Semiconductor Power Devices

AlGaN-GaN power high-electron mobility transistors (HEMTs) with 600-V breakdown voltage are fabricated and demonstrated as switching power devices for motor drive and power supply applications. The fabricated power HEMT realized the high breakdown voltage by optimized field plate technique and the low on-state resistance of 3.3 m/spl Omega/cm/sup 2/, which is 20 times lower than that or silicon MOSFETs, thanks to the high critical field of GaN material and the high mobility in 2DEG channel. The fabricated devices also demonstrated the high current density switching of 850 A/cm/sup 2/ turn-off. These results show that AlGaN-GaN power-HEMTs are one of the most promising candidates for future switching power device for power electronics applications.

High breakdown voltage AlGaN-GaN power-HEMT design and high current density switching behavior

High-power device technology is a key technological factor for wireless communication, which is one of the information network infrastructures in the 21st century, as well as power electronics innovation, which contributes considerably to solving the energy saving problem in the future energy network. Widegap semiconductors, such as SiC and GaN, are strongly expected as high-power high-frequency devices and high-power switching devices owing to their material properties. In this paper, the present status and future prospect of these widegap semiconductor high-power devices are reviewed, in the context of applications in wireless communication and power electronics.

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Present Status and Future Prospect of Widegap Semiconductor High-Power Devices

Recently, a new technology for high voltage power MOSFETs has been introduced: the CoolMOS/sup TM/. Based on the new device concept of charge compensation, the R/sub DS(on)/ area product for e.g. 600 V transistors has been reduced by a factor of 5. The devices show no bipolar current contribution like the well known tail current observed during the turn-off phase of IGBTs. CoolMOS/sup TM/ virtually combines the low switching losses of a MOSFET with the on-state losses of an IGBT. Furthermore, the dependence of R/sub DS(on)/ on the breakdown voltage has been redefined. The more than square-law dependence in the case of standard MOSFET has been broken and a linear voltage dependence achieved. This opens the way to new fields of application even without avalanche operation. System miniaturization, higher switching frequencies, lower circuit parasitics, higher efficiency, and reduced system costs are pointing the way towards future developments. Not only has the new technology achieved breakthrough at reduced R/sub DS(on)/ values, but new benchmarks have also been set for the device capacitances. Due to chip shrinkage and a novel internal structure, the technology shows both a very small input capacitance and a strongly nonlinear output capacitance. The drastically lower gate charge facilitates and reduces the cost of controllability, and the smaller feedback capacitance reduces the dynamic losses. With this new technology, the minimum R/sub DS(on)/ values in all packages are being redefined in the important 600-1000 V categories.

COOLMOS/sup TM/-a new milestone in high voltage power MOS

Superjunction has arguably been the most creative and important concept in the power device field since the introduction of the insulated gate bipolar transistor (IGBT) in the 1980s. It is the only concept known today that has challenged and ultimately proved wrong the well-known theoretical study on the limit of silicon in high-voltage devices. This paper deals with the history, device and process development, and the future prospects of Superjunction technologies. It covers fundamental physics, technological challenges as well as aspects of design and modeling of unipolar devices, such as CoolMOS. The superjunction concept is compared to other methods of enhancing the conductivity of power devices (from bipolar to employment of wide-bandgap materials) to derive its set of benefits and limitations. This paper closes with the application of the superjunction concept to other structures or materials, such as terminations, superjunction IGBTs, or silicon carbide Field Effect Transistors (FETs).

Superjunction Power Devices, History, Development, and Future Prospects

For the first time a new device concept for high voltage power devices has been realized in silicon. Our 600 V-COOLMOS/sup TM/ reaches an area specific on-resistance of typically 3.5 /spl Omega//spl middot/mm/sup 2/. Our technology thus offers a shrink factor of 5 versus the actual state of the art in power MOSFETs. The device concept is based on charge compensation in the drift region of the transistor. We increase the doping of the vertical drift region roughly by one order of magnitude and counterbalance this additional charge by the implementation of fine structured columns of the opposite doping type. The blocking voltage of the transistor remains thus unaltered. The charge compensating columns do not contribute to the current conduction during the turn-on state. Nevertheless the drastically increased doping of the drift region allows the above mentioned reduction of the on-resistance.

A new generation of high voltage MOSFETs breaks the limit line of silicon

High-voltage MOS transistors with blocking voltages of up to 1000 V and turn-on resistances of less than 2 Ω were developed and tested. The transistor structure itself is that of a vertical SIPMOS+(1) power transistor. Retaining this technology, a special design of the cell field and a new type of chip edge construction became necessary in order to achieve the quoted values. The required constructional dimensions were obtained with the aid of a two-dimensional modelling program. (+SIPMOS = Siemens Power MOS)

H. Strack

Papers

A new generation of high voltage MOSFETs breaks the limit line of silicon

Power MOS transistors for 1000 V blocking voltage