An Alternative Kind of Vertical 3D NAND String

Samsung's TCAT 3D NAND flashMy prior 3D NAND post explained how Toshiba’s BiCS cell works, using a silicon nitride charge trap to substitute for a floating gate.  This post will look at an alternative technology used by Samsung and Hynix which is illustrated in the first graphic, a diagram Samsung presented at a technical conference. This cell also uses a charge trap.

Let The Memory Guy warn you, if the process in my prior post seemed tricky, this one promises to put that one to shame!

Part of this stems from the use of a different kind of NAND bit cell.  You can shrink flash cells smaller if you use a high-k gate dielectric (one with a high dielectric constant “k”) since it Continue reading “An Alternative Kind of Vertical 3D NAND String”

3D NAND: Making a Vertical String

Toshiba's Original BiCS Diagram - IEDM 2007Let’s look at how one form of 3D NAND is manufactured.  For this post we will explore the original design suggested by Toshiba at the IEEE’s International Electron Device Meeting (IEDM) in 2007.  It’s shown in the first graphic of this post.  (Click on any of the graphics for a better view.)

Toshiba calls this technology “BiCS” for “Bit Cost Scaling.”  The technique doesn’t scale the process the way the world of semiconductors has always done to date – it scales the cost without shrinking the length and width of the memory cell.  It accomplishes this by going vertically, as is shown in this post’s first graphic.

This takes a special effort. This is where the real Continue reading “3D NAND: Making a Vertical String”

What is a 3D NAND?

Applied Materials' Explanation of 3D NANDIn the prior post we discussed the need to go vertically into the body of the die, since NAND flash can not be scaled much farther in length and width on the die’s surface.  Toshiba invented a 3D NAND which has been adopted and refined by all flash makers.  The idea is simple: Rather than shrink the cell’s length and width, why not turn the NAND string so that it’s standing on its end?

This concept is illustrated by this post’s first graphic, which was provided by Applied Materials.  (Click on the graphic to see the whole thing at a larger size.)  A standard NAND string that normally runs longitudinally is turned on its end to become a vertical string.  Not only that, but it makes things easier if the string is split into two sections and Continue reading “What is a 3D NAND?”

Why Do We Need 3D NAND?

NAND Flash Capped Gate StructureA memory chip of a certain area costs about the same amount to produce, no matter how many bits it holds. Naturally, the more bits you can cram onto this chip, the cheaper the price per bit will be. Low cost is of the utmost importance in the world of memory.

Memory chip makers have shrunk the cost of a bit some nine orders of magnitude since the 1960s largely by shrinking the process, or “scaling” to increasingly tighter process geometries.

Flash has always been expected to reach a scaling limit. Over the past few generations technologists have developed Continue reading “Why Do We Need 3D NAND?”

What is 3D NAND? Why do we need it? How do they make it?

3D NANDIn August 2013 Samsung announced its V-NAND, the first production 3D NAND, kicking off a big change in the way that NAND flash will be manufactured.  This new technology raises a number of important questions:

  • What exactly is a 3D NAND?
  • Why does the industry need to go to a 3D topology?
  • How the heck do they make such a product?

To answer these questions I assembled a series of articles posted as weekly segments on The Memory Guy blog during the fourth quarter of 2013.  The different sections are listed below, with hot links to each section.

Each of these is a topic that is complex enough to warrant its own post, so for the nine Fridays I published a post to explain each one in depth.  I hope you find it engaging and informative.

Samsung’s View on Charge Trap Flash

Samsung's Cheese analogy for Charge Trap FlashAt the Flash Memory Summit yesterday ES Jung, PhD, EVP & GM for the Samsung R&D Center, explained the inner workings of Samsung’s new V-NAND vertical NAND flash technology.  I will shortly be writing a series to explain what a 3D NAND is since there is little on the web that gives clear details about the technology.

One key attribute of most 3D NAND approaches is the use of a charge trapping layer.  This has to do with the difficulty of manufacturing sideways floating gates.

Dr Jung delighted the show’s audience by explaining that a standard floating gate is like Continue reading “Samsung’s View on Charge Trap Flash”

Samsung Announces 3D NAND Production

Toshiba's BiCS 3D NAND 2007 diagramSamsung has announced production of its 3D NAND technology.  This approach, first introduced by Toshiba in 2007, allows NAND flash makers to achieve more bits per chip by building NAND strings, which normally run across the surface of the chip, as vertical stacks.

It’s a fascinating technology, since it harnesses exotic steps invented by DRAM makers in the 1990s to get over scaling problems in that technology.  At the time DRAM had to go vertical to follow Moore’s Law and there were two schools of vertical DRAM: Stacked Capacitor, and Trench Cell.  The stacked capacitor camp layered polysilicon and silicon dioxide into layers to form a vertical capacitor.  The trench camp etched a very narrow and deep hole into the silicon and lined it with the capacitor plates.  Both worked very well, but over time the trench makers have Continue reading “Samsung Announces 3D NAND Production”

Applied’s Take on 3D NAND

Applied Materials expects for 3D NAND to grow the etch & CVD markets by 50%Early this month I was invited to participate in Applied Materials’ (AMAT) Analyst Day.  The sessions were rich in data covering the markets that would profit the company over the next few years.

Naturally, The Memory Guy fixated on those presentations that dealt with memory.  When it came to the upcoming transition to 3D NAND, AMAT had a lot to say.

A later post will explain what 3D NAND actually is.  Suffice it to say that today’s approach to making NAND flash has nearly reached its limit, and the approach that manufacturers plan to use in the future involves making NAND strings that stand on their ends.  This has phenomenal implications on Continue reading “Applied’s Take on 3D NAND”

Hynix and Spansion Join Forces

Spansion and SK Hynix AllianceSK Hynix and Spansion have announced a strategic NAND alliance under which Hynix will serve as a foundry for low-density SLC NAND chips made for Spansion using Hynix’ advanced processing nodes.

These products, aimed at the embedded market, should serve to strengthen Spansion in a market in which the company thrives. In fact,  Spansion expressed this very well in their press release, citing: “Spansion’s recognized customer support and commitment for longevity of supply, which is highly valued in the embedded market, where Spansion has established relationships.”

The new chips will be manufactured in “4x, 3x, and 2xnm” process technologies.

The companies have also agreed to cross-license their patent portfolios.

You may be asking yourself: “What does Hynix Continue reading “Hynix and Spansion Join Forces”

IBM to Build Micron Hybrid Memory Cube

Conceptual Cutaway Drawing of the Hybrid Memory CubeIn a December 1 press release IBM announced that the company will be manufacturing Micron Technology’s Hybrid Memory Cube (HMC) which IBM claims to be “the first commercial CMOS manufacturing technology to employ through-silicon vias (TSVs).”

This device is one that Altera, Intel, Micron, Open Silicon, Samsung, and Xilinx have all presented recently as a plausible solution to the difficulty of increasing the speed of DRAM/processor communications.  The Hybrid Memory Cube Consortium (HMCC) website offers a deep dive into the details of the consortium and the technology.

Continue reading “IBM to Build Micron Hybrid Memory Cube”