Compact RF Research Articles

A Compact RF MEMS Metal-Contact Switch and Switching Networks

A compact RF MEMS metal-contact switch based on a tethered cantilever topology and orthogonal anchors is presented. The switch is a “medium-force” design capable of achieving a simulated contact force of 0.38–0.72 mN for actuation voltages of 90–100 V and a simulated restoring force of 0.46 mN in a 120 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\,$</tex></formula> 160 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\mu {\rm m}^{2}$</tex></formula> area. The pull-in and release voltages are 75 V and 70 V, respectively. In the down-state position, the switch resistance is 1–2 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\Omega $</tex></formula> with a Au/Ru hybrid contact. In the up-state, the capacitance is 16 fF, resulting in an isolation of 20 dB at 10 GHz and 9 dB at 40 GHz for an SPST configuration. For a series/shunt configuration, the switch achieves an isolation of 55 dB at 10 GHz and 35 dB at 40 GHz. Compact SP4T and SP6T switching networks are also implemented. The SP4T is 850 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\,\times\,$</tex></formula> 530 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu {\rm m}^{2}$</tex></formula> (850 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex></formula> 650 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu {\rm m}^{2}$</tex></formula> with bias pads); the SP6T is 850 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex> </formula> 730 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu {\rm m}^{2}$</tex></formula> (850 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\,\times\,$</tex> </formula> 855 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu {\rm m}^{2}$</tex></formula> with bias pads). Both designs achieve an isolation of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\sim 36~{\rm dB}$</tex> </formula> and an insertion loss of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$&lt; 0.3 ~{\rm dB}$</tex></formula> at 3 GHz.

Photo-triggered pulsed cavity compressor for bright electron bunches in ultrafast electron diffraction

Temporally resolved observation of microscopic structural dynamics of solids with ultrafast electron diffraction (UED) requires extremely short pulsed, highly charged, monoenergetic electron beams with sufficient transverse coherence length of several unit cells of the investigated samples. However, Coulomb repulsion defeats these parameters in free propagation of an electron pulse initially bright on the photo cathode. We demonstrate a new electron pulse compressor design based on a simple and compact RF structure incorporating a pair of gallium arsenide photoconductive semiconductor switches that are triggered by femtosecond laser pulses, thereby providing a longitudinal voltage gradient of up to 20 V/ps. Our proof of principle experiment achieved compression of bunches containing 26,000 electrons to a duration of below 750 fs and a beam diameter of 300 μm in the temporal and spatial focus of the device while maintaining the good beam collimation required for time resolved electron diffraction experiments. The simplicity of the compressor provides a strong incentive for its further development toward practical implementation in sub-relativistic UED experiments requiring the highest possible source brightness.

A water-immersible 2-axis scanning mirror microsystem for ultrasound andha photoacoustic microscopic imaging applications.

Fast scanning is highly desired for both ultrasound and photoacoustic microscopic imaging, whereas the liquid environment required for acoustic propagation limits the usage of traditional microelectromechanical systems (MEMS) scanning mirrors. Here, a new water-immersible scanning mirror microsystem has been designed, fabricated and tested. To achieve reliable underwater scanning, flexible polymer torsion hinges fabricated by laser micromachining were used to support the reflective silicon mirror plate. Two efficient electromagnetic microactuators consisting of compact RF choke inductors and high-strength neodymium magnet disc were constructed to drive the silicon mirror plate around a fast axis and a slow axis. The performance of this water-immersible scanning mirror microsystem in both air and water were tested using the laser tracing method. For the fast axis, the resonance frequency reached 224 Hz in air and 164 Hz in water, respectively. The scanning angles in both air and water under ±16 V DC driving were ±12°. The scanning angles in air and water under ±10 V AC driving (at the resonance frequencies) were ±13.6° and ±10°. For the slow axis, the resonance frequency reached 55 Hz in air and 38 Hz in water, respectively. The scanning angles in both air and water under ±10 V DC driving were ±6.5°. The scanning angles in air and water under ±10 V AC driving (at the resonance frequencies) were ±8.5° and ±6°. The feasibility of using such a water-immersible scanning mirror microsystem for scanning ultrasound microscopic imaging has been demonstrated with a 25-MHz ultrasound pulse/echo system and a target consisting of three optical fibers.

Acoustic Wave Filter Based on Periodically Poled Lithium Niobate

Solutions for the development of compact RF passive transducers as an alternative to standard surface or bulk acoustic wave devices are receiving increasing interest. This article presents results on the development of an acoustic band-pass filter based on periodically poled ferroelectric domains in lithium niobate. The fabrication of periodically poled transducers (PPTs) operating in the range of 20 to 650 MHz has been achieved on 3-in (76.2-mm) 500-μm-thick wafers. This kind of transducer is able to excite elliptical as well as longitudinal modes, yielding phase velocities of about 3800 and 6500 ms(-1), respectively. A new type of acoustic band-pass filter is proposed, based on the use of PPTs instead of the SAWs excited by classical interdigital transducers. The design and the fabrication of such a filter are presented, as well as experimental measurements of its electrical response and transfer function. The feasibility of such a PPT-based filter is thereby demonstrated and the limitations of this method are discussed.

Compact RF non-linear electro thermal model of SiGe HBT for the design of broadband ADC's

The design of high speed integrated circuits heavily relies on circuit simulation and requires compact transistor models. This paper presents a non-linear electro-thermal model of SiGe heterojunction-bipolar transistor (HBT). The non-linear model presented in this paper uses a hybrid π topology and it is extracted using IV and S-parameter measurements. The thermal sub-circuit is extracted using low-frequency S-parameter measurements. The model extraction procedure is described in detail. It is applied here to the modeling of npn SiGe HBTs. The proposed non-linear electro-thermal model is expected to be used for the design of high-speed electronic functions such as broadband analog digital converters in which both electrical and thermal aspects are engaged. The main focus and contribution of this paper stands in the fact that the proposed non-linear model covers wideband-frequency range (up to 65 GHz).

Vibration mode observation of piezoelectric disk‐type resonator by high‐frequency laser Doppler vibrometer

AbstractFor future mobile phones based on cognitive radio technology, a compact multiband RF front‐end architecture is strongly required, and an integrated multiband RF filter bank is a key component in it. Contour‐mode resonators are receiving increased attention for a multiband filter solution, because their resonance frequency is mainly determined by their size and shape, which are defined by lithography. However, spurious responses, including flexural vibration, are also excited due to the thin structure of the devices. To improve resonator performance and suppress spurious modes, visual observation with a laser probe system is very effective. In this paper, we prototyped a mechanically coupled disk‐array filter, which consists of a silicon disk and two disk‐type resonators of higher‐order wineglass mode, and observed its vibration modes using a high‐frequency laser Doppler vibrometer (UHF‐120, Polytec, Inc.). It was confirmed that the higher‐order wineglass mode vibration included a compound displacement, and that its out‐of‐plane vibration amplitude was much smaller than that of other flexural spurious modes. The observed vibration modes were compared with FEM (Finite Element Method) simulation results. In addition, it was also confirmed that fabrication error (e.g., misalignment) induced asymmetric vibration. © 2012 Wiley Periodicals, Inc. Electron Comm Jpn, 95(5): 33–41, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.10406

A compact dual-band RF front-end and board design for vehicular platforms

Modern vehicular platforms include several wireless systems that provide navigation, entertainment and road side assistance, among other services. These systems operate at different frequency bands and thus careful system-level design should be followed to minimise the interference between them. In this study, we present a compact dual-band RF front-end module for global positioning system (GPS) operating in the L1-band (1574.42–1576.42 MHz) and satellite digital audio radio system (SDARS) operating in the S-band (2320–2345 MHz). The module provides more than 26 dB of measured gain in both bands and low noise figure values of 0.9 and 1.2 dB in SDARS and GPS bands, respectively. The front-end has interference suppression capability from the advanced mobile phone system and personal communication service cellular bands. The module is designed on a low-cost FR-4 substrate material and occupies a small size of 62 × 29 × 1.3 mm3. It dissipates 235 mW in the SDARS section and 100 mW in the GPS section. Three prototypes have been built to verify a repeatable performance.

Efficiency Enhancement of Pico-cell Base Station Power Amplifier MMIC in GaN HFET Technology Using the Doherty Technique

1 Abstract With the growth of smart-phones, the demand for more broadband, data-centric technologies are being driven higher. As mobile operators worldwide plan and deploy 4 generation (4G) networks such as LTE to support the relentless growth in mobile data demand, the need for strategically positioned pico-sized cellular base stations known as ‘pico-cells’ are gaining traction. In addition to having to design a transceiver in a much compact footprint, pico-cells must still face the technical challenges presented by the new 4G systems, such as reduced power consumptions and linear amplification of the signals. The RF power amplifier (PA) that amplifies the output signals of 4G pico-cell systems face challenges to minimize size, achieve high average efficiencies and broader bandwidths while maintaining linearity and operating at higher frequencies. 4G standards as LTE use nonconstant envelope modulation techniques with high peak to average ratios. Power amplifiers implemented in such applications are forced to operate at a backed off region from saturation. Therefore, in order to reduce power consumption, a design of a high efficiency PA that can maintain the efficiency for a wider range of radio frequency signals is required. The primary focus of this thesis is to enhance the efficiency of a compact RF amplifier suitable for a 4G pico-cell base station. For this aim, an integrated two way Doherty amplifier design in a compact 10x11.5mm monolithic microwave integrated circuit using GaN device technology is presented. Using non-linear GaN HFETs models, the design achieves high efficiencies of over 50% at both back-off and peak power regions without compromising on the stringent linearity requirements of 4G LTE standards. This demonstrates a 17% increase in power added efficiency at 6 dB back off from peak power compared to conventional Class AB amplifier performance. Performance optimization techniques to select between high efficiency and high linearity operation are also presented. Overall, this thesis demonstrates the feasibility of an integrated HFET Doherty amplifier for LTE band 7 which entails the frequencies from 2.62-2.69GHz. The realization of the layout and various issues related to the PA design is discussed and attempted to be solved.

Fully reconfigurable compact RF photonic filters using high-Q silicon microdisk resonators

We present a fully reconfigurable fourth-order RF photonic filter on SOI platform with a tunable 3-dB bandwidth of 0.9-5 GHz, more than 38 dB optical out-of-band rejection, FSR up to 650 GHz, and compact size (total area 0.25 mm(2)). The center wavelength of the filter can be tuned over a wide range with a power consumption of 10 mW/nm. The filter architecture uses a unit-cell based approach to realize the desired filter specifications. The use of high-Q resonator-based components enables a dramatic reduction in size, weight and power (SWaP) of each unit cell, with the possibility of cascading a large number of these unit cells on a single chip. Thermal reconfiguration allows for low insertion loss and therefore results in the scalability of these filters. The demonstrated filter can be used in many different applications including RF photonic front-ends and high speed optical A/D conversion.

Highly integrated antennas and front-ends for 60 GHz WLAN applications

This paper provides an overview of the research carried on in the EASY-A project concerning the design of antennas for different applications in the unlicensed band around 60 GHz, and their integration into compact RF front-ends. Different antenna configurations, in conventional microwave substrate and low-temperature co-fired ceramics (LTCC), were studied and fabricated. The results comply with the requirements established for various scenarios.

Vibration Mode Observation of Piezoelectric Disk-type Resonator by High Frequency Laser Doppler Vibrometer

For future mobile phones based on cognitive radio technology, a compact multi-band RF front-end architecture is strongly required and an integrated multi-band RF filter bank is a key component in it. Contour-mode resonators are receiving increased attention for a multi-band filter solution, because its resonant frequency is mainly determined by its size and shape, which are defined by lithography. However, spurious responses including flexural vibration are also excited due to its thin structure. To improve resonator performance and suppress spurious modes, visual observation with a laser probe system is very effective. In this paper, we have prototyped a mechanically-coupled disk-array filter, which consists of a Si disk and 2 disk-type resonators of higher-order wine-glass mode, and observed its vibration modes using a high-frequency laser-Doppler vibrometer (UHF-120, Polytec, Inc.). As a result, it was confirmed that higher order wine-glass mode vibration included a compound displacement, and that its out-of-plane vibration amplitude was much smaller than other flexural spurious modes. The observed vibration modes were compared with FEM (Finite Element Method) simulation results. In addition, it was also confirmed that the fabrication error, e.g. miss-alignment, induced asymmetric vibration.

3 - 10 GHz Ultra-Wideband Low-Noise Amplifier Using Inductive-Series Peaking Technique with Cascode Common-Source Circuit

The objective of this paper is to investigate a ultra-wideband (UWB) low noise amplifier (LNA) by utilizing a two-stage cascade circuit schematic associated with inductive-series peaking technique, which can improve the bandwidth in the 3-10 GHz microwave monolithic integrated circuit (MMIC). The proposed UWB LNA amplifier was implemented with both co-planer waveguide (CPW) layout and 0.15-μm GaAs D-mode pHEMT technology. Based on those technologies, this proposed UWB LNA with a chip size of 1.5 mm x 1.4 mm, obtained a flatness gain 3-dB bandwidth of 4 - 8 GHz, the constant gain of 4 dB, noise figure lower than 5 dB, and the return loss better than –8.5 dB. Based on our experimental results, the low noise amplifier using the inductive-series peaking technique can obtain a wider bandwidth, low power consumption and high flatness of gain in the 3 - 10 GHz. Finally, the overall LNA characterization exhibits ultra-wide bandwidth and low noise characterization, which illustrates that the proposed UWB LNA has a compact size and favorable RF characteristics. This UWB LNA circuit demonstrated the high RF characterization and could provide for the low noise micro-wave circuit applications.

기생 성분을 고려한 Wi-Fi와 WiMAX용 LTCC 무선 전단부 모듈의 구현

In this paper, a compact RF Front-end module for Wireless Fidelity(Wi-Fi) and Worldwide Interoperability for Microwave Access(WiMAX) applications is realized by low temperature co-fired ceramic(LTCC) technology. The RF Front-end module is composed of three LTCC band-pass filters, a Film Bulk Acoustic Resonator(FBAR) filter, fully embedded matching circuits, an SPDT switch for mode selection, an SPDT switch for Tx/Rx selection, and an SP4T switch for band selection. The parasitic elements of 0.2~0.3 pF are generated by the structure of stacking in the top pad pattern for DC block capacitor of SPDT switch for mode selection. These kinds of parasitic elements break the matching characteristic, and thus, the overall electrical performance of the module is degraded. In order to compensate it, we insert a parallel lumped-element inductor on capacitor pad pattern for DC block, so that we obtain the optimized performance of the RF Front-end module. The fabricated RF front-end module has 12 layers including three inner grounds and it occupies less than .

First Experimental Results from the European Union 2-MW Coaxial Cavity ITER Gyrotron Prototype

The European Union is working toward providing 2-MW, coaxial-cavity, continuous-wave (cw) 170-GHz gyrotrons for ITER. Their design is based on results from an experimental preprototype tube having a pulse length of several milliseconds, in operation at Forschungszentrum Karlsruhe (FZK) for several years now. The first industrial prototype tube was designed for cw operation but, in a first phase, aimed at a pulse length of 1 s at the European Gyrotron Test Facility in Lausanne, Switzerland, as part of a phased testing/development program (1 s, 60 s, cw). The first experimental results of the operation of this prototype gyrotron are reported here. The microwave generation was characterized at very short pulse length (<0.01 s) using a load on loan from FZK, and the highest measured output power was 1.4 MW, at a beam energy significantly lower than the design value (83 kV instead of 90 kV), limited by arcing in the tube. The radio-frequency (rf) beam profile was measured to allow reconstruction of the phase and amplitude profile at the window and to provide the necessary information permitting proper alignment of the compact rf loads prior to pulse extension. Arcs in the tube limited the pulse length extension to a few tens of milliseconds. According to present planning, the tube is going to be opened, inspected, and refurbished, depending on the results of the inspection, to allow testing of an improved version of the mode launcher and replacement of some subassemblies.

Compact RF Model for Transient Characteristics of MEMS Capacitive Switches

A compact model is proposed to facilitate the design and simulation of the control waveform of RF microelectromechanical systems (MEMS) capacitive switches with electrostatically actuated membranes. Following conventional approaches, the pull-in motion of a membrane is simulated by an L-R-C network. However, the present model deviates from conventional approaches by adding another capacitor and a diode to simulate the gradual contact of the membrane with the stationary electrode. After contact, variable mass, spring constant, and damping factor are used to simulate the release process of the membrane. By smoothly bridging the model between pull-in, contact, and release processes, the model can efficiently simulate static and transient S-parameters of the switches up to 50 GHz. The model can be readily installed in popular computer-aided circuit design environments to analyze in the time domain the behavior of the switches and the operation of MEMS-based circuits.

Dual-beam actuation of piezoelectric AlN RF MEMS switches monolithically integrated with AlN contour-mode resonators

This work reports on piezoelectric aluminum nitride (AlN) based dual-beam RF MEMS switches that have been monolithically integrated with AlN contour-mode resonators. The dual-beam switch design presented in this paper intrinsically compensates for the residual stress in the deposited films, requires a low actuation voltage (5 to 20 V) and facilitates active pull-off to open the switch and exhibits fast switching times (1 to 2 µs). This work also presents the combined response (cascaded S parameters) of a resonator and a switch that were co-fabricated on the same substrate. The response shows that the resonator can be effectively turned on and off by the switch. A post-CMOS compatible process was used for the co-fabrication of both the switches and the resonators. The single-chip RF solution presented constitutes an unprecedented step forward towards the realization of compact, low-loss and integrated multi-frequency RF front-ends.

A Compact RF CMOS Modeling for Accurate High-Frequency Noise Simulation in Sub-100-nm MOSFETs

A compact RF CMOS model incorporating an improved thermal noise model is developed. Short-channel effects (SCEs), substrate potential fluctuation effect, and parasitic-resistance-induced excess noises were implemented in analytical formulas to accurately simulate RF noises in sub-100-nm MOSFETs. The intrinsic noise extracted through a previously developed lossy substrate de-embedding method and calculated by the improved noise model can consistently predict gate length scaling effects. For 65- and 80-nm n-channel MOS with f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> above 160 and 100 GHz, NF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> at 10 GHz can be suppressed to 0.5 and 0.7 dB, respectively. Drain current noise S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">id</sub> reveals an apparently larger value for 65-nm devices than that for 80-nm devices due to SCE. On the other hand, the shorter channel helps reduce the gate current noise S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ig</sub> attributed to smaller gate capacitances. Gate resistance R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> -induced excess noise dominates in S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ig</sub> near one order higher than the intrinsic gate noise that is free from R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> for 65-nm devices. The compact RF CMOS modeling can facilitate high-frequency noise simulation accuracy in nanoscale RF CMOS circuits for low-noise design.

Integration of RF MEMS and CMOS IC on a Printed Circuit Board for a Compact RF System Application Based on Wafer Transfer

In this paper, a novel platform technology for integrating radio-frequency microelectromechanical systems (RF-MEMS) and CMOS on a printed circuit board (PCB) is demonstrated. An RF-MEMS switch is constructed on top of a CMOS IC wafer. The stacked structure is subsequently transferred onto a PCB substrate (i.e., FR-4) by thermal compressive bonding, mechanical grinding, and wet removal of bulk silicon. The measurement of the fabricated RF-MEMS switch on the FR-4 substrate shows promising results. It has an insertion loss of 0.25 dB at 20 GHz and an isolation of 25 dB at 20 GHz. At the same time, the performance of CMOS is not degraded during the integration process; the drain current in the p-MOS transistor remained unchanged, whereas that in the n-MOS transistor showed a slight improvement after transfer. This technology is very useful for compact RF system on PCB material with low power consumption and high performance for wearable, wireless, and implantable device applications.

SD-MAC: Design and Synthesis of a Hardware-Efficient Collision-Free QoS-Aware MAC Protocol for Wireless Network-on-Chip

To bridge the widening gap between computation requirements and communication efficiency faced by gigascale heterogeneous SoCs in the upcoming ubiquitous era, a new on-chip communication system, dubbed Wireless Network-on-Chip (WNoC), is introduced by using the recently developed CMOS UWB wireless interconnection technology. In this paper, a synchronous and distributed medium access control (SD-MAC) protocol is designed and implemented. Tailored for WNoC, SD-MAC employs a binary countdown approach to resolve channel contention between RF nodes. The receiver_select_sender mechanism and hidden terminal elimination scheme are proposed to increase the throughput and channel utilization of the system. Our simulation study shows the promising performance of SD-MAC in terms of throughput, latency, and network utilization. We further propose a QoS-aware SD-MAC to ensure the serviceability of the entire system and to improve the bandwidth utilization. As a major component of simple and compact RF node design, a MAC unit implements the proposed SD-MAC that guarantees correct operation of synchronized frames while keeping overhead low. The synthesis results demonstrate several attractive features such as high speed, low power consumption, nice scalability and low area cost.

Investigation of rf power absorption in the plasma of helicon ion source

The simulations of the spatial distribution of rf power absorbed in a helicon ion source reveal a correlation between the depth of penetration of rf power into the plasma and the tilt angle of lines of force of the outer magnetic field. The deeper field penetration and greater power absorption were observed at large tilt angles of the field line to the plasma surface. The evaluations as to the possibility of excitation of helicon waves in compact rf ion sources were performed.