Research On The Temperature Effect On The Electrical Properties Of Two-dimensional Layered Material Field Effect Devices

As it becomes very difficult to sustain the Moore’s law on silicon based devices with the physical limitation of silicon in recent years, searching for novel materials for the next generation microelectronic devices is very important. With many outstanding properties, such as high mobility, unique optoelectronic performance, and thickness on atomic scale, the two-dimensional layered materials, including graphene and metal dichalcogenides, are considered as potential candidates for developing the post-silicon microelectronics. The current research on silicon based microelectronic devices has indicated that the temperature rise related to the Joule heating in devices plays a significant role in the device performance. The thermal management has become a key issue in the design of microelectronic devices. Therefore, studying on the relation between temperature and the performance in device made of two-dimensional layered materials will be helpful for promoting the application of two-dimensional layered materials in microelectronic industry. Moreover, as the building block of the integrated circuits, the field effect device（FET） is an important device category. It is necessary to study the effect of temperature on this fundamental device formed by two-dimensional layered materials.In this dissertation, the temperature effect of two two-dimensional layered FETs, graphene FET and metal dichalcogenide SnS_2-xSe_x FET, are studied respectively. With the measurement of temperature effect during long time operation at different temperatures, the resistance variation caused by desorption of dopants with self-heating effect in graphene FET is observed. By replacing the FET dielectric layer with high thermal conductive AlN thin film, the resistance variation is effectively suppressed by improving the heat dissipation of the FET channel. Using chemical vapor transport method, the SnS_2-xSe_x nanocrystals with different selenium content are successfully synthesized. The transfer and output characteristics of SnS_2-xSe_x FET with different selenium content at different temperatures are measured and analyzed. Based on the transport properties of the FETs and theoretical calculations, the influence of the S/Se ratio on the activation energy of SnS_2-xSe_x nanocrystal is reveled.As for the temperature effect of graphene FET, the fabrication parameters of radio frequency reactive sputtering synthesis of AlN thin film on Si（001） are studied firstly. The high sputtering power is observed to be able to effectively promote the formation of high energy Al-B bond and the growth of c-axis preferred AlN thin film. The influence of Ar/N2 ratio during sputtering on the structure and thermal conductivity of AlN thin film is studied with oxygen impurity and boundary scattering model. The relation between substrate heating temperature, thin film microstructure and thermal conductivity is obtained and explained with series thermal resistance model and scattering model by characterizing the thermal conductivity and AlN/Si interface structure. The higher growth temperature can effectively eliminate the amorphous AlN layer in interface. With the optimized sputtering parameters, the AlN thin film with thermal conductivity as high as 26.7 W/mK is synthesized.The self-heating effect of graphene FET with atmosphere impurities is characterized with the FETs using SiO2 and as-prepared AlN dielectric layers respectively. When the FET is operating with 0.5 W power for 500 s, the channel resistance of FET is observed to keep increasing in hole conduction region and decreasing in electron conduction region. By measuring the shift of charge neutral point and analyzing transport mechanisms, this effect is considered as the result of carrier density change caused by the thermal activated desorption of p-type impurities in graphene. The obvious decrease of channel resistance variation amplitude in FET with AlN dielectric layer shows that the channel resistance instability during long time operation can be suppressed by enhancing the heat dissipation in FET channel with using high thermal conductive dielectric layer.In the study on the temperature effects of SnS_2-xSe_x FETs, the FETs with different selenium content are fabricated with the SnS_2-xSe_x nanocrystals synthesized by chemical vapor transport method. The transport properties of SnS_2-xSe_x FETs are measured at the temperatures ranging from 90 K to 295 K. The increase of selenium content is observed to lead to disapperence of FET ON/OFF funcation and the contact type transformation from Ohmic-like type to Schottky type. The relation between S/Se ratio and the FET transport properties is considered as the result of SnS_2-xSe_x crystal band structure change. The experimental and theoretical analysis indicate that the relative dielectric constant change with the influence of selenium content play a key role on determining the crystal activation energy, which affects the band structure of SnS_2-xSe_x crystal.