Aurelie Humbert

A 1.2-V 8.3-nJ CMOS Humidity Sensor for RFID Applications

This paper presents a fully integrated CMOS humidity sensor for a smart RFID sensor platform. The sensing element is a CMOS-compatible capacitive humidity sensor, which consists of top-metal finger-structure electrodes covered by a humidity-sensitive polyimide layer. Its humidity-sensitive capacitance is digitized by an energy-efficient capacitance-to-digital converter (CDC) based on a third-order delta-sigma modulator. This CDC employs current-efficient operational transconductance amplifiers based on current-starved cascoded inverters, whose limited output swing is accommodated by employing a feedforward loop-filter topology. A programmable offset capacitor is included to remove the sensors baseline capacitance and thus reduce the required dynamic range. To reduce offset errors due to charge injection of the switches, the entire system is auto-zeroed. The proposed humidity sensor has been realized in a 0.16- μm CMOS technology. Measurement results show that the CDC performs a 12.5-bit capacitance-to-digital conversion in a measurement time of 0.8 ms, while consuming only 8.6 μA from a 1.2-V supply. This corresponds to a state-of-the-art figure-of-merit of 1.4 pJ/conversion-step. Combined with the co-integrated humidity sensing element, it provides a resolution of 0.05% RH in the range from 30% RH to 100% RH while consuming only 8.3 nJ per measurement, which is an order-of-magnitude less energy than the state-of-the-art.

A 1.8V 11μW CMOS smart humidity sensor for RFID sensing applications

A fully-integrated humidity sensor for a smart RFID sensor platform has been realized in 0.16μm standard CMOS technology. It consists of a top-metal finger-structure capacitor covered with a humidity-sensitive layer, combined with a micro-power flexible sensor interface based on a second-order incremental delta-sigma converter. The interface can be easily reconfigured to compensate for process variation of the sensing element. In a measurement time of 10.2 ms, the interface performs a 13-bits capacitance-to-digital conversion while consuming only 5.85 μA from 1.8 V supply. In combination with the co-integrated sensor capacitor, it thus provides a humidity-to-digital conversion with a resolution of 0.1% RH in the range of 20% to 90% RH at only 107 nJ per measurement. This represents a significant improvement in energy efficiency compared to existing capacitive-sensor interfaces with comparable performance.

A 1.2V 8.3nJ energy-efficient CMOS humidity sensor for RFID applications

A CMOS fully-integrated humidity sensor for a RFID sensor platform has been realized in 0.16μm CMOS technology. It consists of a top-metal finger capacitor, covered by a humidity-sensitive polyimide layer, and an energy-efficient inverter-based capacitance-to-digital converter (CDC). Measurements show that the CDC performs a 12.5-bit conversion in 0.8ms while consuming only 8.6μA from a 1.2V supply. Together with the co-integrated humidity sensor, this translates into a resolution of 0.05% RH in the range of 30% RH to 90% RH, at an energy consumption of only 8.3nJ per measurement.

P(VDF-HFP) Polymer as Sensing Material for Capacitive Carbon Dioxide Sensors

P(VDF-HFP) polymer is investigated through both theoretical and experimental approaches as a sensing material for capacitive CO2 sensor applications. Analysis based on the Clausius–Mossotti model shows that larger CO2 solubility and larger dielectric constant contribute to high CO2 capacitive sensitivity, which shows that P(VDF-HFP) polymer has significantly higher CO2 sensitivity compared with Teflon when they have comparable CO2 solubility, which is supported by subsequent experimental demonstration. Cross-sensitivity to humidity and temperature are evaluated and discussed for both P(VDF-HFP) and Teflon polymers. Fourier Transform Infrared spectroscopy (FTIR) analysis further reveals that the electrostatic interaction of P(VDF-HFP) with CO2 is stronger than Teflon. The theoretical analyses and experimental demonstration indicate that P(VDF-HFP) is a promising sensing material to be applied for capacitive CO2 sensors operated at room temperature.