應用在無線通訊之低雜訊磷化銦鎵/砷化銦鎵假晶式高電子遷移率電晶體的高線性度之研究發展

Abstract

本篇論文主要目的在於發展應用於無線通訊之低雜訊磷化銦鎵/砷化銦鎵假晶式高電子遷移率電晶體之高線性度研究。 本次實驗在傳統矽平面摻雜元件結構的通道(channel layer)區域中加入微量的雜質濃度摻雜，使得電子在元件通道層中的分布更為均勻及對稱，以期望在不同的閘極偏壓條件下得到較為平坦的轉導值(Transconductance)分布曲線，改善磷化銦鎵/砷化銦鎵假晶式高電子遷移率電晶體的線性度表現。 同時，本研究另外於傳統矽平面摻雜元件結構的磷化銦鎵-蕭特基 層(Schottky layer)中摻雜均勻的雜質濃度以改善元件線性度。此經由均勻摻雜後的磷化銦鎵層可以提升蕭特基接面的費米能階(Fermi level)準位，使元件的轉導值曲線分布(Transconductance)更為平坦，進而獲得較高的輸出三階交叉點功率(OIP3)。 經由等效電路分析理論及量測結果的驗證下，上述的元件結構設 計具有高三階交叉點功率，顯示出其在線性度上的表現獲得顯著的改善。此外，這兩個元件結構所具有的高三階交叉點功率對直流功率比值(IP3/PDC)同時顯示出其在低電壓-高線性度之無線通訊系統的應用上具有卓越的發展潛能。

The purpose of this dissertation is to develop the low noise InGaP/InGaAs PHEMTs with high linearity for wireless communications application. A novel lightly-doped channel approach for linearity improvement of InGaP/InGaAs pseudomorphic high-electron-mobility transistor (PHEMT) device was presented. Light doping in the channel region of the conventional δ-doped InGaP/InGaAs PHEMT was adopted to provide a uniform and symmetric electron distribution in the channel region to achieve flat extrinsic transconductance (Gm) distribution under different gate bias conditions. Another device structure with a uniformly-doped Schottky layer added to the conventional δ-doped InGaP/InGaAs PHEMT to improve device linearity was also studied it this dissertation. This added uniformly doped layer raises the Fermi level of the Schottky layer of the device which in turn contributes to a flatter extrinsic transconductance (Gm) profile, resulting in higher third order intercept point (IP3) . The devices structure were determined based on the third-order intercept point (IP3) performance analysis through simple equivalent circuit model of the device, and the results showed substantial linearity improvement evidenced by much higher IP3. Furthermore, the very high IP3 to PDC ratio of the devices developed will be of great potential for low-voltage high-linearity applications in wireless communications systems.