A Physics of Failure Based Qualification Process for Flexible Display Interconnect Materials
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The next paradigm shift in display technology involves making them flexible, bringing with it many challenges with respect to product reliability. To compound the problem, industry is continuously introducing novel materials and experimenting with device geometries to improve flexibility and optical performance. Hence, a method to rapidly qualify these new designs for high reliability applications is imperative. This dissertation involves the development of a qualification process for gate line interconnects used in flexible displays. The process starts with the observed failure mode of permanent horizontal lines in the displays, followed by the identification of the underlying failure mechanism. Finite element analyses are developed to determine the relationship between the physical flexing and the mechanical stress imposed on the traces. The design of an accelerated life test is performed based on the known agent of failure being cyclic bending that induces a tensile strain. A versatile dedicated test system is designed and integrated in order to rapidly capture changes in resistance of multiple traces during test. Dedicated test structures are also designed and fabricated to facilitate in-situ electrical measurements and direct observations. Since the test structures were consumed during the integration of the test system, random failure times are used in the process of determining a life-stress model. Different models are compared with respect to their applicability to the underlying failure mechanism as well as parameter estimation techniques. This methodology may be applied towards the rapid qualification of other novel materials, process conditions, and device geometries prior to their widespread use in future display systems.