Communications

||Conduction

A quantum wire is about 100 atoms across. However, the conduction of electrons varies in a step-wise manner as the width or length increases. This is an effect of quantum mechanics, where the electrons follow standing wave patterns and are affected by each other’s presence.

||Quantum teleportation

Researchers have been able to teleport information from light to light at a quantum level since 2006. For example, there are two glass containers, each containing a cloud of caesium gas atoms. The two glass containers are enclosed in a magnetic field chamber and are not connected to each other. When the wavelength-specific laser light hits the atoms, the outermost electrons react by pointing up or down. The emitted photons carry this quantum information to the second container. In essence, this behavior mimics computer information delivered with the numbers 0 and 1.

||Image projection

Image and video projection from portable devices, such as cell phones, has been in the works for a while (in particular amongst the MEMS sector). The capability of such designs is limited to lenses and bulky (although micro-scale) mirrors.

By bending light, the use of lenses would not be necessary. This is the main motivation for integrated optical phased arrays (OPAs). It is so far possible to bend infrared light by manipulating its coherence from a single laser diode. Electrical currents would phase shift the light travelling through a silicon chip by influencing the number of electrons joining each light path. The light wave would then recombine coherently after being projected from a chip’s grid arrays.

||Transistors

Ultrafast processes are common at the nanoscale. To combine such processes with a high quantum efficiency–as well as manufacturing simplicity–is a major milestone in energy engineering. From an electronics point of view, transistors have revolutionized global markets for their brilliant electronic switching/amplification capabilities as well as their ever reducing size (up to millions on a single silicon chip). The new transistors will likely need atomically precise electrical contacts.

SiO2 is the most typical transistor material. A higher material dielectric constant is favourable to reduce electron leaking at nm thickness (quantum mechanical tunneling). Silicene transistors of one atom thin silicon are also being developed. Ge, HfO2, and TiO2 are promising materials but require intermediate layers to increase the band offset. Graphene transistors with double-layered striped channels show an improvement over Si in terms of electron mobility and operating temperature.

A new type of transistor uses a nanoscale insulator (boron nitride nanotube, also a popular piezoelectric) with Au QDs. Quantum tunneling, or electron hopping, occurs stably between the Au QDs at a sufficiently high voltage and under liquid helium cooling. It can also occur under plasmonic conditions where light excites surface plasmons, which are then tunneled between molecularly separated plasmonic resonators. The resulting operating frequency is in the scale of 100 THz, about 10,000 times faster than traditional computer processors.

CNTs can also take part in finding an alternative for Si. Usually grown in batches for these applications, some CNTs can be more conductive than semi-conductive with on/off properties. A way around this issue is to switch off the good CNTs first, then burn the conductive CNTs with a surcharge of electricity.

Using light, on the other hand, would address scalability and generated heat issues. One possibility is to use a set of mirrors separated by a wavelength of light. Doing so builds up strong EM fields makes and makes the mirrors essentially transparent. A “gate photon” can be used to excite a single electron of one cesium atom in a super-cooled gas. The higher energy state now would reduce transmitted light to as low as 20%. Alternatively, the Faraday effect exhibited by some materials (e.g. mercury telluride platelets) may be used to rotate the polarization of light at terahertz frequency (induced by a permanent magnet and applied voltage). Magnetite is an alternative material that shows conductive to non-conductive transitions with visible laser light excitation on the ps time scale.

With DRAM memory, each cell consists of a capacitor and a transistor linked to one another (as opposed to only a transistor for NAND Flash memory). Samsung developed a modified double patterning and atomic layer deposition method to scale this DRAM at 20nm, providing a 4Gb DDR3.

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