WHAT IS QUANTUM TUNNELING?

Tunneling of particles (electrons, protons, alpha particles) is an exclusively quantum phenomena arising out of the particle-wave duality. It can only be explained by laws of quantum physics. In the quantum realm particles like an electron can penetrate energy barriers higher then the energy of a particle, and appear on the “other side” in a “ghost-like” manner.

Nobel Prizes in Physics awarded for contributions related to quantum tunneling effect:

• L.-V. de Broglie (1927, particle-wave duality)
• H.A. Bethe (1967, energy production in the Sun and stars)
• B. D. Josephson (1973, theoretical predictions of the properties of a supercurrent through tunnel barrier, Josephson effects)
• L. Esaki and I. Giaever (1973, experimental discoveries regarding tunneling phenomena in semiconductors and superconductors, respectively)
• G. Binnig and H. Rohrer (1986, design of the scanning tunneling microscope).

QUANTUM TUNNELING IN NATURE AND TECHNLOGY: Examples

• Energy production in stars

  The Sun's core temperature is ~13.6 Million K. For hydrogen nuclei the Coulomb barrier is roughly 0.1 MeV. This corresponds to a temperature in excess of 1 Billion K! Luckily, tunneling and the distribution of speeds among nuclei lower the actual temperature required for nuclear reaction. So without tunneling even the Sun's core isn't hot enough for nuclear fusion.

• Magnetoencephalography

  Magnetoencephalography (MEG) is an imaging technique used to measure the magnetic fields produced by electrical activity in the brain via extremely sensitive devices such as superconducting quantum interference devices (SQUIDs).

• Scanning Tunneling Microscope

  Detection of quantum tunneling current flowing between a sample and a scanning tip is the basis of the Scanning Tunneling Microscope (STM), an instrument developed in the IBM Labs in Zurich in early 1980s, which earned its creators the 1986 Nobel Prize in Physics. Experience gained in the last 20 years in the research establishment involved in STM studies will serve as a back-up reservoir of techniques and ideas for Quantum-π commercial sensors and devices.

• Tunnel Magnetoresistance (TMR)

  The effect was discovered in the early 1970s and by 2005 Seagate Technology introduced the first disk drives equipped with TMR read heads. TMR replaced Giant Magnetoresistance (GMR) as the dominant technology in magnetic read heads in disk drives.

DETAILED DESCRIPTION OF Quantum-π TUNNELING DEVICES

Quantum-π technology is based on detecting a quantum tunneling current flowing between arrays of nanowires supported on parallel silicon substrates.The substrates are separated by a soft-matter spacer a few molecular layers thick. The spacer preserves the constant inter-substrate separation, and allows lateral motion of one plate with respect to the other. All the nanowires on each plate are connected in parallel. When a bias of several volts is applied between the plates, tunneling current flows between them. The current is an extremely sensitive measure of an area of overlap or "shadowing" between the nanowires on each substrate. The tunneling current is a linear function of this overlap, and vanishes when the nanowires on the opposite substrate do not overlap. nanoTrek^® in the static mode of operation is a transducer of position, misalignment or translation, very similar to linear encoders based on optics or magnetic effect, but utilizing quantum tunneling instead - and hence much more sensitive. In the dynamic mode it can become an accelerometer, sensor of pressure, flow, vibration and several other quantities.

Many production runs have yielded state of the art devices. The latest devices have 12,000 nanowires, each of 90nm width and 5 mm length (~1:53,000 aspect ratio!) – this is a technological feat, and have tested fabrication capabilities of standard light lithorgaphy to its limits.