The drift-field transistor, also called the drift transistor or graded base transistor, is a type of high-speed
bipolar junction transistor having a
doping-engineered
electric field
An electric field (sometimes E-field) is the physical field that surrounds electrically charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field fo ...
in the base to reduce the
charge carrier
In physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used ...
base transit time.
Invented by
Herbert Kroemer at the Central Bureau of Telecommunications Technology of the German Postal Service, in 1953, it continues to influence the design of modern high-speed bipolar junction transistors.
Early drift transistors were made by diffusing the base dopant in a way that caused a higher doping concentration near the emitter reducing towards the collector.
[Bipolar Transistor. Chenning]
/ref>
This graded base happens automatically with the double diffused planar transistor (so they aren't usually called drift transistors).Fundamentals of Semiconductor Devices.
/ref>
Similar high speed transistors
Another way to speed the base transit time of this type of transistor is to vary the band gap across the base, e.g. in the SiGe pitaxial baseBJT the base of Si1−ηGeη can be grown with η approx 0.2 by the collector and reducing to 0 near the emitter (keeping the dopant concentration constant).[
]
Applications
Germanium diffused junction transistors were used by IBM in their Saturated Drift Transistor Resistor Logic (SDTRL), used in the IBM 1620. (Announced Oct 1959)
References
{{reflist
External links
''Herb’s Bipolar Transistors'' IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 48, NO. 11, NOVEMBER 2001
PDF needs IEEE subscription
Influence of Mobility and Lifetime Variations on Drift-Field Effects in Silicon-Junction Devices
PDF needs IEEE subscription
Transistor types
1953 introductions