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I dont think CMOS is more expensive then BJT.. from where is this information derived....
1) It is cheaper then Bipolar process
2) Better integration
3) The world top foundry are in CMOS process. Huge capacity to drive cost down.
4) Smaller in size.
You need to compare like for like. A typical bipolar technology now would be fairly large geometry and you wouldn't get many devices within a given area. The state of the art CMOS would be packing many times the number of devices in the same area so while it may be more expensive for a given area you have a lot more devices within that area. So, price per transistor is lower for CMOS. However, inherently the bipolar process is simpler - fewer masks and fewer process steps.
Since its manufacturing process is expensive, so we try to design it in smaller size so it is able to integrate large and complex circuits and functions with high yield, and then reduce its cost. Is it?
If I understand you question correctly, the answer is yes. Although it is not quite that simple, the drive to making larger wafers and smaller transistors results in a lower chip cost even though a single wafer can be very expensive. A single die could be as cheap as $0.03 depending on its size and could have a huge number of transistors on it. BUT you need to want a lot of them to justify the costs involved.