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Research was conducted to introduce a frequency-domain model for a diffusion-cooled hot-electron bolometer that takes into account the non-uniform temperature distribution found in superconducting diffusion-cooled devices. In the model, the bolometer was discretized into a finite number of segments while nonlinear large signal response to local oscillator and direct current heating was found by an iterative algorithm.

Superconducting hot-electron bolometer (HEB) mixers were fabricated based on ultra-thin YBCO (10-20 nm) films patterned into 0.1-1x1micron2 microbridges using optical and e-beam lithography and passivated with SiO. High temperature superconductor HEB mixers provide very sensitive, low power heterodyne detectors operating at temperatures approaching 90 K for applications requiring closed-cycle refrigeration. The fabrication of prototype YBCO HEB mixers with lengths as small as 0.1 micron is described.

Josephson currents have been noted to drain instabilities and decrease the sensitivity of a heterodyne superconductor-insulator-superconductor (SIS) receiver operated at submillimeter wavelengths. To reduce the magnitude of its critical Josephson currents and enable quasiparticle mixing, a static magnetic field is usually applied on the SIS junction. The SIS mixer output power at the intermediate frequency was measured versus the dc bias voltage of an array of two 1 square micron Nb/Al-Al2O3/Nb junctions. Results are discussed.

A study was conducted on diffusion-cooled hot-electron bolometer mixers' input and output noise. A noise bandwidth that is larger than the gain bandwidth was observed by simultaneously measuring the noise and gain as function of intermediate frequency for a 0.16 micrometer diffusion cooled Nb device. Results reveal a 340 K DSB mixer noise and a 55 K output noise. Results also demonstrate the THz receiver applications of diffusion cooled devices.

A quasioptical Nb hot-electron bolometer mixer was fabricated for a heterodyne receiver operating a 2.5 THz. The mixer was developed from a 12 nm thick Nb film and has an in-plane size of 0.30 micrometer x 0.15 micrometer. A twin-slot planar antenna on elliptical Si lens was utilized for radio frequency coupling. The receiver's double sideband noise temperature was experimentally measured at less than or equal to 3000 K.

High temperature superconducting hot-electron bolometers (HEB) are proposed for heterodyne mixing at frequencies over 1 terahertz. The frequencies of Nb HEB mixers are not restricted by superconducting energy gap and their performance are comparable to that of tunnel junctions. YBa2Cu3O7-delta HEB mixers may be used in low power heterodyne detectors for 90 K applications in closed-cycle refrigeration.

A quasioptically coupled diffusion-cooled hot-electron bolometric mixer was used to measure receiver noise temperatures at a local oscillator frequency of 1267 GHz and an intermediate frequency of 1.4 GHz. Results reveal a 1880K double-sideband receiver noise temperature with a 945K mixer noise and -19 dB conversion efficiency. Results prove that the mixer's sensitivity is not easily reduced by increasing frequency.

A novel type of transition-edge bolometer mixer is developed for heterodyne measurements at 533 GHz. The mixer, which uses diffusion as a cooling mechanism for hot electrons, is made of niobium and has a critical temperature of 5.5 degrees Kelvin and a receiver noise temperature of approximately 650 degrees Kelvin DSB. The devices' grid current response extends up to 2.0 GHz.

Microwave (30 GHz) measurements on aluminum superconducting hot-electron bolometer (HEB) mixers are discussed. The microwave heterodyne mixing results show good performance with a mixer noise temperature inferred from the conversion efficiency and output noise of T(sub M) more than or equal to 4 K, double size band (DSB).

Experiments were conducted to test device performance as a function of device length under various operating conditions. Measurements of the spectrum of the output noise, mixer noise and conversion efficiency for phonon and diffusion cooled Nb devices of different thermal time constants are presented, and the measurement results are compared to theoretical predictions. Likewise, measurements of the device over a very broad band as well as thermometry measurements in the normal condition are presented. The results are discussed.

Discusses the use of a frequency-domain mixer model to evaluate diffusion-cooled hot electron bolometers. Large-signal and small-signal device models; Calculation of conversion gain; Finite difference simulation results; Bolometer discretization.

Demonstrates heterodyne bolometer mixer with low noise and a large intermediate frequency bandwidth. Description of the bolometer; Composition of the geometry of the bolometer; Dependence of the electrical resistance in the film on the electron temperature.

Measures the effects of dispersion on the resonant mode frequencies of open-ended niobium (Nb)-SiO[sub x]-Nb microstrip transmission lines. Chemicals acting as voltage-controlled oscillators and detectors; Magnitude of the resonator mode spacing; Comparison with the Mattis-Bardeen conductivity of the superconductor line.

Examines the length scaling of bandwidth and noise in hot-electron superconducting bolometric mixers. Variation of the intermediate frequency bandwidth; Mixer noise temperature in short bridges; Use of mixers for low-noise terahertz heterodyne receivers.