Capacitive micromachined ultrasonic transducer (CMUT) is a proven MEMS based gravimetric sensor featuring high mass sensitivity. It can be highly sensitive for relative humidity (RH) measurement when drop-casted with moisture-sensitive graphene oxide (GO) film. However, high hysteresis appears to be a critical problem for the sensor partially due to the non-uniformity of the sensing film. Here, we present miniaturized CMUTs that are functionalized by the inkjet-printed GO film and exhibit high sensitivity and meanwhile low hysteresis. Hexagon CMUTs with a side length of 500 μm were designed and fabricated by the nitride-to-oxide wafer bonding process. GO inks were prepared using a mixture of DI water and ethanol as the solvent. A square pattern formed by a 2D array of ink droplets was inkjet printed on the CMUT membranes. GO films with different thicknesses were deposited on three CMUTs. The humidity sensing performance of the sensors was evaluated by measuring the resonance frequency shifts induced by the added mass of adsorbed water molecules. The sensors delivered high RH sensitivity of up to 3.35 kHz/%RH, short response/recovery time down to 8 s/2 s, and hysteresis as low as 2.6 %RH. This work demonstrates that the inkjet printing technique is an excellent tool to functionalize CMUT with the advantages of minimized material consumption, batch-production capability, and exceptional control over the film thickness and quality. The CMUT printed with GO film has also shown to be a promising candidate as a miniaturized humidity sensing platform.

电容式微加工超声换能器（CMUT）是经过验证的基于MEMS的重量传感器，具有高质量灵敏度。用湿敏性氧化石墨烯（GO）膜滴铸时，它对相对湿度（RH）的测量高度敏感。然而，部分地由于感测膜的不均匀性，高滞后似乎是传感器的关键问题。在这里，我们介绍了通过喷墨印刷的GO膜功能化的小型CMUT，它们具有高灵敏度和低滞后性。边长为500μm的六边形CMUT通过氮化物与氧化物晶片键合工艺设计和制造。使用去离子水和乙醇的混合物作为溶剂制备GO墨水。将由2D墨滴阵列形成的方形图案喷墨打印在CMUT膜上。将具有不同厚度的GO膜沉积在三个CMUT上。通过测量由吸附的水分子的增加质量引起的共振频率偏移，来评估传感器的湿度感测性能。传感器提供高达3.35 kHz /％RH的高RH灵敏度，短至8 s / 2 s的短响应/恢复时间以及低至2.6％RH的磁滞。这项工作表明，喷墨打印技术是使CMUT功能化的出色工具，其优点是将材料消耗最小化，批量生产能力以及对薄膜厚度和质量的出色​​控制。印有GO薄膜的CMUT也已被证明是一种有希望的候选产品，可作为一种小型化的湿度传感平台。通过测量由吸附的水分子的增加质量引起的共振频率偏移，来评估传感器的湿度感测性能。传感器提供高达3.35 kHz /％RH的高RH灵敏度，短至8 s / 2 s的短响应/恢复时间以及低至2.6％RH的磁滞。这项工作表明，喷墨打印技术是使CMUT功能化的出色工具，其优点是将材料消耗最小化，批量生产能力以及对薄膜厚度和质量的出色​​控制。印有GO薄膜的CMUT也已被证明是一种有希望的候选产品，可作为一种小型化的湿度传感平台。通过测量由吸附的水分子的增加质量引起的共振频率偏移，来评估传感器的湿度感测性能。传感器提供高达3.35 kHz /％RH的高RH灵敏度，短至8 s / 2 s的短响应/恢复时间以及低至2.6％RH的磁滞。这项工作表明，喷墨打印技术是使CMUT功能化的出色工具，其优点是将材料消耗最小化，批量生产能力以及对薄膜厚度和质量的出色​​控制。印有GO薄膜的CMUT也已被证明是一种有希望的候选产品，可作为一种小型化的湿度传感平台。磁滞低至2.6％RH。这项工作表明，喷墨打印技术是使CMUT功能化的出色工具，其优点是将材料消耗最小化，批量生产能力以及对薄膜厚度和质量的出色​​控制。印有GO薄膜的CMUT也已被证明是一种有希望的候选产品，可作为一种小型化的湿度传感平台。磁滞低至2.6％RH。这项工作表明，喷墨打印技术是使CMUT功能化的出色工具，其优点是将材料消耗最小化，批量生产能力以及对薄膜厚度和质量的出色​​控制。印有GO薄膜的CMUT也已被证明是一种有希望的候选产品，可作为一种小型化的湿度传感平台。