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Plasma Surface Modification and Etching of Polyimides
Published in Malay K. Ghosh, K. L. Mittal, Polyimides Fundamentals and Applications, 2018
Frank D. Egitto, Luis J. Matienzo
Polyimide films are often used as dielectric materials in the fabrication of thin-film electronic packages, for example, those employing tape-automated bonding (TAB) and flexible circuitry [14]. Flexible circuits are now in common use as low-cost integrated circuit chip carriers. One strategy for reducing cost is to fabricate these carriers in a roll format. Polyimide films are commonly the preferred dielectric for this application because of their high thermal stability and good mechanical properties. One such polyimide is Kapton-H (duPont) film formed from pyromellitic dianhydride (PMDA) and oxydianiline (ODA) precursors. A more recent series of polyimides based on the reaction of biphenyl tetracarboxylic dianhydride (BPDA) and either ODA or para-phenylene diamine (PDA) precursors are commercially available as dry films supplied by Ube Corporation under the names Upilex-R (Ube Industries) (BPDA-ODA) and Upilex-S (BPDA-PDA). Upilex-S has a lower moisture regain and a different thermal coefficient of expansion than the PMDA-ODA polyimide films [27]. The chemical structures of the monomeric units of several polyimide films that are frequently referred to in this chapter are shown schematically in Figure 1.
Draw-spun, photonically annealed Ag fibers as alternative electrodes for flexible CIGS solar cells
Published in Science and Technology of Advanced Materials, 2019
Yujing Liu, Simon Zeder, Sen Lin, Romain Carron, Günter Grossmann, Sami Bolat, Shiro Nishiwaki, Frank Clemens, Thomas Graule, Ayodhya N. Tiwari, Hui Wu, Yaroslav E. Romanyuk
The layout for flexible CIGS solar cells was shown in Figure 1. Polyimide with a thickness of 25 µm (PI, UPILEX-25S) was selected as the substrate. On top of the substrate, as back contact, a layer of 500 nm Mo was prepared via dc magnetron sputtering from metallic target. CIGS absorber layer was fabricated via a three stage coevaporation procedure, as described in details elsewhere [4,14] and the thickness was ca. 2.9 µm. The n-type buffer layer CdS with a thickness of 50 nm was grown via chemical bath deposition in a basic solution containing cadmium acetate (2.3 mM), thiourea (22 mM) and ammonium hydroxide (2 M [NH3]) at 70 °C. A 70 nm layer of intrinsic ZnO (i-ZnO) was deposited with rf-sputtering. According to the cell design, the conductive AZO layer was deposited on top of i-ZnO with rf-sputtering from doped a ZnO target doped with 2 wt% of Al2O3. Three different thicknesses of AZO were considered: (i) 50 nm that does not add possess enough lateral conductivity as compared to the Ag mesh but still warrants an Ohmic contact to Ag, (ii) 200 nm that a standard thickness for the reference device empirically optimized for the highest device efficiency, and (iii) 900 nm that has a sheet resistance of ca. 10 Ohm/sq that is appropriate for larger-area CIGS modules without additional grids. The devices were completed with e-beam evaporated metal grids of 50 nm Ni followed by 2 µm Al in order to warranty identical contacting conditions for all samples. The solar cells were defined by mechanical scribing with an area around 0.55 cm2.
Automated Quality Characterization for Composites Using Hybrid Ultrasonic Imaging Techniques
Published in Research in Nondestructive Evaluation, 2019
Jiangtao Sun, Alvin Yung Boon Chong, Siamak Tavakoli, Guojin Feng, Jamil Kanfoud, Cem Selcuk, Tat-Hean Gan
Ultrasonic testing methods emit stress waves into the material or component to be inspected, and then the transmitted or reflected signals are measured using a separate transducer on the opposite surface of the material or using the same transducer for signal excitation and acquisition, namely through-transmission or pulse-echo technique, respectively [7]. The through-transmission technique requires the two transducers to be installed on the opposite sides of the material under inspection, which may not be practical in many applications. It also cannot provide the depth information of the defects, while the pulse-echo technique can give this information by detecting the arrival time or time of flight (TOF) of ultrasonic echoes reflected from a defect within a test component. Therefore, the research scope of this work focuses on the pulse-echo technique. A-scan data is acquired at each scan position in the composite, which gives the amplitude of received ultrasonic reflection signal against its TOF. A C-scan image is then generated by converting the A-scan raw data at each scan position into a pixel value through appropriate gating and thresholding, which results in a superimposed planar view of the test piece with defect location and size. Ultrasonic C-scan imaging technique has been exploited in many applications for composite inspection. A few examples include characterization of artificial delamination [8], detection of impact damage in carbon or epoxy composite plates [9], characterization of void distribution, size, and shape in composites [10], and extraction of special features of the interfaces between fibres or matrix [11]. To determine the defect sizes in composite materials, guidelines were suggested for the UT inspection which concluded that the efficient estimation of defect size is difficult to achieve, especially in composites with multiple layers and a large thickness [5,12]. Hasiotis et al. located several artificial delamination, which were simulated by embedding “Upilex,” a high heat resistance polyamide material into multiple-layer composite plates, through appropriate tuning of a commercially available UT inspection system. The specimen thickness and the depth position of the defects can be determined with their shapes and sizes attained in some cases.