Direct patterning and electrospray deposition through EHD for fabrication of printed thin film transistors

This paper presents fabrication of thin film transistors using direct write technology following electrohydrodynamic approach for patterning and spray deposition. In this research colloidal solution of Ag nanoparticles is used for patterning of gate, source and drain contacts, while SiO2 and ZnO colloidal solutions are used for dielectric and semiconductor layers of TFTs using EHD printing technology. For direct patterning, different electrode configurations for inkjet head are used and a new nozzle head is developed for getting stable meniscus and uniform patterning. To minimize the disturbances caused by vertically inserted thin electrode, a hollow conductor is used in new setup, which serves both for ink feed and as an actuation electrode. The new configuration helps in minimizing the extraction voltage for jetting and also repeatability of experiment by keeping fixed parameters of the nozzle head is possible. By using metallic enclosed glass capillary head, conductive pattern lines for gate, source and drain contacts with good uniformity and regular boundaries are printed on glass substrate. Conductive lines having width of around 70 μm are achieved with appreciable aspect ratio. A channel length of 50 μm and width of 1.5 mm is obtained by using EHD direct printing of Ag colloidal solution. Layer thickness of SiO2 achieved is around 300 nm while ZnO thickness achieved is around 100 nm. A standard deviation in layer thickness of around 25 nm for SiO2 and 10 nm for ZnO electrosprayed layers is observed. A complete prototype of thin film transistor has been successfully fabricated by using EHD technology in this research. Contact angle analyzer is also used for finding various parameters like contact angle, wetting energy and spreading coefficient of the colloidal solutions which helps in determining the surface properties of the deposited layers. All experiments were performed in ambient conditions and environment.

► Electrohydrodynamic Inkjet steps development for manufacture of thin film transistor.
► Solution based Ag ink for conductive contacts achieving 25 μm channel length and 1.5 mm channel width.
► Electrospray of SiO2 for Dielectric layer around 300 nm thickness.
► Electrospray of ZnO for semiconductor layer around 100 nm thickness.