Microelectromechanical Systems Phase Shifter Research Articles

Fully reconfigurable MEMS-based second-order coupled-resonator optical waveguide (CROW) with ultra-low tuning energy.

Integrated microring resonators are well suited for wavelength-filtering applications in optical signal processing, and cascaded microring resonators allow flexible filter design in coupled-resonator optical waveguide (CROW) configurations. However, the implementation of high-order cascaded microring resonators with high extinction ratios (ERs) remains challenging owing to stringent fabrication requirements and the need for precise resonator tunability. We present a fully integrated on-chip second-order CROW filter using silicon photonic microelectromechanical systems (MEMS) to adjust tunable directional couplers and a phase shifter using nanoscale mechanical out-of-plane waveguide displacement. The filter can be fully reconfigured with regard to both the ER and center wavelength. We experimentally demonstrated an ER exceeding 25 dB and continuous wavelength tuning across the full free spectral range of 0.123 nm for single microring resonator, and showed reconfigurability in second-order CROW by tuning the ER and resonant wavelength. The tuning energy for an individual silicon photonic MEMS phase shifter or tunable coupler is less than 22 pJ with sub-microwatt static power consumption, which is far better than conventional integrated phase shifters based on other physical modulation mechanisms.

Wafer-level hermetically sealed silicon photonic MEMS

The emerging fields of silicon (Si) photonic micro–electromechanical systems (MEMS) and optomechanics enable a wide range of novel high-performance photonic devices with ultra-low power consumption, such as integrated optical MEMS phase shifters, tunable couplers, switches, and optomechanical resonators. In contrast to conventional SiO 2 -clad Si photonics, photonic MEMS and optomechanics have suspended and movable parts that need to be protected from environmental influence and contamination during operation. Wafer-level hermetic sealing can be a cost-efficient solution, but Si photonic MEMS that are hermetically sealed inside cavities with optical and electrical feedthroughs have not been demonstrated to date, to our knowledge. Here, we demonstrate wafer-level vacuum sealing of Si photonic MEMS inside cavities with ultra-thin caps featuring optical and electrical feedthroughs that connect the photonic MEMS on the inside to optical grating couplers and electrical bond pads on the outside. We used Si photonic MEMS devices built on foundry wafers from the iSiPP50G Si photonics platform of IMEC, Belgium. Vacuum confinement inside the sealed cavities was confirmed by an observed increase of the cutoff frequency of the electro-mechanical response of the encapsulated photonic MEMS phase shifters, due to reduction of air damping. The sealing caps are extremely thin, have a small footprint, and are compatible with subsequent flip-chip bonding onto interposers or printed circuit boards. Thus, our approach for sealing of integrated Si photonic MEMS clears a significant hurdle for their application in high-performance Si photonic circuits.

Silicon photonic microelectromechanical phase shifters for scalable programmable photonics.

Programmable photonic integrated circuits are emerging as an attractive platform for applications such as quantum information processing and artificial neural networks. However, current programmable circuits are limited in scalability by the lack of low-power and low-loss phase shifters in commercial foundries. Here, we demonstrate a compact phase shifter with low-power photonic microelectromechanical system (MEMS) actuation on a silicon photonics foundry platform (IMEC's iSiPP50G). The device attains (2.9π±π) phase shift at 1550 nm, with an insertion loss of (0.33-0.10+0.15)dB, a Vπ of (10.7-1.4+2.2)V, and an Lπ of (17.2-4.3+8.8)µm. We also measured an actuation bandwidth f-3dB of 1.03 MHz in air. We believe that our demonstration of a low-loss and low-power photonic MEMS phase shifter implemented in silicon photonics foundry compatible technology lifts a main roadblock toward the scale-up of programmable photonic integrated circuits.

Ku to V-band 4-bit MEMS phase shifter bank using high isolation SP4T switches and DMTL structures

This work presents a micro-electro-mechanical system (MEMS) based on a wide-band 4-bit phase shifter using two back-to-back single-pole-four-throw (SP4T) switches and four different distributed MEMS transmission line (DMTL) structures that are implemented on 635 µm alumina substrate using surface micromachining process. An SP4T switch is designed with a series-shunt configuration and it demonstrates an average return loss of >17 dB, an insertion loss of <1.97 dB and maximum isolation of >28 dB up to 60 GHz. A maximum area of the SP4T switch is ~0.76 mm2. Single-pole-single-throw and SP4T switches are capable of handling 1 W of radio frequency (RF) power up to >100 million cycles at 25° C; they can even sustained up to >70 million cycles with 1 W at 85 °C. The proposed wide-band phase shifter works at 17 GHz (Ku-band), 25 GHz (K-band), 35 GHz (Ka-band) and 60 GHz (V-band) frequencies. Finally,a 4-bit phase shifter demonstrates an average insertion loss of <6 dB, return loss of >10 dB and maximum phase error of ~3.8° at 60 GHz frequency over 500 MHz bandwidth. Total area of the fabricated device is ~11 mm2. In addition, the proposed device works well up to >107 cycles with 1 W of RF power. To the best of the author’s knowledge, this is the best reported wide-band MEMS 4-bit phase shifter in the literature that works with a constant resolution.

Submillimeter-Wave 3.3-bit RF MEMS Phase Shifter Integrated in Micromachined Waveguide

This paper presents a submillimeter-wave 500–550-GHz MEMS-reconfigurable phase shifter, which is based on loading a micromachined rectangular waveguide with 9 E-plane stubs. The phase shifter uses MEMS-reconfigurable surfaces to individually block/unblock the E-plane stubs from the micromachined waveguide. Each MEMS-reconfigurable surface is designed so that in the nonblocking state, it allows the electromagnetic wave to pass freely through it into the stub, while in the blocking state, it serves as the roof of the main waveguide and blocks the wave propagation into the stub. The phase-shifter design comprises three micromachined chips that are mounted in the H-plane cuts of the rectangular waveguide. Experimental results of the first device prototypes show that the microelectromechanical system (MEMS)-reconfigurable phase shifter has a linear phase shift of 20 $\mathbf {^{\circ }}$ in ten discrete steps (3.3 bits). The measured insertion loss is better than 3 dB, of which only 0.5–1.5 dB is attributed to the MEMS surfaces and switched stubs, and the measured return loss is better than 15 dB in the design frequency band of 500–550 GHz. It is also shown that the major part of the insertion loss is attributed to misalignment and assembly uncertainties of the micromachined chips and the waveguide flanges, shown by simulations and reproducibility measurements. The MEMS-reconfigurable phase shifter is also operated in an analog tuning mode for high phase resolution. Furthermore, a detailed study has been carried out identifying the reason for the discrepancy between the simulated (90 $\mathbf {^{\circ }}$ ) and the measured (20 $\mathbf {^{\circ }}$ ) phase shift. Comb-drive actuators with spring constant variations between 2.13 and 8.71 N/m are used in the phase shifter design. An actuation voltage of 21.94 V with a reproducibility better than $\mathbf {\sigma }=$ 0.0503 V is measured for the actuator design with a spring constant of 2.13 N/m. Reliability measurement on this actuator was performed in an uncontrolled laboratory environment and showed no deterioration in the functioning of the actuator observed over one hundred million cycles.

Reliability Analysis of Ku-Band 5-bit Phase Shifters Using MEMS SP4T and SPDT Switches

This work presents a Ku-band microelectromechanical systems (MEMS) based 5-bit phase shifter using dc contact single-pole-four-throw (SP4T) and single-pole-double-throw switches. The design is implemented using a coplanar waveguide transmission line. Two individual 2-bit phase shifters and one 1-bit phase shifter are cascaded to develop the complete 5-bit phase shifter. The phase shifters are fabricated on 635- $\mu{\hbox{m}}$ alumina substrate using a surface micromachining process. The 5-bit phase shifter demonstrates an average insertion loss of 2.65 dB in the 13–18-GHz band with a return loss better than 22 dB and average phase error less than 0.68 $^{\circ}$ at 17 GHz. Total area of the fabricated 5-bit phase shifter is ${\hbox{4.7}}\times {\hbox{2.8}} {\hbox{mm}}^{2}$ . The reliability of the single-pole-single-throw and SP4T switches show more than 10 million cycles with an RF power of 0.1–2 W. Furthermore, reliability of the MEMS phase shifter is extensively investigated and presented with cold and hot switched conditions. To the best of our knowledge, this is the first reported MEMS 5-bit phase shifter in the literature that has undergone different reliability and qualification testing including 3-axis vibrations.

SiGe process integrated full‐360° microelectromechanical systems‐based active phase shifter for W‐band automotive radar

This study presents the implementation of a microelectromechanical systems (MEMS)-based active phase shifter (APS) by using vector sum method. The proposed phase shifter comprises of two variable gain amplifiers (VGAs), a Wilkinson power divider with 90 phase shift lines, a Wilkinson power combiner and two 1-bit (0 degrees/180 degrees) MEMS phase shifters. First, all the components were designed and fabricated individually to check for their proper functionality, then they were brought together in a novel vector sum topology to work as a full-360 degrees span phase shifter. Fabricated VGAs function properly at designed frequency (77 GHz) with gain variation from 0 to 14 dB with the tuned base voltages from 1.8 to 2.3 V. The VGAs not only serve for providing the weighted amplitudes but also compensate 4.3 dB loss from 1-bit MEMS phase shifter and 0.8 dB loss from each power divider and combiner. Active/passive components and MEMS switches are all integrated at one single chip of 3.74 mm(2) and manufactured with IHP 0.25 mu m SiGe BiCMOS technology. As to the author's knowledge, this is the first demonstration of an APS using integrated active components and MEMS technology. Presented phase shifting mechanism can be used at automotive radar system for beam steering purpose.

RF MEMS Switch and Its Applications

RF MEMS (Radio Frequency Microelectromechanical System) has seen an amazing growth in the past 20 years. It has immense commercial and defense potential due to its low loss, low power consumption and superior RF performances. In this article, RF MEMS and its applications are reviewed. Special emphasis is on the RF MEMS switches and MEMS phase shifters investigated in IMETU (Institute of Microelectronics of Tsinghua University). A variety of RF MEMS switches with different configurations are introduced. The MEMS switch present unique properties for the application in future miniaturized antenna and radar system. The prototype illustrates the RF MEMS switch as a fundamental structure in signal path control, structural optimization, and match circuits is very promising to be used in future reconfigurable radar and antenna system, which will address to the application not only in the mobile terminal but also the high end wireless sensor network.

High Resolution Tunable MEMS Phase Shifters for Radar Phased Array Antenna

The paper proposes a high resolution tunable MicroElectroMechanical Systems (MEMS) phase shifters for radar phased array antenna to steer the beam. Two phase shifters are considered the first is a switched line phase shifter; the second is a reflection type phase shifter. The resolution of the designed phase shifters is two degree phase shift using 8 bit control circuitry. The proposed circuit is based on dividing the tuning range into coarse and fine tuning sections which change the phase by 30o and 2o steps respectively to achieve the desired phase. A microstrip phase shifters have been designed at 3 GHz suitable for surveillance radar applications. The development of RF MEMS switches over the past years has enabled system designers to consider replacing the GaAs phase shifters with RF MEMS phase shifters. MEMS phase shifter exhibit excellent characteristics, including low insertion loss and low DC power consumption. The designed phase shifters are simulated and tested using Advance Design System circuit simulation package (ADS) and the results demonstratedusing the graphics capability of Matlab Program. The results show that the worst case insertion loss is less than 0.17 dB and 0.05 dB for switched line and reflection type phase shifters respectively. The return loss for the two proposed phase shifters is less than -60 dB.

A Monolithic Phased Array Using 3-bit Distributed RF MEMS Phase Shifters

This paper presents a novel electronically scanning phased-array antenna with 128 switches monolithically implemented using RF microelectromechanical systems (MEMS) technology. The structure, which is designed at 15 GHz, consists of four linearly placed microstrip patch antennas, 3-bit distributed RF MEMS low-loss phase shifters, and a corporate feed network. MEMS switches and high- <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> metal-air-metal capacitors are employed as loading elements in the phase shifter. The system is fabricated monolithically using an in-house surface micromachining process on a glass substrate and occupies an area of 6 cm times 5 cm. The measurement results show that the phase shifter can provide nearly 20deg/50deg/95deg phase shifts and their combinations at the expense of 1.5-dB average insertion loss at 15 GHz for eight combinations. It is also shown by measurements that the main beam can be steered to required directions by suitable settings of the RF MEMS phase shifters.

An Adaptive Beamforming Method for Phased Array Antenna with MEMS Phase Shifters

Adaptive array antennas, which control their own patterns by means of feed-back or feed-forward control, are effective tools for gain enhancement and interference suppression. However, when applying them to mobile terminals, the problems of hardware complexity and power consumption need to be taken into consideration. One solution is the use of analog device-based adaptive array antennas, such as Reactively Steered Adaptive Array (RESAA) antennas and phased array antennas, which have the attractive characteristics of low cost and power consumption. In this paper, we propose an adaptive beamforming method based on a one-dimension search algorithm for phased array antennas with Micro Electro Mechanical Systems (MEMS) phase shifters, taking into consideration their slow operating speed due to mechanical structure of the devices. Furthermore, a smoothing processing is introduced to prevent the effect of noise and a multi-resolution alogrithm is proposed to help the system form beams more quickly and stably. Numerical results based on the IEEE 802.11 a Wireless Local Area Network (WLAN) standard show that the proposed method has good interference suppression and gain enhancement capabilities in multipath fading channels.

Organic "Wafer-Scale" packaged miniature 4-bit RF MEMS phase shifter

This paper presents for the first time a 4-bit microelectromechanical systems (MEMS) phase shifter fabricated on, integrated, and packaged into an organic flexible low-permittivity material. A microstrip switched-line phase shifter has been optimized at 14 GHz for small size and excellent performance. In addition, the MEMS phase shifter was packaged in an all-organic flexible low-permittivity liquid-crystal polymer (LCP) package. The improved geometry of the reduced size phase shifter is 2.8 times smaller than a traditional switched-line phase shifter and is much less lossy. For the 4-bit phase shifter, the worst case return loss is greater than 19.7 dB and the average insertion loss is less than 0.96 dB (0.24 dB/bit or 280/spl deg//dB). The average phase error is only 3.96/spl deg/. It has been demonstrated that the addition of the LCP package has a negligible effect on the phase-shifter performance, but will enable the device to remain flexible and protected against various environmental conditions.

MEMS 2-Bit Phase-Shifter Failure Mode and Reliability Considerations for Large&amp;gt;tex&amp;lt;$X$&amp;gt;/tex&amp;lt;-Band Arrays

RF microelectromechanical systems (MEMS) switch technology used in the fabrication of phase-shifter circuits is examined from the perspective of failure mode and reliability implications on the performance of large X-band array antennas. Amplitude and phase-state failure probability density functions (pdfs) conditioned on switch probability of failure are formulated for both the hybrid-T (switched line) and coupled-line phase-shifter circuit topologies. The pdfs are used to assess the phase-shifter failure impact on overall array level performance in terms of gain loss and the increase in RMS sidelobe level. Reliability and lifetime implications are addressed through considering a probability of switch failure that increases with cycling. The phase-shifter lifetime switching considerations are related to radar system lifetime beam switching requirements consistent with plausible radar system applications. The key findings are that RF MEMS switch mean time to failure /spl sim/125000 h or longer, consistent with /spl sim/100-125 phase-shifter state switches per second (/spl sim/10/sup 11/ switch operations), are reasonable expectations for RF MEMS phase-shifter technology to meet in order to be considered viable for a broad range of array antenna applications.

Low-loss 2- and 4-bit TTD MEMS phase shifters based on SP4T switches

2- and 4-bit microelectromechanical system (MEMS) X- to K/sub u/-band true-time-delay phase shifters with a very low insertion loss are described. The phase shifters are fabricated on 200-/spl mu/m GaAs substrates and the low loss is achieved using MEMS SP4T switches, which reduce the number of switches in the signal path by half when compared to conventional designs with SP2T switches. Measurements indicate an insertion loss of -0.6/spl plusmn/0.3 and -1.2/spl plusmn/0.5 dB at 10 GHz for the 2- and 4-bit designs, respectively. The measured losses agreed very well with Momentum simulations and are the lowest reported to date. The 2-bit phase shifter performed well from dc-18 GHz, with -0.8/spl plusmn/0.3-dB insertion loss at 18 GHz and a return loss of <-10.5 dB over dc-18 GHz.

A 2-bit RF MEMS phase shifter in a thick-film BGA ceramic package

The development of a thick-film hermetic BGA package for a radio-frequency (RF) microelectromechanical systems (MEMS) 2-bit phase shifter is presented. The measured packaged MEMS phase shifter average in-band insertion loss was 1.14 dB with an average return loss of 15.9 dB. The package transition insertion loss was less than 0.1 dB per transition with excellent agreement between simulated and measured results. It was also demonstrated that the RF MEMS phase shift performance could be improved to obtain a phase error of less than 3.3 degrees. The first reported measurements of the average rise and fall times associated with a MEMS circuit (in this case a 2-bit phase shifter) were 26 and 70 /spl mu/s, respectively. The advent of packaged RF MEMS phase shifters will reduce the cost (both design and building) of future phase arrays.

A compact V-band 2-bit reflection-type MEMS phase shifter

Air-gap overlay CPW couplers and low-loss series metal-to-metal contact microelectromechanical system (MEMS) switches have been employed to reduce the loss of reflection-type MEMS phase shifters at V-band. Phase shift is obtained by changing the lengths of the open-ended stubs using series MEMS switches. A 2-bit [135] reflection-type MEMS phase shifter showed an average insertion loss of 4 dB with return loss better than 11.7 dB from 50 to 70 GHz. The chip is very compact with a chip size as small as 1.5 mm /spl times/ 2.1 mm.

Distributed MEMS phase shifters bymicrostereolithography on silicon substrates for microwave andmillimeter wave applications

A distributed microelectromechanical system (MEMS)phase shifter has been fabricated on a high-resistivity siliconsubstrate using a microstereolithography technique. Thistechnique enables us to decrease the early development cost byremoving the need for photomasks used for defining the MEMSbridges. The distributed MEMS phase shifter fabricated consistsof a high-impedance coplanar waveguide transmission lineand ten MEMS bridges of 4.5 µm height, which givesa phase shift of 6° at 18 GHz with a bias voltage of30 V. This MEMS bridge design can be improved further using themicrostereolithography technique to give a phase shift of nearly90° at 18 GHz with a bias voltage of 20 V. Thefabrication procedure described here shows significant promisefor the use of microstereolithography techniques for RF MEMSdevices for ground and space telecommunication applications.

Low-loss distributed MEMS phase shifter

This letter presents a one-bit low-loss K/K/sub a/-band phase shifter circuit that employs microelectromechanical systems (MEMS) capacitors. The measured results demonstrate a delay line with a 180/spl deg/ phase shift/1.l7 dB loss phase shift at 25 GHz, 270/spl deg/ phase shift/1.69 dB loss at 35 GHz, and a return loss better than 11 dB over a 0-35-GHz band. The state-of-the-art insertion loss performance, 154/spl deg//dB at 25 GHz and 160/spl deg//dB at 35 GHz, demonstrates the potential for the implementation of a very low-loss multibit digital MEMS phase shifter.

K-band 3-bit low-loss distributed MEMS phase shifter

In this work, we present a 3-bit K-band distributed phase shifter circuit that employs microelectromechanical systems (MEMS) capacitive switches. The measured results demonstrate an average 1.7 dB insertion loss at 26 GHz with return loss better than -7 dB. Insertion phase shifts of all switching states are measured and show phase error less than 8.50 for all states. The low loss K-band 3-bit phase shifter demonstrated here can potentially be extended to more-bit-controlled phase shifter applications.

Distributed MEMS true-time delay phase shifters and wide-band switches

Wide-band switches and true-time delay (TTD) phase shifters have been developed using distributed microelectromechanical system (MEMS) transmission lines for applications in phased-array and communication systems. The design consists of a coplanar waveguide (CPW) transmission line (W=G=100 /spl mu/m) fabricated on a 500 /spl mu/m quartz substrate with fixed-fixed beam MEMS bridge capacitors placed periodically over the transmission line, thus creating a slow-wave structure. A single analog control voltage applied to the center conductor of the CPW line can vary the phase velocity of the loaded line by pulling down on the MEMS bridges to increase the distributed capacitive loading. The resulting change in the phase velocity yields a TTD phase shift. Alternatively, the control voltage can be increased beyond the pull-down voltage of the MEMS bridges such that the capacitive loading greatly increases and shorts the line to ground. The measured results demonstrate 0-60 GHz TTD phase shifters with 2 dB loss/118/spl deg/ phase shift at 60 GHz (/spl sim/4.5-ps TTD) and 1.8 dB loss/84/spl deg/ phase shift at 40 GHz. Also, switches have been demonstrated with an isolation of better than 40 dB from 21 to 40 and 40 to 60 GHz. In addition, a transmission-line model has been developed, which results in very close agreement with the measured data for both the phase shifters and switches. The pull-down voltage is 10-23 V, depending on the residual stress in the MEMS bridge. To our knowledge, this paper presents the first wide-band TTD MEMS phase shifters and wide-band switches to date.