Capacitors are electronic devices that use metal plates and non-conductive dielectrics to block direct current (DC) electrical signals while allowing alternating current (AC) signals to pass though them. Thin film capacitors typically use a thin plastic film to serve as a dielectric; however, they can sometimes also use plastic films coated with metals as their plates. Capacitors of this type are often used in high-performance applications.
In a capacitor, at least two metal plates are separated by an insulating layer called a dielectric. This insulating layer prevents a direct current from passing directly between the two plates, which are sometimes called electrodes. Dielectrics, however, can be penetrated by electromagnetic fields, which are created when a difference in charge exists between the plates. When an electromagnetic field is present, such as in AC circuits, the field will induce a voltage between the two plates, which will then pass through the capacitor and onto the rest of the circuit.
Many different materials are used as dielectrics in capacitors. They can range from paper to ceramic to oils. In thin film capacitors, the dielectric is a thin plastic film, most commonly polyester; however, many different plastics, such as polystyrene and polypropylene, see use as dielectrics.
While virtually all thin film capacitors use plastic dielectrics, not all use films as the plates. Many that do typically use plastic films, such as polyester, that have had thin, metallic layers applied to them. Other types of thin film capacitor will actually coat the two opposing faces of the plastic dielectric itself with a metallic compound.
Constructed entirely of very thin layers of different materials deposited on one another, thin film capacitors can be made very small. As a result of their size, and the method of their construction, they are ideal for incorporation into integrated circuit devices to perform a broad range of functions. These functions include the creating of high-speed timing devices, analog-to-digital conversion circuits, and filters used to remove noise from very weak electrical signals.
Thin film capacitors have been frequently incorporated into advanced electronic devices to perform or improve many different functions. They serve in dynamic random access memory chips (DRAM) in computers, improve the detection capabilities of traditional, long-range radio frequency communication devices, and are the prime components in tuning microwave communications equipment. In short, they have become a key building block of all modern microelectronic devices.