Browsing by Author "Hsu, Shawn S. H."

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Impacts of gate recess and passivation on AlGaN/GaN high electron mobility transistors
(2007-02-01)
Chan, Chih-Yuan
;
Lee, Ting-Chi
;
Hsu, Shawn S. H.
;
Chen, Leaf
;
Lin, Yu-Syuan
In this study, the impacts of gate recess and passivation on AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. The trap-related characteristics were studied in detail by several different measurements including dc current-voltage, cur-rent collapse, gate lag, and flicker noise characterizations. With a Cl-2/Ar-recessed gate, drain current collapse factors (Delta I-max) of similar to 37.5 and similar to 6.9% were observed before and after SiN passivation. The gate lag measurements showed that the lagging phenomena almost disappear with SiN passivation for both Cl-2- and Cl-2/Ar-recessed devices. However, the flicker noise measurements revealed distinct noise levels of devices with different processes even after passivation. As the gate voltage (VG) changed from 2 to -4V, the devices recessed by Cl-2 exhibited lower drain noise current densities (S-ID/I-D(2) ranging from 2.8 x 10(-14) to 1.7 x 10(-12) Hz(-1) at 1 kHz) than those etched by Cl-2/Ar mixture gas (S-ID/I-D(2) ranging from 6.3 x 10(-14) to 6.0 x 10(-12) Hz(-1) at 1 kHz), whereas the devices without the recess process showed the lowest noise levels (S-ID/I-D(2) ranging from 2.8 x 10(-15) to 1.3 x 10(-13) Hz(-1) at 1 kHz). It was found that S-ID/I-D(2) increased monotonically when V-G changed from 2 to -4V. A bias dependence of the 1/f(gamma) slope gamma was observed, and a relatively large variation in the range of similar to 1.1 to 1.6 was found for devices recessed by Cl-2/Ar mixture gas. The number fluctuation model was employed to explain the observed trends. The results also indicated that the surface traps play an important role in these devices.
Square-Gate AlGaN/GaN HEMTs With Improved Trap-Related Characteristics
(2009-12-01)
Lin, Yu-Syuan
;
Wu, Jia-Yi
;
Chan, Chih-Yuan
;
Hsu, Shawn S. H.
;
Huang, Chih-Fang
In this brief, the trap-related characteristics of high-breakdown AlGaN/GaN high-electron-mobility transistors (HEMTs) were investigated. Compared with a conventional multifinger layout, the square-gate design presented reduced the current collapse from 19% to 6% and almost eliminated the gate lag. The flicker noise density and the gate leakage decreased from 1.16 x 10(-10) to 1.17 x 10(-11) 1/Hz (f = 100 Hz) and from 7.36 x 10(-5) to 1.80 x 10(-6) A/mm (V(GS) = -4 V and V(DS) = 100 V), respectively. The breakdown voltage was also improved from 350 to 650 V. With the channel area away from the defects generated by the mesa etching process, the square-gate AlGaN/GaN HEMTs demonstrated excellent performance with much less trapping effects.