A miniature micro-machined millimeter-wave bandpass filter by CMOS compatible ICP deep-trench technology

We demonstrate that miniature millimeter-wave (MMW) band-pass filter can be obtained by replacing the traditional eoplanar waveguide structures with the miniature lumped-spiral inductors and metal-insulator-metal (MIM) capacitors. To study the substrate effects on the performances of the spiral inductor and filter, CMOS-compatible backside inductively-coupled-plasma (ICP) deep trench technology was used to selectively remove the silicon underneath them. The results show that a 70.9% (from 5.8 to 9.91) and a 298.7% (from 2.33 to 9.29) increase in Q-factor were achieved at 40 GHz and 60 GHz, respectively, for a 251.7 pH inductor after the ICP etching. In addition, a 0.9 dB (from -5.4 dB to -4.6 dB) improvement in peak insertion loss (S₂₃) was achieved for the miniature bandpass filter with 3-dB bandwidth of 47.7 GHz (18.4 ~ 66.1 GHz) after the ICP etching. The chip area of the miniature filter was only 206 mum x 106 mum excluding the test pads.