RF MEMS Technology Research Articles

A compact and reconfigurable C-band DGS-based power divider using RF MEMS capacitive switch

This article presents a reconfigurable and compact power divider design that utilizes a combination of defect structures in the ground plane (DGS) and capacitance loading using a unique RF MEMS switch on the sapphire substrate. The combination of these two techniques results in a reduced-size reconfigurable power divider, wherein the length of the quarter-wavelength transmission line is reduced to λ/16 from λ/4, and the higher-order harmonics are suppressed up to 40 GHz. The RF MEMS capacitive switch is designed, and its DC characteristics are simulated in coventorware. The RF characteristics of the designed power divider are simulated in Ansys HFSS 19.2. The power divider utilizing RF MEMS technology has been fabricated through surface micromachining, requiring only four masks for fabrication. According to measurement findings, insertion loss and return loss are 3.57 dB and 24.6 dB (at 4.4 GHz) and 3.82 dB and 22.06 dB (at 5.4 GHz) when the switch is on and off, respectively. The total area of the design is 3.1 mm2 (21.3% of the conventional power divider). The proposed design can suppress harmonics up to the 8th order by 10 dB. These features render it a viable option for employment in Radio Frequency Integrated Circuits (RFICs).

Machine Learning-Based Modeling and Generic Design Optimization Methodology for Radio-Frequency Microelectromechanical Devices.

RF-MEMS technology has evolved significantly over the years, during which various attempts have been made to tailor such devices for extreme performance by leveraging novel designs and fabrication processes, as well as integrating unique materials; however, their design optimization aspect has remained less explored. In this work, we report a computationally efficient generic design optimization methodology for RF-MEMS passive devices based on multi-objective heuristic optimization techniques, which, to the best of our knowledge, stands out as the first approach offering applicability to different RF-MEMS passives, as opposed to being customized for a single, specific component. In order to comprehensively optimize the design, both electrical and mechanical aspects of RF-MEMS device design are modeled carefully, using coupled finite element analysis (FEA). The proposed approach first generates a dataset, efficiently spanning the entire design space, based on FEA models. By coupling this dataset with machine-learning-based regression tools, we then generate surrogate models describing the output behavior of an RF-MEMS device for a given set of input variables. Finally, the developed surrogate models are subjected to a genetic algorithm-based optimizer, in order to extract the optimized device parameters. The proposed approach is validated for two case studies including RF-MEMS inductors and electrostatic switches, in which the multiple design objectives are optimized simultaneously. Moreover, the degree of conflict among various design objectives of the selected devices is studied, and corresponding sets of optimal trade-offs (pareto fronts) are extracted successfully.

Performance Exploration of Uncertain RF MEMS Switch Design with Uniform Meanders

The design of RF-MEMS Switch is useful for future artificial intelligence applications. Radio detection and range estimation has been employed with RF MEMS technology. Attenuators, limiters, phase shifters, T/R switches, and adjustable matching networks are components of RF MEMS. The proposed RF MEMS technology has been introduced in T/R modules, lenses, reflect arrays, sub arrays and switching beam formers. The uncertain RF MEMS switches have been faced many issues like switching and voltage alterations. This study aims in the direction of design, simulation, model along with RF MEMS switching analysis including consistent curving or meandering. The proposed RF MEMS Switch is a flexure form of the Meanders that attain minimal power in nominal voltage. Moreover, this research work highlights the materials assortment in case of beam along with signal-based dielectric. The performance analysis is demonstrated for various materials that have been utilized in the design purpose. Further, better isolation is accomplished at the range of -31dB necessary regarding 8.06V pull-in voltage through a spring constant valued at 3.588N/m, switching capacitance analysis has been found to be 103 fF at ON state and 7.03pF at OFF state and the proposed switch is optimized to work at 38GHz. The designed RF MEMS switch is giving 30% voltage improvement; switching frequency is improved by 21.32% had been attained, which are outperformance the methodology and compete with present technology.

압전 액추에이터를 이용한 저전압 구동 MEMS 가변 캐패시터

In this work, low voltage MEMS variable capacitor was presented. Compare with other RF MEMS technologies, piezoelectric MEMS devices offer certain benefits such as low actuation voltage and fast moving, etc. The proposed structure consists of dual piezoelectric actuation bridges of in-plane polarized lead zirconate titanate (PZT) film to improve actuation voltage and reliability of devices. The PZT thin film, deposited on Au structural layer using RF magnetron sputtering method, was poled and driven with interdigitated electrodes(IDEs) to exploit dSUB33/SUB mode actuation. The in-plane polarized PZT films make it possible to develope dSUB33/SUB mode bending devices which lead to about two times improvement in strain performance. The fabricated variable capacitor shows that the tuning range is varied 100.9 to 111.2 nF with control voltage ranging from 0 to 1 V.

Getting ready for beyond-5G, super-IoT and 6G at hardware passive components level: a multi-state RF-MEMS monolithic step attenuator analyzed up to 60 GHz

Looking at 2030, the landscape of technology will be dominated by paradigms like 6G, Super-IoT (Internet of Things) and Tactile Internet (TI). From the perspective of Hardware (HW) components technologies, the turning into reality of such scenarios will demand for a radical reconceptualization of devices, sub-systems and systems, probably modifying the concept of HW itself. Driven by the target of taking initial steps in the direction of such future applications, this work discusses a 4 bit RF power step attenuator entirely realized in RF-MEMS technology. Physical samples are fabricated in a surface micromachining technology and rely on electrostatically actuated cantilevered MEMS ohmic switches to select or short resistive loads placed along the RF line. Fabricated devices are tested and validated up to 30 GHz, while simulations are discussed up to 60 GHz for the full set of allowed configurations. Despite a few technology non-idealities, the network shows levels of attenuation with a flatness as good as 1 dB over 60 GHz frequency span. The measured and simulated data reported in this work offer important indications on how to improve the network concept, both at technology and design level.

Exploitation of response surface method for the optimization of RF-MEMS reconfigurable devices in view of future beyond-5G, 6G and super-IoT applications

The emerging paradigms of the Beyond-5G, 6G and Super-IoT will demand for high-performance Radio Frequency (RF) passive components, and RF-MEMS technology, i.e. Microsystems-based RF passives, is a good candidate to meet such a challenge. As known, RF-MEMS have a complex behavior, that crosses different physical domains (mechanical; electrical; electromagnetic), making the whole design optimization and trimming phases particularly articulated and time consuming. In this work, we propose a novel design optimization approach based on the Response Surface Method (RSM) statistical methodology, focusing on a class of RF-MEMS-based programmable step power attenuators. The proposed method is validated both against physical simulations, performed with Finite Element Method (FEM) commercial software tools, as well as experimental measurements of physical devices. The case study here discussed features 3 DoFs (Degrees of Freedom), comprising both geometrical and material parameters, and aims to optimize the RF performances of the MEMS attenuator in terms of attenuation (S21 Scattering parameter) and reflection (VSWR—Voltage Standing Wave Ratio). When validated, the proposed RSM-based method allows avoiding physical FEM simulations, thus making the design optimization considerably faster and less complex, both in terms of time and computational load.

Q Factor Modeling and Material Selection of a Variable Capacitor based on RF-MEMS Technology

Q Factor Modeling and Material Selection of a Variable Capacitor based on RF-MEMS Technology

RF-MEMS Monolithic K and Ka Band Multi-State Phase Shifters as Building Blocks for 5G and Internet of Things (IoT) Applications.

RF-MEMS, i.e., Micro-Electro-Mechanical Systems (MEMS) for Radio Frequency (RF) passive components, exhibit interesting characteristics for the upcoming 5G and Internet of Things (IoT) scenarios, in which reconfigurable broadband and frequency-agile devices, like high-order switching units, tunable filters, multi-state attenuators, and phase shifters will be necessary to enable mm-Wave services, small cells, and advanced beamforming. In particular, satellite communication systems providing high-speed Internet connectivity utilize the K and Ka bands, which offer larger bandwidth compared to lower frequencies. This paper focuses on two design concepts of multi-state phase shifter designed and manufactured in RF-MEMS technology. The networks feature 4 switchable stages (16 states) and are developed for the K and Ka bands. The proposed phase shifters are realized in a surface micromachining RF-MEMS technology and the experimentally measured parameters are compared with Finite Element Method (FEM) multi-physical electromechanical and RF simulations. The simulated phase shifts at both the operating bands fit well the measured value, despite the measured losses (S21) are larger than 5–7 dB if compared to simulations. However, such a non-ideality has a technological motivation that is explained in the paper and that will be fixed in the manufacturing of future devices.

Modelling, design and fabrication of a novel reconfigurable ultra‐wide‐band impedance matching based on RF MEMS technology

This study proposes an adaptive impedance-matching network with tremendously reduced dimensions and presents its fabrication process. The proposed radio-frequency micro-electromechanical system (RF MEMS) device is based on a coplanar waveguide design and relies on suspended bridges for impedance tuning. The tuning is controlled by a variable applied DC voltage to the bridges. Preliminary tests validate the device's operation mechanism, and simulations were performed on both the mechanical aspects of the device (bridge gap manipulation) and tuning capabilities. This device presents the possibility of operating in a wide band of frequencies, namely [1–6] GHz, and for load impedances in the interval of [30–90] Ω for the real part and [−10–30] for the imaginary part. The device's resonant frequency and its bandwidth can be modified easily by changing the bridge gap in the RF MEMS.

RF-MEMS for 5G applications: a reconfigurable 8-bit power attenuator working up to 110 GHz. Part 2—Experimental characterisation of the RF behaviour

RF-MEMS technology is indicated as a key enabling solution to realise the high-performance and highly-reconfigurable passive components that future 5G communication standards will demand for. In this work, divided in the previous Part 1 and the current Part 2, a novel design concept of an 8-bit reconfigurable power attenuator manufactured in the RF-MEMS technology available at the CMM-FBK, in Italy, is presented, tested and discussed. As reported in Part 1, the device features electrostatically controlled MEMS ohmic switches, in order to select/deselect resistive loads (both in series and shunt configuration) that attenuate the RF signal, and comprises eight cascaded stages (i.e. 8-bit), thus implementing 256 different network configurations. In the current Part 2, fabricated samples are measured (S-parameters) from 10 MHz to 110 GHz in a wide range of different configurations, and modelled/simulated in a full 3D Finite Element Method (FEM) environment. Despite the attenuator complexity, the simulation approach leads to accurate prediction of the experimental behaviour. The device exhibits attenuation levels (S21) in the range from − 10 to − 60 dB, up to 110 GHz. In particular, the S21 shows flatness from 15 down to 3–5 dB, from 10 MHz to 50 GHz, while less linear traces up to 110 GHz. A comprehensive discussion is developed around the voltage standing wave ratio (VSWR), employed as quality indicator for the attenuation levels. Finally, margins of improvement at design level are also discussed, in order to overcome the limitations of the presented RF-MEMS device.

RF-MEMS for 5G applications: a reconfigurable 8-bit power attenuator working up to 110 GHz. Part 1: design concept, technology and working principles

RF-MEMS technology is indicated as a key enabling solution to realise the high-performance and highly-reconfigurable passive components that future 5G communication standards will demand for. In this work, a novel design concept of an 8-bit reconfigurable power attenuator manufactured in the RF-MEMS technology available at the CMM-FBK, in Italy, is tested and discussed. In the current Part 1 of the contribution, the RF-MEMS power attenuator design concept is discussed. The device features electrostatically controlled MEMS ohmic switches, in order to select/deselect resistive loads (both in series and shunt configuration) that attenuate the RF signal, and comprises eight cascaded stages (i.e. 8-bit), thus implementing 256 different network configurations. In Part 2 of the article, fabricated samples are measured (S-parameters) from 10 MHz to 110 GHz in a wide range of different configurations, and modelled/simulated in with a Finite Element Method software tool. Despite the attenuator complexity, the simulation approach leads to accurate prediction of the experimental behaviour. The device exhibits attenuation levels (S21) in the range from − 10 to − 60 dB, up to 110 GHz. In particular, the S21 shows flatness from 15 dB down to 3–5 dB, from 10 MHz to 50 GHz, while less linear traces up to 110 GHz. A comprehensive discussion is developed around the voltage standing wave ratio, employed as quality indicator for the attenuation levels. Finally, margins of improvement at design level are also discussed, in order to overcome the limitations of the presented RF-MEMS device.

Glass Packaging for RF MEMS

Abstract In recent years, advancements in High Performance Computing and Photonics are driving towards high density semiconductor packaging requirements that are creating a need for the adoption of novel material sets. Glass has many attractive properties that help address product level challenges such as low height, and smaller, packages. Glass also offers high resistivity, low dielectric constant, adjustable coefficient of thermal expansion (CTE), and low electrical loss. These properties can also be leveraged for RF and Mobile applications where battery life is paramount. To further utilize glass' material properties for interposers and compact substrates, it is necessary to form precision or Through Glass Vias (TGVs). Mobile cellular networks are rapidly evolving towards fifth generation (5G), which is set to exploit a wider spectrum of frequencies that range into millimeter wave (mmWave). RF MEMS technology is a promising approach to addressing RF Switches, which are key building blocks into Radio Frequency Front Ends (RFFE). In this paper, we show the usage of glass based packaging solutions and TGVs to offer low form factor, broadband RF MEMS switches.

RF-MEMS technology as an enabler of 5G: Low-loss ohmic switch tested up to 110 GHz

Microsystems for Radio Frequency (RF) passive elements, known as RF-MEMS, have been attracting the attention of academic and industrial research since their first discussion, thanks to the remarkable performance they can trigger. Despite the flattering premises, RF-MEMS technology did not score consistent spread into mass-market applications, yet, as technical issues still needed to be managed, but also because consumer products did not use to really need such pronounced characteristics. Nowadays, the application scenarios of 5G (i.e. 5th generation of mobile communications and networks) and of the Internet of Things (IoT), highlight a growing need for cutting edge performance that RF-MEMS are capable of addressing. Given such a context, this short communication discusses an RF-MEMS series ohmic micro-switch, electrostatically driven and fabricated in a surface micromachining process, exhibiting good characteristics up to 110 GHz. In brief details, the micro-relay shows isolation (when OPEN) better than −15 dB and loss (when CLOSE) better than −1 dB up to 40 GHz. The actuation voltage is around 50 V, although it can be lowered acting on the release step temperature. Despite the design concept admits margins for improvement, the characteristics of the micro-switch reported in the following are already quite interesting in the discussion of next generation of RF passive components for 5G and IoT.

Compact modelling-based coupled simulation of RF-MEMS networks for 5G and Internet of Things (IoT) applications

In this work, the exploitation of an on-purpose software library, previously presented by the author, is discussed in order to simulate the coupled behaviour of RF-MEMS (MicroElectroMechanical-Systems for Radio Frequency applications) devices and networks within a commercial integrated circuits (ICs) development framework. After the validation of the proposed tool against electromechanical experimental measurements of an RF-MEMS switch, the software library is exploited to simulate the multiphysics electromechanical and electromagnetic behaviour of a MEMS-based reconfigurable RF power step attenuator (complex network) manufactured within a surface micromachining RF-MEMS technology platform. The dynamic (transient) electromechanical measured behaviour of the MEMS switches comprised in the attenuator is well-predicted by the simulations based on the implemented compact models, proving the latter ones properly take into account all the salient features determining the coupled behaviour of MEMS devices, i.e. electromechanical transduction, elasticity, inertia, as well as dissipative effects, like gas viscous damping. Furthermore, simulation of the RF-MEMS complex network is completed by the inclusion of S-parameters (Scattering parameters) behaviour. To this purpose, frequency analysis of different attenuation levels realised by the network, depending on the configuration of several micro-switches, is performed. The case study reported in this paper represents a comprehensive exploitation example of the MEMS compact model library, aimed to the coupled electromechanical and electromagnetic simulation of RF-MEMS devices and networks within commercial ICs development tools, like Cadence, Keysight advanced design system (ADS), Mentor, and so on. Eventually, the discussion presented in this paper mentions a rather efficient solution to enable the simulation of entire hybrid circuits and blocks, composed of MEMS/RF-MEMS passive elements and standard semiconductor active circuitry (e.g. CMOS), within the same analysis and development environment.

RF-MEMS for high-performance and widely reconfigurable passive components – A review with focus on future telecommunications, Internet of Things (IoT) and 5G applications

Since its first discussions in literature during late ‘90s, RF-MEMS technology (i.e. Radio Frequency MicroElectroMechanical-Systems) has been showing uncommon potential in the realisation of high-performance and widely reconfigurable RF passives for radio and telecommunication systems. Nevertheless, against the most confident forecasts sparkling around the successful exploitation of RF-MEMS technology in mass-market applications, with the mobile phone segment first in line, already commencing from the earliest years of the 2000s, the first design wins for MEMS-based RF passives have started to be announced just in late 2014. Beyond the disappointment of all the most flattering market forecasts and, on the other hand, the effective employment of RF-MEMS in niche applications (like in very specific space and defence scenarios), there were crucial aspects, not fully considered since the beginning, that impaired the success of such a technology in large-market and consumer applications. Quite unexpectedly, the context has changed rather significantly in recent years. The smartphones market segment started to generate a factual need for highly reconfigurable and high-performance RF passive networks, and this circumstance is increasing the momentum of RF-MEMS technology that was expected to take place more than one decade ago. On a broader landscape, the Internet of Things (IoT) and the even wider paradigm of the Internet of Everything (IoE) seem to be potential fields of exploitation for high-performance and highly reconfigurable passive components in RF-MEMS technology.This work frames the current state of RF-MEMS market exploitation, analysing the main reasons impairing in past years the proper employment of Microsystem technology based RF passive components. Moreover, highlights on further expansion of RF-MEMS solutions in mobile and telecommunication systems will be briefly provided and discussed.

RF-MEMS for future mobile applications: experimental verification of a reconfigurable 8-bit power attenuator up to 110 GHz

RF-MEMS technology is proposed as a key enabling solution for realising the high-performance and highly reconfigurable passive components that future communication standards will demand. In this work, we present, test and discuss a novel design concept for an 8-bit reconfigurable power attenuator, manufactured using the RF-MEMS technology available at the CMM-FBK, in Italy. The device features electrostatically controlled MEMS ohmic switches in order to select/deselect the resistive loads (both in series and shunt configuration) that attenuate the RF signal, and comprises eight cascaded stages (i.e. 8-bit), thus implementing 256 different network configurations. The fabricated samples are measured (S-parameters) from 10 MHz to 110 GHz in a wide range of different configurations, and modelled/simulated with Ansys HFSS. The device exhibits attenuation levels (S21) in the range from −10 dB to −60 dB, up to 110 GHz. In particular, S21 shows flatness from 15 dB down to 3–5 dB and from 10 MHz to 50 GHz, as well as fewer linear traces up to 110 GHz. A comprehensive discussion is developed regarding the voltage standing wave ratio, which is employed as a quality indicator for the attenuation levels. The margins of improvement at design level which are needed to overcome the limitations of the presented RF-MEMS device are also discussed.

RF-MEMS Technology for Future Mobile and High-Frequency Applications: Reconfigurable 8-Bit Power Attenuator Tested up to 110 GHz

In this letter, we present and test—to the best of our knowledge, for the first time—, an 8-bit (256-state) reconfigurable RF-MEMS attenuator, from 10 MHz up to 110 GHz, realized in the CMM-FBK technology. Resistive loads, in series and shunt configuration, are selectively inserted on the RF line by means of electrostatic MEMS ohmic switches. The network exhibits several attenuation levels in the range of −10/−45 dB that are rather flat up to 50 GHz, and a certain number of configurations with VSWR smaller than 4 from nearly dc up to 110 GHz, and better than 2 on a frequency span of ~80 GHz.

RF-MEMS Technology for 5G: Series and Shunt Attenuator Modules Demonstrated up to 110 GHz

RF-MEMS technology is emerging as a key enabling solution to address demanding requirements that upcoming 5G standards pose upon passive devices and networks. In this letter, we demonstrate experimentally—to the best of our knowledge, for the first time—, RF-MEMS 2-state basic attenuator modules, from nearly dc up to 110 GHz. Physical samples are realized in the CMM-FBK RF-MEMS technology, and design variations are tested. Resistive loads are placed in series or shunt configuration on the RF line, and the attenuation is ON/OFF switched by electrostatically driven MEMS micro-relays. Tested devices show attenuation levels (S21) from −5 to −10 dB, depending on the resistive load, with flatness of 2–3 dB from 10 MHz to 50 GHz and of $\sim 2$ dB from 60 up to 110 GHz. When OFF, the attenuator modules introduce loss (S21) better than −1 dB up to 50 GHz and better than −6 dB up to 110 GHz.

Advanced Wafer Level Packaging of RF-MEMS with RDL Inductor

Abstract The market for portable and mobile data access devices that are wirelessly connected to the cloud anytime and anywhere is exploding. The trend to access any network from anywhere is driving increased functional convergence in the radio, which translates into increased packaging complexity and sophistication. This is creating unprecedented demand for RF components providing more integration- in smaller package sizes. There are exciting interconnect technologies in wafer level packaging such as wafer level chip scale packaging (WLCSP) or fan-out wafer level packaging (FO-WLP) solutions such as embedded Wafer Level Ball Grid Array (eWLB) to meet these needs. One of the most promising solutions to enable the required RF performance levels in mobile and wearable devices is the use of RF MEMS Tuners. Mobile original equipment manufacturers (OEMs) are rapidly adopting antenna tuning solutions to be able to provide the required signal strength across the large number of LTE spectrum bands used globally. With RF MEMS technology now maturing, the biggest challenge to address the fast growing opportunity was to find a suitable packaging technology that can deliver RF MEMS tuners in the smallest possible form factor, while maintaining the excellent performance characteristics of the RF MEMS technology. After careful analysis, an eWLB/FO-WLP package was adopted and released to volume production in 2015. The commercial eWLB/FO-WLP RF MEMS tuners outperform traditional RF silicon-on-insulator (SOI) switch-based antenna tuning solutions, resulting in much higher data rates (up to 2×) and improved battery life (up to 40%). Redistribution layers (RDL) in eWLB are utilized for higher electrical performance and complex routing to meet electrical requirements. The ability to utilize embedded passives in a multi-layer eWLB structure provides a number of advantages including cost reduction, footprint reduction and increased reliability. Inductors in eWLB offer significantly better performance compared to inductors in standard on-chip technologies. In this paper, we examine the WLCSP and eWLB packaging assembly flow, solutions to RF design challenges as well as characterization of RF performance. Further improvement of the quality factor of the integrated inductor and capacitors by using low-loss thin-film dielectrics and molding compound in eWLB will be reported as well. Package level reliability test results will also be presented in this paper.

RF-MEMS: an enabling technology for modern wireless systems bearing a market potential still not fully displayed

Since its first discussions in literature during late `90 s, RF-MEMS technology (i.e. Radio Frequency MicroElectroMechanical-Systems) has been showing uncommon potential in the realisation of high performance and widely reconfigurable RF passives for radio and telecommunication systems. Nonetheless, against the most confident forecasts for successful exploitation of RF-MEMS technology in mass-market applications, with the mobile phone segment first in line, already commencing from the earliest years of the 2000s, first design wins for MEMS-based RF passives have started to be announced just recently. This paper tries to depict and interpret the substantial circumstances that made RF-MEMS technology fail repeatedly, for about one decade, market forecasts. With the graphical support of the hype cycle concept, it will be shown that missed success of RF-MEMS was first caused by intrinsic (i.e. technology-related) factors. Subsequently, extrinsic elements linked to market acceptance and needs of such a technology, not fully weighted since the beginning, caused the second wave of disappointment around RF-MEMS. Quite unexpectedly, the context has changed rather significantly in recent years. The smartphones market segment started to generate a factual need for highly reconfigurable and high performance RF passive networks, and this circumstance is increasing the momentum of RF-MEMS technology that was expected about one decade ago. This work frames the current state of RF-MEMS market exploitation, also providing highlights on further expansion in mobile and telecommunication systems. Eventually, a focused state of the art report is developed around recent RF-MEMS research findings driven by requirements imposed by current market applications.