arXiv subjects

Alba Centeno

Publications and source records attributed to Alba Centeno.

13 recordsLinked to original sources

arXiv2026

Graphene FET Process and Analysis Optimization in 200 mm Pilot Line Environment

The maturity of the chemical vapor deposition graphene-based device processing has increased from chip level demonstrations to wafer-scale fabrication in the past few years. Due to this wafer-scale, electrical characterization and analysis of the fabricated devices has become increasingly important to enable extraction of multiple parameters with minimal number of measurements for the quality control purposes critical for industrial uptake of 2D materials-based devices. As a crucial step, we demonstrate optimization of complementary metal-oxide semiconductor (CMOS) back-end-of-line (BEOL) compatible graphene field-effect transistor (GFET) fabrication and analysis including the gate stack, bottom contact, graphene patterning and encapsulation process steps. The analysis methods include atomic force microscopy, scanning electron microscopy and most importantly electrical characterization. The electrical characterization focuses on comparing different test structures and extraction methods for mobility, contact resistance, IV-curve hysteresis and doping parameters. The comparison shows that the selected measurement test structures and analysis methods can have a large impact on the extracted values and should thus be considered when comparing data sets between different sources. The analysis shows that the optimized process offers high device yield of 98 % with good doping uniformity, contact resistance and mobility as well as low IV-curve hysteresis values on 200 mm wafers.

cond-mat.mes-hall↗

arXiv2023

Wafer-scale graphene field-effect transistor biosensor arrays with monolithic CMOS readout

The reliability of analysis is becoming increasingly important as point-of-care diagnostics are transitioning from single analyte detection towards multiplexed multianalyte detection. Multianalyte detection benefits greatly from complementary metal-oxide semiconductor (CMOS) integrated sensing solutions, offering miniaturized multiplexed sensing arrays with integrated readout electronics and extremely large sensor counts. The development of CMOS back end of line integration compatible graphene field-effect transistor (GFET) based biosensing has been rapid during the last few years, both in terms of the fabrication scale-up and functionalization towards biorecognition from real sample matrices. The next steps in industrialization relate to improving reliability and require increased statistics. Regarding functionalization towards truly quantitative sensors and on-chip bioassays with improved statistics require sensor arrays with reduced variability in functionalization. Such multiplexed bioassays, whether based on graphene or on other sensitive nanomaterials, are among the most promising technologies for label-free electrical biosensing. As an important step towards that, we report wafer-scale fabrication of CMOS integrated GFET arrays with high yield and uniformity, designed especially for biosensing applications. We demonstrate the operation of the sensing platform array with 512 GFETs in simultaneous detection for sodium chloride concentration series. This platform offers a truly statistical approach on GFET based biosensing and further to quantitative and multi-analyte sensing. The reported techniques can also be applied to other fields relying on functionalized GFETs, such as gas or chemical sensing or infrared imaging.

cond-mat.mes-hall↗

arXiv2023

Wafer-scale Graphene Electro-absorption Modulators Fabricated in a 300mm CMOS Platform

Graphene-based devices have shown great promise for several applications. For graphene devices to be used in real-world systems, it is necessary to demonstrate competitive device performance, repeatability of results, reliability, and a path to large-scale manufacturing with high yield at low cost. Here, we select single-layer graphene electro-absorption modulators as test vehicle and establish their wafer-scale integration in a 300mm pilot CMOS foundry environment. A hardmask is used to shape graphene, while tungsten-based contacts are fabricated using the damascene approach to enable CMOS-compatible fabrication. By analyzing data from hundreds of devices per wafer, the impact of specific processing steps on the performance could be identified and optimized. After optimization, modulation depth of 50 $\pm$ 4 dB/mm is demonstrated on 400 devices measured using 6 V peak-to-peak voltage. The electro-optical bandwidth is up to 15.1 $\pm$ 1 1.8 GHz for 25$\mu$m-long devices. The results achieved are comparable to lab-based record-setting graphene devices of similar design and CVD graphene quality. By demonstrating the reproducibility of the results across hundreds of devices, this work resolves the bottleneck of graphene wafer-scale integration. Furthermore, CMOS-compatible processing enables co-integration of graphene-based devices with other photonics and electronics building blocks on the same chip, and for high-volume low-cost manufacturing.

physics.app-ph↗

arXiv2018

Graphene Reflectarray Metasurface for Terahertz Beam Steering and Phase Modulation

We report a THz reflectarray metasurface which uses graphene as active element to achieve beam steering, shaping and broadband phase modulation. This is based on the creation of a voltage controlled reconfigurable phase hologram, which can impart different reflection angles and phases to an incident beam, replacing bulky and fragile rotating mirrors used for terahertz imaging. This can also find applications in other regions of the electromagnetic spectrum, paving the way to versatile optical devices including light radars, adaptive optics, electro-optical modulators and screens.

physics.app-ph↗

arXiv2018

Very large scale characterization of graphene mechanical devices using a colorimetry technique

We use a scalable optical technique to characterize more than 21000 circular nanomechanical devices made out of suspended single- and double-layer graphene on cavities with different diameters ($D$) and depths ($g$). To maximize the contrast between suspended and broken membranes we used a model for selecting the optimal color filter. The method enables parallel and automatized image processing for yield statistics. We find the survival probability to be correlated to a structural mechanics scaling parameter given by $D^4/g^3$. Moreover, we extract a median adhesion energy of $Γ=$ 0.9 J/m$^2$ between the membrane and the native SiO$_2$ at the bottom of the cavities.

physics.app-ph↗

arXiv2018

Graphene mechanical pixels for Interferometric MOdulator Displays (GIMOD)

Graphene, the carbon monolayer and 2D allotrope of graphite, has the potential to impact technology with a wide range of applications such as optical modulators for high-speed communications. In contrast to modulation devices that rely on plasmonic or electronic effects, MEMS-based modulators can have wider tuning ranges albeit at a lower operating frequency. These properties make electro-optic mechanical modulators ideal for reflective-type display technologies as has been demonstrated previously with SiN membranes in Interferometric MOdulator Displays (IMODs). Despite their low-power consumption and performance in bright environments, IMODs suffer from low frame rates and limited color gamut. Double-layer graphene (DLG) membranes grown by chemical vapor deposition (CVD) can also recreate the interference effect like in IMODs as proven with drumheads displaying Newton's rings. Here, we report on the electro-optical response of CVD DLG mechanical pixels by measuring the change in wavelength-dependent reflectance of a suspended graphene drumhead as a function of electrical gating. We use a spectrometer to measure the wavelength spectrum at different voltages, and find a good agreement with a model based on light interference. Moreover, to verify that gas compression effects do not play an important role, we use a stroboscopic illumination technique to study the electro-optic response of these graphene pixels at frequencies up to 400 Hz. Based on these findings, we demonstrate a continuous full-spectrum reflective-type pixel technology with a Graphene Interferometric MOdulator Display (GIMOD) prototype of 2500 pixels per inch (ppi) equivalent to more than 12K resolution.

physics.app-ph↗

arXiv2017

Magnetoplasmonic Enhancement of Faraday Rotation in Patterned Graphene Metasurfaces

Faraday rotation is a fundamental property present in all non-reciprocal optical elements. In the THz range, graphene displays strong Faraday rotation; unfortunately, it is limited to frequencies below the cyclotron resonance. Here we show experimentally that in specifically design metasurfaces, magneto-plasmons can be used to circumvent this limitation. We find excellent agreement between theory and experiment and provide new physical insights and predictions on these phenomena. Finally, we demonstrate strong tuneability in these metasurfaces using electric and magnetic field biasing.

cond-mat.mes-hall↗

arXiv2017

Image sensor array based on graphene-CMOS integration

Integrated circuits based on CMOS (complementary metal-oxide semiconductors) are at the heart of the technological revolution of the past 40 years, as these have enabled compact and low cost micro-electronic circuits and imaging systems. However, the diversification of this platform into applications other than microcircuits and visible light cameras has been impeded by the difficulty to combine other semiconductors than silicon with CMOS. Here, we show for the first time the monolithic integration of a CMOS integrated circuit with graphene, operating as a high mobility phototransistor. We demonstrate a high-resolution image sensor and operate it as a digital camera that is sensitive to UV, visible and infrared light. The demonstrated graphene-CMOS integration is pivotal for incorporating 2d materials into the next generation microelectronics, sensor arrays, low-power integrated photonics and CMOS imaging systems covering visible, infrared and even terahertz frequencies.. The demonstrated graphene-CMOS integration is pivotal for incorporating 2d materials into the next generation microelectronics, sensor arrays, low-power integrated photonics and CMOS imaging systems covering visible, infrared and even terahertz frequencies.

cond-mat.mes-hall↗

arXiv2017

Upscaling High-Quality CVD Graphene Devices to 100 Micron-Scale and Beyond

We describe a method for transferring ultra large-scale CVD-grown graphene sheets. These samples can be fabricated as large as several cm$^2$ and are characterized by magneto-transport measurements on SiO$_2$ substrates. The process we have developed is highly effective and limits damage to the graphene all the way through metal liftoff, as shown in carrier mobility measurements and the observation of the quantum Hall effect. The charge-neutral point is shown to move drastically to near-zero gate voltage after a 2-step post-fabrication annealing process, which also allows for greatly diminished hysteresis.

cond-mat.mtrl-sci↗

arXiv2017

Non-invasive Scanning Raman Spectroscopy and Tomography for Graphene Membrane Characterization

Graphene has extraordinary mechanical and electronic properties, making it a promising material for membrane based nanoelectromechanical systems (NEMS). Here, chemical-vapor-deposited graphene is transferred onto target substrates to suspend it over cavities and trenches for pressure-sensor applications. The development of such devices requires suitable metrology methods, i.e., large-scale characterization techniques, to confirm and analyze successful graphene transfer with intact suspended graphene membranes. We propose fast and noninvasive Raman spectroscopy mapping to distinguish between freestanding and substrate-supported graphene, utilizing the different strain and doping levels. The technique is expanded to combine two-dimensional area scans with cross-sectional Raman spectroscopy, resulting in three-dimensional Raman tomography of membrane-based graphene NEMS. The potential of Raman tomography for in-line monitoring is further demonstrated with a methodology for automated data analysis to spatially resolve the material composition in micrometer-scale integrated devices, including free-standing and substrate-supported graphene. Raman tomography may be applied to devices composed of other two-dimensional materials as well as silicon micro- and nanoelectromechanical systems.

cond-mat.mtrl-sci↗

arXiv2016

Probing Electron Spin Resonance in Monolayer Graphene

The precise value of the $g$-factor in graphene is of fundamental interest for all spin-related properties and their application. We investigate monolayer graphene on a Si/SiO2 substrate by resistively detected electron spin resonance (ESR). Surprisingly, the magnetic moment and corresponding g-factor of 1.952+/-0.002 is insensitive to charge carrier type, concentration, and mobility.

cond-mat.mtrl-sci↗

arXiv2016

Colorimetry technique for scalable characterization of suspended graphene

Previous statistical studies on the mechanical properties of chemical-vapor-deposited (CVD) suspended graphene membranes have been performed by means of measuring individual devices or with techniques that affect the material. Here, we present a colorimetry technique as a parallel, non-invasive, and affordable way of characterizing suspended graphene devices. We exploit Newton rings interference patterns to study the deformation of a double-layer graphene drum 13.2 micrometer in diameter when a pressure step is applied. By studying the time evolution of the deformation, we find that filling the drum cavity with air is 2-5 times slower than when it is purged.

cond-mat.mes-hall↗

arXiv2012

Optical nano-imaging of gate-tuneable graphene plasmons

The ability to manipulate optical fields and the energy flow of light is central to modern information and communication technologies, as well as quantum information processing schemes. However, as photons do not possess charge, controlling them efficiently by electrical means has so far proved elusive. A promising way to achieve electric control of light could be through plasmon polaritons - coupled excitations of photons and charge carriers - in graphene. In this two-dimensional sheet of carbon atoms, it is expected that plasmon polaritons and their associated optical fields can be readily tuned electrically by varying the graphene carrier density. While optical graphene plasmon resonances have recently been investigated spectroscopically, no experiments so far have directly resolved propagating plasmons in real space. Here, we launch and detect propagating optical plasmons in tapered graphene nanostructures using near-field scattering microscopy with infrared excitation light. We provide real-space images of plasmonic field profiles and find that the extracted plasmon wavelength is remarkably short - over 40 times smaller than the wavelength of illumination. We exploit this strong optical field confinement to turn a graphene nanostructure into a tunable resonant plasmonic cavity with extremely small mode volume. The cavity resonance is controlled in-situ by gating the graphene, and in particular, complete switching on and off of the plasmon modes is demonstrated, thus paving the way towards graphene-based optical transistors. This successful alliance between nanoelectronics and nano-optics enables the development of unprecedented active subwavelength-scale optics and a plethora of novel nano-optoelectronic devices and functionalities, such as tunable metamaterials, nanoscale optical processing and strongly enhanced light-matter interactions for quantum devices and (bio)sensors.

cond-mat.mtrl-sci↗