Flash Memory Summit: Limitless Layers of 3D NAND

SanDisk Technology Roadmap 2014The single most interesting thing I learned at the 2015 Flash Memory Summit was that 3D NAND doesn’t have a natural limit, after which some other memory type will need to be adopted.

For years SanDisk has been presenting a memory roadmap (this post’s graphic is one rendition) that anticipates a move to ReRAM after 3D NAND has run through its natural life, which was expected to be as little as three generations.  This has been backed by the idea that a 3D NAND stack would only be able to reach a certain number of layers before it would encounter difficulties caused by the need to etch a high aspect ratio hole through an increasing number of layers.

The aspect ratio issue is not hard to understand: Let’s assume that the hole in a 24-layer stack has an aspect ratio of 40:1, then a 32-layer hole would have an aspect ratio of about 50:1, and a 64-layer stack would be something close to 100:1.  Today’s technology starts to have trouble etching holes with an aspect ratio higher than 60:1.

These high aspect ratios were thought to be the limiting factor that would prevent 3D NAND from continuing for more than three generations.  3D NAND could only have as many layers as the aspect ratio could support.

On a panel that I moderated at this year’s Flash Memory Summit one panelist, Dr. Myoung Kwan Cho of SK hynix, explained that although there is a limit Continue reading “Flash Memory Summit: Limitless Layers of 3D NAND”

Micron/Intel 3D XPoint Raises More Questions than Answers

Micron-Intel 3D XPoint Memory InternalsMicron and Intel hosted an event in San Francisco Tuesday, July 28, to introduce a new memory technology that they have named “3D XPoint”.  This technology was explained to be “up to 1,000 times faster, with 1,000 times the endurance of NAND flash” while being significantly cheaper than DRAM.

Some technical details:

  • 3D XPoint is a “Fundamentally Different Technology” than current memory types.  It’s an ReRAM that uses material property changes for bit storage where both DRAM and NAND use charge to store a bit
  • The chip currently stores 128Gb in two stacked planes of 64Gb each, storing a single bit per cell
    • Today’s densest production NAND flash chips store 128GB by using MLC, so this chip actually has twice as many bit cells as any production NAND flash
    • The companies do not see a clear limit to the number of planes they can stack, but are optimistic about this
  • The bulk mechanism can be used to store multiple bits on a single cell (MLC)
  • Today’s chip is made using a 20nm process, but can scale well past that
    • There is no clear limit of how far the technology can be scaled
  • It’s 1,000 times faster than NAND flash and offers 1,000 times NAND’s endurance
  • It’s 10 times as dense as today’s “Conventional Memory” (which I suppose to be DRAM)
  • This is not intended to replace either NAND or DRAM, but to coexist as a new memory layer between NAND and DRAM

The companies claim that other Continue reading “Micron/Intel 3D XPoint Raises More Questions than Answers”

Four New Players Join 3D NAND Market

Micron & Intel's 3D NAND Die PhotoThe following is excerpted from an Objective Analysis Alert sent to our clients on March 26: On March 25 SanDisk and Toshiba announced sampling of their 3D NAND flash technology, a 128Gb (gigabit) 48-layer second-generation product based on the BiCS technology that the companies pioneered in 2007.  Pilot production will begin in the second half of 2015 with meaningful production targeted for 2016. This release was issued at the same time that Intel and Micron were briefing the press and analysts for their March 26 announcement of their own 3D NAND offering (pictured), which is currently sampling with select customers, and is to enter full production by year-end.  The Micron-Intel chip is a 32-layer 256Gb device, which the companies proudly point out is the densest flash chip in the industry.

Similarities and Differences

These two joint ventures (Intel-Micron and SanDisk-Toshiba) are taking very different Continue reading “Four New Players Join 3D NAND Market”

Finally! Samsung’s 3-Bit V-NAND Arrives

3-bit V-NANDSamsung has finally introduced the 3-bit 3D NAND chip it revealed at last August’s Flash Memory Summit.  This announcement was made in the form of an SSD announcement.

For those who were unable to attend the Flash Memory Summit, Samsung’s Senior VP of Memory R&D, Bob Brennan, announced in his keynote speech that a 3D 32-layer V-NAND, a chip that would achieve twice the chip density of planar NAND, was entering production and that SSDs would follow in a month.  Now, two months later, Samsung has announced those SSDs.

This week’s release reiterates Continue reading “Finally! Samsung’s 3-Bit V-NAND Arrives”

New Book: Vertical 3D Memory Technologies

Book: Vertical 3D Memory Technologies - Betty PrinceWiley has recently published a new book by Betty Prince titled Vertical 3D NAND Technologies that is one to consider if you want to bring yourself up to speed on recent research behind today’s and tomorrow’s 3D memory technologies.

For those who haven’t previously encountered Dr. Prince, she is the author of a number of key books covering memory design and holds memory patents written over her 30-year career in the field.

The book provides capsule summaries of over 360 papers and articles from scholarly journals on the subject of 3D memories, including DRAM, NAND flash, and stacked chips.

These papers are organized into Continue reading “New Book: Vertical 3D Memory Technologies”

Making 3D NAND Flash – Animated Video

The good people at Coventor have graciously allowed me to post their video of the Pipe-Shaped BiCS 3D NAND flash process onto The Memory Guy blog site.  Click the image to see it play out.

Coventor tells me that they are the leading Continue reading “Making 3D NAND Flash – Animated Video”

Samsung Begins Operations at its Xi’an Fab

Samsung's Xi'an, China fabSamsung has announced that the company’s newest memory fabrication plant (Fab) in Xi’an, China has “begun full-scale production operations”, adding that: “The new facility will manufacture Samsung’s advanced NAND flash memory chips: 3D V-NAND.”

I immediately asked whether the plant will build products other than 3D NAND, and the company has replied that this will be the only product produced in the Xi’an plant.  What Samsung has not said is what is meant by “full-scale production operations.”  Typically wafer fabs start with a very low production capacity as new tools are being qualified, only ramping to high-volume production a year or more after initial production.

Samsung points out that production has begun a mere 20 months after initial groundbreaking, which is quite Continue reading “Samsung Begins Operations at its Xi’an Fab”

Comparing Samsung V-NAND to Micron 16nm Planar NAND

Andrew Walker, SchiltronI 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

ASML chart chowing the lithography used for 4X, 3X, 2X, and 1Xnm planar NAND and 3D NANDNAND 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”

3D NAND: Who Will Make It and When?

SK hynix 3D NAND Cross SectionThis series has looked at 3D NAND technology in a good deal of technical depth.  The last question to be answered centers around the players and the timing of the technology.  A lot has been said about the technology and its necessity.  Will everyone be making 3D NAND?  When will this big transition occur?

This post will provide an update as of its publication (13 December 2013) to show each company’s current status, to the best of The Memory Guy’s understanding.  Readers may want to refer back to the earlier posts in this series, as well as to a June 2013 Nikkei TechON article that gives a good review of the 3D NAND alternatives that have been presented at various technical conferences.

Let’s start with Samsung, the largest producer of NAND flash today.  Just prior to Memcon 2013 last Continue reading “3D NAND: Who Will Make It and When?”