Thin Film Circuits and Products

Thin film circuits and thin film products are metallized or plated onto ceramic or glass substrates. They are fabricated via thin film deposition techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), ion implantation, plasma etching or cleaning, rapid thermal processing (RTP), and vacuum annealing. In specialty electronics manufacturing, thin film deposition is used to create layers of insulators, semiconductors, and conductors to form integrated circuits (IC). For example, a thin film transistor (TFT) is a field effect transistor (FET) made by depositing the metallic contacts, semiconductor active layer, and dielectric layer as thin films. With thin film circuits and thin film products, the metallization layer is made of a conducting material that is selectively deposited or etched to form connections between logic gates. The dielectric layers act as insulating stand-offs between the conducting layers.

Thin film circuits and thin film products are made from layers about 1 µm thick. Specifications include purity, color, nominal density, hardness, surface finish, thickness, coefficient of thermal expansion, thermal conductivity, dielectric constant, and dissipation factor. Removal of heat or heat sinking determines the overall power ratings of thin film circuits. The materials used to mount components to a substrate are crucial for proper power dissipation. For example, eutectic solder has up to 10 times better thermal conductivity than conductive epoxy, and up to 100 times better thermal conductivity than non-conductive epoxy. Some thin film circuits and thin film products require interconnects that are very small and, for portable devices such as cell phones, relatively flexible. Chip-on-flex (COF) is an example of this interconnect technology. Thin film circuits and thin film products that use polyvinylidine difluoride (PVDF) have piezoelectric properties that are useful in sensor circuits. For example, a PVDF thin film sensor can be used to measure stress waves.

The American Society for Testing and Materials (ASTM) publishes standards for thin film circuits and thin film products. ASTM F1711-96 describes the use of four-point probes for measuring the sheet resistance of thin film conductors in flat panel displays (FPDs). ASTM F1709-97 outlines specifications for high-purity titanium sputtering targets for electronic thin film applications. Thin film circuits and thin film products are also covered by British Standards Institute (BSI) standard BS CECC 63200.

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