Integration of inertial MEMS sensors in active smart RFID labels for transport monitoring

Abstract

The transport monitoring of sensitive and valuable goods requires, besides the storage of logistic data, the record of climate and ambient conditions. Therefore the acquisition of physical values like temperature, humidity, pressure, acceleration and inclination is necessary. Commercially available data logger devices are expensive and sizable. A cost effective alternative are active smart radio frequency identification (RFID) label containing microelectromechanical systems (MEMS). By integration of sensors, display and autonomous energy supply in a passive RFID label, wireless smart systems are created. However, the integration of MEMS into smart labels causes special requirements concerning power consumption and packaging. The power consumption of the system is limited due to the autonomous energy supply and so energy efficiency of the sensor is a key requirement. The special demands to the packaging are caused by the assembly of smart labels. The devices are integrated by flip chip bonding on an interposer, which is laminated between the capping layers of the label. Furthermore, usual roll to roll fabrication demands flexibility of the layers. This assembly technique limits the height of the components and hence, no additional housing of the chips is applicable. Therefore, wafer level packaging of the MEMS transducer providing hermetic sealing by minimizing chip geometry is necessary. For realizing a semi-active smart RFID label monitoring temperature, mechanical shock and inclination during transport processes, a MEMS based capacitive inertial sensor has been developed. For low energy consumption of the system sensor functionalities have been integrated and a low-power mixed-signal ASIC for sensor signal processing has been developed. Hermetic sealing of the microstructures has been done by seal glass bonding and a wafer level thin film encapsulation (TFE) technology based on CF-polymer as sacrificial layer material