On chip and freestanding elastic carbon films for micro supercapacitors
Flexible power for flexible electronics A challenge for flexible electronics is to couple devices with power sources that are also flexible. Ideally, they could also be processed in a way that is compatible with current microfabrication technologies. Huang et al. deposited a relatively thick layer of TiC on top of an oxide coated Si film. After chlorination, most, but importantly not all, of the TiC was converted into a porous carbon film that could be turned into an electrochemical capacitor. The carbon films were highly flexible, and the residual TiC acted as a stress buffer with the underlying Si film. The films could be separated from the Si to form free floating films, with the TiC providing a support layer. Science, this issue p. 691 Porous carbon based supercapacitors are directly fabricated onto silicon substrates. Integration of electrochemical capacitors with silicon based electronics is a major challenge, limiting energy storage on a chip. We describe a wafer scale process for manufacturing strongly adhering carbide derived carbon films and interdigitated micro supercapacitors with embedded titanium carbide current collectors, fully compatible with current microfabrication and silicon based device technology. Capacitance of those films reaches 410 farads per cubic centimeter/200 millifarads per square centimeter in aqueous electrolyte and 170 farads per cubic centimeter/85 millifarads per square centimeter in organic electrolyte. We also demonstrate preparation of self supported, mechanically stable, micrometer thick porous carbon films with a Young's modulus of 14.5 gigapascals, with the possibility of further transfer onto flexible substrates. These materials are interesting for applications in structural energy storage, tribology, and gas separation.
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