金刚石/GaN异质外延与键合技术研究进展

Research Progress of Heteroepitaxial and Bonding Technology of Diamond-GaN

氮化镓(GaN)功率器件具有功率高、小型化的优势,但散热问题已经成为限制其高功率输出的新问题。金刚石具有块体材料最高的热导率,是GaN功率器件的理想散热材料,将金刚石与GaN功率器件集成,可以降低器件运行温度,提高功率密度,推进器件小型化发展。但是由于金刚石与GaN存在大的热膨胀失配和晶格失配,以及金刚石的高硬度和稳定的化学性质,其与GaN集成存在很多问题,无法发挥金刚石的超高热导率优势。针对金刚石与GaN的集成已经进行了研究与探索,主要包括GaN功率器件的器件层散热和衬底层散热。器件层散热主要有金刚石钝化散热技术,其在GaN器件层中异质外延金刚石散热层;衬底层散热主要有键合技术、异质外延技术,其中键合技术通常需要在金刚石和GaN表面沉积键合层或形成封端,包括表面活化键合技术、亲水键合技术、原子扩散键合技术和水解辅助固化键合技术等;异质外延技术通常需要在外延表面沉积缓冲层,包括金刚石异质外延GaN技术和GaN底面异质外延金刚石技术。详细介绍了GaN材料的优势、应用领域及面临的挑战,对上述集成技术的研究现状和优缺点进行了归纳,展望了金刚石与GaN功率器件集成技术的未来发展方向。

Gallium nitride(GaN)power devices have the advantages of high power,high frequency and miniaturization,but heat dissipation has become a new problem limiting their high-power output.Diamond has the highest thermal conductivity of bulk materials and is an ideal heat dissipation material for GaN power devices.Integrating diamond with GaN power devices can reduce the operating temperature,improve power density,and promote miniaturization development of devices.However,due to the significant thermal expansion mismatch and lattice mismatch between diamond and GaN,as well as the high hardness and stable chemical properties of diamond,there are many problems in integrating it with GaN power devices.As a result,the ultra-high thermal conductivity advantage of diamond can not be fully utilized.Research and exploration have been conducted on the integration of diamond and GaN power devices,mainly including device layer heat dissipation and substrate layer heat dissipation of GaN power devices.Heat dissipation of the device layer mainly includes diamond passivation heat dissipation technology,with a heteroepitaxial diamond heat dissipation layer in the GaN device layer;Heat dissipation of the substrate layer includes bonding technology and heteroepitaxy technology.Among them,bonding technology usually requires the deposition of bonding layers or the formation of end caps on the surfaces of diamond and GaN,including surface activated bonding technology,hydrophilic bonding technology,atomic diffusion bonding technology,and hydrolysis-assisted solidification bonding technology.Heteroepitaxial technology typically requires the deposition of a buffer layer on the epitaxial surface,includes heteroepitaxial GaN on diamond technology and heteroepitaxial diamond on GaN substrate technology.The advantage of the diamond passivation layer is that the diamond is close to the hot spot,and the heat dissipation efficiency is high,the disadvantage is that the diamond layer is less compatible with the device layer.The diamond is usually deposited under low temperature,resulting in low quality and low thermal conductivity.The advantages of bonding technology lie in the generally low bonding temperature,low thermal stress between diamond and GaN,and minimal thermal damage to the GaN layer in low-temperature environments.The disadvantages include low bonding strength,poor bonding uniformity,difficulty in controlling the quality and thickness of the bonding layer,low thermal conductivity of the bonding layer material,and high cost of obtaining large-sized,low roughness,and high parallelism diamonds.The advantages of heteroepitaxial technology lie in the high bonding strength and good bonding uniformity.However,due to the thermal expansion mismatch and lattice mismatch between diamond and GaN,both heteroepitaxial technologies have problems of high stress between diamond and GaN,high thermal resistance of protective or buffer layers,and poor electrical performance of GaN device layers in diamond heteroepitaxial GaN technology.Currently,most of the research focuses solely on the device layer or the substrate layer.If they are efficiently combined,the use of diamond for three-dimensional heat dissipation in GaN power devices will significantly reduce device temperature.This article provides a detailed introduction to the advantages and application fields of GaN materials,as well as the challenges they face.It summarizes the research status,advantages and disadvantages of the aforementioned integrated technologies,and looks forward to the future development direction of diamond and GaN power device integration technology.