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Biaxial Magnetic Thin Film Memory System and Method of Making Films for Same

IP.com Disclosure Number: IPCOM000095757D
Original Publication Date: 1964-Jun-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 3 page(s) / 57K

Publishing Venue

IBM

Related People

Berkowitz, AE: AUTHOR [+2]

Abstract

The memory system has a biaxial thin film 10, made of, e. g., nickel, which has biaxial anisotropy due to the crystalline properties of substrate 12 on which it is disposed and not as a result of any magnetic interaction between magnetic film 10 and substrate 12. Substrate 12 can be made of nickel oxide disposed on a base or underlayer 14 of magnesium oxide. A first electrically conductive strip line 16 is placed over film 10 in a given direction. A second electrically conductive strip line 18 is placed over film 10 and strip 16 in a direction perpendicular to that of strip 16. Word line drive 20 is connected to strip 18 for selectively passing current pulses through this strip 18. A first switch 22 is operative to connect one end of strip 16 to either ground or to load 24.

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Biaxial Magnetic Thin Film Memory System and Method of Making Films for Same

The memory system has a biaxial thin film 10, made of, e. g., nickel, which has biaxial anisotropy due to the crystalline properties of substrate 12 on which it is disposed and not as a result of any magnetic interaction between magnetic film 10 and substrate 12. Substrate 12 can be made of nickel oxide disposed on a base or underlayer 14 of magnesium oxide. A first electrically conductive strip line 16 is placed over film 10 in a given direction. A second electrically conductive strip line 18 is placed over film 10 and strip 16 in a direction perpendicular to that of strip 16. Word line drive 20 is connected to strip 18 for selectively passing current pulses through this strip 18. A first switch 22 is operative to connect one end of strip 16 to either ground or to load
24. A second switch 26 is operative to connect the other end of strip 16 either to ground or to bit line drive 28.

The biaxial anisotropy is produced in film 10 by first growing epitaxially a single crystal (001) substrate 10 made of nickel oxide on a single crystal (001) underlayer 14 made of magnesium oxide at a temperature of about 600 degrees C. Upon cooling to a temperature below 250 degrees C, the nickel oxide distorts from a cubic lattice 28 to a slightly rhombohedral lattice twinning in the (100) and (010) planes or forming microscopic regions 30 and 32 related to each other crystallographically by a mirror plane. Nickel film 10 is evaporated onto the nickel oxide at room temperature in 10/-5/ Torr.

Film 10 is then annealed at about 260 degrees C or higher for about two minutes in 2 x 10/-6/ Torr.

When film 10 and substrate 12 are cooled to a temperature below 250 degrees C, substrate 12 again distorts from the cubic lattice to the rhombohedral lattice 30, 32 to produce compressive forces 34 in the nickel film 10 in the <110> direction in regions corresponding to the rhombohedral region 30 and compressive forces 36 in the nickel film 10 in the <110> direction in regions corresponding to the rhombohedral region 32. The compressive forces 34 and 36 produce easy axes 38 and 40, respectively. These are parallel to the direction of the compressive force a...