Development of an electret microphone in silicon

We describe a subminiature electret microphone, which has been realized in silicon using wafer processing techniques. The microphone consists of a rigid backplate fabricated in silicon and a 2.5 μm thick metallized Mylar foil (PETP) acting as the diaphragm. Between the diaphragm and the backplate a 20 μm thick air cavity and a 1.1 μm thick charged SiO2 layer are present. The SiO2 layer is used as the electret and generates an electric field in the air gap. The electret has been changed to 300 V using a corona-charging set-up. The time constant of the charge decay amounts to more than 100 years at ambient laboratory conditions.\ud \ud The microphone cartridge, which measures 3 × 3 × 0.3 mm, shows an open-circuit sensitivity of about 2.5 mV/μbar at 1 kHz

A theoretical analysis of the electret air-gap field-effect structure for sensor applications

In order to develop a capacitive solid state sensor that makes use of an electret, a theoretical analysis is given of an electret air-gap field-effect structure.\ud \ud This structure is basically an MOS transistor with a movable gate and can thus be considered as a pressure-sensitive field effect transistor.\ud \ud It is shown that the addition of a metal layer on top of the semiconductor-oxide increases the sensitivity due to charge density multiplication.\ud \ud All calculations are based upon the displacement sensitivity S, which is independent of the mechanical properties of the diaphragm and thus independent of a specific application.\ud \ud Based upon the calculated sensitivities of the several configuration, a well-considered decision can be made as to which configuration is best suited for a specific application. In this paper this has been done for a solid state microphone and a pressure sensor as examples

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

Research and development of miniaturized electrets

A description is given of the realization of small electrets, using techniques generally applied in the fabrication of integrated circuits and microsensors. Attention is paid to the different electret decay mechanisms and their relative contributions to the overall stability of miniaturized electrets. A process is described by which polymer electrets such as Teflon-FEP and PTFE (polytetrafluoroethylene) can be deposited and shaped in a predefined pattern on a silicon wafer. Results on the application of new materials, especially silicon dioxide (SiO2), for use in electret applications, are presented. It appears that after an appropriate treatment of the oxide surface, its charge-stability is at least equal to that of polymer electrets such as Teflon-FEP and PTF

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

Spermatozoa detection and counting on Chip

Semen analysis is usually one of the first tests performed for detecting the cause of infertility of a couple. Therefore the man has to collect his semen in a special container and deliver it within one hour of collection to the hospital. The parameters determined with a semen analysis are the morphology and motility of the spermatozoa in the semen, as well as the concentratio