Sputtered films for display devices

Abstract

Sputter deposition techniques have been developed which yield directly usable films of transparent conductors and of photoconductors for display devices. These devices have been primarily light-valve structures incorporating a ferroelectric ceramic plate or a liquid-crystal layer as the control medium. The deposition techniques may be modified to allow deposition on a variety of substrates including thermally sensitive materials. Transparent electrodes of sputter-deposited In <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</inf> Sn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> O <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3-y</inf> (ITO) have been deposited on PLZT ferroelectric ceramics, glasses, and other substrate materials. These ITO films have excellent adherence and are hard but may readily be polished and etched. The visible-light transmission is excellent and the absorption in the near infrared is controlled by the conductivity. Films of resistivity of 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> Ω ċ cm have routinely been deposited on thermally stable substrates while film resistivity of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> Ω ċ cm may readily be obtained on thermally sensitive substrates. Sputter-deposited CdS, which has a peak photosensitivity near the 514.5-nm line of the Ar laser, has had a photoconductive gain of 4 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and a dark resistivity greater than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> Ω ċ cm. Similar sputter-deposition techniques have been used to fabricate device structures incorporating Cd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Zn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> S as the photoconductor. The Cd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Zn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> S composition has been varied to match film peak photosensitivity with laser emissions between 400 and 500 nm. These films have not been as photosensitive as CdS but they permit greater visible-light transmission, are sufficiently insensitive to projecting light sources so that they may be used in simultaneous read-write systems, and are capable of being used in real-time display systems. The dark resistivity of Cd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> Zn <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> S is dependent on composition but has exceeded 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Ω ċ cm in all films.