Crystallization Rate and Thermal Stability of Te-Based Alloy Thin Films for Erasable Optical Recording
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CRYSTALLIZATION RATE AND THERMAL STABILITY OF TE-BASED ALLOY THIN FILMS FOR ERASABLE OPTICAL RECORDING R.C. ROSS, D.A. STRAND, E.J. BJORNARD, and J.P. DeNEUFVILLE Energy Conversion Devices, Inc., 1675 West Maple Road, Troy, Michigan 48084 ABSTRACT Erasure speed and thermal stability of a number of Te-based alloys have been measured and compared. A distinct trend of increasing crystallization temperature, Tx, and increasing minimum time required for crystallization, Films which Tx, with increasing crosslinking element content is observed. crystallize to form Te are stability limited at Tx=80°C for Tx2lvsec. Films which crystallize to form Sb 4 0 Te4 5Se 1 5 have Tx1600C at Tx=lpsec. Static tester recrystallization kinetics and direct observation of cycled tracks by optical and electron microscopy indicate that recrystallization occurs via epitaxial growth from peripheral crystallities and not from internally dispersed nuclei for all materials studied. Thus, crystallization speed is limited by three factors: the intrinsic maximum crystallization velocity of the pure crystal, the diffusion rate of crystal-insoluble crosslinking elements away from the crystallization front, and the geometry of the amorphous and peripheral crystalline zones. INTRODUCTION Reversible amorphous-crystalline phase change optical recording was conceived by Ovshinsky in the late 1960's [1]. A growing interest in applications of this effect is reflected in recent publications [2-8]. Two important issues for a recording material are related to the crystallization characteristics of amorphous spots: the maximum rate at which intentional
crystallization or erasure can occur (T g
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