Wavy TFTs drive more current, enable increased pixel densities

January 25, 2018 // By Julien Happich
In a paper titled "Wavy Architecture Thin-Film Transistor for Ultrahigh Resolution Flexible Displays", published in the Small journal, Researchers from the King Abdullah University of Science and Technology (KAUST) unveiled a vertically enhanced TFT architecture, where the channel presents multiple vertical fins stretching longitudinally across the transistor's source and drain.

Side view SEM of the planar (top) and wavy
channel (bottom) TFTs with 2µm tall 3µm wide “fins”
at a 6µm fin pitch. For the WTFT, the 3D wavy pattern
means a 70% larger operational width when compared
with coplanar devices.

The 3D wavy structure, with 2µm tall and 3µm wide "fins" repeated at a 6µm pitch give the channel a 70% larger operational width when compared with coplanar devices, allowing the wavy-channel TFTs (WC-TFT) to drive currents 70% higher per unit chip area.

By expanding the transistor's width vertically, through the implementation of grooved trenches, turn-on voltage or the OFF current values remain the same as traditional TFTs while benefiting from higher drive currents, the paper reports.

Device schematics for both coplanar TFT architecture
(top) and the wavy channel TFT architecture (bottom).

The researchers proved their new concept by fabricating WC-TFTs on a silicon substrate with ZnO/Al2O3/Al layers for the gate stack.

Once peeled off and transferred onto a flexible polydimethylsiloxane (PDMS) substrate, the transistors operated well with no degradation in their electrical performance or cracks in the gate stack even when flexed down to a bending radius of 5mm. “ON” current was only slightly lower, 10% lower than when bent to a radius of 1cm.