高效能電阻式記憶體搭配場效電晶體與記憶體可靠度特性提升的研究

Abstract

In this thesis, the improvement of reliability in the transition metal oxide (TMO) based resistive switching random access memory (RRAM) device was investigated. In the first part, we fabricated the ZnO/ZrO2 double layer RRAM device for uniform endurance and high temperature retention property. The stability of resistive switching can be improved by inserting a ZnO thin film with the non-stoichiometric property between Ti top electrode and ZrO2 layer. The oxidation-reduction reaction can be easily performed on the ZnO/ZrO2 double layer RRAM device under an external bias than that on the ZrO2 single layer RRAM device. In addition, the ZnO/ZrO2 double layer RRAM device reveals the stable retention properties exhibited at higher temperature (200 0C). According to the conductive filament model, the control of oxygen ions supply determined by the ZnO inserting layer is the crucial to improve its retention property. Therefore, the ZrO2 RRAM device with an inserting ZnO layer exhibits the stable retention properties at a higher temperature (200 0C). In the second part, we fabricated the HfO2 based RRAM devices with a 1T1R cross bar structure. We discussed the decreasing of resistance in high resistive state (HRS) of HfO2 RRAM device during large endurance test. This phenomenon is due to that no sufficient oxygen ions could recombine with oxygen vacancies for rupturing the conducting filaments. Therefore, the oxygen plasma treatment method is used to increase the available oxygen ions in the HfO2 film for resistive switching. Besides, a thin HfO2 film is inserted to separate them to avoid the Ti top electrode directly absorbs the additional oxygen ions from HfO2 layer with oxygen plasma treatment. Therefore, the endurance degradation can be suppressed in the present structure. High speed (30 ns) and large endurance cycles (up to 1010 cycles) are achieved in this device structure for next generation nonvolatile memory application. In the third part, we fabricated the HfO2 based RRAM devices with a cross bar structure. We discussed the thermal instability of the HfO2 based RRAM device after annealing treatment in vacuum at different temperatures (400 and 500 C) for 30 min. The uniformity of the resistive switching properties degrades after the vacuum annealing treatment. The oxygen ions released from HfO2 resistive switching layers during vacuum annealing leads the unstable resistive switching properties. To overcome this problem, the materials of Al2O3 and TiO2 thin films with different Gibbs free energy are inserted between the Ti top electrode and HfO2 layer to improve the performance of the device. The device with the inserted Al2O3 layer exhibits larger on/off ratios during resistive switching than the single HfO2 layer. Besides, Al2O3 inserted device exhibits good reliability after the high temperature vacuum annealing and post metal annealing (PMA) treatments. Moreover, the endurance and retention properties of the device can also be improved after the PMA treatment. In the fourth part, we fabricated the HfO2 based RRAM cross bar structure devices with an inserting large band gap Al2O3 layer and small band gap TiO2 layer for nonlinear resistive switching property. The HfO2/Al2O3 bilayer device shows the nonlinear resistive switching characteristics, which is performed by inserting the large band gap an Al2O3 tunnel barrier layer. However, the device with a small band gap TiO2 inserting layer shows the typical linear resistive switching property. The nonlinear switching mechanism in the HfO2/Al2O3 bilayer device is caused by Flower–Nordheim (FN) tunneling. We explain the phenomenon by using conductive filament model and energy band diagram. Besides, the influence of different thicknesses of the inserting tunneling barrier layer is also studied. The thicker thickness of both Al2O3 and TiO2 (3nm) tunneling barrier layer device shows the typical linear resistive switching characteristics. Moreover, the nonlinear resistive switching behavior with a large nonlinear factor is also demonstrated in the present device with high performance properties. Finally, we fabricated the metal induced crystallization (MIC) poly-Si based Cu/poly-Si/n+-Si CMOS compatible cross bar CBRAM devices for high performance. We discussed the variation in resistive switching is due to the random formation and rupture of conductive filament in a-Si based device which spoils the repeatability of the devices. The stability of resistive switching can be improved by using MIC poly-Si thin film with the uniform grain boundaries. The MIC process can produce a highly preferred orientation poly-Si film, which can create the exact paths or grain boundaries through the top and down electrodes in the present CBRAM device. The grain boundary in MIC poly-Si layer can confine the conductive filament of metal bridging growth in it, which can improve the switching fluctuation behavior in the nonvolatile memory application. Moreover, the well-behaved memory performance, such as high ON/OFF resistance ratio (4 order), a large AC endurance (106), and good retention characteristics (104 s at 125 ◦C) are achieved in the Cu/poly-Si/n+-Si CMOS compatible cross bar structure.

In this thesis, the improvement of reliability in the transition metal oxide (TMO) based resistive switching random access memory (RRAM) device was investigated. In the first part, we fabricated the ZnO/ZrO2 double layer RRAM device for uniform endurance and high temperature retention property. The stability of resistive switching can be improved by inserting a ZnO thin film with the non-stoichiometric property between Ti top electrode and ZrO2 layer. The oxidation-reduction reaction can be easily performed on the ZnO/ZrO2 double layer RRAM device under an external bias than that on the ZrO2 single layer RRAM device. In addition, the ZnO/ZrO2 double layer RRAM device reveals the stable retention properties exhibited at higher temperature (200 0C). According to the conductive filament model, the control of oxygen ions supply determined by the ZnO inserting layer is the crucial to improve its retention property. Therefore, the ZrO2 RRAM device with an inserting ZnO layer exhibits the stable retention properties at a higher temperature (200 0C). In the second part, we fabricated the HfO2 based RRAM devices with a 1T1R cross bar structure. We discussed the decreasing of resistance in high resistive state (HRS) of HfO2 RRAM device during large endurance test. This phenomenon is due to that no sufficient oxygen ions could recombine with oxygen vacancies for rupturing the conducting filaments. Therefore, the oxygen plasma treatment method is used to increase the available oxygen ions in the HfO2 film for resistive switching. Besides, a thin HfO2 film is inserted to separate them to avoid the Ti top electrode directly absorbs the additional oxygen ions from HfO2 layer with oxygen plasma treatment. Therefore, the endurance degradation can be suppressed in the present structure. High speed (30 ns) and large endurance cycles (up to 1010 cycles) are achieved in this device structure for next generation nonvolatile memory application. In the third part, we fabricated the HfO2 based RRAM devices with a cross bar structure. We discussed the thermal instability of the HfO2 based RRAM device after annealing treatment in vacuum at different temperatures (400 and 500 C) for 30 min. The uniformity of the resistive switching properties degrades after the vacuum annealing treatment. The oxygen ions released from HfO2 resistive switching layers during vacuum annealing leads the unstable resistive switching properties. To overcome this problem, the materials of Al2O3 and TiO2 thin films with different Gibbs free energy are inserted between the Ti top electrode and HfO2 layer to improve the performance of the device. The device with the inserted Al2O3 layer exhibits larger on/off ratios during resistive switching than the single HfO2 layer. Besides, Al2O3 inserted device exhibits good reliability after the high temperature vacuum annealing and post metal annealing (PMA) treatments. Moreover, the endurance and retention properties of the device can also be improved after the PMA treatment. In the fourth part, we fabricated the HfO2 based RRAM cross bar structure devices with an inserting large band gap Al2O3 layer and small band gap TiO2 layer for nonlinear resistive switching property. The HfO2/Al2O3 bilayer device shows the nonlinear resistive switching characteristics, which is performed by inserting the large band gap an Al2O3 tunnel barrier layer. However, the device with a small band gap TiO2 inserting layer shows the typical linear resistive switching property. The nonlinear switching mechanism in the HfO2/Al2O3 bilayer device is caused by Flower–Nordheim (FN) tunneling. We explain the phenomenon by using conductive filament model and energy band diagram. Besides, the influence of different thicknesses of the inserting tunneling barrier layer is also studied. The thicker thickness of both Al2O3 and TiO2 (3nm) tunneling barrier layer device shows the typical linear resistive switching characteristics. Moreover, the nonlinear resistive switching behavior with a large nonlinear factor is also demonstrated in the present device with high performance properties. Finally, we fabricated the metal induced crystallization (MIC) poly-Si based Cu/poly-Si/n+-Si CMOS compatible cross bar CBRAM devices for high performance. We discussed the variation in resistive switching is due to the random formation and rupture of conductive filament in a-Si based device which spoils the repeatability of the devices. The stability of resistive switching can be improved by using MIC poly-Si thin film with the uniform grain boundaries. The MIC process can produce a highly preferred orientation poly-Si film, which can create the exact paths or grain boundaries through the top and down electrodes in the present CBRAM device. The grain boundary in MIC poly-Si layer can confine the conductive filament of metal bridging growth in it, which can improve the switching fluctuation behavior in the nonvolatile memory application. Moreover, the well-behaved memory performance, such as high ON/OFF resistance ratio (4 order), a large AC endurance (106), and good retention characteristics (104 s at 125 ◦C) are achieved in the Cu/poly-Si/n+-Si CMOS compatible cross bar structure.