Fully integrated organic nanocrystal diode as high performance room temperature NO2 sensor
Full integration of nanoscale molecular structures with reliable electrical contacts has remained a persistent challenge in device fabrication procedures. In this work, by employing rolled-up technology we successfully create organic diodes consisting of molecular nano-pyramid structures sandwiched between metal and strained nanomembrane electrodes. The robust and smooth contacts provided by self-curled metal layers render the molecular nano-pyramids efficient channels for detecting nitrogen dioxide airflow. The devices demonstrate a high average sensitivity (151% ppm−1) and a fast recovery time (12 min) for NO2 detection.
High performance tubular GMI sensors
Arrays of rolled-up on-chip-integrated giant magneto-impedance (GMI) sensors equipped with pick-up coils are demonstrated. The geometrical transformation of an initially planar layout into a tubular 3D architecture stabilizes favorable azimuthal magnetic domain patterns. This work creates a solid foundation for further development of CMOS compatible GMI sensorics for magnetoencephalography.
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Biomimetic microelectronics for regenerative neuronal cuff implants
Smart biomimetics, a unique class of devices combining the mechanical adaptivity of soft actuators with the imperceptibility of microelectronics, is introduced. Due to their inherent ability to self-assemble, biomimetic microelectronics can firmly yet gently attach to an inorganic or biological tissue enabling enclosure of, for example, nervous fibers, or guide the growth of neuronal cells during regeneration. This work was carried out in close collaboration with the ETH Zurich, Switzerland.
This work was highlighted in:
- Surgical Tribune (November 2015) URL
Impedemetric sensing of ionic fluids and single cells in a single microtube
Ultracompact three-dimensional tubular structures integrating Au-based electrodes serve as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. The microsensors show a two orders of magnitude improved performance over conventional planar conductivity detection systems integrated in micro fluidic platforms and the capability to detect single HeLa cells. These highly integrated conductivity tubular sensors open new possibilities towards lab-in-a-tube devices for bioapplications such as biosensing and bioelectronics.
Rolled-up field effect transistors
We fabricate inorganic thin film transistors with bending radii of less than 5μm maintaining their high electronic performance with on-off ratios of more than 100.000 and subthreshold swings of 160mV/dec. The fabrication technology relies on the roll-up of highly strained semiconducting nanomembranes, which compacts planar transistors into three-dimensional tubular architectures. The rolled-up transistors are perfectly embedded into the wall of a cylindrical fluidic channel, which may boost the performance of large-scale integrated microfluidics to a level way beyond of what is currently available.
Tunable generation of correlated vortices in open superconductor tubes
We theoretically apply transport currents and magnetic fields to open superconducting tubes. In such tubes, which can be created by rolled-up nanotech, vortices nucleate periodically at one edge of the tube, subsequently move along the tube axis under the action of the Lorentz force and denucleate at the opposite edge of the tube. The characteristic times of the vortex motions are efficiently controlled by the tube radius and are significantly different to the situation in a planar film under the same magnetic field. Our results open perspectives towards tailoring non-equilibrium properties of vortices and their application as tunable superconducting flux generators for fluxon-based information technologies.
*click on pictures to see animation
Spin selective tunneling through SiGe quantum dots
When contacting a quantum dot (QD) with normal metallic leads no spin selective tunnel rates are expected. However, low-temperature magneto-transport measurements through individual SiGe self-assembled QDs have now revealed that this assumption is not always true. Indeed, we have observed that spin-selective tunnel rates through individual QDs can be achieved with normal metallic contacts. The surprising spin selectivity arises from the interplay of the orbital effect of the magnetic field with the strong spin-orbit interaction present in the valence band of the semiconductor. This work was carried out in collaboration with CEA-Grenoble and Yale University.
Hybrid organic/inorganic molecular heterojunctions
We combine self-assembly and top-down methods to create hybrid junctions consisting of single organic molecular monolayers sandwiched between metal and/or single-crystalline semiconductor nanomembrane based electrodes. The fabrication process is fully integrative and produces a yield loss of less than 5% on-chip. The nanomembrane-based electrodes guarantee a soft yet robust contact to the molecules where the presence of pinholes and other defects becomes almost irrelevant. We also pioneer the fabrication and characterization of semiconductor/molecule/semiconductor tunneling heterojunctions which exhibit a double transition from direct tunneling to field emission and back to direct tunneling, a phenomenon which has not been reported previously.
This work was highlighted in:
Nature Materials, 10, 724 (2011) (Sep 23, 2011) URL
The DotFET becomes reality
On May 18, 2001 a patent to speed up Si transistors was filed by Schmidt and Eberl (US 6,498,359), which relies on a SiGe dot positioned below the channel of a Si transistor (see left image). The 3D geometry of the dot provides huge amounts of tensile strain to the Si, which decisively affects the band structure and enhances the mobility of electrons in the channel, and thus the performance of the heart of electronics: The Metal Oxide Semiconductor Field Effect Transistor (MOSFET). In a mutual effort funded by the European Union this concept was eventually brought into reality by a consortium of research groups in Delft, Linz, Jülich, Milano, and Dresden.
Rolled-up mesoscopic Josephson junctions
Josephson junctions are crucial to many areas of high precision science and technology. However, the fabrication of nanoscale Josephson junctions is still tedious and often requires complex preocessing steps such as electron beam lithography with highest resolution. Here, mesoscopic SNS Josephson junctions are developed simply relying on natural metallic film roughnesses, self-assembly and standard optical lithography. We achieve high critical currents, and an IcRn product placing the characteristic frequency in the THz regime. These properties make them interesting candidates for many applications ranging from quantum metrology over THz radiation sensors to flux-qubits.
Photovoltaic effect in ultrathin Si nanomembranes
Under local illumination, ultrathin silicon nanomembranes (SiNMs) on insulator reveal a gate-controlled photovoltaic effect and negative transconductance in Schottky transistors applying both homo- and hetero-contacts. Tiny variations of Schottky barriers between source and drain contacts are responsible for the photovoltaic effect (see the image) and can be enhanced by gate voltage and/or contact design. Our results provide a useful method to disclose contact properties of nanomaterials and open alternative ways for novel nano-optoelectronic devices based on the photovoltaic effect.
Quantum transport through SiGe quantum dots
We have realized single-hole transistors based on self-assembled SiGe quantum dots. Charge transport measurements reveal discrete energy spectra, with the confined hole states displaying anisotropic gyromagnetic factors and strong spin-orbit coupling strength with pronounced gate-voltage and magnetic-field dependence. For strongly coupled devices single-hole supercurrent transistors were realized. Our observations render SiGe quantum dots exciting candidates for the development of spin-based devices and the study of new transport regimes. This work was carried out in collaboration with CEA-Grenoble and CNRS-Grenoble.
Giant persistent photoconductivity in Si nanomembranes
This paper reports the observation of giant persistent photoconductivity from rough Si nanomembranes. When exposed to light, the current in Si nanomembranes is enhanced by roughly 3 orders of magnitude and can persist for days at a high conductive state after the light is switched off. An applied gate voltage can tune the persistent photocurrent and accelerate the response to light. By analyzing the band structure of the devices and the surfaces through various coatings, we attribute the observed effect to the rough surfaces of the nanomembranes, where light activates localised charge carriers.
Integrated microtube resistors
Integrated ohmic devices are fabricated from Si-based microtubes, and linear I-V curves are measured for rolled-up tubes suspended between two electrodes. The combination of tubular geometry, biocompatibility, and good electrical and thermal conductivity render the fabricated devices good candidates for thermoelectric gas sensors or electrically activated micropumps and microfluidic delivery systems.