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，揭示了量子限域效应。通过分析量子点作为浮栅的MOS结构的电特性，证实了其存储操作。本文对硅量子点的电子荷电特性进行了研究，主要成果如下：1.在室温下，硅量子点浮栅MOSFET的存储操作已被证明。在MOSFET的漏极电流-栅极电压（Id-Vg）特性中观察到滞后和电流凸起，导致Si QD浮栅的电子充电。量子点放电后，Id-t特性曲线呈现阶梯状变化，表明量子点的荷电态经过亚稳态到达最终稳定态。此外，还证实了通过施加正的栅极脉冲，可以对Si量子点进行多级电子充电.定量研究了硅量子点浮栅MOS电容的电学特性，揭示了硅量子点的电子充放电特性。量子点的电荷态的双稳态在室温下被证实在零偏压附近。在零栅极偏压附近，每个点的保留电子数被评估为约为1。它还表明，所测量的平带电压漂移后写入操作到量子点是大于均匀板浮栅的情况下。此外，它被认为是库仑排斥力之间的电荷点控制的QD浮栅MOS结构的电子放电动力学。

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.