氧化鋁基覆蓋層應用於氧化鋁鉿鐵電記憶體與電晶體之製程整合與元件電性探討

Abstract

本研究探討單層氧化鋁與不同沉積比的氧化鋁鉿材料於氧化鋁鉿鐵電電容元件之覆蓋層效應，以及比較不同製程條件下之鐵電電容和電晶體特性。在實驗上，我們製備四種條件鐵電電容，使用純氧化鋁覆蓋層與三種不同沉積比的氧化鋁鉿覆蓋層應用於氧化鋁鉿鐵電電容，並於實驗完成後進行電容和電晶體元件電性量測。從實驗結果發現，純氧化鋁覆蓋層能增強氧化鋁鉿鐵電電容的鐵電極化特性，相比於採用氧化鋁鉿覆蓋層，在低量測電壓3.0V下，也有最優異的鐵電極化特性，兩倍殘餘極化值為16 μC/cm2，以及最佳的電荷儲存能力，在100 kHz的操作頻率下，電容值為381 pF，同時能抑制漏電流 約1個數量級。在元件耐久度方面，在量測電壓為±4.0 V條件下，經過4.5×107個循環後仍能保有16 μC/cm2的兩倍殘餘極化量，其鐵電記憶體能具有較佳的儲存性能與更低的功耗表現。而鐵電電容元件採用氧化鋁鉿覆蓋層，則是在低電壓下能些微增強氧化鋁鉿鐵電電容鐵電極化特性，但是將電壓加大後，反而降低氧化鋁鉿鐵電電容鐵電極化特性。此不理想鐵電效應推測是與三元氧化鋁鉿覆蓋熱穩定性不佳，容易在退火過程產生過多界面缺陷有關。在類神經方面，純氧化鋁覆蓋層條件與氧化鋁鉿覆蓋層條件的非線性度皆小於1，其中純氧化鋁覆蓋層條件與沉積比1：9的氧化鋁鉿覆蓋層條件分別為0.58、0.51，更適合應用於類神經網路架構。在鐵電場效電晶體部分，相較於氧化鋁鉿覆蓋層條件，純氧化鋁覆蓋層之鐵電場效電晶體擁有較佳的開關特性，其最小次臨界擺幅為79 mV/decade、開關電流比為1.9 x105，以及響應速度也較優異，轉導值 為7.6 x10-5 mS。In this study, we investigated the capping layer effect of hafnium-aluminum oxide (HfAlO) ferroelectric capacitors using Al2O3 and HfAlO capping materials. The related electrical characteristics of ferroelectric capacitors and transistors (FeFET) with different process conditions were also carried out. In the experiment, we fabricated HfAlO ferroelectric devices with four conditions of capping layers. The capping layer conditions included a single-layer Al2O3 capping layer and three HfAlO capping layers with different deposition ratios. After device fabrication, we performed the electrical characteristic measurements of capacitor and transistor.According to the experimental results, we found that the pure Al2O3 capping layer favorably enhanced the ferroelectric polarization characteristics of HfAlO ferroelectric capacitor. The excellent remanent polarization of about 16 μC/cm2 can be obtained at a low measurement voltage of 3.0V. The capacitance can reach to 381 pf at an operating frequency of 100 kHz, which had a good charge storage capacity. The leakage current of 8.8×10-9 A can be measured at a voltage of -3.5 V., The leakage current can be suppressed by an order of magnitude after adopting an Al2O3 capping layer. From the endurance test, the HfAlO ferroelectric capacitor using Al2O3 capping layer stably switched at an operating voltage of ±4.0V, and the remanent polarization of 16 μC/cm2 can be maintained after 4.5×107 cycles. It showed well-controlled ferroelectric polarization characteristics and better storage performance under the operation of low power consumption. On the other hand, HfAlO capping layer can slightly enhance the ferroelectric polarization characteristics of HfAlO ferroelectric capacitor at low voltage, but reduce ferroelectric polarization characteristics at high voltage. The nonideal ferroelectric polarization effect can be ascribed to the poor thermally-stable ternary material structure of HfAlO capping layer, which easily generate interface defects during the annealing process. In Artificial Neural Network (ANN) analysis, the non-linearity values of HfAlO ferroelectric capacitors using Al2O3 capping layer and HfAlO capping layer were less than 1. The non-linearity values of samples using Al2O3 capping layer and HfAlO capping layer with specific deposition ratio of 1:9 were 0.58 and 0.51, respectively, which was more suitable for ANN. Compared to the FeFET using HfAlO capping layer, the FeFET using Al2O3 capping layer showed better switching characteristic and faster response speed. The lowest subthreshold swing was about 79 mV/decade and the switching on/off current ratio can reach to 1.9x105. Besides, the transconductance was close to 7.6 x10-5 mS, which was also higher than that of FeFET with HfAlO capping layer.