Posted on 06/06/2017 9:40:56 AM PDT by Red Badger
A team of researchers at the Israel Institute of Technology has developed a new capacitor with a metal-insulator-semiconductor (MIS) diode structure that is tunable by illumination. The capacitor, which features embedded metal nanoparticles, is similar to a metal-insulator-metal (MIM) diode, except that the capacitance of the new device depends on illumination and exhibits a strong frequency dispersion, allowing for a high degree of tunability.
This new capacitor has the potential to enhance wireless capability for information processing, sensing and telecommunications. The researchers report their findings this week in the Journal of Applied Physics.
"We have developed a capacitor with the unique ability to tune the capacitance by large amounts using light. Such changes are not possible in any other device," said Gadi Eisenstein, professor and director of the Russell Berrie Nanotechnology Institute at the Technion Israel Institute of Technology in Haifa and a co-author of the paper. "The observed photo sensitivity of this MIS diode structure expands its potential in optoelectronic circuits that can be used as a light-sensitive variable capacitor in remote sensing circuits."
MIM diodes are common elements in electronic devices, especially those utilizing radio frequency circuits. They comprise thin-film metal plate electrodes that are separated by an insulator. Like the MIM structure, the researchers' new MIS capacitor is bias independent, meaning the constant capacitance is independent of its supply voltage. Bias-independent capacitors are important for high linearity, and therefore straightforward predictability, of circuit performance.
"We have demonstrated that our MIS structure is superior to a standard MIM diode," said Vissarion (Beso) Mikhelashvili, senior research fellow at the Israel Institute of Technology and also a co-author of the paper. "On one hand, it has all the features of an MIM device, but the voltage independent capacitance is tunable by light, which means that the tuning functionality can be incorporated in photonic circuits."
"The illumination causes a twofold effect," Eisenstein said. "First, the excitation of trap states enhances the internal polarization. Second, it increases the minority carrier density (due to photo generation) and reduces the depletion region width. This change modifies the capacitance."
The researchers created three MIS structures, fabricated on a bulk silicon substrate, based on a multilayer dielectric stack, which consisted of a thin thermal silicon dioxide film and a hafnium oxide layer. The two layers were separated by strontium fluoride (SrF2) sublayers in which ferrum (Fe, iron) or cobalt (Co) nanoparticles were embedded.
The researchers found that the fluoridation-oxidation process of the iron atoms causes the formation of a gradient in the valence state of iron ions across the active layer, which results in the generation of an electronic polarization. The polarization causes a bias-independent depletion region and hence an MIM-type characteristic.
Four additional structures were prepared for comparison: Two lacked the SrF2 sublayers and one of them was prepared without the iron film. The other two structures contained SrF2: One did not have cobalt and the second included a one-nanometer Co layer.
The comparison with other MIS capacitors that contained the metal nanoparticles with or without the SrF2 sublayers led to the unequivocal conclusion that only devices consisting of the combination of Fe and SrF2 turn the MIS structure into a photo-sensitive MIM-like structure.
More information: "Optical control of capacitance in a metal-insulator-semiconductor diode with embedded metal nanoparticles," Journal of Applied Physics (2017). DOI: 10.1063/1.4983760
Journal reference: Journal of Applied Physics
Strontium fluoride - the primary tooth hardening ingredient in Crest toothpaste.
Seeing that it’s from Israel, you might only get Bob Dylan.................
So, this device is good for your teeth!...............
That's what the "(cough)" indicated. :-)
A new twist on the old varactor diode.
Optical tuning could definitely open up some new possibilities.
The varactor changed capacitance with changes in the bias voltage.
This one keeps the bias constant and the light varying causes change in capacitance. This could be used as a sensor for automatic gradual darkening of windows in homes, buildings and autos according to the brightness of the sun.
Unless this was developed by a diverse group of scientists, it is by definition oppressive
Yes, I agree. I feel the same way.
There are many hidden back roads of modern technology, less stellar inventions than the transistor or the laser, but still important, vital enabling technologies that are buried deep in the chips and modems and materials that have transformed our world... less stellar perhaps, but still deserving of recognition because their invention and commercialization consumed the working lives of very intelligent, passionate, and determined individuals.
On the current subject, it occurs to me that this optical-capacitor nanoparticle invention could — I repeat could — make it possible to make optical elements having optically variable indices of refraction.
This could in turn lead to truly remarkable things, especially when combined with quantum entanglement effects.
The mere mention of the varactor diode makes me think of Yvonne Craig.
OK, I stand corrected.
A stunning accomplishment
I wonder when we will read "Arabic Institute of Technology has developed . . ." (cough)
It was just in the news I think, that the Arabic Institute of Technology had perfected a 5 joule candle developed from camel colostrum.
I was thinking about how this could apply to photography or video.......................
Israelis are very intelligent and want to make the world a better place
Not sure that it would
I wonder what kind of bandwith a “photo-varactor” diode would have as compared to a regular photo diode as a fiber optic receiver.
Or, thinking pushing LED’s, tunnel, or gunn diodes to work to transmit over coax in near the near terrahertz range, as a replacement for the microwave communication bands.
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