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In addition to exploring novel methods for writing, reading and
erasing data in thermomechanical probe recording, research is pursued
in the areas of coding, signal processing and read channel design.
In this context, it has been determined that a limiting factor in
the areal density that can potentially be reached in thermomechanical
probe storage is the intrinsic nonlinear interaction between closely
packed indentations. Upon this realization, the storage capacity
can be increased by applying (d, k)-constrained codes, similar to
the ones used in optical disc recording. The d-constraint in particular
is instrumental in limiting the interference between successive
indentations as well as in increasing the effective areal density
of the storage device.
Continuous advancements on probe-tip fabrication, storage medium
design, and improvements on the writing process and on the read
channel design has lead to the repeated realization of storage of
large amounts of data at densities higher than 1.0 Tb/in² and
reliable retrieval of the data at raw error rates better than 1E-4.
At these error-rate levels, conventional error-correcting codes
(ECC) can successfully correct all errors, guaranteeing that there
will be no loss of user data. These experimental results demonstrate
that the basic thermomechanical read/write process, with some new
improvements, is capable of achieving raw error rates that are suitable
for data-storage products, at extremely high densities. This marks
the first time that a probe-storage technology has reached this
level of technical maturity.
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IBM Research
