高性能氮化镓高压大功率电子器件研制

The wide-bandgap AlGaN/GaN heterostructure possesses unique properties that favour the development of future high-performance HEMT devices. Its high 2-dimensional electron gas (2DEG) with high electron mobility bypasses the hurdle, which hinders the development of the counterpart SiC MOSFET power devices, to produce a highly conductive channel. At the current stage, the research and development on GaN power devices is an emerging topic with very strong interest worldwide. The proposed project scope is to focus on the development of next generation high-performance GaN-based power semiconductor devices on the silicon platform for a cost-effective approach to be suitable for high-voltage power electronics applications, especially for the future renewable energy systems and electric vehicles. The key technologies to be developed will emphasize on the device drift region field manipulation and trench gate formation in order to raise the breakdown voltage, enhance the gate threshold voltage, reduce the specific on-state resistance and minimise the drain current collapse phenomena under high voltage switching operations. There are several technical challenges faced in this project, i.e. (a) near gate high-field breakdown issue which limits the MOS-HEMT high-voltage blocking ability; (b) drain current collapse issue which limits the device's switching speed; (c) how to properly form the multiple gate/gate all-around/multiple 2DEG channels in order to reduce the on-state resistance; (d) finally, on the formation of gate dielectric with interface charge properly controlled for reliability and temperature stability. All these issues will be carefully looked into in order to successfully produce a high-performance GaN power MOS-HEMT device with high breakdown rating, high saturation current level, fast switching speed, and positive threshold voltage above +3V. For the project deliverables, they include the followings. (a) A prototype of GaN high-voltage power MOS-HEMT devices of 1200V rating will be designed, fabricated and installed in the actual power electronic system for field testing. The inverter power rating is to be above 10 kW for solar photovoltaic energy system and electric vehicle traction applications. (b) A suitable current sensor and over-current protection circuit will be designed and built to aid for the prototype system. (c) On the manpower training: 2 postgraduate students and 3 undergraduate students will be trained through this project period. And (d) the research outcome will be published on international conferences and journals.

宽禁带氮化镓异质结构具有优秀的材料特性，适于研制高性功率半导体器件。它的高密度和高迁移率二维电子气赋予器件好的沟道电导率，克服了碳化硅器件中遇到的通态电阻大的难题。为此，目前氮化镓功率器件的研制和发展已经成为国内外一个热门课题。 本课题基于低成本CMOS工艺平台来发展下一代高性能氮化镓高压功率电子器件，重点是实现未来可再生能源系统方面的应用。 其研究重点着重在器件漂移区的电场调节和凹槽栅结构的设计，以克服以下几个难点，如（a）器件耐压能力及栅极边缘高电场集中问题；（b）限制器件开关速度的电流坍塌问题；（c）通态电阻和多重2DEG沟道形成问题；（d）合适的栅极电介质来实现器件可靠性和稳定性问题。以上这些问题将在这个课题中被仔细调研，最后目标是制作1200V等级的高电流，高开关速率和大于+3V阈值电压的高性能氮化镓功率器件。此外，也将着手于过流保护机制的设计和制作，以利其系统应用。

本项目的主要研究工作在于研制和开发高性能氮化镓高压大功率电子器件及其集成技术。其阶段性任务包括（1）开发常闭型氮化镓器件，着重于提高凹槽栅和带电荷介质方法的器件制作细节工艺，以多层势垒层MIS-HEMT器件为设计蓝本，进一步提高在器件沟道漂移区电场调节和栅极的可控性；（2）对氮化镓器件作仿真建模。其过程，依现有的氮化镓外延片材料品质，缺陷校准，再依工艺的过程，校定界面及表面电荷的分布及数量，准确的调适建模；（3）在氟处理之前应用新颖的短氩（Ar）等离子体处理，以有效地增强了Al2O3 电介质内较深层能级处的氟化诱导状态。大幅度提高器件的高温（> 200C）稳定度；（4）高压氮化镓MOS-HEMT器件型换流器试制及过流保护电路及换流器系统整合，优化器件制作细节工艺，并且在氮化镓集成电路的制作上，作必要的技术研究。在研究成果上，已成功开发并制作高性能氮化镓高压大功率电子器件样品，及直流电力换流器集成电路。实测结果，均已达到所预期的规格标准。