New Materials Lower Printed Electronics’ Appetite For Power

To make low cost, bendable electronics and displays for convenient consumer devices, many engineers want to find ways to print electronic circuits like publishers print magazines. Unfortunately, current printed electronics need a lot of power to run properly. A new combination of electronic materials may make the devices less power hungry (Nano Lett., DOI: 10.1021/nl3038773).

Like an iPad, any future bendable or wearable electronic device will run on battery power, says C. Daniel Frisbie, a materials scientist at the University of Minnesota, Twin Cities. But batteries don’t meet the power needs of today’s printed electronics: A typical small battery maxes out at about 3 volts, while high performance printed circuits typically require about 20 volts.

The circuits’ high power needs come from limitations in circuit printing methods; in particular, they produce layers of electronic materials that are too thick. As these layers get thicker, it requires more power to move electrons through them. For example, in transistors, thick layers of a certain insulator mean the circuit needs a lot of power to switch the transistor on and off.

To print transistors that switch at lower voltages even with thick insulating layers, Frisbie’s group tried a new set of materials. For the insulator itself, they used an ionic liquid gel that can store a lot of electrical charge, which lowers the switching voltage. For the transistor’s channel, the part that switches between on and off states, the researchers used semiconducting nanotubes made by Mark C. Hersam, of Northwestern University. Electrons move through these nanotubes very rapidly at low voltages, which further enables fast switching times.

As a demonstration of the new materials’ abilities, the team used aerosol jet printing to make a type of circuit called a ring oscillator. They first sonicated liquid solutions of the electronic materials to form droplets. Then they directed a flow of gas to pick up and deliver those droplets to the circuit’s surface.

To test the printed circuits, the researchers watched how fast elements in the ring oscillator changed states—basically, flipping from a 1 to a 0. This amount of time is called a delay; the lower it is, the better for the circuit’s performance.

When powered with 3 volts of electricity, the printed circuits operated with delays as low as 1 µs, about 10 times faster than previous printed electronics. Frisbie says that the short delays mean the electronic materials and printing method could be used to make circuits with sufficient speeds to drive video displays or chemical sensors.

Zhenan Bao, a materials scientist at Stanford University, says the speed of these circuits is impressive. “The advantage of this approach is that the device can operate at very low voltage, which is important for portable electronics,” she says.