Graduation Year

2012

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Electrical Engineering

Major Professor

Jing Wang

Keywords

Bandwidth, Insertion Loss, MEMS, Piezoelectric, Quality Factor

Abstract

For the past decade, a great deal of research has been focused towards developing a viable on-chip solution to replace the current state-of-the-art VHF and UHF filters based on SAW and FBAR technologies. Although filters based on SAW and FBAR devices are capable of fulfilling the basic requirements needed for IF and RF bandpass filtering and reference signal generation, an alternative solution that can enable the next generation of multi-frequency and multi-mode transceivers while enabling size and price reduction by allowing the manufacturing of single-chip monolithic RF transceivers is highly desired. In response to these new needs, piezoelectrically-transduced micromechanical filters have emerged as a plausible alternative to outperform current dominant technologies in size, cost, and IC manufacturing compatibility without compromising device performance in terms of insertion loss, rejection, power handling and linearity.

This dissertation presents the design, fabrication, characterization and experimental analysis of low-loss VHF and UHF filters for wireless communication applications, based on piezoelectrically-transduced micromechanical resonators. The resonators employed in this work for the implementation of microwave filters, resonate in contour-mode shapes, which differ from commercially available thickness-mode FBAR resonators, for which the thickness sets the resonance frequency. The employment of contour-mode designs facilitate simultaneous synthesis of multiple frequencies on the same substrate through CAD layout-defined lateral dimensions, thus avoiding the complexity demanded by FBAR devices for the precise control of the piezoelectric layer thickness. Moreover, filters composed of acoustically-coupled piezoelectrically-transduced resonators operating at higher order modes with sizes up to 10 times smaller than their SAW counterparts operating at the same UHF range have been successfully implemented, without jeopardizing the key filter specifications.

Throughout this dissertation, piezoelectrically-transduced MEMS filters based on mechanically, electrically and acoustically coupled contour-mode resonator(s) or resonator arrays were designed and fabricated. Filters with insertion loss as low as 2.6 dB at IF frequencies and 4.0 dB at RF frequencies have been demonstrated. Moreover, synthesized filters with extremely narrow bandwidth of 0.1 % and 0.2 % at frequencies between 160 MHz and 215 MHz have been developed, which comply the specifications for IF filters for GSM handsets. This particular type of filters each consist of just one single high-Q resonator, which leverages single crystalline silicon as the major part of their structure to obtain the sufficient quality factor required for the implementation of such small bandwidth.

Among the most significant results, this dissertation presents two thin film piezoelectrically-transduced monolithic filters operating at 482 MHz and 536 MHz, which can be interfaced directly to a 377  antenna without the need of external matching components. This dissertation also has conducted a systematic comparison between commercial available SAW filters and the MEMS filters synthesized using piezoelectrically-transduced resonators. Parameters such as group delay and third intermodulation (IP3) have been measured and carefully compared. Evidentially, most of the fabricated piezoelectrically-transduced filters developed by this work have exhibited a similar or superior performance as compared to their commercial SAW counterparts

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