NAND can't scale below the ONO thickness of 17-18 nm plus the silicon thickness of at least few nm. But that is where NAND is now. To go 3d to expand capacity has yield and ECC consequences which may offset the economic benefit.
I think, about a month back, we were discussing about the future of the NAND memories. Some believe that, the year 2011 is going to be the year of NAND memories. Is there any estimated time frame, by when the memories using newer technologies (such as MRAM, PCM etc.) are going to take place of the conventional memory technologies?