4Mb on-chip-cache bubble memory chips with 4 µm period ion-implanted propagation patterns

4Mb ion-implanted bubble devices (IIBD) with on-chip-cache organization (OCCO) have been designed for 1μm bubbles, and characterized for all functional elements in the devices. The 4Mb memory chip with 9.5×11.8 mm chip size consists of the same two 2Mb units, each of which is divided into 1Mb even and odd sites with 300 strorage loops (s-loops) and cache loops (c-loops), whose bit lengths are 4160 bits and 130 bits, repectively. Basic bit cell size is 4 × 4 μm. The 4Mb chip has an OCCO structure with the following distinguishing functional elements: (1) Bidirectional N-shape transfer gates. (2) A major line replicator with 2 crossed hairpin conductors. (3) DRO detector with folded thin NiFe elements. (4) A hairpin nucleation generator in a 240° super track. (5) Even bit minor loops. Operating margins for the 4Mb IIBD fabricated on (YSmLuBiCa)
3
(FeGe)
5
O
12
are well balanced in all functional elements, and obtained as 25 Oe, sufficient for practical use. It has been found that in-plane holding field applied to stop/start (s/s) direction is necessary for s/s stabilization, and that anisotropy along pattern edges due to stress relief acts a significant role for bit instability and for c-s gate operation. LPE film thickness has been optimized as 1.1 μm for 100-120 keV He+ implantation.