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Semiconductor boffin: 3D NAND don't need NO STEENKIN' TSVs

Cut out 'n' keeper for your storage primer

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Blocks and Files Chip analyst Jim Handy of Objective Analysis took exception to several issues raised in a recent 3D NAND story, and El Reg storage desk asked him a few short questions for clarification.

He provided a few short answers that did just that - and here they are.

El Reg: Are there TSVs (through-silicon vias – vertical electrical connections through a stack of chips) in 3D NAND? And if not, why not?

Jim Handy: There are no TSVs in 3D NAND because there is no need for TSVs. You use TSVs to connect multiple chips, and 3D NAND is single chips.

El Reg: Does 3D NAND use stacks of planar cells?

Jim Handy: 3D NAND uses cells built sideways. These are very different from planar cells. What if you stop calling it "3D" and start calling it "Sideways" NAND (at least to yourself)? That might set your thinking in the right direction.

El Reg: How do the flash cell geometries in planar NAND and 3D NAND compare? How does 3D NAND affect lithographies?

Jim Handy: 3D NAND cells have doughnut-shaped cells and planar cells are flat and square. It's hard to compare the cell "sizes" since they are different things altogether. The process for 3D is not litho-intensive so manufacturers will be using relaxed process technologies like 40-50nm while working to use an aggressive number of layers.

Jim Handy: Samsung has made claims of higher reliability but hasn't released specifications to back that up. One very good reporter I know (you) published an article last August named something like: “Samsung’s cooking 3D NAND flash chips. What Did You Say the Specs Were? Oh right… you didn’t! I have guessed that the use of a charge trap will lower programming energy which should increase endurance, so that's a double benefit: Lower write power and longer life. I'm not positive about that, though."

The analyst seems very keen to get his hands on some, though. "I find it interesting that Samsung's now producing its 2G 3D V-NAND when I have been unable to find anyone outside of the company that has encountered its 1G 3D V-NAND."

Thank you kindly Jim. TSVs are an inter-chip connect and a single chip doesn’t need them. Engrave it on your brain, tattoo it somewhere, or write it on your screen saver. ®

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