Piezo-tunneling strain sensors integrated on plastic by combining vacuum thin film coatings and 3D printing technologies

There is a growing demand for the integration of sensor functions on flexible substrates for wearable electronics, robotics or medical monitoring. For this, it is necessary to develop strain gauges both sensitive and integrable at low cost with a low thermal budget. The gauge factor of metal/insulator/metal piezo-tunneling strain sensors is first measured as a function of applied current and polarity, for different electrode materials (Al, Pt or Pd) and insulator (Al 2 O 3 ) thicknesses. A maximum gauge factor of 90 is obtained with an Al/Al 2 O 3 (10 nm)/Al junction and top electrode injection. Results are discussed based on the Fowler–Nordheim model and it is shown that the electron effective mass in Al 2 O 3 most likely plays a major role in the observed mechano-sensitivity. Next, the feasibility of a low-pressure sensor demonstrator based on a 3D-printing process on a polymer substrate is shown with a sensitivity of 0.19 bar −1 in the 0–450 mbar range.