Guoan Wang

Temperature study of the dielectric polarization effects of capacitive RF MEMS switches

This paper investigates both theoretically and experimentally the dielectric charging effects of capacitive RF microelectromechanical system switches with silicon nitride as dielectric layer. Dielectric charging caused by charge injection under voltage stress was observed. The amphoteric nature of traps and its effect on the switch operation were confirmed under both positive and negative control voltages. It has been confirmed that charging is a complicated process, which can be better described through the stretched exponential relaxation. This mechanism is thermally activated with an activation energy being calculated from the temperature dependence of the capacitance transient response. The charging mechanism, which is responsible for the pull-out voltage and the device failure, is also responsible for the temperature-induced shift of the capacitance minimum bias.

A high performance tunable RF MEMS switch using barium strontium titanate (BST) dielectrics for reconfigurable antennas and phased arrays

In this letter, a tunable RF micro electronic mechanical systems (MEMS) switch used for the development of reconfigurable antennas that is fabricated on sapphire substrate with a barium strontium titanate (BST) dielectric is presented. BST dielectric is deposited by a combustion chemical vapor deposition (CCVD) technology. BST has a very high dielectric constant (>300) making it very appealing for high performance RF MEMS capacitive switches. The tunable dielectric constant of BST provides a possibility of making linearly tunable MEMS capacitor switches. Here for the first time a capacitive tunable RF MEMS switch with a BST dielectric and its characterization and properties up to 40 GHz are presented.

A Small UWB Antenna with Dual Band-Notched Characteristics

A small novel ultrawideband (UWB) antenna with dual band-notched functions is proposed. The dual band rejection is achieved by etching two C-shaped slots on the radiation patch with limited area. A single band-notched antenna is firstly presented, and then an optimized dual band-notched antenna is presented and analyzed. The measured VSWR shows that the proposed antenna could operate from 3.05 to 10.7 GHz with VSWR less than 2, except two stopbands at 3.38 to 3.82 GHz and 5.3 to 5.8 GHz for filtering the WiMAX and WLAN signals. Radiation patterns are simulated by HFSS and verified by CST, and quasiomnidirectional radiation patterns in the H-plane could be observed. Moreover, the proposed antenna has a very compact size and could be easily integrated into portable UWB devices.

Contactless Dielectric Charging Mechanisms in RF-MEMS Capacitive Switches

This paper investigates the possible dielectric layer polarization mechanisms, which contribute to intrinsic charging effects in capacitive RF MEMS switches. The MEMS switches are operated bellow instability point in order to avoid charge injection, hence to allow the dielectric charging to be induced by dipolar or space charge polarization. The possible contribution of interface charge polarization is also examined. The possibility of separating these mechanisms is investigated. Finally it is demonstrated that these polarization mechanisms are responsible for driving a MEMS switch beyond the instability point although the device is biased bellow the pull-in voltage

On the dielectric polarization effects in capacitive RF-MEMS switches

This paper investigates both theoretically and experimentally the dielectric charging effects of capacitive RF MEMS switches. Dielectric charging caused by charge injection under voltage stress was observed. The amphoteric nature of traps and its effect on the switch operation were confirmed under both positive and negative control voltages. Furthermore, it has been confirmed that the charging is a complicated process, which can be better described through the stretched exponential relaxation. This charging mechanism is the one that is responsible for the appearance of the negative pull out voltage and finally for the device failure.

RF characteristics of thin film liquid crystal polymer (LCP) packages for RF MEMS and MMIC integration

A standard non-metallized liquid crystal polymer (LCP) 4 mil thick microwave substrate with depth-controlled laser-micromachined cavities was investigated as a system-level packaging layer for integrated packaging of monolithic microwave integrated circuits (MMICs) and radio frequency microelectromechanical systems (RF MEMS) switches. The RF characteristics of air/dielectric discontinuities at the cavity interfaces were first simulated and the results show that LCPs low dielectric constant enables cavity dimensions to be arbitrarily chosen without significantly affecting the RF performance. To test this packaging concept a 4 mil LCP sheet with twelve 1 mm /spl times/ 2.4 mm /spl times/ 2 mil deep cavities was fabricated. Air-bridge type RF MEMS switches were fabricated on a base LCP substrate and measured before and after introducing the laser-micromachined superstrate layer. The measurements show almost no difference in packaged and unpackaged form for frequencies up to 40 GHz. The concept of a system-level package on a flexible, low-cost, organic substrate has been demonstrated for the first time. The same technique could be used for integrating MMICs all in a near-hermetic low-cost LCP module.

2-D Entropy and Short-Time Fourier Transform to Leverage GPR Data Analysis Efficiency

Accurate detection of singular region using ground-penetrating radar (GPR) is very useful in assessing roadway pavement, bridge deck concrete structure, and railroad ballast conditions. To locate an object within the large radargram involves extensive computational resources and time, especially when the data of interests only possess a small portion of the whole big data set. Therefore, an efficient GPR signal-processing technique is highly demanded. This paper proposes the use of 2-D entropy analysis to narrow down the data scope to the interested regions, which can considerably reduce computational cost for more sophisticated data postprocessing. Joint time-frequency analysis using short-time Fourier transform is then performed for singular region location detection and refinement. The proposed methodology is tested with different laboratory setups. The analysis results show good agreement with physical configurations.

Frequency and Bandwidth Agile Millimeter-Wave Filter Using Ferroelectric Capacitors and MEMS Cantilevers

This paper demonstrates for the first time a tunable bandpass filter with simultaneous frequency and bandwidth control using a combination of ferroelectric barium-strontium-titanate capacitors and cantilever microelectromechanical systems (MEMS) switches. The center frequency of the filter is tuned in a continuous fashion from 30 to 35 GHz with insertion loss ranging from 10 to 2.7 dB. The fractional bandwidth of the filter can also be independently controlled by a tuning scheme that uses MEMS switches to vary the inter-resonator coupling. The two-pole filter prototypes resulted in fractional bandwidths of 9.6% (wideband configuration) and 4.8% (narrowband configuration) for a tuning ratio of approximately 2:1. The third-order filters resulted in bandwidths of 7.8% (wideband configuration) and 3.1% (narrowband configuration) for a passband tunable ratio of approximately 2.5:1

High performance tunable slow wave elements enabled with nano-patterned permalloy thin film for compact radio frequency applications

Slow wave elements are promising structures to design compact RF (radio frequency) and mmwave components. This paper reports a comparative study on different types of coplanar wave-guide (CPW) slow wave structures (SWS). New techniques including the use of defected ground structure and the different signal conductor shape have been implemented to achieve higher slow wave effect with comparative loss. Results show that over 42% and 35% reduction in length is reported in the expense of only 0.3 dB and 0.1 dB insertion loss, respectively, which can end up with 66% and 58% area reduction for the design of a branch line coupler. Implementation of the sub micrometer patterned Permalloy (Py) thin film on top of the simple SWS has been demonstrated for the first time to increase the slow wave effect. Comparing with the traditional slow wave structure, with 100 nm thick Py patterns, the inductance per unit length of the SWS has been increased from 879 nH/m to 963 nH/m. The slow wave effect of the designed structur...

Novel low-cost on-chip CPW slow-wave structure for compact RF components and mm-wave applications

In this paper, an ideal slow wave coplanar waveguide (CPW) structures with low losses, moderate impedance and CMOS fabrication technology have been developed. The slow wave CPW transmission line structures were achieved through IBM 0.13 mum technology with multi-layer metals. The CPW were implemented with narrower signal line or wider separation between signal and ground plane to increase the inductance per unit length, while metal strips on another metal layers cross under/above the CPW lines, which are orthogonal to signal propagation direction. Losses reduction using via bars to increase the thickness of the signal metal layer, structures with metal strip options (above, under and both CPW) to increase the capacitance per unit length of the CPW and provide more flexibility for the proposed structure, effect of the metal strips pitch are also discussed. The slow wave structure discussed in this paper can shrink the side dimension of the mm-wave passive components by up to 35%.