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17 Jan 2005

Volume 86, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 86, 033101 (2005); http://dx.doi.org/10.1063/1.1851002 (3 pages)

Kun Chen, Allen Taflove, Young L. Kim, and Vadim Backman
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Temperature dependence of the dielectric tunability of pyrochlore bismuth zinc niobate thin films

Alexander K. Tagantsev, Jiwei Lu, and Susanne Stemmer

Appl. Phys. Lett. 86, 032901 (2005); http://dx.doi.org/10.1063/1.1853533 (3 pages) | Cited 34 times

Online Publication Date: 7 January 2005

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The change in permittivity of bismuth zinc niobate (BZN) films with the cubic pyrochlore structure under an applied electric field was measured as a function of temperature. Dielectric measurements were performed using parallel-plate capacitor structures with Pt electrodes on sapphire substrates. The electric field tunability of the permittivity was weakly temperature dependent and increased with decreasing temperature up to the onset of dielectric relaxation. At temperatures below the onset of the dielectric relaxation (∼150 K at 1 MHz), larger electric fields were required to achieve the highest tunabilities. A simple model of hopping, noninteracting dipoles was not suited to describe the dielectric tunability of BZN thin films. A better description of the experimentally observed behavior at temperatures above the onset of the dielectric relaxation was obtained using a simple random-field model with hopping dipoles in a uniform distribution of random fields.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

Peculiar temperature aging effects on the piezoelectric constant of Pb(Mg1/3Nb2/3)O3‐PbTiO3 single crystal near the morphotropic phase boundary

Guisheng Xu, Xiaofeng Wang, Danfeng Yang, Ziqing Duan, Chude Feng, and Kai Chen

Appl. Phys. Lett. 86, 032902 (2005); http://dx.doi.org/10.1063/1.1840128 (3 pages) | Cited 2 times

Online Publication Date: 7 January 2005

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After temperature aging, peculiar changes of the piezoelectric response of 0.67 Pb(Mg1/3Nb2/3)O3‐0.33 PbTiO3 crystals appeared. The piezoelectric constant d33 of the (001)-cut crystals with TRT ∼ 35 °C abruptly rose more than 1000 pC/N in some regions after heat treatment at 65 °C for 12 h. For the (001)-cut crystals with TRT ∼ 74 °C, in spite of a fall of 40–100 pC/N after heat treatment at 65 °C for 12 h, the values of d33 rose 50–100 pC/N unexpectedly after the subsequent heat treatment at 85 °C for 4 h. The structure adjustment caused by the internal stress relaxation during heat treatment at T>TRT accounted for the enhancement of d33.
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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)
77.65.Bn Piezoelectric and electrostrictive constants
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
77.80.B- Phase transitions and Curie point
81.40.Gh Other heat and thermomechanical treatments
77.22.Ch Permittivity (dielectric function)

Effect of double-sided (Pb0.72La0.28)Ti0.93O3 buffer layers on the ferroelectric properties of Pb(Zr0.52Ti0.48)O3 thin films

Eun Sun Lee, Hyun Woo Chung, Sung Hoon Lim, and Sang Yeol Lee

Appl. Phys. Lett. 86, 032903 (2005); http://dx.doi.org/10.1063/1.1852086 (3 pages) | Cited 10 times

Online Publication Date: 7 January 2005

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We deposited the Pb(Zr0.52Ti0.48)O3 (PZT) thin films with single and double-sided (Pb0.72La0.28)Ti0.93O3 (PLT) buffers by using a pulsed-laser deposition method. With the PLT buffer layers, the remanent polarization values increased, and a remanent polarization value of 33.4 μC/cm2 was obtained when 10-nm-thick double-sided PLT buffer layers were used. While the coercive field of films slightly increased only with a single-sided PLT buffer, it decreased again by adding the top PLT buffer layer. The film with double-sided PLT buffer also exhibited good fatigue endurance after 109 switching cycles even without oxide electrodes, mainly because the accumulated charges were compensated at the interface junction between the PLT buffer layer and the electrode.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena

Formation and electrical properties of Ni1−xFex nanocrystals embedded in a polyimide layers for applications as nonvolatile flash memories

J. H. Kim, J. Y. Jin, J. H. Jung, I. Lee, T. W. Kim, Sung K. Lim, C. S. Yoon, and Y.-H. Kim

Appl. Phys. Lett. 86, 032904 (2005); http://dx.doi.org/10.1063/1.1850194 (3 pages) | Cited 38 times

Online Publication Date: 10 January 2005

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Self-assembled Ni1−xFex nanoparticles embedded in a polyimide (PI) matrix were formed by curing Ni1−xFex thin films with PI precursor layers. Transmission electron microscopy images and selected area electron-diffraction patterns showed that Ni1−xFex nanocrystals were created inside the PI layer. Capacitance-voltage measurements on Al/PI/nanocrystalline Ni1−xFex/PI/n-Si structures at 300 K showed a metal-insulator-semiconductor behavior with a large flatband voltage shift due to the quantum confinement effect of the Ni1−xFex nanocrystals in spite of the possible existence of a thick tunnel PI layer, and conductance-voltage measurements showed a broad conductance peak around the flatband voltage. The present results suggest that self-assembled Ni1−xFex nanocrystals embedded in a PI layer hold promise for potential applications in nonvolatile flash memories with floating gates consisting of Ni1−xFex nanocrystals embedded in a PI layer.
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81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Cd Deposition by sputtering
81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.37.Lp Transmission electron microscopy (TEM)

Thermal conductivity of porous media

James G. Berryman

Appl. Phys. Lett. 86, 032905 (2005); http://dx.doi.org/10.1063/1.1852718 (3 pages) | Cited 10 times

Online Publication Date: 11 January 2005

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An analytical formulation of Bergman–Milton conductivity bounds is used in a different way to obtain rigorous bounds on the real thermal conductivity of a fluid-saturated porous material. These bounds do not depend explicitly on the porosity, but rather on two formation factors—one associated with the pore space and the other with the solid frame.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Effect of NH3 surface nitridation temperature on mobility of ultrathin atomic layer deposited HfO2

Mohammad S. Akbar, Naim Moumen, Joel Barnett, Johnny Sim, and Jack C. Lee

Appl. Phys. Lett. 86, 032906 (2005); http://dx.doi.org/10.1063/1.1854194 (3 pages) | Cited 7 times

Online Publication Date: 12 January 2005

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Effect of NH3 predeposition anneal (pre-DA) temperature prior to ultrathin atomic layer deposition (ALD) HfO2 deposition (15–30 Å) on equivalent oxide thickness (EOT) and mobility of TiN/HfO2/Si metal-oxide field effect transistors has been studied systematically. At the same physical thickness, reduction of EOT by high temperature NH3 pre-DA treatment ( ∼ 900 °C) has been achieved, with no apparent change in Jg (leakage current density), though no significant channel mobility reduction could be observed. Increase in nitrogen content with pre-DA temperature improved overall dielectric constant and bulk trapping immunity, though slight mobility reduction was attributed to positive charge pile up at the interface. The ultrathin EOT ( ∼ 7.4 Å) with good mobility values sets ALD HfO2 as a very promising candidate for alternate gate oxide.
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85.30.Tv Field effect devices
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ch Permittivity (dielectric function)
73.50.Dn Low-field transport and mobility; piezoresistance
61.72.Cc Kinetics of defect formation and annealing
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Mechanism of polarization enhancement in La-doped Bi4Ti3O12 films

C. Y. Yau, R. Palan, K. Tran, and R. C. Buchanan

Appl. Phys. Lett. 86, 032907 (2005); http://dx.doi.org/10.1063/1.1849422 (3 pages) | Cited 19 times

Online Publication Date: 14 January 2005

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Bi4−xLaxTi3O12 (La-doped BIT, x = 0–0.6) thin films prepared by metalorganic decomposition method, were studied using x-ray diffraction (XRD), polarization hysteresis and Raman scattering techniques. The XRD and polarization studies showed that La substitution reduces structural distortion, relaxes internal strain and enhances polarization, while the Raman data indicate that the added La occupies mainly at A sites in the BIT films. Raman modes also indicate an increase in TiO6 symmetry, internal strain relaxation, lower Ti–O hybridization, and decrease in polarization along the a axis. Further, the polarization in the highly c-oriented BIT films significantly increases with the added La, hence a polarization tilt towards the c axis is implied. The higher polarization observed can be attributed, therefore, to microscopic changes involving decreased distortion in the TiO6 octahedra and a polarization tilt towards the c axis, caused by doping with the electronically less active ion (e.g., La, Y) onto the A sites in the BIT structure. This understanding is important to the commercialization of high-density ferroelectric random access memories.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.B- Phase transitions and Curie point
77.22.Gm Dielectric loss and relaxation
68.55.Nq Composition and phase identification
68.55.-a Thin film structure and morphology
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics

HfO2 high-κ gate dielectrics on Ge (100) by atomic oxygen beam deposition

A. Dimoulas, G. Mavrou, G. Vellianitis, E. Evangelou, N. Boukos, M. Houssa, and M. Caymax

Appl. Phys. Lett. 86, 032908 (2005); http://dx.doi.org/10.1063/1.1854195 (3 pages) | Cited 66 times

Online Publication Date: 14 January 2005

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Thin insulator films of the high-κ dielectric HfO2 are deposited on Ge(100) substrates by evaporating Hf in atomic oxygen beams after in situ thermal desorption of the native oxide in ultrahigh vacuum and subsequent treatment of the clean Ge surface in oxygen and nitrogen. It is shown that HfO2 forms atomically sharp interfaces with Ge and behaves as an excellent insulator with dielectric permittivity κ ∼ 25, which is close to the expected bulk value. Very low equivalent oxide thickness of 0.75 (±0.1) nm with a low gate leakage current of ∼ 4.5×10−4 A/cm2 at 1 V in accumulation is achieved. Strong frequency dispersion of the inversion capacitance and low frequency behavior of the high frequency capacitance–voltage curves is observed. This is attributed to a combined effect of a high generation rate of minority carriers due to impurity traps and the high intrinsic carrier concentration in Ge, which result in a short minority carrier response time.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.22.Ch Permittivity (dielectric function)
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.55.-g Dielectric thin films
68.43.Mn Adsorption kinetics
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Electron-trap centers in ZnO layers grown by molecular-beam epitaxy

D. C. Oh, T. Suzuki, J. J. Kim, H. Makino, T. Hanada, M. W. Cho, and T. Yao

Appl. Phys. Lett. 86, 032909 (2005); http://dx.doi.org/10.1063/1.1849852 (3 pages) | Cited 14 times

Online Publication Date: 14 January 2005

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We have investigated electron-trap centers in ZnO layers grown under different Zn∕O flux ratios by molecular-beam epitaxy. Frequency-dependent capacitance measurements show that ZnO layers grown under Zn-rich and stoichiometric flux conditions suffer from larger dispersion than a ZnO layer grown under an O-rich flux condition. Temperature-dependent capacitance measurements reveal that all the ZnO layers have shallow electron-trap centers ET1 and deep electron-trap centers ET2, while the Zn-rich ZnO layer has another shallow electron-trap center ET3 besides ET1 and ET2: the thermal activation energies of ET1, ET2, and ET3 are estimated to be 0.033–0.046, 0.12–0.15, and 0.065 eV, respectively. Moreover, it is exhibited that the trap density of ET2 is larger than those of ET1 or ET3 in all the cases and increases as the Zn∕O flux ratio increases. Consequently, it is suggested that the large dispersion effect observed in the Zn-rich and stoichiometric ZnO layers is ascribed to the large density of deep electron-trap center ET2.
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81.05.Dz II-VI semiconductors
71.55.Gs II-VI semiconductors
73.61.Ga II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Cc Kinetics of defect formation and annealing
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.A- Nucleation and growth
61.72.J- Point defects and defect clusters

Th4+ donor/Mg2+ acceptor-cosubstituted (Bi,Nd)4Ti3O12 films with excellent ferroelectric properties

Tai-Yi Chiou and Dong-Hau Kuo

Appl. Phys. Lett. 86, 032910 (2005); http://dx.doi.org/10.1063/1.1854734 (3 pages) | Cited 8 times

Online Publication Date: 14 January 2005

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A-site Th4+ donor/B-site Mg2+ acceptor-cosubstituted (Bi3.15Nd0.85)Ti3O12 or (Bi3.15Nd0.85−2xTh2x)(Ti3−xMgx)O12 ferroelectric thin films with x = 0.003 were prepared at 600 °C by a chemical route. A concept of the electrostatic interaction between the positively charged donor and the negatively charged acceptor were introduced for the purpose of enhancing electrical polarization. A (117)-preferred film growth occurred. The 15 min annealed films performed the best with a low coercive field of 45 kV/cm, a large remanent polarization (2Pr) of 70 μC/cm2, and a nonvolatile charge of 58 μC/cm2 after 1010 switching cycles. The excellent ferroelectric properties can be related to the (117)-preferred growth and the tilting of the triple-layered TiO6 octahedral chains.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
68.55.-a Thin film structure and morphology
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)
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