Performance of 1Vlicromechanical Tuning Elements in a 620 GHz Monolithic Integrated Circuit

The submillimeter wave performance of micromechanical tuning elements called sliding planar backshorts (SPB's) is demonstrated in a quasi-optical monolithic integrated circuit. A substrate-lens is used to focus incident radiation onto a circuit consisting of a full-wave resonant slot antenna and a thin-film bismuth detector, joined by coplanar waveguide (CPW) transmission lines with integrated SPB's. The CPW lines act as tuning stubs with electrical lengths which can be varied by mechanically adjusting the position of the SPB's. Two SPB's are used, one to create a variable series reactance in between the antenna and detector, and the other to create a variable susceptance in parallel with the detector. Microwave measurements for a scale model of the SPB show it to have a return loss of as little as 0.02 dB, and less than 0.5 dB over a 30% bandwidth. Measurements at 620 GHz indicate that the micromechanical SPB's perform consistently with the model, and the two tuning elements are used to vary the response of the detector over a range of nearly 15 dB. The impedance matching capability provided by the SP13's allow a circuit of this type to accommodate a wide range of planar submillimeter wave antennas and devices without advance knowledge of their exact electrical characteristics. Such tuning elements can be useful for characterizing components in developmental circuits, and for optimizing the in-use performance of various submillimeter wave integrated circuits.