Vacuum electronic devices and systems, which are based on the control of electron motion through vacuum, have numerous applications including plasma displays, microwave and terahertz radiation sources for communications and imaging, scanning electron microscopes, and electronics for extreme environments. However, devices that efficiently and reliably emit electrons into vacuum have been challenging due to their low current density and poor reliability. The proposed project, a collaboration between Purdue University and Ohio State University, aims to demonstrate new designs for vacuum emitters to enable them to operate reliably at high current densities. Two complementary approaches involving two different semiconductors - Silicon and Gallium Nitride will be used to demonstrate vacuum emitters, guided by detailed electronic and thermal modeling techniques. The proposed work will enable realization of high-performance vacuum electronic devices that can be integrated on semiconductor chips at the micrometer scale. These microscale high current density emitters would surpass the current state-of-art and could enable a large array of new applications that exploit vacuum electronics for display, high data-rate communications, high-temperature electronics, and imaging. The project will lead to training and education of graduate students in a highly interdisciplinary and novel area of semiconductor technology, and could lead to several new commercially relevant applications for vacuum electronic circuits and systems.
This collaborative project will combine the complementary expertise in Si fabrication and vacuum electronics at Purdue University, and III-nitride heterostructure and polarization engineering at Ohio State University to demonstrate reliable high current density emitters. A new approach to Si field emitters will be investigated to take advantage of current saturation effects in Silicon with fairly low carrier concentration, The Si emitters will be designed to control current density through lattice and ionized impurity scattering limited transport. A parallel approach using heterostructure and polarization engineering will be pursued to achieve highly efficient field emission in planar III-nitride semiconductor structures. III-nitride semiconductors have intrinsic polarization that enables large voltages to be dropped across nanometer scale distances. This enables field engineering to align the conduction band within the semiconductor with the vacuum level outside. The polarization engineering concepts will be combined with ballistic transport in ultrascaled structures to achieve efficient field emission from III-nitride semiconductor surfaces. The proposed device will enable high current density field emission in planar geometries that could be advantageous for several applications. Sophisticated modeling techniques including 2-dimensional electro-thermal simulations and Monte Carlo simulations of transport in heterostructures will be developed at Purdue University and Ohio State University to design and evaluate the vacuum emitters in both Silicon and III-nitride material systems. Development and demonstration of micro-fabrication technology for integrated vacuum electronic devices will be done. The proposed work would lead to better understanding of field emission from engineered nanoscale structures and III-nitride semiconductors. The concepts proposed here use promising and novel approaches for overcoming challenges related to high current density emitters, and could therefore have transformative impact on the science and applications of vacuum microelectronics.
