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Summary
The Optomechanical Pressure Sensing project is developing new pressure sensors and transfer standards for the medium vacuum (0.1 Pa to 100 Pa) and high vacuum (10-6 Pa to 0.1 Pa) ranges. Our approach uses optical interferometry to measure the well-known gas-damping response of mechanical oscillators. The mechanical pressure sensors that we create can strengthen calibration chains and improve industrial process control by being simple, robust alternatives to legacy pressure gauges.
Description
Figure 1: Optical microscope image of a silicon nitride trampoline pressure sensor.
Measurement and control of high-vacuum pressure is important for many industrial processes, particularly semiconductor fabrication. Typical process pressure monitors are known to lose accuracy over time and so require repetitive calibration. Pressure transfer standards that support high-vacuum and medium-vacuum calibrations, particularly spinning rotor gauges, are expensive, sensitive to environmental changes, and can be difficult to operate.
We are developing simple, small vacuum pressure sensors based on residual-gas-induced damping of tethered mechanical oscillators. Our mechanical oscillators are approximately 100 nm thick silicon nitride ‘trampoline’ oscillators (see Figure 1). After we excite a mechanical vibration of our trampoline sensor, collisions with gas molecules slowly reduce the mechanical vibration amplitude. We measure the sensor’s vibration amplitude, and thus the gas-induced damping rate, using an optical interferometer. From the measured mechanical damping rate and characterized properties of the trampoline sensor, we can infer the gas vacuum pressure with low uncertainty using the kinetic theory of gases.
Currently, our effort is focused on improving the operating pressure range and readout speed of our sensors. Trampoline sensors with longer, thinner tethers will have both higher sensitivity to gas collisions and reduced parasitic mechanical damping. As a result, they will be able to measure pressure farther into the high vacuum range. We are also developing methods to coherently control the sensor’s mechanical vibration, which will allow fast, repeatable measurements of the mechanical damping rate. We anticipate that, with these two advances, our sensors can match or exceed the performance of the legacy process controllers and transfer standards for high vacuum.
Opportunities: If you are interested in joining our project as a postdoctoral researcher, guest researcher, collaborator, or student, reach out to our technical contacts.