Technical Trends - The Memory Guy Blog

Comparing Samsung V-NAND to Micron 16nm Planar NAND

I was recently directed to a very interesting blog post written by 3D technologist Andrew Walker of Schiltron in which he compares two NAND flash chips that were presented at the IEEE International Solid State Circuits Conference (ISSCC) on February 12.

The post, titled Samsung’s V-NAND Flash at the 2014 ISSCC: Ye Distant Spires… is on the 3D InCites website.

Dr. Walker puts a lot more time and effort into his graphic representations of 3D NAND chips than do others (The Memory Guy included) and this makes it much easier to understand the issues he points out. He shows us that Samsung’s 3D NAND cell is about 5 times the size of a 40nm planar NAND cell and about 30 times that of Micron’s 16nm planar cell, and that the 3D NAND’s physical area is unlikely to change with any future 3D technology generations.

For this and other reasons (given in the article) he states that the Samsung V-NAND is “an impressive achievement but not a realistic foundation for the future.”

After having compiled my series on 3D NAND I can appreciate Dr. Walker’s opinion. This is certainly going to be a difficult technology to master, and it could be quite some time before the cost structure for 3D NAND can compete against that of today’s planar technologies.

Give the Walker post a quick read and judge for yourself whether we are at the brink of a 3D conversion or if this technology can be expected to slip out a few years.

Why NAND is So Difficult to Scale

NAND flash is the process leader in memory technology, and this puts it in a very challenging position: It must ramp to high volume production using techniques that have never been tried before.

The graphic for this post (click to enlarge), supplied by ASML, the semiconductor industry’s leading lithography tool supplier, illustrates the challenge of migrating from one process node to the next. Across the bottom, on the X-axis, are representative process nodes ranging from “2D-45”, or two-dimensional (planar) 45nm NAND, to “3D-5x”, or three-dimensional 5xnm NAND. Below these numbers are the year of volume production.

The vertical axis, labeled “Tolerance” represents the minimum Continue reading “Why NAND is So Difficult to Scale”

What is a “Multilayer Cell”?

From time to time I get questions from investors in the memory business asking: “What is a multilayer cell?”

The answer is: “There is no such thing: It’s a misstatement.”

The term “MLC” has, by a number of people, been mistranslated to “multi-layer cell.” The misunderstanding appears to have originated in the financial community. People in the flash memory business never use the term at all.

Yes, we talk about MLC, but to us the term means “multilevel cell”.

A multilevel cell is a cell that uses varying voltage levels to represent different states. With four voltage levels the resulting four states on a single cell can be turned into Continue reading “What is a “Multilayer Cell”?”

DRAM Inventor Wins Kyoto Prize

This year’s Kyoto Prizes included an Advanced Technology Prize for the father of DRAM, IBM’s Dr. Robert Dennard.

The Kyoto Prize, one of the world’s most prestigious accolades, is an international award bestowed once a year by The Inamori Foundation to honor those who have contributed significantly to the scientific, cultural and spiritual betterment of humankind. Some say it is similar to the Nobel Prize, and seven Kyoto Prize laureates have gone on to win the Nobel Prize.

In addition to the kudos of receiving this honor, Denning was also Continue reading “DRAM Inventor Wins Kyoto Prize”

Why Facebook Can’t Get its Dream Memory Chip

During the Flash Memory Summit last August Facebook’s Jason Taylor, Director of Capacity Engineering and Analysis, asked in his keynote speech for a flash chip with dramatically lower cost per gigabyte, saying that he would readily give up speed and endurance to achieve this lower cost. Taylor called this “Cold Flash” and said he was willing to use something that was “Write Once, Read Many” or WORM for data that was unlikely to change over its lifetime. He said this was Facebook’s “Ask of the Industry.”

That same sentiment was echoed yesterday at Samsung’s Memory Solutions Forum by eBay’s Distinguished Engineer and Technologist Roark Hilomen, who said that he could live with 1/3rd the number of writes that normal flash supports as long as he could get it for 1/4 the price.

Unfortunately this is simply not possible.

Let’s do a little math to understand Continue reading “Why Facebook Can’t Get its Dream Memory Chip”

Samsung’s View on Charge Trap Flash

At 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

Samsung 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

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”

SanDisk & Toshiba Move to Next Process Node

SanDisk and Toshiba, in separate announcements, both today disclosed their next-generation process technology.

The companies introduced their new “1y” processing node that, according to SanDisk, produces 19nm x 19.5nm cell, versus the earlier “19nm” process (or “1x”) that used a 19nm x 26nm cell.

The graphic for this post (click to enlarge) was presented during SanDisk’s May 5th Analyst Day and compares the 24nm process to the 19 x 26nm process, moving to the 19 x 19nm process, and eventually to “1z” which neither company is yet revealing. After the 1z process SanDisk believes Continue reading “SanDisk & Toshiba Move to Next Process Node”

Hybrid Memory Cube Making Progress

On Tuesday the HMC Consortium (that’s short for “Hybrid Memory Cube”) announced that members have agreed upon a specification. The consortium has been moving rapidly, meeting its targets despite the revolutionary nature of the interface.

As a reminder, this technology stacks multiple DRAMs in a single package with a logic chip at the base of the stack that performs all the signalling to the rest of the system. Signals between the DRAMs and logic chip use through-silicon vias (TSVs) as interconnections. This allows the technology to deliver 15 times the performance of DDR3 at only 30% of the power consumption. The Memory Guy first posted about the HMC in late 2011.

The consortium explains that the HMC interface already has 100 adopters, and that a few Continue reading “Hybrid Memory Cube Making Progress”