Search

We experimentally demonstrated >10 dB extinction ratio (ER) at 4 Vpp with a 50µm-long double-layer graphene electro-absorption modulator (DLG EAM) integrated on a silicon slot waveguide. Both the modulation depth (0.2dB/µm) and efficiency (0.070 dBV-1µm-1) exceed state-of-art.

Background: An extreme ultraviolet (EUV)-transparent pellicle must be used during lithography to protect the photomask from fall-on particles. A pellicle made of free-standing carbon nanotube (CNT) films stops particles despite the presence of gaps while demonstrating high EUV transmission, mechanical stability, low EUV scattering and reflectivity, and DUV transmission that enables through-pellicle mask inspection. Aim: The CNT EUV pellicle properties can be tailored based on the diversity of CNT structures and tunability of their configuration within the CNT film (density, bundle size, composition, etc.) as shown in this work. A remaining challenge is extending the CNT EUV pellicle lifetime in the scanner environment of EUV-induced hydrogen-based plasma, and the effects on different CNT films are explored here. Approach: Optical and thermal properties of different CNT pellicles with respect to the CNT material type, density, composition, and bundle size were explored. The ability of uncoated CNT EUV pellicles to withstand high EUV powers in the hydrogen-based environment was tested. Transmission, spectroscopic, and chemical mapping of the exposed CNT membranes were performed to explore the material modifications under various exposure conditions. Results: Uncoated CNT pellicles withstand 600-W source power equivalent in the EUV scanner-like gas environment but exhibit structural changes with prolonged exposure. Multiwalled CNT pellicles exhibit less EUV transmission change as compared to single-walled CNT pellicles under the same exposure conditions. The protection of CNT material from structural degradation by means of coating was shown. Conclusions: These investigations add to the understanding of CNT EUV pellicle tunability for optimal performance and lifetime limiters of CNT pellicles under the influence of EUV radiation and plasma. We anticipate the need for coating the CNT pellicle to protect the CNT material against plasma damage for the current scanner conditions. Optimization of both the CNT membrane and its coating is in progress.

Understanding the energy alignment of electronic bands, which originate from ultrathin MoS2 layers and metal electrodes attached to them, is crucial for the design of MoS2-based electronic devices. We have applied internal photoemission spectroscopy (IPE) to analyze this alignment. We demonstrate that IPE can yield the barrier heights in the metal/ two-dimensional semiconductor/insulator stacks when the top metal electrode is sufficiently thin for allowing both the photoexcitation of electrons and their transport towards the insulator. The electron barrier at the interface between Al and monolayer (1ML) of MoS2 is estimated at 0.7 eV, and this value explains the experimentally observed attenuated quantum yield contribution from the aluminum. Based on the relative energies of the low-energy threshold position and the Fermi level of aluminum at the interface with the SiO2 insulator, we provide a simple explanation for the observed current photoinjection at the interface between aluminum and 1ML MoS2.

The development of silicon semiconductor technology has produced breakthroughs in electronics—from the microprocessor in the late 1960s to early 1970s, to automation, computers and smartphones—by downscaling the physical size of devices and wires to the nanometre regime. Now, graphene and related two-dimensional (2D) materials offer prospects of unprecedented advances in device performance at the atomic limit, and a synergistic combination of 2D materials with silicon chips promises a heterogeneous platform to deliver massively enhanced potential based on silicon technology. Integration is achieved via three-dimensional monolithic construction of multifunctional high-rise 2D silicon chips, enabling enhanced performance by exploiting the vertical direction and the functional diversification of the silicon platform for applications in opto-electronics and sensing. Here we review the opportunities, progress and challenges of integrating atomically thin materials with silicon-based nanosystems, and also consider the prospects for computational and non-computational applications. Progress in integrating atomically thin two-dimensional materials with silicon-based technology is reviewed, together with the associated opportunities and challenges, and a roadmap for future applications is presented.

Scanning tunneling microscopy and spectroscopy experiments under ultrahigh vacuum and low-temperature conditions have been performed on water-intercalated graphene on Pt(111). We find that the confined water layer, with a thickness around 0.35 nm, induces a strong hole doping in graphene, i.e., the Dirac point locates at round 0.64 eV above the Fermi level. This can be explained by the presence of a single "puckered bilayer" of ice-Ih, which has not been experimentally found on bare Pt(111), being confined in between graphene and Pt(111) surface. Moreover, the water intercalation makes graphene highly decoupled from the substrate, allowing us to reveal the intrinsic graphene phonons and double Rydberg series of even and odd symmetry image-potential states. Our work not only demonstrates that the electronic properties of graphene can be tuned by the confined water layer between graphene and the substrate, but also provides a generally applicable method to study the intrinsic properties of graphene as well as of other supported two-dimensional materials.

2D materials such as graphene have attracted a lot of interest in recent years because of their unique electrical and optical properties [1] - [3] . For example, a graphene Mach-Zehnder modulator (MZM) with 2.8Vmm modulation efficiency and 5GHz bandwidth has been demonstrated in the literature [2] . However, one of the challenges for current graphene MZM is graphene’s relatively high insertion loss. Potential solutions have been proposed, such as improving the quality of graphene or operating the device within graphene’s transparency region [4] . Recently, transition metal dichalcogenides (TMDC) have shown a strong electro-refraction effect in the C band, accompanied by only a limited loss increase [3] , which is promising for high efficiency, low loss Mach-Zehnder modulators and switches.

We demonstrate graphene electro-absorption modulators (EAM) integrated on 300mm wafers. The integration is based on imec’s 300mm silicon photonics platform and the full integration sequence is using standard CMOS production tools expect for the 6-inch CVD graphene growth and transfer, transferred by Graphenea. 164x TE EAMs were measured per wafer and demonstrate 90% yield with modulation efficiency (ME) of 41±5.6 dB/mm for 8V voltage swing, after process optimization. The 3dB bandwidth of the EAMs is 14.9±1.2 GHz for the device with 50µm active length. Both parameters show comparable performance with lab-based devices, obtained on coupons using similar CVD graphene. This work paves the way to enable high-volume manufacturing of 2D-material-based photonics devices.

Background: EUV lithography has been introduced for semiconductor fabrication, which makes maximizing yield and throughput increasingly important. One key component is the use of a high-transmission pellicle to keep particles out of the focal plane and thereby minimize their impact on imaging. Imec initiated the development of a promising pellicle approach based on a network of carbon nanotubes (CNT), which has the advantage of many tunable structural parameters to form a pellicle membrane. A balance between membrane robustness and particle nonpermeability on one side and low EUV absorption and membrane scattering on the other must be found. The membrane scatter is important for EUV flare effects during wafer printing. Aim: The experimental measurement of the flare must be determined as a function of the tunable CNT structural parameters. However, this measurement can be very challenging for the low-flare requirements involved. Approach: The EUV scatter measurements on CNT-based pellicle membranes have been performed and optimized in a stand-alone irradiation setup at RWTH Aachen University. The measurement results were compared to flare simulations using a CNT cylinder model, which is used to improve the experimental measurements. Results: With this approach, the flare of pellicles with different CNT structures and network parameters are investigated, as well as CNT pellicles that incorporate protective coatings. Conclusion: The proposed flare measurement procedure can be used to test for acceptable scattering levels for EUV imaging applications.

Single-layer hexagonal boron nitride is produced on 2 inch Pt(111)/sapphire wafers. The growth with borazine vapor deposition at process temperatures between 1000 and 1300 K is in situ investigated by photoelectron yield measurements. The growth kinetics is slower at higher temperatures and follows a tanh2 law which better fits for higher temperatures. The crystal-quality of hexagonal boron nitride (h-BN)/Pt(111) is inferred from scanning low energy electron diffraction (x-y LEED). The data indicate a strong dependence of the epitaxy on the growth temperature. The dominant structure is an aligned coincidence lattice with 10 h-BN on 9 Pt(1 × 1) unit cells and follows the substrate twinning at the millimeter scale.

EUV lithography is introduced in semiconductor fabrication processes, which makes maximizing yield and throughput increasingly important. One key component is the use of a high-transmission pellicle to keep particles out of the focal plane and thereby minimize their impact on imaging. Imec initiated the development of a promising pellicle approach based on a network of carbon nanotubes (CNT), which has the advantage of many tunable structural parameters to form a pellicle membrane. A balance between membrane robustness and particle non-permeability on one side and low EUV absorption and membrane scattering on the other, must be found. The membrane scatter is important for EUV flare effects during wafer printing. Therefore, it is important to verify its magnitude experimentally as a function of the tunable CNT structural parameters. However, this measurement can be very challenging for low-flare requirements. In this work, the EUV scatter measurements on CNT-based pellicle membranes have been performed and optimized in a stand-alone irradiation setup at RWTH Aachen University. Membranes with different CNT structures and network parameters are investigated, as well as membranes with protective coatings. These measurements, in combination with scattering calculations and printing performance, can serve as a guideline on acceptable scattering levels for industrial applications.

2D materials offer a pathway for further scaling of CMOS technology. However, for this to become a reality, both n-MOS and p-MOS should be realized, ideally with the same (standard) material. In the specific case of MoS

Device performance of two dimensional (2D) material based field effect transistors is severely limited by the relatively high contact resistance encountered at the contact-channel interface. Metal-graphene hybrid contacts have been previously used to improve the contact resistance of devices based on thick exfoliated materials. Here we report a novel 2D FET fabrication process entailing the transfer of metal-graphene hybrid contacts on top of 3 monolayer-thick chemical vapor deposition (CVD) MoS2, enabling a lithography free contacting strategy, with respect to MoS2. Three different metal-graphene stacks consisting of Ni, Pd and Ru, have been fabricated, transferred onto MoS2 and characterized extensively using electrical and physical characterization techniques. We find strong correlation between the measured electrical characteristics and physical characterization of the contact interface. From Raman spectra measurement, maximum charge transfer of 1.7 × 1013 cm−2 is observed between graphene and Ru, leading to an improved contact resistance for MoS2 devices with Ru-Gr contacts. Ru-Gr contact shows the lowest contact resistance of 9.34 kΩ · µm among the three metal-graphene contact stacks reported in this article. This contact resistance is also the best among reported CVD grown graphene contacted MoS2 devices. Using more than 400 devices, we study the impact of the different metal-graphene contacts on other electrical parameters such as hysteresis, sub-threshold swing and threshold voltage. The metal-graphene contact stack transfer technique represents a technologically relevant contacting approach which can be further up-scaled to larger wafer areas.

Research on carbon nanotube (CNT) films for the EUV pellicle application was initiated at imec in 2015 triggered by the remarkable optical, mechanical, and thermal properties of the CNT material. Today the advancement of the CNT material synthesis together with matured methods to fabricate thin CNT membranes make free-standing CNT films a very promising EUV pellicle candidate for high volume EUV lithography. Balancing the CNT material properties for the optimal pellicle performance in EUV scanners remains the ongoing research focus. Depending on the density and morphology of the CNTs within the film and individual CNT parameters, like number of walls, bundle size, metal catalyst content, purity etc., the optical and thermal properties of the CNT pellicle can be tuned. It is critical for the pellicle to be stable in the EUV lithography scanner environment which includes hydrogen plasma and heat loads associated with high powers beyond 250 W. Different types of CNTs, i.e. single-, double-, multi-walled CNTs and their combinations, are explored as building blocks of an optimized pellicle membrane. Optical properties of different pellicles and their ability to withstand high EUV powers in the hydrogen-based environment were tested. Transmission, spectroscopic and chemical composition mapping of the exposed free-standing CNT films are used to study the material changes that occur in the scanner-like environment. A solution is needed to extend the CNT pellicle lifetime and coating is discussed as a potential approach to protect the CNT material from hydrogen plasma damage.

Graphene metrology needs to keep up with the fast pace of developments in graphene growth and transfer. Terahertz time-domain spectroscopy (THz-TDS) is a non-contact, fast, and non-destructive characterization technique for mapping the electrical properties of graphene. Here we show several case studies of graphene characterization on a range of different substrates that highlight the versatility of THz-TDS measurements and its relevance for process optimization in graphene production scenarios.

Double gated WS 2 transistors with gate length down to 18 nm are fabricated in a 300mm Si CMOS fab. By using large statistical data sets and mapping uniformity on full 300mm wafer, we built an integration vehicle where impact of each process step can be understood and developed accordingly to enhance device performance. In-depth analysis of V T variability reveals multiple possible sources at different length scales, with the most prominent one being the channel material. The work presented here paves the way towards industrial adoption of 2D materials.

To further understand the interaction of graphene-integrated interconnects, we focus on the interface characterization of graphene-ruthenium hybrid systems. A systematic characterization is performed to quantify the charge transfer between graphene and Ru. By studying the relative band alignment, we measure interface potential barrier height and report an effective work function of 4.9 eV. Carrier concentration of 1.9E13cm−2 is obtained. Surface potential mapping suggests a downward shift of Fermi level in graphene valence band implying hole-doping on Ru substrate. Concurrent physical characterizations complement each other and fully support the conductivity gain demonstrated earlier.

Defect characterization of 2D materials is a critical aspect for their successful integration in future electronic devices. Here, a simple characterization technique is proposed that opens a path for fast, non-invasive, quality assessment of transition metal dichalcogenide (TMDC) layers, such as MoS2, and their interfaces. It relates to the correlation between substrate-induced traps and the indirect-to- direct photoluminescence peak ratio. It is shown that the indirect peak is quenched when interfacial trap sites are present. A physical mechanism is proposed to explain the observations based on different recombination mechanisms.

EUV lithography wafer production has begun and consequently maximizing yield gains importance. One key component to high-yield lithography in manufacturing is using a pellicle to hold particles out of the focal plane and thereby minimize their impact on imaging. Using a pellicle simplifies manufacturing by eliminating wafer inspections that are used to indirectly monitor the presence of printable defects on the mask. The CNT-based pellicle – a membrane consisting of a network of carbon nanotubes – offers the advantage of very high EUV transmission and has demonstrated good durability at high EUV scanner power. Moreover, the microscopic properties of the network can be tuned by modifying several CNT membrane parameters, such as the individual CNT type and diameter, the degree of bundling, the density and the coating. The challenge is balancing these CNT material parameters for optimal performance in the EUV scanner: high transmission, low impact on imaging through scattered light, and low probability for particles to pass. Each of these areas will be addressed along with simulated and experimental data illustrating the value of a CNT-based EUV pellicle solution today and for the future.

ispartof: ECS JOURNAL OF SOLID STATE SCIENCE AND TECHNOLOGY vol:7 issue:12 pages:M195-M200 ispartof: location:WA, Seattle status: published

The mechanism of graphene delamination from a Pt catalyst growth surface with electrochemical methods is studied. After a water intercalation step, an electrochemical graphene delamination process is done with a variety of different electrolytes. It is shown that (hydrogen or oxygen) bubble formation is not the main driving force to decouple graphene from its catalyst growth substrate. Ion intercalation is identified as the primary component for a fast graphene delamination process from its catalytic growth substrate. When the Pt/graphene sample is negatively charged, cations will intercalate, assuming they do not reduce within the electrochemical window of the solvent. This cation intercalation does result in graphene delamination. In the same way, anions intercalate in positively charged Pt/graphene samples when they do not react within the electrochemical window of the solvent. Furthermore, it is shown that applying a potential is sufficient (current is not needed) to induce ion intercalation and, as a result, graphene delamination. These findings open the door to avoid Na+ or K+ contamination introduced during currently described electrochemical graphene delamination. Alternative electrolytes (i.e. ammonium hydroxide and tetraethylammonium hydroxide) are proposed, due to the absence of alkali contaminants and rapid cation intercalation to delaminate graphene.

The effects of oxidants both in the channel and contact regions of MoS2 transistors are discussed through a systematic experimental study. This letter highlights the issues of partial instability in metal-organic chemical vapor deposition MoS2 and proposes a procedure, which considerably improves the electrical characteristics of back-gated transistors. By avoiding ambient exposure and layer oxidation, contact resistance can be reduced and intrinsic mobility increased by 50%.

The key steps of a transfer of two-dimensional (2D) materials are the delamination of the as-grown material from a growth substrate and the lamination of the 2D material on a target substrate. In state-of-the-art transfer experiments, these steps remain very challenging, and transfer variations often result in unreliable 2D material properties. Here, it is demonstrated that interfacial water can insert between graphene and its growth substrate despite the hydrophobic behavior of graphene. It is understood that interfacial water is essential for an electrochemistry-based graphene delamination from a Pt surface. Additionally, the lamination of graphene to a target wafer is hindered by intercalation effects, which can even result in graphene delamination from the target wafer. For circumvention of these issues, a direct, support-free graphene transfer process is demonstrated, which relies on the formation of interfacial water between graphene and its growth surface, while avoiding water intercalation between graphene and the target wafer by using hydrophobic silane layers on the target wafer. The proposed direct graphene transfer also avoids polymer contamination (no temporary support layer) and eliminates the need for etching of the catalyst metal. Therefore, recycling of the growth template becomes feasible. The proposed transfer process might even open the door for the suggested atomic-scale interlocking-toy-brick-based stacking of different 2D materials, which will enable a more reliable fabrication of van der Waals heterostructure-based devices and applications.

As Si-based electronic devices are approaching their projected scaling limits, layered two-dimensional (2D) materials such as transition metal dichalcogenides (TMDs) are extensively studied as potential new channel materials and fundamental building blocks of emerging sensors and devices.[1-2] In this context, MoS2, WS2 and WSe2 to name a few, are now available for deposition trough different top down approaches. However, their outstanding properties are often degraded during the fabrication processes required for the device integration. For example, the selective growth of 2D TMDs their patterning and the electronics properties fine tuning still remain elusive. Here we report on electrical atomic force microcopy (AFM) and beam analysis techniques which are used to develop a framework of analysis for 2D materials. The latter is applied to understand the local properties of MoS2 comparing pristine material and structures which are selectively grown and patterned.[3] Different growth techniques are investigated. After modelling the tip-sample contact system, we assess the impact of the plasma-induced damages combining the electrical AFMs and Auger emission spectroscopy. We study the local electrical properties of grain boundaries and their transport respectively in pristine and patterned structures for FET devices by conductive atomic force microscopy (C-AFM). [1] G. Fiori, F. Bonaccorso, G. Iannaccone, T. Palacios, D. Neumaier, A. Seabaugh, S. K. Banerjee, and L. Colombo, “Electronics based on two-dimensional materials,” Nat. Nanotechnol., vol. 9, no. 10, pp. 768–779, 2014. [2] Desai, S. B., Madhvapathy, S. R., Sachid, A. B., Llinas, J. P., Wang, Q., Ahn, G. H., Javey, A. (2016). MoS 2 transistors with 1-nanometer gate lengths, 354(6308), 2–6. [3] Chiappe, D., Asselberghs, I., Sutar, S., Iacovo, S., Afanas’Ev, V., Stesmans, A., … Thean, A. (2016). Controlled Sulfurization Process for the Synthesis of Large Area MoS2 Films and MoS2/WS2 Heterostructures. Advanced Materials Interfaces, 3(4), 1–10.

Despite the fact that two-dimensional MoS2 films continue to be of interest for novel device concepts and beyond silicon technologies, there is still a lack of understanding on the carrier injection at metal/MoS2 interface and effective mitigation of the contact resistance. In this work, we develop a semi-classical model to identify the main mechanisms and trajectories for carrier injection at MoS2 contacts. The proposed model successfully captures the experimentally observed contact behavior and the overall electrical behavior of MoS2 field effect transistors. Using this model, we evaluate the injection trajectories for different MoS2 thicknesses and bias conditions. We find for multilayer (>2) MoS2, the contribution of injection at the contact edge and injection under the contact increase with lateral and perpendicular fields, respectively. Furthermore, we identify that the carriers are predominantly injected at the edge of the contact metal for monolayer and bilayer MoS2. Following these insights, we have found that the transmission line model could significantly overestimate the transfer length and hence the contact resistivity for monolayer and bilayer MoS2. Finally, we evaluate different contact strategies to improve the contact resistance considering the limiting injection trajectory.

Despite rapid progress in 2D molybdenum disulfide (MoS2) research in recent years, MoS2 field-effect transistors (FETs) still suffer from a high metal-to-MoS2 contact resistance and low intrinsic mobility, which are major hindrances to their future application. We report an efficient technique to dope thin-film MoS2 FETs using a poly(vinyl-alcohol) (PVA) polymeric coating. This results in a reduction of the contact resistance by up to 30% as well as a reduction in the channel resistance to 20 kΩ sq−1. Using a dehydration process, we were able to effectively control the surface interactions between MoS2 and the more electropositive hydroxyl groups (–OH) of PVA, which provided a controllable and yet reversible increase in the charge carrier density to a value of 8.0 × 1012 cm−2. The non-covalent, thus non-destructive, PVA doping of MoS2 increases the carrier concentration without degrading the mobility, which shows a monotonic increase while enhancing the doping effect. The PVA doping technique is then exploited to create heavily doped access regions to the intrinsic MoS2 channel, which yields 200% increase of the ON-state source–drain current. This establishes PVA doping as an effective approach to enhance the transport properties of MoS2 FETs for a variety of applications.

Graphene is considered as potential candidate for future nano-interconnects. In this respect we study the Bronsted acid doping effect of single layer graphene (SLG) and few layer graphene (FLG) synthesized by chemical vapor deposition (CVD). A sheet resistance reduction of 50% is achieved by HNO3 doping of SLG, and the resulting resistivity of 9.1µźźcm is comparable to alternative metals to copper (e.g. Ru). On the other hand, synthetic FLG shows higher sheet resistance due to higher defect density. Mobility degradation at increased carrier concentration is a main limiting factor for sheet resistance reduction of CVD graphene. Display Omitted Doping of graphene with acids can efficiently increase hole concentration through charge transfer process.Resistivity comparable to BEOL metals (e.g. Ru) can be achieved by doping CVD single-layer graphene.Mobility degradation after doping is observed for both single-layer graphene and few-layer graphene.A combination of long range and short range scattering can explain the mobility behavior of single-layer graphene.Doped CVD few-layer graphene shows lower mobility and higher sheet resistance than single-layer graphene.

In this work we are electrically characterizing multilayer graphene ribbons as potential Cu replacement towards future interconnect applications. We are comparing their performance with single-layer ribbons and we are reporting on sheet resistance, mobility and mean free path. We are additionally characterizing the contact properties for Pd contacts in top and edge configuration. Our results show high current carrying capacity for the multilayer ribbons and lower sheet resistance. Edge contacts to multilayer ribbons seem a promising approach for the decrease of the contact resistivity. Values of sheet resistance Rs ~ 280 Ω and contact resistivity Rc*W ~ 325 Ω·μm are measured for multilayer samples and edge contacts. Although the calculated ribbon mean free path is high for single-layer graphene (MFPSLG ~ 60 nm), it is comparable with the MFP of Cu for the multilayer samples (MFPFLG ~ 30 nm). Intercalation is a potential approach for improvement of the multilayer wire properties.

For the integration of two-dimensional (2D) transition metal dichalcogenides (TMDC) with high-performance electronic systems, one of the greatest challenges is the realization of doping and comprehension of its mechanisms. Low-temperature atomic layer deposition of aluminum oxide is found to n-dope MoS

As EUV lithography wafer volumes increase, throughput and yield require more focus. Yield can be enhanced by introducing a pellicle to hold particles out of the focal plane and minimize their impact to imaging. Using a pellicle also minimizes the extra wafer inspections required to ensure that printable mask defects do not increase over time. However, if the associated transmission loss is high, the yield advantage is offset by reduced throughput. The CNT-based pellicle offers the advantage of very high EUV transmission. CNT pellicles have also demonstrated lifetime at 300W EUV scanner power. The challenge is balancing the CNT membrane design in three areas: physical presence/the ability to stop particles, EUV transmission/imaging impact, and lifetime in the scanner/thermal tolerance. Each of these areas will be described along with simulated and experimental data illustrating the value of a CNT-based EUV pellicle solution for the future.

Thin substrate handling has become one of the cornerstone technologies that enabled the development of 3D stacked ICs over the past years. Temporary wafer bonding has continuously improved and reached the maturity level required by volume manufacturing of first-generation devices. Yet the need remains for further development and performance increases. Indeed, the continuous push for denser interconnects has brought new requirements for a through-silicon-via technology on one side but also pushed temporary adhesive and carrier technology into the space of wafer reconstruction and fan-out WLP. On the opposite side of the semiconductor spectrum, at the early steps of the front-end-of-line processing, transistor scaling becomes more and more challenging, including demanding the integration of higher numbers of novel materials. To further increase the options of materials, a growing number of exploratory devices are considering using a layer transfer approach. The advances in temporary bonding and debonding technology is bringing the packaging and nanoscale world together.

Graphene is an ideal material for optoelectronic applications. Its photonic properties give several advantages and complementarities over Si photonics. For example, graphene enables both electro-absorption and electro-refraction modulation with an electro-optical index change exceeding 10$^{-3}$. It can be used for optical add-drop multiplexing with voltage control, eliminating the current dissipation used for the thermal detuning of microresonators, and for thermoelectric-based ultrafast optical detectors that generate a voltage without transimpedance amplifiers. Here, we present our vision for grapheme-based integrated photonics. We review graphene-based transceivers and compare them with existing technologies. Strategies for improving power consumption, manufacturability and wafer-scale integration are addressed. We outline a roadmap of the technological requirements to meet the demands of the datacom and telecom markets. We show that graphene based integrated photonics could enable ultrahigh spatial bandwidth density , low power consumption for board connectivity and connectivity between data centres, access networks and metropolitan, core, regional and long-haul optical communications.

© 2019 Elsevier B.V. Internal photoemission of electrons from uncapped monolayer graphene to insulating SiO 2 has been observed in samples prepared by water-intercalation based graphene transfer. The barrier height between the graphene Fermi level and the oxide conduction band bottom was reproducibly found to be 4.1–4.2 eV. Moreover, this value was weakly sensitive to the contacting metal work function (Al, Cu, Au). This barrier height corresponds to an effective work function of graphene close to 5.0 eV, which is nearly 0.5 eV higher than the usually reported vacuum value. ispartof: THIN SOLID FILMS vol:674 pages:39-43 status: published

We demonstrate three 4-channelWDMtransmitters, each based on four graphenesilicon electro-absorption modulators with passivated graphene, achieving similar to 2.6dB insertion loss, similar to 5.5dB extinction ratio for 8V voltage swing and similar to 10GHz 3dB-bandwidth at 0V DC bias.

Using internal photoemission of electrons, the energy position of the valence band top edge in 1 monolayer WS2 films on top of SiO2 thermally-grown on Si was monitored to evaluate the stability of the WS2 layer with respect to two critically important technological factors: exposure to air and the transfer of WS2 from the growth substrate (sapphire) onto SiO2. Contrary to previous results obtained for WS2 and MoS2 layers synthesized by metal film thermal sulfurization in H2S, the valence band top of metal-organic chemical vapor deposition grown WS2 is found to remain at 3.7 ± 0.1 eV below the conduction band bottom edge of SiO2 through different growth runs, transfer processing, and storage in air for several months. This exceptional stability indicates WS2 as a viable candidate for the wafer-scale technology implementation.

2D materials offer a pathway for further scaling of CMOS technology. However, for this to become a reality, both n-MOS and p-MOS should be realized, ideally with the same (standard) material. In the specific case of MoS2 field effect transistors (FETs), ambipolar transport is seldom reported, primarily due to the phenomenon of Fermi level pinning (FLP). In this study we identify the possible sources of FLP in MoS2 FETs and resolve them individually. A novel contact transfer technique is used to transfer contacts on top of MoS2 flake devices that results in a significant increase in the hole branch of the transfer characteristics as compared to conventionally fabricated contacts. We hypothesize that the pinning not only comes from the contact-MoS2 interface, but also from the MoS2-substrate interface. We confirm this by shifting to an hBN substrate which leads to a 10 fold increase in the hole current compared to the SiO2 substrate. Furthermore, we analyse MoS2 FETs of different channel thickness on three different substrates, SiO2, hBN and Al2O3, by correlating the p-branch I ON/I OFF to the position of oxide defect band in these substrates. FLP from the oxide is reduced in the case of Al2O3 which enables us to observe ambipolar transport in a bilayer MoS2 FET. These results highlight that MoS2 is indeed an ambipolar material, and the absence of ambipolar transport in MoS2 FETs is strongly correlated to its dielectric environment and processing conditions.

In this work, we evaluate the material properties of graphene and assess the potential application of graphene to replace copper wires in Back-End-Of-Line (BEOL) interconnects. Based on circuit and system-level simulations, high restrictions are imposed to graphene with respect to contact resistance and mean free path. Experimentally we evaluate single and multi-layer graphene wires and we measure carrier mean free paths (MFPs) above ~110nm. However, contact engineering will be the key issue for integration of graphene as interconnect. Display Omitted Decrease in mobility and MFP is observed with aggressive scaling of graphene wires.Multilayer graphene stacks need to be considered for advanced interconnects.Experimental results are in agreement with recent simulation results.Lower contact resistance is observed for few-layer graphene.The obtained mean free path in graphene is relatively high compared to Cu.

High performance integrated optical modulators are highly desired for future optical interconnects. The ultrahigh bandwidth and broadband operation potentially offered by graphene based electro-absorption modulators has attracted a lot of attention in the photonics community recently. In this work, we theoretically evaluate the true potential of such modulators and illustrate this with experimental results for a silicon integrated graphene optical electro-absorption modulator capable of broadband 10 Gb/s modulation speed. The measured results agree very well with theoretical predictions. A low insertion loss of 3.8 dB at 1580 nm and a low drive voltage of 2.5 V combined with broadband and athermal operation were obtained for a 50 mu m-length hybrid graphene-Si device. The peak modulation efficiency of the device is 1.5 dB/V. This robust device is challenging best-in-class Si (Ge) modulators for future chip-level optical interconnects.