Graphene inspired sensing devices

Graphene’s exciting characteristics such as high mechanical strength, tuneable electrical prop- erties, high thermal conductivity, elasticity, large surface-to-volume ratio, make it unique and attractive for a plethora of applications including gas and liquid sensing. Adsorption, the phys- ical bonding of molecules on solid surfaces, has huge impact on the electronic properties of graphene. We use this to develop gas sensing devices with faster response time by suspending graphene over large area (cm^2) on silicon nanowire arrays (SiNWAs). These are fabricated by two-step metal-assisted chemical etching (MACE) and using a home-developed polymer-assisted graphene transfer (PAGT) process. The advantage of suspending graphene is the removal of diffusion-limited access to the adsorption sites at the interface between graphene and its support. By modifying the Langmuir adsorption model and fitting the experimental response curves, we find faster response times for both ammonia and acetone vapours. The use of suspended graphene improved the overall response, based on speed and amplitude of response, by up to 750% on average. This device could find applications in biomedical breath analysis for diseases such lung cancer, asthma, kidney failure and more. Taking advantage of the mechanical strength of graphene and using the developed PAGT process, we transfer it on commercial (CMOS) Ion-Sensitive Field-Effect Transistor (ISFET) arrays. The deposition of graphene on the top sensing layer reduces drift that results from the surface modification during exposure to electrolyte while improving the overall performance by up to about 10^13 % and indicates that the ISFET can operate with metallic sensing membrane and not only with insulating materials as confirmed by depositing Au on the gate surface. Post- processing of the ISFET top surface by reactive ion plasma etching, proved that the physical location of trapped charge lies within the device structure. The process improved its overall performance by about 105 %. The post-processing of the ISFET could be applied for sensor performance in any of its applications including pH sensing for DNA sequencing and glucose monitoring.Open Acces

Synthesis And Characterization Of CuS By Laser-Assisted Spray Pyrolysis Deposition For pH Sensor Application

This study involves the novel application of copper sulphide (CuS) films as pH sensors. The synthesized CuS thin films were used as extended gate field effect transistor (EGFET), which was then applied as a pH sensor. The pH sensitivity, hysteresis, repeatability, stability and reliability of the CuS thin films were measured. The effects of thin film material, temperature, illumination, pH sensor thickness, sensor conductivity, sensor surface structure, precursor solvent type on crystal orientation and Metal oxide semiconductor field effect transistor (MOSFET) were studied. The CuS thin films were synthesized on several substrates using spray pyrolysis and laser-assisted spray deposition at substrate temperature of 200°C

A study of langmuir-blodgett films of valinomycin

The deposition and characterisation of Langmuir-Blodgett (LB) films containing the ionophore valinomycin are described. In particular, the thesis concentrates on two specific mixed LB systems incorporating the ionophore, namely, arachidic acid/valinomycin and L-a-phosphatidic acid dipalmitoyl (DPPA)/valinomycin. The extremely sensitive spectroscopic technique of attenuated total reflection (ATR) Fourier transform infrared (FTRIR) spectroscopy is used to investigate the interaction of these ultra-thin LB structures with aqueous solutions containing potassium ions. It is shown that LB layers of pure valinomycin do not complex with potassium ions and that, in order for complexation to occur, the ionophore must be mixed with a secondary component. The formation of the valinomycin-potassium (VM/K(^+)) complex in the arachidic acid/vahnomycin system is demonstrated and the effects of the mole-fraction of arachidic acid, and of the potassium ion concentration upon complexation are described. The IR studies also reveal profound structural changes in the fatty acid matrix upon complexation, and the important result that dissociation of the VM/K(^+) complex does not occur in this mixed system. However, it is shown that if the fatty acid molecule is replaced by the phosphohpid molecule, DPPA, then both formation and dissociation of the complex occur. The results, however, indicate that this system is unstable with loss of the LB film into the aqueous solution during immersion. A number of attempts to eliminate this problem are described. The fabrication and characterisation of ion-selective-field-effect transistors (IS-FETs) are also reported. One of the aims of the research is to develop a potassium- ion sensor, and with this in mind, the deposition of LB films onto the gate surface of the ISFET is demonstrated. The K(^+)-response of the LB film coated devices is described and the results interpreted in terms of the IR evidence

Artificial multiferroic heterostructures: magnetoelectric coupling and dynamics

Artificial multiferroics consist of materials systems engineered to have a coupling between multiple order parameters at the interface, such as between magnetic and ferroelectric order (magnetoelectric coupling) which enable the electric field control of magnetism suitable for applications in energy efficient storage or sensor devices. In this thesis we investigate two types of magnetoelectric coupling, namely, strain-mediated and charge-mediated, with a goal of characterizing their dynamic behaviour. For strain-mediated coupling, we considered a system consisting of Co dots fabricated on a ferroelectric BaTiO3 thin film, where application of an electric field led to a change in magnetic domain structure induced by the piezo-strain; however, we find that the process is stochastic as a consequence of a strong pining of the Co magnetization induced by the high surface roughness of BaTiO3 making it unsuitable for pump and probe dynamical characterization. A second type of system investigated consists of perpendicular magnetic anisotropy (PMA) structures deposited on a silicon nitride membrane gate dielectric, where we used the charge screening effects to modulate the charge carrier density at the metallic/silicon nitride interface. We studied two types of tri-layer structure (i) Pt/Co/Pt/Si3N4 and (ii) Pt/Co/Ta/Si3N4, where the Co thickness is chosen to be at spin reorientation transition. For Pt/Co/Pt, we find the presence of a charge mediated magnetoelectric coupling in the form of domain nucleation and domain wall fluctuations dependency with the electric field; from the latter we estimate a change in energy barrier height of about 10 %. For Ta/Co/Pt heterostructures a net Dzyaloshinskii-Moriya interaction (DMI) is expected and the goal was to investigate the possibility to control the DMI and/or skyrmions with applied electric fields. For these structures we observe the presence of out-of-plane spin structures in an in-plane dominant magnetized surroundings. The out-of-plane spin structures resemble a Neel type skyrmion with a dimension from 200 nm to 2 µm at room temperature under no external magnetic field. We demonstrate that such out-of-plane spin structures can be manipulated by changing the anisotropy of the system with electric fields. The measured capacitive rise time of a 200 nm thick silicon nitride membrane is ~140 ns making it suitable for high frequency characterization; however, we find that the presence of charge traps and/or charge defects in the silicon nitride membranes preclude a systematic control of the magnetization. In this context, we characterize the dielectric time response of different dielectrics, including stoichiometric silicon nitride membranes, AlN, Al2O3, BaTiO3 and MgO grown by physical vapour deposition (PVD) methods. We find that all dielectrics have a significant density of charge defects and/or charge traps. From capacitance vs frequency characterization, we find that the capacitance decreases with increasing frequency; since the mobility of carrier charges such as electrons is independent of the measuring frequency and we measure a higher capacitance at lower frequency, it is likely that we are also moving ions or possible vacancies with the applied electric field along with bound electrons, as ionic mobility with electric field is slower than electron mobility. Our results suggest the importance of characterizing and optimizing the dielectric time response for high frequency charge mediated magnetoelectric devices

Capteur d’hydrogène mos et méthode d’intégration à une technologie de transistor FDSOI

Abstract: hydrogen can be used as an energy carrier (storage) by the renewable energy industry as well as the automotive industry (fuel cell). Other industries already use hydrogen such, food processing and petroleum refineries. Hydrogen is odorless, transparent, and has a lower explosive limit of 4 %. Reliable, fast sensor are essential tools for a hydrogen safe environment. The work of this thesis provides a semiconductor-based hydrogen sensing solution. A MOS capacitor using a CMOS compatible novel Pt/Ti/ALD-Al2O3/p-Si stack. The Pt/Ti/Al2O3 sensing interface materials thicknesses are 100/5/38 nm respectively. The device can detect very low concentrations < 20 ppm. Furthermore, for a concentration of 500 ppm the response time is 56 s. the impact of testing conditions such temperature, and total gas flow have been studied. Results show that at 60℃ the device does not respond to hydrogen. And at 80℃ or higher the sensing response time is significantly reduced with increasing temperature. Furthermore, the total gas flow has an impact on the device response time and shows that a portion of the time response delay can be attributed to the chamber’s volume. Moreover, a heterogeneous integration method has been designed and presented. The latter represents a great tool for a flexible prototyping of sensors using FDSOI transistor technology. The integration has been simulated and results show promising results. The capacitive coupling feature in the FDSOI between the front and back gate is used to amplify the potential variation at the front gate. For instance, a 0.3 V hydrogen induced dipole potential can be amplified by a factor of 14 x.Le travail de cette thèse comprend la conception et la fabrication d’une technologie de capteur d’hydrogène basée sur une structure MOS. La structure est composée d’un empilement de Pt/Ti/Al2O3/p-Si. Les épaisseurs des matériaux utilisés pour la fabrication sont 100/5/38 nm (Pt/Ti/Al2O3) sur un substrat de silicium. Le capteur est capable de détecter de très faibles concentrations < 20 ppm. De plus, pour une concentration de 500 ppm, le temps de réponse est 56 s. L’impact de plusieurs conditions de test, comprenant la température et le débit total dans la chambre a été évalué. Les résultats montrent qu’à 60℃ le dispositive n’est pas capable de détecter la présence d’hydrogène. Cependant, à partir d’une température de 80℃, la réponse est très importante et le temps diminue pour encore des températures plus élevées. Le débit total dans la chambre a aussi démontré un impact sur le temps de réponse du capteur. Ce qui est aussi relié au volume de la chambre. Une intégration hétérogène ensuite a été conçue et présentée. Cette dernière est un outil flexible pour le prototypage avec des technologies de transistor FDSOI. L’intégration des deux dispositifs a été effectuée et montre de résultats prometteurs. Le couplage capacitif entre la grille avant et la grille arrière du transistor FDSOI permet d’amplifier le signal du capteur. Par exemple, une variation de potentiel de 0.3 V peut être amplifier par un facteur de 14 x, donc 4.19 V

Waveguide Mach-Zehnder interferometer for measurement of methane dissolved in water

In this dissertation, we present the development of a novel, compact and highly sensitive waveguide Mach-Zehnder interferometer to measure methane dissolved in water. Methane is a greenhouse gas, like carbon dioxide, and is emitted from both natural sources and human activities. Due to the challenges to measure dissolved methane in the sea and the vast area it covers, much of the methane cycle is unknown. In the last couple of years, there has been an up-swing in the development of subsea methane sensors. These high-end sensors rely on successfully separating the dissolved gas from the water with a membrane before the measurements, effecting the limit of detection, response time and it may give rise to hysteresis effects. Alternatively, samples can be transported to an on-shore laboratory, which can be time-consuming and expensive. We developed a methane sensor with the possibilities of direct and in-situ detection of methane with a relatively cheap and compact optical sensor-chip. A methane sensitive layer, consisting of a host-polymer and cryptophane-A, is deposited onto the chip. Cryptophane-A is a supra-molecular compound that can entrap methane molecules within its structure and thus, induce a change in the refractive index of the host-polymer. This change is detected by the evanescent field from the waveguide, in the sensing arm of the interferometer. Thus, with a change in refractive index in the sensitive layer, a phase change between the reference and the sensing arms of the interferometer is obtained. For obtaining optimal design, simulations were made for shallow silicon nitride rib waveguides with respect to the sensitivity as function of refractive index and the mode-behaviour of the waveguide. Once the design had been established, the waveguides were fabricated externally, with a core thickness of 150 nm, a rib height of 5 nm, rib widths of 1.5, 2 and 3 μm and sensing lengths of 1, 2 and 3 cm. The propagation losses were measured and simulated for tantalum pentoxide (similar to silicon nitride) strip and rib waveguides, to find the dependence of the propagation losses on the waveguide width. The sensitivity of the sensor was characterised with a diluted acid (HCl) and, in a separate measurement, by changing the temperature of the sensor coated with a polymer (PDMS). The sensor was combined with a methane sensitive layer of styrene acrylonitrile (SAN) and cryptophane-A, to detect methane gas. The sensitive layer showed a 17-folded sensitivity increase with a cryptophane-A to SAN ratio of 1:9. Methane gas was measured in the range of 300 ppm to 4.4%(v/v), with a detection limit of 17 ppm. Finally, the sensor was tested with methane in water. It was found that when the sensitive layer was exposed to water, the SAN polymer showed fractures along the surface. In an effort to circumvent the problem, a protecting layer of PDMS was deposited directly onto the SAN layer. However, after some time bubble structures appeared within the layer after exposure to water. Despite this, dissolved methane was successfully and repeatedly detected for concentration in range 9 to 46 μM. A detection limit of 49 nM was obtained, showing that the sensor is suitable for measurements of methane dissolved in water

Chemical Current-Conveyor: a new approach in biochemical computation

Biochemical sensors that are low cost, small in size and compatible with integrated circuit technology play an essential part in the drive towards personalised healthcare and the research described in this thesis is concerned with this area of medical instrumentation. A new biochemical measurement system able to sense key properties of biochemical fluids is presented. This new integrated circuit biochemical sensor, called the Chemical Current-Conveyor, uses the ion sensitive field effect transistor as the input sensor combined with the current-conveyor, an analog building-block, to produce a range of measurement systems. The concept of the Chemical Current-Conveyor is presented together with the design and subsequent fabrication of a demonstrator integrated circuit built on conventional 0.35μm CMOS silicon technology. The silicon area of the Chemical Current-Conveyor is (92μm x 172μm) for the N-channel version and (99μm x 165μm) for the P-channel version. Power consumption for the N-channel version is 30μW and 43μW for the P-channel version with a full load of 1MΩ. The maximum sensitivity achieved for pH measurement was 46mV per pH. The potential of the Chemical Current Conveyor as a versatile biochemical integrated circuit, able to produce output information in an appropriate form for direct clinical use has been confirmed by applications including measurement of (i) pH, (ii) buffer index ( ), (iii) urea, (iv) creatinine and (v) urea:creatinine ratio. In all five cases the device has been demonstrated successfully, confirming the validity of the original aim of this research project, namely to produce a versatile and flexible analog circuit for many biochemical measurement applications. Finally, the thesis closes with discussion of another potential application area for the Chemical Current Conveyor and the main contributions can be summarised by the design and development of the first: ISFET based current-conveyor biochemical sensor, called 'Chemical Current Conveyor, CCCII+' has been designed and developed. It is a general purpose biochemical analog building-block for several biochemical measurements. Real-time buffer capacity measurement system, based on the CCCII+, which exploits the imbedded analog computation capability of the CCCII+. Real-time enzyme based CCCII+ namely, Creatinine-CCCII+ and Urea-CCCII+ for real-time monitoring system of renal system. The system can provide outputs of 3 important parameters of the renal system, namely (i) urea concentration, (ii) creatinine concentration, and (ii) urea to creatinine ratio

Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors

This reprint is a collection of the Special Issue "Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors" published in Nanomaterials, which includes one editorial, six novel research articles and four review articles, showcasing the very recent advances in energy-harvesting and self-powered sensing technologies. With its broad coverage of innovations in transducing/sensing mechanisms, material and structural designs, system integration and applications, as well as the timely reviews of the progress in energy harvesting and self-powered sensing technologies, this reprint could give readers an excellent overview of the challenges, opportunities, advancements and development trends of this rapidly evolving field