Stability of Si impurity in high-κ oxides

The interface structure of a high permittivity (high-κ) oxide with Si substrate affects the electrical properties of the high-κ based transistors. Our theoretical analysis suggests that the formation of a SiO₂ layer at the high-κ/Si interface originates from the instability of a Si impurity in the high-κ oxide. Our computational results revealed that the Si impurity is much more stable in La₂O₃ than in HfO₂, indicating La₂O₃ is a silicate former, while SiO₂ is likely to precipitate at the HfO₂/Si interface.     

Statistical nature of hard breakdown recovery in high-κ dielectric stacks studied using ramped voltage stress

In replacing the conventional SiO₂ gate dielectric with high-κ materials, new challenges emerge on understanding the kinetics of dielectric breakdown due to the different properties of the new bulk oxide and the interfacial layers at the substrate and gate electrode interface as well. Among several complexities, dielectric relaxation and recovery have received a lot of attention due to their promising applications in resistive random access memory (RRAM). In this study, we explore the stochastic nature of hard breakdown recovery in HfO₂, taking advantage of ramped voltage stress (RVS) measurements, which are theoretically equivalent to the widely used constant voltage stress (CVS), while being significantly less time-consuming. We found that the possibility of recovery is largely dependent on the ramp rate during RVS as the dielectric needs adequate time and sufficient thermal budget to recover. The clustering model is found to be a good fit to the RVS data sets for post-recovery subsequent breakdown events and the extent of defect clustering is found to be more intense after increasing number of recovery events. The breakdown mechanism in the stack is confirmed by measuring the resistance change trends with temperature.     

Investigation of dependence between time-zero and time-dependent variability in high-κ NMOS transistors

Bias Temperature Instability (BTI) is a major reliability concern in CMOS technology, especially with High-dielectric constant (High-κ/HK) metal gate (MG) transistors. In addition, the time-independent process-induced variation has also increased because of the aggressive scaling down of devices. As a result, the faster devices at the lower threshold voltage distribution tail experience higher stress, leading to additional skewness in BTI degradation. Since time-dependent dielectric breakdown (TDDB) and stress-induced leakage current (SILC) in NMOS devices are correlated to BTI, it is necessary to investigate the effect of time-zero variability on all of these effects simultaneously. Accordingly, we propose a simulation framework to model and analyze the impact of time-zero variability (in particular, random dopant fluctuations) on different aging effects. For small area devices (~ 1000 nm²) in 30 nm technology, we observe significant effects of Random Dopant Fluctuation (RDF) on BTI-induced variability (σ_ΔVth). In addition, circuit analysis reveals similar trend in performance degradation. However, both TDDB and SILC show weak dependence on RDF. We conclude that the effect of RDF on V_th degradation cannot be disregarded in scaled technology and needs to be considered in variation-tolerant circuit design.     

Physical analysis of breakdown in high-κ/metal gate stacks using TEM/EELS and STM for reliability enhancement (invited)

In this invited paper, we demonstrate how physical analysis techniques that are commonly used in integrated circuits failure analysis can be applied to detect the failure defects associated with ultrathin gate dielectric wear-out and breakdown in high-κ materials and investigate the associated failure mechanism(s) based on the defect chemistry. The key contributions of this work are perhaps focused on two areas: (1) how to correlate the failure mechanisms in high-κ/metal gate technology during wear-out and breakdown to device processing and materials and (2) how the understanding of these new failure mechanisms can be used in proposing “design for reliability” (DFR) initiatives for complex and expensive future CMOS nanoelectronic technology nodes of 22 nm and 15 nm. Hf-based high-κ materials in conjunction with various gate electrode technologies will be used as main examples while other potential high-κ gate materials such as cerium oxide (CeO₂) will also be demonstrated to further illustrate the concept of DFR.     

Time dependent breakdown characteristics of parylene dielectric in metal–insulator–metal capacitors

In this work, we present reliability results of MIM (Metal–Insulator–Metal) capacitors fabricated with parylene as the dielectric, deposited at room temperature. We have evaluated the time dependent dielectric breakdown (TDDB) of parylene-based MIM capacitors as a function of constant DC voltage stress, area and dielectric thickness of the capacitor. Mean-time-to-failure (MTTF) of parylene evaluated at different stress voltages shows a power law distribution over the applied voltage range and device area, with MTTF driven by the number of defects. Defect density in the parylene capacitors is also reported and is calculated to be ～1.2 × 10³ defects/cm².     

High-κ dielectric breakdown in nanoscale logic devices – Scientific insight and technology impact

Dielectric breakdown is one of the key failure mechanisms in front-end silicon-based complementary metal oxide semiconductor (CMOS) technology. With the advent of HfO₂-based high-κ dielectrics replacing SiO₂ and metal gate replacing polysilicon and silicides, the physics of defect generation and breakdown of the oxide has changed significantly, although the mechanisms governing operation of the transistor remain essentially the same. Given the progression towards ultra-thin dielectric films with physical thickness ∼1–2 nm, the overall breakdown process has shifted from a single catastrophic hard breakdown (HBD) event to include various regimes such as soft breakdown (SBD) and progressive (post) breakdown (PBD) which in itself consists of a digital phase with random telegraph noise (RTN) fluctuations and stable average leakage current and an analog phase with gradual wear-out and lateral dilation of the percolation path resulting in a monotonic increase in leakage current. In order to better design and optimize the logic gate stack for enhancing its robustness and immunity to breakdown, it is essential to understand the driving forces and physical mechanisms behind the different phases of dielectric failure. This review is dedicated to the scientific understanding of the various regimes of breakdown in high-κ gate stacks using electrical, physical and statistical techniques along with an application of these findings to predict the impact they will have from a technology perspective.     

Stack engineering of TANOS charge-trap flash memory cell using high-κ ZrO2 grown by ALD as charge trapping layer

ZrO₂ with a κ value of 30 grown by atomic layer deposition has been integrated as charge trapping layer alternative to Si₃N₄ in TANOS-like memory capacitors, with Al₂O₃ as blocking oxide, SiO₂ as tunnel oxide and TaN metal gate. The fabricated device featuring 24 nm ZrO₂ exhibits efficient program and erase operations under Fowler-Nordheim tunneling when compared to a Si₃N₄ based reference device with similar EOT and fabricated under the same process conditions. The effect of stack thermal budget (900-1030 °C range) on memory performance and reliability is investigated and correlated with physical analyses. Finally, scaling ZrO₂ down to 14 nm allows program and erase at lower voltages, even if the trapping efficiency and retention of these device need further improvements for the integration of ZrO₂ in next generation charge trapping nonvolatile memories.     

Optical properties and photoinduced superparamagnetism of γ-Fe2O3 nanoparticles formed in dendrimer

We are presenting the joint investigation of the optical and photoinduced superparamagnetic properties of a single-domain γ-Fe₂O₃ nanoparticles (NPs) formed in poly(propylene imine) (PPI)-dendrimer. The optical absorption studies indicated direct allowed transition with the band gap (4.5 eV), which is "blue"-shift with respect to the value of the bulk material. The influence of pulsed laser irradiation on the superparamagnetic properties of γ-Fe₂O₃ NPs was studied by Electron paramagnetic resonance (EPR) spectroscopy. It has been shown that irradiation of the sample in vacuo and cooled in zero magnetic field to 6.9 K leads to the appearance of a new EPR signal, which decays immediately after the irradiation is stopped. We suppose that the generation of conduction band electrons by irradiation into the band gap of the γ-Fe₂O₃ changes the superparamagnetic properties of NPs.     

Electrical and photoelectric properties of Si-based metal–insulator–semiconductor structures with Au nanoparticles at the insulator–semiconductor interface

It is shown that the formation of Au nanoparticles at the insulator–silicon interface in structures with a high density of surface states results in a shift of the Fermi-level pinning energy at this interface towards the valence-band ceiling in silicon and in increasing the surface-state density at energies close to the Fermi level. In this case, a band with a peak at 0.85 eV arises on the photosensivity curves of the capacitor photovoltage, which is explained by the photoemission of electrons from the formed Au-nanoparticle electron states near the valence-band ceiling in silicon.     

Impact of employees’ demographic characteristics on the awareness and compliance of information security policy in organizations

To protect consumer information, many countries have begun enforcing the Personal Data Protection Act. Organizations are required to comply with this Act, failure of which may result in hefty penalties. To ensure compliance, some organizations have introduced their own information security policy to protect consumer information. A review of the literature shows that many employees are either unaware of the policy or tend to ignore it, which increases the risk of non-compliance. To help organizations manage compliance among their employees, in this study, we used demographic factors to develop profiles of employees’ policy awareness and their intention to comply. By having an understanding of employee profiles, effective and targeted strategies can be devised to educate employees accordingly. Our data from 607 respondents show that age, working industry and education levels have significant effects on information security policy awareness and compliance.     

Analysis of quantum efficiency and optical enhancement in amorphous Si p–i–n solar cells

The effect of i-layer thickness, tin oxide texture, and back reflector (BR) on optical enhancement has been systematically studied in a series of 20 a-Si p–i–n solar cells. The internal quantum efficiency has been analyzed by a simple model based on the work of Schade and Smith. The enhancement of optical absorption is characterized by m, a wavelength-dependent fitting parameter representing the increase in optical pathlength relative to the i-layer thickness d. Solar cells with an Al BR have negligible optical enhancement, with m < 1.5, consistent with large parasitic absorption at the Al/Si interface as reported by others. Solar cells on highly textured SnO₂ with ZnO/Al or ZnO/Ag BR have peak values of m ∼ 3–4, with ZnO/Ag having slightly larger values than ZnO/Al. It was found that m has a strong dependence on the product αd, and that maximum values of m increase with reflectivity of the BR. It is shown that a major source of parasitic absorption loss at long wavelengths is light trapping in the textured SnO₂ front contact. Copyright © 2002 John Wiley & Sons, Ltd.     

Interplay of plasma etch, strip and wet clean in patterning La2O3/HfO2-containing high-κ/metal gate stacks

The removal process of the La₂O₃/HfO₂ dielectric and of the residues after metal gate etch are discussed. The challenges are presented and related to the specific physico-chemical properties of La-containing compounds. Solutions based on optimization of plasma etch, strip and wet clean are demonstrated for both an integrated and delayed etch-clean process. Both processes meet the stringent requirements of complete removal of the high-κ layers and metal-containing sidewall residues without inducing silicon recess or undercut.     

Synthesis of ZnO and Fe2O3 nanoparticles by sol–gel method and their application in dye-sensitized solar cells

ZnO and Fe₂O₃ nanoparticles have been formed in a silica matrix, through the sol–gel method and were used as a photoanode to fabricate dye-sensitized solar cells (DSCs). The obtained oxides were characterized by X-ray diffraction, infrared spectroscopy, scanning electron microscope and UV–visible absorption spectroscopy. The results indicate that ZnO and Fe₂O₃ prepared by this method may be used as photoanodes in photo-electro-chemical energy conversion systems. DSSCs have been built using eosin Y as photosensitizer and their photocurrent, open-circuit voltage, fill factor and efficiency have been measured under direct sunlight illumination (1000 Wcm^?2). A ZnO-film solar cell had the best performance with an open-circuit voltage of V_oc=0.7 V and short-circuit current density of I_sc=490 μA/cm². This was attributed to high optical gap energy and transparency of ZnO compared to Fe₂O₃. The effects of annealing temperature and concentration of Fe₂O₃ on conversion efficiency of the Fe₂O₃ based solar cell were also studied.     

Electrical properties of Ge metal–oxide–semiconductor capacitors with high-k La2O3 gate dielectric incorporated by N or/and Ti

LaON, LaTiO and LaTiON films are deposited as gate dielectrics by incorporating N or/and Ti into La2O3 using the sputtering method to fabricate Ge MOS capacitors, and the electrical properties of the devices are carefully examined. LaON/Ge capacitors exhibit the best interface quality, gate leakage property and device reliability, but a smaller k value (14.9). LaTiO/Ge capacitors exhibit a higher k value (22.7), but a deteriorated interface quality, gate leakage property and device reliability. LaTiON/Ge capacitors exhibit the highest k value (24.6), and a relatively better interface quality (3.1E11 eV^-1cm^-2), gate leakage property (3.6E3 A/cm^2 at Vg = 1 V + Vfb) and device reliability. Therefore, LaTiON is more suitable for high performance Ge MOS devices as a gate dielectric than LaON and LaTiO materials.     

Direction of arrival estimation of sources with intersecting signature in time–frequency domain using a combination of IF estimation and MUSIC algorithm

Time–frequency (TF) approaches are frequently employed for source localization at low signal to noise ratio. However, TF approaches fail to achieve the desired performance for sparsely sampled signals or signals corrupted by heavy noise in an under-determined scenario when sources are not TF separable. In this study, we propose a new TF method for direction of arrival (DOA) estimation of sources with closely spaced and overlapping TF signature. The proposed method uses a combination of a high-resolution time–frequency distribution and instantaneous frequency estimation method for extraction of sources with intersecting and closely spaced time–frequency signatures. Once sources are extracted, their DOAs are estimated using a well known multiple signal classification (MUSIC) algorithm. Experimental results demonstrate that the proposed source localization method achieves better performance as compared to the conventional time–frequency MUSIC algorithm.

     

Implementation of the time delay and integration mode in a scanning 576 × 6 focal-plane array of the long-wave infrared range

The results of the development of a focal-plane array (FPA) of the 576 × 6 format with the time delay and integration (TDI) mode are presented. The comparative analysis of different variants of implementation of the TDI mode in ROIC is conducted. The expedience of the upgrade of existing scanning photodetectors of the 288 × 4 format on the basis of the developed 576 × 6 FPA is justified. The result of this upgrade will be simplification of the optical–mechanical scanning unit and improvement of the quality of thermal image.     

Resource allocation of simultaneous wireless information and power transmission of multi-beam solar power satellites in space–terrestrial integrated networks for 6G wireless systems

Wireless Networks - The technique of simultaneous wireless information and power transmission (SWIPT) has been applied to wireless sensor networks, which employ static or mobile base stations (BSs)...     

Impact of 2D Ligands on Lattice Strain and Energy Losses in Narrow-Bandgap Lead–Tin Perovskite Solar Cells

Mixed lead and tin (Pb/Sn) hybrid perovskites exhibit a great potential in fabricating all-perovskite tandem devices due to their easily tunable bandgaps. However, the energy deficit and instability in Pb/Sn perovskite solar cells (PSCs) constrain their practical applications, which renders defect passivation engineering indispensable to develop highly efficient and long-term stable PSCs. Herein, the mechanisms of strain tailoring and defect passivation in Pb/Sn PSCs by 2D ligands are investigated. The 2D ligands include electroneutral cations with long alkyl chain (LAC), iodates with relatively short alkyl chain (SAC) and their mixtures. This study reveals that LAC ligands facilitate the relaxation of tensile strain in perovskite films while SAC ligands cause strain buildup. By mixing LAC/SAC ligands, tensile strain in perovskite films can be balanced which improves solar cell performance. PSCs with admixed β-guanidinopropionic acid (GUA)/phenethylammonium iodide (PEAI) exhibit enhanced open circuit voltage and fill factor, which is attributed to reduced nonradiative recombination losses in the bulk and at the interfaces. Furthermore, the operational stability of PSCs is slightly improved by the mixed 2D ligands. This work reveals the mechanisms of 2D ligands in strain tailoring and defect passivation toward efficient and stable narrow-bandgap PSCs.     

Impact of crystallization on ferro-, piezo- and pyro-electric characteristics in thin film P(VDF–TrFE)

In this paper, the impact of the crystallization and polymer chain length of the P(VDF–TrFe) on its dielectric, ferroelectric, piezoelectric and pyroelectric properties are studied. X-rays diffraction (XRD) analysis have revealed that a higher β crystalline phase is obtained with a lower polymer chain length corresponding to a higher grain size for a P(VDF–TrFe) composition of 72.2/27.8 mol.%. The polymer chain morphology was characterized by scanning electron microscopy (SEM) where the fibrils orientation and width were extracted. By coupling both XRD analysis and chain morphology analysis, we have established that an increase of the grain size of the polymer chain enhances the ferroelectric and piezoelectric effects of the P(VDF–TrFe) layer. On the other hand, we observed a slight degradation of its pyroelectric properties. In addition, the piezoelectric coefficient (d₃₃) of the P(VDF–TrFe) was enhanced by decreasing the molecular weight (M_w) of the copolymer, exhibiting a maximum value around −50 pC/N for the composition 72.2/27.8 with a molecular weight of 470 kg/mol. On the opposite, the pyroelectric properties were enhanced for the lowest polymer crystalline grain size studied and obtained with the composition 71/29 mol.% with a molecular weight of 505 kg/mol. A pyroelectric coefficient of 37.8 μC/m² K was measured.     

Silane-Mediated Expansion of Domains in Si-Doped κ-Ga2O3 Epitaxy and its Impact on the In-Plane Electronic Conduction

Unintentionally doped (001)-oriented orthorhombic κ-Ga₂O₃ epitaxial films on c-plane sapphire substrates are characterized by the presence of ≈ 10 nm wide columnar rotational domains that can severely inhibit in-plane electronic conduction. Comparing the in- and out-of-plane resistance on well-defined sample geometries, it is experimentally proved that the in-plane resistivity is at least ten times higher than the out-of-plane one. The introduction of silane during metal-organic vapor phase epitaxial growth not only allows for n-type Si extrinsic doping, but also results in the increase of more than one order of magnitude in the domain size (up to ≈ 300 nm) and mobility (highest µ ≈ 10 cm²V⁻¹s⁻¹, with corresponding lowest ρ ≈ 0.2 Ωcm). To qualitatively compare the mean domain dimension in κ-Ga₂O₃ epitaxial films, non-destructive experimental procedures are provided based on X-ray diffraction and Raman spectroscopy. The results of this study pave the way to significantly improved in-plane conduction in κ-Ga₂O₃ and its possible breakthrough in new generation electronics. The set of cross-linked experimental techniques and corresponding interpretation here proposed can apply to a wide range of material systems that suffer/benefit from domain-related functional properties.