Physicists at Russia’s Ioffe Institute published a study today confirming that quantum mechanical tunneling — not the long-favored rival mechanism of electron-collision avalanche — is what drives electrical breakdown in polymer insulators, and the confirmation comes with something engineers have not had before: equations derived from the real physical mechanism that can predict exactly when a polymer dielectric will catastrophically fail, confirmed in Journal of Applied Physics. That result closes a decades-old debate in dielectric physics and simultaneously opens a molecular-design route for engineering polymer insulators that are longer-lived by design — a capability directly relevant to every engineer working with thin-film capacitors, high-voltage cable insulation, or the power electronics that drive electric vehicles.

Why Two Theories Have Competed in Dielectric Physics

When a polymer film breaks down under high voltage, its molecules shed electrons — and explaining precisely how that happens has proved surprisingly contentious. Two mechanisms have competed for decades.

The older explanation, impact ionization, holds that electrons accelerated by an external electric field collide with neutral molecules, releasing additional electrons in an avalanche that ultimately destroys the material. That mechanism is well-established in gases — it governs lightning and the glow of a fluorescent tube — and it operates in some semiconductors. But applying it to dense solid polymers raises a fundamental physical objection that the field has increasingly recognized: in a tightly packed polymer bulk, electrons scatter so frequently and travel such short distances between collisions that they cannot accumulate the kinetic energy required to ionize a polymer macromolecule on impact. The ionization energies of polymer chains are simply out of reach via this route.

The rival explanation, field ionization, requires no external electron source and no collision energy. Instead, the intense electric field itself deforms the potential energy barrier that holds an electron bound to its molecule, narrowing that barrier until quantum mechanics takes over: the electron’s wave function has a non-zero probability of appearing on the other side of the barrier without ever having enough energy to climb over it. This is quantum tunneling — the same phenomenon that enables nuclear fusion in stars, governs radioactive alpha decay, and makes scanning tunneling microscopes possible. In the polymer insulator context, it means that breakdown can ignite spontaneously from within the material, driven by the field alone, without any external charge injection.

The Ioffe Institute group — V. A. Pakhotin, S. E. Semenov, and N. T. Sudar, with affiliations spanning the Ioffe Institute and Peter the Great St. Petersburg Polytechnic University — has been building the case for field ionization in polymer breakdown since at least 2013, when an earlier Fizika Tverdogo Tela paper first proposed the field-ionization mechanism for polymer film degradation. The new Journal of Applied Physics paper delivers the quantitative experimental confirmation that prior work had not fully established — and does so with a precision that produces engineering-usable output.

What Shape Is the Barrier? Triangular vs. Coulomb

Confirming field ionization as the mechanism required more than choosing it over impact ionization. It required choosing the correct mathematical description of the potential energy barrier through which the tunneling electron must pass.

Two barrier geometries are candidates. The triangular barrier is the simpler approximation: it treats the electric field as creating a wedge-shaped potential that rises linearly. It is the natural first-order description and appears in the foundational Fowler-Nordheim formalism for field electron emission from metal surfaces.

The Coulomb barrier is more physically realistic for the polymer case. After a first electron begins to leave a macromolecule, it does not escape into a featureless electric-field landscape. Instead, it experiences an attractive interaction with the positively charged ion it is leaving behind. That electron-ion attraction creates a Coulomb potential — one that falls off as 1/r rather than linearly — and this additional potential well reshapes the effective barrier the departing electron must tunnel through. Accounting for the Coulomb interaction makes the barrier calculation more complex but also more accurate, because it captures a real physical interaction that the triangular approximation ignores.

To distinguish experimentally between the two descriptions, the research team subjected thin films of polyethylene terephthalate (PET) — a polymer familiar from beverage bottles and food packaging, but critically important as a dielectric in film capacitors — to large negative voltage pulses and used an oscilloscope to capture the precise timing of breakdown events. Fitting the lifetime data against both barrier models, the team found that the Coulomb barrier description produced the better match to PET’s measured behavior. That finding validated the field ionization mechanism and calibrated its parameters specifically for PET.

This result extends the group’s own 2018 finding, published in Technical Physics, that PET breakdown field strength increases logarithmically with the steepness of the applied voltage pulse front — a signature inconsistent with impact ionization but naturally explained by field ionization kinetics. The 2026 paper places that earlier observation on rigorous mechanistic ground.

Predicting When Polymer Insulation Will Fail

The engineering payoff of confirming the correct mechanism — and, crucially, the correct barrier model — is a set of lifetime equations: mathematical expressions that relate the applied electric field to the expected time before breakdown.

Among those predictions is a critical feature: the field strength at which a polymer’s lifetime undergoes a sharp, discontinuous jump. Below a certain threshold, lifetime increases gradually with decreasing field. At a specific field strength, the model predicts a step change — a sudden increase in expected lifetime that represents a qualitatively different operating regime.

“The resulting equations for the lifetime lines allow us to predict the exact field strength at which a lifetime jump will occur for a specific polymer, given its parameters,” Pakhotin told AIP SciLights. “In practice, this will allow engineers to more accurately calculate the operating limits and lifespan of thin-film capacitors and cable insulation.”

The accuracy of these predictions depends on correctly capturing two parameters simultaneously: tunneling barrier transparency — how readily the electron’s wave function penetrates the barrier — and charge carrier mobility within the polymer bulk. Getting both right at once is what the Coulomb barrier model enables; this combination is what the triangular approximation misses.

Prior dielectric lifetime modeling relied primarily on empirical accelerated-aging curves: run a batch of capacitors at elevated stress until they fail, fit the failure statistics to a statistical model, and extrapolate to normal operating conditions. That approach works within the range of tested conditions but has no mechanistic grounding that would permit confident extrapolation to new materials, new geometries, or new operating regimes. Equations derived from a confirmed physical mechanism can, in principle, be applied more broadly — because they describe why breakdown happens, not merely when it has happened in past experiments.

How Does the Mechanism Drive Breakdown? A Self-Amplifying Plasma

Field ionization in a polymer does not simply produce a steady trickle of ionized molecules. The 2013 work by the same group described how the process becomes self-amplifying once it begins: positive molecular ions and free electrons accumulating in a local region of the polymer form a quasi-neutral plasma. That plasma screens the local electric field — known as Debye screening — and the screening reduces the effective ionization potential of nearby molecules, making them easier to ionize at even lower field strengths. The result is a runaway: ionization accelerates, the local charge density spikes, and within roughly 100 nanoseconds the polymer transitions in an explosive transition from insulator to conductor.

The mass spectrometry work the group published in Technical Physics 2022 added direct experimental evidence: during PET and polypropylene breakdown in high vacuum, the volatile products emitted from the breakdown channel were exclusively low-molecular-weight destruction products of macromolecule fragmentation — with no lines in the mass spectrum corresponding to carbon molecules, which would indicate carbonization via high-current heating. The absence of a carbonization signature supports the field-ionization picture in which macromolecule destruction begins with electron removal and proceeds through molecular fragmentation, not through thermal incineration of a conducting channel.

Why This Matters for EV Drives and Grid Hardware

Polymer dielectrics are not a niche application. PET film, polypropylene, polyimide, and related materials appear in the thin-film capacitors used in power-factor correction circuits, motor drive inverters, and grid-connected power electronics; in the insulating sheaths of high-voltage transmission cables; and in the motor winding insulation of electric vehicles. The transition to 800-volt EV architectures — where faster-switching wide-bandgap silicon carbide semiconductors generate high-slew-rate voltage pulses — places new and more severe stress on polymer dielectrics than the 400-volt architectures they are replacing, according to IEEE event records.

An estimated 80% of all electric power will flow through power electronics systems by 2030 according to IEEE. In that context, the reliability of polymer insulation at high fields and high repetition rates is not a peripheral engineering concern but a central one. A physics-grounded formula for predicting when a specific polymer will fail under a given field regime — rather than an extrapolation from accelerated aging data gathered at somewhat different conditions — directly improves both design safety margins and the confidence with which those margins can be tightened.

Dielectric failure in solid polymers, unlike failure in gases, is irreversible: the material does not recover once a conductive channel has formed through it. The engineering imperative is therefore predictive: know the failure threshold before deploying the component, not after.

Designing from the Molecule Up

The most consequential implication of these findings for the materials science community is this: because the Coulomb barrier parameters that govern breakdown probability are properties of the macromolecule’s electronic structure — specifically its ionization potential and the geometric shape of the electron-ion attractive potential — the confirmation of field ionization creates a rational molecular-design pathway for ultra-long-lived polymer dielectrics.

Prior to this mechanistic confirmation, improving a polymer dielectric’s breakdown performance required empirical iteration: synthesize a candidate material, measure its dielectric strength, modify the structure, repeat. There was no first-principles guide to which molecular changes would be productive, because the underlying mechanism was not confirmed. Now that the Coulomb barrier parameters are identified as the key variables, chemists and polymer scientists have a specific target. Polymers with higher intrinsic ionization potentials — meaning their macromolecules hold electrons more tightly — should resist field ionization more effectively. Stiffer molecular architectures that reduce the effective polarizability of the macromolecule under an applied field should narrow the Coulomb barrier in ways that reduce tunneling probability. Tailored side-chain structures that reshape the electron-ion potential landscape become rational design objectives rather than shot-in-the-dark modifications.

This is the polymer dielectric equivalent of structure-activity relationships in drug design: a confirmed mechanistic framework that transforms materials discovery from art into targeted engineering science.

What the Team Plans to Test Next

The Pakhotin group was candid that its confirmation applies, so far, specifically to PET. The universality of field ionization as the governing mechanism in polymer dielectrics more broadly depends on confirming the same mechanism in other materials. Pakhotin specifically identified polypropylene as the next priority target, Pakhotin confirmed to AIP.

That choice is significant. Polypropylene is the dominant film dielectric in high-voltage and high-frequency capacitor applications — preferred over PET precisely because of its extremely low dissipation factor (approximately 0.05% at 1 kHz, versus PET’s 0.8%), which makes it suitable for power electronics and audio applications where even small dielectric losses translate into heat and efficiency degradation. If field ionization via the Coulomb barrier mechanism is confirmed in polypropylene, the lifetime equation framework becomes applicable to the largest market segment in film capacitor technology.

Beyond materials expansion, the group’s next steps include extending the model to higher temperature regimes — relevant to EV power electronics, where operating temperatures can stress insulation significantly — and incorporating the effects of mechanical stress, which is a real-world condition that capacitor films and cable insulation both experience in service. Neither extension is routine: the interplay between thermal agitation, mechanical strain, and the quantum-mechanical ionization rate creates a more complex modeling problem than the isothermal, stress-free case addressed in the current paper.

What Does This Mean for Established Dielectric Design Practice?

The confirmation that impact ionization does not govern polymer breakdown has a practical implication beyond the new predictive equations: some existing engineering approaches built on impact-ionization assumptions should be reconsidered. Strategies aimed at reducing free-carrier density by minimizing surface contamination or controlling electrode geometry — which make sense if impact ionization governs breakdown, since they target the external seed electrons needed to start an avalanche — are less directly relevant to a mechanism that requires no external charge injection. The relevant levers are the macromolecular electronic structure and the bulk charge-transport properties, not the electrode-polymer interface.

That is not a refutation of existing engineering practice so much as a reframing: good insulation design has always required controlling bulk material properties, and the field-ionization framework now explains more precisely which bulk properties matter and why.

Frequently Asked Questions

What is field ionization, and why does it matter for electronics?

Field ionization is a quantum mechanical process in which an intense electric field deforms the potential energy barrier that holds an electron bound to a molecule, narrowing it until quantum tunneling allows the electron to escape without the collision energy that classical impact ionization would require. In practical electronics, confirming field ionization as the governing mechanism for polymer breakdown means that the material fails from the inside out — driven by the field acting on the macromolecule’s own electronic structure — rather than by an avalanche of externally injected electrons. That distinction changes which material properties engineers should target to extend insulator lifetime: not purity or surface morphology, but molecular ionization potential and the quantum geometry of the electron-binding potential.

How can engineers actually use the new lifetime equations from this research?

The equations relate the applied electric field strength to the expected time before breakdown for a specific polymer, given its measured Coulomb barrier parameters (tunneling barrier transparency and charge carrier mobility). In practice, this means a capacitor designer can calculate the field strength at which the PET film in a specific component is expected to fail after a given service life — and, critically, identify the exact threshold below which the lifetime undergoes a sudden discontinuous improvement. That threshold is the design target: operating below it moves the component into a qualitatively longer-lived regime. The equations are grounded in the confirmed mechanism rather than in empirical aging data alone, so they can, in principle, be applied to new geometries and operating conditions with greater confidence than purely statistical extrapolations from accelerated tests.

Does this apply to the polymer insulation in EV batteries and motors?

The study directly confirmed the mechanism in polyethylene terephthalate (PET) film, which is widely used in DC-link film capacitors in EV power electronics. The research group’s next planned experiments target polypropylene, the other major film dielectric in that application space. Motor winding insulation, which typically uses polyimide or similar high-temperature polymers rather than PET or PP film, is not directly addressed by this paper — but the field-ionization framework is likely to be applicable to a broad class of polymer dielectrics, and the team’s planned extensions to higher temperature regimes and mechanical stress conditions would move the model closer to the full EV drivetrain environment.

Why has this debate taken so long to resolve?

Impact ionization was mathematically tractable and well-understood from gas discharge physics, so it was the natural first hypothesis to apply to solid dielectrics. The experimental challenge was producing direct evidence that distinguished between the two mechanisms — not just showing that empirical data was consistent with field ionization, but showing that it was inconsistent with impact ionization and that a specific field-ionization model fit the data quantitatively. The 2026 paper achieves both: the physical argument that impact ionization cannot generate sufficient ionization energy in dense polymer solids, combined with the experimental lifetime data fitting the Coulomb barrier model and not the triangular approximation, constitute together a definitive mechanistic case.

Source: “Ionization mechanism of electrical breakdown in polymers. Effect of potential barrier shape and charge mobility,” V. A. Pakhotin, S. E. Semenov, and N. T. Sudar, Journal of Applied Physics (2026). DOI: 10.1063/5.0350895. Coverage via AIP SciLights (American Institute of Physics).