Dielectric Breakdown Strength Research Articles

Electrical tree modelling in dielectric polymers using a phase-field regularized cohesive zone model

Electrical treeing is a leading cause to the eventual breakdown of dielectric polymers under high voltages. This paper presents a simulation scheme developed based on the phase-field regularized cohesive zone model (PF-CZM) for electrical tree modelling. By using the electrical analog of the crack propagation, the localized breakdown is modelled by the evolution of surface energy, and the electrical treeing is driven by the competition between the surface energy and the stored energy following the laws of thermodynamics. The microscopic Weibull distribution of the dielectric breakdown strength is the key factor resulting in the fractal structures of the electrical tree. The model developed is mesh independent and length-scale insensitive when the mesh size is no greater than 2.5μm. The validity of the model was confirmed through experiments, which strengthens its credibility. Three types of composites are designed and compared. The results indicate that the epoxy resin enhanced with 5 vol% silica and 1 vol% graphene sheet has a 3.5 % longer dielectric breakdown time and a 29.2 % higher thermal conductivity than the pure epoxy resin. Overall, the model provides a valuable tool for understanding the physics of electrical treeing and designing new dielectric materials with high withstand voltages.

Realizing high energy density and discharge energy density in high hardness Ba1.938Bi0.375Nb5O15-based glass ceramics

The practical utility of glass-ceramics-based (GCs) energy storage materials is limited due to their low energy density. In this work, we synthesized the unleaded GCs containing two crystalline phases: Ba1.938Bi0.375Nb5O15 and BaNb2O6. An increase in crystallization time at a specific temperature initially leads to a decrease and then an increase in the dielectric permittivity (εr) and breakdown strength (BDS) due to changes in crystallinity. Specifically, at a crystallization temperature of 750 °C for 4 h, the BDS reaches approximately 1422 kV/cm, driven by a lower oxygen density, higher activation energy, and the formation of a fine-grained structure in the compact GCs. Numerical simulation was employed to uncover the underlying mechanism behind the enhanced BDS achieved through changing crystallization time. As a result of the enhanced BDS and polarization, this study achieved remarkable and comprehensive outcomes: a high efficiency (η) of 85.89%, a high energy density (Wrec) of 3.79 J/cm3, an ultrahigh discharge energy density (Wdis) of 3.26 J/cm3 and a high Vickers hardness (Hv) of 6.85 GPa. Meanwhile, this sample crystallized for 4 h demonstrates excellent thermal stability and frequency stability. These results show that these GCs could be highly competitive as lead-free materials for energy storage capacitors.

A new strategy to improve the dielectric properties of cellulose nanocrystals (CNCs): Surface modification of small molecules

Nanocellulose finds various applications in advanced electrical devices due to its impressive mechanical properties, thermal stability, and degradability. Cellulose nanocrystals (CNCs) with excellent dielectric properties may act as a fresh dielectric plastic. In this study, a new strategy of small molecule modification was used to improve the dielectric constant, breakdown strength, and band gap of the CNCs. The dipole moments, dipole density, and the anisotropic impact of surface groups on the dielectric constant were studied. The number of sulfates in the CNCs showed a gradient due to alkali treatment and sulfonation, which allowed for a controlled range of the dielectric constant of nanocellulose between 4.9 and 11.9. TEMPO oxidation (2,2,6,6-tetramethylpiperidine-1-oxyl) and cyanoethylation of the CNCs further increased the dielectric constant to 11.1 and 13.2, respectively, and the dielectric loss 10−1. By understanding and innovating organic polymer dielectrics, we can provide significant benefits to the electronics and device industries.

Rheology-tailored stable aramid nanofiber suspensions for fabricating ultra-strong and electrically insulated additive-free nanopapers

Although aramid nanofiber paper (ANF-P) is a promising alternative to conventional electrical insulation paper, its performance requires further optimization. This study aimed to establish an optimal nanopaper-fabrication process by using rheology-controlled suspensions to achieve remarkably strengthened pure ANF-Ps. The ANF-P was fabricated in two steps: 1) preparing ANF suspension (ANF-SH₂O) by precipitating ANF/dimethyl sulfoxide (DMSO) (ANF-DDMSO), and 2) preparing ANF-P by vacuum-filtrating ANF-SH2O. Under an in-situ homogenization-assisted precipitation in step 1, the concentration of ANF-DDMSO predominantly affected both the suspension stability and nanopaper performance. Semi-dilute ANF-DDMSOs (0.1–0.7 wt%) produced stable suspensions and strong ANF-Ps (mechanical modulus and strength of 4.5–5.1 GPa and 221.4–243.4 MPa, respectively), while concentrated ANF-DDMSOs (1.0–2.0 wt%) yielded unstable suspensions and weak ANF-Ps (0.3–3.2 GPa and 12.6–139.0 MPa, respectively). The former ANF-SH2Os comprised branched or sheet-like precipitated particles that were favorable for structuring the paper, whereas the latter ones consisted of irregular particles. Particularly at a thickness of 17 μm, ANF-Ps from 0.3 wt% ANF-DDMSO exhibited record-high mechanical performances (modulus, strength, and toughness of 7.4 GPa, 382.3 MPa, and 32.5 MJ∙m−3, respectively) compared to previously reported pure ANF-Ps. In addition, ANF-Ps exhibited a remarkable dielectric breakdown strength of ∼200.3 kV∙mm−1. Rheologically, ANF-SH2Os from semi-dilute ANF-DDMSOs provided a higher scaling exponent of elastic modulus, indicating a higher degree of particle entanglement. Moreover, the strain-induced modulus overshoot phenomena revealed a highly structured suspension network. Therefore, linear- and nonlinear-suspension rheology provide a fundamental guideline for fortifying the foundation of industrial production of high-performance nanopapers.

A Novel Polyester Varnish Nanocomposites for Electrical Machines with Improved Thermal and Dielectric Properties Using Functionalized TiO2 Nanoparticles.

Recently, there has been a growing interest in polymer insulating materials that incorporate nanoscale inorganic additives, as they have shown significantly improved dielectric, thermal, and mechanical properties, making them highly suitable for application in high-voltage insulating materials for electrical machines. This study aims to improve the dielectric and thermal properties of a commercial polyester varnish by incorporating different concentrations of titanium dioxide nanoparticles (TiO2) with proper surface functionalization. Permafil 9637 dipping varnish is the varnish used for this investigation, and vinyl silane is the coupling agent used in the surface functionalization of TiO2 nanoparticles. First, nanoparticles are characterized through Fourier transform infrared spectroscopy to validate the success of their surface functionalization. Then, varnish nanocomposites are characterized through field emission scanning electron microscopy to validate the dispersion and morphology of nanoparticles within the varnish matrix. Following characterization, varnish nanocomposites are evaluated for thermal and dielectric properties. Regarding thermal properties, the thermal conductivity of the prepared nanocomposites is assessed. Regarding dielectric properties, both permittivity and dielectric losses are evaluated over a wide frequency range, starting from 20 Hz up to 2 MHz. Moreover, the AC breakdown voltage is measured for varnish nanocomposites, and the obtained data are incorporated into a finite element method to obtain the dielectric breakdown strength. Finally, the physical mechanisms behind the obtained results are discussed, considering the role of nanoparticle loading and surface functionalization.

Novel fabrication of hydrophobic poly(p-phenylene terephthalamide) paper with superior tear strength and high dielectric breakdown strength

Complicated manufacture of poly(p-phenylene terephthalamide) (PPTA) paper limits its wider application. In this study, the facile gelation process was proposed to fabricate PPTA paper by injecting spontaneous-gelling low molecular weight PPTA (LMW-PPTA) solution onto the surface of non-woven PPTA fabric composed of chopped PPTA fibers. Subsequently, the PPTA papers and hydrophobic poly(vinylidene fluoride) (PVDF) doped PPTA paper were eventually obtained by gelation, washing and pressing. The mechanical properties, electric insulation property and hydrophobicity of PPTA papers were apparently affected by the ratio of chopped PPTA fibers to LMW-PPTA polymers and the content of PVDF in the paper. Significantly, the facile-process and low-cost composite PPTA papers were proved with high tear strength, preeminent dielectric breakdown strength, great thermal stability and superior hydrophobicity, which shed light on a promising direction for developing high-performance insulating materials and honeycomb materials.

Phase structure, dielectric and energy storage properties of Na0.5Bi0.5TiO3-BaTiO3 ceramics with Bi(Mg2/3Nb1/3)O3 modification

Na0.5Bi0.5TiO3 (NBT)-based ceramics are promising lead-free candidates for energy-storage applications owing to their individual crystal structure and phase transition information. However, the high coercive field (EC) and large remnant polarization (Pr) are detrimental for practical applications. In this work, the composition-dependent phase structure, micromorphology, dielectric and energy storage properties of (1-x)(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-xBi(Mg2/3Nb1/3)O3 (NBBT-100xBMN, x = 0.18, 0.20, 0.22 and 0.25) ternary ceramics were hereby investigated. The addition of BMN facilitates the phase transformation from rhombohedral (R3c) to tetragonal (P4bm), which is beneficial for the enhancement of relaxation behavior, and meanwhile impels the grain growth. Combined with the influence of grain size on breakdown field strength, an optimal recoverable energy storage density (Wrec) of 1.88 J/cm3 with a high energy storage efficiency (η) of 82.15% was achieved in the NBBT-20BMN ceramic composition under the dielectric breakdown strength (DBS) of 150 kV/cm, accompanied by the excellent temperature stability from room temperature to 200 °C. All these manifest that the NBBT-20BMN ceramics have an attractive application prospect in the energy storage field.

Size effect and electrical ageing of PDMS dielectric elastomer with competing failure modes

Large-scale dielectric elastomer generators dielectric elastomer generators (DEGs) such as those employed in wave energy converter projects require a significant volume of electrically stressed materials. Meanwhile, predictions of energy output from such systems are generally extrapolated from electrical and mechanical breakdown measurements performed on small scale samples, where the presence of small defects can be extremely small. This can lead to overly optimistic upscaled predictions for the performance and reliability of full-scale devices. In this study, multilayer DEGs were prepared to evaluate the dielectric breakdown strength of thin polydimethylsiloxane PDMS elastomer at different values of active areas. The results indicated the presence of two separate breakdown mechanisms resulting in an enhanced size effect and a reduced reliability for the larger samples. Electrical ageing tests were performed on three different sample geometries and the dielectric breakdown strength was found to be marginally affected by the time under stress. A Weibull competing failure model was applied to the distribution of experimental breakdowns and electrical reliability was accurately modeled over more than four decades of variation in the electrode area.

Giant Energy Density via Mechanically Tailored Relaxor Ferroelectric Behavior of Pzt Thick Film.

Relaxor ferroelectrics (RFEs) are being actively investigated for energy storage applications due to their large electric-field-induced polarization with slim hysteresis and fast energy charging-discharging capability. Here, w e report a novel nanograin engineering approach based upon high kinetic energy deposition for mechanically inducing the RFE behavior in a normal ferroelectric Pb(Zr0.52 Ti0.48 )O3 (PZT), which results in simultaneous enhancement in the dielectric breakdown strength (EDBS ) and polarization. Mechanically transformed relaxor thick films with 4μm thickness exhibited an exceptional EDBS of 540 MV/m and reduced hysteresis with large unsaturated polarization (103.6 μC/cm2 ), resulting in a record high energy storage density of 124.1 J/cm3 and a power density of 64.5 MW/cm3 . This fundamental advancement is correlated with the generalized nanostructure design that comprises of nanocrystalline phases embedded within the amorphous matrix. Microstructure-tailored ferroelectric behavior overcomes the limitations imposed by traditional compositional design methods and provides a feasible pathway for realization of high-performance energy storage materials. This article is protected by copyright. All rights reserved.

Achieving significantly enhanced piezoelectricity in aurivillius ceramics by improving initial polarization and dielectric breakdown strength

In this work, the neglected role of the dielectric breakdown strength (BDS) in piezoelectricity of bismuth layer-structured ferroelectrics (BLSFs) is revealed, enhanced initial polarization and BDS work together to improve the piezoelectricity of CaBi4Ti4O15 (CBT) ceramics via Li/Bi co-substitution. The experimental work, first-principles calculations and finite element simulation are carried out to investigate the effect of Li/Bi co-substitution in depth. The stronger spontaneous polarization (Ps) from the lattice distortion and the more favorable domain switching from the improved grain growth both contribute to an enhanced initial polarization. Besides, the changed grain-scale microstructure improves the hardness and inhibits the local discharge, the higher resistivity related to strong defect dipoles suppresses the heat generation during the poling process, all resulting in an increase of BDS by about 100%, and allowing more domains to align. This work demonstrates an effective strategy to develop BLSFs with enhanced piezoelectricity for high temperature piezoelectric applications.

Research progress and prospect of polymer dielectrics

With the increasing demand for energy, how to store and release energy efficiently and stably has become an urgent research topic. Polymer dielectrics have become a kind of ideal dielectric materials in electrostatic capacitors for energy storage due to their advantages of light weight, easy fabrication, low cost, and high breakdown strength. It has a wide application prospect in smart power grids, new energy vehicles, pulse power weapons, electromagnetic guns, and lasers. However, existing polymer dielectrics cannot simultaneously possess the characteristics of high energy density, high breakdown field intensity, high charge and discharge efficiency, and low dielectric loss, thus limiting the development of compact, efficient, and reliable electronic power technology. In addition, the inherent thermal/field charge injection, excitation, and transport phenomena of polymer dielectrics make the resistivity and dielectric energy storage properties of polymer dielectrics decrease sharply under the combined action of high temperature and high electric field. In order to optimize the energy storage performance of polymer dielectrics (including room temperature and high temperature dielectrics), it has been obtained excellent dielectric breakdown strength, energy storage density, energy storage charge, and discharge efficiency from polymer nanocomposites, polymer/small molecule composites, polymer/polymer blends, new synthetic polymers, multilayer polymers, and other material systems. Based on these material systems, this review summarizes and compares these material systems, points out their advantages and disadvantages including the key problems, and puts forward suggestions for the future research.

(Invited) Improvements in Thermal Budget and Film Properties Using Low Pressure Cure Technology for Advanced 3D Integration Packaging

3D advanced integration with Fan-Out Wafer-Level Packaging (FOWLP) and Fan-Out Panel Level Packaging (FOPLP) offers multiple benefits: heterogenous chip design and stacking, increased interconnect density, and improved performance. However, it also brings new requirements for more compact form factors, low thermal budget materials and processing, and lower cost. The materials, process, and fabrication of heterogenous integration on redistribution layers (RDLs) consisting of metal and polymer dielectrics have become important enablers of the move to advanced packaging applications. To achieve the low-stress and low-cost benefits required by advanced integrated devices, thermal budgets must be reduced throughout the heterogenous integration flow -- including the dielectric curing step, which demands the use of low temperature processing and reduced cure times.In this presentation, the low temperature and low pressure thermal polymerization of dielectric polyimides used for redistribution layers (RDLs) is reviewed. Specifically, this presentation illustrates the significant impact of the low pressure cure process in reducing temperature (20° to 50° lower) and cure times (up to a 50% reduction) while providing better mechanical (elongation%, tensile strength, Young’s modulus), thermal (TG, Td 1%, Td 5%), and electrical (Dk, Df, dielectric breakdown strength - DBS) properties for different types of dielectric polyimides, including the Fujifilm LTC-9300 series, the Asahi BL-300 series, and the Toray LT-8300 and PW-1500 series. The post-curing polymerization ratio (FT-IR) and film stress were studied and are described. Finally, a proposed mechanism for the described dielectric polyimides’ polymerization under reduced pressure is discussed.Ongoing developments in design, materials, process and fabrication for FOWLP and FOPLP devices continue to drive progress in 3D heterogenous integration. This study of thermal processing of dielectric polyimides at low pressure and shorter time demonstrates a promising technique to improve overall process flow by reducing thermal budget, stress, and cost.

Development of electrocaloric effect in BT-based lead-free ceramic via density adjustment strategy

Electrocaloric (EC) refrigeration materials have seen significant progress recently, with efficient Barium titanate-based (BT-based) lead-free materials particularly promising for microelectronics applications. However, their performance still lags behind their lead-based counterparts, highlighting the need for further improvements. This study employs a novel density adjustment strategy (DAS) to enhance the EC performance of (0.5-x)BCT-BTZ-xBST ceramics by carefully balancing the relationships among density, dielectric breakdown strength (BDS), and ΔT. Although ΔT intuitively decreases with increasing density, enhanced BDS can partially compensate for this decrease. An excellent EC performance with ΔT of 2.21 K and ΔT/ΔE of 0.471 K mm kV−1 is obtained in x = 0.5, together with a broader temperature span of 50.3 °C near room temperature, which surpasses or is comparable to other lead-free or lead-based ones. The results suggest that the DAS provides a promising approach for developing efficient EC, making speediness of application in EC devices.

Metal ion-assisted fabrication of aramid nanofilm with high strength and toughness for the dye separation

Herein, Fe3+, Co2+, and Ni2+ were respectively introduced into the splitting of aramid fibers, and then the metal hydroxide nanoparticles (NPs) were formed on the aramid nanofibers (ANFs). The nanofilm assembled from NP-grafted ANFs shows high stress, toughness, and dielectric breakdown strength. The results indicate that the ANF nanofilm contained 5 wt% Fe3+ presents the highest enhancing capacity to the mechanical properties of ANF film, with a strength of 312 MPa and a toughness of 61.9 MJ m−3, increased by 73.3% and 215.8%, respectively. The NPs increase the ANF film's dielectric breakdown strength by 40.8%–60.2%. Different from the previous studies, we have not observed the densification of the nanofilm, and the enhanced mechanical properties may be caused by the strong electrostatic and coordinate interactions between NPs and ANFs, evidenced by the large numbers of fiber pull-out on fracture cross-sections. Because of the hydrophilicity of the NPs and the un-densified structures, the composite films show both high flux and rejection to methylene blue (MLB).

Enhancing energy density of poly(vinylidene fluoride) composite film via addition of N-doped carbon modified boron nitride and sandwich-structural engineering

It is a challenge to simultaneously enhance dielectric constant and breakdown strength of dielectrics and achieve a greatly elevated energy density. Herein, polyaniline was first coated onto the surface of boron nitride nanosheets (BN), and then nitrogen-doped carbon (NC) was formed through a carburization process, resulting in BN@NC composite, which was subsequently added to poly(vinylidene fluoride) (PVDF) to prepare a composite film with high dielectric performance. The characterization showed that BN@NC effectively preserved the nanosheet structure of BN and formed strong hydrogen bonding interactions with the PVDF matrix, promoting the β-PVDF formation. This not only improved the compatibility but also enhanced the interfacial polarization between conductive NC and the polymer, leading to a high dielectric constant. Moreover, the electrically insulating BN prevented the formation of leakage current, resulting in a high breakdown strength. Finally, a sandwich-structured film was constructed, and exhibited a dielectric constant of 10.2 (at 1 kHz), a breakdown strength of 380 MV m−1, and an energy density of 6.1 J cm−3, which were 20%, 36%, and 74% higher, respectively, than those of pure PVDF film (8.5, 280 MV m−1, and 3.5 J cm−3). This work highlights significant potential for applications in low-cost and high-energy density dielectric composites.

Effect of Fluorosilicone Rubber on Mechanical Properties, Dielectric Breakdown Strength and Hydrophobicity of Methyl Vinyl Silicone Rubber.

Silicone rubber (SIR) is used in high-voltage insulators because of its insulation, and excellent hydrophobicity is very important in harsh outdoor environments. To enhance the hydrophobicity and low-temperature resistance of silicone rubber, methyl vinyl silicone rubber and fluorosilicone rubber (FSIR) blend composites with different ratios were prepared. The samples were characterized and analyzed using scanning electron microscopy, tensile testing, dynamic mechanical analysis and static contact angle testing. The results showed that after blending, SIR and FSIR were well compatible. FSIR had higher elastic modulus and reduced the tensile strength to some extent in SIR/FSIR composites. The addition of a small amount of FSIR made its crystallization temperature decrease from -30 to -45 °C, meaning that the low-temperature resistance was significantly improved. The breakdown strength of SIR/FSIR composites can still be maintained at a high level when a small amount of FSIR is added. The contact angle of the composites increased from 108.9 to 115.8° with the increase in FSIR content, indicating the enhanced hydrophobicity. When the samples were immersed in water for 96 h, the hydrophobicity migration phenomenon occurred. The static contact angle of the samples with less FSIR content had a weaker decreasing trend, which illustrated that the hydrophobicity was maintained at a high level.

Nanobrick Wall Multilayer Thin Films with High Dielectric Breakdown Strength.

Current thermally conductive and electrically insulating insulation systems are struggling to meet the needs of modern electronics due to increasing heat generation and power densities. Little research has focused on creating insulation systems that excel at both dissipating heat and withstanding high voltages (i.e., have both high thermal conductivity and a high breakdown strength). Herein, a polyelectrolyte-based multilayer nanocomposite is demonstrated to be a thermally conductive high-voltage insulation. Through inclusion of both boehmite and vermiculite clay, the breakdown strength of the nanocomposite was increased by ≈115%. It was also found that this unique nanocomposite has an increase in its breakdown strength, modulus, and hydrophobicity when exposed to elevated temperatures. This readily scalable insulation exhibits a remarkable combination of breakdown strength (250 kV/mm) and thermal conductivity (0.16 W m-1 K-1) for a polyelectrolyte-based nanocomposite. This dual clay insulation is a step toward meeting the needs of the next generation of high-performance insulation systems.

The Influence of Silver Ions on the Dielectric Dispersion Dipolar Relaxation Dynamics and Dielectric Breakdown Strength of Zinc Selenium Phosphate Glass System

Herein, a study on the dielectric properties of ZnO–P2O5–SeO2 glass ceramics containing varied contents of Ag2O is presented. Structural analysis of the samples by X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, Fourier transform infrared spectra, and optical absorption techniques indicated that the glasses are embedded with Ag3PO4, Ag2SeO3, and Zn3(PO4)2 anisotropic crystal phases along with Ag+ ions and Ag0 particles. Dielectric properties, ac conductivity (σac), and dielectric breakdown strength (DBS) are investigated as functions of Ag2O concentration. The results show the maximal concentration of Ag+ ions and Ag0 metallic particles in the sample containing 0.6 mol% of Ag2O. Dielectric parameters and (σac) increase with increasing Ag2O up to 0.6 mol%, while the DBS and electrical impedance decrease. The observed dipolar effects are quantitatively analyzed and possible dipoles are identified. Ionic contribution is predominant up to 0.6 mol% of Ag2O, beyond which the polaronic tunneling phenomenon prevails. These findings indicate that 0.6 mol% of Ag2O is the optimal concentration for using these glass ceramics as solid electrolytes in ionic batteries. Moreover, glass ceramics containing Ag2O beyond 0.6 mol% have exhibited larger polaronic conductivity, hence such glasses can be considered suitable candidates for electrodes in ionic batteries.

Superior and ultrafast energy storage performance of relaxorantiferroelectric HfO2-based supercapacitors

Compared to electrochemical energy storage, dielectric thin film-based capacitors possess the advantages of higher voltage stability and higher break-down voltage as well as lower leakage current etc. Since HfO2 films are compatible to microelectronic process and its ferroelectricity is strategically important in memory device, the realization of their excellent energy storage performance will broaden their applications in microelectronic devices. In this study, we utilized Al3+ dopant, known for its smaller ionic radius compared to Hf4+, to induce lattice disorder in the Hf0.5Zr0.5O2 films, facilitating transformation of the Hf0.5Zr0.5O2 film from ferroelectric to antiferroelectric, and ultimately to a superparaelectric-like relaxation antiferroelectric behaviors. We have experimentally demonstrated that, by introduction of an appropriate Al doping level of x = 4.13%, the Hf0.5Zr0.5O2 thin films with a relaxor antiferroelectric characteristic can achieve a corresponding recoverable energy density of more than 100 J cm−3, an efficiency of more than 80%, and an effective enhancement of the dielectric strength to more than 6 MV cm−1. Compared to HfO2-based amorphous/crystalline films reported previously, this is a record-high energy density in atomic layer deposited HfO2/ZrO2 ternary doped oxides, and beyond that, we also demonstrate their superfast charging/discharging as a capacitor. Targeting at high-speed supercapacitor applications in integrated circuit, HfO2-based dielectric may win the competition with perovskite oxides in terms of dielectric breakdown strength and charging/discharging speed etc. Our fundamental understanding of the physics behind also enriches the knowledge of materials science and dielectric physics.

A simple figure of merit to identify the first layer to degrade and fail in dual layer SiOx/HfO2 gate dielectric stacks

Understanding the degradation dynamics and the breakdown sequence of a bilayer high-k (HK) gate dielectric stack is crucial for the improvement of device reliability. We present a new Figure of Merit (FoM), the IL/HK Degradation Index, that depends on fundamental materials properties (the dielectric breakdown strength and the dielectric constant) and can be used to easily and quickly identify the first layer to degrade and fail in a bilayer SiO2/HK dielectric stack. Its dependence on IL and HK material parameters is investigated and its validity is demonstrated by means of accurate physics-based simulations of the degradation process. The proposed FoM can be easily used to understand the degradation dynamics of the gate dielectric stack, providing critical insights for device reliability improvement.