Buried zener diode having auxiliary zener junction access path

Abstract

A buried Zener diode has an auxiliary Zener junction access path in parallel with the force anode/cathode path. Unlike the force anode/cathode path, the auxiliary path is effectively by-passed by the current flowing between the force anode and cathode during circuit operation, so that there is no accumulation of significant resistance-current products that would otherwise mask the Zener voltage. The Zener diode has an anode region disposed in a first surface portion of a substrate. A `force` anode is formed on a first surface portion of the anode region. A `sense` anode is disposed on a second surface portion of the anode region spaced apart from the force anode. A first cathode region is disposed in a second surface portion of the substrate spaced apart from the anode region, while a sense cathode region is disposed in a third surface portion of the substrate spaced apart from each of the anode region and the first cathode region. A `force` cathode is disposed on the first cathode region and a `sense` cathode is disposed on the sense cathode region. A first N-type region is buried beneath and contiguous with the force cathode region and a second N-type region is buried beneath and contiguous with the sense cathode region. A third N-type region is buried beneath and contiguous with the force anode region. This third buried region has a first portion which defines a buried Zener junction with the anode region and extends to and is contiguous with the first buried region. A portion of the third provides a by-pass path to enable Zener voltage to be measured absent voltage drops of the main current flow path.