Development of Tunable RF Integrated Passive Devices

Abstract

Radio frequency (RF) lumped elements are crucial building blocks for designing any type of passives circuits for RF front-end applications in mobile devices. In particular, high-quality (Q) factor lumped elements are desirable for improving both insertion loss and noise performance. Integrated passive devices (IPD) technology is a platform that can provide miniature inductors, and capacitors with high- Q values that are unattainable with traditional CMOS technologies. Over the past several years, IPD technology has been used to implement devices such as filters, couplers and impedance-matching networks for a wide range of system-in-package applications. However, most of the IPD circuits do not yet have any tunable/reconfigurable functions for use in frequency agile applications.

The objective of this research is to develop tunable integrated passive devices (IPDs) using barium strontium titanate (BST) and micro-electrical-mechanical-systems (MEMS) technologies. Another objective is to develop a fabrication process for monolithic integration of MEMS switches and IPD devices. A 4-mask IPD glass/alumina-based fabrication process is developed at the University of Waterloo for the first time. Details of the modeling and characterization of high-Q lumped elements, L and C, are investigated. The RF performance of these elements is compared with that of similar designs fabricated in a commercial IPD foundry. To highlight the benefits of the IPD process, lumped element bandpass filters are designed, fabricated, and tested.

BST varactors are integrated with IPD circuits to demonstrate a highly miniaturized tunable impedance matching network featuring a wide impedance coverage from 2-3 GHz and an insertion loss of approximately 1 dB. The network promises to be useful in a broad range of wireless applications. A high performance tunable IPD/BST bandstop filter with a wideband balun as a multichip module is also proposed. Reconfigurable IPD/BST bandpass filters with tunable transmission zeros are presented and investigated experimentally for operation under high power levels. Intermodulation test results are presented for the integrated IPD/BST devices.

Making use of the fact that the IPD fabrication process is amenable to the realization of MEMS devices, the IPD process originally developed for realizing passive circuits is further expanded to accommodate monolithic integration of MEMS switches with IPD circuits. Contact-type MEMS switches are developed, fabricated and tested. Also, a monolithically integrated IPD/MEMS 3-bit high resolution true-time delay network and high-Q switched-capacitor bank are fabricated and tested to demonstrate the benefits of integrating MEMS technology with the IPD technology.