Pia Juliane Wessely

Transfer-free fabrication of graphene transistors

The authors invented a method to fabricate graphene transistors on oxidized silicon wafers without the need to transfer graphene layers. To stimulate the growth of graphene layers on oxidized silicon, a catalyst system of nanometer thin aluminum/nickel double layer is used. This catalyst system is structured via liftoff before the wafer enters the catalytic chemical vapor deposition (CCVD) chamber. In the subsequent methane-based growth process, monolayer graphene field-effect transistors and bilayer graphene field-effect transistors are realized directly on oxidized silicon substrate, whereby the number of stacked graphene layers is determined by the selected CCVD process parameters, e.g., temperature and gas mixture. Subsequently, Raman spectroscopy is performed within the channel region in between the catalytic areas and the Raman spectra of five-layer, bilayer, and monolayer graphene confirm the existence of graphene grown by this silicon-compatible, transfer-free and in situ fabrication approach. The...

In-Situ CCVD Grown Bilayer Graphene Transistor

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 MoLGFETs exhibit the expected Dirac point together with the typical low on/off-current ratios of 16. In addition, however, in-situ CCVD grown BiLGFETs possess unipolar p-type device characteristics with an extremely high on/off-current ratio up to 1x10 7 exceeding previously reported values by several orders of magnitude. With this novel fabrication method hundreds of large scale in-situ CCVD grown graphene FETs are realized simultaneously on one 2’’ wafer. Besides the excellent device characteristics, the complete CCVD fabrication process is silicon CMOS compatible. This will allow a simple and low-cost integration of graphene devices for nanoelectronic applications in a hybrid silicon CMOS environment.

In-Situ CCVD Grown Graphene Transistors with Ultra-high On/Off-Current Ratio in Silicon CMOS Compatible Processing

We invented a novel method to fabricate graphene transistors on oxidized silicon wafers without the need to transfer graphene layers. By means of catalytic chemical vapor deposition (CCVD) the in-situ grown monolayer graphene field-effect transistors (MoLGFETs) and bilayer graphene transistors (BiLGFETs) are realized directly on oxidized silicon substrate, whereby the number of stacked graphene layers is determined by the selected CCVD process parameters. In-situ grown MoLGFETs exhibit the expected Dirac point together with the typical low on/off-current ratios between 16 (hole conduction) and 8 (electron conduction), respectively. In contrast, our BiLGFETs possess unipolar p-type device characteristics with an extremely high on/off-current ratio up to 1E7 exceeding previously reported values by several orders of magnitude. We explain the improved device characteristics by a combination of effects, in particular graphene-substrate interactions, hydrogen doping and Schottky-barrier effects at the source/drain contacts as well. Besides the excellent device characteristics, the complete CCVD fabrication process is silicon CMOS compatible. This will allow the usage of BiLGFETs for digital applications in a hybrid silicon CMOS environment.

2nd Generation Bilayer Graphene Transistors for Applications in Nanoelectronics

In this paper we report on in-situ CCVD grown bilayer graphene transistors (BiLGFETs) in a Silicon-CMOS compatible fabrication process. By means of catalytic chemical vapor deposition (CCVD) the BiLGFETs are realized directly on oxidized silicon substrate without transfer. These BiLGFETs possess unipolar p-type device characteristics with a high on/off-current ratio between 1×105 and 1×107 at room temperature [1, 2]. At this stage, the maximal on-state current of a BiLGFET is clearly influenced by the contact resistance. In order to improve the performance of the produced BiLGFETs, an advanced fabrication step has been developed, by which means the contact resistance is lowered by a factor of 10.

Transfer-free grown bilayer graphene memory devices

In this paper we report on the application of in-situ CCVD grown bilayer graphene field effect transistors (BiLGFETs) as memory devices, grown in a Silicon-CMOS compatible fabrication process. By means of catalytic chemical vapor deposition (CCVD) the BiLGFETs are realized directly on oxidized silicon substrate without transfer. These BiLGFETs possess unipolar p-type device characteristics with a high on/off-current ratio between 1×105 and 1×107 at room temperature [1, 2]. The hysteresis of BiLGFETs depends on the cycling range of the applied backgate voltage VBG while the sub-threshold slope is uniform for varied temperatures and varied cycling ranges of the backgate voltage [3]. Based on the observed properties of BiLGFETs it is possible to use BiLGFETS as memory devices.

On/off-current ratios of transfer-free bilayer graphene FETs as a function of temperature

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 bilayer graphene transistors (BiLGFETs) are realized directly on oxidized silicon substrate. These BiLGFETs possess unipolar p-type device characteristics with an extremely high on/off-current ratio between 1×106 and 1×107 at room temperature [1, 2], exceeding previously reported values by several orders of magnitude. Furthermore, when increasing the ambient temperature to 200°C, the on/off-current ratio only degrades by one order of magnitude for BiLGFETs. Besides the excellent device characteristics, the complete CCVD fabrication process is silicon CMOS compatible. This will allow a simple and low-cost integration of graphene devices for nanoelectronic applications in a hybrid silicon CMOS environment.

Transfer-Free Bilayer Graphene FETs: Application as Memory Devices

Introduction In this paper we report on the application of in-situ CCVD grown bilayer graphene transistors (BiLGFETs) as memory devices. By means of catalytic chemical vapor deposition (CCVD) the BiLGFETs are realized directly on oxidized silicon substrate without transfer. These BiLGFETs possess unipolar p-type device characteristics with a high on/off-current ratio between 1x10 and 1x10 at room temperature [1, 2]. The hysteresis of BiLGFETs depends on the cycling range of the applied backgate voltage VBG while the sub-threshold slope is uniform for varied temperatures and varied cycling ranges of the backgate voltage [3]. Based on the observed properties of BiLGFETs it is possible to use BiLGFETS as memory devices.

Feasibility study on in situ CCVD grown CNTs for field-effect power device applications

In this paper we investigate the feasibility of carbon nanotubes (CNTs) for power applications. On the basis of a process which fabricates thousands of carbon nanotube field-effect transistors (CNTFETs) by means of catalytic chemical vapor deposition (CCVD) we will show that CNTFETs are capable to provide a sufficiently high current to drive a light-emitting diode (LED).