Fabrication of organic PVP doping-based Ba0.5Sr0.5TiO3 thick films on silicon substrates for MEMS applications

Barium strontium titanate (BaxSr1−xTiO3, BST) films have been used to develop microwave devices, microsensors, and RF MEMS devices due to the tunable dielectric properties, high dielectric constant, and low loss tangent. However, the most commonly used sol-gel method for BST film preparation has the problem of crack formation. This paper presents a modified sol-gel method to realize crack-free thick films on silicon substrates. The method uses organic macromolecular poly(vinlypyrrolidone) (PVP) dispersed uniformly into the sol-gel precursor solution to avoid crack formation. Due to the hybrid effect of PVP, thick films with thickness up to 1 μm can be achieved by multiple repetitive spin coating and sol-gel method. The preparation process is given in detail, and the effects of PVP and anneal temperature on the maximum film thickness are discussed. The thick films are characterized at frequencies up to 26.5 GHz by using coplanar waveguides. Experimental results show that this method is effective in preparing BST thick films, in particular for porous BST thick films for sensor and RF MEMS applications.