Preparation And Properties Of Charge Trapping Memory Based On TiZrO Thin Film

With the development of semiconductor storage technology,Flash memory based on floating gate structure,as a mainstream product in the non-volatile memory market,is gradually approaching its physical limit.Therefore,the research and design of non-volatile memory with small size,fast reading and writing speed,high storage density,low operating voltage,strong data retention and endurance has become a research hotspot and trend.SONOS charge trapping memory has great potential in the application of next-generation non-volatile semiconductor memory due to its excellent scalability and high density.In addition,a large number of researches have introduced high-K materials into SONOS-type charge trapping memory to improve the storage performance of devices.In this paper,a high-k composite oxide(TiO₂)_0.2(Zr O2)_0.8(TZO)is proposed as the charge trapping layer of the device.The new charge trapping nonvolatile memory with structure of p-Si/Al₂O₃/TZO/Al₂O₃/Pt is prepared by pulse laser deposition technology(PLD).The electrical properties,microstructure and energy band structure of the device have been studied and analyzed.The effects of rapid thermal annealing on the memory window have been emphatically investigated.The main contents are as follows:1.A ceramic target with a mole ratio of TiO₂ to ZrO₂ of 1:4 was prepared.A high-k TZO composite oxide was used as the charge trapping layer,Al₂O₃ as the tunneling layer and blocking layer,successfully fabricated a new type of charge trapping memory device with p-Si/Al₂O₃/TZO/Al₂O₃/Pt structure.Al₂O₃ and TZO films were deposited on p-Si substrate by PLD technology,and the samples prepared at different substrate temperatures were tested by XRD.It is confirmed that the Al₂O₃ and TZO films grown at300?,350?and 400?are amorphous.The AFM test results show that the surface of TZO deposited at 300?and 350?has reached atomic level flatness.The RMS of TZO film deposited at 400?is 2.031nm,and the surface is rough.After comprehensive consideration,the substrate temperature of 350?was selected to prepare TZO films.2.The electrical properties of the TZO memory device were tested.The unannealed device has a memory window of 1.04V at±4V sweeping voltage.For devices undergoing rapid annealing for 90s at 800°C in anO₂ atmosphere,when the sweeping voltage is±4V,±6V,±8V,±10V,and±12V,the corresponding memory windows are 2.5V,5.2V,8.5 V,11.9V and 15.5V,respectively.The charge storage density(N_t)of the device is about1.55×10¹³cm^-2at a sweeping voltage of±12V.Then the effects of annealing temperature and annealing time on the memory window of TZO device were investigated.At a scan voltage of±8V,devices annealed at 700°C and 900°C have a much smaller memory window than devices annealed at 800°C,only 3.92V and 0.24V.On the other hand,the storage Windows of the devices annealed at 800?for 60s,90s and 120s are 7.12V,8.5V and 1.84V,respectively,and the corresponding charge storage densities are 9.61×10¹²cm^-2?8.48×10¹² cm^-2 and 2.74×10¹² cm^-2.3.By XRD analysis,it is found that after rapid annealing at high temperature,the crystallization peak of TZO film appears,which corresponds to the(003)crystal plane of tetragonal ZrO₂.The results of XPS analysis show that the peaks of Zr3d_3/2and Zr3d_5/2are shifted to the direction of low binding energy after rapid annealing at high temperature,and the migration is 0.3e V relative to that of the unannealed films.The XPS spectrum of the sample Ti is fitted by peak splitting,and it is found that there is a weaker peak at the binding energy of 454.3e V after annealing,which belongs to the Ti³⁺-O bond.It is proved that Ti³⁺and Ti⁴⁺exist in the TZO films after rapid annealing at 800?,which helps to improve the charge trapping ability of the composite dielectric.