Novel low-temperature fabrication process for integrated high-aspect ratio zinc oxide nanowire sensors
Novel low-temperature fabrication process for integrated high-aspect ratio zinc oxide nanowire sensors
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DOI：
10.1116/1.4943041
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发表时间：
2016-03-01
影响因子：
1.4
通讯作者：
Pestov, Dmitry
中科院分区：
文献类型：
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作者：
Clavijo, William P.;Atkinson, Gary M.;Pestov, Dmitry
作者提出了一种新的低温纳米线制造工艺，使高纵横比的纳米线很容易与传感器应用的微电子器件集成。这个过程依赖于一种新的方法，形成自组装的高纵横比的纳米孔在阳极氧化铝（AAO）模板在薄（2.5 μ m）铝膜沉积在硅基板上的紧密堆积阵列。该技术与传统的独立厚膜方法形成鲜明对比，并且使用集成薄铝膜极大地提高了这种方法的实用性。作者通过将ZnO纳米线集成到金属氧化物半导体（MOS）晶体管的金属栅极上以形成集成化学场效应晶体管（ChemFET）传感器结构来展示该方法。该新型薄膜AAO工艺使用新型多级铝阳极氧化、氧化铝阻挡层去除、ZnO原子层沉积（ALD）和pH控制的湿法释放蚀刻。这种新工艺选择性地在晶体管的铝栅极上形成ZnO纳米线，同时保持铝膜的其余部分完整，用于其他集成器件组件和互连。这种自组装的高密度AAO模板选择性地形成在通过电子束蒸发沉积的超光滑的2.5 μ m厚的铝层中，而不需要在传统的100 μ m厚的独立膜中形成AAO模板所需的电抛光。所得纳米孔AAO模板由直径为90 nm、高度为1 μ m的纳米孔组成，面密度为1.3 × 10（10）纳米孔/cm（2）。然后在200 ℃下使用ALD用ZnO填充该薄膜AAO模板，在孔内形成多晶ZnO纳米线。然后用缓冲的NaOH溶液除去氧化铝模板，留下1 μ m高和90 nm直径的自立式ZnO纳米线，提供比用于传感应用的标准平坦ZnO膜增加38倍的表面积。铝膜在器件的非选定区域以及下面的ZnO纳米线中保持完整（未阳极化），充当MOS晶体管的栅极。的ZnO纳米线，其特征在于通过扫描电子显微镜，能量色散X射线光谱，和透射电子显微镜，以验证化学计量和晶体结构。此外，使用氨作为目标气体测量ZnO纳米线ChemFET的响应。I-V特性和瞬态响应范围为25-200 ppm的氨进行了检查。对氨的阈值极限值浓度（25 ppm）的氨响应显示阈值电压偏移56 mV，总体灵敏度为14%，响应时间为8 min，并且恢复期为27 min。作者提出的ZnO纳米线制造序列是在低温（< 200摄氏度）下完成的，并且可以选择性地完成，使其易于与标准金属氧化物半导体场效应晶体管工艺以及其他微电子传感器（如表面声波器件）集成。这种新工艺最初是使用ZnO进行演示的，但也适用于使用适当的沉积方法以及选择性纳米线释放方法的各种纳米线材料。这使得有可能方便地制造各种高纵横比纳米线为基础的微电子传感器的应用范围。(C)2016年美国真空学会。
The authors present a new low-temperature nanowire fabrication process that allows high-aspect ratio nanowires to be readily integrated with microelectronic devices for sensor applications. This process relies on a new method of forming a close-packed array of self-assembled high-aspect-ratio nanopores in an anodized aluminum oxide (AAO) template in a thin (2.5 mu m) aluminum film deposited on a silicon substrate. This technique is in sharp contrast to the traditional free-standing thick film methods, and the use of an integrated thin aluminum film greatly enhances the utility of such methods. The authors have demonstrated the method by integrating ZnO nanowires onto the metal gate of a metal-oxide-semiconductor (MOS) transistor to form an integrated chemical field-effect transistor (ChemFET) sensor structure. The novel thin film AAO process uses a novel multistage aluminum anodization, alumina barrier layer removal, ZnO atomic layer deposition (ALD), and pH controlled wet release etching. This new process selectively forms the ZnO nanowires on the aluminum gate of the transistor while maintaining the remainder of the aluminum film intact for other integrated device components and interconnects. This self-assembled high-density AAO template was selectively formed in an ultrasmooth 2.5 mu m thick aluminum layer deposited through e-beam evaporation without the electropolishing required in AAO template formation in traditional 100 mu m thick free standing films. The resulting nanopore AAO template consists of nanopores of 90 nm in diameter and 1 mu m in height at an aerial density of 1.3 x 10(10) nanopores/cm(2). This thin film AAO template was then filled with ZnO using ALD at 200 degrees C, forming polycrystalline ZnO nanowires inside the pores. The alumina template was then removed with a buffered NaOH solution, leaving free standing ZnO nanowires of 1 mu m height and 90 nm diameter, offering an increase in 38 x the surface area over a standard flat ZnO film for sensing applications. The aluminum film remains intact (unanodized) in nonselected regions of the device as well as underlying the ZnO nanowires, acting as the gate of the MOS transistor. The ZnO nanowires were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and transmission electron microscopy to verify stoichiometry and crystal structure. Additionally, the response of a ZnO nanowire ChemFET was measured using ammonia as a target gas. I-V characterization and transient response to ammonia in the range of 25-200 ppm were examined. The ammonia response to the threshold limit value concentration of ammonia (25 ppm) shows a 56mV shift in threshold voltage, an overall sensitivity of 14%, an 8 min response time, and a 27 min recovery period. The ZnO nanowire fabrication sequence that the authors present is accomplished at low-temperature (< 200 degrees C) and can be accomplished selectively, making it readily amenable to integration with standard metal-oxide-semiconductor field-effect transistor processing as well as other microelectronic sensors such as surface acoustic wave devices. This new process has initially been demonstrated using ZnO, but is also adaptable to a variety of nanowire materials using appropriate deposition methods as well as selective nanowire release methods. This allows the potential to conveniently fabricate a variety of high-aspect ratio nanowire based microelectronic sensors for a range of applications. (C) 2016 American Vacuum Society.