Zur Emissivität partiell transparenter, dielektrischer Schichten

Abstract

Die genaue Analyse einer neuartigen Methode zur experimentellen Bestimmung der Wä rmeleitfä higkeit dü nner Schichten aus dielektrischen Materialien hat gezeigt, dass die Wä rmeabstrahlung bei solchen Messungen nicht generell vernachlä ssigt werden darf. Mit einem Finite-Elemente-Modell, das die Abstrahlung durch eine effektive Emissivitä t der Oberflä che als Anpassungsparameter berü cksichtigt, erzielt man hingegen sehr gute Ü bereinstimmung mit den Messergebnissen. In dieser Arbeit wird nachgewiesen, dass dieser Wert der effektiven Emissivitä t mit den Absorptionsdaten der dielektrischen Schicht im Einklang steht. Auf der Grundlage der prä sentierten Berechnungsmethode ist die Abschä tzung der Emissivitä t von flä chenhaften Dü nnschicht-Bauelementen mö glich. Umgekehrt ist aufgrund der bestä tigten Modellvorstellungen die Entwicklung neuer experimenteller Methoden zur Bestimmung der effektiven Emissivitä t als auch der Wä rmeleitfä higkeit mö glich. Schlü sselwö rter: Emissivitä t; Siliziumnitrid; Siliziumdioxid; SandwichschichtenOn the emissivity of partially transparent dielectric layers.The examination of a new experimental method for the determination of the thermal conductivity of thin dielectric layers revealed that thermal radiation may interfere with such measurements. Using an effective emissivity parameter to account for radiative heat loss, an excellent agreement between measurement and related finite element models is achieved. This paper deals with the successful attempt to confirm the mentioned model based on calculations of the emissivity of thin, partially transparent film from infrared absorption data. A reasonable agreement of the emissivity estimates obtained by the different approaches is achieved. Hence, the emissivity of new designs of thin-film devices may be calculated in advance based on infrared absorption data. Futhermore, the presented calculations enable the development of appropriate devices for the determination of the effective emissivity and the thermal conductivity.

Frequency Domain Based Measurement Method for the Thermal Parameters of a Thin-film Diaphragm Embedded in a MEMS Multi-parameter Wind Sensor

“…Once they are calculated, the temperature at the thermistor sites can be derived by averaging # p;i .r/ of the element representing the thermistor over the thermistor surface. Figure 4 comprises analytical, numerical, and measurement results obtained for an imposed power of 1:56 μW of the time-harmonic heating component, an ambient temperature of T 0 D 20 ı C, and thermal thin-film parameters of the conducting paths taken from [2]. The validity of our semi-analytical approach was verified by a comprehensive 3D finite element method (FEM) model of the multi-layer diaphragm sandwich.…”

“…This modeling approach enables an efficient computation of the peak excess temperature # p (i. e, the magnitude of the time-harmonic excess temperature component) in the diaphragm and is justified owing to the following two conditions. First, in view of the high aspect ratio of diameter to thickness of the diaphragm, the heat loss due to radiation leads to imperceptible temperature variations within the thickness [2]. Second, the thin-film conducting paths feature a much higher conductivity than the diaphragm, but a much lower effective cross section yielding a total heat transfer contribution in the same order.…”

“…To quantify this effect and in further consequence to develop optimized devices, reliable values for the thermal thinfilm parameters of the embedded diaphragm are mandatory. However, thin-film parameters typically depend on the production process and can differ considerably from those of bulk material [2,3]. Common techniques for their determination require fabrication of custom test structures (e.g., thin-film cantilevers [3]).…”

Transient measurement method for the thermal properties of the thin-film membrane in a multi-parameter wind sensor

“…4b), where each wedge is identified by a reference number i . The influence of the multi-layer structure on the heat transfer is taken into account by transforming the layered cross section into an equivalent homogeneous cross section with the same resultant thermal conductivity i and diffusivity Ä i while the change in emissivity " i is neglected [7]. A similar ansatz has been previously utilized in [8], [9].…”

Measurement technique for the thermal properties of thin-film diaphragms embedded in calorimetric flow sensors

“…In general, our parameter extraction procedure is expected to be very accurate as all relevant heat transfer effects within the device are taken into account. However, it is important to notice that the emissivity, in general, strongly varies with the temperature and the thin film thickness, particularly for very thin, (semi)transparent films where the whole volume contributes to the radiation (Kohl et al 2008a). Our specimen generates only excess temperatures in fraction of degree centigrade above ambient temperature and therefore all measured values are related to ambient temperature.…”