crystal filter element is also disclosed.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a crystal filter element and a preparation method thereof. Background Art

[0002] Current smartphones, Wi-Fi, etc. all have unique radio frequency (RF) signal receiving systems. In these signal receiving systems, microwave filter elements play the role of selecting the required signals and are therefore indispensable. It has been more than 80 years since thin crystal resonators were used to form filter elements. In recent years, in order to increase the information capacity, the signal transmission frequency has gradually increased. Now 5G technology has been adopted, with a frequency above 2 GHz; and it is gradually transitioning to millimeter waves (frequency above 30 GHz). These technologies require miniaturized, low-loss, high-frequency broadband filters.

[0003] Currently, the products applicable to the above bands on the market are bulk acoustic wave (BAW) filter elements formed by using polycrystalline AlN thin film bulk acoustic resonators (FBAR, or thin film bulk resonators), such as ladder filters (ladder filter, Figure 8 ) and lattice filters (lattice filter, Figure 9 ), which have input terminals (6, 8) and output terminals (7, 8a). In some cases, terminals 8 and 8a are also called ground wires. For a ladder filter, the input terminal 8 and the output terminal 8a are the same because they are both connected to the ground wire. The bulk resonator 1 has a series relationship with the output terminal (7, 8a) and is usually called a series resonator; the bulk resonator 2 has a parallel relationship with the output terminal and is usually called a shunt resonator.

[0004] Polycrystalline AlN thin films have a selective orientation, that is, the C direction of most AlN grains is generally perpendicular to the thin film and has certain piezoelectricity. However, compared with single-crystal AlN thin films, the performance is not high enough. On the other hand, in order to increase the operating frequency to the above 5G / millimeter wave band, it is necessary to reduce the thickness of the polycrystalline AlN thin film, which will cause a decrease in the piezoelectric coefficient and the effective electromechanical coupling coefficient (K 2 eff ) will decrease. Therefore, in order to achieve high-frequency operation and improve the performance and reliability of AlN thin film bulk resonators, such as the effective electromechanical coupling coefficient and reduce noise, etc., single-crystal AlN thin film bulk resonators can be used.

[0005] However, using single-crystal AlN thin film bulk resonators will have a series of problems that have not been realized or solutions have not been proposed: ① All series bulk resonators 1 should have the same resonance frequency, otherwise they cannot work efficiently. However, AlN and its similar III-nitride crystal thin films such as Gax Al 1-x N and Sc x Al 1-x N, etc. are formed by heteroepitaxial growth on growth substrates such as SiC, Si, and sapphire at high temperatures (>1000 °C), such as AlN / SiC and AlN / Si. Stress will be caused during the growth process and cooling. The factors causing stress include heteroepitaxial lattice mismatch, changes in defect concentration during the growth process, thermal expansion mismatch, and the way of heating the substrate, etc. Stress will cause the growth substrate to warp during the growth process, the thickness of the single-crystal thin film will become uneven, and the resonance frequencies of each bulk resonator 1 (FBAR) will be different, and it will be impossible to construct high-quality ladder and lattice filters; ② In order to form electrodes, part of the growth substrate needs to be etched. However, substrates that can be easily etched, such as SiC and Si, are usually conductive, and high-resistance SiC is quite expensive; ③ The internal stress of AlN can reduce the effective electromechanical coupling coefficient; ④ The AlN thin film of the polycrystalline resonator is usually directly deposited on the lower metal electrode, and there is basically no problem with the FBAR connection method. For the single-crystal thin film bulk resonator, its connection method must be optimized to reduce costs and facilitate packaging. Summary of the Invention

[0006] The first technical problem to be solved by the present invention is to provide a crystal filter element that can improve the efficiency in view of the problems existing in the above-mentioned prior art.

[0007] The second technical problem to be solved by the present invention is to provide a preparation method for the above-mentioned filter element.

[0008] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is as follows: A crystal filter element includes a plurality of bulk resonators, a first input endpoint, a second input endpoint, a first output endpoint, and a second output endpoint. The plurality of bulk resonators are divided into two types: a first bulk resonator having a series relationship with the two output endpoints and a second bulk resonator having a parallel relationship with the two output endpoints. Each bulk resonator includes a substrate, a first electrode, and a second electrode. The substrate includes a growth substrate and a crystal thin film layer disposed on the growth substrate. The crystal thin film layer has an upper surface and a lower surface partially exposed outside the growth substrate. Each first electrode is disposed on the corresponding exposed lower surface of the crystal thin film layer, and the second electrode is disposed on the upper surface of the crystal thin film layer. The bulk resonators are connected to each other through a first electrode connection line or a second electrode connection line. The feature is that there are at least two first bulk resonators, and each first bulk resonator is distributed on the same first arc, and the thickness of the position of the crystal thin film layer corresponding to the first arc is the same.

[0009] Further, to enable the second bulk resonator to also have the same frequency and improve the quality of the filtering element, at least two second bulk resonators are provided, and each second bulk resonator is distributed on the same second arc. The position thickness of the crystal thin film layer corresponding to the second arc is the same.

[0010] Further, to facilitate the electrical connection of each bulk resonator, the growth substrate is etched to expose a part of the lower surface of the crystal thin film layer. The growth substrate forms a surface at the etched position and the bottom, and the first electrode connection line extends along the surface of the growth substrate so as to be able to connect the first electrodes to be connected.

[0011] Further, to avoid leakage between the first electrode connection line and the growth substrate and at the same time increase the adhesion between the first electrode connection line and the growth substrate, a first dielectric layer is provided on the surface of the growth substrate, and the first dielectric layer extends between the crystal thin film layer and the first electrode connection line.

[0012] Further, to reduce the influence of the growth substrate on the overall crystal filtering element, the upper surface of the growth substrate includes a high-resistance material layer.

[0013] Further, to reduce the etching cost, the thickness of the growth substrate does not exceed 200 microns.

[0014] Further, to avoid using air resonators and reduce the electrode connection lines for connecting the electrodes on both sides of the substrate, the crystal filtering element is a ladder filter. Between adjacent first bulk resonators, between the first bulk resonator and the second bulk resonator, and between the second bulk resonators, the second electrode connection line on the upper side of the substrate and the first electrode connection line on the lower side are alternately used for connection. The second input endpoint and the second output endpoint are ground connection points and are located on the upper side and the lower side of the substrate respectively.

[0015] Further, to facilitate packaging, when the number of first bulk resonators is even, there is only a second output endpoint on the lower side of the substrate.

[0016] The technical solution adopted by the present invention to solve the above second technical problem is: a preparation method of a crystal filtering element, characterized by including the following steps:

[0017] 1) Providing a substrate: The substrate includes a growth substrate and a crystal thin film layer grown on the growth substrate;

[0018] 2) Removing part of the growth substrate to expose a part of the lower surface of the crystal thin film layer. At the same time, the growth substrate forms a surface at the removed position and the bottom;

[0019] 3) Form the first dielectric layer and the first electrode: Form the first dielectric layer on the surface of the growth substrate, and then form the first electrode after removing the first dielectric layer at the exposed lower surface of the crystal thin film layer; Electrically connect the required first electrodes through the first electrode connection wires;

[0020] 4) Perform mesa etching on the upper surface of the crystal thin film layer;

[0021] 5) Form the second dielectric layer on the upper surface of the crystal thin film layer;

[0022] 6) Form the second electrode: At the position corresponding to the first electrode on the lower surface of the crystal thin film layer, form the second electrode after removing the second dielectric layer on the crystal thin film layer;

[0023] 7) Connect the required second electrodes through the second electrode connection wires, and form the first input endpoint, the second input endpoint, the first output endpoint, and the second output endpoint connected to the first bulk resonator or the second bulk resonator.

[0024] Furthermore, to facilitate supporting the first electrode and enhance the strength, a support layer is formed on the lower surface of the first electrode.

[0025] Compared with the prior art, the advantages of the present invention are as follows: All the series-connected bulk resonators are arranged on the same arc with the same crystal thin film thickness, and the resonance frequencies are the same, which can improve the quality of the crystal filter element; A thinner growth substrate is used to reduce the etching cost. Even if the growth substrate is prone to warping due to large thickness non-uniformity during the growth process because of its thinness, the problem of thickness non-uniformity can also be solved by arranging all the series-connected bulk resonators on the arc with the same thickness; The ground connection points are reasonably set, making the element easy to manufacture, highly reliable, and easy to package. Brief Description of the Drawings

[0026] Figure 1 It is a top view of the crystal filter element of the present invention;

[0027] Figure 2 It is a schematic diagram of the bulk resonator element and the air resonator unit of the crystal filter element of the present invention;

[0028] Figures 3-1 to 3-7 It is a schematic diagram of the manufacturing process of the crystal filter element;

[0029] Figure 4 It is a top view of the crystal filter element of the first specific embodiment of the present invention;

[0030] Figure 5 It is a schematic diagram of the bulk resonator unit of the crystal filter element of the first specific embodiment of the present invention;

[0031] Figure 6Top view of the crystal filter element according to the second specific embodiment of the present invention;

[0032] Figure 7 Schematic diagram of the bulk resonator unit of the crystal filter element according to the second specific embodiment of the present invention;

[0033] Figure 8 Circuit schematic diagram of a bulk acoustic wave (BAW) filter element (ladder filter) composed of thin film bulk acoustic resonators (FBARs) in the prior art;

[0034] Figure 9 Circuit schematic diagram of a bulk acoustic wave (BAW) filter element (form filter) composed of thin film bulk acoustic resonators (FBARs) in the prior art. Detailed description of the specific implementation

[0035] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are 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 specific orientation, be constructed and operated in a specific orientation. Since the disclosed embodiments of the present invention can be arranged in different directions, these terms indicating directions are only for illustration and should not be regarded as limitations. For example, "upper" and "lower" are not necessarily limited to the directions opposite to or consistent with the direction of gravity. In addition, the features defined as "first" and "second" may explicitly or implicitly include one or more of such features.

[0037] See Figure 1 , a crystal filter element, including a first input endpoint 6, a second input endpoint 8, a first output endpoint 7, a second output endpoint 8a, and a crystal thin film bulk acoustic resonator (FBAR, hereinafter referred to as a bulk resonator). The second input endpoint 8 and the second output endpoint 8a can be grounded.

[0038] The crystal filter element as a whole has a circular profile with a center O. In a specific implementation, there are multiple such crystal filter elements on a 4" substrate. The bulk resonators include a first bulk resonator 1 and a second bulk resonator 2. Four first bulk resonators 1 are connected in series between a first input endpoint 6 and a first output endpoint 7, and three second bulk resonators 2 are connected in parallel between the first output endpoint 7 and a second output endpoint 8a. Among them, the four series-connected first bulk resonators 1 are distributed on a first arc 10 with the center O as the center and r2 as the radius, forming a series relationship with the two output endpoints as a whole. The three parallel-connected second bulk resonators 2 are distributed on a second arc 9 with the center O as the center and r1 as the radius, forming a parallel relationship with the two output endpoints as a whole. Preferably, the four series-connected first bulk resonators 1 are evenly distributed in the circumferential direction, and the three parallel-connected second bulk resonators 2 are evenly distributed in the circumferential direction.

[0039] The structures of the first bulk resonator 1 and the second bulk resonator 2 are basically the same, thus reducing the manufacturing cost. The arrangement of the above-mentioned bulk resonators is related to the existing III-group nitride crystal thin film epitaxial growth technology. For example, in the case of uniform heating and substrate spin growth, along the first arc 10 or the second arc 9, the film thickness can be the same. The resonance frequencies of the first bulk resonator 1 and the second bulk resonator 2 are different, and this difference can be controlled. In addition to using the difference in the crystal film thickness, a dielectric layer with a certain thickness can also be added above the second electrode 16 (to be described below) to finely adjust their resonance frequencies.

[0040] The crystal filter element further includes an air resonator 3. There are four air resonators 3, three of which are connected in series between two adjacent first bulk resonators 1, and the other is connected between the first bulk resonator 1 closest to the first output endpoint 7 and the first output endpoint 7, thereby assisting in forming a connection. And the air resonator 3 is located on the first arc 10 with the center O as the center and r1 as the radius.

[0041] See Figure 1 and Figure 2 , Figure 2Shown is the structure of a first bulk resonator 1 and an adjacent empty resonator 3. The second bulk resonator 2 is substantially the same as the first bulk resonator 1 and is not shown for simplicity. Each bulk resonator includes a substrate 11, which includes a crystal thin film layer 13 and a growth substrate 12. The crystal thin film layer 13 is epitaxially grown on the growth substrate 12. The crystal thin film layer 13 has an upper surface and a lower surface. By etching the growth substrate 12, the lower surface of the crystal thin film layer 13 can be exposed outside the growth substrate 12. The growth substrate 12 can be SiC, Si, GaN, sapphire, or AlN, etc. Preferably, the upper surface is high-resistance; otherwise, some measures need to be taken, such as a larger area of etching at the bottom. The growth substrate 12 is preferably capable of being effectively etched by liquid or plasma (ICP). The crystal thin film layer 13 is a group-III nitride thin film, such as AlN, which has a relatively large piezoelectric coefficient. Among group-III nitrides, AlN is a relatively mature material, and Ga or Sc can be doped into AlN. Adding Ga to AlN can reduce the stress of AlN at room temperature, but at the same time, it will reduce the piezoelectric coefficient, generally not exceeding 20%. And the most preferred is to dope Sc, which can reduce the stress at room temperature and will not reduce the piezoelectric coefficient.

[0042] A first electrode 17 and a second electrode 16 are respectively disposed on the upper and lower sides of the crystal thin film layer 13. Usually, the first electrode 17 is larger than the second electrode 16. The crystal thin film layer 13 and the two electrodes form a bulk resonator. The first electrode 17 and the second electrode 16 generally use metal materials with relatively large acoustic impedance, such as Mo, Cr, etc. Mo is more suitable, but it is generally difficult to deposit; while Cr has a better surface adhesion, which is beneficial for deposition. The first bulk resonator 1 and the second bulk resonator 2 must have significantly different frequencies. The frequency can be changed by adding a layer of material, such as SiO2, to the second electrode 16 of one of them. A support layer 18 is disposed on the lower side of the first electrode 17. The support layer 18 can include an acoustic mirror, such as a W / SiO2 multi-layer film structure.

[0043] Each empty resonator 3 shares the growth substrate 12 with the adjacent first bulk resonator 1 and has the same first electrode 17 as the first bulk resonator 1. In addition, it further includes a third electrode 15 located above the first electrode 17. The difference between this structure and the bulk resonator is that no crystal thin film layer 13 is provided between the third electrode 15 and the first electrode 17 of the empty resonator 3, which is convenient for forming electrode connections without increasing the manufacturing cost and is used for optimizing the package. Similarly, the first electrode 17 is exposed outside the growth substrate 12.

[0044] The first electrodes 17 are electrically connected to each other through the first electrode connection lines 5. The first electrode connection lines 5 are preferably made of metal. The first electrode connection lines 5 extend along the surface 20 of the production substrate 12 after etching. A first dielectric layer 19 is provided between the surface 20 of the growth substrate 12 and the first electrode connection lines 5 to prevent leakage between the first electrode connection lines 5 and the growth substrate 12, and at the same time, it can also increase the adhesion between the first electrode connection lines 5 and the growth substrate 12. The first dielectric layer 19 can extend to the lower surface of the exposed crystal thin film layer 13, thereby separating the first electrodes 17 from the growth substrate 12. The crystal thin film layer 13 is coated with a second dielectric layer 14 except for the part (upper side and periphery) in contact with the growth substrate 12. The second dielectric layer 14 can be SiO2 or Si x grown by PECVD (Plasma Enhanced Chemical Vapor Deposition). If the growth substrate 12 is SiC, a thin SiO2 layer can be first formed by plasma oxidation, and then other dielectric materials can be deposited to form the first dielectric layer 19 and the second dielectric layer 14.

[0045] There are two basic forms for the resonator combination to form a filtering element: ladder type ( Figure 8 ) and lattice type ( Figure 9 ). Although each has its own advantages and disadvantages, generally one of the most basic requirements is that the first bulk resonators 1 must have consistent resonance frequencies. However, during the growth process of the crystal thin film layer 13 (also called epitaxial thin film) in this embodiment, it is very difficult to ensure good thickness uniformity of the crystal thin film layer 13 over the entire growth substrate 12, so it will cause changes in the resonance frequency. For example, when the thickness of the crystal thin film layer 13 is about 500 nanometers, a 1-nanometer difference in film thickness may cause a change in the resonance frequency of up to 20 MHz. However, in terms of growth technology (such as MOVPE: Metal-Organic Vapor Phase Epitaxy), the thickness distribution of the crystal thin film layer 13 can be effectively controlled. For example, in a single-chip growth system, when the temperature of the heating body of the growth substrate 12 is uniform, the growth substrate 12 will warp, like a bowl shape, which is caused by the temperature gradient of the growth substrate 12. When the growth substrate 12 rotates, it will ensure that the film thickness is the same on the first arc 10 with the center O of the growth substrate 12 as the center and a radius of r2, so that the corresponding first bulk resonators 1 can have the same frequency, and thus a high-quality filtering element can be formed. There may be frequency differences between the filtering elements, but in practical applications, adjustments can be made in the circuit or wiring. Similarly, the second bulk resonators 2 can also be on the same second arc 9 with the same thickness. The first electrodes 16 and the third electrodes 15 are respectively connected to the electrodes or adjacent endpoints of the adjacent resonators through the same second electrode wires 4. The empty resonators 3 located between the two first bulk resonators 1 are respectively connected to the corresponding second bulk resonators 2 (connecting the corresponding electrodes through electrode connection lines) to achieve the parallel setting of the second bulk resonators 2.

[0046] In Figure 1 Figure 1 , the solid lines between the first input terminal 6 and the first bulk resonator 1, between the dummy resonator 3 and the first bulk resonator 1, between the dummy resonator 3 and the second bulk resonator 2, and between the dummy resonator 3 and the first output terminal 7 represent the second electrode connection 4, and the dashed lines between the dummy resonator 3 and the first bulk resonator 1, and between the second bulk resonator 2 and the second output terminal 8a represent the first electrode connection 5. That is, the second electrode connection 4 is located on the upper side of the substrate 11, and the first electrode connection 5 is located on the lower side of the substrate 11.

[0047] The manufacturing process of the above crystal filter element includes the following steps:

[0048] 1) Provide the substrate 11: Refer to Figure 3-1 , as can be seen from the above, the substrate 11 includes a crystal thin film layer 13 and a growth substrate 12. The growth substrate 12 should not be too thick. For example, if SiC is used, its thickness does not exceed 200 microns; if Si is used, its thickness does not exceed 350 microns; the crystal thin film layer 13 is epitaxially grown on the growth substrate 12;

[0049] 2) Remove part of the growth substrate 12: Refer to Figure 3-2 , thereby, making part of the lower surface of the crystal thin film layer 13 exposed (exposed means that the lower surface is not covered by the growth substrate 12). At the same time, the growth substrate 12 forms a surface 20 at the etching position and the bottom; the exposed part of the lower surface of the crystal thin film layer 13 can have multiple spaced parts. The number of the exposed lower surfaces is related to the number of the first bulk resonator 1, the second bulk resonator 2, and the dummy resonator 3, and the positions ensure that the exposed parts corresponding to the first bulk resonator 1 are located on the same first arc 10 (with the center of the growth substrate 12 as the center and r2 as the radius), and the exposed parts corresponding to the second bulk resonator 2 are located on the same second arc 9 (with the center of the growth substrate 12 as the center and r1 as the radius); in this embodiment, the method of removing part of the growth substrate 12 is preferably to use plasma etching (such as SF6 + O2). The etching rate of SF6 for III-group nitrides is very small, but the etching rates of etching SiC and Si can both reach 2 microns per minute; during etching, it is necessary to first use photolithography and metal deposition to form an etching mask, such as Cr, etc. A reference area can be set, and an optical method can be used to detect the remaining thickness of SiC or Si. Because thin Si wafers and SiC are transparent or semi-transparent in the infrared or visible light region, when the remaining growth substrate 12 is very thin, the upper surface of the substrate 11 can also be bonded to a carrier to play a protective role;

[0050] 3) Form the first dielectric layer 19 and the first electrode 17. After etching, refer to Figure 3-3, the first dielectric layer 19 can be formed on the surface 20 formed by the growth substrate 12. If it is a Si substrate, it is very easy to form the first dielectric layer. If it is a SiC substrate, it is first oxidized using O2 plasma and then the first dielectric layer 19 is deposited. If electron beam evaporation is used, the substrate 11 can be tilted towards the crucible, or the rotation of the substrate 11 can be utilized simultaneously to ensure that the dielectric is deposited on each surface. The most common materials for the first dielectric layer 19 include SiO2 and Si x N; the first dielectric layer 19 not only serves as an insulator but also increases the adhesion between the metal and the growth substrate 12;

[0051] Then, the first electrode 17 is formed on the exposed lower surface of the crystal thin film layer 13: electron beam evaporation or ion beam sputtering can be adopted. This method usually includes photolithography and a relatively thick negative photoresist can be used. First, the first dielectric layer 19 on the lower surface of the crystal thin film layer 13 needs to be removed, and then an electrode such as Cr or Mo is deposited on the newly exposed lower surface of the crystal thin film layer 13 to form the first electrode 17. A support layer 18 can also be formed on the lower surface of the first electrode 17. The support layer 18 includes an acoustic mirror, such as a Cr / SiO2 multilayer film structure. Similarly, if electron beam evaporation or the like is used, the substrate 11 can be tilted towards the crucible to ensure the required deposition. The first electrodes 17 are electrically connected through the first electrode connection line 5. The first electrode connection line 5 extends along the outer side of the first dielectric layer 19 away from the growth substrate 12. The first electrode 17 and the first electrode connection line 5 can use the same metal thin film;

[0052] 4) Perform mesa etching on the crystal thin film layer 13: Refer to Figure 3-4 , and the etching methods include photolithography, forming a mask, and wet etching or dry etching (ICP);

[0053] 5) Form the second dielectric layer 14: Refer to Figure 3-5 , a second dielectric layer 14 is formed on the etched upper surface of the crystal thin film layer 13. SiO2 or the like can be deposited using PECVD (plasma enhanced chemical vapor deposition method). Preferably, flowable oxide is spin-coated, which can weaken the steps on the upper surface;

[0054] 6)) Form the second electrode 16: Refer to Figure 3-6, electron beam evaporation or ion beam sputtering can be adopted, which usually includes photolithography and can be completed using a negative photoresist; at a position corresponding to the first electrode 17 on the lower surface of the crystal thin film layer 13, the second dielectric layer 14 on the crystal thin film layer 13 is removed, and an electrode such as Cr or Mo is deposited to form the second electrode 16; at the same time, at a position corresponding to the first electrode 17 of the air resonator 3, the second dielectric layer 14 at the corresponding position is removed, and an electrode such as Cr or Mo is deposited to form the third electrode 15. The second electrode 16 and the third electrode 15 can be protected by a photoresist;

[0055] 7) Form input terminals and output terminals: Refer to Figure 3-7 , a first input terminal 6 and a first output terminal 7 are formed on the upper side of the substrate 11, a second input terminal 8 and a second output terminal 8a are formed on the lower side of the substrate 11, between the second electrode 16 of a first bulk resonator 1 at the end of the first arc 10 and the first input terminal 6, between the third electrode 15 of an adjacent air resonator 3 and the first electrode 16 of the first bulk resonator 1, between the third electrode 15 of an air resonator 3 at the other end of the first arc 10 and the first output terminal 7, and between the third electrode 15 of the air resonator 3 and the second electrode 16 of the corresponding second bulk resonator 2, a second electrode connection line 4 is formed, and a first electrode connection line 5 is also formed between the first electrode 17 of the second bulk resonator 2 and the second input terminal 8 and the second output terminal 8a, forming a final crystal filter element; each air resonator 3 is connected to two adjacent first bulk resonators 1 respectively through the first electrode connection line 5 and the second electrode connection line 4 (that is, connected to one through the first electrode connection line 5 and to the other through the second electrode connection line 4). Between the above adjacent bulk resonators or air resonators, the connection is realized by the alternating up-and-down manner of the first electrode connection line 5 and the second electrode connection line 4. The formation of each terminal can adopt the photolithography method, and then the deposition of metal is used to form each electrode connection line, so as to avoid large parasitic capacitance; the above process can be adjusted in order or carried out simultaneously. Generally speaking, the metal deposition can be postponed.

[0056] During the whole manufacturing process, the electrodes or connection lines can be protected by a photoresist or a metal (such as Al), because they have etching selectivity relative to the materials used for the electrodes or connection lines.

[0057] Refer to Figure 4 and Figure 5, which is a specific embodiment of the present invention, is a ladder filter. In this embodiment, the substrate 411 includes an AlN crystal thin film (preferably with a thickness of 450 nanometers) 413 grown by MOVPE epitaxy and a high-resistance SiC growth substrate 412 (preferably with a thickness of 150 micrometers). The structural parameters of a single body resonator are as follows: the diameter of the etched part of the growth substrate 12 is 180 micrometers (i.e., the part where the lower surface of the crystal thin film layer 413 is exposed); the diameter of the first electrode 417 (Cr electrode) is 120 micrometers and the thickness is 25 nanometers; the diameter of the second electrode 416 (Cr electrode) is 90 micrometers and the thickness is 25 nanometers. Among them, there can be SiO2 with a thickness of 50 nm above the second electrode 416 of the second body resonator 2. Since there is no empty resonator 3, the support layer 18 can be not required. The crystal thin film layer 413 is covered by a second dielectric layer 414 with a thickness of 100 nanometers, and the second dielectric layer 414 is PECVD SiO2. In addition, the second input endpoint 408 is arranged on the upper side of the substrate 411, and the second output endpoint 408a is arranged on the lower side of the substrate 411 for encapsulation. The second input endpoint 408 and the second output endpoint 408a are both connected to the ground wire, so they are interconnected.

[0058] The manufacturing process of the above-mentioned ladder filter device is as follows, which is similar to the process shown in Figures 3-1 to 3-7 :

[0059] 1) Provide the substrate 411: The substrate 411 includes an AlN crystal thin film layer 413 (450 nanometers thick) grown by MOVPE, epitaxially grown on a high-resistance SiC growth substrate 412 (thickness: 150 micrometers; resistivity: 10 +10 ohm·cm);

[0060] 2) Remove part of the growth substrate 412 to form the surface 420 of the growth substrate 412 and partially expose the lower surface of the crystal thin film layer 413: ① First, use photolithography, lift-off technology, and Cr metal deposition to form an etching mask with a thickness of approximately 500 nanometers; a Ni(100 nanometers) / Ti(10 nanometers) multi-layer film structure can also be used, and it is necessary to first form a 10-nanometer Cr bond on the surface of SiC; ② Use SF6+O2 plasma (ICP) to etch SiC; all masks can be removed or retained for wire connection;

[0061] 3) Connect in the ICP equipment, use oxygen plasma to process the surface 420 of SiC to form a thin SiO2 layer, that is, the first dielectric layer 419. This thin layer acts as a bonding layer, which will help form a more solid metal layer or dielectric layer and avoid the capacitance of the Schottky diode; then use PECVD to increase its thickness to 100 nanometers;

[0062] 4) Form the first electrode 417 on the lower side and the first electrode connection line 405. These can be carried out simultaneously using the same material such as Mo or Cr: First, lithographically form a photoresist mask, and remove the SiO2 layer at the position of the first electrode 417. Electron beam evaporation or ion beam sputtering can be adopted. The substrate 411 should form an angle with the raw material crucible to ensure deposition on the lower surface of the crystal thin film layer 413 and on the adjacent SiC surface 420.

[0063] 5) Perform mesa etching on the crystal thin film layer 413: This includes lithography, electron beam evaporation of a Ti (10 nm) / Ni (80 nm) multilayer film, and a lift-off technique to form a mask with a thickness of approximately 200 nm, and then use Cl2 plasma dry etching (ICP).

[0064] 6) Deposit 100 nm of SiO2 on the mesa of the crystal thin film layer 413 by PECVD to form the second dielectric layer 414.

[0065] 7) Form the second electrode 416 on the upper side: Lithography can be carried out using a negative photoresist; remove the second dielectric layer 414 above the crystal thin film layer 413, deposit an electrode such as Cr or Mo, etc., to form the second electrode 416, and the second electrode 416 can be protected by a photoresist; for the second bulk resonator 402, form a 30-nm-thick SiO2 layer on the second electrode 416 to change its resonance frequency.

[0066] 8) Use necessary lithography and metal deposition to form the required first input endpoint 406, second input endpoint 408, first output endpoint 407, second output endpoint 408a, and second electrode connection line 404: Form the first input endpoint 406, first output endpoint 407, and two second input endpoints 408 on the upper side of the substrate 411, form the second output endpoint 408a on the lower side of the substrate 411. Second electrode connection lines 404 are formed between the second electrode 416 of a first bulk resonator 401 at the end of the first arc 410 and the first input endpoint 406, between the second electrode 416 of a first bulk resonator 401 at the other end of the first arc 410 and the first output endpoint 407, between the two second output endpoints 408, between the second electrode 416 of a second bulk resonator 402 at the end of the second arc 409 and a corresponding second input endpoint 408, and between the second electrode 416 of a second bulk resonator 402 at the other end of the second arc 409 and a corresponding second input endpoint 408. First electrode connection lines 405 are also formed between the first electrodes 417 of each second bulk resonator 402 and the first electrodes 417 of the corresponding first bulk resonators 401, and between a second bulk resonator 402 in the middle of the second arc 409 and the second output endpoint 408a, thus forming the final crystal filter element.

[0067] To avoid using the empty resonator 3 and reduce any electrode connection wires for connecting the electrodes on both sides of the substrate 411, for the ladder filter device, the first input endpoint 408 and the second output endpoint 408a can be formed on the upper and lower sides of the substrate 411 respectively. When the number of bulk resonators in series with the output end is 4, that is, an even number, only the second output endpoint 408a is on the lower side of the substrate 411. This can simplify the device packaging, improve the reliability of the device and reduce the parasitic inductance.

[0068] See Figure 6 and Figure 7 , which is the second specific embodiment of the present invention, namely the format filter. It not only avoids the empty resonator 3, but also the first input endpoint 506 and the second input endpoint 508 are on the upper side of the substrate 511, while the first output endpoint 507 and the second output endpoint 508a are on the lower side. When packaging, there are two connection wires on each of the upper and lower sides, and the device is more miniaturized. There are two first bulk resonators 501, one of which is connected between the first input endpoint 506 and the first output endpoint 507, and the other is connected between the second input endpoint 508 and the second output endpoint 508a. There are two second bulk resonators 502, one of which is connected between the first input endpoint 506 and the second output endpoint 508a, and the other is connected between the second input endpoint 508 and the first output endpoint 507.

[0069] The substrate 511 includes a Ga 0.05 Al 0.95 N crystal thin film layer 413 (preferably 450 nanometers thick) grown by MOVPE, and a high-resistance SiC growth substrate 512 (thickness: 150 micrometers). An appropriate amount of Ga can improve the stress of the thin film. The structural parameters of a single bulk resonator are: the diameter of the etched part of the growth substrate 512 is 150 micrometers (i.e., the part of the lower surface of the crystal thin film layer 513 exposed); the diameter of the first electrode 517 (Cr electrode) is 150 micrometers and the thickness is 25 nanometers; the diameter of the second electrode 516 (Cr electrode) is 90 micrometers and the thickness is 25 nanometers. Among them, there can be a 40-nm-thick SiO2 above the second electrode 516 of the second bulk resonator 2. Since there is no empty resonator 3, the support layer 18 can be not needed. The crystal thin film layer 513 is covered by a 100-nanometer-thick second dielectric layer 514, and the second dielectric layer 514 is PECVD SiO2.

[0070] Its bulk resonator and manufacturing process can be the same as those of the first specific embodiment above. The surface 520 is only treated with oxygen plasma.

Claims

1. A crystal filter element, comprising a plurality of bulk resonators, a first input endpoint, a second input endpoint, a first output endpoint, and a second output endpoint. The plurality of bulk resonators are divided into two types: a first bulk resonator having a series relationship with the two output endpoints and a second bulk resonator having a parallel relationship with the two output endpoints. Each bulk resonator includes a substrate, a first electrode, and a second electrode. The substrate includes a growth substrate and a crystal thin film layer disposed on the growth substrate. The crystal thin film layer has an upper surface and a lower surface partially exposed outside the growth substrate. Each first electrode is disposed on the corresponding exposed lower surface of the crystal thin film layer, and the second electrode is disposed on the upper surface of the crystal thin film layer. The bulk resonators are connected to each other through a first electrode connection line or a second electrode connection line. It is characterized in that: The first bulk resonator has at least two, and each first bulk resonator is distributed on the same first circular arc, and the position thickness of the crystal thin film layer corresponding to the first circular arc is the same.

2. The crystal filter element according to claim 1, characterized in that: The second bulk resonator has at least two, and each second bulk resonator is distributed on the same second circular arc, and the position thickness of the crystal thin film layer corresponding to the second circular arc is the same.

3. The crystal filter element according to claim 1, wherein: The growth substrate is etched to expose a part of the lower surface of the crystal thin film layer, and the growth substrate forms a surface at the etching position and the bottom, and the first electrode connection line extends along the surface of the growth substrate so as to be able to connect the first electrodes to be connected.

4. The crystal filter element according to claim 3, wherein: A first dielectric layer is provided on the surface of the growth substrate, and the first dielectric layer extends between the crystal thin film layer and the first electrode connection line.

5. The crystal filter element according to any one of claims 1 to 4, characterized in that: The upper surface of the growth substrate includes a high-resistance material layer.

6. The crystal filter element according to any one of claims 1 to 4, characterized in that: The thickness of the growth substrate does not exceed 200 microns.

7. The crystal filter element according to claim 1, wherein: The crystal filter element is a ladder filter, and between adjacent first bulk resonators and first bulk resonators, first bulk resonators and second bulk resonators, and second bulk resonators and second bulk resonators, the second electrode connection line on the upper side of the substrate and the first electrode connection line on the lower side are alternately used for connection, and the second input end point and the second output end point are ground connection points and are respectively located on the upper side and the lower side of the substrate.

8. The crystal filter element according to claim 7, characterized in that: When the number of the first bulk resonators is even, there is only a second output end point on the lower side of the substrate.

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