Memory elements are provided that are immune to soft error upset events when subjected to high-energy atomic particle strikes. The memory elements have nonlinear high-impedance two-terminal elements that restrict the flow of discharge currents during a particle strike. By lengthening the switching speed of the memory elements, the presence of the nonlinear high-impedance two-terminal elements prevents the states of the memory elements from flipping during discharge transients. The nonlinear high-impedance two-terminal elements may be formed from polysilicon p-n junction diodes, Schottky diodes, and other semiconductor structures. Data loading circuitry is provided to ensure that memory element arrays using the nonlinear high-impedance two-terminal elements can be loaded rapidly.