“Balsa wood transistors may revolutionize the electronics industry with eco-friendly approach”

This is the next installment in our series highlighting innovative technologies and initiatives that can combat climate change, lessen its impact, or aid communities in adapting to a rapidly changing world.

A group of European scientists is taking a unique approach to wood. Rather than working as carpenters or furniture builders, they are exploring how wood can be utilized to create more environmentally friendly electronic devices that result in fewer greenhouse gas emissions. Their latest invention is a transistor made of balsa wood.

Transistors are crucial components in computers and other electronic devices. They function like miniature switches to regulate the flow of electricity, allowing engineers to process and store data. Modern laptops can contain billions of transistors, each only slightly wider than a DNA strand.

The new transistor developed by Isak Engquist and his team at Linköping University in Sweden is larger than conventional transistors and can only handle low voltage. Additionally, it operates electrochemically by controlling current with ions, or charged particles. While this transistor may not be suitable for traditional computers due to its size, it demonstrates the feasibility of the concept and could potentially be useful in electronics that require low voltage.

Explainer: Understanding electricity

This breakthrough has significant implications, according to physicist Daniel Simon from Linköping University. “Even as a proof of concept, this is a significant development,” he says. Simon envisions a future where living plants could be used to manufacture electronic devices. He suggests imagining “peeling away some bark from a living tree and imprinting electronic circuits onto the wood.”

Engquist echoes this sentiment and emphasizes the vast potential of wood and its components. He envisions wood-based sensors that monitor crop health, measure pollution levels, or assess wildfire risks in forests.

You see a tree. When Van Chinh Tran looks at an image like this, he sees future technology. One day, the trunk or branches could become the basis of a new type of green electronics. Devices could be made from — or even grown inside of — trees. Misha Kaminsky/E+/Getty Images Plus

Why use wood?

“Green electronics” is a trending topic, notes Guido Panzarasa, a materials scientist at ETH Zürich in Switzerland. He explains that it typically refers to devices that rely less on nonrenewable resources, such as minerals obtained through mining. This prompted Panzarasa’s interest in wood-based devices.

Traditional computer transistors are made of silicon, whose production generates significant amounts of pollutants. The process emits carbon dioxide, a greenhouse gas, along with nitrogen oxides that are harmful to the respiratory system and can worsen asthma symptoms. Furthermore, the transformation of silicon into electronic devices involves the use of fluorinated gases, which have a much stronger warming effect on the climate than CO2.

A wood transistor eliminates the need for silicon altogether.

Van Chinh “Robert” Tran, a graduate student who led the design of the wood transistor, acknowledges the initial surprise of using wood for this purpose. The dried wood is an insulator and does not conduct electricity naturally. The Linköping team planned to modify the wood to enhance its electrical conductivity.

There are two primary methods for achieving this, according to Panzarasa. The first involves treating the wood’s surface with specific materials to initiate a chemical reaction that improves electrical conductivity. Panzarasa is currently working on devices that utilize this technique.

The second approach relies on the wood’s structure to support conductive materials, which is the basis for the new Linköping transistor.

The process of discovery involved trial and error, according to Tran. The researchers began by testing balsa, pine, and ash woods, ultimately finding that balsa performed the best. Balsa wood conducted electricity three times more efficiently than the other two types.

Balsa wood is particularly interesting due to its low density, relatively large channels, and relatively thin cell walls, as Panzarasa points out.

The team also had to find the optimal method for removing lignin, the material in cell walls that gives plants their rigidity. In doing so, they created more space in the channels within the wood. Afterwards, they filled these channels with PEDOT:PSS, a conducting material commonly used in solar cells.

a photo of silver transistors against a blue background
These are transistors. They have been used to control the movement of electricity in electronic circuitry. They’re made of silicon, a metal-like substance. Although it’s the second most common element in Earth’s crust (and the main ingredient in sand), silicon’s modification for use in electronics can release a greenhouse gas and produce other pollutants. Jultud/Moment/Getty Images Plus

Performance and further developments

The team assembled the transistor using three small pieces of treated wood—one 1 millimeter thick and 30 millimeters long, the other two 5 millimeters wide, with the third piece measuring 2 millimeters. The narrower piece was inserted between the wider pieces at a right angle, forming a lowercase “t.”

Tests confirmed that this device functioned as an electrical switch, with the top and bottom pieces acting as gates. The middle piece contained channels filled with an electrolyte gel that facilitated the flow of charged ions and generated a current. By applying a voltage between the top and bottom gates, the conductivity of the middle channel could be altered, effectively switching the ion flow “off.”

By controlling the voltage of the gates, the researchers were able to regulate the current flow through the middle piece.

Optimizing the process

Designing an efficient device involved a series of trial and error experiments, says Tran. This included identifying the ideal wood for the transistor. Balsa wood performed the best, conducting electricity three times more effectively than the other types tested.

The researchers also had to develop an optimal method for removing lignin, which required striking a balance between preventing insufficient conductivity and avoiding wood softening and collapsing.

In the future, Engquist and his team aim to further improve the transistor’s performance. They seek to enhance factors such as its voltage handling capabilities by achieving a more even coating of PEDOT:PSS on the interior wood surfaces. Additionally, they plan to investigate methods for removing more lignin.

Panzarasa suggests that researchers could explore other porous materials besides wood to determine if balsa wood transistors still offer superior performance.

Engquist also emphasizes the importance of finding suitable applications for the technology.

Tran proposes an environmental sensor or a tree-based battery as potential applications. The researchers have big dreams for green electricity that include the possibility of growing the transistor directly inside a tree.

This article is part of a series highlighting technology and innovation, made possible by the generous support of the Lemelson Foundation.

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