Thin, physically transferred layers of silicon dioxide (SiO2) thermally grown on the surfaces of silicon wafers offer excellent properties as long-lived, hermetic biofluid barriers in flexible electronic implants. This paper explores materials and physics aspects of the transport of ions through the SiO2 and the resultant effects on device performance and reliability. Accelerated soak tests of devices under electrical bias stress relative to a surrounding phosphate buffered saline (PBS) solution at a pH of 7.4 reveal the field dependence of these processes. Similar experimental protocols establish that coatings of SiNx on the SiO2 can block the passage of ions. Systematic experimental and theoretical investigations reveal the details associated with transport though this bilayer structure, and they serve as the basis for lifetime projections corresponding to more than a decade of immersion in PBS solution at 37 °C for the case of 100/200 nm of SiO2/SiNx. Temperature-dependent simulations offer further understanding of two competing failure mechanisms—dissolution and ion diffusion—on device lifetime. These findings establish a basic physical understanding of effects that are essential to the stable operation of flexible electronics as chronic implants.
Bibliographical noteFunding Information:
E.S. and H.F. contributed equally to this work. This work was supported by Defense Advanced Research Projects Agency Contract HR0011-14-C-0102 and the Center for Bio-Integrated Electronics. This work was supported through the NCN-NEEDS program, which was funded by the National Science Foundation, contract 1227020-EEC. The authors acknowledge the use of facilities in the Micro and Nanotechnology Laboratory for device fabrication and the Frederick Seitz Materials Research Laboratory for Advanced Science and Technology for device measurement at the University of Illinois at Urbana-Champaign. E.S. acknowledges support from China Scholarship Council.
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All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials