Charge Storage MISFET Memory Devices

Abstract

The critical processing parameters for fabricating MNOS nonvolatile charge storage devices are examined and methods for reliable process control are presented. A chemical technique has been found to be the best for preparing the ultra-thin gate oxide especially from the stand-point of reproducibility. This technique results in acceptable yields for LSI and facilitates the overall MNOS/LSI manufacturing process. Design and processing details for 256- and 2240-bit arrays are presented. The charge storage and transfer mechanism of the tunneling mode MNOS is analyzed in terms of device characteristics. A method for optimizing the gate dielectric structures is presented. P- and n-channel MAOS/LSI's, fabricated using pyrolytic aluminum oxide and tested via the tunneling and avalanche injection modes for charge storage, are described. The characteristics of three charge-storage MISFETs are summarized; these are the MNOS, MAOS and FAMOS devices. The advantages and disadvantages of these three device types are computed for nine different structures and operational modes.