Won-Chul Sim

Design and characterization of piezoelectric inkjet for micro patterning of printed electronics

A design verification system based on multiphysics modeling and micro-electro-mechanical systems (MEMS) fabrication has been established to develop piezoelectric inkjet printheads for micro-patterning on printed electronics. Piezoelectric printheads have been fabricated with silicon and silicon on insulator (SOI) wafers by MEMS fabrication and post-processing package. Transient displacements of a piezoelectric actuator according to voltage waveform are measured by Laser Doppler Vibrometer (LDV), and compared with numerical predictions by the three-dimensional piezoelectric-structure interaction modeling. Key issues in design and fabrication of piezoelectric inkjet printheads are investigated: printhead configuration, input voltage waveform, hydrodynamic and structural crosstalks, acoustic wave propagation (or effect of limited compressibility), and meniscus instability at high frequency. The present design verification system has shown its promising applicability to novel-concept designs of inkjet printheads for wide range of printed electronics and bio-applications.

The Effects of Driving Waveform of Piezoelectric Industrial Inkjet Head for Fine Patterns

This paper presents the effect of driving waveform for piezoelectric bend mode inkjet printhead with optimized mechanical design. Experimental and theoretical studies on the applied driving waveform versus jetting characteristics were performed. The inkjet head has been designed to maximize the droplet velocity, minimize voltage response of the actuator and optimize the firing frequency to eject ink droplet. The head design was carried out by using mechanical simulation. The printhead has been fabricated with Si(100) and SOI wafers by MEMS process and silicon direct bonding method. To investigate how performance of the piezoelectric ceramic actuator influences on droplet diameter and droplet velocity, the method of stroboscopy was used. Also we observed the movement characteristics of PZT actuator with LDV(laser doppler vibrometer) system, oscilloscope and dynamic signal analyzer. Missing nozzles caused by bubbles in chamber were monitored by their resonance frequency. Using the water based ink of viscosity of 4.8 cps and surface tension of 0.025N/m, it is possible to eject stable droplets up to 20kHz, 4.4m/s and above 8pL at the different applied driving waveforms.

Modeling and Characterization of an Industrial Inkjet Head for Micro Patterning on Printed Circuit Boards

A conceptual design using computational fluid dynamics (CFD) and micro-electro-mechanical systems (MEMS) fabrication has been performed to develop an industrial inkjet head for micro-patterning on printed circuit boards. The printhead has been fabricated with silicon and silicon on insulator (SOI) wafers by MEMS process and silicon to silicon bonding method. The measured displacement waveform from piezoelectric actuator by Laser Doppler Vibrometer (LDV) was used as input data for the three-dimensional flow solver to simulate the droplet formation. The mechanism of droplet ejection from piezoelectric-type inkjet heads was investigated by simulating two-phase flows of the air and metal inks. Parametric studies are followed by the design optimization process to deduce key factors to inkjet head performance. The effects of nozzle geometry, pulse amplitude, ink viscosity, and micro bubble formation were also investigated based on numerical simulations. The present design tool based on two-phase flow solver and experimental measurements has shown its promising applicability to various concept designs of industrial inkjet system for micro-patterning on electronic chips and boards.Copyright

The Fabrication of Monolithic Micro Droplet Ejector using MEMS

This paper presents the fabrication of a micro droplet ejector for the application of digital printing system. The ejector makes the ink droplets of approximately 80 squaremum diameter on demand. The ejecting system is the type of face-shooter. The method of actuating membrane is bending mode using d31 of PZT. The size of ejector is 27.6 mm x 27.75 mm x 1.1 mm, and the pitch between nozzles is 2.54 mm, 10 npi. The nozzle and restrictor are very important part for the performance of the ejector such as droplet size and velocity. Therefore, the roundness and straightness of nozzle and depth profile of the restrictor have an influence on the characteristic of droplet. Those are made by deep silicon etching technique for the accuracy and uniformity. The ejector is successfully operated and the measured ejection speed, size of droplet and the ejection frequency are 1 m/s, 80 mum and 1 kHz, respectively.

Numerical and Experimental Evaluation of Picoliter Inkjet Head for Micropatterning of Printed Electronics

A design process based on multiphysics modeling and micro-electro-mechanical systems (MEMS) fabrication has been established to develop a picoliter inkjet printhead for micro-patterning for printed electronics. Piezoelectric actuator is designed with numerical analysis using Covent-Ware with consideration of electrical characteristic of piezoelectric material and physical characteristic of silicon structure. The displacements of a piezoelectric actuator according to voltage waveform are evaluated and verified by laser doppler vibrometer (LDV). Piezoelectric printheads have been fabricated with silicon and silicon-on-insulator (SOI) wafers by MEMS process and silicon to silicon bonding method. As a preliminary approach, liquid metal jetting phenomena are identified by simulating droplet ejection and droplet formation in a consequent manner. Parametric studies are followed by the design optimization process to deduce key issues to inkjet head performance: printhead configuration, input voltage amplitude, ink viscosity and meniscus movement using computational fluid dynamics (CFD). By adjusting the driving voltage along with optimizing the drive waveform, the droplet volume and velocity can be controlled and evaluated by a drop watcher system. As a result, inkjet printhead capable of ejecting 1 pL droplet, which is required by electronic applications such as fabricating metal lines on printed circuit board (PCB), is developed.