The comparison of lead β-diketonates as precursors in the CVD deposition of the ferroelectric, pyroelectric, and superconducting oxide films was presented in [[i]]. Vapor pressures, decomposition characteristics, and possible reaction mechanisms were investigated for various Pb β-diketonates in view of their application as precursors for growth of PbO thin films by CVD.
The crystal structures of lead (II) diketonates was presented in [[ii] ] The influence of ligand and crystal structure of the complexes on the thermal properties and volatility was discussed.
[i] V.V. Krisyuk, A.E. Turgambaeva, I.K. Igumenov, Chem.Vap.Dep. 1998, vol.4, Iss.2, p.43, Volatile Lead β- Diketonates as CVD Precursors, DOI:10.1002/(SICI)1521-3862(199803)04:02<43::AID-CVDE43>3.0.CO;2-J
[ii] V. V. Krisyuk, I. A. Baidina, I. K. Igumenov, Main Group Metal Chemistry, Band 21, Heft 4, pp. 199–206, ISSN (Online) 2191-0219, ISSN (Print) 0792-1241, DOI: https://doi.org/10.1515/MGMC.1998.21.4.199, ON THE CRYSTAL STRUCTURE AND SOME STRUCTURE-DEPENDENT PROPERTIES OF LEAD(II) β-DIKETONATES
Lead (II) acetylacetonate can be synthesized by direct reaction of lead (II) oxide and acetylacetone: PbO +2 acacH → Pb(acac)2)
Pb(acac)2 was reported to be used for CVD of Pb-containing layers, despite it has the lowest volatility among lead β –diketonates (volatility increases by increasing the steric bulk of the R group: [Pb(acac)2 ] < [Pb(dhd) 2 ] < [Pb(thd) 2 ] [12] due to the increased shielding of the highly positively charged metal center and reduction of intermolecular oxygen–metal interactions in the solid state. [[i]]
For instance,Pb(acac)2
was applied for the growth of c-axis oriented / epitaxial lead titanate PbTiO3 film on MgO(100) at a substrate temperature of ~280-300° C. The formed lead titanate film is provided with satisfactory dielectric and pyroelectric characteristic comparable
to or surpassing those of bulk material. Lead acetylacetonate Pb(C5 H7 O2)2 was evaporated 130° C (while its co-precursor Ti(OiPr)4 was evaporated at 70° C) and vapor mixture was carried to the reaction chamber by 3.2 sccm N2 carrier gas; 5.8sccm O2
oxygen was supplied to generate plasma of 0.3 W/cm2 of electric power; the CVD growth was carried for 0.5 h at 280° C/ 8.5×10-2
Torr pressure, forming a 2.2µ thick lead titanate PbTiO3 dielectric film on the MgO(100) substrate.. The grown film that the film was shown to be a PbTiO3 film having
perovskite crystal structure fully c-axis oriented (epitaxial growth). The grown PbTiO3 layers had a specific dielectric constant ε*/εo=92, a pyroelectric constant γ=3.4×10-8 C/cm2 K, tanδ* =0.01, and a specific resistance
value of 9.3×109 Ω.cm. [[ii]]
[i] Anthony C. Jones ON THE CRYSTAL STRUCTURE AND SOME STRUCTURE-DEPENDENT PROPERTIES OF LEAD(II) β-DIKETONATES
Vladislav V. Krisyuk, Iraida A. Baidina, Igor K. Igumenov, Main Group Metal Chemistry, Band 21, Heft 4, pp. 199–206, ISSN (Online) 2191-0219, ISSN (Print) 0792-1241, DOI: https://doi.org/10.1515/MGMC.1998.21.4.199.
, J. Mater. Chem., 2002, 12, 2576–2590 , Molecular design of improved precursors for the MOCVD of electroceramic oxides
http://www.chimica.unipd.it/gianandrea.rizzi/privata/documentazione/insegnamenti/Laboratorio%20di%20Preparazione%20e%20Caratt.%20dei%20Materiali%20I/TiO2_CVD.pdf
[ii] Eiji Fujii, Hideo Torii, Masaki Aoki , US5006363A,1988-12-08, Plasma assisted MO-CVD of perooskite dalectric films, https://patents.google.com/patent/US5006363A/en
Bis-1,1,1,5,5,5-hexafluoropentane-2,4-dionatolead Pb(hfac)2 (and for comparison Pb(thd)2 and lead bis-2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionate
Pb(fod)2) was syntzhesized, characterized, and shown to be applicable as precursor for MOCVD growth of lead-containing materials. [[i]]
[i] M.Azad Malik, P.O’Brien, M. Motevalli, A.C. Jones, T. Leedham, Polyhedron, 1999, Vol.18, Iss. 11, p. 1641-1646, « X-ray crystal structures of bis-2,2,6,6-tetramethylheptane-3,5-dionatolead(II) and bis-2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionatolead(II): compounds important in the metalorganic chemical vapour deposition (MOCVD) of lead-containing films » https://doi.org/10.1016/S0277-5387(99)00043-1,
Lead(II) hexafluoroacetylacetonate diglyme adduct Pb(hfac)2(diglyme) hfacH=1,1,1,5,5,5-hexafluoro-2,4-pentanedione, diglyme=MeO(CH2CH2O)2Me) was synthesized and characterized by NMR, mass spectrometry, elemental analysis and infrared spectroscopy. The complex has dimeric structure [Pb(hfa)2·diglyme]2 , as determined by the the single crystal XRD. The adduct has high volatility and good thermal stability with a low residue despite its dimeric nature, as determined by thermal analyses.
Pb(hfac)2(diglyme) has been successfully applied as precursor for the growth of PbO films by MOCVD. It was reported to be the first lead precursor that can be utilised in the liquid phase
without decomposition, thus resulting in constant evaporation rates even for long deposition times.[[i]]
[i]G. Malandrino, R. Lo Nigro, P. Rossi, P. Dapporto, I. L. Fragalà, Inorg. Chim. Acta, 2004, Vol.357, Iss.13, p.927-3933 , “A volatile Pb(II) β-Diketonate diglyme complex as a promising precursor for MOCVD of lead oxide films”, https://doi.org/10.1016/j.ica.2004.06.008
https://www.sciencedirect.com/science/article/pii/S0020169304002968
The structure of lead bis(2,2,6,6-tetramethylheptane-3,5-dionate) Pb(thd)2 was determined by single crystal XRD. Pb(thd)2 has a monomeric structure having chelating thd units distorted away from a stereochemically active lone pair of electrons at the Pb(II) centre. Pb(thd)2 was shown to be useful as a precursor for the growth of Pb-containing thin layers [[i]]
The thermal properties of lead bis(2,2,6,6-tetramethyl-3,5-heptanedionate)Pb(thd)2 were studied by TGA (Table ) [244]. It was found that Pb(thd)2 melts at 130°C, then the most of it evaporates before 305°C, but there some non-evaporated residue ( ~8%) remained.
Thermal
stability of Pb(thd)2 for it application as the Pb source for MOCVD of Pb-based ferroelectric films was investigated. By the TG-DTA at a heating rate of 10 K/min under N2 carrier gas , the endothermic peaks at 132 °C and complete evaporation by 300 °C
were found. No degradation of the sample occurred at temperatures 100-200 °C, according to isothermal mass loss analysis (for example, the specimen remained unchanged after being heated at 150 °C for 1800 h in a sealed vessel). However, at the actual MOCVD process conditions (150 °C over 1500 h), material degradation was detected, however at 140 °C no degradation was detected even after 2400 h. Under CVD operating conditions, at 150 °C, Pb(thd)2 continuously
decomposed, building decomposition products with a higher vapor pressure forming in the source container, what presents a characteristic feature of the MOCVD process using Pb(thd)2 evaporated using carrier gas from the source container. [[ii]]
[i] M.Azad Malik, P.O’Brien, M. Motevalli, A.C. Jones, T. Leedham, Polyhedron, 1999, Vol.18, Iss. 11, p. 1641-1646, « X-ray crystal structures of bis-2,2,6,6-tetramethylheptane-3,5-dionatolead(II) and bis-2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionatolead(II): compounds important in the metalorganic chemical vapour deposition (MOCVD) of lead-containing films » https://doi.org/10.1016/S0277-5387(99)00043-1
[ii] K. Nagashima, H. Funakubo, S. Seki, Y. Sawada, Y. Miura, N. Higuchi, H. Matchida, Chem. Vap. Dep. 2000 , Vol. 6, Iss. 6, p.311–314, « Thermal Stability of Pb(C11H19O2)2 Used as the Lead Source in MOCVD »
DOI: 10.1002/1521-3862(200011)6:6<311::AID-CVDE311>3.0.CO;2-N
http://onlinelibrary.wiley.com/doi/10.1002/1521-3862(200011)6:6%3C311::AID-CVDE311%3E3.0.CO;2-N/full
Pb(thd)2 has been applied as precursor for the growth of PbO films by laser-assisted CVD. [4]
Pb(thd)2 was applied as a precursor for the growth of lead oxides (α- and β-PbO) by MOCVD , by using water vapor as oxygen source. The addition of H2O resulted in
significant increase of growth rate at temperatures below 400 °C (for example, at 300 °C growth rate of 200 nm/h was achieved). Another important advantage of using water is film crystallinity improvement: α-PbO on MgO and
β-PbO on SrTiO3 were grown epitaxially at 380 °C at 300°C, respectively. According to XPS measurements, carbon contamination was undetectable. [[i]]
[i] S. V. Samoilenkov, Chem.Vap.Dep.., Vol. 12, Iss. 4, 2006 , p. 206–208, DOI: 10.1002/cvde.200504212
http://onlinelibrary.wiley.com/doi/10.1002/cvde.200504212/full , « MOCVD of Epitaxial PbO Films Below 400 °C Using Water Vapor »
Bis-tetramethylheptanedionato-lead Pb(thd)2 dissolved in ethylcyclohexane with O2 as oxidant was applied for the growth of lead oxide PbO thin films by liquid delivery MOCVD on Pt/SiO2/Si and Ir/IrO2/SiO2/Si substrates at substrate temperatures 475-525°C, in view of better understanding of the MOCVD behavior of ferroelectric Pb(Zr,Ti)O3 films. Good-quality lead oxide PbO films were grown on the Pt electrodes irrespective of the deposition temperature. However, on the Ir electrodes the growth was hampered by the in situ oxidation of the Ir film at deposition temperatures >500°C. At 525°C the deposited films grown contained metallic Pb components. The oxidation of the Ir layer and enhanced PbO layer growth with a smaller content of metallic Pb were achieved by using smaller oxygen flow.[[i]]
[i] J. Sh. Zhao, J. S. Sim, H. J. Lee, D.-Y. Park, Ch. S. Hwang, J. Electrochem. Soc. 2005, vol. 152, iss. 5, C277-C282, « A Study of Liquid Delivery MOCVD of Lead Oxide Thin Films on Pt and Ir Substrates », doi: 10.1149/1.1877953 , http://jes.ecsdl.org/content/152/5/C277.short
Lead magnesium niobate Pb(Mg0.33Nb0.66)O3 (PMN) is well known as a relaxor-based ferroelectric material, for applications including ferroelectric nonvolatile memory, capacitors, piezoelectric and pyroelectric devices due to quick polarization switching, high dielectric constant, excellent piezoelectric and pyroelectric properties. It is difficult to prepare the perovskite ingle phase PMN films without pyrochlore phase which, even in small quantities, decreases the dielectric constant and worsens ferroelectric and piezoelectric properties of the films. Pb(thd)2 was applied as precursor for the growth of thin layers of Pb(Mg0.33Nb0.66)O3 (PMN) and Pb(Mg0.33Nb0.66)O3-PbTiO3 (PMN-PT) on Si and Pt/Ti/SiO2/Si substrates by MOCVD using ultrasonic nebulization of precursor solution. Nearly single phase perovskite films were obtained at the composition of 80PMN-20PT, which showed a typical butterfly type C-V curve verifying the ferroelectricity; relative dielectric constant was ~60. [175, 176]
Pb(thd)2 has been applied as lead precursor for the growth of Pb(Sc0.5Ta0.5)O3 by direct liquid injection MOCVD, using a of a solution containing Sc and Ta precursors along with Pb(thd)2[4]
Pb(thd)2, combined with Zr2(OPri)6(thd)2 and Ti(OPri)2(thd)2, was successfully applied for the growth of Pb(Zr,Ti)O3 films with improved compositional uniformity by liquid injection MOCVD.
[[i]]
[i] A.C. Jones, T.J. Leedham, P.J Wright, D.J. Williams, M.J. Crosbie, H.O. Davies, K.A Fleeting, P. O’Brien, J. Europ. Ceram. Soc., 1999, Vol. 19, Iss 6–7, p.1431-1434, https://doi.org/10.1016/S0955-2219(98)00456-7, « Metalorganic chemical vapour deposition (MOCVD) of zirconia and lead zirconate titanate using a novel zirconium precursor »
Lead bis-tetramethylheptadionate (Pb(thd)2), combined with Ti(OEt)4 and Zr(thd)4), was applied as precursor for the deposition of thin
layers of lead titanate PbTiO3 and lead zirconate titanate (PZT) using hot-walled MOCVD. Dense, specular and highly transparent films were obtained; the properties of the resulting films were determined by XRD, SEM and UV-VIS-NIR spectrophotometry. Ferroelectric
properties for the PZT films (41% Zr, 9%Ti) annealed at 600 °C were following: spontaneous polarization Ps 23 μC/cm2, coercive field, Ec 65 kV/cm. [[i]]
[i] W.C. Hendricks, S.B. Desu, J. Si, Ch.H. Peng, MRS Symp. Proc, 1993 , Vol 310 (Symposium N – Ferroelectric Thin Films III), , 241, “Metallorganic Chemical Vapor Deposition (Mocvd) of Titanium-Based Ferroelectric Thin Films”, https://doi.org/10.1557/PROC-310-241 , https://www.cambridge.org/core/journals/mrs-online-proceedings-library-archive/article/metallorganic-cheamcal-vapor-deposition-mocvd-of-titaniumbased-ferroelectric-thin-films/F634AE94B2D58B4A2A6C791219D75CE1
Bis-2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionatolead Pb(fod)2 was synthesized and characterised by single crystal X-ray diffraction. It was determined that its structure is based on unusual dimers, having seven co-ordinate lead units bridged by the F atoms of the ligand.
Pb(fod)2 was demonstrated to be are useful as precursor
for the deposition of Pb-containing materials and their structures are useful in understanding their behaviour in materials deposition. [[i]]
[i] M.Azad Malik, P.O’Brien, M. Motevalli, A.C. Jones, T. Leedham, Polyhedron, 1999, Vol.18, Iss. 11, p. 1641-1646, « X-ray crystal structures of bis-2,2,6,6-tetramethylheptane-3,5-dionatolead(II) and bis-2,2-dimethyl-6,6,7,7,8,8,8-heptafluorooctane-3,5-dionatolead(II): compounds important in the metalorganic chemical vapour deposition (MOCVD) of lead-containing films » https://doi.org/10.1016/S0277-5387(99)00043-1
Lead bis(2,2,6,6-tetramethyl-3,5-octanedionate) Pb(tmod)2 was used for liquid injection ALD of Pb-Ti-O films (together with Ti(OiPr)2(thd)2 or Ti(OtAm)2(IBPM)2 and H2O as reactant)
at 240-300°C.[[i]]
[i] T. Watanabe, S. Hoffmann-Eifert, Ch. S. Hwang, R. Waser, J. Electrochem. Soc., 153 (9) F199-F204 (2006)
Liquid lead β-diketonates with ethereal group (ideally saturating the coordination sphere by intramolecular
coordination), among them Pb(tBuC(O)CHC(O)(CH2)3OMe)2 and Pb(MeC(O)CHC(O)(CH2)3OEt)2, have been tested as MOCVD precursors for PbO films. The nature of the tails and substituents of β-diketonates appeared not to be important for the formation of the liquid phase. The volatility and
thermal stability of the complexes was inferior to commercial solid complexes such as Pb(thd)2, probably due to the fact that the ehtereal “scorpion tails”
were not coordinated to the metal. Bulkier tBu-containing complex was unexpectedly less volatile than Me-radical containing complex, probably due to stronger interaction
between bulkier substituent and ethereal tail. The growth rates of PbO films with these complexes by MOCVD at 500°C/3Torr were correspondingly 0.17, 0.33 nm/min, much
lower than with Pb(thd)2 (2 nm/min).[[i]]
[i] J.T. Lim, J.C. Lee, W.I. Lee, I.-M. Lee, Bull. Korean Chem. Soc. 1999, Vol. 20, No. 3, p.355-361
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Pb(thd)4 ??? in combination with Mg, Nb, and Ti tetramethylheptanedionates was used as precursor for the growth of thin epitaxial films of Pb(Mg0.33Nb0.67)O3 (PMN) and Pb(Mg0.33Nb0.67)O3–PbTiO3 (PMN–PT) on (001) SrTiO3 and SrRuO3/SrTiO3 single crystal substrates at 700°C by the solid-source MOCVD method. (see Mg(thd)2). Pure PMN films were prepared using pre-mixed source material (5.5 eq. of Pb(thd)4, 1 eq. of Mg(thd)2 and 2 eq. of Nb(thd)4). Films were single phase perovskite according to XRD. Pb/Mg/Nb/O was 18% /7% /13% /62% by RBS. Films of PMN–10%PT and PMN–20%PT films had dielectric constants 1200–1500 and 600–700, respectively.
Pb(METHD)2, in combination with Zr(METHD) 4 and Ti(MPD)(METHD)2 ( mixed in a cocktail source dissolved in the ECH (ethylcyclohexane) solvent), was applied as zirconium precursor for the growth of ferroelectric Pb(Zr, Ti)O3 (PZT) thin films by liquid delivery MOCVD. Pb(METHD) 2 precursors had decomposition temperature around 300°C, close to the Zr and Ti precursors. The cocktail sources in the ECH solvent were perfectly vaporized above 280°C, and were stable at least for 6 months. The deposited films crystallized into perovskite PZT phase with appropriate composition, however undesirable PbPt x alloy admixture formed at the interface between bottom Pt electrodes and PZT layer at substrate temperature 550°C, reactor pressure 3 Torr, vaporizer temperature 280°C/ vaporizer pressure 115 Torr. The polarization properties of the deposited PZT thin films were not sufficient due to the formation of PbPt x layer.[[i], [ii]]
Pb(METHD)2 dissolved in a cocktail source together with Zr(METHD)4 , and Ti(MPD)(METHD)2 and was examined
for the growth of ferroelectric Pb(Zr, Ti)O3 thin films by liquid delivery MOCVD on 6-inch Pt/Ti/SiO2/Si wafers at 550∘C. PbPtx alloy phase existed in PZT films deposited at 500∘C was disappeared by post-annealing at 600∘C and the annealed film showed hysteresis properties with the 2P r of 56 μ C/cm2 and the 2E c of
181 kV/cm.[[iii] ]
[i] Y. Otani , N. Abe, Y. Ueda , M. Miyake , S. Okamura & T. Shiosaki , Integr. Ferroelectrics, An International Journal , Vol. 46, 2002 - Issue 1, p.115-124, https://doi.org/10.1080/10584580215398
[ii] Y. Otani , N. Abe, Y. Ueda , M. Miyake , S. Okamura & T. Shiosaki , Integrated Ferroelectrics, An International Journal, Vol. 51, 2003 - Issue 1, p.63-72, https://doi.org/10.1080/10584580390229824 , « Fabrication of Pb(Zr,Ti)O 3 Thin Films by Liquid Delivery MOCVD Using a Cocktail Source with Pb(METHD) 2 , Zr(METHD) 4 and Ti(MPD)(METHD) 2 «
http://www.tandfonline.com/doi/abs/10.1080/10584580390229824
[iii] Y. Otani, S. Okamura, T. Shiosaki, J. Electroceram., 2004, Vol. 13, Iss. 1–3, pp 15–22, “Recent Developments on MOCVD of Ferroelectric Thin Films”, https://link.springer.com/article/10.1007/s10832-004-5069-z