Center for Advancing Electronics Dresden cfaed
In 2012, the Center for Advancing Electronics Dresden (cfaed) achieved the status of a cluster of excellence with a funding of 34 million euros until October 2017. It aims inducing breakthroughs in promising technologies which may complement today’s leading CMOS technology, since it will be facing physical limits in performance enhancement soon. Therefore, research teams of 57 investigators from 11 institutions are interdisciplinary cooperating in different scientific fields.
Participating institutions & investigators
- Technische Universität Dresden
- Technische Universität Chemnitz
- Fraunhofer-Institut für Keramische Technologien und Systeme
- Helmholtz-Zentrum Dresden-Rossendorf Leibniz-Institut für Festkörper- und Werkstoffforschung Dresden
- Leibniz-Institut für Polymerforschung Dresden
- Max-Planck-Institut für Molekulare Zellbiologie und Genetik Dresden
- Max-Planck-Institut für Physik komplexer Systeme
- Kurt-Schwabe-Institut für Mess- und Sensortechnik Meinsberg
- Fraunhofer-Institut für Elektronische Nanosysteme Chemnitz.
Within the carbon path, Chemnitz acquired one research group leader and two PhD student positions and therefore represents the center of the technological work package. Moreover, the Center for Microtechnologies at the Technische Universität Chemnitz is involved into the innovative research field of the biomolecular assembled circuits (BAC) path with one PhD student.
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Transistors, being the most important electrical devices, have a wide range of application potential. Due to further shrinking of
integrated circuits, industry increasingly faces problems (e.g. short-channel effect and electromigration) in conventional CMOS technology.
Therefore, the Back-End of Line (BEOL) department at Fraunhofer ENAS in close cooperation with the Center for Microtechnologies at the TU Chemnitz and together with scientists from Dresden, contributes to the design and construction of carbon nanotube based field-effect transistors (CNTFET). Those devices have the potential for outperforming CMOS transistors in terms of linearity and power consumption.
In particular in this project we aim the realization of analog circuits for high frequency applications in the field of wireless communication.
The efforts at Fraunhofer ENAS include designing of different transistor structures for evaluation of their performance as well as fabrication of prototypes on wafer-level. For that purpose a bottom-up approach has been chosen to facilitate detailed characterization of CNTs and devices during preparation. Also the work focuses onto development of a process chain compatible to current fabrication steps in industry and delivery of reliable and reproducible devices, which is quite challenging at the nanoscale. Recently the formation of suitable substrates with embedded gate structures and palladium electrodes have been successfully demonstrated.
For placing the nanotubes between electrodes, the so-called dielectrophoretic approach (DEP) is applied, using dispersed CNTs in solution. This method allows precise positioning of a controlled number of CNTs directly between a pair of electrodes, avoiding extensive wafer contamination.
SEM image of deposited CNTs within a comb-like transistor geometry
A special DEP equipment, designed within the department BEOL allows the ramp up of this procedure to wafer-level and delivers
reproducible results. Characterization of the devices e.g. by I/V measurements, Raman spectroscopy, AFM, TERS and SEM is carried
out at Fraunhofer ENAS and collaborating institutions, like the TU Chemnitz and TU Dresden.
Ongoing work concentrates on improvement of electrical contact formation, process control of CNT assembly and passivation to improve device lifetime.
Within the carbon path, cooperating research groups tackle different aspects of the process chain.
Main work packages and cooperation within the Carbon Path
As synthesis of CNTs always generates different types of nanotubes with a variety of properties accordingly (e.g. length, diameter and band gap), the separation concerning different characteristics is crucial for the performance of CNT-FETs. In this scope, researchers in Dresden apply a density gradient ultracentrifugation to isolate especially long semiconducting CNTs. Moreover, several groups of modeling experts are simulating the transistors. Starting at an atomistic scale to define the influence of single defects in the carbon lattice or molecules attaching to the CNT, up to the device scale with different gap sizes between electrodes, a wide variety of components and parameters are checked to support and improve the fabrication of the transistors.
In the BAC path the development of novel strategies for a controlled bottom-up fabrication of artificial nanostructures
with tailored electronic and optical properties (realized by functionalization with nanoparticles, quantum dots, … ) is proposed by the use
of the unique self-assembly and molecular recognition capabilities of biomolecules.
The self-assembly of deoxyribonucleic acid (DNA) into smallest functional units, the so-called 'transistor pads' (tPads©, produced by TU Dresden, see Fig.) will focus on the development of novel strategies for a hierarchical self-assembly of circuits.
An achievable concept is to develop a self-assembly strategy to integrate tPads© into microsystems, implying recognition interfacing to patterned surfaces and controlled two-dimensional and three-dimensional (2D and 3D) stacking of functional units. This research should bridge the gap between micro and nanotechnology resulting from lacking methods to manipulate inorganic material at molecular scale.
AFM image of a single frame-like tPad© DNA origami (source: Franziska Fischer@Mertig lab, TU Dresden)
In our approach the tPads© will be positioned in geometrical complementary 3D hydrophilic cavities on a hydrophobic substrate. In a first step the structuring of a sub-nm thin hydrophobic layer system to achieve hydrophobic/hydrophilic cavities has been verified with standard silicon microtechnologies. In further steps the adaption of the proved microtechnological processes to lateral nanostructuring technologies at wafer-level such as nano imprint lithography (NIL) will be realized. Therefore, structure dimensions in X, Y and Z, regarding the tPads© itself (100 nm in X,Y and 10 nm in Z) will be achievable and will result in the aimed cavity structure concept. Furthermore, this developed technology concept focuses the electrical connecting of the tPads© which have to be below 50 nm. In addition, in a strong collaboration with TU Dresden, chemical and molecular bond positions are addressed to develop a further and more locally self-assembly opportunity within the described cavity concept of the tPads©.
Schematic of the hierarchical self-assembly of DNA-based circuits
Subsequently, the integration and self-assembly of the tPads© will be accomplished by a microfluidic processing chip in a characterization platform which is used to prove the overall circuit properties of the tPads©.