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Material for Write Once, Read Only Memory

IP.com Disclosure Number: IPCOM000052458D
Original Publication Date: 1981-Jun-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 5 page(s) / 146K

Publishing Venue

IBM

Related People

Cohen, MS: AUTHOR [+3]

Abstract

Squarylium has been employed in the past as a photoconductor film on an aluminized MYLAR* substrate. Here, it is used as a means of providing contrast for an optical read-only memory. The squarylium covers reflective aluminum; where it is removed by a laser, light is reflected. We have shown that 532 nm light can be used to evaporate the film and leave the aluminized MYLAR as a reflective surface. The contrast ratio, R(A1)/R(Sq) between the treated and untreated surface is approx.15:1. This is the expected contrast ratio between a approx. 4-5% reflectance of a dielectric surface and the approx. 80-90% reflectance of aluminum. The squarylium film has a peak absorption coefficient of 2-4 10/5/cm/-1/ in the visible region. This means that a 300 Angstrom thickness wil absorb most of the incident light.

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Material for Write Once, Read Only Memory

Squarylium has been employed in the past as a photoconductor film on an aluminized MYLAR* substrate. Here, it is used as a means of providing contrast for an optical read-only memory. The squarylium covers reflective aluminum; where it is removed by a laser, light is reflected. We have shown that 532 nm light can be used to evaporate the film and leave the aluminized MYLAR as a reflective surface. The contrast ratio, R(A1)/R(Sq) between the treated and untreated surface is approx.15:1. This is the expected contrast ratio between a approx. 4-5% reflectance of a dielectric surface and the approx. 80-90% reflectance of aluminum. The squarylium film has a peak absorption coefficient of 2-4 10/5/cm/-1/ in the visible region. This means that a 300 Angstrom thickness wil absorb most of the incident light. Such a thin film, combined with the low evaporation temperature of 300 degrees C, means that relatively little energy is needed to evaporate the film. We have measured visible reflectance changes with 5 mj/cm/2/ and 10 mj/cm/2/ energy density incident on the surface of uncoated films, and 10 mj/cm on parylene-coated films (coated to protect squarylium from scratching).

The minimum spot size we have achieved so far is 5 Mum diameter. This is the spot size we expect theoretically from the optical system we used (f/10 system for 532 nm light). We expect no difficulty in producing 1 Mum or 0.5 Mum spots with appropriate microscope systems.

The high absorption coefficient of squarylium extends over the visible region (4500-8500 Angstrom) of spectrum and a GaAlAs laser could be used to make micron-size spots with data rates on the order of 10 MHz.

Computer simulations were made of the optical behavior of squarylium in a multilayer stack arrangement. The optical constants which were assumed for this material were n=1.5, k=1 at a wavelength of 550 nm, which corresponds to values reported in the literature.

An example of a multilayer stack which could be used is shown in Fig. 1a. Here, an aluminum underlayer is provided so that when a hole is ablated by the laser, the read beam will encounter a layer of high reflectivity, thus giving a high contrast ratio. The squarylium is covered by a thick layer with anindex of refraction n of about 1.5 in order to keep dust particles out of focus at the active material. In Fig. 2, the reflectivity of squarylium as a function of thickness is shown

It is seen that as the squarylium thickness is increased, the reflectivity rapidly falls, passes through a minimum, and then reaches a saturating value of about 0.1. The minimum corresp...