Fabrication of support structures to prevent SU-8 stiction in high aspect ratio structures

We have previously demonstrated that it is possible to fabricate densely-packed high aspect ratio structures in SU-8 by means of a top-plate support member which stiffens the overall structure and prevents pattern collapse. In this work we have computed the tensile stresses induced in the top-plate structures due to the capillary forces that arise between the columns due to the surface tension of the drying liquid. We have further studied the dynamic behavior of the structure after an instantaneous force. Based on these results, we have shown that the predicted optimal thickness of the top-plate structure is sufficient to maintain structural integrity.     

Effects of Aluminum Concentration on the Oxidation Behaviors of Reactively Sputtered TiAlN Films

Polycrystalline TiAlN films were deposited on a substrate of high-speed steel via a radio-frequency-bias reactive-sputtering process. The effects of aluminum concentration (0–60 at.%) on the high-temperature oxidation behavior of TiAlN films were explored by using in situ thermogravimetric analysis and high-temperature X-ray diffractometry. The composition and distribution of the oxidizing layers over TiAlN films were investigated. Results indicated that the oxidation resistance increased as the aluminum concentration increased. The type and location of oxidizing phases also were dependent on the aluminum concentration. Three major oxides-i.e., Al₂O₃, TiO₂, and TiO-were observed. The thickness of the Al₂O₃ layer increased and the TiO₂ gradually changed to TiO as the aluminum content increased. Thermodynamic calculations were compared to experimental observations, and they showed good agreement.     

Instrumented tracer for Lagrangian measurements in Rayleigh-Bénard convection

We have developed novel instrumentation for making Lagrangian measurements of temperature in diverse fluid flows. A small neutrally buoyant capsule is equipped with on-board electronics which measures temperature and transmits the data via a wireless radio frequency link to a desktop computer. The device has 80 dB dynamic range, resolving millikelvin changes in temperature with up to 100 ms sampling time. The capabilities of these "smart particles" are demonstrated in turbulent thermal convection in water. We measure temperature variations as the particle is advected by the convective motion and analyze its statistics. Additional use of cameras allow us to track the particle position and to report here the first direct measurement of Lagrangian heat flux transfer in Rayleigh-Bénard convection. The device shows promise for opening new research in a broad variety of fluid systems.     

Effects of Structural Isomers of Spermine on the Higher-Order Structure of DNA and Gene Expression

Polyamines are involved in various biological functions, including cell proliferation, differentiation, gene regulation, etc. Recently, it was found that polyamines exhibit biphasic effects on gene expression: promotion and inhibition at low and high concentrations, respectively. Here, we compared the effects of three naturally occurring tetravalent polyamines, spermine (SPM), thermospermine (TSPM), and N⁴-aminopropylspermidine (BSPD). Based on the single DNA observation with fluorescence microscopy together with measurements by atomic force microscopy revealed that these polyamines induce shrinkage and then compaction of DNA molecules, at low and high concentrations, respectively. We also performed the observation to evaluate the effects of these polyamine isomers on the activity of gene expression by adapting a cell-free luciferase assay. Interestingly, the potency of their effects on the DNA conformation and also on the inhibition of gene expression activity indicates the highest for TSPM among spermine isomers. A numerical evaluation of the strength of the interaction of these polyamines with negatively charged double-strand DNA revealed that this ordering of the potency corresponds to the order of the strength of the attractive interaction between phosphate groups of DNA and positively charged amino groups of the polyamines.     

Distinct p53-mediated G1/S checkpoint responses in two NIH3T3 subclone cells following treatment with DNA-damaging agents

N3T3 and P-3T3 cells, originally isolated from a NIH3T3 cell clone on the basis of their negative and positive transformation by v-Abl, v-Src and Bcr-Abl, were previously found to show distinct cyclin activity changes following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment, which is anti-mitogenic for N-3T3 cells and mitogenic for P-3T3 cells. We have found in this study that, while the G1/S arrest and cell death induced by serum starvation and TPA treatment in N-3T3 cells did not involve p53-mediated checkpoint or apoptosis, N-3T3 and P-3T3 cells evidently responded differently in these aspects of cell cycle regulation to DNA-damaging agents, methylmethane sulfonate (MMS) and gamma-radiation. In N-3T3 cells, DNA damages elicit cell growth arrest at G1/S transition with concomitant accumulation of p53 and p53-inducible Waf1/Cip1 proteins and also signs of apoptosis such as DNA ladder patterns and apoptotic (subgenomic) peak in flow cytograph. Conversely, P-3T3 cells treated with the DNA-damaging agents showed no cell cycle interruption nor accumulation of p53 or Waf1/Cip1. However, both P-3T3 and N-3T3 cells showed the same p53 protein half-life of 40 min or less, the same wild-type p53 DNA sequence and the same co-immunoprecipitable cellular proteins in complexes with p53, suggesting that an alteration in a signal transduction pathway upstream of p53 might account for the evasion of p53-mediated G1 checkpoint in P-3T3 cells.     

Association of Methylentetraydrofolate Reductase (MTHFR) 677 C > T gene polymorphism and homocysteine levels in psoriasis vulgaris patients from Malaysia: a case-control study

Background  

The methylenetetrahydrofolate reductase (MTHFR) enzyme catalyzes the reduction of 5, 10-methylenetetrahydrofolate to 5-methyltetrahydrofolate and methyl donors. The methyl donors are required for the conversion of homocysteine to methionine. Mutation of MTHFR 677 C > T disrupts its thermostability therefore leads to defective enzyme activities and dysregulation of homocysteine levels.     

Optimisation of the Plated Through Hole (PTH) Process Using Experimental Design and Response Surface Methodology

The process of producing side-to-side and innerlayer connections for printed circuit boards by metallising with copper is called the plated through hole (PTH) process. The copper deposition rate of the PTH process is one of the major quality characteristics. In this project, experimental design and response surface methodology were employed to investigate the PTH process behaviour and perform the process optimisation. First, a 2_v ⁵⁻¹ fractional factorial design was used to screen out the significant factors as well as their interactions on the response of the copper deposition rate of a PTH process. The location factors were identified to be operation time, temperature, concentration of copper additive and the interaction of operation time and temperature. A normal probability plot of the residuals was used to determine the factors which give the minimum thickness variability of deposited copper in the PTH process. The interaction of operation time and temperature was found to be a dispersion factor. Model adequacy checking was conducted to check the normality, independence, and constant variance assumptions of the model. It is then followed by employing response surface methodology to locate the optimal operating point within the process window for the minimum thickness variability of deposited copper. First, a first-order model was regressed on the standard deviation of copper thickness of the four corners of the process window. The path of steepest descent was found and a new first-order model was then regressed at the point. The lack of fit of the new first-order model indicates that a second-order model is required. A central composite design (CCD) method was used to fit the second-order model. The stationary point obtained by the partial differentiation of the second-order model is 10.623 min in operation time and 24°C in temperature which was characterised by canonical analysis to be a minimum point. The predicted minimum variation of copper deposition rate calculated, based on the second-order model, is 1.02μin. A confirmation experiment was conducted based on the recommended optimal setting. The minimum variation of deposited copper was found to be 1.08 μin. ID="A1"Correspondance and offprint requests to: Dr C. K. Kwong, Department of Industrial and Systems Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong. Email: mfckkong@inet.polyu.edu.hk     

Dosage modeling for deep x-ray lithography application

 A analytical dosage model was established to study exposure parameters of deep x-ray lithography systematically. It provided a reasonable guild line for deciding exposure parameters, selecting masks and filters in radiating process. Calculated results showed a good agreement with experiment results. Both of the single and multiple exposure processes were investigated in present study. Received: 25 August 1997/Accepted: 3 September 1997     

Overcoming SU-8 stiction in high aspect ratio structures

Deep X-ray lithography is a well known technique used for making high aspect ratio structures (HARS). However, well known difficulties arise in the creation of some HARS; adhesion of the developed resist structures to the plating base commonly fails, and when resist structures are densely packed features can clump together. This in turn can exacerbate adhesion failure. The problem of clumping is sometimes known as stiction. In this paper we describe an idea involving a low dose UV second exposure that can help overcome stiction in certain designs and thus promote adhesion and the retention of the designed structure.AGP acknowledges receipt of an Australian Research Council QEII fellowship. This work was supported by the Australian Synchrotron Research Program, which is funded by the Commonwealth of Australia under the Major National Research Facilities Program.     

A study of integration of LIGA and M-EDM technology on the microinjection molding of ink-jet printers’ nozzle plates

Common processes to manufacture nozzle plates of ink-jet printer heads are electroplating or laser machining. In order to reduce the production cost and improve the performance of nozzle plates, a new approach, microinjection molding, is introduced to manufacture nozzle plates in this study. The micro mold was made by integration of the LIGA and M-EDM technology to improve the positioning and alignment accuracy. After assembling the micro mold, microinjection-molding technique was applied to produce four nozzle plates in one shot. There are 60 micro through-holes on each plate. The diameters were measured by an optical microscopy and in the range of 101±1 microns. Experiment and simulation result indicated that the most significant factor for molding these thin films with micro through holes is the mold temperature. This work recommends the mold temperature during filling of the vario-thermal mold system is about 10∼15°C higher than the glass transition temperature of the polymer. The manufacture procedures proposed in this study are believed to be more accurate and economical.