藉由雙閘極製程改善成長於碳化矽基板上氮化鋁鎵/氮化鎵高速電子遷移率電晶體元件之線性度

Abstract

近年來，隨著無線通訊的快速發展，從衛星、汽車雷達、藍芽傳輸到多媒體娛樂，無線傳輸已經被廣泛的利用。然而在大量的使用者情形下，可用的低頻帶已經過度擁擠。為了要降低在開發高頻段上的花費，如何在最小的頻帶下，達成最大的資訊傳輸量，已經成為資訊傳輸技術中關鍵的課題。利用調變技術雖然可以在有限的頻帶下達到最大的資訊傳輸量，但也會造成雜訊的產生。因此對於無線傳輸系統，射頻功率放大器的線性度就成為一個重要性的指標。由於三五族氮化鎵材料的高電子遷移率以及高崩潰電場，氮化鎵高電子遷移率電晶體已在高頻及高功率應用方面展現極大潛力。 本研究先利用非線性電路模型來分析三階截斷點(IP3)與轉導值的關係式，分析製程對於元件特性的改善，以期能在線性度上的提升。接下來依據模擬結果，利用雙閘極製程，透過電子束寫系統，成功的製作出較高轉導跨壓的氮化鎵高電子遷移率電晶體，使元件展現出高線性度的特性。此研究比較了在低操作偏壓下(VDS=10V)使用此先進製程技術的氮化鎵雙閘極場效電晶體與未使用此製程的同等線寬元件，發現透過這些先進製程步驟，能使元件有展現更高的崩潰電壓、更高的轉導值、較佳飽和電流，以及較高的三階截斷點。

In recent years, wireless communication has rapid development, from satellite, automotive radar, bluetooth transmission to multimedia entertainment, the practice of wireless transmission has become widespread. However, due to a large number of users, the available frequency spectrum is over-crowed. In order to reduce the cost in the frequency spectrum, the maximum data transfer rate in minimum bandwidth is necessary. By using complex modulation, we can achieve maximum data transfer rate, but it also cause noise signal. Therefore the linearity of the RF power amplifiers is the one of the important parameters in the modern wireless communication system. GaN material have high electron mobility and high breakdown field which make it show a great potential in high frequency and high power application. In this study, first, using nonlinear circuit model to analyze relationship between the third-order intercept point (IP3) and transconductance. Then, analyzing the process to improve the element characteristics, with a view to enhance the linearity. Next, based on the relationships, the use of double gates process, through the electron beam lithography system, successfully producing a high linearity GaN high electron mobility transistors. This study compared this advanced process technology GaN double gates field effect transistor with the traditional devices with same gate length at low bias (VDS = 10V), found that through these advanced process steps, double gates devices can achieve the higher breakdown voltage, higher transconductance value, better saturation current, and high third-order intercept point (IP3).