2018 AFOSR MURIEmpty State ElectronicsPO: Dr. Jason Marshall, Plasma and Electro Energetic Physics: plasma@us.af.mil PI: Akintunde Ibitayo (Tayo) Akinwande, Massachusetts Institute of Technology (MIT)Website: TBD
Solid-state transistors are inherently limited by two factors ⎯ scattering of carriers by ionized impurities, defects and phonons and dielectric breakdown. Scattering of carriers limits the maximum velocity that could be attained by electrons in a semiconductor channel to 1×107 cm/s < vsat < 2×107 cm/s. Dielectric breakdown limits the electrostatic field that can be applied to the channel 3 × 105 V/cm < FBD < 107 V/cm. These two factors limit the performance semiconductor devices and circuits. Furthermore, solid state transistors are severely limited in high temperature environments and are extremely susceptible to damage and failure in high radiation environments.
The Massachusetts Institute of Technology (MIT), University of Colorado (CU), Southern Methodist University (SMU) and Boise State University (BSU) propose a program on nano vacuum channel transistors (NVCT) to exploit ballistic electron transport in nanoscale vacuum channels. Integrated circuits based on NVCTs have the potential to have low propagation delay and low power-delay product. Electron velocities are expected to approach 5 × 108 cm/s (≈1% the speed of light) at modest voltage biases for devices with short channel length (Lc = 100 nm). The Johnson Figure of Merit (JFoM) of the NVCT is expected to be >20× that of GaN. Furthermore, NVCTs have the potential to operate in extremely harsh environments, including high temperatures and high radiation conditions because both the electron injection mechanism into the channel and transport of electrons in the channel are temperature and radiation insensitive.
Our proposed program addresses fundamental problems that have plagued vacuum nanoelectronic devices for decades ⎯ performance, uniformity, stability, reliability and lifetime. Our program focuses on developing a fundamental understanding of the effects of adsorbates, absorption/desorption processes of gas molecules and variation of emitter tip radius on NVCT performance, stability, reliability and lifetime; through a coordinated study of field emission physics, development of new characterization tools/methods, new materials (IrOx, graphene, graphene oxide, GaN/AlxGa1-xN/AlN heterostructures, p-AlGAN/p-GaN/LaB6 nanostructures) and new device architectures that ensure low transit times and high intrinsic gains. Our program will also develop novel circuit approaches that leverage the strengths of NVCTs to provide very high noise margins and low propagation delays. A critical part of our program is the development of novel mathematical tools for modeling the electron emission processes, surface fields and quantum transport of electrons.
Ultimately, our program will (a) demonstrate simple vacuum integrated circuits based on NVCTs, (b) develop a fundamental understanding of electron emission process (c) develop novel device architectures using novel materials and (d) lay the foundation for future vacuum integrated circuits fabricated by micro/nanotechnology that are temperature and radiation insensitive. These integrated circuit will address DoD need for high speed and low power delay technology that are capable of operating in harsh environments. NVCTs have the opportunity to combine the low cost, stability, uniformity and reliability of silicon ICs with the extreme performance of vacuum electronics, providing DoD with the best of both worlds in an integrated solution.