Power semiconductor device
Power semiconductors are found in systems delivering as little as a few tens of milliwatts for a headphone amplifier, up to around a gigawatt in a high voltage direct current transmission line.
The first electronic device used in power circuits was the electrolytic rectifier - an early version was described by a French experimenter, A. Nodon, in 1904.
These were briefly popular with early radio experimenters as they could be improvised from aluminum sheets, and household chemicals.
Power handling capability evolved rapidly, and by 1954 germanium alloy junction transistors with 100 watt dissipation were available.
[3] Silicon power transistors were not made until 1957, but when available had better frequency response than germanium devices, and could operate up to 150 C junction temperature.
[13] From 1974, Yamaha, JVC, Pioneer Corporation, Sony and Toshiba began manufacturing audio amplifiers with power MOSFETs.
[15] This device allows operation at higher frequencies than a bipolar transistor, but is limited to low voltage applications.
With the vertical structure, the current rating of the device is proportional to its area, and the voltage blocking capability is achieved in the height of the die.
These trade-offs are the same for all power devices; for instance, a Schottky diode has excellent switching speed and on-state performance, but a high level of leakage current in the off-state.
In fact, any power semiconductor relies on a PIN diode structure in order to sustain voltage; this can be seen in figure 2.
The MOSFET is particularly suited to this configuration, because its positive thermal coefficient of resistance tends to result in a balance of current between the individual devices.
Basically, an IGBT is a bipolar transistor driven by a power MOSFET; it has the advantages of being a minority carrier device (good performance in the on-state, even for high voltage devices), with the high input impedance of a MOSFET (it can be driven on or off with a very low amount of power).
Compared to the MOSFET, the operating frequency of the IGBT is relatively low (usually not higher than 50 kHz), mainly because of a problem during turn-off known as current-tail: The slow decay of the conduction current during turn-off results from a slow recombination of a large number of carriers that flood the thick 'drift' region of the IGBT during conduction.
Consequently power is continually dissipated and its design is dominated by the need to remove excess heat from the semiconductor device.
The role of packaging is to: Many of the reliability issues of a power device are either related to excessive temperature or fatigue due to thermal cycling.
Achieving a major improvement over the conventional MOSFET structure by employing the super junction charge-balance principle: essentially, it allows the thick drift region of a power MOSFET to be heavily doped, thereby reducing the electrical resistance to electron flow without compromising the breakdown voltage.
On the other hand, during the on-state, the higher doping of the drift region allows for the easy flow of carriers, thereby reducing on-resistance.
Commercial devices, based on this super junction principle, have been developed by companies like Infineon (CoolMOS products) and International Rectifier (IR).
