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

Gas bubbles electrolytically generated at microcavity electrodes used for the measurement of the dynamic surface tension in liquids

A new method is proposed for the measurement of dynamic surface tension in aqueous solutions. The advantage of this method with respect to the classical method based on sparging is that the use of gas pumps is avoided, resulting in a miniaturized system. This method is based on the in situ generation of gas bubbles by means of electrolysis at microcavity electrodes (MCEs). As a consequence of electrode surface shaping, a single nucleation site for gas bubbles is created. The MCE is used simultaneously as a bubble actuator (generator) and as a bubble size and/or frequency sensor. Measurement results prove the suitability of the electrolytic method for the monitoring of the dynamic surface tension in aqueous solutions

On the mechanical behaviour of thin perforated plates and their application in silicon condenser microphones

In this paper an alternative approach to the modelling of plates with a large number of holes is presented. By means of plate theory, it is shown that perforated plates can be modelled by conventional orthotropic plates with modified elastic properties. The modification of the elastic constants is derived by equalizing the strain-energy of the perforated and the orthotropic plate. The model obtained is then compared with previous methods and applied in the electrochemical simulation of a silicon micromachined microphone structure. The microphone structures are simulated numerically, using an algorithm based on finite differences

A polymer condenser microphone on silicon with on-chip cmos amplifier

In this paper the development of a capacitive microphone with integrated preamplifier is described. The condenser microphone is made by micromachining of polyimide on silicon, and is compatible with CMOS technology. Therefore, the structure can be realised by post processing on substrates containing integrated circuits, independently of the IC process. Microphones with a required DC bias voltage of 4 V have been realised on a CMOS substrate containing PMOS buffer preamplifiers. From the measurements on these structures, it is illustrated how an immediate improvement of 4.8 dB of the microphone sensitivity and noise level can be obtained by using the integrated preamplifier. The measured sensitivity of the integrated condenser microphone was 2.5 mV/Pa and the equivalent noise level (ENL) was 29.5 dB(A) SP

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 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 design, fabrication, and testing of corrugated silicon nitride diaphragms

Silicon nitride corrugated diaphragms of 2 mm×2 mm×1 ¿m have been fabricated with 8 circular corrugations, having depths of 4, 10, or 14 ¿m. The diaphragms with 4-¿m-deep corrugations show a measured mechanical sensitivity (increase in the deflection over the increase in the applied pressure) which is 25 times larger than the mechanical sensitivity of flat diaphragms of equal size and thickness. Since this gain in sensitivity is due to reduction of the initial stress, the sensitivity can only increase in the case of diaphragms with initial stress. A simple analytical model has been proposed that takes the influence of initial tensile stress into account. The model predicts that the presence of corrugations increases the sensitivity of the diaphragms, because the initial diaphragm stress is reduced. The model also predicts that for corrugations with a larger depth the sensitivity decreases, because the bending stiffness of the corrugations then becomes dominant. These predictions have been confirmed by experiments. The application of corrugated diaphragms offers the possibility to control the sensitivity of thin diaphragms by geometrical parameters, thus eliminating the effect of variations in the initial stress, due to variations in the diaphragm deposition process and/or the influence of temperature changes and packaging stres

On the integration of a microdialysis-based microTAS with calibration facility on a silicon-glass sandwich

The integration is discussed of all parts of a microdialysis-based micro Total Analysis System or ¿TAS. In particular a microdialysis probe, a potentiometric and amperometric ion- and enzyme sensor and a calibration dosing pump have been developed separately using different precision machining techniques. By modifying and adapting these parts they can be realized in one generic technology consisting of a stack of a silicon and a glass wafer. The silicon wafer contains the double lumen microdialysis probe connections, a dosing pump chamber with meander formed cavities containing the calibration solutions and small cavities for both the potentiometric and amperometric sensor. The glass wafer contains all the electrical contacts and wires for the sensors, the pump and Interconnections. Both wafers are anodically bonded to each other, yielding a hermetically sealed liquid handling syste

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