Thin-Film-Based Reconfigurable Resonators and Filters for Narrow and Wide Bandwidth Applications

Date of Award

5-5-2024

Degree Name

Ph.D. in Electrical and Computer Engineering

Department

Department of Electrical and Computer Engineering

Advisor/Chair

Guru Subramanyam

Abstract

The advent of 5G technology has catalyzed a spectrum expansion across various frequency bands, including a low band below 1 GHz, a midband spanning 1-7 GHz, and a high band above 24 GHz. Therefore, researchers and engineers are currently engaged in exploring reconfigurable and tunable devices capable of adapting multi-band front-end modules to accommodate this expanded spectrum range. In this work, there are three types of reconfigurable and tunable filters that have been investigated. Each of them has its unique features and advantages. The surface-mounted technology (SMT) 5th-order elliptic tunable filter is first investigated. It exhibits three consecutive tunable bands within and above the L-band frequency range, specifically at 2.0-2.5 GHz, 2.5-3.0 GHz, and 3.0-3.5 GHz. Utilizing PIN diodes and capacitor banks, tunability is achieved through the DC voltage-controlled capacitance of PIN diodes, with in-band insertion loss maintained below 3 dB. This work already met the design limitation of the pure SMT filter in spite of the limited quality factor of the inductor and capacitor components. This dissertation contributed to two other designs. One is the bulk acoustic wave (BAW) filter, using the piezo effect to realize a filter function with high out-of-band rejection. Another one is the microstrip-coplanar waveguide (MS-CPW) filter, utilizing the coupling effect to guarantee a wide bandwidth and low in-band loss. The BAW resonator and filter, integrating tunable dielectric material barium strontium titanate (BST), offer a solution for sub-10 GHz applications. The BST material grants the BAW device a switchable coupling coefficient (Kt2), resulting in a switchable passband. This dissertation delves into the physical behavior and electrical models of the BAW resonator. In this work, the surface-mounted structure is adopted, and a highly efficient Bragg reflector is designed and fabricated to achieve a better isolation for BAW resonator. Furthermore, the performance of the BAW resonator and filter are also analyzed. The BAW filter presents a good out-of-band filter rejection and sharp attenuation. The edge-coupled MS-CPW filter can achieve a wide bandwidth with low insertion loss. The wide bandwidth is guaranteed by strong coupling and transmission line theory. The proposed structure offers a filter solution with ultra-wide bandwidth and low in-band insertion loss. The measured bandwidth is 3 GHz and in-band insertion loss is less than 1 dB. Additionally, the proposed filter can be modified to improve the out-of-band rejection and sharpen the attenuation. Remarkably, the MS-CPW structure also has the potential to realize reconfigurable Ku band and millimeter wave filters. The fabricated tunable Ku band filter presents 7 GHz bandwidth with a tuning ratio of 50%. Additionally, the tested in-band insertion loss is less than 3.5 dB. The proposed Ku band filter also exhibits a linear phase change in the passband, resulting in a constant group delay within 0.1 seconds. All designs are fabricated and characterized. The tunable 5th-order elliptic BPF and MS-CPW filters are first validated on a printed circuit board (PCB). The reconfigurable BAW resonators and tunable millimeter-wave MS-CPW BPF are fabricated on 2-inch wafers. The wafer mask design and fabrication procedures are also presented in this dissertation. In summary, this dissertation meticulously details filter design for diverse frequency, bandwidth, and insertion loss requirements. The incorporation of the tunable dielectric material, BST, contributes to the reconfiguration and tunability of the filter designs.

Keywords

Acoustic filter, Bulk acoustic wave filter (BAW filter), Barium strontium titanite (BST), Thin film fabrication, Elliptical filter, Ferroelectric material, Ku band filter, Millimeter wave filter, Microstrip-CPW line coupling filter, Pulse laser deposit (PLD), Reconfigurable filter, Switchable filter, Tunable filter, Ultra-wide bandwidth filter

Rights Statement

Copyright 2024, author

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