Unlike the monolithic IC's, which are formed within a semiconductor material (substrate), the thin-film circuit is formed on the surface of an insulating substrate. In the thin-film circuit, components such as resistors and capacitors are formed from extremely thin layers of metals and oxides, which are deposited onto a glass or ceramic substrate. Interconnecting wires are also deposited on the substrate as thin strips of metal. Components such as diodes and transistors are formed as separate semiconductor devices and then permanently attached to the substrate at the appropriate locations.
The substrate on which the thin-film circuit is formed is usually less than 2.5cm2. Depositing tantalum or nichrome as thin films or strips on the surface of the substrate forms the resistors. These films are usually less than 0.00254cm thick. The thickness, length and width of each strip that is formed on the substrate determine the value of each resistor. The interconnecting conductors are extremely thin metal strips, which have been deposited on the substrate. Low resistance metals, such as gold. platinum, or aluminium, are generally used as conductors. The substrate is made from an insulating material that will provide a rigid support for the components. Glass or ceramic materials are often used as substrates. Figure shows a portion of a thin-film circuit.