Basic Research on Electronic Properties and Memory Effect of Silicon-Quantum-Dot Array and Its Application to Memory Device

研究了硅量子点阵列的电学和光学性质，揭示了量子约束效应。通过电学特性分析，证实了硅量子点（QD）层作为浮栅嵌入金属氧化物半导体（MOS）结构的存储操作。本文对硅量子点的电子充电特性的研究成果进行了总结。在室温下证明了硅量子点浮栅mosfet的存储工作。在mosfet的漏极电流与栅极电压（Id-Vg）特性中观察到滞后和电流颠簸，导致Si QD浮栅的电子充电。在量子点放电后，观察到Id-t特性的阶梯状变化，表明量子点的带电态通过亚稳态达到最终稳定状态。进一步证实，施加正栅极脉冲可使硅量子点发生多能级电子充电。定量研究了硅量子点浮栅MOS电容器的电学特性，揭示了硅量子点的电子充放电特性。在室温下，零偏压下量子点的充电态具有双稳性。在零栅极偏置附近，每个点保留的电子数估计约为1。实验结果还表明，与均匀板浮栅相比，对量子点进行写入操作后测量到的平带电压位移更大。进一步指出，带电点间的库仑斥力控制着量子点浮栅MOS结构中的电子放电动力学。

Electrical and optical properties of silicon-quantum-dot array have been investigated to reveal the quantum confinement effect. The memory operation of metal-oxide-semiconductor (MOS) structures in which a Si quantum dot (QD) layer is embedded as a floating gate has been confirmed by analyzing the electrical characteristics. The research results on electron charging characteristics of Si QDs are summarized as follows.1. The memory operation of Si QD floating gate MOSFETs has been demonstrated at room temperature. The hysteresis and the current bumps were observed in the drain current versus gate voltage (Id-Vg) characteristics of the MOSFETs, resulting in the electron charging of the Si QD floating gate. After discharging of QDs, stair-like changes in Id-t characteristics were observed, indicating that the charged state of QDs reaches the final stable state via the metastable state. Furthermore it was confirmed that the multilevel electron charging to Si QDs occurs by applying a positive gate pulse.2. The electrical characteristics of Si QD floating gate MOS capacitors have quantitatively investigated to revel the electron charging and discharging characteristics of Si QDs. The bistability of the charging states for the quantum dots was confirmed around zero bias at room temperature. The number of retained electron per dot around zero gate bias was evaluated to be approximately one. It was also demonstrated that the measured flat-band voltage shift after writing operation to QDs is larger than the case of the uniform-plate floating gate. Furthermore it was suggested that Coulombic repulsive force among charged dots controls the electron discharge kinetics in a QD floating gate MOS structure.