Publications
14 results found
Malik FK, Panteli C, Goel K, et al., 2023, Improved Stability of Graphene-Coated CMOS ISFETs for Biosensing., IEEE Trans Biomed Circuits Syst, Vol: 17, Pages: 1293-1304
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 μm 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.
Panteli C, Stylianou M, Anastasiou A, et al., 2023, Rapid Detection of Bacterial Infection Using Gas Phase Time Series Analysis, 2023 IEEE SENSORS, Publisher: IEEE
Fobelets K, Panteli C, Hammour G, 2023, Simultaneous Breathing and ECG Measurements with e-Knits †
Simultaneous recording of breathing and heart rate signals was carried out on a healthy volunteer with a fully knitted, non-sports-type garment. Breathing was recorded using two knitted respiratory inductive plethysmography (RIP) sensors. Electrocardiogram (ECG) recordings were obtained from three knitted electrodes. The knitted garment design was customised for the specific requirements of RIP and ECG by adapting the needle size and/or introducing knit-in-elastic in the sensor areas. RIP was read out using an in-house-developed cross-coupled complementary oscillator circuit. The ECG was recorded using the commercial OpenBCI board. The sensors produced excellent signal quality that allowed for simple signal processing to extract information on heart and breathing rates, showing good correlation between the two.
Ramachandran S, Zhong Y, Robertson S, et al., 2022, Fast in-situ synchrotron X-ray imaging of the interfacial reaction during self-propagating exothermic reactive bonding, MATERIALIA, Vol: 23, ISSN: 2589-1529
Goel K, Panteli C, Moser N, et al., 2022, Reducing Drift in CMOS ISFET Arrays with Monolayer Graphene Sheets, Pages: 139-143
In this paper, we present the scaling of a post-processing method to reduce drift in CMOS Ion-Sensitive Field-Effect Transistor (ISFET) arrays using monolayer graphene sheets. Graphene sheets were transferred using a Polymer Assisted Graphene Transfer (PAGT) process on a 4mm x 4mm chip with a 78x56 dimensional ISFET sensor array. The resulting performance parameters: drift, capacitive attenuation, pH sensitivity, and trapped charge were found, and averaged across all active pixels in the array for 5 dies. The results show, on average, a 55% reduction in drift and an 8% reduction in pH sensitivity for monolayer graphene ISFET arrays compared to plain ISFET arrays, with no effect on trapped charge and capacitive attenuation. Graphene's impermeability limits the modification of the sensing layers while providing physisorption sites to maintain pH sensitivity for the ISFETs. Furthermore, there is no effect on the spatial distribution of performance parameters across the ISFET array associated with transferring monolayer graphene.
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.
Panteli C, Georgiou P, Fobelets K, 2021, Reduced drift of CMOS ISFET pH sensors using graphene sheets, IEEE Sensors Journal, Vol: 21, ISSN: 1530-437X
Reduction of drift in Complementary Metal Oxide-Semiconductor (CMOS) Ion-Sensitive Field-Effect Transistor (ISFET) pH sensors is demonstrated using monolayer and multilayer graphene sheets. Graphene blocks the ion penetration in the CMOS passivation layers and provides the physisorption sites needed for electrical double layer formation allowing sensing. With an in-house polymer-assisted graphene transfer (PAGT) process, monolayer and multilayer graphene sheets were manually transferred on top of the sensing membrane of CMOS ISFET sensors on a 2 by 4 mm chip. Experiments with pH buffers on five different chips were performed to extract the average performance parameters of capacitive attenuation, trapped charge, sensitivity, drift and noise. The stretched exponential function, that describes dispersion processes in amorphous solids such as silicon dioxide and silicon nitride, was modified to model the dynamic drift behaviour and analyse the effect of graphene on the performance of the sensors. The results show that on average the graphene coated ISFET sensors experience about 50% reduction in drift amplitude, up to 3 times slower surface modification and perform overall better compared to the plain unmodified devices.
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.
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.
Moser N, Panteli C, Ma D, et al., 2017, Improving the pH Sensitivity of ISFET Arrays withReactive Ion Etching, BioCAS 2017, Publisher: IEEE
In this paper, we report a method to improvesensitivity for CMOS ISFET arrays using Reactive Ion Etching(RIE) as a post-processing technique. The process etches awaythe passivation layers of the commercial CMOS process, using anoxygen (O2) and sulfur hexafluoride (SF6) plasma. The resultingattenuation and pH sensitivity are characterised for five diesetched for 0 to 15 minutes, and we demonstrate that capacitiveattenuation is reduced by 196% and pH sensitivity increasedby 260% compared to the non-etched equivalent. The spread oftrapped charge is also reduced which relaxes requirements on theanalogue front-end. The technique significantly improves the performanceof the fully-integrated sensing system for applicationssuch as DNA detection.
Panteli C, Georgiou P, Fobelets K, 2017, Optimising the performance of commercial ISFET sensors using Reactive Ion Etching, MNE 2017
Panteli C, Fobelets K, Sydoruk O, 2017, Graphene Suspended on Silicon Nanowire Arrays for Enhanced Gas Sensing, 231st ECS Meeting, ISSN: 2151-2043
Panteli C, Liu D, Sydoruk O, et al., 2016, Through graphene etching of porous Si by electroless metal assisted chemical etching, MNE
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