to a higher on-resistance. On-resistance: A higher current rating lowers the on-resistance due to greater numbers of parallel cells. This increases overall capacitance and slows down the speed. Rise and fall times: The amount of time it takes to switch between the on-state and the off-state. Safe-operating area: This is a thermal dissipation and "latch-up" consideration. Thermal resistance: This is an often ignored but extremely important parameter from the point of view of practical design; a semiconductor does not perform well at elevated temperature, and yet due to large current conduction, a power semiconductor device invariably heats up. Therefore, such a devices needs to be cooled by removing that heat continuously; packaging and heatsink technology provide a means for removing heat from a semiconductor device by conducting it to the external environment. Generally, a large current device has a large die and packaging surface areas and lower thermal resistance. 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, etc.). Many of the reliability issues of a power device are either related to excessive temperature or fatigue due to thermal cycling. Research is currently carried out on the following topics: Cooling performance. Resistance to thermal cycling by closely matching the Coefficient of thermal expansion of the packaging to that of the silicon. 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, because it generates losses during commutation. A low-voltage MOSFET is also limited by the parasitic resistance of its package, as its intrinsic on-state resistance is as low as one or two milliohms. Some of the most common type of power semiconductor packages include the TO-220, TO-247, TO-262, TO-3, D2Pak, etc. Improvement of structures The IGBT design is still under development and can be expected to provide increases in operating voltages. At the high-power end of the range, the MOS-controlled thyristor is a promising device. 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. This is juxtaposed with