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10 Jul 2006

Volume 89, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 89, 023901 (2006); http://dx.doi.org/10.1063/1.2219984 (3 pages)

Nikhil Ganesh, Ian D. Block, and Brian T. Cunningham
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Enhanced tunability of magnetron sputtered Ba0.5Sr0.5TiO3 thin films on c-plane sapphire substrates

E. A. Fardin, A. S. Holland, K. Ghorbani, and P. Reichart

Appl. Phys. Lett. 89, 022901 (2006); http://dx.doi.org/10.1063/1.2220530 (3 pages) | Cited 12 times

Online Publication Date: 10 July 2006

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Thin films of Ba0.5Sr0.5TiO3 (BST) were deposited on c-plane (0001) sapphire by rf magnetron sputtering and investigated by complementary materials analysis methods. Microwave properties of the films, including tunability and Q factor were measured from 1 to 20 GHz by patterning interdigital capacitors (IDCs) on the film surface. The tunability is correlated with texture, strain, and grain size in the deposited films. An enhanced capacitance tunability of 56% at a bias field of 200 kV/cm and total device Q of more than 15 (up to 20 GHz) were achieved following postdeposition annealing at 900 °C.
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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.-e Ferroelectricity and antiferroelectricity
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments

Misfit strain relaxation in (Ba0.60Sr0.40)TiO3 epitaxial thin films on orthorhombic NdGaO3 substrates

W. K. Simon, E. K. Akdogan, and A. Safari

Appl. Phys. Lett. 89, 022902 (2006); http://dx.doi.org/10.1063/1.2214216 (3 pages) | Cited 16 times

Online Publication Date: 10 July 2006

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Strain relaxation in (Ba0.60Sr0.40)TiO3 (BST) thin films on 〈110〉 orthorhombic NdGaO3 substrates is investigated by x-ray diffractometry. Pole figure analysis indicates a [010]BST∥[math10]NGO and [001]BST∥[001]NGO in-plane and [100]BST∥[100]NGO out-of-plane epitaxial relationship. The residual strains are relaxed at h ∼ 200 nm, and for h>600 nm, films are essentially strain free. Two independent dislocations mechanisms operate to relieve the anisotropic misfit strains along the principal directions. The critical thickness for misfit dislocation formation along [001] and [010] are 11 and 15 nm, respectively. Stress analysis indicates deviation from linear elasticity for h<200. The films with 10<h<25 nm are of monoclinic symmetry due to a finite principal shear stress along [110] of the initial orthorhombic cell.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Dynamical slowing down of polar nanoregion in relaxor-based ferroelctric 0.89Pb(Zn2/3Nb1/3)O3–0.11PbTiO3

Yohei Nakata, Yuhji Tsujimi, Kohei Katsuraya, Makoto Iwata, and Toshirou Yagi

Appl. Phys. Lett. 89, 022903 (2006); http://dx.doi.org/10.1063/1.2221387 (3 pages) | Cited 9 times

Online Publication Date: 10 July 2006

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Light scattering experiment has been performed in a single crystal of 0.89Pb(Zn1/3Nb2/3)O3–0.11PbTiO3. The central peak (CP) spectra have been well detected with high resolution over the wide frequency region up to 150 GHz. The distribution is discovered in the relaxation time associated with the CP. Moreover, it is found that the maximum relaxation time indicates the dynamical slowing down near the temperature Tm at which the low-frequency dielectric constant has a maximum. This finding strongly suggests that the physical origin of the CP is “polar nanoregions.”
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ch Permittivity (dielectric function)

In situ transmission electron microscopy study of the nanodomain growth in a Sc-doped lead magnesium niobate ceramic

W. Qu, X. Zhao, and X. Tan

Appl. Phys. Lett. 89, 022904 (2006); http://dx.doi.org/10.1063/1.2219416 (3 pages) | Cited 5 times

Online Publication Date: 10 July 2006

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Sc doping enhances the B-site 1:1 cation ordering in the Pb(Mg1/3Nb2/3)O3 ceramic. At low doping levels, the electrical polar domains remain at the nanometer scale and the relaxor ferroelectric behavior persists. The electric field-induced relaxor to normal ferroelectric phase transition process was directly observed with an in situ transmission electron microscopy technique in a Sc-doped Pb(Mg1/3Nb2/3)O3 polycrystalline sample. It was found that the phase transition started at the grain boundary and took two steps to complete: the gradual coalescence of the polar nanodomains and the abrupt formation of the large wedge-shaped ferroelectric domains.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
68.37.Lp Transmission electron microscopy (TEM)
77.80.Dj Domain structure; hysteresis
61.72.Mm Grain and twin boundaries

Room temperature fabricated ZnO thin film transistor using high-K Bi1.5Zn1.0Nb1.5O7 gate insulator prepared by sputtering

Il-Doo Kim, Mi-Hwa Lim, KyongTae Kang, Ho-Gi Kim, and Si-Young Choi

Appl. Phys. Lett. 89, 022905 (2006); http://dx.doi.org/10.1063/1.2220485 (3 pages) | Cited 37 times

Online Publication Date: 11 July 2006

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In this letter, we report on dielectric and leakage current characteristics of room temperature deposited Bi1.5Zn1.0Nb1.5O7 (BZN) films on the basis of crystallographic structure and suitability of BZN gate insulators as key building blocks in the fabrication of low voltage operating ZnO based thin-film transistors (TFTs). The BZN films exhibited a high dielectric constant ( ∼ 51) and good leakage current characteristics ( ∼ 10−7 A/cm2) at an applied voltage of 5 V. All room temperature processed ZnO based TFTs using BZN gate insulator exhibited field effect mobility of 1.13 cm2/Vs and low voltage device performance less than 4 V.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
85.30.Tv Field effect devices

Resonance enhancement in piezoresponse force microscopy: Mapping electromechanical activity, contact stiffness, and Q factor

Stephen Jesse, Boris Mirman, and Sergei V. Kalinin

Appl. Phys. Lett. 89, 022906 (2006); http://dx.doi.org/10.1063/1.2221496 (3 pages) | Cited 31 times

Online Publication Date: 13 July 2006

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Piezoresponse force microscopy (PFM) and spectroscopy of domain structure and switching dynamics at small excitation voltages require resonance enhancement of the surface displacements. The contact stiffness depends strongly on local elastic properties and topography resulting in significant variations of the resonant frequency. Moreover, the resonant response is determined both by the Q factor and the electromechanical activity. Here we develop a resonance-enhanced PFM that allows mapping of the local electromechanical activity, contact stiffness, and loss factor, thus avoiding limitations inherent to conventional frequency tracking. We anticipate that this method will be instrumental in imaging weakly piezoelectric materials and probing inelastic phenomena in ferroelectrics.
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07.79.-v Scanning probe microscopes and components
77.65.Fs Electromechanical resonance; quartz resonators
77.80.Dj Domain structure; hysteresis
77.22.Gm Dielectric loss and relaxation
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Defect states in the high-dielectric-constant gate oxide LaAlO3

K. Xiong, J. Robertson, and S. J. Clark

Appl. Phys. Lett. 89, 022907 (2006); http://dx.doi.org/10.1063/1.2221521 (3 pages) | Cited 26 times

Online Publication Date: 13 July 2006

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We present calculations of the energy levels of the oxygen vacancy, AlLa antisite, and oxygen interstitial defects in LaAlO3 using density functional methods that do not need an empirical band gap correction. The levels are aligned to those of the Si channel using the known band offsets. The oxygen vacancy gives an energy level near the LaAlO3 conduction band and above the Si gap. It is identified as the main electron trap and the cause of instability. The AlLa antisite gives a state near midgap, neutral when empty, which would be an important trap, with no counterpart in HfO2.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.55.Ht Other nonmetals
77.55.-g Dielectric thin films
61.72.J- Point defects and defect clusters
73.20.At Surface states, band structure, electron density of states
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Permittivity of a ferroelectric film beneath a metal electrode

Christian Bayer and Timothy J. Jackson

Appl. Phys. Lett. 89, 022908 (2006); http://dx.doi.org/10.1063/1.2221524 (3 pages) | Cited 6 times

Online Publication Date: 13 July 2006

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The permittivity of a ferroelectric n-type semiconductor varies smoothly with depth beneath a reversed biased Schottky contact. In partially depleted films, the depletion layer controls the capacitance. In fully depleted films the inverse capacitance is proportional to the thickness, which suggests that Schottky effects do not cause dead-layer behavior.
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77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.80.-e Ferroelectricity and antiferroelectricity
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts

Correlation between reliability of thermal oxides and dislocations in n-type 4H-SiC epitaxial wafers

Junji Senzaki, Kazutoshi Kojima, Tomohisa Kato, Atsushi Shimozato, and Kenji Fukuda

Appl. Phys. Lett. 89, 022909 (2006); http://dx.doi.org/10.1063/1.2221525 (3 pages) | Cited 10 times

Online Publication Date: 13 July 2006

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The correlation between thermal oxide reliability and dislocations in n-type 4H-SiC (0001) epitaxial wafers has been investigated. The thermal oxides were grown by dry oxidation at 1200 °C followed by nitrogen postoxidation annealing. Charge-to-breakdown values of thermal oxides decrease with an increase in the number of the dislocations in a gate-oxide-forming area. Two types of dielectric breakdown modes, edge breakdown and dislocation-related breakdown, were confirmed by Nomarski microscopy. In addition, it is revealed that basal plane dislocation is the most common cause of the dislocation-related breakdown mode.
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77.22.Jp Dielectric breakdown and space-charge effects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Mq Oxidation
61.72.Cc Kinetics of defect formation and annealing

Interfacial varactor characteristics of ferroelectric thin films on high-resistivity Si substrate

Wen-An Lan, Tsan-Chun Wang, Ling-Hui Huang, and Tai-Bor Wu

Appl. Phys. Lett. 89, 022910 (2006); http://dx.doi.org/10.1063/1.2214170 (3 pages) | Cited 6 times

Online Publication Date: 14 July 2006

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Ferroelectric Ba(Zr0.25Ti0.75)O3 (BZT) thin films were deposited on high-resistivity Si substrate without or with inserting a high-k buffer layer of Ta2O5. The varactor characteristics of the BZT capacitors in metal-oxide-semiconductor structure were studied. At low frequency (1 MHz), the capacitors exhibit a negatively tunable characteristic, i.e., [C(V)−C(0)]/C(0)<0, against dc bias V, but opposite tunable characteristics were found at microwave frequencies (>1 GHz). The change of voltage-dependent characteristic is attributed to the effect of low-resistivity interface induced by charged defects formed from interfacial oxidation of Si in screening the microwave from penetrating into the bulk of Si.
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77.55.-g Dielectric thin films
84.32.Tt Capacitors
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
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