Gas sensors are used to determine the concentration of gases, including toxic and explosive (oxygen, nitrogen, carbon dioxide, carbon monoxide, methane, etc.). They are optical, electrochemical, thermocatalytic, semiconductor. Semiconductor gas sensors offer significant advantages such as small size and low power consumption. However, they also have a number of disadvantages, such as low sensitivity (i.e., they are able to respond only to high gas concentrations) and low selectivity (i.e., the sensor responds equally to several gases). Currently, 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 (TFT). To study the gas-sensitive characteristics of these structures, it is necessary to study the change in their current-voltage characteristics (CVC) in the atmosphere of various 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 current-voltage characteristics of TFT transistors. The stand performs the following functions: generates drain-source voltages with the ability to set the range and step and display the current value on the screen, generates gate-source voltages with the ability to set the range and step and display the current value on the screen, registers the current of the conductive channel of the thin-film transistor, and measures channel resistance, saves the measurement results to a file for subsequent processing. For measurements in the presence of gas, the sample is placed in a sealed box filled with gas. To build the I - V characteristic, at a given gate voltage, a sequence of drain-source voltage levels is generated according to the selected range and step, and the corresponding transistor channel current is measured for each set voltage. After passing the entire range of predetermined drain-source voltages, the system changes the gate-source voltage according to the selected range and step, and the process is repeated. The software was developed in the NI LabVIEW programming environment using the 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 PXI-6238 multifunction module, a PXI-4132 power supply, and a PXI-4071 multimeter. As a result, a complex has been created that makes it possible to automate the process of registering the I - V characteristic of TFT transistors, to reduce the time of one change, and to conduct a series of scientific experiments in a short time.