The “Stealth” decoupling capacitor

A new method of construction for a decoupling capacitor with excellent high frequency properties is described. Previous work has demonstrated the poor high frequency performance of conventional chip capacitors, because of their high internal inductance. Capacitors commonly used for decoupling in systems with clock frequencies in the tens of MHz, and thus substantial noise components in the hundreds of MHz, are self-resonant below 25 MHz. They are useless for maintaining low power supply impedance at frequencies above 100 MHz. The new capacitor construction allows capacitors of 25-50 nF to maintain low impedance into the range of several GHz. These capacitors will be useful for both single chip and multichip packaging. Because of very flexible connection options, low inductance connections into package power distribution planes are easily realized. This paper presents the construction details of the new capacitor, as well as test results on devices which have been fabricated. Materials are discussed, and manufacturing methods which should allow the production of the capacitor at very low cost are presented. Various means of using the capacitor in packages are illustrated. Because at high frequencies everything goes in and nothing comes out of the new capacitor, it has been nicknamed “Stealth”