F.E. Prins

Doped silicon single electron transistors with single island characteristics

Uniformly doped single electron transistors nominally consisting of a single island and two silicon tunneling barriers have been fabricated on silicon–on–insulator material. Two operation regimes are found depending upon the gate voltages applied. The structure acts either as a multiple tunnel junction device or as a single electron transistor consisting of a single dot corresponding to the geometrical shape of the device. The multiple tunnel junction behavior is attributed to the formation of additional tunneling barriers, introduced into the structure by the high doping level. We demonstrate that these barriers can be removed by raising the Fermi level via the application of an appropriate gate voltage.

Multicomponent analysis and prediction with a cantilever array based gas sensor

Abstract We present micromechanical cantilever sensor arrays for quantification of individual components in a gas mixture. Using selectively coated cantilevers as mass sensitive transducers, their response to the analyte molecules is obtained by measuring their resonant frequency shift due to the additional mass loading. The responses were used in principal component regression (partial least squares (PLS)) for the quantitative prediction of vapors being analyzed. The results confirm the functionality of our sensor system and motivate for further optimization.

Self-limiting and pattern dependent oxidation of silicon dots fabricated on silicon-on-insulator material

We present a systematic investigation of the oxidation properties of Si dots fabricated on a silicon-on-insulator (SOI) wafer. Dots with diameters varying from 9 to 81 nm were structured on a SOI wafer. These dots were oxidized in a dry oxygen atmosphere at 700, 850, and 1000 °C. The resulting structures were investigated using a side view transmission electron microscopy (TEM) technique in combination with energy filtered TEM. The dimensions of the residual Si and the grown SiO2 were then extracted from the micrographs and analyzed. The oxidation appears to be retarded as compared to the well-known planar oxidation. At 700 and 850 °C a self-limiting effect is observed as well as a clear pattern dependent oxidation at 850 and 1000 °C. We attribute these effects to stress buildup in the oxide. The critical stress, causing the self-limiting effect, is calculated using a model that considers the decrease of the reaction rate with increasing stress perpendicular to the Si surface.

Simultaneous operation of two adjacent double dots in silicon

We have studied the electrical transport through two adjacent double dot structures realized in Si-on-insulator material. The small dimensions of dots and the distance between the centers of the dots, here 100 nm, allow for dc measurements at 4.2 K. We demonstrate that although the structures are entirely doped, we are able to operate both double dot structures simultaneously in the double dot regime. Clear Coulomb blockade characteristics with a Coulomb blockade region of 20 mV are observed in both structures. Using gates, the number of electrons on each individual dot can be manipulated simultaneously. From the measured charging diagrams the capacitances between the gates and the dots are determined.

Parallel frequency readout of an array of mass-sensitive transducers for sensor applications

Polymer coated cantilevers as mass-sensitive transducers for miniaturized gas sensors, an approach for which promising results have been demonstrated recently [1], have been developed and investigated further towards applications. A new detection arrangement has been realized, which enables a simultaneous frequency readout of several cantilevers. In addition, it was possible to coat the cantilevers with different polymers showing specific sensitivity to different gases. Finally, we present the first measurements on the simultaneous application and readout of differently coated cantilevers exposed to a mixture of gases.

Fabrication and characterisation of Coulomb blockade devices in silicon

Silicon Coulomb blockade structures have been fabricated from silicon on insulator substrates and electrically characterised. The devices were realized as a single Si island connected to two electron reservoirs by Si tunnelling barriers. The silicon base substrate served as a backgate. Clear Coulomb blockade behaviour in the I(V) characteristics was observed at temperatures up to 110K with a large Coulomb gap of 1 Volt at zero backgate voltage. The Coulomb gap was found to be strongly dependent on the backgate voltage. Periodic source-drain current oscillations were measured at 4.2K by sweeping the backgate voltage. The geometrical and the electrical shape of the device were found to be different. Despite the designed two tunnelling barriers and a single dot the observed electrical behaviour can only be explained by the assumption of multiple tunnel junctions.

Digital pattern generator for polynomially bordered shape primitives

Abstract We have designed a new Digital Pattern Generator for electron beam lithography applications which is able to generate polynomially bordered shape primitives by hard wired logic. This Pattern Generator has been built and the basic functions have been tested. In connection with an offline spline interpolation program, this device allows the fast generation of deflection signals for structures with arbitrarily curved borders.

New method for fabrication of an array of individually controllable miniaturized electrostatic lenses

Abstract We have fabricated arrays of silicon membranes and structures such as silicon contact pads and interconnecting silicon-wires on borosilicate glass as carrier material and isolator. We propose a new method to align and assemble these basic modules to form electrostatic electron optical components such as lenses and multipoles. This enables the fabrication of arrays of mutually aligned e-beam microcolumns.

How to improve lateral pn-junction electron detectors for microcolumn systems

Design rules for lateral pn-junction detectors have been established and verified by numerical simulations and measurements of the detector efficiency for different geometries. The test devices were fabricated by diffusion of phosphorus into boron-doped silicon substrates. The efficiency was measured by direct electron irradiation in a scanning electron microscope. EBIC imaging was used to obtain the depletion layer width used for calculating the upper limit of the efficiency for the given geometries. All experimental values agree well with the theoretical predictions. It is demonstrated that the efficiency of lateral pn-junction detectors can be improved without reduction of the bandwidth.

Coulomb-blockade-structures in poly-crystalline silicon

Abstract We have defined Coulomb blockade structures in a highly doped poly-crystalline film on top of a SiO 2 layer using electron beam lithography and thermal oxidation. The electrical characterization at 4.2 K revealed a 8 mV wide Coulomb blockade region. The Coulomb blockade can be lifted periodically by applying a voltage to the side as well as the back gate. We conclude that these effects are due to a single electrically active island, which can be directly linked to our lithographically defined structure.