Showing papers on "Contact resistance published in 2019"

Van der Waals contacts between three-dimensional metals and two-dimensional semiconductors

Abstract: As the dimensions of the semiconducting channels in field-effect transistors decrease, the contact resistance of the metal–semiconductor interface at the source and drain electrodes increases, dominating the performance of devices1–3. Two-dimensional (2D) transition-metal dichalcogenides such as molybdenum disulfide (MoS2) have been demonstrated to be excellent semiconductors for ultrathin field-effect transistors4,5. However, unusually high contact resistance has been observed across the interface between the metal and the 2D transition-metal dichalcogenide3,5–9. Recent studies have shown that van der Waals contacts formed by transferred graphene10,11 and metals12 on few-layered transition-metal dichalcogenides produce good contact properties. However, van der Waals contacts between a three-dimensional metal and a monolayer 2D transition-metal dichalcogenide have yet to be demonstrated. Here we report the realization of ultraclean van der Waals contacts between 10-nanometre-thick indium metal capped with 100-nanometre-thick gold electrodes and monolayer MoS2. Using scanning transmission electron microscopy imaging, we show that the indium and gold layers form a solid solution after annealing at 200 degrees Celsius and that the interface between the gold-capped indium and the MoS2 is atomically sharp with no detectable chemical interaction between the metal and the 2D transition-metal dichalcogenide, suggesting van-der-Waals-type bonding between the gold-capped indium and monolayer MoS2. The contact resistance of the indium/gold electrodes is 3,000 ± 300 ohm micrometres for monolayer MoS2 and 800 ± 200 ohm micrometres for few-layered MoS2. These values are among the lowest observed for three-dimensional metal electrodes evaporated onto MoS2, enabling high-performance field-effect transistors with a mobility of 167 ± 20 square centimetres per volt per second. We also demonstrate a low contact resistance of 220 ± 50 ohm micrometres on ultrathin niobium disulfide (NbS2) and near-ideal band offsets, indicative of defect-free interfaces, in tungsten disulfide (WS2) and tungsten diselenide (WSe2) contacted with indium alloy. Our work provides a simple method of making ultraclean van der Waals contacts using standard laboratory technology on monolayer 2D semiconductors. Ultraclean van der Waals bonds between gold-capped indium and a monolayer of the two-dimensional transition-metal dichalcogenide molybdenum disulfide show desirably low contact resistance at the interface, enabling high-performance field-effect transistors.

Microstructured Porous Pyramid-Based Ultrahigh Sensitive Pressure Sensor Insensitive to Strain and Temperature

Abstract: An ultrahigh sensitive capacitive pressure sensor based on a porous pyramid dielectric layer (PPDL) is reported. Compared to that of the conventional pyramid dielectric layer, the sensitivity was drastically increased to 44.5 kPa-1 in the pressure range <100 Pa, an unprecedented sensitivity for capacitive pressure sensors. The enhanced sensitivity is attributed to a lower compressive modulus and larger change in an effective dielectric constant under pressure. By placing the pressure sensors on islands of hard elastomer embedded in a soft elastomer substrate, the sensors exhibited insensitivity to strain. The pressure sensors were also nonresponsive to temperature. Finally, a contact resistance-based pressure sensor is also demonstrated by chemically grafting PPDL with a conductive polymer, which also showed drastically enhanced sensitivity.

Lowering the Schottky Barrier Height by Graphene/Ag Electrodes for High‐Mobility MoS2 Field‐Effect Transistors

Abstract: 2D transition metal dichalcogenides (TMDCs) have emerged as promising candidates for post-silicon nanoelectronics owing to their unique and outstanding semiconducting properties. However, contact engineering for these materials to create high-performance devices while adapting for large-area fabrication is still in its nascent stages. In this study, graphene/Ag contacts are introduced into MoS2 devices, for which a graphene film synthesized by chemical vapor deposition (CVD) is inserted between a CVD-grown MoS2 film and a Ag electrode as an interfacial layer. The MoS2 field-effect transistors with graphene/Ag contacts show improved electrical and photoelectrical properties, achieving a field-effect mobility of 35 cm2 V-1 s-1 , an on/off current ratio of 4 × 108 , and a photoresponsivity of 2160 A W-1 , compared to those of devices with conventional Ti/Au contacts. These improvements are attributed to the low work function of Ag and the tunability of graphene Fermi level; the n-doping of Ag in graphene decreases its Fermi level, thereby reducing the Schottky barrier height and contact resistance between the MoS2 and electrodes. This demonstration of contact interface engineering with CVD-grown MoS2 and graphene is a key step toward the practical application of atomically thin TMDC-based devices with low-resistance contacts for high-performance large-area electronics and optoelectronics.

Transferred via contacts as a platform for ideal two-dimensional transistors

Abstract: Two-dimensional semiconductors have a number of valuable properties that could be used to create novel electronic devices. However, creating 2D devices with good contacts and stable performance has proved challenging. Here we show that transferred via contacts, made from metal embedded in insulating hexagonal boron nitride and dry transferred onto 2D semiconductors, can be used to create high-quality 2D transistors. The approach prevents damage induced by direct metallization and allows full glovebox processing, providing a clean, stable and damage-free platform for 2D device fabrication. Using the approach, we create field-effect transistors (FETs) from bilayer p-type tungsten diselenide (WSe2) that exhibit high hole mobility and low contact resistance. The fabricated devices also exhibit high current and stability for over two months of measurements. Furthermore, the low contact resistance and clean channel allow us to create a nearly ideal top-gated p-FET with a subthreshold swing of 64 mV per decade at 290 K. Bilayer WSe2 field-effect transistors with near ideal device characteristics can be created using transferred via contacts made from metal-embedded hexagonal boron nitride.

Small contact resistance and high-frequency operation of flexible low-voltage inverted coplanar organic transistors

Abstract: The contact resistance in organic thin-film transistors (TFTs) is the limiting factor in the development of high-frequency organic TFTs. In devices fabricated in the inverted (bottom-gate) device architecture, staggered (top-contact) organic TFTs have usually shown or are predicted to show lower contact resistance than coplanar (bottom-contact) organic TFTs. However, through comparison of organic TFTs with different gate-dielectric thicknesses based on the small-molecule organic semiconductor 2,9-diphenyl-dinaphtho[2,3-b:2’,3’-f]thieno[3,2-b]thiophene, we show the potential for bottom-contact TFTs to have lower contact resistance than top-contact TFTs, provided the gate dielectric is sufficiently thin and an interface layer such as pentafluorobenzenethiol is used to treat the surface of the source and drain contacts. We demonstrate bottom-contact TFTs fabricated on flexible plastic substrates with record-low contact resistance (29 Ωcm), record subthreshold swing (62 mV/decade), and signal-propagation delays in 11-stage unipolar ring oscillators as short as 138 ns per stage, all at operating voltages of about 3 V. The widespread adoption of organic thin-film transistors (TFTs) in low-voltage high-frequency device applications is impeded by the contact resistance in the TFTs. Here, the authors report record-low contact resistance in bottom-gate, bottom-contact organic TFTs with an ultrathin gate dielectric.

Carbon-Nanotube-Based Electrical Conductors: Fabrication, Optimization, and Applications

Abstract: DOI: 10.1002/aelm.201800811 and environmentally friendly conductive cables or wires as a replacement for copper. From this view, carbon-based nanomaterial is a potential candidate. Carbon related nanomaterials including fullerenes, carbon nanotubes (CNTs), and graphene are promising due to their exceptional conductive and electronic transport properties, which may accelerate the practical and potential applications for various kinds of novel engineering areas spanning from electronics, energy storage, and advanced materials to nanotechnology and biotechnology. Among the family of carbon nanomaterials, CNTs have been a particularly attractive material since its discovery in 1991 by Iijima,[1] due to their nanoscale 1D shape, excellent mechanical properties, tunable electrical properties either metallic or semiconducting, high current carrying capacity, and many other exciting properties. These properties have highlighted the potential of CNTs use in a plethora of applications, including electrically conductive fillers in polymer composites, flexible and transparent conductive films, microelectronics (transistors, interconnectors, heat dissipaters), and lightweight conducting wires and cables.[2] Figure 1 points out the forecast presented by Endo et al.[3] on the present, near future, and long term applications of CNTs in various fields. An interesting potential application of CNTs is the long-term electrical conductors, which are able to transmit power from plants to plants or households, as well as be used in electronic devices. Compared to conventional copper cables or wires, CNT based cables have several advantages including 1) a lower density of 1.3 g cm−3 for single-walled carbon nanotubes (SWCNTs)[4] and 2.1 g cm−3 for multiwalled carbon nanotubes (MWCNTs),[5] both of which are much lower than that of copper, 8.96 g cm−3;[6] 2) environmental stability, which can stand with severe conditions including high pressure, large temperature changes, etc.; 3) excellent mechanical performance with a Young’s modulus and strength in the ranges of 1.0 TPa and 50 GPa, respectively;[7] 4) ultrahigh electrical conductivity as high as 108 S m−1 for SWCNTs, which is higher than that of copper (≈107 S m−1)).[8] Furthermore, the limited amount of conventional conductive metal resources in nature and their soaring market price greatly increased the need for a desirable alternative solution that are abundant in nature, low-cost, and The lack of progress to obtain commercially available large-scale production of continuous carbon nanotube (CNT) fibers has provided the motivation for researchers to develop high-performance bulk CNT assemblies that could more effectively transfer the superb mechanical, electrical, and other excellent properties of individual CNTs. These wire-like bulk assemblies of CNTs have demonstrated the potential for being used as electrical conductors to replace conventional conductive materials, such as copper and aluminum. CNT conductors are extremely lightweight, corrosive-resistive, and mechanically strong while being potentially cost-effective when compared to other conventional conductive materials. However, great technical challenges still exist in transferring the superior properties of individual CNTs to highly conductive bulk CNT assemblies, such as continuous wires, cables, and sheets. This paper gives an overview of the state-of-the-art advances in CNT-based conductors in terms of fabrication methods, characterization, conduction mechanisms, and applications. In addition, future research directions and possible attempts to improve performance are analyzed. The opportunities and challenges for related nonmetal competitive conductors are also discussed.

MoTe2 Lateral Homojunction Field-Effect Transistors Fabricated using Flux-Controlled Phase Engineering.

Abstract: The coexistence of metallic and semiconducting polymorphs in transition-metal dichalcogenides (TMDCs) can be utilized to solve the large contact resistance issue in TMDC-based field effect transist...

Highly Compressible and Sensitive Pressure Sensor under Large Strain Based on 3D Porous Reduced Graphene Oxide Fiber Fabrics in Wide Compression Strains.

Abstract: The development of highly sensitive wearable and foldable pressure sensors is one of the central topics in artificial intelligence, human motion monitoring, and health care monitors. However, current pressure sensors with high sensitivity and good durability in low, medium, and high applied strains are rather limited. Herein, a flexible pressure sensor based on hierarchical three-dimensional and porous reduced graphene oxide (rGO) fiber fabrics as the key sensing element is presented. The internal conductive structural network is formed by the rGO fibers which are mutually contacted by interfused or noninterfused fiber-to-fiber interfaces. Thanks to the unique structures, the sensor can show an excellent sensitivity from low to high applied strains (0.24-70.0%), a high gauge factor (1668.48) at an applied compression of 66.0%, a good durability in a wide range of frequencies, a low detection limit (1.17 Pa), and anultrafast response time (30 ms). The dominated mechanism is that under compression, the slide of the graphene fibers through the polydimethylsiloxane matrix reduces the connection points between the fibers, causing a surge in electrical resistance. In addition, because graphene fibers are porous and defective, the change in geometry of the fibers also causes a change in the electrical resistance of the composite under compression. Furthermore, the interfused fiber-to-fiber interfaces can strengthen the mechanical stability under 0.01-1.0 Hz loadings and high applied strains, and the wrinkles on the surface of the rGO fibers increased the sensitivity under tiny loadings. In addition, the noninterfused fiber-to-fiber interfaces can produce a highly sensitive contact resistance, leading to a higher sensitivity at low applied strains.

Contact Engineering High-Performance n-Type MoTe2 Transistors.

Abstract: Semiconducting MoTe2 is one of the few two-dimensional (2D) materials with a moderate band gap, similar to silicon. However, this material remains underexplored for 2D electronics due to ambient instability and predominantly p-type Fermi level pinning at contacts. Here, we demonstrate unipolar n-type MoTe2 transistors with the highest performance to date, including high saturation current (>400 μA/μm at 80 K and >200 μA/μm at 300 K) and relatively low contact resistance (1.2 to 2 kΩ·μm from 80 to 300 K), achieved with Ag contacts and AlOx encapsulation. We also investigate other contact metals (Sc, Ti, Cr, Au, Ni, Pt), extracting their Schottky barrier heights using an analytic subthreshold model. High-resolution X-ray photoelectron spectroscopy reveals that interfacial metal-Te compounds dominate the contact resistance. Among the metals studied, Sc has the lowest work function but is the most reactive, which we counter by inserting monolayer hexagonal boron nitride between MoTe2 and Sc. These metal-insulator-semiconductor (MIS) contacts partly depin the metal Fermi level and lead to the smallest Schottky barrier for electron injection. Overall, this work improves our understanding of n-type contacts to 2D materials, an important advance for low-power electronics.

Low Contact Barrier in 2H/1T' MoTe2 In-Plane Heterostructure Synthesized by Chemical Vapor Deposition.

Abstract: Metal–semiconductor contact has been a critical topic in the semiconductor industry because it influences device performance remarkably. Conventional metals have served as the major contact material in electronic and optoelectronic devices, but such a selection becomes increasingly inadequate for emerging novel materials such as two-dimensional (2D) materials. Deposited metals on semiconducting 2D channels usually form large resistance contacts due to the high Schottky barrier. A few approaches have been reported to reduce the contact resistance but they are not suitable for large-scale application or they cannot create a clean and sharp interface. In this study, a chemical vapor deposition (CVD) technique is introduced to produce large-area semiconducting 2D material (2H MoTe2) planarly contacted by its metallic phase (1T′ MoTe2). We demonstrate the phase-controllable synthesis and systematic characterization of large-area MoTe2 films, including pure 2H phase or 1T′ phase, and 2H/1T′ in-plane heterostruc...

Role of contacts in long-range protein conductance.

Abstract: Proteins are widely regarded as insulators, despite reports of electrical conductivity. Here we use measurements of single proteins between electrodes, in their natural aqueous environment to show that the factor controlling measured conductance is the nature of the electrical contact to the protein, and that specific ligands make highly selective electrical contacts. Using six proteins that lack known electrochemical activity, and measuring in a potential region where no ion current flows, we find characteristic peaks in the distributions of measured single-molecule conductances. These peaks depend on the contact chemistry, and hence, on the current path through the protein. In consequence, the measured conductance distribution is sensitive to changes in this path caused by ligand binding, as shown with streptavidin-biotin complexes. Measured conductances are on the order of nanosiemens over distances of many nanometers, orders of magnitude more than could be accounted for by electron tunneling. The current is dominated by contact resistance, so the conductance for a given path is independent of the distance between electrodes, as long as the contact points on the protein can span the gap between electrodes. While there is no currently known biological role for high electronic conductance, its dependence on specific contacts has important technological implications, because no current is observed at all without at least one strongly bonded contact, so direct electrical detection is a highly selective and label-free single-molecule detection method. We demonstrate single-molecule, highly specific, label- and background free-electronic detection of IgG antibodies to HIV and Ebola viruses.

van der Waals Contact Engineering of Graphene Field-Effect Transistors for Large-Area Flexible Electronics

Abstract: Graphene has great potential for high-performance flexible electronics. Although studied for more than a decade, contacting graphene efficiently, especially for large-area, flexible electronics, is still a challenge. Here, by engineering the graphene–metal van der Waals (vdW) contact, we demonstrate that ultralow contact resistance is achievable via a bottom-contact strategy incorporating a simple transfer process without any harsh thermal treatment (>150 °C). The majority of the fabricated devices show contact resistances below 200 Ω·μm with values as low as 65 Ω·μm achievable. This is on par with the state-of-the-art top- and edge-contacted graphene field-effect transistors. Further, our study reveals that these contacts, despite the presumed weak nature of the vdW interaction, are stable under various bending conditions, thus guaranteeing compatibility with flexible electronics with improved performance. This work illustrates the potential of the previously underestimated vdW contact approach for large...

Enhanced Charge Injection Properties of Organic Field Effect Transistor by Molecular Implantation Doping

Abstract: Organic semiconductors (OSCs) have been widely studied due to their merits such as mechanical flexibility, solution processability, and large-area fabrication. However, OSC devices still have to overcome contact resistance issues for better performances. Because of the Schottky contact at the metal-OSC interfaces, a non-ideal transfer curve feature often appears in the low-drain voltage region. To improve the contact properties of OSCs, there have been several methods reported, including interface treatment by self-assembled monolayers and introducing charge injection layers. Here, a selective contact doping of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4 -TCNQ) by solid-state diffusion in poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT) to enhance carrier injection in bottom-gate PBTTT organic field-effect transistors (OFETs) is demonstrated. Furthermore, the effect of post-doping treatment on diffusion of F4 -TCNQ molecules in order to improve the device stability is investigated. In addition, the application of the doping technique to the low-voltage operation of PBTTT OFETs with high-k gate dielectrics demonstrated a potential for designing scalable and low-power organic devices by utilizing doping of conjugated polymers.

MoTe2 van der Waals homojunction p-n diode with low resistance metal contacts.

Abstract: Although many studies have focused on transition metal dichalcogenide heterojunction p–n diodes, homojunction p–n diodes still require more extensive study. We present a van der Waals p-MoTe2/n-MoTe2 homojunction p–n diode with low resistance metal contacts. Such two-dimensional homojunction devices with low contact resistance can be used in various applications in the electronics industry. The device structure consists of stacked nanoflakes of p-MoTe2 and n-MoTe2. In this investigation, we implement a deep ultraviolet light-driven doping technique in a N2 gas environment to modulate the carrier concentration in a multilayered p-MoTe2 flake, which is consequently inverted to n-MoTe2. The deep ultraviolet light-driven doping provides environmental stability in the treated devices. We use ohmic metal contacts for the homojunction p–n diode and achieve excellent gate-dependent rectifying behavior with a rectification ratio of up to 104. Contrary to heterojunctions, the ideality factor is found to be 1.05 for the zero gate bias, indicative of good interface quality at the p-MoTe2/n-MoTe2 junction, owing to low charge trapping sites at the homojunction interface. In addition, low-temperature measurements are performed to determine the barrier height for different gate biases. This study contributes to research on van der Waals homojunction p–n diodes, which show much potential for nanoelectronic and optoelectronic devices.

One-Dimensional Edge Contacts to a Monolayer Semiconductor.

Abstract: Integration of electrical contacts into van der Waals (vdW) heterostructures is critical for realizing electronic and optoelectronic functionalities. However, to date no scalable methodology for gaining electrical access to buried monolayer two-dimensional (2D) semiconductors exists. Here we report viable edge contact formation to hexagonal boron nitride (hBN) encapsulated monolayer MoS2. By combining reactive ion etching, in situ Ar+ sputtering and annealing, we achieve a relatively low edge contact resistance, high mobility (up to ∼30 cm2 V-1 s-1) and high on-current density (>50 μA/μm at VDS = 3V), comparable to top contacts. Furthermore, the atomically smooth hBN environment also preserves the intrinsic MoS2 channel quality during fabrication, leading to a steep subthreshold swing of 116 mV/dec with a negligible hysteresis. Hence, edge contacts are highly promising for large-scale practical implementation of encapsulated heterostructure devices, especially those involving air sensitive materials, and can be arbitrarily narrow, which opens the door to further shrinkage of 2D device footprint.

Corrosion and interfacial contact resistance of 316L stainless steel coated with magnetron sputtered ZrN and TiN in the simulated cathodic environment of a proton-exchange membrane fuel cell

Abstract: To improve the corrosion resistance and electrical conductivity of 316L stainless steel used as a bipolar plate, TiN and ZrN coatings are deposited on the surface through magnetron sputtering in this study. Subsequently, the surface topography, composition, corrosion resistance, and interfacial contact resistance of the coated samples are characterized. The results show that the TiN and ZrN coating can significantly enhance the corrosion resistance of the 316L stainless steel. The corrosion current density of the coated 316L stainless steel with TiN and ZrN in the simulated cathodic environment of a proton-exchange membrane fuel cell (PEMFC) is 0.099 μA/cm2 and 0.209 μA/cm2, respectively, which meets the U.S. DOE 2020 target (

Self-Limited Nanosoldering of Silver Nanowires for High-Performance Flexible Transparent Heaters

Abstract: Silver nanowires (Ag NWs) are key materials to fabricate next-generation flexible transparent electrodes (FTEs). Currently, the applications of Ag NWs are impeded by the large wire-wire contact resistance. Herein, a self-limited nanosoldering method is proposed to reduce the contact resistance by epitaxially depositing silver nanosolders at the Ag NW junctions, which have a negligible effect on the optical transparency, while decreasing the sheet resistance of the Ag NW film from 18.6 to 7.7 Ω/sq at a transmittance of 90%. In addition, the deposited nanosolders at the junctions remarkably improve the electrical and mechanical stabilities of the Ag NW electrodes. Notably, this simple nanosoldering process can be rapidly conducted under room temperature and ambient conditions and is free of any technical support or specific equipment. This technique is easily applied to the nanosoldering of 210 × 297 mm FTEs. Based on these FTEs, a high-performance flexible transparent heater with a sheet resistance 3.7 Ω/sq at a transmittance of 82.5% is constructed. Because of the high heating rate (4.8 °C/s), the heater can produce uniform heating (145 °C) at a short response time (30 s) and low input voltage (6 V).

Electrochemically modified graphite paper as an advanced electrode substrate for supercapacitor application

Abstract: Herein, a novel advanced electrode substrate, electrochemically modified graphite paper (ECM-GP) having a foam-like structure, was developed via the green electrochemical oxidation/exfoliation of pristine graphite paper (PGP). The exfoliation technique greatly enhanced the specific surface area from 28.6 m2 g−1 for PGP to 560.9 m2 g−1 for ECM-GP with a pore volume of 0.766 cm3 g−1. This structural improvement not only enhanced its capacitance (from 108 mF cm−2 for PGP to 156 mF cm−2 for ECM-GP) but also improved its charge storage kinetics from diffusion-controlled to a capacitive nature. These amazing characteristics of ECM-GP allowed it to be extended as an advanced electrode substrate by electrochemically depositing MoO2 nanoparticles, resulting in a high capacitance value of 1409 mF cm−2 (19.6 F cm−3) at a current density of 2 mA cm−2 with 33.7% retention at a current density of 30 mA cm−2. This capacitance value is very high compared to that of previously reported MoO2-based electrodes and other differently designed electrodes. Electrochemical impedance spectroscopy indicated low charge transfer resistance in ECM-GP and low contact resistance between ECM-GP and MoO2. The designed solid-state symmetric supercapacitor (SSC) using the MoO2-decorated ECM-GP electrode showed a high energy density of 0.212 mW h cm−2 (1.41 mW h cm−3) with a power density of 98.46 mW cm−2 (665.41 mW cm−3).

AFM Manipulation of Gold Nanowires To Build Electrical Circuits

Abstract: We introduce scanning-probe-assisted nanowire circuitry (SPANC) as a new method to fabricate electrodes for the characterization of electrical transport properties at the nanoscale. SPANC uses an a...

Scaling-up Atomically Thin Coplanar Semiconductor-Metal Circuitry via Phase Engineered Chemical Assembly

Abstract: Two-dimensional (2D) layered semiconductors, with their ultimate atomic thickness, have shown promise to scale down transistors for modern integrated circuitry. However, the electrical contacts that connect these materials with external bulky metals are usually unsatisfactory, which limits the transistor performance. Recently, contacting 2D semiconductors using coplanar 2D conductors has shown promise in reducing the problematic high contact resistance. However, many of these methods are not ideal for scaled production. Here, we report on the large-scale, spatially controlled chemical assembly of the integrated 2H-MoTe2 field-effect transistors (FETs) with coplanar metallic 1T'-MoTe2 contacts via phase engineered approaches. We demonstrate that the heterophase FETs exhibit ohmic contact behavior with low contact resistance, resulting from the coplanar seamless contact between 2H and 1T'-MoTe2 confirmed by transmission electron microscopy characterizations. The average mobility of the heterophase FETs was measured to be as high as 23 cm2 V-1 s-1 (comparable with those of exfoliated single crystals), due to the large 2H-MoTe2 single-crystalline domain size (486 ± 187 μm). By developing a patterned growth method, we realize the 1T'-MoTe2 gated heterophase FET array whose components of the channel, gate, and contacts are all 2D materials. Finally, we transfer the heterophase device array onto a flexible substrate and demonstrate the near-infrared photoresponse with high photoresponsivity (∼1.02 A/W). Our study provides a basis for the large-scale application of phase-engineered coplanar MoTe2 semiconductor-metal structure in advanced electronics and optoelectronics.

On the Role of Contact Resistance and Electrode Modification in Organic Electrochemical Transistors

Abstract: Contact resistance is renowned for its unfavorable impact on transistor performance. Despite its notoriety, the nature of contact resistance in organic electrochemical transistors (OECTs) remains unclear. Here, by investigating the role of contact resistance in n-type OECTs, the first demonstration of source/drain-electrode surface modification for achieving state-of-the-art n-type OECTs is reported. Specifically, thiol-based self-assembled monolayers (SAMs), 4-methylbenzenethiol (MBT) and pentafluorobenzenethiol (PFBT), are used to investigate contact resistance in n-type accumulation-mode OECTs made from the hydrophilic copolymer P-90, where the deliberate functionalization of the gold source/drain electrodes decreases and increases the energetic mismatch at the electrode/semiconductor interface, respectively. Although MBT treatment is found to increase the transconductance three-fold, contact resistance is not found to be the dominant factor governing OECT performance. Additional morphology and surface energy investigations show that increased performance comes from SAM-enhanced source/drain electrode surface energy, which improves wetting, semiconductor/metal interface quality, and semiconductor morphology at the electrode and channel. Overall, contact resistance in n-type OECTs is investigated, whilst identifying source/drain electrode treatment as a useful device engineering strategy for achieving state of the art n-type OECTs.