Investigation Of Quantum Dot And Nanocrystal-based Nonvolatile Floating Gate Memory

As the continued increasing of semiconductor integrated degree and the further scaling down of feature sizes of semiconductor devices,the nonvolatile memories based on traditional continuous floating gate are facing severe challenges which mainly is the charge leakage caused by the thinner tunneling layer.The nanocrystal floating gate memories enable the size to be further reduced,improve the programing speed and endurance capability due to the realization of discrete charge storage.The nanocrystal floating gate memories are expected to replace the conventional floating gate memories,so they get a lot of attention.In this dissertation,the structure,market and development of memories were thoroughly introduced at first,then the working mechanism of floating gate memory was carefully analyzed.To further improve the performance of memories,the dissertation studied systematically about the nanocrystal floating gate memories in two aspects that are the selection of channel material and the structure construction of floating gate.The specific researches are as followed:1.By employing all inorganic CsPbBr₃ perovskite quantum dots as channel material,gold nanocrystals and PMMA as floating gate and tunneling layer respectively,the all inorganic perovskite quantum dots-based nanocrystal floating gate memory was prepared.From the output and transfer characteristic measurement,the memory window of 2.4V was obtained at±5V programing/erasing voltage,which demonstrated that the employment of ambipolar quantum dots could increase the memory window.Besides,the retention time and endurance capability of the prepared memory were improved as well due to the stability of CsPbBr₃ quantum dots.After 10⁷ s,the memory window could still be distinguished clearly.The performance of our memory kept in good condition through 200 programing/erasing cycles.2.The gold nanocrystal and graphene oxide were used to build double floating gate memory.The graphene oxide sheets could reduce the roughness of tunneling layer surface when they were spin coated on the gold nanocrystals.Meanwhile,the graphene oxide has plenty of groups and defects with which the gold nanocrystals could trap more charges to increase the memory window.From the electrical measurement,as-prepared double floating gates memory achieved a big memory window of 2.02V at the programing/erasing voltage of±10V.what's more,the double floating gates structure provided a high energy barrier caused by the different energy level between upper floating gate and lower floating gate,as a result of which the retention capability was getting better.The results showed that the memory window kept constant basically after10⁵ s.Because of the excellent performance,double floating gates memory based on inorganic quantum dots has a great potential to substitute conventional floating gate memory.