What is a backside-illuminated sensor?

June 7, 2010 5:46 PM

The new iPhone's sensor is backside-illuminated sensor. What does that actually mean? What other cameras offer this technology?

I was hoping the news / Steve would talk a little bit about what it means, not just that it gives better quality, but the best explanation I've been able to find was this highly-technical press release from Sony about doing it on a couple of their cameras, which goes right over my head. If it's as simple as it looks in the illustration -- the "metal wiring" is no longer positioned right in the way of the incoming light -- why hasn't every digital sensor ever made done it this way?

posted by fogster to Technology (7 answers total)

That is exactly what it means -- the sensor is designed to receive light on its back (the "back" of an integrated circuit being defined as the side that doesn't have all the wiring) -- and the reason it hasn't been done that way in the past is that it's not how integrated circuits have been fabricated historically. You also need your substrate to be transparent if you're going to illuminate the back side, and I imagine this was something of a materials challenge.
posted by kindall at 5:51 PM on June 7, 2010

Best answer: On the last question, from this EE Times article:

Anu Pokharna, researcher at iSuppli, said, "This [BSI] has been around in the CCD industry for quite some years especially in the high-end cameras for space programs, astronomy, and scientific imaging." Pokharna added, "Basically it's been used in applications which require extremely high performance." The technology, however, has never trickled down to consumer applications, because "the cost differential has been a factor of 2 to 3 times more."

posted by smackfu at 6:06 PM on June 7, 2010

why hasn't every digital sensor ever made done it this way?

It's technically challenging. The silicon must be "thinned" to allow light to pass directly to the photosites.
posted by fake at 8:40 PM on June 7, 2010

The TX7 camera has it, you can search the reviews for it to see how it performs. I got the impression that the new technology was mostly hype and marketing.
posted by xdvesper at 9:04 PM on June 7, 2010

It is mostly hype and marketing. The low quality of mobile phone pictures is due to the poor optics and small sensor. Notice how professional digicams take good pictures? That's because they have a good lens and a huge sensor.

Apple likes to hype everything they do. The A4 processor, for example, is nothing special. They bought a company that licensed the ARM architecture and made their own ARM chip. Then they suck an Apple logo on it. Big deal, who cares? And yet it's "front page news" because it's Apple.
posted by jrockway at 9:13 PM on June 7, 2010

Best answer: Basically they moved the wiring to the backside of the light sensor (instead in the front) to allow more light in. Easy to understand explanation are here and here.
posted by bbxx at 4:16 AM on June 8, 2010

I'm not sure it's hype as it's a real thing and provides real benefit. It's a tiny benefit due to factors mentioned above but certainly real.
posted by chairface at 12:54 PM on June 8, 2010