That's very surprising, that no-one can produce a 24x36mm sensor without stitching. Why is this?
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The current reason is that all new steppers introduced in the last five years or more have a maximum field size of 26x33mm or smaller, and possibly all are exactly 26x33mm. (There are some current steppers with smaller maximum field size, but they might be older models.) Of the several stepper models once made with larger maximum field size, only one remains available. Its minimum feature size of 500nm should be compared to the current range of mostly 90nm down to 45nm, with 35nm coming soon.
As to why, I can only speculate, but here I go:
1) The vast majority of all IC devices have die sizes no larger than 26x33mm, and in fact mostly far smaller than that. DSLR's as a whole are a tiny fraction of all IC's, and so do not drive design decisions for new steppers, but rely on using steppers designed primarily for other main markets, like CPU's, memory chips and the smaller sensors for mobile phones, compact digicams, video cameras and such.
Memory chips do not need to be large, as it is easy to wire together multiples, and all the recent mainstream CPU's I know of (from Intel in particular) are comfortably under 26x33mm, even the recent dual core ones.
The biggest microprocessors that I know of are the Intel Itanium processors, and the dimensions I can find are die size of 27.72 x 21.5 mm = 596mm^2 for recent dual core models made using 90nm process:
[a href=\"http://www.chiplist.com/Intel_Itanium_2_9000_series_processor_Montecito/tree3f-subsection--2242-/]http://www.chiplist.com/Intel_Itanium_2_90...section--2242-/[/url]
http://en.wikipedia.org/wiki/Montecito_(processor)(This is about as wide as a 1D sensor, but slightly higher.)
The other Intel processors families like Xeon and the mainstream CoreDuo and such have far smaller dies sizes, 143mm^2 or less. (That is far smaller than even 4/3" sensor size of 225MM^2).
The smaller sizes of these other processors is largely due to using new, smaller feature size fabrication technology, like 65nm and 45nm instead of Itanium's 90nm, which for one thing allows higher clock speeds. That diminishing feature size seems to be keeping die size the same or smaller in new CPU models, balancing out increases in transistor counts, even with dual and quad core designs.
2) The remaining larger devices are small volume items that can be most cost effectively handled by stitching rather than having a rarely needed stepper of larger field size: a larger stepper would reduce unit costs for such IC's, but demand for such a stepper would be so low that the cost of designing and building the stepper itself would be too high.
Unless the demand for sensors larger than 26x33mm increases a thousand fold or more, DSLR sensors will be constrained by the size needs of other far larger parts of the IC market.
