A New Macro-Model of Gas Flow and Parameter Extraction for a CMOS-MEMS Vacuum Sensor

Abstract

When using a MEMS sensor to measure the vacuum of a medium, the transition flow between the viscous flow and molar flow is usually used to describe the gas convection due to the physical principle, which is difficult to study through analysis and simulation. In this study, the description of gas flow under different pressures in a CMOS-MEMS vacuum sensors has been incorporated into a new behavioral ANSYS model. The proposed model was built and the characteristic parameters in the model were obtained based on a CMOS-MEMS thermopile patterned with circular symmetry and an embedded heater as a heat source. It contains a characteristic length to describe the effective distance of heat dissipation to the silicon substrate, and the corresponding transition pressure to describe the symmetrical phenomenon of gas heat conduction. The macro-model is based on the description of the physical characteristics of heat transfer and the characteristic parameters of the CMOS-MEMS vacuum sensor. The characteristic length of 49 μm and the corresponding transition pressure of 2396 mTorr for the thermoelectric-type vacuum sensor were extracted and verified successfully. The results show that the average error for the prediction of vacuum sensing by the macro-model we proposed is about 1.11%. This approach provides more applications for vacuum analysis. It can reduce the complexity of simulation and analysis and provide better simulation effects, including gas conduction mechanisms.

A combined MEMS thermal vacuum sensor with a wide pressure range

“…Both heater and thermosensitive element are embedded in the sensitive region and connected to the external circuit via connecting wires which are inside the supporting legs. Based on the thermosensitive element, the MEMS thermal vacuum sensors can be classified into three main categories: thermistor-type [18][19][20], thermopile-type [21][22][23] and diode-type sensors [24][25][26], and the diode-type sensors commonly employ p-n junction diode. Normally, When the thermosensitive element is thermistor or diode, they could be treated as heater simultaneously since they all have Joule effect.…”

Overview of the MEMS Pirani Sensors

“…A thermocouple-based Pirani sensor works based on the Seebeck effect [82], when the hot ends are heated, at the cold ends there forms a voltage, as is shown in Figure 5a. This type of Pirani sensors is usually composed of several pairs of thermocouple strips [83][84][85][86][87][88]. The thermocouple strips are connected in series to form a thermopile, where the hot ends are heated by a heater, while the cold ends are located on heat sinks, which keeps the temperature of the cold ends consistent with the ambient temperature.…”

A Performance Enhancement Method for MEMS Thermopile Pirani Sensors Through In-Situ Integration of Nanoforests

“…Besides, the series connection of multiple thermocouple strips also multiplies the output signal of the sensor. More importantly, they have a wider pressure detection range and higher sensitivity [13], [14]. With all these advantages, the thermopile Pirani sensors are of great research interest.…”