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Squarylium Structures for Optical Recording

IP.com Disclosure Number: IPCOM000052459D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 4 page(s) / 45K

Publishing Venue

IBM

Related People

Jipson, VB: AUTHOR [+2]

Abstract

There is a great deal of interest at the present time in materials appropriate for use in optical data storage systems. The bulk of this effort over the last few years has been concentrated on materials that can be thermally ablated using a tightly focused laser beam. To date the majority of this work has dealt with tellurium and tellurium-based alloys because of their unique thermal properties. Other thin film metals and alloys have also been studied, but tellurium-based systems show the most promise to date. More recently organic-based systems, such as neat dyes and dye- or carbon-loaded polymers, have been explored.

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Squarylium Structures for Optical Recording

There is a great deal of interest at the present time in materials appropriate for use in optical data storage systems. The bulk of this effort over the last few years has been concentrated on materials that can be thermally ablated using a tightly focused laser beam. To date the majority of this work has dealt with tellurium and tellurium-based alloys because of their unique thermal properties. Other thin film metals and alloys have also been studied, but tellurium-based systems show the most promise to date. More recently organic-based systems, such as neat dyes and dye- or carbon-loaded polymers, have been explored.

A suitable optical storage material should meet several criteria simultaneously. The medium should have: (1) low writing energy, (2) archival lifetime, (3) low fabrication cost, (4) high readback signal to noise (i.e., low bit error rate), (5) high resolution and (6) writing sensitivity at the GaAs laser diode line.

The materials that best satisfy the above criteria to date are tellurium-based alloys. However, the lifetime of these materials is in question, and the optimized writing energy is near the cutoff of what can be done with a GaAs laser. Also, the fabrication cost of previously proposed tellurium-based structures is high.

We have identified a structure and medium which potentially satisfy the above criteria. Structures consisting of a squarylium dye, an organic or inorganic spacing layer and a mirror have been designed and fabricated. These structures are highly absorbing from 500-800 nm, and have writing energies comparable to tellurium films and excellent life expectancies. Further, since both the squarylium dye and the spacing layer can be either vacuum-deposited or solvent-coated, they offer fabrication versatility to permit low manufacturing cost.

The basic structure considered is shown in Fig. 1. This is a trilayer structure, as previously described in the literature, with a thin metal film 10, as the active layer, on spacer layer 11 deposited on mirror layer 12 on substrate 13. Due to the high optical absorption of squarylium dyes (Alpha approx.2x10/5/cm), it is possible to use them in this structure. For the design shown, up to 90% of the incident optical energy is absorbed in the active layer


10.

The following structure was tested for Fig. 2: Active Layer Squarylium dye approx. 30 nm

methyl or hydroxy

Spacer Shipley Company's AZ1350J

positive photoresist

Polysulfone approx. 90 nm

SiO(2)

Substrate Fused Quartz 1/2"

In Fig. 2, a measured reflectivity spectrum is shown for the structure of Fig. 1 using hydroxy squarylium as the active layer. It can be seen that at the design wavelength of 647.1 nm very little energy is reflected. The thickness of the

1

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spacing layer and the active layer can be varied to maximize the absorption at any wavelength throughout the absorption spectrum of the dye.

The sample fabrication is straightforward. The mirror 12...