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ECE59I_Project_Instructions-2

ECE59I_Project_Instructions-2 - ECE594I Prof Brown Fall...

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ECE594I, Prof. Brown, Fall Quarter 2009 Course Laboratory Project 1 THz Characterization of a LiTaO 3 Pyroelectric Detector Background The THz field has advanced dramatically during the past 10 years largely in large part because of the development of useful solid-state devices, components, and systems operating at room temperature. Among the successful components are Schottky diode mixers, rectifiers, and varactor multiplier; ultrafast photoconductive (aka “Auston”) switches and photomixers; millimeter-wave low-noise and power amplifiers; and room-temperature thermal detectors (bolometers and pyrolectrics). Among the successful components and systems are varactor multiplier chains, Schottky-diode-based modularized heterodyne receiver front ends, scalar network analyzers, time-domain spectrometers, and photomixing sweep oscillators. The goal of this laboratory project is to give the students “hands-on” experience with one of the most useful and affordable of these devices – the pyroelectric thermal detector. Measuring power – be it thermal or coherent radiation – is one of the most common and important THz tasks, and it has long been somewhat controversial. Researchers developing new THz oscillators have often measured the output power with cryogenic bolometers that are poorly understood and characterized by spectral variations and saturation effects. So they may likely underestimate or overestimate the output of their oscillator, leading to disagreement with other researchers that impedes the progress of the field as a whole. This is a primary reason for the “standardization” that has occurred in nearly every RF band below the THz region over the past 50 years. Unfortunately, the THz field is still a bit too primitive to create such standardization, although there are certain efforts in this direction. If sensitive enough and spectrally uniform, the pyroelectric detector has a good chance of becoming a THz standard in the next few years. The sensitivity requirements are roughly NEP’ ~ 0.1 nW/Hz ½ , and NE T’ ~ 1.0 K/Hz ½ . Both are comparable to the THz sensitivity of the best Golay cells. But the pyroelectric detectors are much more rugged, cost much less (< 10%), and are amenable to fabrication in one- or two-dim arrays. Judging from how important uncooled thermal detector arrays (so-called “focal plane” arrays) have been in the mid-IR bands, a room-temperature THz array is an exciting possibility. Laboratory Procedure The experiments will all be carried out in the Laboratory of 2209 Engineering Sciences Building. Each student will be assigned their own pyroelectric detector, a Model SPH-45 (manufactured by Spectrum Detector, Inc.) mounted in a TO-5 can. The detector is a single- crystal LiTaO 3 capacitor with a front-side chrome electrode that doubles as the absorbing layer.
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