Tae Goo Kang

A four-bit digital microinjector using microheater array for adjusting the ejected droplet volume

In this paper, we present the design, fabrication, and experimental results of 4-bit digital microinjectors, whose ejected droplet volumes are adjusted by the digital operation of a 4-bit microheater array. We design the reference microinjectors as well as its comparative test structures. In the fabrication process, we use a five-mask micromachining process and the total chip size of the fabricated microinjector is 7640 /spl mu/m/spl times/5260 /spl mu/m. We observe the microbubble generation and collapse on the microheater array. The microbubbles initiate and grow individually on top of each operating microheater, however the microbubbles merge together before collapse. We measure the ejected droplet volumes and velocities, which are adjusted from 12.1 /spl ap/ 55.6 pl and 2.3 /spl ap/ 15.7m/s, respectively, depending on the 15 possible combinations of 4-bit microheater array. We also experimentally characterize the effect of geometric variation including the microheater size, intermicroheater gap, microchannel width and sequential operation of microheater array on the ejected droplet volume and velocity. Thus, the present microinjector has a potential for application to the high-resolution inkjet printers with multiple gray levels or high-precision fluid injectors with variable volume control.

Droplet-Volume-Adjustable Microinjectors Using a Digital Combination of Multiple Current Paths Connected to Single Microheater

In this paper, we design, fabricate, and test a single-heater microinjector, whose ejected-droplet volume is adjusted by a digital combination of multiple current paths connected to a single microheater. The novel aspect of the present method includes using the single microheater having multiple current paths to achieve multilevel droplet volume adjustment. In the design process, we design four pairs of current I/O interconnection lines connected to the microheater. We numerically estimate the actually heated area whenever we vary the combination of 4-b current path through the single microheater. On the basis of the numerical and theoretical estimation results, we design the droplet-volume-adjustable microinjector having a rectangular (R)- and a circular (C)-shape single microheater. In the experimental study, we measure the sizes of the generated bubbles, as well as the volumes and velocities of the ejected droplets, according to the digital current-path combination. In the bubble generation test, we use the 1-kHz 15.0-V 3-mus pulsewidth electrical signal and DI water at room temperature. The measured input power is varied from 8.7 to 24.9 muW for the R type and from 8.1 to 43.8 muW for the C type as the current path is changed. The projected area of the generated bubble is varied from 440 to 1,360 mum2 for the R type and from 800 to 3300 mum2 for the C type at six levels, respectively. Under the same experimental condition, we measure the ejected-droplet volumes and velocities. It is found that the ejected-droplet volumes are varied from 9.4 plusmn 0.7 to 20.7 plusmn 1.8 pL at three levels for the R type and from 7.4 plusmn 0.8 to 27.4 plusmn 2.0 pL at five levels for the C type, respectively, while the ejected-droplet velocities are varied from 0.8 plusmn 0.01 to 1.7 plusmn 0.01 m/s for the R type and from 0.5 plusmn 0.02 to 2.8 plusmn 0.03 m/s for the C type, respectively.

Droplet volume adjustable microinjectors using a microheater array

We present the design, fabrication and experimental results of the thermofluidic digital microinjectors, whose ejected droplet volumes are adjusted by the digital operation of a microheater array composed of four microheaters. We measured a life history of the microbubbles generated on the microheater array. The ejected droplet volume is adjusted as 1.4/spl plusmn/0.5, 4.2/spl plusmn/1.0, 6.0/spl plusmn/1.3, 11.0/spl plusmn/1.9 p/depending on the number of active microheaters. Thus, volume adjustable capability of the digital microinjectors has the potential to enhance a image quality as well as printing speed.

Locally Heated Low Temperature Wafer Level MEMS Packaging With Closed-Loop AuSn Solder-Lines

In this paper, locally heated closed-loop AuSn solder-line bonding method was proposed and evaluated for a low-temperature, high strength, and hermetic MEMS packaging. We fabricated two different test specimens including substrate-heated specimen and locally heated specimen in order to verify the performance of locally heated method. In air tightness test, the substrate-heated specimen and locally heated specimen show the maximum leak rate of 13.5±9.8×10−10 mbar-l/s and 18.8±9.9×10−10 mbar-l/s with the same internal volume of 6.89±0.2×10−6 l, respectively. In the critical pressure test, any fracture was not found in the bonded specimens at applied pressure of 10±2bar. From these results, we approximately extracted the bonding strength of the proposed bonding process of 3.53±0.07MPa. By EDS (Energy Dispersive X-ray Spectrometer) analysis at bonded interface, we found that bonded interface (between AuSn solder and Ti/Au layer) of substrate-heated specimen was stronger than that of locally heated specimen.Copyright

A droplet volume adjustable single-heater microinjector based on digital current path control

In this work, we present a novel multilevel droplet volume adjustable single heater microinjector. The present microinjector adjusts droplet volume by controlling current paths in a single microheater, while the previous works use multiple heaters or voltage control method. In the experiment, the input power is changed from 8.7/spl mu/W to 24.9/spl mu/W for R type and from 8.1/spl mu/W to 43.8/spl mu/W for C type as the current path changing. The projected bubble area is also changed from 440/spl mu/m/sup 2/ to 1360/spl mu/m/sup 2/ and from 800/spl mu/m/sup 2/ to 3300/spl mu/m/sup 2/, respectively. It is found that the ejected droplet volume is varied from 9.4pl to 20.7pl at 3 levels for R type and from 7.4pl to 27.4pl at 5 levels for C type, while the droplet velocity is increased from 0.8m/s to 1.7m/s for R type and from 0.5m/s to 2.8m/s for C type microinjector.

Electromagnetic squeezing microactuators using laterally-driven flexible copper strip

In this paper, we present the design, fabrication and testing of an electromagnetic squeezing microactuator, which generates a laterally-driven squeezing motion for application to the microinjectors. A set of electroplated flexible copper microstrip pairs is fabricated by using the thick PR micromold. In the experimental study, we measured the static response of the electromagnetic squeezing microactuators as well as the dynamic response in the vacuum, air and water environments. We also measured the pumping volume of the present electromagnetic squeezing microactuators as 20pl/cycle for DI water.Copyright

A High-Impulse Low-Power Microthruster Using Liquid Propellant with High-Viscous Fluid-Plug

A high-impulse, low-power, continuous-shot micro-thruster has been developed using low-boiling-temperature liquid-propellant with high-viscous fluid-plug. The viscous friction of fluid-plug increases the blast pressure and the low-boiling-temperature liquid-propellant is intended to reduce input power consumption. The three-layer microthruster has been fabricated by surface micromachining as well as bulk micromachining in the size of 7±0.25mm×l3±0.25mm× 1.5±0.25mm. At the continuous operation mode, the output impulse bit of 6.4×10−8N·sec is obtained for the fabricated microthruster using perfluoro normal hexane (FC72) propellant and oil-plug at the continuous operation mode.