Sputter Synthesis of Ferroelectric Films and Heterostructures
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ntroduction Ferroelectric films can display a wide nge of dielectric, ferroelectric, piezoectric, electrostrictive, and pyroelectric operties. The potential utilization of ese properties in a new generation of evices has driven the intensive studies n the synthesis, characterization, and etermination of processing-microstrucre-property relationships of ferroelecc thin films during the last five years. addition there has been an increased ive for integrating ferroelectric filmased heterostructures with different ubstrate materials to demonstrate nuerous devices that exploit the dielectric, rroelectric, piezoelectric, electrostricve, and pyroelectric properties of these aterials. For example the high dielectric ermittivities of perovskite-type mateals can be advantageously used in ynamic random-access memories DRAMs),1"3 while the large values of witchable remanent polarization of ferelectric materials are suitable for nonolatile ferroelectric random-access emories (NVFRAMs).1"3 Various vapor-phase deposition techques such as plasma and ion-beam putter deposition (PSD and IBSD, spectively), pulsed laser-ablation depotion (PLAD), electron-beam or ovenduced evaporation for molecular-beam pitaxy (MBE), and chemical vapor deosition (CVD) have been applied to prouce ferroelectric films and layered eterostructures. See References 4-7 for cent reviews. However, work is still ecessary to optimize the techniques to oduce device-quality films on large miconductor substrates in a way that is lly compatible with existing semiconuctor process technology. Therefore rearch efforts should be focused on the
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optimization of suitable process methods and on the investigation of processingcomposition-microstructure property relationships. These efforts are the focus of this article with emphasis on PSD and IBSD techniques. A manufacturing process for producing ferroelectric thin-film-based devices should at least include the following characteristics: (1) applicability of the processes to deposition of ferroelectric films and integration into devices, including production of as-deposited films with specific microstructures on substrates at the lowest possible temperature, (2) production of device-compatible, highly oriented or polycrystalline films and heterostructures with specific properties (e.g., fatigue-free for a large number of polarization switching cycles, long polarization-retention times, and no polarization-imprint effects), (3) ability to produce patterned structures, superlattices, and layered heterostructures in a reproducible way, and (4) simple and low-cost deposition processes with the capacity for high deposition rates. Plasma Sputter Synthesis and Characterization of Ferroelectric Thin Films and Heterostructures The PSD techniques described in this article are being developed both for use in research laboratories and for commercial production of thin-film-based devices. Basic phenomena occurring during the interaction of plasmas with the targets and substrates during film synthesis are importan
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