Cheap and environmental friendly silicon chips printed on paper
Interview Ryoichi Ishihara
Scientists at TU Delft have succeeded in printing a silicon chip on paper rather than on the usual plastic. It is cheaper, environment friendly and brings new applications a step closer. Such applications would include displays on a carton of milk showing the best-before date.
With the touch of a button, you can transform your wallpaper into a giant screen to watch the latest films or sport games. An 'unsightly' television or projector will no longer be needed thanks to new technology currently under development at TU Delft. The technology will be integrated into the wallpaper itself, enabling you to display moving images on a large surface, such as a wall or ceiling. When the game or film finishes, it reverts to a conventional wall.
This is just one of the remarkable advances this new technology makes possible. Usually, computer chips are printed onto plastic and end up in your computer, television or smartphone, for example. “We print chips on recycled paper,” says TU Delft's Ryoichi Ishihara. “It makes flexible electronics possible, which you can bend.”
It is also better for the environment, the Japanese researcher emphasises. “Increasing numbers of devices will made smart
in the years to come and they will contain electronics and plastic,” says Ishihara. “This so-called e-waste creates a problem that will only increase in the future. We are now printing chips on paper in an environmentally-friendly way, causing the waste problem to disappear.” It also costs much less. Ishihara calculates that paper is ten times cheaper than plastic.
To develop the new technology, it was extremely important for Ishihara and his colleagues to be able to print electronics at room temperature. Otherwise the paper would burn. They recently succeeded in printing the electronics on paper at room temperature (see box). “We are thinking of new ways to market this technology. We are currently talking to companies and considering setting up a consortium,” says Ishihara.
The potential is great, emphasises the researcher. Today, the best-before date is still printed on every milk carton in advance. “But if the milk has been stored cool throughout, it will last longer. The idea is to integrate a temperature sensor into the electronics. It measures how warm or cold the liquid is. From field to refrigerator, so to speak. When the temperature changes, so does the resistance. If you accidentally leave the carton on the table for two hours, the best-before date will be updated immediately.”
It is possible to share this information with consumers in two ways. One of these is Near Field Communication (NFC) on the carton, which you read using your smartphone. NFC is also used for public transport cards and contactless payments. “You can actually use a flexible battery, and these are already being made. They supply power to a display on the carton. They are slightly more expensive and mainly suitable for more expensive products, such as premium cuts of meat.”
Ishihara also envisages possibilities for agriculture. He takes a piece of cardboard from the cupboard in his room. It clearly has electronics printed on it. “We are currently developing these individual transistors. You insert them into the soil next to vegetables that have just been planted. The cardboard contains an antenna, an RFID tag and transistors. They measure the amount of water in the soil, the temperature, and the nitrogen and CO2 levels. The farmer then knows exactly what the plant needs, based on highly localised readings. The RFID tags can even be read remotely using a scanning device.”
Ishihara stresses that it is completely biodegradable. “We print the electronics with silicon, a solid made from sand and rocks that is not harmful for the environment. You can use environmental friendly metal for the conduction, along with biodegradable cardboard, of course. We are talking with companies about marketing this. I am also working with institutes within and outside TU Delft for further discussions on the rate at which these products degrade to determine exactly what the impact on the environment will be.”
Printing on cornflakes
Ishihara believes that the best applications for this new technology would be in health monitoring. You can actually print the electronics on edible paper that you put onto cornflakes, for example. “If you eat it every morning, we will know your sugar levels, body temperature and heart rate on that day. The data are sent wirelessly from your body to the smartphone. The paper and silicon are simply broken down in your body. Vegetables and potatoes already contain cellulose and silicon, so they are obviously edible. I lost my mother at an early age because of poor health. She might have lived longer if we had known about certain indicators of declining health at an earlier stage. This new technology can really make a difference and gives you insight when things are not going as they should. It opens up a new world for healthier living.”
How chips are made
Currently, the chips are still put onto plastic at high temperatures. In order to print electronics onto paper, the temperature needs to be significantly lower, which is what makes this so innovative. How did the scientists achieve it? They put silicon and hydrogen molecules along with liquid silicon onto paper in an oxygen-free atmosphere. Think of it as a type of ink coating. Then they removed the hydrogen using a laser device, leaving silicon in certain places and silicon dioxide in others. “How the silicon is formed determines what you can do with it. This is how you construct and make transistors and thus create a chip,” explains Ishihara.
Text: Robbert Visscher | Photo's: Mark Prins | December 2017