Micromachined CMOS E-band bandpass coplanar filters

In this work, E-band CMOS coplanar filters, whose initial design is made according to quasi- TEM-approximation-based analytical models, are implemented. To study the substrate effects, the CMOS-compatible inductively coupled-plasma (ICP) deep trench technology is used to selectively remove the silicon underneath the filter completely. For the filter with top metal thickness of 0.93 μm after the backside ICP etching, the results show that the input matching bandwidth, i.e. S₁₁ below - 10 dB, moves from lower 39.8-81.4 GHz-band to higher 55.9-94.1 GHz-band, and the 3-dB bandwidth of S₂₁ moves from lower 43.5-76.3 GHz-band to higher 54.5-93.3 GHz-band. In addition, a 4.67 dB improvement [from -8.86 dB (at 58.5 GHz) to -4.19 dB (at 74.5 GHz)] in peak S₂₁ was achieved. These results show that for the design of passive coplanar devices in the E-band, the quasi-TEM- approximation-based analytical models can be used and the backside ICP etching is effective to reduce the substrate loss and parasitic capacitance.