Flexible electrode structures for thermo-tunneling applications

Combined thermionic emission and tunneling of hot electrons (thermo-tunneling) has emerged as a potential new solid-state cooling technology. Practical implementation of thermo-tunneling, however, requires the formation of a nanometer-sized gap spanning macroscopically significant surfaces. Thermo-tunneling of hot electrons across a few-nanometer gap has application to vacuum electronics, flat panel displays, and holds great potential in thermo-electric cooling and energy generation. Development of new thermo-tunneling applications requires creation of a stable nanometer gap between two surfaces. This presentation is focused on our effort to investigate the feasibility of creating such gaps using distributed electro-magnetic forces arising in thin-film flexible structures. Early efforts based on rigid electrodes showed that the effective tunneling approaches 400 square-micrometers, which albeit small, could lead to useful practical systems. In this presentation, we report a theoretical and experimental investigation of a thin-electrode system which could lead to further increase on the effective tunneling area. The device under study consists of a thin membrane collector electrode (anode) suspended over the emitting electrode (cathode). The structure is placed in a vacuum enclosure with an externally generated magnetic field perpendicular to the current flow in the membrane. The resulting Lorentz force is then directed upwards, separating the two surfaces. A mathematical model of the steady-state operation of the device is presented along with predictions of the contact area and tunneling current. Essential output parameters of the model include a central contact area measured by its length (delta) and the thermo-tunneling current. Both parameters are determined as a function of the externally applied external potential and magnetic field. Numerical solutions of the model show two possible operating modes: (1) symmetric deformation with negligibly small current; and (2) asymmetric mode where the B-field controls the current and contact area.