Opinion please – Marketing blabla on quantum film

The US company Invisage has developed a new technique for making image sensors much more efficient, New Scientist reports in this week’s issue.

According to the head of Invisage, nano engineer Ted Sargent, Cmos photodiodes (complementary metal-oxide semiconductor) ‘are not logical platforms for light sensing’, he says in New Scientist magazine, because they are built in such a way that metal tracks (the wiring) must crisscross the surface, and consequently these tracks block much of the light.

This week Sargent’s company revealed a prototype ‘quantum film’ sensor, in which the film is a 2-nanometer thick layer with nanocrystals. The company claims that it can capture up to 95 percent of the light, making it four times more sensitive than Cmos photodiodes and giving it a dynamic range that is twice as high.

The nanocrystal’s light-sensing properties can be tuned by changing its dimensions. “We have tuned ours to absorb the entire visible spectrum and we generate an electron for every photon absorbed,” Sargent claims in New Scientist.

“This quantum film could have some advantages,” says professor Edoardo Charbon (faculty of Electrical Engineering, Mathematics and Computer

Science, EEMCS). “It might indeed function as a kind of funnel for photons onto the underlying Cmos photodiode. But I doubt that it will achieve a factor of four in terms of improvement over Cmos.”

It also remains to be seen how well the film will perform against other technologies, like the ‘back side illuminated’ Cmos sensors that are also currently being developed, Prof. Charbon warns. These sensors also do not have wiring that blocks the photons from reaching the pixels. Moreover, this quantum film would only become successful if it can be perfectly combined with silicon technology.

Professor Albert Theuwissen (EEMCS) is very skeptical about this: “In the 1990s a company added amorphous silicon on top of the silicon layer, which was also supposed to convert the photons into electrons, much like this quantum film is supposed to do. It was a nightmare. There are always some electrical currents leaking in between two such layers. The company went broke.”

And then he adds, laughing: “I think the reason why this company came out with this story is because it’s in great need of money. Their marketing apparatus works – that much is clear. But whether their technology works remains a mystery. Let them make a picture first, and then we’ll see.”

The professor continues: “And what they say about raising the sensitivity of the sensors by a factor four is impossible. It would mean that the current sensors do not register three quarters of the visible light, whereas in fact they do register more than half. In order to gather light from areas covered by metal parts, modern Cmos sensors have micro-lenses on top of each pixel. This story of Invisage is marketing blabla.” 

Verzekeraars keren 118,5 miljoen euro aan de TU uit naar aanleiding van de brand bij Bouwkunde. Bestuursvoorzitter Dirk Jan van den Berg is tevreden met deze overeenkomst. De brand leverde de grootste schade op die ooit in Nederland op een enkele brandpolis stond. De polis was ondergebracht bij een consortium van zes verzekeraars die het risico op hun beurt hadden afgedekt bij herverzekeraars.

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