二氧化鈦膜為一高介電係數材料，並在加入鋇形成鋇摻雜二氧化鈦膜之後會增加其介電係數，因此我們研究以液相沉積法來成長鋇摻雜二氧化鈦膜，並應用於氮化鎵材料上製作氮化鋁鎵/氮化鎵金氧半高電子遷移率電晶體。液相沉積法為一相當低成本且容易使用之氧化層沉積技術，並可於室溫下使用。經由X光譜儀與二次離子質譜儀，可確定鋇摻雜二氧化鈦膜已沉積於氮化鎵材料上，並透過掃描電子顯微鏡及原子力顯微鏡來觀察薄膜的表面狀態。沉積的速率約可達到每小時76奈米，當我們成長76奈米厚的氧化層時，氧化層漏電流密度可達到3.5×10-7A/cm2而電場約為-6MV/cm，崩潰電場則可以達到-9.7MV/cm以上。在經過高純度氮氣環境下的退火處理後，藉由X光繞射我們觀察到鋇摻雜二氧化鈦氧化層由非晶相轉換至金紅石相且結晶顆粒增大，表面粗糙度也有所改善。在經過150℃退火處理後，鋇摻雜二氧化鈦氧化層漏電流密度可達到2×10-8A/cm2而電場約為-4MV/cm，崩潰電場則可以達到-13MV/cm。與液相沉積之二氧化鈦膜相較，不但具有較高介電係數，也能提升介面品質。
在元件應用方面，我們成功利用液相沉積法沉積鋇摻雜二氧化鈦薄膜,並將經過150℃退火後的氧化層應用於氮化鋁鎵/氮化鎵高電子遷移率電晶體形成金氧半高電子遷移率電晶體。與傳統高電子遷移率電晶體比較，金氧半高電子遷移率電晶體最大汲極電流由495 mA/mm 提升到815 mA/mm，最大轉導由150 mS/mm降到130 mS/mm，此外金氧半結構閘極漏電流可以改善超過8千倍，亦可改善次臨界電壓特性，另外，我們亦藉由比較脈衝量測的結果，顯示金氧半結構表面狀態被鈍化層所抑制，進而抑制電流坍塌現象。

Utilizing titanium dioxide as the high-k material constant for dielectric applications, it has been found that dielectric constant can further increase by incorporating barium. In this thesis, Ba-doped TiO2 film is prepared through liquid phase deposition and used as gate dielectric in AlGaN/GaN MOS-HEMT. Liquid phase deposition provides a low-cost and low-complex method in forming oxide layers at room temperature. XPS and SIMS are used to demonstrate that Ba-doped TiO2 film could be deposited successfully on GaN materials. SEM and AFM are also used to observe the surface of the Ba-doped TiO2 film. The deposition rate is about 76 nm/hr. The leakage current is about 3.5×10-7A/cm2 at -6 MV/cm; in addition, the breakdown field is more than -9.7 MV/cm when the oxide thickness is 76 nm. Upon annealing under an atmosphere of high purity N2, the crystal phase of the Ba-doped TiO2 transformed from amorphous to rutile phases accompanied by an increase in crystal size. Surface roughness also improved significantly after thermal treatment. The leakage current is about 2×10-8A/cm2 in a -4 MV/cm electric field, and the breakdown field reached -13 MV/cm after annealing at 150℃ for 30 minutes. Compared with the LPD-TiO2 film, Ba-doped TiO2 film demonstrated higher dielectric constant and better interface quality.
The AlGaN/GaN MOS-HEMT with a liquid phase deposited Ba-doped TiO2 annealed under 150 ℃ as gate insulator is fabricated successfully. Compared with the conventional HEMT, the maximum drain current density increases from 495 mA/mm to 815 mA/mm, whereas the peak extrinsic transconductance increased from 150 mS/mm to 130 mS/mm in the MOS-HEMT structure. The gate leakage current density improved significantly by nearly 8000 times after the insertion Ba-doped TiO2 insulator between gate and channel in MOS-HEMT. Pulse measurement indicates that the MOS-HEMT structure can reduce the effect of the surface state and suppress the current collapse.

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