J. Gest

Analytical expressions for the conductance noise measured with four circular contacts placed in a square array

In the ideal case, noise measurements with four contacts minimize the contribution of the contact interface. There is a need to characterize conductance noise and noise correction factors for the different geometries provided with four contacts, as already is the case for resistivity measurements with van der Pauw structures. Here, we calculate the noise correction factors for two geometries with a pair of sensors and a pair of current driver electrodes placed in a square array. The first geometry investigated is a very large film compared to the distance L between four circular electrodes, which are placed in a square array far away from the borders of the film. The second is a square-shaped conductive film with side length L and provided with four quarter-circle corner contacts with radius l. The effect of the conductance noise in the film can be observed between current free sensors in a four-point measurement or between current carrying drivers in a two-point measurement. Our analytical expressions ar...

Correlations between 1/f noise and thermal treatment of Al-doped ZnO thin films deposited by direct current sputtering

Al-doped ZnO thin films (AZO) have been deposited on amorphous glass substrates by DC sputtering at different substrate temperatures Ts. X-Ray diffraction results reveal that AZO thin films have a hexagonal wurtzite structure with (002) preferred orientation. (002) peaks indicate that the crystalline structure of the films is oriented with c-axis perpendicular to the substrate. Three-dimensional (3D) atomic force microscopy images of AZO thin films deposited on glass substrate at 200u2009°C, 300u2009°C, and 400u2009°C, respectively, shows the improvement of the crystallinity and the homogeneity of AZO thin films with Ts which is in agreement with the noise measurements. The noise was characterized between 1u2009Hz and 100u2009kHz and we have obtained 1/f spectra. The noise is very sensitive to the crystal structure especially to the orientation of the crystallites which is perpendicular to the substrate and to the grain boundaries which generate a high current flow and a sharp increase in noise. Through time, Rsh and [αμ]eff...

NOISE MEASUREMENTS ON NbN THIN FILMS WITH A NEGATIVE TEMPERATURE RESISTANCE COEFFICIENT DEPOSITED ON SAPPHIRE AND ON SiO2

We characterize granular NbNx thin cermet films deposited on either sapphire substrate or on SiO2 and compare the 1/f noise at 300 K and 80 K. The films were characterized with an impedance analyzer from 20 Hz to 1 MHz and analyzed as a resistor R in parallel with a capacitor C. The calculated noise voltage spectral density SvTh of the sample is in agreement with the experimentally observed noise for unbiased samples. The noise measurements on biased samples show 1/f noise. We checked that contact noise does not contribute to our measurements. The 1/f noise was compared for the films deposited on the silicon substrate and on the sapphire. Finally a model is proposed to explain the observed trends in the temperature resistance coefficient (TRC < 0 for all samples) and the relative 1/f noise at 300 K and 80 K with the composition x = N/Nb of the layers.

1/ƒ noise in ZnO films

We have investigated the low-frequency noise of ZnO film deposited by dc sputtering technique on glass substrate. We characterized the noise below 100kHz and obtained classical 1/ƒ spectra. We attempted to verify the validity of Hooges empirical relation and to test its usefulness as a diagnostic tool. The 1/ƒ noise normalized for bias, frequency and unit area, Cus is proportional with the sheet resistance Rsh. We found that the noise results depend strongly on illumination.

Research on the properties of ZnO films by 1/f noise measurement

ZnO films were deposited by dc sputtering technique on glass and Pt/Si substrates. The effect of growth parameters is investigated on sheet resistance and noise. The 1/f noise normalized for bias, frequency and unit area, Cus is proportional with the sheet resistance Rsh. We found that the noise results correlate strongly with the crystalline structure of ZnO. For comparison, we have also studied the ZnO films structural properties.

Dielectric and conductivity properties of composite polyaniline/polyurethane network

In this work, we present the dielectric characterization of polyaniline/polyurethane composite. The samples consisting of 0.5%, 1%, and 5% of polyaniline were deposited on glass fiber, and the measurements were performed in a frequency range of 20u2009Hz to 20u2009GHz. The results showed a dielectric relaxation strongly dependent on the concentration of polyaniline. This phenomenon is explained by a theoretical model. In this model, we assume that the alternative conductivity of the polymer network systems is due to conducting clusters whose lengths followed a Gaussian distribution. Depending on their size and the frequency of the excitation signal, the clusters showed a resistive or capacitive effect.

Effect of substrate temperature deposition on the 1/f noise of Al-doped ZnO thin films

We have investigated the low-frequency noise and the sheet resistance of Al-doped ZnO thin films deposited by DC sputtering technique on glass substrate at different temperature. We characterized the noise below 100 kHz and obtained 1/f spectra. The 1/f noise normalized for bias, frequency and unit area, Cus is proportional with the sheet resistance Rsh· Sheet resistance decreases with the increasing of the substrate temperature Ts. The decrease of the normalized noise showed the improvement of the crystallinity and homogeneity of AZO thin films with Ts which indicates the sensitivity of the noise with the crystalline quality of the thin films.

Noise measurements in NbN semiconductors thin films deposited on sapphire

In this work, we have characterized three NbNx thin films deposited on sapphire substrate and compared their noise properties. The three films were measured in the same conditions. In the first time, the films were characterized with an impedance analyzer from 20 Hz to 1 MHz. The films are then considered as a RC dipole with a resistor R in parallel with a capacitor C. With the Nyquist formula, we calculate the noise voltage spectral density SvTh of the RC dipole considering that only the resistor R exhibits thermal noise in unbiased samples. In the second time, noise measurements were made with the samples biased. Thanks to a four contacts configuration, we checked that contact noise do not contribute to our measurements. The difference between the measured noise and the calculated thermal noise SvTh shows an extra 1/f noise without GR noise contributions. The 1/f noise in the three films extra noise is compared. These results are also compared to the noise measured on NbN thin films deposited on silicon substrate [1].

Influence of thermal annealing of MgO substrate on 1/f noise of YBaCuO superconducting thin films

In this work, we have characterized YBaCuO high Tc superconducting thin films deposited on (001) MgO substrates and compared their noise properties. The films were sputtered on substrates which were annealed at different temperatures prior to deposition. The noise measurements were performed under the same conditions: 1) Without bias, the films are at equilibrium and exhibit only thermal noise proportional to the real part of the impedance for the voltage fluctuations or proportional to the real part of the admittance for the current fluctuations. 2) With bias, the films exhibit 1/f noise due to the conductivity fluctuations. The extra noise is compared with Hooges empirical relation. The normalized noise spectral density (Sv / V2) measured at 300 K as a function of the substrate annealing temperature displays a bell-shaped dependence with a maximum at a critical temperature.