Monolithic Capacitors

Monolithic Capacitors:

Monolithic capacitors are not frequently used in integrated circuits since they are limited in the range of values obtained and their performance. There are, however, two types available, the junction capacitor is a reverse biased PN junction formed by the collector-base or emitter-base diffusion of the transistor. The capacitance is proportional to the area of the junction and inversely proportional to the depletion thickness.

C   α A, where a is the area of the junction and

C  α T , where t is the thickness of the depletion layer.

The capacitance value thus obtainable can be around 1.2nF/mm² .

The thin film or metal oxide silicon capacitor uses a thin layer of silicon dioxide as the dielectric. One plate is the connecting metal and the other is a heavily doped layer of silicon, which is formed during the emitter diffusion. This capacitor has a lower leakage current and is non-directional, since emitter plate can be biased positively. The capacitance value of this method can be varied between 0.3 and 0.8nF/mm² .

Inductors:

No satisfactory integrated inductors exist. If high Q inductors with inductance of values larger than 5μH are required, they are usually supplied by a wound inductor which is connected externally to the chip. Therefore, the use of inductors is normally avoided when integrated circuits are used.