Design & fabrication of electrostatic inkjet head using silicon micromachining technology


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Design & fabrication of electrostatic inkjet head using silicon micromachining technology

  2. 2. Contents:• Introduction• Scope• Objective• Design & Simulation• Fabrication• Experimental Set up• Conclusion• References2
  3. 3. INTRODUCTION• Ink-jet printing technique is very attractive for forming micro-sizepatterns for flat panel displays (FPDS),• Printing circuit board (PCB),• Semiconductor,• Biological,• Optical,• Sensor devices• due to its low temperature process, direct writing, and rapidphotolithography process3
  4. 4. • The inkjet printing mechanisms has been used are• Thermal method• Piezoelectric method• Electrostatic methodINTRODUCTION Cont..4
  5. 5. • Thermal and piezoelectric inkjet printing are based on pushingout the liquid in a chamber through a nozzle by actuators, suchas thermal bubble and piezoelectric actuators.• Thermal bubble actuator has the heat problem when the arrayof nozzle make in a large area• Piezoelectric actuator is difficult to make droplet smaller thannozzle size . The head consisting of piezoelectric or a heaterelement has the disadvantage of the complex structureINTRODUCTION Cont..5
  6. 6. • Electrostatic inkjet are based on protruding through an orificeinduced by an electric field forms a meniscus called the Taylorcone.• Also it can separate from the meniscus tip as fine dropletsmuch smaller than the orifice diameter.• Electrostatic inkjet has a greater advantage than piezoelectricinkjet and thermal inkjet in the ability to eject fine droplets andin the simplicity of structureINTRODUCTION Cont..6
  7. 7. SCOPEThis paper discusses about the design and fabrication ofoptimized geometry structure of Electrostatic Inkjet Head.7
  8. 8. ObjectiveTo design and fabricate inkjet heads to achieve an effectivemicro dripping ejection, to provide concentrated electric forceon nozzle and pole tip.DESIGN & SIMULATION8
  9. 9. • They designed and fabricated the following electrostaticinkjet heads,• electrostatic inkjet heads, hole type• electrostatic inkjet heads, Pole typeHole type Inkjet Head Pole type inkjet headDESIGN & SIMULATION9
  10. 10. • This structure consists of1. Reservoir,2. Nozzle3. Conductive pole to concentrate electric field.DESIGN & SIMULATION Cont…..Hole type Inkjet HeadHole type Inkjet Head10
  11. 11. Schematic of the proposed Pole type inkjet headelectrostatic inkjet head.1. This structure consists of glass electrode part2. Nozzle part with a reservoir.Fig. 3. The structure of the proposed pole type electrostatic inkjethead.11
  12. 12. Δ .Є Δ.Ф = -þĒ= - ΔФWhere• Ē -electric field vector•-Ф- electric potential• Є- permittivity• þ - charge density• Micro droplet is formed from the liquid meniscus due theinduced electric field.• The electric field is obtained by solving the followinggoverning equations. (These equations are solved by FEMmethod)DESIGN & SIMULATION Cont…12
  13. 13. • The inkjet head utilizes electrostatic forces that act betweenelectrode and nozzle tip.• The electrostatic forces are created when a voltage is appliedelectrode and head bottom.• The surface of the inkjet head becomes wet with liquid afterapplying an electric field.• Then charged liquid is separated from the inkjet head tip asfine droplets.Mechanism of Spray formation13
  14. 14. • When the force induced by an electric field on the inkjet headtip is stronger than the resultant force of• surface tension,• ink viscosity and• conductivity,• The meniscus called Taylor cone is generated and fine dropletsis separated from the head by Coulomb force.Mechanism of Spray formation Cont..14
  15. 15. Need For Simulation• In order to verify effect of geometry shape, we simulateelectric field intensity according to the head structure.15
  16. 16. Electric Field Simulation of a Hole type inkjet headwhen DI water is used16
  17. 17. Electric Field Strength Vs. Nozzle height of a Pole type inkjet head17
  18. 18. Result of the Electric field simulation of the hole type inkjet headElectric field simulation of the hole type inkjet head showedthe following results• The electric field strength increases linearly with increasingheight of the micro nozzle.• Also, as the height of the nozzle increases, the electric fieldalong the periphery of the meniscus can be more concentrated.18
  19. 19. • In order to find optimal structure and demonstrateconcentration of electrostatic force at the pole edge, pole typeinkjet head is simulated using FEMLAB.19
  20. 20. Result of the electric field simulation used the DI water as the liquidsolution.20
  21. 21. Result of the Electric field simulation of the hole type inkjet head• The structure of the nozzle inner diameter = 80 μm• Thickness, 20 μm• Pole diameter are, and 40 μm,• The pole height is 50 μm.As the result, the concentration of electrostatic force was shownat the conductive pole edge.21
  22. 22. FABRICATION• Electrostatic inkjet head consist of 2 layers• Glass top layer• Silicon bottom layer.• Fabrication is done using• thermal-oxidation• silicon micromachining technique .22
  23. 23. Fabrication process Cont…• SiO₂ layer on silicon wafer.• Oxide(deep Si etch mask)patterning and deep Si etching.• Reservoir patterning on thebottom silicon wafer.23
  24. 24. • Deep Si etching.• Deep Si etching for poleformation.• SiO₂ removal by HF solution.Fabrication process Cont…24
  25. 25. Fig. 7. Fabrication Process : (a) SiO2 layer on silicon wafer, (b)Oxide(deep Si etch mask) patterning and deep Si etching, (c)reservoir patterning on the bottom silicon wafer, (d) Deep Sietching, (e) Deep Si etching for pole formation, (f) SiO2 removalby the HF solution.25
  26. 26. Photomicrograph of Hole & Pole type nozzleHole type NozzlePole type Nozzle26
  27. 27. SEM Images of NozzleHole type NozzlePole type Nozzle27
  28. 28. EXPERIMENTAL SET UPFig. 11. The schematic of the experimental system.28
  29. 29. • This system consists of• The head system,• High speed camera,• Micro syringe pump,• Power,• ComputerEXPERIMENTAL SET UP Cont….29
  30. 30. • To visualize droplet ejection. high speed camera (IDT XS-4)with a micro-zoom lens and a halogen lamp was used• The high speed camera can image 5000 frames per second at a512 x 512 resolution with a micro-zoom lens and a LED lightsource were used.• .EXPERIMENTAL SET UP Cont….30
  31. 31. • A high voltage power supply (maximum voltage of 3.0 kV)was used with a relay switch to control electrostatic field.• The liquid have been supplied to the nozzle with constantvelocity by micro syringe pump and the voltage has beenprovided to the upper electrodeEXPERIMENTAL SET UP Cont….31
  32. 32. • The jetting mode depends on• the applied voltage,• the flow rate,• liquid properties such as• Electric conductivity,• surface tension,• and viscosity.EXPERIMENTAL SET UP Cont….32
  33. 33. • To make an experiment on the micro ejection of theelectrostatic inkjet head, the conductive liquid of the mixtureof D2O, SDS, and micelle-suspended Carbon Nano Tube (5%wt SWNT) solution is used as ink.• The outer diameter of the nozzle is 50 μm• The gap between the upper electrode• The nozzle orifice is set about 800 μm.• The constant flow rate by a micro pump is kept at0.1 μl/min.EXPERIMENTAL SET UP Cont….33
  34. 34. Results• When flow rate is made constant at 0.1µl/min and 1.7KV issupplied, a droplet 80µm is obtained.Fig. 12. Images taken with high-speed camera showing evemicro ejection from nozzle of inkjet head.34
  35. 35. • When flow rate is made constant at 0.1µl/min and the suppliedvoltage is kept at 2.5 kV. The droplet diameter ejected from thenozzle tip is measured about 10 μm.Results Cont……35
  36. 36. Conclusion• This paper discussed about the design and fabrication of thefollowing electrostatic inkjet heads.• electrostatic inkjet heads hole type• electrostatic inkjet pole type• It was fabricated using thick-thermal oxidation and siliconmicromachining technique such as• the deep reactive ion etching (DRIE)• chemical wet etching process.• The fabrication process used is very simple and reproducible..36
  37. 37. REFERENCES• Design and Fabrication of Electrostatic Inkjet Head using Silicon MicromachiningTechnology Youngmin Kim*, Sanguk Son*, Jaeyong Choi*, Doyoung Byun**, and SukhanLee* JOURNAL OF SEMICONDUCTOR TECHNOLOGY AND SCIENCE, VOL.8,NO.2, JUNE, 2008• Yuji Ishida, Kazunori Hakiai, Akiyoshi Baba and Tanemasa Asano, “Electrostatic InkjetPatterning Using Si Needle Prepared by Anodization,” Japanese Journal of AppliedPhysics, Vol. 44, No. 7B, pp. 5786-5790, July 2005.• S. Lee, D. Byun, S. J. Han, S. U. Son, Y. J. Kim, H. S. Ko, “Electrostatic DropletFormation and Ejection of Colloid,” MHS, July 31, 2004.• S.U.Son, Y.M.Kim, J.Y.Choi, S.H.Lee, H.S.Ko, and D.Y.Byun, “Fabrication of MEMSInkjet Head for Drop-on-Demand Ejection of Electrostatic Force Method,” Trans. KIEE.Vol.56. August, 2007.37
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