Thin-film diode

Thin film diode (TFD) generally refers to any diode produced using thin-film technology.

Within the flat panel display industry TFD more often refers to thin film bi-directional diodes, also known as metal-insulator-metal (MIM) TFDs or nonlinear resistors. Bi-directional MIM TFDs have very low current flow at low applied voltages, but then begin to conduct electricity above a threshold voltage, of either positive or negative polarity. Owing to this behavior these two terminal devices may be used as a switch. The exact threshold voltage at which a MIM TFD switches on and begins to conduct electricity depends on its physical dimensions, such as thickness of the insulating layer, as well as the physical properties of the materials from which it is made, such as the work function of each metal layer.

Commercial applications

Flat panel display manufactures have found use for MIM TFDs as switches in active matrix technology such as active matrix liquid crystal displays (AMLCD). Historically in AMLCDs the switching device of choice for pixels has been the thin-film transistor, however MIM TFD based displays have had some commercial success as they are simpler to make; only requiring two to three photo-lithography steps rather than the typical 5 or more needed to produce thin film transistors.