Leakage currents in Ba0.7Sr0.3TiO3 thin films for ultrahigh-density dynamic random access memories

Self Cite

Thin films of the ͑Ba x Sr 1−x ͒TiO 3 ͑BST͒ solid solution series were grown by metal-organic chemical-vapor deposition ͑MOCVD͒ on platinized silicon wafers with emphasis to ͑Ba 0.7 Sr 0.3 ͒TiO 3 and SrTiO 3 . The nucleation behavior and the size of the stable nuclei were investigated by different scanning probe microscope techniques including local conductivity scanning. The characteristic differences were observed for different deposition temperatures, i.e., a homogeneous nucleation of small BST grains on the larger Pt grains at 565°C and a dominating grain-boundary nucleation at 655°C. X-ray photoelectron spectroscopy indicates a stoichiometric composition from the beginning. The microstructural evolution was investigated by high-resolution transmission electron microscopy and revealed randomly oriented grains ͑typical in-plane size 10-20 nm͒ with a high density of twins at 565°C and ͑100͒-oriented defect-free grains of slightly increased size at 655°C. This remarkably stable ͑100͒ texture seems specific for MOCVD as it is not observed for other deposition methods. The grain structure and surface morphology and their dependence on film stoichiometry ͑group-II/Ti ratio͒ are investigated. The relation between the structural and the electrical properties, capacitance, and leakage current, is finally discussed.

Section: ͑2͒supporting

confidence: 61%

Metal-organic chemical-vapor deposition of (Ba,Sr)TiO3: Nucleation and growth on Pt-(111)

Regnery

Ding

Ehrhart

et al. 2005

Self Cite

“…The leakage current are thus much lower and the break down fields higher than state-of-the art BST films [15].…”

Section: Methodsmentioning

confidence: 99%

Microwave dielectric properties of tunable capacitors employing bismuth zinc niobate thin films

Park

Stemmer

et al. 2005

Parallel plate capacitors employing Bi1.5Zn1.0Nb1.5O7 (BZN) thin films with the pyrochlore structure were fabricated on platinized sapphire substrates. The total device quality factor and capacitance were analyzed in the microwave frequency range (up to 20 GHz) by measuring reflection coefficients with a vector network analyzer. The parasitics due to the probe pads were extracted from the measurements. The total device quality factor, which included losses from the dielectric and the electrodes, was more than 200 up to 20 GHz for devices with an area of 100μm2. Based on the frequency dependence of the impedance, series losses of unknown origin appear to dominate the device quality factor at higher frequencies. No significant dispersion in the device capacitance, as would be associated with a dielectric relaxation of BZN, was measured. The large electric field tunability of the permittivity of BZN films and the high device quality factors make these films attractive for voltage controlled microwave devices.

“…This wear-out process, which is the main limiting factor for the lifetime of multilayer ceramic capacitors, is not destructive and reversible upon annealing. From the large number of studies on oxides and in particular on perovskite ceramics such as SrTiO 3 [24,26,27,28], it appears that the degradation rate is largely influenced by grain size, stoichiometry, doping, second phases, porosity, and electrode properties. In general, doping with donors such as La 3+ , which goes into the A sites (e.g., Sr 2+ ) of the ABO 3 perovskite lattice, leads to an increase of the leakage current and improves or stabilizes the degradation [29].…”

Section: Discussionmentioning

confidence: 99%

Electrical current distribution across a metal–insulator–metal structure during bistable switching

Rossel

Meijer

Brémaud

et al. 2001

202

106

Combining scanning electron microscopy (SEM) and electron-beam-induced current (EBIC) imaging with transport measurements, it is shown that the current flowing across a two-terminal oxide-based capacitor-like structure is preferentially confined in areas localized at defects. As the thin-film device switches between two different resistance states, the distribution and intensity of the current paths, appearing as bright spots, change. This implies that switching and memory effects are mainly determined by the conducting properties along such paths. A model based on the storage and release of charge carriers within the insulator seems adequate to explain the observed memory effect. 61.16.Bg, 72.20.Jv, 73.40.Rw