Hermetic packaging is a suitable means to achieve long lifetime for implantable medical devices. In order to determine the time to failure of the hermetic packages, the prediction of lifetime by helium leakage measurements prior to implantation is state of the art. However, these methods are not applicable to packages with very small internal cavity volumes, as these established methods reach their resolution limits in this case. In these packages, even the smallest amounts of water can lead to corrosion or short circuits and thus to a malfunctioning system with unexpected behavior. Online monitoring of humidity offers the advantage that critical conditions are detected before a failure occurs. A typical maximum limit is 5000 ppm water vapor inside the package, which corresponds to a relative humidity of around 8.1 %RH at 37 °C. This paper presents the design and implementation of capacitive micromachined humidity detectors with a desiccant-based dielectric in different designs. These allow the electrical detection of moisture absorption, especially in the very low humidity regime ≤ 8 %RH. For this humidity range design-dependent sensitivities of 0.08 pF/%RH and 0.25 pF/%RH were achieved. Presented sensor devices facilitate active monitoring of current moisture content in the package cavity and at the same time provide a buffer for ingressing moisture, thus increasing the overall lifetime of the system. The current sensors are designed for miniaturized active medical implants, but can also be transferred to distributed sensors in harsh environments for Internet of Things applications or machine condition monitoring in Industry 4.0 scenarios.

密封包装是实现可植入医疗设备长寿命的合适方法。为了确定密封包装失效的时间，在植入之前通过氦气泄漏测量来预测寿命是现有技术。但是，这些方法不适用于内部空腔体积很小的包装，因为这些既定方法在这种情况下达到了其分辨率极限。在这些包装中，即使最少量的水也可能导致腐蚀或短路，从而导致具有意外行为的系统故障。在线湿度监测具有以下优势：在故障发生之前就可以检测出关键条件。典型的最大限制是包装内的水蒸气含量为5000 ppm，这对应于37°C时约8.1％RH的相对湿度。本文介绍了在不同设计中具有基于干燥剂的电介质的电容式微机械湿度检测器的设计和实现。这些可以实现电学检测水分吸收，特别是在湿度≤8％RH的极低湿度条件下。对于该湿度范围，获得了取决于设计的灵敏度，分别为0.08 pF /％RH和0.25 pF /％RH。提出的传感器装置有助于主动监测包装腔中的当前水分含量，同时提供用于水分进入的缓冲器，从而增加了系统的整体寿命。当前传感器专为小型有源医疗植入物而设计，但也可以在恶劣的环境中转移到分布式传感器，以用于物联网应用或工业4.0场景中的机器状态监控。