Effects of spacer layer elastic properties on metallic thin film edge-induced stress gradients in bubble memory devices

It is well-known that metallization edge-induced stresses can change the uniaxial magnetic anisotropy of a liquid phase epitaxial (LPE) garnet film near the metallization edge. We have investigated this magnetostrictive interaction of patterned metallic films with ion-implanted LPE films by using several different spacer layers such as polyimide, SiO
2
, Si
3
N
4
, and combinations of polyimide and SiO
2
beneath a Cr-Cu-Cr conductor pattern. It is concluded that the stress eliminating capability of a spacer depends on the hardness parameter
K = \frac{E_{s}(1-\nu\min{f}\max{2})}{E_{f}(1-\nu\min{s}\max{2})}
where
E_{s} , E_{f}
are Young's moduli and
\nu_{s}, \nu_{f}
are Poisson's ratios for the spacer and metallic film, respectively. The polyimide spacer with
E_{s} < 10^{11}
dyn/cm
²
and with
K \leq 0.1
transmits an order of magnitude of smaller stress than a SiO
2
spacer with
K \geq 1
with the stress being more uniformly distributed across the spacer.