Building a path toward computer memory written with light

Natia Frank wants to reduce the energy consumption of future computers. The University of Victoria chemist designs and studies novel organic electronic materials, and she recently developed a material that allows computers to write data with light instead of electric current. The material, made of a cobalt dioxolene coupled to a spirooxazine, makes possible a next-generation computer memory known as light-induced random access memory. LI-RAM would be faster than current forms of RAM, require less power, and work for both short-term data processing and long-term data storage. Frank talked with Louisa Dalton about how her LI-RAM material came to be and where she gets her ideas.

Why write computer data with light?

The philosophy behind what we do is trying to decrease energy demands of all of these technologies that people use. That’s important to me on a personal level. Everything is going to be run by little computers, and it’s important that they don’t increase our global electrical energy demands significantly.

The semiconductor industry is up against what’s called the power wall. The industry has been trying to deal with that increase in power consumption by developing resistive memory, which uses a lot less energy to run and doesn’t dump as much heat. There are a lot of different types of resistive technologies that are being looked at, and they all differ in their effectiveness. What we’re trying to do is come up with a resistive magnetic memory, which is good for long-term storage but is written with light.

The reason we chose light is because it is one of the fastest ways to write and transfer energy and information. Less heat, less power demand, and much faster read-write speed are the major advantages of this type of technology.

How does your material make writing binary data with light possible?

We developed a strategy in which we have an electronically bistable metal complex that can exist between a low-spin and a high-spin state. The complex switches between these two states through an intramolecular charge-transfer process. We attached a photochromic ligand to this metal complex, which changes its structure and ligand field when irradiated by light. The change in structure and ligand field causes a change in the redox potential around the metal center, and this in turn changes the driving force for charge transfer in the metal complex.

The coupling of photochromic ligands to these electronically bistable metal complexes gives rise to the photomagnetic effects that we observe at room temperature.

How long have you been working on this material?

This was one of the projects I proposed when I applied for faculty positions way back in 2000. When we started the project, there was essentially no work done on taking a photochromic molecule and complexing it to a transition-metal ion.

I was at Caltech at the time as a postdoc, and a lot of the faculty there and my colleagues read my proposals, and they said, “Oh, this is never going to work because you’re going to excite the system and all the energy is going to get dumped into the metal, and it’s just going to relax down to the ground state.” I wasn’t convinced that all of the excited state energy would get dumped into the metal. And I thought, you know, it’s always worth trying if you don’t know enough to absolutely predict the right answer.

For the ligand, we ended up settling on spirooxazines. Not only were they still photoresponsive once complexed to transition metals, they also showed an increase in photoresponsivity, particularly with cobalt and nickel. I was delighted that it actually worked.

The material that we’re now working on for the light-induced RAM is a cobalt dioxolene attached to a spirooxazine ligand.

What are you doing with the material now?

Now that we can generate these photomagnetic effects at room temperature in the solid state, we can incorporate them into devices. We can start thinking about making other types of magnetic memory devices.

We’re collaborating with semiconductor companies, decreasing the size of the devices, and optimizing the parameters so that the material can be incorporated into semiconductor devices using technologies that are already in place. What’s unique about our material is that it operates on a single molecule level, and because of that, we can, in principle, make a device that is 2 by 2 nm in size and holds one bit.

Where do you get your ideas?

I take advantage of the fact that I’ve moved through a lot of different fields during the course of my career. I’m part of the organic electronics community, the magnetism community, the electron transfer community. I’m sort of on the edge of a lot of communities, and because of that, there’s a lot of cross-fertilization.

In our group, we like to design single-component systems in which there’s a very strong electronic coupling between two different types of processes. We’re perturbing one process and it’s leading to a change in a secondary process. That’s the fundamental philosophy behind what we do on all levels.

Louisa Dalton is a freelance writer. A version of this story appeared in ACS Central Science:cenm.ag/natiafrank. This interview was edited for length and clarity.