This article reviews our work on direct integration of carbon nanotubes (CNTs) in MEMS vehicles and shows initial results in realizing direct CNT integration in CMOS. Extraordinary properties of CNTs are fully exploited if they are closely integrated with signal processing electronics. An example device is a CNT-based gas sensor, where CNTs with their huge surface-to-volume ratio act as a very sensitive sensing element, and the CMOS circuits provide the necessary signal processing for a device to give a standardized, calibrated, low-noise output signal. Direct synthesis of CNTs in CMOS will enable wafer-level, low-cost fabrication of CNT-based devices. A major challenge is the 800–1000 °C CNT synthesis temperature requirement, whereas CMOS-compatible temperature is <300 °C. We synthesized CNTs on purpose-designed MEMS microheaters by local resistive heating to avoid over-heating the bulk of the chip. An applied electric field guides the CNTs to grow towards a second electrode to close electric circuits by making a Si-CNT-Si system. The process is fully controlled through electrical parameters, indicating that the process can be automated and scaled up to wafer-level for a low-cost, high-volume industrial manufacturing process. Characterization of the synthesized CNTs reveals that the hottest region (∼900 °C) ensures low-diameter, less dense and high-quality CNTs. Also, our statistical analysis shows that the electric field guiding is diameter-dependent, ensuring that only well-ordered low-diameter CNTs become part of an electric circuit. Through electrical analysis of the CNT-Si contacts, we found that the Si-CNT-Si systems show either near-ohmic or non-linear (Schottky-like) behaviours depending on the Si doping level. We also demonstrated functionalization of the locally grown CNTs. For direct CNT synthesis on CMOS chips, a high thermal gradient around the CNT growth structure is required to maintain CMOS-compatible temperature. Several promising designs of CNT growth structures and their thermomechanical simulations are presented. Partially suspended microheaters provide thermal isolation to avoid heating the active CMOS region, while keeping reliable mechanical stability. In our attempt to direct CNT-CMOS integration, a purpose-designed CMOS chip is manufactured using a standard AMS 350 nm CMOS process. Layout designs and optical characterization of several fabricated CMOS microstructures are presented.

中文翻译：

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碳纳米管在 CMOS 中的直接集成，迈向工业可行的工艺：综述

本文回顾了我们在 MEMS 车辆中直接集成碳纳米管 (CNT) 的工作，并展示了在 CMOS 中实现直接 CNT 集成的初步结果。如果碳纳米管与信号处理电子设备紧密集成，则可以充分利用碳纳米管的非凡特性。一个示例设备是基于 CNT 的气体传感器，其中具有巨大表面积与体积比的 CNT 作为非常敏感的传感元件，CMOS 电路为设备提供必要的信号处理，以提供标准化、校准、低- 噪声输出信号。在 CMOS 中直接合成碳纳米管将使基于碳纳米管的器件的晶圆级低成本制造成为可能。一个主要挑战是 800–1000 °C CNT 合成温度要求，而 CMOS 兼容温度 <300 °C。我们通过局部电阻加热在专门设计的 MEMS 微型加热器上合成了 CNT，以避免芯片主体过热。施加的电场引导 CNT 向第二电极生长，从而通过制造 Si-CNT-Si 系统来闭合电路。该过程完全通过电气参数控制，表明该过程可以自动化并放大到晶圆级，以实现低成本、大批量的工业制造过程。合成的碳纳米管的表征表明，最热的区域（~900°C）确保了低直径、低密度和高质量的碳纳米管。此外，我们的统计分析表明，电场引导与直径有关，确保只有有序的低直径 CNT 才能成为电路的一部分。通过对 CNT-Si 触点的电学分析，我们发现 Si-CNT-Si 系统根据 Si 掺杂水平显示出近欧姆或非线性（类肖特基）行为。我们还展示了局部生长的碳纳米管的功能化。对于 CMOS 芯片上的直接 CNT 合成，需要围绕 CNT 生长结构的高热梯度来保持 CMOS 兼容温度。介绍了几种有前途的 CNT 生长结构设计及其热机械模拟。部分悬挂的微型加热器提供热隔离以避免加热有源 CMOS 区域，同时保持可靠的机械稳定性。在我们尝试直接进行 CNT-CMOS 集成时，使用标准 AMS 350 nm CMOS 工艺制造了专门设计的 CMOS 芯片。介绍了几种制造的 CMOS 微结构的布局设计和光学特性。