756 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 49, NO. 6, .JUNE 2002

Piezoelectrically Actuated Flextensional Micromachined Ultrasound Droplet Ejectors

Gokhan PerCin, Member, IEEE, and Butrus T. Khuri-Yakub, Fellow, IEEE

Abstract-This paper reports a variation on the design of the flextensional transducer for use in ejecting liquids. The transducer is constructed by depositing a piezoelectric thin film to a thin, edge-clamped, circular annular plate. By placing a fluid behind one face of a vibrating compound plate that has an orifice at its center, we achieve continuous or drop-on-demand ejection of the fluid. We present results of ejection of water and isopropanol. The ejector is harm- less to sensitive fluids and can be used to eject fuels as well as chemical and biological samples. Micromachined two- dimensional array piezoelectrically actuated flextensional droplet ejectors were realized using planar silicon microma- chining techniques. Typical resonant frequency of the mi- cromachined device ranges from 400 kHz to 4.5 MHz. The ejection of water thru a 5-pm diameter orifice at 3.5 MHz was demonstrated by using the developed micromachined two-dimensional array ejectors.

I. INTRODUCTION

URING THE PAST few years, the application of micro- D fabrication techniques has entered the medical field and has initiated the development of powerful new diag- nostic devices used for cancer, AIDS, and genetic diseases [l]. A reliable, fast method for dispensing small volumes of biological and chemical fluids is needed in many emerging areas of biotechnology and biomedicine [a]-[4]. Economi- cal, simple, inexpensive, and fast deposition of materials would have a great impact on the cost and quality control of drug delivery, drug discovery, high throughput screen- ing, assaying, and combinatorial chemistry.

The micromachined arrays of droplet ejectors developed in this research will enable the manufacturing of biochips such as immunoassays and DNA diagnostic assays. Lab- on-chip systems require reliable and robust methods for dispensing the reagents and biological agents on the sub- strates [2], [3] . The developed ejector can deliver femtoliter to nanoliter scale samples of the biological and chemical fluids and small solid particles. By using the microma- chined ejectors developed in this research, it is possible to develop a microspotter system wherein the DNA oligos

Manuscript received April 23, 2001; accepted November 12, 2001. This research was supported by the Defense Advanced Research Projects Agency of the Department of Defense and was monitored by the Air Force Office of Scientific Research under Grant No. F49620- 95-1-0525. This work made use of the National Nanofabrication Users Network facilities funded by the National Science Foundation under award number ECS-9731294.

G. Persin is with ADEPTIENT, Los Altos, CA 94024 (e-mail: percin@adeptient.com).

B. T. Khuri-Yakub is with Edward L. Ginzton Laboratory, Stan- ford University, Stanford CA 94305-4085.

are deposited directly on each cell under computer control. Droplets (as small as 4 pm or smaller) can be deposited from a parallel array of orifices. The linear array of ejectors combined with mechanical scanning will be capable of de- positing single bases (nucleoside phosphoramidites) , pre- determined sequences (oligonucleotides) , cDNAs, or pro- teins over the full size of a biochip in a time interval that is compatible with the manufacturing process.

Conventional pipetting, aspirating syringe, and capil- lary techniques (pins) have been used to withdraw or in- ject samples in automated analysis systems, such as high throughput screening systems. Conventional dispensing is difficult to use in high density micro-array plates, such as 1536 and 3456-well plates. New economical, relia.ble, and robust methods to handle biological and chemical fluids and small solid particles with volumes in the femtoliter to nanoliter scale are needed. The reduced volumes inherently increase the chemical and biological assay speed because of the rapid diffusional mixing of small volumes. Small fluid samples of 0.5 to 100 nL per well (biological samples) and 0.2 to 2 nL per well (reagents) must be distributed over high density assay plates in an efficient way.

The ability to control the placement of cells in an or- ganized pattern on a substrate has become increasingly important for the development of cellular biosensor tech- nology and tissue engineering applications [5], [6]. To build in circuitry to directly monitor the status of sensor cells on a device requires that the cells be properly positioned on the circuit. Automation technologies to perturb and observe cells serially require that cells be positioned into addressable arrays. Tissue function is modulated by the spatial organization of cells on a sub-millimeter scale. For this reason, artificial replication of cellular microstructures is important in understanding, measuring, and simulating their in vivo functions.

Aerosol-mediated pulmonary administration of mono- meric insulin analog (MIA), e.g., by inhalation, provides rapid, painless treatment of diabetes and hyperglycemia [7]. An experimental nasal spray flu vaccine has been proven to protect young children against an influenza strain not covered by the vaccine [8]. Recently, aerosol gene delivery has become popular [9]. This progress in aerosol delivery of drugs and vaccines requires microma- chined ejectors capable of delivering fluids in the form of very small droplets and at a lower velocity than the spray technology currently available on the market. Innovations in biotechnology and recombinant techniques have led to a large increase in the number of macromolecule drugs over the last several years. Because of their large size and sus-

0885-3010/$10.00 @ 2002 IEEE

PERGIN AND KHURI-YAKUB: ULTRASOUND DROPLET EJECTORS

'i

757

heater piezoelectric

Piezoelectric head, roof shooter Bubble jet, roof shooter

heater A

piezoelectric 4

Bubble jet. side shooter Piezoelectric head, side shootei

Fig. 1. Configurations of conventional inkjet printheads.

ceptibility to digestive enzymes, macromolecules typically have been delivered by injection. By enabling the systemic and local lung delivery of large molecule drugs through inhalation into the deep lung, the proposed non-invasive drug delivery module provides a unique and innovative de- livery alternative for therapeutics that must currently be administered by injection. The micromachined ejector de- veloped in this work can be used to easily deliver a range of inhalable drugs, including peptides, proteins, and small molecules, to the deep lung for the treatment of systemic and respiratory diseases.

The main mechanisms of ejecting ink droplets are cat- egorized into two groups as shown in Fig. 1: bubble jet (thermal) and piezoelectric printheads. Thermoelectric ac- tuation (bubble jet) is the dominating ink propulsion mechanism used in inkjet printheads on the market to- day. A small volume of ink is rapidly superheated forming a vapor bubble. The expansion of the bubble pressurizes the surrounding fluid, causing a drop to be ejected from a nearby nozzle. Piezoelectric actuation causes acousto- hydraulic resonance in the ink chamber, i.e., the piezo- electric element is used to abruptly compress the enclosed volume, producing a pressure wave that causes ejection of a drop at a nozzle. Both printhead configurations suffer from some drawbacks, specifically, the piezoelectric priiit- head requires too much power to drive a large array of nozzles, and the bubble jet printhead has limited lifetime because of cavitation damage and burning of the heater re- sistor. In the piezoelectric printhead design, it is difficult to reduce printhead size and to increase the spatial density of array elements. In the micromachined droplet ejector design shown in Fig. 2 , the electric power consumption is very small, because only a thin piezoelectric film is driven. Furthermore, the device can readily be scaled to an array of more than 10000 eject,ors per 1 cm2.

11. DEVICE AND EJECTION SIMULATIONS

We designed the transducer to have maximum displace- ment at the center of the plate at the resonant frequency. Similar ejector designs can be found in Strom [lo], Mae- hara et al. [11]-[14], Ueha et al. [15], Tetsuo [16], and Ivri [17]. However, the complexity of the structure and the fact

zTO Nitride 4

c-150 um

Fig. 2. Configuration of the Type I1 micromachined ultrasound trans- ducers and droplet ejectors.

-, -5 0

IJm

Fig. 3. Typical MEMS device ejection simulation.

5

758 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 49, NO. 6 , JUNE 2002

Electrical input impedance Simulation Average displacement simulation 1 on 10'

1 o5 1 oo

I 0'

IO'

............., ............. , ..........,.... . ................................................. ........... ....... .,........ ........... ,..... ...... ....... .o ............. I ...................... 1 2 3 4 1 2 3 4 5

Frequency (MHz)

lo-';

Frequency (MHz)

Fig. 4. Type I1 micromachined flextensional transducer simulations for a single element (Device E).

that the piezoelectric used is an annular disk rather than a full disk necessitate the use of a more complicated analysis to determine the resonant frequencies of the structure, the input impedance of the transducer, and the normal dis-

shape, this says that droplet size and shape are only a function of this single dimensionless parameter. For in- stance, if f is made larger, then either the orifice radius should be smaller or 0 made larger.

which gives the wavelength X of linear capillary waves driven at frequency f on a plane interface. The param- eters (T and p are surface tension and density of the liquid, respectively. If X is much smaller than the diameter of the orifice, the vibrating plate will simply set up short ripples on the liquid surface. This suggests that a dimensionless surface tension parameter,

where a is the radius of the orifice, should be of order 1 or greater.

A computational model that simulates droplet ejection has been developed using a boundary integral method [21]. The surface equations of motion were made dimensionless using the radius of the orifice as the characteristic length and the period of plate oscillation as the characteristic time. The only parameter that remains in the equations is the surface tension parameter S introduced previously. This provides a scaling law for drop ejection. All other things being equal, such as amplitude and plate mode

locity is about 5.3 m/s based on the distance between the heights of the last two frames. The calculated flow rate is 19.8 nL/s, and the volume of the drop is 14.1 fL. In the computation, the drop pinch-off time was 0.62 ps, and the surface tension parameter was S = 9.3. This simulation shows that a 0.2 pm amplitude of displacement is needed to eject water thru a 4-pm orifice. The electrical input impedance and average displacement simulations for the device used in the previous droplet ejection simulation are given in Fig. 4 for air, one side water-loaded, and two side water-loaded cases. As shown in Fig. 4, the displacement of the compound plate is not enough to eject the water as simulated in Fig. 3.

However, by using a different piezoelectric thin film ma- terial, the average displacement for the one side water- loaded case can be increased as shown in Fig. 5 , where the average displacement at the second resonance is increased approximately 10 times using a piezoelectric material with d,l equal to -32.1 x C/N. In another configuration, the average displacement can be increased by operating at a lower frequency. However, the dimensionless surface tension parameter, S , should be kept constant to obtain the same droplet ejection shown in Fig. 4. By choosing an orifice diameter of 9.6 pm and the ejection frequency

PERGIN A N D KHURI-YAKUB: ULTRASOUND DROPLET EJECTORS

Average displacement simulation, water loaded lo-'

.............. i ................... 3 .................. ................... ...................

759

TABLE I PHYSICAL DIMENSIONS OF THE MICROMACHINED DEVICES.

Dimension (pm) Device Device Device

E F G

Radius of the orifice 2.5 4.8 9.5 Inner radius of the piezoelectric

layer 12.0 30.0 30.0 Outer radius of the piezoelectric

layer 46.2 120.0 120.0 Radius of the device 57.5 150.0 150.0 Thickness of the carrier plate 0.25 0.50 0.30 Thickness of the piezoelectric

layer 0.40 0.50 1.00 Thickness of the electrode

layer 0.10 0.10 0.10

I J 0 1 2 3 4 5

Frequency (MHz)

Fig. 5. Type I1 micromachined flextensional transducer simulations for a single element with different piezoelectric materials (Device E).

Average displacement simulation 10'

... ...... .................. .............. ................. i . . ................

1 IO-'

................................ ................. 0 0.2 0.4 0.6 0.8 1

Frequency (MHz)

Fig. 6. Proposed Type I1 micromachined flextensional transducer simulations for a single element (Device F).

0.38 MHz, the average displacement of the new device is obtained as shown in Fig. 6. The physical dimensions of the devices mentioned in this paper are presented in Ta- ble I.

In Fig. 7, the droplet ejection simulation in Fig. 3 is shown for different mode shapes and excitation displace- ment amplitudes. Generally, the second mode requires more displacement to eject the same fluid than the first mode. For the first mode and an excitation displacement of 0.12 pm, the plate displacement amplitude is so small that the meniscus in the orifice simply oscillates up and down and collapses onto itself. This also happens for the second mode and excitation amplitudes of 0.5 and 0.2 pm, and liquid droplet cannot pinch off from the liquid-air in-

terface. In Fig. 8, the same device is used to eject different fluids with different surface tensions at 1.4 NIHz, and, as the dimensionless surface tension parameter increases, the pinch-off time decreases slowly. For S values of 15.27 or larger, the plate displacement amplitude of 0.2 pm is so small that the meniscus in the orifice simply oscillates up and down and collapses onto itself.

In the following example of ejection simulation, the ob- jective is to design a micromachined device that can eject water droplets 3 to 4 pL with an ejection velocity of 5 to 6 m/s at an ejection rate of 200 kHz. The simulated wa- ter droplet ejections are shown with actual dimensions, at every 0.2 normalized times during a cycle in Fig. 9. The orifice radius is 9.5 pm, the frequency of half-cycle motion of the plate is 280 kHz (period, 3.57 ps), the second flexu- ral axisymmetric mode of the step-wise laminated plate is used for the ejection, and the ejected fluid is water. The diameter of the drop is much smaller than the ori- fice diameter, and the final velocity is about 5.6 m/s in Fig. 9 based on the distance between the heights of the last two frames. In Fig. 9, the volume of the ejected drop is around 3.1 pL after pinching off from the meniscus and snapping off. Because the pinch-off time is greater than the period of excitation, the repetition rate for the ejec- tion is around 200 kHz. The required displacement at the center of the plate is 1.42 pm in Fig. 9. In the computa- tion, the drop pinch-off time was 5 ps in Fig. 9, and the surface tension parameter was S = 2.16. We have used o = 72.7 x N/m, p = 1 g/cm3 for calculating these parameters.

The electrical and mechanical simulations of the step- wise laminated plate (with a radius of 150 pm) designed for the aforementioned water ejection are given in Fig. 10 and 11. The average displacement amplitude of the plate is 0.04 pm/V at 280 kHz for the second mode, loaded with water. By assuming that the mode shapes will be the same for the fluid-loaded case, except for a scaling factor (i.e., the ratio of the average displacement to the center dis- placement should be same for all different loading cases), 0.19 pm/V peak displacement at the center of the plate loaded with water is obtained by using the ratio of the av-

760 IEEE TRANSACTIONS ON III.TRASONJCS, FERROELECTRICS, AND FRRQTJRNCY CONTROL, VOI,. 49, NO. 6, JTJNE 2002

Is1 mode. amplilude=0.Zpm. 1 =0.6Zwec

"V 2

1

0

1

5-2

-3

-4

-5

-6

-71 I

pm -5 0 5

2nd mode, ampiilude=OB)rm. 1 .0.133pec

1st mode, ampllluaB=0.16pm. I =O.SSpSc

3-

-7 -6+5 -5

pm

2nd mode, amplitude=O

1st mode, amplilude=O.l2wn

:L5 -?5 -6

pm

2nd mode. amplitude=O 2pm

1

0

1

5-2 -3

-7 1 I -5 0 5

vm

0

1

-5 5:L5 -6 -7 -5 wm

Fig. 7. Simulation of water ejection for different modes and displacements.

erage displacement at 320 kHz (second mode) in air from Fig. 10 to the center displacement of the plate at the sec- ond mode from Fig 11, and the average displacement at 280 kHz (second mode) loaded with water from Fig. 10 The step-wise laminated plate has a radius of 150 pm, ZnO thickness of 1 pm, and silicon nitride thickness of 0.3 pm. A 10-V amplitude signal can be applied to the 1-pm thick ZnO to obtain the required 1.9-pm peak displacement at the center of the plate. Therefore, the dissipated energy per drop is around 436 pJ for the ejection shown in Fig. 9 based on an electrical calculation. This number for a con- ventional thermal or bubble jet printer is on the order of 1 pJ per drop. The ejection of water droplets with given specifications is demonstrated by using the ejection model and the plate model. The proposed device has a radius of 150 prn and an orifice wilh a radius of 9.5 p i . In addition, the same device can be operated in drop-on-demand mode excited with tone burst to increase the droplet volume.

111. DEVICE FABRICATION

The fabrication process for Type I1 micromachined two- dimensional array flextensional transducers and droplet ejectors is given in Fig. 12. At the right side of the fig- ure, actual pictures of one element from a two-dimensional array are given along with the process flow. The process starts with growing a sacrificial layer, chosen to be silicon oxide (8% phosphorus doped densified low temperature ox- ide [LTO]). A non-piezoelectric carrier plate layer of low pressure chemical vapor deposition (LPCVD) silicon ni- tride is grown on top of the sacrificial layer. Ejection holes are patterned in the silicon nitride carrier plate layer at

the front surface of the wafer by plasma etching. Later, hack side access holes or fluid reservoirs a,re patterned in the silicon nitride and LTO layers a t the back surface of the wafer, and the back side access holes are etched by deep reactive ion etch (DRIE) until reaching the sacrificial silicon oxide layer at the front surface as shown in Fig. 12. The DRIE of silicon has an SFe ambient with a flow rate of 130 sccm, a pressure of 35 mTorr, a radio frequency (RF) power of 120 W in active cycle, a C4Fs ambient with a flow rate of 80 sccm, and a pressure of 18 mTorr in pas- sive cycle. The etching rate is 3.8 pm/min. Because of the material compatibility with the DRIE equipment in our laboratory, we had to choose to etch the back side access holes in bulk silicoii before defining the actual transduc- ers at the front surface of the wafer. The bottom Ti/Au electrode layer is deposited on the non-piezoelectric car- rier plate by e-beam evaporation at 240°C. The degree to which the ZnO c-axis, (0002), is oriented normal to the substrate surface is very sensitive to the degree to which the Au film is (111) oriented. The quality of the ZnO is measured by an X-ray rocking curve scan. The ZnO had a 5.5O-wide rocking curve above Au with a 5"-wide rock- ing curve. Later, the bottom electrode layer is patterned by wet etch, and a piezoelectric ZnO layer is deposited on top of the bottom electrode. The ZnO is deposited by dc planar magnetron sputtering from a 127-mm wide target consisting of 99.99% Zn. The deposition is made in a 20 to 80% argon-oxygen ambient with a flow rate of 26.6 sccm, a pressure of 7. mTorr, a substrate temperature of 150"C, and a dc power of 350 W. The separation between the substrate and the target is 51 mm. The deposition rate is

PERGIN AND KHURI-YAKUB: ULTRASOUND DROPLET EJECTORS 76 1

S7.27, t 0 = 0 . @ w

-% -4 -2 0 2 4 6 I”

5.13 27, tD=O 55pec

2

0

-4

-6

f6 -4 -2 0 2 4 6 w

S-1627

5.8.27, tn=0.e4- S=9 27. lp=O 62+ 4

2

0

-4

-6

-% -4 -2 0 2 4 6 w

S=12 27, ln=O 56pec

0 2 4 6 lun

S=14 27, lD=O 55pec

S117.27 4

2

0

E -2

-4

-6

-% -4 -2 0 2 4 6 lun

S-15 27

2

0

5-2

-4

L -4 -2 0 2 4 6

I”

Fig. 8. Simulation of water ejection for different non-dimensional surface tension parameters.

762 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 49, NO. 6 , J U N E 2002

Water ejection, 1.42pm displacement

Fig. 9. Water ejection simulation through 9.5-pm radius orifice at 280 kHz; pinch-off time is 5 p; drop velocity is 5.6 m/s.

10.5 A/s. The top Cr/Au electrode layer is formed by e- beam evaporation at room temperature and patterned by liftoff. The last step is etching the sacrificial layer by wet etch, and this concludes the front surface micromachining of the devices. Fig. 13 shows a region of final 22 x 22 two- dimensional array devices. The die size is 1 cm x 1 cm. Fig. 14 shows SEM images of the fabricated array element.

Iv. DEVICE OPERATION AND EXPERIMENTS

We have shown that the previously presented version of the ejectors do not have enough displacement nor actua- tion mechanism to eject some fluids at relatively higher frequencies. Because of this fact, a modified version of the device has been developed to provide a bulk actua- tion mechanism along with the individual array element actuation. Two different modes of operation of the devices will be discussed in this section.

The micromachined two-dimensional array droplet ejec- tors with bulk actuation mechanism is shown in Fig. 15. The bulk actuation mechanism in Fig. 15 consists of a

I longitudinal thickness mode piezoelectric transducer. The piezoelectric transducer is in contact with the fluid and bonded above the fluid reservoirs.

In the first type of operation, the bulk actuation mech- anism provides enough actuation to form a fluid menis- cus around the orifice, so that individual array elements,

Average displacement

- in air - - 8 water loaded

10' '

......... .;. .................. ;. ................. -

.............. .:, ................. j ................. ._

: # \ ' 0 \ - -+ .

..... ~- --n.-. -.-: .-. ... i.. .............. ._

I l i I ;

10-8 .................. j.. .............................................................................

200 400 600 800 1000 1 o-8

0 Frequency (kHz)

Fig. 10. Average displacement amplitude and electrical input impedance of the step-wise laminated plate with a radius of 150 pm (Device G).

2nd mode shape 1.2 I

......... -. .

50 100 150 -0.6 0

Fig. 11. Mode shape of the step-wise laminated plate 'with a radius of 150 pm operating in air (Device G).

PERGIN AND KIIURl-YAKUB: ULTRASOUND DROPLET EJECTORS 763

Growing 2.2 microns LTO Growing 0.25 microns LPCVD silicon nitride

-+Nitride 'Oxide -"_ - _ -

+Silicon Patterning 8 microns holes in the nitride by dry etch Etching LOO microns holes from the back side of the wafer by DRIE

,Ti/Au -- ,Nitride

t-lwam e\'aporatioii of 0 1 niicrom hot Ti/Aii bottom electrode Patterning I ' i iAu botruni electrode b) net etrli

DC planar reactive magnetron sputtering of 0.4 microns ZnO Patterning the ZnO layer witti wet etch

Patterning photoresist layer for lop electrode layer liftoff

Patterning e-beam evaporated 0.1 microns CrlAu top electrode layer by liftoff I

Cr/Au

Etching the sacrificial LTO layer by wet etch

Fig. 12. Type I1 micromachined ultrasound transducer and droplet ejector fabrication process flow.

764 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL 49, NO 6, JUNE 2002

Fig. 13. Section of 22 x 22 per 1-cm2 array,

when actuated, will cause fluid to eject thru the orifice. In this mode of operation, the phases of bulk actuation and individual array element actuation should match at the liquid-air interface at the orifice. The frequencies of these actuations should be the same for the continuous mode of ejection, Le., one drop per cycle; however, these frequen- cies may be different for the tone burst mode of ejection, i.e., one drop per several cycles.

In the second type of operation, the bulk actuation mechanism is enough to eject the fluid by itself, and the individual array element when actuated out-of-phase will cause the existing ejection to stop. In this manner, the ejection in two-dimensional array is addressed by individ- ual array elements. The frequencies of bulk and individual array actuations may be different, depending on the appli- cation.

A front view of a typical two-dimensional array flex- tensional transducer is shown in Fig. 13. As mentioned before, these two-dimensional array elements will be used to control ejection spatially. By using the bulk actuation mechanism shown in Fig. 15, the water ejection thru a 5- pm diameter orifice has been achieved, and the ejection pictures for a single array element and 22 x 22 per 1-cm2 array are shown in Fig. 16 and 17, respectively.

V. CONCLUSION

In summary, a novel fluid and solid particle ejector that can be used as a cost-effective miniaturized sample prepa- ration module is designed and demonstrated in this paper and was also silicon micromachined into two-dimensional arrays. The ejector design, based on that of a flextensional ultrasound transducer, is optimized using both a finite el- ement analysis and analytical models that were developed in Perqin et al. [IS].

Fig. 14. SEM images of Type I1 micromachined device array element.

PERGIN AND KHURI-YAKUB: ULTRASOUND DROPLET EJECTORS 765

ACKNOWLEDGMENT

piezoelectric

Silicon

Fluid

Flextensional ejector element

Fig. 15. Configuration of the device.

---.-.-

Fig. 16. Water ejection thru 5-pm diameter orifice at 3.48 MHz

Fig. 17. Water ejection from 22 x 22 per 1-cm2 array.

This research was conducted during G. PerCin’s Ph.D.

The authors would like to thank Tom Lundgren for pro- study at Stanford University.

viding the droplet ejection simulation software.

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766 IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 49, NO. 6, JUNE 2002

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v A “

Phys. Lett., vol. 73, no. 16, pp. 2375-2377,

Gokhan Pergin (S’92-M’00) was born in Ezine, Canakkale, Turkey. He received the B.S. degree in electrical and electronics en- gineering from Bilkent University, Ankara, Turkey in 1994. He received the M.S. degree in electrical engineering in 1996, and the Ph.D. degree in electrical engineering with minor subject in engineering-economic systems and operations research in 2002 both from Stan- ford University, California. He worked in Nu- merical Technologies, Inc., San Jose, Califor- nia, as a senior software enaineer to develop

optical microlithography software. He is cofounder, president and chief technical officer of ADEPTIENT, Los Altos, California. He has years of experience in the areas of fluid ejection, microfluidics, mi- cromachining, micromachined electromechanical systems, ultrasonic actuators, ultrasound transducers, biomedical imaging, software de- velopment, sensors and actuators. Dr. Persin is a member of The Institute of Electrical and Electronics Engineers (IEEE), IEEE U1- trasonics, Ferroelectrics, and Frequency Control Society, IEEE Elec- tron Devices Society, The Electrochemical Society, and American Vacuum Society. His personal interests include Sufism, the Bektashi Order of Dervishes, photography, swimming, hiking, gourmet cook- ing, and collecting coins and stamps.

Butrus T. Khuri-Yakub (S170-S’73-M’76- SM’87-F195) was born in Beirut, Lebanon He received the B.S degree in 1970 from the American University of Beirut, the M.S de- gree in 1972 from Dartmouth College, and the Ph.D. degree in 1975 from Stanford Univer- sity, all in electrical engineering. He joined the research staff a t the E L. Ginzton Laboratory of Stanford University in 1976 as a Research Associate. He was promoted to a Senior Re- search Associate in 1978, and to a Professor of Electrical Engineering (Research) in 1982.

He has served on many university committees in the School of Engi- neering and the Department of Electrical Engineering

Presently, he is the Deputy Director of the E. L. Ginzton Labora- tory. Professor Khuri-Yakub has been teaching both at the graduate and undergraduate levels for over 15 years, and his current research interests include in situ acoustic sensors (temperature, film thickness, resist cure, etc.) for monitoring and control of integrated circuits manufacturing processes, micromachining silicon to make acoustic materials and devices such as airborne and water immersion ultra- sonic transducers and arrays, and fluid ejectors, and in the field of ultrasonic nondestructive evaluation and acoustic imaging and mi- croscopy.

Professor Khuri-Yakub is a fellow of the IEEE, a senior member of the Acoustical Society of America, and a member of Tau Beta Pi. He is associate editor of Research in Nondestructive Evaluation, a Journal of the American Society for Nondestructive Testing. Profes- sor Khuri-Yakub has authored over 300 publications and has been principal inventor or cc-inventor of 52 issued patents. He received the Stanford University School of Engineering Distinguished Advi- sor Award, June 1987 and the Medal of the City of Bordeaux for contributions to NDE, 1983

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