Reconfigurable filter

Abstract

The reconfigurable filter comprises a grounding metal layer and a dielectric substrate, and a spiral resonator and a filter feed structure are arranged on the dielectric substrate; the filter feed structure comprises a first filter feed structure and a second filter feed structure, and the first filter feed structure and the second filter feed structure are both connected with a second BST thin film capacitor; the spiral resonator comprises a first spiral resonator and a second spiral resonator, and a first BST film capacitor is arranged between the first spiral resonator and the second spiral resonator. The interdigital electrodes of the first BST thin film capacitor and the second BST thin film capacitor are arranged above the BST adjustable thin film layer, and the dielectric constant of the BST adjustable thin film material is changed by changing the voltages at the two ends of the interdigital electrodes, so that the capacitance values of the first BST thin film capacitor and the second BST thin film capacitor are adjusted, the center frequency of the filter is changed, and the filter efficiency is improved. And the filtering requirements of different frequency bands are met.

Description

Technical Field

[0001] The present invention relates to the technical field of filters, and in particular to a reconfigurable filter. Background Art

[0002] Reconfigurable filters are advanced components in signal processing that have the flexibility to dynamically adjust their filtering characteristics, such as frequency response, bandwidth, and filter type. Unlike traditional fixed filters whose frequency response is determined during the design phase, reconfigurable filters can reduce the need for multiple dedicated filters by integrating multiple filtering functions into one device, saving space and cost in complex systems and significantly improving the integration of filtering systems. In addition, reconfigurable filters can switch between multiple filtering parameters in real time according to different filtering requirements, dynamically adjust filtering parameters, thereby optimizing filtering performance and enhancing the efficiency and effectiveness of the overall system, which is critical for systems that need to operate across multiple frequency bands or need to adapt to changing signal environments.

[0003] Reconfigurable filters can be implemented through a variety of technologies such as radio frequency micro-electromechanical systems (RF MEMS), digital signal processing (DSP) and adjustable LC circuits. Among them, the adjustable LC circuit changes its resonant frequency by adjusting the inductance (L) and capacitance (C) in the circuit. Traditional LC reconfigurable filters use varactor diodes as adjustable capacitors, which require additional welding micro-assembly. The varactor diodes are large in size, difficult to integrate, and have the risk of nonlinear distortion, which limits the miniaturization of RF microsystems. If the varactor can be integrated on the substrate, the system integration can be effectively improved. Therefore, it is necessary to propose a filter with higher integration and better linearity. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a filter with higher integration and better linearity.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A reconfigurable filter is provided, comprising a grounded metal layer and a dielectric substrate arranged on the grounded metal layer, wherein a spiral resonator and a filter feeding structure are arranged on the dielectric substrate; the filter feeding structure comprises a first filter feeding structure and a second filter feeding structure which are symmetrically arranged, wherein the first filter feeding structure and the second filter feeding structure form an opening for accommodating the spiral resonator, and the first filter feeding structure and the second filter feeding structure are both connected to a second BST film capacitor; the spiral resonator comprises a first spiral resonator and a second spiral resonator which are symmetrically arranged, and wherein a first BST film capacitor is arranged between the first spiral resonator and the second spiral resonator.

[0007] Further, the first BST film capacitor includes a first interdigitated electrode, a second interdigitated electrode, a first DC voltage pad, a second DC voltage pad and a first BST film, the first interdigitated electrode and the second interdigitated electrode are opposite and cross-arranged, the first BST film is arranged at the bottom of the first interdigitated electrode and the second interdigitated electrode, the first interdigitated electrode is connected to the first DC voltage pad, the second interdigitated electrode is connected to the second DC voltage pad, the first interdigitated electrode is connected to the first spiral resonator, and the second interdigitated electrode is connected to the second spiral resonator.

[0008] Furthermore, the first BST film is mounted on the dielectric substrate, a first groove for mounting the first BST film is provided on the dielectric substrate, and the first BST film is embedded in the first groove.

[0009] Furthermore, the second BST film capacitor includes a third interdigitated electrode, a fourth interdigitated electrode, a third DC voltage pad, a fourth DC voltage pad and a second BST film, the third interdigitated electrode and the fourth interdigitated electrode are opposite and cross-arranged, the second BST film is arranged at the bottom of the third interdigitated electrode and the fourth interdigitated electrode, the third interdigitated electrodes of the two second BST film capacitors are connected to the third DC voltage pad, and the fourth interdigitated electrodes of the two second BST film capacitors are connected to the fourth DC voltage pad.

[0010] Furthermore, the second BST film is mounted on the dielectric substrate, a second groove for mounting the second BST film is provided on the dielectric substrate, and the second BST film is embedded in the second groove.

[0011] Furthermore, the first filter feeding structure includes a first feeding segment, an L-shaped second feeding segment and a third feeding segment, and two ends of the second feeding segment are respectively connected to the first feeding segment and the third feeding segment.

[0012] Furthermore, the first feeding section is perpendicular to the second feeding section, and the second feeding section is perpendicular to the third feeding section.

[0013] Furthermore, the first spiral resonator includes a first resonance segment, a second resonance segment, a third resonance segment, a fourth resonance segment and a fifth resonance segment, and the first resonance segment, the second resonance segment, the third resonance segment, the fourth resonance segment and the fifth resonance segment are connected in sequence to form a spiral shape, and the first resonance segments of the first spiral resonator and the second spiral resonator are both connected to the first BST film capacitor.

[0014] Furthermore, the first resonant segment is perpendicular to the second resonant segment, the second resonant segment is perpendicular to the third resonant segment, the third resonant segment is perpendicular to the fourth resonant segment, and the fourth resonant segment is perpendicular to the fifth resonant segment.

[0015] Furthermore, the material of the dielectric substrate is LTCC substrate or high-resistance silicon.

[0016] The beneficial effects of the present invention are:

[0017] Compared with the traditional mechanical or external variable capacitor conventional LC reconfigurable filter, the present invention does not require external welding of variable capacitors, can achieve higher integration, has higher linearity, faster response time, and helps to achieve miniaturization of microwave systems.

[0018] The present invention includes a dielectric substrate, a back grounding layer, a first BST film capacitor, and a second BST film capacitor. The interdigital electrodes of the first BST film capacitor and the second BST film capacitor are arranged above the BST adjustable film layer. By changing the voltage across the interdigital electrodes, the dielectric constant of the BST adjustable film material is changed, thereby adjusting the capacitance values ​​of the first BST film capacitor and the second BST film capacitor, so that the center frequency of the filter is changed to meet the filtering requirements of different frequency bands.

[0019] The present invention constructs a non-uniform open resonant ring hybrid coupling structure in a filter device, controls the size of an adjustable BST film capacitor by applying a DC voltage to achieve a linear change in the center frequency of the filter, and the coupling coefficient between resonators decreases as the resonant frequency increases, thereby achieving a constant absolute bandwidth.

[0020] During use, the present invention applies DC excitation to the BST film of the BST film capacitor by adding a DC voltage pad, changes the dielectric constant of the BST film, thereby affecting the capacitance value of the BST film capacitor, changes the impedance of the filter resonator, thereby affecting the center frequency of the filter, and realizes filtering.

[0021] The present invention connects a first BST film capacitor between the first spiral resonator and the second spiral resonator, changes the capacitance value by applying a DC bias voltage, and changes the coupling coefficient. By controlling the capacitance value of the second BST film capacitor used for coupling the feed input / output, the frequency response of the filter can be optimized, and the stop band can obtain a better suppression level. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the structure of the present invention in the front view direction;

[0023] Figure 2 It is a schematic diagram of the structure of the present invention in a top view;

[0024] Figure 3 is a schematic structural diagram of a first BST film capacitor;

[0025] Figure 4 is a schematic diagram of the structure of a second BST film capacitor;

[0026] Figure 5is a structural schematic diagram of a first filter feeding structure;

[0027] Figure 6 is a schematic structural diagram of a first spiral resonator;

[0028] Figure 7 is the S21 parameter diagram of the filter in the present invention;

[0029] Figure 8 is the S22 parameter diagram of the filter in the present invention;

[0030] The main components in the figure are described as follows:

[0031] 11. First filter feeding structure; 12. Second filter feeding structure; 111. First feeding section; 112. Second feeding section; 113. Third feeding section; 114. Fourth feeding section

[0032] 21, first helical resonator; 22, second helical resonator; 211, first resonant section; 212, second resonant section; 213, third resonant section; 214, fourth resonant section; 215, fifth resonant section;

[0033] 3. First BST film capacitor; 31. First interdigital electrode; 32. Second interdigital electrode; 33. First DC voltage pad; 34. Second DC voltage pad; 35. First BST film;

[0034] 4. Second BST film capacitor; 41. Third interdigital electrode; 42. Fourth interdigital electrode; 43. Third DC voltage pad; 44. Fourth DC voltage pad; 36. Second BST film;

[0035] 5. Dielectric substrate; 6. Ground metal layer. DETAILED DESCRIPTION

[0036] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0037] like Figure 1 and 2As shown, the reconfigurable filter includes a grounding metal layer 6 and a dielectric substrate 5 arranged on the grounding metal layer 6. The dielectric substrate 5 is preferably a polished LTCC substrate or high-resistance silicon, which can avoid the generation of current between the grounding metal 6 and other devices, affecting the performance and life of the device. A spiral resonator and a filter feeding structure are arranged on the dielectric substrate 5. The spiral resonator includes a symmetrically arranged first spiral resonator 21 and a second spiral resonator 22. A first BST film capacitor 3 is arranged between the first spiral resonator 21 and the second spiral resonator 22. The first BST film capacitor 3 is connected between the first spiral resonator 21 and the second spiral resonator 22. The change of the DC bias voltage applied to the first BST film capacitor 3 changes the capacitance value and changes the coupling coefficient. The filter feeding structure includes a symmetrically arranged first filter feeding structure 11 and a second filter feeding structure 12. The first filter feeding structure 11 and the second filter feeding structure 12 form an opening for accommodating the spiral resonator. The first filter feeding structure 11 and the second filter feeding structure 12 are both connected to a second BST film capacitor 4. By controlling the capacitance value of the second BST film capacitor 4 used for coupling the feed input / output, the frequency response of the filter can be optimized, and the stop band can obtain a better suppression level. The length of the spiral resonator is equal to one quarter wavelength of the center frequency of the operating band, the gap between the resonant cavities determines the bandwidth obtained, and the return loss can be improved by using the tap position.

[0038] like Figure 3 As shown, the first BST film capacitor 3 includes a first interdigital electrode 31, a second interdigital electrode 32, a first DC voltage pad 33, a second DC voltage pad 34 and a first BST film 35. The first interdigital electrode 31 is opposite to and cross-arranged with the second interdigital electrode 32. The first BST film 35 is arranged at the bottom of the first interdigital electrode 31 and the second interdigital electrode 32. The first interdigital electrode 31 is connected to the first DC voltage pad 33, the second interdigital electrode 32 is connected to the second DC voltage pad 34, the first interdigital electrode 31 is connected to the first spiral resonator 21, and the second interdigital electrode 32 is connected to the second spiral resonator 22. The first BST film 35 is installed on the dielectric substrate 5, and a first groove for installing the first BST film 35 is provided on the dielectric substrate 5. The first BST film 35 is embedded in the first groove, and the first groove is realized by an etching process. When in use, excitation is applied to the first DC voltage pad 33 and the second DC voltage pad 34 to change the dielectric constant of the first BST film 35, thereby realizing the change of the capacitance value of the first BST film capacitor 3.

[0039] like Figure 4As shown, the second BST film capacitor 4 includes a third interdigital electrode 41, a fourth interdigital electrode 42, a third DC voltage pad 43, a fourth DC voltage pad 44 and a second BST film 45, the third interdigital electrode 41 and the fourth interdigital electrode 42 are opposite and cross-arranged, the second BST film 45 is arranged at the bottom of the third interdigital electrode 41 and the fourth interdigital electrode 42, the third interdigital electrode 41 of the second BST film capacitor 4 at two locations is connected to the third DC voltage pad 43, and the fourth interdigital electrode 42 of the second BST film capacitor 4 at two locations is connected to the fourth DC voltage pad 44. The dielectric substrate 5 is installed on the dielectric substrate 5, and a second groove for installing the second BST film 45 is provided on the dielectric substrate 5, and the second BST film 45 is embedded in the second groove, and the second groove is realized by an etching process. The spiral resonator, the filter feeding structure, the first interdigital electrode 31, the second interdigital electrode 32, the first DC voltage pad33, the second DC voltage pad34, the third interdigital electrode 41, the fourth interdigital electrode 42, the third DC voltage pad43, and the fourth DC voltage pad44 are all located on the same plane to prevent device failure caused by the metal film step. At the same time, the material of the aforementioned components is preferably gold. In the process of preparing the metal layer, a layer of Ti, TiW or Ni is first grown as an adhesion layer to improve the adhesion of the electrode material, but the thickness of the adhesion layer needs to be controlled not to be too high to prevent the generation of large metal stress and ensure that the performance of the electrode material meets the simulation expectations. When used, the excitation is applied to the second DC voltage pad43 and the third DC voltage pad44 to change the dielectric constant of the second BST film 45, thereby realizing the change in the capacitance value of the second BST film capacitor 4. The materials of the first DC voltage pad33, the second DC voltage pad34, the third DC voltage pad43, and the fourth DC voltage pad44 are preferably selected from gold, which has a small resistivity and high stability and will not oxidize or sulfide in the air.

[0040] like Figure 5 As shown, the first filter feeding structure 11 includes a first feeding section 111, an L-shaped second feeding section 112 and a third feeding section 113, and two ends of the second feeding section 112 are respectively connected to the first feeding section 111 and the third feeding section 113. The first feeding section 111 is perpendicular to the second feeding section 112, and the second feeding section 112 is perpendicular to the third feeding section 113.

[0041] like Figure 6As shown, the first helical resonator 21 includes a first resonant section 211, a second resonant section 212, a third resonant section 213, a fourth resonant section 214 and a fifth resonant section 215, which are sequentially connected to form a spiral shape, and the first resonant sections 211 of the first helical resonator 21 and the second helical resonator 22 are both connected to the first BST film capacitor 3. The first resonant section 211 is perpendicular to the second resonant section 212, the second resonant section 212 is perpendicular to the third resonant section 213, the third resonant section 213 is perpendicular to the fourth resonant section 214, and the fourth resonant section 214 is perpendicular to the fifth resonant section 215.

[0042] A first groove and a second groove are etched on the dielectric substrate 5, and a BST film is grown. The film thickness is consistent with the groove depth, so as to keep the interdigitated electrodes of the BST film capacitor and the filter metal layer at the same level to prevent the step effect caused by the inconsistent height of the metal layer from causing device failure. The BST film is grown by magnetron sputtering or pulsed laser deposition technology. After the film deposition is completed, an annealing furnace is used to anneal the film in an oxygen atmosphere, so as to obtain a BST film with a dense structure, so that it has ideal dielectric adjustability and breakdown voltage.

[0043] The input and output of the filter adopts a second BST film capacitor 4 loaded coupling feeding scheme, and the first filter feeding structure 11 is coupled with the second filter feeding structure 12. When the filter is tuned, the quality factor is ensured by changing the capacitance value of the first BST film capacitor 3 of the coupling feeding end load. During the use of the filter, two different DC bias voltages are applied to the third DC voltage pad43 and the fourth DC voltage pad44 of the second BST film capacitor 4.

[0044] The first BST film capacitor 3 and the second BST film capacitor 4 may have different capacitance values. The coupling coefficient M between the first spiral resonator 21 and the second spiral resonator 22 is 12 and the first BST film capacitor 3 satisfy the following relationship:

[0045]

[0046] Where Y re , Y r0 They are respectively represented as the characteristic admittances of the two resonators of the coupled resonator in odd and even modes, λ and f0 are respectively the electrical length of the resonator and the resonant frequency of the filter, and C1 is the capacitance value of the first BST film capacitor 3 .

[0047] Use HFSS software to simulate the performance of the reconfigurable filter. The simulation steps are as follows:

[0048] A1: Specifically, by establishing a finite element simulation model of the first BST film capacitor, the first BST film capacitor, the filter feeding structure and the spiral resonator in the software;

[0049] A2: The dielectric constant of the BST film at different voltages is calculated by measuring the capacitance of the BST film capacitor with an interdigital electrode structure at different voltages after the BST film is prepared;

[0050] A3: Directly set the dielectric constant of the BST material to between 340 and 800 during the simulation;

[0051] A4: The simulation uses wave port feeding, and the solution frequency is 1.4-2.5GHz;

[0052] like Figure 7 and Figure 8 As shown, Figure 7 and Figure 8 The S21 and S11 parameters of the designed reconfigurable filter based on BST tunable film are shown respectively. It can be seen that the reconfigurable filter achieves the center frequency adjustment from 1.75GHz to 2.74GHz. When the DC voltage applied to the BST film capacitor is small, it has a large capacitance value and the center frequency of the filter is low. When the DC voltage applied to the BST film capacitor is large, its capacitance becomes smaller and the center frequency of the filter increases.

[0053] In this embodiment, a method for preparing the above-mentioned reconfigurable filter is provided, and the specific steps are as follows:

[0054] S1: Select a high-resistance silicon substrate as the dielectric substrate 5, use acetone, alcohol, and deionized water ultrasonic cleaning in sequence, and then use a plasma cleaning machine to clean it again in an argon atmosphere, the purpose of which is to ensure that the surface of the dielectric substrate 5 is clean;

[0055] S2: A groove is engraved on the dielectric substrate 5 by reactive ion etching. The size of the groove is determined by the center frequency of the designed filter. The groove depth is preferably 300 nm to ensure the performance of the BST film. The preparation process of the first BST film 35 and the second BST film 45 is the same. In this embodiment, only the method for forming the BST film is described.

[0056] S3: depositing a 200 nm BST film on the dielectric substrate 5, the deposition conditions of the BST film are 3-7 Pa, oxygen atmosphere, 500-800° C., and deposition for about 0.5 hours;

[0057] S4: Then, a positive photoresist is used to pattern the BST film region on the dielectric substrate 5, and a CHF3 / Ar plasma gas is used to perform reactive ion etching;

[0058] S5: then, using negative photoresist to photolithography the interdigital electrodes, DC voltage pad, filter feeding structure and spiral resonator structure on the upper surface of the dielectric substrate 5, and depositing a layer of Ti / Au thin film by magnetron sputtering, wherein the thickness of Ti is preferably 10-20 nm, and the thickness of Au is preferably 150-300 nm;

[0059] S6: Use acetone alcohol to peel off the electrode pattern to obtain the interdigital electrode, DC voltage pad, waveguide feeding structure and spiral resonator pattern;

[0060] S7: A layer of Ti / Au thin film is deposited on the back of the dielectric substrate 5 by magnetron sputtering as the grounding metal layer 6, wherein the thickness of Ti is preferably 10-20 nm, and the thickness of Au is preferably 150-300 nm.

[0061] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A reconfigurable filter, characterized in that: It comprises a grounding metal layer (6) and a dielectric substrate (5) arranged on the grounding metal layer (6), wherein a helical resonator and a filter feeding structure are arranged on the dielectric substrate (5); The filter feeding structure comprises a first filter feeding structure (11) and a second filter feeding structure (12) which are symmetrically arranged, the first filter feeding structure (11) and the second filter feeding structure (12) forming an opening for accommodating the helical resonator, and the first filter feeding structure (11) and the second filter feeding structure (12) are both connected to a second BST film capacitor (4); The spiral resonator comprises a first spiral resonator (21) and a second spiral resonator (22) which are symmetrically arranged, and a first BST film capacitor (3) is arranged between the first spiral resonator (21) and the second spiral resonator (22).

2. The reconfigurable filter according to claim 1, characterized in that: The first BST film capacitor (3) comprises a first interdigitated electrode (31), a second interdigitated electrode (32), a first direct current voltage pad (33), a second direct current voltage pad (34) and a first BST film (35); the first interdigitated electrode (31) and the second interdigitated electrode (32) are arranged opposite to and cross-arranged; the first BST film (35) is arranged at the bottom of the first interdigitated electrode (31) and the second interdigitated electrode (32); the first interdigitated electrode (31) is connected to the first direct current voltage pad (33); the second interdigitated electrode (32) is connected to the second direct current voltage pad (34); the first interdigitated electrode (31) is connected to a first spiral resonator (21); and the second interdigitated electrode (32) is connected to a second spiral resonator (22).

3. The reconfigurable filter according to claim 2, characterized in that: The first BST film (35) is mounted on a dielectric substrate (5); a first groove for mounting the first BST film (35) is provided on the dielectric substrate (5); and the first BST film (35) is embedded in the first groove.

4. The reconfigurable filter according to claim 1, characterized in that: The second BST film capacitor (4) comprises a third interdigitated electrode (41), a fourth interdigitated electrode (42), a third DC voltage pad (43), a fourth DC voltage pad (44) and a second BST film (45); the third interdigitated electrode (41) and the fourth interdigitated electrode (42) are arranged opposite to and cross-arranged; the second BST film (45) is arranged at the bottom of the third interdigitated electrode (41) and the fourth interdigitated electrode (42); the third interdigitated electrode (41) of the second BST film capacitor (4) is connected to the third DC voltage pad (43) at two locations; and the fourth interdigitated electrode (42) of the second BST film capacitor (4) is connected to the fourth DC voltage pad (44) at two locations.

5. The reconfigurable filter according to claim 4, characterized in that: The second BST film (45) is mounted on a dielectric substrate (5); a second groove for mounting the second BST film (45) is provided on the dielectric substrate (5); and the second BST film (45) is embedded in the second groove.

6. The reconfigurable filter according to claim 1, characterized in that: The first filter feeding structure (11) comprises a first feeding section (111), an L-shaped second feeding section (112) and a third feeding section (113), and two ends of the second feeding section (112) are respectively connected to the first feeding section (111) and the third feeding section (113).

7. The reconfigurable filter according to claim 6, characterized in that: The first feeding section (111) is perpendicular to the second feeding section (112), and the second feeding section (112) is perpendicular to the third feeding section (113).

8. The reconfigurable filter according to claim 1, characterized in that: The first helical resonator (21) comprises a first resonant section (211), a second resonant section (212), a third resonant section (213), a fourth resonant section (214) and a fifth resonant section (215); the first resonant section (211), the second resonant section (212), the third resonant section (213), the fourth resonant section (214) and the fifth resonant section (215) are sequentially connected to form a helical shape; the first resonant sections (211) of the first helical resonator (21) and the second helical resonator (22) are both connected to a first BST film capacitor (3).

9. The reconfigurable filter according to claim 8, characterized in that: The first resonant section (211) is perpendicular to the second resonant section (212), the second resonant section (212) is perpendicular to the third resonant section (213), the third resonant section (213) is perpendicular to the fourth resonant section (214), and the fourth resonant section (214) is perpendicular to the fifth resonant section (215).

10. The reconfigurable filter according to claim 1, characterized in that: The material of the dielectric substrate (5) is LTCC substrate or high-resistance silicon.

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