Power-efficient solid-state smart CMOS sensors for RFID applications

Rapidly developing RFID techniques gain various applications in today’s e-life. If integrating CMOS sensors and the RFID tag on the same substrate, functionalities of the tag would be further enhanced, making the RFID tag a promising platform to achieve sensing-system-on-chip. The utmost considerations for RFID embedded sensor design are the energy/power consumption and the sensor robustness under noisy circuit environment. Especially for fully passive RFID tags, whose energy is harvested from the incoming RF signal, which motivates this power-efficient sensor design. In this work, various sensor design constrain for RFID applications are clarified. Tradeoffs between different sensor architectures are studied and analyzed. Meanwhile, sensor solutions suitable for RFID applications are accordingly proposed and justified. Specifically, an ultra-low power CMOS temperature sensor and a capacitive humidity sensor are designed, fabricated and measured to investigate the feasibility of sensing-system-on-chip with the RFID platform. For CMOS temperature sensor, methodologies for low voltage sensor design are investigated and a sub-1V bipolar-based CMOS temperature sensor with full military temperature range is presented. A dual-range sensing scheme is utilized to achieve both low-voltage operation and maintain wide sensing range, without sacrificing the sensor overall SNR. A demonstrative CMOS temperature sensor embedded in the RFID tag with process spread compensation scheme is designed, with optimized power consumption in the order of sub-µW, which would not greatly affect the overall system performance. The embedded temperature sensor is thoroughly characterized with a stable temperature chamber, sensing inaccuracy of ±1°C has been achieved after batch calibration. For CMOS relative humidity sensor, a highly CMOS compatible and reproducible polyimide-based capacitive sensing architecture is selected. A simple modified fully differential first-order sigma-delta data converter readout is designed, which is immune to circuit intrinsic parasitics can also ensure the sensor’s long-term stability. Detailed front-end modeling for preliminary system verification is given. Because of the strong dependency of the relative humidity sensor on its operating temperature, temperature sensor on the same substrate in the RFID tag platform provides another degree of information for more accurate relative humidity sensor design, which potentially enables the sensing-system-on-chip goal. To sum up, several exemplary solid-state sensor designs in a RFID platform are demonstrated and several key design considerations for successfully integrating sensors into such kind of wireless platform are emphasized through this thesis