Researchers from the University of California, Riverside, led by Professor Jianming Huang, have been exploring the behavior of molybdenum disulfide (MoS2) field-effect transistors (FETs) with high-k oxides, which are materials with high dielectric constants used in advanced electronic devices. Their findings, published in the journal Applied Physics Letters, could have significant implications for the energy sector, particularly in the development of advanced memory devices and stable high-temperature electronics.
The team investigated the hysteresis behavior in MoS2 FETs with two different high-k oxides, HfO2 and Al2O3. Hysteresis in this context refers to the dependence of the device’s characteristics on its history of operation, which can be a challenge for logic devices but can be harnessed for memory applications. At room temperature, both types of devices exhibited clockwise (CW) hysteresis, a common issue in MoS2 FETs that can lead to instability.
However, when the temperature was increased to 175°C, the MoS2/HfO2 FETs showed a shift in behavior, with counterclockwise (CCW) hysteresis becoming dominant. This was accompanied by self-doping and negative differential resistance (NDR) effects, which the researchers attributed to the drift of mobile oxygen vacancies within the HfO2 layer. These vacancies caused a negative threshold voltage shift under a constant positive bias stress, effectively overriding the initial CW hysteresis and enabling intrinsic memory functionality. The researchers found that this memory-like behavior could be enhanced by using narrower gate bias sweep ranges.
In contrast, the MoS2/Al2O3 FETs displayed only minor CCW dynamics even at temperatures up to 275°C. This was due to higher drift activation energies for the same oxygen vacancies, which resulted in superior stability. The researchers concluded that Al2O3 layers are better suited for suppressing detrimental negative threshold voltage shifts in MoS2 logic FETs at high temperatures, while HfO2 layers could be used as active memory layers that exploit these abnormal instabilities.
The practical applications of this research for the energy sector are significant. The development of advanced memory devices that can operate at high temperatures could be crucial for energy storage and conversion systems, which often operate in harsh environments. Additionally, the understanding of hysteresis behavior in MoS2 FETs could lead to more stable and reliable high-temperature electronics, which are essential for many energy applications. The researchers’ findings provide a valuable insight into the behavior of MoS2 FETs with high-k oxides and could pave the way for the development of new energy technologies.
Source: Applied Physics Letters, “Mobile charges in MoS2/high-k oxide transistors: from abnormal instabilities to memory-like dynamics”
This article is based on research available at arXiv.