A General Route toward Complete Room Temperature Processing of Printed and High Performance Oxide ElectronicsWhile thin-film transistor (TFT) devices and circuits have existed for decades now, mostly as switching circuit arrays for addressing pixels for display applications, the emergence of flexible and printed sensor device applications have renewed the emphasis for high performance TFT integrated circuits and systems. Common functions for most sensor systems include signal amplification, and analog-to-digital conversion (ADC) prior to data storage or transmission to conventional electronics, which tend to require custom interface designs for standardized silicon chips. Diverging from traditional silicon electronics, a custom printed circuit enabling this functional interface to external silicon electronics provides a versatile approach to standardizing the silicon electronics components that can be readily adapted to a broad range of sensor types and applications. Furthermore, if sensors and TFT circuits and subsystem functions can be readily printed on flexible substrates scalable to high throughput production processes, for example roll-to-roll (R2R) or sheet-to-sheet (S2S) processes, then key challenges associated with cost and performance can be addressed for grand challenge applications such as the Internet of Things (IoT), or wearable health monitoring devices.
Voltage-Controlled Ring Oscillators Based on Inkjet Printed Carbon Nanotubes and Zinc Tin OxideAn approach that has gained a significant amount of attention is the direct printing of TFT device layers and architectures from nanomaterials dispersions or inks that can be readily printed and patterned using predominantly additive approaches such as inkjet, gravure, flexographic, or nanoimprint patterning that are scalable to production platforms. A key challenge has been developing nanoparticle dispersions or inks that are stable and reproducible. One approach to circumvent this is to functionalize the nanoparticles with ligands that provide stable, well-dispersed solutions on the one hand, while not degrading electronic properties of the semiconducting nanomaterial films after printing and curing. An example is the results reported by Baby et. al. where complimentary TFT devices were fabricated using nanoparticles of Indium Oxide (In2O3) for the n-type and Copper Oxide (Cu2O) for the p-type device dispersed using sodium poly acrylic acid (PAANa) ligands. Simple inverter circuits were demonstrated using inkjet printing. In another example, Kim et. al. fabricated double gate voltage controlled ring oscillator circuits using single-wall carbon nanotubes (SWCNT) as the p-channel device and Zinc Oxide (ZnO) nanoparticles for the n-channel device. Inkjet printing of the semiconductor films was complimented by atomic layer deposition (ALD) of the alumina (Al2O3) gate dielectric film. Additionally, Ha et. al. reported on the use of self assembled nano-dielectric film using high-k zirconia (ZrO) and hafnia (HfO) nanoparticle dispersions with polar organic chemistries to create a well-controlled gate dielectric film.
Hybrid Gate Dielectric Materials for Unconventional Electronic CircuitryThus, a range of nanomaterials, dispersion chemistries, and nanomanufacturing processes have been demonstrated recently enabling complete solution-based process compatibility for active TFT devices and circuits. These results will provide key enablers for advancement of flexible printed circuits and subsystems supporting future sensor platforms and networks for applications in wearables, smart textiles, health and infrastructure monitoring, and IoT.
