temperature sensors, positioned symmetrically above and below the heat source,
detect very small temperature differences
with extreme sensitivity. These measurements provide the fundamental information on heat dispersion which can be
directly correlated to the flow rate. Sensirion’s patented CMOSens® technology
enables the miniaturized thermal sensor
and the complete high-precision evaluation circuit to be integrated on a single
Complimentary Metal-Oxide Semiconductor (CMOS) microchip. This ensures
that the sensitive analog sensor signals are
amplified, digitized, and further processed
without interference and with the highest
precision, enabling the chip to provide the
user with a calibrated and linearized signal
via a digital interface.
To isolate our liquid flow sensors
from the medium they’re measuring, we
perform the measurement through the
very thin wall of a specifically designed
flow channel. In this way, the silicon Mi-croelectromechanical systems (MEMS)
chip with the onboard CMOS logic is
media-isolated from the fluid. For any biomedical application, this is very important
as it allows the sensor to measure body
fluids or valuable and possibly aggressive
drugs without the risk of contamination
or damage of the chip.
In order to combine the LD20 sensor
with the micropump, the flow channel
of the sensor had been extended and
modified, allowing a seamless integration of the micropump to be established.
Fluidic connectors barbed fittings have
been chosen to enable a simple connec-
tion with flexible tubes. Our engineers
have gathered over many years a lot of
experience with the requirements for
such customized flow channel designs.
There is no other piece needed to
establish a connection between the two
3. Can you tell us a little more about how
the components were fabricated?
Both components, the sensor and the
micropump, are based on the MEMS
technology and are thus manufactured
on silicon wafer level. Similar processes
are used in a wide variety of electronic
products for constructing integrated
circuits. The economies-of-scales, the
ability, and long term
stability are only some of the
advantages this technology has to
offer for a cost-efficient high-volume
For a wearable, single-use component
in the medical field, low end user costs,
low power consumption, and small size
are the main requirements.
Sensirion has combined the MEMS
with the well-known CMOS technol-
ogy on a single chip in order to allow
for an extremely fast, miniaturized, and
highly precise measurement (CMOS-
ens® Technology). The sensor’s output
is thus a linear, fully calibrated, and
temperature-compensated flow mea-
surement signal with up to 1,000 values
The heart of the micropump is a piezo
actuated micro diaphragm pump made
of silicon. Despite its tiny size (currently
5 x 5 x 0.6 mm3) it reaches type dependent flow rates with water of up to 1,000
µl/min. The current design’s minimum
displaced volume is 50 nanoliters.
4. Why was silicon used to fabricate the
Scientists at the Fraunhofer EMFT research institution have developed various
micro membrane pumps made of silicon,
because they can be manufactured cost-efficient in high volumes at wafer level.
The same holds true for the CMOSens®
Technology from Sensirion.
The deployed silicon processes are
strong and continuously driven by the
computer chip industry for example.
Sensirion and the Fraunhofer EMFT
benefit from the developed innovations.
5. What’s next for this technology?
Sometimes innovative ideas ask for new
solutions and the team of experts at
Sensirion is always keen on finding ways
to make interesting applications happen
through our technology. Our engineers
can develop customized LD20 designs for
high-volume applications to fit different
form factors, materials, flow rates, pressure
ratings, and fluidic connections for a wide
range of applications. MDT
Figure 2. LD20 liquid flow sensor
(Image Credit: Sensirion)
Figure 3. CMOSens Technology of liquid flow sensors (Image Credit: Sensirion)