Distance-controlled tunneling transducer and direct access storage unit employing the transducer

Abstract

A distance-controlled tunneling transducer comprises a plurality of tunnel tips arranged in an array at a tunneling distance from an electrically conductive surface of a storage medium. Each tip is attached to a respective cantilever beam permitting the distance between each tip and the surface to be individually pre-adjusted electrostatically. Arranged in juxtaposition with each cantilever beam is an active control circuit for adjusting the tip-to-surface distance during operation of the storage unit, thus preventing crashes of the associated tip into possible asperities on the surface of the recording medium. Each control circuit is designed such that its operating voltage concurrently serves to pre-adjust its associated cantilever beam and to maintain the tip-to-surface distance essentially constant.

Description

BACKGROUND OF THE INVENTIONThe present invention relates to a distance-controlled tunneling transducer for use in a direct storage unit, having a plurality of tunnel tips arranged facing a recording medium. In particular the invention teaches improved gap control means for implementation in micromechanical techniques. The invention is also applicable to low-voltage field-emission environments where the gap dimension is somewhat larger in the tunneling regime. Therefore, where in the following description reference is made to tunneling phenomena, those skilled in the art will be able to easily apply what is said to field-emission phenomena as well.In the tunneling regime, the tip / surface distance typically is less than 2 nm, and in the field-emission environment, that distance is considered to be on the order of 20 nm. Small local deviations from planarity of the surface of the recording medium, say on the order of tenths of a nanometer, may result in relatively large changes of the ...

AI Technical Summary

Benefits of technology

A primary object of the present invention is to solve this problem by foregoing the idea of perfect feedback regulation, i.e. with zero error. Instead, an open loop circuit is provided which compensates for distance variations though less completely, but which is sufficiently simple to be easily integrated into a multiple-tip scanner head. The achievable reduction in distance variation as result of variation of the tip-to-surface distance typically is a factor of from 30 to greater 100. The result is relaxed manufacturing tolerance requirements with regard to flatness of the recording medium to values that can easily be maintained.

Problems solved by technology

Because of the fact that the operating distances in tunneling as well in in field-emission environments are so small, it may even happen that the tip crashes into a surface it and thus suffers damage, unless some measure is taken to maintain the tip-to-surface distance essentially constant.

While it is acknowledged that the idea has occurred to integrate the tunnel tip feedback loop into the semiconductor chip on which the tunnel tip is formed, it has turned out that conventional control circuitry for scanning tunneling microscope and field emission microscope applications is by far too complex and, hence, too bulky to be installed on the semiconductor chip if the chip is to carry a plurality of tips arranged in a small array.

Such a requirement would, however, impose undesirable constraints with regard to precision of manufacturing and alignment, as well as to the choice of materials for the recording medium.

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