Patent GB-1400961-A (GB)
Title: Magnetic bubble domain sensing device
IPC: H01L29/82
Filed: 1973-02-14
Abstract: 1400961 Magnetic field detection INTERNATIONAL BUSINESS MACHINES CORP 14 Feb 1973 [23 June 1972] 7130/73 Heading G1N [Also in Divisions H1 and H3] A device for sensing the magnetic field associated with a magnetic bubble domain, e.g. representing information, comprises a tunnel junction whose resistance changes with the field magnitude. When the field intercepts the junction the Fermi level of one or more of the materials forming the junction changes, altering the tunnel barrier height and hence altering the junction resistance; this latter change is detected by connecting a constant current or voltage across the junction and measuring the voltage or current respectively across the device. Fig. 7 shows part of a bubble domain sheet 10, on which are two electrodes 20A, 20B separated by a barrier material 18. If desired, the sheet 10 may be part of a magnetic disc or tape for non- bubble applications. The barrier 18, which is preferably less than 100Š thick, may be an insulator, a magnetic insulator, or a magnetic semi-conductor. In Fig. 8 a Schottky barrier is formed between a metal conductor 20A and a semi-conductor or magnetic semi-conductor 18. Fig. 9A shows a double Schottky barrier, a pair of metal contacts 20A, 20B and a pair of semiconductor or magnetic semi-conductor layers S1, S2 being used. The semi-conductors are preferably the same material, e.g. EuS, but have different doping levels. In Fig. 10A, (not shown), an insulating layer is placed between the two semiconductor layers of Fig. 9A, this insulating layer forming the tunnel barrier. In Fig. 11, (not shown) an insulating layer is used to form the barrier between a metal contact and a semi-conductor or magnetic semi-conductor layer. In Fig. 12 the magnetic domain sheet itself, which carries a domain propagating overlay 44 of conventional form, acts as a magnetic insulator between metal electrodes 20A, 20B. The sheet should be less than 100Š thick. Materials: the insulators may be oxides or lightly doped semi-conductors; the metal electrodes may be a highly doped semi-conductor (>10<SP>20</SP> carriers per cc) or, e.g. Indium. The embodiments using semi-conductors preferably employ materials doped in the range 10<SP>17</SP>-10<SP>21</SP> carriers per cc: magnetic semi-conductors which are usable are EuS, EuO, doped with trivalent rare earths or excess Eu to a level around 10<SP>19</SP> carriers per cc. CdCr 2  Se is an alternative magnetic semi-conductor. A magnetic conductor such as Al-Al 2 O 3 -Fe may be used as the metal electrodes, preferably near its Curie point. Magnetic insulators may be undoped EuS or EuO, or garnets. Example: A Schottky barrier between Indium and EuS is formed from single crystals of EuS having sulphur vacancies grown by melting and regrowth in a tungsten crucible. The crystal is vacuum cleaved and the Indium deposited during cleaving to avoid contamination. The second electrode is formed by diffusing a La-Ag alloy into the crystal. In these devices domain movement is not necessary to detection. Any domain having a field component along the sheet may be detected. The detector is the same order of size as the domain and is sensitive enough to detect sub-micron domains.