Charge Trapping Research Articles

Photon-carrier-spin coupling in One-dimensional Ni(II) doped ZnTe Nanostructure.

The transition metal ions doping in II-VI semiconductor can produce exciton magnetic polaron (EMP) and localized EMP, in which contain longitudinal optical (LO) phonon coupling will be discussed in this paper. Transition metal ion doping in II-VI semiconductor for dilute magnetic semiconductor (DMS) show emission by magnetic polarons together with hot carrier effect that need to be understand by its optical properties. The high excitation power responsible for hot carrier effect that suppressed the charge trapping effect for low exciton binding energy (8.12 meV) semiconductor even at room temperature. The large polaron radius exhibits strong interaction between carrier and magnetic polaron results anharmonicty effect in which side-band energy overtone to LO phonon. The photon-like polariton show the polarized spin interaction with LO that show strong spin-phonon polariton at room temperature. The temperature-dependent photoluminescence spectra of Ni-doped ZnTe show free exciton (FX), FX interact with 2LO phonon-spin interaction corresponding to 3T1(3F) → 1T1(1G) and EMP peaks with ferromagnetically coupled Ni ions at 3T1(3F) → 1E(1G). In addition, other d-d transition of single Ni ions (600-900 nm) appears at low energy side. Room temperature energy shift of 14-38 meV due to localized states with density of states tails extending far into bandgap related spin induced localization at valance band. These results show spin-spin magnetic coupling and spin-phonon interaction at room temperature that open a new horizon of optically controlled dilute magnetic semiconductor applications more realistic.

Dual-Adaptive Heterojunction Synaptic Transistors for Efficient Machine Vision in Harsh Lighting Conditions.

Photoadaptive synaptic devices enable in-sensor processing of complex illumination scenes, while second-order adaptive synaptic plasticity improves learning efficiency by modifying the learning rate in a given environment. The integration of above adaptations in one phototransistor device will provide opportunities for developing high-efficient machine vision system. Here, a dually adaptable organic heterojunction transistor as a working unit in the system, which facilitates precise contrast enhancement and improves convergence rate under harsh lighting conditions, is reported. The photoadaptive threshold sliding originates from the bidirectional photoconductivity caused by the light intensity-dependent photogating effect. Metaplasticity is successfully implemented owing to the combination of ambipolar behavior and charge trapping effect. By utilizing the transistor array in a machine vision system, the details and edges can be highlighted in the 0.4% low-contrast images, and a high recognition accuracy of 93.8% with a significantly promoted convergence rate by about 5 times are also achieved. These results open a strategy to fully implement metaplasticity in optoelectronic devices and suggest their vision processing applications in complex lighting scenes.

Observation of Positive Trap Charge by Electron Holography in PMOS Device

Abstract It has been hypothesized that trap charge plays an important role in PMOS (positive-channel metal oxide semiconductor) device reliability. By using electron holography, trap charge in a spacer oxide was observed to cause an inversion of junction in an un-stressed PMOS device prepared using a Ga+ focused ion beam (FIB). Through 400°C annealing for 10 min in vacuum, trap charge in the spacer oxide dispersed and the junction recovered. Technology computer-aided design (TCAD) simulation was used to confirm the positive trap charge effect on the junction. Furthermore, the simulation showed that a low concentration of positive trap charge at the Si/SiO2 interface under the spacer led to a higher tunneling current due to an abrupt junction near the Si surface through a very localized junction inversion.

Fully solution-driven charge trapping synaptic transistor with low energy consumption for neuromorphic computing

Brain-inspired neuromorphic computing has garnered significant attention for going beyond the constraint of von Neumann architecture. To emulate the human brain functions, various artificial synaptic devices have been proposed. Due to the high reliability and the CMOS compatibility, the synaptic transistors based on charge trapping (CT) mechanism have been considered to be one of the most promising candidates. However, most of the synaptic transistors based on CT mechanism were fabricated by costly vacuum-based techniques. In this report, based on a fully solution-driven strategy, the InZnO synaptic transistors, with Nd2O3 as the CT layer and ZrO2 as the dielectric layer, were integrated. The typical synaptic behaviors, including excitatory postsynaptic current, inhibitory postsynaptic current, memory enhancement, potentiation, and depression characteristics, were simulated by modulating presynaptic spikes. It is confirmed that the fabricated synaptic transistor shows low channel conductance and low energy consumption of 0.13 pJ per synaptic event. A recognition accuracy of 93.0% was achieved for the MNIST handwritten digital image dataset by an artificial neural network simulation. This study demonstrates the feasibility of solution-processed synaptic transistors, which exhibit significant potential for the neuromorphic applications.

Photoprogrammed Multifunctional Optoelectronic Synaptic Transistor Arrays Based on Photosensitive Polymer-Sorted Semiconducting Single-Walled Carbon Nanotubes for Image Recognition.

The development of neuromorphic optoelectronic systems opens up the possibility of the next generation of artificial vision. In this work, the novel broadband (from 365 to 940nm) and multilevel storage optoelectronic synaptic thin-film transistor (TFT) arrays are reported using the photosensitive conjugated polymer (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)], F8T2) sorted semiconducting single-walled carbon nanotubes (sc-SWCNTs) as channel materials. The broadband synaptic responses are inherited to absorption from both photosensitive F8T2 and sorted sc-SWCNTs, and the excellent optoelectronic synaptic behaviors with 200 linearly increasing conductance states and long retention time >103s are attributed to the superior charge trapping at the AlOx dielectric layer grown by atomic layer deposition. Furthermore, the synaptic TFTs can achieve IOn/IOff ratios up to 106 and optoelectronic synaptic plasticity with the low power consumption (59aJ per single pulse), which can simulate not only basic biological synaptic functions but also optical write and electrical erase, multilevel storage, and image recognition. Further, a novel Spiking Neural Network algorithm based on hardware characteristics is designed for the recognition task of Caltech 101 dataset and multiple features of the images are successfully extracted with higher accuracy (97.92%) of the recognition task from the multi-frequency curves of the optoelectronic synaptic devices.

Understanding HZO Thickness Scaling in Si FeFETs: Low Operating Voltage, Fast Wake-Up, and Suppressed Charge Trapping

Understanding HZO Thickness Scaling in Si FeFETs: Low Operating Voltage, Fast Wake-Up, and Suppressed Charge Trapping

The Effect of Fluorine Doping in the Charge Trapping Layer on Device Characteristics and Reliability of E-Mode GaN MIS-HEMTs

The Effect of Fluorine Doping in the Charge Trapping Layer on Device Characteristics and Reliability of E-Mode GaN MIS-HEMTs

Performance Projection of Vacuum Gate Dielectric Doping-Free Carbon Nanoribbon/Nanotube Field-Effect Transistors for Radiation-Immune Nanoelectronics.

This paper investigates the performance of vacuum gate dielectric doping-free carbon nanotube/nanoribbon field-effect transistors (VGD-DL CNT/GNRFETs) via computational analysis employing a quantum simulation approach. The methodology integrates the self-consistent solution of the Poisson solver with the mode space non-equilibrium Green's function (NEGF) in the ballistic limit. Adopting the vacuum gate dielectric (VGD) paradigm ensures radiation-hardened functionality while avoiding radiation-induced trapped charge mechanisms, while the doping-free paradigm facilitates fabrication flexibility by avoiding the realization of a sharp doping gradient in the nanoscale regime. Electrostatic doping of the nanodevices is achieved via source and drain doping gates. The simulations encompass MOSFET and tunnel FET (TFET) modes. The numerical investigation comprehensively examines potential distribution, transfer characteristics, subthreshold swing, leakage current, on-state current, current ratio, and scaling capability. Results demonstrate the robustness of vacuum nanodevices for high-performance, radiation-hardened switching applications. Furthermore, a proposal for extrinsic enhancement via doping gate voltage adjustment to optimize band diagrams and improve switching performance at ultra-scaled regimes is successfully presented. These findings underscore the potential of vacuum gate dielectric carbon-based nanotransistors for ultrascaled, high-performance, energy-efficient, and radiation-immune nanoelectronics.

Floating gate potential of gate-all-around floating gate memory cell: parameter extraction and compact model

The compact modeling of flash memories is crucial for integrated circuit designers to carry out efficient and precise circuit-level evaluations, particularly in the case of 3D NAND flash where the 3D geometry leads to significant parasitic coupling impacts on performance. In this work, we proposed a charge-based modeling approach for gate-all-around floating gate memory cells. The compact model is based on the derived unified charge control model where the mobile charge is explicitly solved. By solving the charge balance model and taking into account voltage-dependent parasitic capacitances for accurate coupling effects, the floating gate potential is accurately computed. The simulation results are validated with numerical TCAD simulation and showed good agreement with TCAD simulation. By solving the charge balance model and considering voltage-dependent parasitic capacitances for more accurate coupling effects, the floating gate potential is accurately calculated. Additionally, the results indicate that subthreshold degradation is caused by interface trap charge in the experimental device, and the proposed model successfully replicates experimental data.

Poly‐DADMAC Functionalized Polyethylene Oxide Composite Nanofibrous Mat as Highly Positive Material for Triboelectric Nanogenerators and Self‐Powered Pressure Sensors

AbstractThe triboelectric nanogenerator (TENG) is a promising technology for self‐powered sensors and vibration‐driven energy harvesting, with its development especially influenced by the characteristics of tribomaterials. However, developing tribopositive materials with a strong cationic effect and high electron‐donating capability remains challenging. In this study, a novel polyethylene oxide@poly(diallyldimethylammonium chloride) (PEO@Poly‐DADMAC) composite nanofiber mat (NFM) is successfully fabricated using the electrospinning technique. It functions as a highly tribopositive material, particularly enhancing the performance of nanofiber‐based TENGs (NF‐TENGs). Through investigation of its physical and triboelectric properties, the study revealed that incorporating cationic Poly‐DADMAC with PEO effectively boosts NF‐TENG output by increasing the dielectric constant (twofold), electron‐donating affinities, and surface charge trapping capability. The fabricated NF‐TENG shows excellent output performance generating 980 V, a maximum power density of 5.6 Wm−2, and an ultrahigh sensitivity of 8.923 V kPa−1 which endows composite reliability for power supply and sensing capability. More importantly, the PEO@Poly‐DADMAC‐based self‐powered motion sensor with an NF‐TENG array is successfully demonstrated in multifunctional applications such as athlete activity tracking, and wireless gaming interface control. This study not only offers new insights into optimizing performance and selecting alternative tribomaterials but also provides valuable guidance for developing high‐output TENGs and highly sensitive self‐powered sensors.

Multi-functionality in de-doped poly 3-methylthiophene memristor device

Multi-functional devices are the recent trends in research, as they are cost-effective and reduce e-waste. In this study, detailed current-voltage measurement is performed on electro-polymerized Poly 3-methylthiophene (P3MT) thin film sandwiched between stainless steel (SS) and silver (Ag) electrodes, and the fabricated two-terminal device consisting of geometry SS/P3MT/Ag. Systematic and comparative measurements on partially doped P3MT devices with three dopants (TBAPF6, LiClO4 & TBABF4) helped in realizing multi-functionality. In all the devices the following multifunctional features are demonstrated: negative differential resistance (NDR), sweep voltage-controlled resistive switching, analog memory, and synaptic plasticity. Charge transport in all the devices is modeled based on charge accumulation, trapping, and de-trapping of injected carriers.

Evidence‐Based Understanding of Lateral Hole Transport During OFF‐State Stress Completing Dynamic GaN‐on‐Si Buffer Charging Model

Gallium nitride (GaN)‐on‐Si high electron mobility transistors require insulating GaN buffers, which are prone to charge trapping and result in dynamic ON‐state resistance (dR DS,on) that negatively impacts performance and reliability. Herein, simultaneous measurements of threshold voltage shift (dV TH) and dR DS,on during OFF‐state stress with microsecond time resolution are employed. Ohmic p‐GaN gate contacts enable the use of dV TH to probe charge accumulation under the gate, while dR DS,on probes charge accumulation in the gate‐drain access region. Comparison of dV TH and dR DS,on provides direct evidence of lateral hole transport in the GaN buffer when exposed to a lateral electric field in OFF‐state. This lateral hole transport causes positive charge accumulation in the buffer under the gate and triggers a newly proposed electron injection mechanism into the same region. Only by considering the combination of lateral hole transport and electron injection under the gate the observed up to fivefold dR DS,on increase in OFF‐state stress compared to back‐gating at low biases can be explained. Furthermore, another electron spillover mechanism is introduced that occurs for large positive charge accumulation under the gate and limits the maximum negative dV TH. All known and newly introduced processes during OFF‐state are summarized in a concise dynamic buffer charging model.

Mn-S chemical bond mediated Z-scheme photocatalyst boosting efficient H2 evolution with apparent quantum yield exceeding 32% under visible light

Developing a highly effective solar-to-H2 conversion system is a promising strategy for carbon neutrality. Here, we report a chemically bonded Z-scheme photocatalyst by specifically linking the conduction band site of ZnIn2S4 with the valence band site of Mn0.3Cd0.7S1-x. Deviates from the typical van der Waals interactions between two semiconductors, the in-built robust binding force (Mn-S bond) and charge transfer channel facilitates the electron mobility, minimizes detrimental deep charge trapping, and prolongs the active charge lifetime from 983 ps to 4250 ps. The sulfur vacancies in Mn0.3Cd0.7S1-x are partially refilled by atoms of the same element in ZnIn2S4 during the in-situ formation of heterojunctions, which promotes and solidates the establishment of interfacial chemical bonds. The optimal photocatalyst achieves a high quantum efficiency of 32.71 % at 420 nm. This study offers a new insight into the development of Z-Scheme heterojunctions via a synergistic approach involving doping, vacancy filling and strong interfacial chemical bonds.

A Portable Readout System for Biomarker Detection with Aptamer-Modified CMOS ISFET Array.

Biosensors based on ion-sensitive field effect transistors (ISFETs) combined with aptamers offer a promising and convenient solution for point-of-care testing applications due to the ability for fast and label-free detection of a wide range of biomarkers. Mobile and easy-to-use readout devices for the ISFET aptasensors would contribute to further development of the field. In this paper, the development of a portable PC-controlled device for detecting aptamer-target interactions using ISFETs is described. The device assembly allows selective modification of individual ISFETs with different oligonucleotides. Ta2O5-gated ISFET structures were optimized to minimize trapped charge and capacitive attenuation. Integrated CMOS readout circuits with linear transfer function were used to minimize the distortion of the original ISFET signal. An external analog signal digitizer with constant voltage and superimposed high-frequency sine wave reference voltage capabilities was designed to increase sensitivity when reading ISFET signals. The device performance was demonstrated with the aptamer-driven detection of troponin I in both reference voltage setting modes. The sine wave reference voltage measurement method reduced the level of drift over time and enabled a lowering of the minimum detectable analyte concentration. In this mode (constant voltage 2.4 V and 10 kHz 0.1Vp-p), the device allowed the detection of troponin I with a limit of detection of 3.27 ng/mL. Discrimination of acute myocardial infarction was demonstrated with the developed device. The ISFET device provides a platform for the multiplexed detection of different biomarkers in point-of-care testing.

Field Induced Off‐State Instability in InGaZnO Thin‐Film Transistor and its Impact on Synaptic Circuits

AbstractCharge storage synaptic circuits employing InGaZnO thin‐film transistors (IGZO TFTs) and capacitors are a promising candidate for on‐chip trainable neural network hardware accelerators. However, IGZO TFTs often exhibit bias instability. For synaptic memory applications, the programming transistors are predominantly exposed to asymmetric off‐state biases, and a unique field‐dependent on‐current reduction under off‐scenario is observed which may result in programming current variation. Further examination of the phenomenon is conducted with transmission line‐like method and degradation recovery tests, and current reduction can be attributed to contact resistance increase by charge trapping in the source and drain electrode and the channel region. The current decrease is subsequently formulated with a stretched exponential model with bias‐dependent parameters for quantitative circuit analysis under off‐state degradation. A neural network hardware acceleration simulator is utilized to assess the complicated impact the off‐state current degradation could instigate on on‐chip trainable IGZO TFT‐based synapse arrays. The simulation results generally demonstrate deteriorated training accuracy with aggravated off‐state instability, and the accuracy trend is elucidated from the perspective of weight symmetry point.

In-situ welding and thermal activation enabled robust nanofibers based triboelectric nanogenerator for sustainable energy harvesting

Nanofiber-based triboelectric nanogenerators (TENGs) show great promise in energy harvesting and sensing applications. However, the poor strength and the instability of the nanofiber structures lead to the constraints on the durability and the lack of stability in the output performance. In this study, BaTiO3@PVDF-HFP nanofibers were prepared by electrospinning, in which BaTiO3 nanoparticles enhanced the charge trapping ability of the nanofibers and provided nucleation sites for β-phase growth. Subsequent solvent and annealing treatment in-situ welded the nanofibers, which greatly improved the mechanical strength and stability of the nanofiber membranes. The annealing process further thermally activated the electroactive β-phase in the PVDF-HFP, which increased the surface charge density of the nanofibers. A flexible TENG based on BaTiO3@PVDF-HFP-p nanofiber was prepared to harvest mechanical energy, which could achieve a maximum output of 482.5 V and 1.9 W m−2, the voltage is more than 1.2–1.5 times higher compared to uncrosslinked nanofibers. The BaTiO3@PVDF-HFP-p-based TENG maintains ultra-stable Voc generation over 7000 cycles compared to the nanofibers without solvent and annealing treated. Finally, its practical application in harvesting ambient mechanical energy was demonstrated, which can harvest wind energy to power LEDs and small electronic devices such as temperature and humidity sensors.

Reduced interface effect of proton beam irradiation on the electrical properties of WSe2/hBN field effect transistors

Two-dimensional transition metal dichalcogenide (TMDC) semiconductors are emerging as strong contenders for electronic devices that can be used in highly radioactive environments such as outer space where conventional silicon-based devices exhibit nonideal characteristics for such applications. To address the radiation-induced interface effects of TMDC-based electronic devices, we studied high-energy proton beam irradiation effects on the electrical properties of field-effect transistors (FETs) made with tungsten diselenide (WSe2) channels and hexagonal boron-nitride (hBN)/SiO2 gate dielectrics. The electrical characteristics of WSe2 FETs were measured before and after the irradiation at various proton beam doses of 1013, 1014, and 1015 cm−2. In particular, we demonstrated the dependence of proton irradiation-induced effects on hBN layer thickness in WSe2 FETs. We observed that the hBN layer reduces the WSe2/dielectric interface effect which would shift the transfer curve of the FET toward the positive direction of the gate voltage. Also, this interface effect was significantly suppressed when a thicker hBN layer was used. This phenomenon can be explained by the fact that the physical separation of the WSe2 channel and SiO2 dielectric by the hBN interlayer prevents the interface effects originating from the irradiation-induced positive trapped charges in SiO2 reaching the interface. This work will help improve our understanding of the interface effect of high-energy irradiation on TMDC-based nanoelectronic devices.

The key role of methylenediammonium and tetrahydrotriazinium in the phase stability of FAPbI3

Formamidinium lead triiodide (FAPbI3) is the prime candidate for single-junction perovskite solar cells, despite the metastability of the phase. To improve its ambient-phase stability and produce world-record photoelectric conversion efficiencies, methylenediammonium (MDA) has been used as an additive in FAPbI3. However, the exact function and role of MDA are still uncertain. The MDA doping may exist in the perovskite lattice in either the original structure or the THTZ-H (tetrahydrotriazinium) structure. In this research, the effects of the MDA and THTZ-H doping FAPbI3 perovskite on its stability are explored by first-principles calculations. Both MDA and THTZ-H doping can improve the stability of FAPbI3 perovskite from a structural perspective due to lattice strain and stronger H–I bonds. However, the doping mechanisms differ significantly in terms of electronic properties. The MDA doping acts by the traditional passivation mechanism. It can eliminate the iodine interstitial defect states that trap charge carriers and inhibit iodine interstitial defect migration. The THTZ-H cation can directly contribute to the band edge construction in the FAPbI3 bulk. Electron delocalization in the π-conjugated ring structure lowered the frontier orbital separation of the THTZ-H organic molecule and enabled orbital overlap with the inorganic moiety. The in-depth understanding of the mechanism of improving stability in this study would facilitate the application of FAPbI3 perovskite optoelectronic devices.

Performance and reliability assessment of source work function engineered charge plasma based Ti/HfO2/Al2O3/Ge, double gate TFET

The Tunnel Field Effect Transistor (TFET) often suffers from low ON current (I ON), charge traps, and thermal variability, which limits its performance and reliability. To address these issues, the source work function engineered Ge Charge Plasma Double Gate Tunnel Field Effect Transistor (CP-DGTFET) device structure with HfO2/Al2O3 bilayer gate dielectric is designed and investigated using numerical TCAD simulations. The proposed Ti/HfO2/Al2O3/Ge CP-DGTFET device structure showed excellent DC characteristics with exceptional I ON, I ON/I OFF ratio, and minimal sub-threshold swing (S) of ∼3.04 × 10−4 A μm−1, ∼1.2 × 1010, and ∼3.4 mV/dec, respectively. Furthermore, the device’s analog characteristics displayed good transconductance, cut-off frequency, and gain bandwidth product of ∼0.75 mS/μm, ∼0.97 THz, and ∼102 GHz, respectively. Moreover, the charge trap exploration divulges that positive ITCs can enhance device performance, whereas negative ITCs can adversely impact the electrical characteristics of CP-DGTFET. Additionally, the temperature-dependent analysis showed that the OFF-state leakage current increases from ∼1.7 × 10−15 A μm−1 to 2.4 × 10−10 A μm−1 with temperature fluctuations from 275 K to 375 K. Overall, the work function-engineered CP-based Ti/HfO2/Al2O3/Ge DGTFET device structure shows great potential for improving the performance and reliability of Ge TFET technology.

Charge-Traps, Thermal Stability and Water-Uptakes of CaSiO3/EP and SiO2/EP Nanocomposites from Molecular Simulations and First-Principles Calculations

Various analytical methods were employed to elucidate the effects of filling nano-calcium-silicate or nano-silica on the electronic property, water-uptake, and thermal stability of an amine-crosslinked epoxy (EP) polymer. Molecular-mixture models consisting of a nanofiller or several calcium ions and EP crosslinked macro-molecules were used to simulate local regions of nanofiller/matrix interface or ion-infiltrated matrix, calculating their density of electron-states by first-principles method to determine whether and how the nanofillers introduce charge traps into EP matrix. Calcium cations on nanofiller surface dissociate away from coordinating with silicon-oxygen tetrahedron and infiltrate into void spaces in EP matrix, leaving a larger free volume at filler/matrix interface than in matrix. Calcium cations dissolved in EP matrix are adsorbed in the low electrostatic potential region or coordinate with carbonyl groups in EP matrix and thus introduce a miniband of deep electron traps at energy levels >1 eV lower than conduction band minimum of the amine-crosslinked EP polymer. Even at room temperature, thermal vibrations can break coordinate bonds between calcium cations and silicon-oxygen framework on calcium-silicate nanofiller surface and make considerable calcium ions infiltrating void spaces within EP matrix, leading to comprehensive improvements of cohesive energy, thermal stability, and charge trapping ability in the calcium-silicate/EP nanocomposite.