This paper describes the methods used to evaluate and characterize MNOS arrays and includes test data on the most important parameters of such arrays from the standpoint of large systems. MNOS 256-bit and 2240-bit charge storage memory arrays are evaluated, primarily, in terms of switching speed, level separation uniformity across the chip, nonvolatility, adjacent word disturb during writing, and the effects of temperature and γ-radiation. For a 2240-bit array, a minimum level separation of more than 5 volts across the chip was obtained using a 30 volt pulse with a one millisecond pulse width for writing and erasing and a read cycle time of 500 ns. The information can be stored for more than 10 years. The adjacent word disturb was less than 3% after 20000 successive write-clear cycles and it was not cumulative. There was no degradation of the cell after 109 successive cycles. In the temperature range -55 to +125°C, there was little degradation in the writing, erasing and storage characteristics. Useful information can be stored at radiation levels of up to 5×105 Rads (Si). The window is completely closed after a dosage of 106 Rads (Si), in good agreement with the model developed during this study.
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.
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