Terahertz tuneable filters made by self-releasing deep dry etch process
A novel tuneable filter has been designed for terahertz frequencies, and a self-releasing batch-fabrication process developed for implementing these devices. The filter is made up of two silicon plates that have been patterned with two orthogonal layers of rods and integral mounting lugs and coated with gold. Deep reactive ion etching is achieved with an inductively coupled plasma and a time-multiplexed SF6/O2 and C4F8 chemistry. A deliberate slight over etch is introduced to ensure that the plates separate from the surrounding substrate. It has been demonstrated that the fabrication process is wavelength-scalable by the production of plates for filters operating at 140 GHz (525 ?m thick wafer) and 350 GHz (200 ?m thick wafer). The performance of the 140 GHz device has been measured in good agreement with finite-difference time-domain simulations.
terahertz tuneable filter silicon inductively coupled plasma metallic photonic crystal