High-Current Nanotube Transistors

Abstract

Planar field effect transistors (FET) consisting of a large number of parallel single-walled carbon nanotubes (SWCNT) have been fabricated that allow very high on-currents of the order of several milliamperes and on/off ratios exceeding 500.With these devices it is demonstrated, for the first time, that SWCNTs can be used as transistors to control macroscopic devices, e.g., light emitting diodes and electromotors. Those transistors were fabricated by a very simple process that is based on the catalytic chemical vapor deposition (CCVD) growth of SWCNTs at low temperatures, a single lithographic step to define the source and drain contacts, and a bias pulse to eliminate the metallic SWCNTs.There has been tremendous interest in carbon nanotubes in the past decade 1 due to their superior electronic properties and the possibility that they could replace silicon in future nanoelectronic devices if the integration challenges can be solved. However, carbon nanotubes are also interesting for applications where larger currents have to be switched or detected, e.g., power transistors, flexible electronics, or sensors. Since the maximum current per individual SWCNT is limited to about 25 µA, 2 a parallel arrangement of a large number of SWCNTs is required. Fabrication of such an arrangement requires a process to grow or deposit SWCNTs uniformly on a substrate. Catalytic CVD allows the growth of very clean, amorphous carbon-free SWCNTs on substrates and the control over the density of active catalytic sites and, therefore, the density of the SWCNTs. Control of the SWCNT density is very important in order to achieve transistors with uniform performance, for reasons discussed below. Extensive studies of the CVD growth have shown that this can be achieved by varying the catalyst material, catalyst layer thickness, and the growth parameters. Those results have been published elsewhere. 3,4 The substrate for the SWCNT transistors was p-type silicon with a 50 nm thick atomic-layer-deposited (ALD) Al 2 O 3 with a k-value of about 11. Nickel was chosen as the catalyst metal, since it has been shown that Ni catalyzes the thermal CVD growth of SWCNTs at temperatures as low as 600°C. 5 Ni layers with a nominal thickness of less than 0.2 nm were deposited by a high-precision ion-beam deposition system with a quartz crystal microbalance or by spinon deposition of an ethanol-based nickel-acetate solution. 4 The SWCNTs were grown in a preheated quartz tube furnace at 650°C. After 5-10 min hydrogen pretreatment the growth was initiated by filling the furnace with pure methane to a pressure of 0.3-0.4 bar. After 10 min the growth was stopped by evacuating the furnace and the samples were removed from the furnace after cooling-down to room temperature. Subsequently, the transistors, shown in Figure 1, were defined by e-beam lithography whereby the gap between source and drain, which defines the gate length, was varied ( Figure 2). The smallest gate length was about 90 nm. The total gate width, which is equal to the circumference of the inner ...

Voltage-Induced Dependence of Raman-Active Modes in Single-Wall Carbon Nanotube Thin Films

“…Fig.2a-b show the Raman peaks recorded immediately after releasing each external field used for the measurements shown in While the Raman effects in our experiments are reversible, the conductance does not recover at all after the external field release (Fig.2d). Similar decrease in conductance was found to strongly improve the on/off ratio of thin film transistors and claimed to be due to burning of the metallic SWNTs [4][5][6][7]. In our study, the reversibility in decrease of the peak intensities rules out the burning of large amount of SWNTs.…”

Parallel arrays of individually addressable single-walled carbon nanotube field-effect transistors

“…4͒ at 100 mV is 4.35, which compares with the reported value of 2-4 for asfabricated devices consisting of multiple channels. 17,28 It is worth noting that a value of I on / I off up to 500 can be achieved in such devices, as shown by Seidel et al, 28 after postfabrication treatment, such as selective destruction of metallic SWNTs by high electric field. Also, values as high as 10 5 have been reported by Collins et al, 16 after such modifications to devices with initial I on / I off ratios of ϳ3.…”

“…Recently, there have also been reports 25,26,28 of high output current CNT FETs that take advantage of multiple parallel nanotube channels between metal source and drain contacts. However, in these experiments, the channel-forming CNTs often appear in the form of an entangled network of junctions.…”

Non-destructive characterization of structural hierarchy within aligned carbon nanotube assemblies

“…[1][2][3] Many applications require assemblies of CNTs rather than individual CNTs, and therefore insight into the formation and structure of CNT assemblies is important. In organic electronics such as field effect transistors, 4,5 chemical sensors, 6,7 interconnects, 8,9 and transparent electrodes, 10,11 the contact between the individual CNTs within thin films determines the charge transfer characteristics. Therefore, CNT films with a maximized number of contacts to ensure a percolation path for charge transport are needed.…”