Compositional tailoring of the dielectric and ferroelectric properties of sol-gel derived PLZT thin films

Abstract

PZT films, especially PZT 53/47 films, have been intensively explored for a wide range of applications. A broad range of dopants can be incorporated fairly easily into PZT using sol-gel techniques, resulting in compositional tailoring of material properties. One important dopant is La, forming PLZT compositions which have a larger range of dielectric and ferroelectric properties than the PZT materials. To date, PLZT films have received less attention in electrical applications than PZT films in spite of the wider range of film properties achieveable with the former.

A series of sol-gel derived PLZT films was prepared on platinized Si wafers. Selected compositions were prepared covering the entire PLZT phase diagram, namely PLZT x/y/z with y/z = 20/80, 53/47 and 65/35 and x = 0, 2, 4, 6, 8, 10 and 12; and × = 7.5 with y/z = 0/100, 20/80, 65/35, 53/47, 35/65, 80/20 and 0/100. The films were spincoated on platinized Si wafers and fired to 650 – 700 C to convert them into single phase perovskite films. Top Pt dots were then sputtered to form monolithic PLZT capacitors which were later characterized extensively for their dielectric (dielectric constant, dielectric loss and leakage current) and ferroelectric (remanent polarization, coercive field, fatigue and retention behavior) properties. The PLZT films generally exhibited higher dielectric constants (e.g., up to 2600 for small signal values) and lower dissipation factors (e.g., 0.03) compared to values for PZT films (e.g. 1700 and 0.06 respectively measured for PZT 53/47 films at 1 kHz). The leakage currents can be as low as 3 × 10⁻⁸ A/cm² at 100 kV/cm applied field. These properties of sol-gel films are compared with those of films obtained through sputtering or other physical / chemical vapor deposition techniques and bulk properties of similar compositions.