Bonding Strength of Conductive Inner-Electrode Layers in Piezoelectric Multilayer Ceramics

Multilayer ceramics in which piezoelectric layers of 0.90 Pb(Zr0.48Ti0.52)O3 -0.05 Pb(Mn1/3Sb2/3)O3 -0.05 Pb(Zn1/3Nb2/3)O3 (0.90PZT-0.05PMS-0.05PZN) stack alternately with silver electrode layers were prepared by an advanced low-temperature co-fired ceramic (LTCC) method. The electrical properties and bonding strength of the multilayers were associated with the interface morphologies between the piezoelectric and silver-electrode layers. Usually, the inner silver electrodes are fabricated by sintering silver paste in multi-layer stacks. To improve the interface bonding strength, piezoelectric powders of 0.90PZT-0.05PMS-0.05PZN with an average particle size of 23 μm were added to silver paste to form a gradient interface. SEM observation indicated clear interfaces in multilayer ceramics without powder addition. With the increase of piezoelectric powder addition in the silver paste, gradient interfaces were successfully obtained. The multilayer ceramics with gradient interfaces present greater bonding strength as well as excellent piezoelectric properties for 30~40 wt% of added powder. On the other hand, over addition greatly increased the resistance of the inner silver electrodes, leading to a piezoelectric behavior like that of bulk ceramics in multilayers.