The device builds on a swimmer described at ISSCC 2012, which was propelled by Lorentz forces.
“Instead of Lorentz forces, this chip utilises the gas pressure resulting from electrolytic bubbles as the propulsive force,” said the team in its ISSCC paper. “By appointing voltages to the on-chip electrolysis electrodes, one can decide the electrolysis location and thereby control the bubbles emissions as well as the direction of motion.”
The 21.2mm2 die, made by TSMC on a 0.35µm process, travels at 0.3mm/s.
Four electrodes, one on each edge, make the die steerable. Propulsion and steering requires 82µW, which comes across an 10MHz inductive link from a loop above the liquid to a pair of on-chip coils.
Alongside the coils and electrodes are: power management circuits, a wireless receiver, and a microcontroller – together consuming 125.4µW.
To get plenty of bubbles, the electrode have an inter-digitated pattern to maximise edge length.
Bubble generation is also related to applied voltage, and engineers have provided two levals of drive to give two speeds of travel.
Power from the receiver coils is bridge rectified and regulated by an LDO to 2V for on-chip circuits. This is dropped to 1.3V for the second electrode drive level. Analogue switches control which electrode gets what voltage.
Control signals are amplitude modulated onto the power signal at 1MHz. After demodulation, the MCU decodes the bit stream – which is a simple 8 bit serial stream with four bits enabling each of the four electrodes, one setting the drive voltage, and three error-check bits.
A clock regenerator clocks the MCU, which runs two different bit extraction algorithms to increase the chance of accurate command decoding.
To improve its streamlining, the substrate was thinned.
In-body medical scanning applications for similar future technology were proposed.
The team research team comes from National Taiwan University, National Taipei University of Technology, and Chang Gung University.
ISSCC paper 18.7 ‘A remotely controlled locomotive IC driven by electrolytic bubbles and wireless powering’.
Held every year in San Francisco, the IEEE International Solid-State circuits Conference is the world showcase for circuit design. In 30 multi-paper sessions, selected developments in digital, analogue, RF and data converter circuits are described, alongside sensors ranging from thermometers to video imagers. This year’s theme is ‘Silicon systems bridging the cloud’ but, frankly, whatever the theme, the best in circuits on Earth are always at ISSCC.