Showing papers on "Contact resistance published in 2022"

Effect of multilayer CrN/CrAlN coating on the corrosion and contact resistance behavior of 316L SS bipolar plate for high temperature proton exchange membrane fuel cell

Abstract: Stainless steels have received wide attention as a substitute material for bipolar plates in high temperature proton exchange membrane fuel cell (HT-PEMFC). In the present work, the CrN, CrAlN and multilayer CrN/CrAlN coatings were deposited on 316L SS to increase the corrosion resistance and decrease the interfacial contact resistance. The deposited coatings exhibited face centered cubic phase structure and it was verified from the X-ray diffraction pattern. X-ray photo electron spectroscopy results showed the formation of both CrN and CrAlN layers on 316L SS. CrN/CrAlN coating is more helpful in water management due to low surface roughness and high contact angle in the HT-PEMFC environment. The corrosion resistance behavior of all the samples were studied in 85% H3PO4 solution at 140 °C purged with H2 (HT-PEMFC anode) and O2 (HT-PEMFC cathode) gases. The results showed that all the coatings considerably improved the performance of 316L SS and superior corrosion resistance was observed for CrN/CrAlN multilayer coating, whose protective efficiency was 98.12% and 96.14% in the two simulated HT-PEMFC environments. The results of electrochemical impedance spectroscopic studies demonstrated higher impedance for CrN/CrAlN coating. Surface morphological studies performed after corrosion studies revealed that protection ability of CrN/CrAlN coating still remained acceptable. A very low interfacial contact resistance value of 6 mΩ cm2 at 140 N/cm2 was observed for CrN/CrAlN coating. Moreover, after corrosion studies, the interfacial contact resistance value of CrN/CrAlN coated 316L was much lower than that of CrN and CrAlN coatings due to the increased oxidation resistance. The maximum power density of about 0.93 W/cm2 at 2 A/cm2 and output voltage of 0.96 V was observed for CrN/CrAlN coating.

Assembly‐Free Fabrication of High‐Performance Flexible Inorganic Thin‐Film Thermoelectric Device Prepared by a Thermal Diffusion

Abstract: High relative contact electrical resistance and poor flexibility in inorganic thin‐film thermoelectric devices significantly limit their practical applications. To overcome this challenge, a one‐step thermal diffusion method to fabricate assembly‐free inorganic thin‐film thermoelectric devices is developed, where the in situ grown electrode delivers an excellent leg‐electrode contact, leading to high output power and flexibility in the prepared p‐type Sb2Te3/n‐type Bi2Te3 thin‐film device, which is composed of 8 pairs of p‐n junctions. Such a device shows a very low relative contact electrical resistance of 7.5% and a high power density of 1.42 mW cm–2 under a temperature difference of 60 K. Less than 10% change of the whole electrical resistance before and after bending test indicates the robust bending resistance and stability of the device. This study indicates that the novel assembly‐free one‐step thermal diffusion method can effectively enhance the leg‐electrode contact, the device thermoelectric performance, bending resistance, and stability, which can inspire the development of thin‐film thermoelectric devices.

Reducing Contact Resistance and Boosting Device Performance of Monolayer MoS2 by In Situ Fe Doping

Abstract: 2D semiconductors are emerging as plausible candidates for next‐generation “More‐than‐Moore” nanoelectronics to tackle the scaling challenge of transistors. Wafer‐scale 2D semiconductors, such as MoS2 and WS2, have been successfully synthesized recently; nevertheless, the absence of effective doping technology fundamentally results in energy barriers and high contact resistances at the metal–semiconductor interfaces, and thus restrict their practical applications. Herein, a controllable doping strategy in centimeter‐sized monolayer MoS2 films is developed to address this critical issue and boost the device performance. The ultralow contact resistance and perfect Ohmic contact with metal electrodes are uncovered in monolayer Fe‐doped MoS2, which deliver excellent device performance featured with ultrahigh electron mobility and outstanding on/off current ratio. Impurity scattering is suppressed significantly thanks to the ultralow electron effective mass and appropriate doping site. Particularly, unidirectionally aligned monolayer Fe‐doped MoS2 domains are prepared on 2 in. commercial c‐plane sapphire, suggesting the feasibility of synthesizing wafer‐scale 2D single‐crystal semiconductors with outstanding device performance. This work presents the potential of high‐performance monolayer transistors and enables further device downscaling and extension of Moore's law.

Vertical‐Graphene‐Reinforced Titanium Alloy Bipolar Plates in Fuel Cells

Abstract: The bipolar plate (BP) serves as one of the crucial components in proton exchange membrane fuel cells (PEMFCs). Among BP materials, metallic BPs are widely employed due to their outstanding comprehensive properties. However, the interfacial contact resistance (ICR) between BP and gas diffusion layer together with corrosion of metallic BP under acidic operating conditions degrades the performance and stability of PEMFCs. Herein, an approach is proposed for the surface reinforcement of titanium (Ti) alloy BPs, relying on a directly grown vertical graphene (VG) coating via the plasma‐enhanced chemical vapor deposition method. Compared with bare Ti alloy, the corrosion rate of VG‐coated Ti alloy reduces by 1–2 orders of magnitude in the simulated PEMFC operating environments and ICR decreases by ≈100 times, while its thermal conductivity improves by ≈20% and water contact angle increases by 68.1°. The results can be interpreted that the unique structure of VG enables excellent electrical and thermal conduction in PEMFCs, and the highly hydrophobic VG coating suppresses the penetration of corrosive liquid as well as contributing to water management. This study opens a new opportunity to reinforce metallic surfaces by the robust and versatile VG coating for high‐performance electrodes used in energy and catalyst applications.

Record-high saturation current in end-bond contacted monolayer MoS2 transistors

Abstract: Monolayer two-dimensional (2D) semiconductors are emerging as top candidates for the channels of the future chip industry due to their atomically thin body and superior immunity to short channel effect. However, the low saturation current caused by the high contact resistance (Rc) in monolayer MoS2 field-effect transistors (FETs) limits ultimate electrical performance at scaled contact lengths, which seriously hinders application of monolayer MoS2 transistors. Here we present a scalable strategy with a clean end-bond contact scheme that leads to size-independent electrodes and ultralow contact resistance of 2.5 kΩ·µm to achieve record high performances of saturation current density of 730 µA·µm−1 at 300 K and 960 µA·µm−1 at 6 K. Our end-bond contact strategy in monolayer MoS2 FETs enables the great potential for atomically thin integrated circuitry.

Investigation of ambient temperature and thermal contact resistance induced self-heating effects in nanosheet FET

Abstract: Self-heating effect (SHE) is a severe issue in advanced nano-scaled devices such as stacked nanosheet field-effect transistors (NS-FET), which raises the device temperature (T D), that ultimately affects the key electrical characteristics, i.e. threshold voltage (V T), DIBL, subthreshold slope (SS), I OFF, I ON, etc. SHE puts design constraints in the advanced CMOS logic devices and circuits. In this paper, we thoroughly investigated the impact of ambient temperature and interface thermal contact resistance induced-self heating effect in the NS-FET using extensive numerical simulations. The weak electron–phonon coupling, phonon scattering, and the ambient temperature-induced joule energy directly coupled with thermal contact resistance cause the SHE-induced thermal degradation, which increases the device temperature (T D) and affects the device reliability. The baseline NS-FET is well-calibrated with the experimental data and 3D quantum corrected drift-diffusion coupled hydrodynamic and thermodynamic transport models is used in our TCAD framework to estimate the impact of ambient temperature and interface thermal contact resistance on the device performance. Moreover, we also evaluate the SHE-induced performance comparison of NS-FET with conventional FinFET and found that thermal degradation in NS-FET potentially worsen the electrical characteristics. Thus, a detailed TCAD analysis shows that the ambient temperature and interface thermal contact resistances deteriorate the effective thermal resistance (R eff) and device performance metrics.

Differences in Printed Contacts Lead to Susceptibility of Silicon Cells to Series Resistance Degradation

Abstract: In this case study, we investigate a degradation mode occurring at the cell level in fielded multi-Si modules. The modules exhibit a mix of affected and unaffected cells. Affected cells show a progressive, series-resistance-related power degradation as shown via module- and cell-level IV curves, along with electroluminescence (EL) and PL imaging at the module, cell, and cell core sample scales. Scanning electron microscopy and energy-dispersive X-ray spectroscopy reveal a difference in the oxides in the silver paste used in screen printing of the gridline contacts. The paste in the affected cells is lead rich, whereas the paste in the unaffected cells is zinc rich. This suggests that the cells were screen printed with different silver paste compositions and possibly firing conditions, and that the different composition correlates with the susceptibility to degradation. Our results indicate degradation of the contact at the oxide-silver interface, causing a severe increase in series resistance across the cell that continues to progress over time.

Low-Temperature Cu/SiO2 Hybrid Bonding with Low Contact Resistance Using (111)-Oriented Cu Surfaces

Abstract: We adopted (111)-oriented Cu with high surface diffusivity to achieve low-temperature and low-pressure Cu/SiO2 hybrid bonding. Electroplating was employed to fabricate arrays of Cu vias with 78% (111) surface grains. The bonding temperature can be lowered to 200 °C, and the pressure is as low as 1.06 MPa. The bonding process can be accomplished by a 12-inch wafer-to-wafer scheme. The measured specific contact resistance is 1.2 × 10−9 Ω·cm2, which is the lowest value reported in related literature for Cu-Cu joints bonded below 300 °C. The joints possess excellent thermal stability up to 375 °C. The bonding mechanism is also presented to provide more understanding on hybrid bonding.

Enhanced Performance of WS2 Field-Effect Transistor through Mono and Bilayer h-BN Tunneling Contacts.

Abstract: Transition metal dichalcogenides (TMDs) are of great interest owing to their unique properties. However, TMD materials face two major challenges that limit their practical applications: contact resistance and surface contamination. Herein, a strategy to overcome these problems by inserting a monolayer of hexagonal boron nitride (h-BN) at the chromium (Cr) and tungsten disulfide (WS2 ) interface is introduced. Electrical behaviors of direct metal-semiconductor (MS) and metal-insulator-semiconductor (MIS) contacts with mono- and bilayer h-BN in a four-layer WS2 field-effect transistor (FET) are evaluated under vacuum from 77 to 300 K. The performance of the MIS contacts differs based on the metal work function when using Cr and indium (In). The contact resistance is significantly reduced by approximately ten times with MIS contacts compared with that for MS contacts. An electron mobility up to ≈115 cm2 V-1 s-1 at 300 K is achieved with the insertion of monolayer h-BN, which is approximately ten times higher than that with MS contacts. The mobility and contact resistance enhancement are attributed to Schottky barrier reduction when h-BN is introduced between Cr and WS2 . The dependence of the tunneling mechanisms on the h-BN thickness is investigated by extracting the tunneling barrier parameters.

Detection and Analysis of Corrosion and Contact Resistance Faults of TiN and CrN Coatings on 410 Stainless Steel as Bipolar Plates in PEM Fuel Cells

Abstract: Bipolar Plates (BPPs) are the most crucial component of the Polymer Electrolyte Membrane (PEM) fuel cell system. To improve fuel cell stack performance and lifetime, corrosion resistance and Interfacial Contact Resistance (ICR) enhancement are two essential factors for metallic BPPs. One of the most effective methods to achieve this purpose is adding a thin solid film of conductive coating on the surfaces of these plates. In the present study, 410 Stainless Steel (SS) was selected as a metallic bipolar plate. The coating process was performed using titanium nitride and chromium nitride by the Cathodic Arc Evaporation (CAE) method. The main focus of this study was to select the best coating among CrN and TiN on the proposed alloy as a substrate of PEM fuel cells through the comparison technique with simultaneous consideration of corrosion resistance and ICR value. After verifying the TiN and CrN coating compound, the electrochemical assessment was conducted by the potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests. The results of PDP show that all coated samples have an increase in the polarization resistance (Rp) values (ranging from 410.2 to 690.6 Ω·cm2) compared to substrate 410 SS (230.1 Ω·cm2). Corrosion rate values for bare 410 SS, CrN, and TiN coatings were measured as 0.096, 0.032, and 0.060 mpy, respectively. Facilities for X-ray Diffraction (XRD), Scanning Electron Microscope (FE-SEM, TeScan-Mira III model and made in the Czech Republic), and Energy Dispersive X-ray Spectroscopy (EDXS) were utilized to perform phase, corrosion behavior, and microstructure analysis. Furthermore, ICR tests were performed on both coated and uncoated specimens. However, the ICR of the coated samples increased slightly compared to uncoated samples. Finally, according to corrosion performance results and ICR values, it can be concluded that the CrN layer is a suitable choice for deposition on 410 SS with the aim of being used in a BPP fuel cell system.

High performance millimeter-wave InAlN/GaN HEMT for low voltage RF applications via regrown Ohmic contact with contact ledge structure

Abstract: Benefitting from regrown Ohmic contact with a contact ledge structure, high performance millimeter-wave InAlN/GaN HEMT is fabricated to satisfy low voltage RF applications. Different from the commonly seen fabrication process for regrown Ohmic contact, the scheme proposed in this work features MBE regrowth of n+ GaN on the whole wafer after formation of regrowth well without masks and partial removal of n+ GaN grown on the access region by self-stopping etching. The remaining n+ GaN on the barrier, serving as contact ledges, provides an additional current path to achieve the reduced equivalent source-drain distance and, thus, improved output current, and more current contribution is made by contact ledge as the actual source-drain distance shrinks. With the assistance of contact ledge, the fabricated device demonstrates output current density of 2.8 A/mm, a peak extrinsic transconductance of 823 mS/mm, a knee voltage of 1.6 V, and an on-resistance of 0.47 Ω·mm. Although self-stopping etching is performed on the access region, the device exhibits ignorable current collapse. At 30 GHz and VDS of 6 V, decent power-added-efficiency of 52% together with output power density of 1.2 W/mm is achieved, revealing the great potential of the proposed regrown Ohmic contact with contact ledge structure for low voltage RF applications.

Effect of contact resistance on the electrical conductivity of polymer graphene nanocomposites to optimize the biosensors detecting breast cancer cells

Abstract: This study focuses on the contact regions among neighboring nanoparticles in polymer graphene nanocomposites by the extension of nanosheets. The resistance of graphene and the contact zones represent the total resistance of the prolonged nanosheets. Furthermore, the graphene size, interphase depth, and tunneling distance express the effective volume portion of graphene, while the onset of percolation affects the fraction of percolated nanosheets. Finally, a model is developed to investigate the conductivity of the samples using the graphene size, interphase depth, and tunneling size. In addition to the roles played by certain factors in conductivity, the experimental conductivity data for several samples confirm the conductivity predictions. Generally, the polymer sheet in tunnels determines the total resistance of the extended nanosheets because graphene ordinarily exhibits negligible resistance. In addition, a large tunnel positively accelerates the onset of percolation, but increases the tunneling resistance and attenuates the conductivity of the nanocomposite. Further, a thicker interphase and lower percolation threshold promote the conductivity of the system. The developed model can be applied to optimize the biosensors detecting the breast cancer cells.

High-throughput design of functional-engineered MXene transistors with low-resistive contacts

Abstract: Abstract Two-dimensional material-based transistors are being extensively investigated for CMOS (complementary metal oxide semiconductor) technology extension; nevertheless, downscaling appears to be challenging owing to high metal-semiconductor contact resistance. Here, we propose a functional group-engineered monolayer transistor architecture that takes advantage of MXenes’ natural material chemistry to offer low-resistive contacts. We design an automated, high-throughput computational pipeline that first performs hybrid density functional theory-based calculations to find 16 sets of complementary transistor configurations by screening more than 23,000 materials from an MXene database and then conducts self-consistent quantum transport calculations to simulate their current-voltage characteristics for channel lengths ranging from 10 nm to 3 nm. Performance of these devices has been found to meet the requirements of the international roadmap for devices and systems (IRDS) for several benchmark metrics (on current, power dissipation, delay, and subthreshold swing). The proposed balanced-mode, functional-engineered MXene transistors may lead to a realistic solution for the sub-decananometer technology scaling by enabling doping-free intrinsically low contact resistance.

Atomic transistors based on seamless lateral metal-semiconductor junctions with a sub-1-nm transfer length

Abstract: The edge-to-edge connected metal-semiconductor junction (MSJ) for two-dimensional (2D) transistors has the potential to reduce the contact length while improving the performance of the devices. However, typical 2D materials are thermally and chemically unstable, which impedes the reproducible achievement of high-quality edge contacts. Here we present a scalable synthetic strategy to fabricate low-resistance edge contacts to atomic transistors using a thermally stable 2D metal, PtTe2. The use of PtTe2 as an epitaxial template enables the lateral growth of monolayer MoS2 to achieve a PtTe2-MoS2 MSJ with the thinnest possible, seamless atomic interface. The synthesized lateral heterojunction enables the reduced dimensions of Schottky barriers and enhanced carrier injection compared to counterparts composed of a vertical 3D metal contact. Furthermore, facile position-selected growth of PtTe2-MoS2 MSJ arrays using conventional lithography can facilitate the design of device layouts with high processability, while providing low contact resistivity and ultrashort transfer length on wafer scales.

Towards bifacial silicon heterojunction solar cells with reduced TCO use

Abstract: Reducing indium consumption, which is related to the transparent conductive oxide (TCO) use, is a key challenge for scaling up silicon heterojunction (SHJ) solar cell technology to terawatt level. In this work, we developed bifacial SHJ solar cells with reduced TCO thickness. We present three types of In2O3‐based TCOs, tin‐, fluorine‐, and tungsten‐doped In2O3 (ITO, IFO, and IWO), whose thickness has been optimally minimized. These are promising TCOs, respectively, from post‐transition metal doping, anionic doping, and transition metal doping and exhibit different opto‐electrical properties. We performed optical simulations and electrical investigations with varied TCO thicknesses. The results indicate that (i) reducing TCO thickness could yield larger current in both monofacial and bifacial SHJ devices; (ii) our IWO and IFO are favorable for n‐contact and p‐contact, respectively; and (iii) our ITO could serve well for both n‐contact and p‐contact. Interestingly, for the p‐contact, with the ITO thickness reducing from 75 nm to 25 nm, the average contact resistivity values show a decreasing trend from 390 mΩ cm2 to 114 mΩ cm2. With applying 25‐nm‐thick front IWO in n‐contact, and 25‐nm‐thick rear ITO use in p‐contact, we obtained front side efficiencies above 22% in bifacial SHJ solar cells. This represents a 67% TCO reduction with respect to a reference bifacial solar cell with 75‐nm‐thick TCO on both sides.

The Effect of the Surface Roughness Characteristics of the Contact Interface on the Thermal Contact Resistance of the PP-IGBT Module

Abstract: In this article, the correlation between the thermal contact resistance and the surface roughness characteristics of the contact interface in the press-pack insulated-gate bipolar transistor (PP-IGBT) modules during power cycling was studied by experimental measurements and finite-element (FE) simulation-based factorial design analysis. Thermal transient test technology was applied to examine the change in the thermal characteristic parameters of the PP-IGBT module. This shows that the increase in the thermal contact resistance of the Al metallization/emitter Mo contact interface occurs more dramatically during power cycling. A 3-D surface profilometer was used to evaluate the surface morphology parameters of the Al metallization/emitter Mo contact interface. The equivalent root-mean-square (RMS) roughness increases during power cycling, and the equivalent asperity slope and the equivalent spacing between asperities increase slightly. Additionally, the surface roughening in the corner area of the chip is more obvious than in other regions. A fractional factorial design analysis based on FE simulations was performed. The results indicate that the thermal contact resistance strongly depends on the main effects of the real contact area and the spacing between the asperities, and the RMS roughness and the asperity slope interaction.

Lower Limits of Contact Resistance in Phosphorene Nanodevices with Edge Contacts

Abstract: Edge contacts are promising for improving carrier injection and contact resistance in devices based on two-dimensional (2D) materials, among which monolayer black phosphorus (BP), or phosphorene, is especially attractive for device applications. Cutting BP into phosphorene nanoribbons (PNRs) widens the design space for BP devices and enables high-density device integration. However, little is known about contact resistance (RC) in PNRs with edge contacts, although RC is the main performance limiter for 2D material devices. Atomistic quantum transport simulations are employed to explore the impact of attaching metal edge contacts (MECs) on the electronic and transport properties and contact resistance of PNRs. We demonstrate that PNR length downscaling increases RC to 192 Ω µm in 5.2 nm-long PNRs due to strong metallization effects, while width downscaling decreases the RC to 19 Ω µm in 0.5 nm-wide PNRs. These findings illustrate the limitations on PNR downscaling and reveal opportunities in the minimization of RC by device sizing. Moreover, we prove the existence of optimum metals for edge contacts in terms of minimum metallization effects that further decrease RC by ~30%, resulting in lower intrinsic quantum limits to RC of ~90 Ω µm in phosphorene and ~14 Ω µm in ultra-narrow PNRs.

Investigations in the tape-to-tape contact resistance and contact composition in superconducting CORC® wires

Abstract: Conductor on Round Core (CORC®) wires and cables, constructed from multiple layers of helically wound REBa2Cu3O7−δ tapes, are a promising cable technology for high field magnet applications. An important feature of high-temperature superconductor cables is the ability to share current between conductors, allowing current to bypass drops in I c and minimizing the risk of hot spot formation, which could lead to potential burnout in the superconductor. In contrast to stacked-tape cables, which have continuous contact between tapes, in CORC® the transfer points occur at discrete tape crossovers. The tape-to-tape contact resistance, R c, plays a critical role in the current sharing capabilities and current distribution in cables. For the work reported here, special CORC® wires were manufactured using different winding parameters to investigate variations in R c. Variations comprised inclusion of a lubricant, different lubricant conductivity, inclusion of pre-tinning, and heating briefly to melt the solder. Cables were first tested as straight lengths, followed by bending to a 10 cm diameter. In straight cables R c values ranged from 1 to over 1000 μΩ cm2, depending on cabling parameters, with the highest values being found for cables made by the present ‘standard’ process. Bending the cables to a 10 cm diameter decreased R c by a factor 2–5. Tinning with PbSn decreased R c by three orders of magnitude compared to standard CORC® wires, and heat treating wires with tinned conductor resulted in only a small further decrease in R c. Based on the measured R c at an electric field of 1 μV cm−1 the resulting current transfer length between layers can range from a few millimeters to a tens of centimeters. Examination of contacts with a laser confocal microscope showed plastic deformation of the copper at the edges of the contact overlap area, apparently caused by thicker plating at tape edges digging into the copper of neighboring layers. These images reveal that only a fraction of the total contact surface may actually be touching when there is nothing to compensate for height differential. Images of the PbSn coated tapes indicated that application of solder produces a much more uniform contact surface and higher contact area. Furthermore, imaging of CORC® cross-sections confirmed that in the non-tinned cables there are many regions where tapes are not in contact, while in contrast the PbSn cable shows significantly more contact between the tapes. These different imaging techniques reveal that tape surface morphology is a significant parameter in determining R c.