SnO双极性薄膜晶体管和反相器的载流子注入机理研究

The effective carrier injection between the metal-semiconductor contact is governed by the barrier height, thus it is one of key scientific problems to investigate the efficient and balanced carrier injection existed at the interface between the source/drain electrode and semiconductor channel, in order to research and develop ambipolar thin-film transistors (TFTs) and ambipolar inverters. This project will focus on the well planned research objectives, highlighted as the interface between source/drain and SnO channel, SnO-based ambipolar TFT and ambipolar inverter, to study the hole and electron injection issue by means of modulating the carrier injection barrier height. The approving project implementation is based on uncovering the physical mechanism to tune the barrier height, seeking out the technological approaches to improve the matched injection for both the electrons and holes, clarifying the mechanism of the band alignment between the Fermi level of source/drain electrode and the valence (conduction) band of SnO, making clear the operating principle of SnO ambipolar TFTs, and successfully constructing ambipolar inverters with high gain. On one hand, the research content is a new argument in a sense, since either the experimental data or the related mechanism about the carrier injection in the SnO-based ambipolar TFTs is far from enough to debate in this research community; on the other, the well-designed research method is original, featuring that there is a repeating and self-checking feedback process among the established theoretical prediction model, the real model based on the experimental data, and the extracted performance data from the devices. It is feasible to provide and enrich the theoretical basis to describe the dual carrier injection upon the project implementation, which has important significance for exploring high performance ambipolar TFTs as well as CMOS-like logic circuits.

金属/半导体接触的势垒高度决定了载流子的有效注入，因此载流子在源漏/沟道界面处的高效、匹配注入是研发双极性薄膜晶体管和双极性反相器的关键科学问题。本项目以源漏电极/SnO界面、双极性薄膜晶体管和反相器为研究对象，以调控载流子注入势垒高度为研究手段对空穴和电子的注入问题进行研究，揭示调控载流子注入势垒高度的物理机制，探索改善电子和空穴匹配注入的技术途径，阐明源漏电极费米能级跟SnO价带、导带之间的能带排列的规律，澄清双极性薄膜晶体管的工作原理，构筑高增益的反相器逻辑单元。关于SnO双极性薄膜晶体管的载流子注入问题在实验数据和相关机理方面的工作尚属欠缺，研究内容新颖；构建载流子注入的理论预测模型、实验模型和器件性能之间相互反馈和印证的研究方案，研究方法具有新意。通过本项研究，为双极性电子学器件的研究提供载流子注入的理论依据，对研发高性能双极性薄膜晶体管以及类CMOS逻辑电路有重要意义。

开展氧化物双极性薄膜晶体管研究，突破氧化物在互补型电路应用方面的瓶颈，是近年来最为关注的课题之一。本项目以源漏电极/SnO 界面、双极性薄膜晶体管和反相器为研究对象，以调控载流子注入势垒高度、背沟道表面态为研究手段对载流子的注入与输运问题等关键科学问题进行研究。. 首先，采用反应磁控溅射技术、后退火处理和表面钝化三种工艺相结合，通过系统调控工作气压、溅射功率、氧分压等制备条件，获得了p型和n型SnOx薄膜制备的工艺区间，实现其载流子浓度在大范围内可调；获得了单相p型SnO多晶薄膜，最大室温迁移率约3.6 cm2 V-1 s-1。归纳整理出了制备工艺—薄膜结构、不同价态Sn的百分含量—光学（折射率、带隙、透过率） 、电学（载流子迁移率、浓度和电阻率）性能的对应关系，确定了薄膜导电极性转变的物理机制，即受主与施主缺陷之间的补偿效应。. 其次，系统研究了工作气压、溅射功率、氧分压、沟道厚度、退火时间对薄膜晶体管性能参数的影响规律。特别地，通过覆盖钝化层调控背沟道表面态的方法，可以调控SnO薄膜晶体管从单极p型到双极性工作模式的转变，最优性能为：n区和p区场效应迁移率分别为1.62和0.61 cm2 V-1 s-1。基于双极性薄膜晶体管构筑了双极性反相器，其增益超过100，在未封装的情况下在空气中可长期工作。此外，研究了源漏电极金属功函数对双极性SnO薄膜晶体管性能的影响，发现功函数的变化对器件的对称性影响不大，推测可能是SnO材料表面存在较高浓度的表面态。在源漏电极与SnO沟道之间插入合适的修饰层（如薄层Si和Al2O3），有利于钝化SnO表面态，提高空穴注入势垒高度，从而降低关断电流、提高开关比并改善对称性。. 最后，通过晶体管器件模拟的方法获得了SnO带隙中亚带缺陷态（包括次能隙态和深能级态）密度随能量的分布图。弄清了在横向和纵向电场同时存在情况下源/漏电极费米能级跟SnO价带、导带之间能带排列的规律，以能带结构示意图的形式阐述了SnO双极性薄膜晶体管的工作原理。