Inkjet printed thin and uniform dielectrics for capacitors and organic thin film transistors enabled by the coffee ring effect

• Printed uniform dielectric layers as thin as 70 nm have been demonstrated.
• This is enabled by taking advantage of the coffee ring effect.
• Printing parameters were optimised to enhance the coffee ring effect.
• Fully printed capacitors with high capacitance (230 pF/mm2) were achieved.
• The thin and uniform dielectric enabled high performance TFTs and logic gates.

The deposition of a thin and uniform dielectric layer is required for high performance printed capacitors and thin film transistors (TFTs), however this is difficult to achieve with printing methods. We have demonstrated inkjet-printed dielectrics with a uniform thickness from 70 nm to 200 nm by taking advantage of the coffee ring effect. A high capacitance per unit area of 230 pF/mm2 is achieved from capacitors with linear morphologies fully printed onto flexible substrates. We also demonstrate organic TFTs with an average mobility of 0.86 cm2/Vs and a source drain current of 57 μA obtained with a supply voltage of 15 V. This performance was shown to be consistent, with a standard deviation of 15% obtained from hundreds of printed organic TFTs on PET substrates. This consistency was further validated by the production of functional NAND, NOR, AND and OR logic gates. Our results demonstrate that the coffee ring effect, which is usually viewed as undesirable, can enable higher performance in printed electronic devices.

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