Candidate: Muhammad Ali Martuza
Title: Sensors for Wireless Body Monitoring Applications
Date: November 23, 2017
Time: 10:00 AM
Place: EIT 3142
Supervisor: Karim, Karim S.
Body monitoring systems have recently drawn great attention to modern electronic consumers due to their various health-care and security applications. To demonstrate the feasibility of low-temperature thin-film based sensing systems for these applications, in this thesis, we propose a near-infrared (NIR) photodetector and a humidity sensor (HS) using low-temperature thin-film processes suitable for large-area electronics application. A LC circuit is integrated inside the HS to enable the battery-free wireless sensing feature.
For NIR detection, a novel lateral metal-semiconductor-metal (MSM) photodetector architecture is proposed using nanocrystalline silicon (nc-Si) as a NIR absorption layer and polyimide (PI) as a blocking layer. Experimental results show that addition of PI film reduced the detectors dark current (ID) up to 103-105 times as well as stabilized it. Fabricated devices exhibit a low ID of ~10-10 A, a dynamic range optical intensity of 0.7-2 mW/cm2, a response time of <1.5 ms, and an external quantum efficiency of 35-15% for the 740-850 nm wavelengths of light under 100-150 V biasing conditions. Unlike the standard p-i-n photodetector, our high-performance lateral photodetector does not require doped p+ and n+ layers. Thus, the reported device is compatible with industry standard amorphous silicon (a-Si) thin-film transistor (TFT) fabrication process, which makes it promising for large-area full hand biometric imagers suitable for various non-invasive body monitoring applications.
For humidity detection, a 30 mm diameter passive LC (p-LC) HS is formed by joining an octagonal planer inductor and a moisture sensitive interdigital ZnO capacitor in series. A PCB reader coil is also designed, which is able to sense the HS from <25 mm distance. The HS reads 30-90% of relative humidity (RH) by interrogating change of the resonance frequency (fR) of the reader-sensor system. The reading resolution is ±2.38%RH and the sensitivity is 53.33-93.33 kHz/1%RH for the above 45% RH measurements. Experimental results show that the proposed HS is operational in a range of 0-75 oC as long as recalibration is performed for a temperature drift of above ±3 oC, which makes it suitable for various promising applications operated at different temperatures. Above all, the presented results are promising for the continuous body monitoring applications to observe the humidity wirelessly without any power source on the sensor.
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