Capacitors have broad applications in the design and operation of electrical circuits. For example, capacitors have been used as noise-reduction or cancellation devices on printed circuit boards (“PCBs”) and integrated circuits (“ICs”) substrates. In some applications, capacitors may be surface-mount devices (“SMDs”), such as serving as decoupling capacitors or bypass capacitors for power input terminals. These capacitors may serve to absorb glitches, to reduce radio frequency (“RF”) noise, to stabilize power supply, or to achieve a combination of multiple or other functions.
As semiconductor manufacturing technology continues to evolve, challenges increase for devices operating at high frequencies, such as 10 GHz or more. The increase in signal communication frequency or density also may increase signaling or switching interferences. Therefore, the power delivery system of ICs may need capacitors with high capacitance to reduce noise at low frequency and to offer low impedance paths to reduce noise and interference at high frequency. For example, multiple capacitors with different capacitance may be mounted on the surface of an IC substrate or PCB to reduce noises associated with power delivery system of ICs.
Each capacitor may have its characteristic impedance. When a capacitor is coupled with a signal having an operating frequency lower than the capacitor's resonant frequency, it may still have capacitive characteristics. However, when a capacitor is coupled with a signal having an operating frequency higher than the capacitor's resonant frequency, the capacitor may exhibit inductive characteristics. That is, a capacitor's impedance may increase as the system operating frequency increases. As a result, the capacitor may have little decoupling effect at high frequencies.
To provide decoupling effects or to eliminate undesirable noises for a power supply for ICs or circuitries, a system may be parallel with multiple capacitors, such as SMD capacitors with different capacitances, to reduce noise and glitches at different frequencies. However, as operating frequencies for ICs increase, the required number of SMD capacitors also increases to cover a broader frequency spectrum. Fitting more SMD capacitors on a PCB or an IC substrate can become a challenge due to the limited surface area of the PCB or substrate, especially in the case of portable devices.
As an alternative to the SMD design, PCBs or IC substrates may be designed with embedded capacitors. The design of capacitors embedded in PCBs, in certain applications, may reduce the loop inductance of wiring paths, provide higher capacitance(s), reduce the size of electronic package, or offer additional advantages or a combination of any these advantages. However, some challenges exist in the area of embedded capacitors. For example, the greater the capacitance, the lower the resonant frequency (or the lower the capacitor's impedance curve). In other words, merely providing a larger capacitance might not be able to absorb or reduce interference issues resulted from high-frequency noises or pulses. Although embedded and planar capacitors may be cut into several capacitors designed for absorbing or reducing noises at several frequency bands, the approach may reduce the capacitance values due to reduced areas of capacitor electrodes. Therefore, challenges may exist in providing embedded capacitors suitable for higher or wider frequency coverage of the capacitors noise-reduction (or “decoupling”) effects.
The disclosed embodiments may overcome or be configured to overcome one or more of the problems associated with traditional capacitor designs.