TABLE OF CONTENTS Inductors are key elements in designing high-frequency integrated circuits and have been extensively used in both radio frequency integrated circuits and clock recovery circuits. Traditionally, the use of off-chip inductors was dominant because of their high quality factor Q. However, recently, different types of inductors, including bond wires and on-chip spiral inductors, have been extensively investigated and demonstrated for integrated circuits. Bond wires commonly used for connection between chip and package have been proposed to replace low- Q on-chip inductors to obtain better performance because their quality factor Q can be as high as 40 (Steyaert and Craninckx, 1994). This can definitely help in reducing power consumption and improving the phase noise of VCOs. Nonetheless, bond wires have big problems with accurate modelling, and with their reliability and repeatability, which make them less attractive.
Compared with off-chip inductors and bond wires, on-chip spiral inductors are much more desirable because they can enable single-chip integration. The reproducibility from chip to chip using an on-chip inductor is better than utilizing bond wires. However, the major problem with on-chip inductors is their high loss or low quality factor. Modern CMOS technology with an epitaxial layer makes use of a heavily doped substrate (approximately 0.01 ?-cm) to minimize the latch-up problem. Nevertheless, the magnetic field generated by on-chip inductors induces eddy currents in the substrate and increases the loss to the substrate. Etching out the substrate underneath the spiral coil can alleviate the loss problem (Chang, Abidi...
