G

S

Ad

SD

a

ARRAA

KFPBAFL

1

irsetcfloemeararflaft

S

0h

ARTICLE IN PRESS Model

NA-8490; No. of Pages 6

Sensors and Actuators A xxx (2013) xxx– xxx

Contents lists available at ScienceDirect

Sensors and Actuators A: Physical

jo ur nal homepage: www.elsev ier .com/ locate /sna

MEMS-based passive air flow regulator for handheld breathiagnostics

taffan B. Johansson1, Göran Stemme, Niclas Roxhed ∗

epartment of Micro and Nanosystems, KTH Royal Institute of Technology, Sweden

r t i c l e i n f o

rticle history:eceived 15 April 2013eceived in revised form 19 August 2013ccepted 12 September 2013vailable online xxx

a b s t r a c t

This paper reports on a passive MEMS-based flow regulator designed to maintain a steady flow duringasthma diagnostics. A prototype consisting of six in-plane moving pistons that restrict the flow through sixflow orifices has been fabricated from three wafers using standard silicon micromachining. The in-planedesign enables relatively large flows and tuning of the flow and pressure range to specific applicationrequirements by changing a wafer thickness. In particular, for FENO asthma monitoring, regulatory guide-lines specifies that measurements should be made at steady flow of approximately 50 ml/s and within

eywords:low regulatorassivereath diagnosticssthmaENO

a pressure range of 1–2 kPa. Experimental evaluation of the prototype shows that the flow rate is con-trolled within a dynamic pressure range of 770 Pa compared to only 430 Pa for a dummy structure andthat it can be achieved on a chip measuring only 2 mm × 2 mm × 4 mm. The evaluation also showed thatcondensation of exhaled air that expectedly occurs in the flow regulator at room temperature can beeliminated by local heating of the device to 40 ◦C.

arge flow

. Introduction

Exhaled breath diagnostics as a clinical method is reachingncreasing acceptance in a variety of different diseases. To ensureeproducible measurement results, exhaled breath from patientshould conform to certain protocols dictating the physical param-ters (e.g. flow rate, pressure, temperature, etc.) under which theest should be made. The current trend toward handheld point-of-are devices has brought a need for miniaturized and cost-effectiveow handling systems that can deal with the relatively large flowsf exhaled breath. Specifically for asthma monitoring and fractionalxhaled nitric oxide (FENO) [1], regulatory guidelines dictate thateasurements of nitric oxide concentration should be made at an

xhaled flow rate of 50 ± 5 ml/s [2]. Today this is achieved by bulkynd relatively costly macro scale flow regulators. However, a flowegulator built on MEMS technology could overcome the bulkinessnd potentially be more cost efficient. Passive MEMS-based flowegulators have been demonstrated mainly for controlling liquidows in drug delivery and microfluidic applications [3–5]. It has

Please cite this article in press as: S.B. Johansson, et al., A MEMS-based passA: Phys. (2013), http://dx.doi.org/10.1016/j.sna.2013.09.012

lso been used as self-controlling features to control gas flows inuel cell applications [6] and in adaptive cooling [7]. However, con-rol of large flows in the 50 ml/s regime requires relatively large

∗ Corresponding author at: Micro and Nanosystems, Osquldas Väg 10, SE-100 44tockholm, Sweden. Tel.: +46 87909143.

E-mail addresses: stajoh@kth.se (S.B. Johansson), roxhed@kth.se (N. Roxhed).1 Tel.: +46 87909059.

924-4247/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.sna.2013.09.012

© 2013 Elsevier B.V. All rights reserved.

cross sectional areas of the flow channel and large movements ofthe flow regulating structure. Thus a MEMS implementation thataddresses these challenges while still having a small chip footprintis not straightforward. Recently we have introduced a miniaturizedand passive air flow regulator operating in that flow regime [8]. Thisis the first MEMS-based passive device controlling large air flowsfor breath monitoring. Here this flow regulator is compared to staticflow restricting structures and tested with humid exhaled air.

2. Design and operation

Considering the requirements of a relatively large flow of50 ± 5 ml/s and a pressure of 1–2 kPa, and the consequential geo-metrical requirements such as large cross sectional area of the flowchannel and large movements of the regulating structure, an in-plane design was developed. This allows for long stroke of theregulating structure, enabling better control of large flows. In-planedesigns have previously been suggested for controlling and sensingin microfluidic applications but not for breath diagnostic appli-cations [9]. Multiple-orifice arrangements have been reported toimprove flow performance and reduce footprint area when con-trolling large flows [10]. Hence, a multiple-orifice approach wasutilized in this design by using six pistons creating twelve lin-ear flow orifices. The pistons are connected through two crossbars

ive air flow regulator for handheld breath diagnostics, Sens. Actuators

that are suspended through folded springs as illustrated in Fig. 1.The number of pistons was chosen by first considering the foot-print versus manufacturability balance qualitatively for a successfulproof-of-concept, resulting in a certain minimum piston and spring

ARTICLE ING Model

SNA-8490; No. of Pages 6

2 S.B. Johansson et al. / Sensors and Ac

Airflow

Moving piston

Crossbar

Spring

Stop post

Flow restrictor

Fig. 1. Schematic top view of the flow regulator. Six pistons connected together bytwo crossbars and suspended by springs can move in-plane in the flow direction.Cp

srpfsaaorpplo

5hmu

k

wm

Fs

rossbars and springs are fabricated in the device layer of an SOI-wafer while theistons, stop posts and flow restrictors are fabricated in the handle wafer of the SOI.

ize, and then considering the flow requirements quantitatively,esulting in the actual number of pistons. Hence, the number ofistons can be optimized once the quantitative limitations of manu-acturability such as cost per die are known. The piston and crossbartructure can move up to 200 �m in the direction of the flow. When

pressure is applied at the 2.8 mm wide inlet port, the pistonsre forced to move toward the flow restrictors causing the flowrifices between the pistons and the flow restrictors to be nar-owed, effectively increasing flow resistance. For protection againstressures higher than 2000 Pa, stop posts are designed to restrictiston movement beyond 200 �m. The flow channel is capped by a

id and a bottom substrate, each with a recess to enable movementf the regulating structure as illustrated in Fig. 2.

The dimensions of the pistons seen in the Fig. 1 top view are00 �m × 200 �m and the stop posts are 75 �m × 35 �m while theeight of the structures is 830 �m. To meet the required pistonovement of 100 �m/kPa, the spring constant can be calculated

sing the following expression:

p · A

Please cite this article in press as: S.B. Johansson, et al., A MEMS-based passA: Phys. (2013), http://dx.doi.org/10.1016/j.sna.2013.09.012

=x

(1)

here p is the differential pressure over the pistons i.e. approxi-ately the inlet pressure, A is the surface of the pistons facing the

ig. 2. A 3D illustration showing a cross section of the spring and crossbar structureupporting the moving pistons in scale. The pistons and the posts are 830 �m high.

PRESStuators A xxx (2013) xxx– xxx

inlet pressure and x is the travel. This results in a spring constant ofapproximately 10 N/m. The dimensions of the springs can then becalculated using the following expression [11]:

k =(

nsprings

nfolds

)· kbeam =

(42

)·(

Esi · t · w3

l3

)(2)

where nsprings is the number of springs connected in parallel, nfoldsis the number of folds on each spring, Esi is the Young’s modu-lus of silicon (170 GPa) and t, w and l are the thickness, widthand length of the spring beams respectively. Using a thickness of18.4 �m and a width of 10 �m this results in a beam length (innerdimension of the loop) of approximately 855 �m. Variations in fab-rication such as scalloping and under etching during the Bosch etchprocess was accounted for by designing the beams with a widthof 11 �m.

A simulation was performed in ANSYS to verify the structuraldimensions. Since the fluidic dynamic problem is in the transi-tion regime (Re ∼2000), a model without fluid-structure interactionwas chosen to avoid stability problems. Consequently, it was cho-sen to investigate the flow and pressure behavior at two fix strokepositions: 100 �m and 200 �m at 1 kPa and 2 kPa pressure droprespectively. The simulations were performed using nitrogen at300 K. Since pure nitrogen is a few percent less dense than exhaledair but also simulated at a lower temperature causing a few per-cent higher density, the resulting difference using nitrogen at 300 Kin relation to exhaled air at a temperature of 310 K is expectedto be negligible for the purpose of the simulation. The result-ing data was then used to make minor adjustments to the shapeof the flow restrictors to better fit the flow rate to the targetrequirements.

3. Fabrication

A prototype of the flow regulator was fabricated by standardsilicon micromachining using three 100 mm diameter wafers andthree masks. The essential parts of the device was fabricatedusing an 850 �m thick silicon-on-insulator (SOI) wafer which wasthen sandwiched between a fusion bonded silicon wafer and ananodically bonded borofloat glass wafer acting as bottom andtop capping, respectively. In the 20 �m thick device layer of theSOI, springs and crossbars were fabricated while pistons, stopposts and flow restrictors were etched in the 830 �m thick handlewafer.

The fabrication starts by wet thermal oxidation of the SOI waferat 1100 ◦C to reach 3.5 �m oxide thickness used as a hard maskfor etching. The wafer was then spin coated by photoresist (PR)(Shipley 700-1.2) at 4000 rpm and patterned by UV-lithography(Fig. 3a and b). The oxide and the 20 �m thick device layer werethen etched in two steps to fabricate the spring layer (Fig. 3c).The oxide was etched by reactive ion etching (RIE, Applied Mate-rials, P5000) while the silicon was etched by deep RIE (DRIE, STSICP Multiplex ASE) at 600 W coil power and 12 W low-frequencyplaten power with 130 sccm SF6 flow for 6 min until the 1 �m thickburied oxide (box) layer was reached. A conventional double sidepolished silicon wafer (DSP), 525 �m thick, was processed in thesame way as above excluding the oxide etch step (Fig. 3e–h) to fab-ricate a regulator cover with a 30 �m deep recess to enable pistonand spring movement. The DSP wafer and the SOI wafer were thenfusion bonded into one unit (Fig. 3i) in a substrate bonder (SussMicrotec CB8) in vacuum at room temperature with 1 kN force for1 min followed by annealing and wet thermal oxidation at 1000 ◦C

ive air flow regulator for handheld breath diagnostics, Sens. Actuators

to protect the springs by a 200 nm oxide layer. To define pistonsand posts, a 10 �m thick resist (AZ9260, 2400 rpm) was applied tothe wafer stack and patterned by UV-lithography (1500 mJ/cm2)and developed (AZ 400 K 1:4, 3 min). After etching the oxide hard

ARTICLE IN PRESSG Model

SNA-8490; No. of Pages 6

S.B. Johansson et al. / Sensors and Actuators A xxx (2013) xxx– xxx 3

Si

SiO2

PR

Dicing tape

LinerGlass

n) HF release etch

q) Sand blasting a recess

i) Fusion bonding

a) Spinning PRe) Spinning PR

j) Spinning PRo) Cutting dicing tape

f ) Lithography

k) Lithography p) Transfer to glass wafer

g) Etching a recess to enable piston movement

l) Etching pistons and posts

r) Removing tape

m) Stripping PR

h) Stripping PR

b) Lithography

c) Etching spring layer

d) Stripping PR

s) Anodic bonding

Fig. 3. Process flow of the fabrication scheme. Springs and crossbars are etched inthe 20 �m thick device layer of an SOI wafer and then the flow channel includingpistons and posts are etched in the handle wafer. The device is then capped using aso

mcpflbsoc

Dg(aftd

Fig. 4. SEM pictures of the flow channel captured on wafer level before dicing. Toppicture shows one device between the dashed diagonal lines. 830 �m high pistons

ilicon wafer and a borofloat glass wafer with etched recesses to enable movementf the regulating structure.

ask as described above, the silicon was etched in a two-step pro-ess using DRIE. First, the wafer stack was etched with 600 W coilower and 11 W high-frequency platen power with 130 sccm SF6ow for 3 h until there was approximately 150 �m of silicon leftefore reaching the box layer. At this stage, the platen power waswitched to 12 W low-frequency and etching was continued to stopn the box layer after approximately 2 h. The two-step etching pro-ess finalizes the 830 �m high pistons and posts (Figs. 3j–m).

The top cover of the regulator was fabricated by using a Nittoenko dicing tape as a hard mask on a 500 �m thick borofloatlass wafer before sand blasting the recess to 30 �m depthFig. 3o–r). The dicing tape was cut on a plastic liner foil using

Please cite this article in press as: S.B. Johansson, et al., A MEMS-based passA: Phys. (2013), http://dx.doi.org/10.1016/j.sna.2013.09.012

Graphtec CE5000-60 cutting plotter and subsequently trans-erred to the glass by peeling it off from the liner and taping ito the glass wafer. To be able to easily detach the tape withoutistorting the pattern, an additional layer of the dicing tape was

and flow restricting posts being can be seen. Bottom picture shows a close up of the11 �m wide and 20 �m high spring structures.

used between the liner and the cut dicing tape. The fabricationof the flow regulator was continued by releasing the piston andspring structure from the oxide by etching in buffered hydrogenfluoride (BHF) for 100 min (Fig. 3n). The etch time was chosenlong enough to under etch the pistons and release them from theunderlying springs, but not long enough to release the pistons fromthe wider crossbars. Etching the oxide reduces the thickness ofthe device layer to approximately 18.4 �m. The fabrication wasfinalized by bonding the glass wafer anodically onto the siliconwafer stack at 400 ◦C using 500 V until the current dropped 10%(Fig. 3s). Fig. 4 shows two SEM pictures of the processed SOI waferbefore bonding of the glass wafer while Fig. 5 shows a completediced chip.

4. Evaluation

The fabricated prototype was experimentally evaluated usinga measurement setup that is illustrated in Fig. 6. The chip wasmounted in a chip holder with fluidic ports that was milled anddrilled from a 7 mm thick sheet of PMMA. The chip holder wasdesigned to not disturb the flow by using smooth transitionsbetween the circular tubing system and the rectangular flow chan-nel in the device. The flow output of the chip holder was designedas a smooth expansion to provide a diffusing function, reducing

ive air flow regulator for handheld breath diagnostics, Sens. Actuators

exit losses due to turbulence. The chip holder was connected toa tube system including a differential pressure sensor (MotorolaMPX 5050DP), a flow sensor calibrated for N2 gas (HoneywellAWM5102VN) and a precision manual valve for controlling the

ARTICLE IN PRESSG Model

SNA-8490; No. of Pages 6

4 S.B. Johansson et al. / Sensors and Actuators A xxx (2013) xxx– xxx

Fig. 5. Photograph of the capped prototype showing the size compared to a match.The dimensions are 2 mm × 2 mm × 4 mm.

N2

+-

+-

1 bar

holderChip

sensor

sensor

Flow

Pressure

NeedleValve

Fig. 6. Schematic illustration of the measurement setup. Compressed nitrogen gaswas used to characterize the flow regulator. Pressure was adjusted using a manualpcm

flaetmtootpu

Fig. 7. A 3D streamline plot showing the simulated velocity magnitude in the flowregulator. The simulation was performed with the piston structure at full stroke of200 �m and a pressure of 2 kPa at the inlet. The pitch of the pistons is 500 �m andthe width of the pistons is 200 �m. Streamlines in red color represent flow velocitiesof 65 m/s and streamlines in blue color represent flow velocities below 10 m/s. (For

Fp

recision valve while reading the pressure and flow values off digital voltmetersonnected to pressure and flow sensors, respectively. The device under test wasounted in a PMMA chip holder connected through a fluidic port.

ow. The pressure sensor was connected as close to the chip holders possible, approximately 26 mm from the chip, to reduce anyffects of pressure drop between the sensor and the device underest. The tube system was fed with N2 gas at a pressure of approxi-

ately 1 bar and the gas travel distance between the gas bottle andhe chip holder was made long enough to mitigate cooling effectsf the sudden gas expansion from the gas bottle. To be able to read

Please cite this article in press as: S.B. Johansson, et al., A MEMS-based passA: Phys. (2013), http://dx.doi.org/10.1016/j.sna.2013.09.012

ut the pressure and flow values, the sensors were connected elec-rically to digital volt meters. Characterization of the prototype waserformed by sweeping the pressure up and down in discrete stepssing the valve, reading the flow rate at every step. To be able to

ig. 8. Two cases of pressure drop were simulated on a symmetrical half of the device. Fiston stroke. In the second case (bottom) piston stroke is 100 �m and the inlet pressure

interpretation of the references to color in this figure legend, the reader is referredto the web version of the article.)

evaluate and differentiate the regulating function from static flowresistance, a reference device with pistons fixated in the relaxedposition was also measured.

Although N2 gas was used to evaluate the flow characteristicsof the regulator, the different aspects of exhaled breath, such ashumidity and temperature also need to be considered. In particular,exhaled breath is typically saturated with water vapor which couldpotentially condensate if exhaled through a valve with a temper-ature lower than the body temperature. Investigation of possiblecondensation in the valve was performed in two ways: by blowinginto a room tempered flow regulator and by blowing into a flowregulator that was heated to approximately 40 ◦C. In both cases,exhaled breath was flowing through a short mouth piece 30 mmlong into the regulator for 20 s and then the regulator was inspectedunder microscope.

5. Results

ive air flow regulator for handheld breath diagnostics, Sens. Actuators

Simulated data of the flow velocity at an applied pressure of2000 Pa is shown in Fig. 7. It can be seen in the 3D streamline plotthat flow velocity can become as high as 65 m/s close to the floworifices. At this high flow speed turbulent effects can occur and the

irst case (top) shows the pressure drop (Pa) at 2000 Pa inlet pressure and 200 �m is 1000 Pa. It can be seen that the main pressure drop occurs at the flow orifices.

ARTICLE ING Model

SNA-8490; No. of Pages 6

S.B. Johansson et al. / Sensors and Ac

0 500 1000 1500 2000 25000

10

20

30

40

50

60

70

80

Differential pressure / P a

Flow

rate

/ m

l/s

Theoretical: Flow out from a tubeSimulatedMeasured regulating deviceMeasured reference device

770 Pa

430 Pa

Dynamic range of flow regulator

Dynamic range of reference device with fixed pistons

Fig. 9. Measured flow characteristics of two devices, a reference device with fixedpistons (static flow restriction) and a device with fully moving pistons (dynamic flowrestriction). It can be seen that the regulating device restricts the flow to achieve ahigher dynamic range than the reference device. The flow rate at 2000 Pa is approx-is

ddiofdsp

pat

Fdflv

mately 11% higher than the expected simulated value while it coincides with theimulated value at 1000 Pa.

evice needs to be analyzed using full CFD. The simulated pressurerop over the regulator structure can be seen at two different cases

n Fig. 8. The top illustration shows the pressure drop at a pressuref 2000 Pa applied to the inlet and the pistons are moved to theirull stroke, i.e. 200 �m. The bottom illustration shows the pressurerop at 1000 Pa inlet pressure and 100 �m piston stroke. It can beeen that the flow restriction is effective, indicated by the clearressure drop occurring over the flow orifices.

Experimental evaluation of the fabricated prototype was

Please cite this article in press as: S.B. Johansson, et al., A MEMS-based passA: Phys. (2013), http://dx.doi.org/10.1016/j.sna.2013.09.012

erformed as described in Section 4 and the resulting flow char-cteristics are shown in Fig. 9. The dashed rectangle indicates thearget window for FENO asthma monitoring. As a comparison to

ig. 10. Photographs showing a device prior to blowing exhaled air through it (a), after bevice (c). It can be seen that when blowing through the non heated device (b) the wateow restrictors and a film of water between the pistons and the glass cap, appearing as daisible.

PRESStuators A xxx (2013) xxx– xxx 5

the measured data, the theoretical exit flow from a tube actingas a static flow restriction was calculated using Bernoulli’s equa-tion assuming conservation of energy. The diameter of the tube is0.72 mm corresponding to the same cross sectional area as the flowregulator and it can be seen that the theoretical flow indicated bythe dashed line coincides well with the measured flow rate of thereference device with fixed pistons. However, the regulating devicewith movable pistons restricts the flow rate as pressure increasesresulting in a dynamic range of approximately 770 Pa. This is a 79%increase over the reference device having approximately 430 Pa ofdynamic range. Simulated values for flow rate are also shown in thegraph and indicated by triangles. It can be seen that measured val-ues coincides well with the simulated value at 1000 Pa while themeasured flow rate of the regulating valve is approximately 11%higher than expected at 2000 Pa. A minor increase of the slope of theregulating valve can also be seen at approximately 1800 Pa, indicat-ing the possibility that the spring structure could have reached themaximum stroke length at this pressure. This is supported by thefact that this part of the curve has approximately the same slope asthe reference device.

Potential problems with condensation of exhaled air saturatedby water vapor were also investigated as described in Section4. Condensation was clearly visible when a person was blow-ing into a device at room temperature. In the second experimentwhere breathing air was exhaled into a device that was pre-heated to approximately 40 ◦C, no condensation was visible, asshown in Fig. 10. In current FENO asthma devices, particle fil-ters and humidity absorbing tubes are used [12]. These strategiescan also be applied to the device presented here, eliminatingthe need to preheat the device. Nitric oxide filters are used incurrent FENO asthma detection technologies as well as particlefilters, which could potentially also absorb water vapor, eliminat-ing the need to preheat the device. For other applications wherea filter is not desired, the device could be preheated by inte-grating a resistive layer in the device. The energy required to

ive air flow regulator for handheld breath diagnostics, Sens. Actuators

preheat the device in such applications would be relatively lowdue to the small mass and limited heating requirement (bodytemperature).

lowing through it at room temperature (b) and after blowing through a pre heatedr vapor in the exhaled air condensates and forms small water drops between therk regions on top of the pistons. For the heated device, no condensation of water is

ING Model

S

6 and Ac

6

lsmrcdd

abosd

A

Am

A

R

[

[[

ARTICLENA-8490; No. of Pages 6

S.B. Johansson et al. / Sensors

. Conclusions

A miniaturized, passive flow regulator suitable for controllingarge air flows in portable breath diagnostic tools has been demon-trated. The fabricated prototype was designed for FENO asthmaonitoring applications where flow rates of about 50 ml/s are

equired. Measurements have successfully verified dynamic flowontrol on a chip that measures only 2 mm × 2 mm × 4 mm. Theynamic range was measured to be 79% higher than a referenceevice with static flow restriction.

Condensation of exhaled air was observed in the flow regulatort room temperature. However, this effect can be eliminated eithery preheating the device as verified by the experimental evaluationr by using a filter. In summary the paper demonstrates the fea-ibility of potentially cost-effective MEMS-based flow controllingevices for portable breath diagnostics.

cknowledgements

This work was supported by the Swedish agency VINNOVA anderocrine AB, producer of handheld diagnostic tools for breathonitoring.The authors would like to thank Per Birkestad at FS Dynamics

B for discussions and help with the CFD simulations.

eferences

[1] J.M. Spergel, M.I. Fogg, A. Bokszczanin-Knosala, Correlation of exhalednitric oxide, spirometry and asthma symptoms, J. Asthma 42 (2005)879–883.

[2] ATS/ERS recommendations for standardized procedures for the online andoffline measurement of exhaled lower respiratory oxide and nasal nitric oxide,Am. J. Respir. Crit. Care. Med. 171 (2005) 912–930.

[3] C. Amacker, Y.-S. Leungki, V. Pasquita, C. Madore, M. Haller, P. Renaud, Passivemicro-flow regulator for drug delivery system, in: Proc. Eurosensors XII, 1998,pp. 591–594.

Please cite this article in press as: S.B. Johansson, et al., A MEMS-based passA: Phys. (2013), http://dx.doi.org/10.1016/j.sna.2013.09.012

[4] B. Yang, J.W. Levis, Q. Lin, A PDMS-based constant-flowrate microfluidic controldevice, in: Proc. MEMS, 2004, pp. 379–382.

[5] I. Doh, Y.H. Cho, Passive flow-rate regulators using pressure-dependentautonomous deflection of parallel membrane valves, Lab Chip 9 (2009)2070–2075.

PRESStuators A xxx (2013) xxx– xxx

[6] A. Debray, T. Nakakubo, K. Ueda, S. Mogi, M. Shibata, H. Fujita, A passive microgas regulator for hydrogen flow control, J. Micromech. Microeng. 15 (2005)419–422.

[7] M. McCarthy, N. Tiliakos, V. Modi, L.G. Fréchette, Temperature-regulated non-linear microvalves for self-adaptive MEMS cooling, J. Microelectromech. Syst.17 (2008) 4.

[8] S.B. Johansson, G. Stemme, N. Roxhed, A compact passive air flow regulator forportable breath diagnostics, in: Proc. MEMS, 2013, p. 157-160.

[9] A. Ezkerra, L.J. Fernández, K. Mayora, J.M. Ruano-Lopez, Fabrication of SU-8free-standing structures embedded in microchannels for microfluidic control,J. Micromech. Microeng. 17 (11) (2007) 2264.

10] W. van der Wijngaart, A. Thorsén, G. Stemme, A seat microvalve nozzle foroptimal gas flow capacity at large controlled pressure, J. Microelectromech.Syst. 14 (April (2)) (2005) 200–206.

11] V. Kaajakari, Practical MEMS, Small Gear Publishing, 2009.12] T. Hemmingsson, D. Linnarsson, R. Gambert, Novel hand-held device for

exhaled nitric oxide-analysis in research and clinical applications, J. Clin. Monit.Comput. 18 (2004) 379–387.

Biographies

Staffan B. Johansson was born in Stockholm, Sweden, 1978. He received the M.Sc.degree in microelectronics and biomedical engineering from KTH Royal Instituteof Technology, Sweden, 2009. The thesis work was performed at the Micro andNanosystems Department, School of Electrical Engineering, where he continuedworking as a Ph.D. student the same year. His research is focused on MEMS formedical applications and for use as implants.

Göran Stemme received the M.Sc. degree in electrical engineering and the Ph.D.degree in solid-state electronics from Chalmers University of Technology, Gothen-burg, Sweden, in 1982 and 1987, respectively. In 1981 he joined the Departmentof Solid State Electronics, Chalmers University of Technology, where he becamean Associate Professor (docent) heading the silicon sensor research group in 1990.Since 1991, he has been a professor at KTH Royal Institute of Technology, Stockholm,Sweden, where he heads Department of Micro and Nanosystems in the School ofElectrical Engineering. His research is devoted to microsystem technology based onmicromachining of silicon. He has more than 300 research journal and conferencepapers and has more than 22 patent proposals or granted patents. Dr. Stemme is amember of the Royal Swedish Academy of Sciences (KVA).

Niclas Roxhed was born in Stockholm, Sweden 1978. He received the M.Sc. degreein electrical engineering and the Ph.D. degree in microsystem technology fromKTH Royal Institute of Technology, Stockholm, in 2003 and 2007, respectively. Heis currently an Assistant Professor and a team leader of medical MEMS with the

ive air flow regulator for handheld breath diagnostics, Sens. Actuators

Department of Micro and Nanosystems, School of Electrical Engineering, KTH RoyalInstitute of Technology. His main research fields are sensors for medical diagnosticsand medical-aid Microsystems. He is also involved in high-precision etching usingDRIE for RF-MEMS switches and 3D integration of MEMS on ICs for infrared imagers.He has authored or coauthored more than 50 scientific papers.