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Printed diode can slurp power from phone signals

Boffins get smartphones talking to clothes

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A group of Swedish researchers has created a printed diode that can use the radio output of a smartphone for power – and along the way has answered a long-standing question about how printed diodes work.

In this paper at PNAS, the researchers demonstrate a device created by printing a niobium silicide layer over a silicon paste. Its operating frequency, at 1.6 GHz, is far higher than previous similar efforts – and is fast enough to let the diode work with the kinds of frequencies used by mobile phone transmitters.

As IEEE Spectrum explains, this would let the diode be used to power objects like smart labels.

IEEE Spectrum also notes that other technologies seen as contenders for powering smart labels have cost or fabrication problems that make them impractical. For example, many organic semiconductors are printable, but either work at too low a frequency to operate with smartphone signals as the power source, or need to be deposited under a high vacuum. Nanoparticle semiconducting inks need high temperatures, which make them problematic to print onto clothing labels.

The 1.6 GHz Schottky diode took antimony-doped silicon crushed into particles between 100 nm and 1 micron printed onto an aluminium electrode. The niobium silicide particles were added on top, followed by a carbon electrode and a silver paste. The IEEE article notes that a “brief, mild” heat treatment is needed, but it can be carried out in the open air.

Printed GHz diode

Say hello to your T-shirt: Linköping University's 1.6 GHz printed diode

Linköping University explains while the printed diode has been known of for a long time, its operation has been something of a mystery until the latest work.

The predecessor to the current device was put together at Acreo Swedish ICT in 2001, who followed a process similar to that used in the PNAS study but using just silicon particles. That original device only worked to around 1 MHz, and its operation wasn't well-understood.

The university says PhD student Negar Sani and her collaborators now believe the printed diode uses tunnelling effects: “nano-thin films (1–2 nm) are formed around the micrometer-sized grains of silicon, where the current between anodes (aluminium) and cathodes (silver and carbon) pass through, but only in one direction”, the article states.

Future work will include trying to replace niobium with cheaper materials, and getting a device to operate in the 2.4 GHz band so it can use WiFi and Bluetooth signals.

The work was carried out at Linköping University with collaboration from Acreo Swedish ICT. ®

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