DNA helps electronics to leave flatland

(Press-News.org) Researchers at Columbia Engineering have for the first time used DNA to help create 3D electronically operational devices with nanometer-size features.

"Going from 2D to 3D can dramatically increase the density and computing power of electronics," said corresponding author Oleg Gang, professor of chemical engineering and of applied physics and materials science at Columbia Engineering and leader of the Center for Functional Nanomaterials' Soft and Bio Nanomaterials Group at Brookhaven National Laboratory.

The new manufacturing technique could also contribute to the ongoing effort to develop AI systems that are directly inspired by natural intelligence.

"3D electronic architectures that imitate the natural 3D structure of the brain may prove enormously more effective at running brain-mimicking artificial intelligence systems than existing 2D architectures," Gang said. The researchers detailed their findings March 28 in the journal Science Advances.

From etching to folding Conventional electronics rely on flat circuitry. To help microchips grow more powerful, researchers worldwide are experimenting with approaches to building them in three dimensions. 

However, current electronics manufacturing techniques are top-down in nature — a piece of material is gradually eroded, for example, by an electron beam, until the desired structure is achieved, like sculpting a block of stone. These methods have encountered problems fabricating 3D devices when it comes to creating complex structures and doing so in a cost-effective manner. For instance, they face challenges in assembling multiple layers of circuitry that stack up properly. "Over the course of hundreds of steps during production, errors accumulate that are prohibitive from the point of view of performance and cost," Gang said.

A conceptually different way to build a 3D system is from the bottom up, where many components self-assemble into complex structures. Now Columbia Engineering researchers have developed a new biologically inspired bottom-up way for 3D electronics to build themselves. The key behind the new technique is the way in which strands of DNA can fold themselves into shapes — so-called origami. These building blocks, called frames, are then used to assemble large-scale 3D structures, called frameworks, with nanoscale precision.

DNA is made of strings of four different kinds of molecules, known by the letters A, T, C and G. These stick to each other in highly specific ways — A to T, and C to G. By designing multiple molecules with the right sequences, researchers can get long DNA strands to fold themselves into 2D or 3D shapes. Snippets of DNA stapled onto these strands then hold the folded designs in place.

Building the prototype  In the new study, the study’s first author Aaron Michelson, a staff scientist at Brookhaven National Laboratory's Center for Functional Nanomaterials, who was previously a PhD student at Gang’s group, along with Gang and their colleagues, deposited arrays of gold squares on a surface, onto which they could attach short pieces of DNA. These molecules served as anchors to which they could fasten eight-sided diamond-like octahedral DNA frames that self-assemble into 3D frameworks at these specific surface locations.

"These gold arrays with anchored DNA strands promote the growth of 3D DNA scaffolds on designated areas in desired patterns and orientations, which allows us to establish and integrate this DNA onto an electronic wafer," Gang said.

The researchers, in collaboration with Professor Vald Pribiag’s group at the University of Minnesota, next coated these DNA scaffolds with silicon oxide, laced them with the semiconductor tin oxide, and connected electrodes to each structure. The result — light sensors that respond electrically when illuminated.

"We've demonstrated that not only can we create 3D structures from DNA, but integrate them into microchips as part of the workflow of how electronic devices are fabricated," Gang said. "We can place thousands of these structures at specific sites on silicon wafers in a scalable way. This demonstrates that we can drastically change how we fabricate complex 3D electronic devices."

"For a long time, we have worked on what phenomena might help build a self-assembling electronic device," Gang said. "It's exciting to now actually demonstrate these futuristic ideas, to actually make an operational device using these bottom-up fabrication processes."

In the future, Gang and his colleagues would like to use their new method to create more complex electronic devices using more than one material. "The next dream is creating 3D circuitry," he said.

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