Understanding coupled electro-thermal processes in the catastrophic failure of organic electronic devices

The large-scale application of semiconducting polymers in organic electronics is hindered significantly by catastrophic device failure. Some of these processes are associated with coupled phenomena of electro-migration and thermal localization, which are poorly understood till date. In this paper we identify structural instability and its sources in a simple device configuration consisting of a semiconducting polymer sandwiched between two metal electrodes and subjected to various DC operating voltages. The coupled effect of temperature and electric fields leads to fracture of the polymer layer and the metal electrode layer, interestingly, in mutually exclusive regions. This failure is significantly observable beyond a certain applied voltage. It is observed that defects nucleate in a chain-like pattern with alternating fracture sites of polymer and metal electrode respectively. We subsequently propose a coupled electro-thermal mechanism which explains the observed phenomena. The mechanism is further validated by an analytical model of stress due to thermal and electric field distributions. The model predicts criteria of failure, which are interestingly complementary for the polymer and the electrode films, and hence explains the observation of the chain-like nucleation pattern. The failure criteria are functions of device geometry, operating voltage and temperature. This study will be useful toward reliability-based design of organic electronic devices including important factors such as coupled electro-thermal response and length-scale. The study also opens up important fundamental questions relating to the spatio-temporal evolution of electro-thermally induced minuscule electrical shorts in thin-film electronic devices.