Nano-assembled carbon nanotube thin film based microstructures, field-effect transistors, and acetylcholine biosensors

In this work, we investigate the fabrication and applications of single-walled carbon nanotube (SWNT) based microdevices. The devices are fabricated with an effective technique that combines the "bottom-up" layer-by-layer (LbL) self-assembly process and the "top-down" microfabrication technique. The combinative technique provides a low-cost, fast, simple, and versatile approach to fabricate high-performance SWNT thin-film devices.; The process is highly repeatable and the self-assembled SWNT multilayer films provide both high mechanical strength and flexibility. The assembly of the SWNT thin film can be controlled in nanometer precision of 7.6 nm. The SWNT thin film has a Young's modulus of 17 GPa. Two-dimensional (2D) microstructures and three-dimensional (3D) cantilever arrays are fabricated using photoresist as the sacrificial material. The feature size of the microstructure is 5 mum. The cantilevers are highly flexible and can be deflected to over 90°.; The SWNT multilayers are promising candidates for high-mobility microelectronic devices. Thin-film transistors (TFTs) are fabricated using the self-assembled SWNT thin film as the semiconducting layer and SiO2 nanoparticle thin film as the dielectric layer. The TFT exhibits p-type transistor characteristics and operates in an accumulation mode. The vertically stacked SWNT layers have direct influence on the mobility of the transistors. Mobility enhancement as large as 35 times can be achieved. The highest mobility of the SWNT TFTs is 333.04 cm2/Vs. Furthermore, an increased number of SWNT layers can dramatically enhance the reliability of the devices.; The SWNT thin films and TFTs provide suitable platforms for high-performance biosensors. With self-assembled acetylcholinesterase (AChE) on the surface, both the SWNT thin film and the TFT can be used as acetylcholine (ACh) biosensors. The SWNT thin-film biosensor is capable of detecting ACh at an ultra-low concentration of 100 pM. The sensitivity and the response time of the sensor are measured as 7.2 muA/decade and 6 sec, respectively. The SWNT ion-sensitive field-effect transistor (ISFET) ACh sensor also demonstrates high performance: the resolution, sensitivity, and response time are 10 nM, 378.2 muA/decade, and 15 sec, respectively. Compared with other reported ACh sensors, our two SWNT biosensors have the advantages of higher performance and lower cost.