High Q (Ba, Sr)TiO 3 interdigitated capacitors fabricated on low cost polycrystalline alumina substrates with copper metallization

Dipankar Ghosh, B. Laughlin, J. Nath, A. I. Kingon, M. B. Steer, J. P. Maria

Research output: Contribution to journalConference article

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Barium Strontium Titanate (BST) ferroelectric thin films are attractive for radio frequency and microwave applications. However, for many non-military uses, the high cost of conventionally processed devices is a limiting factor. This high cost stems from the use of single-crystalline sapphire, MgO, or LaAlO 3 substrates and Pt or Au metallization commonly used. Here we present a device process and materials complement offering a low cost alternative. Planar interdigitated capacitors Ba 0.75Sr 0.25TiO 3 (BST) thin films with chromium/copper top electrodes were fabricated on polycrystalline alumina substrates using a single step photolithographic technique and lift-off. RF magnetron sputtering was used for fabrication of BST thin films while Cu thin films were thermally evaporated The dielectric tunability of the Ba 0.75Sr 0.25TiO 3 IDCs was 40 % for an applied electric field of 120 kV/cm, which corresponds to 3 μm electrode gap spacing and a 35 volt dc bias. Low frequency (1MHz) loss measurements reveal a dielectric Q ∼ 100 while a device Q of ∼ 30 is obtained at 26 GHz. The reduction of Q between 0.1 and 26 GHz can be attributed to the metallization. Leakage current measurements of the BST planar varactors show current densities of 1.0 × 10 -6 A / cm 2 for an electric field of 100 kV/cm. These dielectric characteristics (tunability and Q value) are comparable to numerous reports of IDCs with BST films prepared on expensive single crystalline substrates using noble metallization. As such, this technology is significantly less expensive, and amenable to large volume manufacturing.

Original languageEnglish (US)
Pages (from-to)125-132
Number of pages8
JournalCeramic Engineering and Science Proceedings
Issue number5
StatePublished - Dec 1 2005
Event29th International Conference on Advanced Ceramics and Composites - Cocoa Beach, FL, United States
Duration: Jan 23 2005Jan 28 2005


All Science Journal Classification (ASJC) codes

  • Ceramics and Composites
  • Materials Chemistry

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