9 research outputs found
A Percolative Model of Soft Breakdown in Ultrathin Oxides
The degradation of ultrathin oxide layers in the presence of a stress voltage
is modeled in terms of two antagonist percolation processes taking place in a
random resistor network. The resistance and leakage current fluctuations are
studied by MonteCarlo simulations for voltages below the breakdown threshold.
An increase of excess noise together with a noticeable non-Gaussian behavior is
found in the pre-breakdown regime in agreement with experimental results.Comment: accepted for publication on Physica
Resistance and Resistance Fluctuations in Random Resistor Networks Under Biased Percolation
We consider a two-dimensional random resistor network (RRN) in the presence
of two competing biased percolations consisting of the breaking and recovering
of elementary resistors. These two processes are driven by the joint effects of
an electrical bias and of the heat exchange with a thermal bath. The electrical
bias is set up by applying a constant voltage or, alternatively, a constant
current. Monte Carlo simulations are performed to analyze the network evolution
in the full range of bias values. Depending on the bias strength, electrical
failure or steady state are achieved. Here we investigate the steady-state of
the RRN focusing on the properties of the non-Ohmic regime. In constant voltage
conditions, a scaling relation is found between and , where
is the average network resistance, the linear regime resistance
and the threshold value for the onset of nonlinearity. A similar relation
is found in constant current conditions. The relative variance of resistance
fluctuations also exhibits a strong nonlinearity whose properties are
investigated. The power spectral density of resistance fluctuations presents a
Lorentzian spectrum and the amplitude of fluctuations shows a significant
non-Gaussian behavior in the pre-breakdown region. These results compare well
with electrical breakdown measurements in thin films of composites and of other
conducting materials.Comment: 15 figures, 23 page
1/f noise in pentacene and poly-thienylene vinylene thin film transistors
We investigate low frequency conductivity noise in the drain-source channel of organic material field-effect transistors by measuring the spectra of current fluctuations for several values of the gate voltage Vgs and drain voltage Vds and find that it is 1/f. The samples are biased in the ohmic range of the applied Vds. The relative current 1/f noise is inversely proportional to the charge carrier numbers N generated by illumination or by varying the gate-source voltage. Hooge's empirical relation for the 1/f noise is validated for these organic semiconductors with an a¿0.01 for poly-thienylene vinylene and about 100 for pentacene thin film transistors. From geometry dependence of the noise we conclude that series resistance can be ignored for poly-thienylene vinylene field-effect transistors. However, some pentacene samples suffer from a noisy series resistance to the channel resistance. From the 1/f noise dependence on geometry and gate voltage bias we conclude that it can be used as a diagnostic tool for device quality assessment. ©2002 American Institute of Physics