High-performance condenser microphone with fully integrated CMOS amplifier and DC-DC voltage converter

The development of a capacitive microphone with an integrated detection circuit is described. The condenser microphone is made by micromachining of polyimide on silicon. Therefore, the structure can be realized by postprocessing on substrates containing integrated circuits (IC's), independently of the IC process, integrated microphones with excellent performances have been realized on a CMOS substrate containing dc-dc voltage converters and preamplifiers. The measured sensitivity of the integrated condenser microphone was 10 mV/Pa, and the equivalent noise level (ENL) was 27 dB(A) re. 20 ¿Pa for a power supply voltage of 1.9 V, which was measured with no bias voltage applied to the microphone. Furthermore, a back chamber of infinite volume was used in all reported measurements and simulation

Theoretical and experimental determination of cell constants of planar-interdigitated electrolyte conductivity sensors

In this paper, an analytical expression is presented for the cell constant of planar-interdigitated electrodes used as electrolyte conductivity sensors. The result of this expression is compared with results of measurement carried out with several differently shaped planar probes provided with a thin Ta2O5 insulating film, showing good agreement. More than 10 different devices have been fabricated with predicted cell constants ranging from 0.14 to 4.44 cm¿1. The measured cell constants are typically 10¿20% smaller, possibly due to fringing effects

A drift free nernstian iridium oxide PH sensor

A novel way of eliminating drift problems in metal oxide pH sensors is presented. The method employs a FET-structure under the electrode that uses the metal oxide as a gate contact. In addition to the enhanced drift properties, the new sensor has an almost ideal nernstian response. First a theoretical explanation is given, which is then confirmed by measurement

Characterization of proteins by means of their buffer capacity, measured with an ISFET-based coulometric sensor-actuator system

Proteins form the specific selector in many biochemical sensors. A change in one of the properties of such a protein has to be detected by an appropriate transducer, which completes the biochemical sensor. One of these properties is the buffer capacity of a protein. If the binding of a substance to a protein can significantly change the proton binding, which accounts for the buffer capacity of proteins, the detection of this changed buffer capacity enables the construction of a new type of biosensor.\ud \ud It will be shown that the buffer capacity can be measured with an ISFET-based sensor—actuator device. The alternating generation of protons and hydroxyl ions by alternating current coulometry at a porous noble metal actuator electrode causes an associated small pH perturbation, which is detected by the underlying pH-sensitive ISFET. The amplitude of the measured signal is a function of the buffer capacity of the solute, in which proteins can be present (or these proteins can be adsorbed in the porous actuator electrode of the device). A model describing the transfer function from the electrical input signal of the actuator to the resulting chemical output, which is subsequently detected by the ISFET pH sensor, is presented. Preliminary results of the measured buffer capacity of ribonuclease and lysozyme are presented

A bi-directional electrochemically driven micro liquid dosing system with integrated sensor/actuator electrodes

In this contribution a micro liquid dosing system is presented, which allows bi-directional manipulation of fluids (i.e. pushing out and pulling in of liquids) by the electrochemical generation and removal of gas bubbles. Bi-directionality is obtained by reversal of the actuation current thereby causing the earlier produced gasses to react back to water. This reduction of gas volume actively pulls liquid back into the system. The electrochemical actuator electrodes have been specially designed to perform the simultaneous measurement of conductivity, via which the total amount of gas can be estimated. As this amount equals the total dosed volume of liquid, dispensed volumes can be determined on-line during experiment

The application of silicon dioxide as an electret material

The authors have investigated silicon dioxide for its electret properties. It appears that thermally grown silicon dioxide has a large lateral surface conductivity, resulting in poor electret behavior. This can be adequately reduced by chemical surface modification, resulting in an excellent silicon dioxide electret. Experiments have shown that corona-charged SiO2 layers are much more resistant to high temperatures than Teflon-FEP electrets. A 1.1-¿m-thick SiO2 layer, charged up to 150 V, yields a time constant of the charge decay in excess of 400 yr at ambient laboratory condition

Method of calibration for glucose sensor implemented in an integrated microdialysis based system

In this paper the novel method of calibration of glucose amperometric type sensor implemented in an integrated microdialysis based micro system is presented. This method consists in evaluation of the charge, resulting from the glucose consumption in the enzymatic reaction, transferred to the electrode under stop-flow conditions