Visualization of electrons and holes localized in gate thin film of metal SiO2–Si3N4–SiO2 semiconductor-type flash memory using scanning nonlinear dielectric microscopy after writing-erasing cycling

We applied scanning nonlinear dielectric microscopy and succeeded in clarifying the position of the electrons/holes in the gate SiO2–Si3N4–SiO2 (ONO) film of the metal-ONO-semiconductor-type flash memory after the write-erase cycling operation. The electrons were found in the Si3N4 part of the ONO film. The holes, on the other hand, were found in the Si3N4 film as well as at the bottom SiO2 film. We also showed that neither injected electrons nor injected holes accumulate during the write-erase cycling. This indicates that the remaining carrier in the ONO film is space charge and would not be expected to continue to increase infinitely with repeated injections and that most of the injected carriers would recombine with each other. After recombination, they exist separately and are electrically neutralized only.