7.2
CiteScore
3.7
Impact Factor
Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
ABUNDANCE ESTIMATION IN AN ARID ENVIRONMENT
Case Study
Correspondence
Corrigendum
Editorial
Full Length Article
Invited review
Letter to the Editor
Original Article
Retraction notice
REVIEW
Review Article
SHORT COMMUNICATION
Short review
7.2
CiteScore
3.7
Impact Factor
Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
Search in posts
Search in pages
Filter by Categories
ABUNDANCE ESTIMATION IN AN ARID ENVIRONMENT
Case Study
Correspondence
Corrigendum
Editorial
Full Length Article
Invited review
Letter to the Editor
Original Article
Retraction notice
REVIEW
Review Article
SHORT COMMUNICATION
Short review
View/Download PDF

Translate this page into:

29 (
4
); 436-443
doi:
10.1016/j.jksus.2017.06.011

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

 Fondazione Bruno Kessler (FBK), Center for Materials and Microsystems (CMM), Via Sommarive, 18–38123 Povo–Trento, Italy
Received: , Accepted: ,
© The Author(s) 2017
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

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.

Keywords

MEMS
Radio frequency passives (RF)
RF-MEMS
Internet of Things (IoT)
Internet of Everything (IoE)
5G
1

1 Introduction on RF–MEMS technology

MicroElectroMechanical–Systems for Radio Frequency applications, commonly known as RF–MEMS, have been investigated by the research community starting from the late ‘90s. Microsystem (MEMS) technologies, at that time already exploited with a certain maturity in sensors and actuators applications (Bernstein et al., 1993; Zengerle et al., 1992; Aratani et al., 1993), commenced to be ventured for prototyping RF passive components. At first, miniaturisation of microwave and millimetre–wave transmission lines and their implementation in micromachining technologies based on Silicon, emerged as a rather promising research field already at the beginning on ‘90s (McGrath et al., 1993), thanks to the outstanding performance figures in terms of low–loss and compactness, if compared to traditional solutions (Katehi et al., 1993). The possibility to integrate fixed RF signal manipulation functions, e.g. through the realisation of stubs (Weller and Katehi, 1995), appeared as an additional strength of Silicon–based waveguides.

Subsequently, the exploitation of the mechanical deformability, typical of MEMS, within the just mentioned miniaturised waveguides, posed the bases for the inclusion of a crucial characteristic of passive RF components in Silicon–based technologies: tunability/reconfigurability. To this regard, it must be recalled here that from the functional point of view, the multi–physical coupling through which the mechanical behaviour of movable RF–MEMS parts is controlled (and their characteristics reconfigured) can take place basically according to four different actuation principles: electrostatic (Liu, 2011; Lee et al., 2004), electromagnetic (Cho et al., 2005), piezoelectric (Safari and Akdoğan, 2008; Kawakubo et al., 2005), and thermoelectric (Daneshmand et al., 2009; Iannacci et al., 2011a, 2010a).

This is how reconfigurable transmission lines and, more appropriately, RF–MEMS, started to draw increasing attention in the research scenario (Brown, 1997). Shortly after, MEMS technology was demonstrated for the realisation of micro–switches (Goldsmith et al., 1998) and variable capacitors (varactors) (Feng et al., 1999), as well as tunable filters (Katehi et al., 1998), resonators (Katehi et al., 1998) and programmable phase shifters (Malczewski et al., 1999). Fig. 1 shows the microphotograph of a typical varactor configuration realised in RF–MEMS technology (Goldsmith et al., 1998).

Microphotograph of an RF-MEMS varactor in Coplanar Waveguide (CPW) configuration (Goldsmith et al., 1998).
Fig. 1
Microphotograph of an RF-MEMS varactor in Coplanar Waveguide (CPW) configuration (Goldsmith et al., 1998).

The varactor is framed in a Coplanar Waveguide (CPW) structure. A metal overpass (realising an air–gap) crosses the RF line, connecting the two RF ground planes. When no DC bias is imposed between the suspended metal plate and the underlying fixed electrode (i.e. underpass), the shunt capacitance to ground is minimal. Differently, when the DC voltage drop between the two electrodes crosses the pull–in level, the suspended metal membrane collapses onto the underlying electrode, and the shunt capacitance to RF ground reaches its maximum value. In between the two ON/OFF configurations, the vertical position of the MEMS can be controlled in an analogue fashion, by driving the DC bias, thus enabling the continuous tuning of the capacitance, in a range of vertical displacement equal to the 33% of the initial (OFF state) air–gap (Iannacci et al., 2010b).

The remarkable characteristics in terms of low–loss, high–isolation, high quality factor (Q–factor), good linearity and, also importantly, tunability/reconfigurability, indicated since the early days RF–MEMS as a key enabling technology for next generations of radio platforms, spanning from handsets and mobile communications (Nguyen, 1998) to radar systems (Brown, 1998). Fig. 2 shows the schematic block diagram of an RF transceiver (transmitter/receiver), where all the circled components were envisaged to be replaced with MEMS/RF–MEMS implementations, thus enabling better performance of the whole system (Nguyen, 1998).

Schematic block diagram of an RF transceiver (transmitter/receiver). All the circled components were envisioned to be replaced with MEMS and RF-MEMS implementations, thus boosting the performance of the whole system (Nguyen, 1998).
Fig. 2
Schematic block diagram of an RF transceiver (transmitter/receiver). All the circled components were envisioned to be replaced with MEMS and RF-MEMS implementations, thus boosting the performance of the whole system (Nguyen, 1998).

As visible in Fig. 2, the variety of passives to be realised in RF–MEMS technology is quite broad, ranging from switches and varactors, to reconfigurable filters and LC–tanks. Given these premises, the research community has been driven through the years to put significant effort in demonstrating the outstanding performance achievable by means of thoughtful design of basic and complex passives in RF–MEMS technology.

Starting from basic reconfigurable elements, i.e. ohmic (Patel and Rebeiz, 2010; Shalaby et al., 2009) and capacitive (Mahameed and Rebeiz, 2010; Thakur et al., 2009; Martinez et al., 2007) micro–relays with superior characteristics, their proper replication and (cross-)interconnection enabled the realisation of high–performance and widely reconfigurable RF–MEMS passive networks (Iannacci, 2013). Thereafter, switching units ranging from Single Pole Double Throws (SPDTs) (Uno et al., 2009) to more complex Single Pole Multiple Throws (SPMTs) and switching matrices were successfully demonstrated in literature (Gong et al., 2011; Stehle et al., 2009). Fig. 3 shows the Scanning Electron Microscopy (SEM) image of the 60 GHz switched lines proposed and discussed by Gong et al. (2011).

Scanning Electron Microscopy (SEM) image of the reconfigurable RF-MEMS switched line reported by Gong et al. (2011).
Fig. 3
Scanning Electron Microscopy (SEM) image of the reconfigurable RF-MEMS switched line reported by Gong et al. (2011).

The network is realised in CPW configuration. The RF input branch can be redirected on four output lines, by means of a star–like central multiple switching unit, relying on ohmic RF–MEMS switches, that implements a Single Pole Four Throw (SP4T). The network reconfigures the phase shift of the output RF signal with respect to the input one, depending on the length of the selected output branch. Reconfigurable RF power attenuators (Iannacci et al., 2010c) and splitter/couplers (Nishino et al., 2009; Ocera et al., 2007) can also be entirely implemented in RF–MEMS technology, as well as impedance matching tuners covering significant portions of the Smith chart and realising a wide number of different states (Iannacci et al., 2011b; Lu et al., 2005a; Domingue et al., 2010; Larcher et al., 2009). Fig. 4 shows the microphotograph of the RF–MEMS reconfigurable power attenuator reported by Iannacci et al. (2010c).

Microphotograph of the RF-MEMS reconfigurable power attenuator discussed by Iannacci et al. (2010c).
Fig. 4
Microphotograph of the RF-MEMS reconfigurable power attenuator discussed by Iannacci et al. (2010c).

The device, based on a surface micromachining process and framed in a CPW configuration, exploits buried Polycrystalline Silicon (Poly–Si) resistors placed in series on the RF line to attenuate the RF signal flowing across the network. Ohmic contact electrostatically controlled MEMS switches, can selectively short each Poly–Si resistor when actuated (pulled–in), thus reconfiguring the load resistance and, in turn, the attenuation of the RF signal. The experimental testing of the device exhibited rather flat attenuation levels in the range from nearly–DC up to 30 GHz.

Furthermore, RF–MEMS technology was proven to be a key enabling solution also in the realisation of reconfigurable phase shifters (Reinke et al., 2011; Vorobyov et al., 2011) and True Time Delay (TTD) lines (De Angelis et al., 2008; Van Caekenberghe and Vaha-Heikkila, 2008) for electronic antenna steering and radar systems, as well as in the micro–fabrication of tunable filters (Varadan, 2002) for various RF applications (Entesari et al., 2007; Gil et al., 2007; Reines et al., 2010).

The afore–mentioned examples leverage on surface micromachining manufacturing processes, which is proven to be a viable solution for the realisation of highly–reconfigurable RF–MEMS devices. Of course, there exist other technology platforms and solutions, like the so–called bulk micromachining. Since the detailed discussion of pros and cons of each solution steps beyond the purposes of this article, a few references reporting in–depth technology–related discussion are listed (Del Tin et al., 2007; Giacomozzi et al., 2011; Iannacci et al., 2010c; Gao and Gong, 2016).

Despite the focus of this work is mainly aimed to RF–MEMS featuring switching elements, another category of devices that is worth to be mentioned is the one of the so–called Surface Acoustic Wave (SAW), Bulk Acoustic Wave (BAW) filters and (thin-)Film Bulk Acoustic Resonators (FBARs). The just listed classes of devices exploit forth and back transduction between electrical and mechanical (i.e. acoustic) domain, respectively, in order to realise very pronounced filtering functions, and are currently exploited quite frequently in commercial applications. The literature on this topic is wide, therefore just a valuable works are mentioned in this article (Piazza et al., 2007; Gong and Piazza, 2013, 2014; Gao et al., 2016).

2

2 Market exploitation of RF–MEMS: early vision and actual limiting factors

Such a variety of high–performance RF passives stimulated the research and scientific community to picture strategies around market exploitations of RF–MEMS technology in modern wireless systems. To this end, the contribution of Nguyen, with focus on high Q–factor MEMS resonators, is certainly relevant (Nguyen, 2001, 2002). Based on his vision, RF–MEMS passives were bearing the potential for a twofold impact on radio transceivers (transmitters/receivers). First, lumped devices, like switches, resonators and varactors, were meant to substitute standard counterparts in RF circuits, enabling better performance of wireless devices (Nguyen, 2002, 2006), as previously shown in Fig. 2. On a different level, RF–MEMS complex reconfigurable networks, like switching units, tunable filters, reconfigurable LC–tanks and so on, were supposed to make rethink the architecture of transceivers. This would had enabled not only better performance, but also wider reconfigurability of the same platform/terminal, extending services and compliance with different standards, as well as reducing hardware and power consumption (Nguyen, 1998, 2006, 2007, 2013).

Nonetheless, despite the high–expectations triggered in the beginning by RF–MEMS, issues concerned to reliability, packaging and integration, impaired their breaking into large market applications. The just mentioned aspects are going to be briefly discussed in the following.

MEMS are exposed to a wide range of malfunctioning and failure mechanisms (both reversible and irreversible) that are very common in material and mechanical engineering, but rather unknown in the community of electronic and RF engineers. Among them, the most important are fatigue, creep, plastic deformation, corrosion, fracture, stiction (i.e. the missed MEMS release after zeroing the biasing signal) and micro–welding (Iannacci, 2015a,b). All this highlighted explicitly that RF–MEMS technology was demanding for significant further development before being adoptable in market applications (DeNatale and Mihailovich, 2003; Lisec et al., 2004; Melle et al., 2003; Rizk et al., 2002).

Also related to reliability, the issue of packaging and encapsulation emerged as a relevant aspect. MEMS need to be properly isolated from the surrounding environment, by being housed within a protective (hermetic or semi–hermetic) housing (Jourdain et al., 2003; Park et al., 2002, 2003). In the RF–MEMS frame of reference, the application of a package increases the complexity at technology level and the manufacturing costs, as well. The latter ones were estimated to be as high as 80% of the final product price (Cohn et al., 2002). Furthermore, the presence of a protective cap worsens the outstanding RF performance of MEMS passives, because of additional parasitic effects due to capacitive couplings, inductance and resistance of signal underpasses, etc. Therefore, the package must be carefully conceived and counted in as actual part of the device, thus making the design and modelling phases more challenging (Iannacci, 2013; Iannacci et al., 2006, 2008; Margomenos and Katehi, 2002, 2003).

Finally, yet importantly, in several cases MEMS technology is incompatible with standard semiconductor platforms (e.g. Complementary Metal Oxide Semiconductor – CMOS). This happens, for instance, when metals like Gold are used for the MEMS structural parts, or when the thermal budget of the CMOS and MEMS part are significantly different. In–package passive components need to be integrated with active electronics, e.g. through Surface Mount Technologies (SMTs), and ad–hoc circuitry must be developed and deployed, as well, in order to operate them, rising, also in this case, complexity and costs (De Silva and Hughes, 2003; Lu et al., 2005b; Pacheco et al., 2004; Th Rijks et al., 2003; Zhang et al., 2006; Ziegler et al., 2005).

Bearing in mind the just depicted scenario, RF–MEMS started to be gazed across the scientific community as a technology suitable to demonstrate remarkable performance in research–related topics and very–limited niche applications (e.g. space and defence), but at the same time inappropriate for medium/large volume market applications, and, above all, consumer electronics, i.e. mobile phones. Despite the reasons of such a disappointment were attributed to all the additional efforts at reliability, packaging and integration level, necessary to spill out market products from RF–MEMS technology, there exists a more consistent underlying motivation that impaired their spread since the beginning.

In the first years of the 2000s, despite the technical soundness of the vision reported by Nguyen (2001, 2002, 2006, 2007, 2013), there was not a factual need for RF passives with better performance. In other words, the early approach to the commercial exploitation of RF–MEMS was mainly technology push based, rather than market driven (Martin, 1994; Iannacci, 2015a,b).

To conclude this section, a summary of advantages and disadvantages of RF–MEMS technology with respect to standard technologies (both CMOS/semiconductor and miniaturisation e.g. via micro–milling techniques) is reported in Table 1.

Table 1 Summary of advantages and disadvantages of RF-MEMS technology versus standard technologies.
Advantages Disadvantages
Good linearity Fragile (need package)
Large tuning range Large controlling voltages required (CMOS not compatible)
High Q-factor Need ad-hoc electronics to be controlled
Virtually no power consumption (for controlling the device) Technology often incompatible with standard CMOS process (i.e. need to be packaged/integrated)
Good isolation
Low-loss
Small dimensions and reduced weight
High-complexity achievable

In order to provide the reader with a more quantitative understanding of how RF–MEMS technology places with respect to other solutions, Table 2 reports the comparison between micromechanical and semiconductor–based switches (DeLisle, 2015).

Table 2 Performance and characteristics comparison between MEMS and solid state switches (DeLisle, 2015).
Switch type MEMS Solid state
FETa PINb Hybrid
Frequency range DC to max frequency 1–10 MHz to max frequency From kHz
Insertion loss Low High Medium High
Isolation Good across all frequencies Good at low-end frequencies Good at high-end frequencies
Return loss Good
Repeatability Good Excellent
Switching speed Slow Fast
Settling time Slow Good < 350 μs Excellent < 50 μs Good < 350 μs
Rise/fall time ms μs ns μs
ON to OFF switching time ms μs ns μs
Power handling High Low
Operating life Medium High
ESDc immunity High Low Medium Low
Sensitive to Mechanical vibrations Temperature extreme and RF power extreme
a Field Effect Transistor.
b P-type, Intrinsic, N-type semiconductor.
c Electrostatic Discharge.

Following a similar approach, a comparison between RF–MEMS and semiconductor–based variable capacitors (varactors) is shown in Table 3 (Elshurafa and Salama, 2013).

Table 3 Performance and characteristics comparison between MEMS and solid state variable capacitors (varactors) (Elshurafa and Salama, 2013).
CMOS varactors MEMS varactors
Leakage currents No significant leakages
Typical Q–factor of 30–40, in a few cases up to 50–60 Typical Q–factor of 200–300
Decreasing tuning range (Cmax/Cmin) due to continuous downscaling. Maximum ration of about 3 in the millimetre-wave range Tuning ranges typically spanning between 5 and 50
Rather lossy in the millimetre-wave range Always low-loss

3

3 Market exploitation of RF–MEMS: current situation and perspectives

In fact, the recent rapid diffusion of 4th Generation-Long Term Evolution (4G–LTE) smartphones enabled an unwanted degradation trend in voice signal and data transmission quality, due to the integration of the antenna with many other components (Allan, 2013) (see Fig. 5).

Decreasing trend in communication quality stepping from one generation to another, as hopping from early mobile handsets in late ‘90s to modern smartphones (Allan, 2013).
Fig. 5
Decreasing trend in communication quality stepping from one generation to another, as hopping from early mobile handsets in late ‘90s to modern smartphones (Allan, 2013).

Such an unprecedented context made room for exploitation of RF–MEMS characteristics, especially in terms of tunability. To this regard, employment of analogue impedance tuners between the smartphone antennas and the RF Front Ends (RFFEs), enables optimal adaptive matching. Thus, RF–MEMS implementation of impedance tuners is one of the first commercial uptakes of such a technology (Cavendish Kinetics, 2014).

The emerging world of 5G appears to be a field of convergence for diverse demands and challenging requirements as rarely the research and industrial community witnessed before. After all, since the massive diffusion of mobile handsets roughly two decades ago, the trend to integration of more wireless services supported by the same device was relentless. And its pace, rather than linear, has been following an exponential law. To this regard, 5G systems are predicted to deliver up to 1000 times the capacity of current mobile networks (Baldemair et al., 2015). For instance, broadband wireless applications, like high–resolution video streaming and Tactile Internet (Moskvitch, 2015), will urge for data rates that could be 10–100 times wider compared to what 4G wireless networks are able to offer (Fettweis, 2014; Osseiran et al., 2014).

At higher level of abstraction, the Internet of Things (IoT) paradigm portrays an ongoing technology development path through which any object and environment belonging to our daily life experience, earns its own identity in the digital world, by means of the Internet (Econocom, 2016; Uckelmann et al., 2011). Given the IoT frame of reference, 5G mobile systems are expected to accommodate a wider range of wireless connections, supporting emerging applications like Machine–To–Machine (M2M), and, in turn, all the more stringent requirements they bring, in terms of Quality of Service (QoS), concerning reliability, spectral and energy efficiency, and so on (Wu et al., 2011; Bhushan et al., 2014; Boccardi et al., 2014). To this regard, the scenario of smart connected cars for road safety, helps understand how critical delay and reliability constraints might be. In light of the just depicted scenario, it is straightforward that there will be no unique enabling technology capable of addressing all the challenging and often conflicting requirements of next generation 5G applications (Le et al., 2015). From a general point of view, innovation and re–engineering of network architecture and algorithms will be necessary. This, of course, will demand both for novel hardware and software solutions. More in details, just to mention some of the current limitations that will have to be overcome at architectural and implementation level, the currently in use Orthogonal Frequency Multiple Access (OFDM) waveform (exploited in 4G applications) will need to be replaced by more efficient solutions. Moreover, network diversification, employment of large–scale Multiple Input Multiple Output (MIMO) units and use of mmW spectrum to ensure Gigabit (Gb) communications, will have to be ventured (Le et al., 2015).

Bearing in mind the previously discussed market pull scenario that started making RF–MEMS solutions successful (up to now for impedance matching tuners), it is envisaged that 5G communication protocols will demand for higher operation frequencies (e.g. well above 6 GHz) and large reconfigurability to cover different services, while reducing hardware redundancy and power consumption. In order to target these challenges, it is necessary to leverage on passives with boosted characteristics (low–loss, high–isolation, etc.), and RF–MEMS technology is indicated as one of the more promising candidates, both for what concerns 5G smartphones (i.e. RFFEs), and base stations (Lapedus, 2015). Of course, there will be important challenges to be addressed in terms of frequency operation. To this regard, the backhaul portion of the infrastructure closer to end users, is supposed to work at millimetre–wave frequency (60–70 GHz). This is the case of the so–called 5G small cells, which will bring very–wide data rate access (up to the Gbps range) to individual users in confined areas. As discussed below in this paper, RF–MEMS devices featuring micro–relays operating at frequencies as high as 110 GHz and exhibiting good characteristics have already been demonstrated in literature. Further effort will have to be directed towards operation at higher frequencies for resonant classes of MEMS devices, as filters based on electromechanical transduction mechanisms.

From a different perspective, regardless of the specific technology employed for the realisation of RF components, they always need to be packaged and integrated into more complex sub–systems and systems. If, on one side, the primary role of the package is to protect devices from potentially harmful (environmental) factors, like shocks, contaminations, moisture, dust particles, and so on (Jin et al., 2010), it has been realising, on the other hand, more and more functionalities (Kuang et al., 2010). As a matter of fact, the massive growth of RF systems for mobile communication taking place since years, has been driving miniaturisation, high–integration density and low–cost fabrication solutions.

Nowadays, RF Systems on Chip (SoCs) employ hundreds of passive components and only few tens of Integrated Circuits (ICs) (STATS ChipPAC, 2017). Given that such components are often manufactured in diverse, incompatible and non–monolithic technologies, it is easy to understand that their successful integration can only take place through high–performance and high–density Wafer Level Packaging (WLP) solutions. Of course, designing and realising a package that ensures high–reliability (Iannacci, 2015a,b), high–density integration and very–low impact on the performance of RF passive (MEMS and non–MEMS) components (Lahti et al., 2013; Iannacci et al., 2008) is a rather challenging task. This is the reason why, as mentioned above, the packaging/integration phase, in some cases can be more expensive than the realisation of the actual RF components to be packaged.

4

4 Recent findings in the RF–MEMS state of the art research scenario

Since the first years of 2000, the literature on RF–MEMS started to be populated by a few research items reporting high–performance devices and networks working at frequency ranges as high as W–band (i.e. above 75 GHz). The study around the development of such components was mainly driven by the need of demonstrating and disseminating the outstanding characteristics achievable with RF–MEMS technology. For instance, high–isolation RF–MEMS switches (Rizk et al., 2001) and switch–based phase shifters (Stehle et al., 2008) were proven to exhibit high–performance in the range from 70 GHz up to 110 GHz. An interesting solution to improve isolation in the switch OFF state and reduce the losses in the switch ON state is reported by Baghchehsaraei et al. (2012). It is based on a waveguide switch, composed by laterally moving fingers able to short the electric field lines, therefore implementing the OFF state. The 3D schematic of the switch in both ON/OFF states is reported in Fig. 6.

3D schematic of the waveguide RF-MEMS switch proposed by Baghchehsaraei et al. (2012), in both ON/OFF configurations.
Fig. 6
3D schematic of the waveguide RF-MEMS switch proposed by Baghchehsaraei et al. (2012), in both ON/OFF configurations.

The tested samples exhibited losses better than 1 dB and isolation better than 20 dB in the frequency range from 62 GHz to 75 GHz. More recently, RF–MEMS started to be indicated as a key enabling technology for future 5G applications, both for what concerns basic elements (Iannacci et al., 2016a,b) and complex networks (Iannacci et al., 2016c; Iannacci and Tschoban, 2017). This suggests that the interest for high–frequency operating RF–MEMS devices is growing not only in research and niche activities, but in the consumer market segment, as well.

5

5 Conclusions

MicroElectroMechanical–Systems for Radio Frequency applications, i.e. RF–MEMS, after fluctuations about their potential employment as commercial products, are now indicated as a key enabling technology for the next generation of mobile communications. As a matter of fact, 5G communication protocols will demand for higher operation frequencies (e.g. well–above 6 GHz) and large reconfigurability to cover different services, while reducing the hardware redundancy and power consumption. In order to target these challenges, it is necessary to leverage on passives with boosted characteristics (low–loss, high–isolation, etc.), and RF–MEMS technology is indicated as one of the most promising candidates, both for what concerns 5G smartphones, i.e. RF Front Ends (RFFEs), as well as for base stations. 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 framed 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 were provided and discussed.

References

  1. Allan, R., 2013. RF MEMS Switches are Primed for Mass-Market Applications.
  2. Aratani, K., French, P.J., Sarro, P.M., Wolffenbuttel, R.F., Middelhoek, S., 1993. Process and design considerations for surface micromachined beams for a tuneable interferometer array in silicon. In: Proc. IEEE International Conference on Micro Electro Mechanical Systems MEMS, Fort Lauderdale, pp. 230–235.
  3. Baghchehsaraei, Z., Shah, U., Dudorov, S., Stemme, G., Oberhammer, J., Åberg, J., 2012. MEMS 30 µm-thick W-band waveguide switch. In: Proc. 42nd European Microwave Conference, Amsterdam, pp. 1055–1058.
  4. , , , , , , , , , . Ultra-dense networks in millimeter-wave frequencies. IEEE Commun. Mag.. 2015;53:202-208.
    [Google Scholar]
  5. Bernstein, J., Cho, S., King, A.T., Kourepenis, A., Maciel, P., Weinberg M., 1993. A micromachined comb-drive tuning fork rate gyroscope Micro Electro Mechanical Systems. In: Proc. IEEE International Conference on Micro Electro Mechanical Systems MEMS, Fort Lauderdale, pp. 143–148.
  6. , , , , , , , , , . Network densification: the dominant theme for wireless evolution into 5G. IEEE Commun. Mag.. 2014;52:82-89.
    [Google Scholar]
  7. , , , , , . Five disruptive technology directions for 5G. IEEE Commun. Mag.. 2014;52:74-80.
    [Google Scholar]
  8. Brown, E.R., 1997. RF MEMS for digitally-controlled front-end components. In: Proc. IEEE International Conference on Innovative Systems in Silicon, Austin, p. 338.
  9. , . RF-MEMS switches for reconfigurable integrated circuits. IEEE Trans. Microwave Theory Tech.. 1998;46:1868-1880.
    [Google Scholar]
  10. Cavendish Kinetics, 2014. Nubia adopts Cavendish Kinetics' SmarTune Antenna Tuning Solution for its new Z7 LTE Smartphone.
  11. , , , , . A low-voltage and low-power RF MEMS series and shunt switches actuated by combination of electromagnetic and electrostatic forces. IEEE Trans. Microwave Theory Tech.. 2005;53:2450-2457.
    [Google Scholar]
  12. Cohn, M.B., Roehnelt, R., Xu, J.-H., Shteinberg, A., Cheung, S., 2002. MEMS packaging on a budget (fiscal and thermal). In: Proc. IEEE International Conference on Electronics, Circuits and Systems ICECS, Dubrovnik, pp. 287–290.
  13. Daneshmand, M., Fouladi, S., Mansour, R.R., Lisi, M., Stajcer, T., 2009. Thermally-actuated latching RF MEMS switch. In: Proc. IEEE Int. Microwave Symp. MTT-S, Boston, pp. 1217–1220.
  14. De Angelis, G., Lucibello, A., Marcelli, R., Catoni, S., Lanciano, A., Buttiglione, R., Dispenza, M., Giacomozzi, F., Margesin, B., Maglione, A., Erspan, M., Combi, C., 2008. Packaged single pole double thru (SPDT) and true time delay lines (TTDL) based on RF MEMS switches. In: Proc. CAS Semiconductor Conference, Sinaia, pp. 227–230.
  15. , , . The package integration of RF-MEMS switch and control IC for wireless applications. IEEE Trans. Adv. Packag.. 2003;26:255-260.
    [Google Scholar]
  16. Del Tin, L., Iannacci, J., Gaddi, R., Gnudi, A., Rudny, E.B., Greiner, A., Korvink, J.G., 2007. Non linear compact modeling of RE-MEMS switches by means of model order reduction. In: Proc. International Solid-State Sensors, Actuators and Microsystems Conference, 2007, TRANSDUCERS, Lyon, pp. 635–638.
  17. DeLisle, J.-J., 2015. 6 Degrees of Microwave and RF/Microwave Switch Separation.
  18. DeNatale, J., Mihailovich, R., 2003. RF MEMS reliability. In: Proc. International Conference on Solid-State Sensors, Actuators and Microsystems TRANSDUCERS, Boston, pp. 943–946.
  19. Domingue, F., Fouladi, S., Mansour, R.R., 2010. A reconfigurable impedance matching network using dual-beam MEMS switches for an extended operating frequency range. In: Proc. IEEE MTT-S International Microwave Symposium, Anaheim, p. 1.
  20. Econocom, 2016. Internet of Things.
  21. Elshurafa, A.M., Salama, K.N., 2013. RF MEMS Capacitors and Variable Capacitors – The Future of Wireless Communication. http://repository.kaust.edu.sa/kaust/handle/10754/322934 (accessed 28.06.17).
  22. , , , , . A 25–75-MHz RF MEMS tunable filter. IEEE Trans. Microwave Theory Tech.. 2007;55:2399-2405.
    [Google Scholar]
  23. Feng, Z., Zhang, W., Su, B., Harsh, K.F., Gupta, K.C., Bright, V., Lee, Y.C., 1999. Design and modeling of RF MEMS tunable capacitors using electro-thermal actuators. In: Proc. IEEE MTT-S International Microwave Symposium, Anaheim, pp. 1507–1510.
  24. , . The tactile internet: applications and challenges. IEEE Veh. Technol. Mag.. 2014;9:64-70.
    [Google Scholar]
  25. , , . Harnessing mode conversion in AlN laterally vibrating resonators for spurious mode suppression. IEEE J. Microelectromech. Syst.. 2016;25:450-458.
    [Google Scholar]
  26. Gao, A., Lu, R., Gong, S., 2016. Mitigation of A0 spurious modes in AlN MEMS resonators with SiO2 addendums. In: Proc. IEEE International Frequency Control Symposium, New Orleans, pp. 1–5.
  27. , , , , , , . A Flexible fabrication process for RF MEMS devices. Rom. J. Inf. Sci. Technol.. 2011;14:259-268.
    [Google Scholar]
  28. , , , , . Tunable stop-band filter at Q-band based on RF-MEMS metamaterials. IET Electron. Lett.. 2007;43 1153–1153
    [Google Scholar]
  29. , , , , . Performance of low-loss RF MEMS capacitive switches. IEEE Microwave Guided Wave Lett.. 1998;8:269-271.
    [Google Scholar]
  30. , , . Design and analysis of lithium–niobate based high electromechanical coupling RF-MEMS resonators for wideband filtering. IEEE Trans. Microwave Theory Tech.. 2013;61:403-414.
    [Google Scholar]
  31. Gong, S., Piazza, G., 2014. An 880 MHz ladder filter formed by arrays of laterally vibrating thin film lithium niobate resonators. In: Proc. IEEE 27th International Conference on Micro Electro Mechanical Systems (MEMS), San Francisco, pp. 1241–1244.
  32. , , , . A 60-GHz 2-bit switched-line phase shifter using SP4T RF-MEMS switches. IEEE Trans. Microwave Theory Tech.. 2011;59:894-900.
    [Google Scholar]
  33. , , , . Introduction to Microsystem Packaging Technology (first ed.). Boca Raton: CRC Press; .
  34. Jourdain, A., Ziad, H., De Moor, P., Tilmans, H.A.C., 2003. Wafer-scale 0-level packaging of (RF-)MEMS devices using BCB. In: Proc. Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS DTIP, Cannes, pp. 239–244.
  35. Katehi, L.P.B., Rebeiz, G.M., Nguyen, C.T.-C., 1998. MEMS and Si-micromachined components for low-power, high-frequency communications systems. In: Proc. IEEE MTT-S International Microwave Symposium, Baltimore, pp. 331–333.
  36. , , , , , , . Micromachined circuits for millimeter- and sub-millimeter-wave applications. IEEE Antennas Propag. Mag.. 1993;35:9-17.
    [Google Scholar]
  37. Kawakubo, T., Nagano, T., Nishigaki, M., Abe, K., Itaya, K., 2005. Piezoelectric RF MEMS tunable capacitor with 3 V operation using CMOS compatible materials and process. In: Proc. IEEE Int. Electron Dev. Meet. IEDM, Washington, pp. 294–297.
  38. , , , eds. RF and Microwave Microelectronics Packaging (first ed.). Berlin: Springer; .
  39. , . Practical Guide to RF MEMS (first ed.). Weinheim: Wiley VCH; .
  40. , , , , , , . Enhancement of RF-MEMS switch reliability through an active anti-stiction heat-based mechanism. Microelectron. Reliab.. 2010;50:1599-1603.
    [Google Scholar]
  41. , , , . Experimental validation of mixed electromechanical and electromagnetic modeling of RF-MEMS devices within a standard IC simulation environment. IEEE J. Microelectromech. Syst.. 2010;19:526-537.
    [Google Scholar]
  42. Iannacci, J., Faes, A., Mastri, F., Masotti, D., Rizzoli, V., 2010. A MEMS-based wide-band multi-state power attenuator for radio frequency and microwave applications. In: Proc. NSTI Microtech, Anaheim, pp. 328–331.
  43. , , , , , . An active heat-based restoring mechanism for improving the reliability of RF-MEMS switches. Microelectron. Reliab.. 2011;51:1869-1873.
    [Google Scholar]
  44. Iannacci, J., Masotti, D., Kuenzig, T., Niessner, N., 2011. A reconfigurable impedance matching network entirely manufactured in RF-MEMS technology. In: Proc. SPIE Smart Sensors, Actuators, and MEMS V, Prague, pp. 1–12.
  45. , . Reliability of MEMS: a perspective on failure mechanisms, improvement solutions and best practices at development level. Displays. 2015;37:62-71.
    [Google Scholar]
  46. Iannacci, J., Tian, J., Sosin, S., Gaddi, R., Bartek, M., 2006. Hybrid wafer-level packaging for RF-MEMS applications. Proc. In: International Wafer-Level Packaging Conference IWLPC, San Jose, pp. 106–113.
  47. , , , , , . Electromagnetic optimization of an RF-MEMS wafer-level package. Sens. Actuators, A. 2008;142:434-441.
    [Google Scholar]
  48. , . RF-MEMS: an enabling technology for modern wireless systems bearing a market potential still not fully displayed. Microsyst. Technol.. 2015;21:2039-2052.
    [Google Scholar]
  49. Iannacci, J., Tschoban, C., Reyes, J., Maaß, U., Huhn, M., Ndip, I., Pötter, H., 2016. RF-MEMS for 5G mobile communications: a basic attenuator module demonstrated up to 50 GHz. In: Proc. IEEE Sensors 2016, Orlando, pp. 448–450.
  50. , , , , . RF-MEMS technology for 5G: series and shunt attenuator modules demonstrated up to 110 GHz. IEEE Electron Device Lett.. 2016;37 1558–0563
    [Google Scholar]
  51. , , , , . RF-MEMS Technology for future (5G) mobile and high-frequency applications: reconfigurable 8-bit power attenuator tested up to 110 GHz. IEEE Electron Device Lett.. 2016;37:1646-1649.
    [Google Scholar]
  52. , , . RF-MEMS for future mobile applications: experimental verification of a reconfigurable 8-bit power attenuator up to 110 GHz. J. Micromech. Microeng.. 2017;27:1-11.
    [Google Scholar]
  53. Lahti, M., Kautio, K., Ollila, J., Vähä-Heikkilä, T., Kaunisto, M., 2013. Hermetic packaging for millimetre wave applications. In: Proc. European Microelectronics Packaging Conference EMPC, Grenoble, pp. 1–5.
  54. Larcher, L., Brama, R., Ganzerli, M., Iannacci, J., Margesin, B., Bedani, M., Gnudi, A., 2009. A MEMS reconfigurable quad-band class-E power amplifier for GSM standard. In: Proc. IEEE 22nd International Conference on Micro Electro Mechanical Systems MEMS, Sorrento, pp. 864–867.
  55. Lapedus, M., 2015. Inside The 5G Smartphone.
  56. , , , , , , , . Enabling 5G mobile wireless technologies. J. Wireless Commun. Networking 2015:1-14.
    [Google Scholar]
  57. Lee, H.S., Leung, C.H., Shi, J., Chan, S.C., 2004. Micro-electro-mechanical relays design concepts and process demonstrations. In: Proc. the 50th IEEE Holm Conf. on Electrical Contacts and the 22nd Int. Conf. on Electrical Contacts, Seattle, pp. 242–247.
  58. Lisec, T., Huth, C., Wagner, B., 2004. Dielectric material impact on capacitive RF MEMS reliability. In: Proc. 34th European Microwave Conference, Amsterdam, pp. 73–76.
  59. , . Foundations of MEMS (second ed.). London: Pearson Education; .
  60. Lu, Y., Katehi, L.P.B., Peroulis, D., 2005. A novel MEMS impedance tuner simultaneously optimized for maximum impedance range and power handling. In: Proc. IEEE MTT-S International Microwave Symposium, Long Beach, pp. 1–4.
  61. Lu, A.C.W., Chua, K.M., Li, H.G., 2005. Emerging manufacturing technologies for RFIC, antenna and RF-MEMS integration. In: Proc. IEEE International Workshop on Radio-Frequency Integration Technology: Integrated Circuits for Wideband Communication and Wireless Sensor Networks, Singapore, pp. 142–146.
  62. , , . A high-power temperature-stable electrostatic RF MEMS capacitive switch based on a thermal buckle-beam design. IEEE J. Microelectromech. Syst.. 2010;19:816-826.
    [Google Scholar]
  63. , , , , , . X-band RF MEMS phase shifters for phased array applications. IEEE Microwave Guided Wave Lett.. 1999;9:517-519.
    [Google Scholar]
  64. Margomenos, A., Katehi, L.P.B., 2002. DC to 40 GHz on-wafer package for RF MEMS switches. In: Proc. IEEE Topical Meeting on Electrical Performance of Electronic Packaging, Monterey, pp. 91–94.
  65. Margomenos, A., Katehi, L.P.B., 2003. High frequency parasitic effects for on-wafer packaging of RF MEMS switches. In: Proc. IEEE MTT-S International Microwave Symposium, Philadelphia, pp. 1931–1934.
  66. , . Managing Innovation and Entrepreneurship in Technology-Based Firms (first ed.). Hoboken: John Wiley & Sons; .
  67. Martinez, J., Blondy, A., Pothier, A., Bouyge, D., Crunteanu, A., Chatras, M., 2007. Surface and bulk micromachined RF MEMS capacitive series switch for watt-range hot switching operation. In: Proc. 37th European Microwave Conference, Munich, pp. 1237–1240.
  68. , , , , . Silicon micromachined waveguides for millimeter-wave and submillimeter-wave frequencies. IEEE Microwave Guided Wave Lett.. 1993;3:61-63.
    [Google Scholar]
  69. Melle, S., Flourens, F., Dubuc, D., Grenier, K., Pons, P., Pressecq, F., Kuchenbecker, J., Muraro, J.L., Bary, L., Plana, R., 2003. Reliability overview of RF MEMS devices and circuits. In: Proc. 33rd European Microwave Conference, Munich, pp. 37–40.
  70. Moskvitch, K., 2015. Tactile internet: 5G and the Cloud on steroids.
  71. Nguyen, C.T.-C., 1998. Microelectromechanical devices for wireless communications. In: Proc. IEEE 11th International Conference on Micro Electro Mechanical Systems MEMS, Heidelberg, pp. 1–7.
  72. Nguyen, C.T.-C., 2001. Transceiver front-end architectures using vibrating micromechanical signal processors. In: Proc. Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, Ann Arbor, pp. 23–32.
  73. Nguyen, C.T.-C., 2002. RF MEMS for wireless applications. In: Proc. Device Research Conference DRC, Santa Barbara, pp. 9–12.
  74. Nguyen, C.T.-C., 2006. Integrated micromechanical circuits for RF front ends. In: Proc. European Solid-State Circuits Conference ESSCIRC, Montreux, pp. 7–16.
  75. , . MEMS technology for timing and frequency control. IEEE Trans. Ultrason. Ferroelectr. Freq. Control. 2007;54:251-270.
    [Google Scholar]
  76. , . MEMS-based RF channel selection for true software-defined cognitive radio and low-power sensor communications. IEEE Commun. Mag.. 2013;51:110-119.
    [Google Scholar]
  77. Nishino, T., Kitsukawa, Y., Hangai, M., Lee, S.-S., Soda, S.-N., Miyazaki, M., Naitoh, I., Konishi, Y., 2009. Tunable MEMS hybrid coupler and L-band tunable filter. In: Proc. IEEE MTT-S International Microwave Symposium, Boston, pp. 1045–1048.
  78. Ocera, A., Farinelli, P., Mezzanotte, P., Sorrentino, R., Margesin, B., Giacomozzi, F., 2007. Novel RF-MEMS widely-reconfigurable directional coupler. In: Proc. 37th European Microwave Conference, Munich, pp. 122–125.
  79. , , , , , , , , , , , , , , . Scenarios for 5G mobile and wireless communications: the vision of the METIS project. IEEE Commun. Mag.. 2014;52:26-35.
    [Google Scholar]
  80. Pacheco, S., Zurcher, P., Young, S., Weston, D., Dauksher, W., 2004. RF MEMS resonator for CMOS back-end-of-line integration. In: Proc. Topical Meeting on Silicon Monolithic Integrated Circuits in RF Systems, Atlanta, pp. 203–206.
  81. Park, Y.-K., Park, H.-W., Lee, D.-J., Park, J.-H., Song, I.-S., Kim, C.-W., Song, C.-M., Lee, Y.-H., Kim, C.-J., Ju, B.K., 2002. A novel low-loss wafer-level packaging of the RF-MEMS devices. In: Proc. IEEE 15th International Conference on Micro Electro Mechanical Systems MEMS, Las Vegas, pp. 681–684.
  82. Park, Y.-K., Kim, Y.-K., Hoon, K., Lee, D.-J., Kim, C.-J., Ju, B.-K., Park, J.-O., 2003. A novel thin chip scale packaging of the RF-MEMS devices using ultra thin silicon. In: Proc. IEEE 16th International Conference on Micro Electro Mechanical Systems MEMS, Kyoto, pp. 618–621.
  83. Patel, C., Rebeiz, G.M., 2010. An RF-MEMS switch with mN contact forces. In: Proc. IEEE MTT-S International Microwave Symposium, Anaheim, pp. 1242–1245.
  84. , , , . Single-chip multiple frequency AlN MEMS filters based on contour-mode piezoelectric resonators. IEEE J. Microelectromech. Syst.. 2007;16:319-328.
    [Google Scholar]
  85. , , , . Compact low-loss tunable X-band bandstop filter with miniature RF-MEMS switches. IEEE Trans. Microwave Theory Tech.. 2010;58:1887-1895.
    [Google Scholar]
  86. Reinke, J., Wang, L., Fedder, G.K., Mukherjee, T., 2011. A 4-bit RF MEMS phase shifter monolithically integrated with conventional CMOS. In: Proc. IEEE 24th International Conference on Micro Electro Mechanical Systems MEMS, Cancun, pp. 748–751.
  87. Rizk, J.B., Chaiban, E., Rebeiz, G.M., 2002. Steady state thermal analysis and high-power reliability considerations of RF MEMS capacitive switches. In: Proc. IEEE MTT-S International Microwave Symposium, Seattle, pp. 239–243.
  88. , , , , . High-isolation W-band MEMS switches. IEEE Microwave Wireless Compon. Lett.. 2001;11:10-12.
    [Google Scholar]
  89. , , eds. Piezoelectric and Acoustic Materials for Transducer Applications (first ed.). New York: Springer; .
  90. , , , , , , , . Robust design of RF-MEMS cantilever switches using contact physics modeling. IEEE Trans. Ind. Electron.. 2009;56:1012-1021.
    [Google Scholar]
  91. STATS ChipPAC, 2017. Packaging Technology Overview.
  92. Stehle, A., Georgiev, G., Ziegler, V., Schoenlinner, B., Prechtel, U., Schmid, U., Seidel, H., 2009. Broadband single-pole multithrow RF-MEMS switches for Ka-band. In: Proc. German Microwave Conference, Munich, pp. 1–4.
  93. Stehle, A., Georgiev, G., Ziegler, V., Schoenlinner, B., Prechtel, U., Seidel, H., Schmid, U., 2008. RF-MEMS switch and phase shifter optimized for W-band. In: Proc. 38th European Microwave Conference, Amsterdam, pp. 104–107.
  94. Thakur, S., Sumithra Devi, K., Ranjitha, I., 2009. Performance of low loss RF MEMS fixed-fixed capacitive switch characterization. In: Proc. Applied Electromagnetics Conference AEMC, Kolkata, pp. 1–4.
  95. Th Rijks, G.S.M., van Beek, J.T.M., Ulenaers, M.J.E., De Coster, J., Puers, R., den Dekker, A., van Teeffelen, L., 2003. Passive integration and RF MEMS: a toolkit for adaptive LC circuits. In: Proc. European Solid-State Circuits Conference ESSCIRC, Estoril, pp. 269–272.
  96. , , , eds. Architecting the Internet of Things (first ed.). Berlin: Springer; .
  97. Uno, Y., Narise, K., Masuda, T., Inoue, K., Adachi, Y., Hosoya, K., Seki, T., Sato, F., 2009. Development of SPDT-structured RF MEMS switch. In: Proc. International Solid-State Sensors, Actuators and Microsystems Conference TRANSDUCERS, Denver, pp. 541–544.
  98. , , . An analog RF MEMS slotline t-time-delay phase shifter. IEEE Trans. Microwave Theory Tech.. 2008;56:2151-2159.
    [Google Scholar]
  99. , . RF MEMS and Their Applications (first ed.). Hoboken: John Wiley & Sons; .
  100. Vorobyov, A., Sauleau, R., Fourn, E., Oberhammer, J., Baghchehsaraei, Z., 2011. MEMS based waveguide phase shifters for phased arrays in automotive radar applications. In: Proc. European Conference on Antennas and Propagation EUCAP, Rome, pp. 2087–2090.
  101. Weller, T.M., Katehi, L.P.B., 1995. Compact stubs for micromachined coplanar waveguide. In: Proc. 25th European Microwave Conference, Bologna, pp. 589–593.
  102. , , , , , . M2M: From mobile to embedded internet. IEEE Commun. Mag.. 2011;49:36-43.
    [Google Scholar]
  103. Zengerle, R., Richter, A., Sandmaier, H., 1992. A micro membrane pump with electrostatic actuation Micro Electro Mechanical Systems. In: Proc. IEEE International Conference on Micro Electro Mechanical Systems MEMS, Travemünde, pp. 19–24.
  104. Zhang, Q.X., Yu, A.B., Yang, R., Li, H.Y., Guo, L.H., Liao, E.B., Tang, M., Kumar, R., Liu, A.Q., Lo, G.Q., Balasubramanian, N., Kwong, D.L., 2006. Novel monolithic integration of RF-MEMS switch with CMOS-IC on organic substrate for compact RF system. In: Proc. International Electron Devices Meeting IEDM, San Francisco, pp. 1–4.
  105. Ziegler, V., Siegel, C., Schonlinner, B., Prechtel, U., Schumacher, H., 2005. RF-MEMS switches based on a low-complexity technology and related aspects of MMIC integration. In: Proc. European Gallium Arsenide and Other Semiconductor Application Symposium EGAAS, Paris, pp. 289–292.

Fulltext Views
44

PDF downloads
7
View/Download PDF
Download Citations
BibTeX
RIS
Show Sections

Suggested read for related articles:

© Copyright 2025 – Journal of King Saud University – Science.

Published by Scientific Scholar on behalf of King Saud University.

ISSN (Print): 1018-3647
ISSN (Online): 2213-686X

Scientific Scholar CrossRef Creative Commons Open Acess Portico