Atomic Layer Deposition of Complex Oxides for Novel Devices

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As Canada and the rest of the world rapidly moves towards renewable energy, the electronics that support renewable energy is coming into focus. Renewable energy, such as photovoltaics, generates direct current (DC) power that must be converted into alternating current (AC) power to be used by the grid and many household appliances. DC to AC power conversion is accomplished by inverters used in circuits that can generate different types of alternating power (square wave, modified sine wave, pulsed sine wave, pulse width modulated wave or sine wave) depending on circuit design. Other circuits are used in cases where the DC voltage is less than the desired AC voltage and a boost circuit is used to increase the DC voltage to the required level before it is inverted. At heart of these inverters and boost circuits are high power devices, mostly based on silicon. Many silicon inverter circuits used in photovoltaics are only 80% efficient, which means that 20% percent of the solar power is wasted! It is well known that III-V power devices can be used to build high efficiency (>95% efficient) inverters, but these devices are very expensive. We have developed a low-temperature process to fabricate Gallium Nitride (GaN) and (Zinc Oxide) ZnO metal-oxide-semiconductor devices. GaN is used in power devices (inverters) while ZnO is used to fabricate thin film transistors that are used in displays. Our initial research into gate oxides (hafnium oxide, aluminum oxide, zirconium oxide) for these materials has given very promising results. However, the gate oxide requirement for power device is very demanding and some of the binary gate oxide properties can not meet all fo the requirements. For example, we have gate oxides with low interfacial defects but bulk defects that are too high, and we have gate oxides with low bulk defects but high interfacial defects. In order to solve this problem, Dr. Cadien is proposing to look at more complex oxides and oxide structures in order to find a combination that meets all of the required specifications for power and thin film device applications.