Silicon Carbide Transient Voltage Suppressor for Aircraft Use

Silicon Carbide (SiC) power devices are poised to replace silicon (Si) power devices in high voltage and power applications due to the advantages they offer in electrical efficiency and thermal performance. They also offer the same benefits in the low voltage range for devices without gate oxides.  We design, fabricate and market custom silicon carbide power MOSFETs, JFETs, and diodes. We use specially designed versions of these as lightning protection devices. We also design and fabricate SiC avalanche diodes.  We therefore plan to combine the high power and avalanching capabilities of SiC with its thermal advantage to make unidirectional and bidirectional SiC TVS diodes with electrical specifications appropriate for military aircraft. A significant concern in avalanche diode design and fabrication is the prevention of premature breakdown. We employ a beveled mesa structure to circumvent this issue and achieve uniform breakdown. Typically, the breakdown voltage of an avalanche diode for a fixed thickness is higher for wider bandgap materials, and higher if the avalanching region is doped lower. Using a silicon carbide diode, we make the active volume thinner and higher doped, decreasing its overall resistance and capacitance simultaneously.  During the Phase I period, we plan to employ physics-based semiconductor simulation techniques to explore the design parameter space to obtain the pareto optimal designs for unidirectional TVS diodes. To tailor devices for various applications, we use technology computer aided design tools. Detailed maps of the inside of the device are then used in performance and reliability optimization. These maps, which are the visualizations of the calculated variables such as electrostatic potential and carrier concentrations, provide information where experiments cannot reach. Next, we plan to pursue short loop experiments to test different process steps of importance for the fabrication of these diodes. Since the mesa structure is of great importance for our TVS diodes, we will perform experiments to perfect bevel etch recipes. In parallel, other diode process experiments such as dopant profiling will be used to assist diode fabrication and to help guide designs to be fabricated during the option and Phase II periods. During the Phase I option period, the plan is to start the prototype TVS fabrication. We have both in-house and external fabrication capabilities. We are currently performing fabrication runs with commercial foundries. We are also performing internal runs in our own prototyping microfabrication facilities. The fabrication during the option period is set to take place at our facility. Furthermore, the option period is also for planning testing for performance and reliability during Phase II. It is additionally for surveying packaging solutions that are appropriate given the electrical and thermal specifications, as well as environmental constraints.