Development of Electrostatic Field Induced Inkjet Head
-microscale and nanoscale patterning-
Doyoung Byun, Ph. D
Visiting Assistant Professor
Department of Mechanical Engineering and Applied Mechanics
School of Engineering and Applied Science
University of Pennsylvania
(Konkuk University, Seoul, Korea)
Abstract
This study presents a novel mechanism for an electrostatic
field induced drop-on-demand ink-jetting device. Currently, the primary commercial
implementation of inkjet technology is in the field of inkjet image printing.
Recently, there has been a tremendous increase in the use of micro droplets
in physical, chemical, biological, and engineering research areas. Performance
factors such as high frequency jetting, high density of nozzle arrays, size
of droplet, and uniformity of droplet size are required to fulfill the requirements
of various applications. The conventional jetting devices based on thermal
bubble or piezoelectric pumping, however, have some fundamental limitations
to overcome in order to meet the aforementioned requirements for the future
generation of jetting devices: 1) Thermal bubble jetting has fundamentally
limitation in size and density of the nozzle array as well as the ejection
frequency, mainly due to thermal problems. 2) Mechanical jetting, such as
in piezoelectric devices, has limits in the density of the nozzle array,
the ejection frequency limited by physical properties, and the reliability
limited due to the difficulty of fabrication.
Electrostatic jetting of liquids is a physical process caused by an electric
force applied to the surface of a liquid. The electrical shear stress elongates
the liquid meniscus formed at the opening of the nozzle and generates a tiny
droplet as a result of the balance between electrical and surface tension
forces. The electric voltage signal applied allows for a strong electric
field to be concentrated in the vicinity of the apex of the liquid meniscus
and thus micro-dripping ejection of droplet takes place. That is, a tiny
droplet is removed from the peak of the dome-shaped liquid meniscus. Optimal
conditions are introduced for applied voltage, electric conductivity, and
flow rate for generating a stable drop-on-demand droplet using the micro-dripping
mode. It is also verified experimentally that the use of the pole-type nozzle
allows a stable and sustainable micro-dripping mode of droplet ejection for
a wide range of applied voltages, demonstrating the feasibility of an electrostatic
field induced drop-on-demand ink-jetting device as an alternative to conventional
inkjet print heads.
Also the theory is presented for jetting the distilled water and water with
sodium dodecyl surfate (SDS). It has been observed that the droplet size
decreases and the frequency of the droplet formation and the velocity of
the droplet ejection increase with increasing the intensity of the electrostatic
field. The results of the experiments have shown good agreement with those
of numerical analysis.
In general, the limitations of inkjet technology have precluded printing
patterns smaller than 20 um, and it seems that, despite the large pressure
on low-cost manufacturing, the wide application was not opened yet. On the
other hand, since, in 1993, Kumar discovered that a polymer inked with an
alkanethiol can form a monolayer on a gold surface, microcontact printing
has given rise to the development of soft lithography. It is reported that
currently the smallest size moldable with high aspect ratio is 50 nm. Even
if nanoscale high accuracy is achievable with soft lithography, alignment
issues and low printing speed remain challenges. Between microscale printing
approaches and nanoscale soft-lithography approaches, there’s a big
gap from 20 um and around 50 nm. There is a genuine need for nano-to-macro
integration. Therefore, innovations are needed to drive printing technologies
to reduce pattern sizes from 20 um to 50 nm. In this ongoing study, preliminary
results are introduced to enable the patterning of nanoscale elements and
structures and facilitating microscale and nanoscale structures’ integration.
Thursday, September 27th
337 Towne Bldg.
2:00 – 3:00 p.m.
