Hynix - The Memory Guy Blog

Flash Memory Summit: Limitless Layers of 3D NAND

The 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”

DRAM Prices Down, But Not So Bad

For the past ten months DRAM prices have been undergoing a steady slide. Is the market in a crisis? Not really!

Today’s low spot price of $4.30/GB puts us on a par with February 2013, a full two years ago (see chart). DRAM makers have done a lot to reduce their production costs since that time, so their margins this quarter will be much better than they were in the first quarter of 2013.

But we are still a very long way from the bottom of the last market downturn. In late 2012 spot prices reached a low of $2.52/GB, a full 41% lower than today’s lowest spot prices.

The Memory Guy models the production costs of leading memory chips, and DRAM manufacturing costs have been decreasing for the past several years at an average annual rate of about 30%. That means that costs today are about half of what they were two years ago, and one third of their level this time in 2012.

So even though today’s Continue reading “DRAM Prices Down, But Not So Bad”

Four New Players Join 3D NAND Market

The 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”

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”

Did SK hynix Beat Samsung to the 8Gb LPDDR4?

Every so often something very strange happens that puzzles The Memory Guy. On December 29 (or Dec. 30 in Seoul) something odd occurred.

I received two e-mails, one from SK hynix at 3:55 PM Pacific Time, and one from Samsung exactly one hour later. Both were press releases.

The SK hynix release was titled: “SK Hynix Developed the World’s First Next Generation Mobile Memory LPDDR4”. It announced that the company is sampling its 20nm-class 8Gb LPDDR4 DRAM to customers.

The Samsung release was Continue reading “Did SK hynix Beat Samsung to the 8Gb LPDDR4?”

3D NAND: Who Will Make It and When?

This 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?”

Rambus and Micron Sign License Agreement

The following is excerpted from an Objective Analysis Alert that can be downloaded from the company’s website.

Rambus and Micron announced on Tuesday that they have signed a patent cross license agreement. Micron receives rights to Rambus IC patents, including memories. Both Micron and Elpida products will be covered. The companies have thus settled all outstanding patent and antitrust claims in their 13-year court battle.

Micron will make royalty payments to Rambus of up to $10 million per quarter over the next seven years, totaling $280 million, after which Micron will receive a perpetual, paid-up license.

Rambus and Micron both have Continue reading “Rambus and Micron Sign License Agreement”

How Do You Erase and Program 3D NAND?

Some of my readers have asked: “How is 3D NAND programmed and erased? Is it any different from planar NAND?”

In a word: No.

(Before I get too far into this allow me to admit that The Memory Guy doesn’t understand quantum physics, so I will be presenting this only to the depth that I understand it. There will be no band-gap diagrams or equations to wrestle with.)

Both 3D NAND and planar NAND use Fowler Nordheim Tunneling (FN) to both program and erase. This differs from NOR flash which programs bits using Continue reading “How Do You Erase and Program 3D NAND?”

3D NAND: How do You Access the Control Gates?

One of the thornier problems in making 3D NAND is the job of connecting the peripheral logic (the row decoders) to all of those control gates that are on layers buried somewhere within the bit array. Remember that the control gates are the conductive sheets of polysilicon or tantalum nitride at various depths in the chip.

The problem boils down to this: You can’t run connections from each layer up or down the side of the chip to get to the CMOS circuits below. Instead you have to create a terrace structure to expose and connect to each layer.

These connections are made by etching a stair-step pattern into the layers and sinking Continue reading “3D NAND: How do You Access the Control Gates?”

An Alternative Kind of Vertical 3D NAND String

My 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”