Tutorial EQ10: Advanced Memory and Computing Technologies Using Phase Change Materials

Eric Pop, Stanford University

Fundamental, Thermal, and Energy Limits of PCM and RRAM

Written by Mohamed Atwa   

Eric Pop concluded the tutorial with a scintillating session on the fundamental limits of phase change memory (PCM) in terms of thermal confinement. He began the session by providing a historical perspective on “ovonic threshold switching” and its discoverer, Stanford R. Ovshinsky, who first proposed the idea of a memristive device in 1968. He then provided a unique overview of how PCM and resistive random access memory (RRAM) work, and how they are both devices which rely on heating to induce some state change in the memory device. Pop compared different PCM geometries, highlighting the two most common geometries called “mushroom cell” and “confined cell” geometries. The tradeoffs of PCMs in terms of set/reset time, endurance, reset energy, and retention were all briefly touched upon. Pop launched into a detailed timeline of his group’s efforts to explore PCMs, starting with his seminal work on PCMs with carbon nanotube (CNT) electrodes in the 2010s. He detailed the progress his group has achieved since then, including templated synthesis of PCMs with CNT electrodes, an exploration of the thermoelectric effects in PCMs, and his group’s recent exploration of superlattice-based PCM materials. He concluded the talk with a positive outlook regarding the potential of PCMs for future optimization, stressing that the energy and current requirements of PCMs could still be reduced a hundredfold in the future.

Tutorial EQ10: Advanced Memory and Computing Technologies Using Phase Change Materials

Manuel Le Gallo, IBM Research Europe

Deep Learning, Inference, and Training Using Computational Phase Change Memory

Written by Mohamed Atwa   

Manuel Le Gallo gave a detailed talk on the actualization of deep learning using phase change memory (PCM) hardware. He began by describing the differences between conventional computing, which separates processors and memory and “in-memory” processing, in which computations are done directly in the memory device. He cautioned that only certain types of logic and arithmetic can be done in memory, limited by the device physics in such devices. He then introduced charge and resistance based in-memory computing devices, with DRAM and Flash memory being examples of the former, and ReRAM and PCM being examples of the latter. PCM was given as an example of a prototypical “memristor” for such in-memory processing applications. The use-cases of such memristive “in-memory” processing were presented as being somewhere in between stochastic computing applications such as random number generation and those requiring more exacting solutions, such as scientific computing. Le Gallo then tackled the various nuances surrounding the usage of PCM for deep learning as an ideal use case between stochastic and precise computing. He concluded by introducing a newly-unveiled PCM memory chip simulator that IBM has released to open-source, known as the “IBM Analog AI Hardware Acceleration Kit.”

Tutorial EQ10: Advanced Memory and Computing Technologies Using Phase Change Materials

Fabrizio Acriprete, University of Rome Tor Vergata

Molecular Beam Epitaxial Growth and Characterization of Phase Change Memory Materials

Written by Mohamed Atwa     

Fabrizio Acriprete gave a deep-dive talk into the epitaxial growth and materials characterization of the most famous phase change memory material: germanium antimony telluride (GST). He started off by briefly touching on the applications of phase change memory (PCM) to embedded systems storage applications as well as to more exotic applications such as neuromorphic memory and nonvolatile photonics. He then described the various techniques employed in both industry and academia to grow epitaxial films of PCM materials. Specifically, he highlighted the pros and cons of MBE, PLD, and sputtering and showed the most common use cases for each. He moved on to the various crystal structures adopted by GST and its individual constituents: GeTe and Sb₂Te_3­. He touched briefly on the fundamental interest in the metal-insulator transition exhibited by GSTs when they change structure between their amorphous and crystalline phases. While amorphous GSTs are more insulating, crystalline GSTs are more conducting. This, he explained, was due to the change in vacancy ordering between the two phases. He segued into the compositional and structural tuning GSTs by varying the elemental fluxes, substrate types, and deposition temperatures of GSTs during MBE growth. Acriprete ended the talk by discussing a variety of experimental techniques used to probe the electronic structure of GSTs including time-resolved photoemission, angle-resolved photo-spectroscopy, and X-ray photo-spectroscopy. Overall, the session was an excellent exploration of the materials science-side of phase change memory materials.

Tutorial EQ10: Advanced Memory and Computing Technologies Using Phase Change Materials

Andrea Redaelli, STMicroelectronics

Embedded Phase Change Memory: From Material Engineering to Technology

Written by Mohamed Atwa    

Andrea Redaelli kicked off the tutorial with a short and sweet overview of phase change memory (PCM) from the perspective of both materials engineering as well as device fabrication, validation, and benchmarking. He began by introducing the myriad of nonvolatile memory applications of PCMs in the automotive, consumer electronics, and power electronics industries. The strength of PCMS over other nonvolatile memory technologies (such as NOR, NAND, and DRAM) were highlighted. The value proposition of PCMs, Redaelli emphasized, is that they provide the highest capacity per unit cost when compared to these other nonvolatile memory technologies. Redaelli then weighed the pros and cons of different compositions of the most famous PCM material: germanium antimony telluride (GST). While antimony-rich GSTs have the advantage in terms of read-write speed, germanium-rich tellurides are winning out in terms of long-term data retention. The tutorial then touched on the various materials engineering and device fabrication challenges that are present in GST-based PCMs, such as elemental segregation and resulting device aging problems. Redaelli briefly presented some of the statistical methods and metrics devised to quantify elemental segregation in GST-based PCMs. By carefully tuning the “thermal budget,” the thermal energy and heating rate, supplied during read/write cycles, Redaelli reported on his group’s success in limiting the elemental segregation in GST-based PCMs. Redaelli concluded the talk with a summary of the competitiveness of PCM as a nonvolatile memory technology and a positive outlook for the adoption of the technology to industrial and consumer applications in the near future.

Nice tutorial for NequIP from Simon Batzner

Simon Batzner presents the workflow of using NequIP (https://e3nn.org), an equivariant network for molecular dynamics! First time getting my hands on a neural network potential thanks to the easy-to-use colab tutorial (https://colab.research.google.com/drive/1_r348f6oIyKxH4FnpKeD8g4QjwDhP8mT?usp=sharing).

Publishing insights – how does your research get through the editorial process?

 

Researchers communicate their work mainly through publishing peer-reviewed journal articles. The process is rigid to make sure the content is scientifically precise and comprehensible. For a researcher in the training, the editorial process can be daunting. Dr. Stewart Bland, Executive Publisher at Materials Today, walked us through the publishing process and tips for early-career scientists.

Scholarly publishing today

There are around 5000 publishers worldwide generating 3 million peer-reviewed articles, with MRS publishing 35,000 articles each year. Among the publishing landscape, open access articles have occupied an estimated 0.6 million (20%) of the total articles in 2019.

Editorial structures

When authors, i.e. researchers who conduct the research and write the article, submit their manuscript to a publisher, the editorial process works in the workflow:

Author -> Editor in chief -> Associated editor -> Referees review -> Publisher decision

Each of the editorial roles each has a different responsibility to screen, examine, and judge the suitability of publishing.

What does an editor do?

From a publisher’s view, the article curator, the editors, plays an important role. They handle the work from examining technical and language checks, assessing the scope of the content, communicating with referees and authors, and judging and interpreting the quality for publication.

How to work with editors?

One of the key steps for manuscript judgment relies on referees’ comments. To include suitable and qualified referees, editors often use their networks and knowledge to find referees. Other options such as references within the manuscript, recommendations within the author’s cover letter, and search tools.

Therefore from the author’s standpoint, it is crucial to (1) nominate referees who are capable of judging and giving constructive feedback and, (2) optimize the title, abstract, and keywords to improve the process of identifying qualified reviewers.  

Pro-tip: Don’t use unnecessary “buzzwords” because they are popular. This will delay the process.

 

To connect with Chiung-Wei: @cwhuang_sci

Hello December! It’s going to be amazing with Snow and MRS Fall Meeting

Hello MRS attendees, Boston became white and shiny with snow and MRS. As the temperature is going down outside the window, fever is going up for MRS. A great gathering of the Materials Research Society is already started today. A long queue of brilliant researchers at the registration desk showed a desirous enthusiasm for MRS Fall meeting 2019.

In the meantime during a tutorial session of Optical Metasurfaces—Materials, Designs and Advanced Applications , I encountered with very diligent and splendid personality also the Symposium EL01 (Emerging Material Platforms and Approaches for Plasmonics, Metamaterials and Metasurfaces ) organisers Dr. Yu-Jung-lu (Academia Sinica) and Dr. Howard lee ( Baylor University). A deep discussion with them in a short time was remarkable.

I would like to invite all interested researchers tomorrow to take a look at symposium EL01 to dig more into this outstanding research area.

Keep Warm and Cheers.

F19MRS

Tutorial BM01: 3D printing methods for medical applications

Roger J. Narayan, Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University

3D printing technologies for healthcare

Written by Hortense Le Ferrand

Additive manufacturing (AM), commonly called 3D printing (3DP), diverges from traditional subtractive fabrication methods as it aims at building materials in a layer-by-layer fashion. Ten percent of the application fields of AM lies in healthcare, tackling personalized surgery, orthopedic or dental implants, and organ regeneration. In this tutorial, Narayan presented an overview of most common AM methods and described their respective benefits as well as areas demanding improvements for healthcare applications.

Among the four most common AM methods—namely, fused deposition modeling (FDM), ink-jet printing, laser sintering, and photopolymerization—the cheapest and most easily accessible method is FDM. In FDM printers of less than USD$200, a heated polymer filament is extruded through a nozzle, cools down after deposition, and binds to the underlying filament. However, despite the fast fabrication capabilities, the method relies on thermoplastics with low melting temperatures and viscosities, narrowing the range of chemistry available.

Ink-jet methods, however, have a larger range of possible input materials. As an example, mussel adhesive proteins can be printed along with solutions of iron ions playing the role of crosslinkers. This combination produces substrates with controlled crosslinking densities and morphologies.

For high-density materials like ceramics, selective laser sintering is the method of choice. It allows excellent bonding and the mechanical properties achieved are as good as those obtained from cast approaches.

Liquid-based techniques relying on photopolymerization present the advantage of sub-micrometric precision down to 20 µm but might pause the problem of residual radicals and toxic compounds. With recently developed two-photon polymerization techniques using femto-lasers, biocompatible polymers with 200 nm resolution can be printed.

Finally, in bioprinting, one approach particularly interesting for reconstructive surgery or for in vitro testing in replacement of animal testing methods consists in depositing viable cells embedded in polymer matrices. Current challenges are in achieving high-speed fabrication with small feature resolution, without affecting biocompatibility and biological response. On-going development of bioprinting will be discussed this week in the BM01 symposium on 3D Printing of Passive and Active Medical Devices.