Abstract
ABSTRACT In this study, the ammonia gas (NH3) resister type rapid sensor system based on ultrathin (~10 nm) indium nitride (InN) epilayers has been fabricated and demonstrated, and the system applies to the liver lesion diagnosis by detecting sub-ppm lever Volatile Organic Compounds (VOCs) gas: NH3 concentration in human breath. Considering the restriction of the individual respiratory and circulatory system, it is a major challenge to design a system that can practically sense the gas concentration in the patient’s breath. In this article, this gas diagnosis system of liver lesion is discussed mainly in two aspects: first, the improvement of the sensing characteristics of the ultrathin InN sensor itself; and second, design optimization of the measurement system. An annealing process and second heater unit are used in the experiment to improve the characteristics of the ultrathin InN epilayers. An annealing treatment at a 200 ℃ will increase the response of the InN sensor by 6 times, on average, and the drift current of the InN sensor decreases from 6.8% to 1.8%. In addition, the system will be able to increase the current response of the InN sensor and reduce the response time required to reach a stable condition, which increases the response variation by 4 times (from 0.5% to 2%) and reduces the time required to reach stable response by 1.74 times (from 1,011 to 579 seconds). However, through the fitting method, new design only need 30 seconds (15 values) fast to estimate the correct gas concentration by gradients. In system design, the system where the volume of the required patient’s gas sample to be tested is reduced to one tenth of the original volume (from 100 to 9.8125 ml), and a set of Computational Fluid Dynamics (CFD) software from SolidWorks Flow Simulation is used for trajectory simulation of gas molecules in the sensing chamber. In addition, with the valve pump system design and the application of the oxygen oxidation mechanism, the detection process has been successfully reduced by 13 times to a remarkable one of 15 minutes for system stabilization, 1 minute for gas response, and 1 minute for system recovery. Keywords: indium nitrite, InN, ammonia, gas sensor, liver