180 results found
Calvo-Gallego J, Delgado-Notario JA, Minin OV, et al., 2023, Enhancing resolution of terahertz imaging systems below the diffraction limit, Optics and Laser Technology, Vol: 164, ISSN: 0030-3992
We report on resolution enhancement of sub-terahertz (THz) images by using the terajet effect. A mesoscale cuboid dielectric particle, used to establish the terajet, was placed in front of an object located at the focus of the THz beam. The object under study was based on a printed circuit board (PCB) perforated with different holes with diameters ranging from 1.8 to 3.0 mm and separated from each other by a distance that varies from 0.25 to 4 mm. The sample was illuminated by a continuous wave source at a frequency of 0.3 THz and the image was obtained using a sensor based on a strained-Si Field-Effect Transistor. The image was formed pixel-by-pixel in a transmission mode configuration. A clearer image with enhanced resolution was obtained when the mesoscale cube was introduced in the optical path. The terajet effect made possible to resolve a separation between holes of around 0.5 mm (lower than the wavelength, 1 mm), that is, below the diffraction limit. The method described is easy to implement, cost effective and could be used to improve the resolution of any real imaging system.
Malik FK, Panteli C, Goel K, et al., 2023, Improved Stability of Graphene-Coated CMOS ISFETs for Biosensing., IEEE Trans Biomed Circuits Syst, Vol: PP
A polymer-assisted graphene transfer method is used to transfer sheets of monolayer and multilayer graphene onto the passivation layer of ion-sensitive field effect transistor arrays. The arrays are fabricated using commercial 0.35 μ m complementary metal-oxide-semiconductor (CMOS) technology and contain 3874 pixels sensitive to pH changes on the top silicon nitride surface. By inhibiting dispersive ion transport and hydration of this underlying nitride layer, the transferred graphene sheets help address non-idealities in the sensor response while retaining some pH sensitivity due to the presence of ion adsorption sites. Improvements in hydrophilicity and electrical conductivity of the sensing surface after graphene transfer, as well as in-plane molecular diffusion along the graphene-nitride interface, also greatly improve spatial consistency across an array, allowing for ∼20% more pixels to remain within operating range and enhancing sensor reliability. Multilayer graphene offers a better performance trade-off than monolayer graphene, reducing drift rate by ∼25% and drift amplitude by ∼59% with minimal reduction in pH sensitivity. Monolayer graphene offers slightly better temporal and spatial uniformity in performance of a sensing array, which is associated with the consistency in layer thickness and a lower defect density.
Fobelets K, Hammour G, Thielemans K, 2023, Knitted ECG Electrodes in Relaxed Fitting Garments, IEEE Sensors Journal, Vol: 23, Pages: 5263-5269, ISSN: 1530-437X
A wide range of signal quality indices (SQIs) related to statistical methods are used to guide the optimization process of knitted textile electrodes for electrocardiogram (ECG) recordings. The electrode structure and composition as well as their integration into a garment are evaluated in view of a fully knitted garment. The dry electrodes with the best SQIs are obtained by using conductive yarn only with a compact knit structure and a medium level of roughness. The best SQIs for the e-garment were obtained by sewing electrodes at their edges only, into the knitted garment. This implementation outperforms the intarsia and double-knit method as it allows the garment some independent movement from the electrodes, reducing motion artifacts. Tests done on a healthy volunteer demonstrate excellent system performance under gentle ambulation. The advantage of using SQIs in the optimization process of dry textile ECG electrodes is that they offer a quantitative benchmark against which to compare other approaches. The fully knitted clothing allows for more relaxed e-garments when gentle ambulation is considered.
Fobelets K, Panteli C, Hammour G, 2023, Simultaneous Breathing and ECG Measurements with e-Knits, E-Textiles 2022, Publisher: MDPI
Malik FK, Fobelets K, 2022, A review of thermal rectification in solid-state devices, JOURNAL OF SEMICONDUCTORS, Vol: 43, ISSN: 1674-4926
Kiener K, Anand A, Fobelets W, et al., 2022, Low power respiration monitoring using wearable 3D knitted helical coils., IEEE Sensors Journal, Vol: 22, Pages: 1374-1381, ISSN: 1530-437X
We demonstrate a novel low power inductive wearable plethysmography system. This consists of ultra-sensitive 3D knitted helical coils integrated in a garment and an oscillator circuit with high quality factor. The low power oscillator is built using two cross coupled FET pairs with low capacitance drawing only 95 μA during operation and with a response time smaller than 10 μs . The sensor system is linear, with negligible hysteresis. The best compromise in sensitivity and power consumption is obtained with a 3D knitted helical coil using jersey knit with elastic yarn, a lower knitting needle size than recommended for the yarn and minimizing both the number of stitches per winding as well as the stitches containing metal. A sensitivity of 2.7 kHz per mm change in circumference with a power consumption of 6.85 mW per 30 ms measurement time is reported. This system can be used for long term breathing monitoring using a garment indistinguishable from everyday clothing.
Calvo-Gallego J, Delgado-Notario JA, Minin O, et al., 2022, Electromagnetic Simulation to Determine Mesoscopic Dielectric Particle Parameters for Optimal Terajet Effect, 47th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), Publisher: IEEE, ISSN: 2162-2027
Fobelets K, Panteli C, 2022, Ambulatory Monitoring Using Knitted 3D Helical Coils †
We present a highly sensitive wearable angular position sensor to measure joint movement. The sensor is a 3D helical coil knitted in the sleeve of a garment by circularly knitting thin insulated metal wire and yarn simultaneously. The sensing mechanism is based on the variation of the mutual inductance between windings. A 167 μH change is measured for knee movement from fully stretched to completely bent. A double cross coupled FET pair transforms the low-Q coils into a high-Q system giving a maximum frequency variation of 145 kHz for knee bending.
Kiener K, Anand A, Fobelets W, et al., 2022, Respiratory Inductive Plethysmography System for Knitted Helical Coils †
Three-dimensional knitted helical coils are very sensitive inductive sensors that can be used to monitor breathing. Their inductance is high and the quality factor relatively low. A read-out circuit is designed and tested to track the inductance variations during circumference changes of a phantom chest. The challenge of the low-quality factors of the coil is resolved by designing a double cross-coupled FET pair with low capacitance. A digital counter records the frequency. A microprocessor samples the signal every 250 ms to minimize power consumption.
Fobelets K, Sareen KS, Thielemans K, 2021, Magnetic coupling with 3D knitted helical coils, Sensors and Actuators A: Physical, Vol: 332, Pages: 1-9, ISSN: 0924-4247
Continuous power supply for wearable electronics can be facilitated using wireless power transfer (WPT). We use a 3D knitted helical coil as the receiver coil in the wrist or the waist of a garment. This 3D knitted helical coil is a novel approach to integrate coils in garments that maintains full flexibility of the garment. Measurements and simulations of coil-coil coupling give compelling evidence of the feasibility of this approach for wearable WTP. The coupling factor between a closely wound and knitted coil is found to be ~0.25 and ~0.55 for adjacent coils for a knit in the border of a cuff and waist, respectively. Using a simple circuit, we demonstrate a 30% efficiency between a closely wound transmitter coil worn on the wrist and a 3D knitted helical receiver coil integrated in the cuff of a garment at 6 mm distance.
Hamid A, Fobelets K, 2021, Gated silicon nanowire for thermo-electric power generation and temperature sensing, SEMICONDUCTOR SCIENCE AND TECHNOLOGY, Vol: 36, ISSN: 0268-1242
Kang MJ, Kim MS, Jang SH, et al., 2021, Internal Thermoelectric Cooling in Nanosheet Gate-All-Around FETs Using Schottky Drain Contacts, IEEE TRANSACTIONS ON ELECTRON DEVICES, Vol: 68, Pages: 4156-4160, ISSN: 0018-9383
Panteli C, Georgiou P, Fobelets K, 2021, Reduced Drift of CMOS ISFET pH Sensors Using Graphene Sheets, IEEE SENSORS JOURNAL, Vol: 21, Pages: 14609-14618, ISSN: 1530-437X
Minin IV, Minin OV, Salvador-Sanchez J, et al., 2021, Responsivity enhancement of a strained silicon field-effect transistor detector at 0.3 THz using the terajet effect, OPTICS LETTERS, Vol: 46, Pages: 3061-3064, ISSN: 0146-9592
Calvo-Gallego J, Delgado-Notario JA, Velazquez-Perez JE, et al., 2021, Numerical Study of the Coupling of Sub-Terahertz Radiation to n-Channel Strained-Silicon MODFETs, SENSORS, Vol: 21
Calvo-Gallego J, Delgado-Notario JA, Ferrando-Bataller M, et al., 2021, Electromagnetic Simulation of the Sub-THz Radiation Coupling to n-channel strained-silicon MODFETs, 46th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz), Publisher: IEEE, ISSN: 2162-2027
Minin I, Minin O, Salvador-Sanchez J, et al., 2021, Imaging resolution enhancement using terajet effect at 0.3 THz, Conference on Emerging Imaging and Sensing Technologies for Security and Defence VI, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Delgado-Notario JA, Calvo-Gallego J, Velazquez-Perez JE, et al., 2020, Effect of the Front and Back Illumination on Sub-Terahertz Detection Using n-Channel Strained-Silicon MODFETs, APPLIED SCIENCES-BASEL, Vol: 10
Fobelets K, 2020, Knitted coils as breathing sensors, Sensors and Actuators A: Physical, Vol: 306, Pages: 1-5, ISSN: 0924-4247
A new implementation of a wearable respiratory inductive plethysmography garment is obtained by knitting a 250 μm thin insulted Cu wire simultaneously with yarn in the round. This was used to integrate a knitted coil in the body of a baby romper suit. During simulated breathing the diameter of knitted coil changes by stretching the knit circularly, causing a variation of the self-inductance of the coil. Coils with 5 rows of integrated metal wire with different stitch types and patterns were investigated to determine their influence on inductance, series resistance and sensitivity. We observed that knit styles that reduce the resistance of the coil, such as lace and jacquard also reduce the inductance and flexibility of the garment. Jacquard with three colours and one metal wire for each colour, gave the highest coil quality factor but also the poorest flexibility. We found that 1/1 rib stitch has the highest self-inductance for all yarn types. Its sensitivity of 0.5 – 0.6 μH/cm is similar to stockinette stitch except when elastic viscose yarn is used. Coils in stockinette stitch and elastic viscose yarn have the highest sensitivity of 0.84 μH/cm. No hysteresis in self-inductance was observed for circumference variations between 44 and 53 cm of the body of the baby romper in 1/1 rib stitch due to the elasticity of knitted garments.
Kang MJ, Myeong I, Fobelets K, 2020, Geometrical influence on Self Heating in Nanowire and Nanosheet FETs using TCAD Simulations, IEEE Electron Devices Technology and Manufacturing Conference (EDTM), Publisher: IEEE
Inductor coils are integrated in many wearable garments for EM wave screening, heating and health monitoring. This paper presents a critical evaluation of the inductor characteristics of circular weft knitted coils for applications in e-textiles. Inductors are knitted using circular needles with thin insulated metal wire and yarn knitted together. The resulting helical coils are characterized as a function of number of turns, coil diameter, needle size, and insulated metal wire material. The results are compared to wound coils. Simulations of the knitted and wound coils show close agreement with the experimental results and confirm a higher inductance for the knits compared to the wound coils with the same pitch between turns. The parasitic coil capacitance is higher in the knit due to the vertical legs of the stitches, absent in wound coils. Knits with thin Cu and Litz wires result in flexible and wearable textile coils.
Moser N, Panteli C, Fobelets K, et al., 2019, Mechanisms for enhancement of sensing performance in CMOS ISFET arrays using reactive ion etching, Sensors and Actuators B: Chemical, Vol: 292, Pages: 297-307, ISSN: 0925-4005
In this work, we investigate the impact of successively removing the passivation layers of ISFET sensors implemented in a standard CMOS process to improve sensing performance. Reactive ion etching is used as a post-processing technique of the CMOS chips for uniform and accurate etching. The removal of the passivation layers addresses common issues with commercial implementation of ISFET sensors, including pH sensitivity, capacitive attenuation, trapped charge, drift and noise. The process for removing the three standard layers (polyimide, Si3N4 and SiO2) is tailored to minimise the surface roughness of the sensing layer throughout an array of more than 4000 ISFET sensors. By careful calibration of the plasma recipe we perform material-wise etch steps at the top and middle of the nitride layer and top of the oxide layer. The characterisation of the ISFET array proves that the location of the trapped charge in the passivation layers is mainly at the interface of the layers. Etching to the top of the oxide layer is shown to induce an improvement of 80% in the offset range throughout the array and an increase in SNR of almost 40 dB compared to the non-processed configuration. The performance enhancement demonstrates the benefit of a controlled industry-standard etch process on CMOS ISFET array system-on-chips.
Marchese M, Angeli L, Ilieva M, et al., 2019, C-EXTENDED: EXTENDING THE ERASMUS EXPERIENCE BEYOND MOBILITY, 11th International Conference on Education and New Learning Technologies (EDULEARN), Publisher: IATED-INT ASSOC TECHNOLOGY EDUCATION & DEVELOPMENT, Pages: 4053-4061, ISSN: 2340-1117
Fobelets K, Panteli C, Sydoruk O, et al., 2018, Ammonia sensing using arrays of silicon nanowires and graphene, Journal of Semiconductors, Vol: 39, ISSN: 1674-4926
Ammonia (NH3) is a toxic gas released in different industrial, agricultural and natural processes. It is also a biomarker for some diseases. These require NH3 sensors for health and safety reasons. To boost the sensitivity of solid-state sensors, the effective sensing area should be increased. Two methods are explored and compared using an evaporating pool of 0.5 mL NH4OH (28% NH3). In the first method an array of Si nanowires (Si NWA) is obtained via metal-assisted-electrochemical etching to increase the effective surface area. In the second method CVD graphene is suspended on top of the Si nanowires to act as a sensing layer. Both the effective surface area as well as the density of surface traps influences the amplitude of the response. The effective surface area of Si NWAs is 100 × larger than that of suspended graphene for the same top surface area, leading to a larger response in amplitude by a factor of ~7 notwithstanding a higher trap density in suspended graphene. The use of Si NWAs increases the response rate for both Si NWAs as well as the suspended graphene due to more effective NH3 diffusion processes.
Panteli C, Georgiou P, Fobelets K, 2018, Performance improvement of commercial ISFET sensors using reactive ion etching, Microelectronic Engineering, Vol: 192, Pages: 61-65, ISSN: 0167-9317
Reactive Ion Etching (RIE) is used to improve the performance of commercial Complementary Metal Oxide Semiconductor (CMOS) Ion-Sensitive Field-Effect Transistors (ISFETs) by thinning the top passivation layers inherent of the CMOS fabrication process. Using a combination of O2 and SF6 in 50% ratio, both polyimide and Si3N4 layers are etched in one etching step. Etching for different times we find the right remaining layer thickness for best ISFET performance to be ∼1 μm of SiO2. The results show an increase in pH sensitivity of 125%, a 5700% increase in passivation capacitance and a 96% reduction in capacitive attenuation. The RIE etch recipe can be used on multi-project wafers (MPW) to boost CMOS sensor performance.
Plasma waves in gated 2-D systems can be used to efficiently detect THz electromagnetic radiation. Solid-state plasma wave-based sensors can be used as detectors in THz imaging systems. An experimental study of the sub-THz response of II-gate strained-Si Schottky-gated MODFETs (Modulation-doped Field-Effect Transistor) was performed. The response of the strained-Si MODFET has been characterized at two frequencies: 150 and 300 GHz: The DC drain-to-source voltage transducing the THz radiation (photovoltaic mode) of 250-nm gate length transistors exhibited a non-resonant response that agrees with theoretical models and physics-based simulations of the electrical response of the transistor. When imposing a weak source-to-drain current of 5 μA, a substantial increase of the photoresponse was found. This increase is translated into an enhancement of the responsivity by one order of magnitude as compared to the photovoltaic mode, while the NEP (Noise Equivalent Power) is reduced in the subthreshold region. Strained-Si MODFETs demonstrated an excellent performance as detectors in THz imaging.
shougee A, Konstantinou F, Albrecht T, et al., 2018, Cyclic voltammetry peaks due to deep level traps in Si nanowire array electroes, IEEE Transactions on Nanotechnology, Vol: 17, Pages: 154-160, ISSN: 1536-125X
When metal-assisted chemical etching (MACE) is used to increase the effective surface area of Si electrodes for electrochemical capacitors, it is often found that the cyclic voltammetry characteristics contain anodic and cathodic peaks. We link these peaks to the charging-discharging dynamics of deep level traps within the nanowire system. The trap levels are associated with the use of Ag in the MACE process that can leave minute amounts of Ag residue within the nanowire system to interact with the H2O layer surrounding the nanowires in a room temperature ionic liquid. The influence of the traps can be removed by shifting the Fermi level away from the trap levels via spin-on doping. These results in lower capacitance values but improved charge-discharge cycling behavior. Low-frequency noise measurements proof the presence or absence of these deep level traps.
Delgado Notario JA, Javadi E, Velazquez JE, et al., 2017, Detection of terahertz radiation using submicron field effect transistors and their use for inspection applications, Conference on Millimetre Wave and Terahertz Sensors and Technology X, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, ISSN: 0277-786X
Hamid A, Fobelets K, Enrique Velazquez-Perez J, 2017, Thermo-Electric Power Generators using Gated Silicon Nanowires, 11th UKSim-AMSS European Modelling Symposium on Computer Modelling and Simulation (EMS), Publisher: IEEE, Pages: 168-173, ISSN: 2473-3539
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