Design and analysis of a three-dimensional millimeter-wave frequency-shift based CMOS biosensor using vertically stacked spiral inductors in LC oscillators

This paper proposes a novel millimeter-wave frequency-shift based CMOS biosensor capable of providing three-dimensional (3D) resolution. The vertical resolution from the sensor chip surface can be obtained by using vertically stacked on-chip inductors of LC oscillators in dual metal layers, which enables 3D detection of biomolecular target. The LC oscillators with spiral inductors stacked in upper and lower metal layers produce different shifts in the frequencies from the desired resonant frequency of 60 GHz due to frequency dependent complex relative permittivity of targeted bio-molecular structure. The vertical resolution of the sensor can also be improved by changing the supply voltage. The effectiveness of the proposed approach is verified by fabricating a test chip in 65 nm CMOS process. The measurement results show variation in the resonant frequency shifts due to upper and lower spiral inductors of LC oscillators which demonstrates the capability of the proposed biosensor to provide 3D resolution.