Dynamically Reconfigurable Microwave Circuits Leveraging Abrupt Phase-Change Material

• Published in: IEEE transactions on microwave theory and techniques Vol. 68; no. 10; pp. 4188 - 4205
• Main Authors: Connelly, David A., Chisum, Jonathan D.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-10-2020; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Circuits; Conductivity; Coplanar waveguide (CPW); Coplanar waveguides; Dipoles; Equivalent circuits; Inclusions; insulator-metal transition (IMT); material characterization; metal-insulator transition (MIT); Metals; Microwave antennas; Microwave circuits; millimeter wave; Millimeter waves; Phase change materials; phase-change material (PCM); Q factors; reconfigurable antennas; Reconfiguration; Switches; Thick films; Transmission lines; Unit cell; Vanadium dioxide; Vanadium oxides
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2020.3012137

This article proposes a concept for dynamically reconfigurable distributed microwave circuits by leveraging the abrupt conductivity transition in phase-change materials (PCMs). Metallic inclusions (<inline-formula> <tex-math notation="LaTeX">\ll \lambda </tex-math></inline-formula>) are embedded in the PCM film-vanadium dioxide (VO 2 )-to provide low loss and reconfigurability. To validate this concept, a variety of coplanar waveguide transmission lines are designed and fabricated with metallic inclusions in VO 2 films, and the lines' performance are characterized up to 50 GHz. From measurements, a transmission-line-based model and an equivalent circuit model of the VO 2 with inclusions are developed to aid in rapid design. An electromagnetic model was developed, and it indicates that loss can be close to conventional metallic distributed circuits with 100-200-nm-thick VO 2 films. A criterion for maximum operating frequency is defined, and it indicates that 10-<inline-formula> <tex-math notation="LaTeX">\mu \text{m} </tex-math></inline-formula> unit-cells with thicker films could operate up to 60.3 GHz. Unit-cell sizes are proposed for various bands with quality factors from 10.2 to 29.3. Using the models, two applications are presented: a tunable dipole from 2.13 to 9.07 GHz and a tunable triple-stub matching network from 5 to 40 GHz with high <inline-formula> <tex-math notation="LaTeX">|\Gamma | </tex-math></inline-formula>. The proposed method appears viable for the realization of arbitrary programmable distributed circuits and antennas in the microwave and low-millimeter-wave bands.