Metal conductors sintered onto skin at room temperature

Author: EIS Release Date: Oct 26, 2020


Metal conductors can be formed directly onto human skin, according to an international science team which found a way to sinter silver nano-particles into silver conductors at room temperature.

ACS-Electronics-on-skin

The process was used to measure skin temperature and humidity, and to form electrodes for ECGs and conductors to LEDs for blood oxygen measurements (see photo).

The process was also used with paper and cloth to build flexible PCBs, that were used to build a circuit to get data from the subject to a receiver using an SL900A semi-passive tag chip from from AMS.

Sintering is a process of heating powdered material to a temperature below its melting point to the point that it turns into a porous solid as the particles form local bonds where they touch.

Silver particles of various sizes were tried, and a key part of this research was combining these with a novel sintering aid – a paste of the polymer PVA with either TiO2 or CaCO3 additives – all the particles involved were nano-scale powders.

CaCO3 allowed sintering at 25°C – the metal conductors forming at room temperature. With TiO2, tracks formed at 70°C.

The proof-of-concept health monitoring system consisted of sensor circuits printed directly on the back of a hand and a paper-based flexible PCB attached to the inside of a shirt sleeve.

An ink jet printer was used to deposit materials on the paper, and a stamp was used to put the conductors onto skin. Temperature, humidity, blood oxygen, heart rate, blood pressure and electrophysiological signals were measured.

“The signals obtained by these sensors were comparable to or better than those measured by conventional commercial devices,” according to the American Chemical Society, which published the research in Applied Materials & Interfaces as the paper ‘Wearable circuits sintered at room temperature directly on the skin surface for health monitoring‘.

The team came from Pennsylvania State University and Harbin Institute of Technology.

The photograph was provided by ACS. Its printed sensors are:

  • meandering line – temperature
  • inter-digitated lines – humidity
  • curvy crosses – electrodes for measuring EMG or ECG