CN111988010A

CN111988010A - Crystal filter element and preparation method thereof

Info

Publication number: CN111988010A
Application number: CN202010857707.XA
Authority: CN
Inventors: 姜全忠
Original assignee: Suzhou Aopu Haotong Electronic Technology Co ltd
Current assignee: Suzhou Aopu Haotong Electronic Technology Co ltd
Priority date: 2020-08-24
Filing date: 2020-08-24
Publication date: 2020-11-24
Also published as: WO2022042756A1

Abstract

The invention discloses a crystal filter element, which comprises a plurality of bulk resonators, a first input end point, a second input end point, a first output end point and a second output end point, wherein the bulk resonators are divided into a first bulk resonator and a second bulk resonator, the first bulk resonator is connected with the two output end points in series, the second bulk resonator is connected with the two output end points in parallel, each bulk resonator comprises a substrate, a first electrode and a second electrode, the substrate comprises a growth substrate and a crystal thin film layer arranged on the growth substrate, the crystal thin film layer is provided with an upper surface and a lower surface which is partially exposed outside the growth substrate, each first electrode is arranged on the corresponding exposed lower surface of the crystal thin film layer, the second electrode is arranged on the upper surface of the crystal thin film layer, the number of the first resonators is at least two, the first resonators are distributed on the same first arc, and the thicknesses of the positions of the crystal thin film layer corresponding to the first arc are the same. Also discloses a preparation method of the crystal filter element.

Description

Crystal filter element and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductors, in particular to a crystal filter element and a preparation method thereof.

Background

Modern smart phones and WiFi, etc. have unique Radio Frequency (RF) signal receiving systems. In these signal receiving systems, the microwave filter element is indispensable for selecting a desired signal. The use of thin crystal resonators to form filter elements has been known for over 80 years. In recent years, in order to increase the information capacity, the signal transmission frequency has gradually increased. The 5G technology is adopted at present, and the frequency is over 2 GHz; and gradually transition to millimeter waves (frequencies above 30 GHz), these technologies require miniaturized, low-loss, high-frequency, broadband filters.

Products currently on the market that are suitable for the above-mentioned bands are Bulk Acoustic Wave (BAW) filter elements formed using polycrystalline AlN film bulk acoustic resonators (FBARs, or film bulk resonators), such as ladder filters (fig. 8) and lattice filters (fig. 9) having input terminals (6, 8) and output terminals (7, 8a), in some cases the

terminals

8, 8a also being called ground lines. For a ladder filter, input terminal 8 and output terminal 8a are identical because they are both connected to ground. The bulk resonator 1 has a series relationship with the output terminals (7, 8a), commonly referred to as a series resonator; the bulk resonator 2 has a parallel relationship with the output terminal, and is generally called a shunt resonator (shunt resonator).

The polycrystalline AlN film is selectively oriented, i.e., the C direction of most AlN grains is substantially perpendicular to the film, and has a certain piezoelectric property, but the performance is not sufficiently high as compared to a single-crystal AlN film. On the other hand, in order to increase the operating frequency to the above-mentioned 5G/millimeter wave band, it is necessary to thin the thickness of the polycrystalline AlN thin film, which results in a decrease in the piezoelectric coefficient and a decrease in the effective electromechanical coupling coefficient (K)² _eff) It will decrease. Therefore, in order to realize high-frequency operation and to improve the performance and reliability of the AlN thin film bulk resonator, such as an effective electromechanical coupling coefficient, noise reduction, and the like, a single-crystal AlN thin film bulk resonator may be used.

However, there are a number of problems with the use of single crystal AlN thin film bulk resonators, which have not been appreciated or have not addressed solutions: all the series-body resonators 1 should have the same resonance frequencyOtherwise, the work cannot be performed efficiently. However, AlN and similar III-nitride crystal films such as Ga_xAl_1-xN and Sc_xAl_1-xN, etc. at high temperature>Formed by heteroepitaxial growth on a growth substrate of SiC, Si, sapphire, etc., such as AlN/SiC and AlN/Si, etc., at 1000 deg.C. Stress is caused in the growth process and the temperature reduction, the factors for forming the stress comprise heteroepitaxial lattice mismatch, the change of defect concentration in the growth process, thermal expansion mismatch, a substrate heating mode and the like, the stress causes the growth substrate to tilt in the growth process, the thickness of a single crystal film becomes uneven, the resonance frequency of each bulk resonator 1(FBAR) is different, and a high-quality ladder-type filter and a high-quality format filter cannot be constructed; ② to form the electrode, part of the growth substrate needs to be etched, however, substrates such as SiC and Si, etc., which can be easily etched, are usually conductive, and high-resistance SiC is rather expensive; the internal stress of AlN can reduce the effective electromechanical coupling coefficient; AlN thin film of polycrystalline resonators is usually deposited directly on the lower metal electrode, and there is substantially no problem with FBAR connection, and for single crystal thin film resonators, it is necessary to optimize the connection so as to reduce cost and facilitate packaging.

Disclosure of Invention

A first technical problem to be solved by the present invention is to provide a crystal filter device, which can improve the performance of the crystal filter device.

The second technical problem to be solved by the present invention is to provide a method for manufacturing the filter element.

The technical scheme adopted by the invention for solving the first technical problem is as follows: a crystal filter element comprising a plurality of bulk resonators, a first input terminal, a second input terminal, a first output terminal and a second output terminal, the plurality of bulk resonators being divided into two types, a first bulk resonator having a series relationship with the two output terminals and a second bulk resonator having a parallel relationship with the two output terminals, each bulk resonator comprising a substrate, a first electrode and a second electrode, the substrate comprising a growth substrate and a crystal thin-film layer disposed on the growth substrate, the crystal thin-film layer having an upper surface and a lower surface partially exposed outside the growth substrate, each first electrode being disposed on the corresponding exposed lower surface of the crystal thin-film layer, the second electrode being disposed on the upper surface of the crystal thin-film layer, the bulk resonators being connected to each other by a first electrode connection line or a second electrode connection line, characterized in that: the first resonators are at least two, the first resonators are distributed on the same first arc, and the thicknesses of the positions of the crystal thin film layers corresponding to the first arcs are the same.

Furthermore, in order to enable the second bulk resonators to have the same frequency and improve the quality of the filter element, the number of the second bulk resonators is at least two, the second bulk resonators are distributed on the same second circular arc, and the thicknesses of the positions of the crystal thin film layers corresponding to the second circular arc are the same.

Further, in order to facilitate electrical connection of the respective bulk resonators, 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 etching position and the bottom, and the first electrode wiring extends along the surface of the growth substrate so as to be able to connect the first electrodes to be connected.

Furthermore, in order to avoid electric leakage between the first electrode connecting wire and the growth substrate and increase the adhesion between the first electrode connecting wire and the growth substrate, a first dielectric layer is arranged on the surface of the growth substrate and extends to a position between the crystal thin film layer and the first electrode connecting wire.

Further, in order to reduce the influence of the growth substrate on the whole crystal filter element, the upper surface of the growth substrate includes a high-resistance material layer.

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

Further, in order to avoid using empty resonators and reduce electrode connecting lines for connecting electrodes on both sides of the substrate, the crystal filter element is a ladder filter, between adjacent first bulk resonator and first bulk resonator, first bulk resonator and second bulk resonator, second bulk resonator and second bulk resonator, the second electrode connecting line on the upper side of the substrate and the first electrode connecting line on the lower side are respectively and alternately used for connection, and the second input end point and the second output end point are ground wire connecting points and are respectively positioned on the upper side and the lower side of the substrate.

Further, for packaging convenience, when the number of the first bulk resonators is even, the lower side of the substrate has only the second output terminal.

The technical scheme adopted by the invention for solving the second technical problem is as follows: a method for preparing a crystal filter element is characterized in that: the method comprises the following steps:

1) providing a substrate: the substrate comprises a growth substrate and a crystal thin film layer grown on the growth substrate;

2) removing part of the growth substrate to expose a lower surface part of the crystal thin film layer, and simultaneously forming a surface on the removal position and the bottom of the growth substrate;

3) forming a first dielectric layer and a first electrode: forming a first dielectric layer on the surface of the growth substrate, and then removing the first dielectric layer on the exposed lower surface of the crystal thin film layer to form a first electrode; electrically connecting the first electrodes to be connected through the first electrode connecting wires;

4) carrying out mesa corrosion on the upper surface of the crystal thin film layer;

5) forming a second dielectric layer on the upper surface of the crystal thin film layer;

6) forming a second electrode: removing the second dielectric layer on the crystal thin film layer at the position corresponding to the first electrode positioned on the lower surface of the crystal thin film layer to form a second electrode;

7) and connecting the second electrodes to be connected through a second electrode connecting line, and forming a first input terminal, a second input terminal, a first output terminal and a second output terminal which are connected with the first bulk resonator or the second bulk resonator.

Further, in order to facilitate supporting the first electrode and enhance strength, a support layer is formed on a lower surface of the first electrode.

Compared with the prior art, the invention has the advantages that: all the serially connected bulk resonators are arranged on the same arc with the same thickness of the crystal film, the resonance frequency is the same, and the quality of the crystal filter element can be improved; the etching cost is reduced by adopting a thinner growth substrate, and even if the growth substrate is easy to tilt due to the thinner growth substrate and larger thickness nonuniformity in the growth process, the problem of nonuniform thickness can be solved by arranging all the serially connected bulk resonators on an arc with the same thickness; the ground wire connection point is reasonably arranged, so that the element is easy to manufacture, high in reliability and easy to package.

Drawings

FIG. 1 is a top view of a crystal filter element of the present invention;

FIG. 2 is a schematic diagram of bulk and empty resonator elements of a crystal filter element of the present invention;

FIGS. 3-1 to 3-7 are schematic views illustrating a process for fabricating a crystal filter element;

FIG. 4 is a top view of a crystal filter element according to a first embodiment of the present invention;

FIG. 5 is a schematic diagram of a bulk resonator element of a crystal filter element according to a first embodiment of the present invention;

FIG. 6 is a top view of a crystal filter element according to a second embodiment of the present invention;

FIG. 7 is a schematic diagram of a bulk resonator element of a crystal filter element according to a second embodiment of the present invention;

fig. 8 is a schematic circuit diagram of a Bulk Acoustic Wave (BAW) filter element (ladder filter) composed of thin Film Bulk Acoustic Resonators (FBARs) of the prior art;

fig. 9 is a circuit schematic diagram of a Bulk Acoustic Wave (BAW) filter element (format filter) composed of a thin Film Bulk Acoustic Resonator (FBAR) of the related art.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar functions.

In the description of the present invention, it is to be understood that the terms "central," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," and the like are used in the orientations and positional relationships indicated in the drawings for convenience in describing the present invention and to simplify the description, but are not intended to indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and that the directional terms are used for purposes of illustration and are not to be construed as limiting, for example, because the disclosed embodiments of the present invention may be oriented in different directions, "lower" is not necessarily limited to a direction opposite to or coincident with the direction of gravity. Furthermore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

Referring to fig. 1, a crystal filter element includes a first input terminal 6, a second input terminal 8, a first output terminal 7, a second output terminal 8a, and a thin film bulk acoustic resonator (FBAR, hereinafter referred to as bulk resonator), and the second input terminal 8 and the second output terminal 8a may be connected to a ground line.

The crystal filter element has an overall circular profile with a center O. In particular implementations, a 4 "substrate has a plurality of such crystal filter elements thereon. The bulk resonators include first bulk resonators 1 and second bulk resonators 2, four of the first bulk resonators 1 being connected in series between a first input terminal 6 and a first output terminal 7, and three of the second bulk resonators 2 being connected in parallel between the first output terminal 7 and a second output terminal 8 a. Wherein, four first bulk resonators 1 connected in series are distributed on r with the center O as the center of a circle₂Three second bulk resonators 2 connected in parallel are distributed on a first arc 10 with a radius and integrally form a series connection relationship with two output terminals, and the centers of the three second bulk resonators are R₁And a second arc 9 with a radius is integrally connected with the two output end points in parallel. Preferably, four first bulk resonators 1 connected in series are uniformly distributed in the circumferential direction, and three second bulk resonators 2 connected in parallel are uniformly distributed in the circumferential direction.

The first bulk resonator 1 and the second bulk resonator 2 have substantially the same structure, thereby reducing the manufacturing cost. The arrangement of the bulk resonator described above is relevant to existing III-nitride crystal thin film epitaxial growth techniques, for example, in the case of uniform heating and growth of substrate spins, the film thickness may be the same along the first circular arc 10 or the second circular arc 9. The difference between the resonant frequencies of the first bulk resonator 1 and the second bulk resonator 2 can be controlled, and in addition to using the difference in the thickness of the crystal film, a dielectric layer can be added to a certain thickness above the second electrode 16 (described below) to fine-tune their resonant frequencies.

The crystal filter element further includes a hollow resonator 3, and the hollow resonator 3 has four, three, connected in series between two adjacent first body resonators 1, and the other connected between the first body resonator 1 closest to the first output terminal 7 and the first output terminal 7, thereby assisting in forming the connection. And the hollow resonator 3 is positioned r around the center O₁Is on a first circular arc 10 of radius.

Referring to fig. 1 and 2, fig. 2 shows the structure of a first bulk resonator 1 and an adjacent empty resonator 3, the second bulk resonator 2 being substantially identical to the first bulk resonator 1 and not shown for simplicity. Each bulk resonator includes a substrate 11, the substrate 11 including a crystalline thin film layer 13 and a growth substrate 12, the crystalline thin film layer 13 being epitaxially grown on the growth substrate 12. The crystalline thin film layer 13 has an upper surface and a lower surface, and the lower surface of the crystalline thin film layer 13 is exposed outside the growth substrate 12 by etching the growth substrate 12. Growth substrate 12 may be SiC, Si, GaN, sapphire, AlN or the like, and preferably the upper surface is highly resistive, otherwise some measure, such as a large area for lower etching, is taken. Growth substrate 12 is preferably efficiently etchable by liquid or plasma (ICP). The crystal thin film layer 13 is a group III nitride thin film, such as AlN, whose piezoelectric coefficient is large. In group III nitrides, AlN is a relatively mature material and Ga or Sc may be re-doped in AIN. The addition of Ga to AIN can reduce the stress of AIN at room temperature and can also reduce the piezoelectric coefficient, but generally does not exceed 20%. And most preferably Sc, to reduce stress at room temperature without reducing the piezoelectric coefficient.

The first electrode 17 and the second electrode 16 are provided on the upper and lower sides of the crystal thin film layer 13, respectively, and the first electrode 17 is generally larger than the second electrode 16. The crystal thin-film layer 13 and the two electrodes constitute a bulk resonator. The first electrode 17 and the second electrode 16 are generally made of metal material with relatively large acoustic impedance, such as Mo, Cr, and the like. Mo is suitable, but generally difficult to deposit; and the Cr surface has better bonding degree, which is beneficial to deposition. The first bulk resonator 1 and the second bulk resonator 2 must have significantly different frequencies, which can be achieved by adding a layer of material, such as SiO, to the second electrode 16 of either of them₂To change its frequency. On the underside of the first electrode 17 a support layer 18 is arranged, which support layer 18 may comprise an acoustic mirror, such as a W/SiO-mirror₂A multilayer film structure.

Each of the hollow resonators 3 shares the growth substrate 12 with the adjacent first bulk resonator 1, has the same first electrode 17 as the first bulk resonator 1, and further includes the third electrode 15 over the first electrode 17, and the structure is different from the bulk resonator in that the crystal thin-film layer 13 is not provided between the third electrode 15 and the first electrode 17 of the hollow resonator 3, facilitating the formation of electrode connections without increasing the manufacturing cost for optimizing the package. Also, the first electrode 17 is exposed outside the growth substrate 12.

The first electrodes 17 are electrically connected to each other through the first electrode connecting line 5. The first electrode wire 5 is preferably made of metal. The first electrode connecting line 5 extends along the etched surface 20 of the production substrate 12, and a first dielectric layer 19 is arranged between the surface 20 of the growth substrate 12 and the first electrode connecting line 5, so as to avoid electric leakage between the first electrode connecting line 5 and the growth substrate 12, and increase the adhesion between the first electrode connecting line 5 and the growth substrate 12. The first dielectric layer 19 may extend to the lower surface of the exposed crystalline thin film layer 13, thereby separating the first electrode 17 from the growth substrate 12. The crystalline thin film layer 13 is coated with a second dielectric layer 14 except for a portion in contact with the growth substrate 12 (upper and peripheral), and the second dielectric layer 14 may be SiO grown by PECVD (plasma enhanced chemical vapor deposition)₂Or Si_xAnd N is added. If growth substrate 12 is SiC, the plasma may be used firstBulk oxidation to form a SiO₂A thin layer is deposited followed by deposition of additional dielectric material to form the first dielectric layer 19 and the second dielectric layer 14.

There are two basic forms of resonator combination to form a filter element: ladder (fig. 8) and format (fig. 9). Despite the advantages and disadvantages of each, one of the most fundamental requirements in general is that each first body resonator 1 must have a uniform resonance frequency. However, in the growth process of the crystalline thin film layer 13 (also referred to as an epitaxial thin film) of the present embodiment, it is difficult to ensure that the crystalline thin film layer 13 has good thickness uniformity over the entire growth substrate 12, and thus variations in the resonance frequency are caused. For example, when the thickness of the crystalline thin film layer 13 is about 500 nm, a film thickness difference of 1 nm may cause a change in the resonance frequency by 20 MHz. However, the thickness distribution of the crystal thin film layer 13 can be effectively controlled in the growth technique (e.g., MOVPE: organometallic compound vapor phase epitaxy). For example, in a system of monolithic growth, when the temperature of the heating body of the growth substrate 12 is uniform, the growth substrate 12 may be warped like a bowl shape, which is caused by the temperature gradient of the growth substrate 12. When the growth substrate 12 rotates, it is ensured that the center O of the growth substrate 12 is the center of the circle and the radius is r₂The film thickness is the same on the first circular arc 10, so that the corresponding first bulk resonators 1 can have the same frequency, and thus a high quality filter element can be formed. There may be frequency differences between the filter elements, but in practice adjustments may be made in the circuitry or wiring. Similarly, the second bulk resonator 2 may also be on the same second circular arc 9 of the same thickness. The first electrode 16 and the third electrode 15 are connected to the electrodes of the adjacent resonators or the adjacent terminals via the same second electrode wire 4. The empty resonators 3 located between the two first bulk resonators 1 are each connected to a corresponding one of the second bulk resonators 2 (connected to the corresponding electrode by an electrode connection line), and the parallel arrangement of the second bulk resonators 2 is realized.

In fig. 1, the solid lines between the first input terminal 6 and the first bulk resonator 1, between the empty resonator 3 and the second bulk resonator 2, and between the empty resonator 3 and the first output terminal 7 represent the second electrode line 4, and the broken lines between the empty 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 line 5. I.e. the second electrode wire 4 is located on the upper side of the substrate 11 and the first electrode wire 5 is located on the lower side of the substrate 11.

The manufacturing process of the crystal filter element comprises the following steps:

1) providing a substrate 11: referring to fig. 3-1, it can be seen from the above that the substrate 11 includes a crystalline thin film layer 13 and a growth substrate 12, and the growth substrate 12 should not be too thick, if SiC is used, its thickness does not exceed 200 μm; 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;

2) removing part of the growth substrate 12: referring to fig. 3-2, thereby, the lower surface of the crystalline thin film layer 13 is partially exposed (exposed means that the lower surface is not covered by the growth substrate 12), while the growth substrate 12 forms a surface 20 at the etching position and the bottom; the exposed portions of the lower surface of the crystal thin-film layer 13 may have a plurality of positions at intervals, the number of the exposed lower surfaces being related to the number of the first bulk resonators 1, the second bulk resonators 2, and the empty resonators 3, and the positions being such that the exposed portions corresponding to the first bulk resonators 1 are located on the same first circular arc 10 (the center of the growth substrate 12 is the center, r is the center of the circle, r is the center of the growth substrate 12)₂Radius) the exposed portion of the second bulk resonator 2 is located on the same second circular arc 9 (the center of the growth substrate 12 is the center, r)₁Is a radius); in this embodiment, the growth substrate 12 is partially removed, preferably using plasma etching (e.g., SF)₆+O₂)，SF₆The etching rate of III-group nitride is very small, but the etching rate of etching SiC and Si can reach 2 microns/min; when etching, it is necessary to form an etching mask by photolithography and metal deposition, such as Cr, etc., and a reference region can be set, and the thickness of the remaining SiC or Si can be detected by an optical method, because the thin Si sheet and SiC are transparent or translucent in the infrared or visible light region, when the remaining growth substrate 12 is thin, the upper surface of the substrate 11 can also be bonded to a carrier to play a role of protection;

3) forming a first dielectric layer 19 and a first electrode 17, and etchingThereafter, referring to FIGS. 3-3, a first dielectric layer 19 may first be formed on the surface 20 formed by the growth substrate 12, which is quite easy in the case of a Si substrate, and first using O in the case of a SiC substrate₂Oxidizing the plasma, and depositing a first dielectric layer 19; if electron beam evaporation is used, the substrate 11 can be obliquely faced to the crucible, and the rotation of the substrate 11 can be simultaneously utilized to ensure that each face has medium deposition; the most common material for the first dielectric layer 19 comprises SiO₂And Si_xN; the first dielectric layer 19 not only plays an insulating role, but also can increase the adhesion between metal and the growth substrate 12;

then, on the exposed lower surface of the crystalline thin film layer 13, a first electrode 17: electron beam evaporation or ion beam sputtering can be adopted: this approach typically involves photolithography, which can use a thicker negative photoresist; first, it is necessary to remove the first dielectric layer 19 on the lower surface of the crystalline thin film layer 13, and then deposit an electrode, such as Cr or Mo, on the re-exposed lower surface of the crystalline thin film layer 13, thereby forming the first electrode 17; a support layer 18 may then be formed on the lower surface of the first electrode 17, the support layer 18 comprising an acoustic wave mirror, such as Cr/SiO₂A multilayer film structure; also, if electron beam evaporation or the like is used, the substrate 11 may be made to face the crucible obliquely to ensure formation of a desired deposit, the first electrodes 17 are electrically connected through the first electrode connecting wire 5, the first electrode connecting wire 5 is attached to the first dielectric layer 19 to extend away from the outer side of the growth substrate 12, and the first electrodes 17 and the first electrode connecting wire 5 may use the same metal film;

4) performing mesa etching on the crystal thin film layer 13: referring to fig. 3-4, methods of etching include photolithography, forming a mask, and wet or dry etching (ICP);

5) forming the second dielectric layer 14: referring to fig. 3-5, a second dielectric layer 14 is formed on the etched upper surface of the crystalline thin film layer 13, and SiO may be deposited using PECVD (plasma enhanced chemical vapor deposition)₂Etc., preferably spin-coated liquid oxide (flowable oxide), which can weaken the step of the upper surface;

6) forming the second electrode 16: referring to fig. 3-6, electron beam evaporation or ion beam sputtering, typically including photolithography, may be employed, which may be accomplished using a negative photoresist; removing the second dielectric layer 14 on the crystalline thin film layer 13 at the position corresponding to the first electrode 17 on the lower surface of the crystalline thin film layer 13, and depositing an electrode such as Cr or Mo to form a second electrode 16; at the same time, the second dielectric layer 14 is removed at a position corresponding to the position of the first electrode 17 of the hollow resonator 3, 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 may be protected by photoresist;

7) forming input endpoints and output endpoints: referring to fig. 3 to 7, a first input terminal 6 and a first output terminal 7 are formed on the upper side of a substrate 11, forming a second input terminal 8 and a second output terminal 8a on the lower side of the substrate 11, forming a second electrode connecting line 4 between the second electrode 16 of one first bulk resonator 1 positioned at the end of the first arc 10 and the first input terminal 6, between the third electrode 15 of the adjacent empty resonator 3 and the first electrode 16 of the first bulk resonator 1, between the third electrode 15 of one empty resonator 3 positioned at the other end of the first arc 10 and the first output terminal 7, between the third electrode 15 of the empty resonator 3 and the corresponding second electrode 16 of the second bulk resonator 2, and forming a first electrode connecting line 5 between the first electrode 17 of the second bulk resonator 2 and the second input terminal 8 and the second output terminal 8a to form a final crystal filter element; each empty resonator 3 is connected to two adjacent first bulk resonators 1 through a first electrode connection line 5 and a second electrode connection line 4 (i.e., one of them is connected through the first electrode connection line 5, and the other is connected through the second electrode connection line 4). The adjacent bulk resonators or empty resonators are connected by the first electrode connecting wire 5 and the second electrode connecting wire 4 in a vertically alternating manner. All the end points can be formed by adopting a photoetching mode, and then all the electrode connecting wires are formed by a metal deposition mode, so that large parasitic capacitance is avoided; the above processes may be performed in sequence, or simultaneously. Generally, the metal deposition may be dragged.

The electrodes or wires may be protected by photoresist or metal (e.g., Al) or the like throughout the fabrication process because of their etch selectivity with respect to the material used for the electrodes or wires.

Referring to fig. 4 and 5, a ladder filter is an embodiment of the present invention. In this embodiment, the substrate 411 comprises an MOVPE epitaxially grown AlN crystal thin film (preferably 450 nm thick) 413 and a high resistance SiC growth substrate 412 (preferably 150 μm thick). The structural parameters of the single resonator are as follows: the diameter of the etched portion of growth substrate 12 is 180 micrometers (i.e., the portion of lower surface of crystalline thin film layer 413 exposed); first electrode 417(Cr electrode) having a diameter of 120 μm and a thickness of 25 nm; the second electrode 416(Cr electrode) has a diameter of 90 μm and a thickness of 25 nm, wherein a thickness of 50nm of SiO is provided above the second electrode 416 of the second bulk resonator 2₂. The support layer 18 may not be required since there are no empty resonators 3. The crystal thin film layer 413 is covered by a second dielectric layer 414 with a thickness of 100 nm, and the second dielectric layer 414 is PECVD SiO₂. Further, a second input terminal 408 is provided on the upper side of the substrate 411, and a second output terminal 408a is provided on the lower side of the substrate 411 for packaging. The second input terminal 408 and the second output terminal 408a are both connected to ground, and thus are connected to each other.

The manufacturing process of the ladder filter device is as follows, similar to the process shown in fig. 3-1 to 3-7:

1) providing a substrate 411: the base sheet 411 comprises an AlN crystal thin film layer 413(450 nm thick) grown by MOVPE, epitaxially grown on a growth substrate 412 of high-resistance SiC (thickness: 150 μm; resistivity: 10)⁺¹⁰Ohm cm);

2) removing a portion of growth substrate 412 to form surface 420 of growth substrate 412 and partially expose the lower surface of crystalline thin film layer 413: firstly, using photoetching, stripping technique and Cr metal deposition to form an etching mask with the thickness of about 500 nanometers; a Ni (100 nm)/Ti (10 nm) multilayer film structure can also be used, and 10 nm Cr bonding needs to be formed on the surface of SiC; ② use of SF₆+O₂Plasma (ICP) etching SiC; all masks may be removed or may be left for wire connection;

3) connecting in ICP equipment, processing SiC surface 420 by oxygen plasma to form SiO₂Thin layer, i.e. firstA dielectric layer 419, which acts as an adhesive layer and will help to form a stronger metal or dielectric layer and avoid the capacitance of a Schottky diode; then increasing the thickness of the film to 100 nanometers by PECVD;

4) the formation of the lower first electrode 417 and the first electrode wire 405 may be performed simultaneously, using the same material such as Mo or Cr: first, a photoresist mask is formed by photolithography, and SiO at the position of the first electrode 417 is removed₂Layer, which may be electron beam evaporation or ion beam sputtering, the substrate 411 is angled with respect to the source crucible to ensure deposition on the lower surface of the thin crystal film layer 413 and on the adjacent surface 420 of the SiC;

5) mesa etching is performed on the crystalline thin film layer 413: including photolithography, electron beam evaporation of Ti (10 nm)/Ni (80 nm) multilayer film and lift-off technique, forming a mask with a thickness of approximately 200 nm, and then using Cl₂Plasma dry etching (ICP);

6) depositing 100 nm SiO on the 413 table of the crystal film layer by PECVD₂Forming a second dielectric layer 414;

7) second electrode 416 forming upper side: negative photoresist can be used for photoetching; removing the second dielectric layer 414 on the crystalline thin film layer 413, depositing an electrode, such as Cr or Mo, to form a second electrode 416, wherein the second electrode 416 can be protected by photoresist; for the second bulk resonator 402, a 30 nm thick SiO film was formed on the second electrode 416₂A layer, thereby changing its resonant frequency;

8) using the necessary photolithography and metal deposition, the required first input terminal 406, second input terminal 408, first output terminal 407, second output terminal 408a and second electrode connection 404 are formed: a first input terminal 406, a first output terminal 407 and two second input terminals 408 are formed on the upper side of the substrate 411, a second output terminal 408a is formed on the lower side of the substrate 411, a second electrode 416 of one first bulk resonator 401 positioned at an end of the first circular arc 410 and the first input terminal 406, a second electrode 416 of one first bulk resonator 401 positioned at the other end of the first circular arc 410 and the first output terminal 407, two second output terminals 408 are formed, a second bulk resonator 402 positioned at an end of the second circular arc 409 and the corresponding one second input terminal 408, a second bulk resonator 402 positioned at the other end of the second circular arc 409 and the corresponding one second input terminal 408 are formed to form a second electrode connection 404, a first electrode 417 of each second bulk resonator 402 and a first electrode 417 of the corresponding first bulk resonator 401, and a second bulk resonator 402 positioned at an intermediate of the second circular arc 409 and the second output terminal 408a are also formed to form a first electrode connection 404 And pole connections 405 to form the final crystal filter element.

In order to avoid the use of the dummy resonator 3 and reduce any electrode wiring for connecting electrodes on both sides of the substrate 411, for the ladder filter device, the first input terminal 408 and the second output terminal 408a may be formed on both upper and lower sides of the substrate 411, respectively. When the number of bulk resonators in series relation with the output terminals is 4, i.e., even, the lower side of the substrate 411 has only the second output terminal 408 a. This simplifies device packaging, improves device reliability and reduces parasitic inductance.

Referring to fig. 6 and 7, the second embodiment of the present invention, the format filter, not only avoids the empty resonator 3, but also has the first input terminal 506 and the second input terminal 508 on the upper side of the substrate 511, and the first output terminal 507 and the second output terminal 508a on the lower side. Two connecting wires are respectively arranged at the upper side and the lower side during packaging, so that the device is more miniaturized. The first bulk resonator 501 has two, one of which is connected between the first input terminal 506 and the first output terminal 507, and the other of which is connected between the second input terminal 508 and the second output terminal 508 a. The second bulk resonator 502 has two, one of which is connected between the first input terminal 506 and the second output terminal 508a, and the other of which is connected between the second input terminal 508 and the first output terminal 507.

The substrate 511 comprises MOVPE epitaxially grown Ga_0.05Al_0.95An N-crystal thin film layer 413 (thickness preferably 450 nm), and a high resistance SiC growth substrate 512 (thickness: 150 μm). An appropriate amount of Ga may improve the stress of the film. The structural parameters of the single resonator are as follows: the diameter of the etched portion of the growth substrate 512 was 150 μm (i.e., the portion of the lower surface of the crystalline thin film layer 513 exposed)Minute); the first electrode 517(Cr electrode) had a diameter of 150 μm and a thickness of 25 nm; the second electrode 516(Cr electrode) has a diameter of 90 μm and a thickness of 25 nm, wherein a thickness of 40nm of SiO is provided above the second electrode 516 of the second bulk resonator 2₂. The support layer 18 may not be required since there are no empty resonators 3. The crystalline thin film layer 513 is covered by a second dielectric layer 514 with a thickness of 100 nm, the second dielectric layer 514 is PECVD SiO₂。

The bulk resonator and fabrication process may be the same as described above for the first embodiment. Surface 520 is treated only with oxygen plasma.

Claims

1. A crystal filter element comprising a plurality of bulk resonators, a first input terminal, a second input terminal, a first output terminal and a second output terminal, the plurality of bulk resonators being divided into two types, a first bulk resonator having a series relationship with the two output terminals and a second bulk resonator having a parallel relationship with the two output terminals, each bulk resonator comprising a substrate, a first electrode and a second electrode, the substrate comprising a growth substrate and a crystal thin-film layer disposed on the growth substrate, the crystal thin-film layer having an upper surface and a lower surface partially exposed outside the growth substrate, each first electrode being disposed on the corresponding exposed lower surface of the crystal thin-film layer, the second electrode being disposed on the upper surface of the crystal thin-film layer, the bulk resonators being connected to each other by a first electrode connection line or a second electrode connection line, characterized in that: the first resonators are at least two, the first resonators are distributed on the same first arc, and the thicknesses of the positions of the crystal thin film layers corresponding to the first arcs are the same.

2. A crystal filter element according to claim 1, wherein: the second bulk resonators are at least two, the second bulk resonators are distributed on the same second circular arc, and the thicknesses of the positions of the crystal thin film layers corresponding to the second circular arc are the same.

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

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

5. A crystal filter element according to any one of claims 1 to 4, wherein: the upper surface of the growth substrate includes a high resistance material layer.

6. A crystal filter element according to any one of claims 1 to 4, wherein: the growth substrate has a thickness of no more than 200 microns.

7. A crystal filter element according to claim 1, wherein: the crystal filter element is a ladder filter, and is connected between the adjacent first bulk resonator and the first bulk resonator, the first bulk resonator and the second bulk resonator, and the second bulk resonator by respectively and alternately utilizing a second electrode connecting line on the upper side of the substrate and a first electrode connecting line on the lower side of the substrate, and the second input end point and the second output end point are ground wire connecting points and are respectively positioned on the upper side and the lower side of the substrate.

8. The crystal filter element of claim 7, wherein: when the number of the first bulk resonators is even, the lower side of the substrate has only a second output terminal.

9. A method for preparing a crystal filter element is characterized in that: the method comprises the following steps:

10. A method of manufacturing a crystal filter element according to claim 9, wherein: and forming a support layer on the lower surface of the first electrode.