Low-frequency Noise Technique Research Articles

Low-Voltage-Operated Highly Sensitive Graphene Hall Elements by Ionic Gating.

The advanced Hall magnetic sensor using an ion-gated graphene field-effect transistor demonstrates a high current-normalized sensitivity larger than 3000 V/AT and low operation voltages smaller than 0.5 V. From commercially available graphene-on-SiO2 wafers, large-area arrays of ion-gated graphene Hall element (ig-GHE) samples are prepared through complementary metal-oxide-semiconductor-compatible fabrication processes except the final addition of ionic liquid electrolyte covering the exposed graphene channel and the separate gate-electrode area. The enhanced carrier tunability by ionic gating enables this ig-GHE device to be extremely sensitive to magnetic fields in low-voltage-operation regimes. Further electrical characterization indicates that the operation window is limited by the nonuniform carrier concentration over the channel under high bias conditions. The drain-current-normalized magnetic resolution of the device measured using the low-frequency noise technique is comparable to the previously reported values despite its significant low power consumption.

Physical-Based Characterization of Noise Responses in Metal-Oxide Gas Sensors

The noise level in the gas microsensors is a tool for characterizing the electrical conduction under various gases and a means to improve selectivity. Metal-oxide gas microsensors with WO3 sensitive thin film are characterized using a low-frequency noise technique. The spectral form of the noise responses measured using our specific systems is similar for tested gases (ozone and nitrogen dioxide). We observe a clear Lorentzian behavior according to adsorption-desorption (A-D) noise theory. To identify the detected gas, a physical-based characterization model of A-D noise source is proposed and compared with the empirical flicker noise model. We show that the excess noise is due to the A-D processes on the surface of the sensors sensitive film. The Lorentzian parameters depend on the nature of the gases and the noise-level dependence with gas concentration is clearly demonstrated. This confirms the interest on noise spectroscopy to improve the selectivity of gas sensors.

Degradation in InAlN/AlN/GaN heterostructure field-effect transistors as monitored by low-frequency noise measurements: Hot phonon effects

Low-frequency noise technique was applied to analyze performance of nearly lattice-matched InAlN/AlN/GaN heterostructure field-effect transistors and their degradation caused by electrical stress. Nearly identical devices from the same wafer have undergone a 7 h DC electrical stress at a fixed DC drain bias of VDS = 20 V and different gate biases. We noted up to 32 dB/Hz higher low-frequency noise for stressed devices over the entire frequency range of 1 Hz-100 kHz. The measurements showed the minimum degradation at a gate-controlled two-dimensional electron gas density of 9.4 × 1012 cm−2. This result is in good agreement with the reported stress effect on drain-current degradation and current-gain-cutoff-frequency measurements and consistent with the ultrafast decay of hot-phonons due to the phonon–plasmon coupling.

Characterization of traps in the gate dielectric of amorphous and nanocrystalline silicon thin-film transistors by 1/f noise

The low frequency noise technique is used to obtain the volume profile of traps in the SiNx gate dielectric of hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) thin film transistors (TFTs). In both a-Si:H and nc-Si:H TFTs, within the range of probing depth in the gate dielectric, the traps have a uniform spatial distribution which is consistent with the observed pure 1/f noise. The experimental results show that the gate dielectric trap properties near the interface are dependent on the channel material with the trap density in nc-Si:H TFTs being much smaller in comparison with the a-Si:H TFTs.

Identification of traps in an epitaxied AlGaAs/GaAs/AlGaAs quantum well structure

An epitaxied AlGaAs/GaAs/AlGaAs heterostructure is studied by using the low frequency noise technique over a wide range of temperature from 300 K down to 4 K as a function of bias. Emphasis is placed on the generation—recombination noise because it is present on a wide range of temperature and frequency. Thermal activation energies and capture cross sections of traps responsible for this kind of noise are extracted from an arrhenius plot. Six kinds of traps have been identified and their electrical nature has been suggested.

Investigation of single electron traps induced by InAs quantum dots embedded in GaAs layer using the low-frequency noise technique

The properties of the traps induced by InAs quantum dots (QDs), embedded in a GaAs layer grown by molecular beam epitaxy, are investigated by the low-frequency noise measurements using the Au∕n-GaAs Schottky diode as a test device. The forward current noise spectra are composed of two noise components: a 1∕f-like noise at low frequencies and a generation-recombination (g-r) noise at higher frequencies. The 1∕f noise is ascribed to the mobility fluctuations within the space-charge region. The obtained Hooge parameter (αH=6×10−5) is larger than the expected value considering the phonon or impurity scattering mechanism, indicating the presence of the defects associated with QDs. The analysis of the g-r noise gives a single trap of density of about 1.6×1014cm−3 in the part of the GaAs layer located above the QDs.

Low-frequency noise spectroscopy of polycrystalline silicon thin-film transistors

Polycrystalline silicon thin-film transistor (polysilicon TFT's) characteristics are evaluated by using a low-frequency noise technique. The drain current fluctuation caused by trapping and detrapping processes at the grain boundary traps is measured as the current spectral density. Therefore, the properties of the grain boundary traps can be directly evaluated by this technique. The experimental data show a transition from 1/f behavior to a Lorentzian noise. The 1/f noise is explained with an existing model developed for monocrystalline silicon based on fluctuations of the inversion charge near the silicon-oxide interface. The Lorentzian spectrum is explained by fluctuations of the grain boundary interface charge with a model based on a Gaussian distribution of the potential barriers over the grain boundary plane. Quantitative analysis of the 1/f noise and the Lorentzian noise yield the oxide trap density and the energy distribution of the grain boundary traps within the forbidden gap.