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Papers by Laurent A Francis

Sensors and Actuators B …, Jan 1, 2011

14th Biodetection …, 2009

Please be patient while the object screen loads. Change Site View : Select a site UCL FUNDP FUSL... more Please be patient while the object screen loads. Change Site View : Select a site UCL FUNDP FUSL FUCaM. ...

… European Conference of …, Jan 1, 2009

Circuits and Systems …, Jan 1, 2010

Abstract Innovative, simple, miniaturized, low-cost and low-power consumption devices are require... more Abstract Innovative, simple, miniaturized, low-cost and low-power consumption devices are required in future medical applications. In our laboratory we have developed different devices in this field. Firstly, oxide aluminum-coated interdigitated (ID) Al capacitors have been successfully tested for DNA hybridization test (down to 30 pM target concentrations), as well as for specific bacteria recognition (S. Aureus, down to 100 CFU on a sensing area of 200× 200 μm 2) with an appropriate anti-monoclonal antibody (MoAb) and finally for ...

IEEE Sensors Journal, 2000

![Research paper thumbnail of L'apprentissage par projet des microsyst`emes 'electro-m'ecaniques](https://a.academia-assets.com/images/blank-paper.jpg)

IEEE Transactions on Electron Devices, 2015

Procedia Engineering, 2014

ABSTRACT We developed an ultra-low power MEMS hydrogen (H2) sensor performing high dynamics toget... more ABSTRACT We developed an ultra-low power MEMS hydrogen (H2) sensor performing high dynamics together with high sensitivity up to the Lower Explosive Limit (LEL), i.e. 4% vol. H2 in dry air. The architecture consists of Al clamped-clamped beams (700 nm- thick, 800 μm-total width, 140 or 240 μm-length) with both ends made of a Pd/Al bimorph (200/700 nm-thick) on a quarter of its length, acting as actuators, released above a split-bottom electrode. The initial stress defines the initial deflection of the structure while the Pd-hydriding induces compressive stress variation in the Pd actuator layer and therefore the membrane deflection. A capacitive transduction is used to continuously measure the gap variation due to the H2 absorption and hydriding kinetic. Results show a fast response time of less than 5 s for an effective concentration of about 0.2% vol. H2 in dry air or N2 mixture, with no cross sensitivity.

ABSTRACT We have proposed and demonstrated a novel sequence in MEMS fabrication process flow. The... more ABSTRACT We have proposed and demonstrated a novel sequence in MEMS fabrication process flow. The novel MEMS fabrication process flow can be shortly described as a “packaging first, MEMS release second”, whereas a standard process starts form MEMS release and ends up with packaging. The process is explored on a 3D capacitive MEMS sensor (3 × 3 mm2). Unreleased wafer is singulated by sawing on individual dies, then the individual sensor is mounted to the package, wire bonded and encapsulated. Because the sensors are still unreleased there is no damage occurred during the assembly. However the choice for the encapsulant material is not evident. The encapsulant must survive the chemical attack during the MEMS release process (mixture of 73%HF and IPA (isopropanol)), followed by a triple rinse in IPA. We pre-selected 6 different encapsulants: a silicone-, an epoxy- and an urethane-based. At least one encapsulant passed the acceptance criteria: there is no delamination, there is no texture change and the encapsulant maintains a sufficient mechanical adhesion. Additionally to that we measured micro-hardness of the encapsulant before and after the HF release test. We also performed an electrical characterization of the flow meter sensor before and after the HF release and we detected no changes in the sensor's performance caused by HF exposure. We have proposed and demonstrated a novel sequence for MEMS fabrication. We packaged the sensor first, and performed the release after that. The key enabler for the novel process is the encapsulant which can withstand an exposure to the release solution (73%HF:IPA).

2015 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), 2015

Bioinspiration & Biomimetics, 2016

The unique architecture of iridescent Morpho butterfly scales is known to exhibit different optic... more The unique architecture of iridescent Morpho butterfly scales is known to exhibit different optical responses to various vapours. However, the mechanism behind this phenomenon is not fully quantitatively understood. This work reports on process developments in the micro-fabrication of a Morpho-inspired photonic structure in atomic layer deposited (ALD) materials in order to investigate the vapour optical sensitivity of such artificial nanostructures. By developing recipes for dry and wet etching of ALD oxides, we micro-fabricated two structures: one combining Al2O3 and TiO2, and the other combining Al2O3 and HfO2. For the first time, we report the optical response of such ALD Morpho-like structures measured under a controlled flow of either ethanol or isopropyl alcohol (IPA) vapour. In spite of the small magnitude of the effect, the results show a selective vapour response (depending on the materials used).

IEEE Sensors Journal, 2016

We developed a simple and reliable method for the fabrication of sub-10-nm wide nanogaps. The sel... more We developed a simple and reliable method for the fabrication of sub-10-nm wide nanogaps. The self-formed nanogap is based on the stoichiometric solid-state reaction between metal and Si atoms during silicidation process. The nanogap width is deter- mined by the metal layer thickness. Our proposed method produces nanogaps either symmetric or asymmetric electrodes, as well as, multiple nanogaps within one unique process step for application to complex circuits. Therefore, this method provides high throughput and it is suitable for large-scale production. To demonstrate the feasibil- ity of the proposed fabrication method, nanogap resistive switches have been built and characterized. They exhibit a pronounced hysteresis with up to 103 on/off conductance ratios in air. Our results indicate that the voltages for initially electroforming the de- vice to the switch state are determinated by the nanogap sizes. However, the set and reset voltages of the device do not strongly dependent on the nanogap widths. These phenomena could be helpful to understand how the resistive switching is established.

Sensors and Actuators B: Chemical, 2015

Sensors and Actuators B …, Jan 1, 2011

14th Biodetection …, 2009

… European Conference of …, Jan 1, 2009

Circuits and Systems …, Jan 1, 2010

IEEE Sensors Journal, 2000

![Research paper thumbnail of L'apprentissage par projet des microsyst`emes 'electro-m'ecaniques](https://a.academia-assets.com/images/blank-paper.jpg)

IEEE Transactions on Electron Devices, 2015

Procedia Engineering, 2014

2015 4th International Conference on Advancements in Nuclear Instrumentation Measurement Methods and their Applications (ANIMMA), 2015

Bioinspiration & Biomimetics, 2016

IEEE Sensors Journal, 2016

Sensors and Actuators B: Chemical, 2015

"Miniaturized sensors have gained an increasing interest due to smaller sizes and reduced power c... more "Miniaturized sensors have gained an increasing interest due to smaller sizes and reduced power consumption compared to their macroscopic counterparts. Their fabrication technologies are compatible with standard integrated circuits, allowing for the co-integration with intelligent electronics either by a System-on-Chip (SOC) or by a System-in-a-Package (SIP) approach. Microsystems obtained through co-integration can run with minute power and still present excellent performances.
In this work, the design, characterization, and integration of sensing systems are assessed with a generic approach in order to obtain portable, simple, and power efficient solutions. A methodology of the instrumentation system design is proposed in order to push the maturity of the systems technology from the fundamental research to a pre-industrial stage. The proposed interfacing principle is based on the insertion of the sensor into triangular voltage oscillating circuits. The data captured by the sensor deforms the analog output of the oscillator and is extracted by mathematical methods. The methodology is applied for two applicative contexts: 1) liquid sensing, and 2) the detection of variable magnetic fields.
The first system for liquid sensing consists in an interdigitated electrodes (IDE), the sensing device is investigated and modeled using finite elements tools. The interfacing approach consists in stimulating the device with a square current wave; this results in a triangular output voltage with a shape that embeds the liquid properties, i.e., both conductivity and permittivity.
The second system is a detector of magnetic field variations, e.g., for abrupt variations of power line currents. The sensing element is a square planar inductor modeled similarly to the IDE. Being also based on a triangular voltage oscillating system, the interfacing method we built consists in varying the triangular signal frequency for each detected magnetic perturbation. Output characteristics are consequently defined to quantify the amount of magnetic perturbations captured by the inductor. The system has been successfully tested for the detection of arc faults on high-powered current lines. We demonstrate that integrating the interface in current CMOS technologies can lead to data acquisition in the µW regime.
"

Miniaturized sensors have gained an increasing interest due to smaller sizes and reduced power co... more Miniaturized sensors have gained an increasing interest due to smaller sizes and reduced power consumption compared to their macroscopic counterparts. Their fabrication technologies are compatible with standard integrated circuits, allowing for the co-integration with intelligent electronics either by a System-on-Chip (SOC) or by a System-in-a-Package (SIP) approach. Microsystems obtained through co-integration can run with minute power and still present excellent performances.
In this work, the design, characterization, and integration of sensing systems are assessed with a generic approach in order to obtain portable, simple, and power efficient solutions. A methodology of the instrumentation system design is proposed in order to push the maturity of the systems technology from the fundamental research to a pre-industrial stage. The proposed interfacing principle is based on the insertion of the sensor into triangular voltage oscillating circuits. The data captured by the sensor deforms the analog output of the oscillator and is extracted by mathematical methods. The methodology is applied for two applicative contexts: 1) liquid sensing, and 2) the detection of variable magnetic fields.
The first system for liquid sensing consists in an interdigitated electrodes (IDE), the sensing device is investigated and modeled using finite elements tools. The interfacing approach consists in stimulating the device with a square current wave; this results in a triangular output voltage with a shape that embeds the liquid properties, i.e., both conductivity and permittivity.
The second system is a detector of magnetic field variations, e.g., for abrupt variations of power line currents. The sensing element is a square planar inductor modeled similarly to the IDE. Being also based on a triangular voltage oscillating system, the interfacing method we built consists in varying the triangular signal frequency for each detected magnetic perturbation. Output characteristics are consequently defined to quantify the amount of magnetic perturbations captured by the inductor. The system has been successfully tested for the detection of arc faults on high-powered current lines. We demonstrate that integrating the interface in current CMOS technologies can lead to data acquisition in the µW regime.

The impact of different types of radiation on the electromechanical properties of materials used ... more The impact of different types of radiation on the electromechanical properties of materials used in microfabrication
and on the capacitive and piezoresistive transduction mechanisms of MEMS is investigated. MEMS technologies could revolutionize avionics, satellite and space applications provided that the stress conditions which can compromise the reliability of microsystems in these environments are well understood. Initial tests with MEMS revealed a vulnerability of some types of devices to radiation induced dielectric charging, a physical mechanism which also affects microelectronics, however integration of novel functional materials in microfabrication and the current trend to substitute SiO2 with high-k dielectrics in ICs pose new questions regarding
reliability in radiation environments. The performance of MEMS devices with moving parts could also degrade due to radiation induced changes in the mechanical properties of the materials. It is thus necessary to investigate the effects of radiation on the properties of thin films used in microfabrication and here we report on tests with γ, high energy protons and fast neutrons radiation. Prototype SOI based MEMS magnetometers which were developed in UCL are also used as test vehicles to investigate radiation effects on the reliability of magnetically actuated and capacitively coupled MEMS.

Nature provides a wide variety of micro and nanostructures with photonic band-gaps. One can admir... more Nature provides a wide variety of micro and nanostructures with photonic band-gaps. One can admire their spectral properties in some species of butterflies or beetles for instance. Beside their amazing colors, natural photonics structures have also been optimized through ages.
In this talk, we will see how borrowing photonic crystals from Nature with the support of micro and nanotechnologies can lead to new synthetic photonic structures that would improve the performances of solar cells, light-emitting diodes and nanosensors. More specifically, we will show 1) the replication of butterfly wings directly on the surface of silicon to improve the light absorption of silicon solar cells, 2) a new concept inspired by firefly to enhance the light extraction of GaN-based light-emitting diodes, and 3) the Bragg reflectors cavities of butterflies and beetles to develop new types of microsensors.
The different cases will highlight key technologies such as atomic layer deposition, nano-imprint, direct laser writing or colloids to fabricate bio-inspired photonic structures, all along with an in-depth understanding of the optical behavior of natural structures helped by the direct observation of samples, their modeling and simulation.

Nature provides a variety of micro and nano structures which can be used as templates for manufac... more Nature provides a variety of micro and nano structures which can be used as templates for manufacturing photonic sensing surfaces. For example, surfaces replicated from the wings of certain butterfly species can absorb or reflect light over a given spectral range [1]. Nowadays, nanotechnology and biomimetic technology make it possible to obtain a single replica [2], but the challenge is to carry out high throughput, cost-effective replication of such surfaces for practical applications. In this paper, we deposit a layer of Al2O3 on the surface of the butterfly wings by low temperature atomic layer deposition (ALD). The alumina coated wing is used as a mold to imprint butterfly wing pattern on poly(methylmethacrylate) (PMMA) on the surface of a SiO2/Si-wafer stack by nanoimprint lithography. The SiO2 layer is then etched down to the Si wafer using the imprinted PMMA layer as a mask. In such a way, we can obtain a stable and hard SiO2 mold, which can be used to produce in large number the butterfly wing patterns on Si substrates for improving their light absorption and carrier collection ability [3].

Recently, it was reported that Si solar cells with the Al2O3 coating show a high-efficiency [4]. We investigate the optical and electrical properties of the low-temperature ALD Al2O3 layer. According to the flat-band voltage ΔV extracted from the high frequency C-V curve, we also estimate the negative charge density in the Al2O3 layer to be 3 x 1012 /cm2, which will provide an effective field-effect passivation for reducing the surface recombination of the minority carriers. These results demonstrates large potential on applying the replicated butterfly wing patterns on Si wafer with the Al2O3 coating for photovoltaic applications with high antireflection and lower combination properties.

References:
[1] J. Huang et al., Nano Letters, 6, 2325 (2006).
[2] D.P. Gaillot et al., Physical Review E 78, 031922 (2008).
[3] S. Eon et al., Nano Letters, 10 1012 (2010).
[4] B. Hoex et al., J. Appl. Phys. 104, 113703 (2008).

Microtechnologies hold many promises to build a never-ending set of miniaturized components that ... more Microtechnologies hold many promises to build a never-ending set of miniaturized components that can help with sensing and actuation, eventually in direct combination with electronics. Since the early 70’s, they have proved their benefits through the successful commercial stories of inkjet printer heads, accelerometers, pressure sensors, telecom signal filters, data projection micromirrors, and so forth … In the biomedical domain, the concept of lab-on-a-chip (also known as microfluidics and bioMEMS) has quickly emerged as the Holy Grail for in vitro detection - although the term encompasses a very large variety of structures and measurement techniques. Other concepts have been issued and implemented for in vivo applications like cochlear or retinal implants and recording or stimulating neuronal microneedles. Applied to the biomedical field, devices engineered with microtechnologies offer many possibilities and advantages, including drastic time and cost reduction for analytical testing, diagnostics, health monitoring, surgery and re-education. Looking to use or to contribute to biomedical micro-engineering, it requires to get acquainted with the rudiments of microtechnologies and to wonder about the true advantages offered by miniaturization. It also requires to adopt a common language between experts from transverse scientific and technological domains in life sciences and engineering (electrical, material science and informatics) and to look for the societal benefits without losing sight on ethical issues. All in one, it comes to the fundamental question to be answered in this tutorial: is smaller also better?

In order to help you to get an answer to this question, the tutorial will be divided in three main parts divided between operation principles, fabrication techniques and application examples.
The first part will cover the operation principles that have the highest interest for biomedical applications. Going small means basically changing the point of view on physical and chemical behaviors: surface related effects will largely affect body and fluid motions, molecules sensing, thermal flows, … when compared to body related effects to which we, as human beings, are used. Going small is advantageous for faster detection, with minute amount of materials needed, or in order to be less invasive.

The second part will address the basics of fabrication techniques that allow us to obtain micro-engineered biomedical devices. Also, interfacing miniaturized devices with the outer world is often the most difficult part, where the electrical and fluidic continuity between macro and micro worlds has to be considered with the right attention. This last point is often merged with the device packaging; we will see that this point is far from obvious while it critically contributes to a successful real-life application of the microsystem.

The third and last part of the tutorial will address scientific challenges and opportunities offered by a comprehensive approach of microsystems as done in research performed at the Université catholique de Louvain. Examples will be presented like a wireless breath sensor used for the re-education of elderly people, or like devices for bacteria, DNA or protein detection. All in one, they will trend to indicate that small devices are adequate for biomedical applications.

On the page http://www.uclouvain.be/en-202905.html, you can find: - a Booklet of Abstracts with... more On the page http://www.uclouvain.be/en-202905.html, you can find:

- a Booklet of Abstracts with the full day program, the keynote speaker abstracts and bio's, and the list of posters
- a PDF of the following keynotes
o "Inaugural session of the Microsystems Chair " by Laurent Francis, Université catholique de Louvain
o "From Microelectronics to Microsystems " by Jean-Pierre Raskin, Université catholique de Louvain
o "RF-MEMS: an enabling technology for reconfigurable radio front-ends " by Harrie Tilmans, IMEC
o "Surface Acoustic Devices for Wireless Passive Sensors " by Sylvain Ballandras and Jean-Michel Friedt, CNRS FEMTO-ST
o "RF MEMS at EADS: Concept, Designs, and Applications " by Bernhard Schoenlinner, EADS Innovation Works
o "MEMS Industry and Market Overview " by Jérémie Bouchaud, WTC Wicht Technologie Consulting

Microsystems technologies have found their way into an impressive variety of applications, from m... more Microsystems technologies have found their way into an impressive variety of applications, from mobile phones, computers, and displays to smart grids, electric cars, and space shuttles. This multidisciplinary field of research extends the current capabilities of standard integrated circuits in terms of materials and designs and complements them by creating innovative components and smaller systems that require lower power consumption and display better performance. Novel Advances in Microsystems Technologies and their Applications delves into the state of the art and the applications of microsystems and microelectronics-related technologies.

Featuring contributions by academic and industrial researchers from around the world, this book:

Examines organic and flexible electronics, from polymer solar cell to flexible interconnects for the co-integration of micro-electromechanical systems (MEMS) with complementary metal oxide semiconductors (CMOS)
Discusses imaging and display technologies, including MEMS technology in reflective displays, the fabrication of thin-film transistors on glass substrates, and new techniques to display and quickly transmit high-quality images
Explores sensor technologies for sensing electrical currents and temperature, monitoring structural health and critical industrial processes, and more
Covers biomedical microsystems, including biosensors, point-of-care devices, neural stimulation and recording, and ultra-low-power biomedical systems
Written for researchers, engineers, and graduate students in electrical and biomedical engineering, this book reviews groundbreaking technology, trends, and applications in microelectronics. Its coverage of the latest research serves as a source of inspiration for anyone interested in further developing microsystems technologies and creating new applications.