Chalcogenide

NV Stacked Memory: Selectors and Forming (Part 1)

Ron NealeContributor Ron Neale analyzes selector technologies presented by CEA Leti at the 2018 IEDM conference last December.


At the close of last year the IEDM maintained its long-standing reputation for offering across-the-board the right focus at the right time on important and key parts of the electronic device discipline.   For those with an interest in the future of stacked or 3D NV-memory arrays there were a number of important papers and presentations on a variety of thin film memory selectors or matrix isolation devices (MIDs).

Important, because as the move towards stacked memory arrays for storage class memory (SCM) and persistent  memory (PM) applications gains momentum, the thin film selector may be the device which is key in determining the performance and reliability for a number of different types of NV memory arrays or even the very existence of that type of memory array.  One of the important and poorly understood variables in the mix is the selector forming voltage and the structural changes which lead from it to the operating device threshold voltage which, in my view needs a lot more by way of detailed understanding.

As the memory array moves into Continue reading

Accelerating New Memory Materials Research

Intermolecular Characterization ChartWith all the new emerging memories that are being developed there must be quite a number of test runs to study exactly how well these new technologies and materials can perform.  If a batch of 300mm wafers must be used for a single test then the cost multiplies, particularly if no other test can be run on that wafer.

Another great difficulty is that most memory manufacturers run their wafers on very high-efficiency and high-volume wafer fabs.  It is perilous and wasteful to interrupt a production process to inject a batch of test wafers.  Most fab managers would rather have a tooth pulled than to change their flow to accept an experimental lot.

What can be done to improve this situation?

Well the folks at Intermolecular, Inc. (IMI) explained to the Memory Guy that they have a solution: They have built a small fab that allows single wafers to be processed with varying parameters across a single wafer.  In this way one wafer can be used to run 36 or more different experiments all at the same time.  This is clearly more economical than having to run the experiment on 36 wafers or, even worse, 36 batches of wafers!  Intermolecular says that, while production fabs are optimized for manufacturing, their fab is optimized for materials understanding.

The firm calls itself an Continue reading

Monatomic PCMs: A New Direction

Ron Neale[The following is a guest post written by Ron Neale.]

Until now designers of PCM devices have tried to make PCM meet their expectations by experimenting with an almost infinite number of possible multi-element glass compositions, in order to tinker with or emphasise a particular composition-related device characteristic. The apparent advantage of this great variety of materials comes with the baggage of reliability and performance-compromising element separation, driven by the forces of electro-migration, electrostatic effects and phase separation.

Is it possible to cast aside the problems of the multi-element PCM compositions and look at the possibility of monatomic PCMs?  For a team at IBM, Zurich and Aachen University the answer is an unequivocal “Yes!” and recently they have published details of the remarkable progress they have made with amorphous antimony (Sb), as an initial candidate element. This research was published in a June 2018 paper in Nature Materials Letters titled: Monatomic phase change memory, by Martin Salinga et al, IBM and Aachen University).

A difficulty faces those venturing in this new direction: While it is possible to bring many elements to the amorphous state, they very quickly crystallize at room temperature and higher.  The IBM researchers used simulations to find that the keys to obtaining a stable amorphous state is to control the quenching rate and the volume of the sample. That part of the antimony research is underpinned by some very impressive simulations that use only about 200 atoms.

Here’s the issue that this approach Continue reading

IBM Jumps on the “New Memory” Bandwagon

IBM's 3-Bit PCM Read AlgorithmAt a technical conference hosted by the IEEE this week IBM announced the results of nearly a decade of research in which its scientists have been investigating the emerging technology known as “Phase Change Memory” (PCM).  The scientists presented a means of successfully storing three bits per cell for the first time, while also addressing all of PCM’s challenging idiosyncrasies, including resistance drift and temperature drift.

Commonly referred to by the erroneous nickname “TLC” for Triple Level Cell, this technology squeezes three bits of data into the space of a single bit, essentially cutting the cost per gigabyte to about one third of that of a standard memory chip making it closer in cost to flash.

With this step IBM expects to help drive a new memory layer into existence, one that will fit between the cheap and slow NAND flash used in SSDs and the fast but expensive DRAM used for main memory.  Such a layer would improve the cost/performance of all types of Continue reading