Power semiconductor devices are semiconductor devices used as switches or rectifiers in power electronic circuits (switch mode power supplies for example). They are also called power devices or when used in integrated circuits, called power ICs. Semiconductor devices are electronic components that exploit the electronic properties of semiconductor materials, principally silicon, germanium, and gallium arsenide. ... Power electronics is the technology associated with the efficient conversion, control and conditioning of electric power by static means from its available input form into the desired electrical output form. ... An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, and switches. ... A switched-mode power supply, or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator - an internal control circuit that switches the load current rapidly on and off in order to stabilise the output voltage. ...

Some common power devices are the power diode, thyristor, power MOSFET and IGBT (insulated gate bipolar transistor). A power diode or MOSFET, for example, operates on similar principles as its low-power counterpart, but is able to carry a larger amount of current and typically is able to support a larger reverse-bias voltage in the off-state. Types of diodes closeup, showing silicon crystal In electronics, a diode is a component that restricts the direction of movement of charge carriers. ... Circuit symbol for a thyristor The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. ... Two power MOSFETs in the surface-mount package D2PAK. Each of these component can sustain a blocking voltage of 30 volts and a continuous current of 120 amperes. ... The Insulated Gate Bipolar Transistor combines the simple gate drive characteristics of the MOSFET with the high current and low saturation voltage capability of bipolar transistors by combining an isolated gate FET for the control input, and a bipolar power transistor as a switch, in a single device. ... In electronics, voltage bias (sometimes simply called bias) is a steady-state voltage inserted in series with an element of an electronic device like a transistor, coil or other source of load. ...

Structural changes are often made in power devices to accommodate the higher current density, higher power dissipation and/or higher reverse breakdown voltage. The vast majority of the discrete (i.e non integrated) 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]. In electronics, a discrete component is an individual device, either passive (resistor, capacitor, inductor, diode) or active (transistor or vacuum tube), other than an integrated circuit. ...

Power semiconductor devices are only used in commutation mode (i.e they are either on or off), and are therefore optimised for this. Most of them shouldn't be used in linear operation.

History

Power semiconductor devices appeared with the introduction of the thyristor in 1957. They are able to withstand very high reverse breakdown voltage and are also capable of carrying high current. One disadvantage of the thyristor is that once it is 'latched-on' in the conducting state it cannot be turned off by external control. The thyristor turn-off is passive, i.e., the power must be disconnected from the device. This is a major disadvantage for switching circuits. Circuit symbol for a thyristor The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. ...

Although bipolar transistors where invented in 1948, the first devices with substantial power handling capabilities where introduced in the 1960s. These components overcome the limitations of the thyristors, as they can be turned on or off. The schematic symbols for pnp_ and npn_type BJTs. ...

With the improvements of the Metal Oxide Semiconductor technology (initially developed to produce integrated circuits), power MOSFETs became available in the late 1970s. International Rectifier introduced a 25 A, 400 V power MOSFET in 1978.^[1] These devices allow operation at higher frequency than bipolar transistors, but are limited to the low voltage applications. Integrated circuit showing memory blocks, logic and input/output pads around the periphery A monolithic integrated circuit (also known as IC, microchip, silicon chip, computer chip or chip) is a miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as passive components) which has been manufactured in the surface... Two power MOSFETs in the surface-mount package D2PAK. Each of these component can sustain a blocking voltage of 30 volts and a continuous current of 120 amperes. ... International Rectifier Corp. ...

Developed in the 1980s, the Insulated Gate Bipolar Transistor (IGBT) became widely available in the 1990s. This component has the power handling capability of the bipolar transitor, with the advantages of the isolated gate drive of the power MOSFET. It has since almost completely replaced the bipolar transistor in power applications. The Insulated Gate Bipolar Transistor combines the simple gate drive characteristics of the MOSFET with the high current and low saturation voltage capability of bipolar transistors by combining an isolated gate FET for the control input, and a bipolar power transistor as a switch, in a single device. ...

Common power semiconductor devices

Fig. 1: The power devices family, showing the principal power switches.

The realm of power devices is divided into two main categories (see figure 1): Image File history File links Download high-resolution version (3129x1267, 77 KB) Cyril BUTTAY This is a diagram showing the classification of the power devices (MOSFET, IGBT, Diode, Thyristor. ... Image File history File links Download high-resolution version (3129x1267, 77 KB) Cyril BUTTAY This is a diagram showing the classification of the power devices (MOSFET, IGBT, Diode, Thyristor. ...

• The two-terminal devices (diodes), whose state is completely dependent on the external power circuit they are connected to;
• The three-terminal devices, whose state is not only dependent on their external power circuit, but also on the signal on their driving terminal (gate or base). Transistors and thyristors belong to that category.

A second classification is less obvious, but has a strong influence on device performance: Some devices are majority carrier devices (Schottky diode, MOSFET), while the others are minority carrier devices (Thyristor, bipolar transistor, IGBT). The former use only one type of charge carriers, while the latter use both (i.e electrons and holes). The majority carrier devices are faster, but the charge injection of minority carrier devices allows for better On-state performance.

Diodes

An ideal diode should have the following behaviour: Types of diodes closeup, showing silicon crystal In electronics, a diode is a component that restricts the direction of movement of charge carriers. ...

• When forward-biased, the voltage across the end terminals of the diode should be zero, whatever the current that flows through it (on-state);
• When reverse-biased, the leakage current should be zero whatever the voltage (off-state).

Moreover, the transition between on and off states should be instantaneous.

In reality, the design of a diode is a trade-off between performance in on-state, off-state and commutation. Indeed, it is the same area (actually the lightly-doped region of a PiN diode) of the device that has to sustain the blocking voltage in off-state and allow current flow in the on-state. As the requirements for the two state are completely opposite, it can be intuitively seen that a diode has to be either optimised for one of them, or time must be allowed to switch from one state to the other (i.e slow down the commutation speed). A PIN diode (Positive-Intrinsic-Negative diode) is a photodiode with a large, neutrally doped intrinsic region sandwiched between p-doped and n-doped semiconducting regions. ...

This trade-off between on-state, off-state and switching speed is the same for all power devices. A Schottky diode has excellent switching speed and on-state performance, but a high level of leakage current in off-state. PiN diodes are commercially available in different commutation speeds (so-called fast rectifier, ultrafast rectifier...), but any increase in speed is paid by lower performance in on-state. The Schottky diode (named after German physicist Walter H. Schottky) is a semiconductor diode with a low forward voltage drop and a very fast switching action. ... A PIN diode (Positive-Intrinsic-Negative diode) is a photodiode with a large, neutrally doped intrinsic region sandwiched between p-doped and n-doped semiconducting regions. ...

Switches

Fig.2 : Current/Voltage/switching frequency domains of the main power electronics switches.

The trade-off between voltage, current and frequency ratings also exists for the switches. Actually, all power semiconductors rely on a PiN diode structure to sustain voltage. This can be seen in figure 2. The power MOSFET has the advantages of the majority carrier devices, so it can achieve very high operating frequency, but can't be used with high voltages. As it is a physical limit, no improvement is expected from silicon MOSFET concerning their maximum voltage ratings. However, its excellent performance in low voltage make it the device of choice (actually the only choice) for applications below 200 V. By paralleling several devices, it is possible increase the current rating of a switch. The MOSFET is particularly suited to this configuration because its positive thermal coefficient of resistance tends to balance current between individual devices. Image File history File links Switches_domain. ... Image File history File links Switches_domain. ... Two power MOSFETs in the surface-mount package D2PAK. Each of these component can sustain a blocking voltage of 30 volts and a continuous current of 120 amperes. ... The metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET), is by far the most common field-effect transistor in both digital and analog circuits. ...

The IGBT is a relatively new component, so its performance improve regularly as technology evolves. It has already completely replaced the bipolar transistor in power applications, and the availability of power modules (in which several IGBT dice are connected in parallel) makes it attractive for power levels up to several megawatts, pushing further the limit where thyristors and GTO become the only option. 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 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). Its major limitation for low voltage applications is the relatively high voltage drop it exhibits in on-state (2 to 4 V). Compared to the MOSFET, the operating frequency of the IGBT is relatively low (few devices are rated over 50 kHz), mainly because of a so-called 'current-tail' problem during turn-off. The Insulated Gate Bipolar Transistor combines the simple gate drive characteristics of the MOSFET with the high current and low saturation voltage capability of bipolar transistors by combining an isolated gate FET for the control input, and a bipolar power transistor as a switch, in a single device. ... The schematic symbols for pnp_ and npn_type BJTs. ... High power IGBTs (here a 3300V, 1200A switch) are obtained by connecting tens of dice in parallel in a power module. ...

At very high power levels, thyristor-based devices (SCR, GTO, MCT) are still the only choice. The driving a thyristor is somewhat complicated, as this device can only be turned-on. It turns off by itself as soon as no more current flows through it. This requires specific circuit with means to divert current, or specific applications where current is known to cancel regularly (i.e Alternating Current). Different solution have been developed to overcome this limitation (Mos Controlled Thyristors, Gate Turn Off thristor...). These components are widely used in power distribution applications. Circuit symbol for a thyristor The thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. ... SCR can refer to a file extension used for MS Windows screen savers. ... GTO is an abbreviation of: Geostationary transfer orbit Great Teacher Onizuka, the manga and anime series Gran Turismo Omologato, Pontiac GTO. Not to be confused with Mitsubishi GTO Guanajuato, Gto. ... MCT is a three-letter abbreviation with multiple meanings, including: Minnesota Chippewa Tribe Movement Control Team Microsoft Certified Trainer Medium Chain Triglycerides This is a disambiguation page — a navigational aid which lists pages that might otherwise share the same title. ... City lights viewed in a motion blurred exposure. ... Electricity distribution is the penultimate process in the delivery of electric power, the part between transmission and user purchase from an electricity retailer. ...

Parameters of power semiconductor devices

A power device is usually attached to a heatsink to remove the heat caused by operation losses.

The power semiconductor die of a three-terminal device (IGBT, MOSFET or BJT). Two contacts are on top of the die, the remaining one is on the back.

1. Breakdown voltage. Often the trade-off is between breakdown voltage rating and on-resistance because increasing the breakdown voltage by incorporating a thicker and lower doped drift region leads to higher on-resistance.
2. On-resistance. Higher current rating lowers the on-resistance due to greater numbers of parallel cells. This increases overall capacitance and slows down the speed.
3. Rise and fall times for switching between on and off states.
4. Safe-operating area (from thermal dissipation and "latch-up" consideration)

Image File history File links Thermal_stack. ... Image File history File links Thermal_stack. ... A large copper heatsink. ... Image File history File links Power_die. ... Image File history File links Power_die. ...

Research and development

Packaging

The role of packaging is to:

• connect a die to the external circuit;
• provide a way to remove the heat generated by the device;
• protect the die from the external environment (moisture, dust);

Many of the reliability issues of power device are either related to excessive temperature of fatigue due to thermal cycling. Research is currently carried out on the following topics:

• improve the cooling performance.
• improve the resistance to thermal cycling by closely matching the Coefficient of thermal expansion of the packaging to that of the silicon.
• increase the maximum operating temperature of the packaging material.

Research is also ongoing on electrical issues such as reducing the parasitic inductance of packaging. This inductance limits the operating frequency as it generates losses in the devices during commutation. During heat transfer, the energy that is stored in the intermolecular bonds between atoms changes. ...

Low-voltage MOSFETs are also limited by the parasitic resistance of the packages, as their intrinsic on-state resistance can be as low as one or two milliohms.

Improvement of structures

IGBTs are still under development and we can expect increased operating voltages in the future. At the high-power end of the range, Mos-Controlled Thyristor are promising devices.

Wide band-gap semiconductors

The major breakthrough in power semiconductor devices is expected from the replacement of silicon by a wide band-gap semiconductor. At the moment, silicon carbide (SiC) is considered to be the most promising. SiC Schottky diodes with a breakdown voltage of 1200 V are commercially available, as are 1200 V JFETs. As both are majority carrier devices, they can operate at high speed. Bipolar devices are being developed for higher voltages, up to 20 kV. Among its advantages, silicon carbide can operate at higher temperature (up to 400°C) and has a lower thermal resistance than silicon, allowing better cooling. Silicon carbide (SiC) is a ceramic compound of silicon and carbon. ... Electric current flow from source to drain in a JFET is restricted when a voltage is applied to the gate. ... Thermal resistance has two different meanings: 1) the temperature difference across the structure when a unit of heat energy flows through it in unit time or 2) the temperature difference across a unit area of a material of unit thickness when a unit of heat energy flows through it in...

Notes and references

Notes

1. ^ Jacques Arnould, Pierre Merle Dispositifs de l'électronique de puissance, Éditions Hermès, ISBN 2-86601-306-9 (in French)

Reference

• "Power Semiconductor Devices", B. Jayant Baliga, PWS publishing Company, Boston. ISBN 0-534-94098-6