Wednesday, March 17, 2010

CCD Nobel Prize - Commentary and Color by Dana Seccombe

Dana Seccombe has an interesting comment on CCD Nobel Prize post. I'm re-posting it on the front page, thanks Dana!

Nobel Prize - Commentary and Color

As it happened, I worked as a cooperative student from MIT at Bell Laboratories in 1968 (Homdel), and 1969 and 1970 (Murray Hill). My roommate, and fraternity brother, Thomas W. Liu worked in Andy Bobeck’s group, which worked on magnetic bubbles-thought to be a replacement for plated wire memories , and core memories. I occasionally attended presentations in the Murray Hill auditorium discussing progress and status. These informal meetings were typically attended by 15 to 40 people. Bobeck and his group were an outgoing and gregarious group, and enthusiastic about the prospects for magnetic bubbles—which could store data nonvolatily and also could perform some logic (bubbles which interacted at selected points could perform NAND and NOR functions, for example).

I also attended a similar BTL internal meeting, presenting Boyle and Smith’s recent invention of the CCD. This meeting was the first discussion of CCD’s outside the immediate management structure of Boyle and Smith, and was announcing the discovery of the phenomenon/structure of CCD’s. Boyle and Smith did, indeed, say in the meeting that they had been threatened by Bobeck’s discoveries, and weren’t about to let the magnetic group discoveries go unchallenged. Boyle and Smith went on to say that their CCD approach offered three unique advantages:
  1. Memory applications
  2. Imaging applications
  3. Data processing and logic applications
I remember thinking, after the meeting, “who needs a memory that lasts only a few milliseconds and then has to be refreshed?”

At the time, the technologies used 5 micron geometries (though, most people used the alternative measure .2 mils to designate line sizes) It was unclear what the relative future of either technology would be, and both proponents wanted to appear to be developing the superior technology. The initial impetus for both technologies, though, was clearly memory applications—and bubbles appeared, momentarily, superior for that application because it was both nonvolatile, and radiation hardened . However, it was recognized and emphasized in Boyle and Smith’s talk that CCD’s had the additional potentials of image acquisition and complex analog and digital data processing.

By chance, in the summer of 1971, I worked at RCA David Sarnoff Research Laboratories, in Princeton, New Jersey. I worked for Paul Weimer, an inventor of the Silicon Vidicon, and a highly regarded individual at RCA. His lab was solely devoted to successor technologies to the silicon vidicon—including CdSe sensors that were evaporatively deposited in complex arrays by 500 line shadow masks—and CCD and bucket brigade sensors (mostly silicon). As I arrived at that lab, they had already developed CCD line and array image sensors. In Weimer’s group, I worked for Mike Kovac who almost single handedly fabricated masks, processed wafers, did circuit design, and tested the products. There was another group (not reporting to Weimer) also working on CCD’s, with two key contributors, Walter Kosonocky and Jim Carnes. At the end of the summer, Carnes departed for Fairchild where he was to have a responsible position on CCD’s. It is clear to me that Weimer and Kovac definitely thought CCD’s were for imaging. We even made a camera using an area sensor that was the size of a cigarette pack, whose output was fed to a “Z axis modulated ‘scope” to display the output. I still have some of the output photos we made.

My point in bring this history up is to point out that there were many others who were aware of the potential of CCD’s as image sensors, and who had made quite a bit of progress too. The invention of the frame buffer/image transfer section for CCD images was an important, but not foundational part of the technology. It is important for many sensors—particularly where there is no other form of shutter, but there are plenty of CCD sensors that don’t use the frame buffer.

In the early days, perhaps the biggest limiter was smear due to some of the charge being “left behind”, charging and discharging traps. Early sensors would transfer perhaps 99% of their charge per transfer. Today sensors transfer in excess of 99.99% of their charge.

RCA Sarnoff was, however, in financial trouble because of their unsuccessful entry into the computer business, and RCA was beginning to lay off people. As I recall, Weimer’s people were given lower priority, and work on the CCD suffered greatly.

The usefulness of CCD’s for imaging took over 30 years of advances of literally 100’s of people. To be truly useful, CCD’s required at least the following major advances:
  • Silicon gate processing technology (to reduce the “gap” between electrodes that was present in metal gate processes)
  • Radically scaled geometries, including gate oxide thickness (to increase charge), and electrode geometries (to get large enough arrays)
  • Buried channels to reduce surface state induced lag in transfer, and ion implantation to make those channels
  • Consumer demand for still and motion imaging—enabled by a host of still other technologies including: the advanced microprocessor, low cost disk and RAM, related software, design tools, etc.
In many creative processes, there are old concepts combined with some new insights to adapt and combine what is known to a new need. This effect was explored in the PBS program “Connections”, which showed how, for example, the invention of spring steel, and the escapement, lead the development of the chronometer accurate to less than a second—and hence enabled accurate celestial navigation.

CCD development was similar. Many things were incrementally developed.

In my case, work on CCD’s affected my later career at hp, where I eventually ran hp’s Inkjet Supplies Business Unit. Since my goal was to sell more ink, I was interested in developing applications that use more ink. Photography uses perhaps 150% coverage of ink on a page (some each of cyan, magenta, yellow, and black), whereas text is typically 5% dense. I therefore subsidized hp laboratories in developing digital cameras and applications. Later Canon and Epson, with similar printing interests, also invested in digital cameras. Other camera manufacturers could see that cameras would soon all go digital. Hence, the availability of high resolution digital printing drove a huge interest in digital image capture—and helped to drive investment in CCD’s for consumer applications.

As part of the invention tapestry, while at Bell Laboratories, I did my MIT masters thesis on characterizing upconverting phosphors. The goal was to develop a blue light source from phosphors irradiated by high intensity infra-red light. Rare earth oxides (typically Yttrium) were doped with other rare earth oxides (for example, erbium, or thulium, with another oxide, typically ytterbium). Infrared light pumped the ytterbium to an intermediate level, where energy was transferred non-radiatively, to an adjacent thulium or erbium ion. That ion was subsequently pumped a second or third time, to higher levels, ultimately resulting in a radiative decay in the visible (blue or green), though with very low efficiency (in the case of blue, about .1%) Years later, though, these same phosphors are being used to produce white light from UV and visible stimulus. While completely impractical in 1970, improved IR and UV pump sources in conjunction with phosphors in 2010 are making it possible to generate color balanced white solid state lights.

A similar scenario happened with regard to flash memory. Once regarded as an impractical backwater (slower and more expensive than DRAM), flash memory has, 40 years after its initial development, become a paradigm shifting technology. However, it took developments such as radical scaling, series cell memories, multilevel storage, and an explosion in huge, portable applications to make a difference.

Magnetics eventually lost out to electronics, even though it was non-volatile, because it couldn’t scale gracefully. As geometries decreased, the energy density in the bubble wall would have to increase above what is available with realizable materials. Also, generating the required in plane rotating magnetic field was power hungry and bulky. However, today “spintronics” –magnetic effects on an atomic level—may be the basis for the resurgence of magnetism.

Who should get the Nobel Prize? It is up to the commission—and lets recognize that it won’t ever be without controversy. Some (Nobel Peace Prize) winners are reviled as murderers in some countries, while hailed in others. Some scientists received the prize for a single piece of insight. Others worked doggedly for years plowing untilled ground, ultimately developing accurate and groundbreaking, though controversial theories, and then going for additional years ignored or scorned before ultimately being recognized (i.e.,Einstein, Curie).

In the case of CCD’s, much of the insight for how a CCD works was very well understood in 1970. The use of capacitors “in deep depletion” to test doping and trapping, and detecting light, had been standard proceedure for years to characterize semiconductors. In fact, in my first summer at Murray Hill, under Dan Rode, (who reported to John Copeland, the inventor of the Copeland inverse profiler—which used this effect to profile doping densities in semiconductors, including GaAs) I, as a student developed a test setup using hp plotters to do C-V plots. It was well known that charge under the capacitors could be moved (that is how MOS transistors work)—but Boyle and Smith had a flash of insight that a series combination of such transistors could result in a useful, if transient, memory device. That insight wouldn’t have developed if it weren’t for the advent of the bubble memory—something that ultimately had no direct impact.

The fact that it took at least 30 years for CCD’s to become a major factor in the electronic world attests to the fact that many individuals made many important contributions to remove limitations, and provide an environment where CCD’s could contribute. Many of those people have some legitimate claim to a part of the success of CCD’s, though perhaps not rising to the level of the, probably overemphasized, Nobel Prize.

See also Boyle and Smith video fro 1978—admitting that it was a “flash of genius” type discovery:

The video also maintains, as I remember, that from the beginning Boyle and Smith envisioned that CCD's could be used for imaging and digital and analog data processing (typically through the use of tapped delay lines).

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