Micromachined W-band circuits.

Abstract

This dissertation presents a comprehensive demonstration of the ability of membrane-supported transmission lines to provide excellent performance in W-band applications. The design, fabrication, and measurements of micromachined circuits are discussed, with a strong focus on two types of membrane-supported transmission lines: the microshield line and the shielded membrane microstrip (SMM) line. The procedures for the fabrication of these structures are outlined, with treatments of thin dielectric membrane technology and bulk silicon micromachining techniques. Additionally, methods for simulation, analysis, and testing of micromachined circuits are reviewed. A series of experimental investigations demonstrates the excellent performance levels achieved by micromachined W-band circuits. A 90 GHz low-pass filter is developed using the microshield line architecture and achieves one of the first known results of planar filter performance in W-band. Subsequently, a variety of structures are developed using the SMM technology. First, a 25 GHz end-coupled half-wavelength resonator shows conductor loss limited, dispersion-less performance over a 2-octave bandwidth. Second, coupled-line bandpass filters demonstrate excellent signal rejection performance at 94 GHz, with a 6.1% bandwidth filter displaying nearly ideal rolloff characteristics. Finally, the broad-band characteristics of SMM are exploited to create a high-pass 20 dB coupler with uniform response from 8 GHz to 118 GHz. Theoretical comparisons to conventional planar circuit elements show that membrane-supported elements achieve superior W-band performance. Finally, a new direction in micromachining is explored with the development of a micromachined integrated conformal package for a Ka-band HEMT amplifier. The amplifier circuit is realized on silicon, with low-cost processing techniques, and utilizes a flip-chip InP High Electron Mobility Transistor for low noise gain. The measured performance of the amplifier is in good agreement with theoretical predictions, demonstrating the feasibility of creating low-cost Si-based MMICs with flip-chip devices and integrated packaging. This thesis closes with the conclusion that micromachining techniques offer powerful advantages in the development of W-band circuits, including low losses and nearly ideal behavior. Several ideas are proposed for continued work in this area. The appendices provide background on uniplanar circuit development and detail additional fabrication techniques that can be applied to micromachined W-band circuits.