Electromagnetic interference shielding using metal and MXene thin films
Summary
The paper reports the development and characterisation of ultrathin electromagnetic interference (EMI) shields formed from metal–MXene multilayer films (EXIM structures) and pure MXene films. By combining conductive metal walls (Cu, Ag, Au) with Ti3C2Tx MXene layers in sandwich or bilayer geometries, the authors achieve exceptional shielding effectiveness (SE) in electrically thin films (sub-micron to micrometre thickness). Mechanistic analysis points to a mix of surface reflection, enhanced internal absorption and interfacial capacitive effects arising from metal–MXene heterointerfaces. The work includes experimental SE measurements in the X-band, microscopy and spectroscopy characterisation, transmission-line/TMM simulations, environmental stability tests and demonstrations: conformal shielding of ICs in USB 3.0 flash drives and thin flexible Schottky diodes. Protective capping (Cr–Al) improves humidity stability; direct deposition onto flexible substrates is feasible though can induce thermomechanical stress in devices.
Key Points
- Metal–MXene multilayer (EXIM) shields, even when electrically thin, outperform many single-material ultrathin films due to heterointerface effects and combined reflection/absorption mechanisms.
- Sandwich structures (metal/MXene/metal) and multilayer heterostacks increase average SE, with performance tunable by choice of wall metal and MXene thickness.
- MXene-only shields (≈1 μm) are highly conformable and effective for flexible electronics, but EXIM structures offer superior performance for demanding applications.
- Microscopy (SEM, HRTEM, EDS) and electrical modelling show capacitive elements at MXene flakes and resistive–capacitive networks at metal–MXene interfaces, explaining enhanced shielding.
- Environmental stability is a concern: oxidation under high humidity degrades Cu-based films but Cr–Al capping mitigates the effect; edge oxidation remains a vulnerability.
- Practical demos: conformal 1 μm MXene and EXIM shields suppress EM noise from USB 3.0 flash drives (restoring Bluetooth operation) and reduce EMI-induced currents in flexible Schottky diodes.
- Direct formation of EXIM shields on polymer substrates is possible and yields comparable SE to laminated shields, though direct deposition can introduce stress-related device degradation.
Why should I read this?
Short answer: if you care about shrinking EMI shields without losing performance (think wearables, chiplets, flexible electronics), this paper shows how mixing metal and MXene layers gives big gains in tiny thicknesses. It’s hands-on, with real demos (USB drives, diodes) and practical fixes for humidity — so it isn’t just theory.
Context and relevance
This study is timely for anyone working on advanced packaging, flexible/wearable electronics, RF front-ends and chiplet integration where space and conformality are crucial. MXenes have been promising for EMI shielding; this work pushes their utility by showing that carefully engineered metal–MXene heterostructures can beat both single-metal and single-MXene films at sub-micron thicknesses. The combination of experimental SE data, analytical modelling and device demonstrations positions EXIM films as a practical route for next-generation, space-constrained EMI protection. Remaining challenges (humidity-driven oxidation, edge protection and deposition-induced stress) are identified and partly mitigated, pointing to near-term engineering solutions.