Lanthanum(III)hydroxide Nanoparticles and Polyethyleneimine-Functionalized Graphene Quantum Dot Nanocomposites in Photosensitive Silicon Heterojunctions.

Lanthanides are largely used in optoelectronics as dopants to enhance the physical and optical properties of semiconducting devices. In this study, lanthanum(III)hydroxide nanoparticles (La(OH)3NPs) are used as a dopant of polyethylenimine (PEI)-functionalized nitrogen (N)-doped graphene quantum dots (PEI-NGQDs). The La(OH)3NPs-dopedPEI-NGQDs nanocomposites are prepared from La(NO)3 in a single step by a green novel method and are characterized by Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Deposited over an n-type Si wafer, the La(OH)3NPs-dopedPEI-NGQDs nanocomposites form Schottky diodes. The I-V characteristics and the photoresponse of the diodes are investigated as a function of the illumination intensity in the range 0-110 mW cm-2 and at room temperature. It is found that the rectification ratio and ideality factor of the diode decrease, while the Schottky barrier and series resistance increase with the enhancing illuminations. As a photodetector, the La(OH)3NPs-dopedPEI-NGQDs/n-Si heterojunction exhibits an appreciable responsivity of 3.9 × 10-3 AW-1 under 22 mW cm-2 at -0.3 V bias and a maximum detectivity of 8.7 × 108 Jones under 22 mW cm-2 at -0.5 V. This study introduces the green synthesis and presents the structural, electrical, and optoelectronic properties of La(OH)3NPs-dopedPEI-NGQDs, demonstrating that these nanocomposites can be promising for optoelectronic applications.

Achieving Zero-Temperature Coefficient Point Behavior by Defect Passivation for Temperature-Immune Organic Field-Effect Transistors.

Organic field-effect transistors (OFETs) have broad prospects in biomedical, sensor, and aerospace applications. However, obtaining temperature-immune OFETs is difficult because the electrical properties of organic semiconductors (OSCs) are temperature-sensitive. The zero-temperature coefficient (ZTC) point behavior can be used to achieve a temperature-immune output current; however, it is difficult to achieve in organic devices with thermal activation characteristics, according to the existing ZTC point theory. Here, the Fermi pinning in OSCs is eliminated using the defect passivation strategy, making the Fermi level closer to the tail state at low temperatures; thus threshold voltage (VT) is negatively correlated with temperature. ZTC point behaviors in OFETs are achieved by compensation between VT and mobility at different temperatures to improve its temperature immunity. A temperature-immune output current can be realized in a variable-temperature bias voltage test over 50000 s by biasing the device at the ZTC point. This study provides an effective solution for temperature-immune OFETs and inspiration for their practical application.

TCAD Simulation Studies on Ultra-Low-Power Non-Volatile Memory.

Ultra-Low-Power Non-Volatile Memory (UltraRAM), as a promising storage device, has attracted wide research attention from the scientific community. Non-volatile data retention in combination with switching at ≤2.6 V is achieved through the use of the extraordinary 2.1 eV conduction band offsets of InAs/AlSb and a triple-barrier resonant tunnelling structure. Along these lines, in this work, the structure, storage mechanism, and improvement strategies of UltraRAM were systematically investigated to enhance storage window clarity and speed performance. First, the basic structure and working principle of UltraRAM were introduced, and its comparative advantages over traditional memory devices were highlighted. Furthermore, through the validation of the band structure and storage mechanism, the superior performance of UltraRAM, including its low operating voltage and excellent non-volatility, was further demonstrated. To address the issue of the small storage window, an improvement strategy was proposed by reducing the thickness of the channel layer to increase the storage window. The feasibility of this strategy was validated by performing a series of simulation-based experiments. From our analysis, a significant 80% increase in the storage window after thinning the channel layer was demonstrated, providing an important foundation for enhancing the performance of UltraRAM. Additionally, the data storage capability of this strategy was examined under the application of short pulse widths, and a data storage operation with a 10 ns pulse width was successfully achieved. In conclusion, valuable insights into the application of UltraRAM in the field of non-volatile storage were provided. Our work paves the way for further optimizing the memory performance and expanding the functionalities of UltraRAM.

Suppressing the Intrinsic Photoelectric Response of Organic Semiconductors for Highly-Photostable Organic Transistors.

Suppressing the photoelectric response of organic semiconductors (OSs) is of great significance for improving the operational stability of organic field-effect transistors (OFETs) in light environments, but it is quite challenging because of the great difficulty in precisely modulating exciton dynamics. In this work, photostable OFETs are demonstrated by designing the micro-structure of OSs and introducing an electrical double layer at the OS/polyelectrolyte dielectric interface, in which multiple exciton dynamic processes can be modulated. The generation and dissociation of excitons are depressed due to the small light-absorption area of the microstripe structure and the excellent crystallinity of OSs. At the same time, a highly efficient exciton quenching process is activated by the electrical double layer at the OS/polyelectrolyte dielectric interface. As a result, the OFETs show outstanding tolerance to the light irradiation of up to 306 mW·cm-2 , which far surpasses the solar irradiance value in the atmosphere (≈138 mW·cm-2 ) and achieves the highest photostability ever reported in the literature. The findings promise a general and practicable strategy for the realization of photostable OFETs and organic circuits.

Effects of Charge Trapping on Memory Characteristics for HfO2-Based Ferroelectric Field Effect Transistors.

A full understanding of the impact of charge trapping on the memory window (MW) of HfO2-based ferroelectric field effect transistors (FeFETs) will permit the design of program and erase protocols, which will guide the application of these devices and maximize their useful life. The effects of charge trapping have been studied by changing the parameters of the applied program and erase pulses in a test sequence. With increasing the pulse amplitude and pulse width, the MW increases first and then decreases, a result attributed to the competition between charge trapping (CT) and ferroelectric switching (FS). This interaction between CT and FS is analyzed in detail using a single-pulse technique. In addition, the experimental data show that the conductance modulation characteristics are affected by the CT in the analog synaptic behavior of the FeFET. Finally, a theoretical investigation is performed in Sentaurus TCAD, providing a plausible explanation of the CT effect on the memory characteristics of the FeFET. This work is helpful to the study of the endurance fatigue process caused by the CT effect and to optimizing the analog synaptic behavior of the FeFET.

Mechanism of Random Telegraph Noise in 22-nm FDSOI-Based MOSFET at Cryogenic Temperatures.

In the emerging process-based transistors, random telegraph noise (RTN) has become a critical reliability problem. However, the conventional method to analyze RTN properties may not be suitable for the advanced silicon-on-insulator (SOI)-based transistors, such as the fully depleted SOI (FDSOI)-based transistors. In this paper, the mechanism of RTN in a 22-nm FDSOI-based metal-oxide-semiconductor field-effect transistor (MOSFET) is discussed, and an improved approach to analyzing the relationship between the RTN time constants, the trap energy, and the trap depth of the device at cryogenic temperatures is proposed. The cryogenic measurements of RTN in a 22-nm FDSOI-based MOSFET were carried out and analyzed using the improved approach. In this approach, the quantum mechanical effects and diffuse scattering of electrons at the oxide-silicon interface are considered, and the slope of the trap potential determined by the gate voltage relation is assumed to decrease proportionally with temperature as a result of the electron distribution inside the top silicon, per the technology computer-aided design (TCAD) simulations. The fitted results of the improved approach have good consistency with the measured curves at cryogenic temperatures from 10 K to 100 K. The fitted trap depth was 0.13 nm, and the decrease in the fitted correction coefficient of the electron distribution proportionally with temperature is consistent with the aforementioned assumption.

Improved Ferroelectric Properties in Hf0.5Zr0.5O2 Thin Films by Microwave Annealing.

In the doped hafnia(HfO2)-based films, crystallization annealing is indispensable in forming ferroelectric phases. In this paper, we investigate the annealing effects of TiN/Hf0.5Zr0.5O2/TiN metal-ferroelectric-metal (MFM) capacitors by comparing microwave annealing (MWA) and rapid thermal annealing (RTA) at the same wafer temperature of 500 °C. The twofold remanent polarization (2Pr) of the MWA device is 63 µC/cm2, surpassing that of the RTA device (40 µC/cm2). Furthermore, the wake-up effect is substantially inhibited in the MWA device. The orthorhombic crystalline phase is observed in the annealed HZO films in the MWA and RTA devices, with a reduced TiN and HZO interdiffusion in MWA devices. Moreover, the MFM capacitors subjected to MWA treatment exhibit a lower leakage current, indicating a decreased defect density. This investigation shows the potential of MWA for application in ferroelectric technology due to the improvement in remanent polarization, wake-up effect, and leakage current.

Investigation of Radiation Effects on FD-SOI Hall Sensors by TCAD Simulations.

This work investigates the responses of the fully-depleted silicon-on-insulator (FD-SOI) Hall sensors to the three main types of irradiation ionization effects, including the total ionizing dose (TID), transient dose rate (TDR), and single event transient (SET) effects. Via 3D technology computer aided design (TCAD) simulations with insulator fixed charge, radiation, heavy ion, and galvanomagnetic transport models, the performances of the transient current, Hall voltage, sensitivity, efficiency, and offset voltage have been evaluated. For the TID effect, the Hall voltage and sensitivity of the sensor increase after irradiation, while the efficiency and offset voltage decrease. As for TDR and SET effects, when the energy deposited on the sensor during a nuclear explosion or heavy ion injection is small, the transient Hall voltage of the off-state sensor first decreases and then returns to the initial value. However, if the energy deposition is large, the transient Hall voltage first decreases, then increases to a peak value and decreases to a fixed value. The physical mechanisms that produce different trends in the transient Hall voltage have been analyzed in detail.

Performance Optimization of FD-SOI Hall Sensors Via 3D TCAD Simulations.

This work investigates the behavior of fully depleted silicon-on-insulator (FD-SOI) Hall sensors with an emphasis on their physical parameters, namely the aspect ratio, doping concentration, and thicknesses. Via 3D-technology computer aided design (TCAD) simulations with a galvanomagnetic transport model, the performances of the Hall voltage, sensitivity, efficiency, offset voltage, and temperature characteristics are evaluated. The optimal structure of the sensor in the simulation has a sensitivity of 86.5 mV/T and an efficiency of 218.9 V/WT at the bias voltage of 5 V. In addition, the effects of bias, such as the gate voltage and substrate voltage, on performance are also simulated and analyzed. Optimal structure and bias design rules are proposed, as are some adjustable trade-offs that can be chosen by designers to meet their own Hall sensor requirements.

ISFET and Dex-AgNPs based portable sensor for reusable and real-time determinations of concanavalin A and glucose on smartphone.

In this paper, a portable real-time sensing device was built for Concanavalin A (Con A) and glucose detection using a smartphone. The ion-sensitive field-effect transistor (ISFET) functioning at a low working point was selected as a small-size, low-power transducer, and dextran-capped silver nanoparticles (Dex-AgNPs) served as sensitive nanoprobes on the ISFET gate. Using the affinity between Con A and carbohydrates, Con A can be captured, and thus directly detected by the ISFET/Dex-AgNPs unit; then glucose can be determined indirectly by removing Con A from the ISFET/Dex-AgNPs/Con A unit via competition with dextran. The mechanism of this competition does less harm to the sensor, allows the reusability of the sensing device, and overcomes the Debye screening of the FET device in saline solutions. Powered by a button cell, the handheld device attains excellent Con A (0.16 ng mL-1) and glucose (10 nM) detection limit, and can practically be used for at least 20 days.

Carbon dots based photoelectrochemical sensors for ultrasensitive detection of glutathione and its applications in probing of myocardial infarction.

In this work, photoelectrochemical (PEC) sensors based on carbon dots (CDs) were developed for ultrasensitive detection of glutathione (GSH) without additional catalysts. In this PEC sensing system, CDs exhibited both photoelectric and catalytic properties. Silver nanoparticles (AgNPs), graphene oxide (GO), and mesoporous silica (MS) were introduced in order to enhance the sensing properties of CDs for GSH. Among the different hybrid nanocomposites, CDs@MS based PEC sensors exhibited the best sensing properties: the sensitivity and limit of detection (LOD) for GSH were found to be 57.6nAµM- 1 and 6.2nM (S/N = 3), respectively, in the linear range 0.02-4µM. In addition, the developed PEC sensors showed a high selectivity for GSH even with interferences of other biological thiols and amino acids. The PEC sensor was successfully applied for GSH detection in human serum and probing of myocardial infarction (MI) conditions by estimating the amount of GSH in the myocardial cells of mice, which had been treated with different ischemia/ischemia-reperfusion times. These results indicated that the CDs based hybrid nanocomposites are promising candidates for the development of PEC biosensors with enhanced sensing performances.