Summary

Top down is today’s method of choice for manufacturing.

• It requires precise control and many discrete steps.
• Its forward progress is reaching ultimate limitations due to in-built physical restrictions.

Bottom up is a future target since it relies on Nature providing inherent control.

Bottom up from the gas phase uses two prime methods – MBE and CVD.

• Different targets.
• MBE slow and ultra precise, CVD faster but less precise.
• MBE is complicated and CVD is generally simpler and cheaper because of the differing demands on the vacuum systems.