To determine the concentration of gases, including poisonous and explosive (oxygen, nitrogen, carbon dioxide, carbon monoxide, methane, etc.), gas sensors are used. They are optical, electrochemical, thermocatalytic, semiconductor. Semiconductor gas sensors have significant advantages, such as miniature and low power consumption. However, they also have a number of shortcomings, such as low sensitivity (ie they are able to react only to large gas concentrations) and low selectivity (ie, the sensor responds to the same gases in the same way). At present, scientific research is being carried out to increase operational Characteristics of semiconductor gas sensors. There are gas-sensitive thin-film semiconductor structures, which in their structure and principle of operation are identical to thin-film transistors (TFTs). To study the gas-sensitive characteristics of these structures, it is necessary to study the change in their current-voltage characteristics (VAC) in an atmosphere of different gases.
The problem or task
To carry out research work was necessary to develop a system for studying the electrical parameters of thin-film structures (TFT transistors) in the atmosphere of various gases.
To solve the problem, an experimental complex was developed for recording the volt-ampere characteristics of TFT transistors. The stand performs the following functions: generates the drain-source voltages with the possibility of setting the range and step and outputting the current value to the screen, generates the gate-source voltage with the possibility of setting the range and step and outputting the current value to the screen, registers the current of the conducting channel of the thin-film transistor, Resistance of the channel, stores the measurement results in a file for further processing. For measurements in the presence of gas, the sample is placed in a sealed box filled with gas. To construct the current-voltage characteristic, at a given voltage on the gate, a sequence of levels of drain-source voltages is generated according to the selected range and step, and for each set voltage, the corresponding channel current of the transistor is measured. After passing the entire range of the specified drain-source voltages, the system changes the gate-source voltage according to the selected range and step, and the process is repeated. The software is developed in NI LabVIEW programming environment using NI DAQmx, NI DCPower and NI DMM drivers. The complex is built on the basis of a PXI-1031 chassis with a PXI-8108 controller. The chassis also includes a multi-function module PXI-6238, power supply PXI-4132 and multimeter PXI-4071. As a result, a complex has been created that allows to automate the process of registering the I-VTC of TFT transistors, to shorten the time of one change and to conduct a series of scientific experiments in a short time.