Long term investigations of carbon nanotube transistors encapsulated by atomic-layer-deposited Al₂O₃for sensor applications

Abstract

Single-walled carbon nanotube field-effect transistors (CNFETs) are promising functional structures in future micro- or nanoelectronic systems and sensor applications. Research on the fundamental device concepts includes the investigation of the conditions for stable long term CNFET operation. CNFET operation in ambient air leads to on-state current degradation and fluctuating signals due to the well-known sensitivity of the electronic properties of the CNT to many environmental condition changes. It is the goal of device and sensor research to understand various kinds of sensor-environment interactions and to overcome the environmental sensitivity. Here, we show that the encapsulation of CNFETs by a thermal atomic-layer-deposited (ALD) aluminium oxide (Al(2)O(3)) layer of approximately 100 nm leads to stable device operation for 260 days and reduces their sensitivity to the environment. The characteristics of CNFETs prior to and after Al(2)O(3) encapsulation are comparatively investigated. It is found that encapsulation improves the stability of the CNFET characteristics with respect to the gate threshold voltage, hysteresis width and the on-state current, while 1/f noise is lowered by up to a factor of 7. Finally, CNFETs embedded in a dielectric membrane are employed as pressure sensors to demonstrate sensor operation of CNFETs encapsulated by ALD as piezoresistive transducers.

Nanomanufacturing Methods for the Reduction of Noise in Carbon Nanotube-Based Piezoresistive Sensor Systems

“…This source of flicker noise can be reduced in CNT-based sensors and transistors by encapsulating the CNTs in a ceramic coating in order to protect the CNTs from the outside environment. For example, it has been shown that encapsulating CNTs in 100 nm of atomic-layer-deposited aluminum oxide can increase device stability and decrease noise by almost an order of magnitude [26]. Similar results have been demonstrated for top-gated transistors where the ceramic encapsulation layer is used as the gate dielectric and passivation layer [27,28].…”

Hysteresis reduction and measurement range enhancement of carbon nanotube based NO2 gas sensors by pulsed gate voltages

“…The ALD alumina is not removed at the source and drain contact regions. It is a good protection layer for the electrodes against unwanted environmental influences 8 and helps to increase device stability 12 . The ALD alumina layer is grown in a Picosun Sunale R-150B reactor at 150°C and in N 2 atmosphere at low pressure with water and trimethylaluminum (TMA) as source media for the film growth.…”

Large-scale integration of single-walled carbon nanotubes and graphene into sensors and devices using dielectrophoresis: A review

“…Passivation of the devices with a protective layer, generally deposited by atomic layer deposition (ALD), ensures that the nanomaterials are not exposed to any further environmental and/or processing influences. 54 Identification of electrode-bridging nanomaterials is frequently performed by scanning electron microscopy at low acceleration voltages to minimize the risk of inducing any damage during visualization. Additional characterization can be carried out by AFM and electrical measurements.…”