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

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

Recoverable electrical breakdown strength and dielectric constant in ultra-low 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

Specific CD8+ T cell responses correlate with control of simian immunodeficiency virus replication in Mauritian cynomolgus macaques

Specific major histocompatibility complex (MHC) class I alleles are associated with an increased frequency of spontaneous control of human and simian immunodeficiency viruses (HIV and SIV). The mechanism of control is thought to involve MHC class I-restricted CD8+ T cells, but it is not clear whether particular CD8+ T cell responses or a broad repertoire of epitope-specific CD8+ T cell populations (termed T cell breadth) are principally responsible for mediating immunologic control. To test the hypothesis that heterozygous macaques control SIV replication as a function of superior T cell breadth, we infected MHC-homozygous and MHC-heterozygous cynomolgus macaques with the pathogenic virus SIVmac239. As measured by a gamma interferon enzyme-linked immunosorbent spot assay (IFN-γ ELISPOT) using blood, T cell breadth did not differ significantly between homozygotes and heterozygotes. Surprisingly, macaques that controlled SIV replication, regardless of their MHC zygosity, shared durable T cell responses against similar regions of Nef. While the limited genetic variability in these animals prevents us from making generalizations about the importance of Nef-specific T cell responses in controlling HIV, these results suggest that the T cell-mediated control of virus replication that we observed is more likely the consequence of targeting specificity rather than T cell breadth

3D printing of multifunctional metal oxides via a novel photopolymer system

In recent years, 3D printing of ceramics has become a significant area of interest as it has the potential to remove the geometrical limitations assocd. with the current state of the art of ceramic processing. In particular, processes involving photolithog. are esp. promising due to the high resoln. and small feature sizes achievable.These photolithog. systems typically consist of photosensitive slurries, where fine powders of the desired ceramic of choice are dispersed in a photosensitive org. binder. By selectively exposing certain parts of the slurry, a green body can be made. A subsequent high temp. treatment then burns off the org. binder and sinters together the remaining ceramic powders into a dense ceramic part.The advantages of these systems are that it's simple and versatile - as long as the desired ceramic can be obtained in powder form and can be dispersed in the binder, the slurry can be obtained and the part 3D printed. However, the slurry often has to have a high loading of ceramic particles, which increases the viscosity and refractive index of the slurry, making it difficult to print with. In this presentation, a new photopolymer system that circumvents the problems of powder loading is demonstrated. As an example of this technique, we demonstrate the printing of zinc oxide (ZnO) architected structures. ZnO is traditionally deposited as films and can only be made 3D via a multistep process that involves depositing a thick layer of ZnO and then using an ion-mill to cut out the structure desired. Here, we show a two-step process to fabricate monolithic ZnO structures out of any arbitary design. Characterization of these structures verify that the structures are indeed zinc oxide. Compression of these materials also results in a voltage response, showing the piezoelec. behavior of these structures

3D printing of multifunctional metal oxides via a novel photopolymer system

In recent years, 3D printing of ceramics has become a significant area of interest as it has the potential to remove the geometrical limitations assocd. with the current state of the art of ceramic processing. In particular, processes involving photolithog. are esp. promising due to the high resoln. and small feature sizes achievable.These photolithog. systems typically consist of photosensitive slurries, where fine powders of the desired ceramic of choice are dispersed in a photosensitive org. binder. By selectively exposing certain parts of the slurry, a green body can be made. A subsequent high temp. treatment then burns off the org. binder and sinters together the remaining ceramic powders into a dense ceramic part.The advantages of these systems are that it's simple and versatile - as long as the desired ceramic can be obtained in powder form and can be dispersed in the binder, the slurry can be obtained and the part 3D printed. However, the slurry often has to have a high loading of ceramic particles, which increases the viscosity and refractive index of the slurry, making it difficult to print with. In this presentation, a new photopolymer system that circumvents the problems of powder loading is demonstrated. As an example of this technique, we demonstrate the printing of zinc oxide (ZnO) architected structures. ZnO is traditionally deposited as films and can only be made 3D via a multistep process that involves depositing a thick layer of ZnO and then using an ion-mill to cut out the structure desired. Here, we show a two-step process to fabricate monolithic ZnO structures out of any arbitary design. Characterization of these structures verify that the structures are indeed zinc oxide. Compression of these materials also results in a voltage response, showing the piezoelec. behavior of these structures

Enabling Simultaneous Extreme Ultra Low‑<i>k</i> in Stiff, Resilient, and Thermally Stable Nano-Architected Materials

Low dielectric constant (low-<i>k</i>) 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-<i>k</i> 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 <i>k</i> 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-<i>k</i> materials that are simultaneously mechanically resilient and thermally and electrically stable for microelectronics and devices