Compact helical delay lines embedded in a silicon

Small size quasi-lumped-element helical delay lines are presented. The device is disposed in a dielectric-air-metal (DAM) cavity, which consists of a SiNx membrane above a 30-μm-deep hollow cavity made by silicon micromachining process. The delay line is composed of fine segments of a one-turn inductor and a tiny shunt capacitor whose electrode slips into under the ground pattern. The fineness of the segments realizes linear frequency responses up to more than 40GHz, and the optimal LC values of the segment drastically reduce the wavelength. The compact delay line is useful to reduce the size of microwave components such as phase shifters or feedback amplifiers. The 7-turn, 12-turn and 17-turn helical delay lines were fabricated. The 12-turn delay line showed 450°-delay for 1050-μm-long line with 2.5-dB loss at 30 GHz.