EU FP7 Programme
Gasera, University of Turku and VTT developing a MEMS
based gas sensor in an EU project
Pentti Karioja, VTT Technical Research Centre of Finland
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Consortium
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VTT (Finland)
UTU (Finland)
Gasera (Finland)
Ioffe (Russia)
SELEX (Italy)
Dräger (Germany)
Doble (Norway)
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9.4.2015
Process
INSTR
Enabling technologies Technology platforms
Application
System /
module
Component
/ device
Optical Comm.
&
processing
Lighting
&
Displays
Life Sciences
Safety
&
Security
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Energy
&
Environment
Optical measurement & sensor technologies: spectroscopy, machine vision, & imaging, interferometry etc.
Design & characterization: • 3D design & integration • Optics • Thermal Mgt • Electronics • Integrated optics
Precision mechanics • 3D mechanical design & construction • 3D optics design
3D System-in-Package & Integration: • Substrates • Assembly • Hermetic sealing • Thermal management
Polymer Integration: • Multi-layer lamination • Assembled foil over-molding • Nanoimprint
Si technology: MEMS/MOEMS • SOI waveguides
Printing technologies: R2R, UV imprinting, printing processes, materials, devices
11/16/2009
Background: Photoacoustic spectroscopy
 Photoacoustic effect was discovered
in 1880 by Alexander Graham Bell
 The theoretical limitations of this
technology are far from what has been
achieved with any technology today
 The full potential has not been
reached due to the use of
conventional microphones in sensing
the pressure waves.
Photoacoustic spectroscopy is based on the absorption of light leading to the local warming
of the absorbing volume element. The subsequent expansion of the volume element generates
a pressure wave proportional to the absorbed energy, which can be detected via a pressure
detector.
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Background: Cantilever sensor with optical readout
 Finnish SME Gasera has developed a novel
MEMS cantilever approach where the
displacement is 100 that of microphone
membrane [1],
 Cantilever sensor is coupled with interferometric
measurement of the displacement,
 Below picometer (10-12) displacement can be
detected with the optical readout,
 Theoretical predictions indicate cantilever based
PA cell can be miniaturized with sensitivity up to
three orders of magnitude over the prior art.
[1] J. Kauppinen, K. Wilcken, I. Kauppinen, and V. Koskinen,
“High sensitivity in gas analysis with photoacoustic detection,”
Microchem. J. 76, 151-159 (2004).
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Background: Differential photoacoustic measurement
 Silicon cantilever microphone is placed in a twochamber differential gas cell.
 The differential PA cell operates as a differential
IR detector for optical absorption signals
propagating through the measurement and
reference path.
 Pressure difference modulation between the
chambers is monitored by probing the cantilever
movement with an optical interferometer.
 Allows for open-path and flow-through detection
of gases.
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Benefits of the cantilever
enhanced differential PA sensor
 The detection limit is independent on the size of the gas cell which gives
potential for miniaturization.
 The novel cantilever microphone provides high sensitivity from short
absorption path length and highly linear concentration response over a wide
dynamic measurement range.
 Low detection limits can be reached with low power light source,
 The gas inside the differential cell acts like an optical filter (so-called gas
correlation method) providing good selectivity without optical filters or
spectrograph.
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MINIGAS targets
 Compact, rugged gas sensor providing significant
improvement in sensitivity:
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Sensor volume target: 5 cm3
Analysis response time  100 ms
Dynamic range >10 000
Temperature range: - 300C to + 500C
Cost of goods: €100 in high volume production
 Sensors modular structure allows it to be applicable to a
wide range of gases including: CH4, CO2, CO, NH3, …
 Applications including: leak detection, safety, homeland
security and air quality.
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MINIGAS technology roadmap
EU-project
Commercialized
gas sensor
volume < 5 cm3
integrated optic chip
Commercial gas analyzer
19” rack mount analyzer
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Technology portfolio of
sensor subsystems
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IR LEDs with customized wavelengths and performance
Silicon MEMS cantilever pressure sensor
Spatial read-out interferometer
Low Temperature co-fired Ceramics (LTCC)
photoacoustic measurement cell
 On-board drive, detection and readout electronics
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Infrared Light Emitting Diodes
 InAs and InAsSb based diode
structures have been processed
into flip-chip devices with active
areas sized by 300 μm and
reflective contacts by a
multistage wet photolithography
method.
 LEDs are equipped with Si
lenses with shape close to
hyperhemisphere attached to the
contact free surface through the
use of high reflective index glue.
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Silicon MEMS cantilever
mask layout
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Spatial Interferometer for
cantilever readout
 Based on creating interference by wavefront splitting in order to avoid expensive
beam splitting optics.
 High temperature stability is achieved by
using the cantilever frame as the reference
mirror.
 Initial tolerance analysis estimates 0.1 mm
positioning accuracy and 0.5 degrees for
angular alignment accuracy as the tightest
requirement.
 Performance goal: 1.0 pm displacement
sensitivity.
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LTCC photoacoustic
measurement cell
 The vertical cavity is
laminated using a silicone
insert,
 Cells are drilled at the
laminated stage before the
co-fire,
 Reflective metal coating by
thick film coating,
 Sapphire windows are
sealed with solder glass
paste,
 The He-leak rate for the
sealed modules was <2.0
×10-9 atm×cm3/s, which
fulfills the requirements for
the leak rate according MILSTD 883.
Photoacoustic
cell chamber dimensions:
2.5  2.5  10.0 mm
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Predicted performance
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First experiments using sensor platform
Portable methane sensor demonstrator based on LTCC
differential photo acoustic cell and silicon cantilever
 The assembled sensor fitted in a volume
of 40 mm x 40 mm x 35 mm. The
achieved differential pressure signal was
proportional to gas concentration in the
open measurement path of gas flow.
 The sensitivity of the first prototype was
300 ppm for methane with 1 s response
time. Sensitivity is increased to 30 ppm,
when response time of 100 s is used.
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Mr. Juha Palve (VTT)
juha.palve@vtt.fi
+358 400 488 414
www.minigas.eu
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