PZT ‘composite’ ferroelectric thick films

Thick-films of lead zirconate titanate ceramic have been fabricated at low-temperature using a modified sol-gel/ceramic powder technology termed the composite technique. In this process, a ferroelectric powder is suspended in an organometallic solution of the same composition, which is deposited either on metallic or platinised silicon substrates using spin-coating. Dielectric properties have been improved from values around 450–680 by incorporating a novel Cu2O/PbO liquid-phase sintering aid. Rheology studies were carried out to monitor ageing of both the organometallic solution and composite suspension. Over a trial period of 41 days, the organometallic solution was shown to remain stable. Tests further indicated solution stability down to −20°C. Such low temperatures may be experienced during transportation in large-scale manufacturing. By modelling such thick films as 0–3 composites, it is known that electric properties are enhanced with greater powder:solution ratio. This necessary greater loading has been achieved by adjusting the pH of the organometallic solution, allowing the zeta-potential developed on suspended particles to be increased. This considerably lowers the viscosity of the composite suspension and hence allows much greater powder loading. In this way, loadings of up to 2.5 g/ml have been achieved. Optimum permittivities and losses in sintered films of up to 680 and 0.01 have been measured on films 16 μm thick, with associated spontaneous polarisation of 19.8 μC/cm2 with 1.6 V/μm applied.