Their common modes of operation are charge mode, which generates a high-impedance charge output; and voltage mode, which uses an amplifier to convert the high-impedance charge into a low-impedance output voltage. Thin film devices consist of an extremely thin layer of material, usually titanium nitride or polysilicon, deposited on a substrate. Pressure instruments that use microelectromechanical systems (MEMS), variable capacitance, and vibrating elements are commonly available.