FIELD OF THE DISCLOSURE

The present disclosure relates to transistors and specifically to bipolar transistors with improved performance and ruggedness.

BACKGROUND

Transistors such as heterojunction bipolar transistors (HBTs) are widely used in many different applications. For example, one or more HBTs may be provided in a power amplifier (PA) for radio frequency (RF) communications circuitry. As RF communications standards continue to evolve, the performance requirements of RF communications circuitry, and in particular those placed on RF PAs, are becoming increasingly stringent. Accordingly, designers are continually striving to improve RF PA performance parameters such as RF gain and linearity.

To improve the performance of HBTs for RF PAs, designers have previously altered a doping profile of a collector in the device. Generally, these improvements have provided an increase in one performance parameter such as linearity while degrading others such as RF gain and ruggedness. As discussed above, modern RF communications standards demand high performance across a range of different performance parameters. Accordingly, there is a need for an improved bipolar transistor device.

SUMMARY

Disclosed is a transistor having a base, a substrate, and a collector between the substrate and the base. The collector has a first region of a first thickness under the base and is made up of a first dopant type having a substantially constant doping concentration across the first thickness. A second region with a second thickness under the first region is made up of a second dopant type that is different from the first dopant type and has a substantially constant doping concentration across the second thickness. A third region with a third thickness under the second region is made up of the second dopant type with a graded doping concentration that is a function of increasing distance from the second region through the third thickness. An emitter is located over the base opposite the collector.

By providing the collector with the doping profile made up of the doping segments as described, the ruggedness of the transistor is significantly improved while maintaining the radio frequency gain thereof.

Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.

