Voltage Noise Power Spectral Density Research Articles

Metasurface-Enabled Uncooled Silicon Germanium Oxide Infrared Microbolometers for Long-Wave Infrared Detection

This paper investigated metasurface enabled uncooled silicon germanium oxide (Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.425</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.512</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.063</sub> ) infrared (IR) microbolometers. The metasurface was used to engineer the IR absorption to achieve broadband or narrowband spectral response, eliminate the need for Fabry-Perot quarter wave resonant cavity typically used in conventional microbolometer under the pixel, and significantly improve the electrical performance of the temperature-sensing layer. This has facilitated the fabrication of the microbolometer with the supporting arms placed underneath the pixel without disrupting the Fabry-Perot cavity, and as a result, the supporting arms were fabricated with longer length without sacrificing the fill factor. The longer support arms reduced the thermal conductance between the microbolometer pixel and the underlying substrate and thus increased the voltage responsivity. The spectral responsivity and detectivity for the fabricated devices were measured in vacuum and demonstrated tunablility with narrow bands between 7 to 12 μm by changing the metasurface disk diameter and periodicity. The measured voltage responsivity, detectivity and thermal response time were > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> V/W and > 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> /W and 2.01 ms to filtered blackbody infrared radiation between > 2 μm. The voltage noise power spectral density (PSD) of the fabricated devices were reduced by annealing the devices in vacuum.

A novel modem model insensitive to the effect of the modulated carrier and the demodulated-signal phase adapted for capacitive sensors

The differential bridge-type capacitive sensors are widely applied in many precise instrumental measurement fields, where the modem is a key technology to realize the detection for a tiny differential capacitance. A universal structure based on a modulated sine carrier and a switched analog demodulation is adopted, so two factors including the carrier’s stability and the slight phase difference with its fluctuation between demodulated signals will inevitably limit the modem performance, and further deteriorate the capacitance sensitivity. In this paper, a novel modem based on a modulated step sine carrier is proposed, and the theoretical analysis indicates that the novel structure can significantly reduce the effects of aforesaid factors. Finally, a joint evaluation circuit is built to preliminarily measure the modem noise, and experimental results demonstrate a relative voltage noise power spectral density of 7 ppm/Hz1/2 at 1 mHz for the novel modem, two times better than that with a sine carrier.

Uncooled two-microbolometer stack for long wavelength infrared detection

We have investigated an uncooled infrared (IR) detector utilizing a dual level architecture. This was achieved by combining two-microbolometer stack in the vertical direction to achieve high IR absorption over two distinct spectral windows across the long wavelength infrared region (LWIR). In addition, we have studied amorphous silicon germanium oxide (SixGeyO1−x−y) as an IR sensitive material, and metasurface to control IR absorption/reflection in interaction with standard Fabry–Perot cavity. The bottom microbolometer uses a metasurface to selectively absorbs a portion of the spectrum and reflects radiation outside this window range. At the same time, the top microbolometer uses a conventional Fabry–Perot resonant cavity to absorb a different portion of the spectrum and transmit any unabsorbed radiation outside this window. This device can be used to measure the absolute temperature of an object by comparing the relative signals in the two spectral bands. The spectral responsivity and detectivity, and thermal response time were > 105 V/W, > 108 cm Hz1/2/W, and 1.13 ms to filtered blackbody infrared radiation between (2–16) µm. The microbolometer voltage noise power spectral density was reduced by annealing the microbolometers in vacuum at 300 °C.

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

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

Impact of the channel doping on the low-frequency noise of silicon vertical nanowire pFETs

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

Assessment of Fuel Cells’ State of Health by Low-Frequency Noise Measurements

We proposed applying low-frequency (flicker) noise in proton-exchange membrane fuel cells under selected loads to assess their state of health. The measurement set-up comprised a precise data acquisition board and was able to record the DC voltage and its random component at the output. The set-up estimated the voltage noise power spectral density at frequencies up to a few hundred mHz. We observed the evolution of the electrical parameters of selected cells of different qualities. We confirmed that flicker noise intensity varied the most (more than 10 times) and preceded changes in the impedance or a drop in the output DC voltage (less than 2 times). The data were observed for current loads (from 0.5 to 32 A) far from the permissible load. We deduce that the method can be utilised in industrial conditions to monitor the state of health of the selected cells by noise analysis. The method can be used in real-time when the flicker noise is measured within the range of a few Hz and requires a reasonable amount of averaging time to estimate its power spectral density. The presented method of flicker noise measurement has considerable potential for use in innovative ways of fuel cell quality monitoring.

Proton-Induced Effect on AlGaN/GaN HEMTs After Hydrogen Treatment

The effect of proton irradiation on the electrical properties of AlGaN/GaN high electron mobility transistors (HEMTs) with hydrogen treatment is studied. Hydrogen treatment makes the damage caused by proton irradiation worse. The AlGaN/GaN HEMTs with hydrogen treatment at 2.0 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14 </sup> p/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 3-MeV proton irradiation fluence experience a decrease by 37.3% in the saturation current, a 0.55V positive shift of the threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> ) and a notable decrease in reverse gate leakage current. While the AlGaN/GaN HEMTs without hydrogen treatment experience a decrease by 18.2% in the saturation current, a 0.211V positive shift of the V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub> . After extracted by the Low Frequency Noise method (LFN method), the flat-band voltage noise power spectral density (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vfb</sub> ) after hydrogen treatment decreases, and proton irradiation makes the number of defects increased. But the hydrogen treatment causes the S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vfb</sub> to rise rapidly after proton irradiation, comparing with the AlGaN/GaN HEMTs without hydrogen treatment. The main mechanism can be attributed to the hydrogen passivation defect and proton irradiation to stimulate the passivation defect to produce composite defects. And the AlGaN/GaN HEMTs with hydrogen treatment is more sensitive to proton irradiation, compared with the AlGaN/GaN HEMTs without hydrogen treatment.

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

Introduction. The Gate-All-Around (GAA) Nanowire (NW) or nanosheet (NS) architecture provides superior short-channel effects control and is widely considered as one of the most promising candidates to replace finFETs in advanced Logic technology nodes. Compared with their horizontal implementation, vertical NWs (or NSs) FETs [1] offer some clear advantages, appearing promising devices to overcome some of the limitations encountered by conventional CMOS scaling as it reaches its physical limits and faces interconnect routing congestion. They have the potential to yield smaller circuits with reduced power consumption [2], allowing relaxed Lgate without impacting the device footprint. While their fabrication is challenging, several schemes have been proposed for improved process control and device performance [1]. In this work, the static parameters of vertical NW junctionless (JL) nMOSFETs have been studied for devices with two different Replacement Metal Gate (RMG) cap layer widths (see schematics in figure 1), encapsulating the top part of the pillars during processing at the RMG module. It will be shown that this strongly impacts the static device parameters: the threshold voltage (VT), the maximum transconductance (gmmax) and the dynamic output resistance (rout). Moreover, a correlation is shown with the input-referred voltage noise Power Spectral Density (PSD) SVG at 10 Hz, which could be explained in terms of a process-induced variation in the diameter D of the NWs. Experimental. A detailed process description has been recently reported [1]. A 55 nm in situ P-doped n+ layer is deposited by CVD on a low-resistivity silicon substrate (source contact), followed by 90 nm undoped silicon and again 55 nm n+ Si. The RMG stack consists of IL-SiO2/HfO2/TiN/W. An RMG cap consisting of SiO2 is used to encapsulate the top of the pillars. Here, devices with two different cap widths and 100 wires in parallel are compared. On-wafer DC and low-frequency noise measurements have been performed using a BT1500 Parameter Analyzer and an E4727A Advanced Low-Frequency Noise Analyzer from Keysight, respectively. Measurements have been performed in linear operation at a drain voltage VDS=50 mV, while the gate voltage VGS is stepped from weak to strong inversion. Results and Discussion. Figure 1 and 2 compares the linear input ID-VGS characteristics of a set of narrow and wide cap vertical NW nFETs. While there is obvious device-to-device variability, the wide-gap devices (Fig. 2) clearly exhibit a lower VT than their narrow-gap counterparts in Fig. 1. The transconductance (gm) plots of Figs 3 and 4 reveal another trend: devices with a high VT generally exhibit a lower gmmax and vice versa. This is even so within each flavour of devices in Figs 3 and 4. As will be shown, nFETs with a high(er) VT and lower gmmax also tend to exhibit a higher rout. Finally, Figs 5 and 6 demonstrate that the corresponding SVG at f=10 Hz is smaller for the wide-cap devices, especially around VT, where the minimum noise PSD is found. As will be shown, the noise spectra are dominated by 1/f-like noise (f<1 kHz). A possible explanation of the observed parameter variations should provide a consistent picture for the reported correlations. For these particular devices, the NW doping density can be ruled out, as we are studying undoped pillars. The difference in SVG could suggest a difference in oxide/interface trap density, but this is not reflected in the subthreshold swing nor in the PBTI behaviour [1]. On the other hand, it has been reported before that the VT of NW transistors increases for reduce D [3]. This could well explain also the lower gmmax (scales with D) and the higher SVG (scales with 1/D). The different NW diameter could result from the different dummy dielectric removal [1].

Low–Frequency Noise in Vertically Stacked Si n–Channel Nanosheet FETs

This manuscript presents a systematic low–frequency noise analysis of inversion–mode vertically stacked silicon n–channel nanosheet MOSFETs on bulk wafers. Flicker noise due to carrier number fluctuations is shown as the dominant noise source, which is in line with previous reported studies on gate-all-around (GAA) nanowire nMOSFETs. In addition, the benchmark points out that the vertical stacking approach does not deteriorate the oxide trap density, since its normalized input–referred voltage noise Power Spectral Density at flat–band is lower compared to the data on non–stacked horizontal nanowire nMOSFETs. Another finding is that the Coulomb scattering mechanism dominates the mobility.

High-Fluence Proton-Induced Degradation on AlGaN/GaN High-Electron-Mobility Transistors

The electrical characteristics and low-frequency noise (LFN) of AlGaN/GaN high-electron-mobility transistors (HEMTs) after 3-MeV proton irradiation up to a total dose of 5.0 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> p/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> have been studied in this article. The devices experienced a 14.6% decrease in the saturation current, a 0.35-V positive shift in the threshold voltage (Vth), and a significant decrease in the reverse gate leakage current after 3-MeV proton irradiation. Extracted by the LFN method, the flatband voltage noise power spectral density (SVfb) increases from 4.112 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> to 5.603 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> · Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> , and the trap density increases from 2.79 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> to 3.84 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">17</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> · eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> after the radiation. The main degradation mechanism is considered to be the increase of negatively charged trap density in the channel, which depletes more electrons and reduces the carrier mobility in the channel 2-D electron gas (2DEG). We also extracted the radiation-induced trapped charge density according to the theoretical calculation; the result is consistent with the LFN measurement.

Ionizing radiation damage mechanism and biases correlation of AlGaN/GaN high electron mobility transistor devices

In this paper, the total dose effect on AlGaN/GaN high-electron-mobility transistor (HEMT) devices after &lt;sup&gt;60&lt;/sup&gt;Co γ-ray irradiation with a total dose of 1 Mrad(Si) was investigated at different biases (&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;GS&lt;/sub&gt; = –3 V, &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;DS&lt;/sub&gt;&lt;italic/&gt; = 0.5 V; &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;GS&lt;/sub&gt; = –1.9 V, &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;DS&lt;/sub&gt; = 0.5 V; &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;GS&lt;/sub&gt; = 0 V, &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;DS&lt;/sub&gt; = 0 V). The experimental results were analyzed using 1/&lt;i&gt;f&lt;/i&gt; low-frequency noise and direct current electrical characteristics. The electrical parameters degraded mostly under zero bias condition because of the radiation-induced defect charge of the oxide layer and the interface state. Wherein, the saturation drain current was reduced by 36.28%, and the maximum transconductance was reduced by 52.94%. The reason was that the oxide dielectric layer of AlGaN/GaN HEMT devices generated electron-hole pairs under γ-ray irradiation, and most of the electrons were quickly swept out of the oxide region corresponding to the gate-source and gate-drain spacer regions, and most of the holes remained in the oxide. Under the action of the built-in electric field, holes slowly moved towards the interface between the oxide and AlGaN, which depleted the two-dimensional electron gas of the channel.According to the McWhorter model, the low-frequency noise in the AlGaN/GaN HEMT devices results from random fluctuations of carriers, which are caused by the capture and release processes of carriers by traps and defect states in the barrier layer. The extracted defect densities in AlGaN/GaN HEMT devices increased from 4.080 × 10&lt;sup&gt;17 &lt;/sup&gt;cm&lt;sup&gt;–3&lt;/sup&gt;·eV&lt;sup&gt;–1&lt;/sup&gt; to 6.621 × 10&lt;sup&gt;17 &lt;/sup&gt;cm&lt;sup&gt;–3&lt;/sup&gt;·eV&lt;sup&gt;–1&lt;/sup&gt; under the condition of zero bias, and the result was in good agreement with test results of the direct currentelectrical characteristics. The damage mechanism was the radiation-induced defect charge in the oxide layer and the interface state, which increased the flat-band voltage noise power spectral density of the AlGaN/GaN HEMT devices. According to the charge tunneling mechanism, the spatial distribution of defect in the barrier layer was extracted, and the result also proved that the densities of radiation-induced defect charges under zero bias were more than the other biases. The experimental results showed that zero bias was the worst bias for AlGaN/GaN HEMT devices irradiation.

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.

Gate Metal and Cap Layer Effects on Ge nMOSFETs Low-Frequency Noise Behavior

Low-frequency noise is used to estimate the quality of the gate stack for planar Ge nMOSFETs with different effective work function metals and cap layers. It is shown that replacing TiN by a TiAl-based metal gate will induce a significant decline of the threshold voltage VT and noise power spectral density, indicating the introduction of Al will induce an advantageous effect on the trap density in the underlying HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Meanwhile, the application of a LaO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> cap tends to reduce V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and the trap density in the gate oxide, which could attribute to the La in-diffusion in the gate stack. The 1/f noise analysis shows that the noise could mainly be associated with number fluctuations and correlated mobility fluctuations.

Temperature dependence of conduction and low frequency noise characteristics in hydrogenated amorphous silicon thin film transistors

The transfer and low frequency noise characteristics of hydrogenated amorphous silicon thin film transistors (a-Si:H TFTs) were measured in the temperature range of 230–430 K. The variation of threshold voltage, field effect mobility and sub-threshold swing with increasing temperatures were then extracted and analyzed. Moreover, the shifts of low frequency noise in the a-Si:H TFT under various temperatures are reported for the first time. The variation of flatband voltage noise power spectral density with temperature is also calculated and discussed.

(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.

Reduction of Low Frequency Noise Impact to Terahertz Detectors in CMOS

Variation of low frequency noise including 1/f noise and Lorentzian spectra is the dominant source of variations for noise equivalent power (NEP) of THz detectors using a forward biased diode connected NMOS transistor. Elimination of the impact of low frequency noise variation to NEP with 1-V amplitude AC biasing at 44MHz is demonstrated in 830-GHz detectors using a diode connected PMOS transistor. It should be possible to apply this technique to eliminate the impact of low frequency noise variations in THz NMOS and Schottky diode detectors. Lastly, the low frequency noise voltage power spectral density of AC biased diode connected PMOS transistors is comparable to that of commercial GaAs detectors.

Effects of Negative-Bias-Temperature-Instability on Low-Frequency Noise in SiGe ${p}$ MOSFETs

We have measured the low-frequency 1/ ${f}$ noise of Si0.55Ge0.45 ${p}$ MOSFETs with a Si capping layer and SiO2/HfO2/TiN gate stack as a function of frequency, gate voltage, and temperature (100–440 K). The magnitude of the excess drain voltage noise power spectral density ( $\textit{S}_{ {vd}}$ ) is unaffected by negative-bias-temperature stress (NBTS) for temperatures below ~250 K, but increases significantly at higher temperatures. The noise is described well by the Dutta-Horn model before and after NBTS. The noise at higher measuring temperatures is attributed primarily to oxygen-vacancy and hydrogen-related defects in the SiO2 and HfO2 layers. At lower measuring temperatures, the noise also appears to be affected strongly by hydrogen-dopant interactions in the SiGe layer of the device.

Noise Reduction of Amorphous SixGeyO1–x–yThin Films for Uncooled Microbolometers by Si3N4Passivation and Annealing in Vacuum

This paper presents the fabrication and reduction of noise voltage power spectral density (PSD) of Si x Ge y O1– x – y uncooled infrared microbolometers with four different compositions. The noise reduction was achieved by passivating Si x Ge y O1– x – y with Si3N4 layers and by annealing the devices in vacuum at 200 °C, 250 °C, or 300 °C with different time intervals from 1 to 5 h. The voltage noise PSD was measured with a bias current between 0.07 and $0.6~\mathrm {\mu }\text{A}$ before and after annealing. The lowest measured noise voltage PSD before annealing was on devices with Si0.053Ge0.875O0.072 and Si0.041Ge0.902O0.057 films. They were $7.42\times 10^{-15}$ and $2.07\times 10^{-14}~\text{V}^{2}$ /Hz at 23 Hz, respectively. The corresponding 1/ ${f}$ -noise coefficients, $\textit{K}_{f}$ , of the devices were $3.65\times 10^{-14}$ and $3.01\times 10^{-14}$ , respectively. The voltage noise PSD was reduced as the annealing time and temperature were increased. The lowest measured noise was $1.96\times 10^{-14}~\text{V}^{2}$ /Hz at the corner frequency, 12 Hz, on a device with Si0.034Ge0.899O0.067 film annealed at 300 °C for 4 h, before annealing the noise was $4.09\times 10^{-13}~\text{V}^{2}$ /Hz at 12 Hz. This corresponds to a factor of 24 reduction of noise. The testing results demonstrate that annealing at higher temperature 300 °C reduced the low-frequency voltage noise PSD more than that of 200 °C and 250 °C temperatures.

Extraction of density of localized states in indium zinc oxide thin film transistor

Density of localized states (DOS) over the band-gap determines the electrical and instability characteristics in the indium zinc oxide thin film transistor (IZO TFT). In order to propose an accurate extraction method for DOS in the bulk region, low frequency noise and multi-frequency capacitance voltage characteristics are measured and analyzed in this paper. Firstly, the relationship between surface potential and gate voltage is extracted based on subthreshold I-V characteristics. The extraction results show that the surface potential increases with the increase of gate voltage in the sub-threshold region. When the Fermi level is close to the bottom of conduction band, the increase of surface potential should be saturated. Secondly, drain current noise power spectral densities in the IZO TFTs under different operation modes are measured. Based on carrier number fluctuation mechanism, the flat-band voltage noise power spectral density is extracted and localized state near IZO/SiO2 interface is then calculated. By considering the emission and trapping processes of carriers between localized states, the distribution of bulk trap density in the band-gap is extracted based on low frequency noise measurement results. The experimental results show an exponential tail state distribution in the band-gap while NTA is about 3.421020 cm-3eV-1 and TTA is about 135 K. Subsequently, contact resistances are then extracted by combining capacitance-voltage characteristics with I-V characteristics in the linear region. The extrinsic parasitic resistances at gate, source, drain are separated. By considering charges trapped in the localized states and free carriers, the distributions of deep states and tail states in the active layer of IZO TFT are extracted through multi-frequency capacitance-voltage characteristics. The experimental results also show an exponential deep state and tail state distribution in the band-gap while NDA is about 5.41015 cm-3eV-1, TDA is about 711 K, NTA is about 1.991020 cm-3eV-1, and TTA is about 183 K. The above two proposed extraction methods are compared and analyzed. The deviation between two extraction results may relate to the existence of neutral trap in the gate dielectric which is also an important source of low frequency noise in the IZO TFT.

Increase in Oxide Trap Density Due to the Implementation of High-k and Al2O3 Cap Layers in Thick-Oxide Input-Output Transistors for DRAM Applications

Work function engineering by the introduction of cap layers in a high-k gate stack [1],[2] can be successfully implemented in logic and DRAM peripheral MOSFETs. In the latter case, a so-called Diffusion and Gate Replacement (D&GR) integration scheme has recently been proposed [3], whereby an Al2O3 cap is implemented for tuning the threshold voltage of the p-channel transistors. A key step is the diffusion anneal to form a dipole layer at the SiO2/HfO2 interface [1],[2], which is typically carried out in the range of 600 oC to 900 oC [3]. In addition to the peripheral transistors, also input/output (I/O) devices with a larger gate oxide thickness need to be fabricated in a DRAM chip as well. These may undergo also the HfO2 and Al2O3 deposition and subsequent thermal budget. The question addressed in this work is whether the large Equivalent Oxide Thickness (EOT) devices suffer from these additional processing steps, from a viewpoint of gate oxide quality and reliability. To that aim, low-frequency (LF) noise is used as a tool to probe the border trap profile in the thick oxide gate stack [4],[5]. Evidence will be given for the in-diffusion of Hf and Al in the thick SiO2 up to the silicon interface, giving rise to a strong increase of the oxide trap density and hence the 1/f noise Power Spectral Density (PSD). P-channel transistors have been processed on 300 mm wafers following the conditions of Table 1, with 5 nm SiO2 + polysilicon gate as a reference. The Al2O3 cap is deposited on top of the gate stack. LF noise measurements have been performed on 1 mm×0.170 mm area devices in linear operation (drain-to-source voltage VDS=-0.05 V) with the gate voltage VGS stepped from weak to strong inversion. As shown in Fig. 1, the spectra are typically 1/f-like, with occasionally excess Lorentzian noise components. It is also clear, however, that the frequency exponent is not constant in the studied frequency range from 3 Hz to 100 kHz. It will be shown that the 1/f noise is due to number fluctuations, i.e., is caused by trapping in the gate oxide. From Fig. 2, one can derive that the average input-referred voltage noise PSD (<SVG>) at 10 Hz (Fig. 2a) or 10 kHz (Fig. 2b) strongly depends on the process conditions, with the reference wafer showing at least one decade lower values. Using the formulas in Fig. 3, on can convert the 1/f spectra into an oxide trap density profile, showing a strong increase as soon as a high-k layer is present. The increase in trap density points to an in-diffusion of Hf and Al down to the Si/SiO2 interface, while the reference trap densities are typical for SiO2. It will, finally, be shown that there exists a good agreement between the trend in the oxide trap density derived from 1/f noise spectra and the Negative Bias Temperature Instability (NBTI) of similar p-channel devices. It is clear that for optimizing the quality and reliability of I/O transistors, one should suppress this in-diffusion.