Promotie R. Sokolovskij: gassensor

10 december 2019 12:30 - Locatie: Aula, TU Delft - Door: webredactie

AlGaN/GaN high electron mobility transistor (HEMT) based sensors for gas sensing applications. Promotor 1: Prof.dr. G.Q. Zhang (EWI).

Since the first demonstration of a silicon field effect transistor based hydrogen (H2) gas sensor gate numerous modifications were developed in order to expand this technology towards wider range of gases. The maximum operating temperature of these sensors is however limited by the low energy bandgap of silicon. Wide bandgap gallium nitride (GaN) is a highly chemically stable semiconductor suitable for harsh environment applications. Due to strong spontaneous polarization effects of GaN, when a heterojunction of AlGaN/GaN a highly conductive electron channel, called the two-dimensional electron gas (2DEG) is formed at the interface. Transistors that utilize the 2DEG are known as high electron mobility transistors (HEMT). The objective of this research project is to develop a gas sensor based on AlGaN/GaN HEMT.

The fabrication process of GaN HEMTs differs significantly from Si transistors. The sensor designs were made and fabricated in the university cleanroom and necessary processes characterized. The fabricated sensors were successfully applied to detect H2, H2S and NO2 down to low part per million to part per billion levels. Etching a recess of 5 to 15 nm under the gate electrode was investigated to enhance the sensing performance of H2. To obtain such shallow etching depth a cyclic plasma oxidation and chemical etching was developed. Sensing response magnitude was improved by 11x compared to reference sensor, the response time decreased by 3x and the power consumption was reduced by 50x.

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