Influencing factors on the sensitivity of MEMS-based thermal conductivity vacuum gauges

Abstract

The measurement range of thermal conductivity vacuum gauges is mainly influenced by the sensitivity of the sensing element to variations in pressure. An enhanced definition of sensitivity shows its theoretical dependence on the geometric measures of the sensor element at the whole pressure range. This value gives the possibility of direct comparison between different types of sensor structures without the influence of the operating conditions. To study the influencing factors, sensor chips with heated surfaces in the order of some tens of mm2 were realized by microelectromechanical systems-based fabrication techniques. By a silicon-glass hybrid process two cold planes were formed in a distance of 150 μm above and below the heated element. The thermal conductance of devices with different geometric measures was determined in constant temperature operating mode by usage of embedded measurement equipment. In this configuration the sensor signals were sensitive to pressure in a region from 10−5 mbar. The sensitivity was extracted by a fit of the theoretical model to the measurement data and showed the predicted dependencies on the geometric measures.

Optimized MEMS Pirani sensor with increased pressure measurement sensitivity in the fine and rough vacuum regimes

“…This electric circuit is based upon an operation amplifier that keeps R(T) constant [constant temperature (CT) mode], which is a common type of electric circuit for this operation mode that has been used by many other groups with several design variants. 4,8,27,43,44 The sensing nickel resistor RðTÞ follows the equation:…”

“…By miniaturizing the sensor element, new application fields are gathered. The new sensor elements are much smaller in size and are competitive 2,4,5, [11][12][13]21,[28][29][30][31][32][33][36][37][38]42,45 with or even improved 1,3, 15,17,[23][24][25]43 in sensitivity compared to conventional Pirani gauges. Many designs [6][7][8][9][10][14][15][16][17][18][19][20]22,26,34 have been developed for specific pressure ranges.…”

Miniaturized Plasma Actuator Flow Measurements by MEMS-Based Thermal Conductivity Sensors

“…Established measuring methods have the disadvantage that the flow generated by a miniaturized plasma actuator is strongly influenced by the sensor itself, like it is the case with Pitot-tubes [2], whereas techniques like particle imaging velocimetry (PIV) require a more complex setup and signal processing [3]. We present a new measurement method for micro DBD-plasma actuator flow using thermal conductivity MEMS-based surface hotfilms that provide a faster operating time, high frequency response and a less disturbing setup [4]. The measurement of the plasma-induced airflow could then be used to control and compensate the generation of instabilities leading to turbulent flow.…”

Sensor de umidade e vácuo baseado na reflexão interna

“…Vale notar, além disso, que existe a degradação desses, tanto natural quanto pela interação com as amostras estudadas, prejudicando a realização das medidas em longo prazo.No mesmo cenário estão presentes os monitores de vácuo, que são de grande importância em setores como: empacotamento, secagem, destilação, fabricação de lâmpadas, fabricação e operação de sistemas micro eletromecânicos, etc. Nesse caso, os métodos monitoram, em geral, variações na condutividade (térmica ou elétrica) da amostra ou algum tipo de deformação mecânica (18)(19)(20)(21)(22)(23)(24)(25). Seria, portanto, de grande interesse o desenvolvimento de métodos que possibilitem medidas de umidade ou vácuo de uma maneira mais simples e direta, sem a necessidade do uso de filmes finos.…”