Virtual MEchanics GAthering -MEGA- Seminar: Extended lifetime of partially cracked multilayer barriers for implantable electronics


Event details

Date and time 10.12.2020 16:1517:30  
Place and room
Zoom: Room Passcode: 349948
Speaker Kyungjin Kim (LSBI, EPFL)
Category Conferences - Seminars
Abstract: Next-generation bioelectronics develops towards flexible, soft, and lightweight to match dynamics and softness in vivo. Critical challenges in deploying miniaturized and compliant implantable bioelectronic interfaces are the design, synthesis, and validation of barrier coatings that combine hermeticity, biocompatibility, and microfabrication in agreement with physiological and therapeutic timescales. Such barriers are conformally coated thin-films, prepared with vacuum deposition methods, e.g. atomic layer and chemical vapor deposition (ALD and CVD). While the barriers prevent degradation from surroundings (e.g., water vapor, ions.), their interfaces and integrated devices call for providing high reliability under mechanical deformation. In this work, mechanical failure under tensile strain has been thoroughly studied to scrutinize mechanical reliability integrity in brittle, thin barrier films. Time-dependent cracking in flexible coatings under applied strain was characterized using an in-situ microscopy tensile test depending on environmental conditions. Next, nanolaminates with alternative organic and inorganic layers were fabricated, tested, and modeled to produce an optimized crack onset strain. Although an ultrathin metal oxide barrier offers a low water permeability, the presence of pinholes and defects hinder further improvement. Organic-inorganic multilayers were therefore investigated to separate such defects in the inorganic layers by the organic layers. These barrier films' chemical transport properties were assessed in parallel with their mechanical reliability and structural durability during flexural deformation. Channel cracks formed within the organic/inorganic multilayer structure were studied to calculate fracture energies to predict their failure mode. An ion-polished cross-sectional area of a multilayer film which was strained to crack onset strain confirmed the proposed partial channel crack configuration, preserving tortuous pathways even after cracking. Samples were characterized by a thin-film corrosion test, leakage current monitoring of interdigitated electrodes, and lifetime tests of coated optoelectronic devices under accelerated aging. The lifetime of structures coated with cracked multilayers displayed an extended lifetime equivalent to 3 years, exciting results as barriers are considered no longer functioning after cracking.

Bio: Kyungjin is a postdoctoral fellow in the Lacour lab for soft bioelectronic Interfaces at EPFL, working on ultrabarrier encapsulated neuroprosthetics. She received her PhD in 2018 from the Georgia Institute of Technology, USA, and BS in 2014 from KAIST, South Korea, in Mechanical Engineering. She is developing long-term functioning soft and deformable devices using vacuum processed hermetic encapsulations and various quality control methods.

Practical information

  • General public
  • Free


  • MEGA.Seminar Organizing Committee


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