Decrease In Contact Resistance Research Articles

The effect of an auxiliary spring on the decrease of contact resistance and contact temperature for power automotive connector

Power automotive connectors used to connect two electrical systems in an electric vehicle should resist the rising of electric power or electric current. The latter can cause a rise in contact temperature by the Joule effect and can damage a connector improperly designed. The purpose of this work is to study experimentally and numerically the influence of the addition of a second spring on the ability of a power connector to transmit a high current. For this reason, an experimental test has been held on a connector without a second spring to measure contact resistance and contact temperature; then, a finite element model FEM of this connector was developed to compare and validate the numerical results with the experimental results. In addition, another FE model with a second spring was used to minimize contact resistance and contact temperature. Moreover, a theoretical model has shown its effectiveness in contact temperature and contact area calculations; it provides good agreement with experimental and numerical results. Numerical results show that the effect of the addition of a 2nd spring on the decrease of the contact temperature and contact resistance is significant. In addition, the thermo-electrical analysis by finite element shows that the current limit supported by a power connector with an auxiliary spring will equal twice the current supported by a power connector with one spring. FE mechanical analysis shows that the maximum mechanical stress in the connector with an auxiliary spring remains lower than the 2nd spring material yield stress. Finally, experimental and numerical results are in good agreement.

Improving polymer electrolyte membrane fuel cell performance and preventing flooding by exciting gas flow

Effective water management is necessary to prevent the performance degradation of polymer electrolyte membrane fuel cells (PEMFCs). In this study, acoustic pressure waves (AWs) are superimposed on an oxygen gas flow passing through a cathode to evaluate its potential to mitigate the flooding issue in flow channels. The goal is to expedite droplet removal by exciting droplets at frequencies close to their natural frequency. In-situ experiments are conducted to investigate the influence of AWs on two-phase flows in the cathode channel and the corresponding PEMFC performance. When AWs are applied, the frequency of water discharge from the cathode channel increases, and reduces the internal accumulated water, resulting in the pressure drop decreases. The internal flooding is also decreased, resulting in the reduction of the high frequency resistance attributed to decreased contact resistance. The external excitation improves the PEMFC performance owing to the effective and frequent water discharge induced by the increase in the local inertial force related to the droplet oscillation. The water management method propose in this study is considered to be an efficient method not only for PEMFC systems but also for other systems requiring water management.

Quantization Conductance of InSb Quantum-Well Two-Dimensional Electron Gas Using Novel Spilt Gate Structures

Electron transport behaviour in InSb semiconductor significantly changes when the conduction is restricted to two-dimensions. Semiconductor materials are an effective tools to characterize the electron transport in this aspect because the energy separation between transverse modes in a low-dimensional semiconductor device are always inversely proportional to the effective mass, in the same way as for sub-bands in a parabolic potential. Therefore, in this article, a range of novel device geometries were designed, fabricated and characterized to investigate ballistic transport of electrons in low-dimensional InSb structures using surface gated devices to restrict the degrees of freedom (dimensionality) of the active conducting channel. In this framework, designs of gates (i.e., line, loop and solid discussed later) have been used over a range of gate dimensions. Consistent measurement of quantised conductance would be promising for both low power electronics and low temperature transport physics where split gates are typically used for charge sensing. This article presents an experimental results of quantization conductance obtained for the range geometries of novel gates, and some model consideration of the implications of the material choice. Furthermore, the etching techniques (wet and dry) exhibited a significant decrease of ohmic contact resistance from around 35kΩ to only roughly 250Ω at room temperature. Interestingly a possible 0.7 anomaly conduction was observed with a loop gate structure. This work showed perfectly that the two-dimensional electron gases can be formed in narrow gap InSb QWs which makes this configuration device promising candidate for topological quantum computing and next generation integrated circuit applications. Keywords: Quantization conductance, InSb QW, 2DEG, spilt gate structure, ballistic transport.

Surface crystallization effects on tellurium oxide thin films for low-power complementary logic circuit applications

Van-der-Waals-structured tellurium (IV) has demonstrated its potential as a promising building block for complementary logic device due to its superior electrical and optoelectronic features. Here, we demonstrated the novel approach for developing high-performance tellurium oxide (TeOX) thin film through TeOX formation and surface crystallization (SC). The crystalline structures and chemical bindings of the TeOX surfaces were carefully engineered by time- and temperature-dependent UV-ozone treatment and ALD-grown-Al2O3-assisted crystallization. The huge enhancement of device performance was achieved in the optimized SC-TeOX transistor, especially high on–off current ratio of 2.19 × 106, which can be ascribed to the synergistic effects of TeOX formation and SC process resulting in the enlarged bandgap, strong valence band edge localization, and the improved crystallinity. The performance enhancement mechanism was systematically studied by constructing SC-TeOX transistor with different TeOX region, where the TeOX creation in both Te channel and source/drain electrode regions dramatically improved performance owing to the decreased contact resistance and enhanced charge transport. Consequently, we achieved the high-performance low-power complementary logic circuits with SC-TeOX transistors, even reaching the maximum gain of 67.9 and low static power of 0.5 nW. Thus, this work demonstrates the great potentials of SC-TeOX transistor for developing advanced low-power complementary logic circuits.

Study of the demagnetization behavior of no-insulation persistent-current mode HTS coils under external AC fields by 3D FEM simulation

The no-insulation (NI) winding technique is promising for applications in the persistent-current mode (PCM) operation of high-temperature superconducting (HTS) coils. To produce an NI PCM coil, it is essential to understand its demagnetization behavior (i.e. decay of persistent DC current) under an external AC field, which occurs in maglev trains, electric machines and other dynamic magnet systems. For this purpose, a 3D finite-element method (FEM) model, capturing the full electromagnetic properties of NI HTS coils is established. This work studied three kinds of AC fields, observing the impact of turn-to-turn contact resistivity on demagnetization rates, which is attributed to current distribution modulations. Under a transverse AC field, the lower contact resistivity attracts more transport current to flow in the radial pathway to bypass the ‘dynamic resistance’ generated in the superconductor, leading to slower demagnetization. Under an axial AC field, the demagnetization rate exhibits a non-monotonic relation with the contact resistivity: (1) the initial decrease in contact resistivity leads to a concentration of induced AC current on the outer turns, which accelerates the demagnetization; (2) the further decrease in contact resistivity makes the current smartly redistribute to avoid flowing through the loss-concentrated outer turns, thus slowing down the demagnetization. Under a rotating DC field, a hybrid of transverse and axial fields, the impact of contact resistivity on the demagnetization rate exhibits combined characteristics of the transverse and axial components. Additionally, quantitative prediction of the demagnetization rate of NI PCM coil under external AC field is instructive for practical designs and operations, which is tested by this 3D FEM model, and a comparison with experimental results is conducted.

(Digital Presentation) Improving Field-Effect Transistor Performance through Pulsed Laser Irradiation-Mediated MoS2-Metal Contact Engineering

Two-dimensional (2D) layered materials, such as MoS2, with their atomically thin characteristics, offer promising novel solutions for the field of nanoelectronics. MoS2 has been identified as a prospective building block for flexible and transparent nanoelectronics in the future, and has the potential to contribute to the continuation of Moore's law by enabling high integration levels with low power consumption. Although the use of 2D semiconductor materials as contact interfaces presents advantages over conventional Si-based metal-semiconductor contacts practical applications still face several obstacles. One of the biggest concerns being is the presence of the large contact resistance which can caps the available field effect carrier mobility making intrinsic quantum transport phenomena in the material inaccessible. In this work, we demonstrate the use of 1064 nm pulsed-laser to selectively anneal the metal contacts of the CVD synthesized MoS2 based back gated FET. The improved metal–semiconductor interface after laser annealing resulted in higher mobility and improved On-Off ratio (10^6~10^7). This selective contact annealing enhanced back gated MoS2 FET overall performance metrics by increasing peak field effect mobility, improving current saturation due to decreased contact resistance.Our findings suggest that Pulsed laser annealing of metal contacts in TMD-based FETs can significantly reduce contact resistivity without causing channel or substrate distortion, which is not possible with conventional thermal annealing. This approach can provide most promising application in the field of high-performance two-dimensional semiconductor in flexible/ wearable electronics. Keywords: TMDCs, CVD, MoS2 FET, laser annealing, contact resistance.

Thermal stability study of gallium nitride based magnetic field sensor

We investigated the thermal stability and performance of AlGaN/AlN/GaN Hall-effect sensors under industry-relevant atmospheric conditions. The thermal stability and performance of Hall sensors are evaluated by monitoring Hall sensitivity, two-dimensional electron gas density, and Ohmic contact resistance during aging at 200 °C for up to 2800 h under atmospheric conditions. This was accomplished by characterizing AlGaN/AlN/GaN micro-Hall sensors, with and without contacts, and before and after being placed under different thermal aging times. Observed electrical performance was correlated with the micro-structural evolution of AlGaN/AlN/GaN Hall sensor heterostructures. Results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h aging at 200 °C without any significant degradation of (i) Hall sensitivity, (ii) two-dimensional electron gas, and (iii) Ohmic contacts. However, there was a small change in sheet density and mobility, which is due to a decrease in polarization, resulting from local inhomogeneous strain relief at the barrier layer. During the early stage of thermal aging, a decrease in contact resistance was also observed and attributed to (i) out-diffusion of “Ga” at the vicinity of the contact interface, and (ii) a reduction in oxygen concentration and formation of Al–Ti intermediate alloy at the GaN/Ti interface, resulting in a reduced barrier and enhanced electron transport at the contacts. However, despite these small changes, results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h thermal aging at 200 °C.

Q-Carbon as a Corrosion-Resistant Coating.

A newly discovered quenched form of carbon, widely known as Q-carbon, thin films are synthesized by the direct conversion of the amorphous carbon layer using the nanosecond pulsed laser annealing technique, and its corrosion-resistant properties, that is, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy technique, are investigated. The unique microstructure and the existence of defects (sp2 content) in sp3-rich Q-carbon are highly desirable for efficient corrosion-resistant performance. The sp3 percentage of the as-grown Q-carbon is measured to be ∼80.5% from the D and G peaks of the Raman and C-1S X-ray photoelectron spectrum. The anti-corrosion properties with inhibition durability of Q-carbon thin films are systematically investigated in various concentrations of Na2SO4 solutions, and the corrosion potential, corrosion current, and corrosion rate of Q-carbon are determined to be -253 V, 30.1 × 10-5 A/cm2, and 0.00528, respectively, for 1 M Na2SO4 solution. Both series and contact resistance decrease from 5498.6 and 821.1 Ω to 698.8 and 124.3 Ω with an increase of Na2SO4 concentration from 0.1 to 1 M, respectively. The small shift of PDP curves toward more negative potential, the shrinkage of the radius of semicircular arcs in the Nyquist plot (Z″ vs Z'), and negligible loss in corrosion resistance (∼78%) are observed for Q-carbon thin film at the immersion time up to 48 h. The unique sp2-sp3 ratio, shorter bond length, compact atomic arrangement, and minimum porosity, along with the high adhesion strength, due to the ultrafast solid-liquid-solid growth route, of Q-carbon thin film on the substrate signify it as a better alternative compared to the existing corrosion-resistant materials.

Evaluation of Efficiency for Miniscale Thermoelectric Converter under the Influence of Electrical and Thermal Resistance of Contacts

Mass-produced thermoelectric modules are mainly fabricated with Bi2Te3-based materials. Due to the limited world reserves and the high price of tellurium, it must be saved. The miniaturization of thermoelectric converters is one of the modern trends to diminish the use of tellurium, reduce the cost of modules and expand the range of their applications. The main disadvantage of miniature thermoelectric converters operating in cooling or generating modes is their low energy efficiency, caused by the effect of electrical and thermal resistances of contacts, interconnectors and insulating plates. We propose an improved method for evaluating the maximum efficiency that takes into consideration the impact of these unwanted resistances. This method can also be used to design the modules with the optimal structure for cooling and energy generation, and not only to study their performance. The effect of undesirable electrical and thermal resistances on the maximum efficiency of cooling and generating converters made of Bi2Te3-based materials is analyzed. It is shown that the efficiency of miniature modules can be significantly improved if these resistances are reduced to their rational values. The decrease in electrical contact resistance is the predominant factor. The rational values to which it is advisable to decrease the electrical contact resistance have been determined. In the development of miniscale module technology, it is necessary to focus on such rational contact resistance values.

Studying electrical parameters of contact and contactless polarization of particles under the electrochemical treatment of mineral suspensions

Introduction. Electrochemical treatment of mineral suspensions is used in electrochemical conditioning of flotation pulp and electrochemical dissolution of minerals and metals in the processes of gold-bearing products electrochemical chlorination. Research objective is to develop and implement the procedures for determining the values of the liquid phase resistance, contact resistance under contact polarization, and ion discharge energy loss resistance under contactless polarization of the electrically conductive part. Methods of research. Equivalent circuits of electrochemical processes have been built for various electrochemical cells. Circuits for various polarizations of electrically conductive particles are established. A formula is proposed for calculating the electrically conductive particle resistance through the electrical resistivity of a unit of volume. A procedure has been developed for calculating the liquid phase resistance through the resistance increment under changing distance between the electrodes. The contact area and pressure influence on the value of the contact resistance is studied through the contact of pyrite and chalcopyrite with an iron electrode. Results. When studying the electrical resistivity of the liquid phase, it was found that increased distance between the current-carrying electrodes leads to an equivalent increase in the liquid phase resistance. It has been established that increased pressure and contact area between the contacting particles and the current-carrying electrode results in decreased contact resistance. The contact resistance between the particle and the electrode in the electrolyte solution is much less than the contact resistance under dry surfaces contact. This phenomenon is explained by electrons tunneling through the electrolyte film. The obtained experimental data on the determination of the liquid phase resistance, contact resistance and ion discharge energy loss resistance make it possible to mathematically describe the processes of electrochemical chlorination under a large number of particles in the pulp. Conclusions and scope of results. Procedures have been developed and specific data have been obtained on the liquid phase resistance, contact resistance, and ion discharge resistance. They can be used for practical application when implementing electrochemical technologies for mineral suspensions treatment.

Sliding electrical contact properties of highly oriented copper fiber brush

Metal fiber brush is a new electrical brush that has a promising application in high current density and non-lubricating conditions owing to its unique structure. The copper fiber brush comprised of highly oriented and uniformly distributed fibers was prepared by the knitting method with a packing fraction of 20%. The influence of current on the sliding electrical contact properties of the copper fiber brush as sliding against the steel disc was investigated. The worn surfaces of the copper fiber brushes and the steel discs were characterized to reveal the involved wear mechanisms. The results show that the static contact resistance decreases significantly from 55 to 18 mΩ with the gradual increase of contact force from 1 to 8 N, which is attributed to the elastic contact of multiple fibers and good compressive performance. The sliding contact resistance and electrical noise decrease with the increase of current, which is attributed to the micro-welding of contact spots induced by an electric arc. The wear rate of copper fiber brush increases significantly from 1.2 × 10−5 to 5.7 × 10−5 mm3/N·m with the increase of current from 0 to 8 A. The electrical wear caused by arc erosion becomes the dominant wear mechanism, which is more profound than mechanical wear under high currents.

Low Resistance Ohmic Contact on Epitaxial MOVPE Grown β-Ga2O3 and β-(AlxGa1−x)2O3 Films

We report on the realization of record low resistance Ohmic contacts to MOVPE-grown heavily Si-doped $\beta$-Ga$_2$O$_3$ and $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ epitaxial films. Transfer length measurement (TLM) patterns were fabricated on the heavily Si-doped homoepitaxial $\beta$-Ga$_2$O$_3$ films with electron concentration (n) ranging from 1.77 to 3.23e20 cm^-3. Record low specific contact resistance and total contact resistance (Rc) of 1.62e-7 Ohm.cm^2 and 0.023 Ohm.mm were realized for $\beta$-Ga$_2$O$_3$: Si films with n > 3e20 cm^-3. TLM structures were also fabricated on heavily Si doped coherently strained $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$ (x=12%, 17% and 22%) films. The film with 12% Al composition (n=1.23e20 cm^-3) showed \r{ho}c of 5.85e-6 Ohm.cm^2, but it increased to 2.19e-4 Ohm.cm^2 for a layer with a 22% Al composition. Annealing the samples post metal deposition has generally led to a decrease in contact resistance, but for high Al content $\beta$-(Al$_x$Ga$_1-x$)$_2$ O$_3$, the contact resistance did not change significantly after the annealing process. The low contact resistance values measured in this work are very promising for the fabrication of high frequency power devices.

Effect of Magnetic Field on Corrosion Behaviors of Gold-Coated Titanium as Cathode Plates for Proton Exchange Membrane Fuel Cells

Effects of the self-induced magnetic fields generated by the operating current of proton exchange membrane fuel cells (PEMFCs) on metal bipolar plates (BPPs) have hardly been noticed while cannot be ignored. Therefore, corrosion behaviors and surface conductivity of gold-coated titanium (Ti/Au) and bare titanium in simulated PEMFC cathode environment under magnetic fields were evaluated by electrochemical tests and interfacial contact resistance measurements. The results indicated a considerable decrease in corrosion current and interfacial contact resistance of as-received Ti/Au, reaching 1/16 and 1/10 of those of bare titanium, respectively. The applied magnetic field also led to a sharp decline in corrosion current of bare titanium but slight increase for Ti/Au. Electrochemical impedance spectroscopy and scanning electron microscopy results suggested that magnetic field significantly facilitated the corrosion durability of titanium and ameliorating the induced pitting due to coating defects on Ti/Au. Compared to results obtained without MF, interfacial contact resistance of titanium after 24 h potentiostatic polarization under MF further increased by 24%, while a decrease by 8% was recorded for Ti/Au. In sum, effects of self-induced magnetic fields on the corrosion of metal BPPs is significant and these results revised for taking magnetic fields effects in account could be more accurate and realistic.

Understanding the Transport Phenomena in Solid State Battery (SSB)

The state-of-the-art Li-ion battery has energy density plateauing at ~300 Wh/kg. Replacing the graphite-based anode with Li metal is the easiest way to increase energy density. However, a lithium metal anode is prone to non-uniform plating/striping that leads to capacity decay and dendrite formation. Dendrites trigger short-circuiting and possible explosions as the liquid electrolytes that are used in Li-ion batteries are flammable. Solid-state batteries (SSBs) have the potential to enable Li-metal anodes as they are typically less reactive and nonflammable. Additionally, SSBs exhibit greater mechanical stability and can prevent dendritic growth [1,2]. Furthermore, solid electrolytes show much higher thermal stability, are non-toxic, and have high energy density, making the solid-state battery one of the best choices for the next generation of energy storage devices.Solid polymer electrolytes are an important class of materials for making solid-state batteries commercially viable. These have the potential to increase energy density and decrease contact resistance between anode and separator by formation of a suitable solid-electrolyte-interphase (SEI) [1]. However, this technology still has major hurdles to overcome, like lower Li-ion conductivity when compared to state-of-art ceramic separators. In recent years, garnet-type lithium oxide perovskites have gained attractiveness as state-of-art ceramic separators for SSBs. LLZTO is one such ceramic electrolyte that is being thoroughly investigated by researchers as it shows very high Li-ion conductivity at room temperature [2]. However, these materials suffer from poor interfacial contact. Recently, Yang, et al., [3] combined the best of both worlds with a new type of solid polymer separator which has better physical contact between separator and lithium and good li-ion conductivity at room temperature.In this work, we investigate the transport of Li-ions across both a solid polymer electrolyte and LLZTO solid electrolyte using a symmetric Li-cell configuration. Fig. 1 (a) and (c) show the Li plating/stripping cycling performance in a symmetric cell. The cell voltage measured during plating and stripping is to be very high for LLZTO compared to polymer electrolyte. A possible explanation may be due to high interfacial resistance arising between solid ceramic and lithium metal. Impedance spectroscopy was performed on both LLZTO and polymer separators after each current density step (24 h) and shown in Fig. 1 (b) and (d) respectively. The impedance increased with cycling for the LLZTO separator but decreased with cycling for polymer electrolyte. This may indicate that better interfacial contact between Li and polymer exists and that these connections may become more established while cycling. Furthermore, the transport of Li-ions across the separators will be analyzed using the transference number calculated using the Bruce-Vincent method. The influence of temperature and separator thickness on the transference number will also be used to characterize the nature of ion transport across such solid electrolyte separators. Such deep understanding of the transport mechanism is needed to minimize the different losses in SSBs and make it commercially viable.Figure 1: Li plating/stripping cycling performance of the (a) LLZTO electrolyte, and (c) PEO polymer electrolyte at different current density, with 12 minutes for each plating/stripping half cycle, for a total of 72 h at 70 ℃ temperature and their corresponding impedance are shown in (b) and (d) respectively. References R. Sahore, Z. Du, X. C. Chen, W. B. Hawley, A. S. Westover, and N. J. Dudney, Practical considerations for testing polymer electrolytes for high-energy solid-state batteries, ACS Energy Lett. 2021, 6, 2240-2247.A. Parejiya, R. Amin, M. B. Dixit, R. Essehli, C. J. Jafta, D. L. Wood, III, and I. Belharouak, Improving contact impedance via electrochemical pulses applied to lithium−solid electrolyte interface in solid-state batteries, ACS Energy Lett. 2021, 6, 3669−3675.Yang at al, Copper-coordinated cellulose ion conductors for solid-state batteries, Nature, 2021, 598, 590−596. Figure 1

Controlled Hydride Formation on Titanium Porous Transport Layer for Application in PEM Water Electrolysis

Titanium belongs to a group of valve metals that are known to possess a surface layer of passive oxide that protects the material from corrosion. Thanks to this attribute, titanium can withstand even harsh conditions prevailing in the anode compartment of PEM water electrolyzer. This makes titanium, together with its high electrical conductivity, a suitable material for the anode porous transport layer (PTL) and the bipolar plates in PEM water electrolyzers. However, too extensive passivation leads to an increase of contact resistance between the PTL and catalyst layer and consequently decreases the energy efficiency. This is the reason why titanium PTL is usually covered with a thin coating of precious metal (such as iridium or platinum) [1]. This thin coating hinders further titanium oxidation during electrolyzer operation and mediates good electrical contact with the catalyst particles. Recently, a much cheaper alternative approach based on titanium surface etching in acid has been introduced [2]. Titanium hydride that forms during this treatment has been shown to inhibit the passive layer growth, thus decreasing the contact resistance and improving the energy efficiency of the electrolysis.This work aims to further develop the ideas presented in reference [2] and investigate the role of titanium hydride during PEM water electrolysis. The hydridation treatment was done on pieces of titanium foil and consists of two steps. The first step is etching in boiling 35% HCl. This step removes the native oxide layer, increases the surface roughness, and introduces some amount of hydrogen into the crystal lattice of the metal. The second step involves cathodic polarization of the etched samples allowing more pronounced hydridation.By changing the condition of the cathodic polarization process, it is possible to tune the hydrogen uptake. The effects of polarization time, current density, temperature and concentration of electrolyte were studied with respect to the amount of the hydride layer formed, its thickness and penetration into the bulk phase. Treated titanium foils were characterized by various physicochemical techniques. X-ray diffractometry was used for hydride quantification, further analysis was done by scanning electron microscopy and cross-sectional metallography. Electrochemical properties of samples were studied by impedance spectroscopy and linear sweep voltammetry.The hydridation procedure was then used for titanium PTLs treatment which were then tested at the anode side of the PEM water electrolyser. Significant increase of current density was observed for etched and polarized Ti PTLs in comparison with pristine Ti PTL (Figure A). This can be attributed to significantly decreased contact resistance of treated PTLs (Figure B). A further performance increase was achieved when PTLs were treated prior to iridium coating (Figure A, B). It is thus possible to conclude, that the hydridation represents a promising approach to reduce precious metals demands in PEM water electrolysis construction.Financial support by the Czech Science Foundation within the framework of the project No.: 20-06422J is gratefully acknowlegded. Liu, C., et al., Exploring the Interface of Skin-Layered Titanium Fibers for Electrochemical Water Splitting. Advanced Energy Materials, 2021. 11(8): p. 2002926. Bystron, T., et al., Enhancing PEM water electrolysis efficiency by reducing the extent of Ti gas diffusion layer passivation. Journal of Applied Electrochemistry, 2018. 48(6): p. 713-723. Figure 1

Vertical GeSn/Ge Heterostructure Gate-All-Around Nanowire p-MOSFETs

In recent years, Ge-based group-IV alloys (GeSn, SiGeSn) have received a significant amount of attention as candidates to replace Silicon for future low power and high performance nanoelectronics [1]. The interest in these materials stems primarily from the fact that, by varying the Sn-content of the alloy, it is possible to precisely tune its bandgap from indirect to direct [2], which even opens up the possibility to switch the carrier transport from larger mass low mobility L-valley electrons to the lower mass and high mobility Γ-valley electrons. Adding Si atoms into GeSn alloys enables additional strain engineering by decoupling the lattice constant from the band gap and enables the fabrication of devices to target specific applications. Ge exhibits superior hole mobility over Si and GeSn is predicted to further improve carrier mobilities for both electrons and holes, while still retaining Si CMOS compatibility [3]. In this , we present the fabrication and characterization of Ge- and GeSn-based vertical gate-all-around (GAA) nanowire (NW) p-MOSFETs. Multilayer stacks of Ge and GeSn were grown on a Ge virtual substrate (Ge-VS) using industrial CVD reactors and subsequently characterized, confirming the high quality of the alloys.On these GeSn/Ge heterostructures, vertical GAA nanowire FETs were fabricated using a top-down approach. First, nanowires were defined by electron-beam lithography and subsequently etched anisotropically using reactive ion etching (RIE). The diameter of the nanowires was reduced by digital etching, consisting of repeated combined GeOx layer formation by plasma oxidation and removal in diluted HF solution. This way nanowires with a diameter down to 20 nm and a height of 210 nm were fabricated. A two-step process was employed for gate dielectric formation to ensure a low interface trap density: (i), deposition of a thin layer of Al2O3, followed by an O2-plasma post-oxidation step; (ii) deposition of a HfO2 dielectric layer to reach the required EOT (equivalent oxide thickness). TiN deposited by sputtering forms the gate metal. Planarization and isotropic dry etching were performed to remove the TiN on the top of the nanowire. After a second planarization step, NiGe-contacts were formed on the exposed top nanowire by Ni-deposition followed by a forming-gas annealing step. Finally, metal contacts for gate and source/drain were added.The resulting Ge-NW-pMOSFETs exhibit high electrical performances. A low subthreshold slope (SS) of 66 mV/dec, a low drain-induced barrier lowering (DIBL) of 35 mV/V and an I on/I off-ratio of 2.1×106 were measured for nanowires with a diameter of 20 nm. For 65 nm NWs, the I on/I off-ratio improves, which is attributed to the decreased contact resistance on top of the NWs, leading to larger on-currents. The peak transconductance for the Ge NWs reached ~190 µS/µm (V DS=-0.5 V). Adopting a GeSn/Ge-heterostructure, with GeSn on top of the nanowire used as source the device performances are strongly enhanced. The on-current I on was increased by ~32%, mostly due to the reduced contact resistivity of the smaller bandgap of GeSn compared to Ge. It was also observed that adopting GeSn alloys leads to an increase in transconductance, G max, to a respectable value of ~870 µS/µm, almost 3 times larger as reported to date for Ge NWs. Moreover, both SS and DIBL are improved by decreasing the NW diameter as a consequence of improved electrostatic gate control over the channel.These results demonstrate that the incorporation of GeSn into Ge-MOSFET technology yields a significant advantage and confirm its high potential for low-power-high-performance nanoelectronics.Fig. 1: (a) Schematic of the GAA nanowire FET based on a GeSn/Ge-heterostructure. (b) Optical image on the metallic contacts (c) Transfer curve of a Ge nanowire pFET with a diameter of 20 nm. The SS is 68 mV/dec and the DIBL is 35 mV/V. (d) Transfer curves of Ge0.92Sn0.08/Ge nanowire pFETs with a diameter of 65 nm and different EOTs. Acknowledgments The authors acknowledge support from the German BMBF project “SiGeSn NanoFETs”.

Temperature adjustable thermal conductivity and thermal contact resistance for liquid metal/paraffin/olefin block copolymer interface material

The adjustable thermal conductivity and thermal contact resistance are the key ways to realize efficient thermal management of electronic devices. In this work, a low melting-point alloy/paraffin/olefin block copolymer thermal interface material with the above properties was designed and prepared. Low melting-point alloy and paraffin undergo phase transformation with the increase of temperature, resulting in the significant decrease of thermal contact resistance. Moreover, the liquid phase low melting-point alloy particles are connected to reconstruct an efficient heat conduction path, which enhances the thermal conductivity of composites. In addition, this paper studied the thermal conductivity of composites at two different temperatures (30 °C/50 °C) and the effect of temperature or pressure on the thermal contact resistance. Furthermore, the heat dissipation effect of composites was evaluated by infrared thermal imager. The results prove that the thermal conductivity of composites (90 wt% filler) increases from 0.99 W/m⋅Kto 1.87 W/m⋅Kas the temperature increases from 30 °C to 50 °C. The thermal contact resistance of composites (90 wt% filler) is reduced to 0.024 K⋅cm2/W(60 °C, 40 Psi). Moreover, the results of heat dissipation experiments also confirm that the thermal contact resistance decreases with the enhancement of temperature. Therefore, all the results indicate that the thermal conductivity and thermal contact resistance of composites can be adjusted by changing the temperature.

Top-Contact Pentacene-Based Organic Thin Film Transistor with a Rubrene Layer in between Pentacene-Electrode Interface

Top-contact pentacene-based organic thin-film transistor (OTFT) with a rubrene interlayer in between pentacene-electrode [Al, Au] interface is reported. A study of the interlayer behavior of rubrene shows enhanced device performance of OTFT than that of the conventional OTFTs with only metal source-drain electrodes [Al, Au]. The improved performances of the device are attributed to the smoother pentacene surface for high carrier injection and mobility and decrease in contact resistance of the device. The device with a rubrene interlayer in between pentacene/Au interface shows better field-effect mobility of 3.3 cm2 v−1 s−1, On/Off ratio of 1.22 × 107, the threshold voltage of −3.8 V, and sub-threshold-slope of 0.31 V decade−1 respectively.

Healing of donor defect states in monolayer molybdenum disulfide using oxygen-incorporated chemical vapour deposition

Two-dimensional molybdenum disulfide (MoS2) is a semiconductor that could be used to build scaled transistors and other advanced electronic and optoelectronic devices. However, the material typically exhibits strong n-type doping, low photoluminescence quantum yields and high contact resistance with metals, behaviour that is often attributed to the presence of donor states induced by sulfur vacancies. Here we show that oxygen-incorporated chemical vapour deposition can be used to passivate sulfur vacancies and suppress the formation of donor states in monolayer MoS2. First-principles calculations and spectroscopy measurements are used to reveal the formation of molybdenum–oxygen bonding at the sulfur vacancy sites and the absence of donor states in oxygen-incorporated MoS2. Compared with MoS2 fabricated via chemical vapour deposition without oxygen, oxygen-incorporated MoS2 exhibits enhanced photoluminescence, higher work function and improved contact resistance with a lower Schottky barrier (less than 40 meV) at the metal/MoS2 interface. Sulfur vacancies in monolayer molybdenum disulfide can be passivated using an oxygen-incorporated chemical vapour deposition technique, which results in less n-type doping, enhanced photoluminescence and decreased contact resistance compared with growth without oxygen.

Interfacial self-assembly of ultrathin polydiacetylene/graphene oxide nanocomposites: A new method for synergetic enhancement of surface charge transfer without doping

A new method for interfacial self-assembly of graphene oxide (GO) and 10,12-pentacosadiynoic acid into nanometer-thick light-absorbing films exhibiting synergetic enhancement of conductive properties is developed. The blue form of polydiacetylene (PDA) nanopatches with a thickness of 5–10 nm is stabilized through the interactions between GO and PDA. The hole-transferring polymer decreases contact resistance in the GO sublayer through “healing” the gaps between the GO nanosheets. The separation of electron-hole pairs at the PDA/GO interface under applied electric field leads to a doping-free enhancement of the in-plane surface conductivity by 6 orders of magnitude up to 46.4 S·cm−1 with respect to those of individual components. These PDA/GO nanocomposites were applied as ultrathin diodes/photodiodes in a solar cell by creating a PDA/C60 heterojunction and a light-induced cross-layer charge transfer. The method can be adapted to a variety of polymerizable light-absorbing surfactants for fabricating GO-based nanohybrids for photoelectronics.