Low Sheet Resistance Research Articles

Study of phosphorus-doped Si annealed by a multi-wavelength laser

Activation annealing of phosphorus (P)-doped Si was performed with a red–greenblue (RGB) laser to evaluate its potential for the uniform heating of patterned semiconductor devices. Various characteristics of P-doped Si annealed by an RGB laser were experimentally investigated. In addition, a numerical simulation of the multi-wavelength laser annealing process was conducted to predict the temperature distribution during the process. The electrical and crystalline properties were significantly affected by the laser power. Additionally, the wavelength combination considerably affected the electrical and crystalline characteristics under moderate laser powers (27–28 W). However, the effects of the laser power and wavelength on the atomic structure were negligible. Substantial P redistribution and an increase in the surface roughness were only observed for the highest laser power (30 W) using the RGB wavelength, resulting in the highest temperature (∼2076 K) in the simulation. Under this condition, complete melting beyond end-of-range defect zone occurred, leading to a full epitaxial growth of Si and a very low sheet resistance. According to the simulation results, for the same laser power, the RGB wavelength exhibited a higher temperature than the RB wavelength because of the high absorption rate of the green laser in Si.

Freestanding 3D Metallic Micromesh for High-Performance Flexible Transparent Solid-State Zinc Batteries.

Flexible transparent energy supplies are extremely essential to the fast-growing flexible electronic systems. However, the general developed flexible transparent energy storage devices are severely limited by the challenges of low energy density, safety issues, and/or poor compatibility. In this work, a freestanding 3D hierarchical metallic micromesh with remarkble optoelectronic properties (T = 89.59% and Rs = 0.23 Ω sq-1 ) and super-flexibility is designed and manufactured for flexible transparent alkaline zinc batteries. The 3D Ni micromesh supported Cu(OH)2 @NiCo bimetallic hydroxide flexible transparent electrode (3D NM@Cu(OH)2 @NiCo BH) is obtained by a combination of photolithography, chemical etching, and electrodeposition. The negative electrode is constructed by electrodeposition of electrochemically active zinc on the surface of Ni@Cu micromesh (Ni@Cu@Zn MM). The metallic micromesh with 3D hierarchical nanoarchitecture can not only ensure low sheet resistance, but also realize high mass loading of active materials and short electron/ion transmission path, which can guarantee high energy density and high-rate capability of the transparent devices. The flexible transparent 3D NM@Cu(OH)2 @NiCo BH electrode realizes a specific capacity of 66.03 μAh cm-2 at 1mAcm-2 with a transmittance of 63%. Furthermore, the assembled solid-state NiCo-Zn alkaline battery exhibits a desirable energy density/power density of 35.89μWhcm-2 /2000.26μW cm-2 with a transmittance of 54.34%.

Transparent electrodes based on molybdenum–titanium–oxide with increased water stability for use as hole-transport/hole-injection components

Recently, dielectric/metal/dielectric (DMD) transparent electrodes based on MoO3 have been applied in solar cells and organic light emitting diodes, by virtue of the favourable properties of MoO3 as hole-transport/hole-injection material. However, amorphous MoO3 layers are easily dissolved in water, thus inhibiting device processing with water-based solutions. To improve the stability in water, the present study introduces DMD electrodes based on mixed molybdenum–titanium–oxide (MTO), fabricated by DC magnetron sputtering from a conductive oxide target. It is demonstrated that the addition of Ti strongly increases the stability in water, while the desirable electronic properties of MoO3, specifically the high work function and wide bandgap, are maintained. The DMD electrodes, with Ag as metal layer, were fabricated on both rigid and flexible substrates, namely glass and polyethylene terephthalate (PET). The obtained electrodes have low sheet resistance around 5 Ω/sq and high average visible transmittance well above 0.7 (including the substrate). As a result of the MTO stability, processing with water-based solutions takes place without electrode degradation. To demonstrate the process compatibility for large-scale, industrial production, the DMDs were sputter-deposited by a roll-to-roll process on a 300 mm-wide PET foil, achieving similar electrode properties with the laboratory-scale samples.Graphical abstract

Al Reaction-Induced Conductive a-InGaZnO as Pixel Electrode for Active-Matrix Quantum-Dot LED Displays

Thin-film transistors (TFTs) based on amorphous Indium-Gallium-Zinc Oxide (a-IGZO) can be used to drive the quantum-dot light-emitting diodes (QLEDs) for active-matrix (AM) displays. To reduce the fabrication complexity, Al reaction-induced conductive a-IGZO is developed as a common electrode, which simultaneously serves as a drain electrode for the TFT and as a bottom electrode for the QLED. The obtained a-IGZO electrode exhibits a low sheet resistance of 120 <inline-formula> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula>/ and a high transmittance of 92.1&#x0025; at a thickness of 100 nm. With the proposed a-IGZO electrode, QLED demonstrates a high external quantum efficiency of 26&#x0025;. Moreover, because both TFT and QLED share the same a-IGZO electrode, at least two patterning processes can be reduced in making a AM display. Our results suggest that Al reaction-induced conductive a-IGZO could be a promising pixel electrode for AMQLED displays.

Power conversion efficiency of 25.26% for silicon heterojunction solar cell with transition metal element doped indium oxide transparent conductive film as front electrode

AbstractIn this paper, to improve the power conversion efficiency (Eff) of silicon heterojunction (SHJ) solar cells, we developed the indium oxide doped with transition metal elements (IMO) as front transparent conductive oxide (TCO) layer combined with microcrystalline silicon (μ‐Si:H(n+)) for SHJ solar cell. The optical and electrical properties as well as structures of hydrogenated IMO (IMO:H) films were studied and compared to conventional indium tin oxide (ITO) film. Such IMO:H films have high carrier mobility over 70 cm2/V·s, high transmittance, and low free carrier absorption, which leads to a high short circuit current density exceeding 40 mA/cm2. In addition, the low sheet resistance and contact resistivity of the IMO:H films contribute to the high fill factor of the solar cell. The average Eff of solar cells with IMO:H + μ‐Si:H(n+) is improved by 0.4% compared with that of the solar cells with ITO + a‐Si:H(n+). Finally, a certified efficiency up to 25.26% (total area, 274.5 cm2) was achieved.

The effects of an LPCVD SiN x stack on the threshold voltage and its stability in AlGaN/GaN MIS-HEMTs

In this work, we systematically studied the stoichiometry and thickness effects of low-pressure chemical vapor deposited SiN x bilayer stacks on the electrical properties of AlGaN/GaN heterojunction-based metal–insulator-semiconductor high electron mobility transistors. A Si-rich SiN x single layer reduces threshold voltage shift and hysteresis under gate stress but gives rise to high gate leakage. A near-stoichiometric SiN x single layer suppresses gate leakage but causes poor gate stability. A bilayer SiN x stack with an optimized thickness ratio improves both the gate stability and on-resistance while maintaining a low current leakage. The bilayer SiN x stack consisting of a 5 nm Si-rich SiN x interfacial layer and a 15 nm SiN x capping layer resulted in the lowest sheet resistance and the highest gate stability. Such enhanced gate stability is explained by the low density of trap states and the weakened electric field at the Si-rich SiN x /GaN interface and an extra positive charge at the bilayer interface.

Improved light trapping and electrical properties from ZnO:Al seed layer/Ag nanowires/ZnO:Al nanorods composite structure for transparent conducting films

A novel ZnO:Al seed layer/Ag nanowires/ZnO:Al nanorods (AZO SL/Ag NWs/AZO NRs) composite structure for transparent conducting films was successfully obtained to enhance the light trapping and electrical properties concurrently. The morphology of Ag NWs and AZO NRs interlaced composite structure on the AZO SL was observed. Compared with the simplex AZO SL/AZO NRs films, the films with AZO SL/Ag NWs/AZO NRs composite structure had lower average sheet resistance (13.8 Ω/sq) and higher haze value (0.33) at 550 nm, which exhibited the effective improvement of both electrical and light trapping properties. The studies on the AZO SL/Ag NWs/AZO NR composite films in this work provide a novel structure for transparent conducting films applied in solar cells.

H2 based etching of GaN for re-grown gallium-free InAlN barriers giving very low 2DEG sheet resistance of 185 Ω/sq

We have studied two approaches to GaN surface preparation before regrowth of InAlN layers, using Cl2 or H2 based etch conditions to prepare the wafer for barrier regrowth. We have shown that the Cl2 based etching induces layer degradation and higher sheet resistance values, while an H2 based etch, or desorption, does not degrade the surface morphology and yields improved sheet resistance. With additional optimization of the InAlN layers using this approach, increasing the growth temperature to 830 °C, we have achieved excellent sheet resistance values down to 185 Ohm/sq while maintaining gallium free growth. This regrowth optimization could equally be applied to AlGaN regrowth structures for normally off GaN based transistors.

Quantitative Investigation of the Morphologically Corrugated CVD-Grown Graphene Monolayer Surface with a Nanoparticle-on-Mirror System

Graphene can be used as a starting material for the synthesis of useful nano-complexes for flexible, transparent electrodes, therapeutic, bio-diagnostics, and bio-sensing. In order to apply graphene in the medical field, the chemical vapor deposition (CVD) method has been mainly utilized considering its large and near-homogeneous carbon constituents. Especially, the less degree of perturbation of graphene monolayer (GM), which is followed by the underneath catalytic Cu surface morphology, is very crucial in terms of providing the suspended GM and relatively fluent lateral carrier mobility with lower sheet resistance value. In this work, we can suggest a surface-enhanced Raman spectroscopic (SERS) indicator in a quantitative way on the status of z-directional morphological corrugation of a CVD-grown GM (CVD-GM) by applying a nanoparticle-on-mirror (NPoM) system composed of Au nanoparticle (NP)/CVD-GM/Au thin film (TF) plasmonic junction structure. A new (or enhanced) radial breathing-like mode (RBLM) SERS signal around ~ 150 cm−1 from CVD-GM spaced in NPoM is clearly observed by employing a local z-polarized incident field formed at the Au NP–Au TF plasmonic gap junctions. With this observation, the value of I[out-of-plane, RBLM]/I[in-plane, [2D] at certain domains, can be suggested as a new optical nano-metrology value to relatively determine between lower z-directional morphological corrugation (or protrusion) status of a CVD-GM spaced in our NPoM system (lower I[RBLM]/I[2D] value) and a higher degree of lateral carrier mobility of the CVD-GM associated with lower sheet resistance values as a result of higher blue-shifted Raman in-plane (G, 2D) peak maximum position. Furthermore, we will also expect the bio-sensing performances by utilizing the high specific surface area and ultrahigh flexibility of the CVD-GM in one of the future prospective works such as pressure-strain, strain-to-electricity, and chemical-coupled sensor via I[RBLM]/I[2D] values.Graphical abstract

Wet chemical method for highly flexible and conductive fabrics for smart textile applications

This study reports the preparation of highly flexible and conductive fabrics containing zinc oxide (ZnO), silver nanowires (AgNW) and graphene flakes (GFs) by simple vacuum filtration. The ZnO particles prepared with sol-gel method in large sizes with flower-like shape were used as filler and became the first layer to be coated on the fabric surface. These particles covered the gaps at the junction of the fabric fibers, providing a suitable area for the deposition of subsequent layers of AgNW and GFs. The structural, morphological and conductivity properties of the prepared conductive fabric were investigated by XRD, optical and electron microscopy as well as four-point probe conductivity measurement. The optical images showed that a continuous conductive network was obtained that allowed electron transport across the fabric surface. The fabric was found to have a remarkably low sheet resistance of an average of 1.5 Ω/sq. This result displays that promising candidates suitable for conductive textile applications can be prepared by simple vacuum filtration method.

Normally-OFF AlGaN/GaN MIS-HEMTs With Low RON and Vth Hysteresis by Functioning In-situ SiNx in Regrowth Process

Normally-off AlGaN/GaN MIS-HEMTs with a high threshold voltage (<inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula>) more than 2.5 V and a low on- resistance of <inline-formula> <tex-math notation="LaTeX">$5.5\Omega \cdot $ </tex-math></inline-formula>mm have been achieved by an improved regrowth technique with <i>in-situ</i> SiN_<i>x</i> passivation. A thin-barrier heterojunction was used to decrease the two-dimensional electron gas (2DEG) underneath the gate, then regrown Al_0.2Ga_0.8N and <i>in-situ</i> SiN_<i>x</i> were applied to recover 2DEG at the access regions and reduce contact resistance. The O₃-based Al₂O₃ and HfO₂ were employed to cover the recessed-gate with low channel sheet resistances by atomic layer deposition. The other hybrid MIS-HEMT with <i>in-situ</i> SiN_<i>x</i> gate interlayer also enabled a normally-off operation with a <inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> hysteresis lower than 30 mV. The damage-free recessed-gate structures with in- situ SiN_<i>x</i> as passivation and gate dielectric contribute to reducing surface scattering and interface states, resulting in a high <inline-formula> <tex-math notation="LaTeX">$\text{V}_{\text {th}}$ </tex-math></inline-formula> uniformity and channel mobility, low on- resistance and_th hysteresis in normally-off GaN-based MIS-HEMTs.

Plasma enhanced inkjet printing of particle-free silver ink on polyester fabric for electronic devices

Most formulations of metal inks comprise of a suspension of nanoparticles however, these suffer when printed by the formation of unwanted agglomeration. The exploration and optimisation of particle-free silver-complex ink is causing a strong demand for inkjet printing of these formulations over nanoparticle-based suspension inks. This is due to the enhanced printability and rapid conversion via thermal reduction into a conductive material, which can be utilised in electronics manufacture. We developed a silver-complex ink for ‘smart-clothing’ through inkjet printing. The high-quality printing - characterised by no satellite droplet formation and fast speed - is demonstrated upon polyester fabric by the formation of electrical circuitry using a thermal reduction process. Fabric printing is limited by good metal coverage and adhesion, which we demonstrate and improve on in the work by the application of a low temperature, atmospheric air plasma pre-treatment to the polyester surface, which improves printed silver density and coverage using a plasma device which is easy to operate and economic. Printed silver layer reduction and film crystallinity is characterised from high resolution scanning electron microscopy, and spectroscopy (Ultraviolet-visible and Raman) detailing growth mechanisms for high track feature conductivity, producing a low sheet resistivity of 1.378 ± 0.001 Ω/□ and by the lighting of a 1.9 V, 250 mA Light Emitting Device, highlighting its application for conductive features processing. • Conductive films on PET fabric. • Ink jet printing particle-free silver-complex ink. • Conductive thin Ag films, 1.378 ± 0.001 Ω/□. • Enhancement of printed density and coverage by atmospheric plasma pre-treatment.

Nanoscale Electrical Investigation of Transparent Conductive Electrodes Based on Silver Nanowire Network

AbstractPresently, metallic nanowires (NWs) are the most promising materials to fabricate flexible transparent electrodes as an alternative to indium tin oxide. Here, the high performance of transparent conductive electrodes (TCEs) based on silver nanowires (AgNWs) percolation networks is reported. With optimized experimental conditions for the deposition, the AgNWs result in low sheet resistance of 10 Ω sq−1 combined with a high optical transmittance of 92.6% at λ = 550 nm. This leads to a valuable figure of merit as compared to other TCEs. In this study, the nanoscale electrical properties of the AgNWs are measured via conductive atomic force microscopy to characterize the percolation network. The electrical resistivity value calculated for a single AgNW is found to be about 12.35 µΩ cm, while a nanoscale conductivity map over an AgNW network bridging two electrodes has revealed high levels of current within the network over a distance of more than 1000 µm. The favorable determined conductivity results along with the high optical properties of the AgNWs network strongly suggest that thin‐film electrodes based on AgNWs will be a potential approach for future flexible electronic devices.

In‐Depth Investigation of Inkjet‐Printed Silver Electrodes over Large‐Area: Ink Recipe, Flow, and Solidification

AbstractInkjet‐printed flexible transparent conducting electrodes (TCEs) have attracted much recent interest in realizing large‐scale and high‐volume fabrication required by the industrial production protocol. In this paper, an in‐depth investigation and optimization of template‐less inkjet printing for the metal meshes based TCEs are presented. The general principle of conductive ink formulation for inkjet printing, the droplet coalescence and crawling on the substrates, and its solidification processes are thoroughly studied. Ideal silver lines with high conductivity of 3.4 µΩ · cm can be obtained on various substrates, with fine line‐width adjustment by step length of 5 µm. The uniformity of the width, morphology, and conductivity of printed silver lines over large‐area are improved by factors of 3.44, 1.53, and 1.95, respectively. Subsequently, passive matrix organic light emitting diodes based on silver array electrodes are fabricated to successfully light the point, line, and surface. A flexible silver mesh TCE is also printed, with low sheet resistance of 9.56 Ω sq−1 and good flexibility.

Microflow Manipulation by Velocity Field Gradient: Spontaneous Patterning of Silver Nanowires for Tailored Flexible Transparent Conductors

AbstractFlexible transparent conductors (TCs) are the fundamental components for emerging soft optoelectronics because of their excellent optical, electrical, and mechanical properties. These properties are attributed to reasonable alignment of conductive functional nanomaterials, especially 1D inorganic nanowires. Although various patterning technologies are proposed, patterning highly transparent conductors with satisfactory conductivity and flexibility in a facile, scalable, and versatile manner remains an open issue. Here, a directed self‐assembly strategy is presented for patterning silver nanowires (AgNWs) into flexible TCs with a cross‐linked network structure using microflow velocity‐field‐induced alignment at a liquid–solid interface. Under dual‐surface architectonics, the periodically varying internal microflow in the overcoated AgNW suspension facilitates the spontaneous alignment of the AgNWs on the designated regions in a layer‐by‐layer manner, yielding highly ordered AgNW TCs with an ultrahigh transmittance (98.2%), low sheet resistance (29.7 Ω sq−1), and prominent mechanical deformability. The proposed strategy is further applied to fabricate high‐accuracy arbitrary AgNW circuits to realize flexible transparent heaters with adjustable localized heat sources. This is a universal and customizable method for producing functional nanomaterials with hardly any scale or shape limitations in a streamlined fashion and provides great freedom for prototyping and manufacturing high‐performance soft optoelectronics.

A Highly Stretchable and Permeable Liquid Metal Micromesh Conductor by Physical Deposition for Epidermal Electronics.

Stretchable electronics allow functional devices to integrate with human skin seamlessly in an emerging wearable platform termed epidermal electronics. Compliant conductors represent key building components for functional devices. Among the various candidates, gallium-based liquid metals stand out with metallic conductivity and inherent deformability. Currently, the widespread applications of liquid metals in epidermal electronics are hindered by the low steam permeability and hence unpleasant wearing perceptions. In this study, a facile physical deposition approach is established to create a liquid metal micromesh over an elastomer sponge, which exhibits low sheet resistance (∼0.5 Ω sq-1), high stretchability (400% strain), and excellent durability. The porous micromesh shows textile-level permeability to achieve long-term wearing comfort. The conformal interaction of the liquid metal micromesh with the skin gives rise to a low contact impedance. An integrated epidermal sensing sleeve is demonstrated as a human-machine interface to distinguish different hand gestures by recording muscle contractions. The reported stretchable and permeable liquid metal conductor shows promising potentials in next-generation epidermal electronics.

Foldable and highly flexible transparent conductive electrode based on PDMS/ Ag NWs/PEDOT: PSS

In this work, we can transfer poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT: PSS) from the glass substrate to the polydimethylsiloxane (PDMS) substrate by using HNO3 treatment, without losing the resistance and transmittance of the transparent conductive film, which overcome the hydrophobic characteristic of the PDMS substrate. The silver nanowires (Ag NWs) based flexible transparent electrode with PDMS as substrate is prepared. The PDMS/Ag NWs/PEDOT: PSS composite film shows a high transmittance of over 84.07% and low sheet resistance of 9.05 Ω/sq, and its quality factor can reach 218.2. Moreover, the transparent conductive film has an excellent folding performance. After 200 repeated folding experiments, the resistance change rate is only 7.8%. The heater prepared by using the composite film can reach a maximum heating temperature of 184.4 °C, and repeat the on-off operation several times under the condition of 55 °C, which proves the promising application of transparent conductive film in wearable devices for human bodies.

Highly Permeable and Ultrastretchable Liquid Metal Micromesh for Skin-Attachable Electronics

Stretchable electronics represents an emerging technology for next-generation smart wearables toward intimate integration with the human body. In contrast with functional devices constructed over elastomer films with limited moisture permeability, a soft electronic textile may represent the ideal skin-attachable platform to achieve long-term wearing comfort. The advancements in this active area largely hinge on a new generation of permeable conductor. Despite its intrinsic mechanical deformability, gallium-based liquid metal typically represents an impenetrable barrier for gases and liquids. In this study, we introduce a liquid metal micromesh on electrospun microfiber textile as a highly permeable and ultrastretchable conductor. The fabrication process involves dropcasting liquid metal onto an elastomeric microfiber textile followed by high-speed rotation to remove the excessive coating. The liquid metal micromesh exhibits low sheet resistance (0.38 Ω/sq), ultrahigh stretchability (>1000% strain), and mechanical durability. The porous morphology enables a high steam permeability and perception of comfort comparable to those of standard textiles. The conformal interface with the skin gives rise to low contact impedance better than that of state-of-the-art Ag/AgCl gel electrodes. The successful implementation of the liquid micromesh conductor in a multifunctional electronic system demonstrates its practical suitability for a broad range of applications in stretchable and wearable electronics.

Highly conductive and stretching-insensitive transparent electrodes based on CuNWs

Flexible transparent electrode is attracting a lot of attention for various applications due to their versatile ability. However, it is still challenging to apply transparent electrode in stretchable application, because the conductivity will be degraded even lost when the electrode is stretched. Here, a high-performance transparent electrode with stretching-insensitivity is reported. The electrode is obtained by embedding copper nanowires into wrinkled polydimethylsiloxane elastomers via using simple sol–gel transition. The resulting electrode exhibits low sheet resistance of 16 Ω/sq. at an acceptable transmittance of ∼ 74% at visible region, and tensile stability under below 210% strain. In particular, the resistance is almost unchanged after 2500 stretching cycles with a strain of 70%, indicating excellent stretching-insensitively.

Ultra‐robust stretchable electrode for e‐skin: In situ assembly using a nanofiber scaffold and liquid metal to mimic water‐to‐net interaction

AbstractThe development of stretchable electronics could enhance novel interface structures to solve the stretchability–conductivity dilemma, which remains a major challenge. Herein, we report a nano‐liquid metal (LM)‐based highly robust stretchable electrode (NHSE) with a self‐adaptable interface that mimics water‐to‐net interaction. Based on the in situ assembly of electrospun elastic nanofiber scaffolds and electrosprayed LM nanoparticles, the NHSE exhibits an extremely low sheet resistance of 52 mΩ sq−1. It is not only insensitive to a large degree of mechanical stretching (i.e., 350% electrical resistance change upon 570% elongation) but also immune to cyclic deformation (i.e., 5% electrical resistance increases after 330 000 stretching cycles with 100% elongation). These key properties are far superior to those of the state‐of‐the‐art reports. Its robustness and stability are verified under diverse circumstances, including long‐term exposure to air (420 days), cyclic submersion (30 000 times), and resilience against mechanical damages. The combination of conductivity, stretchability, and durability makes the NHSE a promising conductor/electrode solution for flexible/stretchable electronics for applications such as wearable on‐body physiological signal detection, human–machine interaction, and heating e‐skin. image