An image sensor with uniform, well-controlled air gaps is provided. A structure that is at least partially filled with organic material may be formed on the image sensor. A hybrid organic/inorganic film layer may be formed over the organic material. The image sensor may then be exposed to energy, which causes the organic material to sublimate through the hybrid film layer, which itself may become a gas permeable layer when exposed to energy. After sublimation, the regions where the organic material was previously filled become air gaps with a low index of refraction. Air gaps formed in this way can be configured over photodiodes as light guides or focusing structures, as concave/convex microlenses, in between photodiodes as isolation structures, in between color filter elements to reduce crosstalk, and/or over microlenses to enhancing focusing power.