A new method of optically reading domains in Bismuth Titanate for display and memory applications

Abstract

Three previously proposed methods of optically detecting ferroelectric domains in bismuth titanate (Bi <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> Ti <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> ) are reviewed and the merits of each discussed. A fourth method which is introduced involves a tilt of a natural crystal plate about the b axis and utilizes the difference in birefringence between domains. The major advantages of the new read method are its high efficiency and contrast and its insensitivity to the optical degradation or "depoling" which occurs after repeated polarization reversals. Resolution test patterns written into Bi <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> Ti <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</inf> crystals via a photoconductor film show up to 90 lines/mm resolution. In addition, photographic images have been stored, demonstrating a gray-scale capability.