Thin Film Based Gas Sensor for Diabetes Mellitus Applications

Abstract

Diabetes or diabetes mellitus is a group of metabolic diseases in which the level of glucose rises in the human body. This disease results from imperfections in insulin secretion or insulin action in the body. Diabetes can be very dangerous and may even lead to long term damage, non-functioning of organs like heart, kidney and blood vessels. Detection of such a disease is very essential for early treatment. People have been monitoring the glucose level through blood by means of invasive methods. On the contrary, breath analysis has gained recent interest for detection of diabetes. Acetone has been stated to be the biomarker for diabetes mellitus. Breath analysis is a non-invasive method which can be used to detect acetone levels in human breath. For a healthy individual, the level of acetone in breath is less than 0.8 ppm, while it ranges from 1.7 ppm to 3.7 ppm for a diabetic individual. Acetone in breath is found due to the excess formation of ketone bodies in the human body. For detection of diabetes through breath, a very low concentration of 1.7 ppm had to be detected in breath. For this purpose, metal oxide thin films had been considered. A metal oxide gas sensor can be of high importance for the same, since it has been proven that the resistance/electrical conductivity of metal oxides varies when the concentration of surrounding gas changes. MEMS technologies had been used to develop a miniaturized thin film based gas sensor. Four metal oxide thin films, viz., tungsten dioxide (WO2), tungsten trioxide (WO3), tin dioxide (SnO2) and tin-doped tungsten oxide (Sn-doped WO3) were investigated to find the best for detection of acetone gas. After standard cleaning procedure of n-type silicon wafers, a 1 and#61549;m thick layer of silicon dioxide (SiO2) was deposited over them by means of thermal oxidation. 100 nm thin layer of each WO2, WO3, SnO2 and Sn-doped WO3 were deposited over four different oxidized silicon wafers by means of reactive ion sputtering technique. For deposition of WO2, the ratio of argon gas to oxygen