Low temperature inkjet printable transistors can be stacked

Technology News |
By Julien Happich

In a paper titled “Exploiting the colloidal nanocrystal library to construct electronic devices”, co-authors Cherie Kagan, Professor in the School of Engineering and Applied Science, and Ji-Hyuk Choi, then a member of her lab, describe how they exploited the diversity of colloidal nanocrystals to design materials, interfaces, and processes to construct all-nanocrystal electronic devices using solution-based processes.

Tuneable colloidal nanocrystals ink formulations
make for printable transistors
Credit: University of Pennsylvania

The inks formulated with the tuneable colloidal nanocrystals included metallic silver and semiconducting cadmium selenide nanocrystals for the high-conductivity and high-mobility thin-film electrodes and channel layers of a FET, aluminium oxide nanocrystals to form high–dielectric constant gate insulator layers, and a mix of metallic indium nanocrystals and silver nanocrystals to integrate an indium supply in the deposited electrodes, to passivate and dope the cadmium selenide nanocrystal channel layer (through a low temperature dopant diffusion step).

Using a low-temperature multi-step spin coating process involving multiple photolithographic masks, as well as proprietary surface treatments of the nanocrystals, the researchers produced field-effect transistors with electron mobilities of 21.7cm2v-1s-1 on a flexible sheet of plastic.

Transistor fabrication process using multi-step spin coatings of photoresists through photolithographic masks, and colloidal nanocrystal inks with subsequent photoresist removal steps.  Credit: University of Pennsylvania

They are confident that the ink formulations could be used with ink-jet printers to lay transistors and circuits on a wide array of materials, including large and thin substrates for flexible or wearable applications.

In the future, they envisage that such formulations could become part of 3D-printing processes, adding multiple layers of circuits within the bulk of complex 3D objects.

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