Anh-Vu Pham

Selective gas detection using a carbon nanotube sensor

A circular disk resonator is used to study the gas sensing properties of carbon nanotubes. It detects the presence of gases based on the change in the dielectric constant rather than electrical conductivity of single walled carbon nanotubes (SWNTs) upon gas exposure. A conducting circular disk is coated with electric arc prepared SWNTs and degassed by heating under a high vacuum. It exhibits noticeable shifts in resonant frequency to both polar (NH3 and CO) and nonpolar gases (He, Ar, N2, and O2). Gas concentrations as low as 100 ppm can be detected using this sensor configuration.

Carbon-nanotube-based resonant-circuit sensor for ammonia

We present the design and development of highly sensitive and fast-responsive microwave resonant sensors for monitoring the presence of ammonia gas. The sensor consists of a circular disk electromagnetic resonant circuit coated with either single- or multiwalled carbon nanotubes that are highly sensitive to adsorbed gas molecules. Upon exposure to ammonia, the electrical resonant frequency of the sensor exhibits a dramatic downshift of 4.375 MHz. The recovery and response times of these sensors are nominally 10 min. This technology is suitable for designing remote sensor systems to monitor gases inside sealed opaque packages and environmental conditions that do not allow physical wire connections.

A high-gain 60GHz power amplifier with 20dBm output power in 90nm CMOS

In wireless communications, high demand for superb video and audio quality increases the required transfer data rate. The unlicensed 7GHz bandwidth at V-band in North America has been drawing a lot of attention by companies and research institutions. Research topics done using CMOS fabrication, which appears to be a more appealing process due to its high level of integration, have been demonstrated to be a viable semiconductor for gigabit wireless at 60GHz [1]. According to the Federal Communications Commission (FCC) regulations, the maximum radiation power for 60GHz systems can reach up to 40dBm [2]. However, due to device limitations such as low maximum operating frequencies and low breakdown voltage, very few power amplifier (PA) designs using CMOS processes with high output power have been reported. To date, medium- to high-power amplifiers in this frequency range are normally implemented using III–V semiconductor fabrication processes.

Development of three dimensional ceramic-based MCM inductors for hybrid RF/microwave applications

We present the design, development and characterization of planar and multilayer (3-D) inductor structures fabricated on a multi-layer ceramic-based Multi-Chip-Module (MCM-C) technology. We experimentally demonstrate the feasibility of utilizing both planar and compact 3-D helical inductors for hybrid RF and microwave system implementation. For the same numbers of turns and dimensions as the conventional planar inductor, the 3-D helical inductors occupies significantly less area and demonstrate better quality (Q) factor, higher inductance and comparable self resonant frequency (SRF).

Design and Development of a Package Using LCP for RF/Microwave MEMS Switches

We present the development of an ultrahigh moisture-resistant enclosure for RF microelectromechanical system (MEMS) switches using liquid-crystal polymer (LCP). A cavity formed in LCP has been laminated, at low temperature, onto a silicon MEMS switch to create a package. The LCP-cap package has an insertion loss of less than 0.2 dB at X-band. E595 outgas tests demonstrate that the LCP material is suitable for constructing reliable packages without interfering with the operation of the MEMS switch. The package also passes Method 1014, MIL-STD-883 gross leak, and fine leak hermeticity tests

Triple bands antenna and high efficiency rectifier design for RF energy harvesting at 900, 1900 and 2400 MHz

We present the design and development of a novel antenna that effectively radiates at three frequency bands to harvest RF energy from cellular network frequency bands (900 MHz and 1900 MHz) and Wi-Fi sources (2.4 GHz) available in ambience. The antenna is designed using the combination of three different design techniques including composite right/left hand transmission line (CRLH). In addition, a high efficiency, sensitive triple-band rectifier is also proposed in this work. The rectifier provides a maximum conversion efficiency of 80%, 46% and 42% at 940MHz, 1.95GHz and 2.44 GHz, respectively. The experimental results demonstrate that the proposed triple-band RF energy harvesting system can collect 6.6 times more power than the single 900MHz band one and 3.4 times more power than three individual bands combined.

Development of multiband phase shifters in 180-nm RF CMOS technology with active loss compensation

We present the design and development of a novel integrated multiband phase shifter that has an embedded distributed amplifier for loss compensation in 0.18-/spl mu/m RF CMOS technology. The phase shifter achieves a measured 180/spl deg/ phase tuning range in a 2.4-GHz band and a measured 360/spl deg/ phase tuning range in both 3.5- and 5.8-GHz bands. The gain in the 2.4-GHz band varies from 0.14 to 6.6 dB during phase tuning. The insertion loss varies from -3.7 dB to 5.4-dB gain and -4.5 dB to 2.1-dB gain in the 3.5- and 5.8-GHz bands, respectively. The gain variation can be calibrated by adaptively tuning the bias condition of the embedded amplifier to yield a flat gain during phase tuning. The return loss is less than -10 dB at all conditions. The chip size is 1200 /spl mu/m/spl times/2300 /spl mu/m including pads.

Demonstration of Spectral Phase O-CDMA Encoding and Decoding in Monolithically Integrated Arrayed-Waveguide-Grating-Based Encoder

We report on successful spectral phase encoding and decoding operation in a pair of monolithically integrated InP encoder chips, each consisting of an arrayed waveguide grating (AWG) pair and an eight-channel electrooptic phase shifter array. The monolithic fabrication process includes anisotropic reactive ion etching and planarizing hydride-vapor-phase-epitaxy lateral regrowth to realize buried hetero-waveguide structures in AWGs and phase shifters. Electrooptical modulation in the phase shifter arrays in the encoder chip achieved Walsh-code-based optical code-division multiple access (O-CDMA) encoding and decoding. The matched-code encoding-decoding operation resulted in error-free performance in the presence of an interferer, indicating good potential for O-CDMA network applications

Development of microwave package models utilizing on-wafer characterization techniques

A package characterization technique using coplanar waveguide (CPW) probes and line-reflect-match (LRM) calibrations for surface-mountable packages is presented. CPW-to-package adapters (CPA) are fabricated on alumina substrates to mount and measure the high-frequency response of plastic packages. Offset CPA standards in conjunction with an LRM calibration are used to de-embed the response of the adapters from the measured S-parameters. Application of this method is demonstrated by characterizing and modeling surface-mount microwave plastic packages.

Optical-CDMA in InP

This paper describes the InP platforms for photonic integration and the development on these platforms of an optical code division multiple access (O-CDMA) system for local area networks. We demonstrate three building blocks of this system: an optical pulse source, an encoder/decoder pair, and a threshold detector. The optical pulse source consists of an integrated colliding pulse-mode laser with nearly transform-limited 10 Gb/s pulses and optical injection locking to an external clock for synchronization. The encoder/decoder pair is based on arrayed waveguide gratings. Bit-error-rate measurements involving six users at 10 Gb/s showed error-free transmission, while O-CDMA codes were calibrated using frequency resolved optical gating. For threshold detection after the decoder, we compared two Mach--Zehnder interferometer (MZI)-based optical thresholding schemes and present results on a new type of electroabsorber-based MZI.