Effect of oxygen plasma treatment on horizontally aligned carbon nanotube thin film as pH-sensing membrane of extended-gate field-effect transistor

Abstract

The high-performance pH-sensing membrane of extended-gate field-effect transistors (EGFET) composed of high-conductivity horizontally aligned carbon nanotube thin films (HACNTFs) after oxygen plasma treatment is successfully demonstrated. The 10-µm-wide catalytic metal lines with 60 µm interspace produced CNT vertical plates, and the plates were mechanically pulled down and densified to form HACNTFs. A large amount of oxygen-containing functional groups are decorated on the CNTs after the oxygen plasma treatment. These functional groups act as the sensing sites and respond to the H + or OH % ions in solutions with different pH values. Therefore, these functionalized HACNTFs as pH-EGFET-sensing membranes can achieve a high voltage sensitivity of 40 mV/pH and high current sensitivity of 0.78 µA 1/2 /pH. Moreover, large linearity of 0.998 is measured in a wide sensing range from pH 1 to 13. These results reveal that the oxygen plasma treatment is an effective way to improve the CNTsensing characteristics in pH-EGFET sensors.

Interdigitated Extended Gate Field Effect Transistor Without Reference Electrode

“…The channel current can be modified using a concentration of H + ions, while the drain-source voltage V DS is kept constant. Figure 2 shows the transfer characteristics (drain current versus reference electrode voltage, I DS -V ref ) in the linear region for the IEGFET sensor for V DS fixed at 0.2 V and V ref varied from 0 to 4 V. According to the EGFET theory, the V T(IEGFET) could be estimated by using the relationship 5,6 :…”

“…3 An ISFET was employed to replace the fragile glass electrode in pH and ion concentration measurements. 4,5 However, the device suffered from poor isolation between the device and the solution causing the harsh environment in the solutions to degrade the device's reliability. 6,7 To overcome the disadvantages, in 1983, Van der Spiegel et al 8 improved an ISFET structure as an extended gate field effect transistor (EGFET).…”

Densification effects of the carbon nanotube pillar array on field-emission properties

“…The MWCNTs we grew are about 35-37 nm in diameter with about 40 walls. 13) The height of CNT pillars is controlled to be 10, 20, 30, 40, and 50 µm by adjusting synthesis time. The schematic procedure is shown in Figs.…”

The use of a multiple roughening scheme to enhance sensing performance of pH sensors with NiO nanosheets/multi-walled carbon nanotubes on KOH-etched Si substrates

“…Therefore, EGFET reveals many advantages over the conventional ISFET with low cost, simple to package with the FET isolated from its chemical environment, flexible shape of the extended-gate structure, and good long-term stability. [10][11][12] Recently, pH SEs using nanostructured materials such as zinc oxide (ZnO) based materials, 10,13,14) titanium oxide (TiO 2 ), [15][16][17] tin oxide (SnO 2 ), 18) vanadium pentoxide (V 2 O 5 ), 19,20) tungsten oxide (WO 3 ), 21,22) multi-walled carbon nanotube (MWCNT), [23][24][25][26][27] nickel oxide (NiO), 28,29) etc., to enhance the sensitivity of pH sensors was demonstrated. It shows that the increase in the amount of ion adsorption sites through increasing the surface area (SA) of metal oxides and MWCNT nanostructures, in addition to the material itself, is very beneficial for ion sensing.…”