Advanced processing techniques for aluminum gallium nitride/gallium nitride high electron mobility transistors.

摘要

In this dissertation, we have taken an experimental approach to address the main challenges for the use of AlGaN/GaN high electron mobility transistors at millimeter-wave frequencies. Innovative implementation of materials, advanced design techniques and novel processing steps have been employed to overcome the obstacles.;The high frequency performance of these devices is severely limited by parasitic capacitances and access resistances. To minimize the parasitics, we have developed a self-aligned submicron technology where the source and drain regions are self-aligned to the gate. To facilitate this approach, high performance and low temperature annealed ohmic contacts have been developed. The self-aligned technology enabled minimizing the access resistance by reducing the source to drain distance. A nitride based gate transfer technology has been employed to realize high aspect ratio. High performance self-aligned devices with fT 92 GHz and fmax 104 GHz have been realized for the first time. Processing innovations demonstrating the potential to improve device performance have been discussed. A comprehensive study of the low temperature ohmic contact that enables the self-aligned technology has been performed, and an optimized metallization scheme has been identified for high performance and reliability.;A major limitation of AlGaN/GaN transistor technology is the difficulty to achieve normally-off devices. Nonrecessed enhancement mode (normally-off) devices using fluorine plasma pretreatment of the gate region have been fabricated in submicron technology for the first time. An improvement of device performance has been realized by employing the self-aligned technology on these enhancement mode devices. An fT and an fmax of 30 GHz and 52 GHz, respectively, have been demonstrated.;A comprehensive study of the effects of fluorine plasma treatment on the gate leakage and two-dimensional electron gas transport properties has been carried out to obtain insights into the passivation mechanisms of fluorine, and to be able to apply these to optimize device performance.;Using all the processing advancements demonstrated through the research undertaken in this dissertation highlights the potential of GaN-based transistors for next generation millimeter-wave applications, and possibly digital applications.