Abstract
To demonstrate that roll-to-roll (R2R) gravure printing is a suitable advanced manufacturing method for flexible thin film transistor (TFT)-based electronic circuits, three different nanomaterial-based inks (silver nanoparticles, BaTiO3 nanoparticles and single-walled carbon nanotubes (SWNTs)) were selected and optimized to enable the realization of fully printed SWNT-based TFTs (SWNT-TFTs) on 150-m-long rolls of 0.25-m-wide poly(ethylene terephthalate) (PET). SWNT-TFTs with 5 different channel lengths, namely, 30, 80, 130, 180, and 230 μm, were fabricated using a printing speed of 8 m/min. These SWNT-TFTs were characterized, and the obtained electrical parameters were related to major mechanical factors such as web tension, registration accuracy, impression roll pressure and printing speed to determine whether these mechanical factors were the sources of the observed device-to-device variations. By utilizing the electrical parameters from the SWNT-TFTs, a Monte Carlo simulation for a 1-bit adder circuit, as a reference, was conducted to demonstrate that functional circuits with reasonable complexity can indeed be manufactured using R2R gravure printing. The simulation results suggest that circuits with complexity, similar to the full adder circuit, can be printed with a 76% circuit yield if threshold voltage (Vth) variations of less than 30% can be maintained.
Highlights
Directly related to the various trapped charges (Ntr(t)) and the gate oxide capacitance (Co) in printed thin film transistor (TFT) (Δ Vth(t) = eNtr(t)/Co)[3] and to the printed physical dimensions, such as the thickness, surface roughness and edge waviness of printed patterns
The scalability of the R2R gravure system for manufacturing flexible and rollable devices was indirectly proven through the Monte Carlo simulations using the extracted electrical parameters from forward IV measurements in R2R gravure-printed single-walled carbon nanotubes (SWNTs)-TFTs with channel lengths of 30 to 230 μ m
By employing a Vth variation of 30% in the fully R2R gravure-printed SWNT-TFT, the full adder or less than 53 SWNT TFT-based electronic devices can be manufactured with a circuit yield of 76% for the 130 μ m channel length case
Summary
The overlay printing registration accuracy must be controlled within ± 10% of the width of the gate electrodes in both the machine and transverse directions To satisfy these conditions, while providing a sheet resistance of less than 1 Ω /sq for printed electrodes and a capacitance of at least 6 nF/cm[2] for printed dielectric layers, commercially available silver-nanoparticle-based inks and BaTiO3-nanoparticle-based ink were selected because they exhibited good electrical properties for printing TFTs with a web transfer speed of up to 12 m/min[14]. A 1-bit adder circuit integrating 53 SWNT-TFTs was used as a reference circuit and simulated using Monte Carlo simulations with three different ranges of Vth variation (10, 20, and 30%) to refine the optimal device dimension for manufacturing the 1-bit adder circuit using the R2R gravure printing system
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