Accurate Broadband Balanced Terahertz Tripler Design with Thermal and High-Frequency Effects

This paper presents an accurate design method applied to the terahertz broadband multipliers. The design method is divided into two steps: a self-consistent electro-thermal (E-T) model with frequency-dependent spreading resistance and an external matching circuit. The self-consistent electro-thermal model consists of three parts: the steady-state thermal model, the electro-thermal diode circuit model, and the three-dimensional (3-D) electromagnetic (EM) model. The steady-state thermal model and the electro-thermal diode circuit model are used to express the thermal effects of diode. In particular, in the EM model, a frequency-dependent spreading resistance is obtained by the fitting conductivity of actual doped buffer layers and extracted by the auxiliary circuit structures, which is used to express the high-frequency effects. Then, the external matching circuit is designed carefully to match external wideband response instead of single frequency point load-pull. Based on the design approach, a balanced 225–300 GHz frequency tripler with AlN substrate has been designed and manufactured. By introducing the high frequency spreading resistance, a better simulated-measured consistency is achieved compared to the single E-T model, no matter low input power (80 mW) or high input power (160 mW) condition.