Aluminum-based self-powered hyper-fast miniaturized sensor for breath humidity detection

An aluminum-based, self-powered, miniaturized sensor for breath humidity detection is presented. The sensor is designed as an interdigitated capacitor made out of sputtered aluminum 1 % silicon (Al 1 %Si) thin film, 700 nm thickness, with digits 1.5 mm long, 0.01 mm wide and 0.01 mm clearance between them. The voltage on the open end of the sensor is generated when the surface is covered with a thin layer of water vapor, for instance if a person blows on it. The voltage generated is up to 1.5 V. The voltage generation is based on an electrochemical process of interaction between aluminum, water and oxygen from air, similar to the operation of an aluminum-air battery. The rise time of the signal during water vapor (or breath) detection is as small as 10 ms which makes it one of the fastest humidity sensors reported to date. The relaxation time is in the range of 50 ms. To make detection possible, the sensor surface needs to be activated by native oxide removal with the help of electric current and de-mineralized water droplet. Usability of the sensor was demonstrated in the detection of human breathing, where the sensor managed to follow the cycles of inhaling and exhaling.