APPLICATION

The bipolar transistor along with the MOSFET is the most popular transistors in the commercial electronic market. While MOSFETs are more common in high-density circuits, bipolar transistors enable high-speed circuits because of their high transconductance. A good example is the BiCMOS circuit where MOSFETs provide the density and bipolar transistors provide the current drive for large capacitive loads. Another advantage of the bipolar transistor is that the threshold for turn-on is less sensitive to process variation. In bipolar memory applications, soft-error from a-particle is more tolerable. Bipolar transistors are also used in power applications where high voltage (400 V) and high current density are required. The limitations of a bipolar transistor compared to a MOSFET are intrinsic speed constraints due to charge storage, low input impedance, high power dissipation, more complex processing, and large area. For example, in bipolar memory circuits, the chip size is typically 16 times that of MOS technology for the same memory count.

A bipolar transistor can be used as a temperature sensor. It is an improvement over a p-n diode temperature sensor because in a diode, other current components such as recombination current are less predictable and have different temperature dependence. In a bipolar transistor, the collector current is a pure diffusion current from the base-emitter junction while the recombination current only goes to the base.