Aspect ratio design consideration for radiation-hard CMOS inverters

It is known that the device parameters of Metal-Oxide-Semiconductor-Field-Effect-Transistors(M0SFETs) after irradiations are changed due to the trapping of oxide charges and the generation of interface states. These changes cause the degradation of devices and therefore the malfuction of circuit performance. Generally, radiation introduces a negative shift in threshold voltage VTH and a reduction in transconductance G_M. However, for nMOSFETs, a large amount of radiation-induced interface states will cause a "rebound"(or superrecovery) behavior in V_TH. That is to say, the threshold voltage shifts of nMOSFETs may become positive after irradiations when the total dose of irradiation is large enough. Since a negative or a positive threshold voltage shift will cause a different current driving capability in nMOSFETs, the dependency of VTH on the total dose of irradiation is of course important to the circuit design. In this work, an empirical equation describing the above dependence is founded and is applied to the design consideration in radiation hardness for devices with difference parameters.