Armin Tilke

Stable integration of isolated cell membrane patches in a nanomachined aperture

We investigate the microscopic contact of a cell/semiconductor hybrid. The semiconductor is nanostructured with the aim of single channel recording of ion channels in cell membranes. This approach will overcome many limitations of the classical patch-clamp technique. The integration of silicon-based devices on-chip promises novel types of experiments on single ion channels.

Coulomb blockade in quasimetallic silicon-on-insulator nanowires

Using highly doped silicon-on-insulator (SOI) films, we demonstrate metallic Coulomb blockade in silicon nanowires at temperatures up to almost 100 K. We propose a process that leads to island formation inside the wire due to a combination of structural roughness and segregation effects during thermal oxidation. Hence, no narrowing of the SOI wire is necessary to form tunneling contacts to the single-electron transistors.

Microstructured Apertures in Planar Glass Substrates for Ion Channel Research

We have developed planar glass chip devices for patch clamp recording. Glass has several key advantages as a substrate for planar patch clamp devices. It is a good dielectric, is well-known to interact strongly with cell membranes and is also a relatively in-expensive material. In addition, it is optically neutral. However, microstructuring processes for glass are less well established than those for silicon-based substrates. We have used ion-track etching techniques to produce micron-sized apertures into borosilicate and quartz-glass coverslips. These apertures, which can be easily produced in arrays, have been used for high resolution recording of single ion channels as well as for whole-cell current recordings from mammalian cell lines. An additional attractive application that is greatly facilitated by the combination of planar geometry with the optical neutrality of the substrate is single-molecule fluorescence recording with simultaneous single-channel measurements.

A mechanically flexible tunneling contact operating at radio frequencies

We report on a nanomachined electromechanical resonator applied as a mechanically flexible tunneling contact. The resonator was machined out of a single-crystal silicon-on-insulator substrate and operates at room temperature with frequencies up to some 73 MHz, transferring electrons by mechanical motion.

Suspending highly doped silicon-on-insulator wires for applications in nanomechanics

We report on a new method to build suspended silicon nanowires in highly doped silicon films in silicon-on-insulator substrates. The beams are defined by high-resolution, low-energy electron-beam lithography using a two-layer positive electron resist. Micromachining techniques including dry and wet etching are applied to pattern the structures. We show first low-temperature measurements of these novel devices indicating electron-phonon interaction.

Low-energy electron-beam lithography using calixarene

Low-energy electron-beam lithography using calixarene as a negative electron resist has been investigated in the energy range between 0.5 and 20 keV. The suitability of electron energies down to 2 keV with a writing resolution of about 10 nm is clearly demonstrated. At low electron energies the required electron dose is drastically reduced. Moreover, irradiation damage during the exposure of a high-mobility two-dimensional electron gas using calixarene plays no significant role in the low-energy regime.

Nanomechanical resonators operating as charge detectors in the nonlinear regime

We present measurements on nanomechanical resonators machined from silicon-on-insulator substrates. The resonators are designed as freely suspended Au/Si beams of lengths on the order of 1–4 μm and a thickness of 200 nm. The beams are driven into nonlinear response by an applied modulation at radio frequencies and a static magnetic field in plane. The strong hysteresis of the magnetomotive response allows sensitive charge detection by varying the electrostatic potential of a gate electrode.

Single-electron tunneling in highly doped silicon nanowires in a dual-gate configuration

Lateral patterning of highly doped silicon-on-insulator films allows us to observe conductance oscillations due to single-electron charging effects. In our devices, silicon nanostructures are embedded into a metal–oxide–silicon configuration. The single-electron effects can be tuned both by an in-plane sidegate, as well as by a metallic topgate, a technology which is compatible with large-scale integration of single-electron devices with dimensions down to 10 nm. We compare the influence of different gating electrodes, important for ultralarge scale integration, on the electron islands.

Fabrication and transport characterization of a primary thermometer formed by Coulomb islands in a suspended silicon nanowire

We realized bolometers in suspended highly n-doped silicon nanowires with lateral dimensions down to about 40 nm. Random dopant fluctuations in the suspended wires lead to the formation of multiple tunnel junctions, utilized for Coulomb blockade thermometry. In the low bias regime, we observe relaxation via discrete acoustic phonon modes to give a lower bound for the sensitivity.

Analysis of TANOS Memory Cells With Sealing Oxide Containing Blocking Dielectric

In this paper, we investigate the specific impact of an additional silicon oxide layer (sealing oxide) on top of the charge-trap nitride on the electrical performance of small-dimension and large TANOS charge-trapping (CT) memory cells. We observe a significant improvement in charge retention on both our target 48-nm NAND TANOS cells and on large 5 μm long and wide memory cells. However, erase performance is partially degraded by this additional silicon dioxide top-dielectric layer. The presented intrinsic CT stack retention for 3.5-nm sealing oxide, which is visible on large cell structures, clearly shows the potential for multilevel cell operation.We further identified trapping in the Al2O3 states of the blocking dielectric to improve the program and erase performance of conventional TANOS memory cells. However, detrapping from these trap states was found to be the root cause of insufficient retention.