Investigation of Deep Submicron Metamorphic HEMTs and Application on Monolithic Microwave Integrated Circuits
| Autor: | Cheng-Kuo Lin, 林正國 |
|---|---|
| Rok vydání: | 2004 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 93 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. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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