Improved Micro-cantilevers for
AFM Thermo-mechanical Data Storage

Benjamin W. Chui, H. Jonathan Mamin*, Thomas W. Kenny
Bruce D. Terris*, Robert Ried*, Dan Rugar*
Timothy D. Stowe, Stephen C. Minne, Hyongsok T. Soh, Calvin F. Quate
Sung-taek Ju, Kenneth E. Goodson

Stanford University, California 94305

*IBM Almaden Research Center, San Jose, California 95120

A Stanford-IBM collaborative project funded in part by an
IBM Cooperative Fellowship

AFM Thermo-mechanical Data Storage is a data storage scheme invented at IBM in which tiny pits on a plastic disk represent digital data. ("AFM" stands for "Atomic Force Microscope.") At present, bit densities of 25 gigabits per square inch are achievable. A single-crystal silicon micromachined cantilever with a sharp tip can be used to write and read such data 0's and 1's. For reading, we are fabricating such a cantilever with an integrated deflection sensor. For writing, we are incorporating a heating element into the cantilever.


As can be seen from the diagram above, the tip of a cantilever is positioned over a spinning polycarbonate disk which has a melting point of about 120 degrees Celsius. When the tip is heated (as has been demonstrated with a laser pulse), it melts the polycarbonate upon contact, creating a tiny indentation. Heating can also be achieved with an integrated heater, eliminating the need for an external laser. The tip of the cantilever is kept in contact with the spinning disk by means of a very small loading force applied to the base of the cantilever. At a sufficiently small loading force, no wear occurs on either the tip or the disk. The indentations on the polycarbonate disk can be used to represent encoded digital data.


Bit reading depends on the piezoresistivity of the silicon cantilever. Heavily doped silicon exhibits piezoresistivity in that its resistance changes slightly under stress. Therefore a heavily doped cantilever can be used to sense indentations on a disk: whenever the tip rides over an indentation, the cantilever flexes one way or the other. The stress in the cantilever varies accordingly, and so does the resistance. These slight changes in resistance can be converted to voltage signals, amplified and processed to regenerate digital data.

This is a top-view photo of a fabricated cantilever. The cantilever is made of single-crystal silicon and is about 70 microns in length. It has an integrated piezoresistive deflection sensor.

This is an SEM image of a similar, but longer, cantilever:

The following is an SEM close-up image of the cantilever tip. The thickness of the cantilever is about 1 micron, and the tip is about 2 microns tall.

Project Outlook

Active research is continuing in AFM thermo-mechanical data storage. Collaboration on this program between Stanford and IBM is a good example of a partnership between academia and industry. Under this arrangement, Stanford's sophisticated semiconductor fabrication facilities (such as those in CIS, the Center for Integrated Systems) can be used to make advanced components for exploratory studies at IBM.

It is possible that very high bit densities at a low cost per bit can be achieved with AFM thermo-mechanical data storage. Furthermore, the use of cantilever arrays (see photo below) could directly improve the speed of data reading and writing through parallel operation. Finally, the basic technology behind micromachined cantilevers with integrated tips can be applied to other high-density data storage schemes as well.

Click here to see a listing of recent literature on AFM thermomechanical data storage or to download an animated video clip on the subject (courtesy of IBM Almaden Research Center).

Your comments are very welcome.

For further information, please email the following people:
Ben Chui at;
Prof. Thomas Kenny at;
H. Jonathan Mamin at;
Bruce Terris at;
Robert Ried at;
Daniel Rugar at

(Updated December 1995)