Radio Frequency Filters Research Articles

Assessment of the Quality of Radio-Frequency Filters Used in the Organization of Communication in Railway Transport in the Production Process

The article discusses the main types of radio-frequency filters in radio-frequency systems. The errors in the characteristics of radio-frequency filters during the production process are analyzed. The characteristics of the tolerance field and the normal distribution of the production error of the output parameters of products are given. It is shown that in order to reduce the percentage of defective products due to the parameters going beyond the permissible limits, the technological process of filter production should be organized in a certain way.

Trends and Applications of Surface and Bulk Acoustic Wave Devices: A Review.

The past few decades have witnessed the ultra-fast development of wireless telecommunication systems, such as mobile communication, global positioning, and data transmission systems. In these applications, radio frequency (RF) acoustic devices, such as bulk acoustic waves (BAW) and surface acoustic waves (SAW) devices, play an important role. As the integration technology of BAW and SAW devices is becoming more mature day by day, their application in the physical and biochemical sensing and actuating fields has also gradually expanded. This has led to a profusion of associated literature, and this article particularly aims to help young professionals and students obtain a comprehensive overview of such acoustic technologies. In this perspective, we report and discuss the key basic principles of SAW and BAW devices and their typical geometries and electrical characterization methodology. Regarding BAW devices, we give particular attention to film bulk acoustic resonators (FBARs), due to their advantages in terms of high frequency operation and integrability. Examples illustrating their application as RF filters, physical sensors and actuators, and biochemical sensors are presented. We then discuss recent promising studies that pave the way for the exploitation of these elastic wave devices for new applications that fit into current challenges, especially in quantum acoustics (single-electron probe/control and coherent coupling between magnons and phonons) or in other fields.

Heterogeneous integration of lithium tantalate thin film on quartz for high performance surface acoustic wave resonator

Surface acoustic wave (SAW) resonator based on the piezo film on a foreign substrate is promising to enhance the performance of radio frequency filters. In this work, the 4 inch wafer-scale lithium tantalate thin film on quartz (LTOQ) heterogenous substrate was fabricated by ion-cut process. The cut angle of quartz was optimized to achieve high-quality factor (Q) based on finite element analysis. The average film thickness and the film nonuniformity for the whole wafer are 602 nm and ±2.2%, respectively. The lithium tantalate film exhibits single-crystalline quality where the full width at half-maximum of high-resolution X-ray diffraction rocking curve is 47.4 arcsec. The shear horizonal surface acoustic wave resonator based on the LTOQ structure exhibits a maximum Bode-Q exceeding 3000 and the electromechanical coupling coefficient of 10.26%. The temperature coefficient of frequency at resonant frequency and anti-resonant frequency are −25.21 ppm °C−1 and −35.22 ppm °C−1, respectively.

Scandium-Doped Aluminum Nitride for Acoustic Wave Resonators, Filters, and Ferroelectric Memory Applications

Scandium-doped aluminum nitride (AlScN) has generated great research interest owing to its unique properties. The wurtzite-structure AlScN is compatible with the complementary metal oxide semiconductor (CMOS) process and has improved piezoelectricity compared with undoped aluminum nitride (AlN), making it a promising candidate to be used for next-generation radio frequency (RF) microelectromechanical system (MEMS) building blocks. Additionally, the ferroelectricity observed in AlScN can be potentially applied to ferroelectric memory devices. In this spotlight article, we provide a brief introduction of AlScN and summarize the recent progress of AlScN-based applications, including RF acoustic wave resonators, filters, and ferroelectric memory devices. Finally, the current challenges as well as the future opportunities of AlScN materials and related applications are discussed.

Aluminum scandium nitride thin-film bulk acoustic resonators for 5G wideband applications

Bulk acoustic wave (BAW) filters have been extensively used in consumer products for mobile communication systems due to their high performance and standard complementary metal-oxide-semiconductor (CMOS) compatible integration process. However, it is challenging for a traditional aluminum nitride (AlN)-based BAW filter to meet several allocated 5G bands with more than a 5% fractional bandwidth via an acoustic-only approach. In this work, we propose an Al0.8Sc0.2N-based film bulk acoustic wave resonator (FBAR) for the design of radio frequency (RF) filters. By taking advantage of a high-quality Al0.8Sc0.2N thin film, the fabricated resonators demonstrate a large Keff2 of 14.5% and an excellent figure of merit (FOM) up to 62. The temperature coefficient of frequency (TCF) of the proposed resonator is measured to be −19.2 ppm/°C, indicating excellent temperature stability. The fabricated filter has a center frequency of 4.24 GHz, a −3 dB bandwidth of 215 MHz, a small insertion loss (IL) of 1.881 dB, and a rejection >32 dB. This work paves the way for the realization of wideband acoustic filters operating in the 5G band.

Large-Range Spurious Mode Elimination for Wideband SAW Filters on LiNbO₃/SiO₂/Si Platform by LiNbO₃ Cut Angle Modulation.

A LiNbO3 (LN)/SiO2/Si multilayered structure was recently reported as a new platform for achieving wideband radio frequency (RF) filters. However, the in-band ripples in filters resulting from the spurious Rayleigh mode lead to deteriorated performance, and thus, a wide Rayleigh elimination window (REW) is highly desired for realizing spurious-free wideband surface acoustic wave (SAW) filters with a wide design space and good process tolerance. Here, we investigated the spurious mode suppression on the LN/SiO2/Si platform theoretically and experimentally through modulating the cut angle ( θ ) of LN. The K2 dispersion characteristics of the main mode (shear-horizontal wave) and spurious mode (Rayleigh wave) on LN/SiO2/Si substrates were systematically analyzed by the finite-element method (FEM), along with bulk LN for comparison. It is found that the REW is wider on LN/SiO2/Si than bulk LN, as Rayleigh wave can be totally eliminated with Cu electrode normalized thickness ( [Formula: see text]) ranging from 0.1 to 0.19 when θ is between 19° and 22° on the LN/SiO2/Si platform, in contrast to the quite narrow REW on bulk LN restricted to some specific [Formula: see text]. To verify the simulation results, resonators were prepared on 15°YX-LN/SiO2/Si, 20°YX-LN/SiO2/Si, bulk 15°YX-LN, and bulk 20°YX-LN. In addition, the typical spurious-free wideband SAW filter with [Formula: see text] nm based on the 20°YX-LN/SiO2/Si platform demonstrates high performance with a center frequency ( [Formula: see text]) of 1.27 GHz, a minimum insertion loss (ILmin) of 0.7 dB, and a 3-dB fractional bandwidth (FBW) of ~20.1%. This work provides a workable solution in fabricating spurious-free wideband and low-loss SAW filters for fifth-generation (5G) applications.

Homo-epitaxial growth of LiNbO3 thin films by Pulsed Laser deposition

With the deployment of the 5th Generation of mobile applications (5G), the performances of radio-frequency (RF) filters are pushed to their limits. Highly crystalline piezoelectric materials with an electromechanical coupling coefficient higher than aluminium nitride are of high interest. Lithium niobate (LiNbO3), with an electromechanical coupling coefficient from 5 % to 45 % for bulk waves, appears to be a promising candidate for a next generation of RF filters. However, despite decades of research, the growth of single-phased, stoichiometric and highly crystalline LiNbO3 thin films is still very challenging.In the present work, 200 nm-thick LiNbO3 films have been grown by pulsed laser deposition on congruent LiNbO3 substrates with various crystalline orientations: X-cut (i.e. (110)), Y-cut (i.e. (100)) and Z-cut (i.e. (001)). The influence of the substrate’s crystal cut on the physical and chemical properties of the LiNbO3 films is investigated. A High-Resolution X-ray Diffraction methodology is developed to characterize the crystalline properties of the homoepitaxial layers. In all cases, single-phased and epitaxial LiNbO3 thin films are obtained. These results indicate that a standard wafer-based PLD system can be used to grow LiNbO3 thin films with a crystalline quality and a stoichiometry very close to a LiNbO3 monocrystalline substrate.

Perencanaan Rancang Bangun Microstrip Band Pass Filter dengan Struktur Tapped Input Hairpin pada Aplikasi Jaringan Mid-band 5G Telkomsel

Microstrip filter is a type of Radio Frequency (RF) filter that uses a thin electrical conductor separated from the ground plane by using a dielectric called the substrate. Microstrip filters are generally printed on Printed Circuit Boards or PCBs where high-frequency signals are directed from one part of the system to another with high efficiency. There are several types that can be applied to the operation of microstrip filters, one of which is a band pass filter. Band pass filter is a filter that can pass a signal with a certain frequency that is limited by a low cut-off frequency and a high cut-off frequency, and is able to dampen signals that are below the cut-off frequency and above the high cut-off frequency. There are several types of resonator designs that can be used for reference in the manufacture of microstrip filters, such as tapped line input hairpin filters, stub loaded filters, stepped impedance filters, and combline filters. By using the reference form of the tapped line input hairpin, this journal is intended for planning the manufacture of microstrip filters in the application of Telkomsel's 5G technology.

A computer‐aided design tool for RF filters design automation

SummaryIn this paper, we propose a computer‐aided design (CAD) tool in the electronic design automation (EDA) domain. This tool is dedicated for the design and simulation of Radiofrequency (RF) filters that are integrated into Advanced Design System (ADS) software. It includes a graphical user interface (GUI) developed using the design kit feature available under ADS and “Application Extension Language (AEL)” as a programming language. This will extend the existing smart filter design tool under ADS by adding more types of RF filters. The proposed feature will provide to users a rapid and an accurate tool to design and simulate RF filters by presenting interactive menus facilitating the process. As a proof of concept, an application of this tool is presented for the design of a Dual‐Behavior Resonators filter. The tool can be upgraded by adding other RF components and even entire front‐end circuits. In a future step, this tool will be enhanced by adding tuning capabilities to RF filters using ideal capacitors and varactors, which will make it the first one of its kind in the literature.

A Study of Symbolic Analysis of Electrical Circuits on the Example of a Radio Frequency Filter

The year 2022 marks the 175th anniversary of Kirchhoff's theorem on finding a symbolic expression of the current of an electric circuit branch from its contour determinant in the form of a fraction with a denominator and numerator. The first part of Kirchhoff's theorem concerning finding the contour determinant (fraction denominator) marked the beginning of graph theory, while the second part of the theorem on finding the numerator of a fraction remains unused to date. A symbolic circuit analysis calculation of transient processes in the radio frequency filter is carried out at the operator's stepwise and harmonic influences. The computer-aided calculation program developed by the authors is based on the modified Kirchhoff rule for finding the symbolic expression of the current of a branch of an electrical circuit from its contour determinant and it can be useful for researchers, engineers and students of mathematical and technical specialties. The program console is written in the Delphi package and opens in the Windows environment under the name "TINS" and it has an intuitive interface. The expressions for the branch currents can be copied without modification to the Maple computer algebra package, and to the Mathcad package – with the replacement of mathematical symbols. The reliability of the calculations was checked by initial and final conditions by comparing the Laplace transform table with the originals found by the “invlaplace” operation built into the Mathcad package. The presented computer program and calculation methodology allow you to quickly understand certain sections of mathematics and radio electronics and easily choose another object as a study. Computer-aided calculation of electromagnetic processes in radio engineering devices using the "TINS" program reduces the analysis time by obtaining results in symbolic form.

Development and Application of SAW Filter.

With the in-depth advancement of the fifth generation (5G) mobile communication technology, the technical requirements for filters are also constantly improving. Surface acoustic wave (SAW) filters are widely used in home TV, mobile communications, radio frequency filters and radar due to their simple structure, few mask layers, easy miniaturization, and low cost. Through the continuous improvement of communication technology, SAW has developed into various high-performance acoustic filters from bulk SAW with the support of some new architectures, new materials and advanced modeling techniques. This paper analyzes and reviews the research situation of SAW filter technology.

3D visualization of microwave electric and magnetic fields by using a metasurface-based indicator

Visualizations of the microwave electric and magnetic near-field distributions of radio-frequency (RF) filters were performed using the technique of thermoelastic optical indicator microscopy (TEOIM). New optical indicators based on periodic dielectric-metal structures were designed for electric field visualization. Depending on the structure orientation, such metasurface-based indicators allow separately visualization of the Ex and Ey components of the in-plane electric field. Numerical simulations were conducted to examine the working principle of the designed indicator structures, and the results were compared to the experimental, showing good agreement. In addition, the 3D visualization of the microwave near-field distribution was built, to show the field intensity and distribution dependencies on the distance from the RF filter.

Measurement of the electron energy distribution functions in low density RF plasmas through a tunable external RF filter

Abstract The electron energy distribution function (EEDF) measurement in radio frequency (RF) plasmas is of fundamental interests, especially in low-density RF capacitively coupled plasma. For this purpose, a new external filter with very high impedances is developed. The impedance of the filter at the fundamental and its harmonic frequencies (13.56, 27.12 and 40.68 MHz) through careful circuit design is maximized. Experimental verifications are performed by measuring the EEDFs in RF discharges. The result shows that the RF distortion in the EEDF measurement is significantly reduced by tuning the filter under various discharge conditions in an inductively coupled plasma. Accurate plasma densities can be obtained and the electron heating mode transition is observed through high-quality EEDF measurement in an capacitively coupled plasma, where RF plasma potential fluctuates severely.

Development of 3D Wafer Level Hermetic Packaging with Through Glass Vias (TGVs) and Transient Liquid Phase Bonding Technology for RF Filter.

The development of 5G mobile communication created the need for high-frequency communication systems, which require vast quantities of radio frequency (RF) filters with a high-quality factor (Q) and low inband losses. In this study, the packaging of an RF filter with a through-glass via (TGV) interposer was designed and fabricated using a three-dimensional wafer-level package (3D WLP). TGV fabrication is a high-yielding process, which can produce high precision vias without masking and lithography and reduce the manufacturing cost compared with the through silicon via (TSV) solution. The glass interposer capping wafer contains Cu-filled TGV, a metal redistribution layer (RDL), and the bonding layer. The RF filter substrate with Au bump is bonded to the capping wafer based on Au-Sn transient liquid phase (TLP) bonding at 280 °C with a 40 kN (approximately 6.5 MPa) bonding force. Experimental results show that shear strengths of approx. 54.5 MPa can be obtained, higher than the standard requirement (~6 MPa). In addition, a comparison of the electrical performance of the RF filter package after the pre-conditional level three (Pre-Con L3) and unbiased highly accelerated stress (uHAST) tests showed no difference in insertion attenuation across the passband (<0.2 dB, standard value: <1 dB). The final packages passed the reliability tests in the field of consumer electronics. The proposed RF filter WLP achieves high performance, low cost, and superior reliability.

Analysis and Modeling of N-Path Circuits Peak Frequency Shift Caused by Switch Parasitics

The N-path circuit serves both as a mixer and as a radio frequency (RF) filter. Certain performance aspects, such as noise, linearity, and out-of-band (OOB) rejection dictate large switches size. However, such increment raises the value of the parasitic RF capacitance, which causes further in-band (IB) loss and peak frequency shift. In this brief, we derive simplified equations for the assessment of the mentioned non-ideal properties, using the novel linear periodically time-variant (LPTV) state-space analysis, by making derivations and approximations based on realistic circuit parameters. We present closed-form equations for the voltage gain peak frequency shift and a revised linear time-invariant (LTI) model for the assessment of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{11}$ </tex-math></inline-formula> dip frequency shift.

Influence of Etching Trench on Keff2&nbsp;of Film Bulk Acoustic Resonator.

As radio-frequency (RF) communication becomes more ubiquitous globally, film bulk acoustic resonators (FBAR) have attracted great attention for their superior performance. One of the key parameters of an FBAR, the effective electromechanical coupling coefficient (), has a great influence on the bandwidth of RF filters. In this work, we propose a feasible method to tune the of the FBAR by etching the piezoelectric material to form a trench around the active area of the FBAR. The influence of the position of the etching trench on the of the FBAR was investigated by 3D finite element modeling and experimental fabricating. Meanwhile, a theoretical electrical model was presented to test and verify the simulated and measured results. The of the FBAR tended to be reduced when the distance between the edge of the top electrode and the edge of the trench was increased, but the Q value of the FBAR was not degraded. This work provides a new possibility for tuning the of resonators to meet the requirements of different filter bandwidths.

Design and Optimization of the Dual-Mode Lamb Wave Resonator and Dual-Passband Filter.

Radio frequency (RF) filters with multiple passbands can meet the needs of miniaturization and integration for 5G communications. This paper reports a dual-mode Lamb wave resonator (DLWR) and a dual-passband filter based on DLWRs. The DLWR consists of a piezoelectric film and two interdigital electrode (IDT) arrays with different thicknesses, which leads to the coexistence of two main modes in the resonator. The resonance frequencies of the two modes can be adjusted separately by changing the thicknesses of the IDTs, which greatly satisfies the requirements of the dual-passband filter. Four DLWRs with different electrode configurations are designed, and the influences of the periodic length and thicknesses of the IDTs on the performance of the DLWR are studied. When the thickness of the piezoelectric layer is 0.75 μm and the two thicknesses of the IDTs are 0.1 μm and 0.3 μm, the resonance frequency of the second main mode is 1.27 GHz higher than the resonance frequency of the first main mode in the DLWR. Furthermore, a dual-passband filter based on the proposed DLWRs is demonstrated with an insertion loss less than 1 dB and a band rejection of about 15 dB. Moreover, two passbands at 2.45 GHz and 3.88 GHz with bandwidths of 66 MHz and 112 MHz, respectively, are achieved. The presented DLWR shows a potential application that can be used to obtain RF filters with adjustable dual passbands.

Development of the ion cyclotron emission diagnostic on the HL-2A tokamak

An ion cyclotron emission (ICE) diagnostic, which is based on a B-dot probe, has been recently designed and installed on HL-2A tokamak. The diagnostic is used to study various high-frequency magnetic field fluctuations which can be excited by energetic ions and runaway electrons in the plasma. The ICE diagnostic on HL-2A includes a high-frequency B-dot probe, direct current (DC) block, radio frequency splitters, filter bank and power detectors. The filter bank is composed of 16 channels filters, with the center frequency covering from 10 to 160 MHz, 10 MHz step length and 8 MHz bandwidth. The log detectors with a large dynamic range (from −80 dBm to −20 dBm) are used to detect the bandpass power. Test results of the B-dot probe, filters and power detectors are shown. The signals can also be sampled with a fast analog-to-digital converter with a 14-bit depth, 100 MHz bandwidth and 250 MSample/s sampling rate.

Efficient Optimization Based Differential Evolution Algorithm for Accurate Rational Function Modeling of Radio-Frequency Filters

Efficient Optimization Based Differential Evolution Algorithm for Accurate Rational Function Modeling of Radio-Frequency Filters

Structure-Size Optimization and Fabrication of 3.7 GHz Film Bulk Acoustic Resonator Based on AlN Thin Film

Traditional radio frequency filters cannot meet the demands of miniaturization, high frequency operation, integration, and broadband capacity in new-generation communication system owing to their larger volumes. A thin film bulk acoustic resonator (FBAR) is therefore suggested as an optimum solution because of its small volume and a good performance. In this study, the COMSOL multiphysics software was used to build 2 D and 3 D finite element models to analyze the harmonic characteristics of the FBAR. Based on the optimized structural parameters, the FBAR was fabricated with series resonant frequency, parallel resonant frequency, and effective coupling coefficient values of 3.705, and 3.82 GHz, and 7.4%, respectively. Compared with the simulated FBAR results, the effective coupling coefficient of the fabricated FBAR declined by only 0.1%, almost achieving the desired performance.