Hybrid thin-film circuit design
Hybrid circuits — Design

Thin films are deposited under vacuum by evaporation or, more frequently, by sputtering.

Deposited layers are generally less than a few micrometers thick. If greater conductor thicknesses are required, galvanic or chemical growth is generally used, after vacuum deposition of an adhesion layer. This growth can take place before or after photolithography; in the latter case, it is known as selective growth. Galvanic growth uses copper and gold, while chemical growth uses nickel, copper and gold.

Although sputtering allows almost any material to be deposited, there are limitations to these choices:

• the deposited film must adhere to the substrate or to the layer already deposited;

• the deposited film must not react with the substrate or with adjacent layers; in particular, strong galvanic couples must be avoided;

• films must be...