13. High Q (Ba, Sr)TiO3 Interdigitated Capacitors Fabricated on Low Cost Polycrystalline Alumina Substrates with Copper Metallization

  1. Sheng Yao,
  2. Bruce Tuttle,
  3. Clive Randall and
  4. Dwight Viehland
  1. Dipankar Ghosh1,
  2. B. Laughlin1,
  3. J. Nath2,
  4. A. I. Kingon1,
  5. M. B. Steer2 and
  6. J-P. Maria1

Published Online: 26 MAR 2008

DOI: 10.1002/9780470291252.ch13

Advances in Electronic Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 26, Number 5

Advances in Electronic Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 26, Number 5

How to Cite

Ghosh, D., Laughlin, B., Nath, J., Kingon, A. I., Steer, M. B. and Maria, J.-P. (2005) High Q (Ba, Sr)TiO3 Interdigitated Capacitors Fabricated on Low Cost Polycrystalline Alumina Substrates with Copper Metallization, in Advances in Electronic Ceramic Materials: Ceramic Engineering and Science Proceedings, Volume 26, Number 5 (eds S. Yao, B. Tuttle, C. Randall and D. Viehland), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470291252.ch13

Author Information

  1. 1

    The Electroceramic Thin Film Group, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC 27695

  2. 2

    Electrical and Computer Engineering Department, North Carolina State University, Raleigh, NC 27695

Publication History

  1. Published Online: 26 MAR 2008
  2. Published Print: 1 JAN 2005

ISBN Information

Print ISBN: 9781574982350

Online ISBN: 9780470291252

SEARCH

Keywords:

  • conventionally;
  • metallization;
  • polycrystaline;
  • frequency;
  • stoichiometric

Summary

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 LaAlO3 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 Ba0.75Sr0.25TiO3 (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 Ba0.75Sr0.25TiO3 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/cm2 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.