Coaxial shield for a semiconductor device

Abstract

In a semiconductor device, an on chip coaxial cable reduces noise from adversely affecting a signal transmitted by a signal conductor. The signal conductor lies within and is isolated from a second conductor. A dielectric, such as oxide, may provide isolation. In multi level metal devices, such as double level metal devices, the signal conductor can be formed of a first level of metal and a portion of the second conductor can be formed of the first level of metal also. After forming a first level of metal, it is patterned to separate the first signal conductor from a first conductive noise shield and a second conductive noise shield. A second level of metal and a conductive level of material such as polysilicon can complete formation of the second conductor. Oxide insulators can provide isolation between the signal conductor and the second conductor by lying between the top conductive noise shield and the signal conductor and by lying between the bottom conductive noise shield and the signal conductor. Interlevel connectors such as vias and contacts in the oxide insulators provide electrical coupling between the various levels of the second conductor. A signal carrier is centered inside and insulated from an outer conductor on a semiconductor chip and provides an on chip coaxial cable that protects the signal carrier from noise disturbances. The second conductor may be electrically biased, such as to ground, by connecting the bottom conductive noise shield to a voltage source to enhance noise reduction.