Low loss multilayer microstrip line for monolithic microwave integrated circuits applications

Abstract

This paper describes the multilayer microstrip structure using low dielectric constant polyimide as a buffer layer between the microstrip conductor and the GaAs substrate to reduce dissipation loss, especially for very high impedance microstrip lines. The new structure provides about half the dissipation loss and about 40% higher characteristic impedance in comparison to the conventional microstrip line on GaAs substrate having the same conductor widths. An empirical formula for the equivalent dielectric constant compatible with commercial computer-aided design tools was developed to design monolithic microwave integrated circuits (MMICs) using this medium. The multilayer microstrip structure is compatible with ITT's 4′ MSAG® process which uses polyimide for crossovers and scratch protection. The present structure has great potential in realizing low loss and wideband matching networks including low noise, high power, and high efficiency amplifiers, and passive components on GaAs substrate with improved insertion loss and bandwidth performance, and three-dimensional MMICs. © 1998 John Wiley & Sons, Inc. Int J RF and Microwave CAE 8: 441–454, 1998