Contact Resistance Degradation Research Articles

Atomically Precise Graphene Nanoribbon Transistors with Long-Term Stability and Reliability.

Atomically precise graphene nanoribbons (GNRs) synthesized from the bottom-up exhibit promising electronic properties for high-performance field-effect transistors (FETs). The feasibility of fabricating FETs with GNRs (GNRFETs) has been demonstrated, with ongoing efforts aimed at further improving their performance. However, their long-term stability and reliability remain unexplored, which is as important as their performance for practical applications. In this work, we fabricated short-channel FETs with nine-atom-wide armchair GNRs (9-AGNRFETs). We revealed that the on-state (ION) current performance of the 9-AGNRFETs deteriorates significantly over consecutive full transistor on and off logic cycles, which has neither been demonstrated nor previously considered. To address this issue, we deposited a thin ∼10 nm thick atomic layer deposition (ALD) layer of aluminum oxide (Al2O3) directly on these devices. The integrity, compatibility, electrical performance, stability, and reliability, of the GNRFETs before and/or after Al2O3 deposition were comprehensively studied. The results indicate that the observed decline in electrical device performance is most likely due to the degradation of contact resistance over multiple measurement cycles. We successfully demonstrated that the devices with the Al2O3 layer operate well up to several thousand continuous full cycles without any degradation. Our study offers valuable insights into the stability and reliability of GNR transistors, which could facilitate their large-scale integration into practical applications.

Self‐Aligned Contact Doping for Performance Enhancement of Low‐Leakage Carbon Nanotube Field Effect Transistors

AbstractCarbon nanotube (CNT) field effect transistors (CNFETs) show promise for the next generation VLSI systems due to their excellent scalability, energy efficiency, and speed. However, high leakage current is a drawback of large diameter CNTs (diameter (DCNT) ≥ 1.4 nm) due to the small electronic band gap (EG) ≤ 0.6 eV and effective mass. This work investigates the on‐current and off‐current tradeoff for two populations of semiconducting‐enriched CNT with DCNT ≈ 1.0 nm displaying a simultaneous 50x improvement in minimun current (IMIN) with 2.5x degradation in contact resistance compared to DCNT ≈ 1.4 nm using a Pd side‐bonded contact. A method to enhance the performance of low‐leakage CNFETs is demonstrated using sub‐monolayer self‐aligned contact doping with 0.8 nm of MoOX, which delivers a 57% reduction in contact resistance to DCNT ≈ 1.0 nm. Robustness is verified after annealing at 200 °C for 30 min and monitoring stability across 6 months post‐fabrication with no change in electrical behaviors.

Thermal failure analysis of special-shaped crown spring connectors for rail vehicles

With the fast development of the rail transit system and the continuous speed increase of rail vehicles in China, the rated current of the power supply system in the trains rises accordingly, so the thermal reliability of the electrical connection system used in the power supply system has become one of the crucial factors whether the train can run normally for a long time. In this paper, aiming at an ablative failure of a special-shaped crown spring connector during the operation of a subway, both the failure mechanism and the solution method are studied. Firstly, the main influencing factors of the failure, both the cable size and the contact resistance degradation of the connector, were screened by fault tree establishment. Then the capacity of the selected cable was evaluated to be insufficient by current carrying test, with 11.6% lower than the safe margin. Further, the contact resistance degradation of the connector caused by vibration and corrosion was about 23%, studied by the experiments and thermal theory. By combining the theoretical model of temperature rise in the contact interface and the finite element simulation, the heat production of the connection system under actual working conditions was estimated to make the insulating materials near the contacts attain to the decomposition temperature, which was verified by the analysis of the failed samples with various service stages. The thermal analysis results was demonstrated to be consistent (less than 5% error) among the finite element simulation, the experiments and an existed thermal design method. Finally, a solution to increase the cable specification from 50 mm2 to 70 mm2 under complicated service conditions is proposed to reduce bulk resistance of the cables and increase the heat dissipation by cable heat conduction, the maximum temperature rise can reduce 18.4% so that the ablation failure of the connectors can be avoided.

(Invited, Digital Presentation) The Challenges of Overcoming Defects in GaN Hemts for Operation in Extreme Environments

GaN high electron mobility transistors (HEMTs) are known to contain a high density of crystal defects. The material properties of GaN such as high breakdown voltage, carrier mobility, critical electric field strength, and higher thermal conductivity than Si, make it an ideal candidate material for use in power switches in extreme environments. In high power environments (>1.5kV), vertical GaN device geometry is emerging as an effective technique to improve performance, but the more mature lateral GaN HEMT technology is being consistently improved upon to increase breakdown voltage and overall performance in the high-power regime. In high temperature environments, GaNs wide bandgap helps in preventing unwanted thermal generation of carriers, but devices also experience increased gate-leakage current and ohmic contact resistance degradation at high temperatures. The role of defects in these limiting factors of GaN HEMT performance in extreme high power and high temperature environments is reviewed.

Research on the electrical contact degradation model of plug-in connectors under corrosion and wear

Failures due to corrosion are common for connectors operating under atmospheric environment. Results of previous studies lacked universal applicability and neglected the degradation process of contact resistance. Also, wear is rarely considered in studies on corrosion degradation, which is an inevitable mechanical process for plug connectors. Considering these problems, the atmospheric corrosion process and copper dynamics were analyzed. The consistency of the atmospheric corrosion mechanism was used to study the local corrosion degradation law and its influencing factors. The wear mechanism on corrosion degradation was determined through the analysis of the influencing factors. The corrosion model of the gold-plated parts under atmospheric wear was established. To study the degradation process of electrical contacts, a degradation model of contact resistance based on the multi-spot contact mechanism was established combined with the previous corrosion degradation model. Experimentally, the corrosion spot density increases as a function of time and varies with plated thickness, whereas the corrosion spot size distribution is still relatively independent of time. The skew phenomenon appears in the cumulative distribution probability of contact resistance as exposure time increases. Whereas the degradation of electrical contact resistance increases as a function of time, the median remains relatively unchanged. A brief analysis of the contact reliability under wear and corrosive environments was also carried out.

Study on the Wear and Abrasion Effect of Metal Nano-Coating Plug Connectors Under Atmospheric Corrosion Conditions

The plug connector is the most widely used type of separable connector; however, the sliding friction that occurs during the plug-in process causes wear and wiping effects. Wear is a form of damage that occurs to the anti-corrosion coating during the sliding process, and wiping refers to the cleaning effect of corrosion products during the sliding process. Both have negative and positive effects on electrical contact reliability in corrosive environments. Therefore, wear and wiping are key factors in studying the life and reliability of connectors in atmospheric corrosion environments. Atmospheric corrosion is the main mechanism leading to connector contact failure. There have been many related studies on simple connector atmospheric corrosion, but research on the influence of wear and wipe on atmospheric corrosion and the influence of contact resistance degradation is still not comprehensive. To study the influence of wear and wiping on contact reliability during the plug connector-mating process, this work evaluates the metal nano-coating connector plugging process as the object, and the contact resistance degradation model under atmospheric corrosion as the basis, and the effect of wear and wiping on corrosion degradation as the research tool. Ultimately, the influence of wear and wiping on contact resistance is studied in detail. Finally, combined with the actual usage of the plug-in connector, the contact reliability of metal nano-coating plug connectors under the action of abrasion and wiping is studied.

Porównanie obniżenia charakterystyk oraz badanie mechanizmu uszkodzeń materiałów stykowych z kompozytów typu srebro-tlenek metalu stosowanych w przekaźnikach elektromagnetycznych na podstawie danych z symulacji komputerowej

To evaluate the electrical contact behaviors of silver metal oxide contact materials in relays application more accurately, and to guide the selection of contact materials, the test device and testing method for simulating electrical contact performance in relays application were analyzed in this paper. The electrical contact simulation test system was designed and developed, which can easily simulate contact materials. The contact resistance, static force and rebound energy degradation parameters of AgSnO2, AgCdO and AgNi contact materials under the same load conditions were obtained through experimental research, the contact resistance and arcing energy degradation parameters of AgSnO2 under different opening distances were acquired at the same time. The result indicated that accurate data are received by the electrical contact simulation testing method. Finally, based on the test data, the degradation performance of three selected test materials was tested, and the failure mechanism of AgSnO2 materials was analyzed.

Carbon nanotube micro-contactors on ohmic substrates for on-chip microelectromechanical probing applications at wafer level

CNTs can have the ability to act as compliant small-scale springs or as shock resistance micro-contactors. This work investigates the performance of vertically-aligned CNTs (VA-CNTs) as micro-contactors in electromechanical testing applications for testing at wafer-level chip-scale-packaging (WLCSP) and wafer-level-packaging (WLP). Fabricated on ohmic substrates, 500-μm-tall CNT-metal composite contact structures are electromechanically characterized. The probe design and architecture are scalable, allowing for the assembly of thousands of probes in short manufacturing times, with easy pitch control. We discuss the effects of the metallization morphology and thickness on the compliance and electromechanical response of the metal-CNT composite contacts. Pd-metallized CNT contactors show up to 25 μm of compliance, with contact resistance as low as 460 mΩ (3.6 kΩ/μm) and network resistivity of 1.8 × 10−5 Ω cm, after 2500 touchdowns, with 50 μm of over-travel; they form reproducible and repeatable contacts, with less than 5% contact resistance degradation. Failure mechanisms are studied in-situ and after cyclic testing and show that, for top-cap-and-side metallized contacts, the CNT-metal shell provides stiffness to the probe structure in the elastic region, whilst reducing the contact resistance. The stable low resistance achieved, the high repeatability and endurance of the manufactured probes make CNT micro-contacts a viable candidate for WLP and WLCSP testing.

Thermal Analysis Approach for Predicting Power Device Lifetime

The purpose of this paper is to predict the device lifetime under a power cycling test by a simulation method that is based on a distributed self-heating SPICE model. Correlation between numeric extrapolation and experimental data is done by considering the Repetitive Avalanche test, a particular active temperature cycling that evaluates the ruggedness of a power device. The considered failure mechanism is due to front metal aging that produces contact resistance degradation. This phenomenon is strongly dependent on temperature, and by the proposed simulation tool, validated with experimental data, it is possible to evaluate the accurate temperature map and, consequently, predict the lifetime.

A Detailed Study on Light-Induced Degradation of Cz-Si PERC-Type Solar Cells: Evidence of Rear Surface-Related Degradation

A light-induced degradation phenomenon of unknown origin in p-type Cz-Si passivated emitter and rear cell (PERC)-type solar cells is thoroughly investigated by collating results from different measurement techniques and predictions from various simulations. The observed degradation manifests in slight losses in j sc , strong losses in V oc, and devastating losses in FF, and thus massively impacts efficiency. It is found that the series resistance degrades significantly due to a degradation of front contact resistance. This, however, does not explain losses in V oc and j sc , which are attributed to the degradation of a different cell component. Neither a degradation by defect formation in the space charge region, nor the emitter, nor the bulk is found to consistently explain the observations. Only a rear surface-related degradation mechanism explains consistently all experimental findings.

Extremely Thermal Stable Ni/W/TaSi<sub>2</sub>/Pt Simultaneous Ohmic Contacts to n-Type and p-Type 4H-SiC

Studying the ohmic contacts formed on ion-implanted SiC layers is fundamental to understand and to predict the behavior of practical devices. Ohmic contacts to n- (1×1019 cm−3) and p-type (1×1020 cm−3) ion-implanted 4H-SiC using Ni/W/TaSi2/Pt were investigated. No degradation of the specific contact resistance nor a minute change of the surface morphologies was observed after 300 h of 500 oC thermal treatment in air. From auger electron spectroscopy (AES) depth profiles, it was found that the oxidation of the protective platinum silicide overlayer significantly slowed down further migration of oxygen to the SiC interface. In addition, Pt and W played the role of mutual blocking, which guarantees the stability of the contact. This research suggests that the contacts are very promising for applications in harsh environments, where the simultaneously completed both on n-and p-type stability ohmic contacts is crucial.

A simple non-recessed and Au-free high quality Ohmic contacts on AlGaN/GaN: The case of Ti/Al alloy

In this work, non-recessed and Au-free low resistance Ohmic contacts are investigated on AlGaN/GaN on silicon. Based on Ti/Al bilayers, Circular TLM are fabricated and contact values are extracted varying different parameters such as single and combined annealing temperatures and surface treatment. Alloy formation upon annealing has been monitored by XRD. The results indicated that two phases, Ti3AlN and cubic TiAl3, have been formed upon annealing. Furthermore, the increase of Al thickness (up to 240nm) resulted in a tetragonal TiAl3 phase formation, with a contact resistance degradation. Finally, we have shown that a low contact resistance (1Ωmm) is achievable after clean 1 (Caro's + SC1 + HF) and upon annealing at 500°C for 3min and 800°C for 30s when using 70nm and 180nm of Ti and Al, respectively. In this case, the presence of an additional Ti3AlN (111) phase has been identified and is certainly the origin of the high quality of the Ohmic contact.

Graphenic Carbon: A Novel Material to Improve the Reliability of Metal-Silicon Contacts

Contact resistance and thermal degradation of metal-silicon contacts are major challenges in nanoscale CMOS as well as in power device applications. Titanium silicide (TiSi) is commonly used to establish low-barrier height contacts to silicon, in state-of-the-art FinFETs or Schottky diodes. But the metal is known to diffuse into the active region under high current stress, as during an electro-static discharge event. This work shows with a Schottky diode as test vehicle that a carbon–silicon (C–Si) contact has the same low Schottky barrier height as a TiSi–Si junction but is over 100 million times more stable against high current pulses. A Schottky barrier height between 0.36 eV and 0.45 eV can be obtained by a variation of the deposition process. This makes C–Si a promising candidate for future high current density and temperature stable contacts and even for applications that require low contact resistances.

Corrosion Resistance Properties of Cu-Sn Electrodeposits from Cyanide-Free Bath

Cu-Sn alloy is widely known and frequently used to avoid nickel in many decorative, and electronic applications such as connector and terminal. Electrodeposition of Cu-Sn alloys from electrolytes containing uncomplexed, divalent metal ions is difficult because of the large difference in the standard electrode potentials of Cu, 0.340 V and Sn, -0.138 V. At present, Cu-Sn alloy is still plated commercially from cyanide baths, which causes environmental problems in the use and disposal of toxic cyanide. Recently, we demonstrated that silvery white Cu-Sn alloy electrodeposits (40-55mass%Sn), called “speculum alloy,” or “white bronze”. It has been investigated as an promising alternative to an allergenic nickel coating, can be obtained from environmental friendly cyanide-free sulfosuccinate bath [1]. Cu-Sn alloy deposits as an under layer restrained degradation of contact resistance, in particular, thin gold overlay on the Cu-Sn alloy deposits containing 40 to 55 mass% Sn, called “speculum alloy,” maintained a lower contact resistance during the salt spray test for prolonged periods [2]. In addition, gold thickness can be reduced by using the Cu-Sn alloy deposits as an undercoat has been reported [2]. In this study, crystalline structure and anodic property of Cu-Sn alloy electrodeposits were examined. These characteristic features might relate to the corrosion resistance and be important surface properties when using the Cu-Sn layer for the underplating. The Cu-Sn alloy deposits, speculum alloy(40 to 55 mass% Sn) exhibited better corrosion resistance than those of pure Cu, Sn and Ni. The Cu-Sn alloy electrodeposition carried out on copper substrate using sulfosuccinate electrolytes with additives at 1A/dm2. Bath composition were as follows: CuSO4 (0.15mol/L), SnSO4 (0.05mol/L), and HOOCCH2CH(SO3H)COOH (sulfosuccinic acid, 1.0 mol/L), L-methionine (0.4mol/L), and polyoxyethylene-α-naphthol (3g/L). The bath temperature was 298K and the bath pH was adjusted to pH0.5. The anode was Sn sheet. Fig1 shows XRD patterns of the Cu-Sn deposits obtained from the baths containing different concentration ratio of metal ions. According to the Cu-Sn phase diagram, the alloy of 40–55 mass% Sn generally consists of two phases, Cu6Sn5 and Cu3Sn. On the other hand the diffraction peaks of Cu-40mass%Sn and Cu-47mass%Sn electrodeposits were assigned to only Cu6Sn5, and unknown peak(labeled* in Fig.1) near 42° was observed except the peaks derived from copper substrate. All the diffraction peaks of Cu-55mass%Sn electrodeposits was assigned to Cu6Sn5 single-phase. The diffraction peaks of Cu-62mass%Sn or above were assigned to coexistence Cu6Sn5 and β-Sn. Consequently, phase structure of the Cu-Sn alloy deposits containing 40 to 55 mass% Sn, called “speculum alloy,” which exhibited excellent corrosion resistance were identified mainly of Cu6Sn5. It might be related to the corrosion resistance. Figure 2 shows anodic polarization curves for the Cu-40mass%Sn layer obtained in diluted sulfuric acid (50 mmol/L H2SO4) at 25°C. Electrode potential was measured with a Ag/AgCl (sat. KCl) reference electrode. Corrosion potential of Cu-40mass%Sn layer was less noble, -310mV vs. Ag/AgCl, than that of pure Cu and Ni. When polarized positively from the corrosion potentials, the Cu-40mass%Sn layer (almost Cu6Sn5phase) thoroughly passivated, whereas pure Cu, Sn and Ni readily dissolved anodically. Consequently, excellent corrosion resistance of thin gold overlay on the Cu-Sn speculum electrodeposits might be achieved by passivated film formed instantaneously on the Cu-Sn deposits.

Improved Electrochemical Performance in Advanced Lithium-Ion Batteries with Porocarb® As Functional Additive

Electric vehicles face significant battery related challenges such as driving range, recharge time, durability, and cycle life. New concepts for improved and advanced battery technologies are required in order to increase driving range and durability, while simultaneously decreasing recharging time, weight, and cost. In recent years, new cell designs have been developed specifically for large scale applications in the automotive and stationary storage sectors. A new electrode concept is to supplement with Heraeus Porocarb® porous particles as a functional additive to assure optimal mass transport of lithium ions by locally enhancing the effective diffusivity in the volume of the calendared electrode. Thereby achieving higher energy densities with improved cycle life and durability. Heraeus Porocarb is an electrochemically inert carbon with low specific surface with a unique porosity profile with distinct pore size regime. Its fully interconnected macropores allow for rapid ion transport, while the mesopores locally store electrolyte promoting mass transport and the pulse response of the cell. Heraeus Porocarb can be implemented into lithium-ion battery electrodes in two different ways. More conventionally, a percolation-type approach can be taken for Porocarb particles which are smaller than the active material particles. Due to the interconnected and surface-accessible pore network in Porocarb, ionic percolation sets in at the same time as electronic transport, and local improvement of the porosity evolves into a globally interconnected transport pathway of Li+ions with low tortuosity. The second electrode concept is an imprinting-type approach where the Porocarb particles used are larger and the active material is not only slightly imprinted but to a certain degree embedded in the Porocarb after calendaring. Due to the large contact area, very low resistances can be achieved in between the carbon and the active material, which alleviates contact resistance degradation and delamination, thereby extending cycle lifetime of the electrode. The properties of Heraeus Porocarb will be presented with electrochemical data showing the enhanced performance and the so-called “Porocarb effect.” This effect can be seen in lithium ion full cells by adding Porocarb in small quantities to the cathode. Therefore a representative cathode recipe were used, with an active material (NMC-111) content of 93 wt.%, 3 wt.% PVDF binder, 2.5 wt.% carbon black and 1.5 wt.% Porocarb. Reference cells were using a graphite instead of Porocarb. Two different cathode loadings were chosen: 120 g/m2 and 240 g/m2representing high-power and high-energy cell designs, respectively. The unique porous structure of Porocarb increases significantly the kinetics in the electrode and overcomes easily the drawbacks of the low rate capability of high energy cell. Figure 1

Contact resistance to SrRuO3 and La0.67Sr0.33MnO3 epitaxial films

Contact resistance to the metallic oxide electrodes, SrRuO3 (SRO) and La0.67Sr0.33MnO3 (LSMO), is an important parameter that affects the ferroelectric tunnel junction (FTJ) device performance. We have systematically studied the contact resistance between metallic oxide electrodes (SRO, LSMO) and contact metal overlayers (Ti, Pt) after exposure to various processing environments. Specific contact resistivity (ρc) for Ti and Pt contact metals and the sheet resistance (Rsh) of the metallic oxides are measured after exposure to different reactive ion plasma process steps. Sheet resistance degradation was observed for both SRO and LSMO films after exposure to plasma treatment. Severe contact resistance degradation was observed for Ti contacts as compared to Pt after reactive ion etching on LSMO films. The effect of oxygen (O2) plasma on LSMO was observed to be most severe with non-ohmic behavior with Ti contacts, which can affect the functionality of FTJ devices. Finally, the thermal stability of contacts was investigated, Pt contacts to SRO show low resistance ohmic behavior even after annealing at 900 °C, making it a suitable contact for FTJ devices.

Research on fretting Regimes of gold-plated copper alloy electrical contact material under different vibration amplitude and frequency combinations

Gold-plated copper alloy electrical contact materials are widely used in electrical interconnection to meet the requirements of high quality and high reliability for aviation and aerospace engineering. Not much is known about the fretting failure mechanism of such materials when placed in an environment with a high-frequency vibration. This paper investigates the fretting wear and corrosion behavior of gold-plated copper alloy contacts experimentally under different vibration amplitude and frequency combinations. Three typical degradation features are summarized. Relative surface morphology, element distribution, and wear track of worn surfaces are also analyzed. The fretting map, which can discriminate the fretting regimes with vibration amplitude and frequency combinations, is presented. The map can be clearly divided into the infinite electrical contact life zone, the oxidation-dominated failure zone, and the transient unstable conductivity failure zone. The appropriate sliding velocity is the critical condition for the sharply degradation of contact resistance after the gold coating has worn out. The results show that the dynamic contact resistance is significantly influenced by the coarser and irregular profile features of wear track induced by higher sliding speed, as well as the high resistive oxides debris or oxide metal mixture.

Corrosion Studies on Gold-Plated Electrical Contacts

Long-term reliability of electrical connectors are influenced by the type of plating and plating process. In this paper, the authors look for a viable alternative to 400-nm ENIG + EG (electroless Ni, immersion Au + electroless Au) for microelectronic package substrates. In alignment with historical work, the authors choose NiPdAu (electroless Ni, electroless Pd, immersion Au) as the alternative plating with about 85% reduction in Au thickness. The investigation was mainly on contact resistance degradation due to corrosion between the package substrate and socket contacts. Corrosion studies were based on experiments leading to gold wearout and exposure to corrosive test environment, including temperature, humidity, and mixed flowing gas. The scope of investigation was limited to connectors that are infrequently mated once they are shipped to an end user from the assembly factory.

Erratum: “Grain boundary diffusivity of Ni in Au thin films and the associated degradation in electrical contact resistance due to surface oxide film formation” [J. Appl. Phys. 113, 114906 (2013)

Erratum: “Grain boundary diffusivity of Ni in Au thin films and the associated degradation in electrical contact resistance due to surface oxide film formation” [J. Appl. Phys. <b>113</b>, 114906 (2013)

Grain boundary diffusivity of Ni in Au thin films and the associated degradation in electrical contact resistance due to surface oxide film formation

The low temperature diffusion from a nickel strike layer through varying thickness films of gold, a common electrical contact overlayer, was characterized and correlated to changes in electrical contact resistance (ECR). The diffusivity of Ni in Au was determined by the surface accumulation method (type C kinetics) for Au film thicknesses of 280 and 994 nm at an annealing temperature of 150 °C over a 32 day period. X-ray photoelectron spectroscopy (XPS) was used to determine the rate of Ni surface accumulation. The average product of grain boundary width and diffusivity for Ni in polycrystalline Au was calculated to be δbDb≅2.0 × 10−22cm3s using the Hwang-Balluffi model, and δbDb≅2.5×10−22cm3s using the Ma-Balluffi model. ECR measurements were made in parallel to surface accumulation measurements, revealing a correlation between ECR and Ni-O surface concentration; ECR values for both film thicknesses increased by 1 to 2 orders of magnitude at saturation coverage. Film cross-sections were extracted using focused ion beam milling and analyzed via scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy after 32 days of annealing, enabling a direct observation of the composition and thickness of the accumulated Ni-O layer, which was approximately 3 nm thick.