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

功能薄膜支撑着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）薄膜，如氧化铟锡（ITO）和掺铝氧化锌（ZAO）。到2010年，英国的功能性薄膜市场预计将增长到23.4亿美元。如果该设备可以在非常大的吞吐量卷对卷涂布机中直接沉积在聚合物网上，将进一步大幅提高生产率，并开辟新的市场。然而，将TCO薄膜沉积到网络上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，容易出气，并且热敏。后一点特别提出了一个问题，因为为了优化TCO材料的光学和电学性能，通常需要执行沉积后退火工艺（通常在500℃）。一个潜在的解决方案是使用新开发的高功率脉冲磁控溅射（HIPIMS）技术沉积涂层。这个过程包括在短时间内对磁控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，脉冲持续时间通常为80-160微秒，重复频率范围为10秒至100赫兹。对HIPIMS（也称为高功率脉冲磁控溅射/ HPPMS）系统的初步研究表明，这种强脉冲通过这种技术产生了高度电离（钛高达70%）的溅射物质（与传统磁控溅射相比，通常只有不到1%的溅射材料被电离）。HIPIMS中溅射物质的电离程度与阴极电弧放电中产生的电离程度相当；然而，hiims通常不会产生大颗粒。另一个重要的考虑因素是，由于非常低的占空比（~1%）和很长的关闭时间，基片的总热负荷可以非常显着（5-10倍）低于传统的直流和脉冲直流溅射。因此，HIPIMS的潜力是利用高度电离来生产具有显着改善性能的薄膜，同时保持适当的低（低于150摄氏度）衬底体温度，允许涂覆各种衬底材料。因此，HIPIMS技术的引入有可能为沉积在聚合物网上的功能薄膜（如TCO）的性能提供一个阶梯变化。该项目将首次提供机会，在MMU的开发规模系统和牛津大学的工业中试规模的卷对卷涂布机中详细研究这种新的复杂沉积过程。该项目的另一项关键内容是详细研究排放的性质。等离子体特征，如物质浓度和温度的时空演变及其对基底的功率负荷，将使用一系列时间分辨诊断工具和发达的光学成像技术来确定。将具有优化性能的全致密TCO涂层沉积在柔性基材上的能力将是一个重大突破，并将代表卷筒纸涂层技术的重大进步。

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.