Thursday, November 16, 2017

Perovskite Materials for Foveon-like Pixels A group of researchers from Empa and ETH Zurich publish a paper in Nature called "Non-dissipative internal optical filtering with solution-grown perovskite single crystals for full-colour imaging" by Sergii Yakunin, Yevhen Shynkarenko, Dmitry N Dirin, Ihor Cherniukh & Maksym V Kovalenko. The crystals of semiconducting methylammonium lead halide perovskites (MAPbX3, where MA=CH3NH3+, X=Cl−, Br− and Br/I−) are used as absorbers for full-color Foveon-like stacked imaging:

(a) Bayer color sensor design. (b) Vertically stacked color sensor design.
(c) Schematic of the crystal structure of hybrid perovskites
— materials with high optical absorption, efficient charge transport, and
bandgap tunability. (d) Photograph of (from left to right) typical MAPbCl3,
MAPbBr3 and MAPb(Br/I)3 single crystals. (e) Measured light absorption
of each perovskite SC used in a stack.
(a) Sketch of stacked SC photodetector.
(b) Photograph of the prototype detector assembled from three SCs
stacked on a chip carrier. (c) Normalized photoconductivity spectra
of the individual SCs in the stacked detector presented in b.


  1. From image 1e I would expect the crosstalk BG to be higher than BR. Image 2c shows almost same crosstalk for BG and BR. In general crosstalk seems to be quite promising.

    1. Dear reader, thank you for the comment. In fact the tail (Fig.1e)) in low energies for blue-sensitive crystal is not due to absorbance but for the reflective losses. So there is no the reason for the cross-talk between blue and other colors.

  2. "In conclusion, a perovskite-based, one-pixel RGB colour sensor with a vertical layer stacking design was demonstrated. It was shown that this prototype detector could faithfully reproduce simple one-dimensional images and realistic two-dimensional images with excellent colour resolution. Such vertically layered detectors may offer several advantages over traditional Bayer-type dissipative and subtractive optically filtered detectors: a potentially higher spatial resolution, improved optical efficiency and suppressed incidence of colour moiré and de-mosaicing artefacts."

    I like the science. I think it is a big stretch to jump from a one "giant" pixel to replacing Bayer stacked BSI CIS devices when one thinks about all the other issues that need to be overcome. But, I also understand the need to justify exploring new materials and technologies. Perhaps this will find application in some important niche market.

    1. Dear Mr. Fossum. Thank you for your comment, I am totally agree with it. However it is known that from the time when Dick Merrill first patented the idea of Foveon sensor till it came to the market as a real product it took more that ten years, and it is for using well-developed Si technology. Our ETH team is a chemistry-based group with goals to develop novel promising materials for semiconductor sensors. We were first in the world who demonstrated solution-processed material for X-ray and gamma detectors. With current publication we would like attract attention our colleagues to such "wonderful" class materials as metal halide perovskites that have many unique and intriguing properties. Perovskites have few order better absorption than Si, they ae easily for band-gap tuning, they are very cheap in production (simply can be grown on a kitchen in a glass of solution). We hope that this article help us to find collaboration with groups with experience of fabrication of imaging sensor where we going to demonstrate further advantages of this novel material.

    2. I agree that the materials are interesting. BTW, your timeline for Foveon concept to market offering is off. It was a lot shorter than 10 years. It was also a failure from both revenue, market share, and ultimately investor value (perhaps about $100M was lost - but not sure). Now, that was a silicon-based system and had much going for it in terms of manufacturing and materials maturity. While your technology is very interesting, and perhaps will find niche markets eventually, it does not solve any outstanding commercial CMOS image sensor problems in a compelling way. Plus, if it takes you 10 years to come to market, silicon will be 10 years more mature with many engineers worldwide competing to make those improvements as fast as possible. I like the science, but since you come from a chemistry background, you might not be familiar with the formidable challenges it might take to displace the incumbent technology. You should look for some applications where the advantages of this approach, if the technology comes to fruition, would be compelling. The one you picked is not, in my opinion.

  3. This is more similar to Invisage's idea combined with Foveon one. If you want to go further, maybe Prof. Delbruck at your school could help you I guess.


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