A substrate structure is presented that can include a porous polyimide material and electrodes formed in the porous polyimide material. In some examples, a method of forming a substrate can include depositing a barrier layer on a substrate; depositing a resist over the barrier layer; patterning and etching the resist; forming electrodes; removing the resist; depositing a porous polyimide aerogel; depositing a dielectric layer over the aerogel material; polishing a top side of the interposer to expose the electrodes; and removing the substrate from the bottom side of the interposer.