| This thesis is focusing on a study of junction effect transistors (JFETs) in compact pulsed power applications. Pulsed power usually requires switches with high hold-off voltage, high current, low forward voltage drop, and fast switching speed. 4H-SiC, with a bandgap of 3.26 eV (The bandgap of Si is 1.12eV) and other physical and electrical superior properties, has gained much attention in high power, high temperature and high frequency applications. One topic of this thesis is to evaluate if 4H-SiC JFETs have a potential to replace gas phase switches to make pulsed power system compact and portable. Some other pulsed power applications require cathodes of providing stable, uniform, high electron-beam current. So the other topic of this research is to evaluate if Si JFET-controlled carbon nanotube field emitter cold cathode will provide the necessary e-beam source.; In the topic of "4H-SiC JFETs", it focuses on the design and simulation of a novel 4H-SiC normally-off VJFET with high breakdown voltage using the 2-D simulator ATLAS. To ensure realistic simulations, we utilized reasonable physical models and the established parameters as the input into these models. The influence of key design parameters were investigated which would extend pulsed power limitations. After optimizing the key design parameters, with a 50-mum drift region, the predicted breakdown voltage for the VJFET is above 8kV at a leakage current of 1x10-5A/cm2 . The specific on-state resistance is 35 mO·cm 2 at VGS = 2.7 V, and the switching speed is several ns. The simulation results suggest that the 4H-SiC VJFET is a potential candidate for improving switching performance in repetitive pulsed power applications. To evaluate the 4H-SiC VJFETs in pulsed power circuits, we extracted some circuit model parameters from the simulated I-V curves. Those parameters are necessary for circuit simulation program such as SPICE. This method could be used as a test bench without fabricating the devices to minimize the unnecessary cost.; As an extended research of 4H-SiC devices, Metal-Insulator-SiC (MIS) structures were utilized to evaluate the high dielectric constant materials---TiO 2 and Al2O3, as possible gate dielectrics for SiC devices. TiO2 and Al2O3 were chosen because of their high dielectric constants and bandgap energies as well as the acceptance of Ti and Al in most modern CMOS fabrication facilities. MIS devices were fabricated and both their I-V and C-V characteristics were measured and discussed. Our research showed that Al2O3 deposited by e-beam evaporation could be considered as a promising material among the gate insulators for high power SiC devices.; In the topic of "Si JFET-controlled carbon nanotube field emitter cathode arrays", stability, controllability and lifetime are the main issues waiting to be addressed before field emitters find their wide applications. The ideas of connecting Si or metal field emitters with external MOSFETs or built-in active devices were attempted by other researchers, and those devices showed effectiveness in controlling and stabilizing the emission current. We presented the design, simulation, and the fabrication of Si JFETs monolithically integrated with CNTs field emitters. The Si JFET was designed to control and improve the emission of carbon nanotube field emitter arrays. Its electrical characteristics were simulated by the device simulator ATLAS. The fabrication process was developed to be compatible with the last step of growing multiwalled carbon nanotubes at 700°C. Carbon nanotubes field emitters were grown by PECVD (Plasma Enhanced Chemical Vapor Deposition). Preliminary field emission tests were conducted with 50 x 50 emitter arrays, with a resultant emission current of 3 muA (∼40 mA/cm2) at an extraction gate voltage of 50 V and an anode voltage of 300 V. Experimental data shows the linear relationship between ln(I/V2) and l/V consistent with Fowler-Nordheim electron tunneling. Some challenging... |
PDF Full Text Request