Fatigue-free ferroelectric capacitors with platinum electrodes

Abstract

A SIGNIFICANT fraction of the computer memory industry is at present involved in the manufacture of non-volatile memory devices¹—that is, devices which retain information when power is interrupted. For such applications (and also for volatile memories), the use of capacitors constructed from ferroelectric thin films has stimulated much interest¹. In such structures, information is stored in the polarization state of the ferroelectric material itself, which should in principle lead to lower power requirements, faster access time and potentially lower cost¹. But the use of ferroelectrics is not without problems; the memories constructed to date have generally suffered from poor retention of stored information and degradation of performance ('fatigue') with use^1–3. Here we describe the preparation and characterization of thin-film capacitors using ferroelectric materials from a large family of layered perovskite oxides, exemplified by SrBi₂Ta₂O₉, SrBi₂NbTaO₉ and SrBi₄Ta₄O₁₅. The structural flexibility of these materials allows their properties to be tailored so that many of the problems associated with previous ferroelectric memories are avoided. In particular, our capacitors do not show significant fatigue after 10¹² switching cycles, and they exhibit good retention characteristics and low leakage currents even with films less than 100 nm thick.