Patent GB-1367473-A (GB)
Title: Magnetic device using cylindrical magnetic domains
IPC: H03K19/168
Filed: 1971-12-03
Abstract: 1367473 Moving domain storage system INTERNATIONAL BUSINESS MACHINES CORP 3 Dec 1971 [31 Dec 1970] 55704/71 Heading H3B A moving domain magnetic storage system includes decoding devices for switching domains from one propagation channel to another. A complete memory system may be made on a single magnetic chip 10, as shown in Fig. 1, where the write decoder and the read decoder govern the passage of domains from generators 12 to a shift register loop memory 16 and from this memory to a detector 20 respectively. The domain generators 12 may be inhibited by current loop 22 to control the writing of "0" and "1", and the decoders are controlled by lines A, A, B, B connected to address and timing circuitry 24, 26. The latter also controls the rotating in-plane field H which propagates the domains. The detector 20 is preferably a magneto-resistive device as described in Specifications 1,334,603 and 1,358,546. A domain stabilizing bias field Hz is applied; this may be replaced by permanent magnetic layers exchange coupled to the chip surface. The basic switch of a decoder is shown in Fig. 2 where T and I bars define two propagation paths 36 and 38. Current loops 30 and 32 control the passage of domain 34 as the field H rotates. Suppose current is passed through loop 32, but not through loop 30. As the field rotates, the domain passes conventionally along path 36 until it reaches loop 32 whose field diverts the domain along path 42 until it reaches path 38 when it again moves to the left of the Fig. This forms an OR switch. If the loops 30, 32 are placed as in Fig. 2 they do not have to be insulated from the conductive T and I bars. A complete write decoder for four generators is shown in Fig. 3A, each generator having two associated paths like those of Fig. 2 between which domains may be switched. The generators may be rotating permalloy discs, or may be as described in Specification 1,367,288. The generator 12-0 has two paths 44A, 44B, the first being connected to the input of one of the shift registers in the subsequent memory (see Fig. 1) while the other terminates in a bubble buster 48A, 48B comprising permalloy bars on top of and below the chip to destroy the domain as in Specification 1,367,287. The control lines A, A, B, B control the OR switching as in Fig. 2. Thus if a domain is generated by generator 12- 0 it first passes control loop 22, assuming a "1'' is required, and then enters path 44A. It will then either propagate on this path to the associated shift register loop in the memory, or will be switched to path 44B and will terminate at the bubble buster. The complete system is shown in Fig. 5, where one of the shift register loops is detailed. This loop circulates domains in the direction of arrow 82 and has a bubble splitter 76 as described in Specification 1,367,287, as well as a bubble collapsing clear loop 90. The splitter 76 allows non-destructive reading of information in the register, one part of a split bubble remaining in the register and the other part passing to the read decoder. The clear loop 90 allows information to be erased. The read decoder is similar to that shown in Fig. 3A, and passes domains to detecting loops 74. These loops may be replaced by a single detector as in Fig. 1. The system may use other conventional propagation methods such as current loops, Fig. 4 (not shown), herringbone structures, or angel fish patterns in place of the rotating field. Closed loop shift registers are not essential. To minimize power consumption, bubble generators may be added at the end of the write decoder, so that only a single mother domain is passed through the decoder. The shift registers may be accessed singly or in blocks by appropriate control of the lines A, A, B, B.