Conformal Hermetic Sealing of Wireless Microelectronic Implantable Chiplets by Multilayered Atomic Layer Deposition (ALD)

Abstract

A hermetic sealing method of sub-mm sized microelectronic chiplets for wireless body implants is presented by ultrathin and electromagnetically transparent Atomic Layer Deposition (ALD) coatings. Fully 3-dimensional (3D) conformal encapsulation of wirelessly powered microdevices is demonstrated both with and without opening windows for electrophysiological measurements. The chiplets embedding custom CMOS application specific integrated circuits (ASICs) with RF transmitters are encapsulated by a stack of alternating layers of Hafnium oxide (HfO 2 ) and Silicon dioxide (SiO 2 ) as the strategy to maximize impermeability of water and ionic penetration while minimizing the volume of the packaging material. The hermeticity of the devices is characterized through accelerated aging tests in saline at T=87˚C while continued functionality is monitored via evaluation of backscattered RF signals (near 1 GHz) to ascertain possible degradation and electronic failure. Earliest failures of wirelessly functional devices have occurred after more than 180 days of immersion at 87˚C. Wireless device having opening windows through ALD envelope have not shown any signs of degradation for more than 95 days so far. This implies an equivalent lifetime >10 years at T=37˚C. This approach is readily scalable to high throughput batch processing of hundreds of microchiplets, offering a methodology for hermetic packaging of microscale biomedical chronic implants.

A Scalable and Low Stress Post-CMOS Processing Technique for Implantable Microsensors

“…This technique has been demonstrated in the post-processing of wireless microimplant, which mainly requires single-layer lift-off for electrode patterning. However, other microfabrication processes, such as dry etching, can be combined, as shown in our previous work [ 41 ], to make the opening in hermetic packaging. The deformation of PDMS during processing was not observed in this work, even with the use of various chemicals, including photoresists, developers, and stripper.…”

Wireless Ensembles of Sub-mm Microimplants Communicating as a Network near 1 GHz in a Neural Application

“…4b right) for use as intracortical electrodes such as used in the microstimulation experiments. For long term chronic device implantation, not the goal of this paper, we have reported elsewhere the development of ultrathin dielectric coatings, applied by atomic vapor deposition, to obtain biocompatible, hermetically sealed neurograins [36].…”

A Chip Integrity Monitor for Evaluating Long-term Encapsulation Performance Within Active Flexible Implants

“…Despite their long-term reliability, these implants end up having large volumes, are heavy, and unlike biological tissue, are stiff and rigid. For this reason, a great deal of research has been dedicated to replacing the bulky titanium cases with flexible polymers and thin-film coating layers [1], [2]. Recently, these efforts have been further endorsed by the new field of bioelectronic medicine, in which small, flexible, and lightweight implants are needed for targeting the delicate nerve structures within the body [3].…”