BEHAVIOR, an in-home robot, benchmark

As my readers probably already know, I’m a long time benchmark geek. So when I recently read an article out of Stanford (AI Experts Establish the “North Star” for Domestic Robotics Field) where a research team there developed a new robotic benchmark, I was interested. The new robotics benchmark is called BEHAVIOR which was documented in an ARXIV.org article (see: BEHAVIOR: Benchmark for Everyday Household Activities in Virtual, Interactive, and ecOlogical enviRonments). It essentially uses real world data to identify domestic work activities that any robot would need to perform in a home.

The problems with robot benchmarks

The problem with benchmarks are multi-faceted:

  • How realistic are the workloads used to evaluate the systems being measured?
  • How accurate are the metrics used to rank and judge benchmark submissions?
  • How costly/complex is it to run a benchmark?
  • How are submissions audited and are they reproducible?.
  • Where are benchmark results reported and are they public?

And of course robotics brings in it’s own issues that makes benchmarking more difficult:

  • What sensors does the robot have to understand how to complete tasks?
  • What manipulators does the robot have to perform the tasks required of it?
  • Do the robots move in the environment and if so, how do the robots move?
  • Does the robot perform the task in the real world on in a simulated environment.

And of course, when using a simulated environment, how realistic is it.

BEHAVIOR with iGibson (see below) seem to answer many of these concerns for an in home robot benchmarking.

What is BEHAVIOR?

First, BEHAVIOR’s home making tasks were selected from an American Time Use Survey maintained by the USA Bureau of Labor Statistics which identifies tasks Americans perform in their homes. With BEHAVIOR 1.0 there are 100 tasks ranging from building a fruit basket to cleaning a toilet, and just about everything in between. I didn’t see any cooking or mixing drinks tasks but maybe those will be added.

Second, BEHAVIOR uses a predicate logic, called BDDL (BEHAVIOR Domain Definition Language) to define initial conditions for tasks such as tables, chairs, books, etc located in the room, where objects need to be placed, and successful completion goals or what task completion should look like.

BEHAVIOR uses 15 different rooms or scenes in their benchmark, such as a kitchen, garage, study, etc. Each of the 100 tasks are performed in a specific room.

BEHAVIOR incorporates 1217 different objects in 391 categories. Once initial conditions are defined for a task, BEHAVIOR essentially randomly selects different object for the task and randomly locates them throughout the room.

In order to run the benchmark, one could conceivably create a real room, with all the objects and have them placed according to BEHAVIOR BDDL’s randomly assigned locations with a robot physically present in the room and have it perform the assigned task OR one could use a simulation engine and have the robot run the task in the simulation environment, with simulated room, objects and robot.

It appears as if BEHAVIOR could operate in any robotics simulation environment but has been currently implemented in Stanford’s open source robotics simulation engine called iGibson 2.0 (see: iGibson 2.0: Object-Centric Simulation for Robot Learning of Everyday Household Tasks and iGibson 2.0 website). iGibson uses the Bullet real time physics engine for realistic physical environment simulation.

A robot operating within iGibson is provided a 3D rendering of the room and objects in images or LIDAR sensor scans. It can then identify the objects that it needs to manipulate to perform the tasks. One can define the robot simulated sensors and manipulators in iGibnot 2.0 and it’s written in Python, is open source (GitHub Repo) and can be installed to run on (Ubuntu 16.04) Linux, Windows (10) or Mac (10.15) systems.

Finally, BEHAVIOR uses a set of metrics to determine how well a robot has performed its assigned task. Their first metric is success score defined as the fraction of goal conditions satisfied by the robot performing the task. Such as the number of dishes properly cleaned and placed in the drying rack divided by the total number of dishes for a “washing dishes” task. And their second metric is a set of efficiency metrics, like time to complete a task, sum total of object distance moved during the task, how well objects are arranged at task completion (is the toilet seat down…), etc.

Another feature of iGibson 2.0 is that it offers the ability to record a human (in VR) doing a task in its simulated environment. So if your robotic system is able to learn by example, then iGibson could be used to provide training data for an activity.

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A couple of additions to the BEHAVIOR benchmark/iGibson simulation environment that I would like to see:

  • There ought to be a way to construct a house/apartment where multiple rooms are arranged in a hierarchy, i.e., rooms associated with floors with connections using hallways, doors, stairs, etc. between them. This way one could conceivably have a define a set of homes/apartments (let’s say 5) that a robot would perform its tasks in.
  • They need a task list to drive robot activities. Assume that there’s some amount of time let’s say 8-12 hours that a robot is active and construct a series of tasks that need to be accomplished during that period.
  • Robots should be placed in the rooms/apartments/homes at random with random orientation and then they would have to navigate through rooms/passageways to the rooms to perform the tasks.
  • They need to add pet/human avatars in the rooms throughout a home. These would represent real time obstacles to task completion/navigation as well as add more tasks associated with caring for pets/humans.
  • They need the ability to add non-home rooms that could encompass factory floors, emergency response debris fields, grocery stores, etc. and their own unique set of tasks for each of these so that it could be used as a benchmark for more than just domestic robots.

Aside from the above additions to BEHAVIOR/iGibson 2.0, there’s the question of the organization that manages the benchmark and submissions. There needs to be a website/place to publish benchmark results for a robot AND a mechanism to audit results for accuracy to insure fair play.

Typically this would be associated with an organization responsible for publishing and auditing submissions as well as guide further development of BEHAVIOR/iGibson 2.0. BEHAVIOR 1.0 is not the end but it’s a great start at providing realistic tasks that any domestic robot would need to perform. 

Benchmarks have always aided the development and assessment of new technologies. Having a in home robot benchmark like BEHAVIOR makes getting domestic robots that do what we want them to do a more likely possibility someday.

There’s a new benchmark in town and it signals the dawning of the domestic robot age.

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Swarm learning for distributed & confidential machine learning

Read an article the other week about researchers in Germany working with a form of distributed machine learning they called swarm learning (see: AI with swarm intelligence: a novel technology for cooperative analysis …) which was reporting on a Nature magazine article (see: Swarm Learning for decentralized and confidential clinical machine learning).

The problem of shared machine learning is particularly accute with medical data. Many countries specifically call out patient medical information as data that can’t be shared between organizations (even within country) unless specifically authorized by a patient.

So these organizations and others are turning to use distributed machine learning as a way to 1) protect data across nodes and 2) provide accurate predictions that uses all the data even though portions of that data aren’t visible. There are two forms of distributed machine learning that I’m aware of federated and now swarm learning.

The main advantages of federated and swarm learning is that the data can be kept in the hospital, medical lab or facility without having to be revealed outside that privileged domain BUT the [machine] learning that’s derived from that data can be shared with other organizations and used in aggregate, to increase the prediction/classification model accuracy across all locations.

How distributed machine learning works

Distributed machine learning starts with a common model that all nodes will download and use to share learnings. At some agreed to time (across the learning network), all the nodes use their latest data to re-train the common model and share new training results (essentially weights used in the neural network layers) with all other members of the learning network.

Shared learnings would be encrypted with TLS plus some form of homomorphic encryption that allowed for calculations over the encrypted data.

In both federated and swarm learning, the sharing mechanism was facilitated by a privileged block chain (apparently Etherium for swarm). All learning nodes would use this blockchain to share learnings and download any updates to the common model after sharing.

Federated vs. Swarm learning

The main difference between federated and swarm learning is that with federated learning there is a central authority that updates the model(s) and with swarm learning that processing is replaced by a smart contract executing within the blockchain. Updating model(s) is done by each node updating the blockchain with shared data and then once all updates are in, it triggers a smart contract to execute some Etherium VM code which aggregates all the learnings and constructs a new model (or at least new weights for the model). Thus no node is responsible for updating the model, it’s all embedded into a smart contract within the Etherium block chain. .

Buthow does the swarm (or smart contract) update the common model’s weights. The Nature article states that they used either a straight average or a weighted average (weighted by “weight” of a node [we assume this is a function of the node’s re-training dataset size]) to update all parameters of the common model(s).

Testing Swarm vs. Centralized vs. Individual (node) model learning

In the Nature paper, the researchers compared a central model, where all data is available to retrain the models, with one utilizing swarm learning. To perform the comparison, they had all nodes contribute 20% of their test data to a central repository, which ran the common swarm updated model against this data to compute an accuracy metric for the swarm. The resulting accuracy of the central vs swarm learning comparison look identical.

They also ran the comparison of each individual node (just using the common model and then retraining it over time without sharing this information to the swarm versus using the swarm learning approach. In this comparison the swarm learning approach alway seemed to have as good as if not better accuracy and much narrower dispersion.

In the Nature paper, the researchers used swarm learning to manage the machine learning model predictions for detecting COVID19, Leukemia, Tuberculosis, and other lung diseases. All of these used public data, which included PBMC (peripheral blood mono-nuclear cells) transcription data, whole blood transcription data, and X-ray images.

Swarm learning also provides the ability to onboard new nodes in the network. Which would supply the common model and it’s current weights to the new node and add it to the shared learning smart contract.

The code for the swarm learning can be downloaded from HPE (requires an HPE passport login [it’s free]). The code for the models and data processing used in the paper are available from github. All this seems relatively straight forward, one could use the HPE Swarm Learning Library to facilitate doing this or code it up oneself.

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Towards a better AGI – part 3(ish)

Read an article this past week in Nature about the need for Cooperative AI (Cooperative AI: machines must learn to find common ground) which supplies the best view I’ve seen as to a direction research needs to go to develop a more beneficial and benign AI-AGI.

Not sure why, but this past month or so, I’ve been on an AGI fueled frenzy (at leastihere). I didn’t realize this was going to be a multi-part journey otherwise, I would have lableled them AGI part-1 & -2 ( please see: Existential event risks [part-0], NVIDIA Triton GMI, a step to far [part-1] and The Myth of AGI [part-2] to learn more).

But first please take our new poll:

The Nature article puts into perspective what we all want from future AI (or AGI). That is,

  • AI-AI cooperation: AI systems that cooperate with one another while at the same time understand that not all activities are zero sum competitions (like chess, go, Atari games) but rather most activities, within the human sphere, are cooperative activities where one agent has a set of goals and a different agent has another set of goals, some of which overlap while others are in conflict. Sport games like soccer lacrosse come to mind. But there are other card and (Risk & Diplomacy) board games that use cooperating parties, with diverse goals to achieve common ends.
  • AI-Human cooperation: AI systems that cooperate with humans to achieve common goals. Here too, most humans have their own sets of goals, some of which may be in conflict with the AI systems goals. However, all humans have a shared set of goals, preservation of life comes to mind. It’s in this arena where the challenges are most acute for AI systems. Divining human and their own system underlying goals and motivations is not simple. And of course giving priority to the “right” goals when they compete or are in conflict will be an increasingly difficult task to accomplish, given todays human diversity.
  • Human-Human cooperation: Here it gets pretty interesting, but the paper seems to say that any future AI system should be designed to enhance human-human interaction, not deter or interfere with it. One can see the challenge of disinformation today and how wonderful it would be to have some AI agent that could filter all this and present a proper picture of our world. But, humans have different goals and trying to figure out what they are and which are common and thereby something to be enhanced will be an ongoing challenge.

The problem with today’s AI research is that its all about improving specific activities (image recognition, language understanding, recommendation engines, etc) but all are point solutions and none (if any) are focused on cooperation.

Tit for tat wins the award

To that end, the authors of the paper call for a new direction one that attempts to imbue AI systems with social intelligence and cooperative intelligence to work well in the broader, human dominated world that lies ahead.

In the Nature article they mentioned a 1984 book by Richard Axelrod, The Evolution of Cooperation. Perhaps, the last great research on cooperation that was ever produced.

In this book it talked about a world full of simulated prisoner dilemma actors that interacted, one with another, at random.

The experimenters programmed some agents to always do the proper thing for their current partner, some to always do the wrong thing to their partner, others to do right once than wrong from that point forward, etc. The experimenters tried every sort of cooperation policy they could think of.

Each agent in an interaction would get some number of points for an interaction. For example, if both did the right thing they would each get 3 points, if one did wrong, the sucker would get 1 and the bad actor would get 4, both did wrong each got 1 point, etc.

The agents that had the best score during a run (of 1000s of random pairings/interactions) would multiply for the the next run and the agents that did worse would disappear over time in the population of agents in simulated worlds.

The optimal strategy that emerged from these experiments was

  1. Do the right thing once with every new partner, and
  2. From that point forward tit for tat (if the other party did right the last time, then you do right thing the next time you interact with them, if they did wrong the last time, then you do wrong the next time you interact with them).

It was mind boggling at the time to realize that such a simple strategy could be so effective/sustainable in simulation and perhaps in the real world. It turns out that in a (simulated) world of bad agents, there would be this group of Tit for Tat agents that would build up, defend itself and expand over time to succeed.

That was the state of the art in cooperation research back then (1984). I’ve not seen anything similar to this since.

I haven’t seen anything like this that discusses how to implement algorithms in support of social intelligence.

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The authors of the Nature article believe it’s once again time to start researching cooperation techniques and start researching social intelligence so we can instill proper cooperation and social intelligence technology into future AI (AGI) systems .

Perhaps if we can do this, we may create a better AI (or AGI) so that both it and we can live better in our world, galaxy and universe.

Comments?

cOAlition S requires open access to funded research

I read a Science article this last week (A new mandate highlights costs and benefits of making all scientific articles free) about a group of funding organizations that have come together to mandate open access to all peer-reviewed research they fund called Plan S. The list of organizations in cOAlition S is impressive including national R&D funding agencies from UK, Ireland, Norway, and a number of other countries, charitable R&D funding agencies from WHO, Welcome Trust, Bill&Melinda Gates Foundation and more, and the group is also being funded by the EU. Plan S takes effect this year.

Essentially, all research funded by these organizations must be immediately published in open access forum, open access journals or be freely available in an open access section of a publishers website which means it could be free to be read by anyone worldwide with access to the web. Authors and institutions will retain copyright for the work and the work will be published under an open access license such as the CC BY (Creative Commons Attribution) license.

Why open access is important

At this blog, frequently we find ourselves writing about research which is only available on a paid subscription or on a pay per article basis. However, sometimes, if we search long enough, we find a duplicate of the article published in pre-print form in some preprint server or open access journal.

We have written about open access journals before (see our New Science combats Coronavirus post). Much of what we do on this blog would not be possible without open access journals like PLoS, BioRxiv, and PubMed.

Open access mandates are trending

Open access mandates have been around for a while now. And even the US Gov’t got into the act, mandating all research funded by the NIH be open access by 2008, with Dept of Agriculture and Energy following later (see wikipedia Open access mandates).

In addition, given the pandemic emergency, many research publishers like Nature and Elsevier made any and all information about the Coronavirus free access on their websites.

Impacts and R&D research publishing business model

Although research is funded by public organizations such as charities and government agencies, prior to open access mandates, most research was published in peer-reviewed journal magazines which charged a fee for access. For many research organizations, those fees were a cost of doing research. If you were an independent researcher or in an institution that couldn’t afford these fees, attempting to do cutting edge research was impossible without this access.

Yes in some cases, those journal repositories waved these fees for deserving institutions and organizations but this wasn’t the case for individual researchers. Or If you were truly diligent, you could request a copy of a paper from an author and wait.

Of course, journal publishers have real expenses they needed to cover, as well as make a reasonable profit. But due to business consolidation, there were fewer independent journals around and as a result, they charged bundled license fees for vast swathes of research articles. Such a wide bundle may or may not be of interest to an individual or an institution. That plus with consolidation, profits were becoming a more significant consideration.

So open access mandates, often included funding to cover fees for publishers to supply open access. Such fees varied widely. So open access mandates also began to require fees to be published and to be supplied a description how prices were calculated. By doing so, their hope was to make such costs more transparent

Impacts on authors of research articles

Somewhere there’s an aphorism for researchers that says “publish or perish“, which means you must publish research in order to become a recognized expert in your field. Recognition often the main driver behind better academic employment and more research funding.

However, it’s not just about volume of published papers, the quality of research also matters. And the more highly regarded publishing outlets have an advantage here, in that they are de facto gatekeepers to whats published in their journals. As such, where you publish can often lend credibility to any research.

Another thing changed over the last few decades, judging the quality of research has become more quantative. Nowadays, research quality is also dependent on the number of citations it receives. The more popular a publisher is, the more readers it has which increases the possibility for citations.

Thus, most researchers try to publish their best work in highly regarded journals. And of course, these journals have a high cost to provide open access.

Successful research institutions can afford to pay these prices but those further down the totem pole cannot.

Most mandates come with additional funding to support paying the cost to supply open access. But they also require publishing and justifying these. In the belief that in doing this so it will lend some transparency to these costs.

So the researcher is caught in the middle. Funding organizations want open access to research they fund. And publishers want to be paid a profit for that access.

History of research publication

Nature magazine first started publishing research in 1859, Science magazine first published in 1880, the Royal Society first published research in 1665. So publishing research has been going on for 350 years, and at least as a for profit business model, since the mid-1800s.

Research prior to being published in journals was only available in books. And more than likely, the author of the research had to pay to have a book published and the publisher made money only when those books were sold. And prior to that, scientific research was mostly only available in a course of study, also mostly paid for by the student.

So science has always had a cost to access. What open access mandates are doing is moving this cost to something added to the funding of research.

Now if open access can only solve the reproducibility crisis in science we could have us a real scientific revolution.

Comments?

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The beginning of the end of cancer

Read an article today about new research done to apply big data analytics against multiple cancer strains to identify key control mechanisms that allow cancer to survive in the body and multiply. The article Big data analysis find cancer’s key vulnerabilities discusses their discovery of 24 “master regulators” that are present in a number of different cancers. The original research article is in Cell (behind paywall) but I managed to find a preprint on BiorXiv.

From a (software) coding perspective, it’s almost like a majority of cancers are re-using the same modules to perform functions that are needed by the cancer cells. Not all cancers exhibit all master regulator blocks but all the cancers that they have examined have some of them.

The researchers examined the regulatory/signaling networks of proteins in 112 cancer cell lines. They identified 407 master regulatory proteins and further analysis showed that these protiens were associated with 24 master regulatory architectures (oncotectures). A decent laymen description of a cancer oncotecture can be found in an old (2016) Economist Article Cancer’s master criminals…

Master regulatory proteins

According to the Economist article master regulatory proteins are proteins that regulate processes in a cancer cell that cause other proteins to be made, which cause other proteins to be made, etc. which affect the way a cancer cell lives and propagates inside a body.

Biologists call these sorts of proteins transcription factors which controls the copying of DNA information into mRNA which are then taken to protein factories to create proteins from that blueprint.

The research team believe they24 master regulatory (MR) blocks, if they could be disabled somehow, would disrupt the cancer cell and ultimately eliminate that cancer from a body.

It’s almost like a DevOps script that automates the deployment of software inside the cloud. The fact that they have identified 24 master regulatory (MR blocks) architectures (sequences of proteins that are occur) that apply to a wide set of cancer tumor sub-types implies that these could be needed to regulate the functionality of these cancers. If drugs could be devised to interrupt, change or deactivate these master regulatory blocks it’s quite possible that these cancers would be eliminated.

Identifying MR Blocks using (Bio/Life Sciences) Big Data

It all starts with VIPER analysis (GitHub repo) that measures a specific proteins transcriptional activity level. In this fashion they were able to analyze the 112 tumor subtype proteome (the total complement of all proteins active in a cell). And whittle these down, using cluster analysis to those that were especially relevant for the cancer cell transcription activity.

They then used DIGGIT analysis (GitHub repo of R implementation) to identify the MR proteins and identify cellular mutations that led to them. The types of mutations can be copy number, single point or gene fusion. DIGGIT analysis can help identify which of the mutations are responsible for the protein being analyzed. The DIGGIT process is a multi-step, analytical approach to identifying candidate MR proteins.

Then using tumor checkpoint hypothesis and Bayesian analysis/integration they further ranked the MR candidate proteins. Tumor checkpoints are state transitions in the life of a cancer cell where the cell assesses its environment and then determines what actions to take next.

The tumor checkpoint hypothesis says that during the life cycle of a cancer cell it goes through various state transitions. The researchers have shown that these state transitions are managed by the MR blocks they have identified.

In the final step in their analysis, they used tumor checkpoint hypothesis and modularity with saturation & modularity analysis to identify top MR proteins and the MR blocks active in the 112 tumor subtypes.

At the end of their analysis, they had identified 24 MR blocks which solely or in some combination are present in each of the 112 tumor subtypes. If these MR blocks could be attacked by specific drugs then each of these 112 tumor subtypes could essentially be eliminated from a body or rather cure that cancer.

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Where should IoT data be processed – part 2

I wrote a post a while back on Where IOT data should be processed – part 1. We will get back to that post in a moment, but recently I read an article (How big data forced the hunt for ET intelligence to evolve) that mentioned after 20 years, they were shutting down SETI@home.

SETI@home was a crowdsourced computational network that took snippets of radio spectrum, sent them to 1000s of home computers to be analyzed during idle computer time, once processed the analysis was sent back to SETI@home. It was one of the first to use a crowdsourced approach to perform data processing. The data was collected at a radio telescope, sent to SETI@home and distributed from there.

6 Factors for IOT data processing

In my post I talked about 6 factors that should help determine where data is processed. Those 6 factors included

  • Data size which is a measure of the amount (GB, TB or PBs) of data that is being generated at an IOT node
  • Data pipe availability, which is all about the networking bandwidth that’s available at the IOT node. If we are talking some sort of low-bandwidth networking access then it probably makes sense to process the data more locally and send only results of processing up the stack.
  • Processing criticality which indicates how important is the processing of the data. If the processing could save a life then maybe it should be done as close as possible to where the data is generated. If the data processing is less critical it could perhaps be done at other nodes in an IOT network
  • Processing time and infrastructure cost which is all about what sort of computational resources are required to perform the processing and how much would it cost. If processing of the data is to undergo multiple passes or requires multi-core CPUs or GPUs, moving data off the IoT node and onto a more comprehensive server to process it, could make sense.
  • Compliance, governance and archive requirements, which discussed the potential need for all data to be available for regulatory audits and as such may need to be available at a central location anyway so why not perform processing there.
  • Data information funnel, which talked about the fact that an IoT network should be configured in layers and that each layer in the stack should probably be responsible for some portion of the data processing needed by the overall system, if nothing more than compressing the information before it is sent elsewhere.

Now that I review the list, the last, Data information funnel, factor really should be a function of the other factors rather than a separate factor.

In that blog post I promised to follow it up with some examples of the logic applied to real world problems. SETI is the first one I’ve seen in the literature

SETI’s IoT processing problem

Closeup front view of one antenna of the Allan Telescope Array, a radio telescope for combined radio astronomy and SETI (Search for Extraterrestrial Intelligence) research being built by the University of California at Berkeley, outside San Francisco. The first phase, consisting of 42 6 meter dish antennas like the one shown here, was completed in 2007. Eventually it will have 350 antennas. This type of antenna is called an offset Gregorian design. The incoming radio waves are reflected by the large parabolic dish onto a secondary concave parabolic reflector in front of the dish, and then into a feed horn. A metal shroud can be seen along the bottom of the secondary reflector which shields the antenna from ground noise. It covers the frequency range from 0.5 to 11.2 GHz.

The SETI researchers found that “The telescopes are now capable of producing so much data that it’s not possible to get that volume of data out to volunteers,” And “The discovery space is in these massive, massive data streams. And it’s just not efficient to distribute many terabits per second out to volunteers all over the world. It’s more efficient for that data processing to happen at the actual observatory.”

So they moved the data processing for the SETI IoT network from being distributed out to home computers throughout the world to being done at the (telescope) source where the data was originally generated.

This decision seems to rely on a couple of the factors above. Namely the pipe availability and data size factors. They had to move processing because no pipes existed to send Tb of data to 1000s of home computers. And finally, the processing time and infrastructure cost has come down so much, that it was just easier to do the processing onsite.

It doesn’t seem like processing criticality or compliance-governance-archive had any bearing on the decision.

So there’s the first example that seems to fit well into our data processing framework.

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We ought to be able to come up with a formula that uses all these factors and comes up to with a yes or no as to whether to process the data on the node or not.

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New PCM could supply 36PB of memory to CPUs

Read an article this past week on how quantum geometry can enable a new form of PCM (phase change memory) that is based on stacks of metallic layers (SciTech Daily article: Berry curvature memory: quantum geometry enables information storage in metallic layers), That article referred to a Nature article (Berry curvature memory through electrically driven stacking transitions) behind a paywall but I found a pre-print of it, Berry curvature memory through electrically driven stacking transitions.

Figure 1| Signatures of two different electrically-driven phase transitions in WTe2. a, Side view (b–c plane) of unit cell showing possible stacking orders in WTe2 (monoclinic 1T’, polar orthorhombic Td,↑ or Td,↓) and schematics of their Berry curvature distributions in momentum space. The spontaneous polarization and the Berry curvature dipole are labelled as P and D, respectively. The yellow spheres refer to W atoms while the black spheres represent Te atoms. b, Schematic of dual-gate h-BN capped WTe2 evice. c, Electrical conductance G with rectangular-shape hysteresis (labeled as Type I) induced by external doping at 80 K. Pure doping was applied following Vt/dt = Vb/db under a scan sequence indicated by black arrows. d, Electrical conductance G with butterfly-shape switching (labeled as Type II) driven by electric field at 80 K. Pure E field was applied following -Vt/dt = Vb/db under a scan sequence indicated by black arrows. Positive E⊥ is defined along +c axis. Based on the distinct hysteresis observations in c and d, two different phase transitions can be induced by different gating configurations.

The number one challenge in IT today,is that data just keeps growing. 2+ Exabytes today and much more tomorrow.

All that information takes storage, bandwidth and ultimately some form of computation to take advantage of it. While computation, bandwidth, and storage density all keep going up, at some point the energy required to read, write, transmit and compute over all these Exabytes of data will become a significant burden to the world.

PCM and other forms of NVM such as Intel’s Optane PMEM, have brought a step change in how much data can be stored close to server CPUs today. And as, Optane PMEM doesn’t require refresh, it has also reduced the energy required to store and sustain that data over DRAM. I have no doubt that density, energy consumption and performance will continue to improve for these devices over the coming years, if not decades.

In the mean time, researchers are actively pursuing different classes of material that could replace or improve on PCM with even less power, better performance and higher densities. Berry Curvature Memory is the first I’ve seen that has several significant advantages over PCM today.

Berry Curvature Memory (BCM)

I spent some time trying to gain an understanding of Berry Curvatures.. As much as I can gather it’s a quantum-mechanical geometric effect that quantifies the topological characteristics of the entanglement of electrons in a crystal. Suffice it to say, it’s something that can be measured as a elecro-magnetic field that provides phase transitions (on-off) in a metallic crystal at the topological level. 

In the case of BCM, they used three to five atomically thin, mono-layers of  WTe2 (Tungsten Ditelluride), a Type II  Weyl semi-metal that exhibits super conductivity, high magneto-resistance, and the ability to alter interlayer sliding through the use of terahertz (Thz) radiation. 

It appears that by using BCM in a memory, 

Fig. 4| Layer-parity selective Berry curvature memory behavior in Td,↑ to Td,↓ stacking transition. a,
The nonlinear Hall effect measurement schematics. An applied current flow along the a axis results in the generation of nonlinear Hall voltage along the b axis, proportional to the Berry curvature dipole strength at the Fermi level. b, Quadratic amplitude of nonlinear transverse voltage at 2ω as a function of longitudinal current at ω. c, d, Electric field dependent longitudinal conductance (upper figure) and nonlinear Hall signal (lower figure) in trilayer WTe2 and four-layer WTe2 respectively. Though similar butterfly-shape hysteresis in longitudinal conductance are observed, the sign of the nonlinear Hall signal was observed to be reversed in the trilayer while maintaining unchanged in the four-layer crystal. Because the nonlinear Hall signal (V⊥,2ω / (V//,ω)2 ) is proportional to Berry curvature dipole strength, it indicates the flipping of Berry curvature dipole only occurs in trilayer. e, Schematics of layer-parity selective symmetry operations effectively transforming Td,↑ to Td,↓. The interlayer sliding transition between these two ferroelectric stackings is equivalent to an inversion operation in odd layer while a mirror operation respect to the ab plane in even layer. f, g, Calculated Berry curvature Ωc distribution in 2D Brillouin zone at the Fermi level for Td,↑ and Td,↓ in trilayer and four-layer WTe2. The symmetry operation analysis and first principle calculations confirm Berry curvature and its dipole sign reversal in trilayer while invariant in four-layer, leading to the observed layer-parity selective nonlinear Hall memory behavior.
  • To alter a memory cell takes “a few meV/unit cell, two orders of magnitude less than conventional bond rearrangement in phase change materials” (PCM). Which in laymen’s terms says it takes 100X less energy to change a bit than PCM.
  • To alter a memory cell it uses terahertz radiation (Thz) this uses pulses of light or other electromagnetic radiation whose wavelength is on the order of picoseconds or less to change a memory cell. This is 1000X faster than other PCM that exist today.
  • To construct a BCM memory cell takes between 13 and 16  atoms of W and Te2 constructed of 3 to 5 layers of atomically thin, WTe2 semi-metal.

While it’s hard to see in the figure above, the way this memory works is that the inner layer slides left to right with respect to the picture and it’s this realignment of atoms between the three or five layers that give rise to the changes in the Berry Curvature phase space or provide on-off switching.

To get from the lab to product is a long road but the fact that it has density, energy and speed advantages measured in multiple orders of magnitude certainly bode well for it’s potential to disrupt current PCM technologies.

Potential problems with BCM

Nonetheless, even though it exhibits superior performance characteritics with respect to PCM, there are a number of possible issues that could limit it’s use.

One concern (on my part) is that the inner-layer sliding may induce some sort of fatigue. Although, I’ve heard that mechanical fatigue at the atomic level is not nearly as much of a concern as one sees in (> atomic scale and) larger structures. I must assume this would induce some stress and as such, limit the (Write cycles) endurance of BCM.

Another possible concern is how to shrink size of the Thz radiation required to only write a small area of the material. Yes one memory cell can be measured bi the width of 3 atoms, but the next question is how far away do I need to place the next memory cell. The laser used in BCM focused down to ~1.5 μm. At this size it’s 1,000X bigger than the BCM memory cell width (~1.5 nm).

Yet another potential problem is that current BCM must be embedded in a continuous flow of liquid nitrogen (@80K). Unclear how much of a requirement this temperature is for BCM to function. But there are no computers nowadays that require this level of cooling.

Figure 3| Td,↑ to Td,↓ stacking transitions with preserved crystal orientation in Type II hysteresis. a,
in-situ SHG intensity evolution in Type II phase transition, driven by a pure E field sweep on a four-layer and a five-layer Td-WTe2 devices (indicated by the arrows). Both show butterfly-shape SHG intensity hysteresis responses as a signature of ferroelectric switching between upward and downward polarization phases. The intensity minima at turning points in four-layer and five-layer crystals show significant difference in magnitude, consistent with the layer dependent SHG contrast in 1T’ stacking. This suggests changes in stacking structures take place during the Type II phase transition, which may involve 1T’ stacking as the intermediate state. b, Raman spectra of both interlayer and intralayer vibrations of fully poled upward and downward polarization phases in the 5L sample, showing nearly identical characteristic phonons of polar Td crystals. c, SHG intensity of fully poled upward and downward polarization phases as a function of analyzer polarization angle, with fixed incident polarization along p direction (or b axis). Both the polarization patterns and lobe orientations of these two phases are almost the same and can be well fitted based on the second order susceptibility matrix of Pm space group (Supplementary Information Section I). These observations reveal the transition between Td,↑ and Td,↓ stacking orders is the origin of
Type II phase transition, through which the crystal orientations are preserved.

Finally, from my perspective, can such a memory can be stacked vertically, with a higher number of layers. Yes there are three to five layers of the WTe2 used in BCM but can you put another three to five layers on top of that, and then another. Although the researchers used three, four and five layer configurations, it appears that although it changed the amplitude of the Berry Curvature effect, it didn’t seem to add more states to the transition.. If we were to more layers of WTe2 would we be able to discern say 16 different states (like QLC NAND today).

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So there’s a ways to go to productize BCM. But, aside from eliminating the low-temperature requirements, everything else looks pretty doable, at least to me.

I think it would open up a whole new dimension of applications, if we had say 60TB of memory to compute with, don’t you think?

Comments?

[Updated the title from 60TB to PB to 36PB as I understood how much memory PMEM can provide today…, the Eds.]

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