Zhong Sun

Dielectric property studies of multiferroic GaFeO3

Magnetic and dielectric properties of a polycrystalline GaFeO3 sample prepared by a solid-state reaction have been investigated. A ferrimagnetic phase transition TN of the material was identified at a temperature of 225 K. An anomaly on the permittivity as a function of temperature has been observed near its magnetic transition point TN, which could be induced by the magnetoelectric coupling between its electric and magnetic orders. At low temperature, T< T N, the permittivity variation �e depends on magnetization M and shows clearly a linear relationship between �e and M 2 , which indicates that a dielectric and magnetic correlation exists in the compound. Furthermore, its dielectric relaxation process is discussed in the temperature interval of 77–300 K. (Some figures in this article are in colour only in the electronic version)

Effects of film thickness and preferred orientation on the dielectric properties of (Bi1.5Zn0.5) (Zn0.5Nb1.5) O7 films

(Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 (BZN) films with different thicknesses and preferred orientations have been fabricated on Nb doped SrTiO3 substrates by pulsed laser deposition. As the thickness increases, the permittivity increases, and the dielectric loss decreases, while the tunability only has a little variation. The asymmetric behaviour of the electric field dependent permittivity reduces gradually with the increasing thickness, which should be attributed to the decrease in the effect of the interfacial layer between the dielectric film and substrate (electrode). Furthermore, compared with the (1 0 0) oriented BZN film, BZN film with (1 1 1) preferred orientation exhibits high dielectric loss. (Some figures in this article are in colour only in the electronic version)

Effect of Ce substitution on magnetic and dielectric properties of BiMn2O5

Polycrystalline BiMn2O5 and Bi0.9Ce0.1Mn2O5 have been prepared by a solid-state reaction. A crystalline structure study shows that all x-ray diffraction patterns can be indexed successfully in an orthorhombic phase. Substitution of Ce for Bi ions induced in the unit cell a slight distortion and enlargement. Magnetic and dielectric measurements all reveal that Ce substitution induces great effects: BiMn2O5 is in the antiferromagnetic (AFM) phase with a Neel transition temperature at about 42K, whereas Bi0.9Ce0.1Mn2O5 is in the ferromagnetic (FM) phase with a Curie temperature at about 46K. The permittivity of Bi0.9Ce0.1Mn2O5 is much higher than that of BiMn2O5, and two dielectric relaxation peaks have been observed in the former, instead of one dielectric loss peak as observed in BiMn2O5. The valent state of Ce ions has been analyzed mainly as tetravalent by the core-level spectrum of Ce 3d from x-ray photoemission spectroscopy. The possible mechanisms of the magnetic transition from AFM to FM and the pecu...

C-axial oriented (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 thin film grown on Nb doped SrTiO3 substrate by pulsed laser deposition

A c-axial oriented (Bi1.5Zn0.5)(Zn0.5Nb1.5)O-7 thin film has been grown on a (001) Nb doped SrTiO3 substrate by pulsed laser deposition. The permittivity, dielectric loss and tunability of the c-axial oriented film are 187, 0.002 and 6% ( at 750 kV cm(-1) biasing), respectively, indicating a figure of merit of 30. Moreover, an asymmetry behaviour is observed in the dc electric field dependence of permittivity, which could be attributed to the asymmetry of top and bottom electrodes.

Effect of Damage in Source and Drain on the Endurance of a 65-nm-Node NOR Flash Memory

On 12-in wafers of 65-nm-node floating gate NOR flash memory, charge pumping measurements show that compared to those on the edge dies (type A), the devices on the central dies (type B) have more severe damage in the source (S) and drain (D) regions. In type-B devices, the worse damage is due to the generation of interface traps in the S/channel overlapping region and the generation of bulk traps in the S and D junction region. In type-A devices, the damage is much weaker. The generation of interface traps is observed in the S/channel overlapping region. However, it is hardly measurable on the D side. The endurance characteristics have been measured in these two kinds of devices under the channel hot electron program and Fowler-Nordheim erase. In type-B devices, after program/erase cycling the memory window closure is more serious and the junction leakage also degrades greatly with the generation of a lot of bulk traps at S and D regions. The damage in fresh devices is suggested to be due to the plasma etching processes.

Magnetodielectric effect and dielectric relaxation of spinel Cd0.7Fe0.3Cr2S4

Polycrystalline Cd0.7Fe0.3Cr2S4 has been prepared by a solid state reaction. A crystalline structure study shows that the x-ray diffraction pattern can be indexed successfully in a cubic spinel phase. Its magnetic and dielectric properties have been investigated. A ferrimagnetic phase transition of the material was identified at 123K. Larger permittivity and loss tangent are observed than those of CdCr2S4 in the frequency range 300Hz–1MHz. An anomaly cusp induced by the internal magnetic field on e-T and tanδ-T curves is observed near its magnetic transition point, implying an existence of magnetodielectric effect. At low temperature T<TN, the permittivity variation Δe depends on magnetization M and shows clearly a linear relationship between Δe and M2, indicating an interplay of permittivity and magnetism. Furthermore, compared to CdCr2S4, Cd0.7Fe0.3Cr2S4 exhibits smaller values of dielectric relaxation time and activated energy above TC due to Fe2+ doping.

Cycling-Induced Peak-Like Interface State Generation in Si-Nanocrystal Memory Devices

The peaklike behavior of interface trap generation was observed in silicon-nanocrystal (Si-NC) memory during Fowler-Nordheim program/erase cycling. In addition to the two peaks at 0.3 and 0.85 eV from Pb0 centers, two extra peaks (0.45 and 0.7 eV) were also observed and suggested from Pb1 centers. In contrast, only Pb0 centers were observed in reference devices without Si-NCs. The result will be helpful to understand the effect of Si-NCs on the interface reliability.

Comparison of tunneling current assisted by neutral and positive traps with finite ranged core-potential

Trap assisted tunneling current (JTAT) has been computed for neutral and positive traps with finite ranged core-potential in a metal-oxide-semiconductor structure. The calculation is based on Bardeen transfer Hamiltonian approach and the elastic tunneling approximation and includes both direct tunneling at low voltage and tunneling ionization at high voltage. In both regimes, two different forms of transition matrix elements have been presented and their numerical values have been compared. For both kinds of traps, JTAT shows a similar shape for its dependence on the oxide voltage and increases slightly with increasing the radius of the core-potential. However, compared to the neutral traps, JTAT induced by positive traps is enhanced by about half order due to the existence of the long-ranged Coulomb potential tail. The usual δ-function approximation for the core potential of neutral traps underestimates JTAT by a half order.

Magnetism and permittivity properties of spinel Cd0.5Fe0.5Cr2S4

Magnetism and permittivity properties of polycrystalline Cd0.5Fe0.5Cr2S4 have been investigated. Cd0.5Fe0.5Cr2S4 is a ferrimagnet with a Curie temperature of 137u2009K, and exhibits large permittivity and loss tangent in the frequency range 30u2009kHz–1u2009MHz. A kink is observed on the curve of the temperature-dependent permittivity near its magnetic transition point, implying the existence of a magnetodielectric effect.