Junctionless sub-micron silicon wire device fabricated by atomic force microscope lithography and electrically characterized for gas sensing application at room temperature

Fabrication of junctionless sub-micron silicon wire based device using atomic force microscope lithography was presented in this article. The fabricated device consisted of two adjacent probing pads which served as probing pads during electrical characterization. This adjacent probing pads were connected with two parallel sub-micron silicon wires. P-type silicon-on-insulator wafer was used as a raw material in the experiment. The sub-micron silicon wires width between 207 nm and 233 nm was successfully fabricated by means of the aforementioned technique. The fabrication process was conducted in the temperature between 21 °C and 27 °C and relative humidity between 50 % and 70 %. The process was operated in contact mode using standard commercial atomic force microscope without any modification. In addition, 9.0 V of applied voltage and 2 μm/sec of writing speed were used to perform the fabrication process. The fabricated device was realized using wet chemical etching process which involved the usage of tetramethylammonium hydroxide and hydrofluoric acid solution. The bare device was electrically characterized using semiconductor parameter analyzer and the signal was recorded in form of current-voltage characteristic. From the current-voltage characteristic, the fabricated junctionless sub-micron silicon wire device behaved as a resistor where there was a current flow from one contact point to another. To prolong the functionality of the fabricated junctionless sub-micron silicon wire device, the device was tested under gaseous environment at room temperature. Carbon dioxide and nitrous oxide gas were chosen as target gases in the experiment. These two gases were classified as oxidizing agents and act as holes donor to the sub-micron silicon wire device. The current of the fabricated device was decreased upon exposure to both target gases compared with before target gases exposure. In other words, the device resistivity was increased when the t- rget gases were introduced to the fabricated device. Furthermore, the target gases behaved as a chemical gate to the junctionless sub-micron silicon wire device in this study. In addition, applying the target gases (holes donor) to the p-type junctionless sub-micron silicon wire was comparable to applying positive gate voltage to the p-type semiconductor which caused depletion of mobility carrier and reduced the p-type device current. Therefore, the decrease of current value of junctionless sub-micron silicon wire device was expected and observed for this study. In term of sensitivity, the sensitivity of fabricated junctionless sub-micron silicon wire device was 65 % and 57 % when the device was exposed to 9 sccm of carbon dioxide gas and 8 sccm of nitrous oxide gas, respectively. The response and recovery time was observed to be less than one minute for both target gases study.