A Novel Three-Dimensional Thin-film Thermoelectric Generator for Wearable Applications

摘要：热电发电机可以将人体热量转化为电能，为低功耗电子设备提供连续的能量来源。体积小、重量轻的热电发电机可以集成到可穿戴设备中，使无电池设备成为现实。研究表明，很大一部分用户在使用几个月后就不再使用他们的可穿戴设备，部分原因是需要频繁充电。解决方案是使这种可穿戴设备自供电，从而无需充电或更换电池。这样的壮举也将使可穿戴设备在临床应用中得到应用。例如，自供电设备将允许医生在老年病人出院后持续监测他们的状态。除了健康和健康监测之外，自供电传感器的连接网络还可以为工业制造、精准农业、环境监测、测量和土木工程，当然还有智能互联家庭的决策提供信息。到目前为止，商用热电装置的制造方法与50年前的制造方法相似。它们体积庞大，每个设备只有几十个毫米级的元件，因此，它们的输出电压太低（几毫伏），它们的外形因素不适合可穿戴应用。这项研究的目标是制造一种新颖的器件架构，使每平方厘米数千个微尺度热电元件的集成和堆叠成为可能。这种新设备既薄又轻，可以从人体热量中产生几伏特的电压，适合各种可穿戴应用。此外，制造过程将依靠成熟的工业兼容工艺实现晶圆规模，这使其成为商业化的可行技术。技术摘要：本研究的目的是开发一种新型的三维薄膜热电发电机，适用于人体热收集和为可穿戴传感器和电子设备供电。传统的热电发电机仅由12个毫米级元件组成，无法从人体热量中产生足够的电压。提出了一种新的器件结构，可以制造由每平方厘米数千个微尺度热电元件组成的高效薄膜热电器件。因此，新器件可以产生1000X大的输出电压。由于采用了全新的器件结构，它可以在三维结构中堆叠薄膜元件，并通过自真空密封将寄生热损失降至最低，从而实现了性能的增强。该方法不仅可以实现真空封装，还可以制作热电长度与沉积膜厚度无关的薄膜装置。这是对传统结构的重大改进，因为元件的电阻和热阻的优化可以独立于薄膜厚度而实现。工业兼容，晶圆规模的微制造工艺将用于在廉价的硅片上制造所提出的三维热电发电机。制造将依赖于微机电系统集成中使用的成熟工艺和技术。此外，在实现这一目标的过程中，(a)基于碲化铋的热电器件将在氧化硅/硅衬底上生长并表征，(b)将开发一个全面的三维模型，以更好地理解和优化器件结构并最大限度地减少寄生热损失，以及(c)该器件将被表征为人体热收集和可穿戴应用。

Title: A novel high performance thin and light three-dimensional thermoelectric generator harvesting human body heat for powering wearable devicesNontechnical Abstract:Thermoelectric generators can convert body heat to electrical energy providing a continuous source of energy for low power electronics. Small and light weight thermoelectric generators can be integrated into wearable devices making battery-less devices a reality. Studies have shown that a large fraction of the users stop using their wearables after a few months partly caused by the need for frequent charging. The solution is to make such wearables self-powered eliminating the need for recharging or replacing the batteries. Such a feat would also enable the use of wearables in clinical applications. For instance, self-powered devices would allow physicians to monitor continuously the state of their elderly patients after they are discharged from the hospital. In addition to wellness and health monitoring, connected networks of self-powered sensors could inform decisions in industrial manufacturing, precision agriculture, environmental monitoring, surveying and civil engineering, and of course smart and connected homes. To date, commercial thermoelectric devices are fabricated in similar way as they were made fifty years ago. They are bulky with only dozens of millimeter-scale elements per device, as such, their output voltage is too low (a few milli-volts) and their form factor is not appropriate for wearable applications. The objective of this research is to make a novel device architecture that enables integration and stacking of thousands of microscale thermoelectric elements per centimeter square. The new device is thin and light weight, and can generate several volts from body heat appropriate for various wearable applications. Moreover, the fabrication process will be wafer-scale relying on mature industry compatible processes, which makes it a viable technology for commercialization. Technical Abstract:The objective of this research is to develop a novel three-dimensional thin-film thermoelectric generator suitable for body heat harvesting and powering wearable sensors and electronics. A conventional thermoelectric generator consists of only a dozen of millimeter-scale elements, which cannot generate sufficient voltage from body heat. A novel device architecture is proposed that enables fabrication of high efficiency thin film thermoelectric devices consisting of several thousands of microscale thermoelectric elements per square centimeter. Therefore, the new device can generate 1000X larger output voltage. It achieves this performance enhancement thanks to an entirely new device architecture, which allows stacking of thin film elements in a three-dimensional construction, and self-vacuum-sealing that minimizes parasitic heat losses. The approach not only enables vacuum encapsulation, but also allows making a thin-film device in which the thermoelectric length is independent of the thickness of the deposited film. This is a significant improvement over conventional architectures since optimization of the electrical and thermal resistances of the elements can be achieved independent of the film thickness. Industry compatible, wafer-scale micro-fabrication process will be used to fabricate the proposed three-dimensional thermoelectric generator on inexpensive silicon wafers. The fabrication will rely on mature processes and techniques used in micro-electro-mechanical-systems integration. Furthermore, in the path to achieving this goal, (a) bismuth telluride based thermoelectrics will be grown on silicon oxide/silicon substrate and characterized, (b) a comprehensive three-dimensional model will be developed to better understand and optimize the device architecture and minimize the parasitic heat losses, and (c) the device will be characterized for human body heat harvesting and wearable applications.