A Composite-Type MEMS Pirani Gauge for Wide Range and High Accuracy

Abstract

To achieve a wide range and high accuracy detection of the vacuum level, for example, in an encapsulated vacuum microcavity, a composite-type MEMS Pirani gauge has been designed and fabricated. The Pirani gauge consists of two gauges of different sizes connected in series, with one gauge having a larger heat-sensitive area and a larger air gap for extending the lower measurable limit of pressure (i.e., the high vacuum end) and the other gauge having a smaller heat-sensitive area and a smaller air gap for extending the upper measurable limit. The high-resistivity titanium metal was chosen as the thermistor; SiNx was chosen as the dielectric layer, considering the factors relevant to simulation and manufacturing. By simulation using COMSOL Multiphysics and NI Multisim, a range of measurement of 2 × 10−2 to 2 × 105 Pa and a sensitivity of 52.4 mV/lgPa were obtained in an N2 environment. The performance of the fabricated Pirani gauge was evaluated by using an in-house made vacuum test system. In the test, the actual points of measurement range from 6.6 × 10−2 to 1.12×105 Pa, and the highest sensitivity is up to 457.6 mV/lgPa. The experimental results are better in the range of measurement, sensitivity, and accuracy than the simulation results. The Pirani gauge proposed in this study is simple in structure, easy to manufacture, and suitable for integration with other MEMS devices in a microcavity to monitor the vacuum level therein.

Surface Micromachined CMOS-MEMS Pirani Vacuum Gauge With Stacked Temperature Sensor

“…resonators [1], measuring the deflection of membranes [2], and evaluating the thermal conductivity of surrounding gases [3]. Among them, the Pirani vacuum gauge stands out due to its small size, simple structure, wide measurement range, and high resolution, making it a preferred choice for vacuum monitoring in confined spaces [4]. Furthermore, the emergence of microelectromechanical systems (MEMS) has triggered changes in the realm of vacuum sensor technology, enabling the fabrication of low-cost, high-performance, and integrated MEMS Pirani gauges [5], [6], [7], [8], [9].…”

“…To date, significant advances have been made in the research of micro-Pirani gauges, and a variety of different microstructure designs and sensing strategies have been proposed to improve sensor performance. Various sensing paradigms have been explored, including a sensor design that employs heat transfer between a vertically arranged microheater and heat sink, termed vertical heat transfer [4], [10], [11]. Similarly, sensor designs based on lateral heat transfer [12], [13], and hybrid vertical and lateral heat transfer [14] have also been reported.…”

“…Additionally, the performance of the Pirani gauge is also influenced by the number of heat sinks involved. However, most reported designs only incorporate one single heat sink [4], [10], [11], [12], while multiple heat sink designs necessitate more elaborate fabrication techniques [14], [17], [18], resulting in a reduction in sensor yield. Furthermore, in the prevailing research trend of multi-sensor integrated systems, there are very limited reports on integrated designs that combine vacuum gauges with other sensors [19].…”