The reliability in magnetoresistive random access memory (MRAM) write operation was investigated for both toggle and asteroid memory chips developed with 0.18μm CMOS process. Thermally activated magnetization reversal, being the dominant origin of the intrinsic write error, was studied theoretically and experimentally. For asteroid MRAM, the bit line or word line disturbing error on half selected bits was proved to have significant effect on the write operation margin, even in the ideal case free from bit-to-bit switching field distribution and the hysteresis loop shift. For toggle MRAM, on the other hand, the dominant origin of the error occurs for selected bits, although its impact is much smaller than in the case of asteroid MRAM. As was expected from the estimation based on the single domain model, more than 10mA operation margin with the error rate of <10−9, which is sufficiently small for semiconductor IC memory, was achieved for the toggle MRAM.
A fast computation method to correct for the proximity effect in electron-beam lithography is studied for practical uses. Formerly, to compute the proximity effect a double integral of two Gaussian distribution functions was applied. To save computation time and memory size, a simplified computation using the error function is discussed. In this solution the proximity effect correction is determined by two real multiplications, four subtractions and one addition. Not only beam intensity but also a pattern element size is considered in every pattern. A large pattern is divided into small sections. In this method, the computation time is proportional to the number of elements. It takes 105 minutes to compute 10 000 test pattern elements with a minicomputer. The experiment proves that the corrected pattern can be exposed as designed. This procedure has proven effective to design VLSI by using a minicomputer.
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