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15 Sep 2001

Volume 90, Issue 6, pp. 2635-3127

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Domain reversal and nonstoichiometry in lithium tantalate

Sungwon Kim, Venkatraman Gopalan, K. Kitamura, and Y. Furukawa

J. Appl. Phys. 90, 2949 (2001); http://dx.doi.org/10.1063/1.1389525 (15 pages) | Cited 77 times

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Recent studies have shown that lithium nonstoichiometry has a tremendous influence on domain reversal characteristics in ferroelectric lithium tantalate. This work presents a systematic study of the domain reversal characteristics such as threshold coercive fields for domain reversal, domain stabilization times, “backswitching” phenomena, domain switching and wall pinning times, and sideways wall mobility in near-stoichiometric LiTaO3 with Li/(Li+Ta)∼0.498. These properties are contrasted with those of congruent LiTaO3 [Li/(Li+Ta)∼0.485]. A qualitative model is proposed based on nonstoichiometric dipolar defects to explain the dependence of threshold coercive field on defect density, and on repeated field cycling, the origin of domain backswitching, and domain stabilization times. © 2001 American Institute of Physics.
Show PACS
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.66.Bi Elemental solids
61.66.Dk Alloys
77.80.Fm Switching phenomena

Highly conformal ZrO2 deposition for dynamic random access memory application

Jane P. Chang and You-Sheng Lin

J. Appl. Phys. 90, 2964 (2001); http://dx.doi.org/10.1063/1.1389756 (6 pages) | Cited 40 times

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ZrO2 is investigated in this work to replace SiO2 as the dielectric material in metal–oxide–metal capacitors in dynamic random access memory (DRAM) devices for its high dielectric constant, good thermal stability, excellent conformality, and large band gap. ZrO2 films were deposited on planar Si (100) wafers and patterned amorphous silicon cylinders by rapid thermal chemical vapor deposition process using a zirconium (IV) t-butoxide Zr(OC4H9)4 precursor and oxygen. At substrate temperature below 300 °C, no significant deposition was observed. At temperatures between 300 and 400 °C, the reaction is thermally activated with an activation energy of 29 kcal/mol, consistent with a β-hydride elimination mechanism leading to ZrO2 deposition. In this regime, one atomic layer of ZrO2 can be deposited after each alternating exposure to the precursor and oxygen, ideal for achieving conformal coverage of ZrO2 over high aspect ratio features. At temperatures above 400 °C, the deposition rate is less sensitive to temperature with an apparent activation energy of 4 kcal/mol due to decomposition and desorption of the precursors. Stoichiometric, uniform, and amorphous ZrO2 was obtained at all temperatures investigated. Highly conformal step coverage of the deposited ZrO2 was achieved on 300 nm×600 nm cylindrical features with an aspect ratio of 4. The dielectric constant of ZrO2 achieved in this work ranges from 15 to 18 depending upon process conditions and small capacitance–voltage hysteresis is observed, ideal for DRAM application. © 2001 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Dv Thermal stability; thermal effects
73.40.Rw Metal-insulator-metal structures
84.32.Tt Capacitors

Ferroelectric characteristics of oriented Pb(Zr1−xTix)O3 films

San-Yuan Chen and Chia-Liang Sun

J. Appl. Phys. 90, 2970 (2001); http://dx.doi.org/10.1063/1.1394159 (5 pages) | Cited 38 times

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Pb1.2Zr1−xTix)O3 (PZT) films with a variety of compositions were prepared by spin coating on Pt/Ti/SiO2/Si substrate with sol–gel processing. The roles of composition (phase) and orientation in ferroelectric properties of PZT films have been determined. The Zr-rich PZT films with (111)-oriented PZT films have a higher remanent polarization but also show a higher fatigue rate as compared to (100)-oriented films in both Zr-rich(65/35) and Ti-rich(35/65) PZT compositions. The lower fatigue rate of (100)-oriented film can be attributed to its easier reversible domain-wall motions compared to (111)-oriented PZT films due to the absence of internal field stress and less dependence on electrical field. A mode based on domain-wall contribution instead of film–electrode interface is favored to elucidate the role of orientation in fatigue characteristics of PZT films. © 2001 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
77.22.Ej Polarization and depolarization

Effect of neodymium (Nd) doping on the dielectric and ferroelectric characteristics of sol-gel derived lead zirconate titanate (53/47) thin films

S. B. Majumder, B. Roy, R. S. Katiyar, and S. B. Krupanidhi

J. Appl. Phys. 90, 2975 (2001); http://dx.doi.org/10.1063/1.1391416 (10 pages) | Cited 29 times

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The results of the studies on the effect of rare earth Nd doping on the phase formation behavior and electrical properties of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 (PZT) thin films are presented. The perovskite phase is obtained up to 5 at. % doping and beyond that pyrochlore phase was found to coexist with the perovskite phase in all the films. The transition temperature of undoped lead zirconate titanate (PZT) film was found to be reduced with Nd doping. The Nd doped films also exhibited typical relaxor-type behavior and a diffuse phase transition, similar to that observed in relaxor materials. The introduction of Nd into the PZT lattice probably introduces disorder in the B site of ABO3 lattice, which causes the observed dielectric relaxation. Efforts were made to isolate the irreversible component contributions in low field dielectric and high field polarization switching behavior. © 2001 American Institute of Physics.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena
77.80.B- Phase transitions and Curie point
77.22.Gm Dielectric loss and relaxation
77.22.Ej Polarization and depolarization

High temperature x-ray diffraction studies on antiferroelectric and ferroelectric phase transitions in (Pb1−xBax)ZrO3 (x=0.05,0.10)

Bhadra P. Pokharel and Dhananjai Pandey

J. Appl. Phys. 90, 2985 (2001); http://dx.doi.org/10.1063/1.1390308 (10 pages) | Cited 19 times

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We have carried out high temperature x-ray diffraction studies on (Pb1−xBax)ZrO3(PBZ) to correlate the large thermal hysteresis (∼100 °C for x=0.05) and irreversibility (for x=0.10) of the antiferroelectric (AFE)–ferroelectric (FE) phase transition observed in dielectric measurements with structural changes. It is shown that for both the compositions, the sequence of phase transitions during heating is orthorhombic antiferroelectric (AO) to rhombohedral ferroelectric (FR) and then to cubic paraelectric (PC). The wide phase coexistence region (∼80 °C for x=0.05 and ∼160 °C for x=0.10) and the arrest of the FR to AO transition for x=0.10 during cooling strongly indicate first order character of the AO–FR transition. It is shown that the transformation strains associated with the AO to FR transition increases with Ba2+ concentration from a value of 0.6% for x=0 to 0.9% for 0.10. Similarities of the AO–FR transition in PBZ with nonthermoelastic martensitic transformations are pointed out. The FR to PC transition is also shown to be first order but with a small thermal hysteresis (∼10 °C) and a small discontinuous change in the cell volume (∼0.5%). © 2001 American Institute of Physics.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point

Kinetics of polarization reversal in 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3: Heterogeneous nucleation in the vicinity of quenched random fields

Dwight Viehland and Jie-Fang Li

J. Appl. Phys. 90, 2995 (2001); http://dx.doi.org/10.1063/1.1383978 (9 pages) | Cited 31 times

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Polarization reversal and domain dynamics have been investigated in 0.7Pb(Mg1/3Nb2/3) O3–0.3PbTiO3 using a method of current transients. Investigations were performed as a function of applied electric field. The kinetics of the transients have been modeled to an equation of state for heterogeneous nucleation in the vicinity of random fields. Nucleation of polar clusters with a reversed polarization occurs under applied field in the vicinity of randomly quenched defects. © 2001 American Institute of Physics.
Show PACS
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.22.Ej Polarization and depolarization
64.60.Q- Nucleation
77.80.Dj Domain structure; hysteresis
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