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Method for Reducing Friction in Scanning Probe Arrays

IP.com Disclosure Number: IPCOM000074315D
Original Publication Date: 2005-Feb-23
Included in the Prior Art Database: 2005-Feb-23
Document File: 9 page(s) / 1M

Publishing Venue

IBM

Abstract

An activated or intermittent contact read and write technique for a probe storage device is introduced. In such a scheme the array chip is mounted on the scanning system such that the tip-apexes are close to the surface of the media (approx. < 500nm) but not in contact with the media. Two modes of operation are then possible. In the first mode of operation a DC voltage is applied between the substrate carrying the storage media and a group of cantilevers which are to be used for reading or writing. The resulting electrostatic force acting on the cantilevers causes them to move into contact with the storage media allowing these cantilevers to be used for reading or writing data using the same technique as in the pre-bent cantilever implementation. In the second possible mode of operation, the tip of a given cantilever is brought into contact in order to read or write an individual bit and then released again from contact while the scanner moves the media to the next bit position.

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Method for Reducing Friction in Scanning Probe Arrays

In scanning probe array based storage systems, frictional forces acting between the probe tip and the sample result in significant problems. In the current state of the art, the cantilevers in an array are pre-bent out of the plane of the surface of the array by depositing a thin film of stressed silicon nitride at the base of the cantilever. This prebending ensures that when the array is brought into contact with a substrate carrying the storage media, the tips mounted on the end of the cantilevers come into contact with storage media before any of the other topographic features on the array such as the electrical interconnects. The tip apex height uniformity within an array together with the spring constant of the cantilever determines the force on the tip of each cantilever when it is in contact with the storage media, i.e. a minimum average preloading force (or displacement) is required in order to ensure that all tips are in contact with media. Variations in the tip apex height uniformity are dominated by variations in the length of the tip and variations in the cantilever prebending and are expected to increase with increasing array sizes. Controlling the tolerances on these parameters in a manufacturing environment is expected to be challenging (i.e. expensive) and to impact device yield. Controlling and/or minimizing the magnitude and variations in this preloading force are important as it impacts the storage density that can be achieved as well as the friction force acting between the tip and media. Note that the tip-media friction increases with increasing load.

As mentioned above, friction forces acting on the tip result in many problems. On the individual tip level, increasing friction results in increased media and tip wear. In the current approach this is a rather severe problem as all tips are always in contact with the media, such that when data is written or read with a sub-group of the array wear due to friction also occurs on all of the inactive levers. A second problem that arises due to friction involves tracking of the cantilevers during reading and writing. On the individual cantilever level, high levels of friction can result in a slip-stick type of motion of the tip relative to the media making it more difficult to write straight lines of evenly spaced bits and also making it more difficult to readback written data. The cumulative effect of the frictional forces acting between all the tips in the array and the storage media can give rise to a slip-stick type of behavior in the media scanning system. Friction in the scanning system adds complexity to the design of the servo compensator system, and may also impact power consumption in the scanner for very large arrays with high levels of friction.

The problems described above can be significantly reduced through the use of an activated or intermittent contact read and write technique. In such a scheme the...