Bidirectionally propagating fast access bubble memory chips

Bidirectional propagation bubble memory chips have been successfully realized as 78 kb memory chips with 3μm bubbles and 14μm period symmetrical Y-Y propagation patterns. The chips are markedly characterized with the following functional patterns: (1) Transfer gate Ni-Fe patterns with complete symmetry. (2) Operation with no guard rail pattern around the memory area. (3) Collapsing type bubble annihilator. Chips are mainly fabricated in dry etching processes on an (YSmLuCa)3(FeGe)5O12LPE garnet film. Bias field operation margins greater than 18 Oe have been obtained for all functions, including bidirectional bubble propagation in minor loops in a 50 Oe rotating field at 300 kHz within a 0-100°C temperature range. Operation with no guard rail at all is guaranteed by the employment of a thin Ni-Fe detector, set in a major loop, and the collapsing annihilator. The detector, gives an output voltage of 14 mV/2mA at 25°C and -0.29%/°C temperature coefficient. A 64 kB memory system, capable of bidirectional accessing, has been developed using the 8 chips in four 128 kb modules. An average access time of 0.4 msec has been obtained.