基于石墨烯的热电堆器件关键技术研究

Normally, graphene is not considered an effective functional material for thermopile application because of its large thermal conductivity, even though the Seebeck coefficient and electric conductivity of graphene are all high. However, the thickness of graphene is small to only one or several atom layers. The sign and value of the Seebeck coefficient of graphene is electric field dependent. Based on these unique properties, this proposal presents a novel graphene based thermopile design, whose sensing membrane consists of graphene and other materials with low thermal conductivities. Then the composite sensing membrane will have low effective thermal conductivity, but maintain high Seebeck coefficient and electric conductivity. Thus, it is possible to develop a novel graphene thermopile with high sensitivity . Furthermore, because of the electric field dependence of graphene Seebeck coefficient, the output signal of graphene based thermopile can be modulated to an AC voltage if the graphene is biased by an AC signal. This novel readout scheme causes the noise of thermopile sensor system might be low to the theoretical limit. This work will be helpful to push forward the research on the high sensitive thermopile application of graphene, to extend the application of thermopiles to cover environment monitoring, military, and aerospace exploring, and hold the related intelligence right by China.

石墨烯材料具有很高的Seebeck系数和很低的电阻率，但由于其热导率也很高，所以一般认为用石墨烯材料制作的热电堆红外传感器难以达到较高的灵敏度。但是，本项目基于石墨烯超薄的原子层量级厚度，及其独特的热电学特性，提出将石墨烯与低热导率材料相结合构成复合热敏感膜，在保持石墨烯Seebeck系数和电阻率方面的优势的同时，极大降低复合热敏感结构的热导率，达到大幅度提高石墨烯热电堆器件优值和灵敏度的目的。同时，根据石墨烯Seebeck系数及其符号与外加偏置电压的相关性，本项目提出一种新的信号读出方案，使传统热电堆的直流信号输出变为交流信号输出，进一步降低石墨烯热电堆传感器系统的噪声。开展本项目的研究，不仅能够推动石墨烯在热电领域的研究和应用，发展新型的高精度热电堆器件，使热电堆的应用范围扩展到环境监测、军事、航天等高端领域，还有助于中国在该领域内拥有相关自主知识产权。

热电偶以及由多个热电偶级联构成的热电堆，是一种传统的非接触式热传感器，其基本原理是利用导体或半导体的Seebeck效应，将温度梯度转变为电压输出信号。热电堆器件未来的发展方向是采用更高性能的热电材料，与先进半导体技术紧密结合，进一步提高器件精度并小型化。基于石墨烯优良的、独特的热电学特性，石墨烯热电堆器件有比现有的硅热电堆器件具有更高灵敏度的潜力。随着工艺的进步，通过进一步减小介质上石墨烯的电阻率和复合结构的总厚度、甚至提高石墨烯Seebeck系数，石墨烯热电堆器件的灵敏度将有很大的提高空间。石墨烯热电堆同时具有使用简单、成本低、可靠性高、应用范围特别广泛的优点。.本项目重点围绕石墨烯材料的特点，充分发挥其材料的优势，研究开发相应的热电堆器件结构和制造技术，对石墨烯热电堆器件的工作原理、加工工艺和测试技术进行深入研究，并对其相关特性进行剖析，进一步发现和解决石墨烯热电堆器件的若干问题，为石墨烯热电堆器件的应用打下坚实的基础。.项目深入研究了石墨烯热电堆器件的制备工艺流程，获得了热电偶并联、串联等多种结构的石墨烯热电堆器件。通过工艺优化，将影响器件性能的重要参数之一----接触电阻降低到500Ω•μm。针对多个试验样品的实验测试结果表明，当栅控电压在-1 V左右时，石墨烯热电堆的Seebeck系数最大值在50-75μV/K 之间；当栅控电压在0.8 V左右时，Seebeck系数的最小值在-25~-55μV/K 之间。通过静电法成功地实现了对石墨烯Seebeck系数的调控和反相，验证了项目提出的石墨烯热电堆工作和检测基本原理的正确性。