Development of microfluidic chip flowmeter-based constant pressure system for analysing the hydrogen adsorption...

As one of the primary residual gases in vacuum, hydrogen affects the performance of MEMS devices. It commonly uses a non-evaporable getter (NEG) to adsorb hydrogen in this case. One of the standard test methods for NEG is the constant pressure method. However, most constant pressure test systems control the intake flow by valves or small orifices. These methods are crude and limit the reliability of the result. Therefore, it is necessary to provide a stable intake flow method for the constant pressure test system to improve the accuracy of the test.

We demonstrate a constant pressure system based on the microfluidic chip flowmeter to evaluate the hydrogen adsorption performance of non-evaporable getters in this paper. The microfluidic chip features microchannels with a height of around 100 nm. It is encapsulated with standard tube fittings, with leakage of less than 1 × 10^-13 Pa ∙ m³∙ s^-1. The conductance of the flowmeter is 10^-12 m³∙ s^-1, and the upper-pressure limit of the molecular flow is 10⁵ Pa. It can control the intake flow of the adapted constant pressure test system from 10^-11 to 10^-7 Pa ∙ m³∙ s^-1. Using this system, we tested the hydrogen adsorption capability of the Zr-Fe getter at different working pressures/temperatures and the types of gas it adsorbs were analysed. The results showed that the adsorbent has a noticeable adsorption effect on H₂ and a partial adsorption effect on H₂O, CO and CO₂.

The microfluidic chip flowmeter can provide a stable intake molecular flow for the adapted constant pressure test system. It ensures the reliability of the measurement results. The ability of the flowmeter to offer tiny flow rates at 10⁵ Pa can drastically simplify the test system and is more user-friendly for getters tests with poor adsorption performance. It has positive significance for industrial research on the non-evaporable getter.