Millimeter-wave Low-noise Amplifiers Using Cost-effective Ion Implanted MESFETs and Coplanar Transmission Lines

Book excerpt: This dissertation describes the design and implementation of a monolithic 38 GHz low-noise amplifier using 0.25 $mu$m ion-implanted GaAs MESFETs and coplanar waveguide transmission lines. It describes the development of low-noise GaAs FETs, measurement and modeling of active and passive components, circuit design, simulation, fabrication, and characterization of the completed amplifiers. Wireless systems are reshaping the nature of today's telecommunications industry. Millimeter-wave data communication systems provide the large bandwidth which is needed for high information capacity systems. The noise figure of the front ends currently available is a limiting factor in the performance of these systems, due to the lack of commercially available low-noise amplifiers to boost signal levels prior to down conversion. Most systems use a mixer as the first element in the receiver, which results in a noise figure of 7-8 dB. If low-noise amplifiers with a noise figure of less than 4 dB were commercially available, this would result in at least a 3 dB improvement in sensitivity. This would allow for longer links and/or reduced transmitter power, which improve the performance/cost ratio of the link. The use of ion implanted MESFETs as the active devices in MMIC circuits results in a dramatic reduction in material cost and improvement in circuit yields in comparison with those for devices based on epitaxial material. Various industrial foundries currently use high-cost epitaxial material with the goal of obtaining superior high frequency gain and noise performance compared to those for simpler ion-implanted devices. This work explores the benefits and capabilities of ion implanted MESFETs in millimeter-wave integrated circuits and compares their performance to that of p-HEMTs. Low cost ion implanted GaAs MESFETs are demonstrated with performance equivalent to those of high cost p-HEMTs fabricated on epitaxial material with $rm Fsb{t} > 60$ GHz, $rm Fsb{min} 12$ dB at 10 GHz. Coplanar circuits are gaining acceptance as a viable alternative to microstrip circuits for Ka-band applications. Coplanar technology eliminates processing steps associated with backside vias which limit yield in most MMIC processes. This results in high yield and low cost circuits. This work describes the models used to accurately simulate coplanar components at millimeter-wave frequencies. Three-stage coplanar amplifiers are fabricated that have greater than 12 dB of gain at 38 GHz.