Design, test and simulation of self-assembled, micromachined RF inductors

Inductors are essential for fully integrated, complex RF circuits such as single chip radios. Both high Q, Q>15, and high precision, +/-2%, inductors are needed to meet phase noise specifications for on-chip VCO's and for reactive impedance matching to improve power transfer and linearity. We describe the design, test and simulation of self-assembled, micromachined inductors lifted away from the substrate by tensile stress in the metallization. The air gap reduces the capacitive coupling to the substrate, increasing both the Q and self-resonant frequency. For 2nH inductors we have measured Q similar to 14 at 2GHz, with process variation <2%. Increased temperature and current strongly increase the loss, but do not effect the inductance. The inductors are also relatively insensitive to mechanical excitation, with forces similar to 30g's required to significantly modulate the inductor loss under resonant excitation. Extensive EM simulations of this design methodolgy suggests that we should be able to reach Q>25 at 2GHz and maintain Q>10 at 10GHz. We also compare these results with state of the art fully integrated Si RFIC planar inductors.