Effects of N-H2doses in ion-implanted bubble memory test chips

Recently 0.5Mbit 8μm period bubble memory chips based on ion-implanted propagation patterns were reported. In these devices, made with (YSmLuCa)
3
(FeGe)
5
O
12
1.7μm bubble films, 270 keV neon implantation was done. In order to use a commercial implantation system, limited to 200 kV acceleration potential, we have tried 200 keV nitrogen for the medium depth implant in place of the 270 keV neon. We prepared devices with the 200/N and 130/H
2
doses increased proportionally in four steps over 2.7-4.0(10)
¹⁴
cm
^-2
and 2.0- 3.0(10)
¹⁶
cm
^-2
, respectively. We also used an unpatterned 80 keV neon implant of 1.0(10)
¹⁴
cm-2 as was done previously. This paper reports measurements on these devices of (1) perpendicular strain by x-ray diffraction and easy plane anisotropy by FMR vs annealing temperature and (2) bias ranges for propagation vs annealing temperature, drive field, and operating temperature. Annealing lowered the magnitude of the anisotropy and strain of the implanted layer. At a critical anisotropy field H
k
-4πM of about -1.5 kOe, major loop propagation failed. Although the margins change with annealing, the highest dosed devices continued to propagate after anneals of at least 375°C. Functionally complete circuits were processed at temperatures below 300°C and tested in wafer form at 50 kHz. With 40 Oe drive, the major loop and minor loops on test chips overlapped in bias by 24 Oe or better at 40°C for all four doses. At the temperature extremes of 0°C and 85°C, the overlap was ≥ 21 Oe.