T型閘極氮化鋁銦(鎵)/氮化鋁/氮化鎵高電子遷移率電晶體製作與特性分析;Fabrication and Characterization of T-gate AlIn(Ga)N/AlN/GaN High Electron Mobility Transistors

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Title:	T型閘極氮化鋁銦(鎵)/氮化鋁/氮化鎵高電子遷移率電晶體製作與特性分析;Fabrication and Characterization of T-gate AlIn(Ga)N/AlN/GaN High Electron Mobility Transistors
Authors:	林恩碩;Lin, En-Shuo
Contributors:	電機工程學系
Keywords:	氮化鎵高電子遷移率電晶體;T型閘極;氮化鋁銦鎵;基板寄生效應;電流截止增益;功率截止增益;GaN HEMT;T-gate;AlInGaN;substrate parasitic effect;fT;fmax
Date:	2018-11-09
Issue Date:	2019-04-02 15:06:40 (UTC+8)
Publisher:	國立中央大學
Abstract:	現今氮化銦鎵位障層高頻元件因具高二維電子氣且高輸出功率吸引很多團隊應用在高頻元件上。然而其仍受到介面粗糙度以及銦自聚效應等限制，因此發展四元氮化鋁銦鎵位障層，具較少的銦含量，減少銦原子的自聚效應，降低成分不均勻性，加入鎵原子可提高互容性，因此四元位障層具較佳的位障層磊晶品質。於元件結果顯示，四元氮化鋁銦鎵位障層具高能隙特性，在Lgd=2 µm、Lg= 400 nm之元件崩潰達到81 V較三元位障層57 V突出。高頻特性顯示三元與四元磊晶片fT/fmax分別為18/24.5 GHz與35.3/40.3 GHz，萃取小訊號參數發現氮化鋁銦鎵位障層具有較高本質轉導值。為提高元件高頻操作，閘極線寬須微縮，然而將遭遇閘極寄生電阻過大使功率截止增益受限。運用T型閘極的優勢降低閘極寄生電阻與閘極寄生電容，使用三層光阻ZEP-A7/LOR/ZEP-A7開發T型閘極，當閘極線寬由400 nm微縮至160 nm時，T型閘極微影製程需較佳的身寬比才能將金屬鍍完整。元件特性部分相同Lsd下，汲極飽和電流密度由522提升至893 mA/mm，轉導由287上升至370 mS/mm。高頻特性fT/fmax由35.3/40.3提高至83/95 GHz，主要和線寬微縮時本質轉導提升以及閘極寄生電容下降有關。閘極由400 nm微縮至160 nm，因金屬截面積的提高外部閘極寄生電阻由21歐姆降至7歐姆，成功顯示T型閘極製程效果。本論文成功驗證氮化鋁銦鎵材料與T型閘極優勢，適用於高功率放大器之應用。此外吾人考慮基板寄生效應，計算後並利用ADS模擬軟體在小訊號電路上扣除，得到最後的fmax為103GHz，顯示低阻值矽基板將會影響元件高頻特性。 ;Lattice matched Al0.83In0.17N/GaN high electron mobility transistors (HEMTs) have attracted a lot of interests as an alternative to the most matured AlGaN/GaN HEMTs for high power millimeter-wave devices because of its high density two dimensional electron gas (2DEG) at the heterointerface, even with sub-10 nm barrier. However, in spite of having such advantages over its AlGaN counterparts, it suffers from In segregation, compositional inhomogeneity and high off-state leakage current. AlInGaN/GaN HEMTs recently emerges as one of the promising candidate for mm-wave power applications. It is reported to have highest miscibility after AlGaN, among all the III-nitride materials. However, many of its properties and device performances are yet to be explored before its successful commercial deployments. This thesis aims at comparing the DC and RF performances of AlInN/GaN and AlInGaN/GaN HEMTs grown on 150 mm silicon (111) substrates. Devices fabricated with Lg= 0.4 µm/Lgd= 2 µm show off-state breakdown voltage of 81V and 57V with AlInGaN and AlInN barriers respectively. Furthermore, the AlInGaN/GaN and AlInN/GaN HEMTs with the same dimensions exhibit a current gain cut-off frequency (fT) of 35.3 GHz and 18 GHz and a power gain cut-off frequency (fmax) of 40.3 GHz and 24.5 GHz respectively. Extracted small signal parameters indicate, higher intrinsic transconductance (gmi) is one of the reasons for significantly higher fT/fmax in AlInGaN barrier HEMTs. Highly conductive T-gate with low input resistance and small footprint is desirable for devices operating at mm-wave frequency. However, it introduces additional gate parasitic capacitance, resulting lower fT. Therefore, highly optimized T-gates are needed to balance the fT/fmax ratio. A tri-layer photoresist of ZEP-A7/LOR/ZEP-A7 is developed to obtain high profile T-gates. The Idss increases from 522 mA/mm to 893 mA/mm, the transconductance increases from 287 mS/mm to 370 mS/mm and fT/fmax increase from 35.3/40.3 GHz to 83/95 GHz in AlInGaN HEMT by scalling down Lg from 0.4 µm to 0.16 µm. A reduction in parasitic gate capacitance and parasitic gate resistance from 21 ohm to 7 ohm may be attributed to the improved RF performances. This work further demonstrates that the AlInGaN/GaN HEMTs with highly optimized T-gates are excellent candidates for high power mm-wave applications. Furthermore, I consider substrate parasitic effect and remove substrate parasitic parameters by ADS simulation program. The extracted fmax is 103 GHz which indicated low resistivity silicon substrate will reduce high frequency result.
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