All-printed low-power metal oxide gas sensors on polymeric substrates

This paper presents a novel approach for the fabrication of miniaturized and fully printed metal-oxide (MOX) gas sensors on a polyimide (PI) substrate by using digital manufacturing of the functional layers, namely aerosol jet and inkjet printing technologies. We are reporting a stacking approach for all-printed MOX sensors for the first time. High resolution (similar to 20 mu m) printing of metallic patterns is enabled by aerosol jet of gold nanoparticles in solution, which leads to printed resistive thermal transducers with a reduced size of 500 x 500 mu m(2). The wide area printing feature of the aerosol jet is also applied for printing a thin (similar to 2 mu m) inter-dielectric PI layer in between the heater and gold electrodes. The gas sensing layer, i.e. Pd-doped tin oxide (SnO2) nanoparticles, is deposited through drop on demand inkjet printing. Proper operation of the printed sensors is evaluated in both dry and humid conditions under reducing and oxidizing gases i.e. CO and NO2, respectively. All the tests are performed at 250 degrees C, produced by the integrated micro-hotplate at a low power consumption of similar to 78 mW. The chemo-resistive responses of the sensors towards both the gases are found to be in the acceptable range as compared to conventional metal-oxide gas sensor responses. These results are very promising for future integration of MOX gas sensors notably in smart printed electronics, disposable systems and wearables.