Investigating the Nucleation of AlOx and HfOx ALD on Polyimide: Influence of Plasma Activation

There is an increasing interest in atomic layer deposition (ALD) on polymers for the development of membranes, electronics, (3D) nanostructures and specially for the development of hermetic packaging of the new generation of flexible implantable micro-devices. This evolution demands a better understanding of the ALD nucleation process on polymers, which has not been reported in a visual way. Herein, a visual study of ALD nucleation on polymers is presented, based on the different dry etching speeds between polymers (fast) and metal oxides (slow). An etching process removes the polyimide with the nucleating ALD acting as a mask, making the nucleation features visible through secondary electron microscopy analyses. The nucleation of both Al2O3 and HfO2 on polyimide was investigated. Both materials followed an island-coalescence nucleation. First, local islands formed, progressively coalescing into filaments, which connected and formed meshes. These meshes evolved into porous layers that eventually grew to a full layer, marking the end of the nucleation. Cross-sections were analyzed, observing no sub-surface growth. This approach was used to evaluate the influence of plasma-activating polyimide on the nucleation. Plasma-induced oxygen functionalities provided additional surface reactive sites for the ALD precursors to adsorb and start the nucleation. The presented nucleation study proved to be a straightforward and simple way to evaluate ALD nucleation on polymers.

Fabrication of Functionally Graded Diamond/Al Composites by Liquid–Solid Separation Technology

The electronic packaging shell, the necessary material for hermetic packaging of large microelectronic device chips, is made by mechanical processing of a uniform block. However, the property variety requirements at different positions of the shell due to the performance have not been solved. An independently developed liquid–solid separation technology is applied to fabricate the diamond/Al composites with a graded distribution of diamond particles. The diamond content decreases along a gradient from the bottom of the shell, which houses the chips, to the top of the shell wall, which is welded with the cover plate. The bottom of the shell has a thermal conductivity (TC) of 169 W/mK, coefficient of thermal expansion (CTE) of 11.0 × 10−6/K, bending strength of 88 MPa, and diamond content of 48 vol.%. The top of the shell has a TC of 108 W/mK, CTE of 19.3 × 10−6/K, bending strength of 175 MPa, and diamond content of 15 vol.%, which solves the special requirements of different parts of the shell and helps to improve the thermal stability of packaging components. Moreover, the interfacial characteristics are also investigated. This work provides a promising approach for the preparation of packaging shells by near-net shape forming.

A Minimal Volume Hermetic Packaging Design for High-Energy-Density Micro-Energy Systems

Hermetic packaging is critical to the function of many microscale energy storage and harvesting devices. State-of-the-art hermetic packaging strategies for energy technologies, however, are designed for macroscale devices and dramatically decrease the fraction of active materials when applied to micro-energy systems. We demonstrated a minimal volume hermetic packaging strategy for micro-energy systems that increased the volume of active energy storage materials by 2× and 5× compared to the best lab scale microbatteries and commercial pouch cells. The minimal volume design used metal current collectors as a multifunctional hermetic shell and laser-machined hot melt tape to provide a thin, robust hermetic seal between the current collectors with a stronger adhesion to metals than most commercial adhesives. We developed the packaging using commercially available equipment and materials, and demonstrated a strategy that could be applied to many kinds of micro-energy systems with custom shape configurations. This minimal, versatile packaging has the potential to improve the energy density of current micro-energy systems for applications ranging from biomedical devices to micro-robots.