SBIR-STTR Award

We propose to develop a new solid-state, ultra-high frequency metal transistor that exploits the recently discovered dual nature of charge carriers in "goniopolar" materials, where the carrier polarity (electron or hole nature) changes with the crystallographic direction. Such metallic transistors can achieve ultra-high frequencies at unprecedented power levels because they avoid the large capacitive effects that limit high-frequency behavior in semiconductor-based transistors. Capacitive effects are caused by depletion layers at junctions between different materials or doped regions with charge carrier concentrations low enough to act as insulators. Current technology is unable to achieve switching or amplification without the integration of those different materials or doped regions. The proposed single-material all-metal bipolar transistor circumvents this problem and would have the potential for ultra-high frequency and high-power switching not previously thought achievable, since it is a junction-free device made from goniopolar metal with majority electron-conduction along one crystallographic axis and hole-conduction along an orthogonal axis. Efforts will focus on the material Re4Si7 and its implementation into a multistage cascade to optimize gain. Using technology computer aided design (TCAD), we will first design the optimized device structure and operation along with limits for contact resistance, before eventually testing this new device architecture.

Our overall objective was to develop a conceptual design for a solid-state, ultra-high frequency transistor able to perform at 30 THz, with at least 1 W output power, and current densities of 106 A/cm2. This device was based on the topological properties of the Fermi surface of a new class of materials. Modern day electronic devices integrate different material or doped regions together to achieve switching or amplification. In order to do this, a depletion layer is formed in the junction between these materials with charge carrier concentrations so low that it acts as an insulator. This results in large capacitive effects in semiconductor transistors that limit high-frequency behavior. Our team was looking to circumvent this problem by establishing a new single-material all-metal bipolar transistor that would have the potential for ultra-high frequency and high-power switching not previously thought to be achievable. Designed from a new class of single crystalline metals, which has been defined as ‘goniopolar’, these devices will be able to exhibit majority electron-conduction along one crystallographic axis and hole-conduction along an orthogonal axis. Efforts have focused on the material Re4Si7 and its possible implementation into a multistage cascade to optimize gain. The conclusion of the modeling supported by the SBIR Phase I funding is that such a metal transistor is indeed possible. We report a geometry for a single transistor element with a current gain in excess of 2. This device can be put in a cascade of n such elements, given a projected current gain of 2n, so that, in principle, any desirable gain can be designed into a more sophisticated device based on this principle. The simulation results produced in this Phase I SBIR should be a sufficient proof of principle for the transistor, and GonioTech is in the process of patent application for it. Phase II will be focused building a prototype.