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Stretching the Duration of Thermal Pulses for Laser Beam Writing

IP.com Disclosure Number: IPCOM000076792D
Original Publication Date: 1972-Apr-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 34K

Publishing Venue

IBM

Related People

von Gutfeld, RJ: AUTHOR

Abstract

A chalcogenide memory element is shown. Writing is produced by shining a laser light through the transparent substrate at an appropriate amplitude, to produce an amorphous spot on a crystalline film by rapid heating and quenching. The cooling rate is determined essentially by the substrate and for a 5 nsec pulse, cooling occurs in approx. 5 nsec. In addition to the chalcogenide film there are two overlay films on the chalcogenide, one consisting of a poor thermal conductor such as MYLAR* on top of which is evaporated a thin layer of a refractory metal. This metal film is chosen to be highly absorbing at the laser frequency being used for writing and erasing.

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Stretching the Duration of Thermal Pulses for Laser Beam Writing

A chalcogenide memory element is shown. Writing is produced by shining a laser light through the transparent substrate at an appropriate amplitude, to produce an amorphous spot on a crystalline film by rapid heating and quenching. The cooling rate is determined essentially by the substrate and for a 5 nsec pulse, cooling occurs in approx. 5 nsec. In addition to the chalcogenide film there are two overlay films on the chalcogenide, one consisting of a poor thermal conductor such as MYLAR* on top of which is evaporated a thin layer of a refractory metal. This metal film is chosen to be highly absorbing at the laser frequency being used for writing and erasing.

Erasing occurs by shining the laser light on the metal which is sufficiently thick to absorb most of the incident light. The heat is now released slowly from the metal film via the MYLAR and thus the chalcogenide stays in contact with a heated reservoir for a time approx. equal to the time required for heat to travel a diffusion length in the MYLAR. The MYLAR acts as a high-resistance thermal path and causes the heated metal film to release its heat relatively slowly to the chalcogenide and quartz substrate, thereby allowing crystallization which normally requires hundreds of nanoseconds to occur. To obtain slow cooling rates of the metal film on the order of several hundred nsec, the MYLAR film thickness should be approx. 1-1.5 x 10/-5/ cm. The...