Tyndall National Institute - Journal Articles
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Item Enhancing InGaN LED performance via ALD-grown Al2 O3 sidewall passivation(Institute of Physics, 2025) Bayramlı, H. M.; Genc, Muhammet; Yücel, O.; Bulut, B.; Bek, A.; Demirtas, M.; Bursa Uludağ ÜniversitesiInGaN-based light-emitting diodes (LEDs) are at the forefront of solid-state lighting technologies due to their superior efficiency and broad spectral emission. However, their performance is often compromised by leakage currents, which lead to reduced external quantum efficiency. Passivation of surface defect, the need of which arises from either epitaxial growth or mesa etching, emerges as a promising strategy to mitigate leakage currents and enhance LED performance. This study compares the effects of different sidewall passivation using two dielectric materials, Al2O3 and SiO2, on the reliability and long-term stability performance of InGaN LEDs. The study conducts a comprehensive analysis to evaluate the impact of each material on reducing leakage current and improving overall device efficiency. The experimental findings of our study indicate that the LEDs with Al2O3 sidewall passivation have better long-term stability performance, lower series resistance, higher breakdown voltages, significantly lower leakage current, and up to a 19% increase in light output power compared to SiO2 sidewall passivation. These superior properties of Al2O3-passivated LEDs increase device reliability and stability. Conversely, SiO2-passivated LEDs demonstrate relatively higher leakage currents, which can be attributed to lower dielectric constant, non-uniform film deposition and incomplete defect passivation.Item Microneedle electrodes: materials, fabrication methods, and electrophysiological signal monitoring-narrative review(Springer Nature, 2025) Singh, Om Prakash; El-Badawy, Ismail M.; Sundaram, Sornambikai; O'Mahony, Conor; Higher Education Authority; Science Foundation Ireland; European Regional Development FundFlexible, microneedle-based electrodes offer an innovative solution for high-quality physiological signal monitoring, reducing the need for complex algorithms and hardware, thus streamlining health assessments, and enabling earlier disease detection. These electrodes are particularly promising for improving patient outcomes by providing more accurate, reliable, and long-term electrophysiological data, but their clinical adoption is hindered by the limited availability of large-scale population testing. This review examines the key advantages of flexible microneedle electrodes, including their ability to conform to the skin, enhance skin-electrode contact, reduce discomfort, and deliver superior signal fidelity. The mechanical and electrical properties of these electrodes are thoroughly explored, focusing on critical aspects like fracture force, skin penetration efficiency, and impedance measurements. Their applications in capturing electrophysiological signals such as ECG, EMG, and EEG are also highlighted, demonstrating their potential in clinical scenarios. Finally, the review outlines future research directions, emphasizing the importance of further studies to enhance the clinical and consumer use of flexible microneedle electrodes in medical diagnostics.Item Time-resolved eye diagrams to exploit hidden high-energy branches in a nonlinear wideband vibration-energy harvester(American Physical Society, 2023-08-01) Paul, Kankana; Roy, Saibal; Amann, Andreas; Science Foundation Ireland; Horizon 2020A wideband vibration energy harvester with multiple nonlinear forces is investigated. The nonlinearities are due to repulsive magnets and hardening springs, which gives rise to multistabilities between a number of energy branches. Not all branches are accessible by a simple up or down sweep of the driving frequency and in particular the highest energy branch is often hidden, requiring a suitable frequency schedule to be accessed. Detailed theoretical understanding of the energy branch structure along with robust experimental methods are essential for characterizing each of the energy branches to enhance the energy output from such a vibration energy harvesting system. We introduce a graphical representation in the form of eye diagrams based on time-resolved measurements of acceleration and output voltage to study the dynamical features of the different branches. This generic approach allows us to optimize the design, which results in 1.3 mW of power generated at 1 g over the 44-Hz frequency bandwidth while maintaining a small footprint of 1.23 cm3. The energy conversion ratio of the energy harvester at 120-Hz drive frequency is 0.52 for the high-energy branch.Item Low-power actuators for programmable photonic processors(Society of Photo‑Optical Instrumentation Engineers (SPIE), 2023-03-15) Khan, Muhammad Umar; Zand, Iman; Van Iseghem, Lukas; Edinger, Pierre; Jo, Gaehun; Bleiker, Simon J.; Takabayashi, Alain Y.; Antony, Cleitus; Jezzini, Moises; Talli, Giuseppe; Sattari, Hamed; Lee, Jun Su; Mallik, Arun Kumar; Verheyen, Peter; Lerma Arce, Cristina; Garcia Porcel, Marco; Jonuzi, Tigers; Picavet, Ewout; Nagarjun, K. P.; Watté, Jan; Quack, Niels; Niklaus, Frank; Gylfason, K. B.; De Buysser, Klaartje; Beeckman, Jeroen; Bogaerts, Wim; Kitayama, Ken-ichi; Jalali, BahramThe demand for efficient actuators in photonics has peaked with increasing popularity for large-scale general-purpose programmable photonics circuits. We present our work to enhance an established silicon photonics platform with low-power micro-electromechanical (MEMS) and liquid crystal (LC) actuators to enable largescale programmable photonic integrated circuits (PICs).Item Anisotropic magnetic and electrical properties in textured single phase multiferroic Bi4.5Sm0.5Ti3Fe0.8Cr0.2O15 ceramics(Elsevier, 2025) Pritam, Anurag; Abdi, Gisya; Hussian, Sabir; Sikora, Marcin; Shiv Nadar FoundationHere we report the synthesis of single-phase Cr and Sm doped Aurivillius Bi5Ti3FeO15 (SBTFO) ceramics using conventional solid-state route method. The prepared composition exhibits the anticipated four-layered Aurivillius structure having an orthorhombic crystal structure and A21am space group, as confirmed by the XRD in conjunction with the Rietveld refinement. Additionally, the doping-induced crystallite size and strain were analyzed using a Williamson Hall plot, whereas cross-sectional FESEM revealed the plate-like structure having an average crystallite size of 0.5 μm. The SBTFO ceramics demonstrate exemplary ferroelectric and ferromagnetic properties with remnant polarization (2Pr) and remnant magnetization (2Mr) of 0.96 μC/cm2 and 0.06 emug−1, respectively. The temperature and frequency dependence of dielectric study reveals a Maxwell-Wagner relaxation with a higher loss in a low frequency regime perhaps due to leakage current in the system. The frequency dependent AC conductivity investigation adheres to Jonscher's formulation, indicating that the long-range hopping mechanism governs the conduction process, with an activation energy of 0.56 eV. Non-Debye type relaxation mechanism coupled with negative temperature coefficient of resistance (NTCR) behavior was specified by temperature dependent impedance spectroscopy, whereas the modulus spectroscopy revealed the multiple relaxation phenomena. Furthermore, the impedance and modulus processes computed activation energy of 0.74 eV and 0.32 eV, respectively, indicate the involvement of distinct charge carriers in the relaxation and conduction processes. The present work illustrates a versatile approach for designing high-performance, room-temperature multiferroic materials, demonstrating their potential for next-generation industrial applications, including non-volatile memory, spintronic devices, and multifunctional sensors.
