Integrated inductor/capacitor (L-C) circuits are well known in the art. L-C circuits are most often provided for use in high frequency oscillators or filter circuits acting to provide a high quality factor or "Q" for initiating oscillation or feedback.
An integrated L-C tank circuit, such as used with an integrated voltage controlled oscillatory (VCO) is most often formed using a thin film inductor in parallel with a series combination of an metal-insulator-metal (MIM) capacitor and either a voltage dependent metal oxide semiconductor (MOS) capacitor, varactor diode or voltage variable capacitor using a high K dielectric. This is best described in U.S. Pat. No. 5,173,835 herein incorporated by reference. These three components are designed and connect in a way to minimize parasitic interconnection resistance with the tank circuit, providing a substantially high Q resonator.
There is currently an emerging presence of integrated inductors with a high Q in the 1 Gigahertz (Ghz) frequency range and higher. These inductors typically have a Q of 15 to 30 and are integrated on the chip or integrated circuit (IC). It has recently been noted that a thin film spiral inductor consisting of several turns of line loosely wrapped about an open center area provides a higher Q than a comparable value inductor consisting of several turns tightly wrapped about a center. In both structures, a cross-under or cross-over metalization is required to connect the inner turn of the inductor to an outside connection. Because the cross-under metal is thin layer, aluminum alloy is often used in the integrated circuit (IC) fabrication process as compared with a thicker plated copper film which is preferred for the inductor. As can be recognized, this adds a significant resistance that negatively impacts the Q of the circuit. Thus, one reason for the higher performance of an "open" style inductor is that the cross-under required is shorter since it crosses under the inductor with fewer turns.
As seen in prior art FIG. 1 is a schematic diagram of a typical L-C resonator 10 illustrates an inductor 11 in parallel with a combination of a fixed capacitor 13 and voltage variable capacitor 15 forming a resonator. Resistors 17, 19 and 21 are used to control bias voltages in the resonator 10. It will be evident to those skilled in the art that depending on the parallel circuit connection between the inductor 11 and capacitors 13, 15, a cross-over resistance will be created that is located substantially within the tank i.e. the between the inductor capacitor parallel combination.
Thus, it is often necessary to place components in a manner to provide space and Q efficiency. To maximize the Q of the tunable varactor (VVC) element and that of double-poly fixed value capacitors (DPC) used as components in the resonator, an interdigitated finger structure can be employed in order to reduce the resistance of contacting the semiconductor material that includes the capacitor's bottom electrode. The desirable length of fingers would be similar to the length of the cross-under runner needed for a typical open center inductor. However, unless the fingers are positioned in the correct way, cross under resistance will be high, and negatively impact the operation of the resonator.
Therefore, the need exists for a resonator architecture structure that is space and loss efficient by effectively eliminating cross-under and parasitic interconnection resistance from the resonator by selectively positioning components in a predetermined fashion.