Thick electrodes for high frequency high Q tunable ferroelectric thin film varactors

Gregory T. Stauf, Craig Ragaglia, Jeffrey F. Roeder, Dan Vestyck, Jon Paul Maria, Tito Ayguavives, Angus Kingon, Amir Mortazawi, Ali Tombak

Research output: Contribution to journalConference articlepeer-review

11 Scopus citations


Thin film barium strontium titanate (BST) shows great promise for voltage tunable dielectric devices for use at RF and microwave frequencies. An MOCVD process has been developed for production of BST, resulting in films with very low losses (as low as 0.002-0.004) and tunabilities over 50% at low operation voltages. With these values of BST loss, overall device quality factors at RF (100 MHz+) frequencies are primarily limited by losses in the thin metal electrodes, such as Pt, normally used for ferroelectric thin films. The bottom electrode in parallel plate capacitor structures is particularly challenging, since it must provide a good growth surface for BST and be stable at high (600 C) growth temperatures in an oxidizing atmosphere yet have high conductivity and compatibility with Si or SiO2/Si substrates. These challenges have previously prevented use of Pt thicknesses over 0.1-0.2 urn. Our solution to this problem, involves combinations of adhesion layers at the Pt/SiO2 interface and embedded stabilization layers to make functioning Pt bottom electrodes as thick as 2 m. Devices with dielectric Q factors over 150 at 100 MHz (tan 0.006 as measured and modeled by S-parameters) and overall device Q factors over 50 at 30 MHz are described. We have also inserted these devices into tunable filters, achieving tunabilities of 50% and low insertion losses (0.3 dB) at RF frequencies.

Original languageEnglish (US)
Pages (from-to)321-330
Number of pages10
JournalIntegrated Ferroelectrics
Issue number1-4
StatePublished - 2001
Event13th International Symposium on Integrated Ferroelectrics - Colorado Springs, CO, United States
Duration: Mar 11 2006Mar 14 2006

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Control and Systems Engineering
  • Ceramics and Composites
  • Condensed Matter Physics
  • Electrical and Electronic Engineering
  • Materials Chemistry


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