Power semiconductor device

A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics. Such a device is also called a power device or, when used in an integrated circuit, a power IC.
A power semiconductor device is usually used in "commutation mode", and therefore has a design optimized for such usage; it should usually not be used in linear operation. Linear power circuits are widespread as voltage regulators, audio amplifiers, and radio frequency amplifiers.
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.

History

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. They had low withstand voltages and limited efficiency.
The first solid-state power semiconductor devices were copper oxide rectifiers, used in early battery chargers and power supplies for radio equipment, announced in 1927 by L.O. Grundahl and P. H. Geiger.
The first germanium power semiconductor device appeared in 1952 with the introduction of the power diode by R.N. Hall. It had a reverse voltage blocking capability of 200 V and a current rating of 35 A.
Germanium bipolar transistors with substantial power handling capabilities were introduced around 1952; with essentially the same construction as signal devices, but better heat sinking. Power handling capability evolved rapidly, and by 1954 germanium alloy junction transistors with 100 watt dissipation were available. These were all relatively low-frequency devices, used up to around 100 kHz, and up to 85 degrees Celsius junction temperature. 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.
The thyristor appeared in 1957. It is able to withstand very high reverse breakdown voltage and is also capable of carrying high current. However, one disadvantage of the thyristor in switching circuits is that once it becomes 'latched-on' in the conducting state; it cannot be turned off by external control, as the thyristor turn-off is passive, i.e., the power must be disconnected from the device. Thyristors which could be turned off, called gate turn-off thyristors, were introduced in 1960. These overcome some limitations of the ordinary thyristor, because they can be turned on or off with an applied signal.

Power MOSFET

The MOSFET was invented at Bell Labs between 1955 and 1960 Generations of MOSFET transistors enabled power designers to achieve performance and density levels not possible with bipolar transistors. Due to improvements in MOSFET technology, the power MOSFET became available in the 1970s.
In 1969, Hitachi introduced the first vertical power MOSFET, which would later be known as the VMOS. From 1974, Yamaha, JVC, Pioneer Corporation, Sony and Toshiba began manufacturing audio amplifiers with power MOSFETs. International Rectifier introduced a 25 A, 400 V power MOSFET in 1978. This device allows operation at higher frequencies than a bipolar transistor, but is limited to low-voltage applications.
The insulated-gate bipolar transistor was developed in the 1980s, and became widely available in the 1990s. This component has the power handling capability of the bipolar transistor and the advantages of the isolated gate drive of the power MOSFET.

Common devices

Some common power devices are the power MOSFET, power diode, thyristor, and IGBT. The power diode and power MOSFET operate on similar principles to their low-power counterparts, but are able to carry a larger amount of current and are typically able to withstand a larger reverse-bias voltage in the off-state.
Structural changes are often made in a power device in order to accommodate the higher current density, higher power dissipation, and/or higher reverse breakdown voltage. The vast majority of the discrete power devices are built using a vertical structure, whereas small-signal devices employ a lateral structure. 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. With this structure, one of the connections of the device is located on the bottom of the semiconductor die.
The power MOSFET is the most common power device in the world, due to its low gate drive power, fast switching speed, and advanced paralleling capability. It has a wide range of power electronic applications, such as portable information appliances, power integrated circuits, cell phones, notebook computers, and the communications infrastructure that enables the Internet. As of 2010, the power MOSFET accounts for the majority of the power transistor market, followed by the IGBT, then the RF amplifier, and then the bipolar junction transistor.

Solid-state devices

Device	Description	Ratings
Diode	Uni-polar, uncontrolled, switching device used in applications such as rectification and circuit directional current control. Reverse voltage blocking device, commonly modeled as a switch in series with a voltage source, usually 0.7 VDC. The model can be enhanced to include a junction resistance, in order to accurately predict the diode voltage drop across the diode with respect to current flow.	Up to 3000 amperes and 5000 volts in a single silicon device. High voltage requires multiple series silicon devices.
Silicon-controlled rectifier	This semi-controlled device turns on when a gate pulse is present and the anode is positive compared to the cathode. When a gate pulse is present, the device operates like a standard diode. When the anode is negative compared to the cathode, the device turns off and blocks positive or negative voltages present. The gate voltage does not allow the device to turn off.	Up to 3000 amperes, 5000 volts in a single silicon device.
Thyristor	The thyristor is a family of three-terminal devices that include SCRs, GTOs, and MCT. For most of the devices, a gate pulse turns the device on. The device turns off when the anode voltage falls below a value determined by the device characteristics. When off, it is considered a reverse voltage blocking device.
Gate turn-off thyristor	The gate turn-off thyristor, unlike an SCR, can be turned on and off with a gate pulse. One issue with the device is that turn off gate voltages are usually larger and require more current than turn on levels. This turn off voltage is a negative voltage from gate to source, usually it only needs to be present for a short time, but the magnitude s on the order of 1/3 of the anode current. A snubber circuit is required in order to provide a usable switching curve for this device. Without the snubber circuit, the GTO cannot be used for turning inductive loads off. These devices, because of developments in IGCT technology are not very popular in the power electronics realm. They are considered controlled, uni-polar and bi-polar voltage blocking.
Triac	The triac is a device that is essentially an integrated pair of phase-controlled thyristors connected in inverse-parallel on the same chip. Like an SCR, when a voltage pulse is present on the gate terminal, the device turns on. The main difference between an SCR and a Triac is that both the positive and negative cycle can be turned on independently of each other, using a positive or negative gate pulse. Similar to an SCR, once the device is turned on, the device cannot be turned off. This device is considered bi-polar and reverse voltage blocking.
Bipolar junction transistor	The BJT cannot be used at high power; they are slower and have more resistive losses when compared to MOSFET type devices. To carry high current, BJTs must have relatively large base currents, thus these devices have high power losses when compared to MOSFET devices. BJTs along with MOSFETs, and do not block reverse voltage very well, unless installed in pairs with protection diodes. Generally, BJTs are not utilized in power electronics switching circuits because of the I²R losses associated with on resistance and base current requirements. BJTs have lower current gains in high power packages, thus requiring them to be set up in Darlington configurations in order to handle the currents required by power electronic circuits. Because of these multiple transistor configurations, switching times are in the hundreds of nanoseconds to microseconds. Devices have voltage ratings which max out around 1500 V and fairly high current ratings. They can also be paralleled in order to increase power handling, but must be limited to around 5 devices for current sharing.
Power MOSFET	The main benefit of the power MOSFET compared to the BJT is that the MOSFET is a depletion channel device and so voltage, not current, is necessary to create a conduction path from drain to source. At low frequencies this greatly reduces gate current because it is only required to charge gate capacitance during switching, though as frequencies increase this advantage is reduced. Most losses in MOSFETs are due to on-resistance, can increase as more current flows through the device and are also greater in devices that must provide a high blocking voltage. BV_dss. Switching times range from tens of nanoseconds to a few hundred microseconds. Nominal voltages for MOSFET switching devices range from a few volts to a little over 1000 V, with currents up to about 100 A or so, though MOSFETs can be paralleled to increase switching current. MOSFET devices are not bi-directional, nor are they reverse voltage blocking.	-
Insulated-gate bipolar transistor	These devices have the best characteristics of MOSFETs and BJTs. Like MOSFET devices, the insulated gate bipolar transistor has a high gate impedance, thus low gate current requirements. Like BJTs, this device has low on state voltage drop, thus low power loss across the switch in operating mode. Similar to the GTO, the IGBT can be used to block both positive and negative voltages. Operating currents are fairly high, in excess of 1500 A and switching voltage up to 3000 V. The IGBT has reduced input capacitance compared to MOSFET devices which improves the Miller feedback effect during high dv/dt turn on and turn off.
MOS-controlled thyristor	The MOS-controlled thyristor is thyristor like and can be triggered on or off by a pulse to the MOSFET gate. Since the input is MOS technology, there is very little current flow, allowing for very low power control signals. The device is constructed with two MOSFET inputs and a pair of BJT output stages. Input MOSFETs are configured to allow turn on control during positive and negative half cycles. The output BJTs are configured to allow for bidirectional control and low voltage reverse blocking. Some benefits to the MCT are fast switching frequencies, fairly high voltage and medium current ratings.
Integrated gate-commutated thyristor	Similar to a GTO, but without the high current requirements to turn on or off the load. The IGCT can be used for quick switching with little gate current. The devices high input impedance largely because of the MOSFET gate drivers. They have low resistance outputs that do not waste power and very fast transient times that rival that of BJTs. ABB Group company has published data sheets for these devices and provided descriptions of the inner workings. The device consists of a gate, with an optically isolated input, low on resistance BJT output transistors which lead to a low voltage drop and low power loss across the device at fairly high switching voltage and current levels. An example of this new device from ABB shows how this device improves on GTO technology for switching high voltage and high current in power electronics applications. According to ABB, the IGCT devices are capable of switching in excess of 5000 VAC and 5000 A at very high frequencies, something not possible to do efficiently with GTO devices.