Quasi-Integrated Planar Schottky Barrier Diodes for 2.5 THz Receivers

Schottky barrier diodes (SBDs) remain an important device for detecting and mixing at terahertz frequencies, particularly in atmospheric remote sensin g and plasma diagnostics. The hydroxyl radical (OH), which plays a critical role in all cycles of ozone destruction and also acts as an oxidant for harmful gases in the atmosphere, has first significant spectral emissions at 1.8 and 2.5THz. Here we will present a new SBD configuration called a quasi-integrated planar (QUIP) SBD, to be used in 2.5'rHz receivers for measuring spatial distribution of the hydroxyl radical. Submillimetre wave and terahertz applications require sub-micron anode SBDs. Traditionally, whisker-wire contacted diodes, with Schottky and Ohmic contacts at opposite sides of the device, are used in open structures such as corner-cube mixers. Here we propose a "planar" SBD with Schottky and Ohmic contacts on the same side of the device. Instead of mounting a small diode chip on a post, a large chip is used to form the wall of a waveguide which feeds a corrugated conical feedhorn antenna. A small area of this chip consisting of SBD anodes is placed near the feed of the antenna, while the rest of the chip provides the Ohmic contact and acts as a top cover for the waveguide. Thus, the diode is "integrated" into the mixer block. This greatly simplifies mixer block fabrication and assembly, and also minimises losses between the antenna and the diode by allowing the SBD contact to be placed at the feed of the antenna. The diode is then contacted using a planar whisker with an integrated RF/EF filter. QUIP SBDs with anode diameters of 0.25 0.31.tm have been successfully fabricated and mounted into a mixer block for RF performance evaluation. INTRODUCTION Waveguide devices are now being used with some success in the terahertz region [1,2] and waveguide mixers are now showing comparable performance to the more common corner cube mixer configuration at frequencies as high as 2.5THz. The waveguide devices have the additional advantages of rugged construction, in-situ tuning capability and radiation properties that are isolated from the diode embedding circuit. However, the specialist fabrication level of machining required combined with