Charge Trapping In Oxide Research Articles

High-temperature atomic layer deposition of silicon oxide films using Tris(dimethylamino)silane and ozone

Atomic layer deposition (ALD) benefits from high process temperatures when the substrate is not temperature-sensitive because the films deposited at higher temperatures exhibit better electrical properties. In this study, we investigated the ALD process of silicon oxide films by alternating injections of tris(dimethylamino)silane (tris-DMAS) and O3/O2 at temperatures ranging from 400 to 700 °C. The saturation dose of tris-DMAS was 1.5 × 106 L at 400 °C. Self-limiting growth with a growth rate of approximately 0.9 Å/cycle was observed up to 600 °C, allowing excellent step coverage. However, at 700 °C, the growth rate increased significantly to 4.6 Å/cycle, carbon and nitrogen impurities were detected by secondary ion mass spectrometry, and step coverage was poor, supporting the thermal decomposition of tris-DMAS at this temperature. Therefore, the optimum temperature for ALD SiO2 using tris-DMAS is 600 °C for application as an insulating film on high aspect ratio patterns. At this temperature, the leakage current density was 0.58 nA/cm2, and the oxide-trapped charge density was 4.0 × 1010 cm−2.

Effects of co-60 gamma-ray irradiation on the DC and RF characteristics of SiGe HBTs

This study investigates the effects of Co-60 gamma-ray irradiation on the DC and RF characteristics of the SiGe HBTs, with a total dose of up to 4000 krad(Si). The degradation of the forward base current is primarily attributed to surface recombination due to the induced interface traps. The ideality factor of the forward excess base current is affected by the positive oxide-trapped charges at the interface of the emitter-base spacer oxide. TCAD simulation results indicate that the effective integral region of the surface recombination rate is associated with the positive oxide-trapped charge density. The accumulation of positive oxide-trapped charges in the shallow trench isolation oxide has an impact on the potentials of the interface and epi-collector region, subsequently affecting the base diffusion current. Therefore, the ideality factor of the reverse excess base current depends on the device geometry. The RF characterization suggests that the depletion capacitance of the base-emitter junction is more susceptible to gamma-ray irradiation compared to the base-collector junction. And the cut-off frequency experiences a slight degradation as the total dose increases.

IGZO charge trap flash device for reconfigurable logic functions

We fabricated an indium gallium zinc oxide (IGZO) charge trap flash (CTF) device for logic-in-memory (LIM) applications. Initially, the nonvolatile memory characteristics of the IGZO CTF device were investigated under charge trapping and detrapping states in 104 s retention tests. Next, we constructed a common-source amplifier circuit containing the IGZO CTF device and demonstrated various input–output signal relationships by modulating the memory state of the device. Finally, we used interconnected IGZO CTF devices to demonstrate reconfigurable logic functions. Using series- and parallel-connected IGZO CTF devices, we developed 2-input NAND and 2-input NOR gates, respectively. Our experimental results showed that the IGZO CTF device is a promising future memory device and a tool for LIM technology.

14.8% Quantum Efficient Gallium Phosphide Photocatalyst for Hydrogen Evolution.

Gallium phosphide is an established photoelectrode material for H2 or O2 evolution from water, but particle-based GaP photocatalysts for H2 evolution are very rare. To understand the reasons, we investigated the photocatalytic H2 evolution reaction (HER) of suspended n-type GaP particles with iodide, sulfite, ferricyanide, ferrous ion, and hydrosulfide as sacrificial electron donors, and using Pt, RhyCr2-yO3, and Ni2P HER cocatalysts. A record apparent quantum efficiency of 14.8% at 525 nm was achieved after removing gallium and oxide charge trapping states from the GaP surface, adding a Ni2P cocatalyst to reduce the proton reduction overpotential, lowering the Schottky-barrier at the GaP-cocatalyst interface, adjusting the polarity of the depletion layer at the GaP-liquid interface, and optimizing the electrochemical potential of the electron donor. The work not only showcases the main factors that control charge separation in suspended photocatalysts, but it also explains why most known HER photocatalysts in the literature are based on n-type and not p-type semiconductors.

Influence of ionizing radiation on admittance measurements of Au/TiO2/n-Si (MIS) capacitor

This study aimed to investigate the influence of ionizing radiation on the admittance measurements of Titanium dioxide (TiO2)-based metal-insulator-semiconductor (MIS) capacitor. The capacitor was irradiated to a cumulative dose of 100 kGy using a 60Co-gamma (γ) source. The electrical admittance (Y = G + iωC) measurements of the MIS capacitor were performed before and after exposure to gamma irradiation for four different frequencies (1, 10, 100 and 500 kHz). Gamma irradiation leads to changes in the capacitance/conductance versus voltage (C/G–V) characteristics. The C and G showed a decrease by increasing the radiation dose and frequency. This decrease is attributed to the interface traps and oxide-trapped charges created during the gamma irradiation. The obtained results showed that the prepared MIS capacitor have great potential for dosimetry applications.

Total X-ray dose effect on graphene field effect transistor

In this paper, the total dose effects of graphene field-effect transistors (GFETs) with different structures and sizes are studied. The irradiation experiments are carried out by using the 10-keV X-ray irradiation platform with a dose rate of 200 rad(Si)/s. Positive gate bias (<i>V</i><sub>G</sub> = +1 V, <i>V</i><sub>D<i> </i></sub>= <i>V</i><sub>S<i> </i></sub>= 0 V) is used during irradiation. Using a semiconductor parameter analyzer, the transfer characteristic curves of top-gate GFET and back-gate GFET are obtained before and after irradiation. At the same time, the degradation condition of the dirac voltage <i>V</i><sub>Dirac</sub> and the carrier mobility <i>μ</i> are extracted from the transfer characteristic curve. The experimental results demonstrate that <i>V</i><sub>Dirac</sub> and carrier mobility <i>μ</i> degrade with dose increasing. The depletion of <i>V</i><sub>Dirac</sub> and carrier mobility <i>μ</i> are caused by the oxide trap charge generated in the gate oxygen layer during X-ray irradiation. Compared with the back-gate GFETs, the top-gate GFETs show more severely degrade <i>V</i><sub>Dirac</sub> and carrier mobility, therefore top-gate GFET is more sensitive to X-ray radiation at the same cumulative dose than back-gate GFET. The analysis shows that the degradation of top-gate GFET is mainly caused by the oxide trap charge. And in contrast to top-gate GFET, oxygen adsorption contributes to the irradiation process of back-gate GFET, which somewhat mitigates the effect of radiation damage. Furthermore, a comparison of electrical property deterioration of GFETs of varying sizes between the pre-irradiation and the post-irradiation is made. The back-gate GFET, which has a size of 50 μm×50 μm, and the top-gate GFET, which has a size of 200 μm×200 μm, are damaged most seriously. In the case of the top-gate GFET, the larger the radiation area, the more the generated oxide trap charges are and the more serious the damage. In contrast, the back-gate GFET has a larger oxygen adsorption area during irradiation and a more noticeable oxygen adsorption effect, which partially offsets the damage produced by irradiation. Finally, the oxide trap charge mechanism is simulated by using TCAD simulation tool. The TCAD simulation reveals that the trap charge at the interface between Al<sub>2</sub>O<sub>3</sub> and graphene is mainly responsible for the degradation of top-gate GFET property, significantly affecting the investigation of the radiation effect and radiation reinforcement of GFETs.

Effect of 60Coγ ray radiation on electrical properties of SiGe HBTs at low temperatures

In this article, total ionizing dose (TID) irradiation experiments were carried out on germanium-silicon heterojunction bipolar transistors (SiGe HBTs) under different bias and temperature conditions. The electrical performance and noise characteristics of the device were characterized before and after irradiation using a semiconductor parameter analyzer and a 1/f noise test system, respectively. The variation of radiation sensitivity parameters with the TID effect and temperature of the device was obtained, and the mechanism of radiation damage degradation was also identified. Results suggest that the oxide-trap charges and interface states induced by irradiation are the main causes for SiGe HBT electrical parameters degradation. With the decreased temperature, Gummel characteristics and 1/f noise are significantly improved. It's found that oxide-trap charges and interface states generated at 93 K is less than that at 300 K. This work lays the foundation for the application of SiGe HBT in aerospace area.

Optimization of post-annealing temperature for high-performance synaptic transistors based on In–Ga–Zn–O channel and trap layers

Synaptic transistors using an indium–gallium–zinc oxide (IGZO) charge trap layer (CTL) have great potential for high-performance neuromorphic applications due to their excellent stability and high linearity in conductance modulation. Since the high conductivity of the IGZO CTL enhances charge de-trapping performance, the post-annealing process, which directly affects the conductivity of the film, should be carefully conducted. In this study, we investigated the effect of post-annealing temperature (TPA) on the charge de-trapping performance of synaptic transistors. The synaptic transistor showed superior charge de-trapping performance at a TPA of 250 °C, resulting from the increased conductivity of the CTL. Through various electrical and chemical analysis methods, it was revealed that the hydrogen decrease within the CTL and the oxidation–reduction reaction at the interface between the tunneling layer and the CTL contributed to the significant increase in the conductivity of the CTL. The synaptic transistor with the optimal TPA exhibited high linearity of potentiation (αp: 0.56) and depression (αd: −0.65) with 64 conductance levels, enabling the spiking neural network simulation to achieve a high accuracy of 88.75% using a Fashion-MNIST dataset. This work shows that TPA is one of the critical process strategies for the high charge de-trapping performance of the synaptic transistor by inducing the chemical reaction at the CTL interface and hydrogen content change within the CTL.

Study on annealing effect of bipolar transistors at different temperatures after total dose irradiation

The article investigates the annealing process of bipolar transistors after total dose irradiation, using the GLPNP transistor as the research object. After total dose irradiation, room temperature and high temperature annealing tests were carried out. Gummel curve, GS curve and SS curve of bipolar transistor are obtained by I/V scanning, gate scanning and sub-threshold scanning. The evolution behavior of radiation-induced oxide trap charges and interface state damage defects during annealing of bipolar transistors at different temperatures was quantitatively analyzed by different microscopic defect characterization methods. Generally speaking, this study is of great significance to better understand the recovery mechanism of electrical properties of bipolar transistors during annealing after total dose irradiation, and can provide reference for the design, application and radiation-hard of transistors.

Non-ideal program-time conservation in charge trap flash for deep learning

Training deep neural networks (DNNs) is computationally intensive, but arrays of non-volatile memories such as charge trap flash (CTF) can accelerate DNN operations using in-memory computing. Specifically, the resistive processing unit (RPU) architecture uses a voltage-threshold program with stochastic encoded pulse trains and analog memory features to accelerate vector-vector outer product and weight update for gradient descent algorithms. Although CTF, offering high precision, has been regarded as an excellent choice for implementing RPU, the accumulation of charge due to the applied stochastic pulse trains is ultimately of critical significance in determining the final weight update. In this paper, we report on the non-ideal program-time conservation in CTF through pulsing input measurements. We experimentally measure the effect of pulse width and pulse gap, keeping the total ON-time of the input pulse train constant, and report three non-idealities: (1) the cumulative shift reduces when total ON-time is fragmented into a larger number of shorter pulses, (2) the cumulative shift drops abruptly for pulse widths <2 s, (3) the cumulative shift depends on the gap between consecutive pulses and the shift reduction recovers for smaller gaps. We present an explanation based on a transient tunneling field enhancement due to blocking oxide trap-charge dynamics to explain these non-idealities. Identifying and modeling the responsible mechanisms and predicting their system-level effects during learning is critical. This non-ideal accumulation is expected to affect algorithms and architectures relying on devices for implementing mathematically equivalent functions for in-memory computing-based acceleration.

Ultrathin four-quadrant silicon photodiodes for beam position and monitor applications: Characterization and radiation effects

Ultrathin semiconductor photodiodes are of interest for beam position and monitoring in X-ray synchrotron beamlines and particle therapy medical applications. In this work, single and four-quadrant diodes have been fabricated on ultrathin Si films with thicknesses of 10 μm, 5 μm and 3 μm from silicon on insulator (SOI) substrates. Physical and electrical characterization of the devices has been carried out. Good functional electrical characteristics have been obtained for the devices fabricated on the different silicon thicknesses. The impact of electron, neutron and proton irradiations on the electrical characteristics has been studied for the 10 μm-thick devices. In spite of the observed diode leakage current increase and positive charge trapping in interquadrant isolation oxide, functional operation as radiation detector is verified upon illumination with a pulsed laser beam transient current technique.

Effect of Total Dose Irradiation on Parasitic BJT in 130 nm PDSOI MOSFETs.

In this work, the effects of total dose irradiation on the parasitic bipolar junction transistor (BTJ) in 130 nm PDSOI MOSFETs were investigated. The experimental results demonstrate that irradiation-induced oxide-trap charges can modify the E-B junction barrier, and thereby make the common-emitter gain β0 of the parasitic BJT in NMOS device increase, while decreasing it in a PMOS device. Additionally, irradiation-generated oxide-trap charges in shallow trench isolation (STI) elevate the surface electrostatic potential of the gate above the STI sidewall, thus providing an additional channel from the emitter to the collector. Moreover, these charges may generate parasitic reverse conductive paths at the STI/Si interface under high dose irradiation, thereby enhancing the leakage current in the front gate channel and diminishing the significance of the parasitic BJT. Under irradiation, the electric field intensity difference between two biases leads to higher β0 of the parasitic BJT in PG-biased devices than in ON-biased ones. Furthermore, the lifting effect of irradiation on β0 increases in wide or short channel irradiated devices, which can be explained using simulations and an emitter current crowding effect model.

Damage Separation in Proton-Irradiated Bipolar Junction Transistors as a Function of Energy

Damage separation analysis was performed for two types of bipolar junction transistors following proton irradiation over the energy range of 1.6 to 650 MeV. The functional dependence of excess base current on fluence for each device type is consistent with base polarity as it relates to the effect of oxide-trapped charge on surface recombination. For a given fluence, the excess base current decreases with proton energy due to reductions in NIEL and stopping power. Relative damage coefficients, computed from normalized Δ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> vs fluence curves, imply a mix of ionization and displacement damage. The relative amounts of ionization damage and displacement damage as a function of proton energy are consistent with charge yield, stopping power and NIEL. A simple model for the energy dependence of damage contributions, based on charge yield and the relative amounts of deposited ionizing and non-ionizing energy, is described. The model calculations as a function of proton energy are in good agreement with the relative damage contributions estimated from the damage separation analysis.

Charge trapping and photovoltaic characteristics in monocrystalline silicon solar cells employing molybdenum oxide and copper oxide stacked hole-selective contacts

A hole-selective contact (HSC) composed of stacked layers of molybdenum oxide (MoOx) and copper oxide (CuOx), called MOCOSL, has been proposed as passivation booster for screen-printed monocrystalline silicon solar cell (SMSC) applications. The passivation quality of MOCOSL is investigated by characterizing its charge trapping properties, including fixed oxide charge (Qf) and interface trap density (Dit). The conversion efficiency (CE) of SMSCs is improved by MOCOSL, resulting in an increase from 20.66% to 21.76%. This improvement is attributed to an increase in the negative Qf and a decrease in Dit, which result in an increase in the open circuit voltage (Voc) and short circuit current (Jsc). Specifically, the number of negative Qf is increased by MOCOSL, which helps to reduce the recombination of charge carriers.

Realizing improved performance of metal-insulator-semiconductor diodes with high-k MgO/SiOx stack

With the development of metal-insulator-semiconductor (MIS) field-effect transistors, the thickness of silicon dioxide (SiO2) must be scaled down; however, it causes a large gate leakage current and a low on/off current ratio. Magnesium oxide (MgO) exhibits a dielectric constant as high as 11.2, which is about three times larger than that (3.9) of SiO2; thus the thickness of MgO can be three times greater than that of SiO2 and significantly reduces the gate leakage current. Nevertheless, a large lattice mismatch (22.5%) exists between MgO and Si materials. In the study, the MgO/SiOx stack dielectrics are employed to suppress the large lattice mismatch and improve the performance of MIS diodes. The MgO/SiOx stack largely reduces the oxygen vacancy of MgO from 75% to 52.3%; also the fixed oxide charge and interface trap charge density are drastically decreased from 1.3 × 1012 and 1.8 × 1013 to 8.2 × 1011 cm−2 and 7.8 × 1012 cm−2eV−1, respectively. Compared to the MIS diodes with a single MgO, the MgO/SiOx stack dielectrics suppress the gate leakage current by about two orders in MIS diodes; hence the rectification ratio is enhanced from 114 to 1032 at ±2V. Band-diagram shows that Fowler-Nordheim tunneling occurs at a high reverse-bias voltage, and the barrier height increases from 0.18 to 0.42 eV in the MIS diodes with single MgO and MgO/SiOx stack dielectrics, respectively. Nevertheless, the MIS diodes operate through a direct tunneling at low reverse-bias voltages.

Investigation of Anomalous Degradation Tendency of Low-Frequency Noise in Irradiated SOI-NMOSFETs

In this work, we present new evidence of the physical mechanism behind the generation of low-frequency noise with high interface-trap density by measuring the low-frequency noise magnitudes of partially depleted (PD) silicon-on-insulator (SOI) NMOSFETs as a function of irradiation dose. We measure the DC electrical characteristics of the devices at different irradiation doses and separate the threshold-voltage shifts caused by the oxide-trap charge and interface-trap charge. Moreover, the increased densities of the oxide-trap charge projected to the Si/SiO2 interface and interface-trap charge are calculated. The results of our experiment suggest that the magnitudes of low-frequency noise do not necessarily increase with the increase in border-trap density. A novel physical explanation for the low-frequency noise in SOI-NMOSFETs with high interface-trap density is proposed. We reveal that the presence of high-density interface traps after irradiation has a repressing effect on the generation of low-frequency noise. Furthermore, the exchange of some carriers between border traps and interface traps can cause a decrease in the magnitude of low-frequency noise when the interface-trap density is high.

Investigation of heavy ion irradiation effects on a charge trapping memory capacitor by C–V measurement

Heavy ion irradiation effects on charge trapping memory (CTM) capacitors with TiN/Al2O3/HfO2/Al2O3/HfO2/SiO2/p-Si structure have been investigated. The ion-induced interface charges and oxide trap charges were calculated and analyzed by capacitance–voltage (C–V) characteristics. The C–V curves shift towards the negative direction after swift heavy ion irradiation, due to the net positive charges accumulating in the trapping layer. The memory window decreases with the increase of ion fluence at high voltage, which results from heavy ion-induced structural damage in the blocking layer. The mechanism of heavy ion irradiation effects on CTM capacitors is discussed in detail with energy band diagrams. The results may help to better understand the physical mechanism of heavy ion-induced degradation of CTM capacitors.

Bias Dependence of Total Ionizing Dose Response in UTBB FD-SOI Transistors

The impact of continuous bias on the ultra-thin body and buried oxide fully-depleted silicon-on-insulator (UTBB FD-SOI) transistors during total ionizing dose (TID) irradiation is investigated by a device with the single transistor or multiple transistors in parallel. Experimental data of the single transistor shows that the TID bias effect is masked by TID response variation caused by process fluctuation between devices. While the device with multiple transistors in parallel still exhibits a similar TID bias effect as the traditional SOI transistor (TG > OFF > Ground > ON), the process fluctuations between devices are well controlled. Focusing on UTBB FD-SOI parallel transistors, by comparing the results of various bias conditions, the impacts of the drain, gate, and back-gate bias on the TID response of transistors are summarized in detail. Particularly, applying both positive and negative back-gate bias to transistors during TID radiation can obviously increase the TID damage of UTBB FD-SOI parallel transistors, which should be considered in the TID mitigation technique through dynamic back-gate bias. Combined with TCAD simulation, the generation process of oxide-trapped charges in buried oxide (BOX) under different biases is discussed. And, bias dependence of TID response is analyzed from three aspects: fraction of holes escaping initial recombination, holes capture cross section, and spatial distribution of oxide trapped charges. Finally, the TID mitigation calibration law of pMOSFETs is investigated by the empirical model of the back-gate radiation bias effect.

Robustly Stable Ferroelectric Polarization States Enable Long-Term Nonvolatile Storage against Radiation in HfO2-Based Ferroelectric Field-Effect Transistors.

The ferroelectric field-effect transistors (FeFETs) with HfO2-based ferroelectric layers in the gate stacks are emerging as one of the most promising candidates for the next-generation nonvolatile memory devices due to their scalability and compatibility with conventional Si technology. Moreover, owing to the high radiation hardness of the HfO2-based ferroelectric thin films, HfO2-based FeFETs have attracted great interest in the fields of radiation-hard (rad-hard) memory. However, the reliability of their memory states under irradiation, which represents the validity of the stored information, has not been investigated. Here, we focus on the impact of the total ionizing dose (TID) on erased and programmed states of HfO2-based FeFETs. The TID radiation (X-ray) characteristics of erased and programmed HfO2-based FeFETs are characterized using an on-site read operation. Both the erased and programmed states show robust stability under irradiation at a dose rate of 90 rad(Si)/s, and even at 230 rad(Si)/s, only the erased state shows a slight variation. The possible factors contributing to memory state degradation are discussed. Through the analysis of the threshold voltage shift and subthreshold swing evolution, as well as studies of ferroelectric polarization stability under radiation, it is revealed that the erased state degradation is caused by oxide-trapped charges rather than interface degradation or polarization switching. The physical mechanism of the difference in radiation-induced oxide-trapped charges buildup in programmed and erased FeFETs is analyzed to explain different TID radiation characteristics between them. Our work suggests that the HfO2-based FeFETs have great potential in radiation environment applications.

Charge carrier motion and effect of fixed oxide charge in a microstructured silicon radiation detector

Signal formation in a microstructured semiconductor neutron detector is more complex than in planar diode geometry. Three-dimensional microstructures are laterally smaller than the ionization cloud length, and the electric fields may be weak enough to exhibit plasma time effects. This work is the first detailed treatment of charge carrier motion in these complex semiconductor devices to replicate the time profile and signal magnitude. Simulations were performed using COMSOL Multiphysics to investigate various parameters that affect the propagation of the charge cloud. It was observed that the size of the simulated three-dimensional structure had an impact on the induced current pulse, indicating the importance of simulation geometry optimization to accurately simulate charge cloud expansion. COMSOL Multiphysics was used to replicate accurate charge creation profiles using energy deposition information imported from radiation transport codes. A detailed simulation methodology is presented to benchmark preamplifier event pulses along with complexities in modeling the charge carrier motion along the etched microstructured trenches with Si–SiO2 boundary conditions, including fixed oxide charge and interface trapping.