Modeling And Development Of Graphene Transistor Terahertz Modulator

With the development of science and technology,terahertz waves have experienced rapid development in related fields such as materials science,security inspection,medical inspection,and wireless communications,and also shown increasingly broad application prospects.However,as an emerging electromagnetic research band,functional devices that are related to terahertz are still immature,which seriously limits the development and application of terahertz technology.Therefore,it is particularly important to design and develop active modulation terahertz devices.Nowadays,graphene with excellent mechanical and electrical properties,has a significant response to terahertz waves.Artificial electromagnetic metamaterials with unique controllable structures have also been intensively investigated in terahertz waves modulation.The combination of the novel material and artificial metamaterials could achieve a better performance.According to the structure and properties of graphene,we first introduced the general transfer process of graphene,analyzed the problems encountered in the transfer process,and proposed two optimization methods for preparing large-area graphene films that are better for transferring.Then,the structure and principle of the transistorwere discussed in detail according to the traditional transistor structure,and the semiconductor manufacturing process was used to continuously prepare the graphene transistor with buried-gate structure where graphene was used as the channel by continuously optimizing and adjusting the process flow and parameters.Besides,we performed related electrical performance tests on the transistors.Next that,a terahertz modulator based on graphene transistor was designed by CST simulation software.By simulating the size influence on metamaterial structure based modulation characteristics,the optimazed parameters of the metamaterial structure were obtained.Accordingly the designed terahertz modulation device was successfully fabricated through the preparation process of the graphene transistor and its modulation properties including modulation depth and speed were measured by terahertz time domain spectroscopy and space transmission system,respectively.The results showed that the proposed device can achieve a maximum modulation depth of 12.5% at 0.35 THz with the 3 dB bandwidth of 60.1 kHz.Finally,to overcome the limitations of traditional terahertz absorbers,a new material re-constructed by graphene,called as 3D graphene which shows higher absorption to terahertz waves was ultilized to realize a "sandwich" stretchable terahertz absorber,combined with PDMS.According to measurement,the proposed absorber can achieve the terahertz absorption highest to 90% in the range of 0.2 THz to 1.1 THz band.Owing to the flexible stretchability of PDMS,the device also showed better flexibility.By stretching to its 1.2 times in length,the absorption could maintain at a relative high value of 85%-90%,and more importanly,it was reversible for its structure and absorption properties after stretching was revoked and showed the polarization sensitivity to terahertz wave.