一體整合之具無線閘極結構的非晶氧化銦鎵鋅薄膜電晶體之研究

Abstract

本研究以自製線圈、蕭基二極體搭配電容完成無線感應整流結構，製作出具無線供電之閘極結構的非晶氧化銦鎵鋅薄膜電晶體。研究過程中先將線圈、蕭基二極體與非晶氧化銦鎵鋅薄膜電晶體單獨製作於玻璃基板上，確認個別元件的製程參數後，再進行整合元件的製作，最後量測無線感應輸出電壓值與具無線供電之閘極結構的非晶氧化銦鎵鋅薄膜電晶體的輸出與轉換特性曲線。 在單獨於玻璃基板上製作的元件中，自製傳輸與接收線圈外邊長皆為2 cm以達到較佳的感應效果並降低達到最大感應峰對峰電壓值所須施加的訊號頻率。製作蕭基二極體時藉由固定接面有效面積為'20×30' 〖'μm' 〗^'2' 、紫外光臭氧處理鎳金屬表面的時間為5 min，非晶氧化銦鎵鋅薄膜厚度80 nm、退火溫度為200℃於空氣中，可獲得電流整流比為2.22 × 104、理想因子為1.22、蕭基能障高度為0.68 eV的電性表現。製作非晶氧化銦鎵鋅薄膜電晶體時，藉由於空氣與氮氣中進行兩次退火搭配鈍化層沉積，可將薄膜電晶體的臨界電壓降低至2.01 V、場效載子遷移率為7.2 cm2V-1s-1、次臨界擺幅為0.228 V/dec.、電流開關比為1.4 × 108。 最後將接收線圈、蕭基二極體、電容與非晶氧化銦鎵鋅薄膜電晶體於玻璃上進行一體整合，製作出具無線供電之閘極結構的非晶氧化銦鎵鋅薄膜電晶體，並量測其輸出與轉換特性曲線。在輸入給傳輸線圈的弦波振幅為20 VPP、頻率為4 MHz的情況下，經接收線圈感應與蕭基二極體及電容整流後，可供給約1.5 V的近似直流電壓至薄膜電晶體的閘極。整合元件中的薄膜電晶體其電性表現與單獨於玻璃基板上製作時相比下降許多，臨界電壓下降至-0.254 V 使電晶體操作模式自增強型轉為空乏型，場效載子遷移率下降至6.4 cm2V-1s-1，次臨界擺幅上升至0.529 V/dec.，惟電流開關比提升至1.2 × 108，推測原因為薄膜電晶體結構乃於線圈的二氧化矽、氮化矽絕緣層上製作，在後續的退火步驟中，或許有部分成分在加熱過程中向上移動，對薄膜電晶體電性表現造成影響。

In this work, an amorphous indium gallium zinc oxide (a-IGZO) thin film transistor (TFT) with wireless power supply to the gate electrode was fabricated utilizing a handmade coil, a Schottky diode, and a capacitor as the wireless rectifier structure. The coil, Schottky diode, and a-IGZO TFT were first individually fabricated on glass substrate to verify the proper fabrication parameters before monolithically integrating the components. After monolithic integration of the components, the output rectified voltage of the wireless rectifier structure, and both the output and transfer characteristics of the a-IGZO TFT were investigated. After process parameter optimization of the individual components, the physical and functional characteristics of the components were measured. Using a coil with outer side length of 2 cm gave a better coupling effect, and lowered the signal frequency needed to supply the transmit coil. The contact area, duration of UV-Ozone treatment on Ni surface, thickness of the a-IGZO layer, annealing temperature, and gas environment of Schottky diode were determined as 20×30 μm2, 5 min, 80 nm and 200℃ in air. The rectification ratio for the obtained Schottky diode, was 2.22 × 104, with an ideality factor of 1.22 and Schottky barrier height of 0.68 eV. When fabricating the a-IGZO TFT, the threshold voltage was adjusted to 2.01 V by annealing in the air and N2 and depositing an SiO2 film as a passivation layer. The field effect mobility, subthreshold swing, and on/off current ratio of the fabricated a-IGZO TFT were 7.2 cm2V-1s-1, 0.228 V/dec, and 1.4 × 108. Finally, after monolithic integration of the coil, Schottky diode, capacitor, and a-IGZO TFT on glass substrate, an a-IGZO TFT with wireless power supply to gate electrode was fabricated. The output rectified voltage, transfer characteristics, and output characteristics of measured on the completed device. When supplying the transmit coil with 20 VPP, 4 MHz sinewave, the gate of a-IGZO TFT received about 1.5 V approximate DC signal after coil induction and rectification by the Schottky diode and capacitor. After monolithic integration, we observed that the performance of the a-IGZO TFT declined compared to components fabricated on glass, individually. Nevertheless, the on/off current ratio rose to 1.2 × 108, the field effect mobility decreased to 6.4 cm2V-1s-1, the subthreshold swing rose to 0.529 V/dec, and the threshold voltage decreased to -0.254 V, causing the operation mode of the a-IGZO TFT to change from enhancement to depletion mode. The cause was speculated to be that the a-IGZO TFT fabricated on the insulating layer of coil consisted of SiO2 and SiNX, and some constituents may have moved upward in the subsequent annealing process, ultimately affecting the electrical properties of the a-IGZO TFT.