A Review on Electrohydrodynamic inkjet printing technology

International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 4, Issue 5, May 2014)

174

A Review on Electrohydrodynamic-inkjet Printing Technology Pratikkumar Vikramark Raje

1, Naresh Chandra Murmu

2

1Academy of Scientific & Innovative Research, CSIR-CMERI, Durgapur-713209, India

2 Surface Engineering and Tribology, CSIR-CMERI, Durgapur-713209, India

Abstract— Electrohydrodynamic (EHD)-inkjet printing is a

novel high resolution inkjet printing technology with the

advantages of being a maskless, non-contact, direct-write and

additive process. Its printing resolution exceeds by about two

orders of magnitude in comparison to the conventional inkjet

printing systems. It is used in the field of micro/nano

manufacturing for patterning of large class of materials on a

variety of substrates with the options to use either Drop-On-

Demand (D-O-D) or continuous mode. Printable electronics

especially flexible electronics is one of the many fields where

this technology has a lot to offer as the same EHD-inkjet set-

up can be used for electrospraying for thin film layer

deposition, electrospinning for interconnection and EHD

jetting for making electrodes. A lot of research has been

carried out in the recent past to make its transition from a

research tool to a commercial manufacturing process. Many

challenges such as increasing the process throughput (i.e. the

printing speeds) have to be overcome before the

commercialization of this technology. Another major

challenge is to develop a compact, affordable and user

friendly test platform to further develop the process and

associated applications. This review gives a brief account of

the EHD-inkjet technology; the research activities carried out

in recent years and the wide areas of applications of this

technology. The working of the EHD-inkjet system along with

the physics of the process has also been discussed in brief.

Keywords—Drop-on-Demand (D-O-D),

Electrohydrodynamic (EHD)-inkjet printing, Electrospinning,

Electrospraying, Flexible electronics, Inkjet printing systems

I. INTRODUCTION TO THE INKJET BASED MICRO/NANO

PATTERNING TECHNOLOGY

Patterning, i.e. selective deposition, of functional

materials on desired substrates is a basic requirement in

many of the printing based micro/nano manufacturing

operations like the fabrication of microelectronic devices,

research fields like pharmaceutical industries for drug

discovery purposes and in biotechnology to make DNA

microarrays. Controlled generation and deposition of

micro/nano drops at higher and higher resolutions without

adversely affecting the chemical properties of the deposited

materials is the major challenge in micro/nano fabrication.

Traditionally, lithographic processes like

nanolithography or photolithography etc. are used for

achieving micro/nano patterning but these are too time

consuming and expensive [1,2]. As an alternative to the

lithographic processes, non-lithographic direct fabrication

methods like inkjet and roll-to-roll printing are used

because of their reasonable resolutions and higher

throughputs. These direct fabrication methods can be

classified as contact methods i.e. gravure, offset,

flexographic etc. and non-contact methods i.e. inkjet

technology. Because of the inkjet technology’s simple set-

up, cost effectiveness, additive process which reduces

material loss and non-contact nature which nullifies any

adverse effects to the substrate making it suitable for

flexible electronics, it became one of the best choices for

micro/nano fabrication.

Originally invented for printing computer graphic

outputs, from the last few decades inkjet printing

technology is widely used for patterning in the micro/nano

manufacturing industries. It encompasses a wide variety of

different techniques by which micro/nano droplets are

generated and controllably deposited. It has forced its way

from being just a graphic arts printing tool to the paradigm

of micro/nano manufacturing. It has also been successfully

used for the direct 3-D fabrication of micro/nano structures.

Its areas of application includes micro-electronics, drug

discovery, tissue engineering and biomaterials

development, materials science and device preparation,

MEMS, solar cells, mass-spectrometry, sensors and the list

goes on.

Ink-jet printing systems also find its applications in the

rapidly emerging field of flexible electronics. As ink-jet

printers are contact-free (print heads are not in a direct

contact with the substrates), printing can be done on very

flexible and delicate substrates with remarkable precision

and accuracy at higher speeds with minimum feature size in

the sub-micron range.

Inkjet is not a single process but a diverse, versatile and

multi-length scale group of process technologies, and a

variety of mechanisms and energy modes are used to create

material transfer to produce features from nanometer to

micrometer range.



175

It exploits the Plateau-Rayleigh instability (often called

only as the Rayleigh instability), named after Joseph

Plateau and Lord Rayleigh, which explains the

disintegration mechanism of the liquid jet into droplets [3].

Elmqvist of Seimens, in 1951, patented the first ink-jet

device based on this instability [4]. Since then, the ink-jet

technology saw many inventions like Dr. Sweet’s

Continuous Inkjet (CIJ) printing system [5,6] in the early

1960’s and Zoltan (1972), Kyser and Sears’s (1976) Drop-

On-Demand (D-O-D) inkjet printing system [7,8].

Commercially available inkjet printing systems can be

divided into two modes based on the ejection of the inks :

Continuous inkjet (CIJ), where jet emerges from the nozzle

which breaks in stream of droplets and Drop-On-Demand

(D-O-D) wherein the droplets are ejected from the nozzle

orifice as and when required. Many researchers have

reported problems of ink wastage in the start and end of the

printing in continuous mode. This problem of ink wastage

has been addressed by the introduction of D-O-D inkjet

printing. Thermal Inkjet (TIJ) and Piezoelectric Inkjet (PIJ)

printing systems are the predominant players in the area of

inkjet technology (Fig.1).

PIJ printing systems are the piezoelectrically driven

drop-on-demand devices which rely on the mechanical

action of a piezoelectric membrane to generate a pulse

which squeezes the nozzle to eject drops. Epson printers

use this technology.

TIJ , sometimes referred to as bubble jet, is a drop-on-

demand technology wherein a thin layer of liquid is heated

locally by a thin film heater in a few microseconds to form

a rapidly expanding vapour bubble that ejects an ink

droplet. Hewlett Packard and Canon have manufactured

highly successful lines of inkjet printers that have used this

technology for over two decades [53].

However, PIJ and TIJ D-O-D systems are not able to

produce droplets with a broad range of size distributions

from the same nozzle. There resolution is limited to feature

sizes of 20-30 µm [10]. For getting higher and higher

resolutions in terms of the feature size, inkjet systems

requires the use of smaller sized nozzles which faces the

difficulty of manufacturing and also the problem of nozzle

clogging. Also, the droplet placement accuracy for these

processes is not high enough. So, the quest for getting

higher and higher resolutions at higher and higher printing

speeds with more precision and accuracy led to the

development of various novel non-conventional ink-jet

printing methods. One such technology for getting higher

resolutions and better droplet placement accuracy utilizes

externally applied electric fields.

This elegant way of manipulating droplet sizes, their

ejection frequencies and placement on the substrate using

externally applied electric fields is called as the

Electrohydrodynamic inkjet (EHD inkjet) printing

technology.

(a)

(b)

Fig.1. Conventional inkjet printers (a) Piezoelectric inkjet printer (b)

Thermal inkjet printer [9]

II. EHD-INKJET PRINTING TECHNOLOGY: WHAT IT IS

AND WHAT IT CAN DO?

The great experimentalists like Robert Millikan, Lord

Rayleigh and G. I. Taylor [11] have earlier tested the

behavior of liquid jets and liquid drops in electric fields.

Since then many researchers have tried to adapt the

technique of controlling and manipulating the drop

formation process by applying electric fields and EHD

inkjet system has evolved as a prospective technology for

micro/nano patterning.

EHD-inkjet printing technology has been a target of

much research because of its ability to generate drops of

very small size as compared to the other inkjet techniques

like TIJ and PIJ for the same nozzle sizes.

http://en.wikipedia.org/wiki/Joseph_Plateau

http://en.wikipedia.org/wiki/Joseph_Plateau

http://en.wikipedia.org/wiki/John_Strutt,_3rd_Baron_Rayleigh



176

Unlike the conventional inkjet methods, it pulls the

liquid inks out of the nozzle rather than pushing it. As a

result, it is able to produce ink-drops or ink-jets of size 2 to

5 orders of magnitude smaller than the nozzle size [12]

which is not possible in case of the conventional ink-jet

printing systems.

The main components of a EHD inkjet printer can be

classified into four sub-systems.

1) Liquid supply system which consists of a device to

deliver the ink at desired flow rates to the tip of the

conducting needle. The liquid can be supplied by using a

syringe pump or a vacuum pump and the tubings.

2) Positioning system which consists of a motorized stage

on which the substrate is mounted to position it as

desired with respect to the tip of the needle for

patterning. The needle can be mounted on either a

manual or motorized stage to control its distance from

the substrate (called as the stand-off height).

3) Electrical system which consists of a high voltage DC

amplifier for applying voltages across the needle and the

substrate. A function generator is also required to supply

pulsed width modulated (PWM) signals which is the

requirement in case of the D-O-D mode.

4) Visualization system is required to monitor and study the

process of drop formation for various values of the

process parameters. This is helpful in improving the

process. The visualization system consists of a high

speed camera, a microscopic zoom lens system and an

illumination source.

Fig.2. shows the schematic of an EHD-inkjet printing

system.

A wide range of functional organic and inorganic inks,

including suspensions of solid objects can be printed using

this technique with resolutions extending to the submicron

range. The applications in printable electronics require

higher print rates, better resolution and higher reliability

while printing more complex Non-Newtonian and heavily

solid loaded liquids. So, printed electronics represents an

important application area that can take advantage of both

the extremely high-resolution capabilities of EHD-inkjet

printing as well as its compatibility with a range of

functional inks.

Fig.2. Schematic of the EHD inkjet printing system

Also, different devices require different fabrication

processes for eg. Solar cell needs uniform thin film, TFT

needs high resolution line width and uniform structure,

sensors and MEMS need more complex patterns. EHD

inkjet printer uses a fine jet generated at the apex of a

liquid cone in the cone jet mode to create spray by

electrospraying, fibre by electrospinning or inkjet and

droplets by EHD jetting. These three types of EHD printing

hold the same mechanism of EHD and the homologous

experiment setups. Thus, it is promising for all the three

methods used in printed electronics, such as electrospray

for thin film layer, electrospinning for interconnection and

EHD inkjet for making electrodes. Also different types of

materials are required for the fabrication of a single

component. All these requirements can be fulfilled by the

same EHD inkjet printing set-up. Thus, EHD-inkjet

printing has great potential to offer complex and high

resolution printing and is opening new routes to

nanotechnology. Many researchers have shown the

capabilities of EHD-jet printing applied to different

applications from biotechnology to microelectronics.

As with any manufacturing process, throughput rates (in

this case printing speeds) and process robustness are key

decision parameters for the commercialization of this

process. EHD-inkjet printing system has seen recent

advancements in the printing speed and reliability [10, 12].

EHD inkjet printing has emerged from the realm of pure

research into the very early development stages of a

potential commercially viable technology for micro/nano

patterning.



177

Fig.3. shows some of the application areas of the EHD-

inkjet printing technology.

Fig. 3. Some Applications of EHD-inkjet printing technology

III. WORKING OF THE EHD-INKJET SYSTEM AND PHYSICS

OF THE ELECTRIC FIELD DRIVEN JETTING BEHAVIOR

The electrohydrodynamic jetting was first reported by

Bose in 1745 [13]. Many years later, in 1882, Rayleigh [14]

did a theoretical analysis of the break-up of liquid under

electrical stress and derived instability condition for the

electrically charged droplets. Zeleny in 1917 [15]

determined the criterion for the disruption of the jet issuing

from the capillary maintained at high potential. In 1952,

Vonnegut and Neubauer applied the principle of minimum

energy to determine the most probable specific charge of

the droplets. In 1964 and 1969, Taylor showed that the

semi-vertical angle of the cone at the outlet of the capillary

assumes the value of 49.3o.

Rayleigh’s theory is based on the balance between the

repulsive electrostatic force and the surface tension of the

liquid restoring forces. Rayleigh limit for the instability of

charged droplet is given by

1/2

2 3

08Q d

Where Q is the charge on the droplet,0 the permittivity

of the surrounding gas, liquid and d is the diameter of droplet. When the

electrostatic force overcomes the surface tension of the

liquid, electrically charged fine droplets are ejected from

cone [16]. It is also referred to as Coulomb fission [17].

This relationship has been evaluated by a number of

charge-to-mass ratio measurements [18-20] and size

distribution [20-22]. However, Michelson indicated that the

Rayleigh’s analysis considering only the electrical stress

and surface tension is oversimplified [23]. The real process

is greatly influenced by many parameters and these two

forces cannot explain all the phenomena encountered in the

electrospraying.

The control of the droplet size and modes of the

electrospraying offer a wide spectrum of practical

applications. EHD-inkjet printers eject liquid jets due to the

Electrohydrodynamic instability. The main components of

a EHD inkjet printer consists of a liquid supply system to

supply liquids at desired flow rates to the tip of a

conducting nozzle and a DC power source to apply

voltages across the conducting nozzle and the substrates.

Before applying the electric field, the liquid is supplied

to the tip of the nozzle until a hemispherical meniscus is

formed there due to the surface tension between the liquid-

air interface. After the hemispherical meniscus is formed,

electric field is applied. The liquid contains equal number

of positive and negative ions which are its conducting

species. As the voltage is increased, depending on the

polarity of the applied voltage, either the positive or the

negative ions will start moving towards the liquid surface at

the tip of the nozzle. With increase in the voltage, more and

more ions will start accumulating near the liquid surface

and due to the mutual columbic repulsion between them,

the liquid surface starts experiencing a tangential electric

stress.

Fig. 4. Stresses developed in a liquid meniscus under the influence of

external E-field (Kim et al. 2011)



178

Fig. 5. Block diagram showing the Working of the EHD-inkjet printing system

The magnitude of this tangential electric stress goes on

increasing with the increase in voltage. At some voltage

value, the tangential stress on the liquid surface along with

the electrostatic attraction to the substrate deforms the

hemispherical meniscus at the nozzle tip into a cone shaped

pendant called as the famous Taylor’s cone having a semi-

vertical angle of 49.3°. This is the boundary between

stability and instability. A slight increase in the voltage

beyond this value causes the electrostatic stress to

overpower the surface tension resulting in the jet ejection

from the Taylor’s cone. Different jetting modes like

dripping mode, micro-dripping mode, spindle mode, cone-

jet mode etc. are obtained as the voltage is kept on

increasing.

Now depending upon the type of the applied voltage, we

can have either Continuous Inkjet (CIJ) mode or Drop-on-

Demand (D-O-D) mode.

CIJ mode is obtained if the voltage applied between the

conducting nozzle and the substrate is a constant DC one

whereas for the D-O-D mode, pulsed DC voltage is

required. In the CIJ mode, stabilization of the micron size

jet is very difficult. Also, problems in the placement of the

liquid drops at start point and end point of the pattern are

encountered.

The D-O-D mode has the biggest advantage that the jet

emission is controlled, i.e., the jet is ejected from the

Taylor’s cone as and when required. So, the placement

accuracy of the drops on the substrate is high as compared

to the CIJ mode.

IV. VARIOUS JETTING MODES

The application of potential difference between a

conducting needle and a grounded electrode placed

centrally below it with the flow of liquid ink in the region

between gives rise to a phenomenon referred to as

electrohydrodynamic jetting also known as electrospraying.

The liquid ink travelling through the needle acquires a

charge and after exiting the needle, it enters a high intensity

electric field. At the needle’s tip, it can form different

geometries like Taylor’s cone from which a jet or jets or

even monodisperse droplets can evolve. The disruption of

the evolved jets into droplets also depends on the applied

electric field. Choi et al. [24] presented simple scaling laws

that describe the intrinsic pulsation of a liquid jet that forms

at the tips of fine nozzles under electrohydrodynamically

induced flows. They also found that the force of gravity is

negligible compared to the other forces, i.e., electrical and

surface tension in both horizontal and vertical nozzle

orientations. The break-up of the jets into different droplet

sizes can be controlled through the applied potential

difference, the flow rate of the liquid ink to the needle, the

size of the needle and its configuration, i.e., its distance

from the substrate and the ink’s mechanical and electrical

properties; which are called as the process parameters.

The geometrical forms of the jet and the ways in which

it disrupts into droplets have been classified into modes of

spraying. There are various modes of spraying with various

jet structures and break-up mechanisms, depending on the

different values of the process parameters.



179

Classification of jetting modes has been the subject of

intensive work, which can provide insight into the

electrospray [25-27]. The size of liquid droplets ejected

varies from the millimeter to the submicron range.

Several attempts, based on different criteria, have been

undertaken to classify the modes of EHD spraying. [28]

studied the various jetting modes of deionized water using

a high speed camera. [29] studied the various ejection

modes for pulsed-DC EHD inkjet printing using diethylene

glycol (DEG).

[30] proposed a definition of the jetting modes of the

electrohydrodynamic-jet as the way the liquid is dispersed

into droplets, and characterized it by two criteria:

1. The geometrical form of the liquid at the outlet of the

capillary (drop, spindle, jet), and

2. The mechanism of the disintegration of the jet into

droplets (type of instability).

TABLE I

EHD-INKJET PRINTING JETTING MODES [30]

Most of the jetting modes are classified according to

these criteria. For a particular ink, nozzle size and stand-off

height value, each mode commences at certain voltage

value and flow rate, and is sustained within a certain

interval of their values. Outside that interval, the jetting

mode changes into another one. Thus, each jetting mode

has certain intervals of voltage and flow rate values within

which it occurs. [30] divided the jetting modes into two

groups. The first group consists of the modes in which only

fragments of liquid are ejected from the nozzle directly.

This group comprises: the dripping mode, microdripping

mode, spindle mode, multi-spindle mode, and ramified-

meniscus mode.

The second group includes the modes in which the liquid

issues a capillary in the form of a long continuous jet which

disintegrates into droplets only in some distance from the

outlet of the nozzle. This group includes cone-jet mode,

precession mode, oscillating-jet mode, multijet mode and

ramified-jet mode. Majority of the researchers use stable

cone-jet mode or micro-dripping mode for printing

purposes.

V. DROP-ON-DEMAND (D-O-D) MODE

To generate uniform micro-drops for high-resolution

printing, the pulsed-DC voltage method is superior to

continuous-DC voltage methods because of its

controllability. Printing time is cut down by a factor of 30

using the pulsed mode operation as compared to a constant

voltage jet printing mode [12]. Also D-O-D EHD-inkjet

enables on the fly diameter change, i.e., the droplet

diameter is varied while printing the same pattern without

changing the nozzle tips. Using D-O-D mode, Park et al

[31] realized printed dots under 1 µm at 300 Hz, Paine et al

[32] printed 2.886 µm dots at 1 Hz, Wang et al [33] printed

120 µm dots at 1 Hz, and Nguyen et al [34] printed 15 µm

dots at 10 Hz. Young et al [35] investigated

electrohydrodynamic jetting in order to print ultra-fine dots

and lines in drop-on-demand (DOD) mode, using a hybrid

micro-electromechanical system-based printhead with a

piezoelectric actuator. Such hybrid system enabled jetting

without applying an extremely high-voltage pulse.

Scaling laws describing the jet diameter and frequency

have been described by Choi et al [24] through

experimentation and literature results. They propose the

following relationship between the frequency of jetting, f,

the voltage potential, V, and stand-off height, h :

3/2V

f kh

………………………………..(1)

Where k is a scaling factor constant dependent on the

viscosity of the ink, the nozzle diameter, fluid flow rate,

and permittivity of free space.

Due to the relationship between frequency and droplet

diameter according to Equation (1), a method for

controlling them independently was developed in [12]. A

DC voltage is applied to the nozzle which forms the Taylor

cone but does not allow jetting of the ink. When a droplet is

required, the voltage is then pulsed to a much higher value

that guarantees a jet to be formed. A pulse width modulated

(PWM) DC voltage signal which is fed to the nozzle has

the following characteristics:



180

D-O-D : Pulsed voltage characteristics

Voltage pulse peak (Vh) induces a fast EHD-jetting

mode for a short duration while a baseline dc voltage

(Vl) is picked to ensure that the meniscus is always

deformed to nearly a conical shape but not in a jetting

mode

Duration of pulse (Tp) determines the volume of the

droplet, i.e., feature size on the substrate

Droplet frequency is controlled by the time interval

between two successive pulses (Td)

A jet printing regime with a specified droplet size and

droplet spacing can be created through a suitable choice

of the pulse width and frequency

Fig. 6. Pulse width modulated DC signal used for achieving the D-O-D

mode

[29] observed that the higher the frequency of pulsed DC

voltage, the smaller the drop size is. [1,36] observed that

the frequency of the pulsed dc voltage was almost the same

as the pulsating frequency of the liquid in pulsed cone-jet

mode. However, this does not hold good, i.e., jet ejection

does not occur for each input pulse when a pulse duration

time is shorter than the time corresponding to the plateau

frequency. This plateau frequency phenomenon can be

explained with the two characteristic times of transient

electrospray: the charge relaxation time and the

characteristic time for Taylor cone formation. The

characteristic time for Taylor cone formation is suggested

to be the limiting frequency of the drop generation in [36].

Characteristic time of Taylor cone formation is a mystery

but is suggested to be related with electric stress, meniscus

volume, and liquid properties such as surface tension,

viscosity and density. [36] calculated the characteristic

frequency of meniscus formation. As the frequency of

pulsed voltage becomes higher than the characteristic

frequency for the meniscus formation, the meniscus cannot

grow to the typical Taylor cone. And when the input pulse

frequency is larger than the plateau frequency, the drop

generation frequency becomes smaller than input

frequency. [36] also reported that when the input pulse

frequency was larger than the plateau frequency, the drop

generation frequency became smaller than input frequency.

Thus, there is a nonlinear relationship between the

applied voltage frequency and droplet deposition frequency

under pulse voltage at voltage frequency values greater

than the plateau frequency. So, for getting hindrance free

on-demand printing even in the case of pulsed DC voltage,

the frequency of the input signal needs to be set below the

plateau frequency.

The diameter of a ejected drop Ddrop from the nozzle tip

can be calculated by using the following relation :

2 3

8 6

drop drop drop

drop

input

D h hQV

f

Where Vdrop is the volume of one drop, Q is the flow

rate, finput is the frequency of the pulsed voltage and hdrop is

the height of a drop.

VI. MULTI-NOZZLE MULTI-MATERIAL EHD-INKJET

DEPOSITION SYSTEMS

A critical area of continued focus in the EHD-inkjet

technology is the improvement of the process throughput.

Increased throughput is a key for enabling EHD-inkjet as a

viable commercial manufacturing process. There are two

main approaches for increasing the process throughput:

improving the speed of the process also defined as printing

frequency, and increasing the number of nozzles for a

given printhead. As the number of nozzles increases, the

printing time will go down to /t n , where t is the

printing duration of a single nozzle and n is the number of

nozzles. [37] concluded that the use of a 3 nozzle printhead

resulted in a corresponding 3 times reduction in printing

time as compared to a single nozzle printhead for printing a

single device without the loss of part fidelity. So, for large

area printing, multi-nozzle printing system is the need.

Also, heterogeneously integrated functional electronic

systems often require multiple materials (polymers, metals,

biological materials) to be present and collocated on the

same substrate. Thus, it is also this demand for more

complex, multimaterial functionality that leads to the need

for an EHD inkjet printing tool capable of depositing

multiple material inks with same speed and resolution as

with the case of a single nozzle single material deposition

system. Presently, multinozzle printing systems enable upto

4 different types of materials to be patterned on a single

substrate, in rapid fashion and with excellent control over

spatial dimensions and registration. [38] reported a multi-

nozzle multi-material deposition system for heterogeneous

integration of different functionalities on a single substrate.



181

[39] reported the development and evaluation of a EHD

jet printing that uses an addressable multinozzle. The main

issue with the development of a multi-nozzle printhead is

the interaction of electric fields between the multiple

nozzles which affects the print quality. [37] performed the

initial characterization of the electrostatic interference

introduced in the multi-nozzle design.

VII. DEVELOPMENTS IN THE EHD-INKJET TECHNOLOGY

D.H. Choi and I.R. Smith (1998) from the Natural

Imaging Corporation claimed the first patent for EHD

inkjet printing under the US patent 5838349. The process

was not used for high-resolution printing until the

University of Illinois developed a manufacturing system

specifically for that purpose. In January 2009, the

University of Illinois was granted a patent

(WO2009/011709) for high resolution EHD-inkjet printing

for manufacturing systems.

Majority of the research activities for the development of

a commercial EHD inkjet printing system are taking place

in the University of Illinois at the Urbana Champaign. Park

et al. [31] demonstrated high resolution EHD-inkjet

printing using expensive custom built equipments. Barton

et al. [10] developed a desktop system for EHD-inkjet

printing designed from the commercial off-the-shelf

technology (COTS) components. They were able to

generate average droplet size of 2.8 microns from a nozzle

size of 5 microns, i.e., droplets nearly half the size of the

nozzle size. [40] deposited 20 micron circularly shaped

polymeric droplets from 100 micron size nozzle at voltage

frequencies less than 100 Hz, i.e., droplets 5 times less than

the nozzle size. Graf et al [41] developed a second

generation EHD inkjet printing system with a budget less

than USD 50,000 having multi-material capabilities with a

dual print head, interpolation and NC programming for line

writing capabilities in addition to raster-scan printing, and

automated image analysis-based overlay registration

capabilities for quick set-up.

[42] described the application of EHD inkjet in wide-

ranging areas of biotechnology. [43] patterned DNA

without adversely affecting its properties in arrays and

other various complex patterns with printing resolutions

approaching 100 nm. [42] reported the use of EHD inkjet

printing for creating micro and nanoscale patterns of

proteins on various surfaces ranging from flat silica

substrates to structured plasmonic crystals, suitable for

micro/nano array analysis and other applications in both

fluorescent and plasmonic detection modes.

The approaches function well with diverse classes of

proteins, including streptavidin, IgG, fibrinogen and

gamma-gobulin without adversely altering the protein

structure or function. [44] showed that EHD inkjet printing

can be used to process and deposit living cells (Jurkat cells)

in suspensions onto surfaces without having adverse effects

on living cells. Kim et al [45] patterned and then grew

viable Escherichia coli cells. Jayasinghe et al [44] used a

pipette to electrospray cell samples onto a substrate.

[46] reported the applications of inkjet printing in micro

electronics. [2] concluded that EHD inkjet printing can be

used for printing of conductive lines for metallization in

printed circuit boards and backplanes of printable

transistors. [47] showed applications in fabricating

conductive microtracks and microconnects and printed

silver tracks with feature size down to 35 microns. Wang

and Stark [33] demonstrated 3D silver microstructures with

100 µm resolution. Youn et al [48] showed 6 micron silver

lines using a tilted nozzle. [49] printed a set of silver lines

with a few hundred nanometers in thickness and with a few

hundred micrometres in width with EHD inkjet printing.

[50] used EHD-inkjet printing for producing arrays of

colloidal suspensions of colloidal crystalline stripes on

surfaces. [1] generated discrete droplets with 45-55

microns in diameter and continuous tracks with 60 microns

in width by using a 110 micron nozzle. They also

fabricated basic electronic components such as coated

resistors, inter-digitated capacitors and spiral inductors by

printing continuous silver tracks as the conducting leads

using EHD-inkjet. [31] demonstrated the high resolution

EHD-inkjet printing with print feature sizes in the range

from nearly 240 nm to 5 nm. [51] characterized the jetting

rule of polymer solution experimentally under low

frequency pulsation. [12] demonstrated the capability for

printing speeds of 1000 droplets per second, while

producing consistent and controllable droplet sizes of 3-6

microns. [29] Created a map of different ejection modes

with droplet ejection frequencies of 1 Hz, Q= 0.2 ml/h

using a nozzle diameter of dn=1.27mm with DEG as the

working fluid. Muhammad et al 2010 performed thin film

deposition of CIS (Copper-Indium di-Selenide) through

electrospray deposition by using 430 micron ID metallic

nozzle. [52] reported a hybrid EHD inkjet system where

piezoelectric actuator is used to supply a fixed volume of

ink to the nozzle’s exit and electrohydrodynamic technique

is used to form ink droplets.

Thus, lot of research activities have been carried out

which shows the high resolution printing abilities of the

EHD-inkjet with wide range of functional inks.



182

However, a database of printing conditions for different

commercially available functional inks should be built

which will serve as a recipe to the subsequent EHD-inkjet

users. Also, throughput improvement is critical to fully

realize the potential of this emerging manufacturing

process.

VIII. CONCLUDING REMARKS

EHD-inkjet printing is a very powerful tool and process

for the direct patterning of the functional materials on a

large variety of substrates. Its ability to do patterning as

well as thin film deposition can help in fabrication of the

electronic devices such as TFT, OLED or Solar Cells etc.

through a single technology. Its flexibility in terms of

selection of the wide range of ink materials and substrates

together with its high resolution capability and high droplet

registration accuracy makes it a forefront runner for

micro/nano fabrication. However, process throughput

improvements remains to be a major challenge before its

complete transition into a commercial technology. Multi-

nozzle multi-material deposition EHD-inkjet systems can

serve this purpose. Developing this technology will allow

exploring the potential of EHD-inkjet printing in high

resolution fabrication of micro-electronic devices which

appears to be the promising direction for the future.

REFERENCES

[1] Wang X et al. ―Pulsed electrohydrodynamic printing of conductive silver patterns on demand‖, Sci. China Tech. Sci., June 2012,

Vol.55, No.6, 1603-1607

[2] Kyung-Hyun Choi et al. (2011) ―Electrohydrodynamic Inkjet –Micro

Pattern Fabrication for Printed Electronics Applications‖, Recent

Advances in Nanofabrication Techniques and Applications, Prof. Bo Cui (Ed.), ISBN: 978-953-307-602-7, InTech

[3] F. R. S. Rayleigh, ―On the instability of jets‖, in Proc. London Math.

Soc. 10(4), 4–13 (1878).

[4] R. Elmqvist, ―Measuring instrument of the recording type‖, U.S.

Patent 2566443 (1951).

[5] R. G. Sweet, ―High frequency recording with electrostatically

deflected ink-jets‖, Rev. Sci. Instrum. 36, 131 (1965)

[6] R. G. Sweet, ―Signal apparatus with fluid drop recorder‖, U.S. Patent

3596275 (1971).

[7] S. L. Zoltan, (Clevite Corp.), ―Pulse droplet ejection system‖, U.S.

Patent 3683212 (1974).

[8] E. L. Kyser and S. B. Sears, (Silonic Inc.), ―Method and apparatus for recording with writing fluids and drop projection means

therefore‖, U.S. Patent 3946398 (1976).

[9] http://www.imaging.org/ist/resources/tutorials/inkjet_printer.cfm

[10] K. Barton et al. ―A desktop Electrohydrodynamic jet printing

system‖, Mechatronics 20 (2010) 611-616

[11] Sir Geoffrey Taylor , "Disintegration of Water Droplets in an

Electric Field". Proc. Roy. Soc. London. Ser. A Vol. 280 No. 1382 383-397 (1964)

[12] S. Mishra et al ― High speed and Drop-On-Demand printing with a

pulsed electrohydrodynamic jet‖ J. Micromech. Microeng. 20 (2010) 095026 (8pp)

[13] Bailey A.G., Electrostatic spraying of liquids. J. Wiley & Sons 1988

[14] Rayleigh F.R.S., On the Equillibrium of Liquid Conducting Masses

Charged with electricity. Phil. Mag. 14 (1882) Ser.5, 184-6

[15] Zeleny J., Instability of Electrified Liquid Surface. Phys. Rev. 10 (1917) No 1, 1-6

[16] J. N. Smith, R. C. Flagan, and J. L. Beauchamp, "Droplet evaporation and discharge dynamics in electrospray ionization," J.

Phys. Chem. A, vol. 106, pp. 9957-9967, 2002.

[17] K. Tang and A. Gomez, "On the structure of an electrostatic spray of monodisperse droplets," Phys. Fluids, vol. 67, pp. 2317-2332, 1994.

[18] H. M. A. Elghazaly and G. S. P. Castle, "Analysis of the instability of evaporating charged liquid drops," IEEE Trans. Ind. Applicat.,

vol. 22, pp. 892-896, 1986.

[19] A. Doyle, D. R. Moffett, and B. Vonnegut, "Behavior of evaporating electrically charged droplets," J. Colloid Interface Sci., vol. 19, pp.

136-143, 1964.

[20] M. A. Abbas and J. Latham, "The instability of evaporating charged

drops," J. Fluid Mech., vol. 30, pp. 663-670, 1967.

[21] L. D. Juan and J. F. D. L. Mora, "Charged and size distributions of

electrospray drops," J. Colloid Interface Sci., vol. 186, pp. 280-293,

1997.

[22] E. J. Davis and M. A. Bridges, "The Rayleigh limit of charged

revisited: Light scattering from exploding droplets," J. Aerosol. Sci.,

vol. 25, pp. 1179-1199, 1994.

[23] D. Michelson, Electrostatic Atomization. Bristol and New York:

Adam Hilger, 1990.

[24] Choi et al ―Scaling laws for jet pulsations associated with high-

resolution electrohydrodynamic printing‖ Applied Physics Letters

92, 123109 (2008)

[25] S. O. Shiryaeva and A. I. Grigor'ev, "The semiphenomenological

classificationfo the modes of electrostatic dispersion of liquids," J. Electrostat., vol. 34, pp. 51-59, 1995.

[26] M. Cloupeau and B. P. Foch, "Electrostatic spraying of liquids: Main

functioning modes," J. Electrostat., vol. 25, pp. 165-184, 1990.

[27] M. Cloupeau and B. Prunet-Foch, "Electrohydrodynamic spraying

functioning modes: A critical review," J. aerosol. Sci., vol. 25, pp. 1021-1036, 1994.

[28] Hyun-Ha Kim et al 009 Electrostatics Joint Conference, Poster

Session P2. 21

[29] M.W. Lee et al. ―A study of ejection modes for pulsed-DC

electrohydrodynamic inkjet printing‖ Journal of Aerosol Science 46

(2012) 1–6

[30] Jeworek A.et al. ―Main modes of electrohydrodynamic spraying of liquids‖ Third International Conference on Multiphase Flow,

ICMF’98 Lyon, France, June 8-12, 1998

[31] Park J-U et al 2007 ―High-resolution electrohydrodynamic jet printing‖ Nature Mater. 6 782 9

[32] Paine M D, Alexander M S, Smith K L, Wang M and Stark J P W 2007 Controlled electrospray pulsation for deposition of femtoliter

fluid droplets onto surfaces J. Aerosol Sci. 38 315–24

[33] Wang K and Stark J P W 2010 ―Direct fabrication of electrically functional microstructures by fully voltage-controlled

electrohydrodynamic jet printing of silver nano-ink‖ Appl. Phys. A

99 763–6

http://en.wikipedia.org/wiki/Proceedings_of_the_Royal_Society_A#Proceedings_of_the_Royal_Society_A



183

[34] Nguyen V D, Schrlau M G, Tran S B Q, Bau H H, Ko H S and Byun

D 2009 ―Fabrication of nanoscale nozzle for electrohydrodynamic (EHD) inkjet head and high precision patterning by drop-on-demand

operation‖ J. Nanosci. Nanotechnol. 9 7298–302 PMID: 19908776

[35] Young et al 2013 ―Drop-on-demand hybrid printing using a piezoelectric MEMS printhead at various waveforms, high voltages

and jetting frequencies‖ J. Micromech. Microeng. 23 065011 (8pp)

[36] Kim et al. ―Electrohydrodynamic drop-on-demand patterning in

pulsed cone-jet mode at various frequencies‖ Aerosol Science 39

2008 819-825

[37] Erick Sutanto et al ―High throughput Electrohydrodynamic-jet

printing system‖ Proceedings of the ASME 2012 International

Symposium on flexible automation ISFA2012

[38] Sutanto et al ―A multimaterial electrohydrodynamic jet (E-jet)

printing system‖ J. Micromech. Microeng. 22 (2012) 045008 (11pp)

[39] Lee et al ―Design and evaluation of a silicon based multi-nozzle for

addressable jetting using a controlled flow rate in EHD jet printing‖ Appl. Phys. Lett. 93, 243114 (2008)

[40] Lei Xu et al ― Electrohydrodynamic deposition of polymeric droplets

under low-frequency pulsation‖ Langmuir 2011,27, 6541-6548

[41] Graf et al ―A high resolution Electrohydrodynamic jet printing

system‖ Proceedings of NAMRI/SME , Vol. 39, 2011

[42] Shigeta et al ―Functional Protein microarrays by

Electrohydrodynamic jet printing‖ Anal. Chem. 2012 84 10012-

10018

[43] J.U. Park et al ―Nanoscale patterns of oligonucleotides formed by

Electrohydrodynamic jet printing with applications in biosensing and nanomaterials assembly‖ Nano letters 2008 Vol.8, No.12 4210-4216

[44] Jayasinghe et al. ―Electrohydrodynamic jet processing : An

advanced electric-field-driven jetting phenomenon for processing living cells‖ small 2006,2,No.2, 216-219

[45] JH Kim, DY Lee, J Hwang, and HI Jung, "Direct pattern formation

of bacterial cells using microdroplets,"Microfluid Nanofluid, vol. 7, pp. 829-839, 2009.

[46] Chen et al ―Inkjet printing of microcomponents : Theory, Design, Characteristics and applications‖ Features of Liquid Crystal display

materials and processes, Dr. Natalia Kamanina (Ed.), ISBN:978-

953-307-899-1, InTech, 2011

[47] Wang et al ― Fully voltage-controlled electrohydrodynamic jet

printing of conductive silver tracks with a sub-100 micron

linewidth‖ Journal of Applied physics 106, 024907 (2009)

[48] D Youn et al., "Electrohydrodynamic micropatterning of silver ink

using near-field electrohydrodynamic jet printing with tilted-outlet nozzle," Appl Phys A, vol. 96, pp. 933-8, 2009.

[49] Lee et al ―Structuring of conductive silver line by Electrohydrodynamic jet printing and its electrical characterization‖

Journal of Physics: Conference series 142 2008 012039

[50] Poon et al. ―Linear colloidal crystal arrays by electrohydrodynamic printing‖ Applied Physics letters 93, 133114 (2008)

[51] Lei Xu et al ―Electrohydrodynamic deposition of polymeric droplets under low-frequency pulsation‖ Langmuir 2011,27, 6541-6548

[52] Byun et al ―A hybrid inkjet printer utilizing Electrohydrodynamic

jetting and piezoelectric actuation‖ Japanese Journal of Applied Physics 49 2010 060216

[53] Eric R. Lee, 2003, Microdrop Generation, CRC Press

A Review on Electrohydrodynamic inkjet printing technology

Documents

Transcript of A Review on Electrohydrodynamic inkjet printing technology