Low-frequency Noise Properties Research Articles

Optimum Choice of Randomly Oriented Carbon Nanotube Networks for UV-Assisted Gas Sensing Applications.

We investigated the noise and photoresponse characteristics of various optical transparencies of nanotube networks to identify an optimal randomly oriented network of carbon nanotube (CNT)-based devices for UV-assisted gas sensing applications. Our investigation reveals that all of the studied devices demonstrate negative photoconductivity upon exposure to UV light. Our studies confirm the effect of UV irradiation on the electrical properties of CNT networks and the increased photoresponse with decreasing UV light wavelength. We also extend our analysis to explore the low-frequency noise properties of different nanotube network transparencies. Our findings indicate that devices with higher nanotube network transparencies exhibit lower noise levels. We conduct additional measurements of noise and resistance in an ethanol and acetone gas environment, demonstrating the high sensitivity of higher-transparent (lower-density) nanotube networks. Overall, our results indicate that lower-density nanotube networks hold significant promise as a viable choice for UV-assisted gas sensing applications.

Effects of plasmon resonance on the low frequency noise and optoelectronic properties of Au/Cu codoped ZnO based photodetectors

We have investigated the effect of Au nanoparticles on the low frequency noise and current-voltage of Au/Cu doped ZnO nanoparticles (Nps) based photodetectors (PDs). Besides, 1/f noise of Cu doped ZnO is studied with and without Au Nps conditions and varied bias voltages. The Au/Cu codoped ZnO Nps showed much lower 1/f noise and higher normalized photocurrent to the dark current ratio (NPDR) than Cu doped ZnO Nps and undoped ZnO Nps. This enhancement may be attributed to the effect of localized surface Plasmon resonances (LSPR). Furthermore, the noise equivalent power represents the minimum optical power that a photodetector can distinguish from the noise and the detectivity (D*) is an important parameter in evaluating the ability of a photodetector to detect a weak signal. These parameters were determined using low frequency noise measurements. The observed low frequency noise performances could be used for Au/Cu codoped ZnO Nps based UV photodetectors.

Effect of high-pressure D2 and H2 annealing on LFN properties in FD-SOI pTFET

Tunneling field-effect transistors (TFETs) are a promising candidate for the next generation of low-power devices, but their performance is very sensitive to traps near the tunneling junction. This study investigated the effects of high-pressure deuterium (D2) annealing and hydrogen (H2) annealing on the electrical performance and low-frequency noise (LFN) of a fully depleted silicon-on-insulator p-type TFET. Without high-pressure annealing, the typical noise power spectral density exhibited two Lorentzian spectra that were affected by fast and slow trap sites. With high-pressure annealing, the interface trap density related to fast trap sites was reduced. The passivation of traps near the tunneling junction indicates that high-pressure H2 and D2 annealing improves the electrical performance and LFN properties, and it may become a significant and necessary step for realizing integrated TFET technology in the future.

A Study on Dominant Mechanism and Analytical Model of Low-Frequency Noise in FD-SOI pTFET

The origin of low-frequency noise (LFN) properties and the accuracy of LFN model were demonstrated in a fully depleted silicon-on-insulator p-type tunneling field-effect transistor (pTFET). We demonstrated that the origin of LFN properties in pTFET can be deduced and analyzed via the current fluctuation induced by tunneling in the pTFET operation region. Since the trap sites near the tunneling junction contributed to LFN, pTFET must consider the tunneling junction characteristics and channel transportation influences. The tunneling path was not formed at low |VGS| and the carrier transport in pTFET crossed the energy band by Shockley-Read-Hall (SRH) generation-recombination or the trap-assisted tunneling (TAT) mechanism and not through band-to-band tunneling (BTBT). However, with the increase in |VGS|, the tunneling path was formed and the carriers could flow through the energy band by BTBT. The correlation between the simulated model data and experimental data was examined, confirming that the proposed small-signal model accurately represents noise in pTFETs.

Review of Low-Frequency Noise Properties of High-Power White LEDs during Long-Term Aging.

Low-frequency noise investigation is a highly sensitive and very informative method for characterization of white nitride-based light-emitting diodes (LEDs) as well as for the evaluation of their degradation. We present a review of quality and reliability investigations of high-power (1 W and 3 W) white light-emitting diodes during long-term aging at the maximum permissible forward current at room temperature. The research was centered on the investigation of blue InGaN and AlInGaN quantum wells (QWs) LEDs covered by a YAG:Ce3+ phosphor layer for white light emission. The current-voltage, light output power, and low-frequency noise characteristics were measured. A broadband silicon photodetector and two-color (blue and red) selective silicon photodetectors were used for the LED output power detection, which makes it possible to separate physical processes related to the initial blue light radiation and the phosphor luminescence. Particular attention was paid to the measurement and interpretation of the simultaneous cross-correlation coefficient between electrical and optical fluctuations. The presented method enables to determine which part of fluctuations originates in the quantum well layer of the LED. The technique using the two-color selective photodetector enables investigation of changes in the noise properties of the main blue light source and the phosphor layer during the long-term aging.

Noise diagnostics of graphene interconnects for atomic-scale electronics

Graphene nanogaps are considered as essential building blocks of two-dimensional electronic circuits, as they offer the possibility to interconnect a broad range of atomic-scale objects. Here we provide an insight into the microscopic processes taking place during the formation of graphene nanogaps through the detailed analysis of their low-frequency noise properties. Following the evolution of the noise level, we identify the fundamentally different regimes throughout the nanogap formation. By modeling the resistance and bias dependence of the noise, we resolve the major noise-generating processes: atomic-scale junction-width fluctuations in the nanojunction regime and sub-atomic gap-size fluctuations in the nanogap regime. As a milestone toward graphene-based atomic electronics, our results facilitate the automation of an optimized electrical breakdown protocol for high-yield graphene nanogap fabrication.

Low-Frequency Seismic Noise Properties in the Japanese Islands.

The records of seismic noise in Japan for the period of 1997–2020, which includes the Tohoku seismic catastrophe on 11 March 2011, are considered. The following properties of noise are analyzed: The wavelet-based Donoho–Johnston index, the singularity spectrum support width, and the entropy of the wavelet coefficients. The question of whether precursors of strong earthquakes can be formulated on their basis is investigated. Attention is paid to the time interval after the Tohoku mega-earthquake to the trends in the mean properties of low-frequency seismic noise, which reflect the constant simplification of the statistical structure of seismic vibrations. Estimates of two-dimensional probability densities of extreme values are presented, which highlight the places in which extreme values of seismic noise properties are most often realized. The estimates of the probability densities of extreme values coincide with each other and have a maximum in the region: , . The main conclusions of the conducted studies are that the preparation of a strong earthquake is accompanied by a simplification of the structure of seismic noise. It is shown that bursts of coherence between the time series of the day length and the noise properties within annual time window precede bursts of released seismic energy. The value of the lag in the release of seismic energy relative to bursts of coherence is about 1.5 years, which can be used to declare a time interval of high seismic hazard after reaching the peak of coherence.

Magnetic, magnetoresistive and low-frequency noise properties of tunnel magnetoresistance sensor devices with amorphous CoFeBTa soft magnetic layers

Magnetic field sensors using the tunnel magnetoresistance (TMR) effect require linear resistance–magnetic field (R–H) response curves with small hysteresis, for which the soft magnetic property of the free layer (FL) is critical. In this work, we investigated amorphous CoFeBTa (CFBT) as a soft magnetic layer of the FL of CoFeB/MgO/CoFeB-based magnetic tunnel junctions in view of magnetic, TMR, and low-frequency noise properties. A two-step annealing process enabled an orthogonal magnetization configuration between the FL and the reference layer, by which linear R–H curves with small hysteresis were realized. The change in the shape of the R–H curve depending on annealing temperature is explained by the Stoner–Wohlfarth model. The highest TMR ratio of ∼160% and sensitivity of ∼70%/mT were obtained with a CFBT (20 nm)/Ta (0.3 nm)/CoFeB (3 nm) FL. The noise of the TMR devices are dominated by 1/f noise below ∼10 kHz in frequency, which limits the detectivity (D) of the magnetic field of the sensor. The sensor devices patterned to 50 µm diameter circular shapes showed a minimum D of ∼2 nT/ at 10 Hz, which is superior to the previously reported values for the TMR sensors with NiFe soft magnetic layers.

Temperature dependent Schottky barrier characteristics of Al/n-type Si Schottky barrier diode with Au–Cu phthalocyanine interlayer

The Al/n-type Si Schottky barrier diodes (SBDs) were prepared with Au-Cu phthalocyanine (Au-CuPc) interlayers with different Au and CuPc compositional ratios, probed their temperature dependent current-voltage (I–V) and low frequency noise properties. The Schottky barrier properties like barrier height and the ideality factor are strongly temperature dependent, implying the existence of Schottky barrier inhomogeneities. The barrier inhomogeneities was elucidated using thermionic emission theory based on the assumption of Gaussian distribution of the barrier heights. Further, a divergence in the barrier heights evaluated from the I–V characteristics and Norde's method indicates a deviation of the Al/Au–CuPc/n-type Si SBDs behavior from thermionic emission. The Richardson plot evaluated with the Gaussian distribution of barrier heights method yielded Richardson constant values close to theoretical Richardson constant of n-type Si. The room temperature current noise power spectral density (SI) of the Al/Au–CuPc/n-type Si SBDs having various Au and CuPc concentrations showed a reciprocal of frequency (1/f)γ behavior having γ values near to unity. The decrease in SI and γ with increasing Au concentration in Au-CuPc interlayers was indicative of lessening barrier inhomogeneity. This was also correlated with the decrease in the value of standard deviation derived using temperature dependent I–V characteristics. Further investigations revealed that origins of 1/f noise could be associated with the fluctuations of barrier height and carrier mobility for Al/Au–CuPc/n-type Si SBDs with lower and higher Au compositions in Au-CuPc interlayers, respectively.

Rapid Four-Point Sweeping Method to Investigate Hysteresis of MoS2 FET

Hysteresis is a frequently observed phenomenon in the transfer characteristics of thin film transistors. Charge trapping/de-trapping processes of gate oxide and gate-channel interface are commonly known to be the origin of hysteresis and correlated to low frequency noise (LFN) properties of the devices. In this letter, a rapid four-point sweeping method (RFSM) is proposed to reveal the dependence of hysteresis, as well as the distribution of effective trap density on sweeping rate and gate bias range. Based on the RFSM, the hysteresis properties of four-layer MoS2 FETs are studied in detail. The experimental results demonstrate that the hysteresis and trap density at different frequencies and gate voltages, which could further roughly map the traps with different time constants and energy depths, can be obtained by the simple RFSM. Trap density estimated by RFSM shows a comparable range with that extracted from LFN, indicating that the traps inducing the hysteresis may also cause LFN.

Low-frequency noise and thermal equilibrium properties of vacancies

A model explaining Lorentzian low-frequency noise spectra observed in electronic interconnects is presented. The model is based on the interaction of electrons with vacancies, whose thermodynamic equilibrium properties determine the temperature dependence of the noise. The model, therefore, allows calculating vacancy formation and migration enthalpies. It is experimentally verified on copper and tungsten interconnects; the sum of formation and migration enthalpies matches the electromigration activation energy obtained using standard accelerated tests.

Investigation on trap density depending on Si ratio in amorphous SiZnSnO thin-film transistors

High-performance amorphous SiZnSnO thin-film transistors (a-SZTO TFTs) were fabricated using radio-frequency (RF) magnetron sputtering. The noise spectral density of a-SZTO TFTs measured by using the drain current has been reported, and it was found that is possible to apply the conventional 1/fa theory to the low-frequency noise (LFN) of the a-SZTO TFTs. The LFN characteristics of a-SZTO TFTs can be clearly identified by the correlated number fluctuation-mobility fluctuation model. Based on the noise properties, the interfacial trap density (NT) was decreased from 2.32 × 1019 to 1.33 × 1019 cm−3 eV−1 as increasing Si ratio in a-SZTO TFTs. The electrical characteristics and LFN properties of a-SZTO TFTs varied strongly depending on the Si ratio, mainly because the Si atom can act as an oxygen vacancy suppressor.

Free-standing La0.7Sr0.3MnO3 suspended micro-bridges on buffered silicon substrates showing undegraded low frequency noise properties

We report on the microfabrication process of free-standing suspended micro-bridges made of La0.7Sr0.3MnO3 (LSMO) thin films of thicknesses in the range of 10–100 nm. LSMO films were epitaxially grown on either SrTiO3 or CaTiO3 buffer layers on silicon substrates by reactive molecular beam epitaxy. The micro-bridges were patterned using standard UV photolithography then etched by ion beam and released using reactive ion etching of silicon in SF6. LSMO suspended micro-bridges 2 and 4 µm wide and of length ranging from 50 to 200 µm could be fabricated with a high fabrication yield (of about 85% as evaluated over 100 fabricated suspended micro-bridges) without degrading the electrical transport properties and in particular the low frequency noise level, as attested by the normalized Hooge parameter. The latter was measured in the 0.55–7.50 × 10−30 m3 range at 300 K, which is comparable to those measured in non-suspended high quality epitaxial LSMO thin films. This fabrication process could be useful for bolometer fabrication where thermal isolation is needed, or for any microelectromechanical systems devices making use of epitaxial functional oxides.

Low-Frequency Noise Characteristics in Multilayer MoTe2 FETs With Hydrophobic Amorphous Fluoropolymers

This letter investigates the low-frequency noise (LFN) properties of the multilayer MoTe2 field-effect transistors (FETs) before and after hydrophobic amorphous polymer (CYTOP) encapsulation in the subthreshold and linear regimes. The noise spectrum density of drain current (SID) shows that the LFN in the multilayer MoTe2 FETs nicely fits to a 1/ $f^{\gamma }$ power law with $\gamma \sim \textsf {1}$ in the frequency range of 10–200 Hz. From the dependence of SID on the drain current, carrier number fluctuation ( $\Delta n$ ) is considered as a dominant LFN mechanism from all operation regimes in the multilayer MoTe2 FETs. Extracted trap density (Nt) based on the McWhorter model in this letter was reduced at least more than one order level compared with the multilayer MoTe2 FETs without CYTOP passivation.

Cyclic Properties of Seismic Noise and the Problem of Predictability of the Strongest Earthquakes in Japanese Islands

The results of an analysis of the properties of low-frequency seismic noise in the Japanese Islands from early 1997 to March 2018 are presented. The time interval under consideration includes one of the largest seismic disasters of recent times, the Tohoku earthquake of March 11, 2011. The presence of a dense network of seismic observations provides a unique opportunity to investigate how the preparation of a strong earthquake is reflected in changes in the properties of seismic noise in time and space. An analysis of the clustering of the daily multifractal and entropic properties of seismic noise in a 1-year moving time window averaged over all stations of the network made it possible to find a 2.5-year periodicity established since the beginning of 2003. This periodicity correlates with the occurrence of strong earthquakes in Japan. Studying features of the spatial distribution of seismic-noise properties allows us to put forward a hypothesis about the increased danger of the next megaearthquake in Japan in the area of the contact between the northern boundary of the Philippine Sea plate and Honshu Island, in the Nankai deepwater trough area, not far from Tokyo. In the Japanese Islands, in addition to the network of seismic observations, there is a dense network of fixed GPS points for which observations are available from the beginning of March 2015 with a time step of 5 min. The availability of such measurements makes it possible to complement the analysis of seismic-noise properties and to calculate the degree of correlation of GPS data at any point from measurements at neighboring stations. An analysis and processing of measurement results show that the most intense spot of increased correlation of the Earth’s surface tremor, measured using GPS, is located in the Nankai Trough, with the center at the point of 34° N and 138° E.

Downscaling AsTeGeSiN threshold switching devices for high‐density 3D memories

In high-density three-dimensional (3D) memory technology, a stacking method is used to create memory devices and access devices at the intersections of bit lines and word lines. For this application, access devices should have a high on/off ratio, high current density for writing cycles, and high endurance. Consequently, an arsenic–tellurium–germanium–silicon nitride compound (AsTeGeSiN) threshold switching device with a high current density of 10 4 A/cm 2 above the threshold voltage ( V th ) is reported as a good candidate for use in access devices. In addition, scaling down of access devices as well as memory devices is essential for high-density 3D memories. However, in AsTeGeSiN threshold switching devices, fast degradation by pulse cycling in smaller devices is observed. To find the main cause of fast degradation by pulse cycling in smaller devices, the low-frequency noise properties are examined. The rapid increase in the trap density ( N T ) in small devices is the main cause of fast degradation by pulse cycling in AsTeGeSiN devices. On the basis of this evaluation, the author examines the effect of annealing temperature and annealing time on the pulse endurance in smaller devices. Using an annealing temperature of ∼600°C improves the cycling endurance of smaller devices.

Tunable Low-Frequency Noise in Dual-Gate MoS2Transistors

We have systematically studied the effect of the back-gate voltage on the low-frequency noise properties of the MoS2 transistors from 300 to 20 K in this work. The results show that the performance of the top-gate MoS2 transistor can be effectively tuned by the back-gate voltage ${V}_{\text {bg}}$ . When ${V}_{\text {bg}}$ increases to 20 V, the maximum on-current increases up to 588 $\mu \text{A}$ / $\mu \text{m}$ for the 1- $\mu \text{m}$ channel length device, as well as five times reduction of the low-frequency noise and two times reduction in contact resistance. The Fermi-level modulation by adjusting ${V}_{\text {bg}}$ turns out to be an effective way of improving contact resistance and low-frequency noise for future high-quality MoS2 metal-oxide–semiconductor field-effect transistors.

Characterization of Low-Frequency Excess Noise in CH3NH3PbI3-Based Solar Cells Grown by Solution and Hybrid Chemical Vapor Deposition Techniques.

In this study, detailed investigations of low-frequency noise (LFN) characteristics of hybrid chemical vapor deposition (HCVD)- and solution-grown CH3NH3PbI3 (MAPI) solar cells are reported. It has been shown that LFN is a ubiquitous phenomenon observed in all semiconductor devices. It is the smallest signal that can be measured from the device; hence, systematic characterization of the LFN properties can be utilized as a highly sensitive nondestructive tool for the characterization of material defects in the device. It has been demonstrated that the noise power spectral densities of the devices are critically dependent on the parameters of the fabrication process, including the growth ambient of the perovskite layer and the incorporation of the mesoscopic structures in the devices. Our experimental results indicated that the LFN arises from a thermally activated trapping and detrapping process, resulting in the corresponding fluctuations in the conductance of the device. The results show that the presence of oxygen in the growth ambient of the HCVD process and the inclusion of an mp-TiO2 layer in the device structure are two important factors contributing to the substantial reduction in the density of the localized states in the MAPI devices. Furthermore, the lifetimes of the MAPI perovskite-based solar cells are strongly dependent on the material defect concentration. The degradation process is substantially more rapid for the devices with higher initial defect density compared to the devices prepared under optimized conditions and structure that exhibit substantially lower initial trap density.

Low-frequency noise properties of MgZnO nanorod ultraviolet photodetectors with and without UV illumination

Low-frequency current noise measurements were performed on Mg-doped ZnO (MZO) nanorod photodetectors (PD), and 1/f noise was observed in both dark and under ultraviolet (UV) illumination. Results show that the average length and diameter of the nanorods were 609 nm and approximately 50nm, respectively. The X-ray diffraction spectrum showed that the Mg-doped ZnO nanorods had a wurtzite hexagonal sturcture. The photoelectric properties of the nanorods were stable under UV illumination. The resulting Mg-doped ZnO nanorods had excellent potential for UV photodetector applications. Mg-doped ZnO nanorod UV photodetectors had a high UV-to-visible ratio and a fast rise/fall time. The dynamic response of the Mg-doped ZnO nanorod photodetector was stable and reproducible with an on/off current contrast ratio of approximately 4×103. The UV-to-visible rejection ratio of the sample was approximately 400 when biased at 1V, and the fabricated UV photodetector was visible-blind with a sharp cutoff at 350nm. The low-frequency noise spectra obtained from the UV photodetector were caused by the 1/f noise. The noise-equivalent power (NEP) and normalized detectivity (D*) of the Mg-doped ZnO nanorod PD were 3.35×10−10W and 1.49×108 cmHz0.5W−1, respectively. Under UV illumination, the NEP and D* were 1.8×10−6 W and 2.7×106 cmHz0.5W−1, respectively.

Effects of various bias and temperature stresses on low-frequency noise properties of amorphous InGaZnO thin-film transistors

The authors investigate the low-frequency noise (LFN) properties of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) under various bias and temperature stress conditions. After application of a gate-to-source bias (VGS) stress, the LFN properties hardly change. However, the LFN increases (especially, at low drain currents) after application of simultaneous VGS and drain-to-source bias (VDS) stresses. The LFNs measured before and after the stresses are well-fitted using the correlated number fluctuation-mobility fluctuation (Δn-Δμ) model, and the extracted values of the border trap density (NT) and the Coulomb scattering coefficient (αS) increase from 1018 eV−1 cm−3 and 105 V s/C to 1.53 × 1019 eV−1 cm−3 and 106 V s/C, respectively, after application of simultaneous gate- and drain-bias stresses (VGS = VDS = 20 V) for 1000 s at room temperature. This phenomenon is mainly attributed to the high electric-field-induced electronic trap generation inside the a-IGZO active layer. The increase in temperature during application of the simultaneous gate- and drain-bias stress accelerates the increase of LFN after the stress. The values of NT and αS are increased to 9.53 × 1019 eV−1 cm−3 and 8 × 106 V s/C, respectively, after the application of simultaneous gate- and drain-bias stresses for 1000 s at 80 °C, which are much higher than those extracted after the application of simultaneous gate- and drain-bias stresses at room temperature. This result shows that a high electric field combined with a high temperature significantly increases the density of electronic trap states which degrades the LFN properties in a-IGZO TFTs.