Kasper Reck
University of Copenhagen
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Publication
Featured researches published by Kasper Reck.
international conference on micro electro mechanical systems | 2008
Kasper Reck; Jacob Richter; Ole Hansen; Erik Vilain Thomsen
We have designed and fabricated silicon test chips to investigate the piezoresistive properties of both crystalline and polycrystalline nanowires using a top-down approach, in order to comply with conventional fabrication techniques. The test chip consists of 5 silicon nanowires and a reference resistor, each with integrated contacts for electrical 4-point measurements. We show an increase in the piezoresistive effect of 633% compared to bulk silicon. Preliminary temperature measurements indicate a larger temperature dependence of silicon nanowires, compared to bulk silicon. An increase of up to 34% compared to bulk polysilicon is observed in polysilicon nanowires with decreasing dimensions.
Sensors | 2010
Giulio Fragiacomo; Kasper Reck; Lasse Vestergaard Lorenzen; Erik Vilain Thomsen
In the framework of developing innovative microfabricated pressure sensors, we present here three designs based on different readout principles, each one tailored for a specific application. A touch mode capacitive pressure sensor with high sensitivity (14 pF/bar), low temperature dependence and high capacitive output signal (more than 100 pF) is depicted. An optical pressure sensor intrinsically immune to electromagnetic interference, with large pressure range (0–350 bar) and a sensitivity of 1 pm/bar is presented. Finally, a resonating wireless pressure sensor power source free with a sensitivity of 650 KHz/mmHg is described. These sensors will be related with their applications in harsh environment, distributed systems and medical environment, respectively. For many aspects, commercially available sensors, which in vast majority are piezoresistive, are not suited for the applications proposed.
Applied Physics Letters | 2014
Kasper Reck; Ole Hansen
Photon-enhanced thermionic emission (PETE) cells in which direct photon energy as well as thermal energy can be harvested have recently been suggested as a new candidate for high efficiency solar cells. Here, we present an analytic thermodynamical model for evaluation of the efficiency of PETE solar cells including an analysis of the entropy production due to thermionic emission of general validity. The model is applied to find the maximum efficiency of a PETE cell for given cathode and anode work functions and temperatures.
Journal of Micromechanics and Microengineering | 2011
Kasper Reck; Christian Østergaard; Erik Vilain Thomsen; Ole Hansen
While silicon nitride surfaces are widely used in many micro electrical mechanical system devices, e.g. for chemical passivation, electrical isolation or environmental protection, studies on fusion bonding of two silicon nitride surfaces (Si3N4–Si3N4 bonding) are very few and highly application specific. Often fusion bonding of silicon nitride surfaces to silicon or silicon dioxide to silicon surfaces is preferred, though Si3N4–Si3N4 bonding is indeed possible and practical for many devices as will be shown in this paper. We present an overview of existing knowledge on Si3N4–Si3N4 bonding and new results on bonding of thin and thick Si3N4 layers. The new results include high temperature bonding without any pretreatment, along with improved bonding ability achieved by thermal oxidation and chemical pretreatment. The bonded wafers include both unprocessed and processed wafers with a total silicon nitride thickness of up to 440 nm. Measurements of bonding strength, void characterization, oxidation rate and surface roughness are also presented. Bonding strengths for stoichiometric low pressure chemical vapor deposition Si3N4–Si3N4 direct fusion bonding in excess of 2 J cm−2 are found. The stoichiometry is verified indirectly through refractive index and intrinsic stress measurements. The importance of surface oxide in Si3N4–Si3N4 fusion bonding is investigated by x-ray photoelectron spectroscopy measurements.
internaltional ultrasonics symposium | 2013
Mette Funding la Cour; Thomas Lehrmann Christiansen; Christian Dahl-Petersen; Kasper Reck; Ole Hansen; Jørgen Arendt Jensen; Erik Vilain Thomsen
The conventional method of modeling CMUTs use the isotropic plate equation to calculate the deflection, leading to deviations from FEM simulations including anisotropic effects of around 10% in center deflection. In this paper, the deflection is found for square plates using the full anisotropic plate equation and the Galerkin method. Utilizing the symmetry of the silicon crystal, a compact and accurate expression for the deflection can be obtained. The deviation from FEM in center deflection is <;0.1%. The deflection was measured on fabricated CMUTs using a white light interferometer. Fitting the anisotropic calculated deflection to the measurement a deviation of 0.5-1.5% is seen for the fitted values. Finally it was also measured how the device behaved under increasing bias voltage and it is observed that the model including anisotropic effects is within the uncertainty interval of the measurements.
Sensors | 2011
Kasper Reck; Erik Vilain Thomsen; Ole Hansen
We present the design, fabrication and characterization of a new all-optical frequency modulated pressure sensor. Using the tangential strain in a circular membrane, a waveguide with an integrated nanoscale Bragg grating is strained longitudinally proportional to the applied pressure causing a shift in the Bragg wavelength. The simple and robust design combined with the small chip area of 1 × 1.8 mm2 makes the sensor ideally suited for remote and distributed sensing in harsh environments and where miniaturized sensors are required. The sensor is designed for high pressure applications up to 350 bar and with a sensitivity of 4.8 pm/bar (i.e., 350 ×105 Pa and 4.8 × 10−5 pm/Pa, respectively).
Journal of Applied Physics | 2008
Ole Hansen; Kasper Reck; Erik Vilain Thomsen
We show that very high geometrically amplified piezoresistance can indeed be obtained in microstructured metal-semiconductor hybrid devices, even significantly higher amplification factors than the factor of approximately 8 demonstrated recently by Rowe and co-workers may be achieved. However, we also show that this amplification cannot be used to realize high sensitivity sensor devices due to limitation of the applied voltage across the device when the transfer resistance is smaller than the total resistance of the device. In that case, the sensitivity in units of V V−1 Pa−1 is always less than the sensitivity of conventional piezoresistors fabricated in the same piezoresistive material.
29th European Photovoltaic Solar Energy Conference and Exhibition | 2014
Kasper Reck; Fabio Dionigi; Ole Hansen
Photon-enhanced thermionic emission (PETE) is a relatively new concept for high efficiency solar cells that utilize not only the energy of electrons excited across the band gap by photons, as in conventional photovoltaic solar cells, but also the energy usual lost to thermalization of the excited electrons. Efficiencies above 60% have been predicted theoretically for high solar concentration systems. Silicon is an interesting absorber material for high efficiency PETE solar cells, partly due to its mechanical and thermal properties and partly due to its electrical properties, including a close to ideal band gap. The work function of silicon is, however, too high for practical PETE implementations. A well-known method for lowering the work function of silicon (and other materials) is to apply approximately a monolayer of cesium to the silicon surface. We present the first measurements of PETE in cesiated p-type and n-type silicon. It is shown that PETE in average can increase the thermionic emission current by more than an order of magnitude.
Archive | 2013
Kasper Reck; Christian Østergaard; Ole Hansen; Erik Vilain Thomsen
2008 NSTI Nanotechnology Conference and Trade Show | 2008
Kasper Reck; Jacob Richter; Ole Hansen; Erik Vilain Thomsen