Key Issues With Printed Flexible Thin Film Transistors and Their Application in Disposable RF Sensors

Abstract

This paper outlines why hybrid printing processes for fabricating flexible organic thin film transistors is not transferrable to fully scalable printing processes because of threshold voltage (V th ) variations.

Fully Printed and Encapsulated SWCNT-Based Thin Film Transistors via a Combination of R2R Gravure and Inkjet Printing

“…1−3 Realization of these applications requires selection of materials and optimization of printing processes for the fabrication of fully printed thin film transistors (TFTs) with good stability and uniformity of threshold voltage (V th ). 4 Careful selection of semiconducting material such that it provides robust performance via printing will therefore be a key step to provide well-behaved fully printed TFTs. Among many printable semiconducting inks, semiconducting single walled carbon nanotubes (SWCNTs) have attracted the attention of the printed electronics community as a promising printable channel material due to their robustness, flexibility, and high intrinsic carrier mobility.…”

“…21,37−40 Device fabrication has been completed by vacuum deposition of gate dielectric and/or source/drain electrodes in some cases and fully printed TFT material layers in others. 14,34,35 Furthermore, examples of fully printed SWCNT-based TFTs employing rollto-roll (R2R) printing are rare 4,41,42 and have yet to be demonstrated with semiconducting-enriched SWCNT with a printed encapsulation layer to provide environmental stability. Herein, the efficacy of a hybrid printing system comprising R2R gravure and inkjet is examined in order to practically produce SWCNT-based fully printed TFTs with encapsulation to avoid environmental sensitivity of the SWCNT channel.…”

“…The limited on/off ratios at smaller drop spacing likely reflects the contribution of the very low fraction of residual metallic tubes (0.02%) in these highdensity networks (vide supra). For drop spacings above 20 μm the off-current decreased below 10 −7 A, leading to on/off ratios >1 0 4 . The mobility also decreased at higher drop spacing where the amount of SWCNTs deposited on the surface was reduced.…”

“…One method of assessing stability is by monitoring the output of a printed inverter circuit in response to digital ("0" and "1") input signals. 4,42,50 Variation will dictate the complexity of a circuit that can be realized with the present process technology and determine the suitability of printed TFTs in the target application. 4,42,50 Transfer curves from 20 encapsulated fully printed devices along a row show minimal variation ( Figure 9a).…”

“…4,42,50 Variation will dictate the complexity of a circuit that can be realized with the present process technology and determine the suitability of printed TFTs in the target application. 4,42,50 Transfer curves from 20 encapsulated fully printed devices along a row show minimal variation ( Figure 9a). The fully printed encapsulated device was used to construct an inverter (Figure 9b −1 s −1 using the estimated capacitance of 6.5 nF cm −2 .…”