Processing and on-wafer test of ferroelectric film microwave varactors

Abstract

We present comparative characteristics of microwave variable capacitors (varactors) fabricated on Na0.5 K0.5 Nb O3 (NKN), Ag Ta0.5 Nb0.5 O3 (ATN), and Ba0.5 Sr0.5 Ti O3 (BST) ferroelectric films grown by rf-magnetron sputtering (NKN) and pulsed laser deposition (ATN and BST) techniques on the sapphire. Two port 2 μm finger gap coplanar waveguide interdigital capacitors (CPWIDCs) were defined on ferroelectric films surface by photolithographic lift-off technique. Deembedding method was employed to extract properties of CPWIDC from the S parameters measured in microwave range up to 40 GHz. BST films on sapphire substrates show superior tunability of 26% (20 GHz, 200 kVcm), whereas ATN films possess the lowest tan δ=0.06 at 20 GHz and extremely low dispersion of 4.3% in a whole frequency range of 45 MHz-40 GHz. © 2006 American Institute of Physics.