LOW-LOSS MULTILAYER MICROSTRIP LINE FOR MONOLITHIC MICROWAVE INTEGRATED-CIRCUITS APPLICATIONS

This paper describes the multilayer microstrip structure using low die lectric constant polyimide as a buffer layer between the microstrip co nductor and the GaAs substrate to reduce dissipation loss, especially for very high-impedance microstrip lines. The new structure provides a bout half the dissipation loss and about 40% higher characteristic imp edance in comparison to the conventional microstrip line on GaAs subst rate having the same conductor widths. An empirical formula for the eq uivalent dielectric constant compatible with commercial computer-aided design tools was developed to design monolithic microwave integrated circuits (MMICs) using this medium. The multilayer microstrip structur e is compatible with ITT's 4 '' MSAG(R) process which uses polyimide f or crossovers and scratch protection. The present structure has great potential in realizing low loss and wideband matching networks includi ng low noise, high power, and high efficiency amplifiers, and passive components on GaAs substrate with improved insertion loss and bandwidt h performance, and three-dimensional MMICs. (C) 1998 John Wiley & Sons , Inc.