Wireless sensor nodes with ultra-low power consumption for low-frequency vibration monitoring

System scaling down in the viewpoint of both electrical blocks and physical interconnection is essential to wireless sensor nodes for layout-free and maintenance-free ubiquitous applications in wireless sensor networks (WSN). In this work, a piezoresistive planar MEMS sensor with the sensitivity of 0.2-0.3 mV/V/g was developed for the monitoring of vibrations at low-frequency of a few Hz. To reduce power consumption of the system to the lowest limit as well as to reduce the quantity of electrical components, a fully-integrated low-power customized LSI with universal interface to sensors was designed and fabricated by using 0.18 μm 1.8V/3.3V 1P6M logic process for power management, data acquisition, data processing, and data transmission by RF signal. Power supply to the sensor can be managed by the customized LSI for reducing its power consumption. Output analog signal from the sensor can be obtained by the customized LSI through on-chip integrated amplifier and AD convertor. To reduce size of the system to the lowest limit, buried bump interconnection technology (B²it™) was introduced for the integration of above customized LSI, MEMS sensor, crystal oscillator, and passive components into a 3D structure. Those technologies enable the production of the world smallest class wireless sensor nodes with ultra-low power consumption for low-frequency vibration monitoring, and for temperature and humidity measurement.