Design of a High Sensitivity Pirani Gauge Based on Vanadium Oxide Film for High Vacuum Measurement

Abstract

We have designed a hot-plate-type micro-Pirani vacuum gauge with a simple structure and compatibility with conventional semiconductor fabrication processes. In the Pirani gauge, we used a vanadium oxide (VOx) membrane as the thermosensitive component, taking advantage of the high temperature coefficient of resistance (TCR) of VOx. The TCR value of VOx is −2%K−1∼−3%K−1, an order of magnitude higher than those of other thermal-sensitive materials, such as platinum and titanium (0.3%K−1∼0.4%K−1). On one hand, we used the high TCR of VOx to increase the Pirani sensitivity. On the other hand, we optimized the floating structure to decrease the thermal conductivity so that the detecting range of the Pirani gauge was extended on the low-pressure end. We carried out simulation experiments on the thermal zone of the Pirani gauge, the width of the cantilever beam, the material and thickness of the supporting layer, the thickness of the thermal layer (VOx), the depth of the cavity, and the shape and size. Finally, we decided on the basic size of the Pirani gauge. The prepared Pirani gauge has a thermal sensitive area of 130 × 130 μm2, with a cantilever width of 13 μm, cavity depth of 5 μm, supporting layer thickness of 300 nm, and VOx layer thickness of 110 nm. It has a dynamic range of 10−1~104 Pa and a sensitivity of 1.23 V/lgPa. The VOx Pirani was designed using a structure and fabrication process compatible with a VOx-based uncooled infrared microbolometer so that it can be integrated by wafer level. This work contains only our MEMS Pirani gauge device design, preparation process design, and readout circuit design, while the characterization and relevant experimental results will be reported in the future.

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

“…On the other hand, a conventional Pirani gauge has the shortcomings of a relatively narrow range of measurement, low sensitivity, and low accuracy. We have designed a high-sensitivity Pirani gauge in previous work [ 8 ]. In addition, a prior work demonstrates that a composite-type Pirani gauge is promising for a vacuum detection sensor of a wide range: Two gauges of different sizes are connected in series, one with the larger thermal area being more sensitive in the lower-pressure range and the other more sensitive in the higher-pressure range [ 9 ].…”

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

“…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].…”