Measurements of theinitial deflection of anano pressure sensor forbiological applications
In the fabrication of nano pressure sensors for biological applications, thesacrificial layer etching and the sealing of the two membranes separated bya vacuum gap to form a Fabry–Pérot resonator is critical. Knowing the exact
timing of the initial deflection of the membrane after the fabrication process
is also key.

The Barcelona Microelectronics
Institute (IMB) is the National
Microelectronics Centre (CNM)’s
Barcelona location and amember of the Spanish ResearchCouncil. IMB-CNM has a focus
on basic and applied researchand development, in addition toeducation and training in micro andnanotechnologies, components
and systems. Our mission is toexpand the knowledge available
in this field and to contribute tothe implementation of solutions
and new products based in thesetechnologies in order to resolve thechallenges faced by society today.
Project currently being undertaken
by Ms. Marta Duch.

Figure [1] SEM

image of thefabricated pressuresensors. Bar scale
1 µm.
CASE STUDY MEASUREMENTS OF THE INITIAL DEFLECTION OF A NANO PRESSURE SENSOR FOR
BIOLOGICAL APPLICATIONS

1■ Measurements
The pressure sensor is a 6x10 µm chip comprised of a mechanical sensor
deﬁned by two polysilicon membranes separated by a vacuum gap, andan optical reference area. The membranes act as parallel reﬂecting mirrors,
constituting a Fabry–Pèrot resonator that is partially transparent for somewavelengths. An external pressure P deﬂects the membranes and changes
the gap. This device was designed to measure pressure changes inside thedifferent components of a living cell.

Figure [2] Device with a non-collapsed membrane (top) and a device with a collapsed

membrane (bottom). Bar scale 1 µm.

Currently, membrane deflection measurements are carried out using
Scanning Electronic Microscopy (SEM) before being internalized, but in theSEM, samples must be under vacuum pressure which may alter their initialstate.
Using a Sensofar optical profiler we were able to measure,in a quick and non-intrusive way, the deflection of themembranes after manufacturing. The dimensions of
the chip are only a few microns, but the curvature of
the membrane is closer to tens of nanometres, so it’snecessary to use a high magnification lens.
Figure [3] 3D topography of a pressure sensor’s array

before the release from substrate.

2

CASE STUDY MEASUREMENTS OF THE INITIAL DEFLECTION OF A NANO PRESSURE SENSOR FOR
BIOLOGICAL APPLICATIONS

Figure [4] Profile analysis of several pressure sensors.

■ Conclusions
With this technique, it’s possible to obtain a fast and non-destructive
measure of the deflection of the released membrane before and after sealing
to check if membranes have collapsed. Previously, they had to be inspectedby SEM which produced changes in the deflection of the membrane dueto the vacuum and the value of the deflection was not as reliable. These
measurements were obtained with a Plµ 2300 using a confocal techniquewith a 100X brightfield objective.
Sensofar equipment provides non-contact 3D surface profilers based on
three technologies: Confocal, Interferometry and Focus Variation techniques.
With Sensofar equipment, high-resolution measurements can be madequickly and in a non-destructive way, and user-friendly software provides
technical support as needed.

Figure [5] 3D topographyof a 6x10 µm
released pressure
sensor..

CASE STUDY MEASUREMENTS OF THE INITIAL DEFLECTION OF A NANO PRESSURE SENSOR FOR
BIOLOGICAL APPLICATIONS

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