Cd₃As₂ Kinetic Inductance for Miniaturized Terahertz Circuits
Published in Physics
The terahertz (THz) region of the electromagnetic spectrum, long regarded as technologically elusive, is rapidly becoming central to next-generation communication, sensing, and integrated photonic-electronic systems. Its vast bandwidth and potential for ultralow-latency transmission make it an attractive candidate for future 6G networks and dense Internet-of-Things infrastructures. Yet the transition from experimental platforms to scalable chip-level THz technologies continues to face an unglamorous but fundamental obstacle: passive components have not kept pace with advances in sources, detectors, and active devices.
Inductors are a particularly stubborn bottleneck. In conventional electronics, inductance is governed by geometry, magnetic energy stored by currents flowing through patterned metallic conductors. As circuits shrink, geometry alone cannot sustain useful inductance, forcing a trade-off between footprint and performance. High conductivity metals such as aluminium or copper, therefore, impose severe footprint penalties when used in terahertz integrated circuits, limiting the density and scalability of on-chip THz systems. Addressing this constraint requires more than incremental design optimisation; it demands a shift in perspective toward materials that fundamentally alter how inductance is generated.
Our recent work (Discover Electronics 3, 14 (2026). https://doi.org/10.1007/s44291-026-00160-8) exploring spiral inductors fabricated from the Dirac semimetal Cd₃As₂ highlights the promise of such a shift. Instead of relying solely on magnetic-field storage dictated by geometry, this approach exploits carrier dynamics intrinsic to the material itself. Electromagnetic simulations comparing identically patterned aluminium and Cd₃As₂ inductors reveal a striking outcome: the Cd₃As₂ devices exhibit markedly lower resonance frequencies and significantly higher inductance despite identical dimensions. The enhancement arises from kinetic inductance, additional inductance due to inertia of the charge carriers in the oscillating electric fields.
In most conventional metals, kinetic inductance is negligible. High carrier density and rapid scattering allow electrons to follow alternating fields almost instantaneously, suppressing inertial energy storage. Materials hosting low-density, high-mobility carriers with longer relaxation times behave differently. Their carriers respond with finite delay, introducing an additional inductive component that becomes increasingly important at high frequencies. Cd₃As₂, with its linear band dispersion and Dirac-like carriers, falls squarely within this regime. Simulated compact spiral geometries show kinetic contributions dominating the total inductance, yielding values several times greater than those achievable with traditional metals.
This behaviour points to a conceptual pivot: inductance need not remain geometry limited. By embedding functionality in electronic structure rather than physical size, compact THz components can achieve performance previously unattainable through scaling alone. The implications extend well beyond a single material system. Weyl semimetals, topological conductors, and superconducting platforms may offer comparable opportunities, inviting systematic exploration of quantum-material electrodynamics as a design toolkit for passive device engineering.
Equally important is the potential for active tunability. Since kinetic inductance depends on carrier density and scattering dynamics, it can be modulated through optical excitation, temperature variation, or electrostatic gating. This enables frequency-agile resonant circuits and reconfigurable metamaterial elements without modifying the device geometry, which is highly desirable for multifunctional terahertz platforms operating in dynamic environments.
As terahertz technologies progress toward practical deployment, passive components will play a crucial role in determining integration and efficiency. Recent advances in Cd₃As₂-based inductors highlight the broader opportunity of engineering electromagnetic response through quantum-material properties. This approach offers new design flexibility beyond conventional metals, suggesting that future compact terahertz circuits may benefit more from advanced material choices than from geometric optimisation alone.
Sahu, A., Andola, B. & Srivastava, Y.K. Harnessing large kinetic inductance in Cadmium Arsenide (Cd₃As₂) for miniaturised terahertz spiral inductors. Discover Electronics 3, 14 (2026).
Miniaturised spiral inductor: a) Device design, (b) Total inductance of Aluminium and Cd₃As₂ inductor. (c) Kinetic inductance of Cd₃As₂ inductor, (d) Ratio of the total inductance of Cd₃As₂ inductor to that of the aluminium inductor.
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