Hysteresis of In Situ CCVD Grown Graphene Transistors

Abstract

In this paper we report on a novel method to fabricate graphene transistors directly on oxidized silicon wafers without the need to transfer graphene. By means of catalytic chemical vapor deposition (CCVD) the in situ grown monolayer graphene field-effect transistors (MoLGFETs) and bilayer graphene field-effect transistors (BiLGFETs) are realized directly on oxidized silicon substrate. In situ CCVD grown BiLGFETs possess unipolar p-type device characteristics with an extremely high on/off-current ratio up to 1 × 10 7 . With this novel fabrication method hundreds of large scale in situ CCVD grown graphene FETs are realized simultaneously on one 2'' wafer in a silicon CMOS compatible process.

Hysteretic response of chemical vapor deposition graphene field effect transistors on SiC substrates

“…5,6 Hysteretic effects have been widely observed in currentvoltage (I sd -V bg , sd ¼ source-drain, bg ¼ backgate) transfer measurements of GFETs, causing the shape of the transfer curve and the location of the Dirac point to be dependent on direction, speed, and range with which gate voltage sweeps are performed. [7][8][9][10][11] The origin of this hysteresis has been shown to be electrochemical doping of the substrate material on which graphene is deposited. 12 Electrochemical p-type doping may be introduced during device fabrication, or after exposure to environments containing H 2 O and O 2 , or NO 2.…”

Transfer-Free Bilayer Graphene FETs: Application as Memory Devices

“…However, when applying a positive voltage of V BG =15V the BiLGFET is always in the off-state and is completely switched on after ~8V in the back gate cycling range. Using a backgate cycling range of -15V to 15V and reverse yields an average hysteresis of ∆V BG,BiLGFET = 19.5 V± 20% based on 40 examined BiLGFETs (20). However, the hysteresis of BiLGFETs depends on the cycling range of V BG and is caused most likely due to trapping and de-trapping of oxide charges within the backgate oxide or at its interface (22).…”

“…Since the hysteresis of BiLGFETs depends on the cycling range of the applied backgate voltage V BG while the sub-threshold slope is uniform for varied temperatures and varied cycling ranges of the backgate voltage (20,25) a suitable current voltage characteristic can be chosen to use a BiLGFET as a memory device to achieve a reading voltage of V BG = 0V. Figure 3a shows a useful current voltage characteristic for the BiLGFET with a backgate cycling range of -10V to 10V and reverse.…”

“…By annealing the wafer at 800°C to 900°C for 3 to 15 minutes in inert atmosphere, the aluminum transforms itself partially into aluminumoxide-like insulator (Al x O y ) while the nickel (Ni) layer generates several nickel nanoclusters at the border of the catalyst system, as shown schematically in figure 1e. In the subsequent methane-based CCVD process, graphene layers are growing while the number of the stacked graphene layers depends on the adjusted process parameters like time, temperature and gas mixture (20). The SEM analysis in figure 2a of a graphene FET (GFET) channel region shows the source and drain areas which consists of the catalyst.…”

Device Characteristics of In Situ CCVD Grown Bilayer Graphene FETs at Elevated Temperatures

“…The methane flow rates are typically in the range of 4 to 15 litres per minute while the methane can be diluted by hydrogen with a flow rate of 3 litres per minute at maximum at atmospheric pressure. The total processing time for the wafers within the CVD chamber (Applied Materials AMV 1200) is in the range of 30 to 60 minutes [20]. During growth the graphene layer extends a few microns from the catalyst onto the oxidized wafer surface which is sufficient for device fabrication.…”