Translucent Inc had 300mm substrate , The problem isn't the...

Translucent Inc had 300mm substrate ,

The problem isn't the foundry ie IQE it is the fabricators, they tell the foundry what size they want.
https://en.wikipedia.org/wiki/Wafer_(electronics)

Standard wafer sizes

Silicon wafers are available in a variety of diameters from 25.4 mm (1 inch) to 300 mm (11.8 inches).^[11][12] Semiconductor fabrication plants (also known as fabs) are defined by the diameter of wafers that they are tooled to produce. The diameter has gradually increased to improve throughput and reduce cost with the current state-of-the-art fab using 300 mm, with a proposal to adopt 450 mm.^[13][14] Intel, TSMC and Samsung are separately conducting research to the advent of 450 mm "prototype" (research) fabs, though serious hurdles remain.


2-inch (51 mm), 4-inch (100 mm), 6-inch (150 mm), and 8-inch (200 mm) wafers

• 1-inch (25 mm)
• 2-inch (51 mm). Thickness 275 µm.
• 3-inch (76 mm). Thickness 375 µm.
• 4-inch (100 mm). Thickness 525 µm.
• 5-inch (130 mm) or 125 mm (4.9 inch). Thickness 625 µm.
• 150 mm (5.9 inch, usually referred to as "6 inch"). Thickness 675 µm.
• 200 mm (7.9 inch). Thickness 725 µm.
• 300 mm (11.8 inch). Thickness 775 µm.
• 450 mm (17.7 inch). Thickness 925 µm (proposed).^[15]

Wafers grown using materials other than silicon will have different thicknesses than a silicon wafer of the same diameter. Wafer thickness is determined by the mechanical strength of the material used; the wafer must be thick enough to support its own weight without cracking during handling.


Proposed 450mm transition

There is considerable resistance to the 450 mm transition despite the possible productivity improvement, because of concern about insufficient return on investment.^[17] Higher cost semiconductor fabrication equipment for larger wafers increases the cost of 450 mm fabs (semiconductor fabrication facilities or factories). Lithographer Chris Mack claimed in 2012 that the overall price per die for 450 mm wafers would be reduced by only 10-20% compared to 300 mm wafers, because over 50% of total wafer processing costs are lithography-related. Converting to larger 450 mm wafers would reduce price per die only for process operations such as etch where cost is related to wafer count, not wafer area. Cost for processes such as lithography is proportional to wafer area, and larger wafers would not reduce the lithography contribution to die cost.^[18] Nikon plans to deliver 450-mm lithography equipment in 2015, with volume production in 2017.^[19][20] In November 2013 ASML paused development of 450-mm lithography equipment, citing uncertain timing of chipmaker demand.^[21]
The time-line for 450 mm has not been fixed. Mark Durcan, CEO of Micron Technology, said in February 2014 that he expects 450 mm adoption to be delayed indefinitely or discontinued. “I am not convinced that 450mm will ever happen but, to the extent that it does, it’s a long way out in the future.