Resistivity and Structure of Cr–SiO Cermet Films

Abstract

The structure, resistivity, and temperature coefficient of resistance (TCR) of Cr-SiO films with controlled compositions from 0 to 50 at. % SiO have been investigated. Randomly disordered films condense at −196 °C. Higher temperatures introduce varying degrees of order accompanied by disproportionation of SiO and reaction with Cr. This leads to nonhomogeneous structures consisting of amorphous SiO2 and Cr–Si phases according to the binary diagram. Metallic particles of α-Cr and Cr3Si, with either little or no long-range order or at the most partially crystalline, provide conductivity which decreases with increasing SiO2 concentration. The resistance decreases during annealing are proportional to the Cr3Si concentration over a wide composition range. The TCR's of highly disordered films are negative and shift toward positive values upon annealing. Their interpretation requires metallic and thermally activated conduction mechanisms in parallel. The resistivity and TCR changes during annealing are attributed to recrystallization and bridging between islands.

Characterizing and modeling the apparent anomalous behavior of resistivity in Cr–Si–O thin films

“…[2] The silicide precipitates became interconnected as a result of the anneal treatments forming a near continuous web through the matrix. The distribution of precipitates subsequent to annealing for film compositions >55 vol.% SiO 2 in this study aren't described by continuous cluster coalescence.…”

“…For example, silicides were found as precipitates within an amorphous Si-O matrix for vapor deposited cermets. [2] The growth of the precipitates may be a result of segregation of free-Cr from the matrix and/or the coalescence of the nanoprecipitates from the as-deposited condition. Particle coarsening after the anneal correlates with an increase of nearest neighbor spacing, hence an increase in ρ as predicated in the final remarks of Sec.…”

“…1 A general trend is confirmed that the as-deposited Cr-Si-O films are more conductive when the Cr composition increases in the film. [1][2][3] However, anomalous variation in the resistance is observed through a continuous range of Cr-composition. [10] The anomalous variation of resistance with elemental composition doesn't appear when plotted as a function of the insulator volume fraction, i.e.…”

“…2) for all Cr-Si-O films. [1][2][3][4]10] A unified (qualitative and quantitative) variation of both sheet and vertical resistance with vol.% SiO 2 represents a single resistivity. Resistivity values of 10 2 to 10 3 Ω-cm are found over a range of 55 to 80 vol.% SiO 2 with a rapid increase to >10 9 Ω-cm for contents >90 vol.% SiO 2 .…”

“…[1] The general dependence of sheet resistance on composition was investigated for the Cr-Si-O system. [2][3][4][5] The conduction mechanism for these cermets, as for Au-SiO films, can be considered quantum mechanical. [6] For low metallic concentrations, charge transport is proposed to be by electron tunneling between the metallic particles.…”