ABSTRACT

INTRODUCTION Degradation properties such as low voltage breakdown, fatigue, and ageing of ferroelectrics have been pointed out as major problems of ferroelectric films af­ fecting lifetime. Although these properties have been studied for a long time, information is still insufficient for both quality improvement of ferroelectric devices and their lifetime predictions. Materials and fabrication techniques could be de­ veloped by brute force, but techniques for lifetime prediction cannot be developed without understanding degradation. Therefore, degradation mechanisms should be studied for lifetime prediction, as well as for material development. It is also desirable to improve degradation properties simultaneously. For this purpose, com­ mon source(s) of degradation should be understood and correlations among them should be studied. In this paper, general features and the mechanisms of individual degradation properties for ferroelectric materials are briefly reviewed and recent mechanisms for ferroelectric thin films are discussed in detail. Since ageing of ferroelectric thin films (based on the same electrochemical concept as ours) was extensively discussed by G. Arlt in his article entitled “Fatigue and Ageing” in this conference, only electrical degradation and fatigue are discussed in this paper. A semi-quantitative TDDB model is proposed and a quantitative fatigue model is discussed from the viewpoint of correlation studies. Fatigue properties of a fer­ roelectric thin film capacitor with a new electrode material (which was chosen on the basis of the fatigue model) are also presented in conjunction with its currentvoltage characteristics.