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The effect of O2 plasma treatment on the surface property of exposed and unexposed SU8 photoresist has been investigated for the fabrication of a monolithic MEMS microstructure. It can solve the non-uniformity problem of second resist coating on the SU8 with high intrinsic shrinkage after exposure and post-exposure baking (PEB) in the fabrication of the stacked polymer–metal or polymer–polymer structure, which was used in the application of microfluid, bio and chemistry. The thickness difference of untreated SU8 before PEB between the exposed and unexposed SU8 was about 0.3% while that after PEB increased to about 6%. It could result in large non-uniformity of about 18 µm thickness difference for the following second resist coating on the hydrophobic surface without plasma treatment. The surface property of SU8 in terms of the contact angle and surface energy can be adjusted by O2 plasma treatment for enhancing the coating uniformity of the following resist. The measured contact angles of the exposed and unexposed SU8 decrease with O2 plasma time, corresponding to the increased surface energy determined by the Lifshitz–van der Waals/Lewis acid–base approach. It displayed that the similar hydrophilic surface property can minimize the thickness difference of second resist coating on the first shrunken SU8. A monolithic nozzle plate with a physical resolution of 600 dpi in a single column was demonstrated for an inkjet application based on the improved uniformity.

This paper reports the performance comparison of three kinds of thick photoresists used as molds for electroforming of monolithic two-layer microstructure with the nickel nozzle plate on SU8 chambers. The proper selection of mold material is strong relevant to the surface quality of mold and nozzle. The rough surface of mold is made of the JSR THB-430N with high viscosity while the smooth surface of mold is made of the JSR THB-130N with low viscosity. The positive tone SJR-5740 resist is not also a good material for the electroforming mold due to the dimension distortion after development. Good quality of monolithic two-layer microstructure has been achieved by JSR THB-130 N mold for electroforming due to the smooth mold surface, good dimension control and easily removal by acetone. IntroductionMonolithic two-layer microstructure has the advantages of simplified process procedure, high accuracy of alignment, low temperature and low cost with respect to conventional two-layer microstructure by alignment and bonding technology [1]. In addition to MEMS application, microfluidic structure with channels, nozzles and chambers are generally fabricated into two-layer or buried channel microstructure for the use in micro total analysis system, capillary electrophoresis, micro reactor and inkjet printhead [2-4] etc. There are different methods for the above two-layer or buried channel microstructure fabrication. In general, the silicon or glass substrates is chemical etched in solution and then bonded with the cover layer with nozzles or holes to form the two-layer or buried channel structure. This process needs an alignment equipment for precision position control and/or operates at high temperature or electric filed assistance. So it is complex and expensive. Other methods use the SU8 as the first structure layer with chambers or channels, then followed by dry film lamination [5], proton beam secondly exposed SU8 layer with low doses [6] or antireflection coating together with time-controlled UV exposure on the thick SU8 resist [7] to get the buried channel or two-layer microstructure. These processes are at low temperature and only photosensitive polymer followed. But using UV light dosage to control the layer thickness generally suffers the relationship of thickness and dosage with non-linear and abrupt variation at some thickness range [7]. Sometimes, one layer material will be metal, such as the commercial printhead with Ni nozzle plate bonded on polymer dry film, and we should ultilize another method to integrate the two-layer structure instead of conventional alignment and bonding technology. In this paper, we report a new fabrication method by combining two thick photoresists and nickel electroforming processes for the fabrication of monolithic twolayer microstructure with the integrated nozzle plate. The quality of electroformed nickel nozzle plate is strong relevant to the selection of resist mold material. Experimental proceduresThe process flow (Fig. 1) began by patterning the SU8 resist layer of about 35 lm ...

This paper reports that the fabrication of the reflowed microlens by the negative tone JSR THB-130 N photoresist can be treated with different thermal treatments using hotplate and oven. The different disk or thin cylinder arrays with diameters of 40-70 lm and thickness of about 7.4 lm were patterned using photolithography technology, and baked at 220°C by two kinds of thermal treatments using hotplate and oven to form reflowed microlens arrays. The spot size of the refractive microlens was then measured by optical microscopy and the total focal length of refractive microlens was simulated by curve fitting the lens profiles. The resolution of the microlens arrays approaches to 400 dpi as coated with Hexamethyldisilizane material. The smallest spot size of about 2.72 lm at the nominal 40 lm microlensis is obtained by the oven heat treatment, and the shortest total focal length of about 150 lm at the nominal 40 lm microlens is achieved by the hotplate heat treatment. The reduced spot size and total focal length of the microlens could improve the density and performance of optical devices and imaging systems.

Flame-retardant coatings have drawn much attention in recent years. In this study, an inorganic sodium silicate-based intumescent flame-resistance coating with an excellent flameproof properties is developed by mainly utilizing sodium silicate as the ceramizable binder, via hydrolysis and self-condensation reaction. Fly ash, metakaoline, and wollastonite behave as supplement cementing materials. Major formulation encompasses the combination of the ammonium polyphosphate and pentaerythritol as the flame-retardant additives, and aluminum hydroxide or expandable graphite as the intumescence-improving filler agents. Expandable graphite was found to play an important role in the eventual performance of flame-resistance testing. The results showed that solid interaction forces can be formed between metakaoline and sodium silicate, resulting in a similar material to geopolymer with excellent physical properties. After high-temperature flame testing, a densely complex protective layer of carbon-char created on top of the robust silicon dioxide networks offers notable flame resistance. An optimal ratio in this inorganic intumescent coating contains sodium silicate—metakaoline (weight ratio = 9:1)—ammonium polyphosphate and pentaerythritol, aluminum hydroxide (3, 3, 10 wt.%)—expandable graphite (1 wt.%), which can create 4.7 times higher expansion ratio compared with neat sodium silicate matrix. The results of flame testing demonstrate only 387.1 °C and 506.3 °C on the back surface of steel substrate after one and three hours flaming (>1000 °C) on the other surface, respectively, which could meet the requirements according to the level of fire rating.

Monolithic polymer-metal microstructures can be fabricated on the silicon or glass substrate using two kinds of photoresists and electroforming technologies for the inkjet and microfluidic application. However, it suffers from the high shrinkage problem of first SU8 resist after exposure and post exposure baking. This paper reports a novel approach to solve the shrinkage problem by introducing backside exposure of first SU8 resist for the fabrication of the monolithic polymermetal microstructure. In combination with the light absorption layer coating on the unexposed SU8 resist, metal seed layer deposition, frontside exposure for second JSR resist on the seed layer and the nickel (Ni) electroforming together with release process, we have demonstrated a high physical resolution of 1,200 dpi monolithic Ni nozzle plate with negligible shrinkage. It also has the advantages of low cost and high resolution for the improvement of the traditional bonding of polymer and metal nozzle plate, which is generally in need of a complex alignment to stick the metal nozzle plate and dry film polymer on the heating chip together.

This paper reported the effect of seed layer stress on the fabrication of monolithic polymer-metal MEMS microstructure and what is a better material for the seed layer. The monolithic microstructure is gaining more and more attentions in MEMS application, especially in three-dimensional microstructure and inkjet printhead. The polymer-metal MEMS microstructure can be fabricated by combining the lithography and electroforming technologies. It is an integrated technology by batch process at low cost. The metal seed layer with large stress will lead to cracks and failure during the process integration. Several metal materials and thicknesses were studied to find a better candidate as the seed layer for the monolithic MEMS microstructure. The relationship between the monolithic MEMS structure and seed layer selection is also discussed. The lower residual stress of seed layer will result in a better surface condition for the followed integration process. The pure Ti metal and two-layer Ti/Au composite are the better seed layer materials in this study for the followed electroforming process of the monolithic polymer-metal MEMS microstructure.