Nicolaas F. de Rooij

Potential Drifts of Solid‐Contacted Ion‐Selective Electrodes Due to Zero‐Current Ion Fluxes Through the Sensor Membrane

A thin aqueous layer is formed between the polymeric ion-selective membrane and an inner gold electrode. Its composition can be altered upon sample changes, which leads to drifting potentials. It is shown by theory and experiment that interfering ions enter the inner layer much faster than primary ones. Measurement protocols with equal contact times for the sample and the reconditioning solution can therefore not eliminate the effect of changes in the composition of the inner solution. The formation of an inner aqueous film and corresponding drifts for solid-contacted membrane electrodes can be avoided by creating a lipophilic self-assembled monolayer on the surface of the inner electrode.

Assessment of insulated conductive cantilevers for biology and electrochemistry

This paper describes the characterization and application of electrically insulated conductive tips mounted on a cantilever for use in an atomic force microscope and operated in liquid. These multifunctional probes were microfabricated and designed for measurements on biological samples in buffer solution, but they can also be employed for electrochemical applications, in particular scanning electrochemical microscopy. The silicon nitride based cantilevers had a spring constant ≤0.1 N m-1 and a conductive tip, which was insulated except at the apex. The conductive core of the tip consisted of a metal, e.g. platinum silicide, and exhibited a typical radius of 15 nm. The mechanical and electrical characterization of the probe is presented and discussed. First measurements on the hexagonally packed intermediate layer of Deinococcus radiodurans demonstrated the possibility to adjust the image contrast by applying a voltage between a support and the conductive tip and to measure variations of less than 1 pA in faradaic current with a lateral resolution of 7.8 nm.

Thermal optimization of micro-hotplates that have a silicon island

We have performed thermal measurements and electrothermal simulations (finite element modelling) with the aim of optimizing the power consumption and the temperature distribution of micro-hotplates for gas-sensing applications. A silicon island was added underneath the membrane of the micro-hotplate to improve the temperature distribution of drop-coated metal-oxide gas sensors and to thermally isolate MOSFET gas sensors. The temperature distribution over the sensing area and the power consumption depend on the silicon island thickness, which was optimized for both applications using the software MEMCAD from Microcosm Technologies. In the optimization process, we considered the thermal conductivity of silicon and dielectric membrane, the operating temperature, the geometry and the area of the heater, and the processing of the silicon island. The thickness of the silicon island was optimized to ensure a good temperature distribution over the gas-sensing area for metal-oxide and MOSFET gas sensors with specific geometry.

Effects of controlled current on the response behavior of polymeric membrane ion-selective electrodes

The influence of external currents on the potential response of polymeric membrane ion-selective electrodes (ISEs) is analyzed theoretically. The treatment is based on the well-established potential model of ISE membranes, extended by contributions from current flow and corresponding electrodialytic ion fluxes through the membrane. A general implicit solution is derived that describes the potential response in terms of the external current, the selectivity characteristics of the membrane, and the compositions of the membrane, the sample solution, and the inner solution, respectively. Explicit relationships are given for limiting cases, e.g. when only one kind of cation is present in the solution or when the disturbance by interfering cations is small. For the latter case, theoretical curves are compared to experimental ones and are shown to give a good correspondence.

ASEP : a CAD Program for Silicon Anisotropic Etching

Abstract A computer program is describe which simulates silicon single-crystal etching in KOH. Starting from a 2-D mask layout, the program finds the relevant etching planes and delivers a 3-D output of the etched structure with the etch time (or etch depth) as parameter. The resulting output plot is compared with realized test structures.

Low-cost technology for multilayer electroplated parts using laminated dry film resist

Abstract An innovative technology for the realization of key elements of a microfabricated reduction unit is presented. In view of integrating the functions of gear, pinion and axle into one element, multilevel metal electroplating in a negative dry film resist mould (Riston) is used. Easier processing, inherent planarization for multilevel 3-D structures, vertical sidewalls and high thicknesses (20–50 μm/level) are shown to be the main key features of dry films. To demonstrate the process feasibility, a gear and pinion set with upper and lower axle posts has been realized with four levels of nickel.

Development of Insulated Conductive Probes with Platinum Silicide Tips for Atomic Force Microscopy in Cell Biology

A microfabrication process of a multifunctional probe is introduced for atomic force microscopy and various electrochemical measurements on biological samples in buffer solution. The silicon nitride probes have a spring constant lower than 0.1 N/m and a conductive tip, which is tightly insulated except at the apex. The conductive core of the tip consists of PtxSi y and shows a typical radius of curvature of 15 nm. A simultaneous measurement of topography and electrical current on graphite in air was demonstrated.

Making use of ion fluxes through potentiometric sensor membranes: ISEs with step responses at critical ion activities

Note: 246 Reference SAMLAB-ARTICLE-2001-027 Record created on 2009-05-12, modified on 2016-08-08

Wafer level hermetic package and device testing of a SOI-MEMS switch for biomedical applications

We have designed a wafer level chip scale package for a bi-stable SOI-MEMS dc switch using a silicon-glass hermetic seal with through the lid feedthroughs. Bonded at 365 °C, 230 V and 250 kg, they pass the fine/gross leak test after thermal cycling and mechanical shock/vibration according to MIL-STD-833, fulfilling the requirements for biomedical applications. The measured shear strength is 114 ± 26 N in correspondence with the theoretically expected 100 N. Ruthenium microcontacts are a factor of 100 more robust than gold microcontacts, being stable over 106 cycles measured in a N2 atmosphere inside the package presented here. Future work will include a more extensive bond quality assessment and continued microcontact reliability measurements.

Silicon Pressure Sensor Based on a Resonating Element

Note: 51 Reference SAMLAB-ARTICLE-1991-006 Record created on 2009-05-12, modified on 2016-08-08