Voltage-controlled high-frequency oscillations based on suspended semiconducting carbon nanotubes

Abstract

A series of tunable negative differential conductance regions at room temperature is demonstrated in semiconducting carbon nanotubes suspended over a trench with a metallic gate at its bottom. The substrateless carbon nanotube is in fact a wide quantum well that experiences a series of negative differential conductance regions due to the very large difference between the effective masses in the well and the tunneling contacts. The positions of these regions can be tuned by modifying the gate voltage. Since the negative differential conductance is the key element of high-frequency oscillators, the suspended nanotube is a voltage-controlled oscillator able to work up to THz frequencies. This device could have important applications in high-frequency nanoelectronic devices and multivalued logic.Single-walled or multiwalled semiconducting carbon nanotubes ͑CNTs͒ are key elements for CNT diodes or transistors working up to a few terahertz ͑THz͒ since they show a very high mobility and very long mean free paths at room temperature. A review of the physical properties of CNTs and their applications for microwave and millimeterwave devices is found in Ref. 1 while Refs. 2 and 3 report the first experimental data, which demonstrate the huge potential of CNTs in the high-frequency domain.The single-or multiwalled CNTs in a substrateless geometry consisting of a CNT suspended over a trench a few m in depth, which has on the bottom a patterned metallic electrode that plays the role of the gate, are a basic configuration because a multitude of physical effects take place uniquely in this geometry. For example, the ballistic transport of carriers at room temperature over a mean free path exceeding 1.5 m, 4 the ballistic phonon propagation, 5 the electrical generation and absorption of phonons, 6 Fabry-Perot interferences, the single-electron transistor effect, 7 the Coulomb blockade effect, 8 the Aharonov-Bohm effect, 9 and the roomtemperature negative differential conductance ͑NDC͒ at low electric fields, 10 were experimentally evidenced in substrateless CNTs. This wealth of physical phenomena originates in the suspended geometry, which forbids the interactions between the nanotube and the supporting substrate. 11 The NDC at room temperature in semiconducting CNTs due to resonant tunneling was theoretically predicted 12 and experimentally demonstrated in various CNT configurations. 13,14 However, no reference to NDC tunability appears in these works. It is thus the main aim of this paper to investigate the NDC tunability with the gate voltage, due to its paramount importance in miniaturized high-frequency oscillators able to work up to THz. In this context, voltagecontrolled sub-THz oscillations of resonant tunneling diodes implemented with AIII-BV semiconductor heterostructures and integrated with slot antennas were recently evidenced experimentally. 15 The tunability occurs in this case due to the variation of the capacity of the resonant tunneling diode. In contrast, we show that in substrateless gated CNTs several NDC reg...

Negative Differential Resistance in Carbon Nanotube Field-Effect Transistors with Patterned Gate Oxide

“…∼ / , where is the Fermi velocity. 21 In the previous section S4, we extracted the value of the level spacing of the quantum dot, Δ = ℎ /(4 ) ≈ 14 meV.…”

Multiple negative resistances in trenched structures bridged with carbon nanotubes

“…6 Very recently, a NEMS switch using the trench configuration was reported. 7 Tunable NDR was predicted for a single semiconducting CNT suspended over the trench, 8 the tunability being achieved through changes in both gate and drain voltages. Because of the lack of screening in CNTs, the potential profile controls the carrier transport in suspended CNTs.…”

Nanotube-Bridged Wires with Sub-10 nm Gaps

“…For example, in our NBW structure with a gap distance of 50 nm, the gap was connected by multiple CNTs with a diameter of ∼2 nm. Previous work shows that the resistivity of a suspended semiconducting or metallic CNT is ∼0.8 × 10 –4 or ∼1.1 × 10 –5 Ω·m, respectively. , Since we utilized unsorted CNTs, we can assume that the gap of the NBW was connected by a group of CNTs with its semiconducting and metallic CNT composition of 2:1 just like as-grown CNT powders. As a result, we could estimate that the gap of our NBW with a diameter of ∼360 nm was connected by ∼11 CNTs.…”