Design, fabrication and RF performances of two different types of piezoelectrically actuated Ohmic MEMS switches
23 Sep 2005-Journal of Micromechanics and Microengineering (IOP Publishing)-Vol. 15, Iss: 11, pp 2098-2104
TL;DR: In this paper, two different types of piezoelectrically actuated RF MEMS switches have been designed to operate at a low operation voltage for advanced mobile/wireless handset applications.
Abstract: In this paper, we have proposed, fabricated and characterized piezoelectrically actuated RF MEMS (radio-frequency micro-electro-mechanical system) switches. They have been designed to operate at a low operation voltage for advanced mobile/wireless handset applications. The proposed switches are largely composed of piezoelectric cantilever actuators with an Au contact electrode and CPW (coplanar wave) transmission lines suspended over the substrate. Two different types of RF MEMS switches have been suggested to find the better geometry. One has the structure of one single piezoelectric cantilever and a contact electrode attached to its edge with three hinges (type-A), and the other contains four piezoelectric cantilevers that are symmetrically combined through each hinge to support a centered contact electrode (type-B). The two different fabricated (type-A and type-B) RF MEMS switches have insertion losses of −0.22 and −0.23 dB at an operation voltage of 2.5 V and a frequency of 2 GHz, respectively. Although the difference in insertion loss is trivial, there exist different dependences of insertion loss on applied voltage between them. The insertion losses of type-A switches are changed with varying operation voltage because the touching area between the contact electrode and the signal transmission lines is variable. Meanwhile, the type-B switches show nearly constant insertion losses regardless of operation voltage. The type-A and type-B switches have isolation values of −40.8 and −42.5 dB at a frequency of 2 GHz, respectively.
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TL;DR: In this article, the authors reported the implementation of ultrathin (100 nm) aluminum nitride (AlN) piezoelectric layers for the fabrication of vertically deflecting nanoactuators.
Abstract: This letter reports the implementation of ultrathin (100 nm) aluminum nitride (AlN) piezoelectric layers for the fabrication of vertically deflecting nanoactuators. The films exhibit an average piezoelectric coefficient (d31∼−1.9 pC/N), which is comparable to its microscale counterpart. This allows vertical deflections as large as 40 nm from 18 μm long and 350 nm thick multilayer cantilever bimorph beams with 2 V actuation. Furthermore, in-plane stress and stress gradients have been simultaneously controlled. The films exhibit leakage currents lower than 2 nA/cm2 at 1 V, and have an average relative dielectric constant of approximately 9.2 (as in thicker films). These material characteristics and actuation results make the AlN nanofilms ideal candidates for the realization of nanoelectromechanical switches for low power logic applications.
152 citations
TL;DR: In this article, a dual-beam switch design is presented that 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).
Abstract: 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.
105 citations
TL;DR: In this paper, a surface micromachined RF microelectromechanical switch that uses piezoelectric actuators is presented, which exhibits better than 20dB isolation from dc up to 65 GHz and as large as 70 dB below 1 GHz.
Abstract: This paper presents results on a surface micromachined RF microelectromechanical switch that uses piezoelectric actuators. The switch uses solution chemistry-derived lead zirconate titanate thin films spun deposited onto a high-resistivity silicon substrate with coplanar waveguide transmission lines. Actuation voltages, applied via circuits independent of the RF circuitry, average less than 10 V, with switch operation demonstrated as low as 2 V. The series switch exhibits better than 20-dB isolation from dc up to 65 GHz and as large as 70 dB below 1 GHz. In the closed state, the switch has an insertion loss less than 1 dB up to 40 GHz, limited in this demonstration by substrate losses from the elastic layer used to stress control the piezoelectric actuators. Switching speeds for the different designs are in the range of 40-60 ms. Thermal sensitivity measurements show no change in isolation observed for temperatures up to 125degC. However, an increase in actuation voltage is required at elevated temperatures.
98 citations
TL;DR: RF microelectromechani-cal/nanoelectromechanical (MEMS/NEMS) devices are attractive to industry as they offer a means by which performance can be greatly improved for wireless applications while at the same time potentially reducing overall size and weight as well as manufacturing costs.
Abstract: Next-generation military and civilian communication systems will require technologies capable of handling data/ audio, and video simultaneously while supporting multiple RF systems operating in several different frequency bands from the MHz to the GHz range [1]. RF microelectromechani-cal/nanoelectromechanical (MEMS/NEMS) devices, such as resonators and switches, are attractive to industry as they offer a means by which performance can be greatly improved for wireless applications while at the same time potentially reducing overall size and weight as well as manufacturing costs.
92 citations
Cites background from "Design, fabrication and RF performa..."
...Piezoelectric actuation of a 150μm long cantilever beam, yielding deflections up to 5 μm, can be achieved with low voltages (≤5 volts) with PZT film thickness of about 500 nm [33]....
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TL;DR: In this paper, the use of thin-film piezoelectric lead zirconate titanate (PZT) is discussed for millimeter-scale robotics.
Abstract: Thin-film piezoelectric lead zirconate titanate (PZT) is one of the most efficient electromechanical coupling transducer materials currently available for microelectromechanical systems (MEMS). This article reviews piezoelectric MEMS (piezo MEMS) technologies using PZT thin films in radio frequency (RF) devices for communications and radar applications and in the emerging field of millimeter-scale robotics. The electromechanical material properties of thin-film PZT uniquely enable insect-inspired and insect-scale autonomous robots. Recent progress on large force and displacement actuators for robotic leg joints, compact and high torque ultrasonic motors, and bioinspired millimeter-scale flapping wing platforms will be presented. The use of thin-film PZT to achieve high performance and low-voltage RF MEMS switches, ultralow power consumption nanomechanical logic circuits, and high coupling and low loss resonators, filters, and transformers are also reviewed.
85 citations
References
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TL;DR: In this paper, a scaling analysis is performed to demonstrate that the effectiveness of actuators is independent of the size of the structure and evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure.
Abstract: This work presents the analytic and experimental development of piezoelectric actuators as elements of intelligent structures, i.e., structures with highly distributed actuators, sensors, and processing networks. Static and dynamic analytic models are derived for segmented piezoelectric actuators that are either bonded to an elastic substructure or embedded in a laminated composite. These models lead to the ability to predict, a priori, the response of the structural member to a command voltage applied to the piezoelectric and give guidance as to the optimal location for actuator placement. A scaling analysis is performed to demonstrate that the effectiveness of piezoelectric actuators is independent of the size of the structure and to evaluate various piezoelectric materials based on their effectiveness in transmitting strain to the substructure. Three test specimens of cantilevered beams were constructed: an aluminum beam with surface-bonded actuators, a glass/epoxy beam with embedded actuators, and a graphite/epoxy beam with embedded actuators. The actuators were used to excite steady-state resonant vibrations in the cantilevered beams. The response of the specimens compared well with those predicted by the analytic models. Static tensile tests performed on glass/epoxy laminates indicated that the embedded actuator reduced the ultimate strength of the laminate by 20%, while not significantly affecting the global elastic modulus of the specimen.
2,719 citations
TL;DR: In this paper, the design and fabrication of a micromechanical capacitive membrane microwave switching device is described, which consists of a thin metallic membrane, which has two states, actuated or unactuated, depending on the applied bias.
Abstract: The design and fabrication of a micromechanical capacitive membrane microwave switching device is described. The switching element consists of a thin metallic membrane, which has two states, actuated or unactuated, depending on the applied bias. A microwave signal is switched on and off when the membrane is switched between the two states. These switches have a switching on speed of less than 6 /spl mu/s and a switching off speed of less than 4 /spl mu/s. The switching voltage is about 50 V. The switches have a bowtie shape and showed low insertion loss of 0.14 dB at 20 GHz and 0.25 dB at 35 GHz, and isolation of 24 dB at 20 GHz and 35 dB at 35 GHz. These devices offer the potential for building a new generation of low-loss high-linearity microwave circuits for a variety of phased antenna arrays for radar and communications applications.
430 citations
TL;DR: In this paper, the mechanics of a three-layer piezoelectric bimorph is discussed and its dynamic model with hysteresis is presented, which can also be used with other types of actuators with a slight modification.
Abstract: Piezoelectric actuators are usually stacked or bimorph in configuration. In this paper the mechanics of a three-layer piezoelectric bimorph is discussed and its dynamic model with hysteresis is presented. The results can be used to analyze piezoelectric actuators constructed with three-layer piezoelectric bimorphs. A piezoelectric bimorph actuator has been fabricated and experiments have been carried out to verify the model. The calculated results of this model closely matched the tested results. This model can also be used with other types of piezoelectric actuators with a slight modification.
318 citations
TL;DR: In this article, the performance and lifetime of a metal-to-metal shunt RF MEMS switch fabricated on an SI-GaAs substrate is investigated. And the authors have developed a cold switching test method to identify the root cause of sticking as a failure mechanism.
Abstract: This paper investigates the performance and lifetime of a metal-to-metal shunt RF MEMS switch fabricated on an SI-GaAs substrate. The switch is a shunt bridge design that is compatible with standard microelectronic processing techniques. The RF performance of the switch includes actuation voltages of less than 15 V, isolation better than 20 dB from 0.25 to 40 GHz, and switching speeds of less than 22 /spl mu/s. Varying the geometry of the switch affects both switching voltage and reliability, and the tradeoffs are discussed. We have developed a cold switching test method to identify the root cause of sticking as a failure mechanism. The switch structure includes "separation posts" that eliminate sticking failure and has demonstrated lifetimes as high as 7/spl times/10/sup 9/ cold switching cycles. These results show that good reliability is possible with a metal-to-metal RF MEMS switch operated with a low actuation voltage.
154 citations
08 Jun 2003
TL;DR: In this article, the authors present the latest accomplishments in RF MEMS switches, and at the same time, an assessment of their potential applications in defense and commercial systems, particularly at high microwave frequencies.
Abstract: This paper presents the latest accomplishments in RF MEMS switches, and at the same time, an assessment of their potential applications in defense and commercial systems. It is seen that RF MEMS devices offer spectacular performance at microwave frequencies, but suffer from reliability problems and the potential of relatively high-cost hermetic packaging. Still, this technology offers such tremendous advantages over GaAs and silicon switching devices that, in the author's opinion, it will find many applications in satellite, base-station and defense applications, particularly at high microwave frequencies.
138 citations