Current medium format sensors are being fabricated on 150mm wafers. That's really old technology. Even 200mm wafers are rather dated. Current technology is using 300mm wafers.
The trend has not been to smaller chip sizes. It has been to denser chips.
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As someone trained in semiconductor design, albeit a long time ago, I strongly disagree with the contents of the quoted post. Historically, wafer sizes and chip sizes have steadily got bigger.[a href=\"index.php?act=findpost&pid=91674\"][{POST_SNAPBACK}][/a]
Firstly, wafer size has nothing to do with the chip size trend that I was talking about. Clearly it is easy it fit a far larger sensor than current ones onto a wafer, but a dominant limitation on size and cost is the reticle size of the steppers (or the newer fab. options, scanners or stepper-scanners): the maximum size of a chip that can be made in a normal single exposure process. A good hint is the sizes of the chips that are being made and envisioned, which surely influences the capabilities of future stepper/scanner designs.
What is the recent trend in chip sizes? Look for example at the size of the recent dominant microprocessors from Intel and AMD: the trend is to both denser and smaller with the shift to smaller feature sizes such as with 65nm process. Even with the move to two cores on a die, die sizes are smaller now than with single core processors of a few years ago. The new Intel Core Duo processors have a die area of 111-143 sqmm, about half the size of the previous year's dual core Pentium D 900 at 280 sqmm, and distinctly smaller than 183-230 sqmm for recent AMD Opteron dual core processors using the older 90 nm process. (By a sense of scale, 4/3" sensors have die areas of over 243 sqmm, and DX format sensors are over 430 sqmm.)
The biggest IC's that I know of are in the Intel Itanium series, and this year's dual core Itanium 2 processors using the slightly older 90 nm process are 27.72 mm x 21.5 mm = 596 sqmm (about 1D sensor sized). This is down from about 750 sqmm for the first dual core Itanium processors from 2003-2004, which used 130 nm process. Itanium processors are likely to move to the smaller 65 nm process, so even combined with a predicted move to quad core, will likely stay smaller than the dual core Itanium's of a few years ago, staying at about "1D" size. Canon also predicts a move to 45 nm process in three year's a time, further reducing sizes.
The trend seems to be increasing component count without increasing die size, and often decreasing die size.
To Edmund: as a professional scientist, I judge claims more by evidence than by the speaker's educational credentials (so I have not tried to support my claims by reference to my Ph. D. and record of publications in physics journals), so could you provide evidence of a
recent trend to larger reticle sizes in fab. equipment suitable for making sensors, which is what would be required to make larger sensors more likely in the future?