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
At the IEEE’s International Electron Device Meeting (IEDM) in December a start-up named Zeno Semiconductors introduced a 1-transistor (1T) SRAM. Given that today’s SRAMs generally use between six and eight transistors per bit, this alternative promises to squeeze the same amount of SRAM into a space 1/6th to 1/8th the size of current SRAM designs, leading to significant cost savings.
The device is really a single standard NMOS transistor that behaves as if it were two bipolar transistors connected into something like a flip-flop, although the transistors’ bases are open, rather than cross-coupled to the opposite transistors’ collector, as is done in a standard flip-flop.
The cell is selected by activating the gate, and the bit is set or sensed via the source and drain to provide a differential signal.
This is a decidedly clever departure from standard SRAM configurations, and it reflects a careful observation of the actual Continue reading
Naturally, the first question is: “How do they do that?”
To get all the chips into the DIMM format Samsung uses TSV interconnects on the DRAMs. The module’s 36 DRAM packages each contain four 8Gb (1GB) chips, resulting in 144 DRAM chips squeezed into a standard DIMM format. Each package also includes a data buffer chip, making the stack very closely resemble either the High-Bandwidth Memory (HBM) or the Hybrid Memory Cube (HMC).
Since these 36 packages (or worse, 144 DRAM chips) would overload the processor’s address bus, the DIMM uses an RDIMM protocol – the address and control pins are buffered on the DIMM before they reach the DRAM chips, cutting the processor bus loading by an order of magnitude or more. RDIMMs are supported by certain server platforms.
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 (ION) and transconductance (gm) 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
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
Micron 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
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
Last week Toshiba and SK hynix announced an agreement to jointly develop Nano Imprint Lithography (NIL), building on a memorandum of understanding (MOU) that two companies signed in December last year. Development efforts will begin this April and practical adoption is expected to start in 2017. The collaboration is expected to reduce risk and accelerate commercialization of this technology.
NIL is expected to produce next-generation lithography at high throughput rates more economically than established lithography tools. It is should compete against Extreme Ultraviolet (EUV) lithography, an alternative technology whose use has been delayed by numerous technical challenges. EUV, a euphemism for X-Rays, cannot use transmissive optics like glass lenses, so a completely new reflective imaging technology has had to be developed to support its use. The advantage of EUV is that the light wavelength is only 13nm, which is an order of magnitude smaller than the 193nm light currently used to produce leading-edge chips, allowing it to print significantly smaller features.
Unlike today’s lithography, which uses a purely photographic process, NIL mechanically stamps a pattern into the photoresist in a similar manner to the sealing wax stamp shown in the photo (courtesy of BackToZero, a wax stamp maker). The stamp is produced using Continue reading
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
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