Low-frequency Noise Behavior Research Articles

Toward Ideal Low-Frequency Noise in Monolayer CVD MoS2 FETs: Influence of van der Waals Junctions and Sulfur Vacancy Management.

The pursuit of sub-1-nm field-effect transistor (FET) channels within 3D semiconducting crystals faces challenges due to diminished gate electrostatics and increased charge carrier scattering. 2D semiconductors, exemplified by transition metal dichalcogenides, provide a promising alternative. However, the non-idealities, such as excess low-frequency noise (LFN) in 2D FETs, present substantial hurdles to their realization and commercialization. In this study, ideal LFN characteristics in monolayer MoS2 FETs are attained by engineering the metal-2D semiconductor contact and the subgap density of states (DOS). By probing non-ideal contact resistance effects using CuS and Au electrodes, it is uncovered that excess contact noise in the high drain current (ID) region can be substantially reduced by forming a van der Waals junction with CuS electrodes. Furthermore, thermal annealing effectively mitigates sulfur vacancy-induced subgap density of states (DOS), diminishing excess noise in the low ID region. Through meticulous optimization of metal-2D semiconductor contacts and subgap DOS, alignment of 1/f noise with the pure carrier number fluctuation model is achieved, ultimately achieving the sought-after ideal LFN behavior in monolayer MoS2 FETs. This study underscores the necessity of refining excess noise, heralding improved performance and reliability of 2D electronic devices.

Physics-based modeling and characterization of low frequency noise behavior for AlxGa1−xN/GaN HEMT

Physics-based modeling and characterization of low frequency noise behavior for AlxGa1−xN/GaN HEMT

Low Frequency Noise Behavior in Resistive Memory Devices with Hf/HfO2 Stack

Resistive-random-access-memory (RRAM) devices are considered to be one of the most potential candidates of next generation emerging memory technologies due to their excellent device properties, such as high density, low power, low voltage, and high speed. RRAM features simple metal–insulator–metal (MIM) structures and is fully compatible with traditional CMOS fabrication processes. Low-frequency noise (LFN) measurement is a technique to characterize electrically the trap-assisted conduction processes in dielectrics. In this work, we report the LFN characteristics of Hf/HfO2-based bipolar RRAM and investigate the current conduction mechanism and internal physics.

Low-frequency noise behaviors of quasi-two-dimensional electron systems based on complex oxide heterostructures

We report the low-frequency noise behaviors in quasi-two-dimensional (quasi-2D) electron systems based on complex oxide heterostructures. First, the surface 2D electron gas (2DEG) on SrTiO3 (STO) exhibits the 1/fα-type current power spectral density (PSD) with α∼1.39. The non-unity exponent α indicates the discrepancy between the depth distributions of electrons and oxygen vacancies in the STO substrate. Second, the amorphous LaAlO3/KTaO3 (LAO/KTO) interface, another quasi-2D electron system, shows Lorentzian components of PSD at a high-frequency region around 1 kHz, implying that the amorphous overlayer can provide additional shallow charge-trapping sites to the quasi-2D electrons in the crystalline KTO substrate. Lastly, ultrathin SrRuO3 (SRO) film grown on STO substrate exhibits the Lorentzian components of PSD at a low-frequency region around 200 Hz. The slight suppression of the fast charge trapping is attributed to the intrinsic band bending at the interface between film and substrate. These results will provide a guideline for understanding the defect-induced charge trapping and the relevant electron dynamics in the quasi-2D electron systems as well as the oxide-based electronic materials in general.

Improvement of low-frequency noise behavior with chloridic precursor materials at ALD process

This article reports an improvement in the low-frequency noise characteristics in hafnium oxide-based (HfO2) field-effect transistors by different precursor materials at ALD process. The Hafniumoxide on the devices were fabricated once with organic precursor materials and once with chloridic precursor materials. The investigation shows an improvement in the noise behavior when using chloridic precursor materials. Regarding the main noise source, which are divided into fluctuation of the number of carriers (ΔN) and fluctuation of the effective transistor mobility (Δμ), the results show that the devices fabricated with organic precursor materials show typical behavior of ΔN noise, where the devices fabricated with chloridic precursor materials show typical behavior of Δμ noise.

Sensing Remote Bulk Defects through Resistance Noise in a Large-Area Graphene Field-Effect Transistor

The substrate plays a crucial role in determining the transport and low-frequency noise behavior of graphene field-effect devices. Typically, a heavily doped Si/SiO2 substrate is used to fabricate these devices for efficient gating. Trapping-detrapping processes close to the graphene/substrate interface are the dominant sources of resistance fluctuations in the graphene channel, while Coulomb fluctuations arising due to any remote charge fluctuations inside the bulk of the substrate are effectively screened by the heavily doped substrate. Here, we present the electronic transport and low-frequency noise characteristics of a large-area CVD graphene field-effect transistor (FET) prepared on a lightly doped Si/SiO2 substrate (NA ≈ 1015 cm-3). Through a systematic characterization of transport, noise, and capacitance at various temperatures, we reveal that the remote Si/SiO2 interface can affect the charge transport in graphene severely and any charge fluctuations inside the bulk of the silicon substrate can be sensed by the graphene channel. The resistance (R) vs back-gate voltage (Vbg) characteristics of the device show a hump around the depletion region formed at the SiO2/Si interface, confirmed by the capacitance (C)-voltage (V) measurement. A low-frequency noise measurement on these fabricated devices shows a peak in the noise amplitude close to the depletion region. This indicates that due to the absence of any charge layer at the Si/SiO2 interface, the screening ability decreases, and as a consequence, any fluctuations in the deep-level Coulomb impurities inside the silicon substrate can be observed as noise in resistance in the graphene channel via mobility fluctuations. The noise behavior on ionic liquid-gated graphene on the same substrate exhibits no such peak in noise and can be explained by the interfacial trapping-detrapping processes close to the graphene channel. Our study will definitely be useful for integrating graphene with the existing silicon technology, in particular, for high-frequency applications.

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.

Performance Perspective of Gate-All-Around Double Nanosheet CMOS Beyond High-Speed Logic Applications

In this review paper, the performance characteristics of Gate-All-Around (GAA) double nanosheet (NS) MOSFETs are described over a broad temperature range, from 78 K to 473 K (200 oC). Emphasis is on the analog operation, showing good potential. Besides the transistor length, the impact of the metal gate Effective Work Function and the vertical distance between the nanosheets has been studied. Among others, a clear Zero Temperature Coefficient (ZTC) gate voltage has been observed that can be modeled by considering the shift with temperature of the threshold voltage and the maximum transconductance. A trade-off has been noticed between the transistor efficiency and the unit gain frequency, whereby the optimal operation point occurs in strong inversion regime. The feasibility of designing simple analog circuits has also been demonstrated. Finally, a detailed investigation of the low-frequency noise behavior yields good values for the flicker noise Power Spectral Density in comparison with other technology nodes.

(Invited) Impact of Processing Factors on the Low-Frequency Noise of Gate-All-Around Silicon Vertical Nanowire FETs

This paper gives an overview of the impact of certain processing steps on the low-frequency (LF) noise behavior of silicon Gate-All-Around (GAA) Vertical Nanowire (VNW) MOS transistors. It is shown that the width of a Replacement Metal Gate (RMG) cap impacts the flicker noise Power Spectral Density (PSD). The type of source contact, i.e., bulk versus a confined top contact significantly changes the nature and the magnitude of the 1/f noise. Finally, the doping density of the silicon nanowires has a subtle influence, whereby the dominant fluctuation mechanism shifts from number to mobility fluctuations, while increasing the doping density. Optimal noise performance is achieved for intermediate in-situ nanowire B doping density.

Noise behavior of vertical tunnel FETs under the influence of interface trap states

A detailed analysis of low frequency noise behavior of two different vertical TFETs namely n ​+ ​pocket VTFET and dual MOS capacitor (D-MOS) VTFET is presented in this work. Such analysis is performed to understand the limiting factors of their operations. The effect of the presence of both uniform and Gaussian type of interface trap charge distributions on the electrical performance of the devices under consideration are considered in the TCAD simulation study. The results report that the Flicker noise is dominant at low frequency whereas at high frequency, the diffusion noise is the superior noise component. The generation-recombination noise is found to be significant in the entire frequency range considered for the analysis. Lastly, comparison has been done on net drain current noise spectral density (Sid) of some published work and this work.

Quantum-dot semiconductor lasers with prominent relative intensity noise and spectral characteristics.

Relative intensity noise (RIN) behavior of a quantum dot laser (QDL) at free running and under optical injection locking (OIL) has been reported in detail. Considering the mutual effects of the inhomogeneous and homogeneous broadenings, different and also non-routine RIN characteristics of a QDL at low, intermediate, and high homogeneous broadening regimes have been discussed. Results demonstrate that an injection-locked quantum dot laser exhibit enhanced characteristic over free-running operation along with low-frequency noise behavior in a wide range of homogeneous broadening values. RIN reduction of about 25, 55, and 7 dB/Hz have been achieved for low, intermediate, and high values of homogeneous broadening which implies the spontaneous emission noise suppression even at low injection power. The promising impact of the OIL on side-mode suppression for the intermediate homogeneous broadening regime has also been discussed. Our results guarantee the single-mode and low-noise operation of the OIL-QDL at any homogeneous broadening value.

Forward current transport and noise behavior of GaN Schottky diodes

In this work, we first measure the forward temperature-dependent current-voltage (<i>T</i>-<i>I</i>-<i>V</i>) characteristics of the GaN-based Schottky diodes grown on the bulk GaN substrates, and then study the transport mechanisms of the forward current and the low-frequency current noise behaviors under various injection levels. The results are obtained below. 1) In a forward high-bias region the thermionic emission current dominates, and the extracted barrier height is about 1.25 eV at <i>T</i> = 300 K, which is close to the value measured by capacitance-voltage sweeping. 2) In a forward low-bias region (<i>V</i> < 0.8 V) the current is governed by the trap assist tunneling process, having an ideality factor much larger than 1, and the derived barrier height is about 0.92 eV at <i>T</i> = 300 K, which indicates that the conductive dislocation should be mainly responsible for the excessive leakage current, having a reduced barrier around the core of dislocations. 3) The Lorentzian noise appears only at very small current (<i>I</i> < 1 μA) and low frequency (<i>f</i> < 10 Hz), whose typical time constant is extracted to be about 30 ms, depending on the multiple capture and release process of electrons via defects. 4) At a higher frequency and current, the low-frequency 1/<i>f</i> noise becomes important and the corresponding coefficient is determined to be about 1.1, where the transport is affected by the random fluctuation of the Schottky barrier height.

Low-Frequency Noise Behavior of AlGaN/GaN HEMTs with Different Al Compositions

AlxGa1−xN/GaN heterostructures with two kinds of Al composition were grown by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The Al compositions in the AlGaN barrier layer were confirmed to be 13% and 28% using high resolution X-ray diffraction (HRXRD). AlxGa1−xN/GaN high-electron mobility transistors (HEMTs) with different Al compositions were fabricated, characterized, and compared using the Hall effect, direct current (DC), and low-frequency noise (LFN). The device with high Al composition (28%) showed improved sheet resistance (Rsh) due to enhanced carrier confinement and reduced gate leakage currents caused by increased Schottky barrier height (SBH). On the other hand, the reduced noise level and the low trap density (Nt) for the device of 13% of Al composition were obtained, which is attributed to the mitigated carrier density and decreased dislocation density in the AlxGa1−xN barrier layer according to the declined Al composition. In spite of the Al composition, the fabricated devices exhibited 1/ƒ noise behavior with the carrier number fluctuation (CNF) model, which is proved by the curves of both (SId/Id2) versus (gm/Id)2 and (SId/Id2) versus (Vgs–Vth). Although low Al composition is favorable to the reduced noise, it causes some problems like low Rsh and high gate leakage current. Therefore, the optimized Al composition in AlGaN/GaN HEMT is required to improve both noise and DC properties.

Effect of Gate Structure on the Trapping Behavior of GaN Junctionless FinFETs

We investigated the performances of GaN junctionless fin-shaped field-effect transistors (FinFETs) with two different types of gate structures; overlapped- and partially covered-gate. DC, low-frequency noise (LFN), and pulsed I-V characterization measurements were performed and analyzed together in order to identify the conduction mechanism and examine both the interface and buffer traps in the devices. The fabricated GaN junctionless device with overlapped-gate structure exhibits improved DC and noise performance compared to the device with partially covered-gate, even though its gate length is much larger. The LFN behavior was found to be dominated by carrier number fluctuations (CNF). At off-state, the device with partially covered-gate exhibits generation-recombination (g-r) noise on top of 1/ ${f}$ noise. This superposition is correlated with the severe current collapse revealed by pulsed I-V measurements. In contrast, the device with overlapped-gate shows clear 1/ ${f}$ behavior without g-r noise.

On the Correlation Between Static and Low-Frequency Noise Parameters of Vertical Nanowire nMOSFETs

The low-frequency noise behavior of gate-all-around vertical nanowire silicon nMOSFETs is described and discussed with respect to the static device parameters, like the threshold voltage and the maximum transconductance. The spectra are dominated by 1/f noise at low frequencies, followed by white noise. The 1/f noise power spectral density at 10 Hz is correlated with the maximum transconductance and the threshold voltage. This is interpreted in terms of the diameter of the nanowires.

Size-Dependent Photoresponse of Germanium Nanocrystals-Metal Oxide Semiconductor Photodetector

In this article, size-dependent photoresponse characteristics and low-frequency noise behavior of high-speed germanium nanocrystals (nc-Ge) photodetector have been reported. The nc-Ge embedded in SiO2 matrix with different sizes have been synthesized by annealing the cosputtered Ge-SiO2 thin films at 800 °C–900 °C. It has been observed that the photoresponse of the detector increases with the increasing size of nc-Ge. The sample annealed at 900 °C showed maximum responsivity (3.5 A/W) with the fast response time. The low-frequency noise spectral power density in the current fluctuation ( ${S}_{\text {I}}$ ) have been measured for the fabricated nc-Ge photodetectors, and lowest noise equivalent power (NEP) and highest detectivity ( ${D} ^\ast $ ) have been observed in the nc-Ge detector synthesized at 900 °C. Tunable responsivity in nc-Ge has been observed due to size-dependent light absorption, electric field-driven carrier separation, and tunneling through the oxide barriers. The transient photoresponse behavior has also been studied and the best rise time of $6.2~\mu \text{s}$ was observed for nc-Ge synthesized at 900 °C. These results suggest that the nc-Ge are a promising contender for high-performance integrated optoelectronic devices that are fully compatible with silicon technology in terms of fabrication and thermal budget.

Effects of wear characteristics of Ni3Al metal matrix self-lubrication composites on friction-induced vibration and noise properties

An experimental research was performed to study the wear characteristics, as well as the friction-induced vibration and noise behaviors of Ni3Al alloys (NA) and Ni3Al metal matrix composites containing lubricant grephene nanoplatelets (NA-GNPs). Results showed that compared with NA, NA-GNPs exhibited the better tribological performance, as well as the lower amplitudes of friction-induced vibration and noise. The noise signals were closely correlated to the vibration acceleration signals. The occurrence of friction-induced vibration and noise was attributed to friction interface factors, such as asperity deformation, plowing and adhesion. The worn surface of NA with the appearances of peeling and obvious micro-cracks showed high-frequency vibration and noise characteristics. However, the finer GNPs could be filled into the edge of micro-cracks and gaps to repair the worn surface with the sliding of counterpart ball, NA-GNPs exhibited low-frequency vibration and noise behaviors. Moreover, due to the migration and diffusion of GNPs, the friction layer structure was formed easily beneath worn surface of NA-GNPs, which could improve the lubricating effect. GNPs exhibited the excellent potential lubricant for improvement of tribological performance and reduction of vibration and noise.

Low-frequency generation-recombination noise behaviors of blue/violet-light-emitting diode

During the past two decades, GaN-based light-emitting diode has been used as a high-quality light-source. Low-frequency noise as a diagnostic tool for quality control and reliability estimation has been widely accepted and used for semiconductor devices. Understanding the origin of efficiency-droop effect is key to developing the ultimate solid-state light source. Various mechanisms that may cause this effect have been suggested, including carriers’ escape, loses due to dislocations, and the Auger effect. In this study, we investigate the low-frequency noise behaviors of GaN-based blue light-emitting diode with InGaN/GaN multiple quantum wells. The measured currents range from 0.1 mA to 180 mA. According to the characteristics of power spectral density of current noise and the generation-combination mechanism between electrons and holes in the active region of light-emitting diode (LED), we adopt the well-known model of low-frequency noise to fit the relationship between power spectral density of current and frequency, and find that there exists a transition between generation-combination and 1/<i>f</i> noise when the light-emitting diode begins to work. In other words, it can be derived that the low-frequency noise behaviors are dominated by generation-combination noise when the currents are between 0.1 mA and 27 mA; with the current gradually increasing, the origin source of low-frequency noise in blue/violet-light LED will transit to the 1/<i>f</i> noise. Through the analysis of the transport and recombination mechanism of the carriers, and combination with the model of low-frequency noise, we analyze the corner frequency of the generation-recombination noise. The results of this paper provide an effective tool and method to study the conversion of light-emitting diodes.

Empirical and Theoretical Modeling of Low-Frequency Noise Behavior of Ultrathin Silicon-on-Insulator MOSFETs Aiming at Low-Voltage and Low-Energy Regime.

This paper theoretically revisits the low-frequency noise behavior of the inversion-channel silicon-on-insulator metal-oxide-semiconductor field-effect transistor (SOI MOSFET) and the buried-channel SOI MOSFET because the quality of both Si/SiO2 interfaces (top and bottom) should modulate the low-frequency fluctuation characteristics of both devices. It also addresses the low-frequency noise behavior of sub-100-nm channel SOI MOSFETs. We deepen the discussion of the low-frequency noise behavior in the subthreshold bias range in order to elucidate the device’s potential for future low-voltage and low-power applications. As expected, analyses suggest that the weak inversion channel near the top surface of the SOI MOSFET is strongly influenced by interface traps near the top surface of the SOI layer because the traps are not well shielded by low-density surface inversion carriers in the subthreshold bias range. Unexpectedly, we find that the buried channel is primarily influenced by interface traps near the top surface of the SOI layer, not by traps near the bottom surface of the SOI layer. This is not due to the simplified capacitance coupling effect. These interesting characteristics of current fluctuation spectral intensity are explained well by the theoretical models proposed here.

Low-Frequency Noise in Supported and Suspended MoS2 Transistors

Sensitivity of sensors, the phase noise of oscillators, and intrinsic device performance at the nanoscale are primarily limited by fluctuations in resistance at low frequencies, also called flicker noise. These intrinsic fluctuations in resistance become more prominent in two-dimensional materials due to their ultrathin nature. Here, we report the low-frequency noise (LFN) behavior of supported and suspended MoS2 FETs. Carrier-number fluctuation mechanism was found to be responsible for LFN in both configurations. The extracted frequency index ( $\gamma $ in 1/ ${f}^\gamma $ ) indicates the different trap time constants and mechanisms responsible for LFN in MoS2 transistors. A $\gamma $ value of 2 in suspended transistors indicates a tight trap time-constant distribution likely due to recombination–generation through trap states arising only from intrinsic defects and/or extrinsic adsorbates. A wide time-constant distribution ( $\gamma \!\sim \textsf {1}$ to 1.4) in supported transistors indicates the presence of various kinds of traps, such as adsorbates, intrinsic defects, as well as interface and oxide traps. Furthermore, variation in S0 (characterizes the magnitude of noise) with gate voltage in both supported and suspended device configurations was validated analytically using the carrier-number fluctuation model.