@article{azam_tanneeru_lee_misra_2020, title={Engineering a Unified Dielectric Solution for AlGaN/GaN MOS-HFET Gate and Access Regions}, volume={67}, ISSN={["1557-9646"]}, url={https://doi.org/10.1109/TED.2020.2969394}, DOI={10.1109/TED.2020.2969394}, abstractNote={Typically GaN metal-oxide-semiconductor heterojunction-field-effect transistors (MOS-HFETs) have used two separate dielectrics for the gate and access regions. However, as this article shows, with proper gate-stack engineering, a unified dielectric solution can be achieved for the transistor. HfO2 dielectrics were deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H2O) and ozone (O3). It was found that MOS-HFETs with O3 oxidant yielded lower threshold voltage ( ${V}_{\text {TH}}$ ) shifts, higher maximum drain current ( ${I}_{\text {DS,max}}$ ) of 340 mA/mm, 20% lower ON-resistance ( ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ ), higher peak transconductance at 112.66 mS/mm, lower hysteresis, and lower gate leakage ( ${5.4} \times {10}^{-{6}}$ A/cm2) compared to water oxidant based MOS-HFETs with ${I}_{\text {DS},\text {max}}$ of 240 mA/mm, 81.38 mS/mm peak transconductance, and ${1.7} \times {10}^{-{4}}$ A/cm2 gate leakage. DC/RF dispersion tests showed MOS-HFETs with O3 oxidant had ~200 $\times $ better current collapse recovery. Temperature characterization and reliability test results, such as high-temperature reverse bias (HTRB), are published for the first time on ALD-HfO2/AlGaN/GaN MOS-HFETs using tetrakis(dimethylamino)hafnium (TDMAH) and O3 precursor. Using an ozone oxidant provided more stability (i.e., less variability in ${R}_{ {\mathrm {\scriptscriptstyle {ON}}}}$ and ${V}_{\text {TH}}$ ) as a function of temperature. Finally, when devices were electrically stressed in the OFF-state, the HTRB test showed minimal ${V}_{\text {TH}}$ drift (<0.5 V) in the case of O3 oxidant versus much larger ${V}_{\text {TH}}$ drift (2.5 V) in the case of H2O oxidant.}, number={3}, journal={IEEE TRANSACTIONS ON ELECTRON DEVICES}, publisher={Institute of Electrical and Electronics Engineers (IEEE)}, author={Azam, Faisal and Tanneeru, Akhilesh and Lee, Bongmook and Misra, Veena}, year={2020}, month={Mar}, pages={881–887} }
@inproceedings{azam_lee_misra_2017, title={Optimization of ALD high-k gate dielectric to improve AlGaN/GaN MOS-HFET DC characteristics and reliability}, DOI={10.1109/wipda.2017.8170499}, abstractNote={This presents DC electrical characteristics and reliabilities of AlGaN/GaN metal-oxide-semiconductor heterojunction-field-effect transistors (MOS-HFETs) with HfO2 gate dielectric deposited by atomic layer deposition (ALD). Two types of oxidants were investigated, namely, water (H2O) and ozone (O3) for the ALD deposition. The comparison study reveals that GaN MOSHFETs with O3 oxidant results in overall better device performance and reliability than water based oxidant due to improved HfO2/GaN interface quality. For a 20nm ALD HfO2 gate dielectric, MOS-HFET with O3 oxidant has less threshold voltage (VTH) shift with respect to HFET (1.8V), higher transconductance (112.66 mS/mm), less on-resistance, and less gate leakage (5.4×10−6 A/cm2) compared to MOS-HFET with water oxidant where VTH shift with respect to HFET is 9.15V, transconductance is 81.38 mS/mm and gate leakage is 1.7×10−4 A/cm2. Moreover, significant improvement in device reliability (VTH shift is less than 0.5V) is observed with O3 oxidant at high-temperature reverse bias (HTRB).}, booktitle={2017 IEEE 5th Workshop on Wide Bandgap Power Devices and Applications (WIPDA)}, author={Azam, F. and Lee, B. and Misra, Veena}, year={2017}, pages={39–43} }