Suspended Carbon Nanotubes for Humidity Sensing

Abstract

A room temperature microfabrication technique using SU8, an epoxy-based highly functional photoresist as a sacrificial layer, is developed to obtain suspended aligned carbon nanotube beams. The humidity-sensing characteristics of aligned suspended single-walled carbon nanotube films are studied. A comparative study between suspended and non-suspended architectures is done by recording the resistance change in the nanotubes under humidity. For the tests, the humidity was varied from 15% to 98% RH. A comparative study between suspended and non-suspended devices shows that the response and recovery times of the suspended devices was found to be almost 3 times shorter than the non-suspended devices. The suspended devices also showed minimal hysteresis even after 10 humidity cycles, and also exhibit enhanced sensitivity. Repeatability tests were performed by subjecting the sensors to continuous humidification cycles. All tests reported here have been performed using pristine non-functionalized nanotubes.

Ionization Gas Sensor Using Suspended Carbon Nanotube Beams

“…This fabrication process had been adopted from [25] and was derived from the process in [14] used to fabricate CNT humidity sensors. However, the fabrication process diverged from the work in [14] by adding the bottom electrode layer to implement the ionization sensor. The SEM micrograph of the fabricated device is shown in Figure 2a.…”

“…All the processing steps were below a temperature budget of 115 • C, making the process amenable to monolithic integration with electronics or other sensors. This fabrication process had been adopted from [25] and was derived from the process in [14] used to fabricate CNT humidity sensors. However, the fabrication process diverged from the work in [14] by adding the bottom electrode layer to implement the ionization sensor.…”

“…Li et al [13] fabricated suspended CNT microlines on a polymeric substrate using a wet contact printing method. More recently, suspended chemical CNT sensors have been used to sense humidity [14] with minimal hysteretic effects due to the mitigation of substrate effects [15]. The increase in surface area for adsorption of the analyte also results in better sensitivity and long-term stability of the sensor.…”

An Overview of the Recent Progress in the Synthesis and Applications of Carbon Nanotubes

“…The nanosized carbons (or nanocarbons) comprise fullerenes, graphene and CNT [2]. Extraordinary importance is given to graphene and CNTs, as they play a vital role in current advances based on nanomaterials, including conductive and high-strength composites [3], artificial implants [4], drug delivery systems [5], sensors [6], energy conversion and storage devices [7], radiation sources [8] and field emission displays [9], hydrogen storage media [10] and nanometer-sized semiconductor devices [11], probes [12], and interconnects [13]. Radushkevish and Lukyanovich first detected and described CNTs in 1952 [14], and later, the SWCNTs were observed by Oberin in 1976 [15].…”

Chlorinated holey double-walled carbon nanotubes for relative humidity sensors

“…A standard procedure to increase the interaction between a CNT and gaseous H 2 O molecules is the grafting of oxygen containing groups to the outer wall. Humidity sensors based on oxygen functionalized CNTs have a fast response followed by a long recovery (usually between 1 and 2 min) [19,20], unfortunately. This can be due in particular to a strong interaction of H 2 O with car boxylic groups [15].…”