Memristor Materials: Exploring Unusual Sources

From honey in your tea with blood In your veins, the materials around you harbor hidden talent. Some of these substances, if designed in certain ways, can act as memristors—electrical components that can “remember” past states.

Memristors often used in chips that simultaneously perform calculations and store data. These are devices that store data in the form of specific resistance levels. Today they are a thin layer titanium dioxide or similar dielectric material sandwiched between two metal electrodes. Applying enough voltage to the device causes tiny regions in the dielectric layer that lack oxygen atoms to form filaments that connect electrodes or otherwise move in a way that makes the layer more conductive. Changing the voltage cancels the process. So this process essentially gives memristor memory of past electrical activity.

Last month, while exploring the electrical properties of mushrooms, a team from The Ohio State University discovered through personal experience that some organic memristors have advantages over those made from conventional materials. Not only can shiitakes act as a memristorfor example, but it may be useful in aerospace or medical practice as the fungus exhibits high levels of radiation resistance. According to the lead researcher, the project “really turned into something cool.” John LaRocco says with a grin.

Researchers have learned that other unexpected materials may give memristors an advantage. They may be more flexible than typical memristors, or even biodegradable. Here's how they made memristors from strange materials and what potential benefits these strange devices could bring:

Mushrooms

LaRocco and his colleagues were looking for a brain proxy that could be used in electrical stimulation research when they stumbled upon something interesting: Shiitake mushrooms are capable of learning in a similar way to memristors.

The team decided to evaluate how well shiitakes remember electrical states by first growing nine specimens and creating optimal growing conditions, including feeding them a mixture of farro, wheat and hay.

Once fully ripened, the mushrooms were dried and rehydrated to a level where they were moderately conductive. In this state, the mushroom structure includes pathways that mimic oxygen vacancies in commercial memristors. Scientists connected them to circuits and tested voltage, frequency and memory. Result? Mushroom memristors.

It may smell “weird,” but shiitake works surprisingly well compared to conventional memristors, LaRocco says. In about 90 percent of cases, the mushroom maintains ideal memristor behavior for signals up to 5.85 kilohertz. According to him, while traditional materials can operate at frequencies several orders of magnitude faster, for biological materials these numbers are noticeable.

What mushrooms lack in productivity they can compensate for with other properties. First, many mushrooms, including shiitake mushrooms, are highly resistant to radiation and other environmental hazards. “They grow in logs in Fukushima and a lot of very rough parts of the world, and that’s one of the attractions,” LaRocco says.

Shiitake is also an environmentally friendly product that has already been commercialized. “They are already being grown in large quantities,” explains LaRocco. “We could just use existing supply chains” if the industry wanted to commercialize mushroom memristors. In his opinion, the use cases for this product will be niche and will focus on the radiation resistance that shiitake boasts. Mushroom GPUs unlikely, LaRocco says, but he sees potential for aerospace and medical applications.

Honey

In 2022, Washington State University engineers will be interested in green electronics intended study if honey could serve as a good memristor. “Modern electronics generate 50 million tons electronic waste annually, with only about 20 percent being recycled,” says Feng Zhaowho led the work and is now at Missouri University of Science and Technology. “Honey offers a biodegradable alternative.”

The researchers first mixed commercial honey with water and stored it in a vacuum to remove any air bubbles. They then spread the mixture onto a piece of copper, fired the entire stack at 90°C for nine hours to stabilize it, and finally capped it on top with round copper electrodes, completing the honey-based memristor sandwich.

The resulting 2.5-micrometer-thick layer of honey acted as the oxide dielectric in conventional memristors: the site where conductive paths formed and dissolved, changing resistance depending on voltage. In this setup, when voltage is applied, copper threads pass through honey.

The honey memristor was able to switch from low to high resistance in 500 nanoseconds and back to low in 100 nanoseconds, comparable to speeds in some memristive materials of non-food origin.

One advantage of honey is that it is “cheap and widely available, making it an attractive candidate for scalable production,” Zhao says. It is also “fully biodegradable and dissolves in water, creating no toxic waste.” However, in a 2022 paper, the researchers note that for a honey-based device to be truly biodegradable, the copper components would need to be replaced with soluble metals. They offer options such as magnesium And tungstenbut they also write that the performance of memristors made of these metals is still “being studied.”

Blood

Considering it a potential delivery method healthcaregroup in India wondered if blood could become a good memristor in 2011, just three years after first memristor was built.

The experiments were quite simple. The researchers filled a tube with fresh O+ human blood and inserted two conductive wire probes into it. The wires were connected to a power source to form a complete circuit, and voltages of one, two, and three volts were repeatedly applied. Next, to test the memristor properties of blood as it exists in the human body, the researchers set up a “flow mode” that applied a voltage to the blood as it flowed out of the tube, at a rate of up to one drop per second.

The experiments were preliminary and measured only the current passing through the blood, but the resistance could be adjusted by applying a voltage. It is important to note that the resistance changed less than 10 percent in the 30-minute period after voltage was applied. IN International Journal of Medical Engineering and InformaticsThe scientists wrote that these observations make their invention “look like a human blood memristor.”

They suggested that this knowledge could be useful in treating diseases. Sick people may have ionic imbalances in certain parts of the body. Instead of prescribing drugs, why not use a circuit component made from human tissue to solve this problem? In recent years, blood-based memristors have been tested by other scientists as a treatment for various diseases: high blood sugar To myopia.