A Simple, Low-Cost Micro-Coating Method for Accuracy Improvement and Its Application in Pressure Sensors

Defect Filling Method of Sensor Encapsulation Based on Micro-Nano Composite Structure with Parylene Coating

The demand for waterproofing of polymer (parylene) coating encapsulation has increased in a wide variety of applications, especially in the waterproof protection of electronic devices. However, parylene coatings often produce pinholes and cracks, which will reduce the waterproof effect as a protective barrier. This characteristic has a more significant influence on sensors and actuators with movable parts. Thus, a defect filling method of micro-nano composite structure is proposed to improve the waterproof ability of parylene coatings. The defect filling method is composed of a nano layer of Al2O3 molecules and a micro layer of parylene polymer. Based on the diffusion mechanism of water molecules in the polymer membrane, defects on the surface of polymer encapsulation will be filled and decomposed into smaller areas by Al2O3 nanoparticles to delay or hinder the penetration of water molecules. Accordingly, the dense Al2O3 nanoparticles are utilized to fill and repair the surface of the organic polymer by low-rate atomic layer deposition. This paper takes the pressure sensor as an example to carry out the corresponding research. Experimental results show that the proposed method is very effective and the encapsulated sensors work properly in a saline solution after a period of time equivalent to 153.9 days in body temperature, maintaining their accuracy and precision of 2 mmHg. Moreover, the sensors could improve accuracy by about 43% after the proposed encapsulation. Therefore, the water molecule anti-permeability encapsulation would have broad application prospects in micro/nano-device protection.

Ultrathin and Robust Micro-Nano Composite Coating for Implantable Pressure Sensor Encapsulation

Implantable pressure sensors enable more accurate disease diagnosis and real-time monitoring. Their widescale usage is dependent on a reliable encapsulation to protect them from corrosion of body fluids, yet not increasing their sizes or impairing their sensing functions during their lifespans. To realize the above requirements, an ultrathin, flexible, waterproof while robust micro-nano composite coating for encapsulation of an implantable pressure sensor is designed. The composite coating is composed of a nanolayer of silane-coupled molecules and a microlayer of parylene polymers. The mechanism and principle of the composite encapsulation coating with high adhesion are elucidated. Experimental results show that the error of the sensors after encapsulation is less than 2 mmHg, after working continuously for equivalently over 434 days in a simulated body fluid environment. The effects of the coating thickness on the waterproof time and the error of the sensor are also studied. The encapsulated sensor is implanted in an isolated porcine eye and a living rabbit eye, exhibiting excellent performances. Therefore, the micro-nano composite encapsulation coating would have an appealing application in micro-nano-device protections, especially for implantable biomedical devices.