Random Telegraph Signal Noise Research Articles

Radiation hardness of MALTA2 monolithic CMOS imaging sensors on Czochralski substrates

MALTA2 is the latest full-scale prototype of the MALTA family of Depleted Monolithic Active Pixel Sensors (DMAPS) produced in Tower Semiconductor 180 nm CMOS sensor imaging technology. In order to comply with the requirements of high energy physics (HEP) experiments, various process modifications and front-end changes have been implemented to achieve low power consumption, reduce random telegraph signal (RTS) noise, and optimise the charge collection geometry. Compared to its predecessors, MALTA2 targets the use of a high-resistivity, thick Czochralski (Cz) substrates in order to demonstrate radiation hardness in terms of detection efficiency and timing resolution up to 3 ×\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ imes $$\\end{document} 1015\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{15}$$\\end{document} 1 MeV neq/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathrm {n_{eq}/{cm}^2}$$\\end{document} with backside metallisation to achieve good propagation of the bias voltage. This manuscript shows the results that were obtained with non-irradiated and irradiated MALTA2 samples on Cz substrates from the CERN SPS test beam campaign from 2021 to 2023 using the MALTA telescope.

RTS Noise Characterization of Trap Properties in InGaAs nFinFETs

In order to extract and characterize the trap properties in In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\textit{x}}$</tex-math> </inline-formula> Ga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\text{1}-\textit{x}}$</tex-math> </inline-formula> As nFinFET sensitively and effectively, the time-domain and frequency-domain characteristics of low-frequency noise are studied by the random telegraph signal (RTS) method. It is found that the RTS noise in this study originates from the strong electron–phonon coupling mechanism. The activation energies of traps are extracted from the Arrhenius curves, and the results show that these traps mainly come from extended defects, such as dislocation, etc. Furthermore, the relationship between noise characteristics and gate length is explored, it is found that with the reduction of the gate length, the noise contains more RTS components. The noise behavior of devices with different In content is also investigated, it shows that the average of activation energies, as well as the capture cross section of bulk traps, decrease with the increasing In content in the channel. Overall, it can be concluded that the RTS noise is an effective tool to reveal the defect properties of nano-scaled devices. It can be used to provide theoretical guidance in improving the performance and reliability of devices.

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.

Analysis of random telegraph noise in resistive memories: The case of unstable filaments

Through Random Telegraph Noise (RTN) analysis, valuable information can be provided about the role of defect traps in fine tuning and reading of the state of a nanoelectronic device. However, time domain analysis techniques exhibit their limitations in case where unstable RTN signals occur. These instabilities are a common issue in Multi-Level Cells (MLC) of resistive memories (ReRAM), when the tunning protocol fails to find a perfectly stable resistance state, which in turn brings fluctuations to the RTN signal especially in long time measurements and cause severe errors in the estimation of the distribution of time constants of the observed telegraphic events, i.e., capture/emission of carriers from traps. In this work, we analyze the case of the unstable filaments in silicon nitride-based ReRAM devices and propose an adaptive filter implementing a moving-average detrending method in order to flatten unstable RTN signals and increase sufficiently the accuracy of the conducted measurements. The τe and τc emission/capture time constants of the traps, respectively, are then calculated and a cross-validation through frequency domain analysis (Lorentzian fitting) was performed proving that the proposed method is accurate.

Low-frequency noise in β-(AlxGa1−x)2O3 Schottky barrier diodes

We report on the low-frequency electronic noise in β-(AlxGa1−x)2O3 Schottky barrier diodes. The noise spectral density reveals 1/f dependence, characteristic of the flicker noise, with superimposed Lorentzian bulges at the intermediate current levels (f is the frequency). The normalized noise spectral density in such diodes was determined to be on the order of 10−12 cm2/Hz (f = 10 Hz) at 1 A/cm2 current density. At the intermediate current regime, we observed the random telegraph signal noise, correlated with the appearance of Lorentzian bulges in the noise spectrum. The random telegraph signal noise was attributed to the defects near the Schottky barrier. The defects can affect the local electric field and the potential barrier and, correspondingly, impact the electric current. The obtained results help in understanding the noise in Schottky barrier diodes made of ultra-wide bandgap semiconductors and can be used for the material and device quality assessment.

Local electric field perturbations due to trapping mechanisms at defects: What random telegraph noise reveals

As devices scale closer to the atomic size, a complete understanding of the physical mechanisms involving defects in high-κ dielectrics is essential to improve the performance of electron devices and to mitigate key reliability phenomena, such as Random Telegraph Noise (RTN). In fact, crucial aspects of defects in HfO2 are still under investigation (e.g., the presence of metastable states and their properties), but it is well known that oxygen vacancies (V+s) and oxygen ions (O0s) are the most abundant defects in HfO2. In this work, we use simulations to gain insights into the RTN that emerges when a constant voltage is applied across a TiN/(4 nm)HfO2/TiN stack. Signals exhibit different RTN properties over bias and, thus, appear to originate from different traps. Yet, we demonstrate that they can be instead promoted by the same O0s which change their capture (τc) and emission (τe) time constants with the applied bias, which, in turn, changes the extent of their electrostatic interactions with the traps that assist charge transport (V+s). For a certain bias, RTN is given by the modulation of the trap-assisted current at V+s induced by trapping/detrapping events at O0s, which are, in turn, influenced by the bias itself and by trapped charge at nearby O0s. In this work, we demonstrate that accounting for the effect of trapped charge is essential to provide accurate estimation of the RTN parameters, which allow us to retrieve information about traps and to explain key mechanisms behind complex RTN signals.

Modeling With RTS Noise Characterization of Novel Embedded Photogate Single-Photon Avalanche Diode for Circuit Simulations

Single-photon avalanche diodes (SPADs) are widely used for weak light detection due to their high gain and high sensitivity. Unfortunately, SPAD devices have random telegraph signal (RTS) noise during the avalanche transition phase, which makes circuit design more difficult. Therefore, the modeling of RTS noise in SPAD devices is of great significance for the design of signal processing circuits. However, RTS noise is not included in the traditional equivalent circuit model. In response to the above problems, this paper implements an equivalent circuit model with RTS noise based on the Cadence. The model is built based on the basic components in the library, and it has strong application universality. The model is validated in a novel embedded photogate SPAD device (EP-SPAD). It accurately simulates the RTS noise and IV characteristics of the EP-SPAD device. In addition, the threshold voltage of EP-SPAD device operating in Geiger mode is precisely defined based on the characteristics of RTS noise. When the reverse bias voltage is increased from 0 V to 15 V, the IV characteristics of the model are consistent with the EP-SPAD device.

Spatially Controlled Generation and Probing of Random Telegraph Noise in Metal Nanocrystal Embedded HfO2 Using Defect Nanospectroscopy

Random telegraph noise (RTN) is often considered a nuisance or, more critically, a key reliability challenge for miniaturized semiconductor devices. However, this picture is gradually changing as recent works have shown emerging applications based on the inherent randomness of the RTN signals in state-of-the-art technologies, including true random number generator and IoT hardware security. Suitable material platforms and device architectures are now actively explored to bring these technologies from an embryonic stage to practical application. A key challenge is to devise material systems, which can be reliably used for the deterministic creation of localized defects to be used for RTN generation. Toward this goal, we have investigated RTN in Au nanocrystal (Au-NC) embedded HfO2 stacks at the nanoscale by combining conduction atomic force microscopy defect spectroscopy and a statistical factorial hidden Markov model analysis. With a voltage applied across the stack, there is an enhanced asymmetric electric field surrounding the Au-NC. This in turn leads to the preferential generation of atomic defects in the HfO2 near the Au-NC when voltage is applied to the stack to induce dielectric breakdown. Since RTN arises from various electrostatic interactions between closely spaced atomic defects, the Au-NC HfO2 material system exhibits an intrinsic ability to generate RTN signals. Our results also highlight that the spatial confinement of multiple defects and the resulting electrostatic interactions between the defects provides a dynamic environment leading to many complex RTN patterns in addition to the presence of the standard two-level RTN signals. The insights obtained at the nanoscale are useful to optimize metal nanocrystal embedded high-κ stacks and circuits for on-demand generation of RTN for emerging random number applications.

Voltage and temperature dependence of Random Telegraph Noise and their impacts on random number generator

With the continuous decrease in device dimensions, Random Telegraph Noise (RTN) has drawn increasing attention. From the intrinsic stochastic features, RTN signal is adopted as an entropy source for true random number generator (TRNG). In this study, RTN time constants are investigated under various gate voltages and temperatures. Their impacts on the TRNG are revealed by performing the National Institute of Standards and Technology (NIST) test. It is found that the random verification is highly dependent on the maximum frequency (fmax) of the clock signal in TRNG circuit, which shows linear dependence with the RTN time constant (τc + τe). Our findings may make a step towards generating truly random numbers and improving hardware or cyber security based on RTN phenomenon.

Advanced Data Encryption ​using 2D Materials.

Advanced data encryption requires the use of true random number generators (TRNGs) to produce unpredictable sequences of bits. TRNG circuits with high degree of randomness and low power consumption may be fabricated by using the random telegraph noise (RTN) current signals produced by polarized metal/insulator/metal (MIM) devices as entropy source. However, the RTN signals produced by MIM devices made of traditional insulators, i.e., transition metal oxides like HfO2 and Al2 O3 , are not stable enough due to the formation and lateral expansion of defect clusters, resulting in undesired current fluctuations and the disappearance of the RTN effect. Here, the fabrication of highly stable TRNG circuits with low power consumption, high degree of randomness (even for a long string of 224 - 1 bits), and high throughput of 1 Mbit s-1 by using MIM devices made of multilayer hexagonal boron nitride (h-BN) is shown. Their application is also demonstrated to produce one-time passwords, which is ideal for the internet-of-everything. The superior stability of the h-BN-based TRNG is related to the presence of few-atoms-wide defects embedded within the layered and crystalline structure of the h-BN stack, which produces a confinement effect that avoids their lateral expansion and results in stable operation.

Study of RTN signals in resistive switching devices based on neural networks

Random Telegraph Noise (RTN) in Resistive Random Access Memories (RRAM) is an important phenomenon both for the investigation of device physics and for reliability issues. The characteristics of these signals depend on the number of active traps, on the interaction between these traps at different times, on the occurrence of anomalous effects, etc. Using the Locally Weighted Time Lag Plot (LWTLP), a fast numerical procedure, data from RTN current-time (I-t) traces can be represented with a pattern that allows a deeper understanding of the device physics. In the context of self-organizing maps, a neural network devoted to clustering, we have analyzed the LWTLPs to classify the RTN traces obtained from a long measurement with more than 3 million data points. This RTN pattern classification, obtained in an unsupervised learning scheme, allows a comprehensive characterization of the signals and the physics underlying the device operation.

Random Telegraph Noise in Metal‐Oxide Memristors for True Random Number Generators: A Materials Study

AbstractSome memristors with metal/insulator/metal (MIM) structure have exhibited random telegraph noise (RTN) current signals, which makes them ideal to build true random number generators (TRNG) for advanced data encryption. However, there is still no clear guide on how essential manufacturing parameters like materials selection, thicknesses, deposition methods, and device lateral size can influence the quality of the RTN signal. In this paper, an exhaustive statistical analysis on the quality of the RTN signals produced by different MIM‐like memristors is reported, and straightforward guidelines for the fabrication of memristors with enhanced RTN performance are presented, which are: i) Ni and Ti electrodes show better RTN than Au electrodes, ii) the 50 μm × 50 μm devices show better RTN than the 5 μm × 5 μm ones, iii) TiO2 shows better RTN than HfO2 and Al2O3, iv) sputtered‐oxides show better RTN than ALD‐oxides, and v) 10 nm thick oxides show better RTN than 5 nm thick oxides. The RTN signals recorded have been used as entropy sources in high‐throughput TRNG circuits, which have passed the randomness tests of the National Institute of Standards and Technology. The work can serve as a useful guide for materials scientists and electronic engineers when fabricating MIM‐like memristors for RTN applications.

Robust Evaluation of Long-Term Stability of an InAs/GaSb Type II Superlattice Midwave Infrared Focal Plane Array

The temporal stability of the image quality of an infrared focal plane array (FPA) is one key parameter to consider for high-performance imaging applications. It is generally evaluated through residual fixed pattern noise (RFPN) measurements realized after a two-point correction (TPC) and bad pixels exclusion. However, the effect of random telegraph signal (RTS) on temporal stability has never been quantified, the intermittent blinking of RTS pixels making measurements inherently complicated. In this article, we propose a novel protocol and a novel data processing technique to fully characterize the temporal stability of an infrared FPA, thanks to simultaneous RFPN and RTS noise measurements. Using a robust statistics based on median absolute deviation (MAD) leads to a more trustful RFPN evaluation, unaffected by the bad pixels exclusion step. This new protocol can be applied to any FPA technology, cooled or uncooled, operating in the [3, 14] μm spectral domain. We chose to use a type-II superlattice (T2SL) midwave infrared FPA integrated in a cryocooler at 80 K. We show that the long-term stability of this 320 × 256 pixels FPA is excellent. The RFPN only slightly increases over 77 days, using a TPC that has been calculated on the first day of the measurements campaign. A simple offset update, compatible with operational contingencies, can further improve the temporal stability of this FPA. Only 0.3% of the pixels were affected by RTS noise at some moment. Those blinking pixels do not affect the RFPN evolution, which is a very encouraging result for T2SL detector technology.

Employing the Empirical Mode Decomposition to Denoise the Random Telegraph Noise

Random Telegraph Noise (RTN) is a stochastic phenomenon which leads to characteristic variations in electronic devices. Finding features of this signal may result in its modeling and eventually removing the noise in the device. Measuring this signal is accompanied by some noise and therefore we require a method to improve the Signal to Noise Ratio (SNR). As a result, the extraction of an accurate RTN is a remarkable challenge. Empirical Mode Decomposition (EMD) as a fully adaptive and signal dependent method, with no dependency to the specific function, can be an appropriate solution. In this paper, we evaluate the most recent methods and compare them with our proposed approach for the artificial and actual RTN signals. The results show the higher accuracy and efficiency by about 54%, 61% and 39% improvement in SNR, Mean Square Error (MSE) and Percent Root mean square Difference (PRD) respectively for the optimized wited method. Finally, an indicator to evaluate the reliability in digital circuits is introduced.

The Characterization of Electronic Noise in the Charge Transport through Single-Molecule Junctions.

With the goal of creating single-molecule devices and integrating them into circuits, the emergence of single-molecule electronics provides various techniques for the fabrication of single-molecule junctions and the investigation of charge transport through such junctions. Among the techniques for characterization of charge transport through molecular junctions, electronic noise characterization is an effective strategy with which issues from molecule-electrode interfaces, mechanisms of charge transport, and changes in junction configurations are studied. Electronic noise analysis in single-molecule junctions can be used to identify molecular conformations and even monitor reaction kinetics. This review summarizes the various types of electronic noise that have been characterized during single-molecule electrical detection, including the functions of random telegraph signal (RTS) noise, flicker noise, shot noise, and their corresponding applications, which provide some guidelines for the future application of these techniques to problems of charge transport through single-molecule junctions.

An Electrical Model for Trap Coupling Effects on Random Telegraph Noise

Resistive switching (RS) devices are being studied exhaustively for multiple applications such as information storage and bio-inspired computing, but some reliability problems are still hindering their massive use. Among them, random telegraph noise (RTN) is one of the phenomena that still needs to be understood. In this work, we develop a general model to describe RTN in RS devices by demonstrating the existence of coupling effects between multiple traps, and their effect in the current amplitude deviation. We accurately describe anomalous RTN signals observed in high resistive state (HRS) and low-resistance state (LRS) of RS devices based on TiO2 and hexagonal boron nitride (h-BN).

Effect of Interface Traps on the RTS Noise Behavior of Junctionless Nanowires

This work presents a study on the effects of single interface traps throughout the Junctionless Nanowire Transistor (JNT). The results are obtained by analyzing the Random Telegraph Signal noise of the device, which consists of an exception of the generation-recombination noise. The results obtained are mostly from numerical simulation, validated through experimental data. As in physical devices, it is impossible to obtain a single trap in specific locations, we have used a distribution of traps with similar characteristics in a way that they behave like a single trap. The results show the behave considering a set of traps distributions, using an exponential model. The traps are distributed from the conduction band to the valence band.&#x0D; Keywords– JNT; RTS Noise; G-r Noise; Interface Traps.&#x0D;  

Wavelet Analysis of RTS Noise in CMOS Image Sensors Irradiated With High-Energy Photons

This article explores the phenomenon of dark current random telegraph signal (DC-RTS) noise in commercial off-the-shelf CMOS image sensors. Five sensors were irradiated with high-energy photons to a variety of doses and analyzed with a wavelet-based signal reconstruction algorithm. The algorithm is explained in detail and the radiation effects on individual pixels are discussed. Finally, the production rate of RTS pixels as a function of dose is explored, providing information on the underlying defect structure responsible for this noise source.

Human Breast Cancer Cells Demonstrate Electrical Excitability.

Breast cancer is one of the most prevalent types of cancers worldwide and yet, its pathophysiology is poorly understood. Single-cell electrophysiological studies have provided evidence that membrane depolarization is implicated in the proliferation and metastasis of breast cancer. However, metastatic breast cancer cells are highly dynamic microscopic systems with complexities beyond a single-cell level. There is an urgent need for electrophysiological studies and technologies capable of decoding the intercellular signaling pathways and networks that control proliferation and metastasis, particularly at a population level. Hence, we present for the first time non-invasive in vitro electrical recordings of strongly metastatic MDA-MB-231 and weakly/non-metastatic MCF-7 breast cancer cell lines. To accomplish this, we fabricated an ultra-low noise sensor that exploits large-area electrodes, of 2 mm2, which maximizes the double-layer capacitance and concomitant detection sensitivity. We show that the current recorded after adherence of the cells is dominated by the opening of voltage-gated sodium channels (VGSCs), confirmed by application of the highly specific inhibitor, tetrodotoxin (TTX). The electrical activity of MDA-MB-231 cells surpasses that of the MCF-7 cells, suggesting a link between the cells’ bioelectricity and invasiveness. We also recorded an activity pattern with characteristics similar to that of Random Telegraph Signal (RTS) noise. RTS patterns were less frequent than the asynchronous VGSC signals. The RTS noise power spectral density showed a Lorentzian shape, which revealed the presence of a low-frequency signal across MDA-MB-231 cell populations with propagation speeds of the same order as those reported for intercellular Ca2+ waves. Our recording platform paves the way for real-time investigations of the bioelectricity of cancer cells, their ionic/pharmacological properties and relationship to metastatic potential.

Study on random telegraph noise of high-κ/metal-gate gate-all-around poly-Si nanowire transistors

In this paper, we investigated random telegraph noise (RTN) characteristics of gate-all-around poly-Si nanowire (NW) transistors with high-κ oxide/metal-gate (HK/MG) stack. Distinct two-level RTN signals were measured on NW transistors with effective channel length of 150 nm and channel width of 30 nm. Values of time constants for charge emission from and capture by traps were extracted from measured RTN signals. We proposed a new theoretical scheme to evaluate the location and energy level of the corresponding trap. The trap was assessed to be present within the interfacial layer (IL) at a spatial location approximate 1 nm away from the IL/channel interface and 68 nm in proximity to the source side.