Pulsed Laser Deposited KTN Thin Films for Microwave Applications

Abstract : Ferroelectric thin films are attractive materials for electrically tunable high frequency devices, via the variation of the dielectric permittivity driven by a dc voltage. Devices performances strongly depend on the ferroelectrics characteristics: Curie Temperature (Tc) which determines the use in the paraelectric or ferroelectric phase, permittivity , and losses. Integration of such materials implies the control of high quality thin films on substrates suitable for microwaves range. In this frame we investigated KTaxNb1-xO3 (KTN) compound which gives access to various Tc according to x, together with quite low losses. Thin films were epitaxially grown on MgO and LaAlO3 single crystals, as evidenced by x-ray diffraction (XRD). Influence of deposition parameters on thin films composition, orientation and microstructure will be discussed. Although films were epitaxially grown on both substrate a higher crystalline quality was achieved on LaAlO3 because of the better lattice mismatch: XRD rocking curves lin the range 0.5-0.8° were recorded on KTN films on LaAlO3, and around 1.2° on MgO. The response of gold interdigited capacitors realized by screen printing and patterning on KTN films grown on MgO versus an applied dc bias illustrates the potentiality of these compounds for microwaves frequency agility.