Controlled ink-jet printing and deposition of organic polymers and solidparticlesGökhan Perçin, Thomas S. Lundgren, and Butrus T. Khuri-Yakub Citation: Appl. Phys. Lett. 73, 2375 (1998); doi: 10.1063/1.122465 View online: http://dx.doi.org/10.1063/1.122465 View Table of Contents: http://apl.aip.org/resource/1/APPLAB/v73/i16 Published by the American Institute of Physics. Related ArticlesTunable wetting behavior of nanostructured poly(dimethylsiloxane) by plasma combination treatments Appl. Phys. Lett. 101, 221601 (2012) Highly efficient photochemical HCOOH production from CO2 and water using an inorganic system AIP Advances 2, 042160 (2012) Fast photo-switchable surfaces for boiling heat transfer applications Appl. Phys. Lett. 101, 191603 (2012) The interplay of the polyelectrolyte-surface electrostatic and non-electrostatic interactions in the polyelectrolytesadsorption onto two charged objects – A self-consistent field study J. Chem. Phys. 137, 104904 (2012) Voltage-induced deformation in dielectric J. Appl. Phys. 112, 033519 (2012) Additional information on Appl. Phys. Lett.Journal Homepage: http://apl.aip.org/ Journal Information: http://apl.aip.org/about/about_the_journal Top downloads: http://apl.aip.org/features/most_downloaded Information for Authors: http://apl.aip.org/authors

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APPLIED PHYSICS LETTERS VOLUME 73, NUMBER 16 19 OCTOBER 1998

Controlled ink-jet printing and deposition of organic polymersand solid particles

Gokhan Percin,a) Thomas S. Lundgren,b) and Butrus T. Khuri-YakubEdward L. Ginzton Laboratory, Stanford University, Stanford, California 94305-4085

~Received 15 June 1998; accepted for publication 20 August 1998!

In this letter, we present a technique for the deposition of inks, organic polymers and solid particles,using a fluid ejector. The ejector design is based on a flextensional transducer that excitesaxisymmetric resonant modes in a clamped circular membrane. It is constructed by bonding a thinpiezoelectric annular ring to a thin, edge supported, circular membrane. Liquids or solid particles areplaced behind one face of the membrane which has a small orifice~50–200mm diam! at its center.By applying an ac signal across the piezoelectric element, continuous or drop-on-demand ejectionof photoresist~Shipley Microposit S1400-21, S1400-27, S1805, and S1813!, oil-based ink, water, ortalcum powder@Mg3Si4O10~OH!2# has been achieved. Successful deposition of photoresist has beenaccomplished without spinning, and thus without waste. Patterning of 10mm features, by baking,exposure, and developing, has revealed no defects in the deposition process. A boundary integralmethod was used to numerically simulate drop formation from the vibrating orifice. Simulationshave been used to optimize ejection performance. ©1998 American Institute of Physics.@S0003-6951~98!01442-9#

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There is a continuing need for alternative deposittechniques of organic polymers in precision droplet-bamanufacturing and material synthesis, such as the deposof doped organic polymers for organic light emitting devicof flat panel displays,1 there is also need for deposition ophotoresist without spinning on large or oddly shaped sstrates. In addition, small particle ejectors are necessarythe study of heating and combustion behavior of small soparticles, such as coal and metals.2 To date, there has beeno report of a drop-on-demand solid particle ejector thateject fine solid particles with spatial control, althoughpneumatically operated solid particle ejector has beenported by Hwang.2

Of all the needs for a liquid or solid particle ejector, thdeposition of organic polymers used in semiconductor mafacturing and microelectromechanical systems~MEMS! isworth the most attention. Photoresist coating is one ofmost expensive steps in the lithography process of micelectronics fabrication. The photoresist film, after applicatto the substrate, must have uniform thickness and muschemically isotropic so that its response to exposure andvelopment is uniform. In the literature, numerous typesphotoresist coating methods have been reported:3,4 spin coat-ing, spray coating, dip coating, meniscus coating, plasdeposited photoresist, electrodeposited~electrophoretic! pho-toresist, roller, curtain, and extrusion coating. Despite soproblems spin coating is the method of choice of the micelectronic industry. In present applications, over 95% ofphotoresist is wasted and has to be disposed of as amaterial, increasing the cost of this already expensive sRadial thickness variations associated with the spinning p

a!Electronic mail: percin@alumni.stanford.orgb!Also at: Department of Aerospace Engineering and Mechanics, Unive

of Minnesota, 107 Akerman Hall, 110 Union Street S.E., MinneapoMN 55455.

2370003-6951/98/73(16)/2375/3/$15.00

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cess must be avoided. The origin of the potential variatioin physical properties of the photoresist film lies in the spcoating technique. Large amounts of extra free volumetrapped in the film during the spin coating.

The device we developed uses a drop-on-demmethod to dispense photoresist on silicon wafers. Drop-demand coating of a wafer reduces both waste and cosaddition to reducing waste, this method can be used to coddly shaped substrates~i.e., flat panel displays!, to planarizethe resist profile on the wafers~i.e., putting more resist onsome parts of the wafers!, to finely control its spatial distri-bution in real time, and to do direct write for MEMS whercritical dimensions are of the order of microns. The piezelectric fluid ejector can find applications in integrated ccuit manufacturing not only for photoresist coating but afor dispensing chemicals to desired regions, such as liqugaseous materials, and fine solid particles. The ejector dnot damage sensitive fluids.

A schematic of the novel ejector is shown in Fig. 1.thin sheet of brass, a shim, with a small orifice is bondeda piezoelectric ring as described in Perc¸in et al.5 A cylinderattached to the shim serves both as a fluid reservoir an

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FIG. 1. A schematic of the device: the lateral extent is 9 mm.

5 © 1998 American Institute of Physics

cense or copyright; see http://apl.aip.org/about/rights_and_permissions

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2376 Appl. Phys. Lett., Vol. 73, No. 16, 19 October 1998 Percin, Lundgren, and Khuri-Yakub

clamp the ends of the compound membrane formed ofshim and piezoelectric. The reservoir is open, and the fluiat atmospheric pressure. An ac voltage is applied tomembrane to set it into vibration. At the resonant frequencof the fluid loaded compound membrane, the displacemethe center is large. The fluid behind the orifice is acceleraas the membrane moves. When the inertial force is larthan the surface tension force that holds it to the orificedrop is ejected from the orifice. The size of the drop andinitial speed depend on the fluid, the size of the orifice, athe energy supplied to the transducer. A unique feature ofdevice is that the fluid is not pressurized, and the vibratmembrane contains the orifice as the ejection source. Tthe device can be manufactured by surface micromachinand is amenable for implementation in the form of twdimensional arrays. Indeed, a silicon micromachined versof the device is presently under development in olaboratory.6

We designed the transducer to have a maximumplacement at the center of the membrane at the resonanquency described in Perc¸in et al.5 Analyses of similar de-vices such as those of Allaverdievet al.7 and Vassergiseet al.,8 were helpful in identifying the important parameteof the device. Similar ejector designs can be found in Stro¨m,9

Maeharaet al.,10,11 Uehaet al.,12 Tetsuo,13 and Ivri.14

The vibrating membrane raises the pressure in the liqabove atmospheric during part of the cycle, and if this is henough to overcome inertia and surface tension restoforces, drops are ejected through the orifice. If the membrdisplacement amplitude is too small, the meniscus in thefice simply oscillates up and down. If the frequency is thigh, the pressure in the fluid does not remain above atspheric long enough to eject a drop. An estimate of the crect balance can be found by considering the Kelequation15 l(2ps/r f 2)1/3 which gives the wavelengthl oflinear capillary waves driven at frequencyf on a plane inter-face. The parameterss andr are surface tension and densiof the liquid. If l is much smaller than the diameter of thorifice, the vibrating membrane will simply setup shoripples on the liquid surface. This suggests that a dimensless surface tension parameter,S52s/ra3f 2 , wherea is theradius of the orifice, should be of order 1 or greater.

A computational model which simulates droplet ejectihas been developed using a boundary integral method simto one used previously.16,17 The previous work did not havesolid boundaries, however, therefore modifications were nessary. Singular potential flow dipole solutions were distruted along the liquid/air interface in an axially symmetconfiguration, as in the previous work, and singular sousolutions were distributed on the solid membrane surfaEnforcing boundary conditions on these surfaces, pressusurface tension balance on the liquid interface, and specing the velocity on the solid membrane gives integral eqtions to determine the dipole density and the source denfunctions. The use of both dipoles and sources in this manresults in coupled Fredholm equations of the second kwhich can be solved simultaneously by an iterative proce

These equations were made dimensionless using thdius of the orifice as the characteristic length and the peof membrane oscillation as the characteristic time. The o

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parameter which remains in the equations is the surfacesion parameterS introduced previously. This provides a scaing law for drop ejection. All other things being equal, suas amplitude and membrane mode shapes, this showsdroplet size and shape is only a function of this singlemensionless parameter. For instance, iff is made larger, theneither the orifice radius should be smaller ors made larger tocompensate. It should be emphasized that viscous effhave been neglected in this analysis. A Reynolds numRe5a2f/n , which describes the ratio of inertial forces to vicous forces, should be sufficiently large for the analysis tovalid.

In the computation, drop ejection is initiated by pushithe membrane downward from an elevated stationary ption to a depressed position where it is stopped. That ismoves through a half-cycle with a motion which produceflow rate through the orifice ofq5qmax sin(2pt) with 0,t,0.5 andqmax53.1 ml/s for the simulation shown in Fig. 2The simulated droplet ejection closely resembles the acwater droplet ejection picture with a similar elongated taThis is seen in Fig. 2 where the simulated droplet ejectionshown, with actual dimensions, at three times during a cyThe orifice diameter is 60mm, the ejection frequency is 16.

FIG. 2. Droplet ejection simulation: top, simulation; bottom, actual ejecti

cense or copyright; see http://apl.aip.org/about/rights_and_permissions

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2377Appl. Phys. Lett., Vol. 73, No. 16, 19 October 1998 Percin, Lundgren, and Khuri-Yakub

kHz ~period 60.97ms!, and the ejected fluid is water. Thdiameter of the drop is 82% of the orifice diameter andfinal velocity is about 1.64 m/s based on the distancetween the heights of the last two frames. This value ireasonable approximation to 1.54 m/s that was measurethe experiments, at this amplitude and frequency. In the cputation, the drop pinchoff time was 41.95ms, Re514.70,and the surface tension parameterS520.0. We have usedn51.00431026 m2/s, v51.54 m/s, s572.731023 N/m,r51 g/cm3 for calculating these parameters.

Scale model devices were fabricated using the optimconfiguration obtained by finite element analysis asscribed earlier by Perc¸in et al.5 The reservoir was a brascylinder of height 8 mm. A 25mm thin shim was bonded tothe 25mm thick piezoelectric ring. The inner and outer dameters of the ring were 2 and 7 mm, respectively. Thefice diameter ranged from 50 to 200mm and was made usineither a drill in a small lathe, or by chemical etching.

Shipley Microposit S1400-21, S1400-27, S1805, aS1813 photoresists were ejected using the ejector undeconditions described in the previous section, with a 200peak to peak voltage. Figure 3 shows photoresist pattthat were exposed and developed into the wafer. The land spaces are 10mm wide. The ejected photoresist drop siin air is 85% of the orifice size which is 110mm. The resistis 3.5mm thick and has a surface roughness of about 0.2mm.The resist coating was done in a dry laboratory and contdust particles and nonuniformity due to the quick evapotion of the solvent in the resist. Using a chamber withsolvent saturated environment will alleviate both problemsdirt incorporation and nonuniformity. Figure 4 demonstrathe ability to deposit lines of photoresist that are 350mmwide. Narrower lines can be deposited with smaller dro

FIG. 3. Novel ink-jet deposited, exposed, and developed photoresistlines and spaces are 10mm wide.

FIG. 4. Drop-on-demand direct write with photoresist: the lines are 350mmwide.

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Coating in a clean environment will allow the lithographycircuits for microelectronic applications. Figure 5 presethe drop-on-demand direct write of fine solid particles onsticky tape. Talcum powder@Mg3Si4O10~OH!2# with particlesize of 9–18mm was ejected through a 60mm diameterorifice. The deposited solid particle linewidth is 270mm. Thedeposited linewidth can be reduced by decreasing the ejeto sample spacing.

In summary, we have developed a novel fluid and soparticle ejector, and a novel photoresist coating techniqThe ejector was also demonstrated with water, ink, andcum powder. The ejector design, based on that of a flexsional transducer, was optimized using a finite elemanalysis. Simulation software for computing drop formatifrom a vibrating orifice was developed by using a boundintegral method. This novel ejector can be silicon micromchined into two-dimensional arrays.

This research was supported by the Defense AdvanResearch Projects Agency of the Department of Defensewas monitored by the Air Force Office of Scientific Researunder Grant No. F49620-95-1-0525. The authors would lto thank Nagi N. Mansour for his valuable discussions, aH. Tom Soh for his help with the photoresist ejection expements.

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he

FIG. 5. Small solid particle ejection: linewidth is 260mm and individualparticles are 9–18mm in diameter.

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