| In the era of interconnected everything,with the unprecedented rapid dissemination of information and explosive growth of data,memory plays an increasingly important role in people’s work and life.In 2022,memory has accounted for one-third of the global semiconductor market.In addition,transparent,large area and flexible electronics are gradually becoming an important development trend in the future.Compared with traditional silicon-based devices,devices based on metal oxide thin film transistors(MOTFTs)not only have the characteristics of transparency,but also has many advantages,such as large area or flexible substrate,low process temperature,low cost and ultra-low power consumption.Among them,ZnO TFT has been deeply researched because of its high mobility,high stability and low cost,and in the previous work,ZnO based logic circuits have been used in small integrated circuits,such as RFID and fingerprint sensors.However,in the field of transparent and flexible electronics,the non-volatile memory is still lacking.Therefore,developing a compatible process of memory device and logic circuit to realize a NAND flash memory system is necessary and feasible.In response to the above issues and the characteristics and advantages of ZnO materials,this thesis will carry out the following work:1.This article develops a transparent and high-performance ZnO-TFT preparation based on the hydrothermal ALD method,successfully achieving the preparation and testing of ZnO-TFT devices.The test results show that ZnO-TFT exhibits excellent electrical performance,including high mobility and a switching current ratio exceeding 10~8.In addition,this experiment solved the problem of poor stability of ZnO-TFT through a wrapped gate oxide layer structure and multiple annealing processes.The device also demonstrated excellent reliability in multiple tests such as uniformity,retention performance,and gate pressure stress testing.2.Based on the ZnO-TFT in the above work,the transparent nonvolatile memory was fabricated by using one-step atom layer deposition of aluminia tunneling and ZnO charge-trap layers.The test results show that the ZnO-based flash memory exhibits a memory window of up to 15V and excellent fatigue resistance and retention performance.Furthermore,the relationship between the geometrical size of the charge-trapping layer and the memory window is explored.The devices with different memory windows can be controlled simply by designing the area of their trapping layer without any external process,which is much beneficial to the low-cost process fabrication of the memory array and driving circuits,since the memory and switch/digital transistors can be fabricated at the same time.The transparent floating gate memory with the ZnO charge-trap layer has great potential for application of 3D,transparent or multi-value memory.3.This work develops a simple compatible process to fabricate NAND flash memory and driving logic circuits simultaneously based on atomic layer deposition ZnO TFTs,in which the active layer and the floating gate layer both are ZnO thin films.The test results show that ZnO based flash memory has a storage window of 9.8V,long retention time and even excellent multi-level data(2 bits)writing and reading ability.Based on this flash memory,1×4 NAND flash memory array was fabricated and verified.In addition,a novel modulated enhancement/flash(E/F)inverter is proposed and used on the logic circuits.Finally,a fully transparent flash system with NAND memory cell and driving logic circuits is realized successfully,which has great potential for application of 3D integrated circuits,transparent or flexible electronics. |
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