INTEGRATION OF FERROELECTRIC THIN-FILMS INTO NONVOLATILE MEMORIES

Recent advances in the development of high quality thin films of ferroelectric materials have created renewed interest in ferroelectric random access memory (FERRAM) devices. At the present time, several groups are pursuing the development of FERRAMs, where a thin film ferroelectric capacitor memory element is integrated either adjacent to or directly above the circuit elements in a standard silicon or gallium arsenide integrated circuit. However, these designs provide destructive readout (DRO) only. An alternative monolithic device concept, where the ferroelectric thin film is integrated directly into the semiconductor field effect transistor (FET) element, provides not only nonvolatility, but also nondestructive readout (NDRO). For DRO FERRAM structures, lead-zirconate-titanate is the most widely investigated material at present. At Westinghouse, we are concentrating our efforts on the NDRO ferroelectric memory FET approach, using barium magnesium fluoride (BaMgF4) and bismuth titanate (Bi4Ti3O12) thin films. In this paper, we shall review the current status of the integration of ferroelectric thin films into nonvolatile memory devices, with special emphasis on our own results using BaMgF4 and Bi4Ti3O12.