Passivation Layer Thickness Research Articles

Comparison of the Electrical Performance of AlN and HfO<sub>2 </sub>Passivation Layer in AlGaN/GaN HEMT

Different material thickness with medium and high dielectric constant can impact the performance and reliability of high electron mobility transistor device. With varying the thickness of the passivation layer, the effect of it towards the device performance is still unclear. Two different insulator layers with a medium dielectric and a high dielectric constant namely Aluminium Nitride and Hafnium Oxide are used as passivation layer in AlGaN/GaN HEMT. Both material performance was simulated via COMSOL software by varying the thickness and the drain current output were compared. The passivation layer thickness of 10nm at Vds=6 V and Vgs=5 V, HfO2 outperforms AlN with the output drain current of 39 mA compared to 35 mA respectively. It was observed that HfO2 can attain higher threshold voltage, Vth as compared to the AlN because of the influence of its material properties that shows a direct proportional relationship between Vth and dielectric constant. Using high dielectric constant material like HfO2, we observe the ON-voltage gradually decreases as the thickness of the passivation layer increased. Out of all the thickness simulated for HfO2 and AlN, 10nm produced the highest drain current output instead of layer thickness of 20nm.

The atomic oxygen resistant study of a transparent polyimide film containing phosphorus and fluorine

As ideal packaging materials for solar cells of low-Earth orbit (LEO) spacecraft, polyimide (PI) films have to withstand various harsh space environment. Here, we investigate the atomic oxygen (AO)-resistant property of a transparent PI film with side diphenylphosphine oxide and trifluoromethyl. After exposed under AO (1.3 × 1020 atoms·cm−2), most excellent properties of the PI film can be maintained except for partial loss of transmittance. Its erosion yield is 0.56 × 10−24 cm3·atom−1, only 18.7% as that of Kapton film at the same condition. To understand the damage mechanism, the surface and bulk performances of the AO exposed PI film were systematically investigated and compared with those of the prinstine PI film. The results indicate that the relative concentration of phosphorus and oxygen near to the AO exposed surface of the PI film increases, which means the formation of a phosphate passivation layer. The thickness of phosphate passivation layer is about 200 nm with the content of PO3− decreasing in vertical direction of itself, which can reduce the further erosion of the PI film by AO. Such PI films containing P and F are much more AO resistant and expected a candidate as packaging material for LEO spacecraft.

Investigation of effective local contact Al2O3 rear passivation for high-efficiency thin CIGS solar cells

Copper indium gallium selenide (Cu(In,Ga)Se2; CIGS) solar cells with small thicknesses active layer have limits to show high efficiency owing to high carrier recombination and low reflection at the electrode/active layer interface. A passivation layer applied to the rear of the CIGS solar cell is regarded as one of the solutions. However, depending on the thickness of the passivation layer, the surface morphology of the thin CIGS absorber layer can be changed, affecting light absorption and photovoltaic properties. In this study, the optical electrical performances of CIGS solar cells with a thin enough layer of the local contact aluminum oxide (Al2O3) (LC-Al2O3) rear passivation were analyzed and demonstrated. The thin passivation layer with tens of nanometers resulted in higher increased efficiency because of improved open circuit voltage and short circuit current density. In addition, from the experiment, the optimal thickness of the thin passivation layer was derived. Too thin a layer causes a degradation of the performance, providing the surface scattering and parasitic resistance. Our results can be used to develop guidelines for designing high-performance CIGS solar cells with optimized passivation layers.

A Simulation Optimization Factor of Si(111)-Based AlGaN/GaN Epitaxy for High Frequency and Low-Voltage-Control High Electron Mobility Transistor Application.

The effects of barrier layer thickness, Al component of barrier layer, and passivation layer thickness of high-resistance Si (111)-based AlGaN/GaN heterojunction epitaxy on the knee-point voltage (Vknee), saturation current density (Id-sat), and cut-off frequency (ft) of its high electron mobility transistor (HEMT) are simulated and analyzed. A novel optimization factor OPTIM is proposed by considering the various performance parameters of the device to reduce the Vknee and improve the Id-sat on the premise of ensuring the ft. Based on this factor, the optimized AlGaN/GaN epitaxial structure was designed with a barrier layer thickness of 20 nm, an Al component in the barrier layer of 25%, and a SiN passivation layer of 6 nm. By simulation, when the gate voltage Vg is 0 V, the designed device with a gate length of 0.15 μm, gate-source spacing of 0.5 μm, and gate-drain spacing of 1 μm presents a high Id-sat of 750 mA/mm and a low Vknee of 2.0 V and presents ft and maximum frequency (fmax) as high as 110 GHz and 220 GHz, respectively. The designed device was fabricated and tested to verify the simulation results. We demonstrated the optimization factor OPTIM can provide an effective design method for follow-up high-frequency and low-voltage applications of GaN devices.

Spatially isolating Li+ reduction from Li deposition via a Li22Sn5 alloy protective layer for advanced Li metal anodes.

A Li alloy based artificial coating layer can improve the cyclic performance of Li metal anodes. However, the protective mechanism is not well clarified due to multiple components of the artificial layer and complicated interface in liquid electrolytes. Herein, a single-component Li22Sn5 alloy layer buffered Li anode is paired with a solid-state polymer electrolyte, where a metallic Sn film is sputtered onto the Li anode and the subsequent alloying reaction leads to the formation of a Li22Sn5 phase. During the striping/plating process, the thickness and composition of the Li-Sn alloy passivation layer remain unchanged. Meanwhile, Li+ ions are reduced on the top surface of the Li22Sn5 layer, then the reduced Li atoms immediately pass through the alloy layer, and finally dense Li deposition occurs beneath the protective layer, realizing spatial isolation of the electrochemical reduction of Li+ from Li nucleation/growth. This unique protection mechanism can principally avoid the formation of Li dendrites and efficiently mitigate irreversible reactions between the Li anode and the polymer electrolyte. The synergistic effects lead to a clean and flat surface of the protected Li electrode, enabling a prolonged cycle lifetime over 1300 h at 25 °C at 0.1 mA cm-2 and 0.1 mA h cm-2 in a configuration of symmetrical cells.

Role of defect density in the TiOx protective layer of the n-Si photoanode for efficient photoelectrochemical water splitting

Understanding the role of defect density in thick oxide passivation layer in electrolyte/oxide/semiconductor (EOS) junction photoanode system is critical for efficient photo-electrochemical water splitting with long-term stability.

Probing the influence of liquid nitrogen assisted chemical reduction on the nature of passivation layer, magnetic properties, and Cr (VI) remediation performance of nanoscale zero valent iron

Zero valent iron nanoparticles synthesis through sodium borohydride assisted chemical reduction of iron salts is a well-established and fast synthesis process. Zero valent iron nanoparticles possess a core shell structure due to formation of a surface passivation layer and this layer is composed of iron oxides and hydroxides. Depending on the synthesis condition the thickness of the passivation layer varies and effective electron transfer process from the metallic core to the outer surface is restricted if the passivation layer is too thick. Here in this work a liquid nitrogen assisted zero valent iron nanoparticles synthesis is illustrated which is fast, cheap, and highly scalable process to tune the physicochemical properties of the passivation layer and thus overall performance of zero valent iron nanoparticles. Zero valent iron nanoparticles nucleated under liquid nitrogen (ZLN) has passivation layer thickness in the range 3–4 nm and showed higher magnetic saturation value (145.32 emu/g) and better Cr (VI) reduction performance than its room temperature counterpart ZRT with a passivation layer thickness in the range 6 − 7 nm. The spherical ZLN nanoparticles showcased a particle size distribution profile in the range 10–120 nm and were able to reduce the concentration of 10 ppm Cr (VI) in about 15 min for a ZLN loading of 1 g/L at a pH value of 7.

Using of asymmetric cell to monitor corrosion performance of 304 austenitic stainless steel by electrochemical noise method

In this study, corrosion of 304 Austenitic stainless steel (ASS) with varies oxide layers, developed at two temperatures, is investigated by an asymmetric (Asy) cells in 0.05 M FeCl3 solution with time. Therefore, the Asy electrodes system is introduced to perform valuable data. Electrochemical current noise (ECN) signals resulting from the Asy cells are elucidated using the standard deviation of partial signals (SDPS) plot, the recurrence plot (RP), and the statistical procedure which derived from wavelet transform (WT) along with electrochemical impedance spectroscopy (EIS). The Asy electrodes indicated a high advantage and improved the detection of intergranular corrosion (IGC) on the 304 ASS alloy compared with the symmetric (Sym) ones. The trend of signals is eliminated, and then the disintegration of every signal is also performed into 10 crystals. Afterward, the standard deviation of every crystal is shown with the SDPS plots. Besides, ECN signals related to dissimilar crystal numbers are distinguished by the RP, based on the signals population. According to EIS measurements, the thickness of passive oxide layer of sample heated at 0–700 °C is decreased from 57 to 33 nm with immersion time, while it is increased from 9 to 27 nm for sample heated at 1100-700 °C.

Current-induced degradation behaviors of InGaN/GaN multiple quantum well UV photodetectors: Role of electrically active defects

To examine the critical role of electrically active defects and surface states in InGaN/GaN multiple quantum well (MQW) ultraviolet photodetectors (UV-PDs), the study of degradation mechanisms in such devices is very important. In this work, we have fabricated InGaN/GaN MQW UV-PDs with a thick passivation layer of Al 2 O 3 and studied their degradation behaviors by applying high current stress. The origin of degradation processes has been investigated intensively by employing different combined optical and electrical measurements. As a consequence of stress, we noticed that (i) the electroluminescence intensity decreases distinctly (∼ 48 %), suggesting that more of the charge carriers are captured by the newly induced defects in the active region; (ii) the open circuit voltage is mostly accountable for the degradation of photovoltaic properties in treated PDs; (iii) the parasitic current leakage paths increase significantly which in turn reduce the photocurrent generation process largely; (iv) within the temperature range of 100–440 K, the values of the ideality factor and barrier height are found to be always higher and lower in treated PDs, respectively, indicating the presence of generation-recombination centers caused by defects; (v) two major trap levels are identified in treated PDs via Laplace deep level transient spectroscopy analysis; and (vi) the responsivity in treated PDs decreases. The obtained results indicate that degradation is mainly associated with the newly generated defects, mostly Mg-related shallow acceptors, including Mg Ga and Mg-H 2 complexes, which can form the acceptor levels as a result of the breaking of Mg-H chemical complexes due to high heating levels during the stress treatment. • Degradation characteristics of InGaN/GaN MQW UV photodetectors are studied. • Two major trap levels are detected in stressed PDs via Laplace deep level transient spectroscopy analysis. • Newly induced defects in the active region play an important role in worsening the device performances. • Degradation is mostly associated with Mg-related shallow acceptors, including Mg Ga and Mg-H 2 chemical complexes.

Lithium Difluoro(Oxalate)Borate‐Induced Interphase for High‐Voltage LiFe0.15Co0.85PO4@C Cathode by Solid‐State Synthesis

Herein, the effect of lithium difluoro(oxalate)borate (LiDFOB) as an electrolyte additive on the electrochemical performance of LiFe0.15Co0.85PO4@C (LFCP@C) cathode, synthesized by a scalable solid‐state synthesis method is reported. Galvanostatic studies revealed better electrochemical performance among the LFCP@C (LiDFOB: 0.5–2 wt%) in a half‐cell assembly compared to the LiFe0.15Co0.85PO4 in the absence of LiDFOB. Also, among the various concentrations of LiDFOB, the LFCP@C (LiDFOB—1.5 wt%) and LFCP@C (LiDFOB—2 wt%) are optimized as suitable candidates for further electrochemical studies owing to the high discharge capacities of 116 and 118 mAh g−1. In addition, the electrochemical impedance studies (EIS) exhibited an increase in the charge–transfer resistance (R ct) as the amount of LiDFOB was increased, whereas a lower R ct value is observed in the absence of additive. In addition, the diffusion coefficient calculation is calculated using the EIS data, which shows a diffusion coefficient in the order of ≈10−13 cm2 s−1. However, as the amount of LiDFOB is increased from 0 to 2 wt%, a decrease in the diffusion coefficient is observed owing to the formation of a stable and thicker passivation layer.

High Quality Factor and Low Motional Impedance Aluminum Nitride Tuning Fork Resonators Vibrating in In-Plane Flexural Mode

This letter presents a piezoelectric tuning fork resonator vibrating in in-plane flexural mode with a high quality factor (Q) and low motional impedance. A novel double-sided actuating design is implemented based on unimorph structure with a 2.5- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -thick AlN film as passive layer. The design significantly improves the Q and motional impedance compared with the conventional single-sided actuating design thanks to an increase of static capacitance without change of material interfaces. The proposed double-sided actuating device shows an excellent Q measured as 11272 with an extracted motional impedance of 7.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{k}\Omega $ </tex-math></inline-formula> in vacuum. The measured Q-pressure relationship shows that a vacuum level <100 Pa would ensure a sufficiently high Q value, which can be easily achieved through wafer-to-wafer bonding with getters in the future. Furthermore, the impact of AlN passive layer thickness on the resonator performance is analyzed. The proposed device would find applications in sensing fields as miniaturized and high-performance resonator-based solutions, such as gyroscopes, accelerometers and pressure sensors.

Effect of amorphous ternary AlBN passivations on the performance of AlGaN/GaN HEMTs

In this article, an amorphous ternary AlBN dielectric passivation layer is proposed for GaN/AlGaN high-electron mobility transistors (HEMTs). The source–gate–drain access regions with both AlBN and AlN amorphous dielectric films deposited by pulsed laser deposition are investigated to understand their effects on the device performance. Compared with the AlN-passivated HEMTs, the electrical characteristics of AlBN-passivated HEMTs are significantly improved with the same passivation layer thickness. An increase in maximum drain saturation current of AlBN-passivated HEMTs is ∼19.74% at Vgs = 2 V, and the corresponding peak extrinsic transconductance is improved by 38.08% at Vgs = −2 V and Vds = 2 V. Such excellent properties are ascribed to large surface potential change, due to the effect of boron dopants on AlBN films.

Effects of post‐deposition annealing of cerium oxide passivation layer in nitrogen‐oxygen‐nitrogen ambient

Effects of post-deposition annealing temperature (400°C, 600°C, 800°C and 1000°C) onto metal-organic decomposed cerium oxide (CeO2) precursor spin-coated on n-type Si substrate was carried out in nitrogen-oxygen-nitrogen ambient. The capability of nitrogen to inhibit further oxidation of the Si surface by attaching to the oxygen vacancies sites was reported. Excessive formation of SiO2 interfacial layer however occurred at 1000°C, surpassing the thickness of the CeO2 passivation layer, leaving behind nitrogen dangling bonds that were inefficient in restricting further oxidation of the Si surface, and hence a permanent dielectric breakdown happened at an electric field of 0.98 MV/cm. The CeO2 passivation layer annealed at 800°C broke down at 4.85 MV/cm and possessed relatively low Dit, Qeff, and slow trap density with negligible formation of interfacial layer, which promoted its use as a promising high k passivation layer.

Laser-Driven One- and Two-Dimensional Subwavelength Periodic Patterning of Thin Films Made of a Metal–Organic MoS2 Precursor

Laser-based surface processing is an established way for the maskless generation of surface structures and functionalities on a large variety of materials. Laser-driven periodic surface texturing and structuring of thin films is reported for metallic-, semiconductive-, and polymeric films. Here, we introduce subwavelength surface patterning of metal-organic thin films of [Mo2S4(S2CNnBu2)2], a MoS2 precursor. Accurate control of one- and two-dimensional (1D and 2D) periodic patterns is achieved on silicon wafers with a pulsed 532 nm ns laser. With suitable combinations of laser polarization, laser pulse energy, the thickness of the SiO2 passivation layer, and the MoS2 precursor's thin film thickness, high-quality 1D and 2D self-organized periodic structures are obtained in virtually unlimited areas. The material redistribution related to the pattern formation is thermally driven at low laser energies. Increasing pulse energies beyond a threshold level, in our experiments a factor of 2, fully converts the precursor to MoS2.

Precisely nanostructured HfO2 rear passivation layers for ultra‐thin Cu(In,Ga)Se2

AbstractThe quest for material‐efficient Cu(In,Ga)Se2 (CIGS) solar cells encourages the development of ultra‐thin absorbers. Their use reduces material consumption and energy usage during production by increasing the throughput. Thereby, both the bill of materials as well as the energy and capital costs are reduced. However, because thin absorbers are prone to increase back contact recombination, back surface passivation schemes are necessary to reach a similar or higher conversion efficiency than for absorbers with conventional thickness. Here, we investigate nanostructured hafnium oxide (HfO2) rear passivation layers for ultra‐thin CIGS solar cells. We fabricate regular arrays of point contacts with 200 nm diameter through HfO2 layers with thicknesses between 7 and 40 nm using electron beam lithography and reactive ion etching. The current–voltage curves of solar cells with a 500 nm thick CIGS absorber layer and the nanostructured passivation layer show improved performance concerning Voc and Jsc compared to non‐passivated reference devices. Furthermore, external quantum efficiency and optical reflection confirm an effective passivation behavior, with an average efficiency increase of up to 1.2% for the cells with the 40 nm thick HfO2 layer. In addition, simulation work shows that even 40 nm thick HfO2 passivation layers have only a minimal effect on the optical properties of ultra‐thin CIGS solar cells, and hence, the photocurrent increase verified experimentally stems from electrical improvements caused by the HfO2 layer passivation effect. We also investigate the impact of ultra‐thin (0.3, 0.6, 1.3, and 2.5 nm) non‐patterned HfO2 passivation layers on the same type of solar cells. However, these results showed no improvement in solar cell performance, despite an increase in the current density with layer thickness.

Analysis of slow-current transients or current collapse in AlGaN/GaN HEMTs with field plate and high-k passivation layer

We study how the dielectric constant of passivation layer εr and field-plate related parameters (its length LFP, passivation-layer thickness Ti) affect the reduction rates of drain current arising from drain lag, gate lag and current collapse in AlGaN/GaN HEMTs. We plot the current-reduction rates versus Ti for different εr. It is indicated that depending on εr, the drain-lag and current-collapse rates take minimum at certain Ti. When εr is 7, 20, 30 and 50, the current-reduction rates become minimum at Ti = 0.03, 0.1, 0.1, and 0.2 μm, respectively. Hence, at the minimum point, εr/Ti which is proportional to capacitance of the passivation layer takes a nearly constant value at 250 ± 50/μm. At this value of Ti, the lags and current collapse are reduced when LFP becomes long for every εr considered here.

First 18650-format Na-ion cells aging investigation: A degradation mechanism study

Several Hard carbon||Na3V2(PO4)2F3 full-cells in 18650-format are assembled to demonstrate the possible use of SIBs in stationary applications. The cell aging process is investigated in two different conditions: (i) continuous cycling at different current rates, and (ii) storage at different states-of-charge at various temperatures. The obtained results reveal that the cell degradation depends strongly on the temperature, current rates applied in cycling conditions, or state-of-charge of the storage test. Under cycling conditions, the continuous sodiation/desodiation may induce significant mechanical deformation, leading to the detachment of active materials from the current collector. Furthermore, the post-mortem analysis shows that reaction rate and aging process are not homogeneous along the electrode roll. The XRD analysis shows that Na3V2(PO4)2F3 structure is robust; nevertheless, the material cannot recover the initial Na+ content as the cycling progresses, which is the main cause for capacity loss in the positive electrode. The solid-electrolyte interphase present on the hard carbon surface was characterised using XPS. The hard carbon electrode cannot be detected during this study, evidencing the formation of a relatively thick (>5 nm) passivating layer composed of carbonate salts and NaF, which are the main products of electrolyte decomposition.

Access Region Stack Engineering for Mitigation of Degradation in AlGaN/GaN HEMTs With Field Plate

Electric field in a device varies as it switches between ON and OFF states. These states have different intensities of electric field and carrier density. The regions having high electric field affects reliability of a GaN-HEMT. In a AlGaN/GaN HEMT, degradation primarily initiates as a result of electric field crowding near its edges. The present work aims at suppressing high electric field in the SEMI-ON state at the field plate edge by incorporating a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> pocket at its edge. Numerical analysis is performed using a calibrated setup to investigate viability and performance of the proposed device. It is found that the electric field and electron temperature in the SEMI-ON state reduce significantly by incorporating a SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> pocket around the field plate edge in the drain access region. For the device having SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> pocket with diamond and passivation layer thickness kept at 30 nm each, the electric field, carrier temperature, and self heating reduces by 43%, 20%, and 13%, respectively at the field plate edge along with 47% reduction in the thermal resistance.

Communication—Exploration of Plasma Oxidized Copper Oxide as a Copper Passivation Layer

Passivation properties of the plasma oxidized copper oxide on the copper line have been studied using the electromigration stress method. The self-aligned copper oxide passivation layer has the unique property of gettering copper atoms diffused through it at the high temperature raised from the stress current induced Joule heating. On the other hand, the line broken time is shortened with the increase of the copper oxide passivation layer thickness. Therefore, for the passivation application, a thin copper oxide layer is better than a thick copper oxide layer.

Effect of Ald Al2o3 Passivation Layer Thickness on the Surface Treatment of Direct-Bonded Copper Substrates: Wetting, Oxidation, and Mechanical Property Analyses

Effect of Ald Al2o3 Passivation Layer Thickness on the Surface Treatment of Direct-Bonded Copper Substrates: Wetting, Oxidation, and Mechanical Property Analyses