Prof. Zhi Jin received the B.S. degree in Physics from Hebei Normal University, China, in 1993 and the M.S. degree in Physics and Ph.D. degree in Electrical Engineering from Jilin University, in 1996 and 1999, respectively. From 1999 to 2002, he was a postdoctoral fellow with Research Center for Integrated Quantum Electronics, Hokkaido University, Japan, where he worked on the process development of III-V and GaN based devices. He then worked as researcher with Solid-State Electronics Department, Duisburg-Essen University, Germany and with Electrical Engineering Department, The University of Electro-Communications, Japan, where he worked on GaAs- and InP-based Heterojunction Bipolar Transistors. In 2006, he was with Institute of Microelectronics, Chinese Academy of Sciences as Professor. His research interests include III-V semiconductor-based HBTs and HEMTs, microwave circuits, and graphene-based device and circuits. He has authored/coauthored more than 100 papers published in journals and presented at conferences.
演讲题目：Graphene Field-effect Transistor
内容摘要
Since the exfoliation of graphene from HOPG, the properties of graphene have been intensively investigated.[1] The mobility of suspended graphene can reach as high as 105 cm2/Vs. The extremely high mobility is very attractive for radio-frequency (RF) application. Wafer-scale graphene has been grown by decomposition of the surface of SiC substrate and by chemical vapor deposition (CVD) on catalytic metal surfaces. The field-effect transistors (FETs) from wafer-scale graphene have been fabricated and demonstrated very good current gain cutoff frequency, fT.[2-4] The integrated circuit based on graphene FET (GFET) has been also demonstrated.[5] The gate dielectric film is very important for the transistor performances. Here we used a new kind of thin polymer layer as seed layer of dielectric film and fabricated FETs from graphene grown by CVD. The device performances have been investigated.
Fig. 1 shows the diagram of the GFET. Graphene was grown by CVD technology on copper substrate. The GFETs were fabricated by contact-mode photolithography, O2 plasma etching and metal deposition. Ti/Au is used as contact layer, which was evaporated by E-beam evaporation and made by lift-off process. The gate dielectric film was made by spinning a very thin polymer on graphene, followed by an Al2O3 film formed by Atomic Layer Deposition (ALD). The polymer thickness is 5 nm and the thickness of Al2O3 is about 10 nm. A Ti/Au was then evaporated by E-beam evaporation as gate. The DC characteristics of the GFET were measured by HP 4145A semiconductor parameter analyzer and RF characteristics were done by Agilent Vector Network Analyzer.
Fig. 2 shows the drain current as a function of back-gate voltage, Vbg, of the GFET. The black curves are for the pristine GFET, where only the source and drain contacts are fabricated. The Dirac voltage of the back-gate device before processing is ~49 V, showing a highly p-doped effect, which mainly induced by the charges from the adsorbates and residuals on graphene surface. After application of the BCB buffer layer, the Dirac point moves to a moderate p-doping level (red curves). The following deposition of Al2O3 changes the graphene flake to nearly intrinsic properties, which is likely due to the aluminum-rich conditions in Al2O3. Fig. 3 and Fig. 4 show the current gain, H21, and the maximum available gain (MAG) as a function of frequency for the GFET with 300 nm gate length. Both the gains decrease when the measured frequency increases. They finally reach 0 dB at a slope of -20 dB/decade. fT of 40 GHz and fMax of 26 GHz can thus be extrapolated.
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