Gate Width Research Articles

Control mechanism of the back insulated-gate in vacuum nano-electronics

Recently, with the advancement of micronanoscale manufacturing technologies, vacuum electronic devices, which are immune to harsh environments (e.g., high temperatures, severe radiation), have once again entered researchers’ horizons. There have been a lot of reports focused on the impacts of emitter materials and overall consideration of structures on device performances. However, there is less discussion on the influence of the gate with different configuration geometries, even which is an extremely important component in the designed device structure, playing a switching role. In this paper, we discuss the effects of the back insulated-gate structure with different configuration geometries on emission and collection currents. The results show that the emitter emits more electrons when the gate width is larger (i.e., the coupling effect between the gate and the emitter is better), which, in turn, is able to help the collector receive more electrons. The gate has a greater influence than the collector on the local electric field near the emitter, explaining that the gate plays a switching role in such vacuum channel transistors. Moreover, we find that increased gate voltage causes the emitted electron beam to be more dispersed. Different collector voltages lead to different trends in the collection efficiency curve. The effects of widths (in the direction perpendicular to current flow) of the collector and the emitter on the emission and collection currents are also discussed. These studies provide theoretical bases for the future device designing.

Comparative analysis of capacitorless DRAM performance according to stacked junctionless gate-all-around structures

The characteristic comparison of the capacitor-less DRAMs in the structural form variation is investigated. Based on the simulation results of the three basic structures, such as circular, square, and rectangular nanosheets, the gate length (Lg), channel thickness (Tsi), and width of the nanosheet (Wsi) are considered as the main factors in design and the characteristic variations are verified according to the junctionless (JL) gate-all-around (GAA) geometry factors. The channel thickness is a major factor that has a major influence on the sensing margin and the retention time, which are important characteristics of DRAM. The thinner the thickness, the more deteriorated the sensing margin is confirmed. Retention time is due to the influence of the electric field distribution of the JL GAA structure, resulting in differences in structure. Finally, the rectangular type nanosheet is implemented in the stacked structure. As the number of stacks increases, the effective channel width increases compared to the layout footprint. In addition, by stacking vertically, the area where holes can be stored increases. Therefore, the sensing margin tends to increase as the number of stacks increases. However, the difference in diffusion due to the difference in the initially stored hole density, the retention time deteriorates as the number of stacks increases

Nanometer-thick TiO2 channel thin film transistors as radical monitors for plasma enhanced atomic layer deposition

Nanometer-thick-TiO2-channel thin-film transistors (TFTs) are examined as oxidizing-agent monitors for room-temperature atomic layer deposition (RTALD). RTALD is a plasma-based process using plasma-excited humidified argon where OH radicals oxidize the precursor-gas adsorbed surface. In the TFT, the anatase TiO2 channel, with a thickness of 16 nm, is attached to a 300 nm thick gate capacitor of SiO2, while the channel surface is exposed to the ALD ambient. A heavily doped n-type Si substrate attached to the gate SiO2 is used as the gate electrode. The gate width and length are 1000 and 60 μm, respectively. When the TFT is installed in the RTALD chamber, the drain-current waveform is recorded in the course of the metal organic gas adsorption, evacuation of the residual gas, oxidization, and evacuation. In the present study, three kinds of metal organic (MO) precursors, tetrakis(dimethyl)amino titanium, tris(dimethyl)amino silane, and trimethyl aluminum are examined. The drain current exhibits strong responses upon the exposure of the plasma excited humidified argon. This suggests that OH radicals in the plasma might oxidize the adsorbed MO precursors to produce the OH moieties, where the surface polarization of OH moieties might enhance channel conductivity. The experimental results suggest the applicability of the present TFT as a plasma monitor in RTALD.

Modeling of HCI effect in nFinFET for circuit reliability simulation

This paper proposes an equivalent circuit model for simulating the Hot Carrier Injection (HCI) effect. This model is developed based on the N-FinFET in the 12 nm Process Design Kit (PDK) and incorporates arithmetic units and electrical components from the Electronic Design Automatic (EDA) software. Input parameters can be freely modified by the user, such as stress time, ambient temperature, gate length, gate width and process corner. The model also considers the influence of the voltage at each end of the transistor on the HCI effect. The model can be accessed in the EDA tool just like a normal transistor and can be used to evaluate the HCI effect on circuits without modifying the SPICE model. The accuracy and applicability of this model has been verified by comparing it with measured results from other published literature.

Effects of random ferroelectric and dielectric phase distributions on junctionless ferroelectric field effect transistors

In this study, we comprehensively investigated the effects of random ferroelectric (FE) and dielectric (DE) phase distributions on junctionless ferroelectric field-effect transistors (JL-FeFETs). The Poisson–Voronoi tessellation (PVT) algorithm, which corresponds to the physical growth mechanism, was used to obtain grain nucleation in the ferroelectric layer. The simulation results demonstrated that as the probability of FE phase decreased from 80% to 40%, the standard deviation of the memory window (σMW) increased from 62.4 to 99.5 mV, and the possibility of forming a blocking current path from the source to the drain increased, which degraded the memory window (MW). The simulation results indicated that decreasing the gate length and width increased device variations. Furthermore, σMW decreased from 84.5 to 58.9 mV as the grain size decreased from 5 to 3 nm.

Comparison of non-Hermitian three-dimensional quantization line shape in ion-doped microcrystals

In this paper, we studied the relationship between non-Hermitian quantization and line shape in ion-doped microcrystals. We depict the Eu3+: BiPO4 exhibited a broad line shape in contrast to Eu3+: NaYF4, and Dy3+: BiPO4. The line shape is controlled through angle quantization (constructive and destructive quantization) and phonon detuning effects. The Eu3+: BiPO4 and Eu3+: NaYF4 exhibits less sensitivity to line shape as compared to Dy3+: BiPO4. The more sensitivity of Dy3+: BiPO4 is supported by the presence of multiple levels, which disrupt the transition from destructive (out of phase de-phase rate Г) to constructive (in phase dressing Rabi frequency G) three-dimensional quantization. The line shape evolution from out of phase to in phase could be tuned by changing time gate position (the ratio of G and Г regulated largely) and time gate width (the ratio of G and Г regulated on a small scale). We observed that the line shape ratio in Dy3+: BiPO4 is significantly smallest (13.63 %) as compared to Eu3+: NaYF4 (61.29 %) and Eu3+: BiPO4 (85.18 %). Furthermore, the angle quantization affects the line shape evolution of fluorescence and Autler-Townes. However, spontaneous four-wave mixing line shape evolution can not be controlled by the angle quantization. Such results hold significant potential for applications in long band stop filter.

The degradation mechanism of high power S-band AlGaN/GaN HEMTs under high temperature

Abstract The radio frequency (RF) degradation mechanism under high temperature is proposed in this paper. The saturated output power (P sat), power added efficiency (PAE) and gain of the HEMTs deteriorate significantly under high power dissipation operation conditions, which contribute to an elevation of the junction temperature (T j). The high T j causes a negative shift of the threshold voltage and a reduction of electron mobility, as well as enhancing the trapping effects of the devices. As a result, the P sat and PAE of the high-power HEMTs (P sat = 152 W) decreased by 0.76 dB and 8.3%, respectively, which is more severe compared to low-power HEMTs (P sat = 20 W), where P sat and PAE reduced by 0.16 dB and 3.1% when the operation temperature was increased from 25 °C to 150 °C. By increasing the gate-to-drain distance from 1.625 to 2.175 μm, drain current stability and high temperature reverse bias reliability are improved. The results demonstrate that the trapping effect can be suppressed by decreasing the electric field under the gate; therefore, the RF output characteristics are boosted by 1.2 W, 1 dB and 2.6% for a device with gate width of 11.52 mm.

Threshold voltage instability of SiC MOSFETs under very‐high temperature and wide gate bias

AbstractThreshold voltage (VTH) instability affects the reliability of silicon carbide (SiC) MOSFETs. In this article, the influence of gate bias (VGS) and high temperature on VTH instability is investigated under wide VGS and very‐high temperature range (150°C to 275°C). The degradation mechanism of gate oxide under coupling of different electrical and thermal stress is revealed. When the device is subjected to +VGS, the relationship between VTH shift and temperature is not monotonic and there is a temperature turning point. This is mainly related to the capture/release and generation of electron traps. However, the VTH shift increases sharply and gate oxide breakdown for the device bias at +35 V, which is related to Fowler–Nordheim (F–N) tunnelling effect. For a large −VGS, the VTH shift is very small. Moreover, when the negative VGS decreases, the VTH shift is positively correlated with temperature, which may result from the activation and charge exchange of hole traps. However, the influence of moving ions changes the temperature dependence of VTH shift for the device bias at −30 V. Finally, the devices of different manufacturers are studied and similar change patterns are found. This finding provides guidance for the further application of SiC MOSFETs under high temperatures and different voltages.

Selective Rashba spin–orbit coupling manipulation in triple quantum wells

We explore the Rashba (α) spin–orbit coupling (SOC) manipulation in AlInSb/InSb triple quantum wells (QWs) with three subbands occupied in the presence of the external gate voltage V b . Diverse behaviors of α can be demonstrated by adjusting the structural parameters of the wells, which is greatly desirable for the design of multifunctional QW-based spintronic devices. Specifically, the first (lowest) subband always has larger Rashba coupling against the variations in the structural parameters and V b than the other subbands, conducive to spin detection. α ν s (ν = 1, 2, 3 is the subband index) of the second and third subbands take on dual (magnitude and sign) change owing to the regulation of the inner barrier height δ, may facilitating the realization of stretchable persistent spin helix in multiple QWs. Strikingly, α 3 can keep essentially zero in a wide gate range corresponding to asymmetrical QW structural configurations, by adjusting δ. However, when widening the well to a certain extent the δ-dependence of α become fixed, i.e. ∣α 1∣ > ∣α 2∣ > ∣α 3∣ maintains in wide triple-well systems. All these findings may shed light on selective and precise SOC control in QW systems for experiments.

Optimization analysis of gate width for detecting atmospheric turbulence with differential image motion LiDAR

Optimization analysis of gate width for detecting atmospheric turbulence with differential image motion LiDAR

DC and RF analysis of ScAlN/GaN/β-Ga2O3 and ScAlN/InGaN/GaN/β-Ga2O3 HEMTs on SiC substrate

Scandium aluminum nitride (ScxAl1-xN) is a promising material among group III nitrides, offering outstanding polarization properties resulting in very large carrier densities. We report the comparative analysis of Sc0.18Al0.72N/GaN/β-Ga2O3 and Sc0.18Al0.72N/InGaN/GaN/β-Ga2O3 HEMTs on Silicon carbide substrate. LG = 55 nm, Sc0.18Al0.72N/GaN/β-Ga2O3 HEMT demonstrated maximum current density (IDS) of 4.38 A/mm, very large carrier density (ns) of 2.34 × 1013 cm−2, large breakdown voltage (74 V) with low on-resistance (Ron ∼ 0.2 Ω mm), and cut-off frequency (fT)/maximum oscillation frequency (fmax) of 220/242 GHz. Introduction of a very thin 5 nm In0.1Ga0.9N layer in the channel, further improves the 2DEG (two-dimensional electron density), drain current, breakdown voltage. Furthermore, Sc0.18Al0.72N/InGaN/GaN/β-Ga2O3 heterostructure shows stable transconductance (gm) over wide gate bias. A gate voltage swing (GVS) of 7.72, IDS of 6.08 A/mm, and VBR of 105 V with Ron ∼ 0.138 recorded. These findings show the merits of scandium aluminium nitride barrier material, which enables the HEMTs for next generation radar and telecommunications.

High-precision high-stability acousto-optic pulse picking driver with a direct digital synthesis technique.

A method for maintaining a fixed phase relationship between the driving signal of acousto-optic modulator (AOM) and the original mode-locked seed laser is proposed and realized, which stabilizes the amplitude of diffracted signal output from the AOM for subsequent amplification. A field-programmable gate array (FPGA), combined with external summing amplifiers, is used to directly synthesize high-timing-precision driving signals that are synchronized with the seed laser pulses, and the accuracy of signal timing control reaches 160 ps. Using this driver, the standard deviation of the diffracted signal output from the AOM is significantly decreased from 0.52% to 0.18%. This pulse-picking solution also includes a control system that can flexibly control the frequency, gating width, etc., of the driving signal, which makes it more convenient for subsequent laser amplification and makes it suitable for a variety of mode-locked lasers.

Manipulation and applications of ultrafast all-optical switching based on transient absorption and dispersion in KTN crystals.

Potassium tantalate niobate (KTN) represents a noteworthy category of optical crystals known for their superior nonlinear optical properties. In this study, we conducted measurements of femtosecond time-resolved transient absorption (TA) spectra in KTa0.57Nb0.43O3 crystals. Notably, a rapid and pronounced "plateau" phase, ∼1.5 ps in duration, was detected at the onset of the TA kinetics and succeeded by two distinct decay components, exhibiting lifetimes of ∼140 ps and over 10 ns, respectively. We attribute these observations to a decay process involving two-photon absorption, dispersion characteristics, and excited state absorption. Based on this unique TA characteristic of KTN crystals, an all-optical switching strategy was proposed and utilized to measure the ultrafast lasing dynamics of single-crystal CH3NH3PbBr3 nanowires. This polarization-independent TA gate approach offers an adjustable gate width combining ps and ns time scales and introduces a versatile tool for advanced optical applications.

Microwave Power Performance of AlGaN/GaN High‐Electron‐Mobility Transistor on Semi‐Insulating Mn‐Doped GaN Substrate

Herein, a DC and microwave performance of 2 μm gate length AlGaN/GaN high‐electron‐mobility transistor (HEMTs) on a Mn‐doped GaN substrate is demonstrated. The maximum drain current is 670 mA with a threshold voltage of 2.5 V and with good pinch‐off characteristics. The breakdown voltage of the HEMT is ≈80 V. The HEMT shows Δ8% current collapse while referenced HEMT on a SiC substrates which is fabricated simultaneously shows large Δ30% current collapse. When the HEMT with a gate width of 100 μm is tuned for the maximum output power at 2.4 GHz with a drain voltage of 30 V, it delivers 500 mW (5 W mm−1) with the maximum drain efficiency of 54%. These output performances are in good agreement with ideal class‐A operation performance. Therefore, it is concluded that the HEMT on Mn‐doped GaN substrates is promising for future microwave and millimeter‐wave high‐power transistors.

Enhancing Si1-XGex/Si Etch Rate Selectivity Using Etching Inhibitor in Radical Oxidation By Halide-Based Oxidant

As the technology node shrinks, innovation in the metal-oxide-semiconductor field-effect transistor (MOSFET) architecture has been required to mitigate the short-channel effects (SCE). Thus, planar FET had changed to FinFET and now gate-all-around FET (GAAFET) has been introduced with entering the 3-nm-generation. To fabricate GAAFET, selective etching of Si1-xGex- to Si-film is a key technology. According to the International Roadmap for Devices and Systems (IRDS™), the gate width of GAAFET is around 30 nm. Therefore, higher than 30 nm/min of etch rate for throughput and more than 400:1 of selectivity for acquiring a uniform Si-channel layer are required.As is well known, the etch rate in wet etching strongly depends on the standard reduction potential (SRP) of the oxidant. Our research group previously revealed the radical oxidation mechanism of sodium periodate (NaIO4) oxidant. In an acidic medium, NaIO4 can exist in periodate ion (IO4 -) form capable of generating hydroxyl radical (•OH). The high SRP value of hydroxyl radical (2.80 eV) compared to conventional oxidant, hydrogen peroxide (H2O2, 1.76 eV) and peracetic acid (PAA, 1.75 eV), resulted significantly high etch rate. In subsequent research, we introduced inhibitors reducing the Si-film etch rate to enhance Si1-xGex/Si etch rate selectivity when using sodium periodate as an oxidant.Acetic acid is commonly used as an additive in wet etchants to maintain uniform pH and control the etching of Si-film. However, it has several issues, strong vinegar odor, relatively large concentration to act, etc. Therefore, other additives are needed to substitute acetic acid. In selecting inhibitors, 2 factors are considered, i) scavenging effect for hydroxyl radical, and ii) hydrophobicity, as shown in Figure 1. Because the concentration of hydroxyl radical influences not only the Si1-xGex-film etch rate, but the Si-film etch rate, the scavenging effect of an inhibitor can reduce the film etch rate to enhance etch rate selectivity. Furthermore, the hydrophobicity part of inhibitors can build a hindrance layer on Si-film. Generally, Si-film has more hydrophobicity than Si1-xGex-film, inhibitors having hydrophobicity part are more prone to form a hindrance layer on Si-film than Si1-xGex-film. This results in the enhancement of Si1-xGex/Si etch rate selectivity by reducing Si-film considerably than Si1-xGex-film. The qualitative comparison of hydroxyl radical concentration depending on inhibitors and characterization methods to confirm the hindrance layer will be presented in detail. Acknowledgement This work was supported by the Technology Innovation Program (20022475, Development of wet Etchant capable of high selection etching in microprocesses below 10 nm) funded by the Ministry of Trade, Industry & Energy (MOTIE, Korea) References [1] Lee, Seung-Jae, et al. "Extremely high selective Si1−xGex-film wet etchant generating highly dissolved oxygen via peracetic acid oxidant for lateral gate-all-around FETs with a logic node of less than 3-nm." Chemical Engineering Journal 475 (2023): 146257. Figure 1

A mixer architecture using GaN-based split-gate nanowire transistor

Frequency mixer is an essential block in radio-frequency signal processing for frequency translation and phase comparison. The most common mixers are fabricated using passive elements which suffer from significant conversion loss and low isolation. Mixers using active devices are used less frequently and rather less matured on GaN technology. Here, we demonstrate a mixer based on GaN split-gate nanowire transistor, allowing low conversion loss and high isolation. A constriction is formed by electrostatic modulation of the effective gate width. The threshold voltage of the transistor is modified by one of the gate voltages through the width variation, while the other gate voltage biases the transistor in the saturation region. The nonlinear dependency of the transistor characteristics on the two gate voltages facilitates frequency translation. The mixing characteristics of this architecture are verified both experimentally and theoretically. The output power spectral density peaks at the difference frequency with a minimal conversion loss. Extremely high isolation is measured using three-port S-parameter measurements. The proposed architecture shows multiple benefits, additionally facilitating monolithic mixers on the GaN platform.

High linearity AlGaN/GaN HEMTs with Au-free Ti/Al/Ni/Ti ohmic contacts for Ka-band applications

In this study, AlGaN/GaN HEMTs with Au-free Ti/Al/Ni/Ti ohmic contacts were fabricated. The device presents a contact resistance (R c) of 0.64 Ω·mm and high linearity characteristics. The two-tone measurement at 28 GHz shows that the 2 × 50 μm device exhibits an excellent third-order intercept point (OIP3) value of 41.64 dBm at V DS = 28 V, and an OIP3/P DC of 24.2. An OIP3 of 46.59 dBm was achieved when the device’s gate width was increased to 8 × 50 μm at V DS = 48 V. These results demonstrate that AlGaN/GaN HEMTs with Ti/Al/Ni/Ti ohmic contacts have potential for Ka-band applications.

18 A/1020 V p-GaN-gated HEMTs with Isosceles Trapezoidal-Shaped Multi-Finger Structure

In this article, we investigate the effects of gate and drain field plates and isosceles trapezoidal-shaped multi-finger structures on the characteristics of high current p-GaN-gated high-electron-mobility transistors (HEMTs). By optimizing the lengths of gate and drain field plates, the p-GaN-gated HEMTs with 200 μm have a breakdown voltage of 1893 V, a specific on-resistance of 7.0 mΩ-cm2, and a Baliga figure of merit (BFOM) value of 511 MW cm−2. Using the optimized isosceles trapezoidal-shaped multi-finger metallization on the source and drain, the p-GaN-gated HEMT with a 100 mm gate width can reach a current of 2.3 A. Combining all the optimum parameters of field plates and isosceles trapezoidal-shaped multi-finger, the fabricated 600 mm p-GaN-gated HEMT exhibits an output current of 18 A, an on-resistance of 0.7 Ω, and a breakdown voltage of 1020 V. Furthermore, the device also exhibits good thermal stability at high temperatures. These results demonstrate the potential and advantages of p-GaN-gated HEMT for power applications.

Time-domain diffuse correlation spectroscopy at large source detector separation for cerebral blood flow recovery.

Time-domain diffuse correlation spectroscopy (td-DCS) enables the depth discrimination in tissue's blood flow recovery, considering the fraction of photons detected with higher time of flight (TOF) and longer pathlength through the tissue. However, the recovery result depends on factors such as the instrument response function (IRF), analyzed TOF gate start time, gate width and the source-detector separation (SDS). In this research we evaluate the performance of the td-DCS technique at three SDSs of 1.5, 2 and 2.5 cm to recover cerebral blood flow (CBF). To do that we presented comprehensive characterization of the td-DCS system through a series of phantom experiments. First by quality metrices such as coefficient of variation and contrast-to-noise ratios, we identified optimal time gate(s) of the TOF to extract dynamics of particles. Then using sensitivity metrices, each SDS ability to detect dynamics of particles in superficial and deeper layer was evaluated. Finally, td-DCS at each SDS was tested on healthy volunteers during cuff occlusion test and breathing tasks. According to phantom measurements, the sensitivity to estimate perfusion within the deep layer located at depth of 1.5 cm from the surface can be increased more than two times when the SDS increases from 1.5 cm to 2.5 cm.

Natural non-Hermitian interaction alignment with photon-phonon quantization in Eu3+: NaYF4

We investigated the photon and phonon alignment for two dressing interaction profile in Eu+3: NaYF4. The evolution from strong to weak interaction alignment can be controlled by time gate width and time gate position, which shows that time gate position seems more sensitive than time gate width, while changing both can make interaction alignment oscillation due to two phonon and one photon quantization. Fluorescence FL signal switch from dip to peak interaction profile due to strong gamma, while the Super-Fluorescence SFWM signal switch from peak to dip interaction profile due to strong Rabi frequency (G). Comparing single laser spectral alignment to two-laser interaction alignment, the FL and SFWM shows dressing peak dip switch (spectral to interaction profile). In contrast, there is no switch in AT (spectral to interaction profile) because, the phase difference of the second laser balances the destructive and constructive dressing quantization’s. Such results can have potential applications in fine and hyper structure interaction alignment in non-polar ion.