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Current and voltage noise measurements have been carried out on nanoparticle WO3 films. The fluctuation dissipation theorem holds, which indicates that the observed noise is an equilibrium phenomenon. Results on the thinnest films show that noise measurements can be used for quality assessment of nanocrystalline insulating films. ©2002 American Institute of Physics.

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.

Here we investigate dc characteristics, impedance versus frequency, and low frequency noise. The effect of current distribution on 1/f noise in polycrystalline silicon thin film transistors (TFTs) is discussed. We show that the channel impedance versus frequency roll induces spectra that could be misinterpreted above a corner frequency in terms of a frequency index ¿ in 1/f ^¿ with ¿ higher than 2. Moreover, ignoring the inhomogeneous current distribution leads to overestimation of the noise parameter. Whereas it seemed evident that the noise in TFTs can be interpreted in terms of carrier number fluctuation, the noise parameter variation versus the gate bias can be also understood in terms of mobility fluctuations by including the potential barrier evolution. ©2001 American Institute of Physics.

We have investigated the room temperature 1/f noise of microstructured soft magnetic Ni80Fe20 films, showing the anisotropic magnetoresistance effect, and of Ni80Fe20/Cu magnetic multilayers, showing the giant magnetoresistance effect. We find that the 1/f noise in magnetic multilayers is considerably enhanced with respect to the noise of the single domain layer, which sets a limit on the usability of giant magnetoresistance materials for low-frequency applications.

We investigated the dielectric losses of doped and undoped BaSrTiO3 (BST) from thermal noise measurements. The results are compared to impedance measurements. The value for the frequency independent loss angle is about tg δ=2×10−2 in the range 100

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 are based on approximations to solve the integrals (J·)2dA and |J|4dA for the voltage noise measured across a pair of sensors, SVQ, and across the drivers, SVD, respectively. The first and second integrands represent the squared dot product of the current density and adjoint current density and the modulus of the current density to the fourth power, respectively. The current density J in the samples is due to the current I passing through the driver contacts. The calculated expressions are applicable to samples with thickness tl0.1L. Hence, the disturbances in the neighborhood of the sensors on J and of the drivers on are ignored. Noise correction factors for two- and four-point measurements are calculated for sensors on an equipotential (transversal noise) with the driver contacts on the diagonal of a square and for sensors next to each other on one side of the square with the drivers next to each other on the other side of the square (longitudinal noise). In all cases the noise between the sensors is smaller and less sensitive to the contact size 2l/L than the noise between the drivers. The ratio SVQ/SVD becomes smaller with smaller contact radius l. Smaller sensors give a better suppression of interface noise at the contacts. But overly low 2l/L values result in overly high resistance between the sensors and too strong a contribution of thermal noise at the sensors. Therefore, equations are derived to calculate the current level needed to observe 1/f conductance fluctuations on top of the thermal noise. The results from the calculated analytical expressions show good agreement with experimental results obtained from the noise in carbon sheet resistance and numerical results. Transversal noise measurements on a square sample with corner contacts are recommended to characterize the 1/f noise of the layer. This is due to the increased current densities in the sample compared to the open structure, which result in easier detection of the 1/f on top of the thermal noise. ©2007 American Institute of Physics

The low-frequency noise sources are investigated in as-prepared and aged GaN light-emitting diodes (LEDs). Accelerated aging is performed by thermal (300h at 240°C) and electrical forward-bias stressing (20 and 50mA for 2500h). At low currents I

The conductivity fluctuations in 1‐MeV, boron‐implanted layers in silicon have been investigated at room temperature with the anneal temperature as a parameter. The 1/ f noise parameter α has been calculated from conductance, Hall voltage, and noise experiments. Annealing of the implants causes, in addition to an increase in the number of electrically active impurities, a decrease in the 1/ f noise parameter α by a factor of at least 50. The α value is proportional to eΔE/kTan, with an annealing activation energy ΔE=1.1 eV in a temperature range of 722 K

An experimental investigation has been carried out to confirm that contact noise of two crossed semiconductor bars with native oxide films in between can be understood as a volume 1/f noise. Noise and contact resistance have been measured as functions of the force F on the crossed bars. F varies between 6 N and 6×10-5 N. From a simple model, an equation is derived which relates the 1/f noise intensity C to the contact resistance R. The calculations are in agreement with the experimental C-R plots. Two extreme situations are possible: constriction dominated and film dominated. Which situation actually occurs can be seen in the C-R plot as well as in the R-F plot.

Noise measurements on thin bismuth films show that boundary scattering does not contribute to 1/f noise.

The passage of a single‐frequency ac through a nonlinear resistor produces a small voltage at the harmonic frequencies of the exciting signal. The effect of a simultaneously applied dc on the second and third harmonic voltages has been reported. An empirical model is proposed to explain the behavior of the first two harmonic voltages with dc. A physical explanation is put forward based on temperature‐induced changes in mobility. It is shown that this leads to an expression of the same form as the basis of the empirical model.

At present there are two theories of 1/f noise in metal‐oxide‐semiconductor (MOS) transistors. One is based on the McWhorter model (number fluctuations), the other on the Hooge model (mobility fluctuations). In both theories the influence of high electric‐field strengths on the mobility of carriers in the channel were left out of consideration. Here a new model of 1/f noise in MOS transistors is presented which is based on the Hooge model and takes into account the high electric‐field strengths in the channnel. The theoretical results agree well with experimental results.

The patchiness of contacts can be determined from measurements of 1/f noise and contact resistance on a number of contacts of different diameters made by the same method. If a contact consists of k conducting spots with average radius a, k and a can be determined if the distance between the spot centers is at least 2.5 times the spot diameter. Using the developed multispot contact model, the results of the 1/f noise analysis are in good agreement with multispot parameters obtained from microscopic investigations.

The experiments of Kotera et al. on InSb thin‐film Hall elements can be interpreted with existing noise calculations on four‐probe configurations.