Jean-Louis Aucouturier

Acoustic wave devices to measure gas flow: Comparison between surface acoustic wave (SAW) and shear horizontal acoustic plate mode (SH-APM) oscillators

Abstract In recent years there has been growing interest in using acoustic waves for a broad spectrum of physical and chemical sensor applications. In this paper we describe two types of acoustic flow sensors. For both devices, interdigital transducers (IDTs) on a piezoelectric substrate have been used to realize delay lines. The substrate is quartz with a SAW (SH-APM) propagation direction along (normal to) the crystallographic X axis. The delay line, mounted in an oscillator configuration and heated at a constant power with a screen-printed resistor, is placed in the path of the flowing fluid. Cooling caused by fluid motion induces a change in the oscillator frequency. The sensitivity of the two configurations (SAW and SH-APM) to flow rate at various heating power levels is presented and discussed. Taking into account simplified assumptions, we obtain an evaluation of the different heat-loss sources (thermal conduction, natural and forced convections). The interest of the SH-APM oscillator in terms of sensitivity and response time is demonstrated. This is all the more interesting as SH-APM devices are able to work in a liquid environment.

Detection of phosphine at the ppm level by Sr1 — yCayFeO3 — x thick layers pretreated with highly concentrated phosphine in air. Evidence of a transition of the surface conductivity from p- to n-type

Abstract Thick films and pellets of Sr 1 — y Ca y FeO 3 — x ( y = 0, 0.5 and 1) have been tested as sensors for detecting gaseous phosphine. In the absence of PH 3 pretreatment, the three compositions exhibit only small responses. All responses are characteristic of p-type semiconductivity. After pretreating with 2000 ppm PH 3 for 3 h at 360 °C, the semi-conductivity of thick films of SrFeO 3 — x remains of p-type, whereas those of thick films of Sr 0.5 Ca 0.5 FeO 3 — x and CaFeO 2.5 are changed into n-type. The responses of the latter two samples are large enough to allow ppm levels of PH 3 to be detected in air. The change from p- to n-type semiconductivity is verified by Seebeck effect measurements. The pretreatment time is apparently too short to have any effect on the pellets. IR absorption spectra and X-ray microprobe analysis of thick films suggest that part of the samples is converted into phosphate during the PH 3 pretreatment. Although the structure and composition of the bulk remains unaffected, as shown by X-ray diffraction, the surface of the grains is probably covered with thin layers of iron-containing phosphate, which control the transport and detection properties.

Apport de l’analyse technologique à l’enseignement de la microélectronique

RésuméL’analyse technologique des composants électroniques fait appel à des techniques de préparation d’échantillon et d’observation qui à l’heure actuelle permettent une investigation poussée de la conception et des technologies des circuits intégrés. L’objet de cet article est de proposer un document visuel, diaporama puis vidéo, permettant une illustration réaliste d’un enseignement de microélectronique, tout en préparant l’étudiant aux méthodes d’analyse elle-même. Cette approche nous semble particulièrement recommandée pour les futurs équipementiers qui devront procéder à Vévaluation et aux choix des circuits intégrés. Le produit pédagogique peut être utilisé, sous une forme simplifiée et descriptive, dans les cours de microélectronique ou de physique du composant en Maîtrise EEA. Mais il prendra une pleine dimension en DESS, DEA ou en 3e année d’école d’ingénieurs, spécialité microélectronique.AbstractThe technological analysis of electronic components uses different sample preparation and observation techniques which are able to give deep informations about the integrated circuit and technologies. The purpose of this paper is to propose, through a visual document, a method to illustrate realistically a microelectronic course. This approach seems to be especially appropriate for circuits and équipement engineer education, requiring a focussing towards IC’s evaluation and choice.