Deuterium (D-2) annealing was applied to a poly-crystalline silicon thin-film transistor (poly-Si TFT) to improve reliability and performance. The field-effect electron mobility (mu) was extracted using the gate transconductance (gm) method. It was found that mu was improved before and after D-2 annealing. The interface trap density (D-it) as well as the oxide trap density (N-ot) in the poly-Si TFTs was quantitatively extracted using both conventional dc I-V characterization and analysis of low frequency noise (LFN). The profile of N-ot along the depth direction was investigated before and after D-2 annealing using LFN characteristics. It was confirmed that D-it as well as N-ot was reduced by the D-2 annealing, resulting in a reduction in power spectral density and variation.

This study investigated the unique reliability characteristics of tunneling field effect transistors (TFETs) by comparing the effects of positive bias temperature instability (PBTI) and hot carrier injection (HCI) stresses. In case of hot carrier injection (HCI) stress, the interface trap generation near a p/n+ region was the primary degradation mechanism. However, strong recovery after a high-pressure hydrogen annealing and weak degradation at low temperature indicates that the degradation mechanism of TFET under the HCI stress is different from the high-energy carrier stress induced permanent defect generation mechanism observed in MOSFETs. Further study is necessary to identify the exact location and defect species causing TFET degradation; however, a significant difference is evident between the dominant reliability mechanism of TFET and MOSFET.

The electrical characteristics and operation mechanism of a molybdenum disulfide/black phosphorus (MoS2/BP) heterojunction device are investigated herein. Even though this device showed a high on-off ratio of over 1 × 107, with a lower subthreshold swing of ~54 mV/dec and a 1fA level off current, its operating mechanism is closer to a junction field-effect transistor (FET) than a tunneling FET. The off-current of this device is governed by the depletion region in the BP layer, and the band-to-band tunneling current does not contribute to the rapid turn-on and extremely low off-current.

Molybdenum disulfide with atomic-scale flatness has application potential in high-speed and low-power logic devices owing to its scalability and intrinsic high mobility. However, to realize viable technologies based on two-dimensional materials, techniques that enable their large-area growth with high quality and uniformity on wafer cale is a prerequisite. Here, we provide a route toward highly uniform growth of a wafer-scale, four-layered MoS2 film on a 2 in. substrate via a sequential process consisting of the deposition of a molybdenum trioxide precursor film by sputtering followed by postsulfurization using a chemical vapor deposition process. Spatial spectroscopic analyses by Raman and PL mapping validated that the as-synthesized MoS2 thin films exhibit high uniformity on a 2 in. sapphire substrate. The highly uniform MoS2 layers allow a successful integration of devices based on ∼1200 MoS2 transistor arrays with a yield of 95% because of their extreme homogeneity on Si wafers. Moreover, a pulse electrical measurement technique enabled investigation of the inherent physical properties of the atomically thin MoS2 layers by minimizing the charge-trapping effect. Such a facile synthesis method can be possibly applied to other 2D transition metal dichalcogenides to ultimately realize the chip integration of device architectures with all 2D-layered building blocks.

A model to explain the origin of channel width dependent field effect mobility is proposed. According to our model accounting the effect of non-uniform carrier transport in a graphene channel, the field effect mobility of wide channel graphene FET has been severely underestimated as much as two times, even without accounting the fringing field effect. Based on our model, we propose a more accurate protocol to extract the field effect mobility of graphene FET involving the use of narrow channel width devices.

We report the production of a two-dimensional (2D) heterostructured gas sensor. The gas-sensing characteristics of exfoliated molybdenum disulfide (MoS2) connected to interdigitated metal electrodes were investigated. The MoS2 flake-based sensor detected a NO2 concentration as low as 1.2 ppm and exhibited excellent gas-sensing stability. Instead of metal electrodes, patterned graphene was used for charge collection in the MoS2-based sensing devices. An equation based on variable resistance terms was used to describe the sensing mechanism of the graphene/MoS2 device. Furthermore, the gas response characteristics of the heterostructured device on a flexible substrate were retained without serious performance degradation, even under mechanical deformation. This novel sensing structure based on a 2D heterostructure promises to provide a simple route to an essential sensing platform for wearable electronics.

We have investigated the effects of metal decoration on the gas-sensing properties of a device with two-dimensional (2D) molybdenum disulfide (MoS2) flake channels and graphene electrodes. The 2D hybrid-structure device sensitively detected NO2 gas molecules (>1.2 ppm) as well as NH3 (>10 ppm). Metal nanoparticles (NPs) could tune the electronic properties of the 2D graphene/MoS2 device, increasing sensitivity to a specific gas molecule. For instance, palladium NPs accumulate hole carriers of graphene/MoS2, electronically sensitizing NH3 gas molecules. Contrarily, aluminum NPs deplete hole carriers, enhancing NO2 sensitivity. The synergistic combination of metal NPs and 2D hybrid layers could be also applied to a flexible gas sensor. There was no serious degradation in the sensing performance of metal-decorated MoS2 flexible devices before/after 5000 bending cycles. Thus, highly sensitive and endurable gas sensor could be achieved through the metal-decorated 2D hybrid-structure, offering a useful route to wearable electronic sensing platforms.

Defects of graphene are the most important concern for the successful applications of graphene since they affect device performance significantly. However, once the graphene is integrated in the device structures, the quality of graphene and surrounding environment could only be assessed using indirect information such as hysteresis, mobility and drive current. Here we develop a discharge current analysis method to measure the quality of graphene integrated in a field effect transistor structure by analyzing the discharge current and examine its validity using various device structures. The density of charging sites affecting the performance of graphene field effect transistor obtained using the discharge current analysis method was on the order of 10 14 /cm 2 , which closely correlates with the intensity ratio of the D to G bands in Raman spectroscopy. The graphene FETs fabricated on poly(ethylene naphthalate) (PEN) are found to have a lower density of charging sites than those on SiO 2 /Si substrate, mainly due to reduced interfacial interaction between the graphene and the PEN. This method can be an indispensable means to improve the stability of devices using a graphene as it provides an accurate and quantitative way to define the quality of graphene after the device fabrication.

Achieving a low contact resistance for 2D materials is a critical challenge for device applications. In this work, the contact resistance of MoS 2 FETs has been drastically reduced by five times from the reference data using an optimized TiO 2 Fermi level de-pinning layer which reduced the effective Schottky barrier height to 0.1 eV. As a result, a very low contact resistance ~5.4 kΩ·μm was achieved without any doping technique.

The benefits of multi-layer graphene (MLG) capping on Cu interconnects have been experimentally demonstrated. The resistance of MLG capped Cu wires improved by 2-7% compared to Cu wires. The breakdown current density increased by 18%, suggesting that the MLG can act as an excellent capping material for Cu interconnects, improving the reliability characteristics. With a proper process optimization, MLG capped Cu interconnects could become a promising technology for high density back end-of-line interconnects.

SmallVolume 9, Issue 19 p. 3185-3185 Cover PictureFree Access Flexible Electronics: Highly Flexible and Transparent Multilayer MoS2 Transistors with Graphene Electrodes (Small 19/2013) Jongwon Yoon, Jongwon Yoon School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorWoojin Park, Woojin Park School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorGa-Yeong Bae, Ga-Yeong Bae School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorYonghun Kim, Yonghun Kim School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorHun Soo Jang, Hun Soo Jang School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorYujun Hyun, Yujun Hyun School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorSung Kwan Lim, Sung Kwan Lim Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, KoreaSearch for more papers by this authorYung Ho Kahng, Yung Ho Kahng Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju 500-712, KoreaSearch for more papers by this authorWoong-Ki Hong, Corresponding Author Woong-Ki Hong wkh27@kbsi.re.kr Jeonju center, Korea Basic Science Institute, Jeonju, Jeollabuk-do 561-180, Korea Woong-Ki Hong, Jeonju center, Korea Basic Science Institute, Jeonju, Jeollabuk-do 561-180, Korea. Heung Cho Ko, School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorByoung Hun Lee, Byoung Hun Lee School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, Korea Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, KoreaSearch for more papers by this authorHeung Cho Ko, Corresponding Author Heung Cho Ko heungcho@gist.ac.kr School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, Korea Woong-Ki Hong, Jeonju center, Korea Basic Science Institute, Jeonju, Jeollabuk-do 561-180, Korea. Heung Cho Ko, School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this author Jongwon Yoon, Jongwon Yoon School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorWoojin Park, Woojin Park School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorGa-Yeong Bae, Ga-Yeong Bae School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorYonghun Kim, Yonghun Kim School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorHun Soo Jang, Hun Soo Jang School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorYujun Hyun, Yujun Hyun School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorSung Kwan Lim, Sung Kwan Lim Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, KoreaSearch for more papers by this authorYung Ho Kahng, Yung Ho Kahng Research Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju 500-712, KoreaSearch for more papers by this authorWoong-Ki Hong, Corresponding Author Woong-Ki Hong wkh27@kbsi.re.kr Jeonju center, Korea Basic Science Institute, Jeonju, Jeollabuk-do 561-180, Korea Woong-Ki Hong, Jeonju center, Korea Basic Science Institute, Jeonju, Jeollabuk-do 561-180, Korea. Heung Cho Ko, School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this authorByoung Hun Lee, Byoung Hun Lee School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, Korea Department of Nanobio Materials and Electronics, Gwangju Institute of Science and Technology (GIST), Gwangju 500-712, KoreaSearch for more papers by this authorHeung Cho Ko, Corresponding Author Heung Cho Ko heungcho@gist.ac.kr School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, Korea Woong-Ki Hong, Jeonju center, Korea Basic Science Institute, Jeonju, Jeollabuk-do 561-180, Korea. Heung Cho Ko, School of Materials Science and Engineering, Gwangju Institute of Science and Technology (GIST), 261 Cheomdan-gwagiro (Oryong-Dong), Buk-Gu, Gwangju 500-712, KoreaSearch for more papers by this author First published: 04 October 2013 https://doi.org/10.1002/smll.201370112Citations: 120AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract A highly flexible and transparent transistor based on an exfoliated MoS2 channel and CVD-grown graphene electrodes is reported by W.-K. Hong, H. C. Ko, and co-workers on page 3295. Introducing 2D nanomaterials provides high mechanical flexibility (available bending radius: ± 2.2 mm), optical transmittance (74%), and high current on/off ratio (>104) with an average field effect mobility of ≈4.7 cm2 V−1 s−1, all of which cannot be achieved by other transistors consisting of a MoS2 active channel/metal electrodes or graphene channel/graphene electrodes. In particular, the MoS2/graphene interface has a low Schottky barrier of ≈22 meV, which is comparable to the MoS2/metal interface. Citing Literature Volume9, Issue19October 11, 2013Pages 3185-3185 RelatedInformation

The role of the initial defects of graphene characterized by Raman spectroscopy is correlated with the physical mechanisms causing the hysteretic device characteristics of graphene field effect transistors (FETs). Fast charging related to the tunneling-induced charge exchange is found to be closely correlated with the initial defect density, while slow charging related to environmental influences such as the water redox reaction showed a weak correlation. It can be concluded that the intrinsic quality of graphene should be improved to minimize the hysteresis of graphene FETs even in an air-tight environment.

A new touch sensor device has been demonstrated with molybdenum disulfide (MoS2) field effect transistors stacked with a piezoelectric polymer, polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE). The performance of two device stack structures, metal/PVDF-TrFE/MoS2 (MPM) and metal/PVDF-TrFE/Al2O3/MoS2 (MPAM), were compared as a function of the thickness of PVDF-TrFE and Al2O3. The sensitivity of the touch sensor has been improved by two orders of magnitude by reducing the charge scattering and enhancing the passivation effects using a thin Al2O3 interfacial layer. Reliable switching behavior has been demonstrated up to 120 touch press cycles.

A highly flexible and transparent transistor is developed based on an exfoliated MoS2 channel and CVD-grown graphene source/drain electrodes. Introducing the 2D nanomaterials provides a high mechanical flexibility, optical transmittance (approximate to 74%), and current on/off ratio (>10(4)) with an average field effect mobility of approximate to 4.7 cm(2) V-1 s(-1), all of which cannot be achieved by other transistors consisting of a MoS2 active channel/metal electrodes or graphene channel/graphene electrodes. In particular, a low Schottky barrier (approximate to 22 meV) forms at the MoS2/graphene interface, which is comparable to the MoS2/metal interface. The high stability in electronic performance of the devices upon bending up to +/- 2.2 mm in compressive and tensile modes, and the ability to recover electrical properties after degradation upon annealing, reveal the efficacy of using 2D materials for creating highly flexible and transparent devices.

Abstract A highly flexible and transparent transistor is developed based on an exfoliated MoS 2 channel and CVD‐grown graphene source/drain electrodes. Introducing the 2D nanomaterials provides a high mechanical flexibility, optical transmittance (∼74%), and current on/off ratio (>10 4 ) with an average field effect mobility of ∼4.7 cm 2 V −1 s −1 , all of which cannot be achieved by other transistors consisting of a MoS 2 active channel/metal electrodes or graphene channel/graphene electrodes. In particular, a low Schottky barrier (∼22 meV) forms at the MoS 2 /graphene interface, which is comparable to the MoS 2 /metal interface. The high stability in electronic performance of the devices upon bending up to ±2.2 mm in compressive and tensile modes, and the ability to recover electrical properties after degradation upon annealing, reveal the efficacy of using 2D materials for creating highly flexible and transparent devices.

We studied GaN-based optoelectronic devices such as light-emitting diodes (LEDs) and solar cells (SCs) with graphene electrodes. A decoration of Au nanoparticles (NPs) on multi-layer graphene films improved the electrical conductivity and modified the work function of the graphene films. The Au NP-decorated graphene film enhanced the current injection and electroluminescence of GaN-based LEDs through low contact resistance and improved the power conversion efficiency of GaN-based SCs through additional light absorption and energy band alignment. Our study will enhance the understanding of the role of Au NP-decorated graphene electrodes for GaN-based optoelectronic device applications.

The origin of the device instability of chemical vapor deposited graphene metal oxide semiconductor field effect transistor has been investigated while varying the characterization time scale from milliseconds to a few tens of seconds. When oxygen diffusion to the graphene interface was suppressed with Al2O3 passivation layer, the hysteresis activated with a time scale over a few tens of seconds was reduced significantly at both electron and hole branches of current–voltage curves. However, a fast charge trapping process occurring within a few milliseconds was not affected by the passivation and became a dominant mechanism of hysteresis.

Wrinkle free few layer graphene was demonstrated by a graphitization of 4H-SiC substrates using a high power pulsed KrF laser. Wrinkles often observed after thermal graphitization were eliminated with a short heat cycle using a pulse laser anneal. Few layer graphene formed by the laser graphitization appears to have a non-Bernal stack, which leads to on-off ratio of similar to 2 even at a few layer graphene. Drive current of 143 mu A/mu m was obtained at V-d = 100 mV and field effect mobility was 374 cm(2)/Vs. (C) 2011 American Institute of Physics. [doi:10.1063/1.3629785]

Graphene has been considered as a candidate for interconnect metal due to its high carrier mobility and current drivability. In this letter, the breakdown mechanism of single-layer chemical-vapor-deposited (CVD) graphene and triple-layer CVD graphene has been investigated at three different conditions (air exposed, vacuum, and dielectric capped) to identify a failure mechanism. In vacuum, both single- and triple-layer graphenes demonstrated a breakdown current density as high as ~10 8 A/cm 2 , which is similar to that of exfoliated graphene. On the other hand, the breakdown current of graphene exposed to air was degraded by one order of magnitude from that of graphene tested in vacuum. Thus, oxidation initiated at the defect sites of CVD graphene was suggested as a major failure mechanism in air, while Joule heating was more dominant with dielectric capping and in vacuum.