Modeling and Optimization of a High-Tc Hot-Electron Superconducting Mixer for Terahertz Applications

The development of a YBa2Cu307.8 (YBCO) hot-electron bolometer (HEB) quasioptical mixer for a 2.5 l'Hz heterodyne receiver is discussed. The modeled device is a subrnicron bridge made from a 10 nm thick film on a high thermal conductance substrate. The mixer performance expected for this device is analyzed in the framework of a two-temperature model which includes heating both of the electrons and the lattice. Also, the contribution of heat diffusion from the film through the substrate and from the film to the normal metal contacts is evaluated. The intrinsic conversion gain and the noise temperature have been calculated as functions of the device size, substrate material, and ambient temperature. Assuming energy fluctuations and Johnson noise to be the main sources of noise, a single sideband (SSB) mixer noise temperature of less than 2000 K is predicted. For our modeled device, the conversion efficiency at an IF of 2.5 GHz is —10 dB or better and the required local oscillator (LO) power is less than 51.1,W.