RF characteristics of thin film liquid crystal polymer (LCP) packages for RF MEMS and MMIC integration

Abstract

A standard non-metallized liquid crystal poly- mer (LCP) 4 mil thick microwave substrate with depth- controlled laser-micromachined cavities was investigated as a system-level packaging layer for integrated packaging of monolithic microwave integrated circuits (MMICs) and radio frequency microelectromechanical systems (RF MEMS) switches. The RF characteristics of air/dielectric discontinu- ities at the cavity interfaces were first simulated and the results show that LCP's low dielectric constant enables cavity dimensions to be arbitrarily chosen without significantly affecting the RF performance. To test this packaging concept a 4 mil LCP sheet with twelve 1 mm x 2.4 mm x 2 mil deep cavities was fabricated. Air-bridge type RF MEMS switches were fabricated on a base LCP substrate and measured before and after introducing the laser-micromachined super- strate layer. The measurements show almost no difference in packaged and unpackaged form for frequencies up to 40 GHz. The concept of a system-level package on a flexible, low-cost, organic substrate has been demonstrated for the first time. The same technique could be used for integrating MMICs all in a near-hermetic low-cost LCP module. Index Terms— Organic, package, LCP, interconnect, MEMS, laser machining, system-on-package, RF module.