History of semiconductor devices:

 

Fig:  Power semiconductor device variety

 

• Power electronics and converters utilizing them made a head start when the first device the Silicon Controlled Rectifier was proposed by Bell Labs and commercially produced by General Electric in the earlier fifties. The Mercury Arc Rectifiers were well in use by that time and the robust and compact SCR first started replacing it in the rectifiers and cycloconverters.

• The necessity arose of extending the application of the SCR beyond the line-commutated mode of action, which called for external measures to circumvent its turn-off incapability via its control terminals. Various turn-off schemes were proposed and their classification was suggested but it became increasingly obvious that a device with turn-off capability was desirable, which would permit it a wider application. The turn-off networks and aids were impractical at higher powers.

• The Bipolar transistor, which had by the sixties been developed to handle a few tens of amperes and block a few hundred volts, arrived as the first competitor to the SCR.

• The Power MOSFET burst into the scene commercially near the end seventies. Improvements were being tried out on the SCR regarding its turn-off capability mostly by reducing the turn-on gain. The lookout for a more efficient, cheap, fast and robust turn-off-able device proceed in different directions with MOS drives for both the basic thyristor and the Bipolar.

• The Insulated Gate Bipolar Transistor (IGBT) – basically a MOSFET driven Bipolar from its terminal characteristics has been a successful proposition with devices being made available at about 4 KV and 4 KA.

• The IGBT has also pushed up the GTO to applications above 2-5 MVA. Presently there are few hybrid devices and Intelligent Power Modules (IPM) are marketed by some manufacturers. The IPMs have already gathered wide acceptance.

• The 4500 V, 1200 A IEGT (injection-enhanced gate transistor) of Toshiba or the 6000 V, 3500 A IGCT (Integrated Gate Commutated Thyristors) of ABB which are promising at the higher power ranges.

• However these new devices must prove themselves before they are accepted by the industry at large. Silicon carbide is a wide band gap semiconductor with an energy band gap wider than about 2 eV that possesses extremely high thermal, chemical, and mechanical stability.

• The range of power devices thus developed over the last few decades can be represented as a tree, Fig , on the basis of their controllability and other dominant features.

Previous Next