We present the design, fabrication, and characterization of a GLAD-fabricated photonic crystal sensor with a
bandgap located in the visible optical spectrum. The photonic crystal is fabricated from TiO<sub>2</sub> using electron-beam
evaporation in a GLAD capable vacuum deposition system. Changes in humidity over a wide range (from 3% to
90% relative humidity) are detected by a colour change in the film due to movement of the photonic bandgap.
The colour changes are quantified by measuring the transmittance of white light. Coupling the sensitivity of the
film with a simple visual feedback system eliminates the need for complicated measurement techniques. This is
desirable to minimize the cost and power consumption of the sensor device, making it amenable to large-scale
production and deployment.
We have used the glancing angle deposition technique to fabricate highly porous nanostructured optical thin films that
act as humidity sensors. The responsiveness and repeatability of these sensors has been investigated for samples stored
under different environmental conditions. It has been found that samples stored in air have a more stable performance
than those stored in a dry nitrogen environment. It has also been found that annealing impacts the responsiveness of the
optical thin film sensors.