A New Route to high-Performance Functional Films on Polymeric Web

功能膜支撑许多电子和光电器件，包括平板显示器、OLED、图像传感器、薄膜光伏太阳能电池等。对这些器件特别重要的是透明导电氧化物（TCO）膜，例如氧化铟锡（ITO）和铝掺杂氧化锌（ZAO）。到2010年，英国的功能性薄膜市场预计将增长到234亿。如果该装置可以在非常大的吞吐量的卷到卷涂布机中直接沉积到聚合物网上，则生产率将进一步大幅提高，并开辟新的市场。然而，TCO膜在网上的沉积提出了许多重大的技术挑战。与玻璃相比，聚合物网相对粗糙，倾向于显著脱气并且是热敏的。后一点特别提出了一个问题，因为通常需要进行沉积后退火工艺（通常在500摄氏度下），以优化TCO材料的光学和电学性能。该工艺涉及在短时间内向磁控管溅射阴极施加非常大的功率脉冲。峰值脉冲功率可以在兆瓦范围内，并且脉冲持续时间通常为80-160微秒的量级，重复率在10秒至100秒Hz的范围内。HIPIMS的初步研究（也称为高功率脉冲磁控溅射/ HPPMS）系统已经表明，这种强脉冲产生高度电离（对于钛高达70%）的溅射物质（与常规磁控溅射相反，其中通常少于1%的溅射材料被电离）。HIPIMS中溅射物质的电离度与阴极电弧放电中产生的电离度相当;然而，使用HIPIMS通常不产生大颗粒。另一个重要的考虑因素是，由于非常低的占空比（~1%）和长的关断时间，对衬底的总热负荷可以比常规DC和脉冲DC溅射中的低得多（5-10倍）。因此，HIPIMS的潜力是利用高电离度来产生具有显著改善的性质的膜，同时保持适当低（低于150摄氏度）的衬底本体温度，允许涂覆各种各样的衬底材料。因此，HIPIMS技术的引入具有提供沉积在聚合物网上的功能膜（例如TCO）的性能的阶跃变化的潜力。该项目将提供第一次机会，详细研究这种新的，复杂的沉积过程中的发展规模的系统在MMU和工业试验规模的卷到卷涂布机在牛津大学。该项目的另一个关键内容将是详细研究排放的性质。等离子体特性，如浓度和温度的物种和它们的功率负载的基板的空间和时间的演变将使用一系列的时间分辨诊断工具和发达的光学成像技术来确定。将具有优化性能的完全致密TCO涂层存款到柔性基底上的能力将是一个重大突破，并将代表幅材涂覆技术的重大进步。

Functional films underpin many electronic and opto-electronic devices, including flat panel displays, OLED's, image sensors, thin film photovoltaic solar cells, etc. Of particular importance to these devices are transparent conductive oxide (TCO) films, such as indium tin oxide (ITO) and aluminium-doped zinc oxide (ZAO). The UK market for functional films is expected to rise to 23.4B by 2010. Further substantial gains in productivity would be made, and new markets opened up, if the devices could be deposited directly onto polymeric web in very large throughput reel-to-reel coaters. However, the deposition of TCO films onto webs poses many significant technological challenges. In comparison to glass, polymeric webs are relatively rough, tend to outgas significantly and are thermally sensitive. The latter point particularly poses a problem, because it is generally necessary to perform a post-deposition annealing process (typically at 500 degC) in order to optimise the optical and electrical properties of TCO materials.One potential solution to this problem is to deposit coatings using the newly developed technique of high powered impulse magnetron sputtering (HIPIMS). This process involves the application of very large power pulses to magnetron sputter cathodes for short periods of time. The peak pulse power can be in the megawatt range and the pulse duration is typically of the order of 80-160 micro seconds, at repetition rates in the range of 10s to 100s of Hz. Initial studies of the HIPIMS (also referred to as high power pulsed magnetron sputtering / HPPMS) system have shown that this intense pulse creates a high degree of ionization (up to 70% for titanium) of the sputtered species with this technique (in contrast to conventional magnetron sputtering, where usually less than 1% of the sputtered material is ionized).The degree of ionization of the sputtered species in HIPIMS is comparable to that produced in cathodic arc discharges; however, with HIPIMS macroparticles are not normally produced. Another important consideration is that, due to the very low duty cycles (~1%) and long off times, the total heat load to the substrate can be very significantly (5-10 times) lower than in conventional DC and pulsed DC sputtering. Thus, the potential for HIPIMS is to harness the high degree of ionization to produce films with significantly improved properties, whilst maintaining a suitably low (sub-150 degC) substrate bulk temperature, allowing a diverse range of substrate materials to be coated. The introduction of HIPIMS technology, therefore, has the potential to provide a step-change in the performance of functional films, such as TCO's, deposited onto polymeric webs. This project will offer the first opportunity to study this new, complex deposition process in detail in both a development-scale system at MMU and an industrial pilot scale reel-to-reel coater at Oxford University. An additional key element of the project will be a detailed study of the nature of the discharge. Plasma characteristics such as the spatial and temporal evolution of the concentrations and temperatures of the species and their power loading of the substrate will be determined using an array of time-resolved diagnostic tools and well developed optical imaging techniques. The ability to deposit fully dense TCO coatings with optimised properties onto flexible substrates would be a major breakthrough and would represent a significant advancement in web coating technology.