Nonlinearity and parameterization of Schottky diodes-based battery-free harmonic transponder for millimeter-wave 5G applications

Deployment of 5G network infrastructure is a timely opportunity for millimeter-sized battery-free sensors. However, millimeter-wave (mmW) devices often suffer from high conversion loss and path loss that are heavily limiting their communication/detection distance, especially for the case of harmonic transponders based on Schottky diodes. A deep and comprehensive parametric understanding of the second-harmonic generation mechanism of Schottky diodes in the mmW 5G bands can help us to identify suitable diodes or guide diode fabrication to reduce transponder conversion loss. This work reveals that both diode nonlinear junction resistance and capacitance contribute to the second-harmonic generation across the mid-band (sub-7 GHz) and high-band (mmW) 5G frequency bands. However, the nonlinear junction capacitance dominates the second-harmonic generation in the mmW bands. Without Joule heating during the conversion process, the capacitive nonlinearity is more efficient than the resistive nonlinearity, which means that a Schottky diode with a lower junction capacitance will efficiently reduce its associated conversion loss. The VDI GaAs zero bias diode with a low zero bias nonlinear junction capacitance (19.19 fF) shows superior conversion loss performance, which indicates that it can be employed to enhance the detection distance of battery-free harmonic transponders in the mmW 5G bands.