Stefan D. Ilic

This work presents an asymmetric p-i-p silicon diode structure (a-p-i-p) characterized using the Transient Current Technique (TCT) with a scanning pulsed laser system. The device, fabricated on n-type silicon (3–5 Ω·cm) with two identical p+-doped meandering line electrodes (one of which is obscured by a black resin layer), was tested in photovoltaic mode (zero bias) under laser excitation at 660 nm, 980 nm, and 1064 nm wavelengths. The transient photocurrent response was recorded as the laser spot was scanned across the device surface with 0.01 mm spatial resolution. A pronounced wavelength-dependent response was observed: the shortest wavelength (660 nm) produced the largest transient current signals, while longer wavelengths (980 nm, 1064 nm) yielded progressively weaker responses. This study introduces a fundamentally new design paradigm that enables the p-i-p diode to operate in photovoltaic mode.

This work evaluates an MXene-coated PVDF strain sensor for real-time monitoring of finger motion. The sensor was fabricated by vacuum-assisted filtration with titanium contact pads and PDMS encapsulation, then mounted on the back of the index finger centered over the PIP joint. A flexion-extension protocol of approximately 45° was applied. Two acquisition paths were used: a laboratory Keithley 2450 SMU and a compact ADS1220-based readout. Both employed constant-current excitation and identical contact hardware. Raw resistance traces from the two systems exhibited the same periodic waveform associated with repeated flexion and extension. After standard filtering and peak detection, the extracted flexion timings and waveform shapes were closely aligned, with mean flexion frequencies of about 0.83 Hz for the SMU and 0.80 Hz for the ADS1220 over a one-minute record. These results indicate that the custom electronics reproduce the MXene sensor response with fidelity comparable to laboratory instrumentation, capturing strain-dependent amplitude changes. The agreement supports the feasi-bility of MXene-based sensing combined with lightweight readout hardware as a foundation for practical wearable monitoring of body movements.

The development of flexible and wearable sensors for heart rate monitoring has gained significant attention due to the increasing demand for real-time, non-invasive, and continuous cardiovascular health assessment, particularly in sports medicine, athletic performance tracking, and personalized healthcare. Among various candidate materials, polyvinylidene fluoride (PVDF) has emerged as a promising substrate due to its exceptional mechanical flexibility, lightweight nature, chemical stability, and ease of integration into wearable devices. This study introduces an innovative approach by coating PVDF membranes with MXene layers, which act as an electrically conductive channel, facilitating accurate detection of heart rate signals when used in piezoresistive mode, provided the conductive MXene layer was optimized to an appropriate thickness. Structural characterization via XRD, SEM, and SEM-EDX confirmed the successful formation of stable, layered MXene structures without signs of oxidation. Heart rate monitoring tests performed with a MXene-PVDF sensor on a pulse simulator and analyzed with the HeartPy software revealed superior sensor performance, characterized by a high signal-to-noise ratio (SNR~26.78 dB) and excellent accuracy in tracking the preset beats per minute (BPM). The results of heart rate sensing experiments demonstrated that sensors with a thin MXene conductive layer exhibit excellent sensitivity, while those featuring a thicker MXene layer displayed a lack of responsiveness. The obtained results highlight the great potential of MXene-coated polymer sensors for advanced wearable health monitoring applications, particularly in professional sports performance assessment and personalized medical diagnostics.

Flexible, wearable biomedical sensors based on laser-induced graphene (LIG) have garnered significant attention due to a straightforward fabrication process and exceptional electrical and mechanical properties. However, most relevant studies rely on commercial polyimide precursors, which suffer from inadequate biocompatibility and weak adhesion between the precursor material and the LIG layer. To address these challenges, we synthesized cross-linked polyurethanes (PUs) with good biocompatibility and used them as substrates for LIG-based wearable pulse sensors. During fabrication, we employed two methods of LIG transfer to achieve optimal transfer yield. We adjusted the thickness of PU films and tailored their mechanical and physicochemical properties by varying the soft segment content to achieve optimal sensor performance. Our findings demonstrate that the success of LIG transfer is strongly influenced by the structure and composition of the polymeric substrate. Tensile testing revealed that increasing the soft segment content in PU films significantly improved their tensile strength, elongation at break, and flexibility, with PU based on 50 wt.% soft segment content (PU-50) showing the best mechanical properties. LIG exhibited minimal sensitivity to humidity, while PU films maintained high transparency (>80% at 500 nm), and PU-50 was non-toxic, with less than 5% lactate dehydrogenase (LDH) release in endothelial cell cultures, confirming its biocompatibility. Adhesion tests demonstrated that LIG transferred onto PU-50 exhibited significantly stronger adhesion compared to other tested substrates, with only a 30% increase in electrical resistance after the Scotch tape test, ensuring stability for wearable sensors. The optimal substrate, a semicrystalline PU-50, yielded superior transfer efficiency. Among all tested sensors, the LIG/PU-50, featuring a 77 μm thick substrate with good mechanical properties and improved adhesion, exhibited the highest signal-to-noise ratio (SNR). This study showcases a skin-safe LIG/PU-based pulse sensor that has significant potential for applications as a wearable patch in medical and sports monitoring.

We report on a procedure for extracting the SPICE model parameters of a RADFET sensor with a dielectric HfO₂/SiO₂ double-layer. RADFETs, traditionally fabricated as PMOS transistors with SiO₂, are enhanced by incorporating high-k dielectric materials such as HfO₂ to reduce oxide thickness in modern radiation sensors. The fabrication steps of the sensor are outlined, and model parameters, including the threshold voltage and transconductance, are extracted based on experimental data. Experimental setups for measuring electrical characteristics and irradiation are described, and a method for determining model parameters dependent on the accumulated dose is provided. A SPICE model card is proposed, including parameters for two dielectric thicknesses: (30/10) nm and (40/5) nm. The sensitivities of the sensors are 1.685 mV/Gy and 0.78 mV/Gy, respectively. The model is calibrated for doses up to 20 Gy, and good agreement between experimental and simulation results validates the proposed model.