Femtofarad

Femtofarad (symbol fF) is a unit of capacitance in the International System of Units (SI). It equals 10^-15 farads.

Because it denotes an extremely small capacitance, the femtofarad is used mainly in contexts involving nanoscale devices, high-frequency circuits, and certain quantum systems. In nanoscale integrated circuits and MEMS, device parasitics and gate capacitances can fall into the fF range; typical values range from a few femtofarads to a few tens of picofarads in some technologies. One fF equals 1000 attofarads (aF) and 0.001 picofarads (pF).

Measurement and design considerations: At such small scales, parasitic elements, stray capacitances from surroundings, and temperature or humidity can affect measurements. Specialized instruments such as high-precision LCR meters, impedance analyzers, or cryogenic resonators are used, and measurements are often performed in controlled environments or inferred from resonant circuits.

Examples: In superconducting qubits or nanoelectronic devices, capacitances of similar magnitude are used in coupling or shunting elements. Engineers model these values in circuit simulations to predict resonant frequencies and energy storage.

See also: Farad, Picofarad, Attofarad, SI prefixes.