Electronics & Software – Tips & Guide


Why is the MOSFET more preferred for integrated chips than the BJT?

Why is the MOSFET more preferred for integrated chips than the BJT?

mosfet is better than bjt because

switching faster for a given frequency

consumes less power, because it does so only in the on state while bjt does so in both cases.

controlled voltage device

bjts require a continuous bias current and therefore burn energy even when they are at rest, the mosfets use much less power under the same circumstances. This is why mosfets are preferred for low power circuits. However, as the switching speed increases, the mosfets may require more current than the bjts because of the capacity of the door element and the current required to load and unload it in order to perform the switching.

mosfet is a voltage controlled device, bjt is current controlled. MOSFET needs voltage on its door while BJT needs power at its base to turn on. As a result, the losses in bjt are relatively higher than those of the mosfet. The increased losses due to heat also require large heat sinks that increase the overall size of the chips needed. because a large surface offers better heat dissipation.

the two do not work well in an ic done with bjt. they will be bigger and more inefficient compared to a mosfet.

While performance and energy consumption play a role, the economy is now the main driver. the integration density of the cmos process is ahead of that of bipolar processes.

design and manufacture the same complexity in bipolar as in cmos would cost much more.

a note on the power advantage of the mos transistor. While it is true that a static cmos circuit had a virtually zero power dissipation, this is no longer the case. at the deep submicron level, the so-called sub-threshold leakage of millions of individual transistors represents a considerable sum, so that different circuit and system techniques are needed to process it. moreover, the current of non-existent DC current is a thing of the past. Today, designers also have to deal with gate oxide tunneling, which can become important in some cases.