BiCS – The Memory Guy Blog

96-Layer NAND in Perspective: WDC Video

It’s pretty easy to go from talking about the earliest 24-layer 3D NAND to talking about the next-generation 32-layer 3D NAND, and then to progress through 48, 64, and more layers, but the amazing scale of a 96-layer part doesn’t really sink in when you just talk about numbers.

That’s why The Memory Guy was so charmed when Western Digital Corp. (WDC) invited me in for a briefing that gave me a more solid idea of how significant of a number 96 really is. The company brought along a plastic model that replicated the structure of its 96-layer BiCS NAND chip using clear plastic which was dramatically lighted from the inside.

WDC’s model was constructed using standard plastic sheeting, probably 1/8″ thick (~3mm), one sheet to represent the conductive polysilicon and one to represent the insulating silicon dioxide for each layer. Naturally, there are more than 96 layers in 96-layer NAND since there are source select transistors at the bottom and drain select transistors at the top. This adds a little bit to the layer count.

Another layer in the middle of Continue reading “96-Layer NAND in Perspective: WDC Video”

Toshiba Restructuring: New 3D Fab Coming

Beleaguered Toshiba finally unveiled its restructuring plan on Friday. The plan aims to return the company to profitability and growth through management accountability.

A lot of the presentation focused on the memory business, a shining star of the Toshiba conglomerate, which has so far included appliances, nuclear power plants, and medical electronics.

Toshiba has big plans for its Semiconductor & Storage Products Company, calling it “A pillar of income with Memories as a core business”. The company plans to enhance its NAND flash cost competitiveness by accelerating development of BiCS (Toshiba’s 3D NAND technology) and by expanding its SSD business. There are three parts to this effort:

Grow 3D NAND production capacity
Speed up 3D NAND development
Increase SSD development resources

This post’s graphic is an Continue reading “Toshiba Restructuring: New 3D Fab Coming”

New Materials Solve Key 3D NAND Issue

At the IEEE’s IEDM conference last week Belgian research consortium imec showed an improved “gate first” 3D NAND that replaced the conventional polysilicon channel with InGaAs, Indium Gallium Arsenide, a III-V material. This new technique opens the door to higher layer counts in 3D NAND, allowing denser parts to be made in support of further cost reductions.

For those unfamiliar with the term, the “gate first” approach is the foundation of Toshiba’s BiCS NAND, and presumably Micron’s floating gate 3D NAND.

imec explains that “Replacing poly-Si as a channel material is necessary, as it is not suitable for long-term scaling.” Further they report that on-state current (I_ON) and transconductance (g_m) of the III-V channel was better than that of polysilicon devices, without any programming, erase, or endurance degradation. The device’s characteristics are shown in this post’s graphic.

The consortium reports that the current through the Continue reading “New Materials Solve Key 3D NAND Issue”

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”

New Book: Vertical 3D Memory Technologies

Wiley 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 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”

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”

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?”

3D NAND’s Impact on the Equipment Market

A very unusual side effect of the move to 3D NAND will be the impact on the equipment market. 3D NAND takes the pressure off of lithographic steps and focuses more attention on deposition and etch. The reason for going to 3D is that it provides a path to higher density memories without requiring lithographic shrinks.

This sounds like bad news for stepper makers like ASML, Canon, and Nikon while it should be a boon to deposition and etch equipment makers like Applied Materials, Tokyo Electron, and Lam Research.

In its summer 2013 V-NAND announcement, Samsung explained that it would be Continue reading “3D NAND’s Impact on the Equipment Market”