高线性GaN微波功率器件研究

The wide bandgap semiconductor-gallium nitride has exhibited great advantages for high-power, high requency applications during the last decades. However, due to the some limitations from inherent physical mechanisms, transconductor characteristics in GaN HEMTs based on planar structure suffer from a severe degradation after the peak point.This problem would lead to a severe distortion in output signal of designed power amplifiers based on GaN technology, finally resulting in an increase in volume and cost as well as a reduce in operation efficiency of the whole system. In a device level, this project is going to improve the linearity of GaN technology in order to improve the performance of the whole system and boost the technical advantage of GaN semiconductor over others. In order to make precise schemes, the typical transconductor curve is firstly divided into two regions. By revealing the inherent mechanism behind the nonlinear transconductor behavior, establishing a new design rule for high-linearity structures and resolving the key processes, our ultimate goal is to realize novel GaN devices featuring high-linearity characteristics. Furthermore, the issue that GaN devices can not operate well in low voltage will be tackled through the precise improvement in device structrues and processes. By implementing the project, both the advantages of GaN technology in 5G communication base-stations and further development in mobile machines should be enhanced.

宽禁带半导体GaN由于高的饱和电子速度、高的击穿电压等优势，已经在高频、大功率方面显示了巨大优势。然而由于某些物理机制限制，现有平面结构GaN器件的跨导曲线呈现典型峰值特征，导致基于GaN技术的功率放大器的输出信号失真严重、线性度差，结果带来整机系统的设计复杂度、成本的增加及效率的降低。本项目拟在器件级改善GaN技术的线性度，以带动整个系统性能提升，提高GaN半导体技术优势。项目从区域化、细化GaN典型跨导曲线出发，“精准施策”，通过揭示限制GaN器件跨导线性度的主导机制，建立高线性器件结构设计规则，突破相关关键工艺技术，最终研制出高线性、高频率、高效率的GaN新结构器件，解决GaN低压应用技术难题，不仅提升GaN在未来5G移动通信基站的优势，而且将推动GaN在手机移动终端等低压应用的发展，从而能够在理论与应用上获得创新发展。

线性度、输出功率和附加效率是无线通信应用的关键指标。GaN器件具有显著的功率和效率优势，但是线性度存在明显缺陷。为了解决该问题，本项目首先通过理论与实验相结合的方式，揭示了GaN器件跨导非线性的主要机制，包括内在和外在两种因素。在本征上，大电流下导致的沟道内电子迁移率退化是跨导非线性的根本原因；而源极电阻是恶化跨导线性度的关键外部因素。该机理的揭示指导了实际的高线性器件设计与制备。随后，研究了新型CE-PolFET高线性器件，优化了复合沟道器件。最后，将GaN高线性器件的截止频率fT/fmax提高至84/240GHz。通过FinFET和尺度微缩技术，研制出高性能GaN低压器件，最小工作电压可到3V。4GHz时，Vd=4V下，器件输出功率密度Pout=1.94W/mm，附加效率PAE达66.6%；30GHz时，Vd=3V下，器件输出功率密度Pout=1.4W/mm，附加效率PAE=51.5%，这些结果与世界最高水平相媲美。本项目初步建立了高线性器件数值模型，形成了较为完备的GaN线性理论和高线性器件设计方法，为未来5G通信、移动终端等应用奠定了基础。