A miniature micro-machined millimeter-wave bandpass filter by complementary metal-oxide-semiconductor compatible inductively-coupled-plasma deep-trench technology

In this paper, we demonstrate that miniature millimeter-wave band-pass filter can be obtained by replacing the traditional coplanar waveguide structures with the miniature lumped-spiral inductors and metal-insulator-metal (MIM) capacitors. To study the silicon substrate effects on the performances of the miniature spiral inductor and band-pass filter, complementary metal-oxide-semiconductor (CMOS)-process-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 and 60 GHz, respectively, for a 251.7 pH miniature spiral inductor after the backside ICP dry etching. In addition, a 0.9 dB (from -5.4 to -4.6 dB) improvement in peak insertion loss (S₂₁) was achieved for a miniature band-pass filter with 3-dB bandwidth of 47.7GHz (18.4-66.1 GHz) after the backside ICP dry etching. The chip area of the miniature band-pass filter was only 206 × 106 μm² excluding the test pads.