The plates of an isolated parallel plate capacitor with a capacitance C carry a charge Q. The plate separation is d. Initially, the space between the plates contains only air. Then, an isolated metal sheet of thickness 0.5d is inserted between, but not touching, the plates.
Metal-insulator-metal (MIM) capacitors are another class of compact capacitors with distinct advantages. They are like a parallel plate capacitor, in which metal plates (electrodes) are separated by an insulating material (dielectric). These capacitors are widely used because they exhibit high capacitance per unit area.
The standard metal wiring lines (and optionally vias — the plated through holes on a wired board) are used to create the plates of the capacitor, and the lateral (intralayer) capacitive coupling effect between plates produces the required capacitance.
To increase capacitance density, multiple metal layers can be connected in parallel using vias, forming a vertical metal wall or mesh. Typically, the lowest metal layers (such as M1–M5) with the smallest metal line width and spacing are employed in MOM capacitors to maximize capacitance density. Advantages of Metal-Oxide-Metal Capacitors
At the most basic level, all capacitors store energy via electrical conductors (plates) separated by a dielectric (insulating) material. When one plate receives a positive charge and the other plate receives a negative charge, the capacitor is holding a charge.
Metal-oxide-metal (MOM) capacitors are small and versatile devices used in chips. They are interdigitated (interlocking like the fingers of two clasped hands), multi-finger capacitors formed by metal layers.