Most current capacitive RF-MEMS switch technology is based on conventional dielectric materials such as SiO<sub>2</sub> and
Si<sub>3</sub>N<sub>4</sub>. However, they suffer not only from charging problems but also stiction problems leading to premature failure of
an RF-MEMS switch. Ultrananocrystalline diamond (UNCD<sup>(R)</sup> (2-5 nm grains) and nanocrystalline diamond (NCD) (10-
100 nm grains) films exhibit one of the highest Young's modulus (~ 980-1100 GPa) and demonstrated MEMS resonators
with the highest quality factor (Q ≥10,000 in air for NCD) today, they also exhibit the lowest force of adhesion among
MEMS/NEMS materials (~10 mJ/m<sup>2</sup>-close to van der Waals' attractive force for UNCD) demonstrated today. Finally,
UNCD exhibits dielectric properties (fast discharge) superior to those of Si and SiO<sub>2</sub>, as shown in this paper. Thus,
UNCD and NCD films provide promising platform materials beyond Si for a new generation of important classes of
high-performance MEMS/NEMS devices.
This paper discusses issues relating to the reliability and methods for employing high-cycle life testing in capacitive RF
MEMS switches. In order to investigate dielectric charging, transient current spectroscopy is used to characterize and
model the ingress and egress of charges within the switch insulating layer providing an efficient, powerful tool to
investigate various insulating materials without constructing actual MEMS switches. Additionally, an in-situ monitoring
scheme has been developed to observe the dynamic evolution of switch characteristics during life testing. As an
alternative to high-cycle life testing, which may require days or weeks of testing, a method for performing accelerated
life tests is presented. Various methods for mitigating dielectric charging are presented including: reduced operating
voltage, reduced dielectric area, and improved control waveforms. Charging models, accelerated life test results, and
high-cycle life test results for state-of-the-art capacitive RF MEMS switches aid in the better understanding of MEMS
switch reliability providing direction for improving materials and mechanical designs to increase the operation lifetime
of MEMS capacitive switches.
In this paper, we present the design, fabrication and characterization of an inductively-coupled miniaturized RFID transponder using MEMS technology. The micromachined miniaturized transponder consists of a small solenoid inductor with a high permeability magnetic core, a chip capacitor and a RFID chip. They are integrated onto a micromachined SU-8 polymer substrate and it is operated in the frequency range of 13.56 to 27 MHz. Induced voltages of up to 4 V were obtained with a miniaturized 500 nH transponder coil from a 2.2 μH reader coil at 5 mm distance based on a resonant magnetic coupling mechanism. The assembled transponder was tested using a commercial RFID reader at 13.56 MHz and successful communication was established at a distance of 10 mm.
For state-of-the-art RF MEMS capacitive switches, a dielectric-charging model was constructed to predict the amount of charge injected into the dielectric and the corresponding shift in actuation voltage. The model was extracted from measured charging and discharging transient currents on the switch dielectric under different control voltages. The model was verified against the actuation-voltage shift under different control waveforms. Duty factor and peak voltage of the control waveform were found to be critical acceleration factors for the charging effects while actuation frequency is not an acceleration factor. The model is capable of predicting the actuation-voltage shift under complex control waveforms such as the dual-pulse waveforms. For RF MEMS capacitive switches that fail mainly due to dielectric charging, the model can be used to design control waveforms that can either prolong lifetime or accelerate failure.
We have fabricated and characterized radio frequency microelectromechanical systems (RF MEMS) ohmic switches for applications in discrete tunable filters and phase shifters over a frequency range of 0 to 20 GHz. Our previously reported cantilever switches have been redesigned for higher isolation and are now achieving 22 dB of isolation at 10 GHz. The measured insertion loss is 0.15 dB at 10 GHz. We have also fabricated and characterized new devices, designated “crab” switches, to increase isolation and contact forces relative to the cantilever design. The measured insertion loss and isolation are 0.1 dB per switch at 20 GHz and 22 dB at 10 GHz, respectively. A simple and accurate equivalent model has been developed, consisting of a transmission line segment and either a series capacitor to represent the blocking state or a series resistor to represent the passing state. Experimental analysis of the switch shows that high contact and substrate capacitive coupling degrades the isolation performance. Simulations indicate that the isolation improves to 30 dB at 10 GHz by reducing these capacitances. The crab switch design has a measured contact force of 120 μN, which represents a factor of four increase over the cantilever switch contact force and results in consistent, low-loss performance.
An optical time delay network (OTDN) for time delay steering of arrays of various sizes is being developed which features passive waveguides and micromechanical switches monolithically fabricated on silicon. Separately packaged directly modulated lasers and optical envelope detectors perform the RF and optical conversions. Recent developments in the areas of phosphosilicate glass (PSG) waveguides and micromechanical switches are presented. Broadband reactive matching circuits for commercially available directly modulated lasers and optical detectors are described which demonstrate VSWRs of less than 1.5:1 and improvement of 16 dB in overall RF/optical/RF conversion efficiency for an octave bandwidth. Finally, plans for demonstrating the operation of the time delay network in a 4 by 16 element phased array with an operating band of 2 to 4 GHz are presented.
This paper describes laser measurement and modelling techniques pursuant to developing impedance matching networks for bandwidths over an octave. Models presented include a novel large signal model that has a measurement based nonlinear photon resistance term to induce curvature into the L-I characteristic of the laser. It is found that predicted intermodulation performance varied about 1 dB between the linear and nonlinear photon resistance models implying the dominate nonlinearity is due to the I-V characteristic of the laser. Finally, the models are used with microwave design tools to synthesize and optimize a Chebyshev impedance matching network employing a Norton equivalent transformer. The impedance matching circuit results in a simulated 10 dB improvement over resistive matching with a VSWR of less than 1.5 over the band of interest.