Carrier Number Fluctuation Research Articles

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.

Low-Frequency Noise of 4H-SiC CMOS Technology for Analog ICs

To design low-noise analog ICs for nuclear power plants, low-frequency noise (LFN) of 4H-SiC CMOS technology was studied in the frequency range of 3 Hz–10 kHz at room temperature. The LFN of the long-channel MOS devices was systematically studied in terms of gate length, gate width, drain current, and drain voltage. It was found to follow the noise model for carrier number fluctuation regardless of conduction type. In addition, the standard deviation of spectral noise density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${S}_{\text {id}}$ </tex-math></inline-formula> ) at 10 Hz for the p-channel MOS was experimentally found to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.6\times $ </tex-math></inline-formula> larger than that for the n-channel MOS. This was caused by the increase in random telegraph noise (RTN) caused by oxide hole traps with nitrogen incorporation at the SiO2/SiC interface. The flicker noise coefficient (KF) in the noise model was estimated to be <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${4.1} \times {10}^{-{26}}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${1.2} \times {10}^{-{27}}\,\,\text{s}^{\text {1-EF}}\text{A}^{\text {2-AF}}\text{F}^{^{^{^{}}}}$ </tex-math></inline-formula> for the n- and p-channel MOS, respectively.

Low-frequency noise characterization of gate oxide trap depth distribution of MOSFETs

To accurately obtain the depth distribution of the gate oxide traps that cause low-frequency noises, this study developed a discrete form of the low-frequency noise model in MOSFETs based on McWhorter's theory. The non-negative least squares (NNLS) method is employed to numerically solve the designed model. The low-frequency noises of planar Ge nMOSFETs with a gate stack match the prerequisite of the proposed form, which is dominated by carrier number fluctuations and is consistent with the McWhorter model. These transistors are used as the object of analysis in this study. By introducing a La2O3 cap layer to the gate stack, the gate oxide trap profiles calculated by the discrete model and the NNLS method showed obvious suppression of the traps in the HfO2 body and concentration of the traps in and near the SiO2/HfO2 interface. The research on both energy-dispersive x-ray spectroscopy and electron energy-loss spectroscopy has shown during annealing the diffusion of La into HfO2 and the appearance of La-rich layer at the SiO2/HfO2 interface in the Ge nMOSFET with a La2O3 cap. According to the existing first-principles calculations, the substitution of Hf in HfO2 by La increases the formation energy of oxygen vacancies, and the formation energy of oxygen vacancies in the HfnLamSixOy layer formed near the SiO2/HfO2 interface is lower than that of HfO2. The experimental and theoretical results support the physical connotation of the calculations and validate the solution proposed by this study.

(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.

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.

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.

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.

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.

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.

Low-Frequency Noise Modeling of 4H-SiC Metal-Oxide-Semiconductor Field-Effect Transistors

4H-silicon carbide metal-oxide-semiconductor field-effect transistors (4H-SiC MOSFETs) show 1/f low-frequency noise behavior. In this paper, this can be explained by the combination of the mobility fluctuation (Δμ) and the carrier number fluctuation (ΔN) theories. The Δμ theory believes that LFN is generated by the bulk defects, while the ΔN theory holds that LFN originates from the extraordinarily high oxide traps. For 4H-SiC MOSFETs, significant subthreshold noise will appear when only the ΔN theory attempts to model LFN in the subthreshold region. Therefore, we account for the high density of bulk defects (Δμ theory) and characterize the subthreshold noise. The theoretical model allows us to determine the bulk density of the trap states. The proposed LFN model is applicable to SiC MOSFETs and accurately describes the noise experimental data over a wide range of operation regions.

DC and low-frequency noise characteristics of GaN-based HEMTs under cryogenic temperatures

In this work, the device characteristics of GaN-based high-electron-mobility transistors (HEMTs) were systematically investigated by the direct current (DC) and low-frequency noise (LFN) measurements within the temperature ranging from 300 K to 4.2 K. The temperature-dependent behavior of the on- and off-state electrical properties was statistically analyzed, highlighting an overall improved device performance under cryogenic temperatures. In addition, the LFN of the device exhibited an evident behavior of 1/f noise from 10 Hz to 10 kHz in the measured temperature range and can be well described by the carrier number fluctuations with correlated mobility fluctuations (CNF/CMF) model down to 4.2 K. Based on this model, we further extracted and discussed the defect-related behavior in the devices under low-temperature environments. These experimental results provide insights into the device characteristics of GaN-based HEMTs under cryogenic environments, motivating further studies into the GaN-based cryo-devices and systems.

Analysis of Low Frequency Noise in Schottky Junction Trigate Silicon Nanowire FET on Bonded SOI Substrate

In this work, low frequency noise (LFN) in Schottky junction trigate silicon nanowire (SiNW) field-effect transistors (FETs) (SJGFETs) fabricated on bonded silicon on insulator (SOI) substrate is systematically analyzed. The LFN exhibited a typical 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> spectrum and can be well described by the carrier number fluctuation (CNF) with correlated mobility fluctuation (CMF) model. It was found that CNF is the dominant component of the LFN, while CMF associated with the Coulomb scattering near the buried oxide (BOX)/SiNW channel interface plays an insignificant role. Applying a substrate bias can further modulate the LFN of the SJGFETs, and the effect is ascribed to the nonuniform energy distribution of the BOX/SiNW channel interface traps. Confining current path in the channel bulk away from the interface brought limited gain in terms of LFN performance. Finally, our experimental results suggested a possible transition of CMF mechanism from Coulomb scattering to surface roughness scattering when the current path is pushed away from the BOX/SiNW channel interface to the channel bulk.

Understanding random telegraph noise in two-dimensional BP/ReS2 heterointerface

Black phosphorus (BP)-based broken gap heterojunctions have attracted significant attention mainly owing to its wide thickness-dependent Fermi level, offering opportunities to demonstrate various carrier transport characteristics and high performing optoelectronic applications. However, the interfacial effects on the carrier scattering mechanism of the two-dimensional (2D) broken gap heterojunctions are unclear. Herein, we discuss the origin of random telegraph noise of multilayer BP/ReS2 heterojunction diode, in particular, at the direct tunneling (DT) conduction regime. The gate-tunable diode characteristic of BP/ReS2 heterojunction allows one to unveil systematically the transition of the charge fluctuation mechanism from drift-diffusion to the DT regime. Unlike individual BP and ReS2 devices, the current noise histogram obtained from the BP/ReS2 heterojunction device exhibits exclusively two dominant peaks at the DT regime. We ascribed this distinct low-frequency noise feature representing the presence of random telegraph signal to the BP/ReS2 interfacial traps by taking into account of the inherent direct tunneling current conduction mechanism. In addition, the electrostatic bias-dependent power spectrum density manifests clearly that the dominant scattering mechanism is the carrier number fluctuation rather than tunneling barrier height fluctuation at the BP/ReS2 heterointerface. This study elucidates the carrier transport and the charge fluctuation mechanism at the 2D heterostructure interface.

Strong Interfacial Charge Trapping in Ultrathin SrRuO3 on SrTiO3 Probed by Noise Spectroscopy.

SrRuO3 (SRO) has emerged as a promising quantum material due to its exotic electron correlations and topological properties. In epitaxial SRO films, electron scattering against lattice phonons or defects has been considered as only a predominant mechanism accounting for electronic properties. Although the charge trapping by polar defects can also strongly influence the electronic behavior, it has often been neglected. Herein, we report strong interfacial charge trapping in ultrathin SRO films on SrTiO3 (STO) substrates probed by noise spectroscopy. We find that oxygen vacancies in the STO cause stochastic interfacial charge trapping, resulting in high electrical noise. Spectral analyses of the photoinduced noise prove that the oxygen vacancies buried deep in the STO can effectively contribute to the charge trapping process. These results unambiguously reveal that electron transport in ultrathin SRO films is dominated by the carrier number fluctuation that correlates with interfacial charge trapping.

Evaluation of Positive-Bias-Stress-Induced Degradation in InSnZnO Thin-Film Transistors by Low Frequency Noise Measurement

In this letter, degradation of InSnZnO thin-film transistors (TFTs) under positive bias stress (PBS) is evaluated by low frequency noise (LFN) measurement for the first time. With PBS time, the LFN level and trap state density first decrease and then increase, and meanwhile, the dominant fluctuation model changes from carrier number fluctuation model toward to bulk carrier mobility fluctuation model. By considering the interactions of oxygen vacancies, hydrogens and electrons, a degradation model based on the effect of vertical electrical field and water ionization is tentatively proposed and discussed.

Fully integrated FET-type gas sensor with optimized signal-to-noise ratio for H2S gas detection

The focus of gas sensor research has been on improving the response of individual sensors. However, in order to integrate sensors with CMOS circuits, a sensing system composed of an amplifier circuit with a voltage output is required. As such, in this work, we propose a novel gas sensing amplifier circuit composed of resistor- and FET-type gas sensors. Indium-gallium-zinc oxide (IGZO) is used as a sensing material for the detection of hydrogen sulfide (H2S) gas. The H2S gas sensing mechanism of the amplifier circuit is determined by the interplay between the resistor- and FET-type gas sensors. Also, the low-frequency noise characteristics of the resistor- and FET-type gas sensors are analyzed using carrier number fluctuation and Hooge’s mobility fluctuation models, respectively. The signal-to-noise ratio of the amplifier circuit is accurately characterized as a function of the input voltage. The optimal operating bias condition is proposed, and the limit of detection of the amplifier circuit is obtained under this condition. The methodology demonstrated in this work can be applied to other types of amplifier circuits, contributing to the advancement of knowledge about integrated gas sensing systems.

DC and low a frequency noise analysis of p channel gate all around vertically stacked silicon nanosheets

DC and low frequency noise measurements are performed in p-channel gate all around (GAA) vertically stacked silicon nanosheets (NS) at room temperature. The key DC parameters such as threshold voltage, low field mobility, access resistance and subthreshold swing are estimated. Preliminary low frequency noise studies reveal that the 1/f noise may be explained in weak to moderate inversion by the carrier number fluctuation mechanism, while in strong inversion the access resistance noise prevails.

Analysis of Low-Frequency 1/f Noise Characteristics for MoTe2 Ambipolar Field-Effect Transistors.

Low-frequency electronic noise is an important parameter used for the electronic and sensing applications of transistors. Here, we performed a systematic study on the low-frequency noise mechanism for both p-channel and n-channel MoTe2 field-effect transistors (FET) at different temperatures, finding that low-frequency noise for both p-type and n-type conduction in MoTe2 devices come from the variable range hopping (VRH) transport process where carrier number fluctuations (CNF) occur. This process results in the broad distribution of the waiting time of the carriers between successive hops, causing the noise to increase as the temperature decreases. Moreover, we found the noise magnitude for p-type MoTe2 FET hardly changed after exposure to the ambient conditions, whereas for n-FET, the magnitude increased by nearly one order. These noise characteristics may provide useful guidelines for developing high-performance electronics based on the emerging transition metal dichalcogenides.

Single β-Ga2O3 nanowire based lateral FinFET on Si

A fin field-effect transistor (FinFET) based on single β-Ga2O3 nanowire with a diameter of ∼60 nm transferred to Si substrate is demonstrated. The FinFET device shows good saturation performance within a drain-to-source voltage up to 5 V and exhibits a high on/off ratio of ∼4 × 108, a system-limit low leakage current (∼4 fA), and a relatively low subthreshold swing (∼110 mV). Simulation shows that the channel of the FinFET depletes much faster than that of the back-gate FET with negative gate bias, which is consistent with the measurement results. Moreover, trap-related 1/f noise and 1/f2 noise have been identified according to low frequency noise analysis, and a carrier number fluctuation is expected to be the dominant 1/f noise mechanism in the β-Ga2O3 FinFET in this work.