Bond-Pad Charging Protection Design for Charging-Free Reference Transistor Test Structures

A bond-pad charging protection design for charging-free reference transistor test structures was examined. This paper concludes that truly charging-free reference transistors cannot be realized with the one conventional bond-pad charging protection design of protecting transistor gates only. This, however, can be achieved by simultaneously protecting all terminals of the reference transistors. The simulations, in this paper, reconfirm the earlier important experimental conclusion that placing protection device(s) at transistor gates may inflict severe damage to transistor gate oxides instead of protecting them. The implication of the above suggests that attention may be required in a circuit layout design stage for those transistors which gates begin to connect, at high metal layers, to highly efficient leakage paths, such as protection devices, n-type source/drain diffusion regions, and VSS bus lines, which tend to pull transistor gates to low potentials during a backend integrated-circuit manufacturing process. This paper proposes an optimum bond-pad charging protection design for the truly charging-free reference transistor test structures by considering a minimum usage in a layout space and minimum gate oxide stress in the fuse zap-off process.