基于高K浮栅的有机非易失性浮栅存储器件研究

Recently organic flexiable electron devices are extensively investigated due to their low-cost,large area fabrication, flexibility etc. Organic nonvolatile memory is one of the emerging and very important application directions for organic devices. The key problems for its commerical production are high operation voltage and poor long-term stability of the devices. High-K materials are believed to be effetive in reducing their operation voltages. However the high leakage current in the gate insulator layer greatly degraded its long term stability. Therfore to find a high quality insulator layer with high capacitance and low leakage current density is still a big challenge. In this project, we propse high-K materials to replace the conventional Au nanocrytals as the floating gate in the memory device. The advantages of using High-K materials as the floating gate are : 1) It can be used as a flaoting gate to storage charges; 2) It can also be used as a thick insulator layer to drease the leakage current while without degradation of the total gate capacitance density. Therefore devices with low operation voltage and long term stability can be expected. Different high-K floating gate materials with their corrsponding control oxide and tunneling oxides will be fabricated, and their device memory characteristics will be studied comparatively. Through the quantative study on the interfacial structure, band structure among high K floating gate/high k tunneling oxide/organic semiconductor and optimzation of the processing paratemers for film and device fabrication, we will try to clarify those physical mechanisms responsible for their long term stability and discover one to two groups of high K flaoting gate/high K cotrol and tunneling oxides material systems, which can enable the nonvolatile organic memory devices to operate in a low voltage with a long term stability. This project will contribute to provide some useful experimental results and theoretical guidance for the future commercial productions of organic nonvolatile memories.

有机非易失性浮栅存储器目前面临的关键问题是高操作电压和器件的长期稳定性。在器件中引入高K材料作为控制和隧穿层可以有效地降低其工作电压，但栅极漏电流影响了器件的长期稳定性。因此如何获得高电容密度和低漏电流的绝缘栅介质结构是实现其低压稳定工作的一个难题。本项目尝试以高K材料取代金量子点作为器件中电荷存储的浮栅层，其优点是高K浮栅层既可以存储电荷，又可以用作绝缘介质来降低栅极的漏电流。项目拟在有机半导体上制备具有不同介电常数和能带结构的高K浮栅层/高K控制隧穿层体系的器件，理论和实验结合，通过定量表征其不同材料组合体系的电学性能、界面结构和高K浮栅/高K隧穿/有机半导体相互之间的能带结构，优化薄膜材料和器件的制备工艺，力争从实验上确定一至二组同时具有高电容密度和低漏电流的高K浮栅/高K控制隧穿层材料体系，可以使有机非易失性浮栅存储器件低压长期稳定工作，为加速其商业化提供有益的实验结果和理论指导。

电荷俘获型有机浮栅存储器件是一类非常重要的柔性信息存储器件。不仅具有非破坏性读出、集成密度高等目前市场上主流的非易失性存储器产品NAND 闪存的所有优点，而且具备柔性可折叠、大面积制造、低成本等柔性电子器件的优点，是未来非常具有应用前景的一类新型电子器件。虽然经过了近年来的广泛研究，有机浮栅存储器件的商业化生产仍然面临高工作电压和长期稳定性差等诸多挑战。 .项目采用高介电材料来取代金量子点作为有机非易失性浮栅存储器的电荷存储层，以实现低压驱动和高可靠有机薄膜晶体管存储器件。主要开展了如下工作：.1)发展了一种MHOS (Au-HfO2-SiO2-Si)结构电荷俘获型存储器，直接利用HfO2薄膜内的缺陷来俘获和存储电荷，所制备的器件具有非常显著的存储效应和长期可靠性；.2) 采用HfO2/高聚合物驻极体杂化双电荷俘获层体系，制备了高性能的有机存储器件：a) 实现了低压工作(擦写脉冲电压8 V ,宽度<10 ms)。当前绝大部分报道的有机存储器件的工作电压都在数十伏，脉冲宽度大于1s。b) 具有优异长期稳定性。沟道开关电流比经过大于10^4 s保持测试，仍然在2.6×10^4；c) 良好的反复擦写能力。经过2000次反复擦写，器件保持了4.1×10^3的沟道电流开关比；.3) 制备了一种MATS(Metal-Al2O3-TiO2-Al2O3-Silicon)存储器件结构, 展示了优异的电荷存储效应和长期电荷保持能力。利用XPS光电子能谱确定了不同高K材料之间的电子能带结构; .4) 探讨了存储器件中沟道电荷输运对其存储性能的影响。发现少数载流子在沟道中的横向电荷输运对器件存储特性具有非常重要的影响。.5）研究了有机半导体微结构和金属电极/有机半导体界面对有机薄膜晶体管电学特性的影响。发现并五苯的有序度和缺陷密度是影响器件直流和高频响应的重要机制。 .6）基于未来柔性电子的需求，项目也探讨了化学液相法低温制备高介电材料的研究，并成功在柔性衬底上制备了可低压驱动的柔性薄膜晶体管。 .本项目的工作表明，高K栅介质材料作为电荷俘获材料，在未来高性能(低驱动电压、低能耗、高可靠性)有机柔性非易失性存储器件中具有广阔的应用前景。.