Titanium Dioxide Nanoparticle Humidity Microsensors Integrated with Circuitry on-a-Chip

Self Cite

The study develops an integrated humidity microsensor fabricated using the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process. The integrated humidity sensor consists of a humidity sensor and a ring oscillator circuit on-a-chip. The humidity sensor is composed of a sensitive film and branch interdigitated electrodes. The sensitive film is zinc oxide prepared by sol-gel method. After completion of the CMOS process, the sensor requires a post-process to remove the sacrificial oxide layer and to coat the zinc oxide film on the interdigitated electrodes. The capacitance of the sensor changes when the sensitive film adsorbs water vapor. The circuit is used to convert the capacitance of the humidity sensor into the oscillation frequency output. Experimental results show that the output frequency of the sensor changes from 84.3 to 73.4 MHz at 30 °C as the humidity increases 40 to 90 %RH.

“…Hu et al [ 13 ] reported a humidity sensor manufactured by the CMOS process. The sensitive film was nanoparticle titanium dioxide.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Sol-Gel Zinc Oxide Humidity Sensors Integrated with a Ring Oscillator Circuit On-a-Chip

Yang

Dai

2014

Self Cite

“…The ability of the sensing material to be integrated in industrial production depends on the fabrication route used for its deposition and patterning. In the case of humidity sensors, the most standard methods to deposit TiO 2 are the spin-coating, dip coating, or microdroper processes [ 27 , 28 , 29 , 30 , 31 ], which are suitable for prototypes, but cannot be considered for large-scale process. In fabrication route selection, several factors must be considered, such as costs, throughput, and reproducibility, and the procedure ought to be compatible with the substrate, especially in terms of temperature.…”

Section: Introductionmentioning

confidence: 99%

Fabrication and Characterization of Flexible and Miniaturized Humidity Sensors Using Screen-Printed TiO2 Nanoparticles as Sensitive Layer

Dubourg

Segkos

Katona

et al. 2017

This paper describes the fabrication and the characterization of an original example of a miniaturized resistive-type humidity sensor, printed on flexible substrate in a large-scale manner. The fabrication process involves laser ablation for the design of interdigitated electrodes on PET (Poly-Ethylene Terephthalate) substrate and a screen-printing process for the deposition of the sensitive material, which is based on TiO2 nanoparticles. The laser ablation process was carefully optimized to obtain micro-scale and well-resolved electrodes on PET substrate. A functional paste based on cellulose was prepared in order to allow the precise screen-printing of the TiO2 nanoparticles as sensing material on the top of the electrodes. The current against voltage (I–V) characteristic of the sensor showed good linearity and potential for low-power operation. The results of a humidity-sensing investigation and mechanical testing showed that the fabricated miniaturized sensors have excellent mechanical stability, sensing characteristics, good repeatability, and relatively fast response/recovery times operating at room temperature.

“…These types of humidity sensors may be divided into two categories: metal oxide semiconductor MOS- and polymer-based humidity sensors. In recent years, there have been many published research papers on MOS-based humidity sensors [ 14 , 15 , 16 ]; tin dioxide (SnO 2 ) and titanium dioxide (TiO 2 ) are very popular sensing materials for these types of humidity sensors. Polymer-based sensors have also been used for humidity detection for a very long time [ 17 , 18 , 19 ].…”

Section: Introductionmentioning

confidence: 99%

Fabrication and Characterization of a CMOS-MEMS Humidity Sensor

Dennis

Ahmed

Khir

2015

This paper reports on the fabrication and characterization of a Complementary Metal Oxide Semiconductor-Microelectromechanical System (CMOS-MEMS) device with embedded microheater operated at relatively elevated temperatures (40 °C to 80 °C) for the purpose of relative humidity measurement. The sensing principle is based on the change in amplitude of the device due to adsorption or desorption of humidity on the active material layer of titanium dioxide (TiO2) nanoparticles deposited on the moving plate, which results in changes in the mass of the device. The sensor has been designed and fabricated through a standard 0.35 µm CMOS process technology and post-CMOS micromachining technique has been successfully implemented to release the MEMS structures. The sensor is operated in the dynamic mode using electrothermal actuation and the output signal measured using a piezoresistive (PZR) sensor connected in a Wheatstone bridge circuit. The output voltage of the humidity sensor increases from 0.585 mV to 30.580 mV as the humidity increases from 35% RH to 95% RH. The output voltage is found to be linear from 0.585 mV to 3.250 mV as the humidity increased from 35% RH to 60% RH, with sensitivity of 0.107 mV/% RH; and again linear from 3.250 mV to 30.580 mV as the humidity level increases from 60% RH to 95% RH, with higher sensitivity of 0.781 mV/% RH. On the other hand, the sensitivity of the humidity sensor increases linearly from 0.102 mV/% RH to 0.501 mV/% RH with increase in the temperature from 40 °C to 80 °C and a maximum hysteresis of 0.87% RH is found at a relative humidity of 80%. The sensitivity is also frequency dependent, increasing from 0.500 mV/% RH at 2 Hz to reach a maximum value of 1.634 mV/% RH at a frequency of 12 Hz, then decreasing to 1.110 mV/% RH at a frequency of 20 Hz. Finally, the CMOS-MEMS humidity sensor showed comparable response, recovery, and repeatability of measurements in three cycles as compared to a standard sensor that directly measures humidity in % RH.