Mobility Fluctuations Research Articles

Suppression of 1/f noise in graphene due to anisotropic mobility fluctuations induced by impurity motion

Low frequency resistance variations due to mobility fluctuations is one of the key factors of 1/f noise in metallic conductors. According to theory, such noise in a two-dimensional (2D) device can be suppressed to zero at small magnetic fields, implying important technological benefits for low noise 2D devices. In this work, we provide evidence of anisotropic mobility fluctuations by demonstrating a strong field-induced suppression of noise in a high-mobility graphene Corbino disk, even though the device displays only a tiny amount of 1/f noise inherently. The suppression of the 1/f noise depends on charge density, showing less non-uniform mobility fluctuations away from the Dirac point with charge puddles. We model our results using an approach based on impurity clustering dynamics and find our results consistent with the 1/f noise induced by scattering of carriers on mobile impurities forming clusters.

Study on low-frequency noise characteristics of hydrogen-terminated diamond FETs

In this work, the low frequency noise (LFN) characteristics of Hydrogen-terminated diamond FETs are investigated. Both generation-recombination (GR) noise and flicker noise (1/f noise) are found to contribute to the LFN spectrum. The characteristic frequency of f01 = 0.1 Hz, f02 = 30 Hz, f03 = 300 Hz and corresponding effective trap density (Neff) of the GR centers are obtained. By changing the LFN measurement temperature, a trap activation energy level (Ea) of 0.12 eV is extracted from an Arrhenius plot. The dominant mechanism of the 1/f noise for the H-terminated diamond FETs follows the correlated mobility fluctuations (CMF) model. By fitting the experimental data to the CMF model, the trap density and scattering coefficient of the carriers are extracted to be 6.4×1020 eV−1 cm−3 and 4×105 V·s/C. At last, the trap density of the H-terminated diamond FETs is compared with other state-of-the-art GaN and Si based devices. A moderate trap density was obtained without any interface optimization, suggesting that H-terminated diamond FETs could be a promising future technology for power electronics.

Novel Y-function based strategy for parameter extraction in S/D asymmetric architecture devices and low frequency noise characterization in GAA Si VNW pMOSFETs

In this work, DC and low frequency noise measurements are performed in p-channel gate-all-around (GAA) silicon vertical nanowire (Si VNW) MOSFETs. The DC measurements highlight asymmetry in the drain current and transconductance transfer characteristic even in linear operation, at an applied drain voltage of −50 mV. A novel Y-function based strategy for parameter extraction in S/D asymmetric devices is proposed. This novel strategy allows the estimation of the value of each access resistance, from source and from drain sides, respectively, and allows overcoming the device asymmetry to provide an accurate extraction of the main DC parameters. The low-frequency noise studies on forward and reverse operation mode, demonstrate that the 1/f noise in both modes can be explained by the correlated carrier number (Δn) and mobility fluctuation (Δμ) mechanisms, with additional contribution of the access resistance noise in strong inversion.

Second spectrum of 1/f noise due to mobility fluctuations: Simulations vs experiments in suspended graphene

Mobility fluctuations have been observed to influence 1/f noise in mesoscopic two-dimensional conductors in recent experiments. If such mobility noise can be assigned to clustering/declustering of defects/impurities, the second spectrum should also display 1/f character. In this work, we investigate the second spectrum of noise due to mobile impurities on a two-dimensional lattice both using kinetic Monte Carlo simulations (periodic boundary conditions either in one or two directions) and experiments on suspended graphene in Corbino geometry. The simulations indicate 1/fδ behavior with δ≃0.8 ± 0.15 for the second spectrum of noise, while the experiments on suspended graphene yield an exponent δ≃0.7 ± 0.3, independent of the amount of adsorbed atoms.

Exploring the Association between Mobility Fluctuations and Socioeconomic Indicators Using Data Mining Techniques in Indonesia and Malaysia

Human mobility has become a global issue during the Covid-19 pandemic and is believed to be a critical factor in the transmission of Covid -19. The timetable for the government's movement control has stimulated the fluctuation of national mobility. However, the characteristics of variations between regions of the country are not yet understood. The purpose of this study was to characterise community mobility fluctuations in Indonesia and Malaysia and identify the association between socioeconomic indicators and mobility fluctuations in regions. This secondary and exploratory research investigated 34 Indonesian provinces and 14 Malaysian states. Data mining approaches using the CRISP-DM framework and the Knime Analytics platform was used. As a result, Indonesia and Malaysia show the strength of mobility fluctuations in decreasing order: transit stations, workplaces, and residential areas. Malaysia shows higher mobility fluctuations than Indonesia, which may indicate the community's response to the Covid-19 pandemic. As socioeconomic indicators, Human Development Index (HDI), poverty rate, and labor force participation are associated with the fluctuation of mobility. Therefore, regions with high fluctuation in mobility will likely have high HDI, high labour force participation rates, and low poverty rates. High-mobility areas include capitals and other cities with high-density populations. This study provides evidence that socioeconomic indicators are determinants of mobility fluctuation during the pandemic. Regional governments may use the findings to anticipate community mobility and planning policies when similar pandemic conditions occur.

Low-frequency noise in quasi-ballistic monolithic Al–Ge–Al nanowire field effect transistors

In this work, Al2O3-passivated, monolithic, and crystalline Al–Ge–Al heterostructure nanowire field effect transistors (FETs) with Ge channel lengths ranging from 18 to 826 nm are analyzed from a low-frequency noise perspective. 1/f and random telegraph noise (RTN) are analyzed in an accumulation mode, where the hole channel is formed by applying a back-gate potential VG. The normalized power spectral density of drain current fluctuations of 1/f noise (SID/ID2) at medium currents follows nearly an 1/ID trend. 1/f noise is analyzed within both the mobility and carrier number fluctuation models (MFM and CNFM), respectively. Taking the MFM into account, the Hooge noise parameter α spreads in the interval of 1.5 × 10−4 to 4 × 10−2, with lower values for shorter devices. Using the same data and the CNFM, the density of interface states Dit in the Al2O3/GexOy/Ge system was estimated using the transconductance extracted from the quasi-static transfer I/V characteristics. The extracted Dit values range from 5 × 109 to 3 × 1012 cm−2 eV−1. Contact noise has also been observed in some devices at high currents. RTN analyzed in time domain exhibits a relative RTN amplitude in the 0.3%–20% range. Capture and emission time constants as a function of VG exhibit a typical behavior for metal oxide semiconductor FETs. The extracted noise parameters are comparable with Ge and III–V nanodevices of top-down and bottom-up technologies.

Universality of trap-induced mobility fluctuations between 1/f noise and random telegraph noise in nanoscale FD-SOI MOSFETs

Low frequency noise (LFN) and random telegraph noise (RTN) are investigated statistically on nanoscale MOSFETs of 28 nm fully depleted silicon-on-insulator technology. The analysis reveals that the mean noise level is well described by the carrier number fluctuations with a correlated mobility fluctuations model. As for the RTN, it is shown that the mean amplitude of signals is driven by correlated mobility fluctuations in strong inversion. The comparison between the extracted parameters of the LFN and RTN analysis demonstrates that the remote Coulomb scattering impact due to the trapped and detrapped charges remains the same on average for this technology, whether it is the average noise spectrum of all devices or the average amplitude of the detected RTN signals.

Disinformation as a factor of manipulation consciousness

About disinformation and manipulating human consciousness, in particular in the information sphere. It is substantiated that manipulation, as one of the types of information attacks, interferes with the normal life activities of a person, which makes it impossible to form a stable system of information relations, stimulates unpredictable mobility and sharp fluctuations of socio-political orientations and assessments in the population, which, as a result, transforms into instability of social and of political processes in the country as a whole and into significant threats to the security of people, society and the state.

(Invited) In-Depth DC and Low Frequency Noise Characterization of Nanosheet FETs at Room and Cryogenic Temperatures

In this work, an in-depth static and low frequency noise characterization of nanosheet FETs, consisting of two vertically stacked silicon channels per device, is performed. A comparison of the performances from n- versus p-channel FETs operated at 300 K and 78 K, in terms of static and low frequency noise parameters variability, is also discussed. The main electrical parameters are estimated from the I-V characteristics using access resistance robust methodologies. An additional criterion demonstrating that the extracted parameters are not influenced by the second mobility attenuation factor is proposed. The low frequency noise studies prove that the dominant flicker noise mechanism is linked to correlated carrier number and mobility fluctuations, with additional access resistances noise contribution in very strong inversion. The importance of the considered total flicker noise model on the estimation of the Coulomb scattering coefficient is highlighted.

Interface traps, correlated mobility fluctuations, and low-frequency noise in metal–oxide–semiconductor transistors

Interface traps generally are not considered to be likely sources of low-frequency (LF) noise and/or random telegraph noise (RTN) in metal–oxide–semiconductor (MOS) devices because the longer carrier exchange times of border traps are more consistent with experimental observations. In contrast, correlated mobility fluctuations due to remote Coulomb scattering from charged border traps cannot explain the unexpectedly large LF noise and/or RTN observed in some MOS devices. In this Letter it is proposed that equilibrium fluctuations in interface-trap concentrations caused by hydrogen-induced activation and passivation reactions can lead to enhanced LF noise and RTN. This mechanism adds to other noise sources, including border traps, random dopants, and bulk-Si defect clusters.

Low-frequency noise characteristics of indium–gallium–zinc oxide ferroelectric thin-film transistors with metal–ferroelectric–metal–insulator–semiconductor structure

We investigate the low-frequency noise characteristics of indium–gallium–zinc oxide ferroelectric thin-film transistors (FeTFTs) with a metal–ferroelectric–metal–insulator–semiconductor (MFMIS) structure. MFMIS FeTFTs are fabricated with different metal-to-FE area ratios (AM/AF's). It is revealed that the noise generation mechanism differs depending on the operation region [low and high drain current (ID) regions] and AM/AF. Excess noise in the low ID region is observed in the MFMIS FeTFTs with AM/AF's of 4 and 6 due to carrier mobility fluctuations. In the high ID region, the carrier number fluctuation generates the 1/f noise of the devices regardless of the AM/AF.

Optimization of electrical performance and stability of fully solution-driven α-InGaZnO thin-film transistors by graphene quantum dots

• Fully solution-derived GQDs-IGZO TFTs based on ZrO 2 as gate dielectrics have been achieved. • GQDs-IGZO TFTs devices with optimized doping content have demonstrated improved performances, including a μ FE of 35.91 cm 2 V –1 s –1 , a higher I ON / I OFF of 5.04 × 10 8 , a smaller subthreshold swing (SS) of 0.11 V dec –1 and a smaller interfacial trap states of 1.57 × 10 12 cm −2 . • Resistor-loaded unipolar inverter based on GQDs-IGZO/ZrO x has been integrated, demonstrating good dynamic behavior and a high gain of 9.3. • LFN characteristics of GQDs-IGZO/ZrO x TFTs have suggested that the fluctuations in mobility are the noise source. This work presents solution-processed high-performance graphene quantum dots (GQDs) decorated amorphous InGaZnO (α-IGZO) thin-film transistors (TFTs) based on ZrO x as gate dielectrics. Compare with pure IGZO TFTs, GQDs-modified α-IGZO TFTs devices with optimized doping content have demonstrated better performances, including a larger field-effect mobility ( μ FE ) of 35.91 cm 2 V –1 s –1 , a higher on/off current ratio ( I ON / I OFF ) of 5.04 × 10 8 , a smaller subthreshold swing (SS) of 0.11 V dec –1 and a smaller interfacial trap states ( D it , 1.57 × 10 12 cm −2 ). Moreover, the GQDs-doped IGZO TFTs with a doping concentration of 0.5 mg ml –1 have shown excellent stability under bias stress and illumination stress conditions. To demonstrate the potential applications of α-IGZO TFTs in logic circuits, a resistor-loaded unipolar inverter based on GQDs-IGZO/ZrO x has been integrated, demonstrating good dynamic behavior and a high gain of 9.3. Low-frequency noise (LFN) characteristics of GQDs-IGZO/ZrO x TFTs have suggested that the fluctuations in mobility are the noise source. Based on all the experimental findings, it can be concluded that solution-processed GQDs-IGZO/ZrO x TFT may envision promising applications in optoelectronics.

On Reducing LDE Variations in Modern Analog Placement

Layout-dependent (LDEs) introduce an inevitable performance degradation in analog and mixed-signal circuit design with advanced process technologies below 90 nm. The main LDE sources, including the well proximity effect (WPE), length of diffusion (LOD), and the oxide-to-oxide spacing effect (OSE), cause substantial fluctuations in carrier mobility and threshold voltage of transistors. In traditional design flows, impact of these in post-layout simulation, leading to expensive re-design iterations by inspecting the physical locations of devices with respect to one another. In this article, we introduce the concept of an ideal mobility multiplier based on physics models, in order to minimize the LDE effects with a fast simulated annealing algorithm through various LDE alleviating operations. Based on the introduced mobility multiplier and the hierarchical B*-tree (HB*-tree) topological representation, our LDE-aware analog placement methodology can simultaneously optimize not only the area and wire length, but also the LDEs, while maintaining linear-packing time complexity of HB*-trees. Compared to the most recent works on 65 nm-based analog circuits, experimental results show that the proposed method can effectively and efficiently reduce LDE variations, while improving the circuit performance.

On-Wafer Drain Current Variability in GaN MIS-HEMT on 200-mm Silicon Substrates

In this study, a detailed on-wafer (or global) variability analysis of drain current characteristics of GaN MIS-HEMT devices grown on 200 mm silicon substrate is conducted. For the first time to our knowledge, the on-wafer variability sources in GaN technologies due to the manufacturing process are investigated by combining experimental data and analytical variability modeling. The key parameters which affect the variability are oxide the interface charge fluctuations, the mobility fluctuations, the gate oxide thickness and/or the gate area variations and the access resistance fluctuations in the contact as well as in the 2DEG regions (source and drain sides). Due the specificity of GaN MIS HEMT device engineering process, we show that their variability performances are not, for the time being, comparable to the state-of-the art silicon CMOS technologies, and this can be valuable for reliable improvement and optimization of GaN technology fabrication process. This study has been verified over a large range of channel gate lengths for three normally-off GaN MIS-HEMT wafers and having different gate process flows.

In-depth static and low frequency noise assessment of p-channel gate-all-around vertically stacked silicon nanosheets

In this work are investigated the DC and low frequency noise room-temperature operation of p-channel gate-all-around (GAA) vertically stacked silicon nanosheets (NS). The key DC parameters are estimated using methodologies which are not affected by the impact of the access resistance. Low frequency noise studies shown that the carrier number fluctuations correlated to the mobility fluctuations mechanism explain the 1/f behavior from weak to moderate inversion. It is also discussed how access resistance can have an affect on the Coulomb scattering coefficient estimation. In strong inversion, the access resistance noise contribution is seen to dominates the total 1/f noise.

Refined DC and Low-Frequency Noise Characterization at Room and Cryogenic Temperatures of Vertically Stacked Silicon Nanosheet FETs

In this work, two types of gate-all-around (GAA) vertically stacked silicon nanosheet (NS) FETs are investigated, the main difference being the vertical distance between the stacked NSs. Principal electrical parameters are estimated at room and liquid nitrogen temperatures using a refined <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Y}$ </tex-math></inline-formula> -function methodology, the main advantage being that no extra iterative steps are necessary. The results are confirmed using other derivative dc parameter estimation methodologies. Low-frequency noise measurements evidence variability of the flat-band voltage noise and correlation between the noise level and the low field mobility. The dominant flicker noise mechanism is related to the correlated mobility and carrier number fluctuation mechanism with access resistance noise contribution in very strong inversion. The impact of the access resistance on the estimation of the Coulomb scattering coefficient is evidenced.

Low-frequency noise in nanowires.

40 years of research on low-frequency (LF) noise and random-telegraph noise (RTN) in metallic and semiconducting nanowires (NWs) demonstrate the importance of defects and impurities to each system. The fluctuating interference of electrons in the local environment of a mobile bulk defect or impurity can lead to LF noise, RTN, and device-to-device variations in metallic and semiconducting NWs. Scattering centers leading to mobility fluctuations in semiconducting NWs include random dopant atoms and bulk defect clusters. Effective energy distributions for the relevant defects and impurities can be obtained from noise versus temperature measurements in conjunction with the Dutta-Horn model of LF noise for both metallic and semiconducting NWs. In semiconducting NWs configured as metal-oxide-semiconductor field-effect transistors, fluctuations in carrier number due to charge exchange with border traps, such as oxygen vacancies and/or their complexes with hydrogen in adjacent or surrounding dielectrics, often dominate or add to bulk noise sources.

Impact of the channel doping on the low-frequency noise of gate-all-around silicon vertical nanowire pMOSFETs

In this work, the impact of the channel doping density on the low-frequency noise of silicon Gate-All-Around (GAA) Vertical Nanowire (VNW) pMOSFETs on Silicon-on-Insulator (SOI) substrates will be described and discussed. It is demonstrated that the dominant fluctuation mechanism of the 1/f noise in the subthreshold regime changes from number (Δn) to mobility (Δμ) fluctuations with increasing p-type doping density of the silicon nanowires. At the same time, the lowest input-referred voltage noise Power Spectral Density is observed for an intermediate boron concentration in the nanowire of 5 × 1018 cm−3.

New insights into low frequency noise (LFN) sources analysis in GaN/Si MIS-HEMTs

We present a thorough investigation of the low frequency (LF) noise in the access and channel regions in GaN MIS-HEMT devices. The 1/f noise behaviour is caused by trapping/de-trapping processes which are well described by carrier number fluctuations (CNF) and correlated mobility fluctuation (CMF) models. To address the issue of LF noise in the access and channel regions of GaN MIS-HEMT devices, we have tested respectively “non-gated” and “gated” devices with different designs. The border trap density extracted in optimized devices at AlGaN/GaN and Al2O3/GaN interfaces is better than previously reported GaN data and close to silicon CMOS results. This enabled us to show a controlled LF noise level and even improved one, emphasizing the progress in the manufacturing process of advanced GaN technologies. Due to the gate channel shape of GaN MIS-HEMT devices with recessed gate, a new CNF/CMF noise model including access resistance noise source is also proposed. It enables a reliable parameter extraction in each channel region, authorizing device noise modeling over a large set of GaN MIS-HEMT process and design.

Dimensionality reduction of local structure in glassy binary mixtures.

We consider unsupervised learning methods for characterizing the disordered microscopic structure of supercooled liquids and glasses. Specifically, we perform dimensionality reduction of smooth structural descriptors that describe radial and bond-orientational correlations and assess the ability of the method to grasp the essential structural features of glassy binary mixtures. In several cases, a few collective variables account for the bulk of the structural fluctuations within the first coordination shell and also display a clear connection with the fluctuations of particle mobility. Fine-grained descriptors that characterize the radial dependence of bond-orientational order better capture the structural fluctuations relevant for particle mobility but are also more difficult to parameterize and to interpret. We also find that principal component analysis of bond-orientational order parameters provides identical results to neural network autoencoders while having the advantage of being easily interpretable. Overall, our results indicate that glassy binary mixtures have a broad spectrum of structural features. In the temperature range we investigate, some mixtures display well-defined locally favored structures, which are reflected in bimodal distributions of the structural variables identified by dimensionality reduction.