Enabling Durable Ultralow-k Capacitors with Enhanced Breakdown Strength in Density-Variant Nanolattices.

Ultralow-k materials used in high voltage devices require mechanical resilience and electrical and dielectric stability even when subjected to mechanical loads. Existing devices with organic polymers suffer from low thermal and mechanical stability while those with inorganic porous structures struggle with poor mechanical integrity. Recently, 3D hollow-beam nanolattices have emerged as promising candidates that satisfy these requirements. However, their properties are maintained for only five stress cycles at strains below 25%. Here, we demonstrate that alumina nanolattices with different relative density distributions across their height elicit a deterministic mechanical response concomitant with a 1.5-3.3 times higher electrical breakdown strength than nanolattices with uniform density. These density-variant nanolattices exhibit an ultralow-k of ≈1.2, accompanied by complete electric and dielectric stability and mechanical recoverability over 100 cyclic compressions to 62.5% strain. We explain the enhanced insulation and long-term cyclical stability by the bi-phase deformation where the lower-density region protects the higher-density region as it is compressed before the higher-density region, allowing to simultaneously possess high strength and ductility like composites. This study highlights the superior electrical performance of the bi-phase nanolattice with a single interface in providing stable conduction and maximum breakdown strength.

Recoverable Electrical Breakdown Strength and Dielectric Constant in Ultralow-k Nanolattice Capacitors.

The dielectric reliability of low-k materials during mechanical deformation attracts tremendous attention, owing to the increasing demand for thin electronics to meet the ever-shrinking form factor of consumer products. However, the strong coupling between dielectric/electric and mechanical properties limits the use of low-k dielectrics in industrial applications. We report the leakage current and dielectric properties of a nanolattice capacitor during compressive stress cycling. Electrical breakdown measurements during the stress cycling, combined with a theoretical model and in situ mechanical experiments, provide insights to key breakdown mechanisms. Electrical breakdown occurs at nearly 50% strain, featuring a switch-like binary character, correlated with a transition from beam bending and buckling to collapse. Breakdown strength appears to recover after each cycle, concomitant with nanolattice's shape recovery. The compressive displacement at breakdown decreases with cycling due to permanently buckled beams, transforming the conduction mechanism from Schottky to Poole-Frankel emission. Remarkably, our capacitor with 99% porosity, k ∼ 1.09, is operative up to 200 V, whereas devices with 17% porous alumina films breakdown upon biasing based on a percolation model. Similarly with electrical breakdown, the dielectric constant of the capacitor is recoverable with five strain cycles and is stable under 25% compression. These outstanding capabilities of the nanolattice are essential for revolutionizing future flexible electronics.

Additive Manufacturing of 3D-Architected Multifunctional Metal Oxides.

Additive manufacturing (AM) of complex three-dimensional (3D) metal oxides at the micro- and nanoscales has attracted considerable attention in recent years. State-of-the-art techniques that use slurry-based or organic-inorganic photoresins are often hampered by challenges in resin preparation and synthesis, and/or by the limited resolution of patterned features. A facile process for fabricating 3D-architected metal oxides via the use of an aqueous metal-ion-containing photoresin is presented. The efficacy of this process, which is termed photopolymer complex synthesis, is demonstrated by creating nanoarchitected zinc oxide (ZnO) architectures with feature sizes of 250 nm, by first patterning a zinc-ion-containing aqueous photoresin using two-photon lithography and subsequently calcining them at 500 ºC. Transmission electron microscopy (TEM) analysis reveals their microstructure to be nanocrystalline ZnO with grain sizes of 5.1 ± 1.6 nm. In situ compression experiments conducted in a scanning electron microscope show an emergent electromechanical response: a 200 nm mechanical compression of an architected ZnO structure results in a voltage drop of 0.52 mV. This photopolymer complex synthesis provides a pathway to easily create arbitrarily shaped 3D metal oxides that could enable previously impossible devices and smart materials.

Enabling Simultaneous Extreme Ultra Low-k in Stiff, Resilient, and Thermally Stable Nano-Architected Materials.

Low dielectric constant (low-k) materials have gained increasing popularity because of their critical role in developing faster, smaller, and higher performance devices. Their practical use has been limited by the strong coupling among mechanical, thermal, and electrical properties of materials and their dielectric constant; a low-k is usually attained by materials that are very porous, which results in high compliance, that is, silica aerogels; high dielectric loss, that is, porous polycrystalline alumina; and poor thermal stability, that is, Sr-based metal-organic frameworks. We report the fabrication of 3D nanoarchitected hollow-beam alumina dielectrics which k is 1.06-1.10 at 1 MHz that is stable over the voltage range of -20 to 20 V and a frequency range of 100 kHz to 10 MHz. This dielectric material can be used in capacitors and is mechanically resilient, with a Young's modulus of 30 MPa, a yield strength of 1.07 MPa, a nearly full shape recoverability to its original size after >50% compressions, and outstanding thermal stability with a thermal coefficient of dielectric constant (TCK) of 2.43 × 10-5 K-1 up to 800 °C. These results suggest that nanoarchitected materials may serve as viable candidates for ultra low-k materials that are simultaneously mechanically resilient and thermally and electrically stable for microelectronics and devices.