以氧化鉿為介電層的電阻式記憶體之電性與分析

Abstract

在本篇論文中，我們探討以氧化鉿為介電層的電阻式記憶體的電性。首先我們製備有著不同氧化鉿厚度的Ni/HfOx/TiN以及TiN/Ti/HfOx/TiN RRAM元件，並且量測在不同限流(compliance current)以及reset時施加不同大小偏壓對元件電性的影響。接著我們探討不同厚度的鈦緩衝層對元件造成的影響。此外，為了瞭解造成overshoot current的根源，我們利用外接1T1R的量測配置來量測Ni/HfOx/TiN RRAM元件的電性。而為了探討電流的傳導機制以及傳導絲(conductive filament)的性質，我們進行了電流-電壓關係曲線的擬和(fitting)以及變溫量測。 我們觀察到限流的大小對於低組態的電阻有著相當大的影響，並且我們也觀察到在reset時施加不同大小偏壓會影響高組態的電阻以及之後set所需要施加的偏壓大小。這指出一個RRAM元件的電流開關比(on/off ratio)以及操作功率(operation power)是可調變而非定值的。另一方面，在RRAM元件中置入鈦緩衝層對forming所需要施加的偏壓有著相當大的影響，也因此為了使元件有穩定的切換特性，鈦緩衝層以及氧化鉿的厚度是需要被優化的。此外，使用外接1T1R的量測配置去進行量測還是觀察到了overshoot current，這表示去除量測配置中存在的寄生電容是相當重要的。最後，我們觀察到使用不同電極的RRAM元件有著不同的電流傳導機制，也就是說使用不同的電極會影響RRAM元件中傳導絲的性質。

In this thesis, we explore the electrical characteristics of HfOx based-RRAM cells. First, we fabricated Ni/HfOx/TiN and TiN/Ti/HfOx/TiN RRAM cells with various HfOx thickness and investigated the electrical characteristics with various compliance currents and stop voltages during reset. Second, we investigated the effect of Ti buffer layer thickness of TiN/Ti/HfOx/TiN RRAM cells. Third, to investigate the origin of overshoot current during forming and set operations, we measured the electrical characteristics of Ni/HfOx/TiN RRAM cells with external 1T1R configuration. Finally, I-V curves fitting and measurements done at various temperature were carried out in order to investigate the conduction mechanisms and the properties of conductive filaments. We observed that the compliance current has significant influences on LRS resistance. We also observed that the stop voltage during reset operation has influences on the HRS resistance and the set voltage in the following set operation. This indicates that the RRAM cells have tunable on/off ratio and operation power. On the other hand, the insertion of a Ti buffer layer into RRAM cells influences the forming voltage significantly, and thus the thicknesses of the Ti buffer layer and HfOx thin films must be optimized for stable the switching behaviors. Besides, the overshoot current was still observed with the external 1T1R configuration, indicating the importance for eliminating the parasitic capacitance within the measurement configurations. Finally, we observe different current conduction mechanisms in different logic states for the RRAM cells, and the mechanisms are found to be closely related to the electrode materials. From which it can be concluded that the properties of conductive filaments depend on the electrodes of the RRAM cells significantly.