一種用於氧化鎵微結構陣列切割的非等能量雙電阻電容放電電源研製

Development of a dual-resistance-capacitance discharge power source with non-equal energy applied to β-Ga2O3 microstructure array cutting

陳世耀(Chen Shih-Yao)

指導教授 ： 陳順同

國立臺灣師範大學/科技與工程學院/機電工程學系/碩士(2021年)

https://doi.org/10.6345/NTNU202101239

摘要

本研究旨在開發一種「非等能量雙電阻電容放電電源」，並應用於氧化鎵高深寬比微細結構陣列的加工研究。氧化鎵係由氧原子與鎵原子化合而成的寬能隙半導體材料，廣用於高功率元件，具高硬度與高脆性，不易切削加工，目前多以蝕刻方式成形，但蝕刻速度慢，且不易成形高深寬比結構。寬帶隙材料可降低能耗，降低能耗不僅減少了功率損耗，且可使系統微小化，與矽的解決方案相比，降低了成本。不過，常溫狀態下，材料能隙愈大，絕緣性愈高，因此本研究以歐姆接觸原理，於氧化鎵表面製作導電電極，使其呈現微弱導電特性。因此，透由高頻火花熔蝕，將材料中的氧移除，鎵便能從材料中快速剝落，氧化鎵微結構即可被快速成形。所以本研究提出一種「非等能量雙電阻電容放電電源」的電路設計。「非等能量雙電阻電容放電電源」由「元件可程式邏輯閘陣列(FPGA)」控制放電迴路的等頻率放電時間，並以100 pF/200 pF的雙電容當迴路放電電容，以便創造出高頻、高低峰及短脈衝的放電電流波列。高峰值電流負責汽化、熔蝕及移除氧化鎵材料，低峰值電流負責移除氧化鎵的放電殘渣及熔蝕毛邊，並提供介電液將放電殘渣沖離的放電休止時間。實驗結果顯示，就放電加工而言，比較起鋁合金，氧化鎵有更高的材料移除率，主要原因為氧化鎵在放電高溫作用下，會發生熱裂解(Pyrolysis)，當氧被去除後，材料會以小塊狀模式剝落，可加速材料移除。且在設計的「非等能量雙電阻電容放電電源」作用下，可成功切割出柱狀微結構陣列及片狀曲面微結構，且微細結構陣列皆能成形平滑曲面結構，槽寬與表面粗糙度值分別可達24.5 µm與Ra0.188 µm，特徵形狀具高一致性，毛邊與邊緣崩落量都很少;相較於蝕刻技術，不但速度快，更可達高深寬比，加工效率明顯提升，證實「非等能量雙電阻電容放電電源」適用於寬能隙材料的加工，期望此項技術未來能應用於光電產業。

關鍵字

非等能量雙電阻電容放電電源 ； 氧化鎵 ； 熱裂解 ； 寬能隙

並列摘要

The aim of the study is to develop a "dual-resistance-capacitance discharge power source with non-equal energy" for cutting β-Ga2O3 with high-aspect-ratio microstructure array. Gallium oxide which is made of the combination of oxygen atoms and gallium atoms is a wide band gap semiconductor material and widely used in high-power devices. It is characterized by high- hardness, brittleness and not easy to cut. At present, the etching method is mostly used for forming, however, the etching speed is slow, and it is difficult to foFrm a microstructure with high aspect ratio. The wide-bandgap materials allow reduced energy consumption. Reducing energy consumption not only reduces power loss but also makes the system miniaturized, reducing costs compared with silicon solutions. Nevertheless, the greater the energy gap of the material, the higher the insulation under normal temperature condition. An ohmic contact method, in which conductive electrodes are fabricated on the surface of gallium oxide, is carried out to make it possesses weak conductive properties. Therefore, by removing oxygen from the material by high-frequency spark ablation, gallium can be spontaneously and quickly peeled off from the matrix, and the gallium oxide microstructure can be rapidly formed. In view of this, a circuit design of "dual-resistance-capacitance discharge power source with non-equal energy" is proposed in this study. The equal frequency discharge time is controlled by the "component programmable logic gate array (FPGA)" in the power source. Experimental results found that a dual-capacitor with 100pF/200pF used can create a discharge current with high-frequency, high-low-peak and short-pulse train, which is very suitable for cutting the gallium oxide microstructure. High-peak current dominates vaporization, ablation and removal of gallium oxide material, while low-peak current is responsible for removing discharge debris and ablation burrs of gallium oxide. In addition, the pulse off-time of discharge is also designed to be adjustable so that the discharge debris has enough time to be flushed away by dielectric fluid. Experimental results show that in terms of electrical discharge machining, gallium oxide has a higher material removal rate than aluminum alloy. The main reason is that gallium oxide will undergo thermal cracking (i.e. pyrolysis). The gallium oxide will peel off in a small block pattern when oxygen is removed, thereby speeding up the removal of the material. Moreover, by applying the designed "dual-resistance-capacitance discharge power source with non-equal energy", the microstructure arrays with pillar and sheet-like curved can be successfully produced. These microstructure arrays are formed with smooth surface, the slot-widths and surface roughness can reach up to 24.5 µm and Ra0.188 µm, respectively. The microstructure features with high-consistency and low the amount of edge-burrs are realized successfully. Compared with the etching technology, it is not only faster but also achieves a microstructure with high aspect ratio, improving significantly the processing efficiency, proving that the "dual-resistance-capacitance discharge power source with non-equal energy" is suitable for cutting the materials with wide-bandgap. It is expected that this technology can be applied to optoelectronics industry in the future.

並列關鍵字

Dual-resistance-capacitance discharge power source with non-equal energy ； gallium oxide ； pyrolysis ； wide-bandgap

參考文獻

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