| 摘要: | 高速電子移導率電晶體設計概念在1978年被提出，而進一步在1980年利用砷化鋁鎵/砷化鎵(AlGaAs/GaAs) 化合物材料系統成功實現此設計概念。為了進一步提升元件特性，在1985年提出了砷化鎵基板上(GaAs substrate)虛擬式通道(pseudomorphic channel)之概念，使用銦含量最高百分之二十之砷化銦鎵(InGaAs)高電子移導率之材料，進一步提升元件傳導帶之不連續性(Conduction-band discontinuity)，與元件直流與高頻之特性。另一方面在磷化銦(InP)基板上利用晶格常數與高銦含量之砷化銦鎵之材料相近之優點，成長銦含量高達百分之五十之砷化銦鎵之材料，元件高頻特性更可進一步提升。 然而，磷化銦基板機械強度不足，使得基板面積受限於4吋基板，在量產製程上導至良率與價格上受限，因此在砷化鎵基板上成長高銦含量之砷化銦鎵為高速電子移導率電晶體發展之方向。在1989年Alain Cappy提出了在砷化鎵基板上利用變晶式(metamorphic)分子束磊晶式成長技術，成功磊晶高銦含量之砷化銦鎵之材料系統。因此在本論文中是研究在砷化鎵基板上利用變晶式(metamorphic)成長之砷化銦鋁/砷化銦鎵 (InAlAs/InGaAs) 化合物材料系統高電子移導率場效應電晶體。進一步利用磊晶的技術，與製程方法進一步提升元件直流、高頻、崩潰電壓與微波功率特性。 在第二章中，我們與博達科技(Procomp Informatics) 合作利用分子束磊晶技術，在砷化鎵基板上成長變晶式(metamorphic)層，並結合虛擬式通道(pseudomorphic channel)磊晶技術，進一步增加元件砷化銦鋁/砷化銦鎵(InAlAs/InGaAs)傳導帶之不連續性(Conduction-band discontinuity)，電子移導率(electron mobility)。在與傳統晶格常數相通之電晶體比較下元件高頻及功率特性進一步提升。 傳統上提升場效應電晶體特性之方法，就是縮短閘極長度，提升元件高頻特性，因此在第三章，我們改變不同閘極長度在砷化銦鋁/砷化銦鎵(InAlAs/InGaAs)變晶式電晶體上，分析元件短通道效應，與元件傳輸時間之特性，並進一步萃取傳導電子在電子通道層中之飽和速度。另外一方面，我們發展完整的單晶微波積體電路之製作流程，並成功製作出全國學術界第一個次微米變晶式電晶體毫米波積體電路，其中包含了高隔離度之分佈式微波開關以及Ka頻段二級增益放大器。 在第四章中，我們發展出利用閘極高溫滲透之製程方法，改變元件臨界電壓，使得空乏型元件成為增強型元件，並利用小訊號模型之分析方法，研究高頻特性提升之原因。另外，我們開發出只需要一次電子束微影技術，同時達成不對稱之蝕刻與Gamma Gate之閘極外型，使用元件崩潰電壓進一步提升，進一步提升微波功率特性。而在最後一章結論中，整理及歸納出前三章之實驗結果與重點。 The development of HEMTs started in 1978, immediately after successful experiments on modulation-doped AlGaAs/GaAs heterostructures, which revealed the formation of a two-dimensional electron gas (2DEG) with enhanced electron mobility. Earlier HEMTs utilized the AlGaAs/GaAs system, which was the most widely studied and best understood heterojunction system at that time. In the mid 1980s, in order to further improve device characteristics, the AlGaAs/InGaAs pseudomorphic HEMTs and high indium composition of InAlAs/InGaAs on GaAs and InP substrates had been realized owing to the higher conduction band offsets considerably, and excellent electron transport characteristics. However, the AlGaAs/InGaAs pHEMT, In content is restricted to 20-25% to preserve high layer quality. Therefore, the conduction band discontinuity is limited. In addition, InP substrates are available only in small diameters, which make it hard to compete with the cost per chip of GaAs transistors fabricated on 6-inch wafers. Therefore it would be desirable to find a way to fabricate high performance transistors with high In-content channel on the less brittle and larger diameter GaAs substrates. The answer to this is the concept of fabricating metamorphic GaAs HEMTs (GaAs mHEMT). The primary propose of this dissertation is to enhance the InAlAs/InGaAs metamorphic buffer HEMTs performance using molecular beam epitaxial (MBE) techniques, advanced lithography technology and novel fabrication process. In chapter Ⅱ, we used the metamorphic In0.5Al0.5As buffer layer by inserting an pseudomorphic channel (PC) layer to improve device dc and rf performance, which is compared with the lattice matched (LM) In0.5Ga0.5As/In0.5Al0.5As mHEMTs. In recent years, millimeter wave circuit and device technologies are very attractive, which provide a broadband capacity to meet the increasing demands on the wireless mobile communication. Submicron gate-length devices are therefore required to improve the device gain, noise, and power performance. In chapter Ⅲ, in order to characterize and compare the device performance of submicron In0.5Al0.5As/In0.5Ga0.5As mHEMTs, devices with gate-lengths ranging from 0.25-μm to 0.6-μm, written by the e-beam lithography system, were fabricated. The dc, rf, and delay time analysis of these devices will be presented. In addition, we proposed fully process flows of monolithic microwave circuits, which includes high isolation distributed switch and Ka-band two-stage gain amplifier. In this chapter Ⅳ, we developed two device fabrication techniques to improve the InAlAs/InGaAs metamorphic HEMTs dc and rf characteristics without any device structure modification. Firstly, we realized the enhancement-mode (E-mode) InAlAs/InGaAs metamorphic HEMT’s on GaAs substrates by using the thermally annealed Schottky metal diffusion approach so as to further improve rf performance compared with pre-anneal devices. Secondly, we proposed a novel electron beam lithography process flow, which combine an asymmetric wide recess in conjunction with a gamma gate (AG), applying to the fabrication of InAlAs/InGaAs metamorphic HEMTs. The fabricated device using this technique demonstrates the improved off-state breakdown voltage and the reduced impact ionization as compared with the conventional T-gate process. In the final chapter, we summarize the results obtained in this thesis. |
