Non-Contact Writing and Reading for High Density, Power-Efficient Storage/Retrieval Using Scanning Probes
Original Publication Date: 2005-Feb-23
Included in the Prior Art Database: 2005-Feb-23
This article relates to the way of operating probe storage devices. It is preferred to activate levers of probes for bringing in contact with the surface of a storage medium only at specified time-instances and for specified time-durations.
Non-Contact Writing and Reading for High Density, Power -Efficient Storage/Retrieval Using Scanning Probes
Contact recording is currently employed in probe-based storage devices, in which the information carrier is the presence or absence of indentations on a polymer recording surface. In such a storage device, a massive number of probes is employed, and the system is designed to operate with all probes in continuous contact with the recording surface, which is part of a x/y scanner. A probe typically comprises a lever and a tip. The probes are mechanically coupled to an array of probes.
There are several effects observed with the contact mode of operation: Since the probes (also referred to as levers) are in continuous contact with the recording surface, all levers experience continuous wear, even if they are not in use for a particular operation. Note that only a small fraction of all levers are electrically active at a certain time, mainly for limiting power consumption. Moreover, when a tip stays in contact with the recording medium for a long time, adhesion effects take place, and the tip gets contaminated by material on the medium. As a result, the resolution of writing and reading is reduced. It then becomes necessary to "clean" the tip to improve its resolution capability. The lever-array chip and the scanner have to be assembled together, in such a way that all levers are in contact with the recording surface on the scanner. The tolerances of this process are in the order of 100 nm of height uniformity over the entire lever array. Writing at very high densities is limited by interactions between adjacent indentations when they are placed very close to each other. The larger the area/volume of written indentations, the larger the interactions, for a constant distance between adjacent indentations. With contact recording, indentations tend to spread after they are formed on the polymer, thus occupying a large area. This effect limits the achievable storage density. In storage devices, the reliability of retrieved data is of paramount importance. Reliability is enhanced by error correction codes (ECC) and detection methods, but ultimately depends on the quality of the readback signal. With contact reading, at high storage densities, the readback signal-to-noise-ratio (SNR) may deteriorates, and interference between adjacent indentations (smearing of signals) may appear. Both effects can cause deterioration of detection performance, and thus loss of data reliability.
It is now preferred that the levers are not in contact when they are idle, resting at distances typically ranging between 100 nm to several micrometers from the recording surface. When a lever is activated, depending on the operation is performs, it is brought in contact with the surface at specified time-instances and for specified time-durations. Therefore, in applications where lever arrays are employed, only those levers that are activated during a specific o...