A high-frequency tunable bandstop filter based on a YIG substrate

Abstract

A high-frequency tunable bandstop filter based on a YIG substrate belongs to the field of microwave magnetic device technology. It includes a YIG substrate, functional metal layers and ground metal layers formed on the front and back sides of the YIG substrate; the functional metal layers include a microstrip line structure penetrating the YIG substrate, and a square open-loop resonant ring structure disposed on one side of the microstrip line structure. This invention utilizes the tunable permeability of the YIG substrate as a tuning source, overcoming the limitations of traditional fixed resonant structures and methods using semiconductor varactor diodes, ferroelectric materials, or piezoelectric materials, which cannot meet the poor adaptability to high-frequency scenarios and environments. It achieves precise suppression of dynamic electromagnetic interference frequencies at their source; by employing a composite structure of a square open-loop resonant ring and a microstrip line, and YIG substrate-compatible semiconductor wafer technology, it achieves real-time high-frequency signal tuning processing, meeting the current low-cost and high-integration industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of microwave magnetic devices technology, specifically relating to a high-frequency adjustable bandstop filter based on a yttrium iron garnet (YIG) substrate. Background Technology

[0002] With the rapid development of high-frequency electronic technologies such as wireless communication, radar systems, and satellite communication, the requirements for frequency selectivity, tuning flexibility, and environmental adaptability of band-stop filters in radio frequency front-end systems are becoming increasingly stringent. As a core component for suppressing specific interference frequencies and ensuring the quality of useful signal transmission, the performance of band-stop filters directly determines the anti-interference capability and signal integrity of the entire electronic system. Traditional band-stop filters mostly adopt a fixed resonant structure design, and once the stopband frequency is manufactured, it cannot be adjusted. This makes it difficult to adapt to scenarios with dynamically changing interference frequencies in complex electromagnetic environments, and it cannot meet the practical needs of multi-band, wide-range interference suppression.

[0003] To achieve frequency tunability in band-stop filters, existing technologies primarily employ semiconductor varactor diodes, ferroelectric materials, or piezoelectric materials as tunable functional layers. The equivalent dielectric constant or geometric parameters of the resonant unit are adjusted by changing the bias voltage or applying mechanical stress, thereby altering the stopband frequency. However, the parasitic parameters of semiconductor varactor diodes increase insertion loss, and their operating frequency is limited by their cutoff frequency, making them unsuitable for high-frequency applications such as millimeter waves. Ferroelectric materials exhibit temperature-sensitive dielectric tuning characteristics, resulting in poor stability over wide operating temperatures and affecting device performance consistency. Piezoelectric materials have slow mechanical tuning mechanisms, making them unsuitable for applications requiring rapid high-frequency signal switching. Furthermore, the electromagnetic coupling strength between traditional resonant units (such as circular open-circuit resonant rings) and transmission lines is difficult to control precisely, leading to insufficient stopband suppression depth and a large structural size, which is detrimental to the miniaturization and high-density integration of RF systems. Summary of the Invention

[0004] The purpose of this invention is to address the problems of existing adjustable bandstop filters mentioned in the background art by proposing a high-frequency adjustable bandstop filter based on a YIG substrate, which achieves low loss, small size, and high stability with adjustable stopband frequency.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A high-frequency tunable bandstop filter based on a YIG substrate includes a YIG substrate, a functional metal layer formed on the surface of the YIG substrate, and a ground metal layer formed on the back side of the YIG substrate.

[0007] The functional metal layer includes a microstrip line structure penetrating the YIG substrate and a square open-loop resonant ring structure disposed on one side of the microstrip line structure; the square open-loop resonant ring structure includes a plurality of square open-loop resonant rings arranged side by side in the direction of the microstrip line structure.

[0008] Furthermore, the outer side length of the square open-ring resonator is (1 / 5 to 1 / 3)L, where L is the side length of the YIG substrate; the spacing between adjacent square open-ring resonators is 0.1L to 0.5L; the difference in the outer side length of different square open-ring resonators is ±0.2 times the outer side length of the square open-ring resonator; the ring width of the open-ring resonator is the same as the opening gap size.

[0009] Furthermore, the number of the square-opening resonant rings is set according to the size of the substrate.

[0010] Furthermore, the spacing between the square open resonant ring structure and the microstrip line structure is 2-10 μm. As the spacing increases, the electromagnetic coupling strength between the microstrip line and the resonant ring gradually decreases, leading to a weakening of the filter's stopband rejection depth, an increase in insertion loss, and a decline in overall performance.

[0011] Furthermore, a square open resonant ring structure with identical size and position can also be provided on the other side of the microstrip line structure.

[0012] Furthermore, the YIG substrate is a 0.5 mm thick yttrium iron garnet (YIG) substrate grown by liquid phase epitaxy, which has a ferromagnetic resonance linewidth as low as 20 Oe, a saturation magnetization as high as 1750 Gs, and an in-plane Gilbert damping coefficient <10. -4 With a quality factor Q > 100, it possesses high permeability, low hysteresis loss, and significant magnetostriction effect, making it key to achieving magnetic field tuning.

[0013] Furthermore, both the square-shaped open resonant ring structure and the microstrip line structure are made of Cu, a metal material with high conductivity, and are formed by photolithography, sputtering or electroplating processes. The Cu layer thickness is greater than 5 times the Cu skin effect thickness.

[0014] Furthermore, to meet the impedance matching requirements of the RF system, the microstrip line structure uses a 50Ω standard impedance at the port, and its thickness is calculated based on the 50Ω standard impedance matching and the microstrip line structure model.

[0015] Furthermore, the multiple square open-ring resonators in the square open-ring structure are arranged side by side, with the same spacing between them and the microstrip line structure, to ensure uniform electromagnetic coupling strength between the microstrip line and each open-ring resonator, and to avoid distortion of stopband characteristics caused by coupling imbalance.

[0016] Furthermore, the multiple square-opening resonant rings in the square-opening resonant ring structure have the same opening direction and are located on the side away from the microstrip line structure to achieve the effect of enhanced coupling.

[0017] This invention provides a high-frequency tunable bandstop filter based on a YIG substrate. Tuning is achieved by leveraging the tunable permeability of the YIG substrate. An external DC magnetic field parallel to the microstrip line is applied to the YIG substrate, with the magnetic field strength adjustable from 0 to 200 Oe. When the external magnetic field strength changes, the equivalent permeability of the YIG substrate changes dynamically, thereby affecting the electromagnetic coupling coefficient between the microstrip line and the square open-loop resonant ring, as well as the resonant frequency of the resonant ring, thus achieving dynamic adjustment of the stopband frequency.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] This invention provides a high-frequency tunable bandstop filter based on a YIG substrate. Utilizing the tunable permeability of the YIG substrate as a tuning source, it overcomes the limitations of traditional fixed resonant structures and methods using semiconductor varactor diodes, ferroelectric materials, or piezoelectric materials, which cannot meet the poor adaptability to high-frequency scenarios and environments. This achieves precise suppression of dynamic electromagnetic interference frequencies at their source. Furthermore, based on the physical characteristics of YIG magnetostriction and magnetic field changes that precede traditional voltage or mechanical tuning, a highly efficient bandstop filtering mechanism is constructed. Finally, a composite structure of a square open-loop resonant ring and a microstrip line, along with YIG substrate-compatible semiconductor wafer technology, enables real-time tuning of high-frequency signals, making it suitable for current low-cost and highly integrated industrial applications. Attached Figure Description

[0020] Figure 1 This is a top view schematic diagram of the structure of a high-frequency adjustable bandstop filter based on a YIG substrate, as shown in the embodiment.

[0021] Figure 2 Transmission characteristics when the applied magnetic field is zero (S) 21 ) Schematic diagram of the curve;

[0022] Figure 3 To change the transmission characteristics (S) when an external magnetic field is applied 21 ) Schematic diagram of curve changes. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the technical approach of this invention and are therefore only examples, not intended to limit the scope of protection of this invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0024] A high-frequency tunable bandstop filter based on a YIG substrate includes a YIG substrate, a functional metal layer formed on the surface of the YIG substrate, and a ground metal layer formed on the back side of the YIG substrate.

[0025] The functional metal layer includes a microstrip line structure penetrating the YIG substrate and a square open-loop resonant ring structure disposed on one side of the microstrip line structure; the square open-loop resonant ring structure includes a plurality of square open-loop resonant rings arranged side by side in the direction of the microstrip line structure.

[0026] The microstrip line structure extends from one edge of the YIG substrate to the opposite edge, forming a signal input port (left side) and an output port (right side).

[0027] Example

[0028] like Figure 1 The image shows a top view of the tunable bandstop filter based on a YIG substrate described in this embodiment. A functional metal layer is integrated onto the surface of the YIG substrate, including microstrip lines and three independent square-aperture resonant rings A1, A2, and A3. The microstrip lines are used to efficiently couple external microwave signals to the underlying resonant units A1, A2, and A3, and have a standard characteristic impedance of 50Ω. The YIG substrate size is 5×5mm. Resonant ring A1 (the square ring on the left in the image): outer side length 1.08mm, inner side length 0.88mm, ring width 0.1mm (determined by half the difference between the outer and inner side lengths, as indicated in the image), aperture gap 0.2mm (the distance between the two ends of the aperture, as indicated in the image), and the distance between the outer edge of A1 and the edge of the microstrip line is 4μm (aperture indicated in the image). Resonant ring A2 (the middle square ring in the attached diagram): outer side length 1.1mm, inner side length 0.9mm, ring width 0.1mm, opening gap 0.2mm. The distance between the outer side of A2 and the edge of the microstrip line is 4μm (the gap labeling in the attached diagram is consistent with A1). Resonant ring A3 (the right square ring in the attached diagram): outer side length 1.11mm, inner side length 0.91mm, ring width 0.1mm, opening gap 0.2mm. The distance between the inner and outer sides of A3 and the edge of the microstrip line is 4μm (the gap labeling in the attached diagram is consistent). The square opening resonant rings A1, A2, and A3 are arranged in series along the length of the microstrip line. The distance between A1 and A2 is 0.35mm, and the distance between A2 and A3 is 0.25mm. The minimum vertical distance between the edge of the microstrip line and the uppermost edge of the lower resonant unit is precisely controlled at 4μm. Both the square opening resonant ring structure and the microstrip line structure use Cu, a high-conductivity metallic material, with a Cu layer thickness of 30μm. To meet the impedance matching requirements of RF systems, the microstrip line uses a standard impedance design of 50Ω at the port, and the corresponding microstrip line width is determined to be 0.288mm through precise simulation.

[0029] The fabrication method of the tunable bandstop filter based on a YIG substrate in this embodiment specifically includes the following steps:

[0030] Step 1. Select a single-crystal YIG substrate with dimensions of 5×5mm and a thickness of 0.5mm. First, soak the YIG substrate in a solution of concentrated sulfuric acid and hydrogen peroxide in a 1:1 ratio for 15 minutes. Then, clean it in sequence with acetone, alcohol, and deionized water, and blow it dry with nitrogen gas to ensure that the surface of the YIG substrate is clean.

[0031] Step 2. On both sides of the substrate cleaned in Step 1, a Ti film with a thickness of 3 nm is deposited using DC magnetron sputtering to improve the adhesion between the subsequent Cu layer and the YIG substrate;

[0032] Step 3. Continue to deposit a 200nm thick Cu thin film on both sides of the substrate after step 2 as the cathode conductive layer during electroplating;

[0033] Step 4. Spin-coat one side of the substrate after step 3 with positive photoresist AZ4903 at 2800 rpm, pre-bake at 100℃ for 5 min, align with a UV lithography machine, expose and develop.

[0034] Step 5. Use the YIG substrate processed in Step 4 as the cathode and fix it on the electroplating fixture to ensure good contact of the Cu seed layer;

[0035] Step 6. Remove the photoresist by immersing the substrate treated in Step 5 in N-methylpyrrolidone;

[0036] Step 7. The substrate treated in Step 6 is subjected to rapid flash etching with diluted FeCl3 solution, and the Ti adhesion layer is immersed in 0.5% HF solution for 10 seconds.

[0037] Step 8. Clean the substrate treated in Step 7 with deionized water and dry it.

[0038] The tunable bandstop filter based on a YIG substrate in this embodiment is connected to a microwave signal source and a vector network analyzer via a microstrip line port. The microwave signal is fed in through a 50Ω microstrip line, and the energy is efficiently coupled to the lower A1, A2, and A3 via strong capacitive coupling generated by an extremely narrow 4μm gap. Then, the test fixture of the filter in this embodiment is placed between the poles of an electromagnet that provides a uniform DC magnetic field. The direction of the magnetic field is adjusted to ensure that the applied external bias magnetic field is parallel to the propagation direction of the microstrip line. Initially, the external magnetic field strength is set to 0 kA / m, and then gradually increased from 0 kA / m to 150 kA / m. During the magnetic field scanning process, the RF performance parameters (transmission coefficient S) are monitored in real time using a vector network analyzer. 21 Reflection coefficient S11 This describes the tuning effect of the recording device's resonant frequency as it changes with the external magnetic field. It can be observed that as the magnetic field gradually increases from 0 kA / m to 150 kA / m, the center frequency of the notch filter continuously shifts to higher frequencies, from the initial 15.42 GHz to 15.62 GHz, thus achieving tunability of the YIG bandstop filter's operating frequency.

[0039] This invention solves the problems of fixed stopband, high insertion loss, and low integration of traditional bandstop filters by precise structural parameter design, reasonable arrangement, and magnetic field tuning mechanism based on YIG material. It achieves low loss, small size, and high stability with dynamically adjustable stopband frequency, and can be widely used in high-frequency electronic devices such as wireless communication, radar systems, and satellite navigation.

[0040] The present invention has been described in detail above through specific embodiments, but these are not intended to limit the invention. Many modifications and improvements can be made by those skilled in the art without departing from the principles of the invention, and these should also be considered within the scope of protection of the present invention.

Claims

1. A high-frequency tunable bandstop filter based on a YIG substrate, characterized in that, It includes a YIG substrate, a functional metal layer formed on the surface of the YIG substrate, and a ground metal layer formed on the back side of the YIG substrate; The functional metal layer includes a microstrip line structure penetrating the YIG substrate and a square open-loop resonant ring structure disposed on one side of the microstrip line structure; the square open-loop resonant ring structure includes a plurality of square open-loop resonant rings arranged side by side in the direction of the microstrip line structure.

2. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, The outer side length of the square open-ended resonant ring is (1 / 5 to 1 / 3)L, where L is the side length of the YIG substrate; the spacing between adjacent square open-ended resonant rings is 0.1L to 0.5L. The ring width of the open resonator is the same as the size of the opening gap.

3. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, The number of square-aperture resonant rings is determined according to the size of the substrate.

4. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, The spacing between the square open resonant ring structure and the microstrip line structure is 2-10 μm.

5. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, On the other side of the microstrip line structure, a square open resonant ring structure with identical size and position is provided.

6. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, The YIG substrate is grown using liquid-phase epitaxy and exhibits a ferromagnetic resonance linewidth as low as 20 Oe, a saturation magnetization as high as 1750 Gs, and an in-plane Gilbert damping coefficient of <10. -4 Quality factor Q > 100.

7. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, Both the square-shaped open resonant ring structure and the microstrip line structure are made of Cu, and the Cu layer thickness is greater than 5 times the Cu skin effect thickness.

8. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, The multiple square-opening resonant rings in the square-opening resonant ring structure have the same opening direction and are located on the side away from the microstrip line structure.

9. The high-frequency tunable bandstop filter based on a YIG substrate according to claim 1, characterized in that, An external DC magnetic field parallel to the microstrip line is applied to the YIG substrate, with the magnetic field strength adjustable from 0 to 200 Oe. When the external magnetic field strength changes, the equivalent permeability of the YIG substrate changes, which in turn affects the electromagnetic coupling coefficient between the microstrip line and the square open resonant ring and the resonant frequency of the resonant ring, thus achieving dynamic adjustment of the stopband frequency.

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