NPL is supporting industry by providing measurement solutions to underpin the manufacture of advanced MEMS sensors.

Overview

The MEMS sensor market is growing rapidly. However, the metrology that supports the fabrication of MEMS sensors is struggling to keep pace with the expanding limits of MEMS technology. With this in mind NPL recently compiled a report detailing the MEMS sensor industry’s metrology needs and likely future requirements. Their report entitled ‘Overview of MEMS sensors and the metrology requirements for their manufacture’ gauges the metrological requirements of the MEMS sensor industry, reviews current MEMS manufacturing and metrology techniques, and highlights how metrology plays a role when manufacturing some of the key types of MEMS sensor (pressure, RF and microfluidic sensors, accelerometers and gyroscopes). The report details current metrology techniques used in MEMS manufacture such as profilometry, micro co-ordinate measuring machines, electron microscopy, optical microscopy, white light interferometry and laser Doppler velocimetry, and discusses their inherent limitations. Companies that contributed to the report included BAE Systems, Epigem, ETB, GE Sensing, Memsstar, QinetiQ, Rutherford Appleton Laboratory, STS and Tecan.

Research

Following on from the report detailed above, NPL is embarking on the following research projects:

1. Measurement of sidewall roughness, form and angle using micro-CMM technology – this work is being covered by a separate project.
2. Development of methods for measuring the absolute thickness of MEMS structures, for example, cantilevers, membranes and wafers. The preferred method is to use infra-red optical coherence tomography (IR-OCT).
3. Development of traceability routes for the measurement of dynamic response of MEMS structures, both in- and out-of-plane. This will involve the investigation of laser Doppler vibrometry and interferometry, and a comparison of the methods.

Publications

• Reilly, S P, Leach, R K, Cuenat, A, Awan, S A, Lowe, M Overview of MEMS sensors and the metrology requirements for their manufacture. NMS Programme for Engineering Measurement 2005-2008. DEPC-EM 008, October 2006

Collaboration

The vibrometry work is being carried out in collaboration with QinitiQ and that of IR-OCT with Druck and Taylor Hobson.

DMAC, MNT Meas. Club