Noise factors in detection of minute marks by domain wall displacement

Causes of data errors by DWDD and dominant noise factors which determine the density are discussed. Dropout of data mainly occurs during readout by domain wall displacement at mark length less than 110 nm. The bit shift causes serious data error when window width is shorter than 70 nm. A novel method has been introduced to analyze the jitter by reading the signal many times for the same area and by averaging the waveform. The space-dependent jitter obtained by averaging is 8.8 nm and is greater than the time-dependent jitter of 6.7 nm caused by the shot noise, the laser noise, and the system noise as well as caused by the fluctuation of the domain wall displacement. Comparison with the ordinary structured MO media has revealed that a bit length of 77 nm will be available when the space-dependent jitter is reduced to 3.8 nm which is the value for ordinary structured media.