ON THE POSSIBILITY OF STANDING WAVE RESONANCES IN THE BYPASS CAPACITOR STRUCTURE FOR WAFER SCALE PACKAGING.

High-frequency digital circuits such as GaAs E/D MESFET logic exhibit a power supply spiking noise during the charging transient for wires driven by the logic gates or pad drivers. The magnitude of this transient current is of considerable magnitude until the signal lines driven are fully charged. This charge must enter the circuit from its power supply connection. Any spurious inductance in this path can cause noise to appear in the power distribution system. Inductances as low as 40 pH can be objectionable for GaAs MESFETs. To filter this spiking noise and supply the charge needed by the transient, a bypass capacitor is usually required which has a high capacitance-to-self-inductance ratio. The easiest way to incorporate such a capacitor into the circuit is to integrate it directly into the package thus producing a slow wave structure in the power distribution system. This can create standing wave resonances in certain situations, leading to spatial nulls and peaks in the noise of the power distribution system. For GaAs circuits, the critical dimensions can be comparable to wafer size. Hence, this problem can be significant even for wafer-scale packaging. Criteria for determining when this problem will be significant are discussed and some possible solutions are proposed.