Long term investigations of carbonn anotube transistors encapsulated by atomic-layer-deposited Al_2O_3 for sensor applications

摘要

Single-walled carbon nanotube field-effect transistors (CNFETs) are promising functionalstructures in future micro- or nanoelectronic systems and sensor applications. Research on thefundamental device concepts includes the investigation of the conditions for stable long termCNFET operation. CNFET operation in ambient air leads to on-state current degradation andfluctuating signals due to the well-known sensitivity of the electronic properties of the CNT tomany environmental condition changes. It is the goal of device and sensor research tounderstand various kinds of sensor–environment interactions and to overcome theenvironmental sensitivity. Here, we show that the encapsulation of CNFETs by a thermalatomic-layer-deposited (ALD) aluminium oxide (Al_2O_3) layer of approximately 100 nm leadsto stable device operation for 260 days and reduces their sensitivity to the environment. Thecharacteristics of CNFETs prior to and after Al_2O_3encapsulation are comparativelyinvestigated. It is found that encapsulation improves the stability of the CNFET characteristicswith respect to the gate threshold voltage, hysteresis width and the on-state current, while 1/fnoise is lowered by up to a factor of 7. Finally, CNFETs embedded in a dielectric membrane areemployed as pressure sensors to demonstrate sensor operation of CNFETs encapsulated byALD as piezoresistive transducers.