Current Noise Power Spectral Density Research Articles

Low-frequency noise in InSnZnO thin film transistors with high-quality SiO2 gate oxide stacks

Low-frequency noise (LFN) in InSnZnO (ITZO) thin-film-transistors (TFT) with high-quality SiO2 gate oxide (GO) stacks is studied. This stack is fabricated by the plasma enhanced chemical vapor deposition (PECVD) and comprises two single layers. One layer is deposited by a SiH4 source (SiH4–SiO2), and the other uses a tetraethyl-orthosilicate precursor (TEOS-SiO2). The drain current noise power spectral densities follow the typical 1/f rule, and the main origin of LFN changes with the variation of drain current intensities. At low drain current intensities, LFN is affected by grain boundaries in the channel. As the drain current intensities increase, LFN originates from the carrier number fluctuations in devices with single TEOS-SiO2 GOs and from the carrier number with correlated mobility fluctuations in devices with SiO2 stacks GOs. At extremely high drain current intensities, the contact noise acts as a significant source of LFN in devices with SiO2 GO stacks. According to the carrier number with correlated mobility fluctuation (ΔN−Δμ) model, the devices with optimal stacks GOs exhibit a relatively low trap density near the ITZO/SiO2 interface. Additionally, these devices have a lower border trap density in GOs compared to those with single compositions. It demonstrates that high-quality SiO2 stacks reduce traps near the SiO2/ITZO interface, leading to enhanced devices performance. This work provides a precise and efficient method to evaluate the quality of GOs in metal oxide TFTs.

Effect of heavy ion radiation on low frequency noise characteristics of AlGaN/GaN high electron mobility transistors

AlGaN/GaN high election mobility transistor (HEMT) has important application prospects in satellite communication, radar, nuclear reactors and other extreme environments, owing to its excellent electrical performance and strong radiation resistance. Heavy ion radiation mainly causes single-event effect and displacement damage effect in AlGaN/GaN HEMT device. In this work, the displacement damage defects introduced by heavy ion radiation are analyzed in detail. With the increase of heavy ion radiation influence, more defects are introduced by displacement damage. These defects reduce the two-dimensional electron gas (2DEG) concentration through carrier capture and removal effect, and reduce the carrier mobility through scattering mechanism, resulting in gradual degradation of the electrical characteristics of the device. In this work, AlGaN/GaN high electron mobility transistors are irradiated by <sup>181</sup>Ta<sup>32+</sup> ions with fluences of 1×10<sup>8</sup> ions/cm<sup>2</sup>, 1×10<sup>9</sup> ions/cm<sup>2</sup> and 1×10<sup>10</sup> ions/cm<sup>2</sup>. The electrical characteristics, EMMI and low-frequency noise characteristics of the device before and after heavy ion radiation are measured. The results show that heavy ion radiation can lead to the degradation of electrical parameters. When the heavy ion radiation dose reaches 1×10<sup>10</sup> ions/cm<sup>2</sup>, the electrical characteristics of the device deteriorate seriously, the threshold voltage shifts forward by 25%, and the drain saturation current deteriorates obviously. The defect locations introduced by irradiation are analyzed by EMMI test, and it is found that the number of “hot spots” increases significantly after the having been irradiated by heavy ions with a fluence of 1×10<sup>10</sup> ions/cm<sup>2</sup>, indicating that the radiation leads to the increase of defect density and serious damage to the device. Through the noise test, it is found that with the increase of the radiation fluence, the current noise power spectral density gradually increases. When the fluence reaches 1×10<sup>10</sup> ions/cm<sup>2</sup>, the defect density increases to 3.19×10<sup>18</sup> cm<sup>–3</sup>·eV<sup>–1</sup>, and the Hooge parameter increases after having been irradiated by heavy ions. We believe that the radiation leads to the defect density and parasitic series resistance of AlGaN/GaN HEMT device to increases, resulting in larger Hooge parameters. Through analyzing the variation of the normalized power spectral density of the drain current noise with bias voltage, it is found that the defects caused by heavy ion radiation will cause the parasitic series resistance to increase.

Low-Frequency Noise Characteristics in HfO2-Based Metal-Ferroelectric-Metal Capacitors.

The transport mechanism of HfO2-based metal-ferroelectric-metal (MFM) capacitors was investigated using low-frequency noise (LFN) measurements for the first time. The current-voltage measurement results revealed that the leakage behavior of the fabricated MFM capacitor was caused by the trap-related Poole-Frenkel transport mechanism, which was confirmed by the LFN measurements. The current noise power spectral densities (SI) obtained from the LFN measurements followed 1/f noise shapes and exhibited a constant electric field (E) × SI/I2 noise behavior. No polarization dependency was observed in the transport characteristics of the MFM capacitor owing to its structural symmetry.

Shot and Johnson noises in interband cascade infrared photodetectors

Shot and Johnson noises are often incorrectly thought of as two independent noise sources. This incorrect picture has affected the evaluation of detectivities in interband cascade infrared photodetectors (ICIPs). In this work, a unified picture of shot and Johnson noises is developed for ICIPs based on a fundamental framework to understand the origin of Johnson noise and clarify the possible confusion between Johnson and shot noises. General, yet concise expressions are derived to evaluate the current noise power spectral density and detectivity for ICIPs even with complicated structures. Also, simple expressions for the signal current due to absorption of photons and the corresponding photon noise are derived, consistent with the previous results derived from alternative methods. Furthermore, a formula is derived to correctly evaluate the detectivity for conventional photodetectors under a reverse bias. The derived formulas with discussion are expected to improve the understanding of noises in ICIPs and other types of photodetectors and help us to appropriately evaluate their detectivities.

Degradation Characteristics and Reliability Assessment of 1310 nm VCSEL for Microwave Photonic Link

The long-term reliability of the commercially available vertical-cavity surface-emitting laser (VCSEL) at 1310 nm wavelength is investigated. To do so, a high current accelerated life test is used to evaluate the 1310 nm VCSEL reliability. Variations of properties that depend on the operating condition are characterized by the light-current-voltage, leakage current and low-frequency noise. When the aging current is 6 mA, 8 mA and 10 mA, the maximum output power reduces by 5%, 6% and 15% of the initial value, respectively. It is demonstrated theoretically and experimentally that the leakage current increases and reverse bias breakdown voltage decreases after the accelerated current aging test. The current noise power spectral density increases after the device ages, and the noise increases with the augment of the electrical stress. When the bias current of VCSEL is below the threshold, the frequency index factor and noise amplitude gradually increase with the bias current increase. Further, lifetime fitting curves of the devices at an accelerating current of 6 mA, 8 mA and 10 mA are obtained, and the median lifetime of 67 years at the operating current is extrapolated.

Noise behavior and reliability analysis of non-uniform body tunnel FET with dual material source

In this paper the noise analysis of Non-Uniform Body TFET with Dual Material Source is performed incepting both the absence and presence of different types of trap charges when the device undergoes various changes in source material (like Si, Ge, and both Si + Ge), and temperature (200 K–400 K) etc. In this study it has been found that the value of drain current noise power spectral density (Sid) for the device is 9.92 × 10−23 A2/Hz and for entire source region having Si and Ge materials the Sid values are estimated as 3.3 × 10−24 A2/Hz and 1.7 × 10−19 A2/Hz, respectively. In the device noise degradation effect is admissible when different performance parameters are accounted as compared to the cases when source material is completely made of Si or Ge. The aforesaid fact has been validated by normalized Sid (Sid/Ids2) vs. Drain current (Id) and Sid (Sid/Ids2) vs. Subthreshold Swing (SS) plot analysis, which clearly indicates the less effect of noise and superior electrostatic coupling in the device. Furthermore, the systematic study for effect of different types of noise under various trap charge distributions is also reported which showed that the device is negligibly effected by donor trap charges. Lastly to explore the reliability part of the device the temperature analysis including the absence and presence of trap charges for the noise behavior illustrated that the effect of increase in noise due to presence of trap charges is more at low temperatures and low gate to source voltages (Vgs) and the dominating noise component is found to be G-R noise.

Analog Figures of Merit of Vertically Stacked Silicon Nanosheets nMOSFETs With Two Different Metal Gates for the Sub-7 nm Technology Node Operating at High Temperatures

The analysis of vertically stacked nanosheet (NS) n-type transistors with two different metal gate-stacks (with a total thickness of 7.5 and 4.7 nm) is presented in this work from room temperature to 200 °C. The focus in this work is on the classical analog figures of merit (FoM). In all NS devices, superior performance is observed that is confirmed by the subthreshold swing variation with temperature, which is very close to the theoretical thermal limit. The Al-based (n*) gate-stack NS n-channel NS field effect transistors (NSFETs) in general present higher transconductance, transistor efficiency, early voltage, and intrinsic voltage gain (A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> ) thanks to the better electrostatic coupling between the gates and the silicon NSs. An A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> of about 47 dB (gate-stack (n*), L = 200 nm, 200 °C) is obtained. The low-frequency noise analysis demonstrates the presence of flicker noise dominated by carrier number fluctuations as the main type of noise and presents a low current noise power spectral density Sid of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-19</sup> A <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /Hz at a drain current of 1 μA and a drain voltage of 50 mV for a frequency of 10 Hz.

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

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

Low Frequency Noise Analysis of Single Gate Extended Source Tunnel FET

This paper presents the analysis of noise in Single Gate Extended Source TFET (SG-ESTFET) considering the absence and presence of interface trap charges, when the device is subjected to scaling and variation of parameters like device gate length (Lg), extended source length and height, SiGe mole fraction (x), oxide thickness (tox), gate dielectric material, and frequency (f). Furthermore, the influence of variation of dimensionality and material parameters in presence of noise on Drain Current Noise Power Spectral Density (Sid) and Gate Voltage Electron Noise Power Spectral Density (Svgee) are studied for different trap charge conditions. Assuming Gaussian distribution of trap charges at the interface, it is perceived that the effect of noise is more as compared to the case of absence of trap charges. In reference to other FET devices, present paper reports that, the proposed SG-ESTFET device under absence of trap charges, illustrates an improved Sid and Svgee value of 1.4 × 10−29 A2/Hz and 5.21 × 10−16 V2/Hz, respectively whereas under the presence of trap charges, Sid and Svgee value are 6.6 × 10−26 A2/Hz and 8.74 × 10−12 V2/Hz, respectively. Moreover, this study also reports that the generation recombination (G-R) noise is mainly prevailing at low and mid-frequencies in presence of trap charges while diffusion noise is prevailing at high-frequencies. Likewise, the flicker noise is observed to be noteworthy at low and medium-frequencies in absence of trap charges.

Oxide Edge Trap Density Extraction in Silicon Nanowire MOSFET From Tunnel Current Noise Measurement in Gated Diode Like Arrangement

Edge traps in the gate oxide of silicon nanowire MOSFETs have been extracted from tunnel current noise measurement in a gated diode like arrangement. We have found that, low frequency noise in tunnel current results from collective response of the edge traps available within the gate oxide surrounding band-to-band generation (BTBG) region of silicon nanowire, and when the BTBG region is accessed by favorable terminal biases. From detail modeling of the phenomenon, we derived a closed form expression of the tunneling current noise power spectral density (PSD) employing which oxide edge trap density in nanowire MOSFET had been extracted through its fit with the experimental noise PSD data. We furthermore validated our model for different BTBG biases, and contrasted our result with the bulk oxide trap density in identical MOSFET, while the latter was separately estimated from the gate current noise PSD measurement. Mismatch between the oxide bulk trap and edge trap concentrations has been found, whereby actual edge trap density remains otherwise hidden from the widely employed gate current noise measurement technique. It is because, the present scheme improves the resolution of the extracted oxide edge trap concentration in surrounded gate MOSFET owing to constricted tunnel current flow near the corner of the gate which imposes selectivity on the oxide edge traps

Dimension Scaling Effects on Conduction and Low Frequency Noise Characteristics of ITO-Stabilized ZnO Thin Film Transistors

Conduction characteristics and low frequency noises in ITO-stabilized ZnO thin film transistors (TFTs) with constant channel width (W=50 μm) and different channel lengths (L=5, 10, 25, 50 and 100 μm) are measured and analysis. Firstly, dependences of threshold voltage and field effect mobility on channel length are examined. With decreasing channel length, the threshold voltage shifts to the negative direction which may attribute to carrier diffusion from source/drain to the intrinsic device channel. In addition, significant degradation of field effect mobility is observed in short channel device which are induced by the presence of series contact resistance. The value of contact resistance has also been extracted. Secondly, the drain current noise power spectral densities (S ID ) are measured at varied effective gate voltages. The measured noises follow a 1/f γ and y is about -1.1. Moreover, the normalized noises (S ID /I ds ) are dependent linearly on the inverse of channel length and the slope is about -0.75. Finally, the dominant mechanism of low frequency noise in ITO-stabilized ZnO thin film transistor are examined. The slope of normalized noise against effective gate voltage are extracted, which are varied from -1.03 to -1.84 with decreasing channel length and thus it indicates that ITO-stabilized ZnO TFTs varied from bulk dominated devices to interface dominated devices. By using of ΔN-Δμ model, the normalized noises are simulated by considering of contact resistance. Several noise parameters (flat-band voltage noise spectral density, etc) are extracted and analysis.

Noise behavior of ferro electric tunnel FET

In this paper the noise behavior of ferroelectric TFET is explored for the first time. The effect of ferro-thickness, gate length, buffer type, and buffer thickness on current noise power spectral Density (SID) and voltage noise power spectral Density (SVG) along with electrical parameters such as memory window, subthreshold swing along with have been investigated. The normalized SID follows 1/SS2 trend, thus signifies the dominancy of BTBT over TAT in Ferro-TFET. Input referred noise PSD, SVG remains constant for whole range of gate voltage deviating from the nature for conventional MOSFET.Power spectral densities experience a sharp rise for frequency above 0.1 ​GHz due to dominancy of diffusion over other source of noise.

1/f noise analysis in high mobility polymer-based OTFTs with non-fluorinated dielectric

In this paper, Low Frequency Noise (LFN) characterization of SP500 polymer-based Organic Thin Film Transistors with a nonfluorinated dielectric material is presented. The work aimed at identifying the mechanism of 1/f noise as well as inspecting the quality of the gate dielectric interface. Analysis of the LFN experimental data reveals that the 1/f noise power spectral density (PSD) follows 1/f γ frequency dependence over 1 Hz–10 kHz range. The normalized current noise PSD is found to vary similar to the squared-transconductance drain current ratio with respect to drain current, and is inversely related to the gate-area. Furthermore, the high carrier mobility (on the order of 2–3 cm2/Vs) obtained in these devices indicates that low density of traps exists in the semiconducting organic thin film. Such results ascribed the origin of 1/f noise to the dynamic exchange of charge carriers between the gate-dielectric traps and the channel. In addition, Nst values extracted from the 1/f noise experimental data reflect the enhanced quality of the gate dielectric and the interface it forms with the channel material.

Measurements of the size and correlations between ions using an electrolytic point contact

The size of an ion affects everything from the structure of water to life itself. In this report, to gauge their size, ions dissolved in water are forced electrically through a sub-nanometer-diameter pore spanning a thin membrane and the current is measured. The measurements reveal an ion-selective conductance that vanishes in pores <0.24 nm in diameter—the size of a water molecule—indicating that permeating ions have a grossly distorted hydration shell. Analysis of the current noise power spectral density exposes a threshold, below which the noise is independent of current, and beyond which it increases quadratically. This dependence proves that the spectral density, which is uncorrelated below threshold, becomes correlated above it. The onset of correlations for Li+, Mg2+, Na+ and K+-ions extrapolates to pore diameters of 0.13 ± 0.11 nm, 0.16 ± 0.11 nm, 0.22 ± 0.11 nm and 0.25 ± 0.11 nm, respectively—consonant with diameters at which the conductance vanishes and consistent with ions moving through the sub-nanopore with distorted hydration shells in a correlated way.

Noise behaviour of δp+ Si1−xGex layer SELBOX TFET

This paper explores an analysis of low- and high-frequency noise in a heterojunction, selective buried oxide (SELBOX) with high-k gate dielectric TFET. The electrical parameters for different doping concentrations, δp+ layer width and mole fractions have been investigated. The proposed structure has been optimized for different positions of small gap on SELBOX substrate. It has been observed that the presence of small gap on SELBOX near the source region provides the lowest OFF current. The variation of noise (flicker + diffusion + generation − recombination) with frequency has been analysed. Further, the effect of various noise components on the device performance considering the current noise spectral density (SID) and voltage noise spectral density (SVG) is investigated. The impact of germanium mole fractions on noise components has been examined in terms of normalized current noise power spectral density and subthreshold swing.

Scaling Down Effect on Low Frequency Noise in Polycrystalline Silicon Thin-Film Transistors

Scaling down effects on conduction and low frequency noise characteristics are investigated in a set of p-type polycrystalline silicon thin-film transistors (poly-Si TFTs) with fixed channel width ( $W=8 \mu$ m) and different channel lengths ( $L=2, 4, 8, 12, ~\text{and}~ 20 \mu$ m). First, short channel effects on threshold voltage, field effect mobility, and sub-threshold swing are examined, while the presence of contact may induce to the degradation of field effect mobility in the short channel devices. Subsequently, the drain current noise power spectral densities are measured at varied effective gate voltages and drain currents. The slopes of normalized noise against effective gate voltage are varied from −1.1 to −2 with decreasing channel length, which indicates that poly-Si TFTs varied from bulk dominated devices to interface dominated devices. Based on $\Delta N-\Delta \mu$ model, the flat-band voltage noise spectral density and coulomb scattering coefficient are extracted. Therefore, measured normalized noises are simulated by considering of contact resistance. Finally, short channel effects on some noise parameters (such as Hooge’s parameter, etc.) are studied and discussed.

Electrochemical Noise Measurement of Polymer Membrane Fuel Cell under Load

Electrochemical noise of a polymer membrane hydrogen–air fuel cell under different currents is measured. Frequency and amplitude dependences of the current-noise power spectral density are calculated. In the frequency interval from 10 to 200 Hz a linear segment of the frequency characteristic has a slope of ‒2. The current-noise power spectral density is found to be proportional to the 4th power of the fuel cell loading DC current. Thus found frequency dependence of the fuel cell electrochemical noise was shown to differ markedly from that of the electrochemical impedance real component.

Low-Frequency Noise in Hybrid-Phase- Microstructure ITO-Stabilized ZnO Thin-Film Transistors

Low-frequency noise (LFN) in hybrid-phase-microstructure ITO-stabilized ZnO thin-film transistors is investigated. The measured drain current noise power spectral densities obey the classical 1/ $\text{f}^{\gamma }$ noise theory, with $\gamma $ about 0.9. When $V_{\mathrm {\textsf {gs}}} $ - $V_{\mathrm {\textsf {th}}}$ is low, the gate voltage dependent noise data closely follow the carrier number with correlated mobility fluctuation ( $\Delta {N} - \Delta \mu $ ) model, and the average Hooge’s $\vphantom {_{\int }}$ parameter in the channel is extracted to be about $1.1 \times 10^{-2}$ . Moreover, the contribution of contact resistance to LFN is further studied. Dominated by the channel and the contact, the normalized noise varies with two slopes ( ${m} = -1$ .x and 0) with an increase of the effective gate voltage. Finally, the normalized noise versus drain current results are simulated by considering contact resistance.

Analysis and Simulation of Low-Frequency Noise in Indium-Zinc-Oxide Thin-Film Transistors

Low-frequency noise (LFN) is investigated in a set of indium-zinc-oxide thin-film transistors (IZO TFTs) with fixed channel width ( $W$ = $10~\mu \text{m}$ ) and different channel lengths ( $L\,\,=10$ , 20, 30, and $40~\mu \text{m}$ ) from sub-threshold, linear to saturation regions. The drain current noise power spectral density is measured as a function of effective gate voltage and drain current. The variation slopes of normalized noise with effective gate voltage are in the range of −1.27 and −1.48, which are close to the prediction of the mobility fluctuation mechanism. According to the $\Delta N-\Delta \mu $ model, the flat-band voltage noise spectral density and Coulomb scattering coefficient are extracted. Subsequently, variations of noise with the drain current in the above threshold region are analyzed by considering the band-gap distribution of the tail states. Finally, the BSIM model is also used to model 1/ $f$ noise in the IZO TFTs. The noise parameter $NOIB$ is extracted which is inversely proportional to the effective gate voltage. Good agreements are achieved between the simulated and measured results in the linear region.

(Invited) Impact of the Metal Gate on the Oxide Stack Quality Assessed by Low-Frequency Noise

It is well-established that the gate oxide quality and reliability strongly depend on the type of high-k and interfacial oxide layer, the deposition method and the implementation of possible post-deposition heat or passivation treatments. As a result, the low-frequency noise magnitude may be largely affected by the gate stack processing details [1]. What is less studied is the impact of the gate material itself on the gate stack quality. Early assessments already indicated an impact of the number of TiN Atomic Layer Deposition (ALD) cycles on the noise Power Spectral Density (PSD) [2]. It is the aim of the present work to review the low-frequency noise of High-k/Metal Gate (HKMG) MOS transistors with emphasis on the role of the specific gate metal. Devices with different architectures (planar, FinFET and NanoWire (NW) FETs) will be considered in addition to the gate first versus gate last integration [3.4] As a first example, the impact of the W plug processing on the LF noise for planar pMOSFETs is shown in Fig. 1. The current noise PSD (SI) in linear operation (VDS=-0.05 V) at a frequency f=10 Hz is shown to become higher for the B2H6 precursor case, compared with the W deposition with SiH4 precursor. The higher noise is interpreted in terms of a higher oxide trap density, which is evidenced by the hump at about 100 mA drain current (ID), which is thought associated with a gate oxide trap, causing a Random Telegraph Signal (RTS). The impact on the gate stack quality (noise) of high-k Silicon-on-Insulator (SOI) and bulk FinFETs is shown in Figs 2 [5] and 3,4 [6], respectively. In the first case, the effective oxide trap density, derived from the input-referred voltage noise PSD increases with the TiN thickness, which also results in a degradation of the static characteristics, i.e., the low-field electron mobility [5]. Even for input-output (IO) devices with a rather thick thermal oxide, the gate material can play a strong role in the noise: comparing Figs 3 and 4, it is clear that both the magnitude and the slope (frequency index) of the spectra are different for a pFinFET with a standard TiN gate versus a TaN one. It will be shown that the latter devices may yield a better gate stack quality (a lower trap density) which becomes similar to that of a SiO2/polysilicon reference. Ultimately, the NW architecture will take over at the end of the Roadmap due to superior gate control of the short-channel effects. Again, it has been shown that for NWFETs the gate metal may have a strong effect on the oxide trap density, as derived from 1/f noise [7,8]. An example is given in Fig. 5, showing a clear correlation between the DC parameters (low-field mobility) and the oxide trap density (Not) derived from the 1/f noise PSD. A more detailed study of the trap density profile in Fig. 6 reveals an increase of Not towards the metal gate for the TiN device, which is absent for the TiAl case. This suggests a possible oxygen scavenging effect of Ti on the gate stack [9], creating an excess of “noisy” oxygen vacancy centers in the high-k layer.