November 2013 – The Memory Guy Blog

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?”

The Father of Flash Memory

At the Flash Memory Summit in August I had the honor of awarding Fujio Masuoka, the inventor of both NAND and NOR flash, the Flash Memory Summit Lifetime Achievement Award. This award is given to the giants of the flash memory industry to acknowledge their contributions.

Dr. Masuoka first described NOR flash at the 1984 International Electron Device Meeting (IEDM) in San Francisco, and NAND flash at the same venue in 1987. His paper “A new flash EEPROM cell using triple polysilicon technology” introduced a technology that is now used everywhere.

The award has also been given to Intel’s Flash team who brought the first commercial products to the market, and SanDisk co-founder Eli Harari, for devising a way to manufacture a floating gate.

David Schwaderer made a video of the presentation and posted it HERE. Have a watch!

3D NAND: Benefits of Charge Traps over Floating Gates

A prior post in this series (3D NAND: Making a Vertical String) discussed the difficulties of successfully manufacturing a charge trap flash bit. Still, Spansion, and now other flash makers, have determined to take this route. Why is that?

In Spansion’s case, a charge trap was a means of doubling the bit capacity of its products. It was an inexpensive alternative to standard MLC flash. To date this strategy has worked very well.

As mentioned in that earlier post, 3D NAND uses a charge trap because it’s extremely difficult to create features, like a floating gate, sideways – lithography works from the top down. A charge trap, when used to replace a floating gate, doesn’t need to be patterned, since the Continue reading “3D NAND: Benefits of Charge Traps over Floating Gates”

Micron Announces Processor-In-Memory

During the Supercomputing Conference in Denver today Micron Technology announced its new twist on processing: A DRAM chip with an array of built-in processors.

Dubbed: “The Automata Processor” this chip harnesses the inherent internal parallelism of DRAM chips to support a parallel data path of about 50,000 signals to attain processor-DRAM bandwidth that can only be dreamed of using conventional DRAM interfaces. The processor is a Graph-Oriented architecture.

The chip lends itself to Continue reading “Micron Announces Processor-In-Memory”

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?”

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”

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”

SIA: Memories Drive Record Semi Revenues

The SIA yesterday released the WSTS semiconductor sales data for September. Monthly revenues reached a record $27 billion driving third-quarter revenues to their own record of $81 billion. This was the seventh straight month of semiconductor growth, the first such run-up since 2010.

This quote, by SIA CEO Brian Toohey really caught The Memory Guy’s eye: “Sales of memory products have increased sharply compared to last year and continue to be a major driver of industry growth.”

A lot has been happening to drive this increase in memory revenues: The recent SK hynix fire increased DRAM prices, but Continue reading “SIA: Memories Drive Record Semi Revenues”

3D NAND: Making a Vertical String

Let’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”