A direct liquid injection (DLI) metalorganic chemical vapor deposition (MOCVD) technique was devised to deposit ferroelectric lead zirconate titanate (PZT) films for the first time. By utilizing a cheap DLI precursor delivery system, the problems encountered in the conventional precursor delivery system by bubblers were eliminated. Highly uniform PZT films with a spatial variation in film composition of less than ± 3.0% were grown along a range of an 8 cm long substrate holder. The composition and thickness variation within 4 runs was less than ± 5% and ± 8%, respectively. The linear relationship between the composition in precursor solution and in PZT films makes the composition control very easy for the process of DLI-MOCVD preparation of PZT films. The growth temperature had the largest effect on various properties of deposited PZT films. PZT films with (111) orientation were easily deposited at a higher growth temperature while at a low growth temperature, PZT films with (001) orientation tended to form. The effect of annealing on the top electrodes was observed to have the hysterisis loop symmetric and to reduce the leakage current of PZT films. The present DLI-MOCVD grown PZT films showed good ferroelectric properties. Two-remanent polarization from 20 to 50 µC/cm² and two-coercive field from 60 to 100 Kv/cm can be easily obtained from these PZT films which have the thickness range from 300 nm to 1000 nm. The remanent polarization was affected by Lanthanum doping, which decreased from 25µC/cm² at 0% La doping to 12µC/cm² at 8% La doping. No obvious effects on the coercive field and the morphology were observed within these La doping ranges. The leakage current density of our PZT films was decreased as the growth temperature reduced. By reducing the growth temperature from 640°C to 590°C, the leakage current density was reduced one order of magnitude to 5 x 10⁻⁸ A/cm² at an electrical field of 100 Kv/cm. These films also showed high dielectric constants, about 700 for PLZT (4/34/66) and about 1200 for PLZT (4/55/45). The dissipation factors, tan 𝜕, for the above films were 0.023 and 0.03, respectively. The electrical fatigue of the typical PZT films showed 70% switched polarization remained after 10¹⁰ cycles. Surface etching by Ar ion bombardment and H-tetramethylheptadione or H(thd) was applied to get rid of possible PbO which is electrical conducting on the PZT films. No improvement on the leakage current of PZT films was observed. Lead excess from -25% to -10% in the precursor solution was found to produce the PZT films with the strongest (111) orientation and surface flatness. However the best electrical properties were only found in the lead concentration range of -10% to 10% in the precursor solution. PbO may not be the reason for the leakage current of the PZT films. Optical microscopy observation showed that gas phase reaction at higher growth temperature may be the reason for the leakage current of the PZT films. Both the leakage current and morphology were improved obviously by reducing the growth temperature. The non-homogeneous grains of the PZT films may be the other reason to lead the leakage current of our PZT films. Both stochiometry and non-stochiometry two-step-grown PZT films have shown significant improvement in the homogeneity of the grains of PZT films, which should have low leakage current. / Master of Science
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/41028 |
| Date | 13 February 2009 |
| Creators | Tao, Wei |
| Contributors | Materials Science and Engineering |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis, Text |
| Format | xii, 95 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 34230677, LD5655.V855_1995.T36.pdf |
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