Inverting
a semiconducting channel is the basis of all field-effect
transistors. In silicon-based metal-oxide-semiconductor field-effect
transistors (MOSFETs), a gate dielectric mediates this inversion.
Access to inversion layers may be granted by interfacing ultrathin
low-dimensional semiconductors in heterojunctions to advance device
downscaling. Here we demonstrate that monolayer molybdenum disulfide
(MoS2) can directly invert a single-walled semiconducting
carbon nanotube (SWCNT) transistor channel without the need for a
gate dielectric. We fabricate and study this atomically thin one-dimensional/two-dimensional
(1D/2D) van der Waals heterojunction and employ it as the gate of
a 1D heterojunction field-effect transistor (1D-HFET) channel. Gate
control is based on modulating the conductance through the channel
by forming a lateral p–n junction within the CNT itself. In
addition, we observe a region of operation exhibiting a negative static
resistance after significant gate tunneling current passes through
the junction. Technology computer-aided design (TCAD) simulations
confirm the role of minority carrier drift-diffusion in enabling this
behavior. The resulting van der Waals transistor architecture thus
has the dual characteristics of both field-effect and tunneling transistors,
and it advances the downscaling of heterostructures beyond the limits
of dangling bonds and epitaxial constraints faced by III–V
semiconductors.
It has been previously demonstrated that the resonant frequency of the Split Ring Resonator (SRR) reaches a saturation value when its size is continuously scaled down, and at the same time, the resonance is attenuated. Now, it is demonstrated that similar saturation and attenuation phenomena happens to its complementary screen, which is commonly called a Complementary SRR (CSRR). It was found that the saturation frequency of the CSRR is near the saturation frequency of the SRR with equal geometrical dimensions. It is possible to control their saturation levels by tuning the geometry of the resonators. This work is relevant for the design of quasi-optical metamaterials based on one or both kinds of structures (i.e., SRRs and CSRRs) at once, especially when they both are required to resonate at the same frequency.
Abstract. Photolithography for patterns with periodicity in the illumination plane (2.5-D lithography) has seen rapid advances over the past decade, with the introduction of holographic lithography and the further development of phase-contrast and grayscale photolithography methods. However, each of these techniques suffers from substantial difficulties preventing further integration into device fabrication: a lack of parallel processing capabilities and dimension limitations. Here, we present a demonstration of controlled layer topography through modulation of both the exposure dose and exposure focal plane yielding reproducible 2.5-D patterns which are applied to the further development of plasmonic gratings. This process is entirely compatible with commercially available i-line photolithography and etch hardware, enabling a path to ready integration.
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