In an effort said to be aimed at alleviating the environmental burden posed by electronic devices, a team of researchers from the University of Wisconsin-Madison has worked with the US Department of Agriculture's Forest Products Laboratory (FPL) to develop a semiconductor chip made almost entirely of wood.
The research team, led by UW-Madison Professor Zhenqiang Ma, has explored the feasibility of replacing the chip's substrate with cellulose nanofibril (CNF), a flexible, biodegradable material made from wood.
"The majority of material in a chip is support," said Prof Ma. "We only use less than a couple of microns for everything else. The chips are so safe you can put them in the forest and fungus will degrade them; they become as safe as fertilizer."
FPL project leader Zhiyong Cai noted: "If you take a big tree and cut it down to the individual fibre, the most common product is paper. The dimension of the fibre is in the micron stage. But what if we could break it down further to the nano scale? At that scale, you can make very strong and transparent CNF paper."
Cai's group addressed two key barriers to using wood derived materials in electronics – surface smoothness and thermal expansion. "You don't want it to expand or shrink too much. Wood is a natural hydroscopic material and could attract moisture from the air and expand," Cai says. "With an epoxy coating on the surface of the CNF, we solved both the surface smoothness and the moisture barrier."
The group's work also demonstrates a more environmentally friendly process that showed performance similar to existing chips. Most of today's wireless devices use gallium arsenide based chips, but gallium arsenide can be environmentally toxic, particularly in the massive quantities of discarded electronics.
Yei Hwan Jung, a graduate student in electrical and computer engineering, said the new process can greatly reduce use of the material. "I've made 1500 GaAs transistors in a 5 x 6mm chip. Typically, for a microwave chip that size, there are only eight to 40 transistors – the rest of the area is just wasted.
"We take our design and put it on CNF using a deterministic assembly technique and make a completely functional circuit with performance comparable to that of existing chips."
Prof Ma concluded: "Mass producing chips is so cheap and it may take time for the industry to adapt to our design. But flexible electronics are the future and we think we're going to be well ahead of the curve."
Author
Graham Pitcher
Source: www.newelectronics.co.uk