Improving linearity of ferroelectric-based microwave tunable circuits

Jia Shiang Fu, Xinen Alfred Zhu, Jamie D. Phillips, Amir Mortazawi

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


A device architecture for improving the linearity of barium-strontium- titanate (BST) capacitors is proposed, analyzed, and experimentally demonstrated. The basic concept is to reduce the RF swing across the ferroelectric varactors by connecting multiple capacitors in series. With proper biasing networks, the overall device preserves its tunability. In this paper, the proposed architecture is analyzed to derive the equations that relate its quality factor and tuning speed to the design parameters. Parallel-plate BST capacitors are fabricated based on the architecture. Various measurements are performed to demonstrate the efficacy of the technique. The third-order intercept point at input (IIP3) is found to be improved by 16 dB. The hot-tuning test shows that the tunability is maintained for up to 20-V peak-to-peak swing. BST capacitors utilizing the proposed technique are used in a phase-shifter design. The 2.4-GHz phase shifter exhibits high IIP3 greater than 40 dBm.

Original languageEnglish
Pages (from-to)354-360
Number of pages7
JournalIEEE Transactions on Microwave Theory and Techniques
Issue number2
StatePublished - Feb 2007


  • Barium-strontium-titanate (EST)
  • Ferroelectric capacitor
  • Linearity
  • Phase shifter


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