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Comment by amelius | Hacker News Reader

The semiconductor industry has been making pixels much smaller for a very long time. Not for displays, but for camera sensors. The reason why they didn't make them for displays is simply that there wasn't an application that required these kinds of resolutions.

So from a technical point of view, this isn't really that groundbreaking.

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CMOS sensor pixels and LED output pixels aren't the same type of circuitry at all.

You have to look at it from a fabrication perspective. Both CMOS cells and LEDs aren't new, in fact LEDs are older. They can both be mass produced in an array using a very similar process. From a semiconductor fabrication perspective, the LEDs in your TV or smartphone have a laughably low resolution.

Modern CMOS and OLED displays are quite similar, actually. The high end CMOS's that operate at the pitch used in these OLEDs use individually wired pixel 'cells' to capture and convert photons into electrical signals. Those cells/pixels in the sensor are wired up in rows, just like the pixels of an oled, and each pixel transmits 3 or 4 signals along the row, just like oleds receive them. And in fact, each cell of the CMOS sensor is made of a photodiode, which is a lot like a light emiting diode, except it works the other direction, converting photons into electricity.

Then, just like an oled has transitors along its rows and pixels for timing and signaling, so too does the CMOS have a 'rolling shutter' effect caused by the sensor having it's pixels sampled row by row, column by column, just like an oled display draws its pixels.

Here's a few sources in case you'd like to learn more, but clearly if a CMOS sensor of a given resolution is constructable, the only thing preventing its OLED counterpart is the actual organic chemistry driving the pixels, which is a large reason OLEDs are better for fine pitch displays like this than LCDs, they can be made this small.

https://isl.stanford.edu/~abbas/ee392b/lect04.pdf https://isl.stanford.edu/~abbas/ee392b/lect05.pdf

I couldn't find perfectly similar cross sections of an OLED, and the wiring will of course vary a bit, but not enough to blow past the limitations of CMOS's precision lithography process.

https://www.researchgate.net/figure/Cross-section-of-the-pix...

And to give you an idea of how far that can go, Sony has a 61MP sensor that's roughly the same physical size as these displays, but basically 5-6 times as dense with photodiode based pixels instead of oled based ones. Maybe we can't make a 61MP display that size yet, but we can clearly make a 4k one (which is about 12MP, I think...)

Fair point, AMOLED is basically just an inverted CMOS sensor. I was thinking of PMOLED, but I guess these days that's probably less common.

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