Gain-Bandwidth Characteristics of High-Tc Superconducting Millimeter-Wave Hot-Electron Bolometer Mixers
Chao-Te Li, Bascom S. Deaver, Robert M. Weikle +3 more
The conversion gain bandwidth characteristics of millimeter-wave mixers using high-Tc superconducting YBa2Cu307 (YBCO) thin films are presented. The YBCO films are patterned into latticecooled hot-electron bolometers (HEB) coupled to an integrated antenna and transmission line. Direct heterodyne and homodyne down-conversion measurements using local-oscillator frequencies of 75 GHz and 585 GHz show overall conversion gains of -35 dB, which includes a -18 dB coupling loss. The gain bandwidth shows a simple Lorentzian roll-off with -3 dB point of 5 to 8 GHz. No second plateau in the gain spectrum has been observed, in contrast to other reports. The effective volume of the HEB is believed to be significantly smaller than the physical dimensions of the device. Gershenzon, et al. 1 first proposed the design of a lattice-cooled superconducting hot-electron bolometer (HEB) for use as a low-power, wide-band-width heterodyne mixer at millimeter and submillimeter-wave frequencies. This idea has been successfully implemented using NbN , which shows a conversion gain as high as -15 dB using 1 1.tW of pump power at a temperature of 4.2 K. The ultimate speed and bandwidth of the lattice-cooled HEB is determined by the electron-phonon scattering rate. For this reason, Gershenzon 3 suggested that the high normal-state resistivity of the high-Tc superconductor YBa2Cu307 (YBCO) could indicate a very fast electron inelastic scattering, rate and so make this material an ideal candidate to produce a very wide instantaneous bandwidth lattice-cooled HEB operating at 77 K. The first reports of such mixers at 1.5 gm (Ref. 4) and 9.6 gm (Ref. 5) wavelengths showed a very low intrinsic conversion gain of -77 dB (excluding coupling losses) using a relatively large 0.3 mW of absorbed LO power. However, the gain bandwidth showed a twoplateau structure. A low frequency plateau near -77 dB rolled off near 1 GHz intermediate frequency (IF) but gave way to a second plateau near -90 dB that extended to at least 18 GHz, the upper limit of the measurement. Karasik, et al., have done extensive calculations on the conversion gain properties of lattice-cooled HEB mixers for different mixer dimensions, using a two-temperature model. They found that the conversion gain increases
•Mar 1, 1998•1 citation