Walter Smetana

A Wireless Embedded Resonant Pressure Sensor Fabricated in the Standard LTCC Technology

This paper proposes a fully embedded resonant pressure sensor operating in the MHz range and realized in the standard low-temperature co-fired ceramics (LTCC) technology. Buried sensor design and usage of LTCC materials enable application of this sensor in high-temperature and chemically aggressive environments. Upgraded sensor and sensor-antenna models residing on an analytical concept are used for prediction of the system performance. Also, simulation results show that an increase of Youngs modulus for the LTCC tape diminishes the sensor sensitivity. An experimental setup for wireless data retrieval is designed enabling precise measurement of the influence of pressure variation on the sensors resonant frequency. Experimentally attained results are compared with electrical characteristics determined by analytical calculations as well as those derived from electrical simulations.

Processing procedures for the realization of fine structured channel arrays and bridging elements by LTCC-Technology

This report deals with technological procedures to provide channel partition walls of minimum width inside of Low Temperature Co-fired Ceramics (LTCC) micro fluidic devices demonstrated by means of the fabrication of parallel closely-spaced channels which may act as a specific functional part of a fluidic heat exchanger. Furthermore, the realization of single layer bridging elements inside of channels is discussed. Such an element may be introduced as a delicate sensor substrate providing adequate thermal insulation and low thermal mass as well. The technological processing steps under consideration start with laser micromachining of green ceramic tapes using Nd-YAG-laser equipment and are followed by a modified low-pressure lamination step comprising the application of appropriate adhesives and the incorporation of polymer sacrificial volume materials (SVMs). Consequently, the increased fraction of involved organics requires an adequate adaptation of the firing process to provide a residue-free burnout. Great attention is paid to the prevention of channel cross-section distortion and to the integrity of structures, verified by optical inspection of microsectioned samples. The optimized processing procedures enable the fabrication of channel arrays with a partition wall thickness as small as 100 μm, while single layer bridging elements may span a channel width of 4 mm.

End-to-End Differential Contactless Conductivity Sensor for Microchip Capillary Electrophoresis

In this contribution, a novel measurement approach for miniaturized capillary electrophoresis (CE) devices is presented: End-to-end differential capacitively coupled contactless conductivity measurement. This measurement technique is applied to a miniaturized CE device fabricated in low-temperature cofired ceramics (LTCC) multilayer technology. The working principle is based on the placement of two distinct detector areas near both ends of the fluid inlet and outlet of the separation channel. Both output signals are subtracted from each other, and the resulting differential signal is amplified and measured. This measurement approach has several advantages over established, single-end detectors: The high baseline level resulting from parasitic stray capacitance and buffer conductivity is reduced, leading to better signal-to-noise ratio and hence higher measurement sensitivity. Furthermore, temperature and, thus, baseline drift effects are diminished owing to the differentiating nature of the system. By comparing the peak widths measured with both detectors, valuable information about zone dispersion effects arising during the separation is obtained. Additionally, the novel measurement scheme allows the determination of dispersion effects that occur at the time of sample injection. Optical means of dispersion evaluation are ineffective because of the opaque LTCC substrate. Electrophoretic separation experiments of inorganic ions show sensitivity enhancements by about a factor of 30-60 compared to the single-end measurement scheme.

Ceramic capillary electrophoresis chip for the measurement of inorganic ions in water samples.

We present a microchip capillary electrophoresis (CE) device build-up in low temperature co-fired ceramics (LTCC) multilayer technology for the analysis of major inorganic ions in water samples in less than 80 s. Contactless conductivity measurement is employed as a robust alternative to direct-contact conductivity detection schemes. The measurement electrodes are placed in a planar way at the top side of the CE chip and are realized by screen printing. Laser-cutting of channel and double-T injector structures is used to minimize irregularities and wall defects, elevating plate numbers per meter up to values of 110,000. Lowest limit of detection is 6 microM. The cost efficient LTCC module is attractive particularly for portable instruments in environmental applications because of its chemical inertness, hermeticity and easy three-dimensional integration capabilities of fluidic, electrical and mechanical components.

Using integrated capacitive humidity sensors in thick-film technology☆

Abstract An integrated capacitive sensor in thick-film technology is presented, which enables the humidity behaviour of different coating materials for hybrid microcircuits to be evaluated. The capacitance response of different glass and ceramic dielectrics is presented.

Virtual rotor grounding of capacitive angular position sensors

This paper presents a new approach for the design of capacitive angular position and angular speed sensors. The idea is to obtain nonconductive grounding of the rotable part of the sensor. This approach allows the use of conductive rotor blades fixed to a nonconductive shaft. A simple prototype has been developed to show the theory of operation. Model calculations and experimental results show that virtual grounding allows to neglect the rotor-ground resistance in a wide range.

Micro force sensor fabricated in the LTCC technology

This paper presents resonant force sensor designed for the operation in the MHz range and for 0 to 6 N load. The LTCC technology is implemented for the sensor fabrication and a wireless readout of the measured data is provided. Used LTCC tape is characterised in order to demonstrate its mechanical and electrical properties at room temperature. Also, theoretical model of the sensor is developed to predict its behaviour. Fabricated sensor performance is experimentally characterised and obtained results are in good agreement with the ones derived from the presented theoretical model.

Microchip electrophoresis in low-temperature co-fired ceramics technology with contactless conductivity measurement

In this paper a novel micromachined contactless conductivity CE device produced in low temperature co‐fired ceramics (LTCC) is introduced. The application of LTCC multilayer technology provides a promising method for the contactless detection of conductive compounds because of its increased dielectric constant compared with glass or plastics. The capacitive coupling of the excitation signal into the microchannel across the LTCC substrate is improved, resulting in better detection sensitivity. Two silver electrodes located externally at opposite sides at the end of the separation channel act as detector. Impedance variations in the channel are measured without galvanic contact between electrodes and fluid. Inorganic ions are separated in less than 1 min with this novel ceramic device. The limit of detection is 10 μM for potassium.

Designing the performance of a thick-film laser power detector by means of a heat-transfer analysis using finite-element method

Abstract Besides the usual application of thick-film technology to produce circuits of high reliability, this technology is also attractive for the fabrication of sensors. A laser power detector has been realized utilizing the thick-film technique. A special detector configuration provides an exact laser power measurement independent of the position of beam impingement on the detector area and independent of the intensity distribution of the laser beam. The detector, which actually operates as a heat-flow meter, consists of a thermopile circularly applied on an AlN substrate. The geometrical proportions of the detector have been accommodated to an NdYAG laser with a given specification by means of thermal heat-transfer analysis using the finite-element method (FEM). Based on the FEM simulation of steady state and transient temperature distributions on the detector area induced by laser beam impingement, the performance and the operating range of the detector have been specified.

Application of integrated thick-film thermocouples for a laser power detector

Abstract A laser power detector has been developed, where the sensor elements have been built up utilizing standard thick-film technique. The operating principle is based on a heat-flow measurement. Heat flow may be determined by means of temperature differences applying surface temperature sensors. Thick-film thermopiles arranged in a special configuration act as heat-flow meters. Optimizing the geometrical proportions of the detector configuration provides an accurate laser power measurement independent of the position of beam impingement on the detector area and independent of the intensity distribution of the laser beam.