Microwave dielectric properties of W-doped Ba0.6Sr0.4TiO3 thin films grown on (001)MgO by pulsed laser deposition with a variable oxygen deposition pressure

The microwave dielectric properties of Ba0.6Sr0.4TiO3 1 mol% W-doped thin films deposited using pulsed laser deposition, are improved by a novel oxygen deposition profile. The thin films were deposited onto (001) MgO substrates at a temperature of 720 degrees C. A comparison is made between three different oxygen ambient growth conditions. These include growth at a single oxygen pressure (6.7 Pa) and growth at two oxygen pressures, one low (6.7 Pa) and one high (46.7 Pa). Films were deposited in a sequence that includes both a low to high and a high to low transition in the oxygen deposition pressure. Following deposition, all filins were post-annealed in 1 atm of oxygen at 1000 degrees C for 6 h. The dielectric Q (defined as 1/tan delta) and the dielectric constant, epsilon(r), were measured at room temperature, at 2 GHz, using gap oapacitors fabricated on top of the dielectric films. The percent dielectric tuning (defined as (epsilon(r)(0 V) - epsilon(r)(40 V))/epsilon(r)(0 V) x 100) and figure of merit (FOM) (defined as percent dielectric tuning x Q(0 V)) were calculated. The film deposited using the two-stage growth conditions, 6.7/46.7 Pa oxygen, showed a maximum Q(0 V) value with high percent dielectric tuning and gave rise to a microwave FOM twice as large as the single stage growth condition. The improved dielectric properties are due to initial formation of a film with reduced interfacial strain, due to the formation of defects at the film/ substrate interface resulting in a high Q(0 V) value, followed by the reduction of oxygen vacancies which increases the dielectric constant and tuning. (c) 2005 Elsevier B.V. All rights reserved.