Hysteresis Caused by Water Molecules in Carbon Nanotube Field-Effect Transistors

Abstract

Carbon nanotube field-effect transistors commonly comprise nanotubes lying on SiO 2 surfaces exposed to the ambient environment. It is shown here that the transistors exhibit hysteresis in their electrical characteristics because of charge trapping by water molecules around the nanotubes, including SiO 2 surface-bound water proximal to the nanotubes. Hysteresis persists for the transistors in vacuum since the SiO 2bound water does not completely desorb in vacuum at room temperature, a known phenomenon in SiO 2 surface chemistry. Heating under dry conditions significantly removes water and reduces hysteresis in the transistors. Nearly hysteresis-free transistors are obtainable by passivating the devices with polymers that hydrogen bond with silanol groups on SiO 2 (e.g., with poly(methyl methacrylate) (PMMA)). However, nanotube humidity sensors could be explored with suitable water-sensitive coatings. The results may have implications to field-effect transistors made from other chemically derived materials.

Inkjet Printing of MoS2

“…The large hysteresis in Figure 5a should imply the presence of a number of charge traps on the MoS2 flakes. [35] Although MoS2 is intrinsically n-type semiconductor, liquid phase processing often introduces unintentional dopants or traps which may impact the electronic properties of MoS2. As a result, low on/off current ratio (3 ~ 6) as well as p-type gate modulation are often observed in the literature for transistors based on liquid-exfoliated individual MoS2 flakes.…”

Nanoscale Charge Percolation Analysis in Polymer‐Sorted (7,5) Single‐Walled Carbon Nanotube Networks

“…The gate leakage current was always found to be at least two orders of magnitude lower than the channel ON current, while the small operating hysteresis is attributed to atmospheric oxidants/adsorbates that are present even within the nitrogen glovebox, albeit at relatively small concentrations (~ppm). [39,40] Finally, the resulted electron and hole mobility values extracted are ~0.03 cm 2 V -1 s -1 and ~0.02 cm 2 V -1 s -1 respectively.…”

“…The charge transport properties of the as-spun (7,5) SWNT networks were also characterized using a bottom-gate, bottom-contact transistor architecture fabricated on Si ++ /SiO2 (400 nm- Previous reports [39][40][41] have in fact shown that n-type conduction is suppressed in most organic semiconductor-based transistors due to charge traps from the SiO2 interface and especially due to charge transfer to the oxygen/water layer that is strongly bound to the SiO2 surface, where the H2O/O2 redox couple occurs. This is particularly important for SWNTs since the valence band position of the (7,5) SWNT (EV ≈ -5.2 eV) lies very close to the redox potential of oxygen (EREDOX ≈ -5.3 eV) dissolved in slightly acidic water (pH = 6) adsorbed on the SiO2 surface.…”

Tunable conduction type of solution-processed germanium nanoparticle based field effect transistors and their inverter integration

“…Most likely the undesirable hysteresis is originating from trap states in the layer volume or at the semiconductor/dielectric interface 24,25 and/or trapped charges induced by water molecules adsorbed on the semiconductor layer. 6,26 Moreover, the high surface to volume ratio and the porous nature of the nanoparticle layers makes the surface chemistry of the nanoparticles become highly important with respect to the TFT device performance. 7 For this reason, spin coating of polymethyl methacrylate and ALD of alumina as a passivation layer on top of the TFT devices are investigated.…”