SUBJECT: Ph.D. Proposal Presentation
BY: Kyungjin Kim
TIME: Friday, December 1, 2017, 1:00 p.m.
PLACE: MRDC Building, 3510
TITLE: Mechanical Reliability of Thin Barrier Films for Flexible Electronics
COMMITTEE: Dr. Samuel Graham, Co-Chair (ME)
Dr. Olivier N. Pierron, Co-Chair (ME)
Dr. Suresh K. Sitaraman (ME)
Dr. Ting Zhu (ME)
Dr. Mark D. Losego (MSE)


Flexible electronics has been developed as an excellent candidate of next generation devices because of its thin, light-weight features combined with low manufacturing costs which will enable widespread use in mobile and wearable applications. Here, mechanical reliability has been in demand for ensuring stable and accurate functioning of all those applications. Since flexible substrate consists of thin organic materials which are vulnerable to gas permeation, ultrathin barrier films consisting of inorganic brittle materials are deposited as an encapsulation layer to protect the functional layer of the device from oxygen and moisture permeation. Typically, mechanical failure which limits the reliability of thin brittle film under deformation by stretching or bending has been described by the concept of crack onset strain, i.e. applied strain value initiating crack propagation. However, the crack onset strain itself is not sufficient to satisfy the integrity of mechanical reliability in brittle thin film since time dependent deformation can be induced especially in the flexible electronics applications such as bendable or foldable devices which are under applied strain for a period of time. Preliminary result elucidated the origin of subcritical cracking in barriers on polymer substrate by measuring the growth rates as a function of driving force along with presenting numerical models to differentiate the contribution of polymer relaxation from that of environmentally assisted cracking. Testing technique was also further developed to standardize this testing method for future repeatable works which can be applied to all thin film materials undergoing subcritical cracking. Recently, multilayer coating alternating organic and inorganic layer has been suggested to be a smart method optimizing barrier performance by producing both high crack onset strain and high resistance to gas permeation. To optimize the crack onset strain in multilayer barrier structure, besides the materials properties of both organic / inorganic films, thickness of each layer becomes key factor. Proposed work can be summarized as follows: (1) achieve the highest crack onset strain in nanolaminate barriers through the experimental procedure. (2) create a mechanically reliable SiNx barrier that can effectively broaden the usage to harsher mechanical and environmental conditions.