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1 Jan 2002

Volume 91, Issue 1, pp. 1-547

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Material and electrical characterization of carbon-doped Ta2O5 films for embedded dynamic random access memory applications

K. Chu, J. P. Chang, M. L. Steigerwald, R. M. Fleming, R. L. Opila, D. V. Lang, R. B. Van Dover, and C. D. W. Jones

J. Appl. Phys. 91, 308 (2002); http://dx.doi.org/10.1063/1.1418420 (9 pages) | Cited 18 times

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This work is a systematic study of carbon incorporation in Ta2O5 and its effect on the material and electrical properties of Ta2O5, a promising replacement for silicon oxide in embedded dynamic random access memory applications. Using pulsed-dc reactive and rf-magnetron sputtering of Ta2O5 performed in an argon/oxygen/carbon-dioxide plasma, we have methodically doped the Ta2O5 films with carbon. In thick (70 nm) Ta2O5 films, an optimal amount (0.8–1.4 at. %) of carbon doping reduced the leakage current to 10−8 A/cm2 at +3 MV/cm, a four orders of magnitude reduction compared to a leakage current of 10−4 A/cm2 in an undoped Ta2O5 film grown in similar conditions without CO2 in the plasma. This finding suggests that carbon doping can further improve the dielectric leakage property at an optimal concentration. X-ray Photoemission Spectroscopy analysis showed the presence of carbonate (carbon bonded to three oxygen) in these electrically improved carbon-doped films. Analysis by high-resolution transmission electron microscopy and Nomarsky microscopy exhibited no morphological or structural changes in these carbon-doped thin films. Moreover, carbon doping showed no improvement in the leakage current in thin (10 nm) Ta2O5 films. This phenomenon is explained by a defect compensation mechanism in which the carbon-related defects remove carriers at low concentrations but form a hopping conduction path at high concentrations. © 2002 American Institute of Physics.
Show PACS
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Cd Deposition by sputtering
84.30.Sk Pulse and digital circuits
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
77.55.-g Dielectric thin films

Perovskite stabilization and electromechanical properties of polycrystalline lead zinc niobate–lead zirconate titanate

Huiqing Fan and Hyoun-Ee Kim

J. Appl. Phys. 91, 317 (2002); http://dx.doi.org/10.1063/1.1421036 (6 pages) | Cited 64 times

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The perovskite structure of Pb(Zn1/3Nb2/3)O3 (PZN) ceramics was stabilized by adding a Ti-rich side tetragonal Pb(Zr0.47Ti0.53)O3 (PZT) across the morphotropic phase boundary (MPB). The 0.5 PZN–0.5 PZT specimen was found to have a two-phase zone, having a high piezoelectric coefficient, d33 (430 pC/N), an electromechanical coupling factor, kp (0.67), a field-induced strain, S (0.24% at 2 kV/mm), and a remnant polarization, Pr (27 μC/cm2). A phase transition from a rhombohedral to tetragonal phase occurred when a relatively low electrical field was applied to the specimen. This transformation occurred only when the rhombohedral phase coexisted with an equal amount of the tetragonal phase of the perovskite structure. Small rhombohedral domains, which were present around the relatively large tetragonal domains, transformed as a result of the applied field. The excellent electromechanical properties at the MPB composition are attributed to this phase transition in the PZN based ceramics. © 2002 American Institute of Physics.
Show PACS
77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
77.22.Ej Polarization and depolarization

Voltage shift phenomena in a heteroepitaxial BaTiO3 thin film capacitor

K. Abe, N. Yanase, T. Yasumoto, and T. Kawakubo

J. Appl. Phys. 91, 323 (2002); http://dx.doi.org/10.1063/1.1426249 (8 pages) | Cited 16 times

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Voltage shift phenomena of the hysteresis loop were characterized for a c-axis oriented heteroepitaxial BaTiO3 film by means of switching current measurements using various types of pulse sequences. During application of voltage, the hysteresis loop gradually shifted along the voltage axis according to the polarity of the voltage. Even after the application of voltage, while the top and bottom electrodes were short-circuited, the hysteresis loop continued to move. Under certain conditions, a part of the hysteresis loop shifted back, whereas the rest shifted forward. These results were explained, assuming that there is a nonswitching layer between the ferroelectric layer and the bottom electrode, and that the discontinuity of polarization can be compensated by injection of negative charges from the electrode. It was suggested that the nonswitching layer is possibly formed by relaxation of lattice misfit strain in the heteroepitaxial ferroelectric thin film. © 2002 American Institute of Physics.
Show PACS
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Layered planar capacitor based on BaxSr1−xTiO3 with variable parameter x

O. G. Vendik, S. P. Zubko, S. F. Karmanenko, M. A. Nikol’ski, N. N. Isakov, I. T. Serenkov, and V. I. Sakharov

J. Appl. Phys. 91, 331 (2002); http://dx.doi.org/10.1063/1.1421035 (5 pages) | Cited 5 times

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The temperature dependence of a capacitance of a planar capacitor based on Ba1−xSr1−xTiO3 (BSTO) films was investigated and some anomalies were observed. It was experimentally found that the barium concentration decreased across the film thickness in the direction from film/substrate interface to the film surface. The barium concentration, x, of BSTO films grown on sapphire (r-cut) substrates changed from x=0.52 on the film/substrate interface to x=0.3 on the film surface. The investigated films should be considered as a multiphase composition with different phase transition temperatures. The phenomenological model of dielectric response of the film structure has been suggested, which served as a basis for introducing an effective dielectric permittivity of the layered film. © 2002 American Institute of Physics.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
68.55.-a Thin film structure and morphology
77.80.B- Phase transitions and Curie point

Effects of La doping on the cubic–tetragonal phase transition and short-range ordering in PbTiO3

Tae-Yong Kim, Hyun M. Jang, and Seong M. Cho

J. Appl. Phys. 91, 336 (2002); http://dx.doi.org/10.1063/1.1421206 (8 pages) | Cited 8 times

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Effects of cation-site vacancies on the characteristics of the cubic–tetragonal displacive transitions in La-modified PbTiO3 (PLT) were studied using in situ XRD measurements and Raman scattering. For this purpose, two distinct types of PLT series having cation-site vacancies either at the A site (PLT-A) or at the B site (PLT-B) were separately prepared. The PLT-A series exhibited normal ferroelectricity and underwent the cubic-to-tetragonal structural transition for La substitution up to 30 at. %. Contrary to this, the PLT-B became a typical relaxor with the absence of the macroscopic cubic–tetragonal transition. However, for both types of PLTs, Raman-forbidden bands appeared in the high-temperature cubic-phase field at 30 at. % La modification. These observations were attributed to the formation of short-ranged clusters with tetragonal symmetry in a globally cubic matrix and to the reduced dipolar interaction between the clusters in the PLT-B, as compared with the PLT-A. © 2002 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
77.22.Gm Dielectric loss and relaxation
64.70.K- Solid-solid transitions
78.30.Hv Other nonmetallic inorganics
61.72.J- Point defects and defect clusters
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Modeling of laser-induced avalanche in dielectrics

S. R. Vatsya and S. K. Nikumb

J. Appl. Phys. 91, 344 (2002); http://dx.doi.org/10.1063/1.1421207 (8 pages) | Cited 5 times

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A study of the dependence of the laser-induced avalanche behavior on the intensity of irradiation in dielectrics is carried out. The avalanche rate is computed directly from the reduced equations, instead of the time dependent kinetic equations, thereby requiring less computational effort. For comparison, the calculations were carried out for both the flux-doubling model and the linear Fokker–Planck type equation for fused silica material. The flux-doubling model overestimates the avalanche rate by about 8%–10%. The properties of the equations describing the avalanche behavior indicate a nonlinear dependence of the avalanche rate on the intensity. The results for fused silica show an almost linear dependence in the high intensity range from about 1 TW/cm2 to infinity, and in the low intensity range up to about 0.01 TW/cm2, but a significant departure from linearity at the intermediate intensities. For a Gaussian pulse, the exponential growth rate of the electron density distribution in the avalanche regime is still almost directly proportional to the instantaneous fluence. Although the proportionality constant increases with increasing peak intensity, the difference is negligible in the high and low intensity ranges. © 2002 American Institute of Physics.
Show PACS
77.22.Jp Dielectric breakdown and space-charge effects
72.40.+w Photoconduction and photovoltaic effects
73.50.Fq High-field and nonlinear effects
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