The effect of tungsten trioxide thin films at ferroelectric-electrode boundaries on fatigue behaviour

A conventional thin film capacitor heterostructure, consisting of sol-gel deposited lead zirconium titanate (PZT) layers with sputtered platinum top and bottom electrodes, was subjected to fatiguing pulses at a variety of frequencies. The fatigue characteristics were compared to those of a similarly processed capacitor in which a ~20nm tungsten trioxide layer had been deposited, using pulsed laser deposition, between the ferroelectric and upper electrode. The expectation was that, because of its ability to accommodate considerable oxygen non-stoichiometry, tungsten trioxide (WO3) might act as an efficient sink for any oxygen vacancies flushed to the electrode-ferroelectric boundary layer during repetitive switching, and hence would improve the fatigue characteristics of the thin film capacitor. However, it was found that, in general, the addition of tungsten trioxide actually increases the rate of fatigue. It appears that any potential benefit from the WO3, in terms of absorbing oxygen vacancies, is far outweighed by it causing dramatically increased charge injection in the system.

Local atomic structure modulations activate metal oxide as electrocatalyst for hydrogen evolution in acidic water

Modifications of local structure at atomic level could precisely and effectively tune the capacity of materials, enabling enhancement in the catalytic activity. Here we modulate the local atomic structure of a classical but inert transition metal oxide, tungsten trioxide, to be an efficient electrocatalyst for hydrogen evolution in acidic water, which has shown promise as an alternative to platinum. Structural analyses and theoretical calculations together indicate that the origin of the enhanced activity could be attributed to the tailored electronic structure by means of the local atomic structure modulations. We anticipate that suitable structure modulations might be applied on other transition metal oxides to meet the optimal thermodynamic and kinetic requirements, which may pave the way to unlock the potential of other promising candidates as cost-effective electrocatalysts for hydrogen evolution in industry.

LPCVD of tungsten by selective deposition on silicon

Beta-phase W, selectively grown at 440C had resistivity 20 micro-ohm cm and maximum layer thickness 100nm. Hydrogen passivation proved essential in this process. Higher deposition temperatures resulted in increased layer thickness but incorporated WSi2 and alpha- phase W. Self limiting W grown on polycrystalline and heavily doped silicon yielded reduced thickness. Boron is involved in the WF6 reduction reaction but phosphorus is not and becomes incorporated in the W layer. The paper establishes an optimised and novel CVD process suited to IC contact technology. A funded technology transfer contract with National Semiconductor Greenock (M Fallon) resulted from this work.

Tungsten Silicide Contacts to Polycrystalline Silicon and Silicon-Germanium Alloys

Novel CVD WSi2 technology with low series and contact resistance in SiGe HBTs was achieved. Specific contact resistance to Si1-xGex with 0