微波電路 / 期中報告

1. 微波電路/期中報告 A Novel Manufacturing Process of AlGaN/GaN HEMT for X-Band High-Power Application on Si (111) Substrate Cong Wang, Ram Krishna Maharjan, Sung-Jin Cho, and Nam-Young Kim Proceedings of APMC 2012 報告人: 碩研電子一甲 MA130224 李堅誌 Southern Taiwan University Department of Electronic Engineering

2. Abstract • In this paper, successful operation at 10 GHz of 0.5 μm gamma gate AlGaN/GaN high electron mobility transistor (HEMT) is demonstrated on Si (111) substrate. • Various material and processing approaches regarding double surface passivation and post-gate annealing processes are evaluated in terms of device performances. • In order to achieve better immunity to current collapse effects, we conducted experiments that investigate the relationship between the HEMTs electrical characteristics and different passivation films (SiNx or SiO2) using plasma-enhanced chemical vapor deposition (PECVD).

3. Double Surface Passivation Process • The typical I-V output and transfer characteristics of these three AlGaN/GaN HEMTs are shown in Fig. 1 (a) and (b), respectively. Samples A and B exhibit better saturation and pitch-off characteristics than the unpassivated HEMT. • They yielded a maximum saturation current density (IDS max) of 643 and 540 mA/mm, respectively, showing 40% and 17% increases relative to that found for the unpassivated HEMT. Fig. 1. (a) I-V characteristics with varying gate biases, and (b) the transfer characteristics of the SiNX/SiNX-passsivated HEMT and SiO2/SiO2-passivated HEMT compared to the unpassivated HEMT.

4. The I-V output and transfer characteristics of the two type AlGaN/GaN HEMTs are shown in Fig. 2 (a) and (b). An increase in the IDS max (16%) from 643 mA/mm to 750 mA/mm and the gm max (10%) from 200 mS/mm to 220 mS/mm can be observed after the post-gate N2 RTA treatment. • enhancement of these DC characteristics is primarily cause by the RTA process, which reduces the electrically active states at the Schottky metal/AlGaN interfaces. Fig. 2. (a) I-V characteristics with varying gate biases, (b) transfer characteristics

5. After the N2 annealing treatment, the gate-drain breakdown voltage of the HEMTs increased from 113 V to 141 V. increase in the breakdown voltage. • This increase of breakdown voltage is due to the decrease of the gate leakage current. An increase of the forward gate threshold voltage to 2 V has been verified in Sample D. The focused ion beam (FIB) photographs of the cross-sectional gamma gate with double surface passviation structure are shown in Fig. 2 (d) and (e). (c) the gate-drain breakdown voltage of the SiNX/SiNX-passsivated HEMT using post-gate N2 RTA treatment compared to the as-fabricated HEMT, (d) the cross-sectional FIB image of the proposed HEMT, and (e) the enlarged gamma gate with the proposed double passivation structure.

6. Results And Discussions • Fig. 3 (a) shows an optical micrograph of a fabricated 200 μm twofinger freestanding HEMT with a gate length of 0.5 μm, a drain-gate space of 2.5 μm, and a gate-source space of 1 μm. • Fig. 3 (b) shows the short circuit current gain (|h21|) and the maximum stable gain (MSG) for the device with 2 × (200 × 0.5) μm2 gate periphery. The fT and fMAX are determined by the |h21| and the MSG, respectively. The extrinsic fT and fMAX are 24.6 GHz and 45.4 GHz respectively at VDS = 10 V and VGS = -3 V.

7. Large signal measurements have been performed using a load-pull system at 10 GHz. The device was biased at a drain bias of 30 V. • The measured input power (Pin) against the output power (Pout) responses of the device is illustrated in Fig. 3 (c), which illustrates an output power density of 5.8 W/mm, a peak PAE of 51% at 21 dBm Pin with a linear gain of 14.4 dB and a power gain of about 13.68 dB.

8. Conclusion • This paper presents the state-of-the-art results obtained by 0.5 μm gamma-gate AlGaN/GaN HEMTs fabricated on Si (111) substrates. • In order to meet the performance improvement requirements needed for high power applications, these optimized solutions which enhance the characteristics and reduce the cost of HEMTs on Si substrates are proposed. • Excellent performances have been achieved for 0.5 μm gate-length HEMTs. The maximum output power density of 5.8 W/mm is achieved, with an associated power gain of 13.68 dB and a maximum PAE of 51%. Due to these results, this manufacturing process is shown to be an optimal solution for fabricating HEMTs in X-band high-power applications.

9. 心得: 看完這篇ppt後發現跟我目前在做的薄膜有些許相同，不過我們是利用氧化物。這則是一種新製程利用氮化矽，它還利用退火使他的輸出電流電壓，傳輸特性更好，目前我也是利用退火來觀察我的薄膜特性，提高他的耐久。