Extended Barrier Lifetime of Partially Cracked Organic/Inorganic Multilayers for Compliant Implantable Electronics

Abstract

Flexible and soft bioelectronics display conflicting demands on miniaturization, compliance, and reliability. Here, the authors investigate the design and performance of thin encapsulation multilayers against hermeticity and mechanical integrity. Partially cracked organic/inorganic multilayer coatings are demonstrated to display surprisingly year‐long hermetic lifetime under demanding mechanical and environmental loading. The thin hermetic encapsulation is grown in a single process chamber as a continuous multilayer with dyads of atomic layer deposited (ALD) Al2O3‐TiO2 and chemical vapor deposited Parylene C films with strong interlayer adhesion. Upon tensile loading, tortuous diffusion pathways defined along channel cracks in the ALD oxide films and through tough Parylene films efficiently postpone the hermeticity failure of the partially cracked coating. The authors assessed the coating performance against prolonged exposure to biomimetic physiological conditions using coated magnesium films, platinum interdigitated electrodes, and optoelectronic devices prepared on stretchable substrates. Designed extension of the lifetime preventing direct failures reduces from over 5 years yet tolerates the lifetime of 3 years even with the presence of critical damage, while others will directly fail less than two months at 37 °C. This strategy should accelerate progress on thin hermetic packaging for miniaturized and compliant implantable electronics.

Recent Advances in Encapsulation of Flexible Bioelectronic Implants: Materials, Technologies, and Characterization Methods

“…To characterize the influence of the mechanics on the coating's performance, a standard way is to evaluate the mechanical failure induced by the formation and propagation of defects, delamination and tearing effects, and to assess the water diffusion in case of partially cracked/degraded coatings, as reported in. [73,365,366] Hence, (electro-)fragmentation tests associated with residual stress analyses and nanoindentation tests [106] are usually performed to determine the critical strain for failure, the internal stress components, the Young's modulus of the nanosized films, and derive the toughness properties of the film and interfaces. [82,[367][368][369][370][371] (Figure 8D(i)).…”

“…The intrinsic mechanical integrity of the packaging material as well as its compatibility with the substrate, are necessary conditions for its barrier performance. [ 73,74 ] Table 1 lists the main parameters related to the cohesive behavior (crack onset strain (COS), cohesive fracture energy) or the adhesive behavior (crack density at saturation, interfacial shear strength, adhesion peel resistance, adhesive peeling energy).…”

Biomedical Microtechnologies Beyond Scholarly Impact

“…Research in microelectronics has led to the development of microchips with increased computational capacity and better energy efficiency, which will power future implantable devices [29,30]. New engineering strategies are being studied to develop adequate packaging techniques for bioelectronic implants using for instance high barrier performance materials [31] or complex architectures [32]. Advances in organic electronics will supply medical devices with better performing biointerfacing materials for charge transduction in sensing and stimulation applications [33][34][35][36][37].…”

flexLiTE: flexible micro-LED integrated optoelectrodes for long-term chronic deep-brain studies

“…2B:3-4 and C:2-3). The Al2O3 layer was deposited to passivate the traces (30 nm thick) [42][43]. Next, Titanium and Gold metal composites were defined for metal traces by lift-off.…”