MULTILEVEL AND THREEDIMENSIONAL NANOMAGNETIC RECORDING - Bio-Inspired and Nanoscale Integrated Computing - page 188

Patterned recording layer

Continuous recording layer

Recording head
Recording layer

Recording head
Recording layer

L

x-direction

T
(period)

(side band)

Patterned SUL Patterned SUL

(b) (c)

(a)

Figure 6.9. Drawings illustrating integration of a patterned SUL with (a) a
continuous recording layer and (b) a patterned recording layer. (c) A schematic
diagram of the cross-section of a convex patterned SUL in X-direction.

The recording and sensitivity fields remain well localized across the entire
thickness to generate a multitude of signal levels.

The period of the grid T in each direction corresponds to the bit cell dimension
in this direction and thus defines the effective areal density D as 1/T 2 (bit/in 2 )
(Fig. 6.9c). Below, it is shown that at a given grid period, the thickness of the
island, L, could relatively and sensitively control the advantageous effects of the
patterned SUL. To simplify the description, below the ratio of the grid period to
the island thickness L/T is arbitrarily defined as the pattern ''curvature.''
Increased SNR: Figure 6.10a illustrates the simulated perpendicular recording
field versus the distance along the line from the top surface of the patterned SUL
to the ABS of the head (from point s to point e in Fig. 6.10b) at saturation for
three ''curvature'' values of the patterned SUL. The three sets of three parameters,
T, P, and L, are 1) 98, 2, and 200 nm, 2) 98, 2, and 100 nm, and 3) 98, 2, and 25 nm,
for curvature values of 1, 2, and 4, respectively. Curvature values 1 and 4
correspond to the sharpest and flattest surfaces of the island, respectively. In all
these cases, the head is centered with respect to an island in the patterned SUL, as
shown in Figure 6.10b. For comparison, the solid black line in the figure shows an
equivalent field line for the case of a conventional flat-surface continuous SUL. A
pronounced increase of the recording field near the top SUL boundary could be
observed, especially for a curvature of 1. While in the case of a conventionally flat
SUL, the field reaches its maximum at the air bearing surface of the head, in the
case of a patterned SUL, the field reaches its maximum in the vicinity of SUL. The
recording field at SUL exceeds 30000 Oe, while at the air bearing surface of
the head it barely reaches 15000 Oe. For the conventionally flat SUL, the field is
less than approximately 12500 Oe when it reaches the surface of SUL. Such an
increase (by a more than a factor of two) of the recording field in the region of the
recording layer means that a recording media with substantially higher anisotropy
could be used and thus substantially higher recording densities could be achieved.
The fact that the field reaches its maximum at the side of the recording layer
farthest away from the ABS is especially favorable for 3D recording. As described
above, the most trivial form of recording across the thickness of 3D media could