Polymethyl Methacrylate Thickness Research Articles

Investigation of sidewall cracking in PMMA LIGA structures

During x-ray exposure in the LIGA process, the polymethylmethacrylate (PMMA) photoresist undergoes chain scission, which reduces the molecular weight of the exposed materials. Under some exposure and development conditions, sidewall cracking is observed on the PMMA sidewall, creating surface texture that is undesirable. In this research, exposed and developed PMMA sidewalls were examined for evidence of crack formation using optical profilometry. PMMA thickness, exposure dose and delay time between the end of exposure and beginning of development were varied. Our analysis of samples, with three different radiation doses and four different delay times from the end of exposure to the beginning of development, indicate that the first occurrence of cracking and the extent of cracking are affected by both the dose and the development delay time. This work includes the examination of the depth of cracks into the PMMA, distance between cracks, the width of cracks and the relationship between crack occurrence and dose profile. An empirical predictive model to correlate the delay time to the observance of sidewall cracking based on the deposited dose is presented. This information has direct implication for predicting processing conditions and logistics for LIGA fabricated parts.

Dynamic flat panel detector versus image intensifier in cardiac imaging: dose and image quality

The practical aspects of the dosimetric and imaging performance of a digital x-ray system for cardiology procedures were evaluated. The system was configured with an image intensifier (II) and later upgraded to a dynamic flat panel detector (FD). Entrance surface air kerma (ESAK) to phantoms of 16, 20, 24 and 28 cm of polymethyl methacrylate (PMMA) and the image quality of a test object were measured. Images were evaluated directly on the monitor and with numerical methods (noise and signal-to-noise ratio). Information contained in the DICOM header for dosimetry audit purposes was also tested. ESAK values per frame (or kerma rate) for the most commonly used cine and fluoroscopy modes for different PMMA thicknesses and for field sizes of 17 and 23 cm for II, and 20 and 25 cm for FD, produced similar results in the evaluated system with both technologies, ranging between 19 and 589 µGy/frame (cine) and 5 and 95 mGy min−1 (fluoroscopy). Image quality for these dose settings was better for the FD version. The ‘study dosimetric report’ is comprehensive, and its numerical content is sufficiently accurate. There is potential in the future to set those systems with dynamic FD to lower doses than are possible in the current II versions, especially for digital cine runs, or to benefit from improved image quality.

PMMA–Ta2O5 bilayer gate dielectric for low operating voltage organic FETs

This paper reports on a study on pentacene field effect transistors (OFETs) with a gate dielectric made of a bilayer PMMA/Ta2O5 where PMMA (poly(methyl methacrylate)) is spin-coated on top of an evaporated layer of Ta2O5. A comparison with devices with only Ta2O5 is presented. These latter exhibit very low operating voltage associated to the high dielectric constant of this oxide but also show some surface trapping and gate leakage. These two drawbacks can be overcome by depositing a PMMA layer on Ta2O5. With such a bilayer gate dielectric, gate leakage current is considerably reduced and the quality of the interface between pentacene and PMMA was much improved compared to that with Ta2O5 as evidenced from the much higher output drain current. The influence of PMMA thickness in the range 15–250 nm is presented. OFETs with field effect mobility, on/off current ratio, and sub-threshold slope of respectively 0.4 cm2 V−1 s−1, 3 × 105 and 1.2 V/decade were obtained.

PMMA(Poly Methyl Methacrylate) 박막 코팅 층의 마찰 및 마멸 거동

Effects of sliding speed, applied load, and thickness of PMMA (Poly Methyl Methacrylate) coating layers on their dry sliding frictional and wear behavior were investigated. Sliding wear tests were carried out using a pin-on-disk wear tester. The PMMA layer was coated on Si wafer by a spin coating process with two different thicknesses, <TEX>$1.5\mu\textrm{m}$</TEX> and <TEX>$0.8\mu\textrm{m}$</TEX>. AISI 52100 bearing steel balls were used as a counterpart of the PMMA coating during the wear. Normal applied load and sliding speed were varied. Wear mechanisms of the coatings were investigated by examining worn surfaces using an SEM. Friction coefficient of the coatings decreased with the increase of the applied load. Both adhesion and deformation of the coating determined the coefficient. The thicker PMMA layer with the thickness of <TEX>$1.5mutextrm{m}$</TEX> showed lower friction coefficient than the thinner layer under most test conditions. Effects of sliding speed and applied load on the frictional behavior were varied depending on the thickness of the coating layer.

GEM-type detectors using LIGA and etchable glass technologies

Gas electron multipliers (GEMS) have been made by a deep X-ray lithography technique (LIGA process) using synchrotron radiation on polymethylmethacrylate (PMMA) and by ultraviolet (UV) processes using a UV etchable glass. The gain, stability, and rate capability for these detectors are described. The LIGA detectors described consist of PMMA sheets of various thicknesses, 125-350 /spl mu/m, and have 150/spl times/150 /spl mu/m/sup 2/ holes spaced with a pitch of 300 /spl mu/m. Thin copper electrodes are plated on the top and bottom surfaces using a Damascene method, followed by electroless plating of the copper onto a palladium-tin-base layer. For various thicknesses of PMMA, measurements have been made of absolute gain versus voltage, time stability of gain, and rate capability. The operating gas mixture was usually Ar/CO/sub 2/ (70/30) gas, but some tests were also done using P10 gas. We also made GEM-like detectors using the UV etchable glass called Foturan, patterned by exposure to UV light and subsequent etching. A few measurements using these detectors will be reported, including avalanche gain and time stability.

The response of layered aluminum nitride targets subjected to hypervelocity impact

This work presents both experimental and computational ballistic results of layered Aluminum Nitride (AlN) targets. An L/D = 6 tungsten penetrator is used to impact AlN targets at a nominal impact velocity of 2100m/s. The primary objective of this work is to determine the ballistic performance of layered ceramic targets to hypervelocity impact. Various layering configurations are investigated including separating the AlN ceramic layers by thin, low impedance, polymethyl methacrylate (PMMA). PMMA thicknesses of 1 mm, 0.5 mm and 0 mm are used. The number of AlN ceramic layers is also investigated. Target configurations of two, four, six, and twelve layers are considered. All targets consist of 76.2 mm of AlN. The experiments show that target resistance decreases when PMMA is added. Target resistance is also reduced when more layers are used. A secondary objective of this work is to evaluate the ballistic effect of reducing the lateral dimension of the ceramic tile (reduction in self-confinement). The experiments show reduced target resistance when the lateral tile size is decreased. Computations of selected experiments are presented to provide insight into the behavior of the AlN targets. The computations capture the effect of layering, PMMA separation and lateral tile size and provide insight into the behavior of the ceramic when used in these types of configurations.

Film Density Dependence of Polymethylmethacrylate Ablation under Synchrotron Radiation Irradiation

Variations in the etch depth and refractive index of polymethylmethacrylate (PMMA) films of different molecular weights after synchrotron radiation (SR) irradiation are investigated. Reduction of the PMMA film molecular weight, density and thickness are observed after SR irradiation. The amount of film thickness loss depends on not only initial molecular weight but also film density. The PMMA density difference at the start of SR exposure affects the etch depth after SR ablation.

Effect of talc/MMAin situ polymerization on mechanical properties of PVC-matrix composites

In this study, polymethyl methacrylate (PMMA)-coated talc was produced by the insitu polymerization of methyl methacrylate on the talc surface. The polymerization reaction was performed by both batch and semicontinuous emulsion processes. The polymerization kinetics, particle size and distribution, grafting efficiency, and coated-talc morphology were systematically investigated. It was found that the talc particles have no effect on the polymerization of PMMA. The PMMA produced was found to cover the talc surface well. However, only a small amount can be grafted onto the talc. The size distribution of talc particles treated by semicontinuous emulsion polymerization is more uniform than by batch polymerization. The treated talc was subsequently used as filler in a poly(vinyl chloride) (PVC) matrix, and mechanical properties of the PMMA-coated-talc/PVC composites were studied. Morphological structure of PVC-matrix composites revealed that the PMMA coating on talc improved the dispersion of talc in the PVC matrix and enhanced the interfacial adhesion between the talc and PVC. The mechanical properties of the composites, especially the impact strength, were found to be improved. There appears to be a critical covering thickness of PMMA on the talc surface for optimum toughening. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2105–2112, 2001

The influence of feature sidewall tolerance on minimum absorber thickness for LIGA x-ray masks

Minimizing mask absorber thickness is an important practical concern in producing very small features by the LIGA process. To assist in this minimization, we have developed coupled numerical models describing both the exposure and development of a thick polymethyl methacrylate (PMMA) resist. The exposure model addresses multi-wavelength, one-dimensional x-ray transmission through multiple beam filters, through the mask substrate and absorber, and the subsequent attenuation and photon absorption in the PMMA resist. The development model describes one-dimensional dissolution of a feature and its sidewalls, taking into account the variation in absorbed dose through the PMMA thickness. These exposure and development models are coupled in a single interactive code, permitting the automated adjustment of mask absorber thickness to yield a prescribed sidewall taper or dissolution distance. We have used this tool to compute the minimum required absorber thickness yielding a prescribed sidewall tolerance for exposures performed at the ALS, SSRL and NSLS synchrotron sources. Results are presented as a function of the absorbed dose for a range of the prescribed sidewall tolerance, feature size, PMMA thickness, mask substrate thickness and the development temperature.

Design and properties of quartz-based Love wave acoustic sensors incorporating silicon dioxide and PMMA guiding layers

Love wave surface acoustic wave devices are very promising as sensors in gaseous and liquid environments because of their high sensitivity. In this work, two methods of producing the Love wave guiding layer were utilized to fabricate devices based on ST-cut quartz. The methods involved sputter deposition of silicon dioxide films and spin coating of polymethylmethacrylate (PMMA) films. -cut quartz devices with thicknesses up to and PMMA/ST-cut quartz devices with PMMA thicknesses up to have been manufactured and compared. Mass sensitivity, insertion loss, temperature coefficient of oscillation frequency and frequency noise have been studied as a function of layer thickness. A number of hybrid devices consisting of PMMA film/ film/ST-cut quartz have also been assembled and evaluated. These devices exhibit higher sensitivity than the devices and the PMMA devices produced here.

Film Thickness Determination of PMMA on InP by Ellipsometry

The thickness of polymethylmethacrylate (PMMA) films deposited in solution on is measured by ellipsometry to determine its dependence on terminal spin speed. The PMMA solution behaves as a steady‐state Newtonian fluid. Film thickness in excess of the periodic thickness is measured by combining data taken at three angles of incidence; a procedure for applying this technique is discussed. The main feature consists of assigning the film index from data taken at the incident angle where the ellipsometer readings are most sensitive to film index, and using this index in determining the film thickness at the other two angles. The basis supporting this procedure is presented, and the dependence of the ellipsometric model on uncertainties in the assignment of film and substrate optical constants is discussed specifically in terms of its effect on the three‐angle technique.